U.S. patent application number 16/278391 was filed with the patent office on 2020-08-20 for three-dimensional memory device including bit lines between memory elements and an underlying peripheral circuit and methods of .
The applicant listed for this patent is SANDISK TECHNOLOGIES LLC. Invention is credited to Noritaka Fukuo, Masayuki Hiroi.
Application Number | 20200266206 16/278391 |
Document ID | 20200266206 / US20200266206 |
Family ID | 1000005001842 |
Filed Date | 2020-08-20 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200266206 |
Kind Code |
A1 |
Fukuo; Noritaka ; et
al. |
August 20, 2020 |
THREE-DIMENSIONAL MEMORY DEVICE INCLUDING BIT LINES BETWEEN MEMORY
ELEMENTS AND AN UNDERLYING PERIPHERAL CIRCUIT AND METHODS OF MAKING
THE SAME
Abstract
A three-dimensional semiconductor device includes bit lines
formed in the lower-interconnect-level dielectric material layers
located over a substrate, bit-line-connection via structures
contacting a respective one of the bit lines, pillar-shaped drain
regions contacting a respective one of the bit-line-connection via
structures, an alternating stack of insulating layers and
electrically conductive layers located over the pillar-shaped drain
regions, and memory stack structures extending through the
alternating stack. A source layer overlies the alternating stack,
and is electrically connected to an upper end of each vertical
semiconductor channel within a subset of the vertical semiconductor
channels. Vertical bit line interconnections structures extending
through the levels of the alternating stack may be eliminated by
forming the bit lines underneath the alternating stack, and the
footprint of the layout of the three-dimensional memory device may
be reduced.
Inventors: |
Fukuo; Noritaka; (Ofuna,
JP) ; Hiroi; Masayuki; (Yokkaichi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SANDISK TECHNOLOGIES LLC |
ADDISON |
TX |
US |
|
|
Family ID: |
1000005001842 |
Appl. No.: |
16/278391 |
Filed: |
February 18, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/7682 20130101;
H01L 27/11575 20130101; H01L 27/11529 20130101; H01L 27/11565
20130101; H01L 27/11548 20130101; H01L 21/76834 20130101; H01L
27/11582 20130101; H01L 23/5329 20130101; H01L 27/11556 20130101;
H01L 23/5226 20130101; H01L 27/11519 20130101 |
International
Class: |
H01L 27/11575 20060101
H01L027/11575; H01L 27/11519 20060101 H01L027/11519; H01L 27/11565
20060101 H01L027/11565; H01L 27/11548 20060101 H01L027/11548; H01L
27/11556 20060101 H01L027/11556; H01L 27/11582 20060101
H01L027/11582; H01L 23/522 20060101 H01L023/522; H01L 23/532
20060101 H01L023/532; H01L 21/768 20060101 H01L021/768 |
Claims
1. A three-dimensional memory device, comprising: bit lines formed
in a lower-interconnect-level dielectric material layers, laterally
spaced apart along a first horizontal direction, and laterally
extending a long a second horizontal direction that is
perpendicular to the first horizontal direction, and located over a
top surface of a substrate; bit-line-connection via structures
contacting a top surface of a respective one of the bit lines and
formed in a via-level dielectric layer; pillar-shaped drain regions
contacting a respective one of the bit-line-connection via
structures; an alternating stack of insulating layers and
electrically conductive layers located over the pillar-shaped drain
regions; memory opening fill structures vertically extending
through the alternating stack and including a respective memory
stack structure that contains a respective vertical semiconductor
channel and a respective vertical stack of memory elements; a
source layer overlying the alternating stack and electrically
connected to an upper end of each vertical semiconductor channel
within a subset of the vertical semiconductor channels; and field
effect transistors located on or over the top surface of the
substrate, wherein the bit lines are located between the field
effect transistors and the memory opening fill structures.
2. The three-dimensional memory device of claim 1, further
comprising lower-level metal interconnect structures located above,
and electrically connected to, the field effect transistors, formed
within the lower-interconnect-level dielectric material layers, and
underlying the alternating stack.
3. The three-dimensional memory device of claim 2, wherein the bit
lines are electrically connected to a subset of the field effect
transistors that comprise bit line drivers through a subset of the
lower-level metal interconnect structures.
4. The three-dimensional memory device of claim 1, wherein: each
memory stack structure comprises a vertical NAND string; and each
vertical stack of memory elements comprises a vertical stack of
charge storage elements located at levels of the electrically
conductive layers.
5. The three-dimensional memory device of claim 1, wherein the
bit-line-connection via structures are elongated along the second
horizontal direction with a length-to-width ratio in a range from
1.5 to 10.
6. The three-dimensional memory device of claim 1, wherein each of
the pillar-shaped drain regions contacts an entire top surface of
an underlying one of the bit-line-connection via structures and has
a greater horizontal cross-sectional area than a horizontal
cross-sectional area of the underlying one of the
bit-line-connection via structures.
7. The three-dimensional memory device of claim 6, wherein: the
pillar-shaped drain regions comprise a doped semiconductor material
including dopant atoms at an atomic concentration in a range from
5.0.times.10.sup.19/cm.sup.3 to 2.0.times.10.sup.21/cm.sup.3; and
the pillar-shaped drain regions have a circular cylindrical shape
or have a lesser length-to-width ratio than the bit-line-connection
via structures.
8. The three-dimensional memory device of claim 1, further
comprising: source contact via structures contacting an upper end
of a respective one of the vertical semiconductor channels and
contacting a bottom surface of the source layer; and a source
interconnect via structure that electrically connects the source
layer to a lower-level metal interconnect structure formed within
the lower-interconnect-level dielectric material layers.
9. The three-dimensional memory device of claim 1, wherein: the
alternating stack comprises stepped surfaces in a staircase region,
wherein each electrically conductive layer other than a topmost one
of the electrically conductive layers laterally extends farther
than an overlying electrically conductive layer; the electrically
conductive layers comprise word lines for the vertical stacks of
memory elements; and word line contact via structures contact a
respective one of the electrically conductive layers.
10. The three-dimensional memory device of claim 9, further
comprising a word line driver circuit located on a top surface of
the substrate and underlies the alternating stack, wherein the word
line contact via structures are electrically connected to the word
line driver circuit through lower-level metal interconnect
structures formed within the lower-interconnect-level dielectric
material layers.
11. The three-dimensional memory device of claim 1, further
comprising inter-bit-line cavities located between neighboring
pairs of bit lines and laterally extending along the second
horizontal direction, wherein each of the inter-bit-line cavities
is vertically bounded by a curved bottom surface portion of the
via-level dielectric layer.
12. The three-dimensional memory device of claim 11, further
comprising: a dielectric etch stop layer located between the
pillar-shaped drain regions and the bit lines; and a bit-line
dielectric liner that conformally covers sidewalls and top surfaces
of the bit lines, wherein: the via-level dielectric layer comprises
a material selected from undoped silicate glass, a doped silicate
glass, non-porous organosilicate glass, and porous organosilicate
glass; and the bit-line dielectric liner comprises a material
selected from silicon nitride, silicon oxynitride, a dielectric
metal oxide material, and nitrogen-doped organosilicate glass.
13. A method of forming a three-dimensional memory device,
comprising: forming field effect transistors on or over a top
surface of the substrate; forming bit lines within a
lower-interconnect-level dielectric material layers over the field
effect transistors, wherein the bit lines are laterally spaced
apart along a first horizontal direction, and laterally extend a
long a second horizontal direction that is perpendicular to the
first horizontal direction; forming bit-line-connection via
structures within a via-level dielectric layer on a top surface of
a respective one of the bit lines; forming pillar-shaped drain
regions on a respective one of the bit-line-connection via
structures; forming an alternating stack of insulating layers and
spacer material layers over the pillar-shaped drain regions,
wherein the spacer material layers are formed as, or are
subsequently replaced with, electrically conductive layers; forming
memory openings through the alternating stack on a respective one
of the pillar-shaped drain regions; forming memory opening fill
structures including a respective memory stack structure that
contains a respective vertical semiconductor channel and a
respective vertical stack of memory elements in the memory
openings; and forming a source layer over the alternating stack,
wherein the source layer is electrically connected to an upper end
of each vertical semiconductor channel within a subset of the
vertical semiconductor channels.
14. The method of claim 13, further comprising forming lower-level
metal interconnect structures electrically connected to the field
effect transistors in the lower-interconnect-level dielectric
material layers, wherein alternating stack is formed over the
lower-level metal interconnect structures.
15. The method of claim 14, wherein the bit lines are electrically
connected to a subset of the field effect transistors that
comprises bit line drivers through a subset of the lower-level
metal interconnect structures.
16. The method of claim 13, wherein: the bit-line-connection via
structures are elongated along the second horizontal direction with
a length-to-width ratio in a range from 1.5 to 10; and each of the
pillar-shaped drain regions contacts an entire top surface of an
underlying one of the bit-line-connection via structures and has a
greater horizontal cross-sectional area than a horizontal
cross-sectional area of the underlying one of the
bit-line-connection via structures.
17. The method of claim 13, further comprising: forming source
contact via structures on an upper end of a respective one of the
vertical semiconductor channels; and forming a source interconnect
via structure that vertically extends from a lower-level metal
interconnect structure within the lower-interconnect-level
dielectric material layers to a horizontal plane including top
surfaces of the source contact via structures, wherein the source
layer is formed on the source contact via structures and on the
source interconnect via structure.
18. The method of claim 13, wherein: the alternating stack
comprises stepped surfaces in a staircase region, wherein each
electrically conductive layer other than a topmost one of the
electrically conductive layers laterally extends farther than an
overlying electrically conductive layer; the electrically
conductive layers comprise word lines for the vertical stacks of
memory elements; and word line contact via structures contact a
respective one of the electrically conductive layers.
19. The method of claim 18, further comprising: forming a word line
driver circuit on a top surface of the substrate: and forming
lower-level metal interconnect structures within the
lower-interconnect-level dielectric material layers, wherein the
word line contact via structures are electrically connected to the
word line driver circuit through the lower-level metal interconnect
structures.
20. The method of claim 13, further comprising forming a bit-line
dielectric liner that conformally covers sidewalls and top surfaces
of the bit lines, wherein the via-level dielectric layer is formed
over the bit-line dielectric liner with curved bottom surfaces that
overlie inter-bit-line cavities located between neighboring pairs
of bit lines and laterally extending along the second horizontal
direction.
Description
FIELD
[0001] The present disclosure relates generally to the field of
semiconductor devices, and specifically to a three-dimensional
memory device including bit lines located between memory elements
and an underlying peripheral circuit and methods of making the
same.
BACKGROUND
[0002] Recently, ultra-high-density storage devices using
three-dimensional (3D) memory stack structures have been proposed.
For example, a three-dimensional NAND memory device may use an
array of an alternating stack of insulating materials and spacer
material layers that is formed over a substrate containing
peripheral devices (e.g., driver/logic circuits). The spacer
material layers may be formed as electrically conductive layers, or
may be formed as sacrificial material layers that are subsequently
replaced with electrically conductive layers. Memory openings are
formed through the alternating stack, and are filled with memory
stack structures, each of which includes a vertical stack of memory
elements and a vertical semiconductor channel.
[0003] Typically, vertical semiconductor channels of the memory
stack structures are electrically connected to a source line that
underlies the alternating stack. In some configurations, the
vertical semiconductor channels are connected to the source line
through pedestal channel structures that are formed at the bottom
of each memory opening. In some other configurations, the source
line is formed by replacement of a buried sacrificial material
layer that underlies the alternating stack.
SUMMARY
[0004] According to an aspect of the present disclosure, a
three-dimensional semiconductor device is provided, which
comprises: bit lines formed in the lower-interconnect-level
dielectric material layers, laterally spaced apart along a first
horizontal direction, and laterally extending along a second
horizontal direction that is perpendicular to the first horizontal
direction, and located over a substrate; bit-line-connection via
structures contacting a top surface of a respective one of the bit
lines and formed in a via-level dielectric layer; pillar-shaped
drain regions contacting a respective one of the
bit-line-connection via structures; an alternating stack of
insulating layers and electrically conductive layers located over
the pillar-shaped drain regions; memory opening fill structures
vertically extending through the alternating stack and including a
respective memory stack structure that contains a respective
vertical semiconductor channel and a respective vertical stack of
memory elements; a source layer overlying the alternating stack and
electrically connected to an upper end of each vertical
semiconductor channel within a subset of the vertical semiconductor
channels; and field effect transistors located on or over the top
surface of the substrate, wherein the bit lines are located between
the field effect transistors and the memory opening fill
structures.
[0005] According to another aspect of the present disclosure, a
method of forming a three-dimensional semiconductor device is
provided, which comprises forming field effect transistors on or
over a top surface of the substrate; forming bit lines formed in
the lower-interconnect-level dielectric material layers over the
field effect transistors, wherein the bit lines are laterally
spaced apart along a first horizontal direction, and laterally
extend a long a second horizontal direction that is perpendicular
to the first horizontal direction; forming bit-line-connection via
structures formed in a via-level dielectric layer on a top surface
of a respective one of the bit lines; forming pillar-shaped drain
regions on a respective one of the bit-line-connection via
structures; forming an alternating stack of insulating layers and
spacer material layers over the pillar-shaped drain regions,
wherein the spacer material layers are formed as, or are
subsequently replaced with, electrically conductive layers; forming
memory openings through the alternating stack on a respective one
of the pillar-shaped drain regions; forming memory opening fill
structures including a respective memory stack structure that
contains a respective vertical semiconductor channel and a
respective vertical stack of memory elements in the memory
openings; and forming a source layer over the alternating stack,
wherein the source layer is electrically connected to an upper end
of each vertical semiconductor channel within a subset of the
vertical semiconductor channels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1A is a vertical cross-sectional view of an exemplary
structure after formation of field effect transistors,
lower-interconnect-level dielectric material layers, lower-level
metal interconnect structures, and bit lines on a semiconductor
substrate according to an embodiment of the present disclosure.
[0007] FIG. 1B is a top-down view of the exemplary structure of
FIG. 1A. The hinged vertical plane A-A' is the plane of the
vertical cross-sectional view of FIG. 1A.
[0008] FIG. 1C illustrate sequential vertical cross-sectional views
of a region of the exemplary structure during formation of the bit
lines of FIG. 1A
[0009] FIG. 2A is a vertical cross-sectional view of an exemplary
structure after formation of a via-level dielectric layer and
bit-line-connection via structures according to an embodiment of
the present disclosure.
[0010] FIG. 2B is a top-down view of the exemplary structure of
FIG. 2A. The hinged vertical plane A-A' is the plane of the
vertical cross-sectional view of FIG. 2A.
[0011] FIG. 2C is a vertical cross-sectional view of a region of
the exemplary structure after formation of the via-level dielectric
layer according to an embodiment of the present disclosure.
[0012] FIG. 2D is a vertical cross-sectional view of a region of
the exemplary structure after formation of the bit-line-connection
via structures without any overlay error according to an embodiment
of the present disclosure.
[0013] FIG. 2E is a vertical cross-sectional view of a region of
the exemplary structure after formation of the bit-line-connection
via structures with an overlay error according to an embodiment of
the present disclosure.
[0014] FIG. 3A is a vertical cross-sectional view of an exemplary
structure after formation of a drain-level dielectric layer and
pillar-shaped drain regions according to an embodiment of the
present disclosure.
[0015] FIG. 3B is a top-down view of the exemplary structure of
FIG. 3A. The hinged vertical plane A-A' is the plane of the
vertical cross-sectional view of FIG. 3A.
[0016] FIG. 4 is a vertical cross-sectional view of the exemplary
structure after formation of a first-tier alternating stack of
first insulting layers and first spacer material layers according
to an embodiment of the present disclosure.
[0017] FIG. 5 is a vertical cross-sectional view of the exemplary
structure after patterning a first-tier staircase region, a first
retro-stepped dielectric material portion, and an inter-tier
dielectric layer according to an embodiment of the present
disclosure.
[0018] FIG. 6A is a vertical cross-sectional view of the exemplary
structure after formation of first-tier memory openings and
first-tier support openings according to an embodiment of the
present disclosure.
[0019] FIG. 6B is a horizontal cross-sectional of the exemplary
structure along the horizontal plane B-B' of FIG. 6A. The hinged
vertical plane A-A' corresponds to the plane of the vertical
cross-sectional view of FIG. 6A.
[0020] FIG. 7 is a vertical cross-sectional view of the exemplary
structure after formation of various sacrificial fill structures
according to an embodiment of the present disclosure.
[0021] FIG. 8 is a vertical cross-sectional view of the exemplary
structure after formation of a second-tier alternating stack of
second insulating layers and second spacer material layers, second
stepped surfaces, and a second retro-stepped dielectric material
portion according to an embodiment of the present disclosure.
[0022] FIG. 9A is a vertical cross-sectional view of the exemplary
structure after formation of second-tier memory openings and
second-tier support openings according to an embodiment of the
present disclosure.
[0023] FIG. 9B is a horizontal cross-sectional of the exemplary
structure along the horizontal plane B-B' of FIG. 9A. The hinged
vertical plane A-A' corresponds to the plane of the vertical
cross-sectional view of FIG. 9A.
[0024] FIG. 10 is a vertical cross-sectional view of the exemplary
structure after formation of inter-tier memory openings and
inter-tier support openings according to an embodiment of the
present disclosure.
[0025] FIGS. 11A-11F illustrate sequential vertical cross-sectional
views of a memory opening during formation of a memory opening fill
structure according to an embodiment of the present disclosure.
[0026] FIG. 12 is a vertical cross-sectional view of the exemplary
structure after formation of memory opening fill structures and
support pillar structures according to an embodiment of the present
disclosure.
[0027] FIG. 13A is a vertical cross-sectional view of the exemplary
structure after formation of pillar cavities through the
alternating stacks according to an embodiment of the present
disclosure.
[0028] FIG. 13B is a horizontal cross-sectional of the exemplary
structure along the horizontal plane B-B' of FIG. 13A. The hinged
vertical plane A-A' corresponds to the plane of the vertical
cross-sectional view of FIG. 13A.
[0029] FIG. 14 is a vertical cross-sectional view of the exemplary
structure after formation of dielectric pillar structures through
the alternating stacks according to an embodiment of the present
disclosure.
[0030] FIG. 15A is a vertical cross-sectional view of the exemplary
structure after formation of backside trenches through the
alternating stacks according to an embodiment of the present
disclosure.
[0031] FIG. 15B is a horizontal cross-sectional of the exemplary
structure along the horizontal plane B-B' of FIG. 13A. The hinged
vertical plane A-A' corresponds to the plane of the vertical
cross-sectional view of FIG. 13A.
[0032] FIG. 16 is a vertical cross-sectional view of the exemplary
structure after formation of backside recesses according to an
embodiment of the present disclosure.
[0033] FIG. 17 is a vertical cross-sectional view of the exemplary
structure after formation of electrically conductive layers
according to an embodiment of the present disclosure.
[0034] FIG. 18A is a vertical cross-sectional view of the exemplary
structure after formation of insulating wall structures according
to an embodiment of the present disclosure.
[0035] FIG. 18B is a horizontal cross-sectional of the exemplary
structure along the horizontal plane B-B' of FIG. 18A. The hinged
vertical plane A-A' corresponds to the plane of the vertical
cross-sectional view of FIG. 18A.
[0036] FIG. 18C is a vertical cross-sectional view of the exemplary
structure along the vertical plane C-C' of FIG. 18B.
[0037] FIG. 19A is a vertical cross-sectional view of the exemplary
structure after formation of various contact via structures
according to an embodiment of the present disclosure.
[0038] FIG. 19B is a horizontal cross-sectional view of the
exemplary structure along the vertical plane B-B' of FIG. 19A. The
hinged vertical plane A-A' corresponds to the plane of the vertical
cross-sectional view of FIG. 19A.
[0039] FIG. 20A is a vertical cross-sectional view of the exemplary
structure after formation of through-memory-level via structures
and upper-level metal interconnect structures according to an
embodiment of the present disclosure.
[0040] FIG. 20B is a horizontal cross-sectional view of the
exemplary structure along the vertical plane B-B' of FIG. 20A. The
hinged vertical plane A-A' corresponds to the plane of the vertical
cross-sectional view of FIG. 20A.
[0041] FIG. 21 is a layout of a prior art three-dimensional memory
device using bit line tap regions to provide vertical
interconnections through the level of a three-dimensional memory
device.
[0042] FIG. 22 is a layout for the three-dimensional memory device
of the present disclosure, which does not require areas for bit
line tap regions.
[0043] FIG. 23 is a vertical cross-sectional view of an alternative
embodiment of the exemplary structure.
DETAILED DESCRIPTION
[0044] As three-dimensional memory devices scale to smaller device
dimensions, the device area for peripheral devices (which may be
referred to interchangeably as driver devices, driver circuits,
logic circuitry, logic devices, peripheral circuits, etc.) may take
up a significant portion of the total chip area. The peripheral
logic circuitry provides control of the various nodes of the memory
devices. Manufacture of a three-dimensional memory array typically
involves many high temperature processing steps, such as activation
anneals and high temperature layer deposition steps. Such high
temperature processing steps have an adverse impact on logic
devices formed on a same substrate as the three-dimensional memory
array. However, high performance peripheral devices are necessary
to provide high performance for a three-dimensional memory
device.
[0045] A three-dimensional NAND memory device may use an array of
an alternating stack of insulating materials and spacer material
layers that is formed over a substrate containing peripheral
devices (e.g., driver/logic circuits). The spacer material layers
may be formed as electrically conductive layers, or may be formed
as sacrificial material layers that are subsequently replaced with
electrically conductive layers. Memory openings are formed through
the alternating stack, and are filled with memory stack structures,
each of which includes a vertical stack of memory elements and a
vertical semiconductor channel. Typically, vertical semiconductor
channels of the memory stack structures are electrically connected
to each of the source lines. In some configurations, the vertical
semiconductor channels are connected to the source line through
pedestal channel structures that are formed at the bottom of each
memory opening. In some other configurations, the source line is
formed by replacement of a buried sacrificial material layer that
underlies the alternating stack. As the number of electrically
conductive layers increases in the alternating stack, however,
process control for formation of pedestal channel portions and
replacement of the buried sacrificial material layer becomes
difficult due to high aspect ratios of the memory openings or
access trenches. A three-dimensional memory device is desired which
does not require challenging processes that modify structures at
the bottom of high aspect ratio openings through the alternating
stack.
[0046] The embodiments of the present disclosure provide a
three-dimensional memory device including bit lines located between
memory elements and an underlying peripheral circuit and methods of
making the same, the various aspects of which are described herein
in detail. The embodiments of the present disclosure may be used to
form various 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.
[0047] Ordinals such as "first," "second," and "third" are used
merely to identify similar elements, and different ordinals may be
used across the specification and the claims of the instant
disclosure. As used herein, a first element located "on" a second
element may 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. As used herein,
an "in-process" structure or a "transient" structure refers to a
structure that is subsequently modified.
[0048] 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.
[0049] As used herein, a "memory level" or a "memory array level"
refers to the level corresponding to a general region between a
first horizontal plane (i.e., a plane parallel to the top surface
of the substrate) including topmost surfaces of an array of memory
elements and a second horizontal plane including bottommost
surfaces of the array of memory elements. As used herein, a
"through-stack" element refers to an element that vertically
extends through a memory level.
[0050] As used herein, a "semiconducting material" refers to a
material having electrical conductivity in the range from
1.0.times.10.sup.-5 S/m to 1.0.times.10.sup.5 S/m. As used herein,
a "semiconductor material" refers to a material having electrical
conductivity in the range from 1.0.times.10.sup.-5 S/m to 1.0 S/m
in the absence of electrical dopants therein, and is capable of
producing a doped material having electrical conductivity in a
range from 1.0 S/m to 1.0.times.10.sup.7 S/m 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/m. As used herein,
an "insulator material" or a "dielectric material" refers to a
material having electrical conductivity less than
1.0.times.10.sup.-5 S/m. As used herein, a "heavily doped
semiconductor material" refers to a semiconductor material that is
doped with electrical dopant at a sufficiently high atomic
concentration to become a conductive material either as formed as a
crystalline material or if converted into a crystalline material
through an anneal process (for example, from an initial amorphous
state), i.e., to provide electrical conductivity greater than
1.0.times.10.sup.5 S/m. A "doped semiconductor material" may be a
heavily doped semiconductor material, or may be a semiconductor
material that includes electrical dopants (i.e., p-type dopants
and/or n-type dopants) at a concentration that provides electrical
conductivity in the range from 1.0.times.10.sup.-5 S/m to
1.0.times.10.sup.7 S/m. An "intrinsic semiconductor material"
refers to a semiconductor material that is not doped with
electrical dopants. Thus, a semiconductor material may be
semiconducting or conductive, and may be an intrinsic semiconductor
material or a doped semiconductor material. A doped semiconductor
material may be semiconducting or conductive depending on the
atomic concentration of electrical dopants therein. As used herein,
a "metallic material" refers to a conductive material including at
least one metallic element therein. All measurements for electrical
conductivities are made at the standard condition.
[0051] 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 substrate may include integrated circuits fabricated
thereon, such as driver circuits for a memory device
[0052] The various three-dimensional memory devices of the present
disclosure include a monolithic three-dimensional NAND string
memory device, and may be fabricated using the various embodiments
described herein. The monolithic three-dimensional NAND string is
located in a monolithic, three-dimensional array of NAND strings
located over the substrate. At least one memory cell in the first
device level of the three-dimensional array of NAND strings is
located over another memory cell in the second device level of the
three-dimensional array of NAND strings.
[0053] Generally, a semiconductor package (or a "package") refers
to a unit semiconductor device that may be attached to a circuit
board through a set of pins or solder balls. A semiconductor
package may include a semiconductor chip (or a "chip") or a
plurality of semiconductor chips that are bonded throughout, for
example, by flip-chip bonding or another chip-to-chip bonding. A
package or a chip may include a single semiconductor die (or a
"die") or a plurality of semiconductor dies. A die is the smallest
unit that may independently execute external commands or report
status. Typically, a package or a chip with multiple dies is
capable of simultaneously executing as many number of external
commands as the total number of dies therein. Each die includes one
or more planes. Identical concurrent operations may be executed in
each plane within a same die, although there may be some
restrictions. In case a die is a memory die, i.e., a die including
memory elements, concurrent read operations, concurrent write
operations, or concurrent erase operations may be performed in each
plane within a same memory die. In a memory die, each plane
contains a number of memory blocks (or "blocks"), which are the
smallest unit that may be erased by in a single erase operation.
Each memory block contains a number of pages, which are the
smallest units that may be selected for programming. A page is also
the smallest unit that may be selected to a read operation.
[0054] Referring to FIGS. 1A and 1B, an exemplary structure
according to an embodiment of the present disclosure is
illustrated. The exemplary structure includes a substrate 8 and
semiconductor devices 710 formed thereupon. The substrate 8
includes a substrate semiconductor layer 9 at least at an upper
portion thereof. Shallow trench isolation structures 720 may be
formed in an upper portion of the substrate semiconductor layer 9
to provide electrical isolation from the semiconductor devices 710.
The semiconductor devices 710 may include, for example, field
effect transistors including respective transistor active regions
742 (i.e., source regions and drain regions), channel regions 746,
and gate structures 750. The field effect transistors may be
arranged in a CMOS configuration. Each gate structure 750 may
include, for example, a gate dielectric 752, a gate electrode 754,
a dielectric gate spacer 756 and a gate cap dielectric 758. The
semiconductor devices 710 may include any semiconductor circuitry
to support operation of a memory structure to be subsequently
formed, which is typically referred to as a driver circuitry, which
is also known as peripheral circuitry. As used herein, a peripheral
circuitry refers to any, each, or all, of word line decoder
circuitry, word line switching circuitry, bit line decoder
circuitry, bit line sensing and/or switching circuitry, power
supply/distribution circuitry, data buffer and/or latch, or any
other semiconductor circuitry that may be implemented outside a
memory array structure for a memory device. For example, the
semiconductor devices may include word line switching devices for
electrically biasing word lines of three-dimensional memory
structures to be subsequently formed.
[0055] Dielectric material layers are formed over the semiconductor
devices. The dielectric material layers may include, for example, a
dielectric liner 762 (such as a silicon nitride liner that blocks
diffusion of mobile ions and/or apply appropriate stress to
underlying structures) and lower-interconnect-level dielectric
material layers 764 that overlie the dielectric liner 762.
[0056] The lower-interconnect-level dielectric material layers 764
function as a matrix for lower-level metal interconnect structures
780 that provide electrical wiring to and from the various nodes of
the semiconductor devices 710 and landing pads for
through-memory-level contact via structures to be subsequently
formed. The lower-level metal interconnect structures 780 may be
formed within the lower-interconnect-level dielectric material
layers 764. The lower-interconnect-level dielectric material layers
764 may be a plurality of dielectric material layers in which
various elements of the lower-level metal interconnect structures
780 are sequentially formed. Each dielectric material layer
selected from the lower-interconnect-level dielectric material
layers 764 may include any of doped silicate glass, undoped
silicate glass, organosilicate glass, silicon nitride, silicon
oxynitride, and dielectric metal oxides (such as aluminum oxide).
In one embodiment, the lower-interconnect-level dielectric material
layers 764 may comprise, or consist essentially of, dielectric
material layers having dielectric constants that do not exceed the
dielectric constant of undoped silicate glass (silicon oxide) of
3.9. The lower-level metal interconnect structures 780 may include
various device contact via structures 782 (e.g., source and drain
electrodes which contact the respective source and drain nodes of
the device or gate electrode contacts), lower-level metal line
structures 784, lower-level metal via structures 786, and
bit-line-connection metal line structures 788.
[0057] Bit lines 98 may be formed at the topmost level of the
lower-level metal line structures 784. A three-dimensional array of
memory elements is subsequently formed within the areas of the bit
lines 98. Thus, the region in which the bit lines are formed are
herein referred to as a memory array region 100. A region adjacent
to the memory array region 100 is subsequently used to form stepped
surfaces of an alternating stack of insulating layers and
electrically conductive layers, and is herein referred to as a
staircase region 200. A peripheral region 400 may be provided
adjacent to the staircase region 200. The peripheral region 400
includes structures for forming electrical connections between
semiconductor devices 710 and memory devices to be subsequently
formed thereupon. The bit-line-connection metal line structures 788
include metal lines that are electrically connected to the bit
lines 98 and used as components of electrically conductive paths
between a respective bit line 98 and a respective one of the
semiconductor devices 710. The bit lines 98 may be formed on a
respective one of the lower-level metal via structures 786. The bit
lines 98 may be parallel metal line structures that are laterally
spaced apart along the first horizontal direction hd1 with a
uniform pitch (which is herein referred to as a bit line pitch) and
laterally extend along a second horizontal direction hd2 that is
perpendicular to the first horizontal direction hd1.
[0058] Each of the lower-level metal interconnect structures 780
may include a metallic nitride liner and a metal fill structure.
Topmost surfaces of the bit lines 98 and the topmost ones of the
lower-level metal line structures 784 may be formed within a same
horizontal plane, which may, or may not, include a topmost surface
of the lower-interconnect-level dielectric material layers 764. The
region of the semiconductor devices 710 and the combination of the
lower-interconnect-level dielectric material layers 764 and the
lower-level metal interconnect structures 780 is herein referred to
a peripheral device region 700, over which a memory-level assembly
is subsequently formed. The lower-level metal interconnect
structures 780 may be electrically connected to active nodes (e.g.,
transistor active regions 742 or gate electrodes 754) of the
semiconductor devices 710 (e.g., CMOS devices), and are located at
the level of the lower-interconnect-level dielectric material
layers 764.
[0059] The semiconductor devices 710 include field effect
transistors located on a top surface of the substrate 8. The
semiconductor devices 710 comprise a peripheral circuitry for a
three-dimensional array of memory elements to be subsequently
formed. The peripheral circuitry may include a word line driver
circuit and a bit line driver circuit located on the top surface of
the substrate 8. The lower-level metal interconnect structures 780
located in the lower-interconnect-level dielectric material layers
764 are electrically connected to the field effect transistors. The
bit lines 98 are formed in the lower-interconnect-level dielectric
material layers 764. The bit lines 98 are electrically connected to
a subset of the field effect transistors that comprises bit line
drivers through a subset of the lower-level metal interconnect
structures 780.
[0060] Referring to FIG. 1C, an exemplary processing sequence for
forming the bit lines 98 of FIGS. 1A and 1B is illustrated. A bit
line material layer 98L may be deposited on a physically exposed
planar surface of the lower-interconnect-level dielectric material
layers 764. The bit line material layer 98L may include, for
example, a vertical stack of a metallic liner material (such as
TiN, TaN, or WN) and at least one metal (such as Cu, W, Mo, Ru,
and/or Co).
[0061] At least one pattern transfer material layer 771L may be
deposited over the bit line material layer 98L. The at least one
pattern transfer material layer 771L includes at least one material
that may transfer a lithographic pattern with high pattern
fidelity, e.g., without generating line edge roughening. For
example, the at least one pattern transfer material layer 771L may
include a layer stack including, from bottom to top, an undoped
silicate glass layer and an amorphous silicon layer.
[0062] An organic planarization layer (OPL) 774L may be deposited
over the at least one pattern transfer material layer 771L. The OPL
774L contains a self-planarizing organic material that includes
carbon, hydrogen, oxygen, and optionally nitrogen, fluorine, and
silicon. In one embodiment, the self-planarizing organic material
may be a polymer with sufficiently low viscosity so that the top
surface of the applied polymer forms a planar horizontal surface.
In one embodiment, the OPL 774L may include a transparent organic
polymer. The OPL 774L may include a C.sub.xH.sub.y polymer.
Non-limiting examples of materials that may be used for the OPL
774L include, but are not limited to, CHM701B (commercially
available from Cheil Chemical Co., Ltd.), HM8006 and HM8014
(commercially available from JSR Corporation), and ODL-102 and
ODL-401 (commercially available from ShinEtsu Chemical, Co., Ltd.).
The OPL 774L may be applied, for example, by spin-coating. In one
embodiment, the thickness of the OPL 774L may be from about 30 nm
to about 200 nm, although lesser and greater thicknesses may also
be used.
[0063] A photoresist material may be applied over the OPL 774L, and
may be lithographically patterned with a line and space pattern to
form photoresist line structures 778 that laterally extend a
horizontal direction (such as the second horizontal direction hd2
illustrated in FIG. 1B). In one embodiment, the photoresist line
structures 778 may be formed as a one-dimensional periodic array of
line structures that are repeated along a horizontal direction
(such as the first horizontal direction hd1 illustrated in FIG. 1B)
with a minimum lithographic pitch for a deep ultraviolet
lithographic exposure tool or with a lithographic pitch available
through extreme ultraviolet lithographic exposure tool. For
example, the pitch of the photoresist line structures 778 may be in
a range from 20 nm to 60 nm.
[0064] Spacer line structures 776 may be formed on the sidewalls of
the photoresist line structures 778 by conformal deposition and
anisotropic etch of a conformal spacer material layer. The spacer
line structures 776 includes a material that may be used as an etch
mask material for the OPL 774L. For example, the conformal spacer
material layer may include a low temperature oxide material that
may be deposited at a temperature in a range from 150 degrees
Celsius to 300 degrees Celsius by plasma enhanced chemical vapor
deposition. In one embodiment, the spacer line structures 776 may
include silicon oxide or silicon nitride. The photoresist line
structures 778 may be removed selective to the spacer line
structures 776 and the OPL 774L, for example, by ashing.
[0065] An anisotropic etch process is performed, which etches the
materials of the OPL 774L selective to the material of the spacer
line structures 776. The OPL 774L is patterned into organic
planarization material portions 774. Each organic planarization
material portion 774 may have substantially the same area as an
overlying spacer line structure 776. All, or a predominant portion,
of each spacer line structure 776 may be consumed during the
transfer of the pattern in the spacer line structures 776 through
the OPL 774L and patterning of the OPL 774L into the organic
planarization material portions 774. The lateral dimensions of the
photoresist line structures 778 and the spacer line structures 776
may be selected such that the organic planarization material
portions 774 are formed as a one-dimensional periodic array having
a periodic pitch that is one-half of the pitch of the photoresist
line structures 778. Generally, this condition may be satisfied by
setting the thickness of the spacer line structures 776 such that
the width of each photoresist line structure 778 is the same as the
lateral width of a gap between a neighboring pair of spacer line
structures 776. A top surface of the at least one pattern transfer
material layer 771L is physically exposed between each neighboring
pair of organic planarization material portions 774.
[0066] A conformal template material layer may be deposited over
the organic planarization material portions 774. The conformal
template material layer includes a material that may be used as an
etch mask at least for an upper material layer within the at least
one pattern transfer material layer 771L. For example, if the at
least one pattern transfer material layer 771L contains a layer
stack including, from bottom to top, an undoped silicate glass
layer and an amorphous silicon layer, the conformal template
material layer may include low temperature oxide (silicon oxide)
that may be subsequent used as an etch mask material for patterning
the amorphous silicon layer. An anisotropic etch process may be
performed to remove horizontal portions of the conformal template
material layer selective to the at least one pattern transfer
material layer 771L (e.g., selective to the amorphous silicon
layer). Each remaining vertical portion of the conformal template
material layer constitutes a template line structure 772 that
laterally extend along a horizontal direction (such as the second
horizontal direction hd2 in FIG. 1B). The lateral dimensions of the
template line structures 772 and the organic planarization material
portions 774 may be selected such that the template line structures
772 are formed as a one-dimensional periodic array having a
periodic pitch that is one-quarter of the pitch of the photoresist
line structures 778. Generally, this condition may be satisfied by
setting the thickness of the template line structure 772 such that
the width of each organic planarization material portion 774 is the
same as the lateral width of a gap between a neighboring pair of
template line structures 772. A top surface of the at least one
pattern transfer material layer 771L is physically exposed between
each neighboring pair of organic planarization material portions
774.
[0067] The organic planarization material portions 774 may be
removed selective to the template line structures 772 by an
anisotropic etch process. The pattern in the template line
structures 772 may be subsequently transferred through the at least
one pattern transfer material layer 771L by an anisotropic etch
process. If the at least one pattern transfer material layer 771L
contains a layer stack including, from bottom to top, an undoped
silicate glass layer and an amorphous silicon layer, the
anisotropic etch process may sequentially etch through the
physically exposed portions of the amorphous silicon layer and the
undoped silicate glass layer. All, or a predominant portion, of
each template line structure 772 may be consumed during the pattern
transfer through the at least one pattern transfer material layer
771L by the anisotropic etch process. Each remaining discrete
portion of the at least one pattern transfer material layer 771L
constitutes pattern transfer line structures 771 that laterally
extend along a horizontal direction (such as the second horizontal
direction hd2 in FIG. 1B).
[0068] A subsequent step of the anisotropic etch process may use
the pattern transfer line structures 771 (and any remaining portion
of the template line structures 771, if any) as an etch mask to
pattern the bit line material layer 98L into the bit lines 98.
Optionally, a dielectric material layer that is incorporated into
the lower-interconnect-level dielectric material layers 764 may be
formed between the bit lines 98. In this case, the dielectric
material layer may be planarized to provide a top surface that is
coplanar with the top surfaces of the bit lines 98. Alternatively,
gaps may be present between the bit lines 98 until a subsequent
anisotropic deposition of a dielectric material for forming a
via-level dielectric layer. Remaining portions of the pattern
transfer line structures 771 and any template line structure 772,
if present, are removed selective to the bit lines 98 by an
anisotropic etch process.
[0069] Referring back to FIGS. 1A and 1B, the bit lines 98 may have
the bit line pitch along the first horizontal direction hd1. In one
embodiment, the bit line pitch hd1 may be one-quarter of the pitch
of the patterned photoresist line structures 778, which may use a
minimum lithographic pitch of deep ultraviolet lithographic
exposure tool or a pitch of an extreme ultraviolet lithographic
exposure tool. Thus, the bit lines 98 may be formed with a
sub-lithographic pitch, which is necessary to provide a
one-dimensional periodic array of high density bit lines 98 that
provides a high density three-dimensional array of memory elements
to be subsequently fabricated.
[0070] Referring to FIGS. 2A and 2B, a via-level dielectric layer
768A may be formed over the bit lines 98 and the
lower-interconnect-level dielectric material layers 764. In one
embodiment, unfilled gaps may be present between neighboring pairs
of bit lines 98, and a dielectric material of the via-level
dielectric layer 768A may be anisotropically deposited to provide
voids between neighboring pairs of bit lines 98.
Bit-line-connection via structures 188 may be formed through the
via-level dielectric layer 768A. Each bit-line-connection via
structure 188 may be elongated along the second horizontal
direction hd2. The width of each bit-line-connection via structure
188 along the first horizontal direction hd1 may be about the same
as the width of each bit line 98. In one embodiment, the
bit-line-connection via structures 188 may be elongated along the
second horizontal direction hd2 with a length-to-width ratio in a
range from 1.5 to 10, such as from 2 to 5.
[0071] The general pattern of the bit-line-connection via
structures 188 may be the same as the pattern of memory stack
structures to be subsequently formed in the memory array region
100. In one embodiment, the bit-line-connection via structures 188
may be arranged as multiple clusters that are laterally spaced
apart along the second horizontal direction hd2. Each cluster of
bit-line-connection via structures 188 may include a number N of
rows that extend along the first horizontal direction hd1. The
number N may be in a range from 2 to 16. Each bit line 98 may
contact a respective bit-line-connection via structure 188 within
each cluster of bit-line-connection via structures 188. The pattern
of the bit-line-connection via structures 188 may repeat at every
N-th bit line 98 along the first horizontal direction within each
cluster of bit-line-connection via structures 188. The total number
of the bit-line-connection via structures 188 may be the same as
the total number of memory stack structures to be subsequently
formed.
[0072] FIGS. 2C-2E illustrates an exemplary processing sequence for
forming the bit-line-connection via structures 188 and the
via-level dielectric layer 768A of FIGS. 2A and 2B.
[0073] Referring to FIG. 2C, the bit lines 98 as provided at the
processing steps of FIG. 1C may have gaps throughout. According to
an embodiment of the present disclosure, a bit-line dielectric
liner 765 that conformally covers sidewalls and top surfaces of the
bit lines 98 may be formed by a conformal deposition process. The
bit-line dielectric liner 765 includes a non-porous dielectric
material such as silicon nitride, silicon oxynitride, a dielectric
metal oxide material, and nitrogen-doped organosilicate glass. The
bit-line dielectric liner 765 may be formed by a conformal
deposition process such as atomic layer deposition (ALD) or low
pressure chemical vapor deposition. The thickness of the bit-line
dielectric liner 765 may be in a range from 3% to 30% of the
spacing between a neighboring pair of bit lines 98. For example,
the thickness of the bit-line dielectric liner 765 may be in a
range from 1 nm to 5 nm, although lesser and greater thicknesses
may also be used.
[0074] A via-level dielectric layer 768A may be formed over the
bit-line dielectric liner 765 by an anisotropic deposition process
such as plasma enhanced chemical vapor deposition. The via-level
dielectric layer 768A may include a dielectric material such as
undoped silicate glass, a doped silicate glass, non-porous
organosilicate glass, and porous organosilicate glass. The
thickness of the via-level dielectric layer 768A over the top
surfaces of the bit lines 98 may be in a range from 50 nm to 300
nm, although lesser and greater thicknesses may also be used. The
narrow width of each gap between neighboring pairs of vertical
portions of the bit-line dielectric liner 765 and the anisotropic
nature of the deposition process cause pinch off of the deposited
dielectric material above each gap. Discrete dielectric strip
portions 766 are formed on recessed horizontal surfaces of the
bit-line dielectric liner 765 underneath each gap between
neighboring pairs of vertical portions of the bit-line dielectric
liner 765.
[0075] Unfilled volumes of the gaps between neighboring pairs of
vertical portions of the bit-line dielectric liner 765 are herein
referred to as inter-bit-line cavities 767. The via-level
dielectric layer 768A is formed with curved bottom surfaces that
overlie the inter-bit-line cavities 767. The inter-bit-line
cavities 767 are formed between neighboring pairs of bit lines 98.
The inter-bit-line cavities 767 laterally extend along the second
horizontal direction hd2, which is the lengthwise direction of the
bit lines 98. Each of the inter-bit-line cavities 767 is vertically
bounded by a curved bottom surface portion of the via-level
dielectric layer 768A and a convex surface of a respective
dielectric strip portion 766. The inter-bit-line cavities 767 are
freed of any solid or liquid material, and provides regions of
relative permittivity of 1.0. Capacitive coupling between the bit
lines 98 may be reduced due to the presence of the inter-bit-line
cavities 767, and RC delay of electrical signals through the bit
lines 98 may be reduced.
[0076] Referring to FIGS. 2D and 2E, a photoresist layer (not
shown) may be applied over the via-level dielectric layer 768A, and
may be lithographically patterned to form an array of openings
therethrough. FIG. 2D illustrates a case in which the overlay error
between the lithographic pattern in the photoresist layer relative
to the bit lines 98 is zero. FIG. 2E illustrates a case in which
the overlay error between the lithographic pattern in the
photoresist layer relative to the bit lines 98 is at a maximum
tolerance.
[0077] The pattern of the openings in the photoresist layer may be
transferred through the via-level dielectric layer 768A to form an
array of elongated via cavities. At least one conductive material
may be deposited in the array of elongated via cavities. Excess
portions of the at least one conducive material may be removed from
above the horizontal plane including the top surface of the
via-level dielectric layer 768A by a planarization process, which
may use a recess etch and/or chemical mechanical planarization
(CMP). Each remaining portion of the at least one conductive
material in a respective elongated via cavity constitutes a
bit-line-connection via structure 188. Each bit-line-connection via
structure 188 may include a metallic nitride liner (such as a TiN
layer) and a metallic fill material portion (such as a tungsten
portion).
[0078] According to an aspect of the present disclosure, the
presence of the bit-line dielectric liner 765 between bit lines 98
prevents electrical short between neighboring pairs of bit lines 98
in case the elongated via cavities extending through the via-level
dielectric layer 768A connect to a respective one of the
inter-bit-line cavities 767. In a configuration in which the
bit-line dielectric liner 765 is not present, the at least one
conductive material that is deposited into the elongated via
cavities through the via-level dielectric layer 768A may
continuously extend into an adjoining inter-bit-line cavity 767 and
may be deposited on sidewalls of a neighboring pair of bit lines
98, thereby forming an electrically conductive path between the
neighboring pair of bit lines 98. The bit-line dielectric liner 765
of the present disclosure cover the sidewalls of the bit lines 98
around each inter-bit-line cavity 767. Thus, even when an elongated
via cavity extending through the via-level dielectric layer 768A is
connected to a respective one of the inter-bit-line cavities 767,
the deposited conductive material of the bit-line-connection via
structures 188 physically contacts only one bit line 98, and is
spaced from any other bit line 98 at least by a vertical portion of
the bit-line dielectric liner 765. Thus, the bit-line dielectric
liner 765 of the present disclosure provides short-free electrical
connection to underlying bit lines 98.
[0079] Referring to FIGS. 3A and 3B, a drain-level dielectric layer
768B may be deposited on the via-level dielectric layer 768A. The
drain-level dielectric layer 768B includes a dielectric material
such as undoped silicate glass, a doped silicate glass, or a porous
or non-porous organosilicate glass. The thickness of the
drain-level dielectric layer 768B may be in a range from 50 nm to
300 nm, although lesser and greater thicknesses may also be used.
The drain-level dielectric layer 768B and the via-level dielectric
layer 768A are collectively referred to as drain-side dielectric
layers 768.
[0080] Cylindrical cavities may be formed through the drain-level
dielectric layer 768B. For example, a photoresist layer (not shown)
may be applied over the drain-level dielectric layer 768B, and may
be lithographically patterned to form openings therein. Each
opening in the photoresist layer overlies one, and only one, of the
bit-line-connection via structures 188. Each opening in the
photoresist layer may have a circular cylindrical shape or may have
a lesser length-to-width ratio than the bit-line-connection via
structures 188. The pattern in the photoresist layer may be
transferred through the drain-level dielectric layer 768B by an
anisotropic etch process. The photoresist layer may be subsequently
removed, for example, by ashing. The cylindrical cavities may be
formed over a respective one of the bit-line-connection via
structures 188. The entire top surface of each bit-line-connection
via structure 188 may be physically exposed to the cylindrical
cavities. In one embodiment, the cylindrical cavities have a
circular cylindrical shape or have a lesser length-to-width ratio
than the bit-line-connection via structures 188. In one embodiment,
the cylindrical cavities may be circular cylindrical cavities
having circular horizontal cross-sectional shapes.
[0081] A conductive material may be deposited in the cylindrical
cavities. In one embodiment, the conductive material may include a
doped semiconductor material such as doped silicon. In one
embodiment, the doped semiconductor material may include electrical
dopants at an atomic concentration in a range from
5.0.times.10.sup.19/cm.sup.3 to 2.0.times.10.sup.21/cm.sup.3.
Excess portions of the conductive material may be removed from
above the horizontal plane including the top surface of the
drain-level dielectric layer 768B by a planarization process, which
may use a recess etch and/or chemical mechanical planarization.
Each remaining portion of the conductive material constitutes a
pillar-shaped drain region 88. Each pillar-shaped drain region 88
is formed directly on a top surface of a respective one of the
bit-line-connection via structures 188.
[0082] The pillar-shaped drain regions 88 are formed through the
drain-level dielectric layer 768B. The pillar-shaped drain regions
88 may be formed in multiple clusters. Each cluster of
pillar-shaped drain regions 88 may be formed over a respective
cluster of bit-line-connection via structures 188. Each cluster of
pillar-shaped drain regions 88 may be formed as a periodic
two-dimensional array of pillar-shaped drain regions 88. The
geometrical centers of the bit-line-connection via structures 188
may be offset from geometrical centers of the pillar-shaped drain
regions 88 so that periodic two-dimensional array of
bit-line-connection via structures 188 overlie a set of
bit-line-connection via structures 188 that do not form a periodic
two-dimensional array. In one embodiment, each of the pillar-shaped
drain regions 88 contacts an entire top surface of an underlying
one of the bit-line-connection via structures 188, and has a
greater horizontal cross-sectional area than a horizontal
cross-sectional area of the underlying one of the
bit-line-connection via structures 188. In one embodiment, the
pillar-shaped drain regions 88 have a circular cylindrical shape or
have a lesser length-to-width ratio than the bit-line-connection
via structures 188.
[0083] Referring to FIG. 4, an alternating stack of first material
layers and second material layers is subsequently formed. Each
first material layer may include a first material, and each second
material layer may include a second material that is different from
the first material. In case at least another alternating stack of
material layers is subsequently formed over the alternating stack
of the first material layers and the second material layers, the
alternating stack is herein referred to as a first-tier alternating
stack. The level of the first-tier alternating stack is herein
referred to as a first-tier level, and the level of the alternating
stack to be subsequently formed immediately above the first-tier
level is herein referred to as a second-tier level, etc.
[0084] The first-tier alternating stack may include first insulting
layers 132 as the first material layers, and first spacer material
layers as the second material layers. In one embodiment, the first
spacer material layers may be sacrificial material layers that are
subsequently replaced with electrically conductive layers. In
another embodiment, the first spacer material layers may be
electrically conductive layers that are not subsequently replaced
with other layers. While the present disclosure is described using
embodiments in which sacrificial material layers are replaced with
electrically conductive layers, embodiments in which the spacer
material layers are formed as electrically conductive layers
(thereby obviating the need to perform replacement processes) are
expressly contemplated herein.
[0085] In one embodiment, the first material layers and the second
material layers may be first insulating layers 132 and first
sacrificial material layers 142, respectively. In one embodiment,
each first insulating layer 132 may include a first insulating
material, and each first sacrificial material layer 142 may include
a first sacrificial material. An alternating plurality of first
insulating layers 132 and first sacrificial material layers 142 is
formed over the drain-side dielectric layers 768. As used herein, a
"sacrificial material" refers to a material that is removed during
a subsequent processing step.
[0086] 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 throughout, or may have
different thicknesses. The second elements may have the same
thickness throughout, 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.
[0087] The first-tier alternating stack (132, 142) may 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 may be at least one
insulating material. Insulating materials that may be used 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 may be silicon oxide.
[0088] The second material of the first sacrificial material layers
142 is a sacrificial material that may 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.
[0089] 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 may be subsequently replaced with electrically
conductive electrodes which may function, for example, as control
gate electrodes of a vertical NAND device. In one embodiment, the
first sacrificial material layers 142 may be material layers that
comprise silicon nitride.
[0090] In one embodiment, the first insulating layers 132 may
include silicon oxide, and sacrificial material layers may include
silicon nitride sacrificial material layers. The first material of
the first insulating layers 132 may be deposited, for example, by
chemical vapor deposition (CVD). For example, if silicon oxide is
used for the first insulating layers 132, tetraethylorthosilicate
(TEOS) may be used as the precursor material for the CVD process.
The second material of the first sacrificial material layers 142
may be formed, for example, CVD or atomic layer deposition
(ALD).
[0091] The thicknesses of the first insulating layers 132 and the
first sacrificial material layers 142 may be in a range from 20 nm
to 50 nm, although lesser and greater thicknesses may be used 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 may be in a range from 2 to 1,024, and typically from 8 to 256,
although a greater number of repetitions may also be used. In one
embodiment, each first sacrificial material layer 142 in the
first-tier alternating stack (132, 142) may have a uniform
thickness that is substantially invariant within each respective
first sacrificial material layer 142.
[0092] A first insulating cap layer 170 is subsequently formed over
the first alternating stack (132, 142). The first insulating cap
layer 170 includes a dielectric material, which may be any
dielectric material that may be used for the first insulating
layers 132. In one embodiment, the first insulating cap layer 170
includes the same dielectric material as the first insulating
layers 132. The thickness of the first insulating cap layer 170 may
be in a range from 20 nm to 300 nm, although lesser and greater
thicknesses may also be used.
[0093] Referring to FIG. 5, the first insulating cap layer 170 and
the first-tier alternating stack (132, 142) may be patterned to
form first stepped surfaces in the staircase region 200. The
staircase region 200 may include a respective 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) and/or additional tier structures. The first
stepped surfaces may 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 170, 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. In one embodiment, top
surfaces of the first sacrificial material layers 142 may be
physically exposed at the first stepped surfaces. The cavity
overlying the first stepped surfaces is herein referred to as a
first stepped cavity.
[0094] A dielectric fill material (such as undoped silicate glass
or doped silicate glass) may be deposited to fill the first stepped
cavity. Excess portions of the dielectric fill material may be
removed from above the horizontal plane including the top surface
of the first insulating cap layer 170. A remaining portion of the
dielectric fill material that fills the region overlying the first
stepped surfaces constitute a first retro-stepped dielectric
material portion 165. 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. The first-tier alternating stack (132, 142) and
the first retro-stepped dielectric material portion 165
collectively constitute a first-tier structure, which is an
in-process structure that is subsequently modified.
[0095] An inter-tier dielectric layer 180 may be optionally
deposited over the first-tier structure (132, 142, 170, 165). The
inter-tier dielectric layer 180 includes a dielectric material such
as silicon oxide. In one embodiment, the inter-tier dielectric
layer 180 may include a doped silicate glass having a greater etch
rate than the material of the first insulating layers 132 (which
may include an undoped silicate glass). For example, the inter-tier
dielectric layer 180 may include phosphosilicate glass. The
thickness of the inter-tier dielectric layer 180 may be in a range
from 30 nm to 300 nm, although lesser and greater thicknesses may
also be used.
[0096] Referring to FIGS. 6A and 6B, various first-tier openings
(149, 129) may be formed through the inter-tier dielectric layer
180 and the first-tier structure (132, 142, 170, 165) and into the
drain-side dielectric layers 768. A photoresist layer (not shown)
may be applied over the inter-tier dielectric layer 180, and may be
lithographically patterned to form various openings therethrough.
The pattern of openings in the photoresist layer may be transferred
through the inter-tier dielectric layer 180 and the first-tier
structure (132, 142, 170, 165) and into the drain-side dielectric
layers 768 by a first anisotropic etch process to form the various
first-tier openings (149, 129) concurrently, i.e., during the first
isotropic etch process. The various first-tier openings (149, 129)
may include first-tier memory openings 149 and first-tier support
openings 129. Locations of steps S in the first alternating stack
(132, 142) are illustrated as dotted lines in FIG. 4B.
[0097] The first-tier memory openings 149 are openings that are
formed in the memory array region 100 through each layer within the
first alternating stack (132, 142) and are subsequently used to
form memory stack structures therein. The first-tier memory
openings 149 may be formed in clusters of first-tier memory
openings 149 that are laterally spaced apart along the second
horizontal direction hd2. Each cluster of first-tier memory
openings 149 may be formed as a two-dimensional array of first-tier
memory openings 149.
[0098] The first-tier support openings 129 are openings that are
formed in the staircase region 200 and are subsequently used to
provide mechanical support during subsequent processing steps. A
subset of the first-tier support openings 129 may be formed through
the first retro-stepped dielectric material portion 165 and through
a respective horizontal surface of the first stepped surfaces.
[0099] In one embodiment, the first anisotropic etch process may
include an initial step in which the materials of the first-tier
alternating stack (132, 142) are etched concurrently with the
material of the first retro-stepped dielectric material portion
165. The chemistry of the initial etch step may alternate to
optimize etching of the first and second materials in the
first-tier alternating stack (132, 142) while providing a
comparable average etch rate to the material of the first
retro-stepped dielectric material portion 165. The first
anisotropic etch process may use, for example, a series of reactive
ion etch processes or a single reaction etch process (e.g.,
CF.sub.4/O.sub.2/Ar etch). The sidewalls of the various first-tier
openings (149, 129) may be substantially vertical, or may be
tapered. The photoresist layer may be subsequently removed, for
example, by ashing.
[0100] Optionally, the portions of the first-tier memory openings
149 and the first-tier support openings 129 at the level of the
inter-tier dielectric layer 180 may be laterally expanded by an
isotropic etch. In this case, the inter-tier dielectric layer 180
may comprise a dielectric material (such as borosilicate glass)
having a greater etch rate than the first insulating layers 132
(that may include undoped silicate glass) in dilute hydrofluoric
acid. An isotropic etch (such as a wet etch using HF) may be used
to expand the lateral dimensions of the first-tier memory openings
149 at the level of the inter-tier dielectric layer 180. The
portions of the first-tier memory openings 149 located at the level
of the inter-tier dielectric layer 180 may be optionally widened to
provide a larger landing pad for second-tier memory openings to be
subsequently formed through a second-tier alternating stack (to be
subsequently formed prior to formation of the second-tier memory
openings).
[0101] Referring to FIG. 7, sacrificial first-tier opening fill
portions (148, 128) may be formed in the various first-tier
openings (149, 129). For example, a sacrificial first-tier fill
material is deposited concurrently deposited in each of the
first-tier openings (149, 129). The sacrificial first-tier fill
material includes a material that may be subsequently removed
selective to the materials of the first insulating layers 132 and
the first sacrificial material layers 142.
[0102] In one embodiment, the sacrificial first-tier fill material
may include a semiconductor material such as silicon (e.g., a-Si or
polysilicon), a silicon-germanium alloy, germanium, a III-V
compound semiconductor material, or a combination thereof.
Optionally, a thin etch stop liner (such as a silicon oxide layer
or a silicon nitride layer having a thickness in a range from 1 nm
to 3 nm) may be used prior to depositing the sacrificial first-tier
fill material. The sacrificial first-tier fill material may be
formed by a non-conformal deposition or a conformal deposition
method.
[0103] In another embodiment, the sacrificial first-tier fill
material may include a silicon oxide material having a higher etch
rate than the materials of the first insulating layers 132, the
first insulating cap layer 170, and the inter-tier dielectric layer
180. For example, the sacrificial first-tier fill material may
include borosilicate glass or porous or non-porous organosilicate
glass having an etch rate that is at least 100 times higher than
the etch rate of densified TEOS oxide (i.e., a silicon oxide
material formed by decomposition of tetraethylorthosilicate glass
in a chemical vapor deposition process and subsequently densified
in an anneal process) in a 100:1 dilute hydrofluoric acid. In this
case, a thin etch stop liner (such as a silicon nitride layer
having a thickness in a range from 1 nm to 3 nm) may be used prior
to depositing the sacrificial first-tier fill material. The
sacrificial first-tier fill material may be formed by a
non-conformal deposition or a conformal deposition method.
[0104] In yet another embodiment, the sacrificial first-tier fill
material may include amorphous silicon or a carbon-containing
material (such as amorphous carbon or diamond-like carbon) that may
be subsequently removed by ashing, or a silicon-based polymer that
may be subsequently removed selective to the materials of the first
alternating stack (132, 142).
[0105] Portions of the deposited sacrificial material may be
removed from above the topmost layer of the first-tier alternating
stack (132, 142), such as from above the inter-tier dielectric
layer 180. For example, the sacrificial first-tier fill material
may be recessed to a top surface of the inter-tier dielectric layer
180 using a planarization process. The planarization process may
include a recess etch, chemical mechanical planarization (CMP), or
a combination thereof. The top surface of the inter-tier dielectric
layer 180 may be used as an etch stop layer or a planarization stop
layer.
[0106] Remaining portions of the sacrificial first-tier fill
material comprise sacrificial first-tier opening fill portions
(148, 128). For example, each remaining portion of the sacrificial
material in a first-tier memory opening 149 constitutes a
sacrificial first-tier memory opening fill portion 148. Each
remaining portion of the sacrificial material in a first-tier
support opening 129 constitutes a sacrificial first-tier support
opening fill portion 128. The various sacrificial first-tier
opening fill portions (148, 128) are concurrently formed, i.e.,
during a same set of processes including the deposition process
that deposits the sacrificial first-tier fill material and the
planarization process that removes the first-tier deposition
process from above the first alternating stack (132, 142) (such as
from above the top surface of the inter-tier dielectric layer 180).
The top surfaces of the sacrificial first-tier opening fill
portions (148, 128) may be coplanar with the top surface of the
inter-tier dielectric layer 180. Each of the sacrificial first-tier
opening fill portions (148, 128) may, or may not, include cavities
therein.
[0107] Referring to FIG. 8, a second-tier structure may be formed
over the first-tier structure (132, 142, 170, 148). The second-tier
structure may include an additional alternating stack of insulating
layers and spacer material layers, which may be sacrificial
material layers. For example, a second alternating stack (232, 242)
of material layers may be subsequently formed on the top surface of
the first alternating stack (132, 142). The second alternating
stack (232, 242) includes an alternating plurality of third
material layers and fourth material layers. Each third material
layer may include a third material, and each fourth material layer
may include a fourth material that is different from the third
material. In one embodiment, the third material may be the same as
the first material of the first insulating layer 132, and the
fourth material may be the same as the second material of the first
sacrificial material layers 142.
[0108] In one embodiment, the third material layers may be second
insulating layers 232 and the fourth material layers may 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 may 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 may 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 may
be subsequently replaced with electrically conductive electrodes
which may function, for example, as control gate electrodes of a
vertical NAND device.
[0109] In one embodiment, each second insulating layer 232 may
include a second insulating material, and each second sacrificial
material layer 242 may include a second sacrificial material. In
this case, the second alternating stack (232, 242) may include an
alternating plurality of second insulating layers 232 and second
sacrificial material layers 242. The third material of the second
insulating layers 232 may be deposited, for example, by chemical
vapor deposition (CVD). The fourth material of the second
sacrificial material layers 242 may be formed, for example, CVD or
atomic layer deposition (ALD).
[0110] The third material of the second insulating layers 232 may
be at least one insulating material. Insulating materials that may
be used for the second insulating layers 232 may be any material
that may be used for the first insulating layers 132. The fourth
material of the second sacrificial material layers 242 is a
sacrificial material that may be removed selective to the third
material of the second insulating layers 232. Sacrificial materials
that may be used for the second sacrificial material layers 242 may
be any material that may be used for the first sacrificial material
layers 142. In one embodiment, the second insulating material may
be the same as the first insulating material, and the second
sacrificial material may be the same as the first sacrificial
material.
[0111] The thicknesses of the second insulating layers 232 and the
second sacrificial material layers 242 may be in a range from 20 nm
to 50 nm, although lesser and greater thicknesses may be used 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 may be in a range from 2 to 1,024, and typically from 8 to 256,
although a greater number of repetitions may also be used. In one
embodiment, each second sacrificial material layer 242 in the
second alternating stack (232, 242) may have a uniform thickness
that is substantially invariant within each respective second
sacrificial material layer 242.
[0112] Second stepped surfaces in the second stepped area may be
formed in the staircase region 200 using a same set of processing
steps as the processing steps used to form the first stepped
surfaces in the first stepped area with suitable adjustment to the
pattern of at least one masking layer. A second retro-stepped
dielectric material portion 265 may be formed over the second
stepped surfaces in the staircase region 200.
[0113] A second insulating cap layer 270 may be subsequently formed
over the second alternating 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 second insulating cap layer 270 may include silicon
oxide. In one embodiment, the first and second sacrificial material
layers (142, 242) may comprise silicon nitride.
[0114] Generally speaking, at least one alternating stack of
insulating layers (132, 232) and spacer material layers (such as
sacrificial material layers (142, 242)) may be formed over the
drain-side dielectric layers 768, and at least one retro-stepped
dielectric material portion (165, 265) may be formed over the
staircase regions on the at least one alternating stack (132, 142,
232, 242).
[0115] Optionally, source-select-level isolation structures 72 may
be formed through a subset of layers in an upper portion of the
second-tier alternating stack (232, 242). The second sacrificial
material layers 242 that are cut by the source-select-level
isolation structures 72 correspond to the levels in which
drain-select-level electrically conductive layers are subsequently
formed. The source-select-level isolation structures 72 include a
dielectric material such as silicon oxide. The source-select-level
isolation structures 72 may laterally extend along a first
horizontal direction hd1, and may be laterally spaced apart along a
second horizontal direction hd2 that is perpendicular to the first
horizontal direction hd1. The combination of the second alternating
stack (232, 242), the second retro-stepped dielectric material
portion 265, the second insulating cap layer 270, and the optional
source-select-level isolation structures 72 collectively constitute
a second-tier structure (232, 242, 265, 270, 72).
[0116] Referring to FIGS. 9A and 9B, various second-tier openings
(249, 229) may be formed through the second-tier structure (232,
242, 265, 270, 72). A photoresist layer (not shown) may be applied
over the second insulating cap layer 270, and may be
lithographically patterned to form various openings therethrough.
The pattern of the openings may be the same as the pattern of the
various first-tier openings (149, 129), which is the same as the
sacrificial first-tier opening fill portions (148, 128). Thus, the
lithographic mask used to pattern the first-tier openings (149,
129) may be used to pattern the photoresist layer.
[0117] The pattern of openings in the photoresist layer may be
transferred through the second-tier structure (232, 242, 265, 270,
72) by a second anisotropic etch process to form various
second-tier openings (249, 229) concurrently, i.e., during the
second anisotropic etch process. The various second-tier openings
(249, 229) may include second-tier memory openings 249 and
second-tier support openings 229.
[0118] The second-tier memory openings 249 are formed directly on a
top surface of a respective one of the sacrificial first-tier
memory opening fill portions 148. The second-tier support openings
229 are formed directly on a top surface of a respective one of the
sacrificial first-tier support opening fill portions 128. Further,
each second-tier support openings 229 may be formed through a
horizontal surface within the second stepped surfaces, which
include the interfacial surfaces between the second alternating
stack (232, 242) and the second retro-stepped dielectric material
portion 265. Locations of steps S in the first-tier alternating
stack (132, 142) and the second-tier alternating stack (232, 242)
are illustrated as dotted lines in FIG. 7B.
[0119] The second anisotropic etch process may include an etch step
in which the materials of the second-tier alternating stack (232,
242) are etched concurrently with the material of the second
retro-stepped dielectric material portion 265. The chemistry of the
etch step may alternate to optimize etching of the materials in the
second-tier alternating stack (232, 242) while providing a
comparable average etch rate to the material of the second
retro-stepped dielectric material portion 265. The second
anisotropic etch process may use, for example, a series of reactive
ion etch processes or a single reaction etch process (e.g.,
CF.sub.4/O.sub.2/Ar etch). The sidewalls of the various second-tier
openings (249, 229) may be substantially vertical, or may be
tapered. A bottom periphery of each second-tier opening (249, 229)
may be laterally offset, and/or may be located entirely within, a
periphery of a top surface of an underlying sacrificial first-tier
opening fill portion (148, 128). The photoresist layer may be
subsequently removed, for example, by ashing.
[0120] Referring to FIG. 10, the sacrificial first-tier fill
material of the sacrificial first-tier opening fill portions (148,
128) may be removed using an etch process that etches the
sacrificial first-tier fill material selective to the materials of
the first and second insulating layers (132, 232), the first and
second sacrificial material layers (142,242), the first and second
insulating cap layers (170, 270), and the inter-tier dielectric
layer 180. A memory opening 49, which is also referred to as an
inter-tier memory opening, is formed in each combination of a
second-tier memory openings 249 and a volume from which a
sacrificial first-tier memory opening fill portion 148 is removed.
A support opening 19, which is also referred to as an inter-tier
support opening, is formed in each combination of a second-tier
support openings 229 and a volume from which a sacrificial
first-tier support opening fill portion 128 is removed.
[0121] FIGS. 11A-11F provide sequential cross-sectional views of a
memory opening 49 during formation of a memory opening fill
structure. The same structural change occurs in each of the memory
openings 49 and the support openings 19.
[0122] Referring to FIG. 11A, a memory opening 49 in the exemplary
device structure of FIG. 10 is illustrated. The memory opening 49
extends through the first-tier structure and the second-tier
structure.
[0123] Referring to FIG. 11B, a stack of layers including a
blocking dielectric layer 52, a charge storage layer 54, a
tunneling dielectric layer 56, and an optional first semiconductor
channel layer 601 may be sequentially deposited in the memory
openings 49.
[0124] The blocking dielectric layer 52 may include a single
dielectric material layer or a stack of a plurality of dielectric
material layers. In one embodiment, the blocking dielectric layer
may include a dielectric metal oxide layer consisting essentially
of a dielectric metal oxide. As used herein, a dielectric metal
oxide refers to a dielectric material that includes at least one
metallic element and at least oxygen. The dielectric metal oxide
may consist essentially of the at least one metallic element and
oxygen, or may consist essentially of the at least one metallic
element, oxygen, and at least one non-metallic element such as
nitrogen. In one embodiment, the blocking dielectric layer 52 may
include a dielectric metal oxide having a dielectric constant
greater than 7.9, i.e., having a dielectric constant greater than
the dielectric constant of silicon nitride.
[0125] Non-limiting examples of dielectric metal oxides include
aluminum oxide (Al.sub.2O.sub.3), hafnium oxide (HfO.sub.2),
lanthanum oxide (LaO.sub.2), yttrium oxide (Y.sub.2O.sub.3),
tantalum oxide (Ta.sub.2O.sub.5), silicates thereof, nitrogen-doped
compounds thereof, alloys thereof, and stacks thereof. The
dielectric metal oxide layer may be deposited, for example, by
chemical vapor deposition (CVD), atomic layer deposition (ALD),
pulsed laser deposition (PLD), liquid source misted chemical
deposition, or a combination thereof. The thickness of the
dielectric metal oxide layer may be in a range from 1 nm to 20 nm,
although lesser and greater thicknesses may also be used. The
dielectric metal oxide layer may subsequently function as a
dielectric material portion that blocks leakage of stored
electrical charges to control gate electrodes. In one embodiment,
the blocking dielectric layer 52 includes aluminum oxide. In one
embodiment, the blocking dielectric layer 52 may include multiple
dielectric metal oxide layers having different material
compositions.
[0126] Alternatively or additionally, the blocking dielectric layer
52 may include a dielectric semiconductor compound such as silicon
oxide, silicon oxynitride, silicon nitride, or a combination
thereof. In one embodiment, the blocking dielectric layer 52 may
include silicon oxide. In this case, the dielectric semiconductor
compound of the blocking dielectric layer 52 may be formed by a
conformal deposition method such as low pressure chemical vapor
deposition, atomic layer deposition, or a combination thereof. The
thickness of the dielectric semiconductor compound may be in a
range from 1 nm to 20 nm, although lesser and greater thicknesses
may also be used. Alternatively, the blocking dielectric layer 52
may be omitted, and a backside blocking dielectric layer may be
formed after formation of backside recesses on surfaces of memory
films to be subsequently formed.
[0127] Subsequently, the charge storage layer 54 may be formed. In
one embodiment, the charge storage layer 54 may be a continuous
layer or patterned discrete portions of a charge trapping material
including a dielectric charge trapping material, which may be, for
example, silicon nitride. Alternatively, the charge storage layer
54 may include a continuous layer or patterned discrete portions of
a conductive material such as doped polysilicon or a metallic
material that is patterned into multiple electrically isolated
portions (e.g., floating gates), for example, by being formed
within lateral recesses into sacrificial material layers (142,
242). In one embodiment, the charge storage layer 54 includes a
silicon nitride layer. In one embodiment, the sacrificial material
layers (142, 242) and the insulating layers (132, 232) may have
vertically coincident sidewalls, and the charge storage layer 54
may be formed as a single continuous layer.
[0128] In another embodiment, the sacrificial material layers (142,
242) may be laterally recessed with respect to the sidewalls of the
insulating layers (132, 232), and a combination of a deposition
process and an anisotropic etch process may be used to form the
charge storage layer 54 as a plurality of memory material portions
that are vertically spaced apart. While the present disclosure is
described using an embodiment in which the charge storage layer 54
is a single continuous layer, embodiments are expressly
contemplated herein in which the charge storage layer 54 is
replaced with a plurality of memory material portions (which may be
charge trapping material portions or electrically isolated
conductive material portions) that are vertically spaced apart.
[0129] The charge storage layer 54 may be formed as a single charge
storage layer of homogeneous composition, or may include a stack of
multiple charge storage layers. The multiple charge storage layers,
if used, may 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 charge storage layer
54 may comprise an insulating charge trapping material, such as one
or more silicon nitride segments. Alternatively, the charge storage
layer 54 may comprise conductive nanoparticles such as metal
nanoparticles, which may be, for example, ruthenium nanoparticles.
The charge storage layer 54 may 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 charge
storage layer 54 may be in a range from 2 nm to 20 nm, although
lesser and greater thicknesses may also be used.
[0130] The tunneling dielectric layer 56 includes a dielectric
material through which charge tunneling may 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 may 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 may include a stack of a first silicon oxide
layer, a silicon oxynitride layer, and a second silicon oxide
layer, which is commonly known as an ONO stack. In one embodiment,
the tunneling dielectric layer 56 may include a silicon oxide layer
that is substantially free of carbon or a silicon oxynitride layer
that is substantially free of carbon. The thickness of the
tunneling dielectric layer 56 may be in a range from 2 nm to 20 nm,
although lesser and greater thicknesses may also be used.
[0131] The optional first semiconductor channel layer 601 includes
a semiconductor material such as at least one elemental
semiconductor material, at least one III-V compound semiconductor
material, at least one II-VI compound semiconductor material, at
least one organic semiconductor material, or other semiconductor
materials known in the art. In one embodiment, the first
semiconductor channel layer 601 includes amorphous silicon or
polysilicon. The first semiconductor channel layer 601 may be
intrinsic, or may have a doping of a first conductivity type. The
atomic concentration of dopants of the first conductivity type in
the first semiconductor channel layer 601 may be in a range from
1.0.times.10.sup.14/cm.sup.3 to 1.0.times.10.sup.18/cm.sup.3. The
first conductivity type may be the opposite of the conductivity
type of electrical dopants in the pillar-shaped drain regions 88.
The conductivity type of dopants in the pillar-shaped drain regions
88 is herein referred to as a second conductivity type. For
example, if the first conductivity type is p-type, the second
conductivity type is n-type, and vice versa. The first
semiconductor channel layer 601 may be formed by a conformal
deposition method such as low pressure chemical vapor deposition
(LPCVD). The thickness of the first semiconductor channel layer 601
may be in a range from 2 nm to 10 nm, although lesser and greater
thicknesses may also be used. A memory cavity 49' is formed in the
volume of each memory opening 49 that is not filled with the
deposited material layers (52, 54, 56, 601).
[0132] Referring to FIG. 11C, the optional first semiconductor
channel layer 601, the tunneling dielectric layer 56, the charge
storage layer 54, the blocking dielectric layer 52 are sequentially
anisotropically etched using at least one anisotropic etch process.
The portions of the first semiconductor channel layer 601, the
tunneling dielectric layer 56, the charge storage layer 54, and the
blocking dielectric layer 52 located above the top surface of the
second insulating cap layer 270 may be removed by the at least one
anisotropic etch process. Further, the horizontal portions of the
first semiconductor channel layer 601, the tunneling dielectric
layer 56, the charge storage layer 54, and the blocking dielectric
layer 52 at a bottom of each memory cavity 49' may be removed to
form openings in remaining portions thereof. Each of the first
semiconductor channel layer 601, the tunneling dielectric layer 56,
the charge storage layer 54, and the blocking dielectric layer 52
may be etched by a respective anisotropic etch process using a
respective etch chemistry, which may, or may not, be the same for
the various material layers.
[0133] Each remaining portion of the first semiconductor channel
layer 601 may have a tubular configuration. The charge storage
layer 54 may comprise a charge trapping material or a floating gate
material. In one embodiment, each charge storage layer 54 may
include a vertical stack of charge storage regions that store
electrical charges upon programming. In one embodiment, the charge
storage layer 54 may be a charge storage layer in which each
portion adjacent to the sacrificial material layers (142, 242)
constitutes a charge storage region.
[0134] A top surface of a pillar-shaped drain region 88 may be
physically exposed underneath the opening through the first
semiconductor channel layer 601, the tunneling dielectric layer 56,
the charge storage layer 54, and the blocking dielectric layer 52.
Optionally, the physically exposed semiconductor surface at the
bottom of each memory cavity 49' may be vertically recessed by a
recess distance. A tunneling dielectric layer 56 is located over
the charge storage layer 54. A set of a blocking dielectric layer
52, a charge storage layer 54, and a tunneling dielectric layer 56
in a memory opening 49 constitutes a memory film 50, which includes
a plurality of charge storage regions (comprising the charge
storage layer 54) that are insulated from surrounding materials by
the blocking dielectric layer 52 and the tunneling dielectric layer
56. In one embodiment, the first semiconductor channel layer 601,
the tunneling dielectric layer 56, the charge storage layer 54, and
the blocking dielectric layer 52 may have vertically coincident
sidewalls.
[0135] Referring to FIG. 11D, a second semiconductor channel layer
602 may be deposited directly on a top surface of an underlying
pillar-shaped drain region 88 and directly on the first
semiconductor channel layer 601. The second semiconductor channel
layer 602 includes a semiconductor material such as at least one
elemental semiconductor material, at least one III-V compound
semiconductor material, at least one II-VI compound semiconductor
material, at least one organic semiconductor material, or other
semiconductor materials known in the art. In one embodiment, the
second semiconductor channel layer 602 includes amorphous silicon
or polysilicon. The second semiconductor channel layer 602 may be
intrinsic, or may have a doping of the first conductivity type. The
atomic concentration of dopants of the first conductivity type in
the second semiconductor channel layer 602 may be in a range from
1.0.times.10.sup.14/cm.sup.3 to 1.0.times.10.sup.18/cm.sup.3. The
second semiconductor channel layer 602 may be formed by a conformal
deposition method such as low pressure chemical vapor deposition
(LPCVD). The thickness of the second semiconductor channel layer
602 may be in a range from 2 nm to 10 nm, although lesser and
greater thicknesses may also be used. The second semiconductor
channel layer 602 may partially fill the memory cavity 49' in each
memory opening, or may fully fill the cavity in each memory
opening.
[0136] The materials of the first semiconductor channel layer 601
and the second semiconductor channel layer 602 are collectively
referred to as a semiconductor channel material. In other words,
the semiconductor channel material is a set of all semiconductor
material in the first semiconductor channel layer 601 and the
second semiconductor channel layer 602.
[0137] Referring to FIG. 11E, in case the memory cavity 49' in each
memory opening is not completely filled by the second semiconductor
channel layer 602, a dielectric core 62 may be deposited in the
memory cavity 49' to fill any remaining portion of the memory
cavity 49' within each memory opening. The dielectric core 62
includes a dielectric material such as silicon oxide or
organosilicate glass. The dielectric core 62 may be deposited by a
conformal deposition method such as low pressure chemical vapor
deposition (LPCVD), or by a self-planarizing deposition process
such as spin coating.
[0138] The horizontal portion of the dielectric core 62 may be
removed, for example, by a recess etch from above the top surface
of the second insulating cap layer 270. The dielectric core 62 may
be further recessed within each memory opening 49, for example, by
a recess etch to a depth that is located between the top surface of
the second insulating cap layer 270 and the bottom surface of the
second insulating cap layer 270. Further, the horizontal portion of
the second semiconductor channel layer 602 located above the top
surface of the second insulating cap layer 270 may be removed by a
planarization process, which may use a recess etch or chemical
mechanical planarization (CMP). Each remaining portion of the
second semiconductor channel layer 602 may be located entirety
within a memory opening 49 or entirely within a support opening
19.
[0139] Each adjoining pair of a first semiconductor channel layer
601 and a second semiconductor channel layer 602 may collectively
form a vertical semiconductor channel 60 through which electrical
current may flow when a vertical NAND device including the vertical
semiconductor channel 60 is turned on. The average atomic
concentration of dopants of the first conductivity type in the
vertical semiconductor channel 60 may be in a range from
1.0.times.10.sup.14/cm.sup.3 to 1.0.times.10.sup.18/cm.sup.3. A
tunneling dielectric layer 56 is surrounded by a charge storage
layer 54, and laterally surrounds a portion of the vertical
semiconductor channel 60. Each adjoining set of a blocking
dielectric layer 52, a charge storage layer 54, and a tunneling
dielectric layer 56 collectively constitute a memory film 50, which
may store electrical charges with a macroscopic retention time. In
some embodiments, a blocking dielectric layer 52 may not be present
in the memory film 50 at this step, and a blocking dielectric layer
may be subsequently formed after formation of backside recesses. As
used herein, a macroscopic retention time refers to a retention
time suitable for operation of a memory device as a permanent
memory device such as a retention time in excess of 24 hours.
[0140] Referring to FIG. 11F, source regions 61 may be formed by
depositing a doped semiconductor material within each recessed
region above the dielectric cores 62. The source regions 61 may
have a doping of the second conductivity type, which is the
opposite of the first conductivity type. The dopant concentration
in the source regions 61 may be in a range from
5.0.times.10.sup.19/cm.sup.3 to 2.0.times.10.sup.21/cm.sup.3,
although lesser and greater dopant concentrations may also be used.
The doped semiconductor material may be, for example, doped
polysilicon. Excess portions of the deposited semiconductor
material may 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 source regions
61.
[0141] Each combination of a memory film 50 and a vertical
semiconductor channel 60 within a memory opening 49 constitutes a
memory stack structure 55. The memory stack structure 55 is a
combination of a semiconductor channel, a tunneling dielectric
layer, a plurality of memory elements comprising portions of the
charge storage layer 54, and an optional blocking dielectric layer
52. Each combination of a memory stack structure 55, a dielectric
core 62, and a source region 61 within a memory opening 49 is
herein referred to as a memory opening fill structure 58. Each
combination of a memory film 50, a vertical semiconductor channel
60, a dielectric core 62, and a source region 61 within each
support opening 19 fills the respective support openings 19, and
constitutes a support pillar structure.
[0142] Referring to FIG. 12, the exemplary structure is illustrated
after formation of memory opening fill structures 58 and support
pillar structure 20 within the memory openings 49 and the support
openings 19, respectively. An instance of a memory opening fill
structure 58 may be formed within each memory opening 49 of the
structure of FIGS. 10A and 10B. An instance of the support pillar
structure 20 may be formed within each support opening 19 of the
structure of FIGS. 10A and 10B.
[0143] Each memory stack structure 55 includes a vertical
semiconductor channel 60, which may comprise multiple semiconductor
channel layers (601, 602), and a memory film 50. The memory film 50
may comprise a tunneling dielectric layer 56 laterally surrounding
the vertical semiconductor channel 60, a vertical stack of charge
storage regions (comprising a charge storage layer 54) laterally
surrounding the tunneling dielectric layer 56, and an optional
blocking dielectric layer 52. While the present disclosure is
described using the illustrated configuration for the memory stack
structure, the methods of the present disclosure may be applied to
alternative memory stack structures including different layer
stacks or structures for the memory film 50 and/or for the vertical
semiconductor channel 60.
[0144] Referring to FIGS. 13A and 13B, a first contact level
dielectric layer 280 may be formed over the second-tier structure
(232, 242, 270, 265, 72). The first contact level dielectric layer
280 includes a dielectric material such as silicon oxide, and may
be formed by a conformal or non-conformal deposition process. For
example, the first contact level dielectric layer 280 may include
undoped silicate glass and may have a thickness in a range from 100
nm to 600 nm, although lesser and greater thicknesses may also be
used.
[0145] A photoresist layer (not shown) may be applied over the
first contact level dielectric layer 280, and may be
lithographically patterned to form discrete openings within the
area of the memory array region 100 in which memory opening fill
structures 58 are not present. An anisotropic etch may be performed
to form vertical interconnection region cavities 585 having
substantially vertical sidewalls that extend through the first
contact level dielectric layer 280, the second-tier structure (232,
242, 270, 265, 72), and the first-tier structure (132, 142, 170,
165) may be formed underneath the openings in the photoresist
layer. A top surface of a lower-level metal interconnect structure
780 may be physically exposed at the bottom of each vertical
interconnection region cavity 585. The photoresist layer may be
removed, for example, by ashing.
[0146] Referring to FIG. 14, a dielectric material such as silicon
oxide may be deposited in the vertical interconnection region
cavities 585 by a conformal deposition process (such as low
pressure chemical vapor deposition) or a self-planarizing
deposition process (such as spin coating). Excess portions of the
deposited dielectric material may be removed from above the top
surface of the first contact level dielectric layer 280 by a
planarization process. Remaining portions of the dielectric
material in the vertical interconnection region cavities 585
constitute interconnection region dielectric fill material portions
584.
[0147] Referring to FIGS. 15A and 15B, a photoresist layer may be
applied over the first contact level dielectric layer 280 and may
be lithographically patterned to form elongated openings that
extend along the first horizontal direction hd1 between clusters of
memory opening fill structures 58. Backside trenches 79 may be
formed by transferring the pattern in the photoresist layer through
the first contact level dielectric layer 280, the second-tier
structure (232, 242, 270, 265, 72), and the first-tier structure
(132, 142, 170, 165), and into the drain-side dielectric layers
768. Portions of the first contact level dielectric layer 280, the
second-tier structure (232, 242, 270, 265, 72), and the first-tier
structure (132, 142, 170, 165) that underlie the openings in the
photoresist layer may be removed to form the backside trenches 79.
In one embodiment, the backside trenches 79 may be formed between
clusters of memory stack structures 55. The clusters of the memory
opening fill structures 58 may be laterally spaced apart along the
second horizontal direction hd2 by the backside trenches 79. A top
surface of the drain-side dielectric layers 768 may be physically
exposed at the bottom of each backside trench 79.
[0148] Referring to FIG. 16, the sacrificial material layers (142,
242) are may be removed selective to the insulating layers (132,
232), the first and second insulating cap layers (170, 270), the
first contact level dielectric layer 280, and the drain-side
dielectric layers 768. For example, an etchant that selectively
etches the materials of the sacrificial material layers (142, 242)
with respect to the materials of the insulating layers (132, 232),
the first and second insulating cap layers (170, 270), the
retro-stepped dielectric material portions (165, 265), and the
material of the outermost layer of the memory films 50 may be
introduced into the backside trenches 79, for example, using an
isotropic etch process. For example, the sacrificial material
layers (142, 242) may include silicon nitride, the materials of the
insulating layers (132, 232), the first and second insulating cap
layers (170, 270), the retro-stepped dielectric material portions
(165, 265), and the outermost layer of the memory films 50 may
include silicon oxide materials.
[0149] The isotropic etch process may be a wet etch process using a
wet etch solution, or may be a gas phase (dry) etch process in
which the etchant is introduced in a vapor phase into the backside
trenches 79. For example, if the sacrificial material layers (142,
242) include silicon nitride, the etch process may be a wet etch
process in which the exemplary structure is immersed within a wet
etch tank including phosphoric acid, which etches silicon nitride
selective to silicon oxide, silicon, and various other materials
used in the art.
[0150] Backside recesses (143, 243) are formed in volumes from
which the sacrificial material layers (142, 242) are removed. The
backside recesses (143, 243) include first backside recesses 143
that are formed in volumes from which the first sacrificial
material layers 142 are removed and second backside recesses 243
that are formed in volumes from which the second sacrificial
material layers 242 are removed. Each of the backside recesses
(143, 243) may 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 backside
recesses (143, 243) may be greater than the height of the
respective backside recess (143, 243). A plurality of backside
recesses (143, 243) may be formed in the volumes from which the
material of the sacrificial material layers (142, 242) is removed.
Each of the backside recesses (143, 243) may extend substantially
parallel to the top surface of the substrate semiconductor layer 9.
A backside recess (143, 243) may be vertically bounded by a top
surface of an underlying insulating layer (132, 232) and a bottom
surface of an overlying insulating layer (132, 232). In one
embodiment, each of the backside recesses (143, 243) may have a
uniform height throughout.
[0151] Referring to FIG. 17, a backside blocking dielectric layer
(not shown) may be optionally deposited in the backside recesses
(143, 243) and the backside trenches 79 and over the first contact
level dielectric layer 280. The backside blocking dielectric layer
includes a dielectric material such as a dielectric metal oxide,
silicon oxide, or a combination thereof. For example, the backside
blocking dielectric layer may include aluminum oxide. The backside
blocking dielectric layer may be formed by a conformal deposition
process such as atomic layer deposition or chemical vapor
deposition. The thickness of the backside blocking dielectric layer
may be in a range from 1 nm to 20 nm, such as from 2 nm to 10 nm,
although lesser and greater thicknesses may also be used.
[0152] At least one conductive material may be deposited in the
plurality of backside recesses (243, 243), on the sidewalls of the
backside trenches 79, and over the first contact level dielectric
layer 280. The at least one conductive material may be deposited by
a conformal deposition method, which may be, for example, chemical
vapor deposition (CVD), atomic layer deposition (ALD), electroless
plating, electroplating, or a combination thereof. The at least one
conductive material may include 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.
[0153] In one embodiment, the at least one conductive material may
include at least one metallic material, i.e., an electrically
conductive material that includes at least one metallic element.
Non-limiting exemplary metallic materials that may be deposited in
the backside recesses (143, 243) include tungsten, tungsten
nitride, titanium, titanium nitride, tantalum, tantalum nitride,
cobalt, and ruthenium. For example, the at least one conductive
material may include a conductive metallic nitride liner that
includes a conductive metallic nitride material such as TiN, TaN,
WN, or a combination thereof, and a conductive fill material such
as W, Co, Ru, Mo, Cu, or combinations thereof. In one embodiment,
the at least one conductive material for filling the backside
recesses (143, 243) may be a combination of titanium nitride layer
and a tungsten fill material.
[0154] Electrically conductive layers (146, 246) may be formed in
the backside recesses (143, 243) by deposition of the at least one
conductive material. A plurality of first electrically conductive
layers 146 may be formed in the plurality of first backside
recesses 243, a plurality of second electrically conductive layers
246 may be formed in the plurality of second backside recesses 243,
and a continuous metallic material layer (not shown) may be formed
on the sidewalls of each backside trench 79 and over the first
contact level dielectric layer 280. Each of the first electrically
conductive layers 146 and the second electrically conductive layers
246 may include a respective conductive metallic nitride liner and
a respective conductive fill material. Thus, the first and second
sacrificial material layers (142, 242) may be replaced with the
first and second electrically conductive layers (146, 246),
respectively. For example, each first sacrificial material layer
142 may be replaced with an optional portion of the backside
blocking dielectric layer and a first electrically conductive layer
146, and each second sacrificial material layer 242 may be replaced
with an optional 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.
[0155] Residual conductive material may be removed from inside the
backside trenches 79. For example, the deposited metallic material
of the continuous metallic material layer may be etched back from
the sidewalls of each backside trench 79 and from above the first
contact level dielectric layer 280, for example, by an anisotropic
or isotropic etch. Each remaining portion of the deposited metallic
material in the first backside recesses constitutes a first
electrically conductive layer 146. Each remaining portion of the
deposited metallic material in the second backside recesses
constitutes a second electrically conductive layer 246.
[0156] Each electrically conductive layer (146, 246) may be a
conductive sheet including openings therein. A first subset of the
openings through each electrically conductive layer (146, 246) may
be filled with memory opening fill structures 58. A second subset
of the openings through each electrically conductive layer (146,
246) may be filled with the support pillar structures 20. Each
electrically conductive layer (146, 246) may have a lesser area
than any underlying electrically conductive layer (146, 246)
because of the first and second stepped surfaces. Each electrically
conductive layer (146, 246) may have a greater area than any
overlying electrically conductive layer (146, 246) because of the
first and second stepped surfaces.
[0157] Each alternating stack {(132, 146), (232, 246)} comprises
respective stepped surfaces in the staircase region 200. For
example, the first alternating stack (132, 146) may include first
stepped surfaces contacting the first retro-stepped dielectric
material portion 165, and the second alternating stack (232, 246)
may include second stepped surfaces contacting the second
retro-stepped dielectric material portion 265. Each electrically
conductive layer (146, 246) other than a topmost one of the
electrically conductive layers 246 laterally extends farther than
an overlying electrically conductive layer (146, 246). The
electrically conductive layers (146, 246) comprise word lines for
the vertical stacks of memory elements contained within the memory
stack structures 55.
[0158] In some embodiment, source-select-level isolation structures
72 may be provided at topmost levels of the second electrically
conductive layers 246. A subset of the second electrically
conductive layers 246 located at the levels of the
source-select-level isolation structures 72 constitutes drain
select gate electrodes. A subset of the electrically conductive
layer (146, 246) located underneath the drain select gate
electrodes may function as combinations of a control gate and a
word line 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.
[0159] Each of the memory stack structures 55 comprises a vertical
stack of memory elements located at each level of the electrically
conductive layers (146, 246). A subset of the electrically
conductive layers (146, 246) may comprise word lines for the memory
elements. The semiconductor devices in the underlying peripheral
device region 700 may comprise word line switch devices configured
to control a bias voltage to respective word lines. The
memory-level assembly is located over the substrate semiconductor
layer 9. The memory-level assembly includes at least one
alternating stack (132, 146, 232, 246) and memory stack structures
55 vertically extending through the at least one alternating stack
(132, 146, 232, 246).
[0160] Referring to FIGS. 18A-18C, a dielectric material is
deposited in the backside trenches 79 to form dielectric wall
structures 76. Each of the dielectric wall structures 76 may
laterally extend along the first horizontal direction hd1 and may
vertically extend through each layer of an alternating stack of the
insulating layers (132, 232) and the word-line-level electrically
conductive layers 46. Each dielectric wall structure 76 may contact
sidewalls of the first and second insulating cap layers (170,
270).
[0161] Referring to FIGS. 19A and 19B, a second contact level
dielectric layer 282 may be formed over the first contact level
dielectric layer 280. The second contact level dielectric layer 282
includes a dielectric material such as silicon oxide, and may have
a thickness in a range from 100 nm to 600 nm, although lesser and
greater thicknesses may also be used.
[0162] A photoresist layer (not shown) may be applied over the
second contact level dielectric layer 282, and may be
lithographically patterned to form various contact via openings.
For example, openings for forming source contact via structures may
be formed in the memory array region 100, and openings for forming
staircase region contact via structures may be formed in the
staircase region 200. An anisotropic etch process is performed to
transfer the pattern in the photoresist layer through the second
and first contact level dielectric layers (282, 280) and underlying
dielectric material portions. The source regions 61 and the
electrically conductive layers (146, 246) may be used as etch stop
structures. Source contact via cavities may be formed over each
source region 61, and staircase-region contact via cavities may be
formed over each electrically conductive layer (146. 246) at the
stepped surfaces underlying the first and second retro-stepped
dielectric material portions (165, 265). The photoresist layer may
be subsequently removed, for example, by ashing.
[0163] Source contact via structures 68 are formed in the source
contact via cavities and on a top surface of a respective one of
the source regions 61. Staircase-region contact via structures 86
are formed in the staircase-region contact via cavities and on a
top surface of a respective one of the electrically conductive
layers (146, 246). The staircase-region contact via structures 86
may include drain select level contact via structures that contact
a subset of the second electrically conductive layers 246 that
function as drain select level gate electrodes. Further, the
staircase-region contact via structures 86 may include word line
contact via structures that contact electrically conductive layers
(146, 246) that underlie the drain select level gate electrodes and
function as word lines for the memory stack structures 55.
[0164] Referring to FIGS. 20A and 20B, peripheral-region via
cavities may be formed through the second and first contact level
dielectric layers (282, 280), the second and first retro-stepped
dielectric material portions (265, 165), and the drain-side
dielectric layers 768 to top surfaces of a first subset of the
lower-level metal interconnect structure 780 in the peripheral
region 400. Source interconnect via cavities may be formed through
the interconnection region dielectric fill material portions 584
and the drain-side dielectric layers 768 to top surfaces of a
second subset of the lower-level metal interconnect structure 780.
At least one conductive material may be deposited in the
peripheral-region via cavities and in the source interconnect via
cavities. Excess portions of the at least one conductive material
may be removed from above the horizontal plane including the top
surface of the second contact level dielectric layer 282. Each
remaining portion of the at least one conductive material in a
peripheral-region via cavity constitutes a peripheral-region
contact via structure 488. Each remaining portion of the at least
one conductive material in a source interconnect via cavity
constitutes a source interconnect via structure 588.
[0165] At least one additional dielectric layer may be formed over
the contact level dielectric layers (280, 282), and additional
metal interconnect structures (herein referred to as upper-level
metal interconnect structures) may be formed in the at least one
additional dielectric layer. For example, the at least one
additional dielectric layer may include a line-level dielectric
layer 284 that is formed over the contact level dielectric layers
(280, 282). The upper-level metal interconnect structures may
include source layers 92 contacting, or electrically connected to,
a respective one of the source interconnect via structures 588 and
a respective subset of the source contact via structures 68, and
interconnection line structures 96 contacting, and/or electrically
connected to, at least one of the staircase-region contact via
structures 86 and/or the peripheral-region contact via structures
488. The word line contact via structures (which are provided as a
subset of the staircase-region contact via structures 86) may be
electrically connected to the word line driver circuit through a
subset of the lower-level metal interconnect structures 780 and
through a subset of the peripheral-region contact via structures
488.
[0166] Each source interconnect via structure 588 vertically
extends from a lower-level metal interconnect structure 780 formed
within the lower-interconnect-level dielectric material layers 764
to a horizontal plane including top surfaces of the source contact
via structures 68. Each source layer 92 overlies the alternating
stacks {(132, 146), (232, 246)}. Each source layer 92 is
electrically connected to an upper end of each vertical
semiconductor channel within a subset of the vertical semiconductor
channels 60 that underlies the source layer 92. In one embodiment,
each subset of the memory opening fill structures 58 may be located
between a neighboring pair of backside trenches 79. In another
embodiment, each subset of the memory opening fill structures 58
may be located between a neighboring pair of a backside trench 79
and a source-select-level isolation structure 72 or between a
neighboring pair of source-select-level isolation structures
72.
[0167] FIG. 21 is a layout of a prior art three-dimensional memory
device using power supply connection (C4 tap) regions 302 and bit
line tap (BL tap) regions 304 to provide vertical interconnections
through the level of a three-dimensional memory device. Each of the
C4 tap regions 302 and the BL tap regions 304 may include a
respective dielectric pillar or dielectric filled trench structure
and at least one vertical interconnection via structure that
vertically extends through the entire thickness range of a
three-dimensional memory array within the prior at
three-dimensional memory device. For example, the BL tap regions
304 may comprise a large dielectric filled trench extending in the
word line direction and vertical interconnection via structure
connecting bit lines which overly the prior art memory array region
100 and driver circuit devices 710 located under the memory array
region 100. Each "MH" represents a memory array region 100 and
"Staircase" represents staircase region 200. Direction "WL"
represents the word line direction (e.g., the first horizontal
direction hd1). Direction "BL" represents the bit line direction
(e.g., the second horizontal direction hd2). The BL tap regions are
provided because each bit line in the prior art three-dimensional
memory device needs to be individually connected to a respective
node of a bit line driver circuitry through the entire thickness
range of a three-dimensional memory array within the prior at
three-dimensional memory device.
[0168] FIG. 22 is a layout for the three-dimensional memory device
of an embodiment of the present disclosure, which does not require
areas for bit line tap regions 304. This is because the bit lines
98 are provided below the three-dimensional memory array in the
memory array region 100 of the embodiments of the present
disclosure. Thus, vertical wiring for bit lines 98 through the
level of the three-dimensional memory array may be eliminated in
the three-dimensional memory device of the present disclosure. The
area of the C4 tap regions 302 may be used to form interconnection
region dielectric fill material portions 584 and source
interconnect via structures 588 to connect the source lines 92 with
the driver circuit devices 710 in addition to various power supply
connections to the driver circuit devices 710 in the
three-dimensional memory device of the embodiments of the present
disclosure. The layout for the three-dimensional memory device of
the embodiments of the present disclosure may be smaller than the
prior art layout of FIG. 21 and/or may contain more space for the
memory array regions 100 through elimination of areas for the BL
tap regions 304 of the layout of FIG. 21.
[0169] Referring to FIG. 23, an alternative embodiment of the
exemplary structure of the present disclosure is illustrated, which
can be derived from the exemplary structure described above by
forming an etch stop layer 769 on the physically exposed top
surfaces of the lower-interconnect-level dielectric material layers
764, the lower-level metal line structures 784, and the bit lines
98 after the processing steps of FIGS. 1A and 1B. In one
embodiment, the etch stop layer 769 can be formed after formation
of the bit line material layer 98L and prior to formation of the at
least one pattern transfer material layer 771L illustrated in FIG.
1C. The etch stop layer 769 includes a dielectric material that can
function as an etch stop material during subsequent anisotropic
etch processes. The etch stop layer 769 can be employed to
effectively increase the etch selectivity of anisotropic etch
processes that are employed to form various patterns that extend to
the top surface of the bit line material layer 98L or to the top
surfaces of the bit lines 98. In one embodiment, the etch stop
layer 769 can include silicon nitride or a dielectric metal oxide
material such as aluminum oxide, hafnium oxide, and/or titanium
oxide. The thickness of the etch stop layer 769 can be in a range
from 5 nm to 30 nm, such as from 10 nm to 20 nm, although lesser
and greater thicknesses can also be employed. In case the etch stop
layer 769 is included, each anisotropic etch process that etches
cavities that extend to the bit lines 98 can be modified to include
a first etch step that stops on the etch stop layer 769 and a
second etch step that etches through the etch stop layer 769.
Further, etch steps that form the cavities for forming the
peripheral-region contact via structure 488 and/or the source
interconnect via structure 588 can be appropriately modified to
etch through the etch stop layer 769. In one embodiment, the
thickness of the etch stop layer 769 can be minimized to reduce
parasitic capacitance among the bit lines 98 and between the bit
lines 98 and adjacent conductive structures as long as the etch
stop layer 769 provides the function of an etch stopper
material.
[0170] Referring to all drawings and according to various
embodiments of the present disclosure, a three-dimensional
semiconductor device is provided, which comprises: bit lines 98
formed in the lower-interconnect-level dielectric material layers
764, laterally spaced apart along a first horizontal direction hd1,
and laterally extending a long a second horizontal direction hd2
that is perpendicular to the first horizontal direction hd1, and
located over a top surface of a substrate 8; bit-line-connection
via structures 188 contacting a top surface of a respective one of
the bit lines 98 and formed in a via-level dielectric layer 768A;
pillar-shaped drain regions 88 contacting a respective one of the
bit-line-connection via structures 188; an alternating stack of
insulating layers (132 and/or 232) and electrically conductive
layers (146 and/or 246) located over the pillar-shaped drain
regions 88; memory opening fill structures 58 vertically extending
through the alternating stack {(132, 146), (232, 246)} and
including a respective memory stack structure 55 that contains a
respective vertical semiconductor channel 60 and a respective
vertical stack of memory elements (for example, comprising portions
of a charge storage layer 54 located at levels of the electrically
conductive layers (146, 246)); and a source layer 92 overlying the
alternating stack {(132, 146), (232, 246)} and electrically
connected to an upper end of each vertical semiconductor channel 60
within a subset of the vertical semiconductor channels 60. Field
effect transistors (as a subset of the semiconductor devices 710)
are located on or over a top surface of the substrate 8, such that
the bit lines 98 are located between the field effect transistors
and the memory opening fill structures 58.
[0171] In one embodiment, the three-dimensional memory device
comprises: lower-level metal interconnect structures 780 located
above, and electrically connected to, the field effect transistors,
formed within the lower-interconnect-level dielectric material
layers 164, and underlies the alternating stack {(132, 146), (232,
246)}.
[0172] In one embodiment, the bit lines 98 are electrically
connected to a subset of the field effect transistors that
comprises bit line drivers through a subset of the lower-level
metal interconnect structures 780.
[0173] In one embodiment, each memory stack structure 55 comprises
a vertical NAND string; and each vertical stack of memory elements
comprises a vertical stack of charge storage elements located at
levels of the electrically conductive layers (146, 246).
[0174] In one embodiment, the bit-line-connection via structures
188 are elongated along the second horizontal direction hd2 with a
length-to-width ratio in a range from 1.5 to 10.
[0175] In one embodiment, each of the pillar-shaped drain regions
88 contacts an entire top surface of an underlying one of the
bit-line-connection via structures 188 and has a greater horizontal
cross-sectional area than a horizontal cross-sectional area of the
underlying one of the bit-line-connection via structures 188.
[0176] In one embodiment, the pillar-shaped drain regions 88
comprise a doped semiconductor material including dopant atoms at
an atomic concentration in a range from
5.0.times.10.sup.19/cm.sup.3 to 2.0.times.10.sup.21/cm.sup.3; and
the pillar-shaped drain regions 88 have a circular cylindrical
shape or have a lesser length-to-width ratio than the
bit-line-connection via structures 188.
[0177] In one embodiment, the three-dimensional memory device
comprises: source contact via structures 68 contacting an upper end
of a respective one of the vertical semiconductor channels 60 and
contacting a bottom surface of the source layer 92; and a source
interconnect via structure 588 that electrically connects the
source layer 92 to a lower-level metal interconnect structure 780
formed within the lower-interconnect-level dielectric material
layers 764.
[0178] In one embodiment, the alternating stack {(132, 146), (232,
246)} comprises stepped surfaces in a staircase region 200, wherein
each electrically conductive layer (146, 246) other than a topmost
one of the electrically conductive layers 246 laterally extends
farther than an overlying electrically conductive layer (146, 246);
the electrically conductive layers (146, 246) comprise word lines
for the vertical stacks of memory elements; and word line contact
via structures (comprising a subset of the staircase-region contact
via structures 86) contact a respective one of the electrically
conductive layers (146, 246).
[0179] In one embodiment, the three-dimensional memory device
comprises a word line driver circuit (comprising a subset of the
semiconductor devices 710) located on a top surface of the
substrate 8 and underlies the alternating stack {(132, 146), (232,
246)}, wherein the word line contact via structures are
electrically connected to the word line driver circuit through
lower-level metal interconnect structures 780 formed within the
lower-interconnect-level dielectric material layers 764.
[0180] In one embodiment, the three-dimensional memory device
comprises inter-bit-line cavities 767 located between neighboring
pairs of bit lines 98 and laterally extending along the second
horizontal direction hd2, wherein each of the inter-bit-line
cavities 767 is vertically bounded by a curved bottom surface
portion of the via-level dielectric layer 768A.
[0181] In one embodiment, the three-dimensional memory device
comprises a dielectric etch stop layer 769 located between the
pillar-shaped drain regions 88 and the bit lines and a bit-line
dielectric liner 765 that conformally covers sidewalls and top
surfaces of the bit lines 98. The via-level dielectric layer 768A
comprises a material selected from undoped silicate glass, a doped
silicate glass, non-porous organosilicate glass, and porous
organosilicate glass; and the bit-line dielectric liner 765
comprises a material selected from silicon nitride, silicon
oxynitride, a dielectric metal oxide material, and nitrogen-doped
organosilicate glass.
[0182] Various embodiments provided herein disclose semiconductor
memory devices having bit lines formed in lower-interconnect-level
dielectric material layers under a memory hole array. Various
embodiments disclose bit lines that may be formed between memory
elements and an underlying peripheral circuit. By providing bit
lines in lower-interconnect-level dielectric material layers under
a memory hole array, cell source lines may be formed on top of
memory holes. In such embodiments, the process to connect cell
source lines to memory holes is significantly eased. Thus, the
overall formation and connection process is easier and the overall
yield may be improved. Bit line performance may also be improved
due to improved resistance characteristics.
[0183] Furthermore, typically, vertical semiconductor channels of
the memory stack structures are electrically connected to a source
line that underlies the alternating stack. In that case, a lot of
long contact vias are needed to supply power to the source line.
However, in the embodiments of the present invention, such long
contact vias are not needed. As a result, chip area is reduced.
[0184] Moreover, by forming bit lines under the cell array, the bit
line tap area of conventional devices is not needed. The bit lines
may be directly connected with bit line switching transistors. The
impact of the bit line tap area in conventional devices is large.
Thus, the various embodiments provide for more efficient use of
space by reducing the die size.
[0185] Although the foregoing refers to particular 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. Compatibility is presumed among all embodiments that
are not alternatives of one another. The word "comprise" or
"include" contemplates all embodiments in which the word "consist
essentially of" or the word "consists of" replaces the word
"comprise" or "include," unless explicitly stated otherwise. Where
an embodiment using 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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