U.S. patent application number 15/183195 was filed with the patent office on 2017-09-21 for three-dimensional memory device containing annular etch-stop spacer and method of making thereof.
The applicant listed for this patent is SANDISK TECHNOLOGIES LLC. Invention is credited to Ryoichi EHARA, Kota FUNAYAMA, Youko FURIHATA, Zhenyu LU, Tadashi NAKAMURA, Masanori TSUTSUMI, Tong ZHANG.
Application Number | 20170271261 15/183195 |
Document ID | / |
Family ID | 58191610 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170271261 |
Kind Code |
A1 |
TSUTSUMI; Masanori ; et
al. |
September 21, 2017 |
THREE-DIMENSIONAL MEMORY DEVICE CONTAINING ANNULAR ETCH-STOP SPACER
AND METHOD OF MAKING THEREOF
Abstract
A method of forming a monolithic three-dimensional memory device
includes forming a first alternating stack over a substrate,
forming an insulating cap layer, forming a first memory opening
through the insulating cap layer and the first alternating stack,
forming a sacrificial pillar structure in the first memory opening,
forming a second alternating stack, forming a second memory
opening, forming an inter-stack memory opening, forming a memory
film and a first semiconductor channel layer in the inter-stack
memory opening, anisotropically etching a horizontal bottom portion
of the memory film and the first semiconductor channel layer to
expose the substrate at the bottom of the inter-stack memory
opening such that damage to portions of the first semiconductor
channel layer and the memory film located adjacent to the
insulating cap layer is reduced or avoided, and forming a second
semiconductor channel layer in contact with the exposed substrate
in the inter-stack memory opening.
Inventors: |
TSUTSUMI; Masanori;
(Yokkaichi, JP) ; FUNAYAMA; Kota; (Yokkaichi,
JP) ; EHARA; Ryoichi; (Yokkaichi, JP) ;
FURIHATA; Youko; (Yokkaichi, JP) ; LU; Zhenyu;
(Milpitas, CA) ; ZHANG; Tong; (Palo Alto, CA)
; NAKAMURA; Tadashi; (Yokkaichi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SANDISK TECHNOLOGIES LLC |
PLANO |
TX |
US |
|
|
Family ID: |
58191610 |
Appl. No.: |
15/183195 |
Filed: |
June 15, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15071575 |
Mar 16, 2016 |
|
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15183195 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 27/1157 20130101;
H01L 27/11582 20130101; H01L 21/76816 20130101; H01L 27/11565
20130101 |
International
Class: |
H01L 23/528 20060101
H01L023/528; H01L 23/522 20060101 H01L023/522; H01L 21/768 20060101
H01L021/768; H01L 27/115 20060101 H01L027/115 |
Claims
1-33. (canceled)
34. A monolithic three-dimensional memory device, comprising: a
first alternating stack of first insulating layers and first
electrically conductive layers located over a top surface of a
substrate; an insulating cap layer overlying the first alternating
stack; a second alternating stack of second insulating layers and
second electrically conductive layers overlying the insulating cap
layer; and a memory stack structure extending through the second
alternating stack, the insulating cap layer, and the first
alternating stack and comprising a semiconductor channel and a
memory film including a plurality of charge storage regions,
wherein: the insulating cap layer comprises a first concave surface
having a first radius of curvature, laterally surrounding the
memory stack structure, and adjoined to an upper periphery of a
substantially vertical sidewall of the memory stack structure; and
the insulating cap layer comprises a second concave surface having
a second radius of curvature that is greater than the first radius
of curvature, laterally surrounding the memory stack structure, and
adjoined to an upper periphery of the first concave surface
35. The monolithic three-dimensional memory device of claim 34,
wherein the memory stacks structure contains a tapered portion
adjacent to the insulating cap layer.
36. The monolithic three-dimensional memory device of claim 34,
wherein: an upper periphery of the second concave surface is
adjoined to a lower periphery of a substantially vertical sidewall
of the insulating cap layer; a first convex sidewall of the memory
stack structure contacts the first concave sidewall of the
insulating cap layer; and a second convex sidewall of the memory
stack structure contacts the second concave sidewall of the
insulating cap layer.
37. The monolithic three-dimensional memory device of claim 34,
further comprising an annular spacer that laterally surrounds the
memory stack structure, wherein: a first convex sidewall of the
annular spacer contacts the first concave sidewall of the
insulating cap layer; and a second convex sidewall of the annular
spacer contacts the second concave sidewall of the insulating cap
layer.
Description
FIELD
[0001] The present application is a continuation-in-part
application of U.S. application Ser. No. 15/071,575 filed on Mar.
16, 2016, the entire contents of which are incorporated herein by
reference.
FIELD
[0002] The present disclosure relates generally to the field of
three-dimensional memory devices and specifically to
three-dimensional memory devices including a vertical stack of
multilevel memory arrays and methods of making the same.
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
monolithic three-dimensional memory device is provided, which
comprises: a first alternating stack of first insulating layers and
first electrically conductive layers located over a top surface of
a substrate; an insulating cap layer overlying the first
alternating stack; a second alternating stack of second insulating
layers and second electrically conductive layers overlying the
insulating cap layer; a memory stack structure extending through
the second alternating stack, the insulating cap layer, and the
first alternating stack and comprising a semiconductor channel and
a memory film including a plurality of charge storage regions; and
an annular spacer located within the insulating cap layer and
laterally surrounding the memory stack structure.
[0005] According to another aspect of the present disclosure, a
method of forming a monolithic three-dimensional memory device
includes forming a first alternating stack of first insulating
layers and first spacer material layers over a substrate, forming
an insulating cap layer over the first alternating stack, forming a
first memory opening through the insulating cap layer and the first
alternating stack, forming a sacrificial pillar structure in the
first memory opening, forming a second alternating stack of second
insulating layers and second spacer material layers over the
insulating cap layer, forming a second memory opening through the
second alternating stack, forming an inter-stack memory opening by
removing the sacrificial pillar structure, forming a memory film
and a first semiconductor channel layer in the inter-stack memory
opening, anisotropically etching a horizontal bottom portion of the
memory film and the first semiconductor channel layer to expose the
substrate at the bottom of the inter-stack memory opening such that
damage to portions of the first semiconductor channel layer and the
memory film located adjacent to the insulating cap layer is reduced
or avoided, and forming a second semiconductor channel layer in
contact with the exposed substrate in the inter-stack memory
opening.
[0006] According to yet another aspect of the present disclosure, a
monolithic three-dimensional memory device is provided, which
comprises: a first alternating stack of first insulating layers and
first electrically conductive layers located over a top surface of
a substrate; an insulating cap layer overlying the first
alternating stack; a second alternating stack of second insulating
layers and second electrically conductive layers overlying the
insulating cap layer; and a memory stack structure extending
through the second alternating stack, the insulating cap layer, and
the first alternating stack and comprising a semiconductor channel
and a memory film including a plurality of charge storage regions.
The insulating cap layer comprises a first concave surface having a
first radius of curvature, laterally surrounding the memory stack
structure, and adjoined to an upper periphery of a substantially
vertical sidewall of the memory stack structure. The insulating cap
layer comprises a second concave surface having a second radius of
curvature that is greater than the first radius of curvature,
laterally surrounding the memory stack structure, and adjoined to
an upper periphery of the first concave surface.
[0007] According to still another aspect of the present disclosure,
a method of forming a device includes forming a first alternating
stack of first insulating layers and first spacer material layers
over a substrate; forming an insulating cap layer over the first
alternating stack; forming a sacrificial material portion in a
first memory opening extending through the insulating cap layer and
the first alternating stack; performing a set of etch steps at
least twice, the set of etch steps comprising a recess etch step
that vertically recesses the top surface of the sacrificial
material portion downward, and an isotropic etch step that
isotropically etches a material of the insulating cap layer
selective to the sacrificial material portion, wherein a remaining
portion of the sacrificial material portion constitutes a
sacrificial pillar structure; forming an fill material portion in
an upper portion of the memory opening that overlies the
sacrificial pillar structure; forming a second alternating stack of
second insulating layers and second spacer material layers over the
insulating cap layer; forming a second memory opening through the
second alternating stack; and forming an inter-stack memory opening
by removing the sacrificial pillar structure from below the second
memory opening.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a vertical cross-sectional view of a first
exemplary structure after formation of a first alternating stack of
first insulating layers and first sacrificial material layers and
formation of an overlying first insulating cap layer according to
an embodiment of the present disclosure.
[0009] FIG. 2 is a vertical cross-sectional view of the first
exemplary structure after formation of lower memory openings,
optional epitaxial channel portions, and semiconductor oxide
portions according to an embodiment of the present disclosure.
[0010] FIG. 3 is a vertical cross-sectional view of the first
exemplary structure after deposition of a sacrificial fill material
layer according to an embodiment of the present disclosure.
[0011] FIG. 4 is a vertical cross-sectional view of the first
exemplary structure after formation of sacrificial pillar
structures according to an embodiment of the present
disclosure.
[0012] FIG. 5 is a vertical cross-sectional view of the first
exemplary structure after recessing the first insulating cap layer
according to an embodiment of the present disclosure.
[0013] FIG. 6 is a vertical cross-sectional view of the first
exemplary structure after formatting of annular spacers around
protruding portions of the sacrificial pillar structures according
to an embodiment of the present disclosure.
[0014] FIG. 7 is a vertical cross-sectional view of the first
exemplary structure after deposition and planarization of a second
insulating cap layer according to an embodiment of the present
disclosure.
[0015] FIG. 8 is a vertical cross-sectional view of the first
exemplary structure after formation of a second alternating stack
of second insulating layers and second sacrificial material layers
according to an embodiment of the present disclosure.
[0016] FIG. 9 is a vertical cross-sectional view of the first
exemplary structure after formation of second memory openings
according to an embodiment of the present disclosure.
[0017] FIG. 10 is a vertical cross-sectional view of the first
exemplary structure after removal of the sacrificial pillar
structures to form memory openings according to an embodiment of
the present disclosure.
[0018] FIG. 11 is a vertical cross-sectional view of the first
exemplary structure after formation of memory stack structures,
dielectric cores, and drain regions according to an embodiment of
the present disclosure.
[0019] FIG. 12A-12D are sequential vertical cross-sectional views
of a joint region during formation of a second memory opening,
removal of an underlying sacrificial pillar structure, and
formation of a memory stack structure and a dielectric core
according to an embodiment of the present disclosure.
[0020] FIG. 13 is a vertical cross-sectional view of a reference
structure for comparison with the first exemplary structure
according to an embodiment of the present disclosure.
[0021] FIG. 14 is a vertical cross-sectional view of the first
exemplary structure after formation of backside trenches according
to an embodiment of the present disclosure.
[0022] FIG. 15 is a vertical cross-sectional view of the first
exemplary structure after formation of backside recesses by removal
of the sacrificial material layers according to an embodiment of
the present disclosure.
[0023] FIG. 16 is a vertical cross-sectional view of the first
exemplary structure after formation of a gate dielectric layer
according to an embodiment of the present disclosure.
[0024] FIG. 17 is a vertical cross-sectional view of the first
exemplary structure after formation of electrically conductive
layers according to an embodiment of the present disclosure.
[0025] FIG. 18 is a vertical cross-sectional view of the first
exemplary structure after removal of residual materials from the
backside trenches, formation of source regions, and formation of
insulating spacers and backside contact structures according to an
embodiment of the present disclosure.
[0026] FIG. 19 is vertical cross-sectional view of an alternate
embodiment of the first exemplary structure after formation of
upper sacrificial pillar structures and backside contact structures
according to an embodiment of the present disclosure.
[0027] FIG. 20 is a vertical cross-sectional view of the alternate
embodiment of the first exemplary structure after removal of the
sacrificial pillar structures according to an embodiment of the
present disclosure.
[0028] FIG. 21 is a vertical cross-sectional view of the alternate
embodiment of the first exemplary structure after formation of
memory stack structures, dielectric cores, and drain regions
according to an embodiment of the present disclosure.
[0029] FIG. 22 is a vertical cross-sectional view of a second
exemplary structure after formation of sacrificial pillar
structures according to an embodiment of the present
disclosure.
[0030] FIG. 23 is a vertical cross-sectional view of the second
exemplary structure after a first isotropic etch process that
etches a first insulating cap layer according to an embodiment of
the present disclosure.
[0031] FIG. 24 is a vertical cross-sectional view of the second
exemplary structure after recessing the sacrificial pillar
structures according to an embodiment of the present
disclosure.
[0032] FIG. 25 is a vertical cross-sectional view of the second
exemplary structure after a second isotropic etch process that
etches the first insulating cap layer according to an embodiment of
the present disclosure.
[0033] FIG. 26 is a vertical cross-sectional view of the second
exemplary structure after formation of an etch stop material
portion according to an embodiment of the present disclosure.
[0034] FIG. 27 is a vertical cross-sectional view of the second
exemplary structure after formation of a second alternating stack
of second insulating layers and second sacrificial material layers
according to an embodiment of the present disclosure.
[0035] FIG. 28 is a vertical cross-sectional view of the second
exemplary structure after formation of inter-stack memory openings
according to an embodiment of the present disclosure.
[0036] FIG. 29A is a vertical cross-sectional view of the second
exemplary structure after formation of memory stack structures and
backside contact via structures according to an embodiment of the
present disclosure.
[0037] FIG. 29B is a magnified view of a region of the second
exemplary structure of FIG. 29A.
[0038] FIG. 30 is a vertical cross-sectional view of an alternative
embodiment of the second exemplary structure according to an
embodiment of the present disclosure.
[0039] FIG. 31 is a vertical cross-sectional view of a third
exemplary structure after isotropically etching a first insulating
cap layer according to an embodiment of the present disclosure.
[0040] FIG. 32 is a vertical cross-sectional view of the third
exemplary structure after formation of a conformal spacer material
layer according to an embodiment of the present disclosure.
[0041] FIG. 33 is a vertical cross-sectional view of the third
exemplary structure after formation of annular spacers according to
an embodiment of the present disclosure.
[0042] FIG. 34 is a vertical cross-sectional view of the third
exemplary structure after formation of fill material portions
according to an embodiment of the present disclosure.
[0043] FIGS. 35A and 35B are vertical cross-sectional views of the
third exemplary structure after formation of memory stack
structures and backside contact structures according to an
embodiment of the present disclosure.
[0044] FIG. 36 is a vertical cross-sectional view of a fourth
exemplary structure after formation of etch stop material portions
according to an embodiment of the present disclosure.
[0045] FIG. 37 is a vertical cross-sectional view of the fourth
exemplary structure after formation of a second alternating stack
of second insulating layers and second sacrificial material layers
according to an embodiment of the present disclosure.
[0046] FIG. 38 is a vertical cross-sectional view of the fourth
exemplary structure after formation of second memory openings
according to an embodiment of the present disclosure.
[0047] FIG. 39 is a vertical cross-sectional view of the fourth
exemplary structure after formation of memory stack structures and
backside contact structures according to an embodiment of the
present disclosure.
[0048] FIGS. 40A-40C illustrate an exemplary processing sequence
that can be employed to form substantially vertical sidewalls of
first memory openings through the first alternating stack of any of
the exemplary structures of the present disclosure.
[0049] FIGS. 41A and 41B are vertical cross-sectional views of an
alternative embodiment of the fourth exemplary structure after
formation of the recess regions and the etch stop material
portions, respectively, according to an embodiment of the present
disclosure.
[0050] FIGS. 42A and 42B are vertical cross-sectional views of the
alternative embodiment of the fourth exemplary structure after
formation of a second alternating stack and second memory openings
according to an embodiment of the present disclosure.
[0051] FIG. 43 is a vertical cross-sectional view of the
alternative embodiment of the fourth exemplary structure after
formation of memory stack structures according to an embodiment of
the present disclosure.
[0052] FIG. 44 is a vertical cross-sectional view of a fifth
exemplary structure after formation of etch stop material portions
according to an embodiment of the present disclosure.
[0053] FIGS. 45A and 45B are vertical cross-sectional views of the
fifth exemplary structure after formation of a second alternating
stack and second memory openings according to an embodiment of the
present disclosure.
[0054] FIG. 46 is a vertical cross-sectional view of the fifth
exemplary structure after formation of memory stack structures
according to an embodiment of the present disclosure.
DETAILED DESCRIPTION
[0055] As discussed above, the present disclosure is directed to
three-dimensional memory devices including a vertical stack of
multilevel memory arrays and methods of making the same, the
various aspects of which are described below. An embodiment of the
disclosure can be employed to form 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.
[0056] As used herein, a "layer" refers to a material portion
including a region having a thickness. A layer may extend over the
entirety of an underlying or overlying structure, or may have an
extent less than the extent of an underlying or overlying
structure. Further, a layer may be a region of a homogeneous or
inhomogeneous continuous structure that has a thickness less than
the thickness of the continuous structure. For example, a layer may
be located between any pair of horizontal planes between, or at, a
top surface and a bottom surface of the continuous structure. A
layer may extend horizontally, vertically, and/or along a tapered
surface. A substrate may be a layer, may include one or more layers
therein, and/or may have one or more layer thereupon, thereabove,
and/or therebelow.
[0057] 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.
[0058] Referring to FIG. 1, a first 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 first exemplary
structure includes a substrate, which can be a semiconductor
substrate. The substrate can include a substrate semiconductor
layer 10. The substrate semiconductor layer 10 can be 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
semiconductor layer 10 can comprise a single crystalline
semiconductor material, such as a single crystal silicon wafer.
[0059] 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 conductivity 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 "insulating 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 10. While the substrate semiconductor
layer 10 is alternatively referred to as the substrate 10 in the
present disclosure, it is understood that the substrate 10 may
optionally include additional material layers (such as a handle
substrate and a buried insulator layer as in the case of a
semiconductor-on-insulator substrate).
[0060] The first exemplary structure includes a device region, in
which memory devices can be subsequently formed, and a contact
region (not shown), in which stepped surfaces are subsequently
formed. As used herein, a "contact region" refers to a region in
which contact via structures are to be formed. At least one
semiconductor device for a peripheral circuitry can be formed in a
peripheral device region (not shown). The at least one
semiconductor device can include, for example, one or more field
effect transistors. 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.
[0061] Optionally, a doped semiconductor well (not separately
shown) can be provided in an upper portion of the substrate
semiconductor layer 10. The doped semiconductor well can be formed,
for example, by implantation of electrical dopants (p-type dopants
or n-type dopants) into an upper portion of the substrate
semiconductor layer 10, or by deposition of a single crystalline
semiconductor material, for example, by selective epitaxy. In one
embodiment, the doped semiconductor well can include a single
crystalline semiconductor material (e.g., p-well).
[0062] An alternating stack of first material layers and second
material layers is subsequently formed. Each first material layer
can include a first material, and each second material layer can
include a second material that is different from the first
material. The alternating stack is herein referred to as a first
alternating stack. In one embodiment, the first material layers and
the second material layers can be first insulating layers 132 and
first sacrificial material layers 142, respectively. In one
embodiment, each first insulating layer 132 can include a first
insulating material, and each first sacrificial material layer 142
can include a first sacrificial material. An alternating plurality
of first insulating layers 132 and first sacrificial material
layers 142 is formed over the semiconductor substrate layer 10,
which is a portion of a substrate. As used herein, a "sacrificial
material" refers to a material that is removed during a subsequent
processing step.
[0063] As used herein, an alternating stack 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.
[0064] The first alternating stack (132, 142) can include first
insulating layers 132 composed of the first material, and first
sacrificial material layers 142 composed of the second material,
which is different from the first material. The first material of
the first insulating layers 132 can be at least one insulating
material. Insulating materials that can be employed for the first
insulating layers 132 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 first
insulating layers 132 can be silicon oxide.
[0065] The second material of the first sacrificial material layers
142 is a sacrificial material that can be removed selective to the
first material of the first insulating layers 132. 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.
[0066] The first sacrificial material layers 142 may comprise an
insulating material, a semiconductor material, or a conductive
material. The second material of the first sacrificial material
layers 142 can be subsequently replaced with electrically
conductive electrodes which can function, for example, as control
gate electrodes of a vertical NAND device. In one embodiment, the
first sacrificial material layers 142 can be material layers that
comprise silicon nitride.
[0067] In one embodiment, the first insulating layers 132 can
include silicon oxide, and sacrificial material layers can include
silicon nitride sacrificial material layers. The first material of
the first insulating layers 132 can be deposited, for example, by
chemical vapor deposition (CVD). For example, if silicon oxide is
employed for the first insulating layers 132,
tetraethylorthosilicate (TEOS) can be employed as the precursor
material for the CVD process. The second material of the first
sacrificial material layers 142 can be formed, for example, CVD or
atomic layer deposition (ALD).
[0068] The thicknesses of the first insulating layers 132 and the
first sacrificial material layers 142 can be in a range from 20 nm
to 50 nm, although lesser and greater thicknesses can be employed
for each first insulating layer 132 and for each first sacrificial
material layer 142. The number of repetitions of the pairs of a
first insulating layer 132 and a first sacrificial material layer
142 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. In
one embodiment, each first sacrificial material layer 142 in the
first alternating stack (132, 142) can have a uniform thickness
that is substantially invariant within each respective first
sacrificial material layer 142.
[0069] A first insulating cap layer 170A is sequentially formed.
The first insulating cap layer 170A includes a dielectric material,
which can be any dielectric material that can be employed for the
first insulating layers 132. In one embodiment, the first
insulating cap layer 170A includes the same dielectric material as
the first insulating layers 132. The thickness of the insulating
cap layer 170A can be in a range from 20 nm to 300 nm, although
lesser and greater thicknesses can also be employed.
[0070] Optionally, the first insulating cap layer 170A and the
first alternating stack (132, 142) can be patterned to form first
stepped surfaces in a contact region (not shown). The contact
region includes a first stepped area in which the first stepped
surfaces are formed, and a second stepped area in which additional
stepped surfaces are to be subsequently formed in a second tier
structure (to be subsequently formed over a first tier structure).
The first stepped surfaces can be formed, for example, by forming a
mask layer with an opening therein, etching a cavity within the
levels of the first insulating cap layer 170A, and iteratively
expanding the etched area and vertically recessing the cavity by
etching each pair of a first insulating layer 132 and a first
sacrificial material layer 142 located directly underneath the
bottom surface of the etched cavity within the etched area. A
dielectric material can be deposited to fill the first stepped
cavity to form a first retro-stepped dielectric material portion
(not shown). 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.
[0071] Referring to FIG. 2, lower memory openings 121 extending to
a top surface of the substrate 10 are formed through the first
alternating stack (132, 142). The lower memory openings 121 can be
formed in the device region. For example, a lithographic material
stack (not shown) including at least a photoresist layer can be
formed over the first insulating cap layer 170A, and can be
lithographically patterned to form openings within the lithographic
material stack. The pattern in the lithographic material stack can
be transferred through the first insulating cap layer 170A and
through the entirety of the first alternating stack (132, 142) by
at least one anisotropic etch that employs the patterned
lithographic material stack as an etch mask. Portions of the first
insulating cap layer 170A and the first alternating stack (132,
142) underlying the openings in the patterned lithographic material
stack are etched to form the lower memory openings 121. In other
words, the transfer of the pattern in the patterned lithographic
material stack through the first insulating cap layer 170A and the
first alternating stack (132, 142) forms the lower memory openings
121.
[0072] In one embodiment, the chemistry of the anisotropic etch
process employed to etch through the materials of the first
alternating stack (132, 142) can alternate to optimize etching of
the first and second materials in the first alternating stack (132,
142). The anisotropic etch can be, for example, a series of
reactive ion etches. The sidewalls of the lower memory openings 121
can be substantially vertical, or can be tapered. Subsequently, the
patterned lithographic material stack can be subsequently removed,
for example, by ashing.
[0073] A selective epitaxy process can be performed to deposit a
semiconductor material on physically exposed semiconductor
surfaces. Specifically, epitaxial channel portions 11 can grow from
the semiconductor surfaces at the bottom of the lower memory
openings 121 during the selective epitaxy process. The epitaxial
channel portions 11 comprise a single crystalline semiconductor
material in epitaxial alignment with the single crystalline
substrate semiconductor material of the substrate semiconductor
layer 10.
[0074] In one embodiment, the deposited semiconductor material may
be doped with in-situ doping of a p-type dopant or an n-type
dopant. Thus, the epitaxial channel portions 11 can be doped with
electrical dopants of a suitable conductivity type. In one
embodiment, the substrate semiconductor layer 10 and the epitaxial
channel portions 11 can have a doping of the first conductivity
type (e.g., p-type). The epitaxial channel portions 11 may comprise
silicon.
[0075] The selective epitaxy process can be performed, for example,
by sequentially or simultaneously flowing a reactant gas (such as
SiH.sub.4, SiH.sub.2Cl.sub.2, SiHCl.sub.3, SiCl.sub.4,
Si.sub.2H.sub.6, GeH.sub.4, Ge.sub.2H.sub.6, other semiconductor
precursor gases, or combinations there) with an etchant gas (such
as HCl). The deposition rate of the semiconductor material on
amorphous surfaces (such as the surfaces of dielectric materials)
is less than the etch rate of the semiconductor material by the
etchant, while the deposition rate of the semiconductor material on
crystalline surfaces (such as the top surface of the substrate
semiconductor layer 10) is greater than the etch rate of the
semiconductor material by the etchant. Thus, the semiconductor
material is deposited only on the semiconductor surface, which is
the physically exposed portion of the top surface of the substrate
semiconductor layer 10. The process conditions (such as the
deposition temperature, the partial pressure of the various gases
in a process chamber, etc.) can be selected such that the deposited
semiconductor material is epitaxial, i.e., single crystalline
silicon or another semiconductor material with atomic alignment
with the single crystalline structure of the substrate
semiconductor layer 10 (e.g., p-well). Each epitaxial channel
portion 11 can be formed at a bottom portion of a respective lower
memory opening 121.
[0076] Subsequently, a thermal oxidation process or a plasma
oxidation process can be performed to oxidize a surface portion of
each epitaxial channel portion 11, thereby converting the surface
portion into a respective semiconductor oxide portion 13. The
thickness of the semiconductor oxide portion 13 can be in a range
from 1 nm to 10 nm, although lesser and greater thicknesses can
also be employed.
[0077] Referring to FIG. 3, a sacrificial fill material layer 131L
can be deposited over the epitaxial channel portions 11 in the
lower memory openings 121. The sacrificial fill material layer 131L
includes a temporary material, i.e., a sacrificial material, which
is subsequently removed selective to the materials of the first
insulator layers 132 and the first sacrificial material layers 142.
In one embodiment, the sacrificial fill material layer 131L
includes a semiconductor material such as silicon, a
silicon-germanium alloy, germanium, a III-V compound semiconductor
material, or a combination thereof. The sacrificial fill material
layer 131L may be formed by a non-conformal deposition or a
conformal deposition method. In one embodiment, a cavity may be
formed inside one or more of the lower memory openings 121 in case
a non-conformal deposition method is employed to form the
sacrificial fill material layer 131L. In one embodiment, the
sacrificial fill material layer 131L can be formed directly on the
semiconductor oxide portions 13.
[0078] In one embodiment, the sacrificial fill material layer 131L
can include an undoped semiconductor material. As used herein, an
"undoped" semiconductor material refers to a semiconductor material
that is intrinsic, or not intentionally doped, and thus, having a
low dopant concentration such as less than
1.0.times.10.sup.17/cm.sup.3. In one embodiment, the sacrificial
fill material layer 131L can be an amorphous or polycrystalline
silicon layer including undoped amorphous or polycrystalline
silicon.
[0079] Referring to FIG. 4, portions of the deposited sacrificial
material can be removed from above the first insulating cap layer
170A. Specifically, the sacrificial fill material layer 131L can be
recessed to a top surface of the first insulating cap layer 170A
employing a planarization process. The planarization process can
include a recess etch, chemical mechanical planarization (CMP), or
a combination thereof. The top surface of the first insulating
layer 170A can be employed as an etch stop layer or a planarization
stop layer. Each remaining portion of the sacrificial material in a
lower memory opening constitutes a sacrificial pillar structure 3A.
The top surfaces of the sacrificial pillar structures 3A can be
coplanar with the top surface of the first insulating cap layer
170A. The sacrificial pillar structures 3A may, or may not, include
cavities therein.
[0080] Referring to FIG. 5, the first insulating cap layer 170A can
be recessed selective to the material of the sacrificial pillar
structures 3A. The recessing of the first insulating cap layer 170A
with respect to the top surfaces of the sacrificial pillar
structures 3A can be performed employing a selective etch process,
which can be an isotropic etch or an anisotropic etch. In an
illustrative example, if the first insulating cap layer 170A
includes silicon oxide and if the sacrificial pillar structures 3A
include semiconductor materials, the first insulating cap layer
170A can be recessed by a wet etch employing KOH. The recess depth
can be in a range from 10% to 90% of the initial thickness of the
first insulating cap layer 170A, and may be in a range from 25% to
75% of the initial thickness of the first insulating cap layer
170A. The recess depth is the same as the height of the protruding
portions 3P of the sacrificial pillar structures above the recessed
top surface of the first insulating cap layer 170A. In an
illustrative example, the recess depth can be in a range from 20 nm
to 200 nm, although lesser and greater thicknesses can also be
employed.
[0081] Referring to FIG. 6, annular spacers 172 can be formed
around protruding portions 3P of the sacrificial pillar structures
3A. As used herein, an "annular" element refers to an element that
is topologically homeomorphic to a torus, and thus, topologically
homeomorphic to a ring with a single hole. As used herein, a first
element is "topologically homeomorphic" to a second element if the
first element can be continuously stretched into the second element
without destroying a pre-existing hole and without creating a new
hole. Each annular spacer 172 can be formed on sidewalls of the
protruding portion 3P of a respective sacrificial pillar structure
3A above a recessed top surface of the first insulating cap layer
170A. For example, a spacer material layer can be formed over the
sacrificial pillar structures 3A and over the recessed top surface
of the first insulating cap layer and around the protruding portion
of the sacrificial pillar structures 3A. The spacer material layer
includes a material that is different from the material of the
sacrificial pillar structures 3A. In one embodiment, the
sacrificial material layer includes a semiconductor material that
is different from the material of the sacrificial pillar structures
3A. In one embodiment, the sacrificial pillar structures 3A include
undoped amorphous or polycrystalline silicon, and the spacer
material layer includes a heavily doped semiconductor material
(such as heavily doped silicon, such as heavily doped amorphous or
polycrystalline silicon). As used herein, a "heavily doped"
semiconductor material refers to a semiconductor material that is
doped with p-type dopants or n-type dopants at a dopant
concentration greater than 1.0.times.10.sup.18 /cm.sup.3, such as
1.0.times.10.sup.19 /cm.sup.3 to 1.0.times.10.sup.22 /cm.sup.3,
including 1.0.times.10.sup.20 /cm.sup.3 to 1.0.times.10.sup.21
/cm.sup.3. In one embodiment, the spacer material layer can be a
conformal material layer having a uniform thickness in a range from
20 nm to 100 nm, although lesser and greater thicknesses can also
be employed.
[0082] The spacer material layer can be anisotropically etched
using any suitable sidewall spacer anisotropic etch to remove
horizontal portions of the spacer material layer from above the top
surfaces of the sacrificial pillar structures 3A and from portions
of the recessed top surface of the first insulating cap layer 170A
that are spaced from the sidewalls of the sacrificial pillar
structures 3A by more than the thickness of the spacer material
layer. Each remaining annular portion of the spacer material layer
constitutes an annular spacer 172. The lateral thickness of each
annular spacer 172, as measured at the bottom portion thereof
between the outer sidewall and a most proximate portion of the
inner sidewall, can be substantially the same as the initial
thickness of the sacrificial material layer.
[0083] Referring to FIG. 7, a second insulating cap layer 170B can
be deposited over the annular spacers 172, the sacrificial pillar
structures 3A, and the physically exposed surfaces of the first
insulating cap layer 170A. The second insulating cap layer 170B
includes a dielectric material that can be subsequently planarized.
For example, the second insulating cap layer 170B can include doped
silicate glass, undoped silicate glass (e.g., silicon oxide
deposited by CVD using a TEOS source), or organosilicate glass. The
second insulating cap layer 170B can be formed employing chemical
vapor deposition (CVD) or spin-on coating.
[0084] Subsequently, the second insulating cap layer 170B can be
planarized to remove portions above a horizontal plane including
the top surfaces of the sacrificial pillar structures 3A. The
planarization of the second insulating cap layer 170B can be
performed, for example, by chemical mechanical planarization
employing the sacrificial pillar structures 3A as stopping
structures. In one embodiment, a planarized top surface of the
second insulating cap layer 170B can be within a same horizontal
plane as the topmost surfaces of each annular spacer 172. The first
insulating cap layer 172A and the second insulating cap layer 172B
are collectively referred to a first insulating cap layer 170. The
first alternating stack (132, 142), the first insulating cap layer
170, and elements embedded in the first alternating stack (132,
142) (e.g., elements 3A and 172) collectively constitute a first
tier structure (132, 142, 170, 3A).
[0085] Referring to FIG. 8, a second tier structure can be formed
over the first tier structure (132, 142, 170, 3A). The second tier
structure can include an additional alternating stack of insulating
layers and spacer material layers, which can be sacrificial
material layers. For example, a second alternating stack (232, 242)
of material layers can be subsequently formed on the top surface of
the first alternating stack (132, 142). The second stack (232, 242)
includes an alternating plurality of third material layers and
fourth material layers. Each third material layer can include a
third material, and each fourth material layer can include a fourth
material that is different from the third material. In one
embodiment, the third material can be the same as the first
material of the first insulating layer 132, and the fourth material
can be the same as the second material of the first sacrificial
material layers 142.
[0086] In one embodiment, the third material layers can be second
insulating layers 232 and the fourth material layers can be second
spacer material layers that provide vertical spacing between each
vertically neighboring pair of the second insulating layers 232. In
one embodiment, the third material layers and the fourth material
layers can be second insulating layers 232 and second sacrificial
material layers 242, respectively. The third material of the second
insulating layers 232 may be at least one insulating material. The
fourth material of the second sacrificial material layers 242 may
be a sacrificial material that can be removed selective to the
third material of the second insulating layers 232. The second
sacrificial material layers 242 may comprise an insulating
material, a semiconductor material, or a conductive material. The
fourth material of the second sacrificial material layers 242 can
be subsequently replaced with electrically conductive electrodes
which can function, for example, as control gate electrodes of a
vertical NAND device.
[0087] In one embodiment, each second insulating layer 232 can
include a second insulating material, and each second sacrificial
material layer 242 can include a second sacrificial material. In
this case, the second stack (232, 242) can include an alternating
plurality of second insulating layers 232 and second sacrificial
material layers 242. The third material of the second insulating
layers 232 can be deposited, for example, by chemical vapor
deposition (CVD). The fourth material of the second sacrificial
material layers 242 can be formed, for example, CVD or atomic layer
deposition (ALD).
[0088] The third material of the second insulating layers 232 can
be at least one insulating material. Insulating materials that can
be employed for the second insulating layers 232 can be any
material that can be employed for the first insulating layers 132.
The fourth material of the second sacrificial material layers 242
is a sacrificial material that can be removed selective to the
third material of the second insulating layers 232. Sacrificial
materials that can be employed for the second sacrificial material
layers 242 can be any material that can be employed for the first
sacrificial material layers 142. In one embodiment, the second
insulating material can be the same as the first insulating
material, and the second sacrificial material can be the same as
the first sacrificial material.
[0089] The thicknesses of the second insulating layers 232 and the
second sacrificial material layers 242 can be in a range from 20 nm
to 50 nm, although lesser and greater thicknesses can be employed
for each second insulating layer 232 and for each second
sacrificial material layer 242. The number of repetitions of the
pairs of a second insulating layer 232 and a second sacrificial
material layer 242 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. In one embodiment, each second sacrificial material layer
242 in the second stack (232, 242) can have a uniform thickness
that is substantially invariant within each respective second
sacrificial material layer 242.
[0090] A second insulating cap layer 270 can be subsequently formed
over the second stack (232, 242). The second insulating cap layer
270 includes a dielectric material that is different from the
material of the second sacrificial material layers 242. In one
embodiment, the insulating cap layer 70 can include silicon oxide.
In one embodiment, the first and second sacrificial material layers
(142, 242) can comprise silicon nitride. Optionally, second stepped
surfaces (not shown) can be region in the contact region in the
same manner as formation of the first stepped surfaces. A second
retro-stepped dielectric material portion may be formed over the
second stepped surfaces.
[0091] Referring to FIG. 9, second memory openings 221 can be
formed through the second tier structure (232, 242, 270) in an area
overlying the lower memory openings 121, i.e., in areas that
substantially coincides with the areas of the lower memory openings
121. The second memory openings 221 can be formed to the top
surface of the sacrificial pillar structures 3A. For example, a
lithographic material stack (not shown) including at least a
photoresist layer can be formed over the second insulating cap
layer 270 and the second tier structure (232, 242, 270), and can be
lithographically patterned to form openings within the lithographic
material stack. The pattern in the lithographic material stack can
be transferred through the entirety of the second tier structure
(232, 242, 270) by at least one anisotropic etch that employs the
patterned lithographic material stack as an etch mask. Portions of
the second insulating cap layer 270 and the second tier structure
(232, 242, 270) underlying the openings in the patterned
lithographic material stack are etched to form the second memory
openings 221. In other words, the transfer of the pattern in the
patterned lithographic material stack through the second insulating
cap layer 270 and the second tier structure (232, 242, 270) forms
the second memory openings 221. While not illustrated in FIG. 9, a
misalignment can occur between the second memory openings 221 and
the lower memory openings 121 due to overlay variations that are
inherent in lithographic alignment of a new pattern (the pattern of
the openings for the second memory openings) with a pre-existing
pattern (the pattern of the sacrificial fill structures 3A).
[0092] In one embodiment, the chemistry of the anisotropic etch
process employed to etch through the materials of the second stack
(232, 242) can alternate to optimize etching of the third and
fourth materials in the second stack (232, 242). The anisotropic
etch can be, for example, a series of reactive ion etches. The
sidewalls of the second memory openings 221 can be substantially
vertical, or can be tapered. In one embodiment, the sacrificial
pillar structures 3A may be employed as stopping structures for the
anisotropic etch process that forms the second memory openings 221.
An overetch into upper portions of the sacrificial pillar
structures 3A can occur during the anisotropic etch. In other
words, the second memory openings 221 can be formed employing an
anisotropic etch process that stops at a height between a first
horizontal plane including topmost surfaces of the annular spacers
172 and a second horizontal plane including bottom surfaces of the
annular spacers 172.
[0093] Referring to FIG. 10, the sacrificial pillar structures 3A
can be removed selective to the materials of the annular spacers
172, the first and second insulating cap layers (170, 270), the
lower and second tier structures (132, 142, 232, 242), and the
semiconductor oxide portions 13. In case the sacrificial pillar
structures 3A comprise an undoped semiconductor material (such as
undoped amorphous silicon or polycrystalline silicon), an etch
chemistry that removes the undoped semiconductor material selective
to dielectric materials and to the material of the annular spacers
172 can be employed. If the annular spacers 172 includes heavily
doped semiconductor material (such as heavily doped amorphous or
polycrystalline silicon), a wet etch employing hot trimethyl-2
hydroxyethyl ammonium hydroxide ("hot TMY") can be employed. A
plurality of memory openings 49 can be formed through the first and
second tier structures (132, 142, 232, 242, 170, 270).
[0094] In one embodiment, removal of the sacrificial pillar
structures 3A can be performed selective to the annular spacers 172
such that the spacers 172 are substantially retained employing an
etch chemistry that provides differential etch rates that depend on
the concentration of electrical dopants (e.g., which etches the
pillar structures 3A at a rate that is at least 50 times greater,
such as 100 to 150 times greater, than the spacers 172). In one
embodiment, the sacrificial pillar structures 3A can include a
first semiconductor material that does not include electrical
dopants or includes electrical dopants at an atomic concentration
less than 1.0.times.10.sup.17/cm.sup.3, and the annular spacers 172
can include a second semiconductor material that includes
electrical dopants at an atomic concentration greater than
1.0.times.10.sup.18/cm.sup.3. In one embodiment, the sacrificial
pillar structures 3A can include amorphous or polycrystalline
silicon that does not include electrical dopants or includes
electrical dopants at an atomic concentration less than
1.0.times.10.sup.17/cm.sup.3, the annular spacers 172 can include
amorphous or polycrystalline silicon that includes electrical
dopants at an atomic concentration greater than
1.0.times.10.sup.18/cm.sup.3, and removal of the sacrificial pillar
structures 3A selective to the annular spacers 172 can be performed
employing hot trimethyl-2 hydroxyethyl ammonium hydroxide.
[0095] Subsequently, semiconductor oxide portions 13 may be
optionally removed to physically expose the top surfaces of the
epitaxial channel portions 11. In one embodiment, the semiconductor
oxide portions 13 can be removed by a wet etch employing
hydrofluoric acid. In another embodiment, the semiconductor oxide
portions are not removed.
[0096] Referring to FIG. 11, memory stack structures 55 can be
formed in the memory openings 49. In an illustrative example, each
memory stack structure 55 can include a memory film 50 and a
vertical semiconductor channel 60. In one embodiment, each memory
film 50 can include a blocking dielectric layer 52, a memory
material layer 54, and a tunneling dielectric layer 56. In one
embodiment, each vertical semiconductor channel 60 can include a
first semiconductor channel 601 and a second semiconductor channel
602.
[0097] The blocking dielectric layer 52 includes a blocking
dielectric layer material such as silicon oxide, a dielectric metal
oxide (such as aluminum oxide), or a combination thereof.
Alternatively, the blocking dielectric layer 52 may be omitted
during this processing step and instead be formed through backside
recesses as will be described in more detail below. In one
embodiment, the memory material layer 54 can be a charge trapping
material including a dielectric charge trapping material, which can
be, for example, silicon nitride.
[0098] The memory material layer 54 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 54 may comprise an insulating charge trapping
material, such as one or more silicon nitride segments.
Alternatively, the memory material layer 54 may comprise conductive
nanoparticles such as metal nanoparticles, which can be, for
example, ruthenium nanoparticles. The memory material layer 54 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 54 can be in a
range from 2 nm to 20 nm, although lesser and greater thicknesses
can also be employed. Each portion of the memory material layer 54
located at the levels of the electrically conductive layers (146,
246).
[0099] The tunneling dielectric layer 56 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 56 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 56 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. The thickness of
the tunneling dielectric layer 56 can be in a range from 2 nm to 20
nm, although lesser and greater thicknesses can also be
employed.
[0100] A first semiconductor channel layer can be deposited over
the memory films 50 by a conformal deposition method such as low
pressure chemical vapor deposition (LPCVD). The thickness of the
first semiconductor channel layer can be in a range from 2 nm to 10
nm, although lesser and greater thicknesses can also be employed.
The first semiconductor channel layer and the memory films 50 can
be anisotropically etched to remove horizontal portions thereof. A
horizontal bottom portion of each memory film 50 can be removed
from the bottom of each memory opening. Each remaining portion of
the first semiconductor channel layer constitutes a first
semiconductor channel 601. The first semiconductor channels can
include 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 channels 601 can include amorphous silicon or
polysilicon. The memory film 50 and the first semiconductor channel
601 are anisotropically etched to remove the memory film 50 and the
first semiconductor channel 601 (and layer 13 if present) at the
bottom of the memory opening 49 to expose the structures 11, while
leaving the memory film 50 and the first semiconductor channel 601
on the sidewalls of the memory opening 49.
[0101] A second semiconductor channel layer can be deposited on the
first semiconductor channels 601 (i.e., the remaining vertical
portions of the first semiconductor channel layer) and on top
surface of the epitaxial channel portions 11 (or of the substrate
semiconductor layer 10 in case the epitaxial channel portions 11
are not present). The second semiconductor channel layer includes a
semiconductor material, which can be any semiconductor material
that can be employed for the first semiconductor channel layer. The
first and second semiconductor channel layers can have a doping of
the first conductivity type (i.e., the same conductivity type as
the substrate semiconductor layer 10) or can be substantially
intrinsic, i.e., having a dopant concentration that does not exceed
1.0.times.1017/cm3. In one embodiment, the second semiconductor
channel layer can include amorphous silicon or polysilicon. The
thickness of the second semiconductor channel layer can be in a
range from 2 nm to 10 nm, although lesser and greater thicknesses
can also be employed.
[0102] A dielectric material can be deposited in cavities
surrounded by the second semiconductor channel layer, and
subsequently recessed below the top surface of the second
dielectric tier cap layer 270. Each remaining portion of the
dielectric material in the memory openings constitutes a dielectric
core 62. A doped semiconductor material having a second
conductivity type (which is the opposite of the first conductivity
type) can be deposited over the dielectric cores 62 and within the
cavities in the memory openings to form drain regions 63. 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 second insulating cap
layer 270, for example, by chemical mechanical planarization (CMP)
or a recess etch to form the drain region 63. Each remaining
portion of the second semiconductor channel layer constitutes a
second semiconductor channel 602. A combination of a first
semiconductor channel 601 and a second semiconductor channel 602
inside a memory opening constitutes a vertical semiconductor
channel 60.
[0103] Each memory film 50 can include a blocking dielectric layer
52 contacting a sidewall of the memory opening, a plurality of
charge storage regions (embodied as portions of a memory material
layer 54 at each level of the sacrificial material layers (142,
242)) located on an inner sidewall of the blocking dielectric layer
52, and a tunneling dielectric layer 56 located inside the
plurality of charge storage regions.
[0104] FIGS. 12A-12D illustrate a joint region between the first
tier structure (132, 142, 170) and the second tier structure (232,
242, 270) during formation of a second memory opening 221
(corresponding to the processing steps of FIG. 9), removal of an
underlying sacrificial pillar structure 3A (corresponding to the
processing steps of FIG. 10), and formation of a memory stack
structure 55 and a dielectric core 62 (corresponding to the
processing steps of FIG. 11), respectively. While FIGS. 9-11
illustrate a configuration in which the overlay variation between
the sacrificial pillar structure 3A and the second memory opening
221 is zero, overlay variations that are inherent in the
lithographic process that provides the pattern for the second
memory openings 221 with respect to the underlying pattern of the
sacrificial pillar structures 3A can cause the lateral offset
between an underlying sacrificial pillar structure 3A and an
overlying second memory opening 221 as illustrated in FIG. 12A. In
other words, sidewalls of the underlying sacrificial pillar
structure 3A can be laterally offset with respect to sidewalls of
the second memory opening 221 that is formed through the second
alternating stack (w32, 242). In this case, a first side of the
annular spacer 172 can be partly etched during an anisotropic etch
that forms the second memory opening 221, and a second side of the
annular spacer 172 that faces the first side may not be etched
during the anisotropic etch.
[0105] Referring to FIG. 12B, the processing steps of FIG. 10 can
be performed to form a memory opening 49 that extends through the
first tier structure (132, 142, 170) and the second tier structure
(232, 242, 270). The memory opening 49 has first horizontal ledge
49A at an interface between the insulating cap layer 170 and the
second alternating stack (232, 242), and a second horizontal ledge
49B that contacts a horizontal surface of the annular spacer 172
between a top surface of the annular spacer 172 and a bottom
surface of the annular spacer 172.
[0106] Referring to FIGS. 12C and 12D, the processing steps of FIG.
11 can be performed to form a memory film 50, a vertical
semiconductor channel 60, and a dielectric core 62. In the first
exemplary structure illustrated in FIGS. 11 and 12D, the memory
film 50 is formed inside a remaining portion of the annular spacer
172 within each memory opening 49.
[0107] Referring to FIG. 13, a reference structure is illustrated
for comparison with the first exemplary structure of embodiments of
the present disclosure. The reference structure can be derived from
the first exemplary structure of FIG. 12A by removing the annular
spacers 172 concurrently with removal of the sacrificial pillar
structure 3A. In that case, substantially horizontal portions (60A,
60B) of the semiconductor channel 60 can face each other in the
memory opening. Portions 60A, 60B are connected by a substantially
vertical portion 60C which together form a convex portion of the
semiconductor channel 60 which bows in an outward direction from
the dielectric fill 62. The convex portion (60A, 60B, 60C)
increases the channel 60 resistance, decreases cell current and
increases electric field concentration. By not removing the annular
spacer 172 and depositing the memory film 50 on the inner sidewalls
of the annular spacer 172 in each memory opening 49, as shown in
FIG. 12D, decreases the channel 60 resistance, increases cell
current and decreases electric field concentration.
[0108] Referring to FIG. 14, a planarization material layer 280 can
be formed over the second insulating cap layer 270. The
planarization material layer 280 may be selected as an in-process
structure that is consumed during subsequent planarization
processes. In one embodiment, the planarization material layer 280
can include a silicon oxide material deposited by chemical vapor
deposition such as tetraethylorthosilicate (TEOS) silicon oxide.
The thickness of the planarization material layer 280 can be in a
range from 50 nm to 300 nm, although lesser and greater thicknesses
can also be employed.
[0109] At least one backside trench 79 can be formed through the
upper and first tier structures, for example, by applying a
photoresist layer (not shown), lithographically patterning the
photoresist layer, and transferring the pattern in the photoresist
layer through the upper and first tier structures employing an
anisotropic etch. The anisotropic etch that forms the at least one
backside trench 79 can stop on the substrate 10. The photoresist
layer can be subsequently removed, for example, by ashing.
[0110] Referring to FIG. 15, an etchant that selectively etches the
materials of the first and second sacrificial material layers (142,
242) with respect to the materials of the first and second
insulating layers (132, 232), the material of the dielectric oxide
layer 51L, and the first and second insulating cap layers (170,
270) can be introduced into the backside trench 79, for example,
employing an isotropic etch process. First backside recesses 143
are formed in volumes from which the first sacrificial material
layers 142 are removed. Second backside recesses 243 are formed in
volumes from which the second sacrificial material layers 242 are
removed. The removal of the materials of the first and second
sacrificial material layers (142, 242) can be selective to the
materials of the first and second insulating layers (132, 232), and
the material of the dielectric oxide layer 51L. In one embodiment,
the first and second sacrificial material layers (142, 242) can
include silicon nitride, and the materials of the first and second
insulating layers (132, 232), can be silicon oxide. In another
embodiment, the first and second sacrificial material layers (142,
242) can include a semiconductor material such as germanium or a
silicon-germanium alloy, and the materials of the first and second
insulating layers (132, 232) can be selected from silicon oxide and
silicon nitride.
[0111] The isotropic etch process 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 backside trench 79. For example, if the first and second
sacrificial material layers (142, 242) include silicon nitride, the
etch process can be a wet etch process in which the first 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.
[0112] Each of the first and second backside recesses (143, 243)
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 of the first and second backside
recesses (143, 243) can be greater than the height of the
respective backside recess (143, 243). A plurality of first
backside recesses 143 can be formed in the volumes from which the
material of the first sacrificial material layers 142 is removed. A
plurality of second backside recesses 243 can be formed in the
volumes from which the material of the second sacrificial material
layers 242 is removed. Each of the first and second backside
recesses (143, 243) can extend substantially parallel to the top
surface of the substrate 10. A backside recess (143, 243) can be
vertically bounded by a top surface of an underlying insulating
layer (132 or 232) and a bottom surface of an overlying insulating
layer (132 or 232). In one embodiment, each of the first and second
backside recesses (143, 243) can have a uniform height
throughout.
[0113] In one embodiment, a sidewall surface of each epitaxial
channel portion 11 and a top surface of a semiconductor material
layer in the substrate (i.e., the substrate semiconductor layer 10)
can be physically exposed below the bottommost first backside
recess 143 after removal of the first and second sacrificial
material layers (142, 242).
[0114] Referring to FIG. 16, a gate dielectric layer 12 can be
formed by converting surface portions of the epitaxial channel
portions 11 and the semiconductor material layer (the substrate
semiconductor layer 10) into a continuous dielectric material
layer. In one embodiment, the gate dielectric layer 12 can be
formed by thermal conversion of the surface portions of the
epitaxial channel portions 11 and the substrate semiconductor layer
10. In one embodiment, the thermal conversion process can include a
thermal oxidation process and/or a thermal nitridation process. In
one embodiment, the gate dielectric layer 12 can include a thermal
oxide of the semiconductor material of the substrate semiconductor
layer 10. The gate dielectric layer 12 can be formed as a single
continuous layer.
[0115] Referring to FIG. 17, a backside blocking dielectric layer
(not shown) can be optionally deposited in the backside recesses
(143, 243) and the backside trenches 79 and over the planarization
dielectric layer 280. The backside blocking dielectric layer can be
deposited on the physically exposed portions of the outer surfaces
of the memory stack structures 55. The backside blocking dielectric
layer includes a dielectric material such as a dielectric metal
oxide, silicon oxide, or a combination thereof. If employed, the
backside blocking dielectric layer can be formed by a conformal
deposition process such as atomic layer deposition or chemical
vapor deposition. The thickness of the backside blocking dielectric
layer can be in a range from 1 nm to 60 nm, although lesser and
greater thicknesses can also be employed.
[0116] At least one conductive material can be deposited in the
plurality of backside recesses (143, 243), on the sidewalls of the
backside trench 79, and over the planarization dielectric layer
280. The at least one conductive material can include at least one
metallic material, i.e., an electrically conductive material that
includes at least one metallic element.
[0117] A plurality of first electrically conductive layers 146 can
be formed in the plurality of first backside recesses 143, a
plurality of second electrically conductive layers 246 can be
formed in the plurality of second backside recesses 243, and a
continuous metallic material layer 46L can be formed on the
sidewalls of each backside trench 79 and over the planarization
dielectric layer 280. In embodiments in which the first spacer
material layers and the second spacer material layers are provided
as first sacrificial material layers 142 and second sacrificial
material layers 242, the first and second sacrificial material
layers (142, 242) can be replaced with the first and second
conductive material layers (146, 246), respectively. Specifically,
each first sacrificial material layer 142 can be replaced with a
portion of the backside blocking dielectric layer and a first
electrically conductive layer 146, and each second sacrificial
material layer 242 can be replaced with a portion of the backside
blocking dielectric layer and a second electrically conductive
layer 246. A backside cavity is present in the portion of each
backside trench 79 that is not filled with the continuous metallic
material layer 46L.
[0118] The metallic material can be deposited by a conformal
deposition method, which can be, for example, chemical vapor
deposition (CVD), atomic layer deposition (ALD), electroless
plating, electroplating, or a combination thereof. The metallic
material can be an elemental metal, an intermetallic alloy of at
least two elemental metals, a conductive nitride of at least one
elemental metal, a conductive metal oxide, a conductive doped
semiconductor material, a conductive metal-semiconductor alloy such
as a metal silicide, alloys thereof, and combinations or stacks
thereof. Non-limiting exemplary metallic materials that can be
deposited in the backside recesses (143, 243) include tungsten,
tungsten nitride, titanium, titanium nitride, tantalum, tantalum
nitride, cobalt, and ruthenium. In one embodiment, the metallic
material can comprise a metal such as tungsten and/or metal
nitride. In one embodiment, the metallic material for filling the
backside recesses (143, 243) can be a combination of titanium
nitride layer and a tungsten fill material. In one embodiment, the
metallic material can be deposited by chemical vapor deposition or
atomic layer deposition.
[0119] Referring to FIG. 18, residual material can be removed from
each backside trench 79. Specifically, the deposited metallic
material of the continuous metallic material layer 46L can be
etched back from the sidewalls of each backside trench 79 and from
above the planarization dielectric layer 280, for example, by an
isotropic etch. Each remaining portion of the deposited metallic
material in the first backside recesses 143 constitutes a first
electrically conductive layer 146. Each remaining portion of the
deposited metallic material in the second backside recesses 243
constitutes a second electrically conductive layer 246. Each
electrically conductive layer (146, 246) can be a conductive line
structure.
[0120] Each electrically conductive layer (146, 246) except the
bottommost electrically conductive layer (i.e., the bottommost
first electrically conductive layer 146) can function as a
combination of a plurality of control gate electrodes located at a
same level and a word line electrically interconnecting, i.e.,
electrically shorting, the plurality of control gate electrodes
located at the same level. The control gate electrodes within each
electrically conductive layer (146, 246) are the control gate
electrodes for a vertical memory device including the memory stack
structure 55.
[0121] The bottommost first electrically conductive layer 146 can
be a source select gate electrode located over the gate dielectric
layer 12, which can control activation of a horizontal channel
portion of a semiconductor channel that extends between a source
region 61 (which is previously formed or which will be subsequently
formed underneath each backside trench 79) and drain regions 63. In
one embodiment, the backside blocking dielectric layer may be
present as a single continuous material layer. In another
embodiment, the vertical portions of the backside blocking
dielectric layer may be removed from within the backside trenches
79, and the backside blocking dielectric layer can have a plurality
of physically disjoined backside blocking dielectric layer portions
that are located at each level of the electrically conductive
layers (146, 246).
[0122] Dopants of a second conductivity type, which is the opposite
of the first conductivity type of the substrate semiconductor layer
10, can be implanted into a surface portion of the substrate
semiconductor layer 10 to form a source region 61 underneath the
bottom surface of each backside trench 79. An insulating spacer 74
including a dielectric material can be formed at the periphery of
each backside trench 79, for example, by deposition of a conformal
insulating material (such as silicon oxide) and a subsequent
anisotropic etch. The planarization dielectric layer 280 may be
thinned due to a collateral etch during the anisotropic etch that
removes the vertical portions of horizontal portions of the
deposited conformal insulating material.
[0123] A backside contact via structure 76 can be formed in the
remaining volume of each backside trench 79, for example, by
deposition of at least one conductive material and removal of
excess portions of the deposited at least one conductive material
from above a horizontal plane including the top surface of the
planarization dielectric layer 80 by a planarization process such
as chemical mechanical planarization or a recess etch. Optionally,
each backside contact via structure 76 may include multiple
backside contact via portions such as a lower backside contact via
portion and an upper backside contact via portion. In an
illustrative example, the lower backside contact via portion can
include a doped semiconductor material (such as doped polysilicon),
and can be formed by depositing the doped semiconductor material
layer to fill the backside trenches 79 and removing the deposited
doped semiconductor material from upper portions of the backside
trenches 79. The upper backside contact via portion can include at
least one metallic material (such as a combination of a TiN liner
and a W fill material), and can be formed by depositing the at
least one metallic material above the lower backside contact via
portions, and removing an excess portion of the at least one
metallic material from above the horizontal plane including the top
surface of the planarization dielectric layer 280. The
planarization dielectric layer 280 can be thinned and removed
during a latter part of the planarization process, which may employ
chemical mechanical planarization (CMP), a recess etch, or a
combination thereof. Each backside contact via structure 76 can be
formed through the at least one tier structure (132, 146, 232, 246)
and on a source region 61, which may be a source region. The top
surface of each backside contact via structure 76 can be formed
within the horizontal plane that includes the top surfaces of the
memory stack structures 55.
[0124] Referring to FIG. 19, an alternate embodiment of the first
exemplary structure can be derived from the first exemplary
structure of FIG. 9 by forming upper sacrificial pillar structures
3B in the second memory openings 221. The sacrificial pillar
structures 3A underlying the upper sacrificial pillar structures
are herein referred to as lower sacrificial pillar structures. The
upper sacrificial pillar structures 3B can include any material
that may be employed for the lower sacrificial pillar structures 3A
as described above. The upper sacrificial pillar structures 3B may
include the same material as, or may include a material different
from, the lower sacrificial pillar structures 3A. For example, the
upper and lower sacrificial pillar structures (3A, 3B) can include
polycrystalline or amorphous undoped silicon. Each adjoining pair
of a lower sacrificial pillar structure 3A and an upper sacrificial
pillar structure 3B constitutes a pillar structure stack (3A,
3B).
[0125] The processing steps of FIGS. 14-18 can be performed to form
electrically conductive layers (146, 246), source regions 61,
insulating spacers 74, and backside contact via structures 76.
While the illustrated embodiment corresponds to a case in which the
second insulating cap layer 280 is not employed or is thinned and
removed, embodiments are expressly contemplated herein, in which
the second insulating cap layer 280 is present after the processing
steps of FIG. 19.
[0126] Referring to FIG. 20, the pillar structure stacks (3A, 3B)
can be removed selective to the annular spacers 172, the first and
second insulating layers (132, 142), the first and second
electrically conductive layers (146, 246), the first and second
insulating cap layers (170, 270), and the epitaxial channel
portions 11. The same etch chemistry can be employed as the etch
chemistry employed at the processing steps of FIG. 10.
[0127] In one embodiment, removal of the pillar structure stacks
(3A, 3B) can be performed selective to the annular spacers 172
employing an etch chemistry that provides differential etch rates
that depend on the concentration of electrical dopants. In one
embodiment, the pillar structure stacks (3A, 3B) can include a
first semiconductor material that does not include electrical
dopants or includes electrical dopants at an atomic concentration
less than 1.0.times.1017/cm3, and the annular spacers 172 can
include a second semiconductor material that includes electrical
dopants at an atomic concentration greater than 1.0.times.1018/cm3.
In one embodiment, the pillar structure stacks (3A, 3B) can include
amorphous or polycrystalline silicon that does not include
electrical dopants or includes electrical dopants at an atomic
concentration less than 1.0.times.1017/cm3, the annular spacers 172
can include amorphous or polycrystalline silicon that includes
electrical dopants at an atomic concentration greater than
1.0.times.1018/cm3, and removal of the pillar structure stacks (3A,
3B) selective to the annular spacers 172 can be performed employing
hot trimethyl-2 hydroxyethyl ammonium hydroxide.
[0128] Referring to FIG. 21, the processing steps of FIG. 11 can be
performed to form memory stack structures 55, dielectric cores 62,
and drain regions 63. The first exemplary structures illustrated in
FIGS. 18 and 21 can include a monolithic three-dimensional memory
device. The monolithic three-dimensional memory device can include
a first alternating stack of first insulating layers 132 and first
electrically conductive layers 146 located over a top surface of a
substrate 10; an insulating cap layer 270 overlying the first
alternating stack (132, 146); a second alternating stack located
over the insulating cap layer 170 and comprising a second
alternating stack of second insulating layers 232 and second
electrically conductive layers 246; a memory opening extending
through the second alternating stack (232, 246), the insulating cap
layer 170, and the firsts tier structure (132, 146); a memory stack
structure 55 located within the memory opening and comprising a
memory film 50 including a plurality of charge storage regions (as
embodied as portions of the memory material layer 54) located at
the levels of the electrically conductive layers (146, 246); and an
annular spacer 172 located within the insulating cap layer 170 and
laterally surrounding the memory stack structure 55.
[0129] In one embodiment, an inner sidewall of the annular spacer
172 contacts a portion of an outer sidewall of the memory film 50.
In one embodiment, a bottom surface of the annular spacer 172 is
vertically spaced from a bottom surface of the insulating cap layer
170. In one embodiment, the annular spacer 172 has a horizontal
bottom surface and a tapered sidewall surface. In one embodiment,
the insulating cap layer 170 can comprise a first insulating cap
layer 170A having a top surface that is coplanar with a bottom
surface of the annular spacer 172, and a second insulating cap
layer 170B having a top surface that is coplanar with a topmost
surface of the annular spacer 172. In one embodiment, the annular
spacer 172 can comprise a doped semiconductor material.
[0130] In one embodiment, the memory opening 49 can have a first
horizontal ledge 49A at an interface between the insulating cap
layer 170 and the second alternating stack (232, 246), and a second
horizontal ledge 49B that contacts a horizontal surface of the
annular spacer 172 between a top surface of the annular spacer 172
and a bottom surface of the annular spacer 172, as illustrated in
FIG. 12B. The first and second horizontal ledges (49A, 49B) extend
substantially parallel to the top surface of the substrate 10, and
the second horizontal ledge 49B is located closer to the top
surface of the substrate 10 than the first horizontal ledge 49A. In
one embodiment, first sidewalls of the memory opening 49 located in
a lower portion of the insulating cap layer 170 (e.g., in layer
170A) can be laterally offset with respect to second sidewalls of
the memory opening located in the upper portion of the insulating
cap layer (e.g., in layer 170B) and in the second alternating stack
(232, 246), which is derived from the structure of FIG. 12D by
replacement of the sacrificial material layers (142, 242) with
electrically conductive layers (146, 246). In one embodiment, one
of the first sidewalls of the memory opening 49 can extend to a
horizontal plane including an interface (e.g., ledge 49A in FIG.
12B) between the insulating cap layer 170 and the second
alternating stack (232, 246), and one of the second sidewalls of
the memory opening 49 can extend into a middle portion of the
annular spacer 172 at ledge 49B, as illustrated in FIG. 12B. The
memory film 50 has the same contour as the memory opening 49.
[0131] According to another aspect of the present disclosure, a
second exemplary structure according to an embodiment of the
present disclosure can be derived from the first exemplary
structure of FIG. 4 by performing a set of etch steps at least
twice, such as twice, three times, four times, etc. The set of etch
steps includes a recess etch step that vertically recesses the top
surfaces of sacrificial material portions (such as the sacrificial
pillar structures 3A as provided at the processing step of FIG. 4)
downward, and an isotropic etch step that isotropically etches the
material of the insulating cap layer 170A selective to the
sacrificial material portions. After performing the set of etch
steps at least twice, each remaining portion of the sacrificial
pillar structures 3A constitutes a sacrificial pillar structure
3A.
[0132] Exemplary implementation of the set of etch steps twice is
illustrated in FIGS. 22-25. Referring to FIG. 22, the sacrificial
pillar structures 3A in the first exemplary structure of FIG. 4 are
vertically recessed such that the recessed top surfaces of the
sacrificial pillar structures 3A are located between a first
horizontal plane including the top surface of the first insulating
cap layer 170A and a second horizontal plane including the bottom
surface of the first insulating cap layer 170A. A recess region 169
is formed above each recessed top surface of the sacrificial pillar
structures 3A. Each recess region 169 can have a substantially
vertical sidewall having a top periphery and a bottom periphery
that are congruent. The sacrificial pillar structures 3A are
sacrificial material portions that are subsequently removed
selective to the first alternating stack (132, 142) and the first
insulating cap layer 170A.
[0133] Referring to FIG. 23, a first isotropic etch process is
performed, which etches the material of the first insulating cap
layer 170A selective to the sacrificial material portions (i.e.,
the sacrificial pillar structures 3A). The volume of each recess
region 169 can be expanded by etching the material of the first
insulating cap layer 170A selective to the sacrificial pillar
structures 3A. Each recess region 169 can have a vertical surface
adjoined by a concave surface having an initial radius of curvature
R0 due to the isotropic nature of the first isotropic etch process.
In one embodiment, the foci of the center of radius of curvature of
the concave surfaces can coincide with the peripheral edge of the
top surface of each sacrificial pillar structure 3A. The processing
steps of FIGS. 22 and 23 collectively correspond to one instance of
implementation of the set of etch steps, such as wet etching steps
using dilute hydrofluoric acid to selectively etch silicon oxide
material of layer 170A. If layer 170A comprises material other than
silicon oxide, then another etching fluid may be used to
selectively etch layer 170A.
[0134] Referring to FIG. 24, the sacrificial pillar structures 3A
are vertically recessed selective to the dielectric material of the
first insulating cap layer 170A. The recessed top surfaces of the
sacrificial pillar structures 3A are located above the horizontal
plane including the bottom surface of the first insulating cap
layer 170A. Each recessed top surfaces of the sacrificial pillar
structures 3A may be located below a peripheral bottom edge of the
concave surfaces of the overlying recess region 169. A selective
dry or wet etch may be used to selectively etch back the material
of structures 3A (e.g., amorphous silicon) compared to the
insulating materials of layers 132, 142 and 170A.
[0135] Referring to FIG. 25, a second isotropic etch process is
performed, which etches the material of the first insulating cap
layer 170A selective to the sacrificial material portions (i.e.,
the sacrificial pillar structures 3A). The volume of each recess
region 169 can be expanded by etching the material of the first
insulating cap layer 170A selective to the sacrificial pillar
structures 3A. Each recess region 169 can have a first concave
surface having a first radius of curvature R1 and adjoined to a
sidewall of an underlying sacrificial pillar structure 3A, a second
concave surface having a second radius of curvature R2 and adjoined
to a top periphery of the first concave surface, and a vertical
sidewall adjoined to a top periphery of the second concave surface.
For each recess region 169, the foci of the center of first radius
of curvature R1 of the first concave surface can coincide with the
peripheral edge of the top surface of each sacrificial pillar
structure 3A. The processing steps of FIGS. 24 and 25 collectively
correspond to another instance of implementation of the set of etch
steps. The second radius of curvature R2 can be the same as the sum
of the initial radius of curvature R0 and the first radius of
curvature due to the isotropic nature of the second isotropic etch.
The net etch distance for the vertical sidewalls can be the same as
the first radius of curvature R1. The foci of the second radius of
curvature R2 can coincide with the foci of the initial radius of
curvature R0 because the second isotropic etch proceeds
isotropically by a distance that is equal to the first radius of
curvature R1.
[0136] Optionally, the processing steps of FIGS. 24 and 25 can be
repeated once or a plurality of times. As illustrated in FIGS.
22-25, each recess region 169 can be formed by expanding a first
memory opening 121 within the first insulating cap layer 170A by
performing the set of etch steps at least twice. Thus, the set of
etch steps is performed at least twice through the processing steps
of FIGS. 22-25 and any additional repetitions of the processing
steps of FIGS. 24 and 25. The set of etch steps includes a recess
etch step that vertically recesses the top surface of each
sacrificial material portion (i.e., each sacrificial pillar
structure 3A) downward; and an isotropic etch step that
isotropically etches the material of the first insulating cap layer
170A selective to the sacrificial material portions.
[0137] At least two concave sidewalls are formed around each recess
region 169, which is a portion of the volume of the expanded first
memory opening 121. In one embodiment, the at least two concave
sidewalls can include a first concave sidewall having a first
radius of curvature R1 and adjoining a substantially vertical
sidewall of the first insulating cap layer 170A that contacts a
vertical sidewall of a respective sacrificial pillar structure 3A.
The at least two concave sidewalls can further include a second
concave sidewall having a second radius of curvature R2 that is
greater than the first radius of curvature R1 and adjoining an
upper edge (i.e., the top periphery) of the first concave
sidewall.
[0138] Referring to FIG. 26, a fill material portion 3B can be
formed in each recess region 169 by deposition of a fill material
and removal of excess portions of the fill material from above a
horizontal plane including the top surface of the first insulating
cap layer 170A. The fill material portions 3B include a sacrificial
material that can be removed selected to the dielectric material of
the first insulating cap layer 170A. The fill material portions 3B
can include the same material as, or a different material from, the
material of the sacrificial pillar structures 3A.
[0139] In one embodiment, the fill material portions 3B includes a
material that can function as an etch stop material during a
subsequent anisotropic etch process to be employed to form second
memory openings through a second tier structure during a subsequent
processing step. In this case, the fill material portions 3B can be
etch stop material portions. In an illustrative example, the fill
material portions 3B can include a doped semiconductor material
(such as doped polysilicon or doped amorphous silicon) or an
undoped semiconductor material (such as undoped polysilicon or
undoped amorphous silicon). The sacrificial pillar structures 3A
can include a material that can be removed concurrently with
removal of the fill material portions 3B, or a material that can be
removed selective to the fill material portions 3B. For example, if
the sacrificial pillar structures 3A include a silicon-germanium
alloy, the fill material portions 3B can include silicon to enable
selective removal of the sacrificial pillar structures 3A. If the
sacrificial pillar structures 3A include undoped silicon, the fill
material portions 3B can include boron-doped silicon to enable
selective removal of the sacrificial pillar structures. In some
embodiments, the fill material portions 3B and the sacrificial
pillar structures 3A include materials that can be simultaneously
etched.
[0140] Referring to FIG. 27, the processing steps of FIG. 8 can be
performed to form a second alternating stack of second insulating
layers and second sacrificial material layers and a second
insulating cap layer. Stepped terraces (not shown) can be formed by
patterning the second alternating stack in a contact region located
at a periphery of the array region including the sacrificial pillar
structures 3A.
[0141] Referring to FIG. 28, the processing steps of FIG. 9 can be
performed to form second memory openings through the second tier
structure. In one embodiment, the fill material portions 3B can be
etch stop material portions. In this case, an anisotropic etch
process employed to form the second memory openings can utilize the
etch stop material portions as material portions that provide a
greater etch resistance than the second insulating layers 232 and
the second spacer material layers (i.e., the second sacrificial
material layers 242). In another embodiment, the fill material
portions 3B do not function as etch stop material portions.
[0142] The fill material portions 3B are subsequently removed,
wholly or in part, to physically expose top surfaces of the
sacrificial pillar structures 3A. The sacrificial pillar structures
3A are subsequently removed selective to the materials of the first
alternating stack (132, 142), the second alternating stack (232,
242), and the first and second insulating cap layers (170A, 270).
Any remaining portion of the fill material portions 3B can be
removed, for example, employing an etch including an isotropic
component prior to, during, or after, removal of the sacrificial
pillar structures 3A. An inter-stack memory opening 49 is formed by
removing the underlying sacrificial pillar structure 3A from below
each second memory opening. Subsequently, the semiconductor oxide
portions 13 can be removed, for example, by an etch process that
employs HF chemistry. A top surface of an epitaxial channel portion
11 can be physically exposed at the bottom of each inter-stack
memory opening 49.
[0143] Referring to FIGS. 29A and 29B, the processing steps of
FIGS. 11 and 13-18 can be subsequently performed to form memory
stack structures 55, a dielectric core 62, and a drain region 63
within each inter-stack memory opening 49, to form backside contact
trenches 79 through the alternating stacks (132, 142, 232, 242), to
replace the sacrificial material layers (142, 242) with
electrically conductive layers (146, 246), to form source regions
61 within surface portions of the substrate 10, and insulating
spacers 74 and backside contact via structures 76 in the backside
contact trenches 79.
[0144] The second exemplary structure includes a monolithic
three-dimensional memory device that includes a first alternating
stack of first insulating layers 132 and first electrically
conductive layers 146 located over a top surface of a substrate 10;
an insulating cap layer 170A overlying the first alternating stack
(132, 146); a second alternating stack of second insulating layers
232 and second electrically conductive layers 246 overlying the
insulating cap layer 170A; and a memory stack structure 55
extending through the second alternating stack (232, 246), the
insulating cap layer 170A, and the first alternating stack (132,
146) and comprising a semiconductor channel 60 and a memory film 50
including a plurality of charge storage regions (as embodied as
portions of the memory material layer 54 located at levels of the
electrically conductive layers (146, 246)). The insulating cap
layer 170A comprises a first concave surface having a first radius
of curvature R1, laterally surrounding the memory stack structure
55, and adjoined to an upper periphery of a substantially vertical
sidewall of the memory stack structure 55 (that contacts the
insulating cap layer 170A). The insulating cap layer 170A also
comprises a second concave surface having a second radius of
curvature R2 that is greater than the first radius of curvature R1,
laterally surrounding the memory stack structure 55, and adjoined
to an upper periphery of the first concave surface.
[0145] In one embodiment, an upper periphery of the second concave
surface is adjoined to a lower periphery of a substantially
vertical sidewall of the insulating cap layer 170A, of which the
upper periphery is adjoined to the top surface of the insulating
cap layer 170A. A first convex sidewall of the memory stack
structure 55 contacts the first concave sidewall of the insulating
cap layer 170A, and a second convex sidewall of the memory stack
structure 55 contacts the second concave sidewall of the insulating
cap layer 170A. Each the memory stack structure 55 can have a first
periphery PR1 at which a substantially vertical outer sidewall of
the structure 55 adjoins a top surface of the structure 55, and
each memory stack structure 55 can have a second periphery PR2 at
which a substantially vertical inner sidewall of the structure 55
adjoins a convex bottom surface of the structure 55.
[0146] The convex sidewall(s) of the structure 55 forms a thicker,
sloped (i.e., tapered) surface which extends between a vertical and
horizontal direction in structure 55 at the junction of openings
121 and 221 in layer 170A. This thicker, sloped surface of
structure 55 prevents or reduces etching damage during the
anisotropic etch of the horizontal surface of the bottom of the
structure 55 at the interface of opening 121 and structure 11. In
other words, the damage to the sloped surface of the structure 55
is reduced or avoided during the anisotropic etch of the first
semiconductor channel layer 601 and the memory films 50 to remove
the horizontal bottom portion of each memory film 50 from the
bottom of each memory opening before the step of forming the second
semiconductor channel layer 602 in contact with the structure 11.
As shown in FIG. 29B, in case of a lateral offset between a second
memory opening 221 and an underlying first memory opening 121, the
effective thickness of the first semiconductor channel layer 601
along the direction of ions of the anisotropic etch of the bottom
portion of the memory film is given by
t.sub.1=t.sub.0/cos(.theta.), in which t.sub.0 is the thickness of
the as-deposited first semiconductor channel layer 601, and the
angle .theta. is the taper angle of the first semiconductor channel
layer 601 at the location at which the ions of the anisotropic etch
impinges, where 0<.theta.<90 degrees, such as
20.ltoreq..theta..ltoreq.70 degrees. Thus, the tapered
configuration of the first semiconductor channel layer 601 in the
structure 55 provides a greater protection against collateral
damage during the anisotropic etch that forms the second memory
openings 221.
[0147] Referring to FIG. 30, an alternative embodiment of the
second exemplary structure can be derived from the second exemplary
structure by anisotropically etching regions of the fill material
portions 3B that underlie the second openings. An annular spacer
472 including a remaining annular portion of a fill material
portion 3B can be formed underneath each second memory opening by
etching through a portion of a fill material portion 3B (which may,
or may not, be an etch stop material portion). In case the fill
material portions 3B are employed as etch stop material portions,
the second memory openings can be formed through the second
alternating stack (232, 242) employing the etch stop material
portion as a material portion that provides a greater etch
resistance than the second insulating layers 232 and the second
spacer material layers (such as the second sacrificial material
layers 242). The etch stop material portion is patterned into an
annular spacer 472.
[0148] A memory stack structure 55 can be formed on each annular
spacer 472. Upon formation of the memory stack structures 55, the
dielectric cores 62, and the drain regions 63, each annular spacer
472 laterally surrounds a respective memory stack structure 55. A
first convex sidewall of the annular spacer 472 can contact the
first concave sidewall of the insulating cap layer 170A, and a
second convex sidewall of the annular spacer 472 can contact the
second concave sidewall of the insulating cap layer 170A.
[0149] The alternate embodiment of the second exemplary structure
includes a monolithic three-dimensional memory device, which
comprises: a first alternating stack of first insulating layers 132
and first electrically conductive layers 146 located over a top
surface of a substrate 10; an insulating cap layer 170A overlying
the first alternating stack (132, 146); a second alternating stack
of second insulating layers 232 and second electrically conductive
layers 246 overlying the insulating cap layer 170A; a memory stack
structure 55 extending through the second alternating stack (232,
246), the insulating cap layer 170A, and the first alternating
stack (132, 146) and comprising a semiconductor channel 60 and a
memory film 50 including a plurality of charge storage regions; and
an annular spacer 472 located within the insulating cap layer 170A
and laterally surrounding the memory stack structure 55. In one
embodiment, the annular spacer 472 can have a planar top surface
that contacts a bottommost layer within the second alternating
stack (232, 246). In one embodiment, the annular spacer 472 can
have a bottommost surface that is located above a horizontal plane
including an interface between the first alternating stack (132,
146) and the insulating cap layer 170A. In one embodiment, a
substantially vertical outer sidewall of the annular spacer 472 can
laterally protrude farther outward than any portion of the memory
stack structure 55 within the first alternating stack (132, 146).
In one embodiment, the annular spacer 472 can include a material
selected from a doped semiconductor material (such as undoped
silicon or doped silicon) and a dielectric material (such as
silicon oxide, silicon nitride, or a dielectric metal oxide).
[0150] In one embodiment, each annular spacer 472 can have a first
periphery PR1 at which a substantially vertical outer sidewall of
the annular spacer 472 adjoins a top surface of the annular spacer
472, and the annular spacer 472 can have a second periphery PR2 at
which a substantially vertical inner sidewall of the annular spacer
472 adjoins a convex bottom surface of the annular spacer 472. The
annular spacer 472 has a substantially vertical upper outer surface
and a convex lower outer surface.
[0151] Referring to FIG. 31, a third exemplary according to an
embodiment of the present disclosure can be derived from the second
exemplary structure of FIG. 23 or FIG. 25. Specifically, a
sacrificial material portion (such as a sacrificial pillar
structure 3A) is formed in each first memory opening, and a recess
region 169 is formed by recessing a top surface of the sacrificial
material portions below a top surface of the first insulating cap
layer 170A at least once. The volume of each recess region 169 is
laterally expanded by etching the material of the first insulating
cap layer 170A selective to the sacrificial pillar structures 3A.
Thus, the first insulating cap layer 170A is isotropically etched
at least once to form the recess regions 169. A remaining portion
of the sacrificial material portion after the recess regions 169
are expanded constitutes a sacrificial pillar structure 3A
illustrated in FIG. 31.
[0152] Referring to FIG. 32, a conformal spacer material layer 272L
is formed in the recess regions 169 and over the first insulating
cap layer 170A. In one embodiment, the conformal spacer material
layer 272L may comprise a silicon nitride layer. In another
embodiment, the conformal spacer material layer 272L can be an etch
stop material layer that includes a material that can be employed
as an etch stop material. For example, the conformal spacer
material layer 272L can include a semiconductor material (such as
silicon or a silicon-germanium alloy) or a dielectric material
(such as a dielectric metal oxide). In one embodiment, the
conformal spacer material layer 272L can include aluminum
oxide.
[0153] Referring to FIG. 33, an anisotropic sidewall spacer etch
can be performed to remove horizontal portions of the conformal
spacer material layer 272L. Each remaining vertical portion of the
conformal spacer material layer 272L constitutes an annular spacer
272 located at a periphery of a respective recess region 169. In
one embodiment, the annular spacers 272 can be etch stop material
portions that are subsequently employed as an etch stop structure
during formation of second memory openings through a second
alternating stack to be subsequently formed over the first
alternating stack. In this case, the annular spacers 272 can be
formed directly on a sidewall of the recess regions 169 by
deposition of an etch stop material layer (i.e., the conformal
spacer material layer) and an anisotropic etch of the etch stop
material layer. If the annular spacers 272 comprise silicon nitride
(e.g., not an etch stop material), then the top of the spacers 272
may be recessed below the top of layer 170A.
[0154] Referring to FIG. 34, fill material portions 3B can be
formed by performing the processing steps of FIG. 26. In one
embodiment, the fill material portions 3B can be additional etch
stop material portions that function as additional etch stop
structure during subsequent formation of second memory openings. In
one embodiment, the fill material portions 3B can be additional the
etch stop material portions that are formed by depositing a second
semiconductor material a greater dopant concentration than the
first semiconductor material of the sacrificial pillar structures
3A. In one embodiment, the second semiconductor material can be
boron-doped silicon.
[0155] A combination of a sacrificial pillar structure 3A and at
least one etch stop material portion is formed in each first memory
opening. The at least one etch stop material portion can be
embodied as an annular spacer 272, and/or can be embodied as a fill
material portion 3B.
[0156] Referring to FIG. 35A, the processing steps of FIG. 8 can be
performed to form a second alternating stack of second insulating
layers 232 and second spacer material layers (such as second
sacrificial material layer 246). The processing steps of FIG. 9 can
be performed to form second memory openings through the second tier
structure. In an embodiment in which the annular spacers 272 are
employed as etch stop material portions, the second memory openings
can be formed through the second alternating stack (232, 242)
employing the etch stop material portion as a material portion that
provides a greater etch resistance than the second insulating
layers 232 and the second spacer material layers (such as the
second sacrificial material layers 242). In this case, the etch
stop material portion is provided as an annular spacer 272. In one
embodiment, the fill material portions 3B can be etch stop material
portions. In this case, an anisotropic etch process employed to
form the second memory openings can utilize the etch stop material
portions (272 and/or 3B) as material portions that provide a
greater etch resistance than the second insulating layers 232 and
the second spacer material layers (i.e., the second sacrificial
material layers 242). In another embodiment, the fill material
portions 3B do not function as etch stop material portions.
[0157] The fill material portions 3B and the sacrificial pillar
structures 3A are subsequently removed to form inter-stack memory
openings 49 employing additional etch processes. The fill material
portions 3B and the sacrificial pillar structures 3A are
subsequently removed selective to the materials of the first
alternating stack (132, 142), the second alternating stack (232,
242), the second insulating cap layer 270, and the annular spacers
272.
[0158] Subsequently, the processing steps of FIGS. 11 and 13-18 can
be performed to form memory stack structures 55, a dielectric core
62, and a drain region 63 within each inter-stack memory opening
49, to form backside contact trenches 79 through the alternating
stacks (132, 142, 232, 242), to replace the sacrificial material
layers (142, 242) with electrically conductive layers (146, 246),
to form source regions 61 within surface portions of the substrate
10, and insulating spacers 74 and backside contact via structures
76 in the backside contact trenches 79. As shown in the close up
view of one memory stack structure 55 in FIG. 35B, the layers of
the memory stack structure 55 (i.e., the memory film 50, the first
semiconductor channel layer 601 and the second semiconductor
channel layer 602) have an outward taper in the joint section
adjacent to the annular spacer 272 in the insulating pad layer 170A
between the first and the second alternating stacks because the
layers follow the tapered contour of the inner sidewalls of the
annular spacer 272.
[0159] The third exemplary structure can include a monolithic
three-dimensional memory device, which can include: a first
alternating stack of first insulating layers 132 and first
electrically conductive layers 146 located over a top surface of a
substrate 10; an insulating cap layer 170A overlying the first
alternating stack (132, 146); a second alternating stack of second
insulating layers 232 and second electrically conductive layers 246
overlying the insulating cap layer 170A; a memory stack structure
55 extending through the second alternating stack (232, 246), the
insulating cap layer 170A, and the first alternating stack (132,
146) and comprising a semiconductor channel 60 and a memory film 50
including a plurality of charge storage regions; and an annular
spacer 272 located within the insulating cap layer 170A and
laterally surrounding the memory stack structure 55.
[0160] In one embodiment, the annular spacer 272 has a bottommost
surface that is located above a horizontal plane including an
interface between the first alternating stack (132, 146) and the
first insulating cap layer 170A. In one embodiment, a substantially
vertical outer sidewall of the annular spacer 272 can laterally
protrude farther outward than any portion of the memory stack
structure 55 within the first alternating stack (132, 146). In one
embodiment, the annular spacer 272 can comprise a first periphery
PR1 at which a substantially vertical outer sidewall of the annular
spacer 272 adjoins a top surface of the annular spacer 272. In one
embodiment, the annular spacer 272 can comprise a second periphery
PR2 at which a substantially vertical inner sidewall of the annular
spacer 272 adjoins a convex bottom surface of the annular spacer
272.
[0161] In one embodiment, the top surface of the annular spacer 272
can be a tapered convex surface adjoined to the substantially
vertical inner sidewall of the annular spacer 272. In one
embodiment, the annular spacer 272 can comprise a material selected
from a doped semiconductor material and a dielectric material.
[0162] Referring to FIG. 36, a fourth exemplary structure according
to an embodiment of the present disclosure can be derived from the
second exemplary structure of FIG. 23 or FIG. 25. Specifically, a
sacrificial material portion (such as a sacrificial pillar
structure 3A) is formed in each first memory opening, and a recess
region 169 is formed by recessing a top surface of the sacrificial
material portions below a top surface of the first insulating cap
layer 170A at least once. The volume of each recess region 169 is
laterally expanded by etching the material of the first insulating
cap layer 170A selective to the sacrificial pillar structures 3A.
Thus, the first insulating cap layer 170A is isotropically etched
at least once to form the recess regions 169. A remaining portion
of the sacrificial material portion after the recess regions 169
are expanded constitutes a sacrificial pillar structure 3A
illustrated in FIG. 31.
[0163] Etch stop material portions 3C can be formed by depositing a
material that can be employed as an etch stop material during
subsequent formation of second memory openings. In one embodiment,
the etch stop material having portions 3C can be formed by
depositing a second semiconductor material a greater dopant
concentration than the first semiconductor material of the
sacrificial pillar structures 3A. In one embodiment, the second
semiconductor material can be boron-doped silicon (e.g., boron
doped amorphous silicon). A combination of a sacrificial pillar
structure 3A and an etch stop material portion 3C is formed in each
first memory opening. Each etch stop material portion 3C can fill
the entire volume of a recess region 169.
[0164] Referring to FIG. 37, the processing steps of the processing
steps of FIG. 8 can be performed to form a second alternating stack
of second insulator layers 232 and second spacer material layers,
which can be second sacrificial material layers 242. A second
insulating cap layer 270 can be formed over the second alternating
stack (232, 242). Stepped terraces can be formed at a periphery of
an array region including the sacrificial pillar structures 3A.
[0165] Referring to FIG. 38, the processing steps of the processing
steps of FIG. 9 can be performed to form second memory openings 221
through the second tier structure that includes the second
alternating stack (232, 242) and the second insulating cap layer
270. The second memory openings 221 can be formed through the
second alternating stack (232, 242) employing the etch stop
material portions 3C as material portions that provide a greater
etch resistance than the second insulating layers 232 and the
second spacer material layers (such as the second sacrificial
material layers 242). In this case, an anisotropic etch process
employed to form the second memory openings 221 can utilize the
etch stop material portions 3C as material portions that provide a
greater etch resistance than the second insulating layers 232 and
the second spacer material layers (i.e., the second sacrificial
material layers 242).
[0166] Another anisotropic etch process can be performed to remove
regions of the etch stop material portions 3C that underlie the
second memory openings 221. Each remaining portion of the etch stop
material portions 3C can constitute an annular spacer 372.
[0167] Referring to FIG. 39, the sacrificial pillar structures 3A
can be removed selective to the annular spacers, the first
alternating stack (132, 142), the second alternating stack (232,
242), and the first and second insulating cap layers (170A, 270),
and optionally selective to the semiconductor oxide portions 13.
Subsequently, the processing steps of FIGS. 11 and 13-18 can be
performed to form memory stack structures 55, a dielectric core 62,
and a drain region 63 within each inter-stack memory opening 49, to
form backside contact trenches 79 through the alternating stacks
(132, 142, 232, 242), to replace the sacrificial material layers
(142, 242) with electrically conductive layers (146, 246), to form
source regions 61 within surface portions of the substrate 10, and
insulating spacers 74 and backside contact via structures 76 in the
backside contact trenches 79.
[0168] FIGS. 40A-40C illustrate an exemplary processing sequence
that can be employed to form substantially vertical sidewalls at
least the upper parts of first memory openings 121 through the
first alternating stack (132, 142) of any of the exemplary
structures of the present disclosure. After formation of the first
alternating stack (132, 142) and the first insulating cap layer
170A, a patterning film 37, such as Advanced Patterning Film.TM. by
Applied Materials, Inc., can be employed as a patterned masking
layer that defines the patterns of the first memory openings 121.
An anisotropic etch is performed through the first insulating cap
layer 170A and the first alternating stack (132, 142), and
optionally through an upper portion of the semiconductor material
of the substrate 10 to form bottle-shaped first memory openings
having a widening downward taper in an upper portion and a
narrowing downward taper in a lower portion of the first
alternating stack (132, 142) as illustrated in FIG. 40A.
[0169] Referring to FIG. 40B, the patterning film 37 can be trimmed
(i.e., slimmed) employing an isotropic etch process that removes
the material of the patterning film 37 isotropically. Referring to
FIG. 40C, another anisotropic etch process can be performed to etch
the upper portions of the first memory openings 121 to provide a
substantially vertical sidewall at least in the upper portion of
each first memory opening. In one embodiment, each first memory
opening 121 can include a substantially vertical sidewall in an
upper portion and a tapered sidewall in a lower portion. In another
embodiment, each first memory opening 121 can include a
substantially vertical sidewall that extends through the first
alternating stack (132, 142). As used herein, a surface or a line
is "substantially vertical" if the deviation of the surface or the
line from a vertical line is less than 4 degrees. Subsequently, the
patterning film 37 can be removed, for example, by ashing. The
exemplary processing sequence can be employed in conjunction with
any of the previously described processing sequences, or with any
of the processing sequences to be subsequently described.
[0170] Referring to FIG. 41A, subsequent processing steps of the
fourth embodiment can be employed to laterally expand (i.e., widen)
the recess regions 169 using any of the methods described above,
such as the methods described above with respect to FIG. 23 or 25.
Then, as shown in FIG. 41B, a combination of a sacrificial pillar
structure 3A and an etch stop material portion 3C are formed in
each first memory opening 121 and recessed region 169,
respectively. The lower portion of each first memory opening 121
can have a tapered sidewall. In one embodiment, each sacrificial
pillar structure 3A can be a sacrificial material portion formed by
depositing a first semiconductor material, and each etch stop
material portion 3C can be formed by depositing a second
semiconductor material a greater dopant concentration than the
first semiconductor material (such as boron-doped polysilicon
having an atomic concentration of boron of at least
1.0.times.10.sup.19/cm.sup.3, and preferably at least
1.0.times.10.sup.20/cm.sup.3).
[0171] Referring to FIG. 42A, the processing steps of FIGS. 37 and
38 can be sequentially performed to form a second alternating stack
(232, 242) and second memory openings 221. Each remaining portion
of the etch stop material portions 3C can constitute an annular
spacer 372.
[0172] Referring to FIG. 42B, after removal of the sacrificial
pillar structures 3A, the memory film 50 and the first
semiconductor channel layer 601 are formed in the memory openings
49 (i.e., in the lower and upper openings 121, 221). The first
semiconductor channel layer 601 and the memory film 50 are
anisotropic ally etched to remove the horizontal bottom portion of
each memory film 50 (and the horizontal bottom portion of layer
601) from the bottom of each memory opening 49 to expose the
epitaxial channel portions 11. The damage to the portion of the
structure 55 located adjacent to layer 170A between the lower 121
and upper 221 openings is reduced or avoided by not having an
exposed horizontal portion of the memory stack structure 55 (i.e.,
horizontal shoulder portion of the first semiconductor channel
layer 601) located adjacent to layer 170A between lower 121 and
upper 221 openings during the anisotropic etch the bottom portion
of the memory film 50. In this embodiment, the annular spacer 372
forms a protective etch stop located above the horizontal portion
of structure 55 (i.e., horizontal shoulder portion of the first
semiconductor channel layer 601) adjacent to layer 170A, during the
anisotropic etching of the bottom portion of the memory film 50 in
the circled region in FIG. 42B.
[0173] Referring to FIG. 43, the processing steps of FIG. 39 can be
performed to provide an alternative embodiment of the fourth
exemplary structure.
[0174] Referring to FIG. 44, a fifth exemplary structure can be
derived from the forth exemplary structure by omitting the
processing step(s) of FIG. 41A that laterally expand the recess
regions 169. For example, after performing the processing steps of
FIG. 22, the processing steps of FIGS. 23, 24, and 25 can be
omitted. Subsequently, the processing steps of FIG. 26 or the
processing steps of FIG. 36 can be performed to form an etch stop
material portion 3C within the volume of each recess region 169. In
this case, each etch stop material portion 3C can include a
substantially vertical sidewall surface having a first periphery
that adjoins a horizontal top surface of the etch stop material
portion 3C and having a second periphery that adjoins a bottom
surface of the etch stop material portion 3C. A substantially
vertical sidewall of each etch stop material portion 3C can
coincide with a substantially vertical sidewall of the underlying
sacrificial pillar structure 3A.
[0175] Referring to FIG. 45A, the processing steps of FIGS. 37 and
38 can be sequentially performed to form a second alternating stack
(232, 242) and second memory openings 221. Each remaining portion
of the etch stop material portions 3C can constitute an annular
spacer 372.
[0176] Referring to FIG. 45B, after removal of the sacrificial
pillar structures 3A, the memory film 50 and the first
semiconductor channel layer 601 are formed in the memory openings
49 (i.e., in the lower and upper openings 121, 221). The first
semiconductor channel layer 601 and the memory film 50 are
anisotropic ally etched to remove the horizontal bottom portion of
each memory film 50 (and the horizontal bottom portion of layer
601) from the bottom of each memory opening 49 to expose the
epitaxial channel portions 11. The damage to the portion of the
structure 55 located adjacent to layer 170A between the lower 121
and upper 221 openings is reduced or avoided by not having an
exposed horizontal portion of the memory stack structure 55 (i.e.,
horizontal shoulder portion of the first semiconductor channel
layer 601) located adjacent to layer 170A between lower 121 and
upper 221 openings during the anisotropic etch the bottom portion
of the memory film 50. In this embodiment, the annular spacer 372
forms a protective etch stop located above the horizontal portion
of structure 55 (i.e., horizontal shoulder portion of the first
semiconductor channel layer 601) adjacent to layer 170A, during the
anisotropic etching of the bottom portion of the memory film 50 in
the circled region in FIG. 42B
[0177] Referring to FIG. 46, the processing steps of FIG. 39 can be
performed to provide the fifth exemplary structure. A substantially
vertical sidewall of each etch stop material portion 3C can
coincide with a substantially vertical sidewall of an underlying
portion of a memory stack structure 55.
[0178] Each of the fourth and fifth exemplary structures or
alternative embodiments thereof can include a monolithic
three-dimensional memory device. The monolithic three-dimensional
memory device can include a first alternating stack of first
insulating layers 132 and first electrically conductive layers 146
located over a top surface of a substrate 10; an insulating cap
layer 170A overlying the first alternating stack (132, 146); a
second alternating stack of second insulating layers 232 and second
electrically conductive layers 246 overlying the insulating cap
layer 170A; a memory stack structure 55 extending through the
second alternating stack (232, 246), the insulating cap layer 170A,
and the first alternating stack (132, 146) and comprising a
semiconductor channel 60 and a memory film 50 including a plurality
of charge storage regions; and an annular spacer 372 located within
the insulating cap layer 170A and laterally surrounding the memory
stack structure 55.
[0179] In one embodiment, the annular spacer 372 has a planar top
surface that contacts a bottommost layer within the second
alternating stack (232, 246). In one embodiment, the annular spacer
372 has a bottommost surface that is located above a horizontal
plane including an interface between the first alternating stack
(132, 146) and the insulating cap layer 170A.
[0180] In one embodiment, a substantially vertical outer sidewall
of the annular spacer 372 laterally protrudes farther outward than
any portion of the memory stack structure 55 within the first
alternating stack (132, 146) as illustrated in FIGS. 39 and 43.
[0181] In one embodiment, a substantially vertical outer sidewall
of the annular spacer 372 is vertically coincident with a portion
of the memory stack structure 55 within the first alternating stack
(132, 146) located directly underneath the annular spacer 372 as
illustrated in FIG. 46.
[0182] In one embodiment, a bottom surface of the annular spacer
372 contacts a portion (e.g., a horizontal portion) of the memory
stack structure 55 within the first alternating stack (132, 146)
located directly underneath the annular spacer 372 within a
horizontal plane as illustrated in FIGS. 43 and 46.
[0183] In one embodiment, the annular spacer 372 comprises a first
periphery PR1 at which a substantially vertical outer sidewall of
the annular spacer 372 adjoins a top surface of the annular spacer
372; and a second periphery PR2 at which a substantially vertical
inner sidewall of the annular spacer adjoins a convex bottom
surface of the annular spacer 372 as illustrated in FIG. 39. In one
embodiment, the top surface of the annular spacer 372 can be a
horizontal surface that contacts a bottommost layer in the second
alternating stack (232, 246). In another embodiment, the bottom
surface of the annular spacer 372 is horizontal (e.g.,
substantially horizontal to include unavoidable non-uniformities
that occur during photolithography, etching and layer deposition),
as shown in FIG. 46.
[0184] In one embodiment, the annular spacer 372 comprises a
material selected from a doped semiconductor material and a
dielectric material.
[0185] Each of the monolithic three-dimensional memory structures
of the present disclosure can comprise a monolithic
three-dimensional NAND memory device. The first and second
electrically conductive layers can comprise, or can be electrically
connected to, a respective word line of the monolithic
three-dimensional NAND memory device. The substrate 10 can comprise
a silicon substrate. The monolithic three-dimensional NAND memory
device can comprise an array of monolithic three-dimensional NAND
strings over the silicon substrate. At least one memory cell in a
first device level of the array of monolithic three-dimensional
NAND strings can be located over another memory cell in a second
device level of the array of monolithic three-dimensional NAND
strings. The silicon substrate can contain an integrated circuit
comprising a driver circuit for the memory device located thereon.
The array of monolithic three-dimensional NAND strings can
comprises a plurality of semiconductor channels. At least one end
portion of each of the plurality of semiconductor channels extends
substantially perpendicular to a top surface of the substrate. The
array of monolithic three-dimensional NAND strings can comprises a
plurality of charge storage elements. Each charge storage element
can be located adjacent to a respective one of the plurality of
semiconductor channels. The array of monolithic three-dimensional
NAND strings can comprise 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
can 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.
[0186] The embodiments of the present disclosure reduce or prevent
etching damage during the anisotropic etch of the horizontal
surface of the bottom of the memory stack structure 55 at the
interface of opening 121 and the epitaxial channel portion 11. In
other words, the damage to the portions of the first semiconductor
channel layer 601 and the memory film 50 located adjacent to layer
170A between the lower 121 and upper 221 openings is reduced or
avoided during the anisotropic etch of the first semiconductor
channel layer 601 and the memory films 50 to remove the horizontal
bottom portion of each memory film 50 from the bottom of each
memory opening before the step of forming the second semiconductor
channel layer 602 in contact with the epitaxial channel portions
11. The damage to the portion of the structure 55 located adjacent
to layer 170A between the lower 121 and upper 221 openings is
reduced or avoided by not having an exposed horizontal portion of
the memory stack structure 55 (i.e., horizontal shoulder portion of
the first semiconductor channel layer 601) located adjacent to
layer 170A between lower 121 and upper 221 openings during the
anisotropic etch the bottom portion of the memory film 50. In one
embodiment, the thicker tapered (i.e., non-horizontal) portion of
the structure 55 is formed adjacent to layer 170A, as shown in
FIGS. 29 and 35B. In another embodiment, an annular spacer 372 or
472 is used to form the structure 55 which is substantially
vertical adjacent to layer 170A, shown in FIGS. 30 and 39. In
another embodiment, an annular spacer 372 forms a protective etch
stop located above the horizontal portion of structure 55 (i.e.,
horizontal shoulder portion of the first semiconductor channel
layer 601) adjacent to layer 170A, during the anisotropic etching
of the bottom portion of the memory film, as shown in FIGS. 42B and
45B.
[0187] Therefore, in the above described embodiment, the step of
anisotropically etching a horizontal bottom portion of the memory
film 50 and the first semiconductor channel layer 601 such that
damage to portions of the first semiconductor channel layer and the
memory film located adjacent to the insulating cap layer 170A is
reduced or avoided comprises not having a horizontal portion of the
first semiconductor channel layer 601 located adjacent to the
insulating cap layer 170A exposed in the inter-stack memory opening
49.
[0188] In one embodiment, not having a horizontal portion of the
first semiconductor channel layer located adjacent to the
insulating cap layer exposed in the inter-stack memory opening
comprises forming a tapered non-horizontal portion of the first
semiconductor channel layer 601 adjacent to the insulating cap
layer 170A, as shown in FIG. 29B. In another embodiment, not having
a horizontal portion of the first semiconductor channel layer
located adjacent to the insulating cap layer exposed in the
inter-stack memory opening comprises forming an annular spacer 272
in the first memory opening 121 and forming the non-horizontal
tapered portion of the first semiconductor channel layer 601
adjacent to annular spacer 272, as shown in FIG. 35B.
[0189] In another embodiment, not having a horizontal portion of
the first semiconductor channel layer located adjacent to the
insulating cap layer exposed in the inter-stack memory opening
comprises forming an annular spacer 372 or 472 in the first memory
opening 121 and forming substantially vertical memory stack
structure 55 adjacent to annular spacer, as shown in FIGS. 30 and
39.
[0190] In another embodiment, not having a horizontal portion of
the first semiconductor channel layer located adjacent to the
insulating cap layer exposed in the inter-stack memory opening
comprises forming a protective etch stop annular spacer 372 in the
first memory opening 121 which covers the horizontal portion of the
first semiconductor channel 601 in the inter-stack memory opening
49.
[0191] 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.
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