U.S. patent application number 13/611817 was filed with the patent office on 2014-03-13 for novel rram structure at sti with si-based selector.
This patent application is currently assigned to GLOBALFOUNDRIES Singapore Pte. Ltd.. The applicant listed for this patent is Elgin Quek, Shyue Seng Tan, Eng Huat Toh. Invention is credited to Elgin Quek, Shyue Seng Tan, Eng Huat Toh.
Application Number | 20140070159 13/611817 |
Document ID | / |
Family ID | 50232304 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140070159 |
Kind Code |
A1 |
Tan; Shyue Seng ; et
al. |
March 13, 2014 |
NOVEL RRAM STRUCTURE AT STI WITH SI-BASED SELECTOR
Abstract
An RRAM at an STI region is disclosed with a vertical BJT
selector. Embodiments include defining an STI region in a
substrate, implanting dopants in the substrate to form a well of a
first polarity around and below an STI region bottom portion, a
band of a second polarity over the well on opposite sides of the
STI region, and an active area of the first polarity over each band
of second polarity at the surface of the substrate, forming a
hardmask on the active areas, removing an STI region top portion to
form a cavity, forming an RRAM liner on cavity side and bottom
surfaces, forming a top electrode in the cavity, removing a portion
of the hardmask to form spacers on opposite sides of the cavity,
and implanting a dopant of the second polarity in a portion of each
active area remote from the cavity.
Inventors: |
Tan; Shyue Seng; (Singapore,
SG) ; Toh; Eng Huat; (Singapore, SG) ; Quek;
Elgin; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tan; Shyue Seng
Toh; Eng Huat
Quek; Elgin |
Singapore
Singapore
Singapore |
|
SG
SG
SG |
|
|
Assignee: |
GLOBALFOUNDRIES Singapore Pte.
Ltd.
Singapore
SG
|
Family ID: |
50232304 |
Appl. No.: |
13/611817 |
Filed: |
September 12, 2012 |
Current U.S.
Class: |
257/4 ;
257/E21.006; 257/E45.003; 438/382 |
Current CPC
Class: |
H01L 45/146 20130101;
H01L 27/2445 20130101; H01L 27/2436 20130101; H01L 45/08 20130101;
H01L 45/124 20130101; H01L 45/1683 20130101 |
Class at
Publication: |
257/4 ; 438/382;
257/E45.003; 257/E21.006 |
International
Class: |
H01L 21/02 20060101
H01L021/02; H01L 45/00 20060101 H01L045/00 |
Claims
1. A method comprising: defining a shallow trench isolation (STI)
region in a substrate; implanting dopants in the substrate to form
a well of a first polarity around and below a bottom portion of the
STI region, a band of a second polarity over the well on opposite
sides of the STI region, and an active area of the first polarity
over each band of second polarity at the surface of the substrate;
forming a hardmask on the active areas; removing a top portion of
the STI region to form a cavity; forming an RRAM liner on side and
bottom surfaces of the cavity; forming a top electrode in the
cavity; removing a portion of the hardmask to form spacers on
opposite sides of the cavity; and implanting a dopant of the second
polarity in a portion of each active area remote from the
cavity.
2. The method according to claim 1, wherein the bottom surface of
the cavity is above a top surface of the band of a second
polarity.
3. The method according to claim 1, comprising forming the active
areas with a shallow implant and implanting the dopant of the
second polarity in each active area using multiple energies.
4. The method according to claim 3, comprising activating all of
the dopants after implanting the dopant of the second polarity in
each active area.
5. The method according to claim 4, comprising forming the hardmask
of silicon nitride.
6. The method according to claim 1, comprising forming the RRAM
liner to a thickness of 3 nanometers (nm) to 900 nm.
7. The method according to claim 1, wherein the RRAM liner
comprises an oxide of a transition metal.
8. The method according to claim 1, wherein the top electrode
comprises a transition metal, titanium nitride (TiN), TiN/Ti, or
polysilicon.
9. A method comprising: defining a shallow trench isolation (STI)
region in a substrate; implanting dopants in the substrate to form
a well of a first polarity around and below a bottom portion of the
STI region, a band of a second polarity over the well on opposite
sides of the STI region, and an active area of the first polarity
over each band of second polarity at the surface of the substrate;
forming a hardmask on the active areas; removing a top portion of
the STI region to form a cavity; forming a sacrificial top
electrode in the cavity; removing a portion of the hardmask to form
spacers on opposite sides of the cavity; implanting a dopant of the
second polarity in a portion of each active area remote from the
cavity; removing the sacrificial top electrode; forming an RRAM
liner on side and bottom surfaces of the cavity; and forming a top
electrode in the cavity.
10. The method according to claim 9, wherein the bottom surface of
the cavity is above a top surface of the band of a second
polarity.
11. The method according to claim 9, comprising forming the active
areas with a shallow implant and implanting the dopant of the
second polarity in each active area using multiple energies.
12. The method according to claim 9, comprising activating all of
the dopants prior to removing the sacrificial top electrode.
13. The method according to claim 12, comprising forming a
protection layer over the active areas prior to removing the
sacrificial top electrode.
14. The method according to claim 9, comprising forming the
hardmask of silicon nitride.
15. The method according to claim 9, comprising forming the RRAM
liner of an oxide of a transition metal and to a thickness of 3
nanometers (nm) to 900 nm.
16. The method according to claim 9, wherein the top electrode
comprises a transition metal, titanium nitride (TiN), TiN/Ti, or
polysilicon.
17. A device comprising: a substrate; a well of a first polarity in
the substrate; a shallow trench isolation (STI) region formed in
the substrate extending partially into the well; a band of a second
polarity in the substrate, over the well, at opposite sides of the
STI region; an area of the first polarity in the substrate over the
band at opposite sides of each STI region; an area of the second
polarity in the substrate over the band adjacent each area of the
first polarity, remote from the STI region; a recess in a top
surface of a portion of the STI region; an RRAM liner on side and
bottom surfaces of the recess; and a top electrode in the recess,
wherein the bottom surface of the recess is above a top surface of
the band.
18. The device according to claim 17, wherein the RRAM liner
comprises an oxide of a transition metal.
19. The device according to claim 17, wherein a thickness of the
RRAM liner is 3 nm to 900 nm.
20. The device according to claim 17, wherein the top electrode
comprises a transition metal, titanium nitride (TiN), TiN/Ti, or
polysilicon.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to semiconductor memories.
The present disclosure is particularly applicable to nonvolatile
resistive random access memories (RRAMs).
BACKGROUND
[0002] Present flash technologies have encountered significant
challenges for scaling such as scaling of program/erase (P/E)
voltage, speed, reliability, number of charges stored per floating
gate and their variability. Attempts to solve such issues have
included employing RRAMs due to their scalability, highly
competitive speed, endurance, and retention properties. RRAMs have
been placed within contacts, above contacts, between M2 and M3
layers, and above backend layers. Single transistor single resistor
(1T1R) RRAMs, which are desirably bipolar and have a high access
current, also have a large cell size of 8F.sup.2 or higher and are
not easily scalable. Single diode single resistor (1D1R) RRAMs, on
the other hand, have a smaller cell size of 4F.sup.2 or higher, and
are easily scalable, but are unipolar and have a low access
current. In addition, 1D1R RRAMs employ metal oxide diodes or
organic diodes, which are compatible with back-end-of-line (BEOL)
processes because of processing temperatures less than 400.degree.
C. However, the diodes of such materials are not tunable, have
inferior diode performance (i.e., low forward current due to large
band-gap), which leads to larger cell area and a high Vdd of 3 to
4.5 V, which is not compatible with low Vdd technology.
[0003] A need therefore exists for methodology enabling fabrication
of RRAMs which have a small cell size, are easily scalable, have a
high access current, and are bipolar, and the resulting
product.
SUMMARY
[0004] An aspect of the present disclosure is a method of
fabricating a compact RRAM using an embedded vertical bipolar
junction transistor (BJT).
[0005] Another aspect of the present disclosure is a compact RRAM
using an embedded vertical BJT.
[0006] Additional aspects and other features of the present
disclosure will be set forth in the description which follows and
in part will be apparent to those having ordinary skill in the art
upon examination of the following or may be learned from the
practice of the present disclosure. The advantages of the present
disclosure may be realized and obtained as particularly pointed out
in the appended claims.
[0007] According to the present disclosure, some technical effects
may be achieved in part by a method including: defining a shallow
trench isolation (STI) region in a substrate; implanting dopants in
the substrate to form a well of a first polarity around and below a
bottom portion of the STI region, a band of a second polarity over
the well on opposite sides of the STI region, and an active area of
the first polarity over each band of second polarity at the surface
of the substrate; forming a hardmask on the active areas; removing
a top portion of the STI region to form a cavity; forming an RRAM
liner on side and bottom surfaces of the cavity; forming a top
electrode in the cavity; removing a portion of the hardmask to form
spacers on opposite sides of the cavity; and implanting a dopant of
the second polarity in a portion of each active area remote from
the cavity.
[0008] Aspects of the present disclosure include the bottom surface
of the cavity being above a top surface of the band of a second
polarity. Further aspects include forming the active areas with a
shallow implant and implanting the dopant of the second polarity in
each active area using multiple energies. Other aspects include
activating all of the dopants after implanting the dopant of the
second polarity in each active area. Another aspect includes
forming the hardmask of silicon nitride. An additional aspect
includes forming the RRAM liner to a thickness of 3 nanometers (nm)
to 900 nm. Further aspects include the RRAM liner including an
oxide of a transition metal. Other aspects include the top
electrode including a transition metal, titanium nitride (TiN),
TiN/Ti, or polysilicon.
[0009] Another aspect of the present disclosure is a method
including defining a shallow trench isolation (STI) region in a
substrate; implanting dopants in the substrate to form a well of a
first polarity around and below a bottom portion of the STI region,
a band of a second polarity over the well on opposite sides of the
STI region, and an active area of the first polarity over each band
of second polarity at the surface of the substrate; forming a
hardmask on the active areas; removing a top portion of the STI
region to form a cavity; forming a sacrificial top electrode in the
cavity; removing a portion of the hardmask to form spacers on
opposite sides of the cavity; implanting a dopant of the second
polarity in a portion of each active area remote from the cavity;
removing the sacrificial top electrode; forming an RRAM liner on
side and bottom surfaces of the cavity; and forming a top electrode
in the cavity.
[0010] Aspects include the bottom surface of the cavity being above
a top surface of the band of a second polarity. Additional aspects
include forming the active areas with a shallow implant and
implanting the dopant of the second polarity in each active area
using multiple energies. Other aspects include activating all of
the dopants prior to removing the sacrificial top electrode.
Another aspect includes forming a protection layer over the active
areas prior to removing the sacrificial top electrode. Further
aspects include forming the hardmask of silicon nitride. Additional
aspects include forming the RRAM liner of an oxide of a transition
metal and to a thickness of 3 nm to 900 nm. Further aspects include
the top electrode including a transition metal, titanium nitride
(TiN), TiN/Ti, or polysilicon.
[0011] Another aspect of the present disclosure is a device
including: a substrate; a well of a first polarity in the
substrate; a shallow trench isolation (STI) region formed in the
substrate extending partially into the well; a band of a second
polarity in the substrate, over the well, at opposite sides of the
STI region; an area of the first polarity in the substrate over the
band at opposite sides of each STI region; an area of the second
polarity in the substrate over the band adjacent each area of the
first polarity, remote from the STI region; a recess in a top
surface of a portion of the STI region; an RRAM liner on side and
bottom surfaces of the recess; and a top electrode in the recess,
wherein the bottom surface of the recess is above a top surface of
the band.
[0012] Aspects include the RRAM liner including an oxide of a
transition metal. Further aspects include a thickness of the RRAM
liner being 3 nm to 900 nm. Other aspects include the top electrode
including a transition metal, titanium nitride (TiN), TiN/Ti, or
polysilicon.
[0013] Additional aspects and technical effects of the present
disclosure will become readily apparent to those skilled in the art
from the following detailed description wherein embodiments of the
present disclosure are described simply by way of illustration of
the best mode contemplated to carry out the present disclosure. As
will be realized, the present disclosure is capable of other and
different embodiments, and its several details are capable of
modifications in various obvious respects, all without departing
from the present disclosure. Accordingly, the drawings and
description are to be regarded as illustrative in nature, and not
as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present disclosure is illustrated by way of example, and
not by way of limitation, in the figures of the accompanying
drawing and in which like reference numerals refer to similar
elements and in which:
[0015] FIGS. 1A through 4A and 1B through 4B schematically
illustrate top views and cross-sectional views, respectively, of a
process flow, in accordance with an exemplary embodiment;
[0016] FIGS. 5A through 7A and 5B through 7B schematically
illustrate top views and cross-sectional views, respectively, of a
process flow, in accordance with another exemplary embodiment;
and
[0017] FIGS. 8A through 8C schematically illustrate a layout scheme
for the structures formed by the processes of the first and second
embodiments.
DETAILED DESCRIPTION
[0018] In the following description, for the purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of exemplary embodiments. It
should be apparent, however, that exemplary embodiments may be
practiced without these specific details or with an equivalent
arrangement. In other instances, well-known structures and devices
are shown in block diagram form in order to avoid unnecessarily
obscuring exemplary embodiments. In addition, unless otherwise
indicated, all numbers expressing quantities, ratios, and numerical
properties of ingredients, reaction conditions, and so forth used
in the specification and claims are to be understood as being
modified in all instances by the term "about."
[0019] The present disclosure addresses and solves the current
problems of difficult scalability, low access current, large cell
size and/or unipolarity attendant upon fabricating a 1T1R or a 1D1R
RRAM. In accordance with embodiments of the present disclosure, a
compact RRAM is formed using an embedded vertical BJT.
[0020] Methodology in accordance with embodiments of the present
disclosure includes defining a shallow trench isolation (STI)
region in a substrate, implanting dopants in the substrate to form
a well of a first polarity around and below a bottom portion of the
STI region, a band of a second polarity over the well on opposite
sides of the STI region, and an active area of the first polarity
over each band of second polarity at the surface of the substrate.
A hardmask is then formed on the active areas, a top portion of the
STI region is removed to form a cavity, an RRAM liner is formed on
side and bottom surfaces of the cavity, a top electrode is formed
in the cavity, a portion of the hardmask is removed to form spacers
on opposite sides of the cavity, and a dopant of the second
polarity is implanted in a portion of each active area remote from
the cavity.
[0021] Still other aspects, features, and technical effects will be
readily apparent to those skilled in this art from the following
detailed description, wherein preferred embodiments are shown and
described, simply by way of illustration of the best mode
contemplated. The disclosure is capable of other and different
embodiments, and its several details are capable of modifications
in various obvious respects. Accordingly, the drawings and
description are to be regarded as illustrative in nature, and not
as restrictive.
[0022] FIGS. 1A through 4A schematically illustrate a top view of a
process flow in accordance with an exemplary embodiment, and FIGS.
1B through 4B schematically illustrate corresponding
cross-sectional views of the process flow. Adverting to FIGS. 1A
and 1B, STI regions 103 are defined on a p-type substrate 101. The
STI regions may be formed to a depth of 100 nanometer (nm) to 1000
nm and to a width of 50 nm to 200 nm, depending on the technology
node, and may be formed, for example, of silicon dioxide
(SiO.sub.2), silicon nitride (Si.sub.3N.sub.4), or silicon
oxynitride (SiON). N-wells 105 are formed around the bottom
portions of the STI regions by implanting N-type dopants (e.g.,
phosphorus (P), arsenic (As), etc.) at a dosage of 1E12 to 9E13
with an energy of 10 keV to 900 keV depending on the STI depth.
Next, a p-band 107 is formed over the n-wells on opposite sides of
the STI region by implanting P-type dopant (e.g., boron (B), boron
difluoride (BF.sub.2), indium (In), etc.) at a dosage of 1E12 to
9E13 and with an energy of 10 keV to 100 keV. Then, a shallow
n-type implant is performed over the p-band on opposite sides of
the STI region by implanting N-type dopants (e.g., P, As, etc.) at
a dosage of 1E12 to 9E13 and with an energy of 1 keV to 10 keV,
forming n-type active area 109.
[0023] As illustrated in FIGS. 2A and 2B, a hardmask, such as
silicon nitride (SiN) 201 is deposited over the entire substrate.
Then, using a mask with openings 203, the portion of hardmask 201
over STI regions 103 and a top portion of STI regions 103 are
removed, such as by etching, forming cavities 205. After the
etching is complete, the bottom surface 207 of cavities 205 must be
above a top surface 209 of p-band 107, to prevent short-circuit
paths to other terminals.
[0024] An RRAM liner 301 is then conformally deposited in cavities
205, as illustrated in FIGS. 3A and 3B. RRAM liner 301 may be
formed of titanium oxide (TiO.sub.x), nickel oxide (NiO.sub.x),
hafnium oxide (HfO.sub.x), tungsten oxide (WO.sub.x), tantalum
oxide (TaO.sub.x), vanadium oxide (VO.sub.x), and copper oxide
(CuO.sub.x). The RRAM liner 301 may be formed to a thickness of a
few nm to hundreds of nm. The remainder of each cavity 205 is then
filled with a top electrode 303, followed by an etch-back or
chemical mechanical polishing (CMP). Top electrode 303 may be
formed of a material such as tungsten (W), platinum (Pt), titanium
nitride (TiN), TiN/titanium (Ti), ruthenium (Ru), nickel (Ni), or
polysilicon.
[0025] Adverting to FIGS. 4A and 4B, hardmask 201 is etched to form
spacers 401 on opposite sides of top electrode 303. Then, multiple
implantation steps are performed, implanting, for example, P-type
dopant (e.g., B, BF.sub.2, In, etc.), with different energies
ranging from between sub keV (<1 keV) and 1 keV to between 2 keV
and 10 keV, depending on the dopant used, to establish a desired
implant profile for p-type regions 403. Once the implantations are
complete, the dopants may be activated by heating to a temperature
of 900.degree. C. to 1100.degree. C. for 1 millisecond (ms) to less
than 5 seconds. Alternatively, a laser anneal may be performed to
activate the dopants. Nickel silicide (NiSi) is then formed on
p-type regions 403, and back-end-of line (BEOL) processing may
continue.
[0026] FIGS. 5A through 7A schematically illustrate a top view of a
process flow in accordance with another exemplary embodiment, in
which a gate last approach is utilized, and FIGS. 5B through 7B
schematically illustrate corresponding cross-sectional views of the
process flow. The process begins the same as the first embodiment,
through the formation of cavities 205 by removing both the portion
of hardmask 201 over STI regions 103 and also a top portion of STI
regions 103, such as by etching. Adverting to FIGS. 5A and 5B,
cavities 205 are filled with a sacrificial top electrode 501,
formed, for example by depositing polysilicon or amorphous silicon
(a-Si).
[0027] As illustrated in FIGS. 6A and 6B, hardmask 201 is etched to
form spacers 601 on opposite sides of sacrificial top electrode
501. Then, multiple implantation steps are performed, implanting,
P-type dopant (e.g., B, BF.sub.2, In, etc.), with different
energies ranging from between sub keV (<1 keV) and 1 keV to
between 2 keV and 10 keV, depending on the dopant used, to
establish a desired implant profile for p-type regions 603. Once
the implantations are complete, the dopants may be activated by
heating to a temperature of 900.degree. C. to 1100.degree. C. for 1
millisecond (ms) to less than 5 seconds. Alternatively, a laser
anneal may be performed to activate the dopants.
[0028] A protection layer (not shown for illustrative convenience),
formed for example of SiO2 or SiON, is then deposited over p-type
regions 603 (the active regions), and sacrificial top electrode 501
is removed. As illustrated in FIGS. 7A and 7B, an RRAM liner 701 is
then conformally deposited in cavities 205. RRAM liner 301 may be
formed of titanium oxide (TiO.sub.x), nickel oxide (NiO.sub.x),
hafnium oxide (HfO.sub.x), tungsten oxide (WO.sub.x), tantalum
oxide (TaO.sub.x), vanadium oxide (VO.sub.x), and copper oxide
(CuO.sub.x). The RRAM liner 701 may be formed to a thickness of a
few nm to hundreds of nm. The remainder of each cavity 205 is then
filled with a top electrode 703, followed by an etch-back or
chemical mechanical polishing (CMP). Top electrode 703 may be
formed of a material such as tungsten (W), platinum (Pt), titanium
nitride (TiN), TiN/titanium (Ti), ruthenium (Ru), nickel (Ni), or
polysilicon. Nickel silicide (NiSi) is then formed on p-type
regions 603, and back-end-of line (BEOL) processing may
continue.
[0029] Adverting to FIGS. 8A through 8C, a layout of RRAMs of FIGS.
4A and 4B is illustrated. As shown in FIGS. 8A through 8C, a first
bit line 801 is connected to the p-type region 403 on one side of
the STI region, and a second bit line 803 is connected to the
p-type region 403 on the other side of the STI region. A first word
line 805 is connected to a first column of top electrodes 303, and
a second word line 809 is connected to a second column of top
electrodes 303. A select line 807 is formed in n-wells 105.
[0030] Read, set, and reset operations of the RRAM at the STI can
be achieved by passing current through selected BJTs and RRAM. For
example, for a read operation, a high read voltage may be applied
to the selected word line, a select read voltage may be applied to
the selected bit line, and a low voltage may be applied to the
select line. Similarly, for a set operation, a high set voltage may
be applied to the selected word line, a select set voltage may be
applied to the selected bit line, and a low voltage may be applied
to the select line. For reset operations, a select reset voltage
may be applied to the selected bit line. Then, for a unipolar reset
operation, a high reset voltage may be applied to the selected word
line and a low voltage may be applied to the select line, whereas
for a bipolar operation, a low reset voltage may be applied to the
selected word line and a high voltage may be applied to the select
line. In addition, for forming operations, a high forming voltage
may be applied to the selected word line, a select forming voltage
may be applied to the selected bit line, and a low voltage may be
applied to the select line. For all forming, read, set, and reset
operations, unselected word lines and unselected bit lines may be
floating.
[0031] The embodiments of the present disclosure can achieve
several technical effects, such as direct access to the RRAM with a
high access current through a silicon-based selector (the vertical
BJT), cell performance and scalability being independent from the
gate oxide and gate length, thereby reducing cell size and
increasing scalability, bidirectionality of the RRAM without
increasing cell size, and compatibility with both gate first and
gate last approaches. Embodiments of the present disclosure enjoy
utility in various industrial applications as, for example,
microprocessors, smart phones, mobile phones, cellular handsets,
set-top boxes, DVD recorders and players, automotive navigation,
printers and peripherals, networking and telecom equipment, gaming
systems, digital cameras, or in any memory product. The present
disclosure therefore enjoys industrial applicability in any of
various types of highly integrated semiconductor devices.
[0032] In the preceding description, the present disclosure is
described with reference to specifically exemplary embodiments
thereof. It will, however, be evident that various modifications
and changes may be made thereto without departing from the broader
spirit and scope of the present disclosure, as set forth in the
claims. The specification and drawings are, accordingly, to be
regarded as illustrative and not as restrictive. It is understood
that the present disclosure is capable of using various other
combinations and embodiments and is capable of any changes or
modifications within the scope of the inventive concept as
expressed herein.
* * * * *