U.S. patent application number 14/613956 was filed with the patent office on 2017-10-05 for cobalt-containing conductive layers for control gate electrodes in a memory structure.
The applicant listed for this patent is SANDISK TECHNOLOGIES INC.. Invention is credited to Johann ALSMEIER, Senaka Krishna KANAKAMEDALA, Sateesh KOKA, Yao-Sheng LEE, Raghuveer S. MAKALA, George MATAMIS, Genta MIZUNO, Rahul SHARANGPANI, Naoki TAKEGUCHI.
Application Number | 20170287925 14/613956 |
Document ID | / |
Family ID | 53400927 |
Filed Date | 2017-10-05 |
United States Patent
Application |
20170287925 |
Kind Code |
A9 |
MAKALA; Raghuveer S. ; et
al. |
October 5, 2017 |
COBALT-CONTAINING CONDUCTIVE LAYERS FOR CONTROL GATE ELECTRODES IN
A MEMORY STRUCTURE
Abstract
A memory film and a semiconductor channel can be formed within
each memory opening that extends through a stack including an
alternating plurality of insulator layers and sacrificial material
layers. After formation of backside recesses through removal of the
sacrificial material layers selective to the insulator layers, a
metallic barrier material portion can be formed in each backside
recess. A cobalt portion can be formed in each backside recess.
Each backside recess can be filled with a cobalt portion alone, or
can be filled with a combination of a cobalt portion and a metallic
material portion including a material other than cobalt.
Inventors: |
MAKALA; Raghuveer S.;
(Campbell, CA) ; SHARANGPANI; Rahul; (Fremont,
CA) ; KOKA; Sateesh; (Milpitas, CA) ; MIZUNO;
Genta; (Yokkaichi, JP) ; TAKEGUCHI; Naoki;
(Yokkaichi, JP) ; KANAKAMEDALA; Senaka Krishna;
(San Jose, CA) ; MATAMIS; George; (Danville,
CA) ; LEE; Yao-Sheng; (Tampa, FL) ; ALSMEIER;
Johann; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SANDISK TECHNOLOGIES INC. |
PLANO |
TX |
US |
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Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20150179662 A1 |
June 25, 2015 |
|
|
Family ID: |
53400927 |
Appl. No.: |
14/613956 |
Filed: |
February 4, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14587368 |
Dec 31, 2014 |
9230976 |
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14613956 |
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14283431 |
May 21, 2014 |
8946810 |
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14587368 |
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|
14086139 |
Nov 21, 2013 |
8829591 |
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14283431 |
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14051627 |
Oct 11, 2013 |
8765543 |
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14086139 |
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13875854 |
May 2, 2013 |
8580639 |
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14051627 |
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13693337 |
Dec 4, 2012 |
8461000 |
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13875854 |
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12827761 |
Jun 30, 2010 |
8349681 |
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13693337 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/76841 20130101;
H01L 27/11582 20130101; H01L 27/11578 20130101; H01L 29/7889
20130101; H01L 29/4958 20130101; H01L 29/7926 20130101; H01L
27/11519 20130101; H01L 29/4966 20130101; H01L 27/1157 20130101;
H01L 27/11563 20130101; H01L 27/11556 20130101; H01L 27/11568
20130101; H01L 29/66833 20130101; H01L 29/7883 20130101; H01L
29/40117 20190801; H01L 27/11524 20130101; H01L 21/76877 20130101;
H01L 21/32133 20130101; H01L 29/40114 20190801; H01L 29/66825
20130101; H01L 27/11565 20130101 |
International
Class: |
H01L 27/115 20060101
H01L027/115; H01L 21/3213 20060101 H01L021/3213; H01L 21/768
20060101 H01L021/768; H01L 29/788 20060101 H01L029/788; H01L 29/49
20060101 H01L029/49; H01L 21/28 20060101 H01L021/28 |
Claims
1. A three-dimensional memory device comprising: a stack of
alternating layers comprising insulator layers and electrically
conductive layers and located over a substrate; an opening
extending through the stack; a blocking dielectric, at least one
charge storage element and a tunneling dielectric located within
the opening; and a semiconductor channel located within the
opening, wherein each of the electrically conductive layers
comprises at least a cobalt portion.
2. The three-dimensional memory device of claim 1, wherein the
electrically conductive layers comprise: a first control gate
electrode located in a first device level; and a second control
gate electrode located in a second device level that is located
below the first device level.
3. The three-dimensional memory device of claim 1, wherein each of
the electrically conductive layers further comprises a metallic
barrier material portion contacting an overlying insulator layer,
an underlying insulator layer, and a sidewall of a blocking
dielectric layer.
4. The three-dimensional memory device of claim 3, further
comprising a backside contact structure extending through a
backside contact trench in the stack, electrically isolated from
the electrically conductive layers, and electrically shorted to the
semiconductor channel.
5. The three-dimensional memory device of claim 4, wherein a
proximal sidewall of each cobalt portion is laterally spaced from
the blocking dielectric by a vertical portion of a respective
metallic barrier material portion, and each cobalt portion is
laterally recessed from the backside contact trench.
6. The three-dimensional memory device of claim 3, wherein each
cobalt portion contacts a surface of a respective metallic barrier
material portion.
7. The three-dimensional memory device of claim 6, wherein each
cobalt portion contacts a pair of horizontal surfaces of the
respective metallic barrier material portion and an outer sidewall
of the respective metallic barrier material portion.
8. The three-dimensional memory device of claim 6, wherein each
electrically conductive layer consists of a respective cobalt
portion and a respective metallic barrier material portion.
9. The three-dimensional memory device of claim 6, wherein each of
the electrically conductive layers further comprises a metallic
material portion containing a material other than cobalt and
contacting a respective cobalt portion.
10. The three-dimensional memory device of claim 9, wherein each
metallic material portion is laterally spaced from a metallic
barrier material portion located at a same level by a respective
cobalt portion, and comprises tungsten or a tungsten alloy.
11. The three-dimensional memory device of claim 9, wherein each
metallic material portion is vertically spaced from a metallic
barrier material portion located at a same level by a respective
cobalt portion.
12. The three-dimensional memory device of claim 9, wherein each
metallic material portion contacts a pair of horizontal surfaces of
a respective metallic barrier material portion located at a same
level.
13. The three-dimensional memory device of claim 9, wherein each
metallic material portion contacts a horizontal surface of an
overlying dielectric layer and a horizontal surface of an
underlying dielectric layer.
14. The three-dimensional memory device of claim 9, wherein each
cobalt portion contacts a horizontal surface of an overlying
dielectric layer and a horizontal surface of an underlying
dielectric layer.
15. The three-dimensional memory device of claim 9, wherein each
cobalt portion is laterally spaced from a vertical portion of a
metallic barrier material portion located at a same level by a
respective metallic material portion that comprises tungsten or a
tungsten alloy.
16. The three-dimensional memory device of claim 1, wherein each of
the electrically conductive layers comprises: a metallic barrier
material portion contacting an outer sidewall of the blocking
dielectric; a metallic material portion containing a material other
than cobalt and contacting the metallic barrier material portion;
and a respective cobalt portion contacting horizontal surfaces of
the metallic material portion and not contacting the metallic
barrier material portion.
17. The three-dimensional memory device of claim 1, wherein each of
the electrically conductive layers comprises: a metallic barrier
material portion contacting an outer sidewall of the blocking
dielectric; a cobalt material portion contacting the metallic
barrier material portion; and a metallic material portion
containing a material other than cobalt contacting horizontal
surfaces of the cobalt material portion and not contacting the
metallic barrier material portion.
18. The three-dimensional memory device of claim 1, wherein each of
the electrically conductive layers contacts surfaces of a backside
blocking dielectric layer.
19. The three-dimensional memory device of claim 18, wherein each
electrically conductive layer comprises a metallic barrier material
portion contacting a backside blocking dielectric layer and a
respective cobalt portion.
20. The three-dimensional memory device of claim 1, wherein: the
three-dimensional memory device comprises a vertical NAND device
located in a device region; and the electrically conductive layers
comprise, or are electrically connected to a respective word line
of the NAND device.
21. The three-dimensional memory device of claim 20, wherein: the
device region comprises: a plurality of semiconductor channels,
wherein at least one end portion of each of the plurality of
semiconductor channels extends substantially perpendicular to a top
surface of the substrate; a plurality of charge storage regions,
each charge storage region located adjacent to a respective one of
the plurality of semiconductor channels; and a plurality of control
gate electrodes having a strip shape extending substantially
parallel to the top surface of the substrate; the plurality of
control gate electrodes comprise at least a first control gate
electrode located in a first device level and a second control gate
electrode located in a second device level; the electrically
conductive layers in the stack are in electrical contact with the
plurality of control gate electrode and extend from the device
region to a contact region including the plurality of electrically
conductive via connections; and the substrate comprises a silicon
substrate containing a driver circuit for the NAND device.
22. A method of manufacturing a three-dimensional memory device,
comprising: forming a stack of alternating layers comprising
insulator layers and sacrificial material layers over a substrate;
forming an opening through the stack; forming a blocking dielectric
at a periphery of the opening; forming at least one charge storage
element over the blocking dielectric; forming a tunneling
dielectric over the at least one charge storage element; forming a
semiconductor channel over the tunneling dielectric in the opening;
forming backside recesses around the blocking dielectric by
removing the sacrificial material layers; and forming electrically
conductive layers within the backside recesses, wherein each of the
electrically conductive layers is formed by depositing at least a
cobalt portion within a respective backside recess.
23. The method of claim 22, further comprising forming a metallic
bather material portion in each backside recess prior to forming
the cobalt portions.
24. The method of claim 23, further comprising forming a backside
contact trench through the stack, wherein the backside recesses are
formed by removing the sacrificial material layers through the
backside contact trench.
25. The method of claim 24, wherein the metallic barrier material
portions are formed by: depositing a metallic barrier material
layer in the backside recesses and on a sidewall of the backside
contact trench; and removing vertical portions of the metallic
barrier material layer from the sidewall of the backside contact
trench, wherein remaining portions of the metallic barrier material
layer constitutes the metallic barrier material portions.
26. The method of claim 25, further comprising: depositing a
contiguous cobalt layer on the metallic barrier material layer; and
etching back portions of the contiguous cobalt layer from the
backside contact trench prior to removing the vertical portions of
the metallic barrier material layer, wherein each remaining portion
of the contiguous cobalt layer constitutes the cobalt portions of
the electrically conductive layers.
27. The method of claim 24, wherein each cobalt portion of the
electrically conductive layers is formed on a surface of a
respective metallic barrier material portion.
28. The method of claim 27, wherein each cobalt portion of the
electrically conductive layers is formed on a pair of horizontal
surfaces of the respective metallic barrier material portion and an
outer sidewall of the respective metallic barrier material
portion.
29. The method of claim 28, further comprising: depositing a
metallic barrier material layer in the backside recesses and on a
sidewall of the backside contact trench; depositing a contiguous
cobalt layer on the metallic barrier material layer; and removing
vertical portions of the metallic barrier material layer and the
contiguous cobalt layer from a sidewall of the backside contact
trench, wherein remaining portions of the metallic barrier material
layer constitute metallic barrier material portions, and remaining
portions of the contiguous cobalt layer constitute the cobalt
portions.
30. The method of claim 29, further comprising forming a metallic
material portion comprising a material other than cobalt in a
vacant portion of each backside recess.
31. The method of claim 30, wherein each metallic material portion
is vertically and laterally spaced from a metallic barrier material
portion located at a same level by a respective cobalt portion, and
comprises tungsten or a tungsten alloy.
32. The method of claim 30, wherein each metallic material portion
contacts a pair of horizontal surfaces of a metallic barrier
material portion located at a same level.
33. The method of claim 29, wherein each electrically conductive
layer consists of a respective cobalt portion and a metallic
barrier material portion.
34. The method of claim 29, further comprising selectively
depositing cobalt after formation of the metallic barrier material
portions as a plurality structures vertically disjoined from one
another, wherein each deposited portion of cobalt constitutes one
of the cobalt portions.
35. The method of claim 29, further comprising: depositing a
metallic barrier material layer in the backside recesses and on a
sidewall of the backside contact trench; depositing a contiguous
metallic material layer comprising a material other than cobalt;
and removing vertical portions of the metallic barrier material
layer and the contiguous metallic material layer from a sidewall of
the backside contact trench, wherein remaining portions of the
metallic barrier material layer constitute metallic barrier
material portions, and remaining portions of the contiguous
metallic material layer constitute metallic material portions.
36. The method of claim 35, wherein each cobalt portion is formed
directly on a respective metallic material portion located at a
same level.
37. The method of claim 22, wherein the electrically conductive
layers are formed directly on horizontal surfaces of the insulating
layers and an outer sidewall of the blocking dielectric.
38. The method of claim 22, further comprising: forming a metallic
barrier material layer in the backside recesses; filling the
backside recesses by depositing a disposable material layer on the
metallic barrier material layer; forming a metallic barrier
material portion and a disposable material portion at each level of
the of backside recesses by removing vertical portions of the
disposable material layer and the metallic barrier material layer;
removing the disposable material portions; and forming the cobalt
portions over the respective metallic barrier material
portions.
39. The method of claim 38, further comprising forming backside
dielectric material layer in the backside recesses prior to forming
the metallic barrier material layer, wherein the metallic barrier
material layer is formed on the backside dielectric material
layer.
40. The method of claim 22, wherein: the three-dimensional memory
device comprises a vertical NAND device formed in a device region;
and the electrically conductive layers comprise, or are
electrically connected to a respective word line of the NAND
device.
41. The method of claim 42, wherein: the device region comprises: a
plurality of semiconductor channels, wherein at least one end
portion of each of the plurality of semiconductor channels extends
substantially perpendicular to a top surface of the substrate; a
plurality of charge storage regions, each charge storage region
located adjacent to a respective one of the plurality of
semiconductor channels; and a plurality of control gate electrodes
having a strip shape extending substantially parallel to the top
surface of the substrate; the plurality of control gate electrodes
comprise at least a first control gate electrode located in a first
device level and a second control gate electrode located in a
second device level; the electrically conductive layers in the
stack are in electrical contact with the plurality of control gate
electrode and extend from the device region to a contact region
including the plurality of electrically conductive via connections;
and the substrate comprises a silicon substrate containing a driver
circuit for the NAND device.
42. A three-dimensional memory device comprising: a stack of
alternating layers comprising insulator layers and electrically
conductive layers and located over a substrate; a memory opening
extending through the stack; and a memory film and a semiconductor
channel located within the memory opening, wherein each of the
electrically conductive layers comprises at least a cobalt portion.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of U.S.
application Ser. No. 14/578,368, filed Dec. 31, 2014, which is a
continuation of U.S. application Ser. No. 14/283,431, filed May 21,
2014, which is a continuation of U.S. application Ser. No.
14/086,139, filed Nov. 21, 2013, now U.S. Pat. No. 8,829,591, which
is a continuation of U.S. application Ser. No. 14/051,627, filed
Oct. 11, 2013, which is a divisional of U.S. application Ser. No.
13/875,854, filed May 2, 2013, now U.S. Pat. No. 8,580,639, which
is a divisional of U.S. application Ser. No. 13/693,337, filed Dec.
4, 2012, now U.S. Pat. No. 8,461,000, which is a divisional of U.S.
application Ser. No. 12/827,761 filed on Jun. 30, 2010, now U.S.
Pat. No. 8,349,681. All of the priority applications are
incorporated herein by reference in their entirety.
FIELD
[0002] The present disclosure relates generally to the field of
semiconductor devices and specifically to three-dimensional memory
structures, such as vertical NAND strings and other
three-dimensional devices, and methods of making thereof.
BACKGROUND
[0003] Three-dimensional vertical NAND strings having one bit per
cell are disclosed in an article by T. Endoh, et. al., titled
"Novel Ultra High Density Memory With A Stacked-Surrounding Gate
Transistor (S-SGT) Structured Cell", IEDM Proc. (2001) 33-36.
SUMMARY
[0004] According to an aspect of the present disclosure, a
three-dimensional memory device is provided, which comprises a
stack of alternating layers comprising insulator layers and
electrically conductive layers and located over a substrate, a
memory opening extending through the stack, and a memory film and a
semiconductor channel located within the memory opening. Each of
the electrically conductive layers comprises a cobalt portion.
[0005] According to an aspect of the present disclosure, a
three-dimensional memory device is provided, which comprises a
stack of alternating layers comprising insulator layers and
electrically conductive layers and located over a substrate, an
opening extending through the stack, a blocking dielectric, at
least one charge storage element and a tunneling dielectric located
within the opening, and a semiconductor channel located within the
opening. Each of the electrically conductive layers comprises at
least a cobalt portion.
[0006] According to another aspect of the present disclosure, a
method of manufacturing a three-dimensional memory device is
provided. A stack of alternating layers comprising insulator layers
and sacrificial material layers is formed over a substrate. A
memory opening is formed through the stack. A memory film and a
semiconductor channel are formed in the memory opening. Backside
recesses are formed around the memory film by removing the
sacrificial material layers. Electrically conductive layers are
formed within the backside recesses. Each of the electrically
conductive layers is formed by depositing at least a cobalt portion
within a respective backside recess.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a vertical cross-sectional view of an exemplary
structure after formation of a stack including an alternating
plurality of material layers and memory openings extending through
the stack according to an embodiment of the present disclosure.
[0008] FIGS. 2A-2F are sequential vertical cross-sectional views of
a memory opening within the exemplary structure during various
processing steps employed to form a memory stack structure
according to an embodiment of the present disclosure.
[0009] FIG. 3 is a vertical cross-sectional view of the exemplary
structure after formation of memory stack structures according to
an embodiment of the present disclosure.
[0010] FIG. 4 is a vertical cross-sectional view of the exemplary
structure after formation of a set of stepped surfaces and a
retro-stepped dielectric material portion according to an
embodiment of the present disclosure.
[0011] FIG. 5A is a vertical cross-sectional view of the exemplary
structure after formation of a backside via cavity and backside
recesses according to an embodiment of the present disclosure.
[0012] FIG. 5B is a see-through top-down view of the exemplary
structure of FIG. 5A. The vertical plane A-A' is the plane of the
vertical cross-sectional view of FIG. 5A.
[0013] FIGS. 6A-6D are sequential vertical cross-sectional views of
a magnified region M in FIGS. 5A and 5B during formation of first
exemplary electrically conductive layers according to a first
embodiment of the present disclosure.
[0014] FIGS. 7A and 7B are sequential vertical cross-sectional
views of a magnified region M in FIGS. 5A and 5B during formation
of second exemplary electrically conductive layers according to a
second embodiment of the present disclosure.
[0015] FIGS. 8A-8C are sequential vertical cross-sectional views of
a magnified region M in FIGS. 5A and 5B during formation of third
exemplary electrically conductive layers according to a third
embodiment of the present disclosure.
[0016] FIGS. 9A-9C are sequential vertical cross-sectional views of
a magnified region M in FIGS. 5A and 5B during formation of fourth
exemplary electrically conductive layers according to a fourth
embodiment of the present disclosure.
[0017] FIGS. 10A and 10B are sequential vertical cross-sectional
views of a magnified region M in FIGS. 5A and 5B during formation
of fifth exemplary electrically conductive layers according to a
fifth embodiment of the present disclosure.
[0018] FIGS. 11A-11C are sequential vertical cross-sectional views
of a magnified region M in FIGS. 5A and 5B during formation of
sixth exemplary electrically conductive layers according to a sixth
embodiment of the present disclosure.
[0019] FIGS. 12A-12C are sequential vertical cross-sectional views
of a magnified region M in FIGS. 5A and 5B during formation of
seventh exemplary electrically conductive layers according to a
seventh embodiment of the present disclosure.
[0020] FIGS. 13A and 13B are sequential vertical cross-sectional
views of a magnified region M in FIGS. 5A and 5B during formation
of eighth exemplary electrically conductive layers according to an
eighth embodiment of the present disclosure.
[0021] FIGS. 14A-14E are sequential vertical cross-sectional views
of a magnified region M in FIGS. 5A and 5B during formation of
ninth exemplary electrically conductive layers according to a ninth
embodiment of the present disclosure.
[0022] FIG. 15 is a vertical cross-sectional view of the exemplary
structure after formation of electrically conductive lines
according to an embodiment of the present disclosure.
[0023] FIG. 16 is a vertical cross-sectional view of the exemplary
structure after formation of a backside via space and a backside
contact via structure according to an embodiment of the present
disclosure.
[0024] FIGS. 17A and 17B are vertical cross-sectional views of
regions of the exemplary structure after formation of conductive
line structures according to an embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0025] As discussed above, the present disclosure is directed to
three-dimensional memory structures, such as vertical NAND strings
and other three-dimensional devices, and methods of making thereof,
the various aspects of which are described below. The embodiments
of the disclosure can be employed to form various structures
including a multilevel memory structure, non-limiting examples of
which include semiconductor devices such as three-dimensional
monolithic memory array devices comprising a plurality of NAND
memory strings. The drawings are not drawn to scale. Multiple
instances of an element may be duplicated where a single instance
of the element is illustrated, unless absence of duplication of
elements is expressly described or clearly indicated otherwise.
Ordinals such as "first," "second," and "third" are employed merely
to identify similar elements, and different ordinals may be
employed across the specification and the claims of the instant
disclosure. As used herein, a first element located "on" a second
element can be located on the exterior side of a surface of the
second element or on the interior side of the second element. As
used herein, a first element is located "directly on" a second
element if there exist a physical contact between a surface of the
first element and a surface of the second element.
[0026] A monolithic three-dimensional memory array is one in which
multiple memory levels are formed above a single substrate, such as
a semiconductor wafer, with no intervening substrates. The term
"monolithic" means that layers of each level of the array are
directly deposited on the layers of each underlying level of the
array. In contrast, two-dimensional arrays may be formed separately
and then packaged together to form a non-monolithic memory device.
For example, non-monolithic stacked memories have been constructed
by forming memory levels on separate substrates and vertically
stacking the memory levels, as described in U.S. Pat. No. 5,915,167
titled "Three-dimensional Structure Memory." The substrates may be
thinned or removed from the memory levels before bonding, but as
the memory levels are initially formed over separate substrates,
such memories are not true monolithic three-dimensional memory
arrays. The various three-dimensional memory devices of the present
disclosure include a monolithic three-dimensional NAND string
memory device, and can be fabricated employing the various
embodiments described herein.
[0027] Tungsten is widely employed for the material of conductive
metal lines. The inventors of the present disclosure recognized
that high tensile stress generated by tungsten can generate warpage
of a device structure. Further, the inventors of the present
disclosure recognized that cobalt is a softer metal than tungsten,
and may be deposited employing a thinner metallic barrier material
layer than a metallic barrier metal layer required for tungsten
deposition. Use of a thinner metallic barrier material layer for
cobalt deposition relative to tungsten deposition is possible
because cobalt can be deposited employing precursor gases that do
not contain fluorine. For example, bis(cyclopentadienyl)cobalt,
bis(ethylcyclopentadienyl)cobalt, bis(ethylcyclopentadienyl)cobalt,
or bis(pentamethylcyclopentadienyl)cobalt may be employed to
deposit cobalt. In addition, cobalt has a bulk resistivity of 6.24
.mu.Ohm-cm, which is comparable with the bulk resistivity of
tungsten of 5.28 .mu.Ohm-cm. As the thickness of conductive metal
layers decreases, therefore, it is possible to provide a metal
interconnect structure having a lesser or comparable total
resistance employing a combination of a thinner metallic barrier
layer and a cobalt portion than a combination of a thicker metallic
barrier layer and a tungsten portion.
[0028] Referring to FIG. 1, an exemplary structure according to an
embodiment of the present disclosure is illustrated, which can be
employed, for example, to fabricate a device structure containing
vertical NAND memory devices. The exemplary structure includes a
substrate, which can be a semiconductor substrate. The substrate
can include a substrate semiconductor layer 9. The substrate
semiconductor layer 9 is a semiconductor material layer, and can
include at least one elemental semiconductor material, at least one
III-V compound semiconductor material, at least one II-VI compound
semiconductor material, at least one organic semiconductor
material, or other semiconductor materials known in the art. The
substrate can have a major surface 7, which can be, for example, a
topmost surface of the substrate semiconductor layer 9. The major
surface 7 can be a semiconductor surface. In one embodiment, the
major surface 7 can be a single crystalline semiconductor
surface.
[0029] As used herein, a "semiconductor material" refers to a
material having electrical conductivity in the range from
1.0.times.10.sup.-6 S/cm to 1.0.times.10.sup.5 S/cm, and is capable
of producing a doped material having electrical resistivity in a
range from 1.0 S/cm to 1.0.times.10.sup.5 S/cm upon suitable doping
with an electrical dopant. As used herein, an "electrical dopant"
refers to a p-type dopant that adds a hole to a valence band within
a band structure, or an n-type dopant that adds an electron to a
conduction band within a band structure. As used herein, a
"conductive material" refers to a material having electrical
conductivity greater than 1.0.times.10.sup.5 S/cm. As used herein,
an "insulator material" or a "dielectric material" refers to a
material having electrical conductivity less than
1.0.times.10.sup.-6 S/cm. All measurements for electrical
conductivities are made at the standard condition. Optionally, at
least one doped well (not expressly shown) can be formed within the
substrate semiconductor layer 9.
[0030] At least one semiconductor device for a peripheral circuitry
can be formed on a portion of the substrate semiconductor layer 9.
The at least one semiconductor device can include, for example,
field effect transistors. For example, at least one shallow trench
isolation structure 120 can be formed by etching portions of the
substrate semiconductor layer 9 and depositing a dielectric
material therein. A gate dielectric layer, at least one gate
conductor layer, and a gate cap dielectric layer can be formed over
the substrate semiconductor layer 9, and can be subsequently
patterned to form at least one gate structure (150, 152, 154, 158),
each of which can include a gate dielectric 150, at least one gate
electrode (152, 154), and a gate cap dielectric. A gate electrode
(152, 154) may include a stack of a first gate electrode portion
152 and a second gate electrode portion 154. At least one gate
spacer 156 can be formed around the at least one gate structure
(150, 152, 154, 158) by depositing and anisotropically etching a
conformal dielectric layer. Active regions 130 can be formed in
upper portions of the substrate semiconductor layer 9, for example,
by introducing electrical dopants employing the at least one gate
structure (150, 152, 154, 158) as masking structures. Additional
masks may be employed as needed. The active region 130 can include
source regions and drain regions of field effect transistors. A
first dielectric liner 161 and a second dielectric liner 162 can be
optionally formed. Each of the first and second dielectric liners
(161, 162) can comprise a silicon oxide layer, a silicon nitride
layer, and/or a dielectric metal oxide layer. In an illustrative
example, the first dielectric liner 161 can be a silicon oxide
layer, and the second dielectric liner 162 can be a silicon nitride
layer. The least one semiconductor device for the peripheral
circuitry can contain a driver circuit for memory devices to be
subsequently formed, which can include at least one NAND
device.
[0031] A dielectric material such as silicon oxide can be deposited
over the at least one semiconductor device, and can be subsequently
planarized to form a planarization dielectric layer 170. In one
embodiment the planarized top surface of the planarization
dielectric layer 170 can be coplanar with a top surface of the
dielectric liners (161, 162). Subsequently, the planarization
dielectric layer 170 and the dielectric liners (161, 162) can be
removed from an area to physically expose a top surface of the
substrate semiconductor layer 9.
[0032] An optional semiconductor material layer 10 can be formed on
the top surface of the substrate semiconductor layer 9 by
deposition of a single crystalline semiconductor material, for
example, by selective epitaxy. The deposited semiconductor material
can be the same as, or can be different from, the semiconductor
material of the substrate semiconductor layer 9. The deposited
semiconductor material can be any material that can be employed for
the semiconductor substrate layer 9 as described above. The single
crystalline semiconductor material of the semiconductor material
layer 10 can be in epitaxial alignment with the single crystalline
structure of the substrate semiconductor layer 9. Portions of the
deposited semiconductor material located above the top surface of
the planarization dielectric layer 70 can be removed, for example,
by chemical mechanical planarization (CMP). In this case, the
semiconductor material layer 10 can have a top surface that is
coplanar with the top surface of the planarization dielectric layer
170.
[0033] Optionally, a dielectric pad layer 12 can be formed above
the semiconductor material layer 10 and the planarization
dielectric layer 170. The dielectric pad layer 12 can be, for
example, silicon oxide layer. The thickness of the dielectric pad
layer 12 can be in a range from 3 nm to 30 nm, although lesser and
greater thicknesses can also be employed.
[0034] At least one optional shallow trench can be formed through
the dielectric pad layer 12 and an upper portion of the
semiconductor material layer 10. The pattern of the at least one
shallow trench can be selected such that lower select gate
electrodes can be subsequently formed therein. For example, a lower
select gate device level may be fabricated as described in U.S.
patent application Ser. No. 14/133,979, filed on Dec. 19, 2013,
U.S. patent application Ser. No. 14/225,116, filed on Mar. 25,
2014, and/or U.S. patent application Ser. No. 14/225,176, filed on
Mar. 25, 2014, all of which are incorporated herein by
reference.
[0035] A lower select gate structure 20 can be formed in each of
the at least one shallow trench, for example, by forming a gate
dielectric layer and at least one conductive material layer, and
removing portions of the gate dielectric layer and the at least one
conductive material layer from above the top surface of the
dielectric pad layer 12, for example, by chemical mechanical
planarization. Each lower select gate structure 20 can include a
gate dielectric 22 and a gate electrode (24, 26). In one
embodiment, each gate electrode (24, 26) can include an
electrically conductive liner 24 and a conductive material portion
26. The electrically conductive liner 24 can include, for example,
TiN, TaN, WN, or a combination thereof. The conductive material
portion 26 can include, for example, W, Al, Cu, or combinations
thereof. At least one optional shallow trench isolation structure
(not shown) and/or at least one deep trench isolation structure
(not shown) may be employed to provide electrical isolation among
various semiconductor devices that are present, or are to be
subsequently formed, on the substrate.
[0036] A dielectric cap layer 31 can be optionally formed. The
dielectric cap layer 31 includes a dielectric material, and can be
formed directly on top surfaces of the gate electrodes (24, 26).
Exemplary materials that can be employed for the dielectric cap
layer 31 include, but are not limited to, silicon oxide, a
dielectric metal oxide, and silicon nitride (in case the material
of second material layers to be subsequently formed is not silicon
nitride). The dielectric cap layer 31 provides electrical isolation
for the gate electrodes (24, 26).
[0037] A stack of an alternating plurality of first material layers
(which can be insulating layers 32) and second material layers
(which can be sacrificial material layer 42) is formed over the top
surface of the substrate, which can be, for example, on the top
surface of the dielectric cap layer 31. As used herein, an
alternating plurality of first elements and second elements refers
to a structure in which instances of the first elements and
instances of the second elements alternate. Each instance of the
first elements that is not an end element of the alternating
plurality is adjoined by two instances of the second elements on
both sides, and each instance of the second elements that is not an
end element of the alternating plurality is adjoined by two
instances of the first elements on both ends. The first elements
may have the same thickness thereamongst, or may have different
thicknesses. The second elements may have the same thickness
thereamongst, or may have different thicknesses. The alternating
plurality of first material layers and second material layers may
begin with an instance of the first material layers or with an
instance of the second material layers, and may end with an
instance of the first material layers or with an instance of the
second material layers. In one embodiment, an instance of the first
elements and an instance of the second elements may form a unit
that is repeated with periodicity within the alternating
plurality.
[0038] Each first material layer includes a first material, and
each second material layer includes a second material that is
different from the first material. In one embodiment, each first
material layer can be an insulator layer 32, and each second
material layer can be a sacrificial material layer. In this case,
the stack can include an alternating plurality of insulator layers
32 and sacrificial material layers 42.
[0039] The stack of the alternating plurality is herein referred to
as an alternating stack (32, 42). In one embodiment, the
alternating stack (32, 42) can include insulator layers 32 composed
of the first material, and sacrificial material layers 42 composed
of a second material different from that of insulator layers 32.
The first material of the insulator layers 32 can be at least one
electrically insulating material. As such, each insulator layer 32
can be an electrically insulating material layer. Electrically
insulating materials that can be employed for the insulator layers
32 include, but are not limited to, silicon oxide (including doped
or undoped silicate glass), silicon nitride, silicon oxynitride,
organosilicate glass (OSG), spin-on dielectric materials,
dielectric metal oxides that are commonly known as high dielectric
constant (high-k) dielectric oxides (e.g., aluminum oxide, hafnium
oxide, etc.) and silicates thereof, dielectric metal oxynitrides
and silicates thereof, and organic insulating materials. In one
embodiment, the first material of the insulator layers 32 can be
silicon oxide.
[0040] The second material of the sacrificial material layers 42 is
a sacrificial material that can be removed selective to the first
material of the insulator layers 32. As used herein, a removal of a
first material is "selective to" a second material if the removal
process removes the first material at a rate that is at least twice
the rate of removal of the second material. The ratio of the rate
of removal of the first material to the rate of removal of the
second material is herein referred to as a "selectivity" of the
removal process for the first material with respect to the second
material.
[0041] The sacrificial material layers 42 may comprise an
electrically insulating material, a semiconductor material, or a
conductive material. The second material of the sacrificial
material layers 42 can be subsequently replaced with electrically
conductive electrodes, which can function, for example, as control
gate electrodes of a vertical NAND device. Non-limiting examples of
the second material include silicon nitride, an amorphous
semiconductor material (such as amorphous silicon), and a
polycrystalline semiconductor material (such as polysilicon). In
one embodiment, the sacrificial material layers 42 can be material
layers that comprise silicon nitride or a semiconductor material
including at least one of silicon and germanium.
[0042] In one embodiment, the insulator layers 32 can include
silicon oxide, and sacrificial material layers can include silicon
nitride sacrificial material layers. The first material of the
insulator layers 32 can be deposited, for example, by chemical
vapor deposition (CVD). For example, if silicon oxide is employed
for the insulator layers 32, tetraethyl orthosilicate (TEOS) can be
employed as the precursor material for the CVD process. The second
material of the sacrificial material layers 42 can be formed, for
example, CVD or atomic layer deposition (ALD).
[0043] The sacrificial material layers 42 can be suitably patterned
so that conductive material portions to be subsequently formed by
replacement of the sacrificial material layers 42 can function as
electrically conductive electrodes, such as the control gate
electrodes of the monolithic three-dimensional NAND string memory
devices to be subsequently formed. The sacrificial material layers
42 may comprise a portion having a strip shape extending
substantially parallel to the major surface 7 of the substrate.
[0044] The thicknesses of the insulator layers 32 and the
sacrificial material layers 42 can be in a range from 20 nm to 50
nm, although lesser and greater thicknesses can be employed for
each insulator layer 32 and for each sacrificial material layer 42.
The number of repetitions of the pairs of an insulator layer 32 and
a sacrificial material layer (e.g., a control gate electrode or a
sacrificial material layer) 42 can be in a range from 2 to 1,024,
and typically from 8 to 256, although a greater number of
repetitions can also be employed. The top and bottom gate
electrodes in the stack may function as the select gate electrodes.
In one embodiment, each sacrificial material layer 42 in the
alternating stack (32, 42) can have a uniform thickness that is
substantially invariant within each respective sacrificial material
layer 42.
[0045] Optionally, an insulating cap layer 70 can be formed over
the alternating stack (32, 42). The insulating cap layer 70
includes a dielectric material that is different from the material
of the sacrificial material layers 42. In one embodiment, the
insulating cap layer 70 can include a dielectric material that can
be employed for the insulator layers 32 as described above. The
insulating cap layer 70 can have a greater thickness than each of
the insulator layers 32. The insulating cap layer 70 can be
deposited, for example, by chemical vapor deposition. In one
embodiment, the insulating cap layer 70 can be a silicon oxide
layer.
[0046] Subsequently, a lithographic material stack (not shown)
including at least a photoresist layer can be formed over the
insulating cap layer 70 and the alternating stack (32, 42), and can
be lithographically patterned to form openings therein. The pattern
in the lithographic material stack can be transferred through the
insulating cap layer 70 and through entirety of the alternating
stack (32, 42) by at least one anisotropic etch that employs the
patterned lithographic material stack as an etch mask. Portions of
the alternating stack (32, 42) underlying the openings in the
patterned lithographic material stack are etched to form memory
openings 49. In other words, the transfer of the pattern in the
patterned lithographic material stack through the alternating stack
(32, 42) forms the memory openings 49 that extend through the
alternating stack (32, 42). The chemistry of the anisotropic etch
process employed to etch through the materials of the alternating
stack (32, 42) can alternate to optimize etching of the first and
second materials in the alternating stack (32, 42). The anisotropic
etch can be, for example, a series of reactive ion etches.
Optionally, the dielectric cap layer 31 may be used as an etch stop
layer between the alternating stack (32, 42) and the substrate. The
sidewalls of the memory openings 49 can be substantially vertical,
or can be tapered. The patterned lithographic material stack can be
subsequently removed, for example, by ashing.
[0047] The memory openings 49 are formed through the dielectric cap
layer 31 and the dielectric pad layer 12 so that the memory
openings 49 extend from the top surface of the alternating stack
(32, 42) to the top surface of the semiconductor material layer 10
within the substrate between the lower select gate electrodes (24,
26). In one embodiment, an overetch into the semiconductor material
layer 10 may be optionally performed after the top surface of the
semiconductor material layer 10 is physically exposed at a bottom
of each memory opening 49. The overetch may be performed prior to,
or after, removal of the lithographic material stack. In other
words, the recessed surfaces of the semiconductor material layer 10
may be vertically offset from the unrecessed top surfaces of the
semiconductor material layer 10 by a recess depth. The recess depth
can be, for example, in a range from 1 nm to 50 nm, although lesser
and greater recess depths can also be employed. The overetch is
optional, and may be omitted. If the overetch is not performed, the
bottom surface of each memory opening 49 can be coplanar with the
topmost surface of the semiconductor material layer 10. Each of the
memory openings 49 can include a sidewall (or a plurality of
sidewalls) that extends substantially perpendicular to the topmost
surface of the substrate. The region in which the array of memory
openings 49 is formed is herein referred to as a device region. The
substrate semiconductor layer 9 and the semiconductor material
layer 10 collectively constitutes a substrate (9, 10), which can be
a semiconductor substrate. Alternatively, the semiconductor
material layer 10 may be omitted, and the memory openings 49 can be
extend to a top surface of the semiconductor material layer 10.
[0048] A memory stack structure can be formed in each of the memory
opening employing various embodiments of the present disclosure.
FIGS. 2A-2F illustrate sequential vertical cross-sectional views of
a memory opening within the exemplary structure during formation of
an exemplary memory stack structure according to a first embodiment
of the present disclosure. Formation of the exemplary memory stack
structure can be performed within each of the memory openings 49 in
the exemplary structure illustrated in FIG. 1.
[0049] Referring to FIG. 2A, a memory opening 49 is illustrated.
The memory opening 49 extends through the insulating cap layer 70,
the alternating stack (32, 42), the dielectric cap layer 31, the
dielectric pad layer 12, and optionally into an upper portion of
the semiconductor material layer 10. The recess depth of the bottom
surface of each memory opening with respect to the top surface of
the semiconductor material layer 10 can be in a range from 0 nm to
30 nm, although greater recess depths can also be employed.
Optionally, the sacrificial material layers 42 can be laterally
recessed partially to form lateral recesses (not shown), for
example, by an isotropic etch.
[0050] A series of layers including at least one blocking
dielectric layer (501L, 503L), a memory material layer 504L, a
tunneling dielectric layer 505L, and an optional first
semiconductor channel layer 601L can be sequentially deposited in
the memory openings 49. The at least one blocking dielectric layer
(501L, 503L) can include, for example, a first blocking dielectric
layer 501L and a second blocking dielectric layer 503L.
[0051] The first blocking dielectric layer 501L can be deposited on
the sidewalls of each memory opening 49 by a conformal deposition
method. The first blocking dielectric layer 501L includes a
dielectric material, which can be a dielectric metal oxide. As used
herein, a dielectric metal oxide refers to a dielectric material
that includes at least one metallic element and at least oxygen.
The dielectric metal oxide may consist essentially of the at least
one metallic element and oxygen, or may consist essentially of the
at least one metallic element, oxygen, and at least one
non-metallic element such as nitrogen. In one embodiment, the first
blocking dielectric layer 501L can include a dielectric metal oxide
having a dielectric constant greater than 7.9, i.e., having a
dielectric constant greater than the dielectric constant of silicon
nitride.
[0052] Non-limiting examples of dielectric metal oxides include
aluminum oxide (Al.sub.2O.sub.3), hafnium oxide (HfO.sub.2),
lanthanum oxide (LaO.sub.2), yttrium oxide (Y.sub.2O.sub.3),
tantalum oxide (Ta.sub.2O.sub.5), silicates thereof, nitrogen-doped
compounds thereof, alloys thereof, and stacks thereof. The first
blocking dielectric layer 501L can be deposited, for example, by
chemical vapor deposition (CVD), atomic layer deposition (ALD),
pulsed laser deposition (PLD), liquid source misted chemical
deposition, or a combination thereof. The thickness of the first
blocking dielectric layer 501L can be in a range from 1 nm to 20
nm, although lesser and greater thicknesses can also be employed.
The first blocking dielectric layer 501L can subsequently function
as a dielectric material portion that blocks leakage of stored
electrical charges to control gate electrodes. In one embodiment,
the first blocking dielectric layer 501L includes aluminum
oxide.
[0053] The second blocking dielectric layer 503L can be formed on
the first blocking dielectric layer 501L. The second blocking
dielectric layer 503L can include a dielectric material that is
different from the dielectric material of the first blocking
dielectric layer 501L. In one embodiment, the second blocking
dielectric layer 503L can include silicon oxide, a dielectric metal
oxide having a different composition than the first blocking
dielectric layer 501L, silicon oxynitride, silicon nitride, or a
combination thereof. In one embodiment, the second blocking
dielectric layer 503L can include silicon oxide. The second
blocking dielectric layer 503L can be formed by a conformal
deposition method such as low pressure chemical vapor deposition,
atomic layer deposition, or a combination thereof. The thickness of
the second blocking dielectric layer 503L can be in a range from 1
nm to 20 nm, although lesser and greater thicknesses can also be
employed. Alternatively, the first blocking dielectric layer 501L
and/or the second blocking dielectric layer 503L can be omitted,
and a blocking dielectric layer can be formed after formation of
backside recesses on surfaces of memory films to be subsequently
formed.
[0054] The memory material layer 504L, the tunneling dielectric
layer 505L, and the optional first semiconductor channel layer 601L
can be sequentially formed. In one embodiment, the memory material
layer 504L can be a charge trapping material including a dielectric
charge trapping material, which can be, for example, silicon
nitride. Alternatively, the memory material layer 504L can include
a conductive material such as doped polysilicon or a metallic
material that is patterned into multiple electrically isolated
portions (e.g., floating gates), for example, by being formed
within lateral recesses into sacrificial material layers 42. In one
embodiment, the memory material layer 504L includes a silicon
nitride layer.
[0055] The memory material layer 504L can be formed as a single
memory material layer of homogeneous composition, or can include a
stack of multiple memory material layers. The multiple memory
material layers, if employed, can comprise a plurality of
spaced-apart floating gate material layers that contain conductive
materials (e.g., metal such as tungsten, molybdenum, tantalum,
titanium, platinum, ruthenium, and alloys thereof, or a metal
silicide such as tungsten silicide, molybdenum silicide, tantalum
silicide, titanium silicide, nickel silicide, cobalt silicide, or a
combination thereof) and/or semiconductor materials (e.g.,
polycrystalline or amorphous semiconductor material including at
least one elemental semiconductor element or at least one compound
semiconductor material). Alternatively or additionally, the memory
material layer 504L may comprise an insulating charge trapping
material, such as one or more silicon nitride segments.
Alternatively, the memory material layer 504L may comprise
conductive nanoparticles such as metal nanoparticles, which can be,
for example, ruthenium nanoparticles. The memory material layer
504L can be formed, for example, by chemical vapor deposition
(CVD), atomic layer deposition (ALD), physical vapor deposition
(PVD), or any suitable deposition technique for storing electrical
charges therein. The thickness of the memory material layer 504L
can be in a range from 2 nm to 20 nm, although lesser and greater
thicknesses can also be employed.
[0056] The tunneling dielectric layer 505L includes a dielectric
material through which charge tunneling can be performed under
suitable electrical bias conditions. The charge tunneling may be
performed through hot-carrier injection or by Fowler-Nordheim
tunneling induced charge transfer depending on the mode of
operation of the monolithic three-dimensional NAND string memory
device to be formed. The tunneling dielectric layer 505L can
include silicon oxide, silicon nitride, silicon oxynitride,
dielectric metal oxides (such as aluminum oxide and hafnium oxide),
dielectric metal oxynitride, dielectric metal silicates, alloys
thereof, and/or combinations thereof. In one embodiment, the
tunneling dielectric layer 505L can include a stack of a first
silicon oxide layer, a silicon oxynitride layer, and a second
silicon oxide layer, which is commonly known as an ONO stack. In
one embodiment, the tunneling dielectric layer 505L can include a
silicon oxide layer that is substantially free of carbon or a
silicon oxynitride layer that is substantially free of carbon. The
thickness of the tunneling dielectric layer 505L can be in a range
from 2 nm to 20 nm, although lesser and greater thicknesses can
also be employed.
[0057] The optional first semiconductor channel layer 601L includes
a semiconductor material such as at least one elemental
semiconductor material, at least one III-V compound semiconductor
material, at least one II-VI compound semiconductor material, at
least one organic semiconductor material, or other semiconductor
materials known in the art. In one embodiment, the first
semiconductor channel layer 601L includes amorphous silicon or
polysilicon. The first semiconductor channel layer 601L can be
formed by a conformal deposition method such as low pressure
chemical vapor deposition (LPCVD). The thickness of the first
semiconductor channel layer 601L can be in a range from 2 nm to 10
nm, although lesser and greater thicknesses can also be employed. A
cavity 49' is formed in the volume of each memory opening 49 that
is not filled with the deposited material layers (501L, 503L, 504L,
505I, 601L).
[0058] Referring to FIG. 2B, the optional first semiconductor
channel layer 601L, the tunneling dielectric layer 505L, the memory
material layer 504L, the at least one blocking dielectric layer
(501L, 503L) are sequentially anisotropically etched employing at
least one anisotropic etch process. The portions of the first
semiconductor channel layer 601L, the tunneling dielectric layer
505L, the memory material layer 504L, and the at least one blocking
dielectric layer (501L, 503L) located above the top surface of the
insulating cap layer 70 can be removed by the at least one
anisotropic etch process. Further, the horizontal portions of the
first semiconductor channel layer 601L, the tunneling dielectric
layer 505L, the memory material layer 504L, and the at least one
blocking dielectric layer (501L, 503L) at a bottom of each cavity
49' can be removed to form openings in remaining portions thereof.
Each of the first semiconductor channel layer 601L, the tunneling
dielectric layer 505L, the memory material layer 504L, and the at
least one blocking dielectric layer (501L, 503L) can be etched by
anisotropic etch process.
[0059] Each remaining portion of the first semiconductor channel
layer 601L constitutes a first semiconductor channel portion 601.
Each remaining portion of the tunneling dielectric layer 505L
constitutes a tunneling dielectric 505. Each remaining portion of
the memory material layer 504L is herein referred to as a charge
storage element 504. In one embodiment, the charge storage element
504 can be a contiguous layer, i.e., can be a charge storage layer.
Each remaining portion of the second blocking dielectric layer 503L
is herein referred to as a second blocking dielectric 503. Each
remaining portion of the first blocking dielectric layer 501L is
herein referred to as a first blocking dielectric 501. A surface of
the semiconductor material layer 10 can be physically exposed
underneath the opening through the first semiconductor channel
portion 601, the tunneling dielectric 505, the charge storage
element 504, and the at least one blocking dielectric (501, 503).
Optionally, the physically exposed semiconductor surface at the
bottom of each cavity 49' can be vertically recessed so that the
recessed semiconductor surface underneath the cavity 49' is
vertically offset from the topmost surface of the semiconductor
material layer 10 by a recess distance rd. A tunneling dielectric
505 is embedded within a charge storage element 504. The charge
storage element 504 can comprise a charge trapping material or a
floating gate material.
[0060] In one embodiment, the first semiconductor channel portion
601, the tunneling dielectric 505, the charge storage element 504,
the second blocking dielectric 503, and the first blocking
dielectric 501 can have vertically coincident sidewalls. As used
herein, a first surface is "vertically coincident" with a second
surface if there exists a vertical plane including both the first
surface and the second surface. Such a vertical plane may, or may
not, have a horizontal curvature, but does not include any
curvature along the vertical direction, i.e., extends straight up
and down.
[0061] Referring to FIG. 2C, a second semiconductor channel layer
602L can be deposited directly on the semiconductor surface of the
semiconductor material layer 10 in the substrate (9, 10), and
directly on the first semiconductor channel portion 601. The second
semiconductor channel layer 602L includes a semiconductor material
such as at least one elemental semiconductor material, at least one
III-V compound semiconductor material, at least one II-VI compound
semiconductor material, at least one organic semiconductor
material, or other semiconductor materials known in the art. In one
embodiment, the second semiconductor channel layer 602L includes
amorphous silicon or polysilicon. The second semiconductor channel
layer 602L can be formed by a conformal deposition method such as
low pressure chemical vapor deposition (LPCVD). The thickness of
the second semiconductor channel layer 602L can be in a range from
2 nm to 10 nm, although lesser and greater thicknesses can also be
employed. The second semiconductor channel layer 602L may partially
fill the cavity 49' in each memory opening, or may fully fill the
cavity in each memory opening.
[0062] The materials of the first semiconductor channel portion 601
and the second semiconductor channel layer 602L are collectively
referred to as a semiconductor channel material. In other words,
the semiconductor channel material is a set of all semiconductor
material in the first semiconductor channel portion 601 and the
second semiconductor channel layer 602L.
[0063] Referring to FIG. 2D, in case the cavity 49' in each memory
opening is not completely filled by the second semiconductor
channel layer 602L, a dielectric core layer 62L can be deposited in
the cavity 49' to fill any remaining portion of the cavity 49'
within each memory opening. The dielectric core layer 62L includes
a dielectric material such as silicon oxide or organosilicate
glass. The dielectric core layer 62L can be deposited by a
conformal deposition method such as low pressure chemical vapor
deposition (LPCVD), or by a self-planarizing deposition process
such as spin coating.
[0064] Referring to FIG. 2E, the horizontal portion of the
dielectric core layer 62L can be removed, for example, by a recess
etch from above the top surface of the insulating cap layer 70.
Further, the horizontal portion of the second semiconductor channel
layer 602L located above the top surface of the insulating cap
layer 70 can be removed by a planarization process, which can
employ a recess etch or chemical mechanical planarization (CMP).
Each remaining portion of the second semiconductor channel layer
602L within a memory opening constitutes a second semiconductor
channel portion 602.
[0065] Each adjoining pair of a first semiconductor channel portion
601 and a second semiconductor channel portion 602 can collectively
form a semiconductor channel 60 through which electrical current
can flow when a vertical NAND device including the semiconductor
channel 60 is turned on. A tunneling dielectric 505 is embedded
within a charge storage element 504, and laterally surrounds a
portion of the semiconductor channel 60. Each adjoining set of a
first blocking dielectric 501, a second blocking dielectric 503, a
charge storage element 504, and a tunneling dielectric 505
collectively constitute a memory film 50, which can store
electrical charges with a macroscopic retention time. In some
embodiments, a first blocking dielectric 501 and/or a second
blocking dielectric 503 may not be present in the memory film 50 at
this step, and a blocking dielectric may be subsequently formed
after formation of backside recesses. As used herein, a macroscopic
retention time refers to a retention time suitable for operation of
a memory device as a permanent memory device such as a retention
time in excess of 24 hours.
[0066] The top surface of the remaining portion of the dielectric
core layer 62L can be further recessed within each memory opening,
for example, by a recess etch to a depth that is located between
the top surface of the insulating cap layer 70 and the bottom
surface of the insulating cap layer 70. Each remaining portion of
the dielectric core layer 62L constitutes a dielectric core 62.
[0067] Referring to FIG. 2F, drain regions 63 can be formed by
depositing a doped semiconductor material within each recessed
region above the dielectric cores 62. The doped semiconductor
material can be, for example, doped polysilicon. Excess portions of
the deposited semiconductor material can be removed from above the
top surface of the insulating cap layer 70, for example, by
chemical mechanical planarization (CMP) or a recess etch to form
the drain regions 63.
[0068] The exemplary memory stack structure can be embedded into
the exemplary structure illustrated in FIG. 1. FIG. 3 illustrates
the exemplary structure that incorporates multiple instances of the
exemplary memory stack structure of FIG. 2F. The exemplary
structure includes a semiconductor device, which comprises a stack
(32, 42) including an alternating plurality of material layers
(e.g., the sacrificial material layers 42) and insulator layers 32
located over a semiconductor substrate (9, 10), and a memory
opening extending through the stack (32, 42). The semiconductor
device further comprises a first blocking dielectric 501 vertically
extending from a bottommost layer (e.g., the bottommost sacrificial
material layer 42) of the stack to a topmost layer (e.g., the
topmost sacrificial material layer 42) of the stack, and contacting
a sidewall of the memory opening and a horizontal surface of the
semiconductor substrate. While the present disclosure is described
employing the illustrated configuration for the memory stack
structure, the methods of the present disclosure can be applied to
alternative memory stack structures including a polycrystalline
semiconductor channel.
[0069] Referring to FIG. 4, at least one dielectric cap layer 71
can be optionally formed over the planarization dielectric layer
70. In one embodiment, the at least one dielectric cap layer 71 can
include dielectric materials through which deuterium atoms can
permeate. For example, the at least one dielectric cap layer can
include silicon oxide and/or a dielectric metal oxide.
[0070] Optionally, a portion of the alternating stack (32, 42) can
be removed, for example, by applying and patterning a photoresist
layer with an opening and by transferring the pattern of the
opening through the alternating stack (32, 42) employing an etch
such as an anisotropic etch. An optional trench extending through
the entire thickness of the alternating stack (32, 42) can be
formed within an area that includes a peripheral device region 200
and a portion of a contact region 300, which is adjacent to a
device region 100 that includes an array of memory stack structures
55. Subsequently, the trench can be filled with an optional
dielectric material such as silicon oxide. Excess portions of the
dielectric material can be removed from above the top surface of
the at least one dielectric cap layer 71 by a planarization process
such as chemical mechanical planarization and/or a recess etch. The
top surfaces of the at least one dielectric cap layer 71 can be
employed as a stopping surface during the planarization. The
remaining dielectric material in the trench constitutes a
dielectric material portion 64.
[0071] A stepped cavity can be formed within the contact region
300, which can straddle the dielectric material portion 64 and a
portion of the alternating stack (32, 42). Alternatively, the
dielectric material portion 64 may be omitted and the stepped
cavity 69 may be formed directly in the stack (32, 42). The stepped
cavity can have various stepped surfaces such that the horizontal
cross-sectional shape of the stepped cavity changes in steps as a
function of the vertical distance from the top surface of the
substrate (9, 10). In one embodiment, the stepped cavity can be
formed by repetitively performing a set of processing steps. The
set of processing steps can include, for example, an etch process
of a first type that vertically increases the depth of a cavity by
one or more levels, and an etch process of a second type that
laterally expands the area to be vertically etched in a subsequent
etch process of the first type. As used herein, a "level" of a
structure including alternating plurality is defined as the
relative position of a pair of a first material layer and a second
material layer within the structure.
[0072] The dielectric material portion 64 can have stepped surfaces
after formation of the stepped cavity, and a peripheral portion of
the alternating stack (32, 42) can have stepped surfaces after
formation of the stepped cavity. As used herein, "stepped surfaces"
refer to a set of surfaces that include at least two horizontal
surfaces and at least two vertical surfaces such that each
horizontal surface is adjoined to a first vertical surface that
extends upward from a first edge of the horizontal surface, and is
adjoined to a second vertical surface that extends downward from a
second edge of the horizontal surface. A "stepped cavity" refers to
a cavity having stepped surfaces.
[0073] A retro-stepped dielectric material portion 65 (i.e., an
insulating fill material portion) can be formed in the stepped
cavity by deposition of a dielectric material therein. A dielectric
material such as silicon oxide can be deposited in the stepped
cavity. Excess portions of the deposited dielectric material can be
removed from above the top surface of the at least one dielectric
cap layer 71, for example, by chemical mechanical planarization
(CMP). The remaining portion of the deposited dielectric material
filling the stepped cavity constitutes the retro-stepped dielectric
material portion 65. As used herein, a "retro-stepped" element
refers to an element that has stepped surfaces and a horizontal
cross-sectional area that increases monotonically as a function of
a vertical distance from a top surface of a substrate on which the
element is present. If silicon oxide is employed for the
retro-stepped dielectric material portion 65, the silicon oxide of
the retro-stepped dielectric material portion 65 may, or may not,
be doped with dopants such as B, P, and/or F.
[0074] Referring to FIGS. 5A and 5B, at least one dielectric
support pillar 7P may be optionally formed through the
retro-stepped dielectric material portion 65 and/or through the
alternating stack (32, 42). The plane A-A' in FIG. 5B corresponds
to the plane of the vertical cross-sectional view of FIG. 5A. In
one embodiment, the at least one dielectric support pillar 7P can
be formed in the contact region 300, which is located adjacent to
the device region 100. The at least one dielectric support pillar
7P can be formed, for example, by forming an opening extending
through the retro-stepped dielectric material portion 65 and/or
through the alternating stack (32, 42) and at least to the top
surface of the substrate (9, 10), and by filling the opening with a
dielectric material that is resistant to the etch chemistry to be
employed to remove the sacrificial material layers 42. In one
embodiment, the at least one dielectric support pillar can include
silicon oxide and/or a dielectric metal oxide such as aluminum
oxide. In one embodiment, the portion of the dielectric material
that is deposited over the at least one dielectric cap layer 71
concurrently with deposition of the at least one dielectric support
pillar 7P can be present over the at least one dielectric cap layer
71 as a dielectric pillar material layer 73. The dielectric pillar
material layer 73 and the at least one dielectric support pillar 7P
can be formed as a single contiguous structure of integral
construction, i.e., without any material interface therebetween. In
another embodiment, the portion of the dielectric material that is
deposited over the at least one dielectric cap layer 71
concurrently with deposition of the at least one dielectric support
pillar 7P can be removed, for example, by chemical mechanical
planarization or a recess etch. In this case, the dielectric pillar
material layer 73 is not present, and the top surface of the at
least one dielectric cap layer 71 can be physically exposed.
[0075] A photoresist layer (not shown) can be applied over the
alternating stack (32, 42) and/or the retro-stepped dielectric
material portion 65, and optionally over the and lithographically
patterned to form at least one backside contact trench 79 in an
area in which formation of a backside contact via structure is
desired. The pattern in the photoresist layer can be transferred
through the alternating stack (32, 42) and/or the retro-stepped
dielectric material portion 65 employing an anisotropic etch to
form the at least one backside contact trench 79, which extends at
least to the top surface of the substrate (9, 10). In one
embodiment, the at least one backside contact trench 79 can include
a source contact opening in which a source contact via structure
can be subsequently formed. If desired, a source region (not shown)
may be formed by implantation of dopant atoms into a portion of the
semiconductor material layer 10 through the backside contact trench
79.
[0076] An etchant that selectively etches the second material of
the sacrificial material layers 42 with respect to the first
material of the insulator layers 32 can be introduced into the at
least one backside contact trench 79, for example, employing an
etch process. Backside recesses 43 are formed in volumes from which
the sacrificial material layers 42 are removed. The removal of the
second material of the sacrificial material layers 42 can be
selective to the first material of the insulator layers 32, the
material of the at least one dielectric support pillar 7P, the
material of the retro-stepped dielectric material portion 65, the
semiconductor material of the semiconductor material layer 10, and
the material of the outermost layer of the memory films 50. In one
embodiment, the sacrificial material layers 42 can include silicon
nitride, and the materials of the insulator layers 32, the at least
one dielectric support pillar 7P, and the retro-stepped dielectric
material portion 65 can be selected from silicon oxide and
dielectric metal oxides. In another embodiment, the sacrificial
material layers 42 can include a semiconductor material such as
polysilicon, and the materials of the insulator layers 32, the at
least one dielectric support pillar 7P, and the retro-stepped
dielectric material portion 65 can be selected from silicon oxide,
silicon nitride, and dielectric metal oxides. In this case, the
depth of the at least one backside contact trench 79 can be
modified so that the bottommost surface of the at least one
backside contact trench 79 is located within the dielectric pad
layer 12, i.e., to avoid physical exposure of the top surface of
the semiconductor substrate layer 10.
[0077] The etch process that removes the second material selective
to the first material and the outermost layer of the memory films
50 can be a wet etch process employing a wet etch solution, or can
be a gas phase (dry) etch process in which the etchant is
introduced in a vapor phase into the at least one backside contact
trench 79. For example, if the sacrificial material layers 42
include silicon nitride, the etch process can be a wet etch process
in which the exemplary structure is immersed within a wet etch tank
including phosphoric acid, which etches silicon nitride selective
to silicon oxide, silicon, and various other materials employed in
the art. The at least one dielectric support pillar 7P, the
retro-stepped dielectric material portion 65, and the memory stack
structures 55 provide structural support while the backside
recesses 43 are present within volumes previously occupied by the
sacrificial material layers 42.
[0078] Each backside recess 43 can be a laterally extending cavity
having a lateral dimension that is greater than the vertical extent
of the cavity. In other words, the lateral dimension of each
backside recess 43 can be greater than the height of the backside
recess 43. A plurality of backside recesses 43 can be formed in the
volumes from which the second material of the sacrificial material
layers 42 is removed. The memory openings in which the memory stack
structures 55 are formed are herein referred to as front side
recesses or front side cavities in contrast with the backside
recesses 43. In one embodiment, the device region 100 comprises an
array of monolithic three-dimensional NAND strings having a
plurality of device levels disposed above the substrate (9, 10). In
this case, each backside recess 43 can define a space for receiving
a respective word line of the array of monolithic three-dimensional
NAND strings.
[0079] Each of the plurality of backside recesses 43 can extend
substantially parallel to the top surface of the substrate (9, 10).
A backside recess 43 can be vertically bounded by a top surface of
an underlying insulator layer 32 and a bottom surface of an
overlying insulator layer 32. In one embodiment, each backside
recess 43 can have a uniform height throughout. Optionally, a
backside blocking dielectric layer can be formed in the backside
recesses.
[0080] FIGS. 6A-6D illustrate processing steps that can be employed
to form first exemplary electrically conductive layers according to
a first embodiment of the present disclosure. Referring to FIG. 6A,
a vertical cross-sectional magnified view of a magnified region M
in FIGS. 5A and 5B is illustrated, which includes a portion of the
backside contact trench 79 and a plurality of backside recesses 43.
In one embodiment, a sidewall surface of at least one blocking
dielectric (501, 503) can be physically exposed at end portions of
backside recesses 43. The sidewall surface of the at least one
blocking dielectric (501, 503) is an outer sidewall surface of a
memory film 50 illustrated in FIG. 2F. Optionally, a backside
blocking dielectric layer (not shown) including a blocking
dielectric material can be formed on the physically exposed
surfaces of the insulator layers 32 and the physically exposed
sidewalls of the memory film 50 (See FIG. 2F).
[0081] An optional metallic barrier material layer 148L can be
deposited in the backside recesses 43 and over the sidewall of the
backside contact trench 79. The metallic barrier material layer
148L includes a metallic barrier material, which is a metallic
material that blocks diffusion of metal elements therethrough. The
metallic barrier material layer 148L can be a conductive metallic
nitride layer such as TiN, TaN, WN, or a combination or an alloy
thereof. The thickness of the metallic barrier material layer 148L
can be in a range from 0.5 nm to 1.5 nm, although lesser and
greater thicknesses can also be employed. The metallic barrier
material layer 148L can be deposited, for example, by chemical
vapor deposition (CVD) or atomic layer deposition (ALD). In
general, the thickness of the metallic barrier material layer 148L
can be thinner if cobalt is to be subsequently deposited on the
sidewalls of the metallic barrier material layer 148L than if
tungsten is to be subsequently deposited on the sidewalls of the
metallic barrier material layer 148L. A backside cavity 43' is
present in each unfilled volume of the backside recess 43, i.e., in
each volume of the backside recess 43 that is not filled with the
metallic barrier material layer 148L.
[0082] Referring to FIG. 6B, an anisotropic etch is performed to
remove vertical portions of the metallic barrier material layer
148L from the sidewalls of each backside contact trench 79. The
anisotropic etch can be a reactive ion etch that removes the
material of the metallic barrier material layer 148L selective to
the material of the insulator layers 32 and the material of the
semiconductor material layer 10. Vertical portions of the metallic
barrier material layer 148L are removed from the sidewall of the
backside contact trench 79. Portions of the metallic barrier
material layer 148L inside the backside recesses 43 are not removed
by the anisotropic etch. Each remaining portion of the metallic
barrier material layer 148L inside the backside recesses 43
constitutes a metallic barrier portion 148. Each metallic barrier
material portion 148 can be a conformal material portion having a
uniform thickness throughout. Sidewalls of the insulator layers 32
are physically exposed within each backside contact trench 79. The
metallic barrier material portions 148 are formed as a plurality
structures that are vertically disjoined from one another.
[0083] Referring to FIG. 6C, cobalt can be selectively deposited
inside the backside cavities to form cobalt portions 48. Deposition
of cobalt can be performed by chemical vapor deposition (CVD) or
atomic layer deposition (ALD). Chemical vapor deposition or atomic
layer deposition of cobalt employs a cobalt precursor that can be
easily vaporized to leave high-purity cobalt on a surface without
causing surface damage. In one embodiment, an organometallic
compound with relatively high vapor pressures and good thermal
stability can be employed as the cobalt precursor gas to deposit
cobalt without requiring hydrogen. In a non-limiting example,
bis(cyclopentadienyl)cobalt, bis(ethylcyclopentadienyl)cobalt,
bis(ethylcyclopentadienyl)cobalt, or
bis(pentamethylcyclopentadienyl)cobalt can be employed as a cobalt
precursor gas in a CVD or ALD process. Alternatively, different
precursor gases (such as Co.sub.2(CO).sub.8) can also be employed
for cobalt deposition.
[0084] Cobalt may be selectively nucleated on a metallic surface
such as the surfaces of the metallic barrier material portions 148.
Thus, cobalt portions 48 can grow selectively only from the
surfaces of the metallic barrier material portions 148, and do not
grow from the sidewalls of the insulator layers 32. As such, the
cobalt deposition process is a selective deposition process that
proceeds from the surfaces of the metallic barrier material
portions 148, while cobalt is not deposited on the surfaces of the
insulator layers 32. Each cobalt portion 48 can be formed on
surfaces of a respective metallic barrier material portion 148, and
specifically, on a pair of horizontal surfaces of the respective
metallic barrier material portion 148 and an outer sidewall of the
respective metallic barrier material portion 148. Each deposited
portion of cobalt constitutes one of the cobalt portions 48.
[0085] The duration of the cobalt deposition process can be
selected such that the cobalt portions 48 completely fill the
backside cavities 43'. In one embodiment, a convex sidewall of each
cobalt portion 48 can protrude into the backside contact trench 79
due to the selective nature of the cobalt deposition process. A
combination of a metallic barrier material portion 148 and a cobalt
portion 48 embedded within the metallic barrier material portion
148 constitutes an electrically conductive layer 46 at each level.
Thus, each electrically conductive layer 46 can consist of a cobalt
portion 48 and a metallic barrier material portion 148. Each
electrically conductive layer 46 can be formed directly on
horizontal surfaces of the insulating layers 32 and directly on an
outer sidewall of the memory film 50. In one embodiment, the
electrically conductive layers 46 can be employed as is, and
subsequent processing steps of FIG. 16 can be performed.
[0086] Alternatively, the cobalt portions 48 can be laterally
recessed. FIG. 6D illustrates the optional step of laterally
recessing the cobalt portions 48, in which cobalt can be
isotropically etched employing an isotropic etch chemistry. The
lateral recessing of the cobalt portions 48 can be performed by an
isotropic dry etch or a wet etch. The lateral recess distance lrd,
as measured between a vertical plane including a sidewall of the
backside contact trench 79 and a sidewall of a cobalt portion 48
after the lateral recess, can be in a range from 3 nm to 5 nm,
although lesser and greater thickness can be employed. A proximal
sidewall of each cobalt portion 48 is laterally spaced from the
memory film 50 (See FIG. 2F) by a vertical portion of a respective
metallic barrier material portion 148. Each cobalt portion 48 can
be laterally recessed from the backside contact trench 79.
Specifically, a distal sidewall of each cobalt portion 48 (e.g., a
left side sidewall in FIG. 6D) is more proximal to the memory film
50 than the sidewall of the backside contact trench 79 is to the
memory film 50 by the lateral recess distance lrd. The lateral
recessing of the sidewalls of the cobalt portions 48 is an optional
process.
[0087] FIGS. 7A and 7B illustrate processing steps for forming
second exemplary electrically conductive layers according to a
second embodiment of the present disclosure. The structure of FIG.
7A can be derived from the structure of FIG. 6A by depositing a
cobalt layer 48L on the metallic barrier material layer 148L. The
cobalt layer 48L can be deposited employing the same deposition
methods as the deposition methods employed to deposit the cobalt
portions 48. Because the surfaces of the metallic barrier material
layer 148L are present within the backside recesses 43 and in the
backside contact trench 79, the cobalt layer 48L can be deposited
as a contiguous layer filling the backside cavities 43' and
extending through the entire height of the backside contact trench
79.
[0088] Referring to FIG. 7B, the cobalt layer 48L can be etched to
physically expose sidewalls of the insulator layers 32. The etch of
cobalt can be performed by an isotropic dry etch process or a wet
etch process. The isotropic etch of cobalt may, or may not, be
selective to the material of the metallic barrier material layer
148L. The cobalt layer 48L can be divided into disjoined discrete
material portions located within each respective level. Each
disjoined discrete material portion of the cobalt layer 48L is
herein referred to as a cobalt portion 48. In one embodiment, an
outer sidewall of each cobalt portion 48 can be laterally recessed
from the sidewall of the backside contact trench 79 by a lateral
recess distance lrd. A proximal sidewall of each cobalt portion 48
is laterally spaced from the memory film 50 (See FIG. 2F) by a
vertical portion of a respective metallic barrier material portion
148. Each cobalt portion 48 can be laterally recessed from the
backside contact trench 79. Specifically, a distal sidewall of each
cobalt portion 48 is more proximal to the memory film 50 than the
sidewall of the backside contact trench 79 is to the memory film 50
by the lateral recess distance lrd.
[0089] Subsequent to the etching of the cobalt layer 48L or
concurrently with etching of the cobalt layer 48L, an anisotropic
etch can be performed to remove vertical portions of the metallic
barrier material layer 148L from the sidewalls of each backside
contact trench 79. The anisotropic etch can be a reactive ion etch
that removes the material of the metallic barrier material layer
148L selective to the material of the insulator layers 32 and the
material of the semiconductor material layer 10. Portions of the
metallic barrier material layer 148L inside the backside recesses
43 are not removed by the anisotropic etch. Each remaining portion
of the metallic barrier material layer 148L inside the backside
recesses 43 constitutes a metallic barrier portion 148.
[0090] Thus, portions of the contiguous cobalt layer 48L are etched
back prior to removing the vertical portions of the metallic
barrier material layer 148L. Each remaining portion of the
contiguous cobalt layer 48L constitutes a cobalt portion 48 of the
electrically conductive layers 46. The cobalt portions 48 may have
distal sidewalls that are laterally recessed from the sidewalls of
the backside trench 79, or may have distal sidewalls that are
vertically coincident with the sidewalls of the backside trench 79.
Each metallic barrier material portion 148 can be a conformal
material portion having a uniform thickness throughout. Sidewalls
of the insulator layers 32 are physically exposed within each
backside contact trench 79. Each cobalt portion 48 can be formed on
surfaces of a respective metallic barrier material portion 148, and
specifically, on a pair of horizontal surfaces of the respective
metallic barrier material portion 148 and an outer sidewall of the
respective metallic barrier material portion 148. A combination of
a metallic barrier material portion 148 and a cobalt portion 48
embedded within the metallic barrier material portion 148
constitutes an electrically conductive layer 46 at each level. Each
electrically conductive layer 46 can consist of a cobalt portion 48
and a metallic barrier material portion 148.
[0091] FIGS. 8A-8C illustrate processing steps for forming third
exemplary electrically conductive layers according to a third
embodiment of the present disclosure. The structure of FIG. 8A can
be derived from the structure of FIG. 6A by depositing a metallic
material layer 47L on the metallic barrier material layer 148L. The
metallic material layer 47L can be a contiguous layer extending
through the entire vertical height of the backside contact trench
79. The metallic material layer 47L can include any metallic
material other than cobalt. In one embodiment, the metallic
material layer 47L can consist essentially of a single elemental
metal or an intermetallic alloy of at least two elemental metals.
For example, the metallic material layer 47L can comprise
molybdenum, tungsten, copper, ruthenium, or titanium, or a
combination thereof. In one embodiment, the metallic material layer
47L can comprise tungsten or a tungsten-containing intermetallic
alloy. The thickness of the metallic material layer 47L can be
selected such that the backside cavities 43' are not completely
filled with the metallic material layer 47L.
[0092] Referring to FIG. 8B, an anisotropic etch is performed to
remove vertical portions of the metallic barrier material layer
148L and the metallic material layer 47L from the sidewalls of each
backside contact trench 79. The anisotropic etch can be a reactive
ion etch that removes the materials of the metallic barrier
material layer 148L and the metallic material layer 47L selective
to the material of the insulator layers 32 and the material of the
semiconductor material layer 10. Portions of the metallic barrier
material layer 148L and the metallic material layer 47L inside the
backside recesses 43 are not removed by the anisotropic etch. Each
remaining portion of the metallic barrier material layer 148L
inside the backside recesses 43 constitutes a metallic barrier
portion 148. Each remaining portion of the metallic material layer
47L inside the backside recesses 43 constitutes a metallic material
portion 47. Each metallic barrier material portion 148 can be a
conformal material portion having a uniform thickness throughout.
Likewise, each metallic material portion 47 can be a conformal
material portion having another uniform thickness throughout.
Sidewalls of the insulator layers 32 are physically exposed within
each backside contact trench 79. The metallic barrier material
portions 148 are formed as a plurality structures that are
vertically disjoined from one another. Further, the metallic
material portions 47 are formed as a plurality structures that are
vertically disjoined from one another. Alternately, the processing
steps of FIGS. 6A and 6B can be performed, and the metallic
material portions 47 can be deposited by a selective deposition
process.
[0093] Referring to FIG. 8C, cobalt can be deposited inside the
backside cavities 43' to form cobalt portions 48. Deposition of
cobalt can be performed employing the same methods as in the first
embodiment. Cobalt portions 48 grow only from the surfaces of the
metallic material portions 47 and the metallic barrier material
portions 148, and do not grow from the sidewalls of the insulator
layers 32. As such, the cobalt deposition process is a selective
deposition process that proceeds from the surfaces of the metallic
material portions 47, while cobalt is not deposited on the surfaces
of the insulator layers 32. Each cobalt portion 48 can be formed on
surfaces of a respective metallic material portion 47, and
specifically, on a pair of horizontal surfaces of the respective
metallic material portion 47 and an outer sidewall of the
respective metallic material portion 47. Each deposited portion of
cobalt constitutes one of the cobalt portions 48.
[0094] The duration of the cobalt deposition process can be
selected such that the cobalt portions 48 completely fill the
backside cavities 43'. A combination of a metallic barrier material
portion 148, a metallic material portion 47 embedded within the
metallic barrier material portion 148, and a cobalt portion 48
embedded within the metallic material portion 47 constitutes an
electrically conductive layer 46 at each level. Thus, each
electrically conductive layer 46 can comprise a cobalt portion 48,
a metallic material portion 47 including a metallic material other
than cobalt, and a metallic barrier material portion 148. Each
electrically conductive layer 46 can be formed directly on
horizontal surfaces of the insulating layers 32 and directly on an
outer sidewall of the memory film 50. Optionally, the cobalt
portions 48 and/or the metallic material portions 47 can be
laterally recessed from the sidewall of the backside contact trench
79. In this case, each of the electrically conductive layers 46
comprises a metallic barrier material portion 148 contacting an
outer sidewall of the memory film 50, a metallic material portion
47 containing a material other than cobalt and contacting the
metallic barrier material portion 148, and a respective cobalt
portion 48 contacting horizontal surfaces of the metallic material
portion 47 and not contacting the metallic barrier material portion
148.
[0095] FIGS. 9A-9C illustrate processing steps for forming fourth
exemplary electrically conductive layers according to a fourth
embodiment of the present disclosure. The structure of FIG. 9A can
be derived from the structure of FIG. 6A by depositing a metallic
material layer 47L on the metallic barrier material layer 148L. The
metallic material layer 47L can include any metallic material other
than cobalt. In one embodiment, the metallic material layer 47L can
consist essentially of a single elemental metal or an intermetallic
alloy of at least two elemental metals. For example, the metallic
material layer 47L can comprise molybdenum, tungsten, copper,
titanium, ruthenium, or a combination thereof. In one embodiment,
the metallic material layer 47L can comprise tungsten or a
tungsten-containing intermetallic alloy. The thickness of the
metallic material layer 47L can be selected such that the backside
cavities 43' are completely filled with the metallic material layer
47L.
[0096] Referring to FIG. 9B, vertical portions of the metallic
material layer 47L and the metallic barrier material layer 148L are
removed from the sidewall of the backside contact trench 79. The
metallic material layer 47L can be isotropically etched to
physically expose the sidewall of the metallic barrier material
layer 148L located adjacent to the sidewall of each backside
contact trench 79. The isotropic etch of tungsten can be performed
by an isotropic dry etch process or a wet etch process. The
isotropic etch of the metallic material layer 47L can be selective
to the material of the metallic barrier material layer 148L. The
duration of the isotropic etch can be selected such that remaining
portions of the metallic material layer 47L are laterally recessed
from the sidewall of the backside contact trench 79 by a lateral
recess distance lrd. The metallic material layer 47L is divided
into disjoined discrete material portions located within each
respective level. Each disjoined discrete material portion of the
metallic material layer 47L constitutes a metallic material portion
47.
[0097] Subsequently, an anisotropic etch is performed to remove
vertical portions of the metallic barrier material layer 148L from
the sidewalls of each backside contact trench 79. The anisotropic
etch can be a reactive ion etch that removes the material of the
metallic barrier material layer 148L selective to the material of
the insulator layers 32 and the material of the semiconductor
material layer 10. Portions of the metallic barrier material layer
148L inside the backside recesses 43 are not removed by the
anisotropic etch. Each remaining portion of the metallic barrier
material layer 148L inside the backside recesses 43 constitutes a
metallic barrier portion 148. Thus, portions of the metallic
material layer 47L are etched back prior to removing the vertical
portions of the metallic barrier material layer 148L. Each
remaining portion of the metallic material layer 47L constitutes a
metallic material portion 47 of electrically conductive layers to
be formed. Alternately, an anisotropic etch may be employed to
remove the vertical portions of the metallic material layer 47L and
the metallic barrier material layer 148L, and an isotropic etch may
be employed to laterally recess the metallic material portions
47.
[0098] In one embodiment, the lateral recess distance lrd can be
greater than the height of a backside recess 43, which is the same
as the height of a metallic barrier material portion 148 within the
backside recess 43. In one embodiment, the lateral recess distance
lrd can be in a range from 15% to 85% of the lateral distance
between the sidewall of the backside contact trench 79 and the
outer sidewall of the memory film 50, e.g., the outer sidewall of
the at least one blocking dielectric layer (501L, 503L). In one
embodiment, the lateral recess distance lrd can be determined to
optimize the resistance of the electrically conductive layers to be
formed in the backside recesses and the overall stress that the
electrically conductive layers will generate. A distal sidewall of
each metallic material portion 47 is more proximal to the memory
film 50 than the sidewall of the backside contact trench 79 is to
the memory film 50 by the lateral recess distance lrd. A proximal
sidewall of each metallic material portion 47 can contact an outer
sidewall of a metallic barrier material portion 148.
[0099] Referring to FIG. 9C, cobalt can be deposited inside the
backside cavities 43' to form cobalt portions 48. Deposition of
cobalt can be performed employing the same methods as in the first
embodiment. Cobalt portions 48 grow only from the surfaces of the
metallic material portions 47 and the metallic barrier material
portions 148, and do not grow from the sidewalls of the insulator
layers 32. As such, the cobalt deposition process is a selective
deposition process that proceeds from the surfaces of the metallic
barrier material portions 148 and the surfaces of the metallic
material portions 47, while cobalt is not deposited on the surfaces
of the insulator layers 32. Thus, each cobalt portion 48 can be
formed on a respective metallic material portion 47 and a
respective metallic barrier material portion 148, and specifically,
on a pair of horizontal surfaces of the respective metallic barrier
material portion 148 and an outer sidewall of the respective
metallic material portion 47. Each deposited portion of cobalt
constitutes one of the cobalt portions 48.
[0100] In one embodiment, the duration of the cobalt deposition
process can be selected such that the cobalt portions 48 completely
fill the backside cavities 43'. A combination of a metallic barrier
material portion 148, a cobalt portion 48 contacting horizontal
surfaces of the metallic barrier material portion 148, and a
metallic material portion 47 encapsulated by the metallic barrier
material portion 148 and the cobalt portion 48 constitutes an
electrically conductive layer 46 at each level. Thus, each
electrically conductive layer 46 can comprise a cobalt portion 48,
a metallic material portion 47 including a metallic material other
than cobalt, and a metallic barrier material portion 148. Each
electrically conductive layer 46 can be formed directly on
horizontal surfaces of the insulating layers 32 and directly on an
outer sidewall of the memory film 50. Optionally, an anisotropic
etch or an isotropic etch can be performed to remove regions of the
cobalt portions 48 inside backside contact trench 79. In this case,
the cobalt portions 48 can have sidewalls that are vertically
coincident with sidewalls of the insulator layers 32 around the
backside contact trench 79. Optionally, the cobalt portions 48 may
be laterally recessed from the sidewall of the backside contact
trench 79, for example, by a recess etch. In one embodiment, each
cobalt portion 48 is laterally spaced from a vertical portion of a
metallic barrier material portion 148 located at a same level by a
respective metallic material portion 47 that comprises tungsten or
a tungsten alloy.
[0101] FIGS. 10A and 10B illustrate processing steps for forming
fifth exemplary electrically conductive layers according to a fifth
embodiment of the present disclosure. The structure of FIG. 10A can
be derived from the structure of FIG. 9B by etching physically
exposed portions of the metallic barrier material portions 148.
[0102] Alternatively, the structure of FIG. 10A can be derived from
the structure of FIG. 9A by simultaneously etching, or by
sequentially etching, the metallic material layer 47L and the
metallic barrier material layer 148L. At least one isotropic etch
process can be employed to laterally recess the metallic material
layer 47L and the metallic barrier material layer 148L, and to form
backside recesses 43'. After the isotropic etching of the metallic
material layer 47L, the metallic material layer 47L can be divided
into disjoined discrete material portions located within each
respective level. Each disjoined discrete material portion of the
metallic material layer 47L is herein referred to as a metallic
material portion 47.
[0103] Subsequently, an isotropic etch process is employed to etch
the physically exposed portions of the metallic barrier material
layer 148L. In other words, an isotropic etch is employed to remove
physically exposed portions of the metallic barrier material layer
148L at the processing step of FIG. 10A in lieu of an anisotropic
etch that is employed to remove the portions of the metallic
barrier material layer 148L within the backside contact trench 79
at the processing steps of FIG. 9B. The isotropic etch process that
etches the physically exposed portions of the metallic barrier
material layer 148L can be an isotropic dry etch or a wet etch.
[0104] The isotropic etch divides the metallic barrier material
layer 148L into disjoined discrete material portions located within
each respective level. Each disjoined discrete material portion of
the metallic barrier material layer 148L is herein referred to as a
metallic barrier material portion 148. Thus, portions of the
metallic material layer 47L are etched back prior to removing the
physically exposed portions of the metallic barrier material layer
148L. A distal sidewall of each metallic material portion 47 and a
distal sidewall of each metallic barrier material portion 148 can
be more proximal to the memory film 50 than the sidewall of the
backside contact trench 79 is to the memory film 50 by the lateral
recess distance lrd. A proximal sidewall of each metallic material
portion 47 can contact an outer sidewall of a metallic barrier
material portion 148.
[0105] Referring to FIG. 10B, cobalt can be deposited inside the
backside cavities 43' to form cobalt portions 48. Deposition of
cobalt can be performed employing the same methods as in the first
embodiment. Cobalt portions 48 grow only from the surfaces of the
metallic material portions 47 and the metallic barrier material
portions 148, and do not grow from the sidewalls of the insulator
layers 32. As such, the cobalt deposition process is a selective
deposition process that proceeds from the surfaces of the metallic
barrier material portions 148 and the surfaces of the metallic
material portions 47, while cobalt is not deposited on the surfaces
of the insulator layers 32. Thus, each cobalt portion 48 can be
formed on a respective metallic material portion 47 and a
respective metallic barrier material portion 148, and specifically,
on vertical sidewalls of the respective metallic material portion
47 and the respective metallic barrier material portion 148. Each
deposited portion of cobalt constitutes one of the cobalt portions
48.
[0106] In one embodiment, the duration of the cobalt deposition
process can be selected such that the cobalt portions 48 completely
fill the backside cavities 43'. A combination of a metallic barrier
material portion 148, a cobalt portion 48 contacting horizontal
surfaces of a pair of insulator layers 32, and a metallic material
portion 47 encapsulated by the metallic barrier material portion
148 and the cobalt portion 48 constitutes an electrically
conductive layer 46 at each level. Thus, each electrically
conductive layer 46 can comprise a cobalt portion 48, a metallic
material portion 47 including a metallic material other than
cobalt, and a metallic barrier material portion 148. Each
electrically conductive layer 46 can be formed directly on
horizontal surfaces of the insulating layers 32 and directly on an
outer sidewall of the memory film 50. Optionally, an anisotropic
etch or an isotropic etch can be performed to remove regions of the
cobalt portions 48 inside backside contact trench 79. In this case,
the cobalt portions 48 can have sidewalls that are vertically
coincident with sidewalls of the insulator layers 32 around the
backside contact trench 79. Optionally, the cobalt portions 48 may
be laterally recessed from the sidewall of the backside contact
trench 79, for example, by a recess etch. Each cobalt portion 48
contacts a horizontal surface of an overlying dielectric layer
(e.g., an overlying insulator layer 32) and a horizontal surface of
an underlying dielectric layer (e.g., an underlying insulator layer
32).
[0107] FIGS. 11A and 11B illustrate processing steps for forming
sixth exemplary electrically conductive layers according to a sixth
embodiment of the present disclosure. The structure of FIG. 11A can
be derived from the structure of FIG. 6A by depositing a cobalt
layer 48L on the metallic barrier material layer 148L. The cobalt
layer 48L can be deposited employing the same deposition methods as
the deposition methods employed to deposit the cobalt portions 48
of FIG. 6C or the cobalt layer 48L of FIG. 7A. The thickness of the
cobalt layer 48L can be selected such that the backside cavities
43' are not completely filled with the cobalt layer 48L. For
example, the duration of the cobalt deposition process in a
chemical vapor deposition process or the number of cycles in an
atomic layer deposition process can be selected such that the
backside recesses 43 are not completely filled at the end of the
deposition process. Thus, a backside cavity 43' is present within
each backside recess 43 after formation of the cobalt layer
48L.
[0108] Referring to FIG. 11B, an anisotropic etch is performed to
remove vertical portions of the metallic barrier material layer
148L and the cobalt layer 48L from the sidewalls of each backside
contact trench 79. The anisotropic etch can be a reactive ion etch
that removes the materials of the metallic barrier material layer
148L and the cobalt layer 48L selective to the material of the
insulator layers 32 and the material of the semiconductor material
layer 10. Portions of the metallic barrier material layer 148L and
the cobalt layer 48L inside the backside recesses 43 are not
removed by the anisotropic etch. Each remaining portion of the
metallic barrier material layer 148L inside the backside recesses
43 constitutes a metallic barrier portion 148. Each remaining
portion of the cobalt layer 48L inside the backside recesses 43
constitutes a cobalt portion 48. Each metallic barrier material
portion 148 can be a conformal material portion having a uniform
thickness throughout. Likewise, each cobalt portion 48 can be a
conformal material portion having another uniform thickness
throughout. Sidewalls of the insulator layers 32 are physically
exposed within each backside contact trench 79. The metallic
barrier material portions 148 are formed as a plurality structures
that are vertically disjoined from one another. Further, the cobalt
portions 48 are formed as a plurality structures that are
vertically disjoined from one another. Each cobalt portion 48 of
the electrically conductive layers 46 is formed on surfaces of a
respective metallic barrier material portion 148.
[0109] Referring to FIG. 11C, a metallic material can be deposited
inside the backside cavities 43' to form metallic material portions
47. The metallic material portions 47 can include any metallic
material other than cobalt. In one embodiment, the metallic
material portions 47 can consist essentially of a single elemental
metal or an intermetallic alloy of at least two elemental metals.
For example, the metallic material portions 47 can comprise
molybdenum, tungsten, copper, titanium, ruthenium, or a combination
thereof. In one embodiment, the metallic material portions 47 can
comprise tungsten or a tungsten-containing intermetallic alloy.
[0110] Deposition of the metallic material can be performed
employing the same methods as in the third embodiment. In one
embodiment, the metallic material portions 47 grow from the
surfaces of the cobalt portions 48, and do not grow from the
sidewalls of the insulator layers 32. As such, the metallic
material deposition process is a selective deposition process that
proceeds from the surfaces of the cobalt portions 48, while the
metallic material is not deposited on the surfaces of the insulator
layers 32. Thus, each metallic material portion 47 can be formed on
surfaces of a respective cobalt portion 48, and specifically, on a
pair of horizontal surfaces of the respective cobalt portion 48 and
an outer sidewall of the respective cobalt portion 48. Each
deposited portion of metallic material constitutes one of the
metallic material portions 47.
[0111] The duration of the metallic material deposition process can
be selected such that the metallic material portions 47 completely
fill the backside cavities 43'. A metallic material portion 47 is
formed on a respective cobalt portion 48 in each backside cavity
43', i.e., in the vacant portion of each backside recess. A
combination of a metallic barrier material portion 148, a cobalt
portion 48 embedded within the metallic bather material portion
148, and a metallic material portion 47 embedded within the cobalt
portion 48 constitutes an electrically conductive layer 46 at each
level. Thus, each electrically conductive layer 46 can comprise a
cobalt portion 48, a metallic material portion 47 including a
metallic material other than cobalt, and a metallic barrier
material portion 148. Each electrically conductive layer 46 can be
formed directly on horizontal surfaces of the insulating layers 32
and directly on an outer sidewall of the memory film 50. Each
metallic material portion 47 is vertically and laterally spaced
from a metallic barrier material portion 148 located at a same
level by a respective cobalt portion 48. Optionally, the cobalt
portions 48 and/or the metallic material portions 47 can be
laterally recessed from the sidewall of the backside contact trench
79.
[0112] FIGS. 12A-12C illustrate processing steps for forming
seventh exemplary electrically conductive layers according to a
seventh embodiment of the present disclosure. The structure of FIG.
12A can be the same as the structure of FIG. 7A according to the
second embodiment, and can be formed employing the same method as
the second embodiment. In one embodiment, the cobalt layer 48L can
consist essentially of cobalt.
[0113] Referring to FIG. 12B, the cobalt layer 48L can be
isotropically etched to physically expose the sidewall of the
metallic barrier material layer 148L located adjacent to the
sidewall of each backside contact trench 79. The isotropic etch of
cobalt can be performed by an isotropic dry etch process or a wet
etch process. The isotropic etch of the cobalt layer 48L can be
selective to the material of the metallic barrier material layer
148L. The duration of the isotropic etch can be selected such that
remaining portions of the cobalt layer 48L are laterally recessed
from the sidewall of the backside contact trench 79 by a lateral
recess distance lrd. The cobalt layer 48L is divided into disjoined
discrete material portions located within each respective level.
Each disjoined discrete material portion of the cobalt layer 48L is
herein referred to as a cobalt portion 48. Each cobalt portion 48
of the electrically conductive layers 46 is formed on surfaces of a
respective metallic barrier material portion 148. Alternatively, a
combination of an anisotropic etch and an isotropic etch can be
employed to form the structure of FIG. 12B.
[0114] In one embodiment, the lateral recess distance lrd can be
greater than the height of a backside recess 43, which is the same
as the height of a metallic barrier material portion 148 within the
backside recess 43. In one embodiment, the lateral recess distance
lrd can be in a range from 15% to 85% of the lateral distance
between the sidewall of the backside contact trench 79 and the
outer sidewall of the memory film 50, e.g., the outer sidewall of
the at least one blocking dielectric layer (501L, 503L). In one
embodiment, the lateral recess distance lrd can be determined to
optimize the resistance of the electrically conductive layers to be
formed in the backside recesses and the overall stress that the
electrically conductive layers will generate. A distal sidewall of
each cobalt portion 48 is more proximal to the memory film 50 than
the sidewall of the backside contact trench 79 is to the memory
film 50 by the lateral recess distance lrd. A proximal sidewall of
each cobalt portion 48 can contact an outer sidewall of a metallic
barrier material portion 148. A proximal sidewall of each cobalt
portion 48 is laterally spaced from the memory film 50 by a
vertical portion of a respective metallic barrier material portion
148, and each cobalt portion 48 is laterally recessed from the
backside contact trench 79.
[0115] Subsequently, an anisotropic etch is performed to remove
vertical portions of the metallic barrier material layer 148L from
the sidewalls of each backside contact trench 79. The anisotropic
etch can be a reactive ion etch that removes the material of the
metallic barrier material layer 148L selective to the material of
the insulator layers 32 and the material of the semiconductor
material layer 10. Portions of the metallic barrier material layer
148L inside the backside recesses 43 are not removed by the
anisotropic etch. Each remaining portion of the metallic barrier
material layer 148L inside the backside recesses 43 constitutes a
metallic bather portion 148. Thus, portions of the cobalt layer 48L
are etched back prior to removing the vertical portions of the
metallic barrier material layer 148L. Each remaining portion of the
cobalt layer 48L constitutes a cobalt portion 48 of electrically
conductive layers to be formed.
[0116] Referring to FIG. 12C, a metallic material can be deposited
inside the backside cavities 43' to form metallic material portions
47. The metallic material portions 47 can include any metallic
material other than cobalt. In one embodiment, the metallic
material portions 47 can consist essentially of a single elemental
metal or an intermetallic alloy of at least two elemental metals.
For example, the metallic material portions 47 can comprise
molybdenum, tungsten, copper, titanium, ruthenium, or a combination
thereof. In one embodiment, the metallic material portions 47 can
comprise tungsten or a tungsten-containing intermetallic alloy.
Deposition of metallic material can be performed employing the same
methods as in the third embodiment. The metallic material portions
47 grow only from the surfaces of the cobalt portions 48 and the
metallic barrier material portions 148, and do not grow from the
sidewalls of the insulator layers 32. As such, the metallic
material deposition process is a selective deposition process that
proceeds from the surfaces of the metallic barrier material
portions 148 and the surfaces of the cobalt portions 48, while the
metallic material is not deposited on the surfaces of the insulator
layers 32. Thus, each metallic material portion 47 can be formed on
a respective cobalt portion 48 and a respective metallic barrier
material portion 148, and specifically, on a pair of horizontal
surfaces of the respective metallic barrier material portion 148
and an outer sidewall of the respective cobalt portion 48. Each
deposited portion of metallic material constitutes one of the
metallic material portions 47.
[0117] In one embodiment, the duration of the metallic material
deposition process can be selected such that the metallic material
portions 47 completely fill the backside cavities 43'. A metallic
material portion 47 is formed on a respective cobalt portion 48 in
each backside cavity 43', i.e., in the vacant portion of each
backside recess. A combination of a metallic barrier material
portion 148, a metallic material portion 47 contacting horizontal
surfaces of the metallic barrier material portion 148, and a cobalt
portion 48 encapsulated by the metallic barrier material portion
148 and the metallic material portion 47 constitutes an
electrically conductive layer 46 at each level. Thus, each
electrically conductive layer 46 can comprise a metallic material
portion 47, a cobalt portion 48 including cobalt, and a metallic
barrier material portion 148 including a metallic material other
than cobalt. Each electrically conductive layer 46 can be formed
directly on horizontal surfaces of the insulating layers 32 and
directly on an outer sidewall of the memory film 50. Each metallic
material portion 47 contacts a pair of horizontal surfaces of a
metallic barrier material portion 148 located at the same level and
a distal sidewall of the cobalt portion 48 located at the same
level. Optionally, an anisotropic etch can be performed to remove
regions of the metallic material portions 47 inside backside
contact trench 79. In this case, the metallic material portions 47
can have sidewalls that are vertically coincident with sidewalls of
the insulator layers 32 around the backside contact trench 79.
Optionally, the metallic material portions 47 may be laterally
recessed from the sidewall of the backside contact trench 79, for
example, by a recess etch.
[0118] FIGS. 13A-13B illustrate processing steps for forming eighth
exemplary electrically conductive layers according to an eighth
embodiment of the present disclosure. The structure of FIG. 13A can
be derived from the exemplary structure of FIG. 12B by
isotropically etching physically exposed portions of each metallic
barrier material portion 148. Alternately, the metallic barrier
material portions 148 can be laterally recessed at about the same
etch rate as the cobalt portion 48 from the exemplary structure of
FIG. 12A.
[0119] Referring to FIG. 13B, the processing steps of FIG. 12C can
be performed to form the metallic material portions 47, which can
be, for example, tungsten portions. The metallic material portions
47 grow from the respective vertical metallic surfaces of the
metallic barrier material portion 148 and the cobalt portion 48 at
each level. Each metallic material portion 47 can contact a
horizontal surface of an underlying dielectric layer (which can be,
for example, an underlying insulator layer 32) and a horizontal
surface of an overlying dielectric layer (which can be, for
example, an overlying insulator layer 32).
[0120] FIGS. 14A-14E illustrate processing steps for forming ninth
exemplary electrically conductive layers according to a ninth
embodiment of the present disclosure. The structure of FIG. 14A can
be derived from the structure of FIGS. 5A and 5B by forming a
backside blocking dielectric layer 51 prior to formation of a
metallic barrier material layer 148L. The backside blocking
dielectric layer 51 includes a dielectric material, which can
comprise a high dielectric constant (high-k) dielectric material
having a dielectric constant greater than 7.9 (such as aluminum
oxide), and/or silicon oxide and/or silicon nitride. The backside
blocking dielectric layer 51 can be formed, for example, by
chemical vapor deposition (CVD) or atomic layer deposition (ALD).
The thickness of the backside blocking dielectric layer 51 can be
in a range from 0.5 nm to 1.5 nm, although lesser and greater
thicknesses can also be employed. The metallic barrier material
layer 148L can be formed in the same manner as in the first
embodiment.
[0121] Referring to FIG. 14B, a disposable material layer 143L is
formed in the backside cavities 43'. The disposable material layer
143L can fill the entirety of the backside cavities 43'. As used
herein, a "disposable" material refers to a temporary material that
is subsequently removed. The disposable material layer 143L
includes a material that can be removed selective to the material
of the metallic barrier material layer 148L. In one embodiment, the
disposable material layer 143L can comprise a semiconductor
material such as polysilicon, amorphous silicon, a
silicon-germanium alloy, or a combination thereof. The disposable
material layer 143L can be deposited, for example, by chemical
vapor deposition.
[0122] Referring to FIG. 14C, the material of the disposable
material layer 143L and the metallic barrier material layer 148L
are isotropically or anisotropically etched to physically expose
sidewalls of the backside blocking dielectric layer 51. The etch of
the disposable material layer 143L can be performed by a dry etch
or a wet etch. For example, if the disposable material layer 143L
comprises silicon, the disposable material layer 143L can be etched
by an etch process employing one or more of BCl.sub.3; a
combination of SiCl.sub.4, Cl.sub.2, and HCl; a combination of
O.sub.2, SiCl.sub.4, and HCl; SF.sub.6; and NF.sub.3. Each
remaining portion of the disposable material layer 143L within a
backside recess is herein referred to as a disposable material
portion 143.
[0123] Subsequent to, or concurrently with, the etch of the
vertical portion of the disposable material layer 143L, physically
exposed portions of the metallic barrier material layer 148L is
removed by an etch selective to the backside blocking dielectric
layer 51. Each remaining portion of the metallic barrier material
layer 148L constitutes a metallic barrier material portion 148. In
other words, a metallic barrier material portion 148 and a
disposable material portion 143 can be formed at each level of the
of backside recesses by removing vertical portions of the
disposable material layer 143L and the metallic barrier material
layer 148L, respectively.
[0124] Referring to FIG. 14D, the disposable material portions 143
can be removed by an isotropic etch that etches the material of the
disposable material portions 143. A backside cavity 43' can be
formed within the volume of each backside recess.
[0125] Referring to FIG. 14E, the processing step of FIG. 6C can be
performed to form cobalt portions 48. Each cobalt portion 48 is
embedded within a metallic barrier material portion 148.
Optionally, the processing steps of FIG. 6D may be performed.
[0126] A combination of a metallic barrier material portion 148 and
a cobalt portion 48 embedded within the metallic barrier material
portion 148 constitutes an electrically conductive layer 46 at each
level. Thus, each electrically conductive layer 46 can consist of a
cobalt portion 48 and a metallic barrier material portion 148. Each
electrically conductive layer 46 can be vertically spaced from an
overlying insulating layer 32, an underlying insulating layer 32,
and the memory film 50 by the backside blocking dielectric layer
51. Each cobalt portion 48 of the electrically conductive layers 46
is formed on surfaces of a respective metallic barrier material
portion 148. Specifically, each cobalt portion 48 of the
electrically conductive layers 46 is formed on a pair of horizontal
surfaces of the respective metallic barrier material portion and an
outer sidewall of the respective metallic barrier material
portions. The disposable material layer 143L may be used in
conjunction with other embodiments.
[0127] Referring to FIG. 15, the exemplary structure is shown after
formation of a plurality of electrically conductive layers 46,
which can be any of the electrically conductive layers 46 according
to the first through ninth embodiments as described above.
[0128] Each electrically conductive layer 46 can function as a
combination of a plurality of control gate electrodes and a word
line electrically connecting, i.e., electrically shorting, the
plurality of control gate electrodes. The plurality of control gate
electrodes within each electrically conductive layer 46 can include
control gate electrodes located at the same level for the vertical
memory devices including the memory stack structures 55. In other
words, each electrically conductive layer 46 can be a word line
that functions as a common control gate electrode for the plurality
of vertical memory devices.
[0129] Referring to FIG. 16, an insulating spacer 74 can be formed
on the sidewalls of the backside contact trench 79 by deposition of
a contiguous dielectric material layer and an anisotropic etch of
its horizontal portions. The insulating spacer 74 includes a
dielectric material, which can comprise, for example, silicon
oxide, silicon nitride, a dielectric metal oxide, a dielectric
metal oxynitride, or a combination thereof. The thickness of the
insulating spacer 74, as measured at a bottom portion thereof, can
be in a range from 1 nm to 50 nm, although lesser and greater
thicknesses can also be employed. In one embodiment, the thickness
of the insulating spacer 74 can be in a range from 3 nm to 10
nm.
[0130] A photoresist layer (not shown) can be applied over the
topmost layer of the exemplary structure (which can be, for
example, the dielectric pillar material layer 73) and in the cavity
laterally surrounded by the insulating spacer 74, and is
lithographically patterned to form various openings in a peripheral
device region. The locations and the shapes of the various openings
are selected to correspond to electrical nodes of the semiconductor
devices in the peripheral device region 200 to be electrically
contacted by contact via structures. An anisotropic etch is
performed to etch through the various layers overlying the
electrical nodes of the semiconductor devices. For example, at
least one gate via cavity can be formed such that the bottom
surface of each gate via cavity is a surface of a gate electrode
(152, 154), and at least one active region via cavity can be formed
such that the bottom surface of each active region via cavity is a
surface of an active region 130. In one embodiment, different types
of via cavities can be formed separately employing multiple
combinations of photoresist layers and anisotropic etch processes.
The vertical extent of each gate via cavity, as measured from the
top surface of the dielectric pillar material layer 73 to the
bottom surface of the gate via cavity, can be less than the
vertical distance between the top surface of the dielectric pillar
material layer 73 and the topmost surface of the alternating
plurality (32, 46) of the insulator layers 32 and the electrically
conductive layers 46. The photoresist layer can be subsequently
removed, for example, by ashing.
[0131] Another photoresist layer (not shown) can be applied over
the exemplary structure, and can be lithographically patterned to
form openings within the contact region 200 in which formation of
contact via structures for the electrically conductive layers 46 is
desired. Control gate contact via cavities can be formed through
the retro-stepped dielectric material portion 65 by transfer of the
pattern of the opening by an anisotropic etch. Each via cavity can
vertically extend to a top surface of a respective electrically
conductive layer 46.
[0132] In addition, another photoresist layer (not shown) can be
applied over the exemplary structure, and can be lithographically
patterned to form openings that overlie the array of drain regions
63 in the device region 100. Drain contact via cavities can be
formed through the dielectric pillar material layer 73 and the at
least one dielectric cap layer 71.
[0133] The cavity laterally surrounded by the insulating spacer 74,
the various via cavities in the peripheral device region 200, the
control gate contact via cavities in the contact region 300, and
the drain contact via cavities in the device region 100 can be
filled with a conductive material to form various contact via
structures. For example, a backside contact via structure 76 can be
formed in the cavity surrounded by the insulating spacer 74. A gate
contact via structure 8G can be formed in each gate via cavity in
the peripheral device region 200. An active region via structure 8A
is formed in each active region via cavity in the peripheral device
region 200. Drain contact via structures 88 can be formed in the
drain contact via cavities in the device region 100. Further,
control gate contact via structures (not shown) can be formed
within each contact via cavity that extends to a top surface of the
electrically conductive layers 46 in the contact region 300.
Similarly, drain contact via structures 88 can be formed to provide
electrical contact to the drain regions 63.
[0134] Referring to FIGS. 17A and 17B, an optional passivation
layer 82 and a line-level dielectric layer 90 can be formed over
the dielectric pillar material layer 73. The optional passivation
layer 82 can include a low permeability material such as silicon
nitride. The thickness of the passivation layer 82 can be in a
range from 3 nm to 30 nm, although lesser and greater thicknesses
can also be employed. The line-level dielectric layer 90 can
include silicon oxide or organosilicate glass. The thickness of the
line-level dielectric layer 90 can be in a range from 30 nm to
1,000 nm, although lesser and greater thicknesses can also be
employed. Control gate contact via structures 8C can contact the
electrically conductive layers 46.
[0135] Various conductive line structures 92 can be formed in the
line-level dielectric layer 90 to provide electrical contact to the
various contact via structures (76, 8G, 8A, 88, 8C). A subset of
the electrically conductive layers 46 can function as control gate
electrodes for the memory stack structures 55 in the device region.
Optionally, at least one subset of the electrically conductive
layers 46 can be employed as at least one drain select gate
electrode and/or at least one source select gate electrode.
[0136] Additional metal interconnect structures (not shown) can be
optionally formed, which can include at least one dielectric
material layer, at least one conductive via structure, and at least
one additional conductive line structure. The additional metal
interconnect structure can be formed on the top surface of the
conductive line structure 92 and the line-level dielectric layer
90.
[0137] The exemplary structure is a multilevel structure including
a stack (32, 46) of an alternating plurality of electrically
conductive layers 46 and insulator layers 32 located over a
semiconductor substrate including the semiconductor material layer
10. An array of memory stack structures 55 can be located within
memory openings through the stack (32, 46).
[0138] In one embodiment, the device located on the semiconductor
substrate can include a vertical NAND device located in the device
region 100, and at least one of the electrically conductive layers
46 in the stack (32, 46) can comprise, or can be electrically
connected to, a word line of the NAND device. The device region 100
can include a plurality of semiconductor channels (601, 602). At
least one end portion of each of the plurality of semiconductor
channels (601, 602) extends substantially perpendicular to a top
surface of the semiconductor substrate. The device region 100
further includes a plurality of charge storage regions located
within each memory layer 50. Each charge storage region is located
adjacent to a respective one of the plurality of semiconductor
channels (601, 602). The device region 100 further includes a
plurality of control gate electrodes having a strip shape extending
substantially parallel to the top surface of the substrate (9, 10).
The plurality of control gate electrodes comprise at least a first
control gate electrode located in the first device level and a
second control gate electrode located in the second device level.
The plurality of electrically conductive layers 46 in the stack
(32, 46) can be in electrical contact with, or can comprise, the
plurality of control gate electrodes, and extends from the device
region 100 to a contact region 300 including a plurality of
electrically conductive contact via structures.
[0139] In case the exemplary structure includes a three-dimensional
NAND device, a stack (32, 46) of an alternating plurality of word
lines 46 and insulating layers 32 can be located over a
semiconductor substrate. Each of the word lines 46 and insulating
layers 32 is located at different levels that are vertically spaced
from a top surface of the semiconductor substrate by different
distances. An array of memory stack structures 55 is embedded
within the stack (32, 46). Each memory stack structure 55 comprises
a semiconductor channel (601, 602) and at least one charge storage
region located adjacent to the semiconductor channel (601, 602). At
least one end portion of the semiconductor channel (601, 602)
extends substantially perpendicular to the top surface of the
semiconductor substrate through the stack (32, 46).
[0140] In a non-limiting illustrative example, the insulating
layers 32 can comprise silicon oxide layers, the plurality of word
lines 46 can comprise tungsten, ruthenium, a combination or an
alloy of ruthenium and tungsten, or a combination of titanium
nitride, ruthenium, and tungsten, the at least one charge storage
region can comprises a tunneling dielectric, a blocking dielectric
layer, and either a plurality of floating gates or a charge
trapping layer located between the tunneling dielectric layer and
the blocking dielectric layer. An end portion of each of the
plurality of word lines 46 in a device region can comprise a
control gate electrode located adjacent to the at least one charge
storage region. A plurality of contact via structures contacting
the word lines 46 can be located in a contact region 300. The
plurality of word lines 46 extends from the device region 100 to
the contact region 300. The backside contact via structure 76 can
be a source line that extends through a dielectric insulated
trench, i.e., the backside contact trench 79 filled with the
dielectric spacer 74 and the backside contact via structure 76, in
the stack to electrically contact the source region (not shown).
The source region can be in contact with the horizontal portion of
the semiconductor channel in an upper portion of the semiconductor
material layer 10.
[0141] A drain line, as embodied as a conductive line structure 92
that contacts a drain contact via structure 88, electrically
contacts an upper portion of the semiconductor channel (601, 602).
As used herein, a first element "electrically contacts" a second
element if the first element is electrically shorted to the second
element. An array of drain regions 63 contacts a respective
semiconductor channel (601, 602) within the array of memory stack
structures 55. A top surface of the dielectric material layer,
i.e., the insulating cap layer 70, can be coplanar with top
surfaces of the drain regions 63.
[0142] The exemplary structure of the present disclosure can
comprise a three-dimensional memory device, which comprises a stack
(32, 46) of alternating layers comprising insulator layers 32 and
electrically conductive layers 46 and located over a substrate (9,
10), a memory opening extending through the stack (32, 46), and a
memory film 50 and a semiconductor channel (601, 602) located
within the memory opening. Each of the electrically conductive
layers 46 comprises at least a cobalt portion 48. The electrically
conductive layers 46 comprise a first control gate electrode
located in a first device level, and a second control gate
electrode located in a second device level that is located below
the first device level.
[0143] Although the foregoing refers to particular preferred
embodiments, it will be understood that the disclosure is not so
limited. It will occur to those of ordinary skill in the art that
various modifications may be made to the disclosed embodiments and
that such modifications are intended to be within the scope of the
disclosure. Where an embodiment employing a particular structure
and/or configuration is illustrated in the present disclosure, it
is understood that the present disclosure may be practiced with any
other compatible structures and/or configurations that are
functionally equivalent provided that such substitutions are not
explicitly forbidden or otherwise known to be impossible to one of
ordinary skill in the art. All of the publications, patent
applications and patents cited herein are incorporated herein by
reference in their entirety.
* * * * *