U.S. patent application number 17/061563 was filed with the patent office on 2021-01-21 for 3d semiconductor device and structure.
This patent application is currently assigned to Monolithic 3D Inc.. The applicant listed for this patent is Monolithic 3D Inc.. Invention is credited to Brian Cronquist, Zvi Or-Bach, Deepak Sekar.
Application Number | 20210020457 17/061563 |
Document ID | / |
Family ID | 1000005123700 |
Filed Date | 2021-01-21 |
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United States Patent
Application |
20210020457 |
Kind Code |
A1 |
Or-Bach; Zvi ; et
al. |
January 21, 2021 |
3D SEMICONDUCTOR DEVICE AND STRUCTURE
Abstract
A 3D semiconductor device, the device comprising: a first level,
wherein said first level comprises a first layer, said first layer
comprising first transistors, and wherein said first level
comprises a second layer, said second layer comprising first
interconnections; a second level overlaying said first level,
wherein said second level comprises a third layer, said third layer
comprising second transistors, and wherein said second level
comprises a fourth layer, said fourth layer comprising second
interconnections; and a plurality of connection paths, wherein said
plurality of connection paths provides connections from a plurality
of said first transistors to a plurality of said second
transistors, wherein said second level is bonded to said first
level, wherein said bonded comprises oxide to oxide bond regions,
wherein said bonded comprises metal to metal bond regions, wherein
said second level comprises at least one memory array, wherein said
second level comprises at least one Phase Lock Loop ("PLL) circuit,
and wherein said third layer comprises crystalline silicon.
Inventors: |
Or-Bach; Zvi; (San Jose,
CA) ; Cronquist; Brian; (Klamath Falls, OR) ;
Sekar; Deepak; (Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Monolithic 3D Inc. |
San Jose |
CA |
US |
|
|
Assignee: |
Monolithic 3D Inc.
San Jose
CA
|
Family ID: |
1000005123700 |
Appl. No.: |
17/061563 |
Filed: |
October 1, 2020 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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16114211 |
Aug 28, 2018 |
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17061563 |
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15913917 |
Mar 6, 2018 |
10115663 |
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16114211 |
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15470872 |
Mar 27, 2017 |
9941275 |
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15913917 |
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13864245 |
Apr 17, 2013 |
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15470872 |
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13803437 |
Mar 14, 2013 |
9385058 |
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13864245 |
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13731108 |
Dec 30, 2012 |
9871034 |
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13803437 |
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13730897 |
Dec 29, 2012 |
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13731108 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 25/0657 20130101;
H01L 23/60 20130101; H01L 21/4871 20130101; H01L 23/3732 20130101;
H01L 23/49827 20130101; H01L 27/092 20130101; H01L 27/0207
20130101; H01L 23/367 20130101; H01L 23/49838 20130101; H01L
27/0688 20130101; H01L 21/823487 20130101; H01L 23/5226 20130101;
H01L 25/50 20130101; H01L 2924/0002 20130101; H01L 2225/06589
20130101; H01L 27/098 20130101; H01L 23/3677 20130101; H01L 23/34
20130101; H01L 2225/06541 20130101; H01L 23/373 20130101; H01L
2225/06527 20130101; H01L 27/0248 20130101 |
International
Class: |
H01L 21/48 20060101
H01L021/48; H01L 23/498 20060101 H01L023/498; H01L 23/34 20060101
H01L023/34; H01L 27/02 20060101 H01L027/02; H01L 21/8234 20060101
H01L021/8234; H01L 27/06 20060101 H01L027/06; H01L 27/098 20060101
H01L027/098; H01L 23/522 20060101 H01L023/522; H01L 23/367 20060101
H01L023/367; H01L 27/092 20060101 H01L027/092; H01L 25/00 20060101
H01L025/00; H01L 23/60 20060101 H01L023/60; H01L 25/065 20060101
H01L025/065 |
Claims
1. A 3D semiconductor device, the device comprising: a first level,
wherein said first level comprises a first layer, said first layer
comprising first transistors, and wherein said first level
comprises a second layer, said second layer comprising first
interconnections; a second level overlaying said first level,
wherein said second level comprises a third layer, said third layer
comprising second transistors, and wherein said second level
comprises a fourth layer, said fourth layer comprising second
interconnections; and a plurality of connection paths, wherein said
plurality of connection paths provides connections from a plurality
of said first transistors to a plurality of said second
transistors, wherein said second level is bonded to said first
level, wherein said bonded comprises oxide to oxide bond regions,
wherein said bonded comprises metal to metal bond regions, wherein
said second level comprises at least one memory array, wherein said
second level comprises at least one Phase Lock Loop ("PLL) circuit,
and wherein said third layer comprises crystalline silicon.
2. The device according to claim 1, wherein at least one of said
second transistors comprises a raised source and drain.
3. The device according to claim 1, wherein said second level
comprises at least one SerDes circuit.
4. The device according to claim 1, further comprising: a heat
removal path from said third level to an external surface of said
device.
5. The device according to claim 1, wherein said first level
comprises a plurality of trench capacitors, and wherein said
plurality of trench capacitors are connected to at least one power
supply line.
6. The device according to claim 1, wherein said first level
comprises at least one control circuit, and wherein said at least
one control circuit controls read operations of said at least one
memory array.
7. The device according to claim 1, wherein at least one of said
second transistors is a FinFET type transistor.
8. A 3D semiconductor device, the device comprising: a first level,
wherein said first level comprises a first layer, said first layer
comprising first transistors, and wherein said first level
comprises a second layer, said second layer comprising first
interconnections; a second level overlaying said first level,
wherein said second level comprises a third layer, said third layer
comprising second transistors, and wherein said second level
comprises a fourth layer, said fourth layer comprising second
interconnections; a plurality of connection paths, wherein said
plurality of connection paths provides connections from a plurality
of said first transistors to a plurality of said second
transistors, wherein said second level is bonded to said first
level, wherein said bonded comprises oxide to oxide bond regions,
wherein said bonded comprises metal to metal bond regions, wherein
said second level comprises at least one memory array, wherein said
third layer comprises crystalline silicon, wherein a plurality of
said first transistors are circumscribed by a first guard ring,
wherein a plurality of said second transistors are circumscribed by
a second guard ring, and wherein said second guard ring overlays
said first guard ring.
9. The device according to claim 8, wherein said second level
comprises at least one PLL circuit.
10. The device according to claim 8, wherein said second level
comprises at least one SerDes circuit.
11. The device according to claim 8, wherein at least one of said
second transistors comprises a raised source and drain.
12. The device according to claim 8, wherein said first level
comprises a plurality of trench capacitors, and wherein said
plurality of trench capacitors are connected to at least one power
supply line.
13. The device according to claim 8, wherein said first level
comprises at least one control circuit, and wherein said at least
one control circuit controls read operations of said memory
array.
14. The device according to claim 8, wherein at least one of said
second transistors is a FinFET type transistor.
15. A 3D semiconductor device, the device comprising: a first
level, wherein said first level comprises a first layer, said first
layer comprising first transistors, and wherein said first level
comprises a second layer, said second layer comprising first
interconnections; a second level overlaying said first level,
wherein said second level comprises a third layer, said third layer
comprising second transistors, and wherein said second level
comprises a fourth layer, said fourth layer comprising second
interconnections; and a plurality of connection paths, wherein said
plurality of connection paths provides connections from a plurality
of said first transistors to a plurality of said second
transistors, wherein said second level is bonded to said first
level, wherein said bonded comprises oxide to oxide bond regions,
wherein said bonded comprises metal to metal bond regions, wherein
said second level comprises at least one memory array, wherein said
third layer comprises crystalline silicon, and wherein said second
layer comprises an Electro-Static-Discharge ("ESD") protection
structure connected to at least one of said connection paths.
16. The device according to claim 15, further comprising: a heat
removal path from said third level to an external surface of said
device.
17. The device according to claim 15, wherein said second level
comprises at least one SerDes circuit.
18. The device according to claim 15, wherein at least one of said
second transistors comprises a raised source and drain.
19. The device according to claim 15, wherein said first level
comprises at least one control circuit, and wherein said at least
one control circuit controls read operations of said memory
array.
20. The device according to claim 15, wherein at least one of said
second transistors is a FinFET type transistor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] This application relates to the general field of Integrated
Circuit (IC) devices and fabrication methods, and more particularly
to multilayer or Three Dimensional Integrated Circuit (3D-IC)
devices and fabrication methods.
2. Discussion of Background Art
[0002] Over the past 40 years, there has been a dramatic increase
in functionality and performance of Integrated Circuits (ICs). This
has largely been due to the phenomenon of "scaling"; i.e.,
component sizes within ICs have been reduced ("scaled") with every
successive generation of technology. There are two main classes of
components in Complementary Metal Oxide Semiconductor (CMOS) ICs,
namely transistors and wires. With "scaling", transistor
performance and density typically improve and this has contributed
to the previously-mentioned increases in IC performance and
functionality. However, wires (interconnects) that connect together
transistors degrade in performance with "scaling". The situation
today is that wires dominate the performance, functionality and
power consumption of ICs.
[0003] 3D stacking of semiconductor devices or chips is one avenue
to tackle the wire issues. By arranging transistors in 3 dimensions
instead of 2 dimensions (as was the case in the 1990s), the
transistors in ICs can be placed closer to each other. This reduces
wire lengths and keeps wiring delay low.
[0004] There are many techniques to construct 3D stacked integrated
circuits or chips including: [0005] Through-silicon via (TSV)
technology: Multiple layers of transistors (with or without wiring
levels) can be constructed separately. Following this, they can be
bonded to each other and connected to each other with
through-silicon vias (TSVs). [0006] Monolithic 3D technology: With
this approach, multiple layers of transistors and wires can be
monolithically constructed. Some monolithic 3D and 3DIC approaches
are described in U.S. Pat. Nos. 8,273,610, 8,298,875, 8,362,482,
8,378,715, 8,379,458, 8,450,804, 8,557,632, 8,574,929, 8,581,349,
8,642,416, 8,669,778, 8,674,470, 8,687,399, 8,742,476, 8,803,206,
8,836,073, 8,902,663, 8,994,404, 9,023,688, 9,029,173, 9,030,858,
9,117,749, 9,142,553, 9,219,005, 9,385,058, 9,406,670, 9,460,978,
9,509,313, 9,640,531, 9,691,760, 9,711,407, 9,721,927, 9,799,761,
9,871,034, 9,953,870, 9,953,994, 10,014,292, 10,014,318; and
pending U.S. patent application Publications and applications, Ser.
Nos. 14/642,724, 15/150,395, 15/173,686, 62/651,722; 62/681,249,
62/713,345, 62/770,751, 62/952,222, 2020/0013791, Ser. No.
16/558,304; and PCT Applications (and Publications):
PCT/US2010/052093, PCT/US2011/042071 (WO2012/015550),
PCT/US2016/52726 (WO2017053329), PCT/US2017/052359 (WO2018/071143),
PCT/US2018/016759 (WO2018144957), and PCT/US2018/52332 (WO
2019/060798). The entire contents of the foregoing patents,
publications, and applications are incorporated herein by
reference. [0007] Electro-Optics: There is also work done for
integrated monolithic 3D including layers of different crystals,
such as U.S. Pat. Nos. 8,283,215, 8,163,581, 8,753,913, 8,823,122,
9,197,804, 9,419,031, 9,941,319, and 10,679,977. The entire
contents of the foregoing patents, publications, and applications
are incorporated herein by reference.
[0008] Regardless of the technique used to construct 3D stacked
integrated circuits or chips, heat removal is a serious issue for
this technology. For example, when a layer of circuits with power
density P is stacked atop another layer with power density P, the
net power density is 2P. Removing the heat produced due to this
power density is a significant challenge. In addition, many heat
producing regions in 3D stacked integrated circuits or chips have a
high thermal resistance to the heat sink, and this makes heat
removal even more difficult.
[0009] Several solutions have been proposed to tackle this issue of
heat removal in 3D stacked integrated circuits and chips. These are
described in the following paragraphs.
[0010] Publications have suggested passing liquid coolant through
multiple device layers of a 3D-IC to remove heat. This is described
in "Microchannel Cooled 3D Integrated Systems", Proc. Intl.
Interconnect Technology Conference, 2008 by D. C. Sekar, et al.,
and "Forced Convective Interlayer Cooling in Vertically Integrated
Packages," Proc. Intersoc. Conference on Thermal Management
(ITHERM), 2008 by T. Brunschweiler, et al.
[0011] Thermal vias have been suggested as techniques to transfer
heat from stacked device layers to the heat sink. Use of power and
ground vias for thermal conduction in 3D-ICs has also been
suggested. These techniques are described in "Allocating Power
Ground Vias in 3D ICs for Simultaneous Power and Thermal Integrity"
ACM Transactions on Design Automation of Electronic Systems
(TODAES), May 2009 by Hao Yu, Joanna Ho and Lei He.
[0012] Other techniques to remove heat from 3D Integrated Circuits
and Chips will be beneficial.
[0013] Additionally the 3D technology according to some embodiments
of the invention may enable some very innovative IC alternatives
with reduced development costs, increased yield, and other
illustrative benefits.
SUMMARY
[0014] The invention may be directed to multilayer or Three
Dimensional Integrated Circuit (3D IC) devices, structures, and
fabrication methods.
[0015] In one aspect, a 3D semiconductor device, the device
comprising: a first level, wherein said first level comprises a
first layer, said first layer comprising first transistors, and
wherein said first level comprises a second layer, said second
layer comprising first interconnections; a second level overlaying
said first level, wherein said second level comprises a third
layer, said third layer comprising second transistors, and wherein
said second level comprises a fourth layer, said fourth layer
comprising second interconnections; and a plurality of connection
paths, wherein said plurality of connection paths provides
connections from a plurality of said first transistors to a
plurality of said second transistors, wherein said second level is
bonded to said first level, wherein said bonded comprises oxide to
oxide bond regions, wherein said bonded comprises metal to metal
bond regions, wherein said second level comprises at least one
memory array, wherein said second level comprises at least one
Phase Lock Loop ("PLL) circuit, and wherein said third layer
comprises crystalline silicon.
[0016] In another aspect, a 3D semiconductor device, the device
comprising: a first level, wherein said first level comprises a
first layer, said first layer comprising first transistors, and
wherein said first level comprises a second layer, said second
layer comprising first interconnections; a second level overlaying
said first level, wherein said second level comprises a third
layer, said third layer comprising second transistors, and wherein
said second level comprises a fourth layer, said fourth layer
comprising second interconnections; a plurality of connection
paths, wherein said plurality of connection paths provides
connections from a plurality of said first transistors to a
plurality of said second transistors, wherein said second level is
bonded to said first level, wherein said bonded comprises oxide to
oxide bond regions, wherein said bonded comprises metal to metal
bond regions, wherein said second level comprises at least one
memory array, wherein said third layer comprises crystalline
silicon, wherein a plurality of said first transistors are
circumscribed by a first guard ring, wherein a plurality of said
second transistors are circumscribed by a second guard ring, and
wherein said second guard ring overlays said first guard ring.
[0017] In another aspect, a 3D semiconductor device, the device
comprising: a first level, wherein said first level comprises a
first layer, said first layer comprising first transistors, and
wherein said first level comprises a second layer, said second
layer comprising first interconnections; a second level overlaying
said first level, wherein said second level comprises a third
layer, said third layer comprising second transistors, and wherein
said second level comprises a fourth layer, said fourth layer
comprising second interconnections; and a plurality of connection
paths, wherein said plurality of connection paths provides
connections from a plurality of said first transistors to a
plurality of said second transistors, wherein said second level is
bonded to said first level, wherein said bonded comprises oxide to
oxide bond regions, wherein said bonded comprises metal to metal
bond regions, wherein said second level comprises at least one
memory array, wherein said third layer comprises crystalline
silicon, and wherein said second layer comprises an
Electro-Static-Discharge ("ESD") protection structure connected to
at least one of said connection paths.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Various embodiments of the invention will be understood and
appreciated more fully from the following detailed description,
taken in conjunction with the drawings in which:
[0019] FIG. 1 is an exemplary drawing illustration of a 3D
integrated circuit;
[0020] FIG. 2 is an exemplary drawing illustration of another 3D
integrated circuit;
[0021] FIG. 3 is an exemplary drawing illustration of the power
distribution network of a 3D integrated circuit;
[0022] FIG. 4 is an exemplary drawing illustration of a NAND
gate;
[0023] FIG. 5 is an exemplary drawing illustration of a thermal
contact concept;
[0024] FIG. 6 is an exemplary drawing illustration of various types
of thermal contacts;
[0025] FIG. 7 is an exemplary drawing illustration of another type
of thermal contact;
[0026] FIG. 8 is an exemplary drawing illustration of the use of
heat spreaders in 3D stacked device layers;
[0027] FIG. 9 is an exemplary drawing illustration of the use of
thermally conductive shallow trench isolation (STI) in 3D stacked
device layers;
[0028] FIG. 10 is an exemplary drawing illustration of the use of
thermally conductive pre-metal dielectric regions in 3D stacked
device layers;
[0029] FIG. 11 is an exemplary drawing illustration of the use of
thermally conductive etch stop layers for the first metal layer of
3D stacked device layers;
[0030] FIG. 12A-12B are exemplary drawing illustrations of the use
and retention of thermally conductive hard mask layers for
patterning contact layers of 3D stacked device layers;
[0031] FIG. 13 is an exemplary drawing illustration of a 4 input
NAND gate;
[0032] FIG. 14 is an exemplary drawing illustration of a 4 input
NAND gate where substantially all parts of the logic cell can be
within desirable temperature limits;
[0033] FIG. 15 is an exemplary drawing illustration of a
transmission gate;
[0034] FIG. 16 is an exemplary drawing illustration of a
transmission gate where substantially all parts of the logic cell
can be within desirable temperature limits;
[0035] FIG. 17A-17D is an exemplary process flow for constructing
recessed channel transistors with thermal contacts;
[0036] FIG. 18 is an exemplary drawing illustration of a pMOS
recessed channel transistor with thermal contacts;
[0037] FIG. 19 is an exemplary drawing illustration of a CMOS
circuit with recessed channel transistors and thermal contacts;
[0038] FIG. 20 is an exemplary drawing illustration of a technique
to remove heat more effectively from silicon-on-insulator (SOI)
circuits;
[0039] FIG. 21 is an exemplary drawing illustration of an
alternative technique to remove heat more effectively from
silicon-on-insulator (SOI) circuits;
[0040] FIG. 22 is an exemplary drawing illustration of a recessed
channel transistor (RCAT);
[0041] FIG. 23 is an exemplary drawing illustration of a 3D-IC with
thermally conductive material on the sides;
[0042] FIG. 24 is an exemplary procedure for a chip designer to
ensure a good thermal profile for a design;
[0043] FIG. 25 is an exemplary drawing illustration of a monolithic
3D-IC structure with CTE adjusted through layer connections;
[0044] FIGS. 26A-26F are exemplary drawing illustrations of a
process flow for manufacturing fully depleted Recessed Channel
Array Transistors (FD-RCAT);
[0045] FIGS. 27A-27B, 27B-1, 27C-27F are exemplary drawing
illustrations of the integration of a shield/heat sink layer in a
3D-IC;
[0046] FIGS. 28A-28G, 28G-1 are exemplary drawing illustrations of
a process flow for manufacturing fully depleted Recessed Channel
Array Transistors (FD-RCAT) with an integrated shield/heat sink
layer;
[0047] FIGS. 29A-29G, 29G-1 are exemplary drawing illustrations of
a process flow for manufacturing fully depleted MOSFET (FD-MOSFET)
with an integrated shield/heat sink layer;
[0048] FIGS. 30A-30G are exemplary drawing illustrations of another
process flow for manufacturing fully depleted MOSFET (FD-MOSFET)
with an integrated shield/heat sink layer;
[0049] FIGS. 31A-31E, 31E-1, 31F, 31G are exemplary drawing
illustrations of a process flow for manufacturing horizontally
oriented JFET or JLT with an integrated shield/heat sink layer;
[0050] FIG. 32 is an exemplary illustration of a partially
processed 3D device with substrate being processed with topside
illumination and including thermally conductive paths; and
[0051] FIG. 33 is an exemplary illustration of some additional
embodiments and combinations of devices, circuits, paths, and
connections of a 3D device.
DETAILED DESCRIPTION
[0052] An embodiment of the invention is now described with
reference to the drawing figures. Persons of ordinary skill in the
art will appreciate that the description and figures illustrate
rather than limit the invention and that in general the figures are
not drawn to scale for clarity of presentation. Such skilled
persons will also realize that many more embodiments are possible
by applying the inventive principles contained herein and that such
embodiments fall within the scope of the invention which is not to
be limited except by the appended claims.
[0053] Some drawing figures may describe process flows for building
devices. The process flows, which may be a sequence of steps for
building a device, may have many structures, numerals and labels
that may be common between two or more adjacent steps. In such
cases, some labels, numerals and structures used for a certain
step's figure may have been described in the previous
steps'figures.
[0054] FIG. 1 illustrates a 3D integrated circuit. Two crystalline
layers, 0104 and 0116, which may include semiconductor materials
such as, for example, mono-crystalline silicon, germanium, GaAs,
InP, and graphene, are shown. For this illustration,
mono-crystalline (single crystal) silicon may be used. Silicon
layer 0116 could be thinned down from its original thickness, and
its final thickness could be in the range of about 0.01 um to about
50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5
um. Silicon layer 0104 could be thinned down from its original
thickness, and its final thickness could be in the range of about
0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um,
1 um, 2 um or 5 um; however, due to strength considerations,
silicon layer 0104 may also be of thicknesses greater than 100 um,
depending on, for example, the strength of bonding to heat removal
apparatus 0102. Silicon layer 0104 may include transistors such as,
for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include
gate electrode region 0114, gate dielectric region 0112, source and
drain junction regions (not shown), and shallow trench isolation
(STI) regions 0110. Silicon layer 0116 may include transistors such
as, for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may
include gate electrode region 0134, gate dielectric region 0132,
source and drain junction regions (not shown), and shallow trench
isolation (STI) regions 0130. A through-silicon via (TSV) 0118
could be present and may have an associated surrounding dielectric
region 0120. Wiring layers 0108 for silicon layer 0104 and wiring
dielectric regions 0106 may be present and may form an associated
interconnect layer or layers. Wiring layers 0138 for silicon layer
0116 and wiring dielectric 0136 may be present and may form an
associated interconnect layer or layers. Through-silicon via (TSV)
0118 may connect to wiring layers 0108 and wiring layers 0138 (not
shown). The heat removal apparatus 0102 may include a heat spreader
and/or a heat sink. The heat removal problem for the 3D integrated
circuit shown in FIG. 1 is immediately apparent. The silicon layer
0116 is far away from the heat removal apparatus 0102, and it may
be difficult to transfer heat among silicon layer 0116 and heat
removal apparatus 0102. Furthermore, wiring dielectric regions 0106
may not conduct heat well, and this increases the thermal
resistance among silicon layer 0116 and heat removal apparatus
0102. Silicon layer 0104 and silicon layer 0116 may be may be
substantially absent of semiconductor dopants to form an undoped
silicon region or layer, or doped, such as, for example, with
elemental or compound species that form a p+, or p, or p-, or n+,
or n, or n- silicon layer or region. The heat removal apparatus
0102 may include an external surface from which heat transfer may
take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0055] It should be noted that while in general a heat sink may be
an extra heat conducting element bonded with good heat conductivity
(or made to be in contact with) to the back side of the base layer
or substrate, such as for example, mono-crystalline bulk silicon or
the bulk substrate of an SOI wafer, in many cases the base layer
itself could be an effective heat sink. For example, many silicon
wafers are many hundreds of microns thick before extra thinning or
back-grinding, and has a relatively high heat capacity in
comparison to the transistor layer, which may be less than one
micron thick. Accordingly the heat sink structure for some devices
discussed herein might be the bulk substrate or base layer itself.
In addition, when the term `bulk body` is used herein, it may refer
to the base layer or substrate such as a mono-crystalline bulk
silicon substrate or the bulk substrate of an SOI wafer, such that
the bulk body has a greater heat capacity than the 3D layer/region
structure to which it is thermally connected. Of course, the bulk
body may additionally be connected to a heat sink.
[0056] FIG. 2 illustrates an exemplary 3D integrated circuit that
could be constructed, for example, using techniques described in
U.S. Pat. No. 8,273,610, US patent publications 2012/0091587 and
2013/0020707, and pending U.S. patent application Ser. Nos.
13/441,923 and 13/099,010. The contents of the foregoing patent and
applications are incorporated herein by reference. Two crystalline
layers, 0204 and 0216, which may include semiconductor materials
such as, for example, mono-crystalline silicon, germanium, GaAs,
InP, and graphene, are shown. For this illustration,
mono-crystalline (single crystal) silicon may be used. Silicon
layer 0216 could be thinned down from its original thickness, and
its final thickness could be in the range of about 0.01 um to about
50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5
um. Silicon layer 0204 could be thinned down from its original
thickness, and its final thickness could be in the range of about
0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um,
1 um, 2 um or 5 um; however, due to strength considerations,
silicon layer 0204 may also be of thicknesses greater than 100 um,
depending on, for example, the strength of bonding to heat removal
apparatus 0202. Silicon layer 0204 may include transistors such as,
for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include
gate electrode region 0214, gate dielectric region 0212, source and
drain junction regions (not shown for clarity) and shallow trench
isolation (STI) regions 0210. Silicon layer 0216 may include
transistors such as, for example, MOSFETS, FinFets, BJTs, HEMTs,
HBTs, which may include gate electrode region 0234, gate dielectric
region 0232, source and drain junction regions (not shown for
clarity), and shallow trench isolation (STI) regions 0222. It can
be observed that the STI regions 0222 can go right through to the
bottom of silicon layer 0216 and provide good electrical isolation.
This, however, may cause challenges for heat removal from the STI
surrounded transistors since STI regions 0222 are typically
composed of insulators that do not conduct heat well. Therefore,
the heat spreading capabilities of silicon layer 0216 with STI
regions 0222 are low. A through-layer via (TLV) 0218 may be present
and may include an associated surrounding dielectric region 0220.
Wiring layers 0208 for silicon layer 0204 and wiring dielectric
regions 0206 may be present and may form an associated interconnect
layer or layers. Wiring layers 0238 for silicon layer 0216 and
wiring dielectric 0236 may be present and may form an associated
interconnect layer or layers. Through-layer via (TLV) 0218 may
connect to wiring layers 0208 and wiring layers 0238 (not shown).
The heat removal apparatus 0202 may include a heat spreader and/or
a heat sink. The heat removal problem for the 3D integrated circuit
shown in FIG. 2 is immediately apparent. The silicon layer 0216 may
be far away from the heat removal apparatus 0202, and it may be
difficult to transfer heat among silicon layer 0216 and heat
removal apparatus 0202. Furthermore, wiring dielectric regions 0206
may not conduct heat well, and this increases the thermal
resistance among silicon layer 0216 and heat removal apparatus
0202. The heat removal challenge is further exacerbated by the poor
heat spreading properties of silicon layer 0216 with STI regions
0222. Silicon layer 0204 and silicon layer 0216 may be may be
substantially absent of semiconductor dopants to form an undoped
silicon region or layer, or doped, such as, for example, with
elemental or compound species that form a p+, or p, or p-, or n+,
or n, or n- silicon layer or region. The heat removal apparatus
0202 may include an external surface from which heat transfer may
take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0057] FIG. 3 and FIG. 4 illustrate how the power or ground
distribution network of a 3D integrated circuit could assist heat
removal. FIG. 3 illustrates an exemplary power distribution network
or structure of the 3D integrated circuit. As shown in FIGS. 1 and
2, a 3D integrated circuit, could, for example, be constructed with
two silicon layers, first silicon layer 0304 and second silicon
layer 0316. The heat removal apparatus 0302 could include, for
example, a heat spreader and/or a heat sink. The power distribution
network or structure could consist of a global power grid 0310 that
takes the supply voltage (denoted as V.sub.DD) from the
chip/circuit power pads and transfers V.sub.DD to second local
power grid 0308 and first local power grid 0306, which transfers
the supply voltage to logic/memory cells, transistors, and/or gates
such as second transistor 0314 and first transistor 0315. Second
layer vias 0318 and first layer vias 0312, such as the previously
described TSV or TLV, could be used to transfer the supply voltage
from the global power grid 0310 to second local power grid 0308 and
first local power grid 0306. The global power grid 0310 may also be
present among first silicon layer 0304 and second silicon layer
0316. The 3D integrated circuit could have a similarly designed and
laid-out distribution networks, such as for ground and other supply
voltages, as well. The power grid may be designed and constructed
such that each layer or strata of transistors and devices may be
supplied with a different value Vdd. For example, first silicon
layer 0304 may be supplied by its power grid to have a Vdd value of
1.0 volts and second silicon layer 0316 a Vdd value of 0.8 volts.
Furthermore, the global power grid 0310 wires may be constructed
with substantially higher current conduction, for example 30%
higher, 50% higher, 2.times. higher, than local power grids, for
example, such as first local power grid 0306 wires and second local
power grid 0308 wires. The thickness, linewidth, and material
composition for the global power grid 0310 wires may provide for
the higher current conduction, for example, the thickness of the
global power grid 0310 wires may be twice that of the local power
grid wires and/or the linewidth of the global power grid 0310 wires
may be 2.times. that of the local power grid wires. Moreover, the
global power grid 0310 may be optimally located in the top strata
or layer of transistors and devices. Noise on the power grids, such
as the Vss and/or Vdd supply grids, may be mitigated by
attaching/connecting decoupling capacitors onto the power
conducting lines of the grid(s), such as global power grid 0310,
first local power grid 0306 wires and second local power grid 0308
wires. The decoupling caps may include, for example, trench
capacitors such as described by Pei, C., et al., "A novel, low-cost
deep trench decoupling capacitor for high-performance, low-power
bulk CMOS applications," ICSICT (9.sup.th International Conference
on Solid-State and Integrated-Circuit Technology) 2008, October
2008, pp. 1146-1149, of IBM. The decoupling capacitors may include,
for example, planar capacitors, such as poly to substrate or poly
to poly, or MiM capacitors (Metal-Insulator-Metal).
[0058] Typically, many contacts may be made among the supply and
ground distribution networks and first silicon layer 0304. Due to
this, there could exist a low thermal resistance among the
power/ground distribution network and the heat removal apparatus
0302. Since power/ground distribution networks may be typically
constructed of conductive metals and could have low effective
electrical resistance, the power/ground distribution networks could
have a low thermal resistance as well. Each logic/memory cell or
gate on the 3D integrated circuit (such as, for example, second
transistor 0314) is typically connected to V.sub.DD and ground, and
therefore could have contacts to the power and ground distribution
network. The contacts could help transfer heat efficiently (for
example, with low thermal resistance) from each logic/memory cell
or gate on the 3D integrated circuit (such as, for example, second
transistor 0314) to the heat removal apparatus 0302 through the
power/ground distribution network and the silicon layer 0304.
Silicon layer 0304 and silicon layer 0316 may be may be
substantially absent of semiconductor dopants to form an undoped
silicon region or layer, or doped, such as, for example, with
elemental or compound species that form a p+, or p, or p-, or n+,
or n, or n- silicon layer or region. The heat removal apparatus
0302 may include an external surface from which heat transfer may
take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0059] FIG. 4 illustrates an exemplary NAND logic cell or NAND gate
0420 and how substantially all portions of this logic cell or gate
could be designed and laid-out with low thermal resistance to the
V.sub.DD or ground (GND) contacts. The NAND gate 0420 could include
two pMOS transistors 0402 and two nMOS transistors 0404. The layout
of the NAND gate 0420 is indicated in exemplary layout 0422.
Various regions of the layout may include metal regions 0406, poly
regions 0408, n type silicon regions 0410, p type silicon regions
0412, contact regions 0414, and oxide regions 0424. pMOS
transistors 0416 and nMOS transistors 0418 may be present in the
layout. It can be observed that substantially all parts of the
exemplary NAND gate 0420 could have low thermal resistance to
V.sub.DD or GND contacts since they may be physically very close to
them, within a few design rule lambdas, wherein lamda is the basic
minimum layout rule distance for a given set of circuit layout
design rules. Thus, substantially all transistors in the NAND gate
0420 can be maintained at desirable temperatures, such as, for
example, less than 25 or 50 or 70 degrees Centigrade, if the
V.sub.DD or ground contacts are maintained at desirable
temperatures.
[0060] While the previous paragraph described how an existing power
distribution network or structure can transfer heat efficiently
from logic/memory cells or gates in 3D-ICs to their heat sink, many
techniques to enhance this heat transfer capability will be
described herein. Many embodiments of the invention can provide
several benefits, including lower thermal resistance and the
ability to cool higher power 3D-ICs. As well, thermal contacts may
provide mechanical stability and structural strength to low-k Back
End Of Line (BEOL) structures, which may need to accommodate shear
forces, such as from CMP and/or cleaving processes. The heat
transfer capability enhancement techniques may be useful and
applied to different methodologies and implementations of 3D-ICs,
including monolithic 3D-ICs and TSV-based 3D-ICs. The heat removal
apparatus employed, which may include heat sinks and heat
spreaders, may include an external surface from which heat transfer
may take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0061] FIG. 5 illustrates an embodiment of the invention, wherein
thermal contacts in a 3D-IC is described. The 3D-IC and associated
power and ground distribution network may be formed as described in
FIGS. 1, 2, 3, and 4 herein. For example, two crystalline layers,
0504 and 0516, which may include semiconductor materials such as,
for example, mono-crystalline silicon, germanium, GaAs, InP, and
graphene, may have transistors. For this illustration,
mono-crystalline (single crystal) silicon may be used. Silicon
layer 0516 could be thinned down from its original thickness, and
its final thickness could be in the range of about 0.01 um to about
50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5
um. Silicon layer 0504 could be thinned down from its original
thickness, and its final thickness could be in the range of about
0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um,
1 um, 2 um or 5 um; however, due to strength considerations,
silicon layer 0504 may also be of thicknesses greater than 100 um,
depending on, for example, the strength of bonding to heat removal
apparatus 0202. Silicon layer 0504 may include transistors such as,
for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include
STI regions 0510, gate dielectric regions 0512, gate electrode
regions 0514 and several other regions that may be necessary for
transistors such as source and drain junction regions (not shown
for clarity). Silicon layer 0516 may include transistors such as,
for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include
STI regions 0530, gate dielectric regions 0532, gate electrode
regions 0534 and several other regions that may be necessary for
transistors such as source and drain junction regions (not shown
for clarity). Heat removal apparatus 0502 may include, for example,
heat spreaders and/or heat sinks. In the example shown in FIG. 5,
silicon layer 0504 is closer to the heat removal apparatus 0502
than other silicon layers such as silicon layer 0516. Wiring layers
0542 for silicon layer 0504 and wiring dielectric 0546 may be
present and may form an associated interconnect layer or layers.
Wiring layers 0522 for silicon layer 0516 and wiring dielectric
0506 may be present and may form an associated interconnect layer
or layers. Through-layer vias (TLVs) 0518 for power delivery and
interconnect and their associated dielectric regions 0520 are
shown. Dielectric regions 0520 may include STI regions, such as STI
regions 0530. A thermal contact 0524 may connect the local power
distribution network or structure to the silicon layer 0504. The
local power distribution network or structure may include wiring
layers 0542 used for transistors in the silicon layer 0504. Thermal
junction region 0526 can be, for example, a doped or undoped region
of silicon, and further details of thermal junction region 0526
will be given in FIG. 6. The thermal contact 0524 can be suitably
placed close to the corresponding through-layer via 0518; this
helps transfer heat efficiently as a thermal conduction path from
the through-layer via 0518 to thermal junction region 0526 and
silicon layer 0504 and ultimately to the heat removal apparatus
0502. For example, the thermal contact 0524 could be located within
approximately 2 um distance of the through-layer via 0518 in the
X-Y plane (the through-layer via 0518 vertical length direction is
considered the Z plane in FIG. 5). While the thermal contact 0524
is described above as being between the power distribution network
or structure and the silicon layer closest to the heat removal
apparatus, it could also be between the ground distribution network
and the silicon layer closest to the heat sink. Furthermore, more
than one thermal contact 0524 can be placed close to the
through-layer via 0518. The thermal contacts can improve heat
transfer from transistors located in higher layers of silicon such
as silicon layer 0516 to the heat removal apparatus 0502. While
mono-crystalline silicon has been mentioned as the transistor
material in this document, other options are possible including,
for example, poly-crystalline silicon, mono-crystalline germanium,
mono-crystalline III-V semiconductors, graphene, and various other
semiconductor materials with which devices, such as transistors,
may be constructed within. Moreover, thermal contacts and vias may
not be stacked in a vertical line through multiple stacks, layers,
strata of circuits. Thermal contacts and vias may include materials
such as sp2 carbon as conducting and sp3 carbon as non-conducting
of electrical current. Thermal contacts and vias may include
materials such as carbon nano-tubes. Thermal contacts and vias may
include materials such as, for example, copper, aluminum, tungsten,
titanium, tantalum, cobalt metals and/or silicides of the metals.
Silicon layer 0504 and silicon layer 0516 may be may be
substantially absent of semiconductor dopants to form an undoped
silicon region or layer, or doped, such as, for example, with
elemental or compound species that form a p+, or p, or p-, or n+,
or n, or n- silicon layer or region. The heat removal apparatus
0502 may include an external surface from which heat transfer may
take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0062] FIG. 6 describes an embodiment of the invention, wherein
various implementations of thermal junctions and associated thermal
contacts are illustrated. P-wells in CMOS integrated circuits may
be typically biased to ground and N-wells may be typically biased
to the supply voltage V.sub.DD. A thermal contact 0604 between the
power (V.sub.DD) distribution network and a P-well 0602 can be
implemented as shown in N+ in P-well thermal junction and contact
example 0608, where an n+ doped region thermal junction 0606 may be
formed in the P-well region at the base of the thermal contact
0604. The n+ doped region thermal junction 0606 ensures a reverse
biased p-n junction can be formed in N+ in P-well thermal junction
and contact example 0608 and makes the thermal contact viable (for
example, not highly conductive) from an electrical perspective. The
thermal contact 0604 could be formed of a conductive material such
as copper, aluminum or some other material with a thermal
conductivity of at least 100 W/m-K. A thermal contact 0614 between
the ground (GND) distribution network and a P-well 0612 can be
implemented as shown in P+ in P-well thermal junction and contact
example 0618, where a p+ doped region thermal junction 0616 may be
formed in the P-well region at the base of the thermal contact
0614. The p+ doped region thermal junction 0616 makes the thermal
contact viable (for example, not highly conductive) from an
electrical perspective. The p+ doped region thermal junction 0616
and the P-well 0612 may typically be biased at ground potential.
The thermal contact 0614 could be formed of a conductive material
such as copper, aluminum or some other material with a thermal
conductivity of at least 100 W/m-K. A thermal contact 0624 between
the power (V.sub.DD) distribution network and an N-well 0622 can be
implemented as shown in N+ in N-well thermal junction and contact
example 0628, wherein an n+ doped region thermal junction 0626 may
be formed in the N-well region at the base of the thermal contact
0624. The n+ doped region thermal junction 0626 makes the thermal
contact viable (for example, not highly conductive) from an
electrical perspective. The n+ doped region thermal junction 0626
and the N-well 0622 may typically be biased at V.sub.DD potential.
The thermal contact 0624 could be formed of a conductive material
such as copper, aluminum or some other material with a thermal
conductivity of at least 100 W/m-K. A thermal contact 0634 between
the ground (GND) distribution network and an N-well 0632 can be
implemented as shown in P+ in N-well thermal junction and contact
example 0638, where a p+ doped region thermal junction 0636 may be
formed in the N-well region at the base of the thermal contact
0634. The p+ doped region thermal junction 0636 makes the thermal
contact viable (for example, not highly conductive) from an
electrical perspective due to the reverse biased p-n junction
formed in P+ in N-well thermal junction and contact example 0638.
The thermal contact 0634 could be formed of a conductive material
such as copper, aluminum or some other material with a thermal
conductivity of at least 100 W/m-K. Note that the thermal contacts
are designed to conduct negligible electricity, and the current
flowing through them is several orders of magnitude lower than the
current flowing through a transistor when it is switching.
Therefore, the thermal contacts can be considered to be designed to
conduct heat and conduct negligible (or no) electricity.
[0063] FIG. 7 describes an embodiment of the invention, wherein an
additional type of thermal contact structure is illustrated. The
embodiment shown in FIG. 7 could also function as a decoupling
capacitor to mitigate power supply noise. It could consist of a
thermal contact 0704, an electrode 0710, a dielectric 0706 and
P-well 0702. The dielectric 0706 may be electrically insulating,
and could be optimized to have high thermal conductivity.
Dielectric 0706 could be formed of materials, such as, for example,
hafnium oxide, silicon dioxide, other high k dielectrics, carbon,
carbon based material, or various other dielectric materials with
electrical conductivity below 1 nano-amp per square micron.
[0064] A thermal connection may be defined as the combination of a
thermal contact and a thermal junction. The thermal connections
illustrated in FIG. 6, FIG. 7 and other figures in this document
are designed into a chip to remove heat, and are designed to not
conduct electricity. Essentially, a semiconductor device including
power distribution wires is described wherein some of said wires
have a thermal connection designed to conduct heat to the
semiconductor layer and the wires do not substantially conduct
electricity through the thermal connection to the semiconductor
layer.
[0065] Thermal contacts similar to those illustrated in FIG. 6 and
FIG. 7 can be used in the white spaces of a design, for example,
locations of a design where logic gates or other useful
functionality may not be present. The thermal contacts may connect
white-space silicon regions to power and/or ground distribution
networks. Thermal resistance to the heat removal apparatus can be
reduced with this approach. Connections among silicon regions and
power/ground distribution networks can be used for various device
layers in the 3D stack, and may not be restricted to the device
layer closest to the heat removal apparatus. A Schottky contact or
diode may also be utilized for a thermal contact and thermal
junction. Moreover, thermal contacts and vias may not have to be
stacked in a vertical line through multiple stacks, layers, strata
of circuits.
[0066] FIG. 8 illustrates an embodiment of the invention, which can
provide enhanced heat removal from 3D-ICs by integrating heat
spreader regions in stacked device layers. The 3D-IC and associated
power and ground distribution network may be formed as described in
FIGS. 1, 2, 3, 4, and 5 herein. For example, two crystalline
layers, 0804 and 0816, which may include semiconductor materials
such as, for example, mono-crystalline silicon, germanium, GaAs,
InP, and graphene, are shown. For this illustration,
mono-crystalline (single crystal) silicon may be used. Silicon
layer 0816 could be thinned from its original thickness, and its
final thickness could be in the range of about 0.01 um to about 50
um, for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5 um.
Silicon layer 0804 could be thinned down from its original
thickness, and its final thickness could be in the range of about
0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um,
1 um, 2 um or 5 um; however, due to strength considerations,
silicon layer 0804 may also be of thicknesses greater than 100 um,
depending on, for example, the strength of bonding to heat removal
apparatus 0802. Silicon layer 0804 may include transistors such as,
for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include
gate electrode region 0814, gate dielectric region 0812, shallow
trench isolation (STI) regions 0810 and several other regions that
may be necessary for transistors such as source and drain junction
regions (not shown for clarity). Silicon layer 0816 may include
transistors such as, for example, MOSFETS, FinFets, BJTs, HEMTs,
HBTs, which may include gate electrode region 0834, gate dielectric
region 0832, shallow trench isolation (STI) regions 0822 and
several other regions that may be necessary for transistors such as
source and drain junction regions (not shown for clarity). A
through-layer via (TLV) 0818 may be present and may include an
associated surrounding dielectric region 0820. Wiring layers 0808
for silicon layer 0804 and wiring dielectric 0806 may be present
and may form an associated interconnect layer or layers. Wiring
layers 0838 for silicon layer 0816 and wiring dielectric 0836 may
be present and may form an associated interconnect layer or layers.
Through-layer via (TLV) 0818 may connect to wiring layers 0808 and
wiring layers 0838 (not shown). The heat removal apparatus 0802 may
include, for example, a heat spreader and/or a heat sink. It can be
observed that the STI regions 0822 can go right through to the
bottom of silicon layer 0816 and provide good electrical isolation.
This, however, may cause challenges for heat removal from the STI
surrounded transistors since STI regions 0822 are typically
composed of insulators that do not conduct heat well. The buried
oxide layer 0824 typically does not conduct heat well. To tackle
heat removal issues with the structure shown in FIG. 8, a heat
spreader 0826 may be integrated into the 3D stack. The heat
spreader 0826 material may include, for example, copper, aluminum,
graphene, diamond, carbon or any other material with a high thermal
conductivity (defined as greater than 10 W/m-K). While the heat
spreader concept for 3D-ICs is described with an architecture
similar to FIG. 2, similar heat spreader concepts could be used for
architectures similar to FIG. 1, and also for other 3D IC
architectures. Silicon layer 0804 and silicon layer 0816 may be may
be substantially absent of semiconductor dopants to form an undoped
silicon region or layer, or doped, such as, for example, with
elemental or compound species that form a p+, or p, or p-, or n+,
or n, or n- silicon layer or region. The heat removal apparatus
0802 may include an external surface from which heat transfer may
take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0067] FIG. 9 illustrates an embodiment of the invention, which can
provide enhanced heat removal from 3D-ICs by using thermally
conductive shallow trench isolation (STI) regions in stacked device
layers. The 3D-IC and associated power and ground distribution
network may be formed as described in FIGS. 1, 2, 3, 4, 5 and 8
herein. For example, two crystalline layers, 0904 and 0916, which
may include semiconductor materials such as, for example,
mono-crystalline silicon, germanium, GaAs, InP, and graphene, are
shown. For this illustration, mono-crystalline (single crystal)
silicon may be used. Silicon layer 0916 could be thinned from its
original thickness, and its final thickness could be in the range
of about 0.01 um to about 50 um, for example, 10 nm, 100 nm, 200
nm, 0.4 um, 1 um, 2 um or 5 um. Silicon layer 0904 could be thinned
down from its original thickness, and its final thickness could be
in the range of about 0.01 um to about 50 um, for example, 10 nm,
100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5 um; however, due to
strength considerations, silicon layer 0904 may also be of
thicknesses greater than 100 um, depending on, for example, the
strength of bonding to heat removal apparatus 0802. Silicon layer
0904 may include transistors such as, for example, MOSFETS,
FinFets, BJTs, HEMTs, HBTs, which may include gate electrode region
0914, gate dielectric region 0912, shallow trench isolation (STI)
regions 0910 and several other regions that may be necessary for
transistors such as source and drain junction regions (not shown
for clarity). Silicon layer 0916 may include transistors such as,
for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include
gate electrode region 0934, gate dielectric region 0932, shallow
trench isolation (STI) regions 0922 and several other regions that
may be necessary for transistors such as source and drain junction
regions (not shown for clarity). A through-layer via (TLV) 0918 may
be present and may include an associated surrounding dielectric
region 0920. Dielectric region 0920 may include a shallow trench
isolation region. Wiring layers 0908 for silicon layer 0904 and
wiring dielectric 0906 may be present and may form an associated
interconnect layer or layers. Wiring layers 0938 for silicon layer
0916 and wiring dielectric 0936 may be present and may form an
associated interconnect layer or layers. Through-layer via (TLV)
0918 may connect to wiring layers 0908 and wiring layers 0938 (not
shown). The heat removal apparatus 0902 may include a heat spreader
and/or a heat sink. It can be observed that the STI regions 0922
can go right through to the bottom of silicon layer 0916 and
provide good electrical isolation. This, however, may cause
challenges for heat removal from the STI surrounded transistors
since STI regions 0922 are typically composed of insulators such as
silicon dioxide that do not conduct heat well. To tackle possible
heat removal issues with the structure shown in FIG. 9, the STI
regions 0922 in stacked silicon layers such as silicon layer 0916
could be formed substantially of thermally conductive dielectrics
including, for example, diamond, carbon, or other dielectrics that
have a thermal conductivity higher than silicon dioxide and/or have
a thermal conductivity higher than 0.6 W/m-K. This structure can
provide enhanced heat spreading in stacked device layers. Thermally
conductive STI dielectric regions could be used in the vicinity of
the transistors in stacked 3D device layers and may also be
utilized as the dielectric that surrounds TLV 0918, such as
dielectric region 0920. While the thermally conductive shallow
trench isolation (STI) regions concept for 3D-ICs is described with
an architecture similar to FIG. 2, similar thermally conductive
shallow trench isolation (STI) regions concepts could be used for
architectures similar to FIG. 1, and also for other 3D IC
architectures and 2D IC as well. Silicon layer 0904 and silicon
layer 0916 may be may be substantially absent of semiconductor
dopants to form an undoped silicon region or layer, or doped, such
as, for example, with elemental or compound species that form a p+,
or p, or p-, or n+, or n, or n- silicon layer or region. The heat
removal apparatus 0902 may include an external surface from which
heat transfer may take place by methods such as air cooling, liquid
cooling, or attachment to another heat sink or heat spreader
structure.
[0068] FIG. 10 illustrates an embodiment of the invention, which
can provide enhanced heat removal from 3D-ICs using thermally
conductive pre-metal dielectric regions in stacked device layers.
The 3D-IC and associated power and ground distribution network may
be formed as described in FIGS. 1, 2, 3, 4, 5, 8 and 9 herein. For
example, two crystalline layers, 1004 and 1016, which may include
semiconductor materials such as, for example, mono-crystalline
silicon, germanium, GaAs, InP, and graphene, are shown. For this
illustration, mono-crystalline (single crystal) silicon may be
used. Silicon layer 1016 could be thinned from its original
thickness, and its final thickness could be in the range of about
0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um,
1 um, 2 um or 5 um. Silicon layer 1004 could be thinned down from
its original thickness, and its final thickness could be in the
range of about 0.01 um to about 50 um, for example, 10 nm, 100 nm,
200 nm, 0.4 um, 1 um, 2 um or 5 um; however, due to strength
considerations, silicon layer 1004 may also be of thicknesses
greater than 100 um, depending on, for example, the strength of
bonding to heat removal apparatus 1002. Silicon layer 1004 may
include transistors such as, for example, MOSFETS, FinFets, BJTs,
HEMTs, HBTs, which may include gate electrode region 1014, gate
dielectric region 1012, shallow trench isolation (STI) regions 1010
and several other regions that may be necessary for transistors
such as source and drain junction regions (not shown for clarity).
Silicon layer 1016 may include transistors such as, for example,
MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include gate
electrode region 1034, gate dielectric region 1032, shallow trench
isolation (STI) regions 1022 and several other regions that may be
necessary for transistors such as source and drain junction regions
(not shown for clarity). A through-layer via (TLV) 1018 may be
present and may include an associated surrounding dielectric region
1020, which may include an STI region. Wiring layers 1008 for
silicon layer 1004 and wiring dielectric 1006 may be present and
may form an associated interconnect layer or layers. Wiring layers
1038 for silicon layer 1016 and wiring dielectric 1036 may be
present and may form an associated interconnect layer or layers.
Through-layer via (TLV) 1018 may connect to wiring layers 1008 (not
shown). The heat removal apparatus 1002 may include, for example, a
heat spreader and/or a heat sink. It can be observed that the STI
regions 1022 can go right through to the bottom of silicon layer
1016 and provide good electrical isolation. This, however, can
cause challenges for heat removal from the STI surrounded
transistors since STI regions 1022 are typically filled with
insulators such as silicon dioxide that do not conduct heat well.
To tackle this issue, the inter-layer dielectrics (ILD) 1024 for
contact region 1026 could be constructed substantially with a
thermally conductive material, such as, for example, insulating
carbon, diamond, diamond like carbon (DLC), and various other
materials that provide better thermal conductivity than silicon
dioxide or have a thermal conductivity higher than 0.6 W/m-K.
Thermally conductive pre-metal dielectric regions could be used
around some of the transistors in stacked 3D device layers. While
the thermally conductive pre-metal dielectric regions concept for
3D-ICs is described with an architecture similar to FIG. 2, similar
thermally conductive pre-metal dielectric region concepts could be
used for architectures similar to FIG. 1, and also for other 3D IC
architectures and 2D IC as well. Silicon layer 1004 and silicon
layer 1016 may be may be substantially absent of semiconductor
dopants to form an undoped silicon region or layer, or doped, such
as, for example, with elemental or compound species that form a p+,
or p, or p-, or n+, or n, or n- silicon layer or region. The heat
removal apparatus 1002 may include an external surface from which
heat transfer may take place by methods such as air cooling, liquid
cooling, or attachment to another heat sink or heat spreader
structure.
[0069] FIG. 11 describes an embodiment of the invention, which can
provide enhanced heat removal from 3D-ICs using thermally
conductive etch stop layers or regions for the first metal level of
stacked device layers. The 3D-IC and associated power and ground
distribution network may be formed as described in FIGS. 1, 2, 3,
4, 5, 8, 9 and 10 herein. For example, two crystalline layers, 1104
and 1116, which may include semiconductor materials such as, for
example, mono-crystalline silicon, germanium, GaAs, InP, and
graphene, are shown. For this illustration, mono-crystalline
(single crystal) silicon may be used. Silicon layer 1116 could be
thinned from its original thickness, and its final thickness could
be in the range of about 0.01 um to about 50 um, for example, 10
nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5 um. Silicon layer 1104
could be thinned down from its original thickness, and its final
thickness could be in the range of about 0.01 um to about 50 um,
for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5 um;
however, due to strength considerations, silicon layer 1104 may
also be of thicknesses greater than 100 um, depending on, for
example, the strength of bonding to heat removal apparatus 1102.
Silicon layer 1104 may include transistors such as, for example,
MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include gate
electrode region 1114, gate dielectric region 1112, shallow trench
isolation (STI) regions 1110 and several other regions that may be
necessary for transistors such as source and drain junction regions
(not shown for clarity). Silicon layer 1116 may include transistors
such as, for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which
may include gate electrode region 1134, gate dielectric region
1132, shallow trench isolation (STI) regions 1122 and several other
regions that may be necessary for transistors such as source and
drain junction regions (not shown for clarity). A through-layer via
(TLV) 1118 may be present and may include an associated surrounding
dielectric region 1120. Wiring layers 1108 for silicon layer 1104
and wiring dielectric 1106 may be present and may form an
associated interconnect layer or layers. Wiring layers for silicon
layer 1116 may include first metal layer 1128 and other metal
layers 1138 and wiring dielectric 1136 and may form an associated
interconnect layer or layers. The heat removal apparatus 1102 may
include, for example, a heat spreader and/or a heat sink. It can be
observed that the STI regions 1122 can go right through to the
bottom of silicon layer 1116 and provide good electrical isolation.
This, however, can cause challenges for heat removal from the STI
surrounded transistors since STI regions 1122 are typically filled
with insulators such as silicon dioxide that do not conduct heat
well. To tackle this issue, etch stop layer 1124 as part of the
process of constructing the first metal layer 1128 of silicon layer
1116 can be substantially constructed out of a thermally conductive
but electrically isolative material. Examples of such thermally
conductive materials could include insulating carbon, diamond,
diamond like carbon (DLC), and various other materials that provide
better thermal conductivity than silicon dioxide and silicon
nitride, and/or have thermal conductivity higher than 0.6 W/m-K.
Thermally conductive etch-stop layer dielectric regions could be
used for the first metal layer above transistors in stacked 3D
device layers. While the thermally conductive etch stop layers or
regions concept for 3D-ICs is described with an architecture
similar to FIG. 2, similar thermally conductive etch stop layers or
regions concepts could be used for architectures similar to FIG. 1,
and also for other 3D IC architectures and 2D IC as well. Silicon
layer 1104 and silicon layer 1116 may be may be substantially
absent of semiconductor dopants to form an undoped silicon region
or layer, or doped, such as, for example, with elemental or
compound species that form a p+, or p, or p-, or n+, or n, or n-
silicon layer or region. The heat removal apparatus 1102 may
include an external surface from which heat transfer may take place
by methods such as air cooling, liquid cooling, or attachment to
another heat sink or heat spreader structure.
[0070] FIG. 12A-B describes an embodiment of the invention, which
can provide enhanced heat removal from 3D-ICs using thermally
conductive layers or regions as part of pre-metal dielectrics for
stacked device layers. The 3D-IC and associated power and ground
distribution network may be formed as described in FIGS. 1, 2, 3,
4, 5, 8, 9, 10 and 11 herein. For example, two crystalline layers,
1204 and 1216, are shown and may have transistors. For this
illustration, mono-crystalline (single crystal) silicon may be
used. Silicon layer 1216 could be thinned from its original
thickness, and its final thickness could be in the range of about
0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um,
1 um, 2 um or 5 um. Silicon layer 1204 could be thinned down from
its original thickness, and its final thickness could be in the
range of about 0.01 um to about 50 um, for example, 10 nm, 100 nm,
200 nm, 0.4 um, 1 um, 2 um or 5 um; however, due to strength
considerations, silicon layer 1204 may also be of thicknesses
greater than 100 um, depending on, for example, the strength of
bonding to heat removal apparatus 1202. Silicon layer 1204 may
include transistors such as, for example, MOSFETS, FinFets, BJTs,
HEMTs, HBTs, which may include gate electrode region 1214, gate
dielectric region 1212, shallow trench isolation (STI) regions 1210
and several other regions that may be necessary for transistors
such as source and drain junction regions (not shown for clarity).
Silicon layer 1216 may include transistors such as, for example,
MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include gate
electrode region 1234, gate dielectric region 1232, shallow trench
isolation (STI) regions 1222 and several other regions that may be
necessary for transistors such as source and drain junction regions
(not shown for clarity). A through-layer via (TLV) 1218 may be
present and may include an associated surrounding dielectric region
1220. Wiring layers 1208 for silicon layer 1204 and wiring
dielectric 1206 may be present and may form an associated
interconnect layer or layers. Through-layer via (TLV) 1218 may
connect to wiring layers 1208 and future wiring layers such as
those for interconnection of silicon layer 1216 transistors (not
shown). The heat removal apparatus 1202 may include a heat spreader
and/or a heat sink. It can be observed that the STI regions 1222
can go right through to the bottom of silicon layer 1216 and
provide good electrical isolation. This, however, can cause
challenges for heat removal from the STI surrounded transistors
since STI regions 1222 are typically filled with insulators such as
silicon dioxide that do not conduct heat well. To tackle this
issue, a technique is described in FIG. 12A-B. FIG. 12A illustrates
the formation of openings for making contacts to the transistors of
silicon layer 1216. A hard mask layer 1224 or region is typically
used during the lithography step for contact formation and hard
mask layer 1224 or region may be utilized to define contact opening
regions 1226 of the pre-metal dielectric 1230 that is etched away.
FIG. 12B illustrates the contact 1228 formed after metal is filled
into the contact opening regions 1226 shown in FIG. 12A, and after
a chemical mechanical polish (CMP) process. The hard mask layer
1224 or region used for the process shown in FIG. 12A-B may include
a thermally conductive but electrically isolative material.
Examples of such thermally conductive materials could include
insulating carbon, diamond, diamond like carbon (DLC), and various
other materials that provide better thermal conductivity than
silicon dioxide and silicon nitride, and/or have thermal
conductivity higher than 0.6 W/m-K and can be left behind after the
process step shown in FIG. 12B (hence, electrically
non-conductive). Further steps for forming the 3D-IC (such as
forming additional metal layers) may be performed (not shown).
While the thermally conductive materials for hard mask concept for
3D-ICs is described with an architecture similar to FIG. 2, similar
thermally conductive materials for hard mask concepts could be used
for architectures similar to FIG. 1, and also for other 3D IC
architectures and 2D IC as well. Silicon layer 1204 and silicon
layer 1216 may be may be substantially absent of semiconductor
dopants to form an undoped silicon region or layer, or doped, such
as, for example, with elemental or compound species that form a p+,
or p, or p-, or n+, or n, or n-silicon layer or region. The heat
removal apparatus 1202 may include an external surface from which
heat transfer may take place by methods such as air cooling, liquid
cooling, or attachment to another heat sink or heat spreader
structure.
[0071] FIG. 13 illustrates the layout of an exemplary 4-input NAND
gate 1300, where the output OUT is a function of inputs A, B, C and
D. 4-input NAND gate 1300 may include metal 1 regions 1306, gate
regions 1308, N-type silicon regions 1310, P-type silicon regions
1312, contact regions 1314, and oxide isolation regions 1316. If
the 4-input NAND gate 1300 is used in 3D IC stacked device layers,
some regions of the NAND gate (such as, for example, sub-region
1318 of N-type silicon regions 1310) are far away from V.sub.DD and
GND contacts of 4-input NAND gate 1300. The regions, such as
sub-region 1318, could have a high thermal resistance to V.sub.DD
and GND contacts, and could heat up to undesired temperatures. This
is because the regions of the NAND gate far away from V.sub.DD and
GND contacts cannot effectively use the low-thermal resistance
power delivery network to transfer heat to the heat removal
apparatus.
[0072] FIG. 14 illustrates an embodiment of the invention wherein
the layout of exemplary 3D stackable 4-input NAND gate 1400 can be
modified so that substantially all parts of the gate are at
desirable temperatures during chip operation. Desirable
temperatures during chip operation may depend on the type of
transistors, circuits, and product application & use, and may
be, for example, sub-150.degree. C., sub-100.degree. C.,
sub-75.degree. C., sub-50.degree. C. or sub-25.degree. C. Inputs to
the 3D stackable 4-input NAND gate 1400 are denoted as A, B, C and
D, and the output is denoted as OUT. The 4-input NAND gate 1400 may
include metal 1 regions 1406, gate regions 1408, N-type silicon
regions 1410, P-type silicon regions 1412, contact regions 1414,
and oxide isolation regions 1416. As discussed above, sub-region
1418 could have a high thermal resistance to V.sub.DD and GND
contacts and could heat up to undesired temperatures. Thermal
contact 1420 (whose implementation can be similar to those
described in FIG. 6 and FIG. 7) may be added to the layout, for
example as shown in FIG. 13, to keep the temperature of sub-region
1418 within desirable limits by reducing the thermal resistance
from sub-region 1418 to the GND distribution network. Several other
implementations of adding and placement of thermal contacts that
would be appreciated by persons of ordinary skill in the art can be
used to make the exemplary layout shown in FIG. 14 more desirable
from a thermal perspective.
[0073] FIG. 15 illustrates the layout of an exemplary transmission
gate 1500 with control inputs A and A' (A' typically the inversion
of A). Transmission gate 1500 may include metal 1 regions 1506,
gate regions 1508, N-type silicon regions 1510, P-type silicon
regions 1512, contact regions 1514, and oxide isolation regions
1516. If transmission gate 1500 is used in 3D IC stacked device
layers, some regions of the transmission gate could heat up to
undesired temperatures since there are no V.sub.DD and GND
contacts. There could be a high thermal resistance to V.sub.DD and
GND distribution networks. Thus, the transmission gate cannot
effectively use the low-thermal resistance power delivery network
to transfer heat to the heat removal apparatus. Transmission gate
is one example of transistor function that might not include any
connection to the power grid and accordingly there may not be a
good thermal path to remove the built-up heat. Sometimes in a 3D
structure the transistor isolation may be achieved by etching
around the transistor or transistor function substantially all of
the silicon and filling it with an electrically isolative material,
such as, for example, silicon oxides, which might have a poor
thermal conduction. As such, the transistor or transistor function
may not have an effective thermal path to remove heat build-up.
There are other functions, such as, for example, SRAM select
transistors and Look-Up-Table select transistors, which may use
transistors with no power grid (Vdd, Vss) connections (may only
have signal connections) which may be subject to the same heat
removal problem.
[0074] FIG. 16 illustrates an embodiment of the invention wherein
the layout of exemplary 3D stackable transmission gate 1600 can be
modified so that substantially all parts of the gate, channel, and
transistor body are at desirable temperatures during chip
operation. Desirable temperatures during chip operation may depend
on the type of transistors, circuits, and product application &
use, and may be, for example, sub-150.degree. C., sub-100.degree.
C., sub-75.degree. C., sub-50.degree. C. or sub-25.degree. C.
Control signals to the 3D stackable transmission gate 1600 are
denoted as A and A' (A' typically the inversion of A). 3D stackable
transmission gate 1600 may include metal 1 regions 1606, gate
regions 1608, N-type silicon regions 1610, P-type silicon regions
1612, contact regions 1614, and oxide isolation regions 1616.
Thermal contacts, such as, for example thermal contact 1620 and
second thermal contact 1622 (whose implementation can be similar to
those described in FIG. 6 and FIG. 7) may be added to the layout
shown in FIG. 15 to keep the temperature of 3D stackable
transmission gate 1600 within desirable limits (by reducing the
thermal resistance to the V.sub.DD and GND distribution networks).
The thermal paths may use a reverse bias diode in at least one
portion so that the thermal path may conduct heat but does not
conduct current or an electric signal, and accordingly does not
interfere with the proper operation of the transistor function.
Several other implementations of adding and placement of thermal
contacts that would be appreciated by persons of ordinary skill in
the art can be used to make the exemplary layout, such as shown in
FIG. 16, more desirable from a thermal perspective.
[0075] The techniques illustrated with FIG. 14 and FIG. 16 are not
restricted to cells such as transmission gates and NAND gates, and
can be applied to a number of cells such as, for example, SRAMs,
CAMs, multiplexers and many others. Furthermore, the techniques
illustrated with at least FIG. 14 and FIG. 16 can be applied and
adapted to various techniques of constructing 3D integrated
circuits and chips, including those described in U.S. Pat. No.
8,273,610, US patent publications 2012/0091587 and 2013/0020707,
and pending U.S. patent application Ser. Nos. 13/441,923 and
13/099,010. The contents of the foregoing applications are
incorporated herein by reference. Furthermore, techniques
illustrated with FIG. 14 and FIG. 16 (and other similar techniques)
need not be applied to substantially all such gates on the chip,
but could be applied to a portion of gates of that type, such as,
for example, gates with higher activity factor, lower threshold
voltage or higher drive current. Moreover, thermal contacts and
vias may not have to be stacked in a vertical line through multiple
stacks, layers, strata of circuits.
[0076] When a chip is typically designed a cell library consisting
of various logic cells such as NAND gates, NOR gates and other
gates is created, and the chip design flow proceeds using this cell
library. It will be clear to one skilled in the art that a cell
library may be created wherein each cell's layout can be optimized
from a thermal perspective and based on heat removal criteria such
as maximum allowable transistor channel temperature (for example,
where each cell's layout can be optimized such that substantially
all portions of the cell have low thermal resistance to the
V.sub.DD and GND contacts, and therefore, to the power bus and the
ground bus).
[0077] FIG. 24 illustrates a procedure for a chip designer to
ensure a good thermal profile for his or her design. After a first
pass or a portion of the first pass of the desired chip layout
process is complete, a thermal analysis may be conducted to
determine temperature profiles for active or passive elements, such
as gates, on the 3D chip. The thermal analysis may be started
(2400). The temperature of any stacked gate, or region of gates,
may be calculated, for example, by simulation such as a
multi-physics solver, and compared to a desired specification value
(2410). If the gate, or region of gates, temperature is higher than
the specification, which may, for example, be in the range of
65.degree. C.-150.degree. C., modifications (2420) may be made to
the layout or design, such as, for example, power grids for stacked
layers may be made denser or wider, additional contacts to the gate
may be added, more through-silicon (TLV and/or TSV) connections may
be made for connecting the power grid in stacked layers to the
layer closest to the heat sink, or any other method to reduce
stacked layer temperature that may be described herein or in
referenced documents, which may be used alone or in combination.
The output (2430) may give the designer the temperature of the
modified stacked gate (`Yes` tree), or region of gates, or an
unmodified one (`No` tree), and may include the original
un-modified gate temperature that was above the desired
specification. The thermal analysis may end (2440) or may be
iterated. Alternatively, the power grid may be designed (based on
heat removal criteria) simultaneously with the logic gates and
layout of the design, or for various regions of any layer of the 3D
integrated circuit stack. The density of TLVs may be greater than
10.sup.4 per cm.sup.2, and may be 10.times., 100.times.,
1000.times., denser than TSVs.
[0078] Recessed channel transistors form a transistor family that
can be stacked in 3D. FIG. 22 illustrates an exemplary Recessed
Channel Transistor 2200 which may be constructed in a 3D stacked
layer using procedures outlined in U.S. Pat. No. 8,273,610, US
patent publications 2012/0091587 and 2013/0020707, and pending U.S.
patent application Ser. Nos. 13/441,923 and 13/099,010. The
contents of the foregoing patent and applications are incorporated
herein by reference. Recessed Channel Transistor 2200 may include
2202 a bottom layer of transistors and wires 2202, oxide layer
2204, oxide regions 2206, gate dielectric 2208, n+ silicon regions
2210, gate electrode 2212 and region of p- silicon region 2214. The
recessed channel transistor is surrounded on substantially all
sides by thermally insulating oxide layers oxide layer 2204 and
oxide regions 2206, and heat removal may be a serious issue.
Furthermore, to contact the p- silicon region 2214, a p+ region may
be needed to obtain low contact resistance, which may not be easy
to construct at temperatures lower than approximately 400.degree.
C.
[0079] FIG. 17A-D illustrates an embodiment of the invention
wherein thermal contacts can be constructed to a recessed channel
transistor. Note that numbers used in FIG. 17A-D are inter-related.
For example, if a certain number is used in FIG. 17A, it has the
same meaning if present in FIG. 17B. The process flow may begin as
illustrated in FIG. 17A with a bottom layer or layers of
transistors and copper interconnects 1702 being constructed with a
silicon dioxide layer 1704 atop it. Layer transfer approaches
similar to those described in U.S. Pat. No. 8,273,610, US patent
publications 2012/0091587 and 2013/0020707, and pending U.S. patent
application Ser. Nos. 13/441,923 and 13/099,010 may be utilized.
The contents of the foregoing patent and applications are
incorporated herein by reference. An activated layer of p+ silicon
1706, an activated layer of p- silicon 1708 and an activated layer
of n+ silicon 1710 can be transferred atop the structure
illustrated in FIG. 17A to form the structure illustrated in FIG.
17B. FIG. 17C illustrates a next step in the process flow. After
forming isolation regions such as, for example, STI-Shallow Trench
Isolation (not shown in FIG. 17C for simplicity) and thus forming
p+ regions 1707, gate dielectric regions 1716 and gate electrode
regions 1718 could be formed, for example, by etch and deposition
processes, using procedures similar to those described in U.S. Pat.
No. 8,273,610, US patent publications 2012/0091587 and
2013/0020707, and pending U.S. patent application Ser. Nos.
13/441,923 and 13/099,010. Thus, p- silicon region 1712 and n+
silicon regions 1714 may be formed. FIG. 17C thus illustrates an
RCAT (recessed channel transistor) formed with a p+ silicon region
atop copper interconnect regions where the copper interconnect
regions are not exposed to temperatures higher than approximately
400.degree. C. FIG. 17D illustrates a next step of the process
where thermal contacts could be made to the p+ silicon region 1707.
FIG. 17D may include final p- silicon region 1722 and final n+
silicon regions 1720. Via 1724 may be etched and constructed, for
example, of metals (such as Cu, Al, W, degenerately doped Si),
metal silicides (WSi.sub.2) or a combination of the two, and may
include oxide isolation regions 1726. Via 1724 can connect p+
region 1707 to the ground (GND) distribution network. Via 1724
could alternatively be connected to a body bias distribution
network. Via 1724 and final n+ silicon regions 1720 may be
electrically coupled, such as by removal of a portion of an oxide
isolation regions 1726, if desired for circuit reasons (not shown).
The nRCAT could have its body region connected to GND potential (or
body bias circuit) and operate correctly or as desired, and the
heat produced in the device layer can be removed through the
low-thermal resistance GND distribution network to the heat removal
apparatus (not shown for clarity).
[0080] FIG. 18 illustrates an embodiment the invention, which
illustrates the application of thermal contacts to remove heat from
a pRCAT device layer that is stacked above a bottom layer of
transistors and wires 1802. The p-RCAT layer may include 1804
buried oxide region 1804, n+ silicon region 1806, n- silicon region
1814, p+ silicon region 1810, gate dielectric 1808 and gate
electrode 1812. The structure shown in FIG. 18 can be constructed
using methods similar to those described in respect to FIG. 17A-D
above. The thermal contact 1818 could be constructed of, for
example, metals (such as Cu, Al, W, degenerately doped Si), metal
silicides (WSi.sub.2) or a combination of two or more types of
materials, and may include oxide isolation regions 1816. Thermal
contact 1818 may connect n+ region 1806 to the power (V.sub.DD)
distribution network. The pRCAT could have its body region
connected to the supply voltage (V.sub.DD) potential (or body bias
circuit) and operate correctly or as desired, and the heat produced
in the device layer can be removed through the low-thermal
resistance V.sub.DD distribution network to the heat removal
apparatus. Thermal contact 1818 could alternatively be connected to
a body bias distribution network (not shown for clarity). Thermal
contact 1818 and p+ silicon region 1810 may be electrically
coupled, such as by removal of a portion of an oxide isolation
regions 1816, if desired for circuit reasons (not shown).
[0081] FIG. 19 illustrates an embodiment of the invention that
describes the application of thermal contacts to remove heat from a
CMOS device layer that could be stacked atop a bottom layer of
transistors and wires 1902. The CMOS device layer may include
insulator regions 1904, sidewall insulator regions 1924, thermal
via insulator regions 1930, such as silicon dioxide. The CMOS
device layer may include nMOS p+ silicon region 1906, pMOS p+
silicon region 1936, nMOS p- silicon region 1908, pMOS buried p-
silicon region 1912, nMOS n+ silicon regions 1910, pMOS n+ silicon
1914, pMOS n- silicon region 1916, p+ silicon regions 1920, pMOS
gate dielectric region 1918, pMOS gate electrode region 1922, nMOS
gate dielectric region 1934 and nMOS gate electrode region. A nMOS
transistor could therefore be formed of regions 1934, 1928, 1910,
1908 and 1906. A pMOS transistor could therefore be formed of
regions 1914, 1916, 1918, 1920 and 1922. This stacked CMOS device
layer could be formed with procedures similar to those described in
U.S. Pat. No. 8,273,610, US patent publications 2012/0091587 and
2013/0020707, and pending U.S. patent application Ser. Nos.
13/441,923 and 13/099,010 and at least FIG. 17A-D herein. The
thermal contact 1926 may be connected between n+ silicon region
1914 and the power (V.sub.DD) distribution network and helps remove
heat from the pMOS transistor. This is because the pMOSFET could
have its body region connected to the supply voltage (V.sub.DD)
potential or body bias distribution network and operate correctly
or as desired, and the heat produced in the device layer can be
removed through the low-thermal resistance V.sub.DD distribution
network to the heat removal apparatus as previously described. The
thermal contact 1932 may be connected between p+ silicon region
1906 and the ground (GND) distribution network and helps remove
heat from the nMOS transistor. This is because the nMOSFET could
have its body region connected to GND potential or body bias
distribution network and operate correctly or as desired, and the
heat produced in the device layer can be removed through the
low-thermal resistance GND distribution network to the heat removal
apparatus as previously described.
[0082] FIG. 20 illustrates an embodiment of the invention that
describes a technique that could reduce heat-up of transistors
fabricated on silicon-on-insulator (SOI) substrates. SOI substrates
have a buried oxide (BOX) or other insulator between the silicon
transistor regions and the heat sink. This BOX region may have a
high thermal resistance, and makes heat transfer from the
transistor regions to the heat sink difficult. The nMOS transistor
in SOI may include buried oxide regions 2036, BEOL metal insulator
regions 2048, and STI insulator regions 2056, such as silicon
dioxide. The nMOS transistor in SOI may include n+ silicon regions
2046, p- silicon regions 2040, gate dielectric region 2052, gate
electrode region 2054, interconnect wiring regions 2044, and highly
doped silicon substrate 2004. Use of silicon-on-insulator (SOI)
substrates may lead to low heat transfer from the transistor
regions to the heat removal apparatus 2002 through the buried oxide
regions 2036 (generally a layer) that may have low thermal
conductivity. The ground contact 2062 of the nMOS transistor shown
in FIG. 20 can be connected to the ground distribution network
wiring 2064 which in turn can be connected with a low thermal
resistance connection 2050 to highly doped silicon substrate 2004.
This enables low thermal conductivity, a thermal conduction path,
between the transistor shown in FIG. 20 and the heat removal
apparatus 2002. While FIG. 20 described how heat could be
transferred among an nMOS transistor and the heat removal
apparatus, similar approaches can also be used for pMOS
transistors, and many other transistors, for example, FinFets,
BJTs, HEMTs, and HBTs. Many of the aforementioned transistors may
be constructed as fully depleted channel devices. The heat removal
apparatus 2002 may include an external surface from which heat
transfer may take place by methods such as air cooling, liquid
cooling, or attachment to another heat sink or heat spreader
structure.
[0083] FIG. 21 illustrates an embodiment of the invention which
describes a technique that could reduce heat-up of transistors
fabricated on silicon-on-insulator (SOI) substrates. The nMOS
transistor in SOI may include buried oxide regions 2136, BEOL metal
insulator regions 2148, and STI insulator regions 2156, such as
silicon dioxide. The nMOS transistor in SOI may include n+ silicon
regions 2146, p- silicon regions 2140, gate dielectric region 2152,
gate electrode region 2154, interconnect wiring regions 2144, and
highly doped silicon substrate 2104. Use of silicon-on-insulator
(SOI) substrates may lead to low heat transfer from the transistor
regions to the heat removal apparatus 2102 through the buried oxide
regions 2136 (generally a layer) that may have low thermal
conductivity. The ground contact 2162 of the nMOS transistor shown
in FIG. 21 can be connected to the ground distribution network 2164
which in turn can be connected with a low thermal resistance
connection 2150 to highly doped silicon substrate 2104 through an
implanted and activated region 2110. The implanted and activated
region 2110 could be such that thermal contacts similar to those in
FIG. 6 can be formed. This may enable low thermal conductivity, a
thermal conduction path, between the transistor shown in FIG. 21
and the heat removal apparatus 2102. This thermal conduction path,
whilst thermally conductive, may not be electrically conductive
(due to the reverse biased junctions that could be constructed in
the path), and thus, not disturb the circuit operation. While FIG.
21 described how heat could be transferred among the nMOS
transistor and the heat removal apparatus, similar approaches can
also be used for pMOS transistors, and other transistors, for
example, FinFets, BJTs, HEMTs, and HBTs.
[0084] FIG. 23 illustrates an embodiment of the invention wherein
heat spreading regions may be located on the sides of 3D-ICs. The
3D integrated circuit shown in FIG. 23 could be potentially
constructed using techniques described in U.S. Pat. No. 8,273,610,
US patent publications 2012/0091587 and 2013/0020707, and pending
U.S. patent application Ser. Nos. 13/441,923 and 13/099,010. For
example, two crystalline layers, 2304 and 2316, which may include
semiconductor materials such as, for example, mono-crystalline
silicon, germanium, GaAs, InP, and graphene, are shown. For this
illustration, mono-crystalline (single crystal) silicon may be
used. Silicon layer 2316 could be thinned from its original
thickness, and its final thickness could be in the range of about
0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um,
1 um, 2 um or 5 um. Silicon layer 2304 could be thinned down from
its original thickness, and its final thickness could be in the
range of about 0.01 um to about 50 um, for example, 10 nm, 100 nm,
200 nm, 0.4 um, 1 um, 2 um or 5 um; however, due to strength
considerations, silicon layer 2304 may also be of thicknesses
greater than 100 um, depending on, for example, the strength of
bonding to heat removal apparatus 2302. Silicon layer 2304 may
include transistors such as, for example, MOSFETS, FinFets, BJTs,
HEMTs, HBTs, which may include gate electrode region 2314, gate
dielectric region 2312, and shallow trench isolation (STI) regions
2310 and several other regions that may be necessary for
transistors such as source and drain junction regions (not shown
for clarity). Silicon layer 2316 may include transistors such as,
for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include
gate electrode region 2334, gate dielectric region 2332, and
shallow trench isolation (STI) regions 2322 and several other
regions that may be necessary for transistors such as source and
drain junction regions (not shown for clarity). It can be observed
that the STI regions 2322 can go right through to the bottom of
silicon layer 2316 and provide good electrical isolation. A
through-layer via (TLV) 2318 may be present and may include an
associated surrounding dielectric region 2320. Dielectric region
2320 may include a shallow trench isolation region. Wiring layers
2308 for silicon layer 2304 and wiring dielectric 2306 may be
present and may form an associated interconnect layer or layers.
Wiring layers 2338 for silicon layer 2316 and wiring dielectric
2336 may be present and may form an associated interconnect layer
or layers. Through-layer via (TLV) 2318 may connect to wiring
layers 2308 and wiring layers 2338 (not shown). The heat removal
apparatus 2302 may include a heat spreader and/or a heat sink.
Thermally conductive material regions 2340 could be present at the
sides of the 3D-IC shown in FIG. 23. Thermally conductive material
regions 2340 may be formed by sequential layer by layer etch and
fill, or by an end of process etch and fill. Thus, a thermally
conductive heat spreading region could be located on the sidewalls
of a 3D-IC. The thermally conductive material regions 2340 could
include dielectrics such as, for example, insulating carbon,
diamond, diamond like carbon (DLC), and other dielectrics that have
a thermal conductivity higher than silicon dioxide and/or have a
thermal conductivity higher than 0.6 W/m-K. Another method that
could be used for forming thermally conductive material regions
2340 could involve depositing and planarizing the thermally
conductive material at locations on or close to the dicing regions,
such as potential dicing scribe lines (described in U.S. Patent
Application Publication 2012/0129301) of a 3D-IC after an etch
process. The wafer could be diced. Those of ordinary skill in the
art will appreciate that one could combine the concept of having
thermally conductive material regions on the sidewalls of 3D-ICs
with concepts shown in other figures of this patent application,
such as, for example, the concept of having lateral heat spreaders
shown in FIG. 8. Silicon layer 2304 and silicon layer 2316 may be
may be substantially absent of semiconductor dopants to form an
undoped silicon region or layer, or doped, such as, for example,
with elemental or compound species that form a p+, or p, or p-, or
n+, or n, or n- silicon layer or region. The heat removal apparatus
2302 may include an external surface from which heat transfer may
take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0085] FIG. 25 illustrates an exemplary monolithic 3D integrated
circuit. The 3D integrated circuit shown in FIG. 25 could be
potentially constructed using techniques described in U.S. Pat. No.
8,273,610, US patent publications 2012/0091587 and 2013/0020707,
and pending U.S. patent application Ser. Nos. 13/441,923 and
13/099,010. For example, two crystalline layers, 2504 and 2516,
which may include semiconductor materials such as, for example,
mono-crystalline silicon, germanium, GaAs, InP, and graphene, are
shown. For this illustration, mono-crystalline (single crystal)
silicon may be used. Silicon layer 2516 could be thinned from its
original thickness, and its final thickness could be in the range
of about 0.01 um to about 50 um, for example, 10 nm, 100 nm, 200
nm, 0.4 um, 1 um, 2 um or 5 um. Silicon layer 2504 could be thinned
down from its original thickness, and its final thickness could be
in the range of about 0.01 um to about 50 um, for example, 10 nm,
100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5 um; however, due to
strength considerations, silicon layer 2504 may also be of
thicknesses greater than 100 um, depending on, for example, the
strength of bonding to heat removal apparatus 2502. Silicon layer
2504, or silicon substrate, may include transistors such as, for
example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include
gate electrode region 2514, gate dielectric region 2512, transistor
junction regions 2510 and several other regions that may be
necessary for transistors such as source and drain junction regions
(not shown for clarity). Silicon layer 2516 may include transistors
such as, for example, MOSFETS, FinFets, BJTs, HEMTs, HBTs, which
may include gate electrode region 2534, gate dielectric region
2532, transistor junction regions 2530 and several other regions
that may be necessary for transistors such as source and drain
junction regions (not shown for clarity). A through-silicon
connection 2518, or TLV (through-silicon via) could be present and
may have a surrounding dielectric region 2520. Surrounding
dielectric region 2520 may include a shallow trench isolation (STI)
region, such as one of the shallow trench isolation (STI) regions
typically in a 3D integrated circuit stack (not shown). Silicon
layer 2504 may have wiring layers 2508 and wiring dielectric 2506.
Wiring layers 2508 and wiring dielectric 2506 may form an
associated interconnect layer or layers. Silicon layer 2516 may
have wiring layers 2538 and wiring dielectric 2536. Wiring layers
2538 and wiring dielectric 2536 may form an associated interconnect
layer or layers. Wiring layers 2538 and wiring layers 2508 may be
constructed of copper, aluminum or other materials with bulk
resistivity lower than 2.8 uohm-cm. The choice of materials for
through-silicon connection 2518 may be challenging. If copper is
chosen as the material for through-silicon connection 2518, the
co-efficient of thermal expansion (CTE) mismatch between copper and
the surrounding mono-crystalline silicon layer 2516 may become an
issue. Copper has a CTE of approximately 16.7 ppm/K while silicon
has a CTE of approximately 3.2 ppm/K. This large CTE mismatch may
cause reliability issues and the need for large keep-out zones
around the through-silicon connection 2518 wherein transistors
cannot be placed. If transistors are placed within the keep-out
zone of the through-silicon connection 2518, their current-voltage
characteristics may be different from those placed in other areas
of the chip. Similarly, if Aluminum (CTE=23 ppm/K) is used as the
material for through-silicon connection 2518, its CTE mismatch with
the surrounding mono-crystalline silicon layer 2516 could cause
large keep-out zones and reliability issues. Silicon layer 2504 and
silicon layer 2516 may be may be substantially absent of
semiconductor dopants to form an undoped silicon region or layer,
or doped, such as, for example, with elemental or compound species
that form a p+, or p, or p-, or n+, or n, or n- silicon layer or
region.
[0086] An embodiment of the invention utilizes a material for the
through-silicon connection 2518 (TSV or TLV) that may have a CTE
closer to silicon than, for example, copper or aluminum. The
through-silicon connection 2518 may include materials such as, for
example, tungsten (CTE approximately 4.5 ppm/K), highly doped
polysilicon or amorphous silicon or single crystal silicon (CTE
approximately 3 ppm/K), conductive carbon, or some other material
with CTE less than 15 ppm/K. Wiring layers 2538 and wiring layers
2508 may have materials with CTE greater than 15 ppm/K, such as,
for example, copper or aluminum.
[0087] Persons of ordinary skill in the art will appreciate that
the illustrations in FIG. 25 are exemplary only and are not drawn
to scale. Such skilled persons will further appreciate that many
variations are possible such as, for example, the through-silicon
connection 2518 may include materials in addition to those (such as
Tungsten, conductive carbon) described above, for example, liners
and barrier metals such as TiN, TaN, and other materials known in
the art for via, contact, and through silicon via formation.
Moreover, the transistors in silicon layer 2504 may be formed in a
manner similar to silicon layer 2516. Furthermore, through-silicon
connection 2518 may be physically and electrically connected (not
shown) to wiring layers 2508 and wiring layers 2538 by the same
material as the wiring layers 2508/2538, or by the same materials
as the through-silicon connection 2518 composition, or by other
electrically and/or thermally conductive materials not found in the
wiring layers 2508/2538 or the through-silicon connection 2518.
Many other modifications within the scope of the invention will
suggest themselves to such skilled persons after reading this
specification. Thus the invention is to be limited only by the
appended claims.
[0088] Alignment is a basic step in semiconductor processing. In
most cases it is part of the flow that every successive layer is
patterned and aligned to a previous or underneath layer. This
alignment of each layer could all be done to one common alignment
mark, such as for example the zero mark utilized by some ASML
equipment, or to some other alignment mark or marks that are
embedded in a layer underneath the masking layer being aligned. In
today's equipment such alignment would be precise to below 40
nanometers, or 10 nanometers or a few nanometers. In general such
alignment could be observed outside the manufacturing fabrication
facility by comparing two devices processed using the same mask
set. If two layers in one device maintain their relative positions
the same--to few nanometers--as the other device, it is a clear
indication that these layers are one aligned to the other. This
could be achieve by either aligning to the same alignment mark or
one is using alignment mark embedded in the other or using
different alignment marks of layers that are aligned to each other.
Within the manufacturing fabrication facility alignment may be
observed and measured by scanning the post develop, and sometime
post etch, alignment structures such as for example fiducial marks,
or box in box, crosses, etc. as understood by those skilled in the
art.
[0089] When formation of a 3D-IC is discussed herein, crystalline
layers, for example, two crystalline layers, 2504 and 2516, are
utilized to form the monolithic 3D-IC, generally utilizing layer
transfer techniques. Similarly, donor layers and acceptor layers of
crystalline materials which are referred to and utilized in the
referenced US patent documents including U.S. Pat. Nos. 8,273,610,
9,099,526, 9,219,005, 8,557,632 and 8,581,349 may be utilized to
form a monolithic 3D-IC, generally utilizing layer transfer
techniques. The crystalline layers, whether donor or acceptor
layer, may include regions of compound semiconductors, such as, for
example, InP, GaAs, and/or GaN, and regions of mono-crystalline
silicon and/or silicon dioxide. Heterogeneous integration with
short interconnects between the compound semiconductor transistors
and the silicon based transistors (such as CMOS) could be enabled
by placing or constructing Si--CS hetero-layers into a monolithic
3D-IC structure.
[0090] One compelling advantage of the Excico's laser annealing
machine is its output optical system. This optical system forms a
large rectangular window of uniform laser energy with less than 10%
variation over the surface to be annealed, and with sharp edges of
less than 100 micron between the uniform energy and almost no
energy as illustrated in FIG. 49 of incorporated patent reference
U.S. Pat. No. 9,385,058. Accordingly a whole die or even reticle
could be exposed in one shot. By setting the window size and
aligning the laser to the wafer properly, it could allow the laser
annealing process to have the stitching of optical energy, such as
pulsed laser exposures, at a desired area, such as the scribe
street, such as for example lines 104, potential dicing line 104-1,
potential dicing lines 104-2, in FIG. 10 of incorporated patent
reference U.S. Pat. No. 8,273,610 to Or-Bach, et al. Thus, the
laser stitch may be placed between dies, thereby reducing the risk
from uneven exposure at the stitching area affecting any of the
desired circuit transistors or elements. Additionally, the window
size may be set to cover a multiplicity of dice or tiles, such as
end-device 3611 of FIG. 36 of incorporated patent reference U.S.
Pat. No. 8,273,610 to Or-Bach, et al., which may also have
potential dice lines, such as potential dice lines 3602 and/or
actual dice lines, such as actual dice lines 3612. The optical
annealing could be done sequentially across the wafer or in
steppings that substantially cover the entire wafer area but spread
the heat generation to allow better heat removal. Such spreading of
heat generation could be done, for example, by scanning the wafer
surface like a checkerboard, first exposing rectangles or areas
such as the `blacks` of the checkerboard, and then the `white`
locations.
[0091] A planar fully depleted n-channel Recessed Channel Array
Transistor (FD-RCAT) suitable for a monolithic 3D IC may be
constructed as follows. The FD-RCAT may provide an improved source
and drain contact resistance, thereby allowing for lower channel
doping (such as undoped), and the recessed channel may provide for
more flexibility in the engineering of channel lengths and
transistor characteristics, and increased immunity from process
variations. The buried doped layer and channel dopant shaping, even
to an un-doped channel, may allow for efficient adaptive and
dynamic body biasing to control the transistor threshold and
threshold variations, as well as provide for a fully depleted or
deeply depleted transistor channel. Furthermore, the recessed gate
allows for an FD transistor but with thicker silicon for improved
lateral heat conduction. FIG. 26A-F illustrates an exemplary
n-channel FD-RCAT which may be constructed in a 3D stacked layer
using procedures outlined below and in U.S. Pat. Nos. 8,273,610,
9,099,526, 9,219,005, 8,557,632 and 8,581,349. The contents of the
foregoing patent and applications are incorporated herein by
reference.
[0092] As illustrated in FIG. 26A, a P- substrate donor wafer 2600
may be processed to include wafer sized layers of N+ doping 2602,
P- doping 2606, channel 2603 and P+ doping 2604 across the wafer.
The N+ doped layer 2602, P- doped layer 2606, channel layer 2603
and P+ doped layer 2604 may be formed by ion implantation and
thermal anneal. P- substrate donor wafer 2600 may include a
crystalline material, for example, mono-crystalline (single
crystal) silicon. P- doped layer 2606 and channel layer 2603 may
have additional ion implantation and anneal processing to provide a
different dopant level than P- substrate donor wafer 2600. P-
substrate donor wafer 2600 may be very lightly doped (less than
1e15 atoms/cm.sup.3) or nominally un-doped (less than 1e14
atoms/cm.sup.3). P- doped layer 2606, channel layer 2603, and P+
doped layer 2604 may have graded or various layers doping to
mitigate transistor performance issues, such as, for example, short
channel effects, after the FD-RCAT is formed, and to provide
effective body biasing, whether adaptive or dynamic. The layer
stack may alternatively be formed by successive epitaxially
deposited doped silicon layers of N+ doped layer 2602, P- doped
layer 2606, channel layer 2603 and P+ doped layer 2604, or by a
combination of epitaxy and implantation. Annealing of implants and
doping may include, for example, conductive/inductive thermal,
optical annealing techniques or types of Rapid Thermal Anneal (RTA
or spike). The N+ doped layer 2602 may have a doping concentration
that may be more than 10.times. the doping concentration of P-
doped layer 2606 and/or channel layer 2603. The P+ doped layer 2604
may have a doping concentration that may be more than 10.times. the
doping concentration of P- doped layer 2606 and/or channel layer
2603. The P- doped layer 2606 may have a doping concentration that
may be more than 10.times. the doping concentration of channel
layer 2603. Channel layer 2603 may have a thickness and/or doping
that may allow fully-depleted channel operation when the FD-RCAT
transistor is substantially completely formed, such as, for
example, less than 5 nm, less than 10 nm, or less than 20 nm.
[0093] As illustrated in FIG. 26B, the top surface of the P-
substrate donor wafer 2600 layer stack may be prepared for oxide
wafer bonding with a deposition of an oxide or by thermal oxidation
of P+ doped layer 2604 to form oxide layer 2680. A layer transfer
demarcation plane (shown as dashed line) 2699 may be formed by
hydrogen implantation or other methods as described in the
incorporated references. The P- substrate donor wafer 2600 and
acceptor wafer 2610 may be prepared for wafer bonding as previously
described and low temperature (less than approximately 400.degree.
C.) bonded. Acceptor wafer 2610, as described in the incorporated
references, may include, for example, transistors, circuitry, and
metal, such as, for example, aluminum or copper, interconnect
wiring, a metal shield/heat sink layer, and thru layer via metal
interconnect strips or pads. Acceptor wafer 2610 may be
substantially comprised of a crystalline material, for example
mono-crystalline silicon or germanium, or may be an engineered
substrate/wafer such as, for example, an SOI (Silicon on Insulator)
wafer or GeOI (Germanium on Insulator) substrate. The portion of
the N+ doped layer 2602 and the P- substrate donor wafer 2600 that
may be above (when the layer stack is flipped over and bonded to
the acceptor wafer) the layer transfer demarcation plane 2699 may
be removed by cleaving or other low temperature processes as
described in the incorporated references, such as, for example,
ion-cut or other layer transfer methods.
[0094] As illustrated in FIG. 26C, oxide layer 2680, P+ doped layer
2604, channel layer 2603, P- doped layer 2606, and remaining N+
layer 2622 have been layer transferred to acceptor wafer 2610. The
top surface of N+ layer 2622 may be chemically or mechanically
polished. Now transistors may be formed with low effective
temperature (less than approximately 400.degree. C. exposure to the
acceptor wafer 2610 sensitive layers, such as interconnect and
device layers) processing and aligned to the acceptor wafer
alignment marks (not shown) as described in the incorporated
references.
[0095] As illustrated in FIG. 26D, the transistor isolation regions
2605 may be formed by mask defining and plasma/RIE etching
remaining N+ layer 2622, P- doped layer 2606, channel layer 2603,
and P+ doped layer 2604 substantially to the top of oxide layer
2680 (not shown), substantially into oxide layer 2680, or into a
portion of the upper oxide layer of acceptor wafer 2610 (not
shown). Additionally, a portion of the transistor isolation regions
2605 may be etched (separate step) substantially to P+ doped layer
2604, thus allowing multiple transistor regions to be connected by
the same P+ doped region 2624. A low-temperature gap fill oxide may
be deposited and chemically mechanically polished, the oxide
remaining in isolation regions 2605. The recessed channel 2686 may
be mask defined and etched thru remaining N+ doped layer 2622, P-
doped layer 2606 and partially into channel layer 2603. The
recessed channel surfaces and edges may be smoothed by processes,
such as, for example, wet chemical, plasma/RIE etching, low
temperature hydrogen plasma, or low temperature oxidation and strip
techniques, to mitigate high field effects. The low temperature
smoothing process may employ, for example, a plasma produced in a
TEL (Tokyo Electron Labs) SPA (Slot Plane Antenna) machine. Thus N+
source and drain regions 2632, P- regions 2626, and channel region
2623 may be formed, which may substantially form the transistor
body. The doping concentration of N+ source and drain regions 2632
may be more than 10.times. the concentration of channel region
2623. The doping concentration of the N- channel region 2623 may
include gradients of concentration or layers of differing doping
concentrations. The doping concentration of N+ source and drain
regions 2632 may be more than 10.times. the concentration of P-
regions 2626. The etch formation of recessed channel 2686 may
define the transistor channel length. The shape of the recessed
etch may be rectangular as shown, or may be spherical (generally
from wet etching, sometimes called an S-RCAT: spherical RCAT), or a
variety of other shapes due to etching methods and shaping from
smoothing processes, and may help control for the channel electric
field uniformity. The thickness of channel region 2623 in the
region below recessed channel 2686 may be of a thickness that
allows fully-depleted channel operation. The thickness of channel
region 2623 in the region below N+ source and drain regions 2632
may be of a thickness that allows fully-depleted transistor
operation.
[0096] As illustrated in FIG. 26E, a gate dielectric 2607 may be
formed and a gate metal material may be deposited. The gate
dielectric 2607 may be an atomic layer deposited (ALD) gate
dielectric that may be paired with a work function specific gate
metal in the industry standard high k metal gate process schemes
described in the incorporated references. Alternatively, the gate
dielectric 2607 may be formed with a low temperature processes
including, for example, LPCVD SiO.sub.2 oxide deposition or low
temperature microwave plasma oxidation of the silicon surfaces and
a gate material with proper work function and less than
approximately 400.degree. C. deposition temperature such as, for
example, tungsten or aluminum may be deposited. The gate material
may be chemically mechanically polished, and the gate area defined
by masking and etching, thus forming the gate electrode 2608. The
shape of gate electrode 2608 is illustrative; the gate electrode
may also overlap a portion of N+ source and drain regions 2632.
[0097] As illustrated in FIG. 26F, a low temperature thick oxide
2609 may be deposited and planarized, and source, gate, and drain
contacts, P+ doped region contact (not shown) and thru layer via
(not shown) openings may be masked and etched preparing the
transistors to be connected via metallization. P+ doped region
contact may be constructed thru isolation regions 2605, suitably
when the isolation regions 2605 is formed to a shared P+ doped
region 2624. Thus gate contact 2611 connects to gate electrode
2608, and source & drain contacts 2640 connect to N+ source and
drain regions 2632. The thru layer via (not shown) provides
electrical coupling among the donor wafer transistors and the
acceptor wafer metal connect pads or strips (not shown) as
described in the incorporated references.
[0098] Persons of ordinary skill in the art will appreciate that
the illustrations in FIGS. 26A through 26F are exemplary only and
are not drawn to scale. Such skilled persons will further
appreciate that many variations are possible such as, for example,
a p-channel FD-RCAT may be formed with changing the types of
dopings appropriately. Moreover, the P- substrate donor wafer 2600
may be n type or un-doped. Further, P- doped channel layer 2603 may
include multiple layers of different doping concentrations and
gradients to fine tune the eventual FD-RCAT channel for electrical
performance and reliability characteristics, such as, for example,
off-state leakage current and on-state current. Furthermore,
isolation regions 2605 may be formed by a hard mask defined process
flow, wherein a hard mask stack, such as, for example, silicon
oxide and silicon nitride layers, or silicon oxide and amorphous
carbon layers, may be utilized. Moreover, CMOS FD-RCATs may be
constructed with n-JLRCATs in a first mono-crystalline silicon
layer and p-JLRCATs in a second mono-crystalline layer, which may
include different crystalline orientations of the mono-crystalline
silicon layers, such as for example, <100>, <111> or
<551>, and may include different contact silicides for
optimum contact resistance to p or n type source, drains, and
gates. Furthermore, P+ doped regions 2624 may be utilized for a
double gate structure for the FD-RCAT and may utilize techniques
described in the incorporated references. Further, efficient heat
removal and transistor body biasing may be accomplished on a
FD-RCAT by adding an appropriately doped buried layer (N- in the
case of a n-FD-RCAT), forming a buried layer region underneath the
P+ doped region 2624 for junction isolation, and connecting that
buried region to a thermal and electrical contact, similar to what
is described for layer 1606 and region 1646 in FIGS. 16A-G in the
incorporated reference pending U.S. patent application Ser. No.
13/441,923 and U.S. Patent Publication 2012/0091587. Many other
modifications within the scope of the invention will suggest
themselves to such skilled persons after reading this
specification. Thus the invention is to be limited only by the
appended claims.
[0099] Defect annealing, such as furnace thermal or optical
annealing, of thin layers of the crystalline materials generally
included in 3D-ICs to the temperatures that may lead to substantial
dopant activation or defect anneal, for example above 600.degree.
C., may damage or melt the underlying metal interconnect layers of
the stacked 3D-IC, such as copper or aluminum interconnect layers.
An embodiment of the invention is to form 3D-IC structures and
devices wherein a heat spreading, heat conducting and/or optically
reflecting or absorbent material layer or layers (which may be
called a shield) is incorporated between the sensitive metal
interconnect layers and the layer or regions being optically
irradiated and annealed, or annealed from the top of the 3D-IC
stack using other methods. An exemplary generalized process flow is
shown in FIGS. 27A-F. An exemplary process flow for an FD-RCAT with
an optional integrated heat shield/spreader is shown in FIGS.
28A-G. An exemplary process flow for a FD-MOSFET with an optional
integrated heat shield/spreader is shown in FIGS. 29A-G. An
exemplary process flow for a planar fully depleted n-channel MOSFET
(FD-MOSFET) with an optional integrated heat shield/spreader and
back planes and body bias taps is shown in FIGS. 30A-G. An
exemplary process flow for a horizontally oriented JFET or JLT with
an optional integrated heat shield/spreader is shown in FIGS.
31A-G. The 3D-ICs may be constructed in a 3D stacked layer using
procedures outlined herein (such as, for example, FIGS. 39, 40, 41
of incorporated patent reference U.S. Pat. No. 9,385,058) and in
U.S. Pat. Nos. 8,273,610, 9,099,526, 9,219,005, 8,557,632 and
8,581,349. The contents of the foregoing applications are
incorporated herein by reference. The topside defect anneal may
include optical annealing to repair defects in the crystalline
3D-IC layers and regions (which may be caused by the ion-cut
implantation process), and may be utilized to activate
semiconductor dopants in the crystalline layers or regions of a
3D-IC, such as, for example, LDD, halo, source/drain implants. The
3D-IC may include, for example, stacks formed in a monolithic
manner with thin layers or stacks and vertical connection such as
TLVs, and stacks formed in an assembly manner with thick (>2 um)
layers or stacks and vertical connections such as TSVs. Optical
annealing beams or systems, such as, for example, a laser-spike
anneal beam from a commercial semiconductor material oriented
single or dual-beam continuous wave (CW) laser spike anneal DB-LSA
system of Ultratech Inc., San Jose, Calif., USA (10.6 um laser
wavelength), or a short pulse laser (such as 160 ns), with 308 nm
wavelength, and large area (die or step-field sized, including 1
cm.sup.2) irradiation such as offered by Excico of Gennevilliers,
France, may be utilized (for example, see Huet, K., "Ultra Low
Thermal Budget Laser Thermal Annealing for 3D Semiconductor and
Photovoltaic Applications," NCCAVS 2012 Junction Technology Group,
Semicon West, San Francisco, Jul. 12, 2012). Additionally, the
defect anneal may include, for example, laser anneals (such as
suggested in Rajendran, B., "Sequential 3D IC Fabrication:
Challenges and Prospects", Proceedings of VLSI Multi Level
Interconnect Conference 2006, pp. 57-64), Ultrasound Treatments
(UST), megasonic treatments, and/or microwave treatments. The
topside defect anneal ambient may include, for example, vacuum,
high pressure (greater than about 760 torr), oxidizing atmospheres
(such as oxygen or partial pressure oxygen), and/or reducing
atmospheres (such as nitrogen or argon). The topside defect anneal
may include temperatures of the layer being annealed above about
400.degree. C. (a high temperature thermal anneal), including, for
example, 600.degree. C., 800.degree. C., 900.degree. C.,
1000.degree. C., 1050.degree. C., 1100.degree. C. and/or
1120.degree. C., and the sensitive metal interconnect (for example,
may be copper or aluminum containing) and/or device layers below
may not be damaged by the annealing process, for example, which may
include sustained temperatures that do not exceed 200.degree. C.,
exceed 300.degree. C., exceed 370.degree. C., or exceed 400.degree.
C. As understood by those of ordinary skill in the art,
short-timescale (nanosceonds to miliseconds) temperatures above
400.degree. C. may also be acceptable for damage avoidance,
depending on the acceptor layer interconnect metal systems used.
The topside defect anneal may include activation of semiconductor
dopants, such as, for example, ion implanted dopants or PLAD
applied dopants. It will also be understood by one of ordinary
skill in the art that the methods, such as the heat sink/shield
layer and/or use of short pulse and short wavelength optical
anneals, may allow almost any type of transistor, for example, such
as FinFets, bipolar, nanowire transistors, to be constructed in a
monolithic 3D fashion as the thermal limit of damage to the
underlying metal interconnect systems is overcome. Moreover,
multiple pulses of the laser, other optical annealing techniques,
or other anneal treatments such as microwave, may be utilized to
improve the anneal, activation, and yield of the process. The
transistors formed as described herein may include many types of
materials; for example, the channel and/or source and drain may
include single crystal materials such as silicon, germanium, or
compound semiconductors such as GaAs, InP, GaN, SiGe, and although
the structures may be doped with the tailored dopants and
concentrations, they may still be substantially crystalline or
mono-crystalline.
[0100] As illustrated in FIG. 27A, a generalized process flow may
begin with a donor wafer 2700 that may be preprocessed with wafer
sized layers 2702 of conducting, semi-conducting or insulating
materials that may be formed by deposition, ion implantation and
anneal, oxidation, epitaxial growth, combinations of above, or
other semiconductor processing steps and methods. For example,
donor wafer 2700 and wafer sized layers 2702 may include
semiconductor materials such as, for example, mono-crystalline
silicon, germanium, GaAs, InP, and graphene. For this illustration,
mono-crystalline (single crystal) silicon and associated silicon
oriented processing may be used. The donor wafer 2700 may be
preprocessed with a layer transfer demarcation plane (shown as
dashed line) 2799, such as, for example, a hydrogen implant cleave
plane, before or after (typical) wafer sized layers 2702 are
formed. Layer transfer demarcation plane 2799 may alternatively be
formed within wafer sized layers 2702. Other layer transfer
processes, some described in the referenced patent documents, may
alternatively be utilized. Damage/defects to the crystalline
structure of donor wafer 2700 may be annealed by some of the
annealing methods described, for example the short wavelength
pulsed laser techniques, wherein the donor wafer 2700 wafer sized
layers 2702 and portions of donor wafer 2700 may be heated to
defect annealing temperatures, but the layer transfer demarcation
plane 2799 may be kept below the temperate for cleaving and/or
significant hydrogen diffusion. Dopants in at least a portion of
wafer sized layers 2702 may also be electrically activated. Thru
the processing, donor wafer 2700 and/or wafer sized layers 2702
could be thinned from its original thickness, and their/its final
thickness could be in the range of about 0.01 um to about 50 um,
for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5 um.
Donor wafer 2700 and wafer sized layers 2702 may include
preparatory layers for the formation of horizontally or vertically
oriented types of transistors such as, for example, MOSFETS,
FinFets, FD-RCATs, BJTs, HEMTs, HBTs, JFETs, JLTs, or partially
processed transistors (for example, the replacement gate HKMG
process described in the referenced patent documents). Donor wafer
2700 and wafer sized layers 2702 may include the layer transfer
devices and/or layer or layers contained herein this document or
referenced patent documents, for example, DRAM Si/SiO.sub.2 layers,
RCAT doped layers, multi-layer doped structures, or starting
material doped or undoped monocrystalline silicon, or
polycrystalline silicon. Donor wafer 2700 and wafer sized layers
2702 may have alignment marks (not shown). Acceptor wafer 2710 may
be a preprocessed wafer, for example, including monocrystalline
bulk silicon or SOI, that may have fully functional circuitry
including metal layers (including aluminum or copper metal
interconnect layers that may connect acceptor wafer 2710
transistors and metal structures, such as TLV landing strips and
pads, prepared to connect to the transferred layer devices) or may
be a wafer with previously transferred layers, or may be a blank
carrier or holder wafer, or other kinds of substrates suitable for
layer transfer processing. Acceptor wafer 2710 may have alignment
marks 2790 and metal connect pads or strips 2780 and ray blocked
metal interconnect 2781. Acceptor wafer 2710 may include
transistors such as, for example, MOSFETS, FinFets, FD-RCATs, BJTs,
JFETs, JLTs, HEMTs, and/or HBTs. Acceptor wafer 2710 may include
shield/heat sink layer 2788, which may include materials such as,
for example, Aluminum, Tungsten (a refractory metal), Copper,
silicon or cobalt based silicides, or forms of carbon such as
carbon nanotubes or DLC (Diamond Like Carbon), and may be layered
itself as described herein FIG. 50. Shield/heat sink layer 2788 may
have a thickness range of about 50 nm to about mm, for example, 50
nm, 100 nm, 200 nm, 300 nm, 500 nm, 0.1 um, 1 um, 2 um, and 10 um.
Shield/heat sink layer 2788 may include isolation openings 2786,
and alignment mark openings 2787, which may be utilized for short
wavelength alignment of top layer (donor) processing to the
acceptor wafer alignment marks 2790. Shield/heat sink layer 2788
may include shield path connect 2785 and shield path via 2783.
Shield path via 2783 may thermally and/or electrically couple and
connect shield path connect 2785 to acceptor wafer 2710
interconnect metallization layers such as, for example, metal
connect pads or strips 2780 (shown). If two shield/heat sink layers
2788 are utilized, one on top of the other and separated by an
isolation layer common in semiconductor BEOL, such as carbon doped
silicon oxide, shield path connect 2785 may also thermally and/or
electrically couple and connect each shield/heat sink layer 2788 to
the other and to acceptor wafer 2710 interconnect metallization
layers such as, for example, metal connect pads or strips 2780,
thereby creating a heat conduction path from the shield/heat sink
layer 2788 to the acceptor wafer substrate, and a heat sink (shown
in FIG. 27F). The topmost shield/heat sink layer may include a
higher melting point material, for example a refractory metal such
as Tungsten, and the lower heat shield layer may include a lower
melting point material such as copper.
[0101] As illustrated in FIG. 27B, two exemplary top views of
shield/heat sink layer 2788 are shown. In shield/heat sink portion
2720 a shield area 2722 of the shield/heat sink layer 2788
materials described above and in the incorporated references may
include TLV/TSV connects 2724 and isolation openings 2786.
Isolation openings 2786 may be the absence of the material of
shield area 2722. TLV/TSV connects 2724 are an example of a shield
path connect 2785. TLV/TSV connects 2724 and isolation openings
2786 may be drawn in the database of the 3D-IC stack and may formed
during the acceptor wafer 2710 processing. In shield/heat sink
portion 2730 a shield area 2732 of the shield/heat sink layer 2788
materials described above and in the incorporated references may
have metal interconnect strips 2734 and isolation openings 2786.
Metal interconnect strips 2734 may be surrounded by regions, such
as isolation openings 2786, where the material of shield area 2732
may be etched away, thereby stopping electrical conduction from
metal interconnect strips 2734 to shield area 2732 and to other
metal interconnect strips. Metal interconnect strips 2734 may be
utilized to connect/couple the transistors formed in the donor
wafer layers, such as 2702, to themselves from the `backside` or
`underside` and/or to transistors in the acceptor wafer
level/layer. Metal interconnect strips 2734 and shield/heat sink
layer 2788 regions such as shield area 2722 and shield area 2732
may be utilized as a ground plane for the transistors above it
residing in the donor wafer layer or layers and/or may be utilized
as power supply or back-bias, such as Vdd or Vsb, for the
transistors above it residing in the transferred donor wafer layer
or layers. The strips and/or regions of shield/heat sink layer 2788
may be controlled by second layer transistors when supplying power
or other signals such as data or control. For example, as
illustrated in FIG. 27B-1, the topmost shield/heat sink layer 2788
may include a topmost shield/heat sink portion 2770, which may be
configured as fingers or stripes of conductive material, such as
top strips 2774 and strip isolation spaces 2776, which may be
utilized, for example, to provide back-bias, power, or ground to
the second layer transistors above it residing in the donor wafer
layer or layers (for example donor wafer device structures 2750). A
second shield/heat sink layer 2788, below the topmost shield/heat
sink layer, may include a second shield/heat sink portion 2772,
which may be configured as fingers or stripes of conductive
material, such as second strips 2778 and strip isolation spaces
2776, may be oriented in a different direction (although not
necessarily so) than the topmost strips, and may be utilized, for
example, to provide back-bias, power, or ground to the second layer
transistors above it residing in the donor wafer layer or layers
(for example donor wafer device structures 2750). Openings, such as
opening 2779, in the topmost shield/heat sink layer may be designed
to allow connection from the second layer of transistors to the
second shield/heat sink layer, such as from donor wafer device
structures 2750 to second strips 2778. The strips or fingers may be
illustrated as orthogonally oriented layer to layer, but may also
take other drawn shapes and forms; for example, such as diagonal
running shapes as in the X-architecture, overlapping parallel
strips, and so on. The portions of the shield/heat sink layer 2788
or layers may include a combination of the strip/finger shapes of
FIG. 27B-1 and the illustrated via connects and fill-in regions of
FIG. 27B.
[0102] Bonding surfaces, donor bonding surface 2701 and acceptor
bonding surface 2711, may be prepared for wafer bonding by
depositions (such as silicon oxide), polishes, plasma, or wet
chemistry treatments to facilitate successful wafer to wafer
bonding. The insulation layer, such as deposited bonding oxides
and/or before bonding preparation existing oxides, between the
donor wafer transferred layer and the acceptor wafer topmost metal
layer, may include thicknesses of less than 1 um, less than 500 nm,
less than 400 nm, less than 300 nm, less than 200 nm, or less than
100 nm.
[0103] As illustrated in FIG. 27C, the donor wafer 2700 with wafer
sized layers 2702 and layer transfer demarcation plane 2799 may be
flipped over, aligned, and bonded to the acceptor wafer 2710. The
donor wafer 2700 with wafer sized layers 2702 may have alignment
marks (not shown). Various topside defect anneals may be utilized.
For this illustration, an optical beam such as the laser annealing
previously described is used. Optical anneal beams may be optimized
to focus light absorption and heat generation at or near the layer
transfer demarcation plane (shown as dashed line) 2799 to provide a
hydrogen bubble cleave with exemplary cleave ray 2751. The laser
assisted hydrogen bubble cleave with the absorbed heat generated by
exemplary cleave ray 2751 may also include a pre-heat of the bonded
stack to, for example, about 100.degree. C. to about 400.degree.
C., and/or a thermal rapid spike to temperatures above about
200.degree. C. to about 600.degree. C. The laser assisted ion-cut
cleave may provide a smoother cleave surface upon which better
quality transistors may be manufactured. Reflected ray 2753 may be
reflected and/or absorbed by shield/heat sink layer 2788 regions
thus blocking the optical absorption of ray blocked metal
interconnect 2781 and potentially enhancing the efficiency of
optical energy absorption of the wafer sized layers 2702.
Additionally, shield/heat sink layer 2788 may laterally spread and
conduct the heat generated by the topside defect anneal, and in
conjunction with the dielectric materials (low heat conductivity)
above and below shield/heat sink layer 2788, keep the interconnect
metals and low-k dielectrics of the acceptor wafer interconnect
layers cooler than a damage temperature, such as, for example,
400.degree. C. Annealing of dopants or annealing of damage, such as
from the H cleave implant damage, may be accomplished by optical
annealing rays, such as repair ray 2755. A small portion of the
optical energy, such as unblocked ray 2757, may hit and heat, or be
reflected, by (a few rays as the area of the heat shield openings,
such as 2724, is small compared to the die or device area) such as
metal connect pads or strips 2780. Heat generated by absorbed
photons from, for example, cleave ray 2751, reflected ray 2753,
and/or repair ray 2755 may also be absorbed by shield/heat sink
layer 2788 regions and dissipated laterally and may keep the
temperature of underlying metal layers, such as ray blocked metal
interconnect 2781, and other metal layers below it, cooler and
prevent damage. Shield/heat sink layer 2788 may act as a heat
spreader. A second layer of shield/heat sink layer 2788 (not shown)
may have been constructed (during the acceptor wafer 2710
formation) with a low heat conductive material sandwiched between
the two heat sink layers, such as silicon oxide or carbon doped
`low-k` silicon oxides, for improved thermal protection of the
acceptor wafer interconnect layers, metal and dielectrics.
Electrically conductive materials may be used for the two layers of
shield/heat sink layer 2788 and thus may provide, for example, a
Vss and a Vdd plane and/or grid for power delivery that may be
connected to the donor layer transistors above, as well may be
connected to the acceptor wafer transistors below. Shield/heat sink
layer 2788 may include materials with a high thermal conductivity
greater than 10 W/m-K, for example, copper (about 400 W/m-K),
aluminum (about 237 W/m-K), Tungsten (about 173 W/m-K), Plasma
Enhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD DLC
(about 1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene
(about 5000 W/m-K). Shield/heat sink layer 2788 may be sandwiched
and/or substantially enclosed by materials with a low thermal
conductivity less than 10 W/m-K, for example, silicon dioxide
(about 1.4 W/m-K). The sandwiching of high and low thermal
conductivity materials in layers, such as shield/heat sink layer
2788 and under & overlying dielectric layers, spreads the
localized heat/light energy of the topside anneal laterally and
protect the underlying layers of interconnect metallization &
dielectrics, such as in the acceptor wafer, from harmful
temperatures or damage. Further, absorber layers or regions, for
example, including amorphous carbon, amorphous silicon, and phase
changing materials (see U.S. Pat. Nos. 6,635,588 and 6,479,821 to
Hawryluk et al. for example), may be utilized to increase the
efficiency of the optical energy capture in conversion to heat for
the desired annealing or activation processes. Photoresist may also
be utilized to attenuate the optical energy. For example,
pre-processed layers 2702 may include a layer or region of optical
absorbers such as transferred absorber region 2775, acceptor wafer
2710 may include a layer or region of optical absorbers such as
acceptor absorber region 2773, and second device layer 2705 may
include a layer or region of optical absorbers such as post
transfer absorber regions 2777 (shown in FIG. 27E). Transferred
absorber region 2775, acceptor absorber region 2773, and/or post
transfer absorber regions 2777 may be permanent (could be found
within the device when manufacturing is complete) or temporary so
is removed during the manufacturing process.
[0104] As illustrated in FIG. 27D, the donor wafer 2700 may be
cleaved at or thinned to (or past, not shown) the layer transfer
demarcation plane 2799, leaving donor wafer portion 2703 and the
pre-processed layers 2702 bonded to the acceptor wafer 2710, by
methods such as, for example, ion-cut or other layer transfer
methods. The layer transfer demarcation plane 2799 may instead be
placed in the pre-processed layers 2702. Optical anneal beams, in
conjunction with reflecting layers and regions and absorbing
enhancement layers and regions, may be optimized to focus light
absorption and heat generation within or at the surface of donor
wafer portion 2703 and provide surface smoothing and/or defect
annealing (defects may be from the cleave and/or the ion-cut
implantation), and/or post ion-implant dopant activation with
exemplary smoothing/annealing ray 2766. The laser assisted
smoothing/annealing with the absorbed heat generated by exemplary
smoothing/annealing ray 2766 may also include a pre-heat of the
bonded stack to, for example, about 100.degree. C. to about
400.degree. C., and/or a thermal rapid spike to temperatures above
about 200.degree. C. to about 600.degree. C. Moreover, multiple
pulses of the laser may be utilized to improve the anneal,
activation, and yield of the process. Reflected ray 2763 may be
reflected and/or absorbed by shield/heat sink layer 2788 regions
thus blocking the optical absorption of ray blocked metal
interconnect 2781. Annealing of dopants or annealing of damage,
such as from the H cleave implant damage, may be also accomplished
by a set of rays such as repair ray 2765. A small portion of the
optical energy, such as unblocked ray 2767, may hit and heat, or be
reflected, by a few rays (as the area of the heat shield openings,
such as 2724, is small) such as metal connect pads or strips 2780.
Heat generated by absorbed photons from, for example,
smoothing/annealing ray 2766, reflected ray 2763, and/or repair ray
2765 may also be absorbed by shield/heat sink layer 2788 regions
and dissipated laterally and may keep the temperature of underlying
metal layers, such as ray blocked metal interconnect 2781, and
other metal layers below it, cooler and prevent damage. A second
layer of shield/heat sink layer 2788 may be constructed with a low
heat conductive material sandwiched between the two heat sink
layers, such as silicon oxide or carbon doped `low-k` silicon
oxides, for improved thermal protection of the acceptor wafer
interconnect layers, metal and dielectrics. Shield/heat sink layer
2788 may act as a heat spreader. When there may be more than one
shield/heat sink layer 2788 in the device, the heat conducting
layer closest to the second crystalline layer may be constructed
with a different material, for example a high melting point
material, for example a refractory metal such as tungsten, than the
other heat conducting layer or layers, which may be constructed
with, for example, a lower melting point material such as aluminum
or copper. Electrically conductive materials may be used for the
two layers of shield/heat sink layer 2788 and thus may provide, for
example, a Vss and a Vdd plane and/or grid that may be connected to
the donor layer transistors above, as well may be connected to the
acceptor wafer transistors below. Noise on the power grids, such as
the Vss and Vdd plane power conducting lines/wires, may be
mitigated by attaching/connecting decoupling capacitors onto the
power conducting lines of the grids. The decoupling caps, which may
be within the second layer (donor, for example, donor wafer device
structures 2750) or first layer (acceptor, for example acceptor
wafer transistors and devices 2793), may include, for example,
trench capacitors such as described by Pei, C., et al., "A novel,
low-cost deep trench decoupling capacitor for high-performance,
low-power bulk CMOS applications," ICSICT (9.sup.th International
Conference on Solid-State and Integrated-Circuit Technology) 2008,
October 2008, pp. 1146-1149, of IBM. The decoupling capacitors may
include, for example, planar capacitors, such as poly to substrate
or poly to poly, or MiM capacitors (Metal-Insulator-Metal).
Furthermore, some or all of the layers utilized as shield/heat sink
layer 2788, which may include shapes of material such as the strips
or fingers as illustrated in FIG. 27B-1, may be driven by a portion
of the second layer transistors and circuits (within the
transferred donor wafer layer or layers) or the acceptor wafer
transistors and circuits, to provide a programmable back-bias to at
least a portion of the second layer transistors. The programmable
back bias may utilize a circuit to do so, for example, such as
shown in FIG. 17B of U.S. Pat. No. 8,273,610, the contents
incorporated herein by reference; wherein the `Primary` layer may
be the second layer of transistors for which the back-bias is being
provided, the `Foundation` layer could be either the second layer
transistors (donor) or first layer transistors (acceptor), and the
routing metal lines connections 1723 and 1724 may include portions
of the shield/heat sink layer 2788 layer or layers. Moreover, some
or all of the layers utilized as shield/heat sink layer 2788, which
may include strips or fingers as illustrated in FIG. 27B-1, may be
driven by a portion of the second layer transistors and circuits
(within the transferred donor wafer layer or layers) or the
acceptor wafer transistors and circuits to provide a programmable
power supply to at least a portion of the second layer transistors.
The programmable power supply may utilize a circuit to do so, for
example, such as shown in FIG. 17C of U.S. Pat. No. 8,273,610, the
contents incorporated herein by reference; wherein the `Primary`
layer may be the second layer of transistors for which the
programmable power supplies are being provided to, the `Foundation`
layer could be either the second layer transistors (donor) or first
layer transistors (acceptor), and the routing metal line
connections from Vout to the various second layer transistors may
include portions of the shield/heat sink layer 2788 layer or
layers. The Vsupply on line 17C12 and the control signals on
control line 17C16 may be controlled by and/or generated in the
second layer transistors (donor, for example donor wafer device
structures 2750) or first layer transistors (acceptor, for example
acceptor wafer transistors and devices 2793), or off chip circuits.
Furthermore, some or all of the layers utilized as shield/heat sink
layer 2788, which may include strips or fingers as illustrated in
FIG. 27B-1 or other shapes such as those in FIG. 27B, may be
utilized to distribute independent power supplies to various
portions of the second layer transistors (donor, for example donor
wafer device structures 2750) or first layer transistors (acceptor,
for example acceptor wafer transistors and devices 2793) and
circuits; for example, one power supply and/or voltage may be
routed to the sequential logic circuits of the second layer and a
different power supply and/or voltage routed to the combinatorial
logic circuits of the second layer. Moreover, the power
distribution circuits/grid may be designed so that Vdd may have a
different value for each stack layer. Patterning of shield/heat
sink layer 2788 or layers can impact their heat-shielding capacity.
This impact may be mitigated, for example, by enhancing the top
shield/heat sink layer 2788 areal density, creating more of the
secondary shield/heat sink layers 2788, or attending to special CAD
rules regarding their metal density, similar to CAD rules that are
required to accommodate Chemical-Mechanical Planarization (CMP).
These constraints would be integrated into a design and layout EDA
tool. Moreover, the second layer of circuits and transistors, for
example, donor wafer device structures 2750, may include I/O logic
devices, such as SerDes (Serialiser/Deserialiser), and conductive
bond pads (not shown). The output or input conductive pads of the
I/O circuits may be coupled, for example by bonded wires, to
external devices. The output or input conductive pads may also act
as a contact port for the 3D device output to connect to external
devices. The emf generated by the I/O circuits could be shielded
from the other layers in the stack by use of, for example, the heat
shield/heat sink layer 2788. Placement of the I/O circuits on the
same stack layer as the conductive bond pad may enable close
coupling of the desired I/O energy and lower signal loss.
Furthermore, the second layer of circuits and transistors, for
example, donor wafer device structures 2750, may include RF (Radio
Frequency) circuits and/or at least one antenna. For example, the
second layer of circuits and transistors, for example, donor wafer
device structures 2750, may include RF circuits to enable an
off-chip communication capability to external devices, for example,
a wireless communication circuit or circuits such as a Bluetooth
protocol or capacitive coupling. The emf generated by the RF
circuits could be shielded from the other layers in the stack by
use of, for example, the heat shield/heat sink layer 2788.
[0105] As illustrated in FIG. 27E, the remaining donor wafer
portion 2703 may be removed by polishing or etching and the
transferred layers 2702 may be further processed to create second
device layer 2705 which may include donor wafer device structures
2750 and metal interconnect layers (such as second device layer
metal interconnect 2761) that may be precisely aligned to the
acceptor wafer alignment marks 2790. Donor wafer device structures
2750 may include, for example, CMOS transistors such as N type and
P type transistors, or at least any of the other transistor or
device types discussed herein this document or referenced patent
documents. The details of CMOS in one transferred layer and the
orthogonal connect strip methodology may be found as illustrated in
at least FIGS. 30-27, 73-80, and 94 and related specification
sections of U.S. Pat. No. 8,273,610. As discussed above and herein
this document and referenced patent documents, annealing of dopants
or annealing of damage, such as from the dopant application such as
ion-implantation, or from etch processes during the formation of
the transferred layer transistor and device structures, may be
accomplished by optical annealing. Donor wafer device structures
2750 may include transistors and/or semiconductor regions wherein
the dopant concentration of the regions in the horizontal plane,
such as shown as exemplary dopant plane 2749, may have regions that
differ substantially in dopant concentration, for example,
10.times. greater, and/or may have a different dopant type, such
as, for example p-type or n-type dopant. Additionally, the
annealing of deposited dielectrics and etch damage, for example,
oxide depositions and silicon etches utilized in the transferred
layer isolation processing, for example, STI (Shallow Trench
Isolation) processing or strained source and drain processing, may
be accomplished by optical annealing. An optical step may be
performed to densify and/or remove defects from gate dielectric,
anneal defects and activate dopants such as LDD and S/D implants,
densify ILDs, form DSS junctions (Dopant Segregated Schottky such
as NiSi.sub.2), and/or form contact and S/D silicides (not shown).
The optical anneal may be performed at each sub-step as desired, or
may be done at prior to the HKMG deposition (such as after the
dummy gate but before the HKMG formation), or various combinations.
Second device layer metal interconnect 2761 may include
electrically conductive materials such as copper, aluminum,
conductive forms of carbon, and tungsten. Donor wafer device
structures 2750 may utilize second device layer metal interconnect
2761 and thru layer vias (TLVs) 2760 to electrically couple
(connection paths) the donor wafer device structures 2750 to the
acceptor wafer metal connect pads or strips 2780, and thus couple
donor wafer device structures (the second layer transistors) with
acceptor wafer device structures (first layer transistors). Thermal
TLVs 2762 may be constructed of thermally conductive but not
electrically conductive materials, for example, DLC (Diamond Like
Carbon), and may connect donor wafer device structures 2750
thermally to shield/heat sink layer 2788. TLVs 2760 may be
constructed out of electrically and thermally conductive materials,
such as Tungsten, Copper, or aluminum, and may provide a thermal
and electrical connection path from donor wafer device structures
2750 to shield/heat sink layer 2788, which may be a ground or Vdd
plane in the design/layout. TLVs 2760 and thermal TLVs 2762 may be
also constructed in the device scribelanes (pre-designed in base
layers or potential dicelines) to provide thermal conduction to the
heat sink, and may be sawed/diced off when the wafer is diced for
packaging. Shield/heat sink layer 2788 may be configured to act as
an emf (electro-motive force) shield to prevent direct layer to
layer cross-talk between transistors in the donor wafer layer and
transistors in the acceptor wafer. In addition to static ground or
Vdd biasing, shield/heat sink layer 2788 may be actively biased
with an anti-interference signal from circuitry residing on, for
example, a layer of the 3D-IC or off chip. TLVs 2760 may be formed
through the transferred layers 2702. As the transferred layers 2702
may be thin, on the order of about 200 nm or less in thickness, the
TLVs may be easily manufactured as a typical metal to metal via may
be, and said TLV may have state of the art diameters such as
nanometers or tens to a few hundreds of nanometers, such as, for
example about 150 nm or about 100 nm or about 50 nm. The thinner
the transferred layers 2702, the smaller the thru layer via
diameter obtainable, which may result from maintaining
manufacturable via aspect ratios. Thus, the transferred layers 2702
(and hence, TLVs 2760) may be, for example, less than about 2
microns thick, less than about 1 micron thick, less than about 0.4
microns thick, less than about 200 nm thick, less than about 150 nm
thick, less than about 100 nm thick, less than about 50 nm thick,
less than about 20 nm thick, or less than about 5 nm thick. The
thickness of the layer or layers transferred according to some
embodiments of the invention may be designed as such to match and
enable the most suitable obtainable lithographic resolution (and
enable the use of conventional state of the art lithographic
tools), such as, for example, less than about 10 nm, 14 nm, 22 nm
or 28 nm linewidth resolution and alignment capability, such as,
for example, less than about 5 nm, 10 nm, 20 nm, or 40 nm alignment
accuracy/precision/error, of the manufacturing process employed to
create the thru layer vias or any other structures on the
transferred layer or layers. The above TLV dimensions and alignment
capability and transferred layer thicknesses may be also applied to
any of the discussed TLVs or transferred layers described elsewhere
herein. Transferred layers 2702 may be considered to be overlying
the metal layer or layers of acceptor wafer 2710. Alignment marks
in acceptor wafer 2710 and/or in transferred layers 2702 may be
utilized to enable reliable contact to transistors and circuitry in
transferred layers 2702 and donor wafer device structures 2750 and
electrically couple them to the transistors and circuitry in the
acceptor wafer 2710. Transferred layer or layers may have regions
of STI or other transistor elements within it or on it when
transferred, but would then use alignment and connection schemes
for layer transfer of patterned layers as described in incorporated
patent references. The donor wafer 2700 may now also be processed,
such as smoothing and annealing, and reused for additional layer
transfers. The transferred layers 2702 and other additional regions
created in the transferred layers during transistor processing are
thin and small, having small volumes on the order of
2.times.10.sup.-16 cm.sup.3 (2.times.10.sup.5 nm.sup.3 for a 100 nm
by 100 nm.times.20 nm thick device). As a result, the amount of
energy to manufacture with known in the art transistor and device
formation processing, for example, annealing of ion-cut created
defects or activation of dopants and annealing of doping or etching
damages, is very small and may lead to only a small amount of
shield layer or layers or regions or none to effectively shield the
underlying interconnect metallization and dielectrics from the
manufacturing processing generated heat. The energy may be supplied
by, for example, pulsed and short wavelength optical annealing
techniques described herein and incorporated references, and may
include the use of optical absorbers and reflectors and
optical/thermal shielding and heat spreaders, some of which are
described herein and incorporated references. The optical anneal
may be performed at each sub-step as desired, or may be done at
prior to the HKMG deposition (such as after the dummy gate but
before the HKMG formation), or various combinations. Moreover,
multiple pulses of the laser may be utilized to improve the anneal,
activation, and yield of the process.
[0106] As illustrated in FIG. 27F, a thermal conduction path may be
constructed from the devices in the upper layer, the transferred
donor layer and formed transistors, to the acceptor wafer substrate
and associated heat sink. The thermal conduction path from the
donor wafer device structures 2750 to the acceptor wafer heat sink
2797 may include second device layer metal interconnect 2761, TLVs
2760, shield path connect 2785, shield path via 2783, metal connect
pads or strips 2780, first (acceptor) layer metal interconnect
2791, acceptor wafer transistors and devices 2793, and acceptor
substrate 2795. The elements of the thermal conduction path may
include materials that have a thermal conductivity greater than 10
W/m-K, for example, copper (about 400 W/m-K), aluminum (about 237
W/m-K), and Tungsten (about 173 W/m-K), and may include material
with thermal conductivity lower than 10 W/m-K but have a high heat
transfer capacity due to the wide area available for heat transfer
and thickness of the structure (Fourier's Law), such as, for
example, acceptor substrate 2795. The elements of the thermal
conduction path may include materials that are thermally conductive
but may not be substantially electrically conductive, for example,
Plasma Enhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD
DLC (about 1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene
(about 5000 W/m-K). The acceptor wafer interconnects may be
substantially surrounded by BEOL dielectric 2796. In general,
within the active device or devices (that are generating the heat
that is desired to be conducted away thru at least the thermal
conduction path), it would be advantageous to have an effective
conduction path to reduce the overall space and area that a
designer would allocate for heat transfer out of the active
circuitry space and area. A designer may select to use only
materials with a high thermal conductivity (such as greater than 10
W/m-K), much higher for example than that for monocrystalline
silicon, for the desired thermal conduction path. However, there
may need to be lower than desired thermal conductivity materials in
the heat conduction path due to requirements such as, for example,
the mechanical strength of a thick silicon substrate, or another
heat spreader material in the stack. The area and volume allocated
to that structure, such as the silicon substrate, is far larger
than the active circuit area and volume. Accordingly, since a
copper wire of 1 um.sup.2 profile is about the same as a 286
um.sup.2 profile of a column of silicon, and the thermal conduction
path may include both a copper wire/TLV/via and the bulk silicon
substrate, a proper design may take into account and strive to
align the different elements of the conductive path to achieve
effective heat transfer and removal, for example, may attempt to
provide about 286 times the silicon substrate area for each Cu
thermal via utilized in the thermal conduction path. The heat
removal apparatus, which may include acceptor wafer heat sink 2797,
may include an external surface from which heat transfer may take
place by methods such as air cooling, liquid cooling, or attachment
to another heat sink or heat spreader structure.
[0107] Formation of CMOS in one transferred layer and the
orthogonal connect strip methodology may be found as illustrated in
at least FIGS. 30-33, 73-80, and 94 and related specification
sections of U.S. Pat. No. 8,273,610, and may be applied to at least
the FIG. 27 formation techniques. Transferred layer or layers may
have regions of STI or other transistor elements within it or on it
when transferred, but would then use alignment and connection
schemes for layer transfer of patterned layers as described in
incorporated patent references.
[0108] A planar fully depleted n-channel Recessed Channel Array
Transistor (FD-RCAT) with an integrated shield/heat sink layer
suitable for a monolithic 3D IC may be constructed as follows. The
FD-RCAT may provide an improved source and drain contact
resistance, thereby allowing for lower channel doping (such as
undoped), and the recessed channel may provide for more flexibility
in the engineering of channel lengths and transistor
characteristics, and increased immunity from process variations.
The buried doped layer and channel dopant shaping, even to an
un-doped channel, may allow for efficient adaptive and dynamic body
biasing to control the transistor threshold and threshold
variations, as well as provide for a fully depleted or deeply
depleted transistor channel. Furthermore, the recessed gate allows
for an FD transistor but with thicker silicon for improved lateral
heat conduction. Moreover, a heat spreading, heat conducting and/or
optically reflecting material layer or layers may be incorporated
between the sensitive metal interconnect layers and the layer or
regions being optically irradiated and annealed to repair defects
in the crystalline 3D-IC layers and regions and to activate
semiconductor dopants in the crystalline layers or regions of a
3D-IC without harm to the sensitive metal interconnect and
associated dielectrics. FIG. 28A-G illustrates an exemplary
n-channel FD-RCAT which may be constructed in a 3D stacked layer
using procedures outlined below and in U.S. Pat. Nos. 8,273,610,
9,099,526, 9,219,005, 8,557,632 and 8,581,349. The contents of the
foregoing applications are incorporated herein by reference.
[0109] As illustrated in FIG. 28A, a P- substrate donor wafer 2800
may be processed to include wafer sized layers of N+ doping 2802,
P- doping 2806, channel 2803 and P+ doping 2804 across the wafer.
The N+ doped layer 2802, P- doped layer 2806, channel layer 2803
and P+ doped layer 2804 may be formed by ion implantation and
thermal anneal. P- substrate donor wafer 2800 may include a
crystalline material, for example, mono-crystalline (single
crystal) silicon. P- doped layer 2806 and channel layer 2803 may
have additional ion implantation and anneal processing to provide a
different dopant level than P- substrate donor wafer 2800. P-
substrate donor wafer 2800 may be very lightly doped (less than
1e15 atoms/cm.sup.3) or nominally un-doped (less than 1e14
atoms/cm.sup.3). P- doped layer 2806, channel layer 2803, and P+
doped layer 2804 may have graded or various layers doping to
mitigate transistor performance issues, such as, for example, short
channel effects, after the FD-RCAT is formed, and to provide
effective body biasing, whether adaptive or dynamic. The layer
stack may alternatively be formed by successive epitaxially
deposited doped silicon layers of N+ doped layer 2802, P- doped
layer 2806, channel layer 2803 and P+ doped layer 2804, or by a
combination of epitaxy and implantation, or by layer transfer.
Annealing of implants and doping may include, for example,
conductive/inductive thermal, optical annealing techniques or types
of Rapid Thermal Anneal (RTA or spike). The N+ doped layer 2802 may
have a doping concentration that may be more than 10.times. the
doping concentration of P- doped layer 2806 and/or channel layer
2803. The P+ doped layer 2804 may have a doping concentration that
may be more than Ox the doping concentration of P- doped layer 2806
and/or channel layer 2803. The P- doped layer 2806 may have a
doping concentration that may be more than Ox the doping
concentration of channel layer 2803. Channel layer 2803 may have a
thickness and/or doping that may allow fully-depleted channel
operation when the FD-RCAT transistor is substantially completely
formed, such as, for example, less than 5 nm, less than 10 nm, or
less than 20 nm.
[0110] As illustrated in FIG. 28B, the top surface of the P-
substrate donor wafer 2800 layer stack may be prepared for oxide
wafer bonding with a deposition of an oxide or by thermal oxidation
of P+ doped layer 2804 to form oxide layer 2880. A layer transfer
demarcation plane (shown as dashed line) 2899 may be formed by
hydrogen implantation or other methods as described in the
incorporated references. The P- substrate donor wafer 2800 and
acceptor wafer 2810 may be prepared for wafer bonding as previously
described and low temperature (less than approximately 400.degree.
C.) bonded. Acceptor wafer 2810, as described in the incorporated
references, may include, for example, transistors, circuitry, and
metal, such as, for example, aluminum or copper, interconnect
wiring, a metal shield/heat sink layer, and thru layer via metal
interconnect strips or pads. Acceptor wafer 2810 may be
substantially comprised of a crystalline material, for example
mono-crystalline silicon or germanium, or may be an engineered
substrate/wafer such as, for example, an SOI (Silicon on Insulator)
wafer or GeOI (Germanium on Insulator) substrate. SOI Acceptor
wafer 2810 may include transistors such as, for example, MOSFETS,
FinFets, FD-RCATs, BJTs, HEMTs, and/or HBTs. The portion of the N+
doped layer 2802 and the P- substrate donor wafer 2800 that may be
above (when the layer stack is flipped over and bonded to the
acceptor wafer) the layer transfer demarcation plane 2899 may be
removed by cleaving or other low temperature processes as described
in the incorporated references, such as, for example, ion-cut or
other layer transfer methods. Damage/defects to crystalline
structure of N+ doped layer 2802, P- doped layer 2806, channel
layer 2803 and P+ doped layer 2804 may be annealed by some of the
annealing methods described, for example the short wavelength
pulsed laser techniques, wherein the N+ doped layer 2802, P- doped
layer 2806, channel layer 2803 and P+ doped layer 2804 or portions
of them may be heated to defect annealing temperatures, but the
layer transfer demarcation plane 2899 may be kept below the
temperate for cleaving and/or significant hydrogen diffusion. The
optical energy may be deposited in the upper layer of the stack,
for example in P+ doped layer 2804, and annealing of the other
layer may take place via heat diffusion. Dopants in at least a
portion of N+ doped layer 2802, P- doped layer 2806, channel layer
2803 and P+ doped layer 2804 may also be electrically activated by
the anneal.
[0111] As illustrated in FIG. 28C, oxide layer 2880, P+ doped layer
2804, channel layer 2803, P- doped layer 2806, and remaining N+
layer 2822 have been layer transferred to acceptor wafer 2810. The
top surface of N+ layer 2822 may be chemically or mechanically
polished. Thru the processing, the wafer sized layers such as N+
layer 2822 P+ doped layer 2804, channel layer 2803, and P- doped
layer 2806, could be thinned from its original total thickness, and
their/its final total thickness could be in the range of about 0.01
um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1
um, 2 um or 5 um. Acceptor wafer 2810 may include one or more (two
are shown in this example) shield/heat sink layers 2888, which may
include materials such as, for example, Aluminum, Tungsten (a
refractory metal), Copper, silicon or cobalt based silicides, or
forms of carbon such as carbon nanotubes, and may be layered itself
as described herein FIG. 50. Each shield/heat sink layer 2888 may
have a thickness range of about 50 nm to about 1 mm, for example,
50 nm, 100 nm, 200 nm, 300 nm, 500 nm, 0.1 um, 1 um, 2 um, and 10
um. Shield/heat sink layer 2888 may include isolation openings
2887, and alignment mark openings (not shown), which may be
utilized for short wavelength alignment of top layer (donor)
processing to the acceptor wafer alignment marks (not shown).
Shield/heat sink layer 2888 may include one or more shield path
connect 2885 and shield path via 2883. Shield path via 2883 may
thermally and/or electrically couple and connect shield path
connect 2885 to acceptor wafer 2810 interconnect metallization
layers such as, for example, acceptor metal interconnect 2881
(shown). Shield path connect 2885 may also thermally and/or
electrically couple and connect each shield/heat sink layer 2888 to
the other and to acceptor wafer 2810 interconnect metallization
layers such as, for example, acceptor metal interconnect 2881,
thereby creating a heat conduction path from the shield/heat sink
layer 2888 to the acceptor substrate 2895, and a heat sink (shown
in FIG. 28G.). Isolation openings 2887 may include dielectric
materials, similar to those of BEOL isolation 2896. Acceptor wafer
2810 may include first (acceptor) layer metal interconnect 2891,
acceptor wafer transistors and devices 2893, and acceptor substrate
2895. Various topside defect anneals may be utilized. For this
illustration, an optical beam such as the laser annealing
previously described is used. Optical anneal beams may be optimized
to focus light absorption and heat generation within or at the
surface of N+ layer 2822 and provide surface smoothing and/or
defect annealing (defects may be from the cleave and/or the ion-cut
implantation) with exemplary smoothing/annealing ray 2866. The
laser assisted smoothing/annealing with the absorbed heat generated
by exemplary smoothing/annealing ray 2866 may also include a
pre-heat of the bonded stack to, for example, about 100.degree. C.
to about 400.degree. C., and/or a rapid thermal spike to
temperatures above about 200.degree. C. to about 600.degree. C.
Additionally, absorber layers or regions, for example, including
amorphous carbon, amorphous silicon, and phase changing materials
(see U.S. Pat. Nos. 6,635,588 and 6,479,821 to Hawryluk et al. for
example), may be utilized to increase the efficiency of the optical
energy capture in conversion to heat for the desired annealing or
activation processes. Reflected ray 2863 may be reflected and/or
absorbed by shield/heat sink layer 2888 regions thus blocking the
optical absorption of ray blocked metal interconnect 2881.
Annealing of dopants or annealing of damage, such as from the H
cleave implant damage, may be also accomplished by a set of rays
such as repair ray 2865. Heat generated by absorbed photons from,
for example, smoothing/annealing ray 2866, reflected ray 2863,
and/or repair ray 2865 may also be absorbed by shield/heat sink
layer 2888 regions and dissipated laterally and may keep the
temperature of underlying metal layers, such as metal interconnect
2881, and other metal layers below it, cooler and prevent damage.
Shield/heat sink layer 2888 and associated dielectrics may
laterally spread and conduct the heat generated by the topside
defect anneal, and in conjunction with the dielectric materials
(low heat conductivity) above and below shield/heat sink layer
2888, keep the interconnect metals and low-k dielectrics of the
acceptor wafer interconnect layers cooler than a damage
temperature, such as, for example, 400.degree. C. A second layer of
shield/heat sink layer 2888 may be constructed (shown) with a low
heat conductive material sandwiched between the two heat sink
layers, such as silicon oxide or carbon doped `low-k` silicon
oxides, for improved thermal protection of the acceptor wafer
interconnect layers, metal and dielectrics. Shield/heat sink layer
2888 may act as a heat spreader. Electrically conductive materials
may be used for the two layers of shield/heat sink layer 2888 and
thus may provide, for example, a Vss and a Vdd plane and/or grid
that may be connected to the donor layer transistors above, as well
may be connected to the acceptor wafer transistors below. Noise on
the power grids, such as the Vss and Vdd plane power conducting
lines/wires, may be mitigated by attaching/connecting decoupling
capacitors onto the power conducting lines of the grids. The
decoupling caps, which may be within the second layer (donor, for
example, donor wafer device structures) or first layer (acceptor,
for example acceptor wafer transistors and devices 2893), may
include, for example, trench capacitors such as described by Pei,
C., et al., "A novel, low-cost deep trench decoupling capacitor for
high-performance, low-power bulk CMOS applications," ICSICT
(9.sup.th International Conference on Solid-State and
Integrated-Circuit Technology) 2008, October 2008, pp. 1146-1149,
of IBM. The decoupling capacitors may include, for example, planar
capacitors, such as poly to substrate or poly to poly, or MiM
capacitors (Metal-Insulator-Metal). Shield/heat sink layer 2888 may
include materials with a high thermal conductivity greater than 10
W/m-K, for example, copper (about 400 W/m-K), aluminum (about 237
W/m-K), Tungsten (about 173 W/m-K), Plasma Enhanced Chemical Vapor
Deposited Diamond Like Carbon-PECVD DLC (about 1000 W/m-K), and
Chemical Vapor Deposited (CVD) graphene (about 5000 W/m-K).
Shield/heat sink layer 2888 may be sandwiched and/or substantially
enclosed by materials with a low thermal conductivity (less than 10
W/m-K), for example, silicon dioxide (about 1.4 W/m-K). The
sandwiching of high and low thermal conductivity materials in
layers, such as shield/heat sink layer 2888 and under &
overlying dielectric layers, spreads the localized heat/light
energy of the topside anneal laterally and protect the underlying
layers of interconnect metallization & dielectrics, such as in
the acceptor wafer, from harmful temperatures or damage. When there
may be more than one shield/heat sink layer 2888 in the device, the
heat conducting layer closest to the second crystalline layer or
oxide layer 2880 may be constructed with a different material, for
example a high melting point material, for example a refractory
metal such as tungsten, than the other heat conducting layer or
layers, which may be constructed with, for example, a lower melting
point material, for example, such as aluminum or copper. Now
transistors may be formed with low effective temperature (less than
approximately 400.degree. C. exposure to the acceptor wafer 2810
sensitive layers, such as interconnect and device layers)
processing, and may be aligned to the acceptor wafer alignment
marks (not shown) as described in the incorporated references. This
may include further optical defect annealing or dopant activation
steps. The donor wafer 2800 may now also be processed, such as
smoothing and annealing, and reused for additional layer transfers.
The insulator layer, such as deposited bonding oxides (for example
oxide layer 2880) and/or before bonding preparation existing oxides
(for example the BEOL isolation 2896 on top of the topmost metal
layer of shield/heat sink layer 2888), between the donor wafer
transferred monocrystalline layer and the acceptor wafer topmost
metal layer, may include thicknesses of less than 1 um, less than
500 nm, less than 400 nm, less than 300 nm, less than 200 nm, or
less than 100 nm.
[0112] As illustrated in FIG. 28D, transistor isolation regions
2805 may be formed by mask defining and plasma/RIE etching
remaining N+ layer 2822, P- doped layer 2806, channel layer 2803,
and P+ doped layer 2804 substantially to the top of oxide layer
2880 (not shown), substantially into oxide layer 2880, or into a
portion of the upper oxide layer of acceptor wafer 2810 (not
shown). Additionally, a portion of the transistor isolation regions
2805 may be etched (separate step) substantially to P+ doped layer
2804, thus allowing multiple transistor regions to be connected by
the same P+ doped region 2824. A low-temperature gap fill oxide may
be deposited and chemically mechanically polished, the oxide
remaining in isolation regions 2805. An optical step, such as
illustrated by exemplary STI ray 2867, may be performed to anneal
etch damage and densify the STI oxide in isolation regions 2805.
The recessed channel 2886 may be mask defined and etched thru
remaining N+ doped layer 2822, P- doped layer 2806 and partially
into channel layer 2803. The recessed channel surfaces and edges
may be smoothed by processes, such as, for example, wet chemical,
plasma/RIE etching, low temperature hydrogen plasma, or low
temperature oxidation and strip techniques, or optical annealing
(such as illustrated by exemplary channel smoothing ray 2868, which
may induce local short term high temperatures) as described herein,
to mitigate high field effects (see Kim, J. Y., et al., "The
breakthrough in data retention time of DRAM using
Recess-Channel-Array Transistor (RCAT) for 88 nm feature size and
beyond," 2003 Symposium on VLSI Technology Digest of Technical
Papers, pp. 11-12, 10-12 Jun. 2003, for CDE (chemical dry etch)
smoothing). The low temperature smoothing process may employ, for
example, a plasma produced in a TEL (Tokyo Electron Labs) SPA (Slot
Plane Antenna) machine. Thus N+ source and drain regions 2832, P-
regions 2826, and channel region 2823 may be formed, which may
substantially form the transistor body. The doping concentration of
N+ source and drain regions 2832 may be more than 10.times. the
concentration of channel region 2823. The doping concentration of
the N- channel region 2823 may include gradients of concentration
or layers of differing doping concentrations. The doping
concentration of N+ source and drain regions 2832 may be more than
10.times. the concentration of P- regions 2826. The etch formation
of recessed channel 2886 may define the transistor channel length.
The shape of the recessed etch may be rectangular as shown, or may
be spherical (generally from wet etching, sometimes called an
S-RCAT: spherical RCAT), or a variety of other shapes due to
etching methods and shaping from smoothing processes, and may help
control for the channel electric field uniformity. The thickness of
channel region 2823 in the region below recessed channel 2886 may
be of a thickness that allows fully-depleted channel operation. The
thickness of channel region 2823 in the region below N+ source and
drain regions 2832 may be of a thickness that allows fully-depleted
transistor operation. Any additional doping, such as ion-implanted
halo implants, may be activated and annealed with optical
annealing, such as illustrated by exemplary implant ray 2869, as
described herein. The optical anneal, such as exemplary STI ray
2867, exemplary channel smoothing ray 2868, and/or exemplary
implant ray 2869 may be performed at separate times and processing
parameters (such as laser energy, frequency, etc.) or may be done
in combination or as one optical anneal.
[0113] As illustrated in FIG. 28E, a gate dielectric 2807 may be
formed and a gate metal material may be deposited. The gate
dielectric 2807 may be an atomic layer deposited (ALD) gate
dielectric that may be paired with a work function specific gate
metal in the industry standard high k metal gate process schemes
described in the incorporated references. Alternatively, the gate
dielectric 2807 may be formed with a low temperature processes
including, for example, LPCVD SiO.sub.2 oxide deposition (see Ahn,
J., et al., "High-quality MOSFET's with ultrathin LPCVD gate
SiO.sub.2," IEEE Electron Device Lett., vol. 13, no. 4, pp.
186-188, April 1992) or low temperature microwave plasma oxidation
of the silicon surfaces (see Kim, J. Y., et al., "The excellent
scalability of the RCAT (recess-channel-array-transistor)
technology for sub-70 nm DRAM feature size and beyond," 2005 IEEE
VLSI-TSA International Symposium, pp. 33-28, 25-27 Apr. 2005) and
agate material with proper work function and less than
approximately 400.degree. C. deposition temperature such as, for
example, tungsten or aluminum may be deposited. An optical step,
such as represented by exemplary gox ray 2821, may be performed to
densify and/or remove defects from gate dielectric 2807. The gate
material may be chemically mechanically polished, and the gate area
defined by masking and etching, thus forming the gate electrode
2808. The shape of gate electrode 2808 is illustrative, the gate
electrode may also overlap a portion of N+ source and drain regions
2832. An optical step, such as represented by exemplary gox ray
2821, may be performed to anneal defects and activate dopants such
as LDD and S/D implants, densify an ILD thick oxide 2809, form DSS
junctions (Dopant Segregated Schottky such as NiSi.sub.2), and/or
form contact and S/D silicides (not shown). The optical anneal may
be performed at each sub-step as desired, or may be done at prior
to the HKMG deposition (such as after the dummy gate but before the
HKMG formation), or various combinations. Moreover, multiple pulses
of the laser may be utilized to improve the anneal, activation, and
yield of the process.
[0114] As illustrated in FIG. 28F, a low temperature thick oxide
2809 may be deposited and planarized. Source, gate, and drain
contacts, P+ doped region contact (not shown) openings may be
masked and etched preparing the transistors to be connected via
metallization. P+ doped region contact may be constructed thru
isolation regions 2805, suitably when the isolation regions 2805 is
formed to a shared P+ doped region 2824. Thus gate contact 2811
connects to gate electrode 2808, and source & drain contacts
2840 connect to N+ source and drain regions 2832. An optical step,
such as illustrated by exemplary STI ray 2831, may be performed to
anneal contact etch damage and densify the thick oxide 2809.
[0115] As illustrated in FIG. 28G, thru layer vias (TLVs) 2860 may
be formed by etching thick oxide 2809, gate dielectric 2807,
isolation regions 2805, oxide layer 2880, into a portion of the
upper oxide layer BEOL isolation 2896 of acceptor wafer 2810 BEOL,
and filling with an electrically and thermally conducting material
or an electrically non-conducting but thermally conducting
material. Second device layer metal interconnect 2861 may be formed
by conventional processing. TLVs 2860 may be constructed of
thermally conductive but not electrically conductive materials, for
example, DLC (Diamond Like Carbon), and may connect the FD-RCAT
transistor device and other devices on the top (second) crystalline
layer thermally to shield/heat sink layer 2888. TLVs 2860 may be
constructed out of electrically and thermally conductive materials,
such as Tungsten, Copper, or aluminum, and may provide a thermal
and electrical connection path from the FD-RCAT transistor device
and other devices on the top (second) crystalline layer to
shield/heat sink layer 2888, which may be a ground or Vdd plane in
the design/layout. TLVs 2860 may be also constructed in the device
scribelanes (pre-designed in base layers or potential dicelines) to
provide thermal conduction to the heat sink, and may be sawed/diced
off when the wafer is diced for packaging not shown). Shield/heat
sink layer 2888 may be configured to act (or adapted to act) as an
emf (electro-motive force) shield to prevent direct layer to layer
cross-talk between transistors in the donor wafer layer and
transistors in the acceptor wafer. In addition to static ground or
Vdd biasing, shield/heat sink layer 2888 may be actively biased
with an anti-interference signal from circuitry residing on, for
example, a layer of the 3D-IC or off chip. A thermal conduction
path may be constructed from the devices in the upper layer, the
transferred donor layer and formed transistors, to the acceptor
wafer substrate and associated heat sink. The thermal conduction
path from the FD-RCAT transistor device and other devices on the
top (second) crystalline layer, for example, N+ source and drain
regions 2832, to the acceptor wafer heat sink 2897 may include
source & drain contacts 2840, second device layer metal
interconnect 2861, TLV 2860, shield path connect 2885 (shown as
twice), shield path via 2883 (shown as twice), metal interconnect
2881, first (acceptor) layer metal interconnect 2891, acceptor
wafer transistors and devices 2893, and acceptor substrate 2895.
The elements of the thermal conduction path may include materials
that have a thermal conductivity greater than 10 W/m-K, for
example, copper (about 400 W/m-K), aluminum (about 237 W/m-K), and
Tungsten (about 173 W/m-K). The heat removal apparatus, which may
include acceptor wafer heat sink 2897, may include an external
surface from which heat transfer may take place by methods such as
air cooling, liquid cooling, or attachment to another heat sink or
heat spreader structure.
[0116] It should be noted that one of the design requirements for a
monolithic 3D IC design may be that substantially all of the
stacked layers and the base or substrate would have their
respective dice lines (may be called scribelines) aligned. As the
base wafer or substrate is processed and multiple circuits may be
constructed on semiconductor layers that overlay each other, the
overall device may be designed wherein each overlaying layer would
have its respective dice lines overlying the dice lines of the
layer underneath, thus at the end of processing the entire layer
stacked wafer/substrate could be diced in a dicing step. There may
be test structures in the streets between dice lines, which overall
may be called scribelanes or dicelanes. These scribelanes or
dicelanes may be 10 um wide, 20 um wide, 50 um wide 100 um wide, or
greater than 100 um wide depending on design choice and die
singulation process capability. The scribelanes or dicelanes may
include guard-ring structures and/or other die border structures.
In a monolithic 3D design each layer test structure could be
connected through each of the overlying layers and then to the top
surface to allow access to these `buried` test structure before
dicing the wafer. Accordingly the design may include these vertical
connections and may offset the layer test structures to enable such
connection. In many cases the die borders comprise a protection
structure, such as, for example, a guard-ring structure, die seal
structure, ESD structure, and others elements. Accordingly in a
monolithic 3D device these structures, such as guard rings, would
be designed to overlay each other and may be aligned to each other
during the course of processing. The die edges may be sealed by a
process and structure such as, for example, described in relation
to FIG. 183C of incorporated U.S. Pat. No. 8,273,610, and may
include aspects as described in relation to FIG. 183A and 183B of
same reference. One skilled in the art would recognize that the die
seal can be passive or electrically active. On each 3D stack layer,
or stratum, the electronic circuits within one die, that may be
circumscribed by a dicelane, may not be connected to the electronic
circuits of a second die on that same wafer, that second die also
may be circumscribed by a dicelane. Further, the
dicelane/scribelane of one stratum in the 3D stack may be aligned
to the dicelane/scribelane of another stratum in the 3D stack, thus
providing a direct die singulation vector for the 3D stack of
stratums/layers.
[0117] Furthermore, some or all of the layers utilized as
shield/heat sink layer 2888, which may include shapes of material
such as the strips or fingers as illustrated in FIG. 27B-1, may be
driven by a portion of the second layer transistors and circuits
(within the transferred donor wafer layer or layers) or the
acceptor wafer transistors and circuits, to provide a programmable
back-bias to at least a portion of the second layer transistors.
The programmable back bias may utilize a circuit to do so, for
example, such as shown in FIG. 17B of U.S. Pat. No. 8,273,610, the
contents incorporated herein by reference; wherein the `Primary`
layer may be the second layer of transistors for which the
back-bias is being provided, the `Foundation` layer could be either
the second layer transistors (donor) or first layer transistors
(acceptor), and the routing metal lines connections 1723 and 1724
may include portions of the shield/heat sink layer 2888 layer or
layers. Moreover, some or all of the layers utilized as shield/heat
sink layer 2888, which may include strips or fingers as illustrated
in FIG. 27B-1, may be driven by a portion of the second layer
transistors and circuits (within the transferred donor wafer layer
or layers) or the acceptor wafer transistors and circuits to
provide a programmable power supply to at least a portion of the
second layer transistors. The programmable power supply may utilize
a circuit to do so, for example, such as shown in FIG. 17C of U.S.
Pat. No. 8,273,610, the contents incorporated herein by reference;
wherein the `Primary` layer may be the second layer of transistors
for which the programmable power supplies are being provided to,
the `Foundation` layer could be either the second layer transistors
(donor) or first layer transistors (acceptor), and the routing
metal line connections from Vout to the various second layer
transistors may include portions of the shield/heat sink layer 2888
layer or layers. The Vsupply on line 17C12 and the control signals
on control line 17C16 may be controlled by and/or generated in the
second layer transistors (for example donor wafer device structures
such as the FD-RCATs formed as described in relation to FIG. 28) or
first layer transistors (acceptor, for example acceptor wafer
transistors and devices 2893), or off chip circuits. Furthermore,
some or all of the layers utilized as shield/heat sink layer 2888,
which may include strips or fingers as illustrated in FIG. 27B-1 or
other shapes such as those in FIG. 27B, may be utilized to
distribute independent power supplies to various portions of the
second layer transistors (for example donor wafer device structures
such as the FD-RCATs formed as described in relation to FIG. 28 of
incorporated patent reference U.S. Pat. No. 9,385,058) or first
layer transistors (acceptor, for example acceptor wafer transistors
and devices 2893 of incorporated patent reference U.S. Pat. No.
9,385,058) and circuits; for example, one power supply and/or
voltage may be routed to the sequential logic circuits of the
second layer and a different power supply and/or voltage routed to
the combinatorial logic circuits of the second layer. Moreover, the
power distribution circuits/grid may be designed so that Vdd may
have a different value for each stack layer. Patterning of
shield/heat sink layer 2888 or layers can impact their
heat-shielding capacity. This impact may be mitigated, for example,
by enhancing the top shield/heat sink layer 2888 areal density,
creating more of the secondary shield/heat sink layers 2888, or
attending to special CAD rules regarding their metal density,
similar to CAD rules that are required to accommodate
Chemical-Mechanical Planarization (CMP). These constraints would be
integrated into a design and layout EDA tool
[0118] TLVs 2860 may be formed through the transferred layers. As
the transferred layers may be thin, on the order of about 200 nm or
less in thickness, the TLVs may be easily manufactured as a typical
metal to metal via may be, and said TLV may have state of the art
diameters such as nanometers or tens to a few hundreds of
nanometers, such as, for example about 150 nm or about 100 nm or
about 50 nm. The thinner the transferred layers, the smaller the
thru layer via diameter obtainable, which may result from
maintaining manufacturable via aspect ratios. The thickness of the
layer or layers transferred according to some embodiments of the
invention may be designed as such to match and enable the most
suitable obtainable lithographic resolution (and enable the use of
conventional state of the art lithographic tools), such as, for
example, less than about 10 nm, 14 nm, 22 nm or 28 nm linewidth
resolution and alignment capability, such as, for example, less
than about 5 nm, 10 nm, 20 nm, or 40 nm alignment
accuracy/precision/error, of the manufacturing process employed to
create the thru layer vias or any other structures on the
transferred layer or layers.
[0119] As illustrated in FIG. 28G-1, at least one conductive bond
pad 2864 for interfacing electrically (and may thermally) to
external devices may be formed on top of the completed device and
may include at least one metal layer of second device layer metal
interconnect 2861. Bond pad 2864 may overlay second device layer
metal interconnect 2861 or a portion of (some of the metal and
insulator layers of) second device layer metal interconnect 2861.
Bond pad 2864 may be directly aligned to the acceptor wafer
alignment marks (not shown) and the I/O driver circuitry may be
formed by the second layer (donor) transistors, for example, donor
wafer device structures such as the FD-RCATs formed as described in
relation to FIG. 28. Bond pad 2864 may be connected to the second
layer transistors thru the second device layer metal interconnect
2861 which may include vias 2862. The I/O driver circuitry may be
formed by transistors from the acceptor wafer transistors and
devices 2893, or from transistors in other strata if the 3DIC
device has more than two layers of transistors. I/O pad control
metal segment 2867 may be formed directly underneath bond pad 2864
and may influence the noise and ESD (Electro Static Discharge)
characteristics of bond pad 2864. The emf influence of I/O pad
control metal segment 2867 may be controlled by circuitry formed
from a portion of the second layer transistors. I/O pad control
metal segment 2867 may be formed with second device layer metal
interconnect 2861.
[0120] Formation of CMOS in one transferred layer and the
orthogonal connect strip methodology may be found as illustrated in
at least FIGS. 30-33, 73-80, and 94 and related specification
sections of U.S. Pat. No. 8,273,610, and may be applied to at least
the FIG. 28 formation techniques herein. Transferred layer or
layers may have regions of STI or other transistor elements within
it or on it when transferred, but would then use alignment and
connection schemes for layer transfer of patterned layers as
described in incorporated patent references.
[0121] Persons of ordinary skill in the art will appreciate that
the illustrations in FIGS. 28A through 28G are exemplary only and
are not drawn to scale. Such skilled persons will further
appreciate that many variations are possible such as, for example,
a p-channel FD-RCAT may be formed with changing the types of
dopings appropriately. Moreover, the P- substrate donor wafer 2800
may be n type or un-doped. Further, P- doped channel layer 2803 may
include multiple layers of different doping concentrations and
gradients to fine tune the eventual FD-RCAT channel for electrical
performance and reliability characteristics, such as, for example,
off-state leakage current and on-state current. Furthermore,
isolation regions 2805 may be formed by a hard mask defined process
flow, wherein a hard mask stack, such as, for example, silicon
oxide and silicon nitride layers, or silicon oxide and amorphous
carbon layers, may be utilized. Moreover, CMOS FD-RCATs may be
constructed with n-JLRCATs in a first mono-crystalline silicon
layer and p-JLRCATs in a second mono-crystalline layer, which may
include different crystalline orientations of the mono-crystalline
silicon layers, such as for example, <100>, <111> or
<551>, and may include different contact silicides for
optimum contact resistance to p or n type source, drains, and
gates. Furthermore, P+ doped regions 2824 may be utilized for a
double gate structure for the FD-RCAT and may utilize techniques
described in the incorporated references. Further, efficient heat
removal and transistor body biasing may be accomplished on a
FD-RCAT by adding an appropriately doped buried layer (N- in the
case of a n-FD-RCAT), forming a buried layer region underneath the
P+ doped regions 2824 for junction isolation, and connecting that
buried region to a thermal and electrical contact, similar to what
is described for layer 1606 and region 1646 in FIGS. 16A-G in the
incorporated reference pending U.S. patent application Ser. No.
13/441,923 and U.S. Patent Publication 2012/0091587. Moreover,
implants after the formation of the isolation regions 2805 may be
annealed by optical (such as pulsed laser) means as previously
described and the acceptor wafer metallization may be protected by
the shield/heat sink layer 2888. Furthermore, raised source and
drain contact structures, such as etch and epi SiGe and SiC, may be
utilized for strain and contact resistance improvements and the
damage from the processes may be optically annealed. Moreover, the
optical anneal may be performed at each sub-step as desired, or may
be done at prior to the HKMG deposition (such as after the dummy
gate but before the HKMG formation), or various combinations.
Moreover, multiple pulses of the laser may be utilized to improve
the anneal, activation, and yield of the process. Many other
modifications within the scope of the invention will suggest
themselves to such skilled persons after reading this
specification. Thus the invention is to be limited only by the
appended claims.
[0122] A planar fully depleted n-channel MOSFET (FD-MOSFET) with an
optional integrated heat shield/spreader suitable for a monolithic
3D IC may be constructed as follows. The FD-MOSFET may provide an
improved transistor variability control and conduction channel
electrostatic control, as well as the ability to utilize an updoped
channel, thereby improving carrier mobility. In addition, the
FD-MOSFET does not demand doping or pocket implants in the channel
to control the electrostatic characteristics and tune the threshold
voltages. Sub-threshold slope, DIBL, and other short channel
effects are greatly improved due to the firm gate electrostatic
control over the channel. Moreover, a heat spreading, heat
conducting and/or optically reflecting material layer or layers may
be incorporated between the sensitive metal interconnect layers and
the layer or regions being optically irradiated and annealed to
repair defects in the crystalline 3D-IC layers and regions and to
activate semiconductor dopants in the crystalline layers or regions
of a 3D-IC without harm to the sensitive metal interconnect and
associated dielectrics. FIG. 29A-G illustrates an exemplary
n-channel FD-MOSFET which may be constructed in a 3D stacked layer
using procedures outlined below and in U.S. Pat. Nos. 8,273,610,
9,099,526, 9,219,005, 8,557,632 and 8,581,349. The contents of the
foregoing applications are incorporated herein by reference.
[0123] As illustrated in FIG. 29A, a P- substrate donor wafer 2900
may be processed to include a wafer sized layer of doping across
the wafer. The channel layer 2902 may be formed by ion implantation
and thermal anneal. P- substrate donor wafer 2900 may include a
crystalline material, for example, mono-crystalline (single
crystal) silicon. P- substrate donor wafer 2900 may be very lightly
doped (less than 1e15 atoms/cm.sup.3) or nominally un-doped (less
than 1e14 atoms/cm.sup.3). Channel layer 2902 may have additional
ion implantation and anneal processing to provide a different
dopant level than P- substrate donor wafer 2900 and may have graded
or various layers of doping concentration. The layer stack may
alternatively be formed by epitaxially deposited doped or undoped
silicon layers, or by a combination of epitaxy and implantation, or
by layer transfer. Annealing of implants and doping may include,
for example, conductive/inductive thermal, optical annealing
techniques or types of Rapid Thermal Anneal (RTA or spike). The
preferred crystalline channel layer 2902 will be undoped to
eventually create an FD-MOSFET transistor with an updoped
conduction channel.
[0124] As illustrated in FIG. 29B, the top surface of the P-
substrate donor wafer 2900 layer stack may be prepared for oxide
wafer bonding with a deposition of an oxide or by thermal oxidation
of channel layer 2902 to form oxide layer 2980. A layer transfer
demarcation plane (shown as dashed line) 2999 may be formed by
hydrogen implantation or other methods as described in the
incorporated references. The P- substrate donor wafer 2900, such as
surface 2982, and acceptor wafer 2910 may be prepared for wafer
bonding as previously described and low temperature (less than
approximately 400.degree. C.) bonded. Acceptor wafer 2910, as
described in the incorporated references, may include, for example,
transistors, circuitry, and metal, such as, for example, aluminum
or copper, interconnect wiring, a metal shield/heat sink layer or
layers, and thru layer via metal interconnect strips or pads.
Acceptor wafer 2910 may be substantially comprised of a crystalline
material, for example mono-crystalline silicon or germanium, or may
be an engineered substrate/wafer such as, for example, an SOI
(Silicon on Insulator) wafer or GeOI (Germanium on Insulator)
substrate. Acceptor wafer 2910 may include transistors such as, for
example, MOSFETS, FD-MOSFETS, FinFets, FD-RCATs, BJTs, HEMTs,
and/or HBTs. The portion of the channel layer 2902 and the P-
substrate donor wafer 2900 that may be above (when the layer stack
is flipped over and bonded to the acceptor wafer 2910) the layer
transfer demarcation plane 2999 may be removed by cleaving or other
low temperature processes as described in the incorporated
references, such as, for example, ion-cut with mechanical or
thermal cleave or other layer transfer methods, thus forming
remaining channel layer 2903. Damage/defects to crystalline
structure of channel layer 2902 may be annealed by some of the
annealing methods described, for example the short wavelength
pulsed laser techniques, wherein the channel layer 2902 or portions
of channel layer 2902 may be heated to defect annealing
temperatures, but the layer transfer demarcation plane 2999 may be
kept below the temperate for cleaving and/or significant hydrogen
diffusion. The optical energy may be deposited in the upper layer
of the stack, for example near surface 2982, and annealing of a
portion of channel layer 2902 may take place via heat
diffusion.
[0125] As illustrated in FIG. 29C, oxide layer 2980 and remaining
channel layer 2903 have been layer transferred to acceptor wafer
2910. The top surface of remaining channel layer 2903 may be
chemically or mechanically polished, and/or may be thinned by low
temperature oxidation and strip processes, such as the TEL SPA tool
radical oxidation and HF:H.sub.2O solutions as described herein and
in referenced patents and patent applications. Thru the processing,
the wafer sized layer remaining channel layer 2903 could be thinned
from its original total thickness, and its final total thickness
could be in the range of about 5 nm to about 20 nm, for example, 5
nm, 7 nm, 10 nm, 12 nm, 15 nm, or 20 nm. Remaining channel layer
2903 may have a thickness and doping that may allow fully-depleted
channel operation when the FD- MOSFET transistor is substantially
completely formed. Acceptor wafer 2910 may include one or more (two
are shown in this example) shield/heat sink layers 2988, which may
include materials such as, for example, Aluminum, Tungsten (a
refractory metal), Copper, silicon or cobalt based silicides, or
forms of carbon such as carbon nanotubes, and may be layered itself
as described herein FIG. 50. Each shield/heat sink layer 2988 may
have a thickness range of about 50 nm to about 1 mm, for example,
50 nm, 100 nm, 200 nm, 300 nm, 500 nm, 0.1 um, 1 um, 2 um, and 10
um. Shield/heat sink layer 2988 may include isolation openings
2987, and alignment mark openings (not shown), which may be
utilized for short wavelength alignment of top layer (donor)
processing to the acceptor wafer alignment marks (not shown).
Shield/heat sink layer 2988 may include one or more shield path
connects 2985 and shield path vias 2983. Shield path via 2983 may
thermally and/or electrically couple and connect shield path
connect 2985 to acceptor wafer 2910 interconnect metallization
layers such as, for example, exemplary acceptor metal interconnect
2981 (shown). Shield path connect 2985 may also thermally and/or
electrically couple and connect each shield/heat sink layer 2988 to
the other and to acceptor wafer 2910 interconnect metallization
layers such as, for example, acceptor metal interconnect 2981,
thereby creating a heat conduction path from the shield/heat sink
layer 2988 to the acceptor substrate 2995, and a heat sink (shown
in FIG. 29G.). Isolation openings 2987 may include dielectric
materials, similar to those of BEOL isolation 2996. Acceptor wafer
2910 may include first (acceptor) layer metal interconnect 2991,
acceptor wafer transistors and devices 2993, and acceptor substrate
2995. Various topside defect anneals may be utilized. For this
illustration, an optical beam such as the laser annealing
previously described is used. Optical anneal beams may be optimized
to focus light absorption and heat generation within or at the
surface of remaining channel layer 2903 and provide surface
smoothing and/or defect annealing (defects may be from the cleave
and/or the ion-cut implantation) with exemplary smoothing/annealing
ray 2966. The laser assisted smoothing/annealing with the absorbed
heat generated by exemplary smoothing/annealing ray 2966 may also
include a pre-heat of the bonded stack to, for example, about
100.degree. C. to about 400.degree. C., and/or a rapid thermal
spike to temperatures above about 200.degree. C. to about
600.degree. C. Additionally, absorber layers or regions, for
example, including amorphous carbon, amorphous silicon, and phase
changing materials (see U.S. Pat. Nos. 6,635,588 and 6,479,821 to
Hawryluk et al. for example), may be utilized to increase the
efficiency of the optical energy capture in conversion to heat for
the desired annealing or activation processes. Moreover, multiple
pulses of the laser may be utilized to improve the anneal,
activation, and yield of the process. Reflected ray 2963 may be
reflected and/or absorbed by shield/heat sink layer 2988 regions
thus blocking the optical absorption of ray blocked metal
interconnect 2981. Annealing of dopants or annealing of damage,
such as from the H cleave implant damage, may be also accomplished
by a set of rays such as repair ray 2965. Heat generated by
absorbed photons from, for example, smoothing/annealing ray 2966,
reflected ray 2963, and/or repair ray 2965 may also be absorbed by
shield/heat sink layer 2988 regions and dissipated laterally and
may keep the temperature of underlying metal layers, such as metal
interconnect 2981, and other metal layers below it, cooler and
prevent damage. Shield/heat sink layer 2988 and associated
dielectrics may laterally spread and conduct the heat generated by
the topside defect anneal, and in conjunction with the dielectric
materials (low heat conductivity) above and below shield/heat sink
layer 2988, keep the interconnect metals and low-k dielectrics of
the acceptor wafer interconnect layers cooler than a damage
temperature, such as, for example, 400.degree. C. A second layer of
shield/heat sink layer 2988 may be constructed (shown) with a low
heat conductive material sandwiched between the two heat sink
layers, such as silicon oxide or carbon doped `low-k` silicon
oxides, for improved thermal protection of the acceptor wafer
interconnect layers, metal and dielectrics. Shield/heat sink layer
2988 may act as a heat spreader. Electrically conductive materials
may be used for the two layers of shield/heat sink layer 2988 and
thus may provide, for example, a Vss and a Vdd plane and/or grid
that may be connected to the donor layer transistors above, as well
may be connected to the acceptor wafer transistors below, and/or
may provide below transferred layer device interconnection. Noise
on the power grids, such as the Vss and Vdd plane power conducting
lines/wires, may be mitigated by attaching/connecting decoupling
capacitors onto the power conducting lines of the grids. The
decoupling caps, which may be within the second layer (donor, for
example, donor wafer device structures) or first layer (acceptor,
for example acceptor wafer transistors and devices 2993), may
include, for example, trench capacitors such as described by Pei,
C., et al., "A novel, low-cost deep trench decoupling capacitor for
high-performance, low-power bulk CMOS applications," ICSICT
(9.sup.th International Conference on Solid-State and
Integrated-Circuit Technology) 2008, October 2008, pp. 1146-1149,
of IBM. The decoupling capacitors may include, for example, planar
capacitors, such as poly to substrate or poly to poly, or MiM
capacitors (Metal-Insulator-Metal). Shield/heat sink layer 2988 may
include materials with a high thermal conductivity greater than 10
W/m-K, for example, copper (about 400 W/m-K), aluminum (about 237
W/m-K), Tungsten (about 173 W/m-K), Plasma Enhanced Chemical Vapor
Deposited Diamond Like Carbon-PECVD DLC (about 1000 W/m-K), and
Chemical Vapor Deposited (CVD) graphene (about 5000 W/m-K).
Shield/heat sink layer 2988 may be sandwiched and/or substantially
enclosed by materials with a low thermal conductivity (less than 10
W/m-K), for example, silicon dioxide (about 1.4 W/m-K). The
sandwiching of high and low thermal conductivity materials in
layers, such as shield/heat sink layer 2988 and under &
overlying dielectric layers, spreads the localized heat/light
energy of the topside anneal laterally and protects the underlying
layers of interconnect metallization & dielectrics, such as in
the acceptor wafer 2910, from harmful temperatures or damage. When
there may be more than one shield/heat sink layer 2988 in the
device, the heat conducting layer closest to the second crystalline
layer or oxide layer 2980 may be constructed with a different
material, for example a high melting point material, for example a
refractory metal such as tungsten, than the other heat conducting
layer or layers, which may be constructed with, for example, a
lower melting point material, for example, such as aluminum or
copper. Now transistors may be formed with low effective
temperature (less than approximately 400.degree. C. exposure to the
acceptor wafer 2910 sensitive layers, such as interconnect and
device layers) processing, and may be aligned to the acceptor wafer
alignment marks (not shown) as described in the incorporated
references. This may include further optical defect annealing or
dopant activation steps. The donor wafer 2900 may now also be
processed, such as smoothing and annealing, and reused for
additional layer transfers. The insulator layer, such as deposited
bonding oxides (for example oxide layer 2980) and/or before bonding
preparation existing oxides (for example the BEOL isolation 2996 on
top of the topmost metal layer of shield/heat sink layer 2988),
between the donor wafer transferred monocrystalline layer and the
acceptor wafer topmost metal layer, may include thicknesses of less
than 1 um, less than 500 nm, less than 400 nm, less than 300 nm,
less than 200 nm, or less than 100 nm.
[0126] As illustrated in FIG. 29D, transistor isolation regions
2905 may be formed by mask defining and plasma/RIE etching
remaining channel layer 2903 substantially to the top of oxide
layer 2980 (not shown), substantially into oxide layer 2980, or
into a portion of the upper oxide layer of acceptor wafer 2910 (not
shown). Thus channel region 2923 may be formed, which may
substantially form the transistor body. A low-temperature gap fill
dielectric, such as SACVD oxide, may be deposited and chemically
mechanically polished, the oxide remaining in isolation regions
2905. An optical step, such as illustrated by exemplary STI ray
2967, may be performed to anneal etch damage and densify the STI
oxide in isolation regions 2905. The doping concentration of the
channel region 2923 may include gradients of concentration or
layers of differing doping concentrations. Any additional doping,
such as ion-implanted channel implants, may be activated and
annealed with optical annealing, such as illustrated by exemplary
implant ray 2969, as described herein. The optical anneal, such as
exemplary STI ray 2967, and/or exemplary implant ray 2969 may be
performed at separate times and processing parameters (such as
laser energy, frequency, etc.) or may be done in combination or as
one optical anneal. Optical absorber and or reflective layers or
regions may be employed to enhance the anneal and/or protect the
underlying sensitive structures. Moreover, multiple pulses of the
laser may be utilized to improve the anneal, activation, and yield
of the process.
[0127] As illustrated in FIG. 29E, a transistor forming process,
such as a conventional HKMG with raised source and drains (S/D),
may be performed. For example, a dummy gate stack (not shown),
utilizing oxide and polysilicon, may be formed, gate spacers 2930
may be formed, raised S/D regions 2932 and channel stressors may be
formed by etch and epitaxial deposition, for example, of SiGe
and/or SiC depending on P or N channel, LDD and S/D
ion-implantations may be performed, and first ILD 2936 may be
deposited and CMP'd to expose the tops of the dummy gates. Thus
transistor channel 2933 and S/D & LDD regions 2935 may be
formed. The dummy gate stack may be removed and a gate dielectric
2907 may be formed and a gate metal material gate electrode 2908,
including a layer of proper work function metal
(Ti.sub.xAl.sub.y,N.sub.z for example) and a conductive fill, such
as aluminum, and may be deposited and CMP'd. The gate dielectric
2907 may be an atomic layer deposited (ALD) gate dielectric that
may be paired with a work function specific gate metal in the
industry standard high k metal gate process schemes, for example,
as described in the incorporated references. Alternatively, the
gate dielectric 2907 may be formed with a low temperature processes
including, for example, LPCVD SiO.sub.2 oxide deposition (see Ahn,
J., et al., "High-quality MOSFET's with ultrathin LPCVD gate
SiO.sub.2," IEEE Electron Device Lett., vol. 13, no. 4, pp.
186-188, April 1992) or low temperature microwave plasma oxidation
of the silicon surfaces (see Kim, J. Y., et al., "The excellent
scalability of the RCAT (recess-channel-array-transistor)
technology for sub-70 nm DRAM feature size and beyond," 2005 IEEE
VLSI-TSA International Symposium, pp. 33-29, 25-27 Apr. 2005) and a
gate material with proper work function and less than approximately
400.degree. C. deposition temperature such as, for example,
tungsten or aluminum may be deposited. An optical step, such as
represented by exemplary anneal ray 2921, may be performed to
densify and/or remove defects from gate dielectric 2907, anneal
defects and activate dopants such as LDD and S/D implants, densify
the first ILD 2936, form DSS junctions (Dopant Segregated Schottky
such as NiSi.sub.2), and/or form contact and S/D silicides (not
shown). The optical anneal may be performed at each sub-step as
desired, or may be done at prior to the HKMG deposition (such as
after the dummy gate but before the HKMG formation), or various
combinations. Moreover, multiple pulses of the laser may be
utilized to improve the anneal, activation, and yield of the
process. Raised S/D regions 2932 may be formed by low temperature
(less than 400.degree. C.) deposition of in-situ doped polysilicon
or amorphous silicon into the S/D openings, an optical anneal to
further crystallize and dopant activate the raised S/D material,
and removal of excess raised S/D material
[0128] As illustrated in FIG. 29F, a low temperature thick oxide
2909 may be deposited and planarized. Source, gate, and drain
contacts openings may be masked and etched preparing the
transistors to be connected via metallization. Thus gate contact
2911 connects to gate electrode 2908, and source & drain
contacts 2940 connect to raised S/D regions 2932. An optical step,
such as illustrated by exemplary ILD anneal ray 2951, may be
performed to anneal contact etch damage and densify the thick oxide
2909.
[0129] As illustrated in FIG. 29G, thru layer vias (TLVs) 2960 may
be formed by etching thick oxide 2909, first ILD 2936, isolation
regions 2905, oxide layer 2980, into a portion of the upper oxide
layer BEOL isolation 2996 of acceptor wafer 2910 BEOL, and filling
with an electrically and thermally conducting material (such as
tungsten or cooper) or an electrically non-conducting but thermally
conducting material (such as described elsewhere within). Second
device layer metal interconnect 2961 may be formed by conventional
processing. TLVs 2960 may be constructed of thermally conductive
but not electrically conductive materials, for example, DLC
(Diamond Like Carbon), and may connect the FD-MOSFET transistor
device and other devices on the top (second) crystalline layer
thermally to shield/heat sink layer 2988. TLVs 2960 may be
constructed out of electrically and thermally conductive materials,
such as Tungsten, Copper, or aluminum, and may provide a thermal
and electrical connection path from the FD- MOSFET transistor
device and other devices on the top (second) crystalline layer to
shield/heat sink layer 2988, which may be a ground or Vdd plane in
the design/layout. TLVs 2960 may be also constructed in the device
scribelanes (pre-designed in base layers or potential dicelines) to
provide thermal conduction to the heat sink, and may be sawed/diced
off when the wafer is diced for packaging not shown). Shield/heat
sink layer 2988 may be configured to act (or adapted to act) as an
emf (electro-motive force) shield to prevent direct layer to layer
cross-talk between transistors in the donor wafer layer and
transistors in the acceptor wafer. In addition to static ground or
Vdd biasing, shield/heat sink layer 2988 may be actively biased
with an anti-interference signal from circuitry residing on, for
example, a layer of the 3D-IC or off chip. The formed FD-MOSFET
transistor device may include semiconductor regions wherein the
dopant concentration of neighboring regions of the transistor in
the horizontal plane, such as traversed by exemplary dopant plane
2934, may have regions, for example, transistor channel 2933 and
S/D & LDD regions 2935, that differ substantially in dopant
concentration, for example, a 10 times greater doping concentration
in S/D & LDD regions 2935 than in transistor channel 2933,
and/or may have a different dopant type, such as, for example
p-type or n-type dopant, and/or may be doped and substantially
undoped in the neighboring regions. For example, transistor channel
2933 may be very lightly doped (less than 1e15 atoms/cm.sup.3) or
nominally un-doped (less than 1e14 atoms/cm.sup.3) and S/D &
LDD regions 2935 may be doped at greater than 1e15 atoms/cm.sup.3
or greater than 1e16 atoms/cm.sup.3. For example, transistor
channel 2933 may be doped with p-type dopant and S/D & LDD
regions 2935 may be doped with n-type dopant.
[0130] A thermal conduction path may be constructed from the
devices in the upper layer, the transferred donor layer and formed
transistors, to the acceptor wafer substrate and associated heat
sink. The thermal conduction path from the FD-MOSFET transistor
device and other devices on the top (second) crystalline layer, for
example, raised S/D regions 2932, to the acceptor wafer heat sink
2997 may include source & drain contacts 2940, second device
layer metal interconnect 2961, TLV 2960, shield path connect 2985
(shown as twice), shield path via 2983 (shown as twice), metal
interconnect 2981, first (acceptor) layer metal interconnect 2991,
acceptor wafer transistors and devices 2993, and acceptor substrate
2995. The elements of the thermal conduction path may include
materials that have a thermal conductivity greater than 10 W/m-K,
for example, copper (about 400 W/m-K), aluminum (about 237 W/m-K),
and Tungsten (about 173 W/m-K), and may include material with
thermal conductivity lower than 10 W/m-K but have a high heat
transfer capacity due to the wide area available for heat transfer
and thickness of the structure (Fourier's Law), such as, for
example, acceptor substrate 2995. The elements of the thermal
conduction path may include materials that are thermally conductive
but may not be substantially electrically conductive, for example,
Plasma Enhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD
DLC (about 1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene
(about 5000 W/m-K). The acceptor wafer interconnects may be
substantially surrounded by BEOL isolation 2996 dielectric. The
heat removal apparatus, which may include acceptor wafer heat sink
2997, may include an external surface from which heat transfer may
take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0131] Furthermore, some or all of the layers utilized as
shield/heat sink layer 2988, which may include shapes of material
such as the strips or fingers as illustrated in FIG. 27B-1, may be
driven by a portion of the second layer transistors and circuits
(within the transferred donor wafer layer or layers) or the
acceptor wafer transistors and circuits, to provide a programmable
back-bias to at least a portion of the second layer transistors.
The programmable back bias may utilize a circuit to do so, for
example, such as shown in FIG. 17B of U.S. Pat. No. 8,273,610, the
contents incorporated herein by reference; wherein the `Primary`
layer may be the second layer of transistors for which the
back-bias is being provided, the `Foundation` layer could be either
the second layer transistors (donor) or first layer transistors
(acceptor), and the routing metal lines connections 1723 and 1724
may include portions of the shield/heat sink layer 2988 layer or
layers. Moreover, some or all of the layers utilized as shield/heat
sink layer 2988, which may include strips or fingers as illustrated
in FIG. 27B-1, may be driven by a portion of the second layer
transistors and circuits (within the transferred donor wafer layer
or layers) or the acceptor wafer transistors and circuits to
provide a programmable power supply to at least a portion of the
second layer transistors. The programmable power supply may utilize
a circuit to do so, for example, such as shown in FIG. 17C of U.S.
Pat. No. 8,273,610, the contents incorporated herein by reference;
wherein the `Primary` layer may be the second layer of transistors
for which the programmable power supplies are being provided to,
the `Foundation` layer could be either the second layer transistors
(donor) or first layer transistors (acceptor), and the routing
metal line connections from Vout to the various second layer
transistors may include portions of the shield/heat sink layer 2988
layer or layers. The Vsupply on line 17C12 and the control signals
on control line 17C16 may be controlled by and/or generated in the
second layer transistors (for example donor wafer device structures
such as the FD-MOSFETs formed as described in relation to FIG. 29)
or first layer transistors (acceptor, for example acceptor wafer
transistors and devices 2993), or off chip circuits. Furthermore,
some or all of the layers utilized as shield/heat sink layer 2988,
which may include strips or fingers as illustrated in FIG. 27B-1 or
other shapes such as those in FIG. 27B, may be utilized to
distribute independent power supplies to various portions of the
second layer transistors (for example donor wafer device structures
such as the FD-MOSFETs formed as described in relation to FIG. 29
of incorporated patent reference U.S. Pat. No. 9,385,058) or first
layer transistors (acceptor, for example acceptor wafer transistors
and devices 2993 of incorporated patent reference U.S. Pat. No.
9,385,058) and circuits; for example, one power supply and/or
voltage may be routed to the sequential logic circuits of the
second layer and a different power supply and/or voltage routed to
the combinatorial logic circuits of the second layer. Moreover, the
power distribution circuits/grid may be designed so that Vdd may
have a different value for each stack layer. Patterning of
shield/heat sink layer 2988 or layers can impact their
heat-shielding capacity. This impact may be mitigated, for example,
by enhancing the top shield/heat sink layer 2988 areal density,
creating more of the secondary shield/heat sink layers 2988, or
attending to special CAD rules regarding their metal density,
similar to CAD rules that are required to accommodate
Chemical-Mechanical Planarization (CMP). These constraints would be
integrated into a design and layout EDA tool. Second layer
metallization and power grid wires (such as second device layer
metal interconnect 2961) may be constructed thicker and wider than
the first layer metal interconnect (such as metal interconnect
2981), and hence have a higher current conduction capacity.
Moreover, the second layer of circuits and transistors, for
example, for example donor wafer device structures such as the
FD-MOSFETs formed as described in relation to FIG. 29, may include
I/O logic devices, such as SerDes (Serialiser/Deserialiser), and
conductive bond pads (not shown) (herein such as FIG. 33). The
output or input conductive pads of the I/O circuits may be coupled,
for example by bonded wires, to external devices. The output or
input conductive pads may also act as a contact port for the 3D
device output to connect to external devices. The emf generated by
the I/O circuits could be shielded from the other layers in the
stack by use of, for example, the shield/heat sink layer 2988.
Placement of the I/O circuits on the same stack layer as the
conductive bond pad may enable close coupling of the desired I/O
energy and lower signal loss. Furthermore, the second layer of
circuits and transistors, for example donor wafer device structures
such as the FD-MOSFETs formed as described in relation to FIG. 29,
may include RF (Radio Frequency) circuits and/or at least one
antenna. For example, the second layer of circuits and transistors
may include RF circuits to enable an off-chip communication
capability to external devices, for example, a wireless
communication circuit or circuits such as a Bluetooth protocol or
capacitive coupling. The emf generated by the RF circuits could be
shielded from the other layers in the stack by use of, for example,
the shield/heat sink layer 2988.
[0132] TLVs 2960 may be formed through the transferred layers. As
the transferred layers may be thin, on the order of about 200 nm or
less in thickness, the TLVs may be easily manufactured as a typical
metal to metal via may be, and said TLV may have state of the art
diameters such as nanometers or tens to a few hundreds of
nanometers, such as, for example about 150 nm or about 100 nm or
about 50 nm. The thinner the transferred layers, the smaller the
thru layer via diameter obtainable, which may result from
maintaining manufacturable via aspect ratios. The thickness of the
layer or layers transferred according to some embodiments of the
invention may be designed as such to match and enable the most
suitable obtainable lithographic resolution (and enable the use of
conventional state of the art lithographic tools), such as, for
example, less than about 10 nm, 14 nm, 22 nm or 28 nm linewidth
resolution and alignment capability, such as, for example, less
than about 5 nm, 10 nm, 20 nm, or 40 nm alignment
accuracy/precision/error, of the manufacturing process employed to
create the thru layer vias or any other structures on the
transferred layer or layers.
[0133] As illustrated in FIG. 29G-1, at least one conductive bond
pad 2964 for interfacing electrically (and may thermally) to
external devices may be formed on top of the completed device and
may include at least one metal layer of second device layer metal
interconnect 2961. Bond pad 2964 may overlay second device layer
metal interconnect 2961 or a portion of (some of the metal and
insulator layers of) second device layer metal interconnect 2961.
Bond pad 2964 may be directly aligned to the acceptor wafer
alignment marks (not shown) and the I/O driver circuitry may be
formed by the second layer (donor) transistors, for example, donor
wafer device structures such as the FD-MOSFETs formed as described
in relation to FIG. 29. Bond pad 2964 may be connected to the
second layer transistors thru the second device layer metal
interconnect 2961 which may include vias 2962. The I/O driver
circuitry may be formed by transistors from the acceptor wafer
transistors and devices 2993, or from transistors in other strata
if the 3DIC device has more than two layers of transistors. I/O pad
control metal segment 2967 may be formed directly underneath bond
pad 2964 and may influence the noise and ESD (Electro Static
Discharge) characteristics of bond pad 2964. The emf influence of
I/O pad control metal segment 2967 may be controlled by circuitry
formed from a portion of the second layer transistors. I/O pad
control metal segment 2967 may be formed with second device layer
metal interconnect 2961. Furthermore, metal segment 2989 of the
topmost shield/heat sink layer 2988 may be used to influence the
FD-MOSFET transistor or transistors above it by emf, and influence
the noise and ESD (Electro Static Discharge) characteristics of
bond pad 2964. Metal segment 2989 may be controlled by second layer
(donor) transistors, for example, donor wafer device structures
such as the FD-MOSFETs formed as described in relation to FIG. 29
and/or by transistors from the acceptor wafer transistors and
devices 2993, or from transistors in other strata if the 3DIC
device has more than two layers of transistors. Power from external
sources may be routed to conductive bond pad 2964 to the 3D device,
wherein at least a portion of the second layer interconnections
such as second device layer metal interconnect 2961 and associated
vias, may be constructed as a power distribution grid/network, and
the power distribution grid/network may be connected electrically
and thermally via TLVs 2960 to the transistor layer below's (such
as acceptor wafer transistors and devices 2993) power distribution
grid/network, the power distribution grid/network may include for
example, shield/heat sink layer 2988 or Vss/Vdd strategy as
described herein at least FIG. 32, and it's associated portion of a
thermal conduction path (shield path connect 2985, shield path vias
2983, metal interconnect 2981, first (acceptor) layer metal
interconnect 2991) to acceptor wafer transistors and devices 2993,
acceptor substrate 2995, and acceptor wafer heat sink 2997.
[0134] Formation of CMOS in one transferred layer and the
orthogonal connect strip methodology may be found as illustrated in
at least FIGS. 30-33, 73-80, and 94 and related specification
sections of U.S. Pat. No. 8,273,610, and may be applied to at least
the FIG. 29 formation techniques herein. Transferred layer or
layers may have regions of STI or other transistor elements within
it or on it when transferred, but would then use alignment and
connection schemes for layer transfer of patterned layers as
described in incorporated patent references.
[0135] Persons of ordinary skill in the art will appreciate that
the illustrations in FIGS. 29A through 29G are exemplary only and
are not drawn to scale. Such skilled persons will further
appreciate that many variations are possible such as, for example,
a p-channel FD-MOSFET may be formed with changing the types of
dopings appropriately. Moreover, the P- substrate donor wafer 2900
may be n type or un-doped. Furthermore, isolation regions 2905 may
be formed by a hard mask defined process flow, wherein a hard mask
stack, such as, for example, silicon oxide and silicon nitride
layers, or silicon oxide and amorphous carbon layers, may be
utilized. Moreover, CMOS FD MOSFET s may be constructed with
n-MOSFETs in a first mono-crystalline silicon layer and p- MOSFET s
in a second mono-crystalline layer, which may include different
crystalline orientations of the mono-crystalline silicon layers,
such as for example, <100>, <111> or <551>, and
may include different contact silicides for optimum contact
resistance to p or n type source, drains, and gates. Further,
dopant segregation techniques (DST) may be utilized to efficiently
modulate the source and drain Schottky barrier height for both p
and n type junctions formed. Furthermore, raised source and drain
contact structures, such as etch and epi SiGe and SiC, may be
utilized for strain and contact resistance improvements and the
damage from the processes may be optically annealed. Many other
modifications within the scope of the invention will suggest
themselves to such skilled persons after reading this
specification. Thus the invention is to be limited only by the
appended claims.
[0136] A planar fully depleted n-channel MOSFET (FD-MOSFET) with an
optional integrated heat shield/spreader and back planes and body
bias taps suitable for a monolithic 3D IC may be constructed as
follows. The FD-MOSFET may provide an improved transistor
variability control and conduction channel electrostatic control,
as well as the ability to utilize an updoped channel, thereby
improving carrier mobility. In addition, the FD-MOSFET does not
demand doping or pocket implants in the channel to control the
electrostatic characteristics and tune the threshold voltages.
Sub-threshold slope, DIBL, and other short channel effects are
greatly improved due to the firm gate electrostatic control over
the channel. In this embodiment, a ground plane is constructed that
may provide improved electrostatics and/or Vt adjustment and/or
back-bias of the FD-MOSFET. In addition, selective regions may be
constructed to provide body bias and/or partially
depleted/bulk-like transistors. Moreover, a heat spreading, heat
conducting and/or optically reflecting material layer or layers may
be incorporated between the sensitive metal interconnect layers and
the layer or regions being optically irradiated and annealed to
repair defects in the crystalline 3D-IC layers and regions and to
activate semiconductor dopants in the crystalline layers or regions
of a 3D-IC without harm to the sensitive metal interconnect and
associated dielectrics. FIG. 30A-G illustrates an exemplary
n-channel FD-MOSFET which may be constructed in a 3D stacked layer
using procedures outlined below and in U.S. Pat. Nos. 8,273,610,
9,099,526, 9,219,005, 8,557,632 and 8,581,349. The contents of the
foregoing applications are incorporated herein by reference.
[0137] As illustrated in FIG. 30A, SOI donor wafer substrate 3000
may include back channel layer 3002 above Buried Oxide BOX layer
3001. Back channel layer 3002 may be doped by ion implantation and
thermal anneal, may include a crystalline material, for example,
mono-crystalline (single crystal) silicon and may be heavily doped
(greater than 1e16 atoms/cm.sup.3), lightly doped (less than 1e16
atoms/cm.sup.3) or nominally un-doped (less than 1e14
atoms/cm.sup.3). SOI donor wafer substrate 3000 may include a
crystalline material, for example, mono-crystalline (single
crystal) silicon and at least the upper layer near BOX layer 3001
may be very lightly doped (less than 1e15 atoms/cm.sup.3) or
nominally un-doped (less than 1e14 atoms/cm.sup.3). Back channel
layer 3002 may have additional ion implantation and anneal
processing to provide a different dopant level than SOI donor wafer
substrate 3000 and may have graded or various layers of doping
concentration. SOI donor wafer substrate 3000 may have additional
ion implantation and anneal processing to provide a different
dopant level than back channel layer 3002 and may have graded or
various layers of doping concentration. The layer stack may
alternatively be formed by epitaxially deposited doped or undoped
silicon layers, or by a combination of epitaxy and implantation, or
by layer transfer. Annealing of implants and doping may include,
for example, conductive/inductive thermal, optical annealing
techniques or types of Rapid Thermal Anneal (RTA or spike). The
preferred at least top of SOI donor wafer substrate 3000 doping
will be undoped to eventually create an FD-MOSFET transistor with
an updoped conduction channel. SOI donor wafer may be constructed
by layer transfer techniques described herein or elsewhere as known
in the art, or by laser annealed SIMOX at a post donor layer
transfer to acceptor wafer step. BOX layer 3001 may be thin enough
to provide for effective back and/or body bias, for example, 25 nm,
or 20 nm, or 10 nm, or 35 nm.
[0138] As illustrated in FIG. 30B, the top surface of the SOI donor
wafer substrate 3000 layer stack may be prepared for oxide wafer
bonding with a deposition of an oxide or by thermal oxidation of
back channel layer 3002 to form oxide layer 3080. A layer transfer
demarcation plane (shown as dashed line) 3099 may be formed by
hydrogen implantation or other methods as described in the
incorporated references, and may reside within the SOI donor wafer
substrate 3000. The SOI donor wafer substrate 3000 stack, such as
surface 3082, and acceptor wafer 3010 may be prepared for wafer
bonding as previously described and low temperature (less than
approximately 400.degree. C.) bonded. Acceptor wafer 3010, as
described in the incorporated references, may include, for example,
transistors, circuitry, and metal, such as, for example, aluminum
or copper, interconnect wiring, a metal shield/heat sink layer or
layers, and thru layer via metal interconnect strips or pads.
Acceptor wafer 3010 may be substantially comprised of a crystalline
material, for example mono-crystalline silicon or germanium, or may
be an engineered substrate/wafer such as, for example, an SOI
(Silicon on Insulator) wafer or GeOI (Germanium on Insulator)
substrate. Acceptor wafer 3010 may include transistors such as, for
example, MOSFETS, FD-MOSFETS, FinFets, FD-RCATs, BJTs, HEMTs,
and/or HBTs. The portion of the SOI donor wafer substrate 3000 that
may be above (when the layer stack is flipped over and bonded to
the acceptor wafer 3010) the layer transfer demarcation plane 3099
may be removed by cleaving or other low temperature processes as
described in the incorporated references, such as, for example,
ion-cut with mechanical or thermal cleave or other layer transfer
methods, thus forming remaining channel layer 3003. Damage/defects
to crystalline structure of back channel layer 3002 may be annealed
by some of the annealing methods described, for example the short
wavelength pulsed laser techniques, wherein the back channel layer
3002 and/or portions of the SOI donor wafer substrate 3000 may be
heated to defect annealing temperatures, but the layer transfer
demarcation plane 3099 may be kept below the temperate for cleaving
and/or significant hydrogen diffusion. The optical energy may be
deposited in the upper layer of the stack, for example near surface
3082, and annealing of back channel layer 3002 and/or portions of
the SOI donor wafer substrate 3000 may take place via heat
diffusion. Moreover, multiple pulses of the laser may be utilized
to improve the anneal, activation, and yield of the process and/or
to control the maximum temperature of various structures in the
stack.
[0139] As illustrated in FIG. 30C, oxide layer 3080, back channel
layer 3002, BOX layer 3001 and channel layer 3003 may be layer
transferred to acceptor wafer 3010. The top surface of channel
layer 3003 may be chemically or mechanically polished, and/or may
be thinned by low temperature oxidation and strip processes, such
as the TEL SPA tool radical oxidation and HF:H.sub.2O solutions as
described herein and in referenced patents and patent applications.
Thru the processing, the wafer sized layer channel layer 3003 could
be thinned from its original total thickness, and its final total
thickness could be in the range of about 5 nm to about 20 nm, for
example, 5 nm, 7 nm, 10 nm, 12 nm, 15 nm, or 20 nm. Channel layer
3003 may have a thickness and/or doping that may allow
fully-depleted channel operation when the FD-MOSFET transistor is
substantially completely formed. Acceptor wafer 3010 may include
one or more (two are shown in this example) shield/heat sink layers
3088, which may include materials such as, for example, Aluminum,
Tungsten (a refractory metal), Copper, silicon or cobalt based
silicides, or forms of carbon such as carbon nanotubes, and may be
layered itself as described in FIG. 50 of incorporated patent
reference U.S. Pat. No. 9,385,058. Each shield/heat sink layer 3088
may have a thickness range of about 50 nm to about 1 mm, for
example, 50 nm, 100 nm, 200 nm, 300 nm, 500 nm, 0.1 um, 1 um, 2 um,
and 10 um. Shield/heat sink layer 3088 may include isolation
openings 3087, and alignment mark openings (not shown), which may
be utilized for short wavelength alignment of top layer (donor)
processing to the acceptor wafer alignment marks (not shown).
Shield/heat sink layer 3088 may include one or more shield path
connects 3085 and shield path vias 3083. Shield path via 3083 may
thermally and/or electrically couple and connect shield path
connect 3085 to acceptor wafer 3010 interconnect metallization
layers such as, for example, exemplary acceptor metal interconnect
3081 (shown). Shield path connect 3085 may also thermally and/or
electrically couple and connect each shield/heat sink layer 3088 to
the other and to acceptor wafer 3010 interconnect metallization
layers such as, for example, acceptor metal interconnect 3081,
thereby creating a heat conduction path from the shield/heat sink
layer 3088 to the acceptor substrate 3095, and a heat sink (shown
in FIG. 30G.). Isolation openings 3087 may include dielectric
materials, similar to those of BEOL isolation 3096. Acceptor wafer
3010 may include first (acceptor) layer metal interconnect 3091,
acceptor wafer transistors and devices 3093, and acceptor substrate
3095. Various topside defect anneals may be utilized. For this
illustration, an optical beam such as the laser annealing
previously described is used. Optical anneal beams may be optimized
to focus light absorption and heat generation within or at the
surface of channel layer 3003 and provide surface smoothing and/or
defect annealing (defects may be from the cleave and/or the ion-cut
implantation) with exemplary smoothing/annealing ray 3066. The
laser assisted smoothing/annealing with the absorbed heat generated
by exemplary smoothing/annealing ray 3066 may also include a
pre-heat of the bonded stack to, for example, about 100.degree. C.
to about 400.degree. C., and/or a rapid thermal spike to
temperatures above about 200.degree. C. to about 600.degree. C.
Additionally, absorber layers or regions, for example, including
amorphous carbon, amorphous silicon, and phase changing materials
(see U.S. Pat. Nos. 6,635,588 and 6,479,821 to Hawryluk et al. for
example), may be utilized to increase the efficiency of the optical
energy capture in conversion to heat for the desired annealing or
activation processes. Moreover, multiple pulses of the laser may be
utilized to improve the anneal, activation, and yield of the
process. Reflected ray 3063 may be reflected and/or absorbed by
shield/heat sink layer 3088 regions thus blocking the optical
absorption of ray blocked metal interconnect 3081. Annealing of
dopants or annealing of damage in back channel layer 3002 and/or
BOX 3010 and/or channel layer 3003, such as from the H cleave
implant damage, may be also accomplished by a set of rays such as
repair ray 3065, illustrated is focused on back channel layer 3002.
Heat generated by absorbed photons from, for example,
smoothing/annealing ray 3066, reflected ray 3063, and/or repair ray
3065 may also be absorbed by shield/heat sink layer 3088 regions
and dissipated laterally and may keep the temperature of underlying
metal layers, such as metal interconnect 3081, and other metal
layers below it, cooler and prevent damage. Shield/heat sink layer
3088 and associated dielectrics may laterally spread and conduct
the heat generated by the topside defect anneal, and in conjunction
with the dielectric materials (low heat conductivity) above and
below shield/heat sink layer 3088, keep the interconnect metals and
low-k dielectrics of the acceptor wafer interconnect layers cooler
than a damage temperature, such as, for example, 400.degree. C. A
second layer of shield/heat sink layer 3088 may be constructed
(shown) with a low heat conductive material sandwiched between the
two heat sink layers, such as silicon oxide or carbon doped `low-k`
silicon oxides, for improved thermal protection of the acceptor
wafer interconnect layers, metal and dielectrics. Shield/heat sink
layer 3088 may act as a heat spreader. Electrically conductive
materials may be used for the two layers of shield/heat sink layer
3088 and thus may provide, for example, a Vss and a Vdd plane
and/or grid that may be connected to the donor layer transistors
above, as well may be connected to the acceptor wafer transistors
below, and/or may provide below transferred layer device
interconnection. Noise on the power grids, such as the Vss and Vdd
plane power conducting lines/wires, may be mitigated by
attaching/connecting decoupling capacitors onto the power
conducting lines of the grids. The decoupling caps, which may be
within the second layer (donor, for example, donor wafer device
structures) or first layer (acceptor, for example acceptor wafer
transistors and devices 3093), may include, for example, trench
capacitors such as described by Pei, C., et al., "A novel, low-cost
deep trench decoupling capacitor for high-performance, low-power
bulk CMOS applications," ICSICT (9.sup.th International Conference
on Solid-State and Integrated-Circuit Technology) 2008, October
2008, pp. 1146-1149, of IBM. The decoupling capacitors may include,
for example, planar capacitors, such as poly to substrate or poly
to poly, or MiM capacitors (Metal-Insulator-Metal). Shield/heat
sink layer 3088 may include materials with a high thermal
conductivity greater than 10 W/m-K, for example, copper (about 400
W/m-K), aluminum (about 237 W/m-K), Tungsten (about 173 W/m-K),
Plasma Enhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD
DLC (about 1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene
(about 5000 W/m-K). Shield/heat sink layer 3088 may be sandwiched
and/or substantially enclosed by materials with a low thermal
conductivity (less than 10 W/m-K), for example, silicon dioxide
(about 1.4 W/m-K). The sandwiching of high and low thermal
conductivity materials in layers, such as shield/heat sink layer
3088 and under & overlying dielectric layers, spreads the
localized heat/light energy of the topside anneal laterally and
protects the underlying layers of interconnect metallization &
dielectrics, such as in the acceptor wafer 3010, from harmful
temperatures or damage. When there may be more than one shield/heat
sink layer 3088 in the device, the heat conducting layer closest to
the second crystalline layer or oxide layer 3080 may be constructed
with a different material, for example a high melting point
material, for example a refractory metal such as tungsten, than the
other heat conducting layer or layers, which may be constructed
with, for example, a lower melting point material, for example such
as aluminum or copper. Now transistors may be formed with low
effective temperature (less than approximately 400.degree. C.
exposure to the acceptor wafer 3010 sensitive layers, such as
interconnect and device layers) processing, and may be aligned to
the acceptor wafer alignment marks (not shown) as described in the
incorporated references. This may include further optical defect
annealing or dopant activation steps. The remaining SOI donor wafer
substrate 3000 may now also be processed, such as smoothing and
annealing, and reused for additional layer transfers. The insulator
layer, such as deposited bonding oxides (for example oxide layer
3080) and/or before bonding preparation existing oxides (for
example the BEOL isolation 3096 on top of the topmost metal layer
of shield/heat sink layer 3088), between the donor wafer
transferred monocrystalline layer and the acceptor wafer topmost
metal layer, may include thicknesses of less than 1 um, less than
500 nm, less than 400 nm, less than 300 nm, less than 200 nm, or
less than 100 nm.
[0140] As illustrated in FIG. 30D, transistor and back channel
isolation regions 3005 and/or transistor isolation regions 3086 may
be formed. Transistor isolation region 3086 may be formed by mask
defining and plasma/RIE etching channel layer 3003, substantially
to the top of BOX layer 3001 (not shown), substantially into BOX
layer 3001, or back channel layer 3002 (not shown). Transistor and
back channel isolation regions 3005 may be formed by mask defining
and plasma/RIE etching channel layer 3003, BOX layer 3001 and back
channel layer 3002, substantially to the top of oxide layer 3080
(not shown), substantially into oxide layer 3080, or further into
the top BEOL dielectric layer in acceptor wafer 3010 (not shown).
Thus channel region 3023 may be formed, which may substantially
form the transistor body, back-channel region 3022 may be formed,
which may provide a back bias and/or Vt control by doping or bias
to one or more channel regions 3023, and BOX region 3031.
Back-channel region 3022 may be ion implanted for Vt control and/or
body bias efficiency. A low-temperature gap fill dielectric, such
as SACVD oxide, may be deposited and chemically mechanically
polished, the oxide remaining in transistor and back channel
isolation regions 3005 and transistor isolation regions 3086.
Back-channel region 3022 may be ion implanted for Vt control and/or
body bias efficiency. An optical step, such as illustrated by
exemplary STI ray 3067, may be performed to anneal etch damage and
densify the STI oxide in transistor and back channel isolation
regions 3005. The doping concentration of channel region 3023 may
include vertical or horizontal gradients of concentration or layers
of differing doping concentrations. The doping concentration of
back-channel region 3022 may include vertical or horizontal
gradients of concentration or layers of differing doping
concentrations. Any additional doping, such as ion-implanted
channel implants, may be activated and annealed with optical
annealing, such as illustrated by exemplary implant ray 3069, as
described herein. The optical anneal, such as exemplary STI ray
3067, and/or exemplary implant ray 3069 may be performed at
separate times and processing parameters (such as laser energy,
frequency, etc.) or may be done in combination or as one optical
anneal. Optical absorber and or reflective layers or regions may be
employed to enhance the anneal and/or protect the underlying
sensitive structures. Moreover, multiple pulses of the laser may be
utilized to improve the anneal, activation, and yield of the
process. BOX region 3031 may be a relatively thin dielectric,
including the thickness range of 5 nm to 100 nm, at least a portion
of which being between the back-channel region 3022 and channel
region 3023. Back-channel region 3022 could be constructed from a
material that would not be damaged by the optical anneal process.
Such could be a refractory metal or doped silicon in crystallized
form, poly or amorphous, or other conductive material that are
acceptable for semiconductor processing and can withstand high
temperature of 700.degree. C. or higher.
[0141] As illustrated in FIG. 30E, a transistor forming process,
such as a conventional HKMG with raised source and drains (S/D),
may be performed. For example, a dummy gate stack (not shown),
utilizing oxide and polysilicon, may be formed, gate spacers 3030
may be formed, raised S/D regions 3032 and channel stressors may be
formed by etch and epitaxial deposition, for example, of SiGe
and/or SiC depending on P or N channel (and may be doped in-situ or
ion-implantation and optical anneal activation), LDD and S/D
ion-implantations may be performed, and first ILD 3036 may be
deposited and CMP'd to expose the tops of the dummy gates. Thus
transistor channel region 3033 and S/D & LDD regions 3035 may
be formed. The dummy gate stack may be removed and a gate
dielectric 3007 may be formed and a gate metal material gate
electrode 3008, including a layer of proper work function metal
(Ti.sub.xAl.sub.y,N.sub.z for example) and a conductive fill, such
as aluminum, and may be deposited and CMP'd. The gate dielectric
3007 may be an atomic layer deposited (ALD) gate dielectric that
may be paired with a work function specific gate metal in the
industry standard high k metal gate process schemes, for example,
as described in the incorporated references. Alternatively, the
gate dielectric 3007 may be formed with a low temperature processes
including, for example, LPCVD SiO.sub.2 oxide deposition (see Ahn,
J., et al., "High-quality MOSFET's with ultrathin LPCVD gate
SiO.sub.2," IEEE Electron Device Lett., vol. 13, no. 4, pp.
186-188, April 1992) or low temperature microwave plasma oxidation
of the silicon surfaces (see Kim, J. Y., et al., "The excellent
scalability of the RCAT (recess-channel-array-transistor)
technology for sub-70 nm DRAM feature size and beyond," 2005 IEEE
VLSI-TSA International Symposium, pp. 33-30, 25-27 Apr. 2005) and
agate material with proper work function and less than
approximately 400.degree. C. deposition temperature such as, for
example, tungsten or aluminum may be deposited. An optical step,
such as represented by exemplary anneal ray 3021, may be performed
to densify and/or remove defects from gate dielectric 3007, anneal
defects and activate dopants such as LDD and S/D implants, densify
the first ILD 3036, form DSS junctions (Dopant Segregated Schottky
such as NiSi.sub.2), and/or form contact and S/D silicides (not
shown). The optical anneal may be performed at each sub-step as
desired, or may be done at prior to the HKMG deposition (such as
after the dummy gate but before the HKMG formation), or various
combinations. Optionally, portions of transistor isolation region
3086 and BOX region 3031 may be lithographically defined and etched
away, thus forming second transistor isolation regions 3076 and PD
transistor area 3068. Partially depleted transistors (not shown)
may be constructed in a similar manner as the FD-MOSFETs
constructed on transistor channel region 3033 herein, but now with
the thicker back-channel region 3022 silicon as its channel body.
PD transistor area 3068 may also be utilized to later form a direct
connection thru a contact to the back-channel region 3022 for back
bias and Vt control of the transistor with transistor channel
region 3033. If no PD devices are desired, then it may be more
efficient to later form a direct connection thru a contact to the
back-channel region 3022 for back bias and Vt control of the
transistor with transistor channel region 3033 by etching a contact
thru transistor isolation region 3086. Raised S/D regions 3032 may
be formed by low temperature (less than 400.degree. C.) deposition
of in-situ doped polysilicon or amorphous silicon into the S/D
openings, an optical anneal to further crystallize and dopant
activate the raised S/D material, and removal of excess raised S/D
material.
[0142] As illustrated in FIG. 30F, a low temperature thick oxide
3009 may be deposited and planarized. Source, gate, drain, two
types of back contact openings may be masked, etched, and filled
with electrically conductive materials preparing the transistors to
be connected via metallization. Thus gate contact 3011 connects to
gate electrode 3008, source & drain contacts 3040 connect to
raised S/D regions 3032, back channel contact 3044 may connect to
back-channel region 3022, and direct back contact 3045 may connect
to back-channel region 3022. An optical step, such as illustrated
by exemplary ILD anneal ray 3051, may be performed to anneal
contact etch damage and densify the thick oxide 3009. Back channel
contact 3044 and direct back contact 3045 may be formed to connect
to shield/heat sink layer 3088 by further etching, and may be
useful for hard wiring a back bias that may be controlled by, for
example, the second layer or first layer circuitry into the FD
MOSFET.
[0143] As illustrated in FIG. 30G, thru layer vias (TLVs) 3060 may
be formed by etching thick oxide 3009, first ILD 3036, transistor
and back channel isolation regions 3005, oxide layer 3080, into a
portion of the upper oxide layer BEOL isolation 3096 of acceptor
wafer 3010 BEOL, and filling with an electrically and thermally
conducting material (such as tungsten or cooper) or an electrically
non-conducting but thermally conducting material (such as described
elsewhere within). Second device layer metal interconnect 3061 may
be formed by conventional processing. TLVs 3060 may be constructed
of thermally conductive but not electrically conductive materials,
for example, DLC (Diamond Like Carbon), and may connect the
FD-MOSFET transistor device and other devices on the top (second)
crystalline layer thermally to shield/heat sink layer 3088. TLVs
3060 may be constructed out of electrically and thermally
conductive materials, such as Tungsten, Copper, or aluminum, and
may provide a thermal and electrical connection path from the
FD-MOSFET transistor device and other devices on the top (second)
crystalline layer to shield/heat sink layer 3088, which may be a
ground or Vdd plane in the design/layout. TLVs 3060 may be also
constructed in the device scribelanes (pre-designed in base layers
or potential dicelines) to provide thermal conduction to the heat
sink, and may be sawed/diced off when the wafer is diced for
packaging not shown). Shield/heat sink layer 3088 may be configured
to act (or adapted to act) as an emf (electro-motive force) shield
to prevent direct layer to layer cross-talk between transistors in
the donor wafer layer and transistors in the acceptor wafer. In
addition to static ground or Vdd biasing, shield/heat sink layer
3088 may be actively biased with an anti-interference signal from
circuitry residing on, for example, a layer of the 3D-IC or off
chip. The formed FD-MOSFET transistor device may include
semiconductor regions wherein the dopant concentration of
neighboring regions of the transistor in the horizontal plane, such
as traversed by exemplary dopant plane 3034, may have regions, for
example, transistor channel region 3033 and S/D & LDD regions
3035, that differ substantially in dopant concentration, for
example, a 10 times greater doping concentration in S/D & LDD
regions 3035 than in transistor channel region 3033, and/or may
have a different dopant type, such as, for example p-type or n-type
dopant, and/or may be doped and substantially undoped in the
neighboring regions. For example, transistor channel region 3033
may be very lightly doped (less than 1e15 atoms/cm.sup.3) or
nominally un-doped (less than 1e14 atoms/cm.sup.3) and S/D &
LDD regions 3035 may be doped at greater than 1e15 atoms/cm.sup.3
or greater than 1e16 atoms/cm.sup.3. For example, transistor
channel region 3033 may be doped with p-type dopant and S/D &
LDD regions 3035 may be doped with n-type dopant.
[0144] A thermal conduction path may be constructed from the
devices in the upper layer, the transferred donor layer and formed
transistors, to the acceptor wafer substrate and associated heat
sink. The thermal conduction path from the FD-MOSFET transistor
device and other devices on the top (second) crystalline layer, for
example, raised S/D regions 3032, to the acceptor wafer heat sink
3097 may include source & drain contacts 3040, second device
layer metal interconnect 3061, TLV 3060, shield path connect 3085
(shown as twice), shield path via 3083 (shown as twice), metal
interconnect 3081, first (acceptor) layer metal interconnect 3091,
acceptor wafer transistors and devices 3093, and acceptor substrate
3095. The elements of the thermal conduction path may include
materials that have a thermal conductivity greater than 10 W/m-K,
for example, copper (about 400 W/m-K), aluminum (about 237 W/m-K),
and Tungsten (about 173 W/m-K), and may include material with
thermal conductivity lower than 10 W/m-K but have a high heat
transfer capacity due to the wide area available for heat transfer
and thickness of the structure (Fourier's Law), such as, for
example, acceptor substrate 3095. The elements of the thermal
conduction path may include materials that are thermally conductive
but may not be substantially electrically conductive, for example,
Plasma Enhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD
DLC (about 1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene
(about 5000 W/m-K). The acceptor wafer interconnects may be
substantially surrounded by BEOL isolation 3096, which may be a
dielectric such as, for example, carbon doped silicon oxides. The
heat removal apparatus, which may include acceptor wafer heat sink
3097, may include an external surface from which heat transfer may
take place by methods such as air cooling, liquid cooling, or
attachment to another heat sink or heat spreader structure.
[0145] Furthermore, some or all of the layers utilized as
shield/heat sink layer 3088, which may include shapes of material
such as the strips or fingers as illustrated in FIG. 27B-1, may be
driven by a portion of the second layer transistors and circuits
(within the transferred donor wafer layer or layers) or the
acceptor wafer transistors and circuits, to provide a programmable
back-bias to at least a portion of the second layer transistors.
The programmable back bias may utilize a circuit to do so, for
example, such as shown in FIG. 17B of U.S. Pat. No. 8,273,610, the
contents incorporated herein by reference; wherein the `Primary`
layer may be the second layer of transistors for which the
back-bias is being provided, the `Foundation` layer could be either
the second layer transistors (donor) or first layer transistors
(acceptor), and the routing metal lines connections 1723 and 1724
may include portions of the shield/heat sink layer 3088 layer or
layers. Moreover, some or all of the layers utilized as shield/heat
sink layer 3088, which may include strips or fingers as illustrated
in FIG. 27B-1, may be driven by a portion of the second layer
transistors and circuits (within the transferred donor wafer layer
or layers) or the acceptor wafer transistors and circuits to
provide a programmable power supply to at least a portion of the
second layer transistors. The programmable power supply may utilize
a circuit to do so, for example, such as shown in FIG. 17C of U.S.
Pat. No. 8,273,610, the contents incorporated herein by reference;
wherein the `Primary` layer may be the second layer of transistors
for which the programmable power supplies are being provided to,
the `Foundation` layer could be either the second layer transistors
(donor) or first layer transistors (acceptor), and the routing
metal line connections from Vout to the various second layer
transistors may include portions of the shield/heat sink layer 3088
layer or layers. The Vsupply on line 17C12 and the control signals
on control line 17C16 may be controlled by and/or generated in the
second layer transistors (for example donor wafer device structures
such as the FD-MOSFETs formed as described in relation to FIG. 30)
or first layer transistors (acceptor, for example acceptor wafer
transistors and devices 3093), or off chip circuits. Furthermore,
some or all of the layers utilized as shield/heat sink layer 3088,
which may include strips or fingers as illustrated in FIG. 27B-1 or
other shapes such as those in FIG. 27B, may be utilized to
distribute independent power supplies to various portions of the
second layer transistors (for example donor wafer device structures
such as the FD-MOSFETs formed as described in relation to FIG. 30)
or first layer transistors (acceptor, for example acceptor wafer
transistors and devices 3093) and circuits; for example, one power
supply and/or voltage may be routed to the sequential logic
circuits of the second layer and a different power supply and/or
voltage routed to the combinatorial logic circuits of the second
layer. Moreover, the power distribution circuits/grid may be
designed so that Vdd may have a different value for each stack
layer. Patterning of shield/heat sink layer 3088 or layers can
impact their heat-shielding capacity. This impact may be mitigated,
for example, by enhancing the top shield/heat sink layer 3088 areal
density, creating more of the secondary shield/heat sink layers
3088, or attending to special CAD rules regarding their metal
density, similar to CAD rules that are required to accommodate
Chemical-Mechanical Planarization (CMP). These constraints would be
integrated into a design and layout EDA tool. Moreover, the second
layer of circuits and transistors, for example, for example donor
wafer device structures such as the FD-MOSFETs formed as described
in relation to FIG. 30, may include I/O logic devices, such as
SerDes (Serialiser/Deserialiser), and conductive bond pads (not
shown) (herein such as FIG. 33). The output or input conductive
pads of the I/O circuits may be coupled, for example by bonded
wires, to external devices. The output or input conductive pads may
also act as a contact port for the 3D device output to connect to
external devices. The emf generated by the I/O circuits could be
shielded from the other layers in the stack by use of, for example,
the shield/heat sink layer 3088. Placement of the I/O circuits on
the same stack layer as the conductive bond pad may enable close
coupling of the desired I/O energy and lower signal loss.
Furthermore, the second layer of circuits and transistors, for
example donor wafer device structures such as the FD-MOSFETs formed
as described in relation to FIG. 30, may include RF (Radio
Frequency) circuits and/or at least one antenna. For example, the
second layer of circuits and transistors may include RF circuits to
enable an off-chip communication capability to external devices,
for example, a wireless communication circuit or circuits such as a
Bluetooth protocol or capacitive coupling. The emf generated by the
RF circuits could be shielded from the other layers in the stack by
use of, for example, the shield/heat sink layer 3088.
[0146] TLVs 3060 may be formed through the transferred layers. As
the transferred layers may be thin, on the order of about 200 nm or
less in thickness, the TLVs may be easily manufactured as a typical
metal to metal via may be, and said TLV may have state of the art
diameters such as nanometers or tens to a few hundreds of
nanometers, such as, for example about 150 nm or about 100 nm or
about 50 nm. The thinner the transferred layers, the smaller the
thru layer via diameter obtainable, which may result from
maintaining manufacturable via aspect ratios. The thickness of the
layer or layers transferred according to some embodiments of the
invention may be designed as such to match and enable the most
suitable obtainable lithographic resolution (and enable the use of
conventional state of the art lithographic tools), such as, for
example, less than about 10 nm, 14 nm, 22 nm or 28 nm linewidth
resolution and alignment capability, such as, for example, less
than about 5 nm, 10 nm, 20 nm, or 40 nm alignment
accuracy/precision/error, of the manufacturing process employed to
create the thru layer vias or any other structures on the
transferred layer or layers.
[0147] Formation of CMOS in one transferred layer and the
orthogonal connect strip methodology may be found as illustrated in
at least FIGS. 30-33, 73-80, and 94 and related specification
sections of U.S. Pat. No. 8,273,610, and may be applied to at least
the FIG. 30 formation techniques herein. Transferred layer or
layers may have regions of STI or other transistor elements within
it or on it when transferred, but would then use alignment and
connection schemes for layer transfer of patterned layers as
described in incorporated patent references.
[0148] Persons of ordinary skill in the art will appreciate that
the illustrations in FIGS. 30A through 30G are exemplary only and
are not drawn to scale. Such skilled persons will further
appreciate that many variations are possible such as, for example,
a p-channel FD-MOSFET may be formed with changing the types of
dopings appropriately. Moreover, the SOI donor wafer substrate 3000
may be n type or un-doped. Furthermore, transistor and back channel
isolation regions 3005 and transistor isolation region 3086 may be
formed by a hard mask defined process flow, wherein a hard mask
stack, such as, for example, silicon oxide and silicon nitride
layers, or silicon oxide and amorphous carbon layers, may be
utilized. Moreover, CMOS FD MOSFETs may be constructed with
n-MOSFETs in a first mono-crystalline silicon layer and p-MOSFETs
in a second mono-crystalline layer, which may include different
crystalline orientations of the mono-crystalline silicon layers,
such as for example, <100>, <111> or <551>, and
may include different contact silicides for optimum contact
resistance to p or n type source, drains, and gates. Further,
dopant segregation techniques (DST) may be utilized to efficiently
modulate the source and drain Schottky barrier height for both p
and n type junctions formed. Furthermore, raised source and drain
contact structures, such as etch and epi SiGe and SiC, may be
utilized for strain and contact resistance improvements and the
damage from the processes may be optically annealed. Many other
modifications within the scope of the invention will suggest
themselves to such skilled persons after reading this
specification. Thus the invention is to be limited only by the
appended claims.
[0149] A planar n-channel JFET or JLT with an optional integrated
heat shield/spreader suitable for a monolithic 3D IC may be
constructed as follows. Being bulk conduction devices rather than
surface conduction devices, the JFET and JLT may provide an
improved transistor variability control and conduction channel
electrostatic control. Sub-threshold slope, DIBL, and other short
channel effects are greatly improved due to the firm gate
electrostatic control over the channel. Moreover, a heat spreading,
heat conducting and/or optically reflecting material layer or
layers may be incorporated between the sensitive metal interconnect
layers and the layer or regions being optically irradiated and
annealed to repair defects in the crystalline 3D-IC layers and
regions and to activate semiconductor dopants in the crystalline
layers or regions of a 3D-IC without harm to the sensitive metal
interconnect and associated dielectrics. Furthermore, a buried
doped layer and channel dopant shaping, even to an un-doped
channel, may allow for efficient adaptive and dynamic body biasing
to control the transistor threshold and threshold variations, the
concepts shown in FIG. 26 herein may be applied to the JFET. As
well, the back plane and body bias tap concepts shown in FIG. 30
herein may be utilized for the JFET and JLT devices. As one of
ordinary skill in the art would understand, many other types of
transistors, such as a FinFet transistor, could be made utilizing
similar concepts in their construction. FIG. 31A-G illustrates an
exemplary n-channel JFET which may be constructed in a 3D stacked
layer using procedures outlined below and in U.S. Pat. Nos.
8,273,610, 9,099,526, 9,219,005, 8,557,632 and 8,581,349. The
contents of the foregoing applications are incorporated herein by
reference.
[0150] As illustrated in FIG. 31A, an N- substrate donor wafer 3100
may be processed to include a wafer sized layer of doping across
the wafer, N- doped layer 3102. The N- doped layer 3102 may be
formed by ion implantation and thermal anneal. N- substrate donor
wafer 3100 may include a crystalline material, for example,
mono-crystalline (single crystal) silicon. N- doped layer 3102 may
be very lightly doped (less than 1e15 atoms/cm.sup.3) or lightly
doped (less than 1e16 atoms/cm.sup.3) or nominally un-doped (less
than 1e14 atoms/cm.sup.3). N- doped layer 3102 may have additional
ion implantation and anneal processing to provide a different
dopant level than N- substrate donor wafer 3100 and may have graded
or various layers of doping concentration. The layer stack may
alternatively be formed by epitaxially deposited doped or undoped
silicon layers, or by a combination of epitaxy and implantation, or
by layer transfer. Annealing of implants and doping may include,
for example, conductive/inductive thermal, optical annealing
techniques or types of Rapid Thermal Anneal (RTA or spike).
[0151] As illustrated in FIG. 31B, the top surface of N- substrate
donor wafer 3100 layer stack may be prepared for oxide wafer
bonding with a deposition of an oxide or by thermal oxidation of N-
doped layer 3102 to form oxide layer 3180. A layer transfer
demarcation plane (shown as dashed line) 3199 may be formed by
hydrogen implantation or other methods as described in the
incorporated references. The N- substrate donor wafer 3100, such as
surface 3182, and acceptor wafer 3110 may be prepared for wafer
bonding as previously described and low temperature (less than
approximately 400.degree. C.) bonded. Acceptor wafer 3110, as
described in the incorporated references, may include, for example,
transistors, circuitry, and metal, such as, for example, aluminum
or copper, interconnect wiring, a metal shield/heat sink layer or
layers, and thru layer via metal interconnect strips or pads.
Acceptor wafer 3110 may be substantially comprised of a crystalline
material, for example mono-crystalline silicon or germanium, or may
be an engineered substrate/wafer such as, for example, an SOI
(Silicon on Insulator) wafer or GeOI (Germanium on Insulator)
substrate. Acceptor wafer 3110 may include transistors such as, for
example, MOSFETS, FD-MOSFETS, FinFets, FD-RCATs, BJTs, HEMTs,
and/or HBTs. The portion of the N- doped layer 3102 and the N-
substrate donor wafer 3100 that may be above (when the layer stack
is flipped over and bonded to the acceptor wafer 3110) the layer
transfer demarcation plane 3199 may be removed by cleaving or other
low temperature processes as described in the incorporated
references, such as, for example, ion-cut with mechanical or
thermal cleave or other layer transfer methods, thus forming
remaining N- layer 3103. Damage/defects to crystalline structure of
N- doped layer 3102 may be annealed by some of the annealing
methods described herein, for example the short wavelength pulsed
laser techniques, wherein the N- doped layer 3102 may be heated to
defect annealing temperatures, but the layer transfer demarcation
plane 3199 may be kept below the temperate for cleaving and/or
significant hydrogen diffusion. The optical energy may be deposited
in the upper layer of the stack, for example near surface 3182, and
annealing of the N- doped layer 3102 may take place via heat
diffusion. Moreover, multiple pulses of the laser may be utilized
to improve the anneal, activation, and yield of the process.
[0152] As illustrated in FIG. 31C, oxide layer 3180 and remaining
N- layer 3103 have been layer transferred to acceptor wafer 3110.
The top surface of remaining N- layer 3103 may be chemically or
mechanically polished, and/or may be thinned by low temperature
oxidation and strip processes, such as the TEL SPA tool radical
oxidation and HF:H.sub.2O solutions as described herein and in
referenced patents and patent applications. Thru the processing,
the wafer sized layer remaining N- layer 3103 could be thinned from
its original total thickness, and its final total thickness could
be in the range of about 3 nm to about 30 nm, for example, 3 nm, 5
nm, 7 nm, 10 nm, 150 nm, 20 nm, or 30 nm. Remaining N- layer 3103
may have a thickness that may allow full gate control of channel
operation when the JFET (or JLT) transistor is substantially
completely formed. Acceptor wafer 3110 may include one or more (two
are shown in this example) shield/heat sink layers 3188, which may
include materials such as, for example, Aluminum, Tungsten (a
refractory metal), Copper, silicon or cobalt based silicides, or
forms of carbon such as carbon nanotubes, and may be layered itself
as described herein FIG. 50. Each shield/heat sink layer 3188 may
have a thickness range of about 50 nm to about mm, for example, 50
nm, 100 nm, 200 nm, 300 nm, 500 nm, 0.1 um, 1 um, 2 um, and 10 um.
Shield/heat sink layer 3188 may include isolation openings 3187,
and alignment mark openings (not shown), which may be utilized for
short wavelength alignment of top layer (donor) processing to the
acceptor wafer alignment marks (not shown). Shield/heat sink layer
3188 may include one or more shield path connects 3185 and shield
path vias 3183. Shield path via 3183 may thermally and/or
electrically couple and connect shield path connect 3185 to
acceptor wafer 3110 interconnect metallization layers such as, for
example, exemplary acceptor metal interconnect 3181 (shown). Shield
path connect 3185 may also thermally and/or electrically couple and
connect each shield/heat sink layer 3188 to the other and to
acceptor wafer 3110 interconnect metallization layers such as, for
example, acceptor metal interconnect 3181, thereby creating a heat
conduction path from the shield/heat sink layer 3188 to the
acceptor substrate 3195, and a heat sink (shown in FIG. 31G.).
Isolation openings 3187 may include dielectric materials, similar
to those of BEOL isolation 3196. Acceptor wafer 3110 may include
first (acceptor) layer metal interconnect 3191, acceptor wafer
transistors and devices 3193, and acceptor substrate 3195. Various
topside defect anneals may be utilized. For this illustration, an
optical beam such as the laser annealing previously described is
used. Optical anneal beams may be optimized to focus light
absorption and heat generation within or at the surface of
remaining N- layer 3103 and provide surface smoothing and/or defect
annealing (defects may be from the cleave and/or the ion-cut
implantation) with exemplary smoothing/annealing ray 3166. The
laser assisted smoothing/annealing with the absorbed heat generated
by exemplary smoothing/annealing ray 3166 may also include a
pre-heat of the bonded stack to, for example, about 100.degree. C.
to about 400.degree. C., and/or a rapid thermal spike to
temperatures above about 200.degree. C. to about 600.degree. C.
Additionally, absorber layers or regions, for example, including
amorphous carbon, amorphous silicon, and phase changing materials
(see U.S. Pat. Nos. 6,635,588 and 6,319,821 to Hawryluk et al. for
example), may be utilized to increase the efficiency of the optical
energy capture in conversion to heat for the desired annealing or
activation processes. Moreover, multiple pulses of the laser may be
utilized to improve the anneal, activation, and yield of the
process. Reflected ray 3163 may be reflected and/or absorbed by
shield/heat sink layer 3188 regions thus blocking the optical
absorption of ray blocked metal interconnect 3181. Annealing of
dopants or annealing of damage in remaining N- layer 3103, such as
from the H cleave implant damage, may be also accomplished by a set
of rays such as repair ray 3165. Heat generated by absorbed photons
from, for example, smoothing/annealing ray 3166, reflected ray
3163, and/or repair ray 3165 may also be absorbed by shield/heat
sink layer 3188 regions and dissipated laterally and may keep the
temperature of underlying metal layers, such as metal interconnect
3181, and other metal layers below it, cooler and prevent damage.
Shield/heat sink layer 3188 and associated dielectrics may
laterally spread and conduct the heat generated by the topside
defect anneal, and in conjunction with the dielectric materials
(low heat conductivity) above and below shield/heat sink layer
3188, keep the interconnect metals and low-k dielectrics of the
acceptor wafer interconnect layers cooler than a damage
temperature, such as, for example, 400.degree. C. A second layer of
shield/heat sink layer 3188 may be constructed (shown) with a low
heat conductive material sandwiched between the two heat sink
layers, such as silicon oxide or carbon doped `low-k` silicon
oxides, for improved thermal protection of the acceptor wafer
interconnect layers, metal and dielectrics. Shield/heat sink layer
3188 may act as a heat spreader. Electrically conductive materials
may be used for the two layers of shield/heat sink layer 3188 and
thus may provide, for example, a Vss and a Vdd plane and/or grid
that may be connected to the donor layer transistors above, as well
may be connected to the acceptor wafer transistors below, and/or
may provide below transferred layer device interconnection. Noise
on the power grids, such as the Vss and Vdd plane power conducting
lines/wires, may be mitigated by attaching/connecting decoupling
capacitors onto the power conducting lines of the grids. The
decoupling caps, which may be within the second layer (donor, for
example, donor wafer device structures) or first layer (acceptor,
for example acceptor wafer transistors and devices 3193), may
include, for example, trench capacitors such as described by Pei,
C., et al., "A novel, low-cost deep trench decoupling capacitor for
high-performance, low-power bulk CMOS applications," ICSICT
(9.sup.th International Conference on Solid-State and
Integrated-Circuit Technology) 2008, October 2008, pp. 1146-1149,
of IBM. The decoupling capacitors may include, for example, planar
capacitors, such as poly to substrate or poly to poly, or MiM
capacitors (Metal-Insulator-Metal). Shield/heat sink layer 3188 may
include materials with a high thermal conductivity greater than 10
W/m-K, for example, copper (about 400 W/m-K), aluminum (about 237
W/m-K), Tungsten (about 173 W/m-K), Plasma Enhanced Chemical Vapor
Deposited Diamond Like Carbon-PECVD DLC (about 1000 W/m-K), and
Chemical Vapor Deposited (CVD) graphene (about 5000 W/m-K).
Shield/heat sink layer 3188 may be sandwiched and/or substantially
enclosed by materials with a low thermal conductivity (less than 10
W/m-K), for example, silicon dioxide (about 1.4 W/m-K). The
sandwiching of high and low thermal conductivity materials in
layers, such as shield/heat sink layer 3188 and under &
overlying dielectric layers, spreads the localized heat/light
energy of the topside anneal laterally and protects the underlying
layers of interconnect metallization & dielectrics, such as in
the acceptor wafer 3110, from harmful temperatures or damage. When
there may be more than one shield/heat sink layer 3188 in the
device, the heat conducting layer closest to the second crystalline
layer or oxide layer 3180 may be constructed with a different
material, for example a high melting point material, for example a
refractory metal such as tungsten, than the other heat conducting
layer or layers, which may be constructed with, for example, a
lower melting point material, for example such as aluminum or
copper. Now transistors may be formed with low effective
temperature (less than approximately 400.degree. C. exposure to the
acceptor wafer 3110 sensitive layers, such as interconnect and
device layers) processing, and may be aligned to the acceptor wafer
alignment marks (not shown) as described in the incorporated
references. This may include further optical defect annealing or
dopant activation steps. The N- donor wafer 3100 may now also be
processed, such as smoothing and annealing, and reused for
additional layer transfers. The insulator layer, such as deposited
bonding oxides (for example oxide layer 3180) and/or before bonding
preparation existing oxides (for example the BEOL isolation 3196 on
top of the topmost metal layer of shield/heat sink layer 3188),
between the donor wafer transferred monocrystalline layer and the
acceptor wafer topmost metal layer, may include thicknesses of less
than 1 um, less than 500 nm, less than 400 nm, less than 300 nm,
less than 200 nm, or less than 100 nm.
[0153] As illustrated in FIG. 31D, transistor isolation regions
3105 may be formed by mask defining and plasma/RIE etching
remaining N- layer 3102 substantially to the top of oxide layer
3180 (not shown), substantially into oxide layer 3180, or into a
portion of the upper oxide layer of acceptor wafer 3110 (not
shown). Thus N- channel region 3123 may be formed. A
low-temperature gap fill dielectric, such as SACVD oxide, may be
deposited and chemically mechanically polished, the oxide remaining
in isolation regions 3105. An optical step, such as illustrated by
exemplary STI ray 3167, may be performed to anneal etch damage and
densify the STI oxide in isolation regions 3105. The doping
concentration of N- channel region 3123 may include gradients of
concentration or layers of differing doping concentrations. Any
additional doping, such as ion-implanted channel implants, may be
activated and annealed with optical annealing, such as illustrated
by exemplary implant ray 3169, as described herein. The optical
anneal, such as exemplary STI ray 3167, and/or exemplary implant
ray 3169 may be performed at separate times and processing
parameters (such as laser energy, frequency, etc.) or may be done
in combination or as one optical anneal. Optical absorber and or
reflective layers or regions may be employed to enhance the anneal
and/or protect the underlying sensitive structures. Moreover,
multiple pulses of the laser may be utilized to improve the anneal,
activation, and yield of the process.
[0154] As illustrated in FIG. 31E, a JFET transistor forming
process with raised source and drains (S/D), may be performed. For
example, a shallow P+ region 3177 may be performed to create a JFET
gate by utilizing a mask defined implant of P+ type dopant, such
as, for example, Boron. A laser or other method of optical
annealing may be utilized to activate the P+ implanted dopant.
Alternatively, a directly in contact with the silicon channel P+
doped poly gate may be formed, with appropriate isolation from the
source and drains, and dopant from that gate may also be utilized
to form shallow P+ region 3177, for example, by diffusion from an
optical anneal. S/D ion-implantations may be performed and laser
annealed to create N+ regions 3135, and thus forming N- channel
region 3133. The N+ regions 3135 may have a doping concentration
that may be more than Ox the doping concentration of N- channel
region 3133. First ILD 3136 may be deposited and CMP'd, and then
openings may be etched to enable formation of gate 3178 and raised
S/D regions 3132. Raised S/D regions 3132 and channel stressors may
be formed by etch and epitaxial deposition, for example, of SiGe
and/or SiC depending on P or N channel, and may be doped in-situ or
ion-implantation and optical anneal activation. Gate 3178 may be
formed with a metal to enable an optimal Schottky contact, for
example aluminum, or may make an electrical connection to shallow
P+ region 3177. An optical step, such as represented by exemplary
anneal ray 3121, may be performed to densify and/or remove defects
from gate 3178 and its connection to shallow P+ region 3177, anneal
defects and activate dopants such as S/D and other buried channel
tailoring implants, densify the first ILD 3136, form DSS junctions
(Dopant Segregated Schottky such as NiSi.sub.2), and/or form
contact and S/D silicides (not shown). The optical anneal may be
performed at each sub-step as desired, or may be done at prior to
Schottky metal deposition, or various combinations. Moreover,
multiple pulses of the laser may be utilized to improve the anneal,
activation, and yield of the process. Raised S/D regions 3132 may
be formed by low temperature (less than 400.degree. C.) deposition
of in-situ doped polysilicon or amorphous silicon into the S/D
openings, an optical anneal to further crystallize and dopant
activate the raised S/D material, and removal of excess raised S/D
material.
[0155] As illustrated in FIG. 31E-1, an alternate transistor
forming process to form a JLT with a conventional HKMG with raised
source and drains (S/D), may be performed. For example, a dummy
gate stack (not shown), utilizing oxide and polysilicon, may be
formed, gate spacers 3130 may be formed, raised S/D regions 3132
and channel stressors may be formed by etch and epitaxial
deposition, for example, of SiGe and/or SiC depending on P or N
channel (and may be doped in-situ or ion-implantation and optical
anneal activation), LDD and N++ S/D ion-implantations may be
performed, and first ILD 3136 may be deposited and CMP'd to expose
the tops of the dummy gates. Thus JLT transistor channel 3133-1 and
N++ S/D & LDD regions 3135-1 may be formed. N- doped layer in
FIG. 31A may be doped to N+, concentrations in excess of
1.times.10.sup.19 atms/cm.sup.3, to enable a conductive JLT channel
(JLT transistor channel 3133-1) and has been described elsewhere in
referenced patents and patent applications. JLT transistor channel
3133-1 may also be doped by implantation after the layer transfer,
and activated/annealed with optical techniques. The dummy gate
stack may be removed and a gate dielectric 3107 may be formed and a
gate metal material gate electrode 3108, including a layer of
proper work function metal to enable channel cut-off at 0 gate bias
(described in referenced U.S. Pat. No. 8,273,610) and a conductive
fill, such as aluminum, and may be deposited and CMP'd. The gate
dielectric 3107 may be an atomic layer deposited (ALD) gate
dielectric that may be paired with a work function specific gate
metal in the industry standard high k metal gate process schemes,
for example, as described in the incorporated references.
Alternatively, the gate dielectric 3107 may be formed with a low
temperature processes including, for example, LPCVD SiO.sub.2 oxide
deposition (see Ahn, J., et al., "High-quality MOSFET's with
ultrathin LPCVD gate SiO2," IEEE Electron Device Lett., vol. 13,
no. 4, pp. 186-188, April 1992) or low temperature microwave plasma
oxidation of the silicon surfaces (see Kim, J. Y., et al., "The
excellent scalability of the RCAT (recess-channel-array-transistor)
technology for sub-70 nm DRAM feature size and beyond," 2005 IEEE
VLSI-TSA International Symposium, pp. 33-31, 25-27 Apr. 2005) and a
gate material with proper work function and less than approximately
400.degree. C. deposition temperature such as, for example,
tungsten or aluminum may be deposited. An optical step, such as
represented by exemplary anneal ray 3121, may be performed to
densify and/or remove defects from gate dielectric 3107, anneal
defects and activate dopants such as N+ channel, LDD and N++ S/D
implants, densify the first ILD 3136, form DSS junctions (Dopant
Segregated Schottky such as NiSi.sub.2), and/or form contact and
S/D silicides (not shown). The optical anneal may be performed at
each sub-step as desired, or may be done at prior to the HKMG
deposition (such as after the dummy gate but before the HKMG
formation), or various combinations. Raised S/D regions 3132 may be
formed by low temperature (less than 400.degree. C.) deposition of
in-situ doped polysilicon or amorphous silicon into the S/D
openings, an optical anneal to further crystallize and dopant
activate the raised S/D material, and removal of excess raised S/D
material. The following steps may be applied to the JFET or JLT
flows.
[0156] As illustrated in FIG. 31F, a low temperature thick oxide
3109 may be deposited and planarized. Source, gate, and drain
contacts openings may be masked and etched preparing the
transistors to be connected via metallization. Thus gate contact
3111 connects to gate 3178, and source & drain contacts 3140
connect to raised S/D regions 3132. An optical step, such as
illustrated by exemplary ILD anneal ray 3151, may be performed to
anneal contact etch damage and densify the thick oxide 3109.
[0157] As illustrated in FIG. 31G, thru layer vias (TLVs) 3160 may
be formed by etching thick oxide 3109, first ILD 3136, isolation
regions 3105, oxide layer 3180, into a portion of the upper oxide
layer BEOL isolation 3196 of acceptor wafer 3110 BEOL, and filling
with an electrically and thermally conducting material (such as
tungsten or cooper) or an electrically non-conducting but thermally
conducting material (such as described elsewhere within). Second
device layer metal interconnect 3161 may be formed by conventional
processing. TLVs 3160 may be constructed of thermally conductive
but not electrically conductive materials, for example, DLC
(Diamond Like Carbon), and may connect the JFET or JLT transistor
device and other devices on the top (second) crystalline layer
thermally to shield/heat sink layer 3188. TLVs 3160 may be
constructed out of electrically and thermally conductive materials,
such as Tungsten, Copper, or aluminum, and may provide a thermal
and electrical connection path from the JFET or JLT transistor
device and other devices on the top (second) crystalline layer to
shield/heat sink layer 3188, which may be a ground or Vdd plane in
the design/layout. TLVs 3160 may be also constructed in the device
scribelanes (pre-designed in base layers or potential dicelines) to
provide thermal conduction to the heat sink, and may be sawed/diced
off when the wafer is diced for packaging not shown). Shield/heat
sink layer 3188 may be configured to act (or adapted to act) as an
emf (electro-motive force) shield to prevent direct layer to layer
cross-talk between transistors in the donor wafer layer and
transistors in the acceptor wafer. In addition to static ground or
Vdd biasing, shield/heat sink layer 3188 may be actively biased
with an anti-interference signal from circuitry residing on, for
example, a layer of the 3D-IC or off chip. The formed JFET (or JLT)
transistor device may include semiconductor regions wherein the
dopant concentration of neighboring regions of the transistor in
the horizontal plane, such as traversed by exemplary dopant plane
3134, may have regions, for example, N- channel region 3133 and S/D
N+ regions 3135, that differ substantially in dopant concentration,
for example, a 10 times greater doping concentration in N+ regions
3135 than in N- channel region 3133, and/or may be doped and
substantially undoped in the neighboring regions.
[0158] A thermal conduction path may be constructed from the
devices in the upper layer, the transferred donor layer and formed
transistors, to the acceptor wafer substrate and associated heat
sink. The thermal conduction path from the JFET or JLT transistor
device and other devices on the top (second) crystalline layer, for
example, raised S/D regions 3132, to the acceptor wafer heat sink
3197 may include source & drain contacts 3140, second device
layer metal interconnect 3161, TLV 3160, shield path connect 3185
(shown as twice), shield path via 3183 (shown as twice), metal
interconnect 3181, first (acceptor) layer metal interconnect 3191,
acceptor wafer transistors and devices 3193, and acceptor substrate
3195. The elements of the thermal conduction path may include
materials that have a thermal conductivity greater than 10 W/m-K,
for example, copper (about 400 W/m-K), aluminum (about 237 W/m-K),
and Tungsten (about 173 W/m-K), and may include material with
thermal conductivity lower than 10 W/m-K but have a high heat
transfer capacity due to the wide area available for heat transfer
and thickness of the structure (Fourier's Law), such as, for
example, acceptor substrate 3195. The elements of the thermal
conduction path may include materials that are thermally conductive
but may not be substantially electrically conductive, for example,
Plasma Enhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD
DLC (about 1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene
(about 5000 W/m-K). The acceptor wafer interconnects may be
substantially surrounded by BEOL isolation 3196. The heat removal
apparatus, which may include acceptor wafer heat sink 3197, may
include an external surface from which heat transfer may take place
by methods such as air cooling, liquid cooling, or attachment to
another heat sink or heat spreader structure.
[0159] Furthermore, some or all of the layers utilized as
shield/heat sink layer 3188, which may include shapes of material
such as the strips or fingers as illustrated in FIG. 27B-1, may be
driven by a portion of the second layer transistors and circuits
(within the transferred donor wafer layer or layers) or the
acceptor wafer transistors and circuits, to provide a programmable
back-bias to at least a portion of the second layer transistors.
The programmable back bias may utilize a circuit to do so, for
example, such as shown in FIG. 17B of U.S. Pat. No. 8,273,610, the
contents incorporated herein by reference; wherein the `Primary`
layer may be the second layer of transistors for which the
back-bias is being provided, the `Foundation` layer could be either
the second layer transistors (donor) or first layer transistors
(acceptor), and the routing metal lines connections 1723 and 1724
may include portions of the shield/heat sink layer 3188 layer or
layers. Moreover, some or all of the layers utilized as shield/heat
sink layer 3188, which may include strips or fingers as illustrated
in FIG. 27B-1, may be driven by a portion of the second layer
transistors and circuits (within the transferred donor wafer layer
or layers) or the acceptor wafer transistors and circuits to
provide a programmable power supply to at least a portion of the
second layer transistors. The programmable power supply may utilize
a circuit to do so, for example, such as shown in FIG. 17C of U.S.
Pat. No. 8,273,610, the contents incorporated herein by reference;
wherein the `Primary` layer may be the second layer of transistors
for which the programmable power supplies are being provided to,
the `Foundation` layer could be either the second layer transistors
(donor) or first layer transistors (acceptor), and the routing
metal line connections from Vout to the various second layer
transistors may include portions of the shield/heat sink layer 3188
layer or layers. The Vsupply on line 17C12 and the control signals
on control line 17C16 may be controlled by and/or generated in the
second layer transistors (for example donor wafer device structures
such as the JFETs or JLTs formed as described in relation to FIG.
31) or first layer transistors (acceptor, for example acceptor
wafer transistors and devices 3193), or off chip circuits.
Furthermore, some or all of the layers utilized as shield/heat sink
layer 3188, which may include strips or fingers as illustrated in
FIG. 27B-1 or other shapes such as those in FIG. 27B, may be
utilized to distribute independent power supplies to various
portions of the second layer transistors (for example donor wafer
device structures such as the JFETs or JLTs formed as described in
relation to FIG. 31) or first layer transistors (acceptor, for
example acceptor wafer transistors and devices 3193) and circuits;
for example, one power supply and/or voltage may be routed to the
sequential logic circuits of the second layer and a different power
supply and/or voltage routed to the combinatorial logic circuits of
the second layer. Moreover, the power distribution circuits/grid
may be designed so that Vdd may have a different value for each
stack layer. Patterning of shield/heat sink layer 3188 or layers
can impact their heat-shielding capacity. This impact may be
mitigated, for example, by enhancing the top shield/heat sink layer
3188 areal density, creating more of the secondary shield/heat sink
layers 3188, or attending to special CAD rules regarding their
metal density, similar to CAD rules that are required to
accommodate Chemical-Mechanical Planarization (CMP). These
constraints would be integrated into a design and layout EDA tool.
Moreover, the second layer of circuits and transistors, for
example, for example donor wafer device structures such as the
JFETs or JLTs formed as described in relation to FIG. 31, may
include I/O logic devices, such as SerDes
(Serialiser/Deserialiser), and conductive bond pads (not shown)
(herein such as FIG. 33). The output or input conductive pads of
the I/O circuits may be coupled, for example by bonded wires, to
external devices. The output or input conductive pads may also act
as a contact port for the 3D device output to connect to external
devices. The emf generated by the I/O circuits could be shielded
from the other layers in the stack by use of, for example, the
shield/heat sink layer 3188. Placement of the I/O circuits on the
same stack layer as the conductive bond pad may enable close
coupling of the desired I/O energy and lower signal loss.
Furthermore, the second layer of circuits and transistors, for
example donor wafer device structures such as the JFETs or JLTs
formed as described in relation to FIG. 31, may include RF (Radio
Frequency) circuits and/or at least one antenna. For example, the
second layer of circuits and transistors may include RF circuits to
enable an off-chip communication capability to external devices,
for example, a wireless communication circuit or circuits such as a
Bluetooth protocol or capacitive coupling. The emf generated by the
RF circuits could be shielded from the other layers in the stack by
use of, for example, the shield/heat sink layer 3188
[0160] TLVs 3160 may be formed through the transferred layers. As
the transferred layers may be thin, on the order of about 200 nm or
less in thickness, the TLVs may be easily manufactured as a typical
metal to metal via may be, and said TLV may have state of the art
diameters such as nanometers or tens to a few hundreds of
nanometers, such as, for example about 150 nm or about 100 nm or
about 50 nm. The thinner the transferred layers, the smaller the
thru layer via diameter obtainable, which may result from
maintaining manufacturable via aspect ratios. The thickness of the
layer or layers transferred according to some embodiments of the
invention may be designed as such to match and enable the most
suitable obtainable lithographic resolution (and enable the use of
conventional state of the art lithographic tools), such as, for
example, less than about 10 nm, 14 nm, 22 nm or 28 nm linewidth
resolution and alignment capability, such as, for example, less
than about 5 nm, 10 nm, 20 nm, or 40 nm alignment
accuracy/precision/error, of the manufacturing process employed to
create the thru layer vias or any other structures on the
transferred layer or layers.
[0161] Formation of CMOS, such as for the described JFETs or JLTs,
in one transferred layer and the orthogonal connect strip
methodology may be found as illustrated in at least FIGS. 30-33,
73-80, and 94 and related specification sections of U.S. Pat. No.
8,273,610, and may be applied to at least the FIG. 31 formation
techniques herein. Transferred layer or layers may have regions of
STI or other transistor elements within it or on it when
transferred, but would then use alignment and connection schemes
for layer transfer of patterned layers as described in incorporated
patent references.
[0162] Persons of ordinary skill in the art will appreciate that
the illustrations in FIGS. 31A through 31G are exemplary only and
are not drawn to scale. Such skilled persons will further
appreciate that many variations are possible such as, for example,
a p-channel JFET or JLT may be formed with changing the types of
dopings appropriately. Moreover, the N- substrate donor wafer 3100
may be p type or un-doped. Furthermore, isolation regions 3105 may
be formed by a hard mask defined process flow, wherein a hard mask
stack, such as, for example, silicon oxide and silicon nitride
layers, or silicon oxide and amorphous carbon layers, may be
utilized. Moreover, CMOS JFETs or JLTs may be constructed with
n-JFETs or JLTs in a first mono-crystalline silicon layer and
p-JFETs or JLTs in a second mono-crystalline layer, which may
include different crystalline orientations of the mono-crystalline
silicon layers, such as for example, <100>, <111> or
<551>, and may include different contact silicides for
optimum contact resistance to p or n type source, drains, and
gates. Further, dopant segregation techniques (DST) may be utilized
to efficiently modulate the source and drain Schottky barrier
height for both p and n type junctions formed. Furthermore, raised
source and drain contact structures, such as etch and epi SiGe and
SiC, may be utilized for strain and contact resistance improvements
and the damage from the processes may be optically annealed. Back
gated and/or multi Vt JFETs or JLTs may be constructed utilizing
the inventive concepts in FIGS. 46A-G herein. Many other
modifications within the scope of the invention will suggest
themselves to such skilled persons after reading this
specification. Thus the invention is to be limited only by the
appended claims.
[0163] An embodiment of the invention may include an exemplary
partially processed 3D device with substrate being processed with
topside illumination as illustrated in FIG. 32. The topside
illumination 3299 may be an optical anneal for purposes, such as,
for example, dopant annealing, STI densification and annealing,
silicidation, and/or ion-cut damage repair, which have been
described at least herein and in incorporated patents and patent
publications. Furthermore, topside illumination 3299 may be an
optical anneal that is die sized, or reticle sized, or other size
and shape as has been described at least herein and in incorporated
patents and patent publications. A transferred layer 3203, which
may be a transferred layer or layers as described at least herein
and in incorporated patents and patent publications, may have been
transferred and bonded to an acceptor wafer or substrate, and may
include bonding at the interface between donor bonding oxide 3280
and acceptor bonding oxide 3281. Transferred layer 3203 may have a
protect layer 3266 (or region) atop it, which may function as a
optical absorber, reflector, or energy spreader as described in at
least herein and in incorporated patents and patent publications,
and may remain a part of the device at the end of device processing
or be sacrificial (removed). Transferred layer 3203 may include its
entirety or portions, isotopically enriched silicon (such as, for
example, >99% .sup.28Si) or germanium to enable a greater heat
conductivity. The relatively higher cost of the isotopically
enriched layer or regions can be mitigated by the reuse of a donor
wafer comprised wholly or partially with the material. The acceptor
wafer at the time of bonding to the donor wafer and at exposure to
topside illumination 3299 may include acceptor bonding oxide 3281,
top shield layer 3285, inter-shield insulator layer 3298, bottom
shield layer 3288, second inter-shield insulator layer 3296, eight
`2.times.` interconnect layers 3283 that may be interspersed with
four `2.times.` insulator layers 3294, a `1.times.` interconnect
layer 3287, a `1.times.` insulator layer 3292, device die thermal
conduction paths 3245, device scribe-lane thermal conduction paths
3246, second device die thermal conduction paths 3244, second
device scribe-lane thermal conduction paths 3247, and a base wafer
with transistors and circuits 3295. The acceptor wafer may have
another combination of these layers and regions as would be clear
to one skilled in the art. The elements of the exemplary acceptor
wafer may include the materials, process flows, construction, use,
etc. as has been described herein and in incorporated patents and
patent publications, for example, transferred layer 3203 may be
doped or undoped silicon, and may have regions of STI or other
transistor elements within it or on it, and may include multiple
layers or regions of doping. Moreover, transferred layer 3203 may
include layers or regions that have materials with melting points
higher than 900.degree. C. (for example doped mono-crystalline
silicon or polysilicon or amorphous silicon, tungsten, tantalum
nitride) that may be used, for example, as a back-bias or body bias
region or layer, as has been described herein and in incorporated
patents and patent publications. Top shield layer 3285 may have
layered shield regions wherein the horizontal thermal conduction is
substantially greater than the vertical heat conduction. The bonded
stack of the acceptor wafer and transferred layers may include
scribe regions 3265, either preformed and/or predetermined
scribelanes and/or dicelines, or may include custom function
definition and etching, or a combination of both. Scribe regions
3265 may be constructed with device scribe-lane thermal conduction
paths 3246 that may provide a thermal conduction path from the top
shield layer 3285 to the base wafer with transistors and circuits
3295, which could then conduct heat that may be generated from
topside illumination 3299 to the illumination machine heat
sink/chuck 3240 and thus help prevent damage from the topside
illumination 3299 of the acceptor interconnect layers, such as, for
example, the eight `2.times.` interconnect layers 3283, four
`2.times.` insulator layers 3294, 1X' interconnect layer 3287,
`1.times.` insulator layer 3292, and the transistors and circuits
of base wafer with transistors and circuits 3295. Second device
scribe-lane thermal conduction paths 3247 may thermally conduct
from bottom shield layer 3288 to the base wafer with transistors
and circuits 3295 and the illumination machine heat sink/chuck
3240. Device die thermal conduction paths 3245 within the device
die, may provide a thermal conduction path from the top shield
layer 3285 to the base wafer with transistors and circuits 3295,
which could then conduct heat that may be generated from topside
illumination 3299 to the illumination machine heat sink/chuck 3240
and thus help prevent damage from the topside illumination 3299 of
the acceptor interconnect layers, such as, for example, the eight
`2.times.` interconnect layers 3283, four `2.times.` insulator
layers 3294, 1.times.` interconnect layer 3287, `1.times.`
insulator layer 3292, and the transistors and circuits of base
wafer with transistors and circuits 3295, and has been described
herein and in incorporated patents and patent publications. Second
device die thermal conduction paths 3244 may thermally conduct from
bottom shield layer 3288 to the base wafer with transistors and
circuits 3295 and the illumination machine heat sink/chuck 3240.
Device scribe-lane thermal conduction paths 3246 may be removed in
the later dice singulation processes whereas the device die thermal
conduction paths 3245 may remain in the finished device and provide
cooling of the second layer and above transistor and circuit layers
when the device is in operation and generating heat from the device
operation. The density of device die thermal conduction paths 3245,
device scribe-lane thermal conduction paths 3246, second device die
thermal conduction paths 3244, and second device scribe-lane
thermal conduction paths 3247 is a device design and thermal
architecture calculation, but may be on the order of 1 every 100
um.sup.2 (Wei H., et al., "Cooling Three-Dimensional Integrated
Circuits Using Power Delivery Networks", IEDM 2012, 14.2, December
2012. incorporated by reference in entirety). Scribelanes (or
dicelanes), such as scribe regions 3265, may be 10 um wide, 20 um
wide, 50 um wide 100 um wide, or greater than 100 um wide depending
on design choice and die singulation process capability.
[0164] Persons of ordinary skill in the art will appreciate that
the illustrations in FIG. 32 are exemplary and are not drawn to
scale. Such skilled persons will further appreciate that many
variations may be possible such as, for example, bottom shield
layer 3288 may also be formed as a layered shield/heat sink layer
or region. Moreover, although many of the elements in the FIG. 32
may be called layers, they main include within them regions.
Furthermore, device scribe-lane thermal conduction paths 3246 and
device die thermal conduction paths 3245 may be formed so that
there is no electrical connection to bottom shield layer 3288,
unless they are designed to do so as the same circuit node.
Further, the choice of eight `2.times.` interconnect layers 3283
that may be interspersed with four `2.times.` insulator layers
3294, a `1.times.` interconnect layer 3287, a `1.times.` insulator
layer 3292 is a design choice and may be different according to the
design considerations, both device functionally and thermally.
Moreover, the various semiconductor layers within the 3D device may
have various circuitry, functions and connection, for example, as
described herein (such as FIG. 33) or in incorporated patent
references. Thus the invention is to be limited only by the
appended claims.
[0165] The various layers of a 3D device may include many types of
circuitry, which may be formed by regions of transistors and other
semiconductor device elements within that layer or in combination
with other layers of the 3D device, and connections between the
transistors within the same region, region to region and vertically
(layer to layer) may be provided by layers of interconnect
metallization and vertical connections such as TLVs and TSVs. In
addition, power routing within the 3D device may utilize thicker
and more conductive interconnect metallization than another layer,
especially if the layer is closest to the source of external power
and/or has a greater current load/supply requirement. Many
individual device and interconnect embodiments for 3D devices have
been described herein and in the incorporated patent references. As
illustrated in FIG. 33, some additional embodiments and
combinations (further embodiments) of devices, circuits, paths, and
connections are described and may utilize similar materials,
constructions and methods as the incorporated references or
discussed herein. With reference to embodiments described herein,
for example with respect to FIG. 46, and in the incorporated patent
references, a substrate layer, which may have a thicker body than
other semiconductor layers above or within the 3D device, such as
acceptor 3310 may be formed and may include heat sink 3397,
acceptor substrate 3395, acceptor wafer transistors and circuits
3393, first (acceptor) layer metal interconnect 3381 which may
include first layer contacts 3391, first layer vias 3383, at least
one shield layer/region 3388 (two layers and many regions, such as
lower level shield layer region 3385, shown), interconnect
insulator regions 3396 and ESD diode structures 3307. A second
semiconductor layer may be transferred and constructed on top of
the first layer with isolation layer 3380 in-between and vertical
layer to layer interconnections may be provided by TLV/TSV 3335,
only one is shown. A layer of transistors and circuits 3322 may
include second layer input device structures 3376, FD ESD
structures 3317, Phase Lock Loop circuits PLL 3318, SERDES
circuitry 3319, and output device structure 3351. Second
interconnections layer 3330 may include at least one layer/regions
of metallization and associated contacts and via, for example,
second layer metallization M1 segments 3328, 3321, 3323, 3325,
second layer contacts 3326, second layer vias 3352, and conductive
pads 3390. The 3D device may be connected to external devices
utilizing many structures known to those skilled in the art, for
example, bond wires 3399. Input device structures 3376 and output
device structure 3351 may be connected to external devices through,
for example, second layer contacts 3326, second layer metallization
M1 segments 3328, second layer vias 3352, conductive pads 3390, and
bond wires 3399. A portion of the transistors within input device
structures 3376 and output device structure 3351 may be larger in
either or both width and length than most transistors within
acceptor wafer transistors and circuits 3393. Input device
structures 3376 (and output device structure 3351) may be subjected
to voltage and/or current transients from external devices or
generated externally and traveling to the 3D device along bond
wires 3399. Input device structures 3376 (and output device
structure 3351) may be protected by dissipating the transient
energy in diode structures, such as ESD diode structures 3307 on
the relatively thicker (than for example, the second semiconductor
layer) acceptor substrate 3395, which may be connected by a
multiplicity of connection stacks such as first (acceptor) layer
metal interconnect 3381 which may include first layer contacts
3391, first layer vias 3383, at least one shield layer/region 3388,
TLV/TSV 3335, and second layer metallization M1 segments 3328.
Input device structures 3376 (and output device structure 3351) may
be protected by dissipating the transient energy in a transient
filtering circuitry such as for example, FD ESD structures 3317,
which may reside on a relatively thin semiconductor layer in the 3D
device and may effectively utilize fully depleted transistors in
the filter circuitry. FD ESD structures 3317 may be coupled to
input device structures 3376 (and output device structure 3351) by
second layer interconnections (not shown). Input device structures
3376 may be connected to PLL 3318, for example, thru second layer
metallization M1 segment 3321 and second layer contacts 3326. Input
device structures 3376 may be connected to SERDES circuitry 3319,
for example, thru second layer metallization (not shown). Output
device structures 3351 may be connected to SERDES circuitry 3319,
for example, thru second layer metallization M1 segment 3323 and
second layer contacts 3326. Output device structures 3351 may drive
signals thru the connection to conductive pads 3390 and then out to
external devices thru bond wires 3399. Transistors within a lower
layer, for example within acceptor wafer transistors and circuits
3393, may be connected (not shown) to the output device structure
3351 and drive a signal to the output device structure 3351, and a
portion of the transistors of output device structure 3351 may have
a larger width and/or length than the transistors within acceptor
wafer transistors and circuits 3393. Power from external sources
may be routed thru bond wires 3399 to conductive pads 3390 to the
3D device, wherein at least a portion of the second
interconnections layer 3330 may be constructed with thicker and/or
wider metallization wiring (for example 4.times. wiring as
described in incorporated patent references) so to provide the
higher current carrying capability required for the second layer
power distribution grid/network than that of the lower layer, in
this example, first layer metallization wiring (for example
1.times. or 2.times. wiring as described in incorporated patent
references). The width and/or length of the transistors of the
second layer of transistors and circuits 3322, for example a
portion of those in second layer input device structures 3376
and/or FD ESD structures 3317 and/or output device structures 3351,
may be substantially larger than the width and/or length of
transistors in acceptor wafer transistors and circuits 3393.
[0166] Persons of ordinary skill in the art will appreciate that
the illustrations in FIG. 33 are exemplary and are not drawn to
scale. Such skilled persons will further appreciate that many
variations may be possible such as, for example, a thick enough
semiconductor layer to enable ESD diode style protection circuitry
to be constructed need not only be on the base or substrate layer,
but may reside elsewhere in the 3D device stack. Moreover, the
output circuitry including output device structures 3351 may wholly
or partially reside on a semiconductor transistor layer that is not
on top, and vertical connections including TLVs/TSV may be utilized
to connect the output device structures 3351 to conductive pads
3390. Furthermore, the input circuitry including input device
structures 3376 may wholly or partially reside on a semiconductor
transistor layer that is not on top, and vertical connections
including TLVs/TSV may be utilized to connect the input device
structures 3376 to conductive pads 3390. Similarly, SERDES
circuitry and 3319 PLL 3318 may wholly or partially reside on a
semiconductor transistor layer that is not on top, thee choices
being one of design choice and device characteristics driven.
Furthermore, connection to external devices (signal and/or power
supply) may be made on the backside of acceptor substrate 3395.
Moreover, connection to external devices form the 3D device may
utilize many types of structures other than bond wires 3399 shown
in the illustration, for example, flipchip and bumps, wireless
circuitry. Thus the invention is to be limited only by the appended
claims.
[0167] Some embodiments of the invention may include alternative
techniques to build IC (Integrated Circuit) devices including
techniques and methods to construct 3D IC systems. Some embodiments
of the invention may enable device solutions with far less power
consumption than prior art. The device solutions could be very
useful for the growing application of mobile electronic devices and
mobile systems such as, for example, mobile phones, smart phone,
and cameras, those mobile systems may also connect to the internet.
For example, incorporating the 3D IC semiconductor devices
according to some embodiments of the invention within the mobile
electronic devices and mobile systems could provide superior mobile
units that could operate much more efficiently and for a much
longer time than with prior art technology.
[0168] Smart mobile systems may be greatly enhanced by complex
electronics at a limited power budget. The 3D technology described
in the multiple embodiments of the invention would allow the
construction of low power high complexity mobile electronic
systems. For example, it would be possible to integrate into a
small form function a complex logic circuit with high density high
speed memory utilizing some of the 3D DRAM embodiments of the
invention and add some non-volatile 3D NAND charge trap or RRAM
described in some embodiments of the invention. Mobile system
applications of the 3DIC technology described herein may be found
at least in FIG. 156 of U.S. Pat. No. 8,273,610, the contents of
which are incorporated by reference.
[0169] In this document, the connection made between layers of,
generally single crystal, transistors, which may be variously named
for example as thermal contacts and vias, Thru Layer Via (TLV), TSV
(Thru Silicon Via), may be made and include electrically and
thermally conducting material or may be made and include an
electrically non-conducting but thermally conducting material or
materials. A device or method may include formation of both of
these types of connections, or just one type. By varying the size,
number, composition, placement, shape, or depth of these connection
structures, the coefficient of thermal expansion exhibited by a
layer or layers may be tailored to a desired value. For example,
the coefficient of thermal expansion of the second layer of
transistors may be tailored to substantially match the coefficient
of thermal expansion of the first layer, or base layer of
transistors, which may include its (first layer) interconnect
layers.
[0170] Base wafers or substrates, or acceptor wafers or substrates,
or target wafers substrates herein may be substantially comprised
of a crystalline material, for example, mono-crystalline silicon or
germanium, or may be an engineered substrate/wafer such as, for
example, an SOI (Silicon on Insulator) wafer or GeOI (Germanium on
Insulator) substrate.
[0171] It will also be appreciated by persons of ordinary skill in
the art that the invention is not limited to what has been
particularly shown and described hereinabove. For example, drawings
or illustrations may not show n or p wells for clarity in
illustration. Moreover, transistor channels illustrated or
discussed herein may include doped semiconductors, but may instead
include undoped semiconductor material. Further, any transferred
layer or donor substrate or wafer preparation illustrated or
discussed herein may include one or more undoped regions or layers
of semiconductor material. Moreover, epitaxial regrow of source and
drains may utilize processes such as liquid phase epitaxial
regrowth or solid phase epitaxial regrowth, and may utilize flash
or laser processes to freeze dopant profiles in place and may also
permit non-equilibrium enhanced activation (superactivation).
Further, transferred layer or layers may have regions of STI or
other transistor elements within it or on it when transferred.
Rather, the scope of the invention includes both combinations and
sub-combinations of the various features described hereinabove as
well as modifications and variations which would occur to such
skilled persons upon reading the foregoing description. Thus the
invention is to be limited only by the appended claims.
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