U.S. patent application number 12/493515 was filed with the patent office on 2010-06-24 for vertical channel type nonvolatile memory device and method for fabricating the same.
Invention is credited to Jung-Ryul Ahn, Heung-Jae Cho, Won-Joon Choi, Beom-Yong Kim, Yong-Soo Kim.
Application Number | 20100155818 12/493515 |
Document ID | / |
Family ID | 42264767 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100155818 |
Kind Code |
A1 |
Cho; Heung-Jae ; et
al. |
June 24, 2010 |
VERTICAL CHANNEL TYPE NONVOLATILE MEMORY DEVICE AND METHOD FOR
FABRICATING THE SAME
Abstract
A method for fabricating, a vertical channel type nonvolatile
memory device includes: alternately forming a plurality of
sacrificial layers and a plurality of interlayer dielectric layers
over a semiconductor substrate; etching the sacrificial layers and
the interlayer dielectric layers to form a plurality of first
openings for channel each of which exposes the substrate; filling
the first openings to form a plurality of channels protruding from
the semiconductor substrate; etching the sacrificial layers and the
interlayer dielectric layers to form second openings for removal of
the sacrificial layers between the channels; exposing sidewalls of
the channels by removing the sacrificial layers exposed by the
second openings; and forming a tunnel insulation layer, a charge
trap layer, a charge blocking layer, and a conductive layer for
gate electrode on the exposed sidewalls of the channels.
Inventors: |
Cho; Heung-Jae;
(Gyeonggi-do, KR) ; Kim; Yong-Soo; (Gyeonggi-do,
KR) ; Kim; Beom-Yong; (Gyeonggi-do, KR) ;
Choi; Won-Joon; (Gyeonggi-do, KR) ; Ahn;
Jung-Ryul; (Gyeonggi-do, KR) |
Correspondence
Address: |
IP & T Law Firm PLC
7700 Little River Turnpike, Suite 207
Annandale
VA
22003
US
|
Family ID: |
42264767 |
Appl. No.: |
12/493515 |
Filed: |
June 29, 2009 |
Current U.S.
Class: |
257/324 ;
257/E21.21; 257/E29.309; 438/287; 438/591 |
Current CPC
Class: |
H01L 27/11578 20130101;
H01L 29/7926 20130101; H01L 27/088 20130101; H01L 27/11582
20130101; H01L 29/792 20130101 |
Class at
Publication: |
257/324 ;
438/591; 438/287; 257/E29.309; 257/E21.21 |
International
Class: |
H01L 29/792 20060101
H01L029/792; H01L 21/28 20060101 H01L021/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 2008 |
KR |
10-2008-0133015 |
Apr 13, 2009 |
KR |
10-2009-0031902 |
Claims
1. A method for fabricating a vertical channel type nonvolatile
memory device, the method comprising: alternately forming a
plurality of sacrificial layers and a plurality of interlayer
dielectric layers over a semiconductor substrate; etching the
sacrificial layers and the interlayer dielectric layers to form a
plurality of first openings for channel, each of which exposes the
semiconductor substrate; filling the first openings to form a
plurality of channels protruding from the semiconductor substrate;
etching the sacrificial layers and the interlayer dielectric layers
to form second openings for removal of the sacrificial layers
between the channels; exposing sidewalls of the channels by
removing the sacrificial layers exposed by the second openings; and
forming a tunnel insulation layer, a charge trap layer, a charge
blocking layer, and a conductive layer for gate electrode on the
exposed sidewalls of the channels.
2. The method of claim 1, wherein the sacrificial layers comprise a
material having a high etch selectivity ratio to the interlayer
dielectric layers.
3. The method of claim 2, wherein the sacrificial layers comprise a
nitride layer or an amorphous carbon layer, and the interlayer
dielectric layers comprise an oxide layer.
4. The method of claim 1, wherein the second openings for removal
of the sacrificial layers comprise a plurality of line type
openings expending in parallel in a certain direction, or a
plurality of hole type openings arranged in a first direction and a
second direction intersecting with the first direction.
5. The method of claim 1, wherein the second openings for removal
of the sacrificial layers are formed to a depth at which at least
the most lowest sacrificial layer is exposed.
6. The method of claim 1, wherein the channels comprise a single
crystal silicon layer or a polycrystal silicon layer.
7. The method of claim 1, wherein the tunnel insulation layer, the
charge trap layer, and the charge blocking layer are formed as
spacers between the conductive layer for gate electrode and the
interlayer dielectric layer.
8. The method of claim 7, wherein the spacers comprises an
oxide-nitride-oxide (ONO) layer.
9. The method of claim 1, wherein forming the tunnel insulation
layer, the charge trap layer, the charge blocking layer, and the
conductive layer for gate electrode comprises: forming the tunnel
insulation layer, the charge trap layer, and the charge blocking
layer on a space having a opened region between the interlayer
dielectric layers where the sacrificial layers are removed; forming
the conductive layer for gate electrode over a resulting structure
to fill the opened region between the interlayer dielectric layers;
forming a plurality of mask patterns over a resulting structure
including the conductive layer for gate electrode, wherein the mask
patterns covering a region where memory cells are to be formed and
extending in a certain direction; and forming a plurality of gate
electrodes by etching the conductive layer for gate electrode using
the mask patterns as an etch barrier.
10. The method of claim 1, further comprises: forming the tunnel
insulation layer, the charge trap layer, and the charge blocking
layer over a resulting structure where the sidewalls of the
channels are exposed, a region between the interlayer dielectric
layers being opened; filling the opened region between the
interlayer dielectric layers with the conductive layer for gate
electrode to form a plurality of gate electrodes of memory cells;
and filling the second openings for removal of the sacrificial
layers with a insulation layer where the gate electrodes are
formed.
11. The method of claim 10, wherein the forming the plurality of
gate electrodes comprises: forming the conductive layer for gate
electrode to open a center region of the second openings for
removal of the sacrificial layers; and separating the gate
electrodes by removing the conductive layers for gate electrode
which are formed along inner sidewalls of the opened center
region.
12. The method of claim 1, wherein the forming the tunnel
insulation layer, the charge trap layer, the charge blocking layer,
and the conductive layer for gate electrode comprises: forming the
tunnel insulation layer, the charge trap layer, and the charge
blocking layer over a resulting structure where the sidewalls of
the channels are exposed, a region between the interlayer
dielectric layers being opened; forming the conductive layer for
gate electrode over a resulting structure to fill the opened region
between the interlayer dielectric layers; selectively etching the
conductive layer for gate electrode to separate a plurality of gate
electrodes of memory cells; and forming an insulation layer to fill
a region where the conductive layer for gate electrode is
etched.
13. The method of claim 1, further comprising: forming a plurality
of bit lines connected to the channels, after forming the tunnel
insulation layer, the charge trap layer, the charge blocking layer,
and the conductive layer for gate electrode.
14. The method of claim 1, wherein forming the tunnel insulation
layer, the charge trap layer, the charge blocking layer, and the
conductive layer for gate electrode comprises: patterning the
previously formed layers to expose a plurality of gate electrodes
of memory cells; and forming a plurality of word lines connected to
the gate electrodes of the memory cells.
15. A method for fabricating a vertical channel type nonvolatile
memory device, the method comprising: alternately forming a
plurality of sacrificial layers and a plurality of interlayer
dielectric layers over a semiconductor substrate; etching the
sacrificial layers and the interlayer dielectric layers to form a
plurality of first openings for channel, each of which exposes the
semiconductor substrate; filling the first openings to form a
plurality of rectangular pillar type channels protruding from the
substrate; etching the sacrificial layers and the interlayer
dielectric layers to form second openings for removal of the
sacrificial layers which are disposed between the channels;
exposing sidewalls of the channels by removing the sacrificial
layers exposed by the second openings; and forming a tunnel
insulation layer, a charge trap layer, a charge blocking layer, and
a conductive layer for gate electrode on the exposed sidewalls of
the channels.
16. The method of claim 15, wherein the forming the plurality of
first openings for channel comprises: etching the sacrificial
layers and the interlayer dielectric layers to form a plurality of
line type openings extending in parallel in a first direction;
filling the line type openings with an insulation layer; forming a
plurality of mask patterns extending in parallel in a second
direction intersecting with the first direction over a resulting
structure where the insulation layer is formed; and forming the
plurality of rectangular pillar type first openings by etching the
insulation layer using the mask patterns as an etch barrier.
17. The method of claim 15, wherein the forming a plurality of
rectangular pillar type channels comprises: filling the line type
first openings to form the channels; forming a plurality of mask
patterns extending in parallel in a second direction intersecting
with the first direction over a resulting structure where the layer
for channel is formed; forming the plurality of rectangular pillar
type channels by etching the channels using the mask patterns as an
etch barrier; and forming an insulation layer to fill a region
where the layer for channel is etched.
18. The method of claim 15, wherein the second openings for removal
of the sacrificial layer comprise a plurality of line type openings
extending in parallel in a certain direction, or a plurality of
hole type openings arranged in a first direction and a second
direction intersecting with the first direction.
19. The method of claim 15, wherein the tunnel insulation layer,
the charge trap layer, and the charge blocking layer are formed, as
a spacer, between the conductive layer for gate electrode and the
interlayer dielectric layer.
20. The method of claim 19, wherein the spacer comprises an
oxide-nitride-oxide (ONO) layer.
21. The method of claim 15, wherein the forming the tunnel
insulation layer, the charge trap layer, the charge blocking layer,
and the conductive layer for gate electrode comprises: forming the
tunnel insulation layer, the charge trap layer, and the charge
blocking layer over a resulting structure where the sacrificial
layers are removed, a region between the interlayer dielectric
layers being opened; forming the conductive layer for gate
electrode over a resulting structure to fill the opened region
between the interlayer dielectric layers; forming a plurality of
mask patterns over a resulting structure where the conductive layer
for gate electrode is formed, the mask patterns covering a region
where memory cells are to be formed and extending in a certain
direction; and forming a plurality of gate electrodes by etching
the conductive layer for gate electrode using the mask patterns as
an etch barrier.
22. The method of claim 15, wherein the forming the tunnel
insulation layer, the charge trap layer, the charge blocking layer,
and the conductive layer for gate electrode comprises: sequentially
forming the tunnel insulation layer, the charge trap layer, and the
charge blocking layer over a resulting structure where the
sidewalls of the channels are exposed, a region between the
interlayer dielectric layers being opened; filling the opened
region between the interlayer dielectric layers with the conductive
layer for gate electrode to form a plurality of gate electrodes of
memory cells stacked along the channels; and forming an insulation
layer to fill the second openings where the gate electrodes are
formed.
23. The method of claim 22, wherein the forming the plurality of
gate electrodes comprises: forming the conductive layer for gate
electrode to open a center region of the second openings; and
separating the gate electrodes by removing the conductive layers
for gate electrode which are formed along inner sidewalls of the
opened center region.
24. The method of claim 15, wherein the forming the tunnel
insulation layer, the charge trap layer, the charge blocking layer,
and the conductive layer for gate electrode comprises: forming the
tunnel insulation layer, the charge trap layer, and the charge
blocking layer over a resulting structure where the sidewalls of
the channels are exposed, a region between the interlayer
dielectric layers being opened; forming the conductive layer for
gate electrode over a resulting structure to fill the opened region
between the interlayer dielectric layers; selectively etching the
conductive layer for gate electrode to separate a plurality of gate
electrodes of memory cells stacked along the channels; and forming
an insulation layer to fill a region where the conductive layer for
gate electrode is etched.
25. A vertical channel type nonvolatile memory device, comprising:
a plurality of channels protruding from a semiconductor substrate;
and a plurality of strings comprising a plurality of memory cells
stacked along the channels, wherein at least two of the strings
share one channel.
26. The vertical channel type nonvolatile memory device of claim
25, wherein the channels are arranged in a first direction and a
second direction intersecting with the first direction, and an
insulation layer is buried in a region between the channels
arranged in the first direction.
27. The vertical channel type nonvolatile memory device of claim
25, wherein the channels have a rectangular pillar type, and the
two strings sharing one channel are formed on both sides of the
rectangular pillar type channels.
28. A vertical channel type nonvolatile memory device, comprising:
a channel protruding from a semiconductor substrate; a string
comprising a plurality of memory cells stacked along the channel;
and a spacer on sidewalls of gate electrodes of the memory
cells.
29. The vertical channel type nonvolatile memory device of claim
28, wherein the spacer comprises an oxide-nitride-oxide (ONO)
layer.
30. A vertical channel type nonvolatile memory device, comprising:
a channel protruding from a semiconductor substrate; and a string
comprising a plurality of memory cells stacked along the channel,
wherein the memory cells disposed on the same layer operate as one
page.
31. The vertical channel type nonvolatile memory device of claim
30, wherein the memory cells disposed on the same layer share a
gate electrode.
32. The vertical channel type nonvolatile memory device of claim
30, wherein the memory cell comprises: a gate electrode alternately
stacked with interlayer dielectric layer over a semiconductor
substrate; a channel buried within a plurality of gate electrode
and interlayer dielectric layer and protruding from the
semiconductor substrate; and a tunnel insulation layer, a charge
trap layer, and a charge blocking layer disposed between sidewalls
of the channels of the gate electrodes, and the gate electrodes in
the memory cells stacked along the channels are separated by a gate
electrode separation layer buried within the gate electrode and the
interlayer dielectric layer.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority of Korean Patent
Application Nos. 10-2008-0133015 and 10-2009-0031902, filed on Dec.
24, 2008, and Apr. 13, 2009, respectively, the disclosure of each
of which is incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a nonvolatile memory device
and a method for fabricating the same, and more particularly, to a
vertical channel type nonvolatile memory device and a method for
fabricating the same.
[0003] Memory devices are classified into volatile memory devices
and nonvolatile memory devices according to whether data is
retained when power is interrupted. Volatile memory devices lose
data when power is interrupted. Examples of volatile memory devices
include dynamic random access memory (DRAM) and static random
access memory (SRAM). In contrast, nonvolatile memory devices
retain stored data even when power is interrupted. Examples of
nonvolatile memory devices include flash memory.
[0004] Nonvolatile memory devices are classified into floating gate
type nonvolatile memory devices and charge trap type nonvolatile
memory devices according to data storing methods.
[0005] A floating gate type nonvolatile memory device includes a
plurality of memory cells, each of which has a tunnel insulation
layer, a floating gate electrode, a charge blocking layer, and a
control gate electrode being formed over a substrate. The floating
gate type nonvolatile memory device stores data by accumulating
charges within a conduction band of the floating gate
electrode.
[0006] A charge trap type nonvolatile memory device includes a
plurality of memory cells, each of which has a tunnel insulation
layer, a charge trap layer, a charge blocking layer, and a control
gate electrode being formed over a substrate. The charge trap type
nonvolatile memory device stores data by trapping charges in a
deep-level trap site within the charge trap layer.
[0007] However, planar nonvolatile memory devices fabricated in a
single layer over a silicon substrate have limitations in improving
integration density due to fine pattern formation as patterning
technologies have reached limitations in some aspects.
[0008] Therefore, there have been proposed vertical channel type
nonvolatile memory devices in which strings are vertically arranged
over a substrate. A vertical channel type nonvolatile memory device
includes a lower selection transistor, a plurality of memory cells,
and an upper selection transistor, which are sequentially formed
over a substrate. The vertical channel type nonvolatile memory
device can improve integration density because the strings are
arranged vertically over the substrate.
[0009] Hereinafter, a conventional method for fabricating a
vertical channel type nonvolatile memory device will be described
with reference to the accompanying drawings.
[0010] FIGS. 1A to 4B are exemplary diagrams illustrating a
conventional method for fabricating a vertical channel type
nonvolatile memory device. For the sake of convenience, a
description about a process of forming a lower selection transistor
and an upper selection transistor is omitted, and the following
description will be focused on a process of forming a plurality of
memory cells. In particular, figures "A" are cross-sectional views
illustrating intermediate results, and figures "B" are plan views
at height A-A' of figures "A".
[0011] Referring to FIGS. 1A and 1B, a plurality of interlayer
dielectric layers 11 and a plurality of conductive layers 12 for
gate electrode are alternately formed over a substrate 10 where a
lower structure including a source line, a lower selection
transistor, and the like is formed. The interlayer dielectric
layers 11 and the conductive layers 12 are selectively etched to
form a plurality of contact holes H exposing the substrate 10.
[0012] Referring to FIGS. 2A and 2B, a charge blocking layer 13 is
formed on inner walls of the contact holes H. The charge blocking
layer 13 prevents charges from passing through the charge trap
layer 14 and moving toward the gate electrode.
[0013] A charge trap layer 14 is formed over the charge blocking
layer 13. The charge trap layer 14 traps charges in a deep-level
trap site and serves as a substantial data storage. The charge trap
layer 14 is formed of nitride.
[0014] A tunnel insulation layer 15 is formed within the contact
holes H in which the charge blocking layer 13 and the charge trap
layer 14 are formed. The tunnel insulation layer 15 serves as an
energy barrier layer because of tunneling of charges.
[0015] Referring to FIGS. 3A and 3B, a center region of the tunnel
insulation layer 15 is etched to form openings for channel which
expose the substrate 10. The openings for channel are filled with a
layer for channel to form a plurality of channels 16 protruding
from the substrate 10.
[0016] Referring to FIGS. 4A and 4B, a plurality of mask patterns
(not shown) are formed over a resulting structure where the
channels 16 are formed. The plurality of mask patterns cover a
region for memory cells MC and extend in a first direction I-I'.
Using the mask patterns as an etch barrier, the interlayer
dielectric layer 11 and the conductive layer 12 for gate electrode
are etched to form a plurality of gate electrodes 12A. The etched
region is filled with an insulation layer 17.
[0017] In this way, a plurality of memory cells MC each including
the tunnel insulation layer 15, the charge trap layer 14, the
charge blocking layer 13, and the gate electrode surrounding the
outer surface of the vertical channel 16 are formed. At this point,
the memory cells MC stacked along the same channel 16 constitute
one string. In addition, the memory cells MC connected to the gate
electrode 12A (memory cells arranged in the first direction I-I')
operate as one page. That is, a plurality of memory cells MC formed
in each layer operate as a plurality of pages.
[0018] FIG. 5 is a perspective view explaining a process of forming
word lines in the conventional vertical channel type nonvolatile
memory device.
[0019] Referring to FIG. 5, the interlayer dielectric layers 11 and
the gate electrodes 12A are patterned to expose the gate electrodes
12A of the memory cells stacked along the channels 16. Word lines
18 connected to the gate electrodes of the memory cells are
formed.
[0020] As described above, since the plurality of memory cells
formed on the same layer operate as the plurality of pages, the
word lines 18 must be formed in each page even though the gate
electrodes 12A are formed on the same layer.
[0021] According to the prior art, the channels 16 are formed after
forming the conductive layers 12 for gate electrode, the charge
blocking layer 13, the charge trap layer 14, and the tunnel
insulation layer 15. That is, since the fabrication process of the
vertical channel type nonvolatile memory device is performed in
reverse order of that of the planar nonvolatile memory device, the
characteristics of the memory device are degraded, which will be
described hereinafter in more detail.
[0022] First, degradation in the layer quality of the tunnel
insulation layer 15 causes degradation in date retention
characteristic and reliability. Since the nonvolatile memory device
stores and erases data by using Fowler-Nordheim (F-N) tunneling,
the layer quality of the tunnel insulation layer 15 serving as the
energy barrier in the F-N tunneling has a great influence on the
characteristics of the memory device.
[0023] However, the layer quality of the tunnel insulation layer 15
is degraded because the tunnel insulation layer 15 is formed at the
last time and the openings for channel are formed by etching the
center region of the tunnel insulation layer 15.
[0024] Second, since the channels 16 formed of polysilicon are
formed in order to prevent damage of the charge blocking layer 13,
the charge trap layer 14, and the tunnel insulation layer 15 in a
process of forming the layer for channel within the openings, the
current flow in the channels 16 is lowered and the uniformity of a
threshold voltage distribution is degraded.
[0025] A single crystal silicon growth process is typically
performed using a silicon source gas and an HCl gas at high
temperature. The silicon source gas supplies silicon source for
growing single crystal silicon, and removes a natural oxide layer
formed on the substrate 10 through an oxidation-reduction reaction,
or removes silicon deposited on the insulation layer, thereby
growing single crystal silicon only on the surface of the substrate
10.
[0026] If the single crystal silicon growth process is applied to
the process of forming the channels 16 of the conventional vertical
channel type nonvolatile memory device, the charge blocking layer
13, the charge trap layer 14, and the tunnel insulation layer 15
are damaged. Therefore, there is a difficulty in forming the
channels 16 of single crystal silicon.
[0027] Meanwhile, since the tunnel insulation layer 15, the charge
trap layer 14, the charge blocking layer 13, and the gate electrode
are formed to surround the outer surface of the channel 16, one
string ST is formed with respect to one channel 16. Therefore,
there is a limitation in increasing the integration density of the
nonvolatile memory device.
[0028] Furthermore, it is necessary to form the word lines 18 at
each page with respect to the gate electrodes 12A formed on each
layer. Thus, an area for formation of the word lines 18 at each
page is required and thus there is another limitation in increasing
the integration density of the memory device.
SUMMARY OF THE INVENTION
[0029] An embodiment of the present invention is directed to
providing a vertical channel type nonvolatile memory device, which
has a channel, a tunnel insulation layer, a charge trap layer, and
a charge blocking layer being sequentially formed, and a method for
fabricating the same.
[0030] Another embodiment of the present invention is directed to
providing a vertical channel type nonvolatile memory device, which
has at least two strings sharing one channel, and a method for
fabricating the same.
[0031] Another embodiment of the present invention is directed to
providing a vertical channel type nonvolatile memory device, in
which a plurality of memory cells formed on the same layer operate
as one page, and a method for fabricating the same.
[0032] In accordance with an aspect of the present invention, there
is provided a method for fabricating a vertical channel type
nonvolatile memory device, the method including: alternately
forming a plurality of sacrificial layers and a plurality of
interlayer dielectric layers over a substrate; etching the
sacrificial layers and the interlayer dielectric layers to form a
plurality of first openings for channel, each of which exposes the
substrate; filling the first openings with a layer for a channel to
form a plurality of channels protruding from the substrate; etching
the sacrificial layers and the interlayer dielectric layers to form
second openings for removal of the sacrificial layers between the
channels; exposing sidewalls of the channels by removing the
sacrificial layers exposed by the second openings for removal of
the sacrificial layers; and sequentially forming a tunnel
insulation layer, a charge trap layer, a charge blocking layer, and
a conductive layer for gate electrode on the exposed sidewalls of
the channels.
[0033] In accordance with another aspect of the present invention,
there is provided a method for fabricating a vertical channel type
nonvolatile memory device, the method including: alternately
forming a plurality of sacrificial layers and a plurality of
interlayer dielectric layers over a substrate; etching the
sacrificial layers and the interlayer dielectric layers to form a
plurality of first openings for channel each of which exposes the
substrate; filling the first openings with a layer for a channel to
form a plurality of rectangular pillar type channels protruding
from the substrate; etching the sacrificial layers and the
interlayer dielectric layers to form second openings for removal of
the sacrificial layers which are disposed between the channels;
exposing sidewalls of the channels by removing the sacrificial
layers exposed by the second openings for removal of the
sacrificial layers; and sequentially forming a tunnel insulation
layer, a charge trap layer, a charge blocking layer, and a
conductive layer for gate electrode on the exposed sidewalls of the
channels.
[0034] In accordance with another aspect of the present invention,
there is provided a vertical channel type nonvolatile memory
device, which includes: a plurality of channels protruding from a
substrate; and a plurality of strings including a plurality of
memory cells stacked along the channels, wherein at least two of
the strings share one channel.
[0035] In accordance with another aspect of the present invention,
there is provided a vertical channel type nonvolatile memory
device, which includes: a channel protruding vertically from a
substrate; a string comprising a plurality of memory cells stacked
along the channel; and a spacer on sidewalls of gate electrodes of
the memory cells.
[0036] In accordance with another aspect of the present invention,
there is provided a vertical channel type nonvolatile memory
device, which includes: a channel protruding vertically from a
substrate; and a string comprising a plurality of memory cells
stacked along the channel, wherein the memory cells disposed on the
same layer operate as one page.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIGS. 1A to 4B are diagrams illustrating a conventional
method for fabricating a vertical channel type nonvolatile memory
device.
[0038] FIG. 5 is a perspective view explaining a process of forming
word lines in the conventional vertical channel type nonvolatile
memory device.
[0039] FIGS. 6A to 11B are diagrams illustrating a method for
fabricating a vertical channel type nonvolatile memory device in
accordance with a first embodiment of the present invention.
[0040] FIGS. 12A to 18B are diagrams illustrating a method for
fabricating a vertical channel type nonvolatile memory device in
accordance with a second embodiment of the present invention.
[0041] FIGS. 19A to 26B are diagrams illustrating a method for
fabricating a vertical channel type nonvolatile memory device in
accordance with a third embodiment of the present invention.
[0042] FIGS. 27A to 27C are diagrams illustrating a process of
forming a bit line and a word line in accordance with an embodiment
of the present invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0043] Other objects and advantages of the present invention can be
understood by the following description, and become apparent with
reference to the embodiments of the present invention.
[0044] Referring to the drawings, the illustrated thickness of
layers and regions are exaggerated to facilitate explanation. When
a first layer is referred to as being "on" a second layer or "on" a
substrate, it could mean that the first layer is formed directly on
the second layer or the substrate, or it could also mean that a
third layer may exist between the first layer and the substrate.
Furthermore, the same or like reference numerals represent the same
or like constituent elements, although they appear in different
embodiments or drawings of the present invention.
[0045] For the sake of convenience, a description about a process
of forming a lower selection transistor and an upper selection
transistor is omitted, and the following description will be
focused on a process of forming a plurality of memory cells.
[0046] A first embodiment of the present invention provides a
nonvolatile memory device which has a channel, a tunnel insulation
layer, a charge trap layer, a charge blocking layer, and a gate
electrode being sequentially formed, and a method for fabricating
the same. A second embodiment of the present invention provides a
nonvolatile memory device which has at least two strings sharing
one channel, and a method for fabricating the same. A third
embodiment of the present invention provides a nonvolatile memory
device in which a plurality of memory cells formed on the same
layer operate as one page, and a method for fabricating the
same.
[0047] FIGS. 6A to 11B are diagrams illustrating a method for
fabricating a vertical channel type nonvolatile memory device in
accordance with a first embodiment of the present invention. In
particular, a case of using line type openings for removal of
sacrificial layers is illustrated. Figures "A" are cross-sectional
views illustrating intermediate results, and figures "B" are plan
views at height A-A' of figures "A".
[0048] Referring to FIGS. 6A and 6B, a plurality of interlayer
dielectric layers 21 and a plurality of sacrificial layers 22 are
alternately formed on a substrate 20 where a lower structure
including a source line, a lower selection transistor, and the like
is formed.
[0049] The source line may include a silicon substrate, a
conductive material layer, a material layer formed by doping
impurities into an insulator, or a metal layer. The interlayer
insulation layer 21 separates a plurality of memory cells from one
another, where the plurality of memory cells constitutes a string,
and may be formed of oxide, for example, SiO.sub.2.
[0050] The sacrificial layer 22 ensures a space necessary for
forming a tunnel insulation layer, a charge trap layer, a charge
blocking layer, and a gate electrode in a subsequent process. The
sacrificial layer 22 may be formed repetitively as many as the
memory cells constituting a string.
[0051] The space necessary for forming the tunnel insulation layer,
the charge trap layer, the charge blocking layer, and the gate
electrode is ensured by selectively removing only the sacrificial
layer 22 in a subsequent process while a plurality of interlayer
dielectric layers 21 are remaining. Therefore, the sacrificial
layer 22 may be formed of a material having a high etch selectivity
ratio to the interlayer dielectric layers 21. For example, when the
interlayer dielectric layers 21 are formed of oxide, the
sacrificial layer 22 may be formed of amorphous carbon or nitride,
for example, Si.sub.3N.sub.4.
[0052] The interlayer dielectric layers 21 and the sacrificial
layers 22 are selectively etched to form a plurality of openings
for channel, each of which expose the substrate 20.
[0053] The openings for channel may be arranged in a first
direction and a second direction intersecting with the first
direction. The interval between the openings may be determined,
considering the thickness of a tunnel insulation layer, a charge
trap layer, a charge blocking layer, and a gate electrode which
will be formed in a subsequent process.
[0054] A plurality of hole type openings for channel are
exemplarily illustrated in the drawings, and it is apparent that
the openings for channel can be modified in various forms, for
example, a rectangular pillar type, according to intention of those
skilled in the art.
[0055] The openings for channel are filled with a layer for channel
to form a plurality of channels 23 protruding from the substrate
20.
[0056] The channels 23 may be formed of polycrystal silicon or
single crystal silicon. For example, when the channels 23 are
formed of single crystal silicon, the channels 23 may be formed
using a silicon source gas and an HCl gas at high temperature. In
accordance with the first embodiment of the present invention, the
channels 23 are formed prior to formation of the tunnel insulation
layer, the charge trap layer, and the charge blocking layer. Thus,
the tunnel insulation layer, the charge trap layer, and the charge
blocking layer will not be damaged in the process of forming the
channels 23. Consequently, the channels 23 can be formed of single
crystal silicon without any defect.
[0057] Referring to FIGS. 7A and 7B, the multi-layered sacrificial
layers 22 and the multi-layered interlayer dielectric layers 21 are
selectively etched so that openings T1 for removal of the
sacrificial layers are formed between a plurality of the channels
23.
[0058] The openings T1 are formed for removing the sacrificial
layers 22. The openings T1 may be formed to a depth D1 at which at
least the lowermost sacrificial layer 22 is exposed. In this case,
all the sacrificial layers 22 may be exposed through inner walls of
the openings T1, and therefore, all the sacrificial layers 22 can
be removed.
[0059] While a case where line type openings T1 for removal of the
sacrificial layers, which extend in parallel in a certain
direction, is illustrated as one exemplary embodiment, it is
apparent to those skilled in the art that various types of the
openings T1 for removal of the sacrificial layers may also be
formed.
[0060] Referring to FIGS. 8A and 8B, the sacrificial layers 22
exposed by the openings T1 are removed to expose sidewalls of the
channels 23. At this point, due to the removal of the sacrificial
layers 22, the openings T1' for removal of the sacrificial layers
extend up to the sidewalls of the channels 23.
[0061] The removal of the sacrificial layers 22 is performed to
selectively remove only the sacrificial layers 22 while the
interlayer dielectric layers 21 are remaining substantially in
their original shapes. Therefore, the sidewalls of the channels 23
are exposed at a certain interval with the space where the
sacrificial layers 22 are removed (see, {circle around (1)} of FIG.
8A), and the tunnel insulation layer, the charge trap layer, the
charge blocking layer, and the gate electrode are formed in the
space, where the sacrificial layers 22 are removed, in a subsequent
process.
[0062] As mentioned above, when the interlayer insulation layers 21
are formed of SiO.sub.2 and the sacrificial layers are formed of
Si.sub.3N.sub.4, the removal of the sacrificial layers 22 may be
performed using a phosphoric acid, for example, H.sub.3PO.sub.4, at
a temperature ranging from approximately 50.degree. C. to
approximately 200.degree. C. In this case, only the sacrificial
layers 22 can be selectively removed through the chemical formula 1
described as follows.
Si.sub.3N.sub.4+4H.sub.3PO.sub.4+12H.sub.2O.fwdarw.3Si(OH).sub.4+4NH.sub-
.4H.sub.2PO.sub.4 SiO.sub.2+2H.sub.2O.fwdarw.Si(OH).sub.4 [Chemical
Formula 1]
[0063] Referring to FIGS. 9A and 9B, the tunnel insulation layer,
the charge trap layer, and the charge blocking layer 24 are
sequentially formed over a resulting structure where the channels
23 are exposed. Therefore, the tunnel insulation layer, the charge
trap layer, and the charge blocking layer 24 are sequentially
formed on sidewalls of the exposed channels 23. The tunnel
insulation layer, the charge trap layer, and the charge blocking
layer are illustrated as one layer and represented by a reference
numeral "24".
[0064] In sequentially forming the tunnel insulation layer, the
charge trap layer, and the charge blocking layer 24 over the
resulting structure where the sacrificial layers 22 are removed,
the tunnel insulation layer, the charge trap layer, and the charge
blocking layer 24 may be formed to a certain thickness at which the
space between the interlayer dielectric layers 21 is not completely
filled. That is, the tunnel insulation layer, the charge trap
layer, and the charge blocking layer 24 may be formed to a certain
thickness at which the space between the interlayer dielectric
layers 21 is opened to some degree so that the space for gate
electrode may be ensured. In this way, spacers may be formed
between the interlayer dielectric layer 21 and conductive layers 25
for gate electrode which will be formed in a subsequent
process.
[0065] The formation of the tunnel insulation layer may be
performed by an oxidation process or a chemical vapor deposition
(CVD) process The charge trap layer may include a charge trapping
layer for trapping charges or a charge storage layer for storing
charges. The charge trapping layer may be formed of nitride, and
the charge storage layer may be formed of polycrystal silicon. In
particular, the charge trapping layer may include a
high-dielectric-constant material, for example, Si.sub.xN.sub.y,
Hf, Zr, La, Dy or Sc. The charge blocking layer may include a
two-component material, for example, SiO.sub.2, Al.sub.2O.sub.3,
HfO.sub.2, ZrO.sub.2, GdO, DyO, or ScO, or a three-component
material, for example, HfAlO, HfLaO, AlLaO, GdAlO, or GdLaO.
[0066] Referring to FIGS. 1-A and 10B, a conductive layer 25 for
gate electrode is formed over a resulting structure where the
tunnel insulation layer, the charge trap layer, and the charge
blocking layer 24 are formed, and a planarization process is
performed on the conductive layer. The conductive layer 25 for gate
electrode is buried in an opened region between the interlayer
dielectric layers 21.
[0067] The conductive layer 25 for gate electrode may include metal
silicide, metal, metal oxide, or metal nitride. For example, the
conductive layer 25 may include TiN, WN, TiAlN, TaN, TaCN, or MoN.
In particular, the conductive layer 25 may further include a
low-resistance material, for example, W, Al, or Cu.
[0068] The formation of the conductive layer 25 for gate electrode
may be performed by a CVD process or an atomic layer deposition
(ALD) process.
[0069] Referring to FIGS. 11A and 11B, a plurality of mask patterns
(not shown) are formed on a resulting structure where the
conductive layer 25 for gate electrode is formed. The mask patterns
(not shown) cover a region where memory cells MC will be formed,
and extend in parallel in a first direction I-I'. A plurality of
gate electrodes 25A are formed by etching the conductive layer 25
using the mask patterns as an etch barrier.
[0070] At this point, the width of the mask patterns may be
determined considering the thickness of the gate electrodes 25A. In
etching the conductive layer 25 for gate electrode, the adjacent
layers 21 and 24 may also be etched along the width of the mask
patterns.
[0071] The etched region is filled with an insulation layer 26. In
this way, a plurality of memory cells MC each including the channel
23, the tunnel insulation layer, the charge trap layer, and the
charge blocking layer 24 are formed. Furthermore, a plurality of
strings ST including the plurality of memory cells MC stacked along
the channels 23 are formed.
[0072] A plurality of spacers SP each including the tunnel
insulation layer, the charge trap layer, and the charge blocking
layer 24 are formed on sidewalls of the gate electrodes 25A of the
memory cells MC. The spacers SP may include an oxide-nitride-oxide
(ONO) layer.
[0073] Although not shown, the interlayer dielectric layers 21 and
the gate electrodes 25A are patterned to form a plurality of metal
lines connected to the respective gate electrodes.
[0074] As mentioned above, after the channels 23 are formed, the
tunnel insulation layer, the charge trap layer, and the charge
blocking layer 24 can be sequentially formed. Therefore, the layer
quality of the tunnel insulation layer can be improved. By forming
the channels 23 of the single crystal silicon, the current flow in
the channels 23 can be improved, and the uniformity of the
threshold voltage distribution can also be improved.
[0075] FIGS. 12A to 18B are diagrams illustrating a method for
fabricating a vertical channel type nonvolatile memory device in
accordance with a second embodiment of the present invention. In
particular, a case of forming rectangular pillar type channels is
illustrated. Figures "A" are cross-sectional views illustrating
intermediate results, and figures "B" are plan views at height A-A'
of figures "A". Since a detailed fabrication process of the
vertical channel type nonvolatile memory device in accordance with
the second embodiment of the present invention is identical to that
in accordance with the first embodiment of the present invention,
its detailed description will be omitted.
[0076] Referring to FIGS. 12A and 12B, a plurality of interlayer
dielectric layers 31 and a plurality of sacrificial layers 32 are
alternately formed on a substrate 30. The sacrificial layer 32 may
be formed of amorphous carbon or nitride, for example,
Si.sub.3N.sub.4.
[0077] The interlayer dielectric layers 31 and the sacrificial
layers 32 are selectively etched to form a plurality of line type
openings T2 exposing the substrate 30 and extending in parallel in
a first direction I-I'.
[0078] Referring to FIGS. 13A and 13B, the line type openings are
filled with a layer for channel to form a plurality of rectangular
pillar type channels 34 protruding from the substrate 30. A method
for forming the channels 34 will be described hereinafter.
[0079] First, the line type openings T2 are filled with an
insulation layer 33. The insulation layer 33 may be formed of
oxide. A plurality of line type mask patterns (not shown) extending
in parallel in a second direction II-II' are formed on a resulting
structure where the insulation layer 33 is formed. The insulation
layer 33 is etched using the mask patterns (not shown) as an etch
barrier. In this way, the openings for rectangular pillar type
channels are formed to expose the substrate 30. The openings for
channels are filled with a layer for channel to form a plurality of
channels 34 protruding vertically from the substrate 30. At this
point, the channels 34 have a rectangular pillar shape, and the
insulation layer 33 is buried in the region between the channels 34
arranged in the first direction I-I'.
[0080] Second, after the line type openings T2 are filled with the
layer for channel, a plurality of mask patterns (not shown)
extending in parallel in the second direction II-II' are formed on
a resulting structure where the layer for channel is buried. Using
the mask patterns (not shown) as an etch barrier, the buried layer
for channel is etched to form rectangular pillar type channels 34.
The etched region is filled with an insulation layer 33. In this
way, the rectangular pillar type channels are formed, and the
insulation layer 33 is buried in the region between the channels 34
arranged in the first direction I-I'.
[0081] Referring to FIGS. 14A and 14B, the multi-layered
sacrificial layers 32 and the multi-layered interlayer dielectric
layers 31 are selectively etched to form openings T3 for removal of
the sacrificial layers disposed between a plurality of the channels
34.
[0082] Referring to FIGS. 15A and 15B, the multi-layered
sacrificial layers 32 exposed by the openings T3 for removal of the
sacrificial layers are removed to expose sidewalls of the channels
34. At this point, due to the removal of the multi-layered
sacrificial layers 32, the openings T3' for removal of the
sacrificial layers extend up to the sidewalls of the channels 34.
Therefore, the sidewalls of the channels 23 are exposed at certain
intervals through the space where the sacrificial layers 32 are
removed, and a tunnel insulation layer, a charge trap layer, a
charge blocking layer, and a gate electrode are formed in a
subsequent process in the space where the sacrificial layers 32 are
removed.
[0083] Referring to FIGS. 16A and 16B, the tunnel insulation layer,
the charge layer, and the charge blocking layer 35 are sequentially
formed over a resulting structure where the sidewalls of the
channels 34 are exposed. In this way, the tunnel insulation layer,
the charge trap layer, and the charge blocking layer 35 are
sequentially formed on the exposed sidewalls of the channels 34.
The tunnel insulation layer, the charge trap layer, and the charge
blocking layer are illustrated as one layer and represented by a
reference numeral "35".
[0084] In sequentially forming the tunnel insulation layer, the
charge trap layer, and the charge blocking layer 35 over the
resulting structure where the sacrificial layers 32 are removed,
the tunnel insulation layer, the charge trap layer, and the charge
blocking layer 35 may be formed to a certain thickness at which the
space between the multi-layered interlayer dielectric layers 31 is
not completely filled. That is, the tunnel insulation layer, the
charge trap layer, and the charge blocking layer 35 may be formed
to a certain thickness at which the space between the multi-layered
interlayer dielectric layers is opened to some degree, that is, the
space for gate electrode is ensured therebetween. In this way,
spacers may be formed between the interlayer dielectric layer 31
and conductive layers 36 for gate electrode which will be formed in
a subsequent process.
[0085] In addition, since the insulation layer 33 is buried in the
region between the channels 34 arranged in the first direction, the
tunnel insulation layer, the charge trap layer, and the charge
blocking layer 35 are formed only on the sidewalls having the
rectangular pillar shape (see a reference numeral {circle around
(3)}). That is, the charge trap layer may be separately formed on
either sidewall of the channel 34.
[0086] Referring to FIGS. 17A and 17B, a conductive layer 36 for
gate electrode is formed over a resulting structure where the
tunnel insulation layer, the charge trap layer, and the charge
blocking layer 35 are formed, and a planarization process is
performed on the conductive layer 36. The conductive layer 36 for
gate electrode is buried in an opened region between the
multi-layered interlayer dielectric layers 31.
[0087] Referring to FIGS. 18A and 18B, a plurality of mask patterns
(not shown) are formed on a resulting structure where the
conductive layer 36 for gate electrode is formed. The mask patterns
(not shown) cover the channels 34 and a region where memory cells
MC will be formed, and extend in parallel in a first direction
I-I'. A plurality of gate electrodes 36A are formed by etching the
conductive layer 36 using the mask patterns as an etch barrier.
[0088] The etched region is filled with an insulation layer 37. In
this way, a plurality of memory cells MC each including the channel
34, the tunnel insulation layer, the charge trap layer, the charge
blocking layer 35, and the gate electrode 36A are formed. A
plurality of spacers SP, each including the tunnel insulation
layer, the charge trap layer, and the charge blocking layer 35, are
formed on sidewalls of the gate electrodes 36A of the memory cells
MC. The spacers SP may include an oxide-nitride-oxide (ONO)
layer.
[0089] In this way, a plurality of strings ST, each including the
plurality of memory cells MC stacked along the channels 34, are
formed. In particular, due to the insulation layer 33 buried in the
region between the channels 34 arranged in the first direction, two
strings ST sharing one channel 34 are separated from each other.
Therefore, the strings ST are formed on both sides of the
rectangular pillar type channel 34, and two strings ST can be
formed with respect to one channel 34. That is, two strings ST1 and
ST2 (ST3 and ST4) share one channel 34.
[0090] Although not shown, the multi-layered interlayer dielectric
layers 31 and the gate electrodes 36A are patterned to form a
plurality of metal lines connected to the respective gate
electrodes.
[0091] As mentioned above, since at least two strings ST are formed
to share one channel 34, the integration density of the vertical
channel type nonvolatile memory device can be increased.
[0092] FIGS. 19A to 26B are diagram illustrating a method for
fabricating a vertical channel type nonvolatile memory device in
accordance with a third embodiment of the present invention.
Figures "A" are cross-sectional views illustrating intermediate
results, and figures "B" are plan views at height A-A' of figures
"A". Since a detailed fabrication process of the vertical channel
type nonvolatile memory device in accordance with the third
embodiment of the present invention is identical to that in
accordance with the first embodiment of the present invention, its
detailed description will be omitted.
[0093] Referring to FIGS. 19A and 19B, multi-layered interlayer
dielectric layers 41 and multi-layered sacrificial layers 42 are
alternately formed on a substrate 40 where a lower structure (not
shown) including a source line, a lower selection transistor and
the like is formed. The sacrificial layers 42 may be formed of a
material having a high etch selectivity to the interlayer
dielectric layers 41. For example, the sacrificial layers 42 may be
formed of amorphous carbon or nitride, specifically,
Si.sub.3N.sub.4.
[0094] The interlayer dielectric layers 41 and the sacrificial
layers 42 are selectively etched to form a plurality of openings
for channel which expose the substrate 40.
[0095] The interval between the openings for channel may be
determined, considering the thickness of a tunnel insulation layer,
a charge trap layer, a charge blocking layer, and a gate electrode
which will be formed in a subsequent process. In particular, the
openings for channel may be formed in a hole type, and the width of
the openings for channel may be approximately 1 .mu.m or less. As
such, when the hole type openings for channel are formed, the
interval between the channels is reduced and thus the integration
density of the memory device can be further increased.
[0096] The openings for channel are filled with the layer for
channel to form a plurality of channels 43 protruding from the
substrate 40. As mentioned above, when the hole type openings for
channel are filled with the layer for channel, the pillar type
channels 43 are formed and thus subsequent processes are performed
more easily.
[0097] The channels 43 may be formed by growing single crystal
silicon or depositing polycrystal silicon.
[0098] Referring to FIGS. 20A and 20B, the multi-layered
sacrificial layers 42 and the multi-layered interlayer dielectric
layers 41 are selectively etched to form a plurality of hole type
openings T3 for removal of the sacrificial layers disposed between
the channels 43.
[0099] The openings T3 are formed for removing the multi-layered
sacrificial layers 42. The openings T3 may be formed in various
shapes such as a line type, in addition to the hole type. However,
when the openings T3 are formed in the hole type, the integration
density of the memory device can be further increased, which will
be described hereinafter in more detail.
[0100] When the hole type openings T3 for removal of the
sacrificial layer are formed between the channels 43 arranged in
the first direction I-I' and the second direction II-II'
intersecting with the first direction I-I', the hole type openings
T3 and the channels 43 are arranged to cross each other. In this
way, a distance D2 between the openings T3 and the channels 43 can
be further reduced.
[0101] When the line type openings extending in the first direction
I-I' are formed, the distance D2 between the openings and the
channels 43 must be considered. On the other hand, when the hole
type openings T3 and the channels 43 are arranged to cross each
other, a distance D1 between the openings T3 and the channels 43 in
a diagonal direction must be considered.
[0102] That is, as illustrated in FIG. 20B, a distance D3 between
the openings T4 for removal of the sacrificial layers and the
channels 43 can be further reduced. Hence, the integration density
of the channels 43 and the openings for removal of the sacrificial
layers can be further increased.
[0103] The distance D1 between the openings T3 for removal of the
sacrificial layer and the channels 43 may be determined,
considering the thickness of the tunnel insulation layer, the
charge trap layer, and the charge blocking layer 44 which are
formed on the sidewalls of the channels 43 in the subsequent
process.
[0104] For illustrative purposes, the sectional view showing the
cross section of the channels 43 and the openings T3 for removal of
the sacrificial layers is illustrated in FIG. 20A. However, as
mentioned above, when the distance D3 between the channels 43 and
the openings T4 for removal of the sacrificial layer is reduced,
the channels 43 and the openings T4 for removal of the sacrificial
layers may be arranged to overlap each other in view of the cross
section.
[0105] The hole type openings T3 for removal of the sacrificial
layers may be formed to have a width of 1 .mu.m or less.
[0106] Referring to FIGS. 21A and 21B, the multi-layered
sacrificial layers 42 exposed by the openings T3 for removal of the
sacrificial layer are removed to expose the sidewalls of the
channels 43. At this point, due to the removal of the sacrificial
layers 42, the openings T3' for removal of the sacrificial layers
extend up to the sidewalls of the channels 43. Therefore, the
sidewalls of the channels 43 are exposed at certain intervals
through the space where the sacrificial layers 42 are removed (see
{circle around (1)} of FIG. 21A), and a tunnel insulation layer, a
charge trap layer, a charge blocking layer, and a gate electrode
are formed in the space, where the sacrificial layers 42 are
removed, in a subsequent process.
[0107] Referring to FIGS. 22A and 22B, the tunnel insulation layer,
the charge trap layer, and the charge blocking layer 44 are
sequentially formed over a resulting layer where the channels 43
are exposed. In this way, the tunnel insulation layer, the charge
trap layer, and the charge blocking layer 44 are sequentially
formed on the sidewalls of the exposed channels 43, and the width
of the openings T3'' for removal of the sacrificial layers between
the multi-layered interlayer dielectric layers 41 is reduced. The
tunnel insulation layer, the charge trap layer, and the charge
blocking layer are illustrated as one layer and represented by a
reference numeral "44"
[0108] In sequentially forming the tunnel insulation layer, the
charge trap layer, and the charge blocking layer 44 over the
resulting structure where the sacrificial layers 42 are removed,
the tunnel insulation layer, the charge trap layer, and the charge
blocking layer 44 may be formed to a certain thickness at which the
space between the multi-layered interlayer dielectric layers 41 is
not completely filled. That is, the tunnel insulation layer, the
charge trap layer, and the charge blocking layer 44 may be formed
to a certain thickness at which the space between the interlayer
dielectric layers is opened to some degree, that is, the space for
gate electrode is ensured.
[0109] The tunnel dielectric layer may be formed to a thickness
ranging from approximately 1 .ANG. to approximately 200 .ANG., and
the charge trap layer may be formed to a thickness ranging from
approximately 1 .ANG. to approximately 500 .ANG.. The charge
blocking layer may be formed to a thickness ranging from
approximately 1 .ANG. to approximately 500 .ANG.. Moreover, the
charge trap layer may be formed of nitride or polycrystal silicon,
and the charge blocking layer may be formed of a material having a
high dielectric constant.
[0110] A process of forming gate electrodes of the memory cells
stacked along the channels is performed. The gate electrode is
formed by filling the opened region between the interlayer
dielectric layers, that is, the opened region between the charge
blocking layers, with a conductive layer for gate electrode. A gate
electrode separation layer is formed by filling the openings for
removal of the sacrificial layer, where the gate electrodes are
formed, with an insulation layer.
[0111] As the method for forming the gate electrode in accordance
with the first embodiment, a case of forming the conductive layer
for gate electrode so that the center region is opened will be
described hereinafter with reference to FIGS. 23A to 24B. As the
method for forming the gate electrode in accordance with the second
embodiment, a case of forming the conductive layer for gate
electrode so that the openings T3'' for removal of the sacrificial
layers are completely filled will be described hereinafter with
reference to FIGS. 25A to 26B.
[0112] A method for forming a gate electrode in accordance with a
first embodiment of the present invention will be described
hereinafter.
[0113] Referring to FIGS. 23A and 23B, conductive layers 45 for
gate electrode are formed so that the opened regions between the
interlayer dielectric layers, that is, the opened regions between
the charge blocking layers, are filled and the center regions C of
the openings T3'' for removal of the sacrificial region are opened.
Therefore, the center regions C have a hole type trench shape, and
the conductive layers 45 for gate electrode are formed along the
inner walls of the center regions C.
[0114] The conductive layers 45 for gate electrode may be formed of
polysilicon, metal, a combination thereof, or a metal compound. The
metal compound may include CoSix or NiSi.
[0115] Referring to FIGS. 24A and 24B, the conductive layers 45 for
gate electrode, which are formed along the inner walls, may be
removed by a dry etch process or a wet etch process.
[0116] The center regions C where the conductive layers 45 formed
along the inner walls are filled with an insulation layer. The
insulation layer 46 is a gate separation layer for separating the
multi-layered gate electrodes, and may include an oxide layer.
[0117] A method for forming a gate electrode in accordance with a
second embodiment of the present invention will be described
hereinafter.
[0118] Referring to FIGS. 25A and 25B, conductive layers 45 for
gate electrode are formed over a resulting structure where the
tunnel insulation layer, the charge trap layer, the charge blocking
layer 44 are formed, so that the opened region between the
multi-layered interlayer dielectric layers are filled. At this
point, the openings T3'' for removal of the sacrificial layer are
completely filled with the conductive layers 45 for gate
electrode.
[0119] Referring to FIGS. 26A and 26B, the conductive layers 45 for
gate electrode are selectively etched to separate gate electrodes
45A of the memory cells from one another, the memory cells being
stacked along the channels 43.
[0120] The conductive layers 45 for gate electrode may be etched by
a blanket etch process. When the blanket etch process is performed,
the tunnel insulation layer, the charge trap layer, and the charge
blocking layer 44 formed at the uppermost portion of the memory
cell MC serve as an etch barrier, and only the conductive layers 45
buried between the memory cells MC are selectively etched.
Therefore, the gate electrodes of the memory cells MC can be
separated from one another, without forming separate mask
patterns.
[0121] The regions, where the conductive layers 45 for gate
electrode are etched, are filled with an insulation layer 46. The
insulation layer 46 serves as a gate electrode separation layer for
separating the multi-layered gate electrodes and may include an
oxide layer.
[0122] In this way, the semiconductor memory device is fabricated
which includes the gate electrode 45A alternately stacked with the
interlayer insulation layer 41 on the substrate 40, the channel 43
buried within a plurality of gate electrode 45A and the interlayer
dielectric layer 41 and protruding vertically from the substrate
40, and the memory cell including the tunnel insulation layer, the
charge trap layer, and the charge blocking layer 44 between the
gate electrode 45A and the channel 43. Furthermore, the string (ST)
structure arranged vertically from the substrate 40 is formed by
the memory cells MC stacked along the channel 43.
[0123] In the memory cells MC stacked along the channel 43, the
gate electrodes 45A are separated by the insulation layer 46 buried
within the gate electrodes 45A and the interlayer dielectric layers
41, that is, the gate electrode separation layer. Moreover, since
the memory cells MC formed on the same layer share the gate
electrode 45A, they operate as one page in a read operation.
[0124] As mentioned above, the integration density of the memory
device can be increased by forming the hole type openings for
removal of the sacrificial layer. Furthermore, since the memory
cells formed on the same layer operate as one page, the area
necessary for the formation of the word lines is reduced and thus
the integration density of the memory device is further
increased.
[0125] FIGS. 27A to 27C are diagrams illustrating a process of
forming a plurality of bit lines and a plurality of word lines in
accordance with an embodiment of the present invention.
[0126] FIG. 27A is a cross-sectional view of an intermediate
resulting structure, where a plurality of bit lines are formed.
Referring to FIG. 27A, after exposing the surfaces of the channels
43, a plurality of bit lines connected to the channels 43 are
formed. That is, the bit lines may be formed after forming a
plurality of contact plugs connected to the channels 43.
[0127] FIG. 27B is a cross-sectional view of an intermediate
resulting structure where a plurality of word lines are formed, and
FIG. 27C is a perspective view of the intermediate resulting
structure where the word lines are formed. Referring to FIG. 27B,
the previously formed layers such as the interlayer dielectric
layer 41, the tunnel insulation layer, the charge trap layer, and
the charge blocking layer 44, and the gate electrode 45A are
patterned to expose the gate electrodes of the memory cells stacked
along the channels 43.
[0128] A plurality of word lines 48 connected to the gate
electrodes of the memory cells are formed. The word lines may be
formed after forming a plurality of contact plugs connected to the
gate electrodes.
[0129] At this point, since the memory cells formed on the same
layer are formed to operate as one page, one word line 48 is formed
one layer. Thus, compared with the prior art, the number of the
word lines 48 is reduced and therefore the area necessary for
formation of the word lines may be effectively reduced. That is,
the integration density of the memory device can be further
increased.
[0130] In accordance with the embodiments of the present invention,
the tunnel insulation layer, the charge trap layer, and the charge
blocking layer can be sequentially formed after forming the
channels. Thus, the layer quality of the tunnel insulation layer
can be improved, and the current flow in the channels can be
improved by forming the channels of single crystal silicon. In
addition, the uniformity of the threshold voltage distribution can
be improved.
[0131] Furthermore, the integration density of the vertical channel
type nonvolatile memory device can be improved because at least two
strings share one channel.
[0132] Moreover, the area necessary for formation of the word lines
can be reduced because the plurality of memory cells formed on the
same layer operate as one page. Thus, the integration density of
the memory device can be further increased.
[0133] While the present invention has been described with respect
to the specific embodiments, it will be apparent to those skilled
in the art that various changes and modifications may be made
without departing from the spirit and scope of the invention as
defined in the following claims.
* * * * *