U.S. patent application number 12/417127 was filed with the patent office on 2009-08-13 for fabrication method and structure for providing a recessed channel in a nonvolatile memory device.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Kwang-soo Kim, Heon-Kyu Lee, Chan-Kwang Park, Sang-Pil Sim.
Application Number | 20090200596 12/417127 |
Document ID | / |
Family ID | 38088052 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090200596 |
Kind Code |
A1 |
Sim; Sang-Pil ; et
al. |
August 13, 2009 |
FABRICATION METHOD AND STRUCTURE FOR PROVIDING A RECESSED CHANNEL
IN A NONVOLATILE MEMORY DEVICE
Abstract
A method of fabricating a nonvolatile memory device includes
preparing a semiconductor substrate including a cell array region.
The method also includes forming a recessed region in the cell
array region by etching the semiconductor substrate. The method
includes etching at least a portion of the semiconductor substrate
that partially includes the recessed region and forming first and
second trenches that differ in depth, intersect the recessed
region, and link with each other. The method includes forming a
device isolation layer having rugged bottoms and defining an active
region by filling an insulating material in the first and second
trenches. The method includes forming a gate insulation layer on
the semiconductor substrate of the active region including the
recessed region and forming a gate structure on the gate insulation
layer, to fill the recessed region, the gate structure including a
floating gate, an intergate insulating pattern, and a control
gate.
Inventors: |
Sim; Sang-Pil; (Seongnam-si,
KR) ; Kim; Kwang-soo; (Wansan-gu, KR) ; Park;
Chan-Kwang; (Seoul, KR) ; Lee; Heon-Kyu;
(Suwon-si, KR) |
Correspondence
Address: |
VOLENTINE & WHITT PLLC
ONE FREEDOM SQUARE, 11951 FREEDOM DRIVE SUITE 1260
RESTON
VA
20190
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
38088052 |
Appl. No.: |
12/417127 |
Filed: |
April 2, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11583796 |
Oct 20, 2006 |
7531409 |
|
|
12417127 |
|
|
|
|
Current U.S.
Class: |
257/316 ;
257/E29.3 |
Current CPC
Class: |
H01L 27/115 20130101;
H01L 27/0207 20130101; H01L 27/11519 20130101; H01L 27/11524
20130101; H01L 29/40114 20190801; H01L 27/11521 20130101 |
Class at
Publication: |
257/316 ;
257/E29.3 |
International
Class: |
H01L 29/788 20060101
H01L029/788 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2005 |
KR |
2005-103866 |
Jun 19, 2006 |
KR |
2006-55061 |
Claims
1. A nonvolatile memory device comprising: a semiconductor
substrate including a cell array region; a device isolation layer
having a rugged bottom profile with shallower and deeper bottoms,
intersecting the semiconductor substrate in the cell array region
and defining an active region, wherein the active region comprises
a recessed region; a gate insulation layer on the active region;
and a gate structure including a control gate, an intergate
insulating layer, and a floating gate on the gate insulation layer,
wherein the gate insulation layer is conformably provided along a
profile of the recessed region and the floating gate is provided to
fill the recessed region.
2. The nonvolatile memory device as set forth in claim 1, wherein
an intergate insulating pattern is smaller than the control gate in
width and the floating gate is in contact with the control
gate.
3. The nonvolatile memory device as set forth in claim 1, wherein a
difference between the shallower and deeper bottoms in the device
isolation layer corresponds to a depth of the recessed region.
4. A nonvolatile memory device as set forth in claim 1, wherein the
recessed region comprises a bottom and a sidewall, the corner
between the bottom and the sidewall being rounded.
5. A nonvolatile memory device comprising: device isolation layers
provided in parallel with each other in a semiconductor substrate,
defining active regions; pluralities of parallel word lines
intersecting the device isolation layers on the semiconductor
substrate; a floating gate interposed between the word lines and
the active regions; an intergate insulating pattern interposed
between the word lines and the floating gate; a gate insulation
layer interposed between the floating gate and the active regions;
drain regions provided in the active regions at a first side of the
word lines, the drain regions being isolated from each other
through the device isolation layers; a common source line provided
by connecting the active regions with each other at the second side
of the word lines, being parallel with the word lines; and a bit
line conductively connected to the drain regions, crossing over the
word lines, wherein the active region under the floating gate
comprises a recessed region, wherein the gate insulation layer is
conformably provided along a profile of the recessed region and the
floating gate is provided to fill the recessed region, wherein the
device isolation layer has a rugged bottom profile, with shallower
and deeper bottoms, along the bit line.
6. The nonvolatile memory device as set forth in claim 5, wherein a
difference between the shallower and deeper bottoms in the device
isolation layer corresponds to a depth of the recessed region.
7. The nonvolatile memory device as set forth in claim 5, wherein
the recessed region and the deeper bottom of the device isolation
layer are placed under the word line.
8. The nonvolatile memory device as set forth in claim 5, which
further comprises: a common source contact in contact with the
common source line, wherein the word line is adjacent to the common
source line contact and has a sidewall concaved toward the common
source line contact.
9. The nonvolatile memory device as set forth in claim 8, wherein
the recessed region extends to be under the word line adjacent to
the common source line contact and has a sidewall concaved toward
the common source line contact along a profile of the concaved
sidewall of the word line.
10. The nonvolatile memory device as set forth in claim 8, wherein
the recessed region is excluded from the semiconductor substrate
under the word line adjacent to the common source line contact.
11. A nonvolatile memory device as set forth in claim 5, wherein
the recessed region comprises a bottom and a sidewall, the corner
between the bottom and the sidewall being rounded.
12. A nonvolatile memory device comprising: a semiconductor
substrate; device isolation layers formed in parallel with each
other in the semiconductor substrate, defining an active region;
string and ground selection lines in parallel with each other,
crossing over the active region; pluralities of parallel word lines
interposed between the string and ground selection lines, crossing
over the active region; a first floating gate interposed between
the word lines and the active region; a first intergate insulating
pattern interposed between the word lines and the first floating
gate; a first gate insulation layer interposed between the first
floating gate and the active region; a second gate insulation layer
interposed between the first floating gate and the active region;
and a bit line conductively connected to the active region adjacent
to the selection lines, intersecting the selection lines, wherein
the active region under the selection lines comprises a recessed
region, wherein the second gate insulation layer is conformably
provided along a profile of the recessed region, wherein the device
isolation layers have a rugged bottom profile with shallower and
deeper bottoms along the bit line.
13. The nonvolatile memory device as set forth in claim 12, wherein
a difference between the shallower and deeper bottoms in the device
isolation layers corresponds to a depth of the recessed region.
14. The nonvolatile memory device as set forth in claim 12, wherein
the recessed region and the deeper bottom of the device isolation
layers are arranged in a line.
15. A nonvolatile memory device as set forth in claim 12, wherein
the recessed region comprises a bottom and a sidewall, the corner
between the bottom and the sidewall being rounded.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of U.S. non-provisional application
Ser. No. 11/583,796, filed Oct. 20, 2006, which is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present disclosure relates to manufacturing methods for
semiconductor memory devices and, more particularly, to fabrication
methods and structures for providing recessed channels in
nonvolatile memory devices.
[0004] This U.S. non-provisional patent application claims priority
under 35 U.S.C. .sctn. 119 to Korean Patent Application No.
2005-103866 filed on Nov. 1, 2005, and Korean Patent Application
No. 2006-55061 filed on Jun. 19, 2006, the entire contents of which
are hereby incorporated by reference.
[0005] 2. Description of Related Art
[0006] With higher integration of semiconductor devices, various
physical limitations may affect the performance of the
semiconductor devices. For example, because of high integration
densities, a channel length of the device may become shorter. The
shorter channel length of the device may lead to problems such as,
for example, a punch-through effect. In order to overcome such
limitations associated with the channel length of the semiconductor
device, various structures and fabrication methods for extending a
channel length in a highly integrated semiconductor device have
been studied.
[0007] One such example of a highly integrated semiconductor device
includes a recessed channel array transistor (RCAT). The structure
of the RCAT includes sidewalls and a recessed region. Specifically,
the bottom of the recessed region is used for a channel region.
[0008] A conventional method for fabricating a nonvolatile memory
device having the recessed channels is as follows. A device
isolation layer is formed in a semiconductor substrate. This device
isolation layer may be used to define an active region.
Furthermore, the defined active region may include the channel for
the semiconductor device. Specifically, the recessed region for the
channel is formed in the active region. In addition, the recessed
region may have a width smaller than that of the active region.
Thus, it may be beneficial to form a photoresist pattern having an
opening that is smaller than the dimensions of the active region.
In particular, the opening of the photoresist pattern defines the
recessed region.
[0009] While the disclosed RCAT provides for higher integration
densities in semiconductor devices, it suffers from several
shortcomings. For example, with higher integration of semiconductor
devices, it may become more difficult to precisely arrange the
photoresist pattern having a smaller opening.
[0010] In addition, the higher integration of nonvolatile
semiconductor devices also leads to narrower widths of floating
gates. The narrow widths of floating gates may also cause many
problems. For example, the narrow floating gates may have
insufficient processing margins because of the gates' reduced
width. This reduction in processing margins may make it difficult
to compensate for the misalignment that occurs when patterning the
floating gates. In order to solve this problem, the floating gates
may be arranged in self-alignment with the device isolation layer.
In this case, the device isolation layer is designed to have a
height corresponding to a height of the floating gates. However, it
may be practically very difficult to implement such a precise
photoresist pattern for the recessed regions in the structure of
the device isolation layer having a high surface. This is because
the depth of focus (DOF) margin becomes smaller because of such a
physical limitation.
[0011] The present disclosure is directed towards overcoming one or
more problems associated with the prior art semiconductor
devices.
SUMMARY OF THE INVENTION
[0012] One aspect of the present disclosure includes a method of
fabricating a nonvolatile memory device. The method includes
preparing a semiconductor substrate including a cell array region.
The method also includes forming a recessed region in the cell
array region by etching the semiconductor substrate. In addition,
the method includes etching at least a portion of the semiconductor
substrate that partially includes the recessed region and forming
first and second trenches that differ in depth, intersect the
recessed region, and link with each other. The method also includes
forming a device isolation layer having rugged bottoms and defining
an active region by filling an insulating material in the first and
second trenches. The method also includes forming a gate insulation
layer on the semiconductor substrate of the active region including
the recessed region. The method also includes forming a gate
structure on the gate insulation layer, to fill the recessed
region, the gate structure including a floating gate, an intergate
insulating pattern, and a control gate.
[0013] Another aspect of the present disclosure includes a method
of fabricating a nonvolatile memory device. The method includes
preparing a semiconductor substrate including a cell array region.
The method also includes forming a pad oxide layer and a first hard
mask layer on the semiconductor substrate. The method also includes
forming first hard mask patterns and pad oxide patterns by
patterning the first hard mask layer and the pad oxide layer in the
cell array region, the first hard mask patterns being formed in
parallel with each other and crossing over the semiconductor
substrate, and the pad oxide patterns being formed under the first
hard mask patterns. In addition, the method includes forming
pluralities of recessed regions in the semiconductor substrate by
patterning the semiconductor substrate by using the first hard mask
patterns as an etch mask. The method also includes exposing the pad
oxide patterns by removing the first hard mask patterns. The method
also includes forming pluralities of second hard mask patterns such
that the pluralities of second hard mask patterns are parallel with
each other and intersect the recessed regions on the semiconductor
substrate where the pad oxide patterns are exposed. The method also
includes etching the pad oxide patterns and the semiconductor
substrate to form a first trench, and etching the semiconductor
substrate at the bottoms of the recessed regions to form a second
trench deeper than the first trench, by using the second hard mask
patterns as an etch mask. The method also includes forming a device
isolation layer having rugged bottoms and defining an action region
by filling an insulating material in the first and second trenches.
The method also includes exposing the semiconductor substrate
including the recessed regions adjacent to the device isolation
layer by removing the second hard mask patterns and the pad oxide
patterns. In addition the method includes forming a gate insulation
layer on the exposed semiconductor substrate. The method also
includes forming gate structures on the gate insulation layer to
fill the recessed regions, each of the gate structures including a
floating gate, an interlevel gate insulation pattern, and a control
gate.
[0014] Another aspect of the present disclosure includes a
nonvolatile memory device. The nonvolatile memory device includes a
semiconductor substrate including a cell array region. The memory
device also includes a device isolation layer having a rugged
bottom profile with shallower and deeper bottoms, intersecting the
semiconductor substrate in the cell array region and defining an
active region, wherein the active region comprises a recessed
region. The memory device also includes a gate insulation layer on
the active region. The memory device also includes a gate structure
including a control gate, an intergate insulating layer, and a
floating gate on the gate insulation layer, wherein the gate
insulation layer is conformably provided along a profile of the
recessed region and the floating gate is provided to fill the
recessed region.
[0015] Yet another aspect of the present disclosure includes a
nonvolatile memory device. The memory device includes device
isolation layers provided in parallel with each other in a
semiconductor substrate, defining active regions. The memory device
also includes pluralities of parallel word lines intersecting the
device isolation layers on the semiconductor substrate. The memory
device also includes a floating gate interposed between the word
lines and the active regions, an intergate insulating pattern
interposed between the word lines and the floating gate, a gate
insulation layer interposed between the floating gate and the
active regions, drain regions provided in the active regions at a
first side of the word lines, the drain regions being isolated from
each other through the device isolation layers, a common source
line provided by connecting the active regions with each other at
the second side of the word lines, being parallel with the word
lines, a bit line conductively connected to the drain regions,
crossing over the word lines, wherein the active region under the
floating gate comprises a recessed region, wherein the gate
insulation layer is conformably provided along a profile of the
recessed region and the floating gate is provided to fill the
recessed region, and wherein the device isolation layer has a
rugged bottom profile, with shallower and deeper bottoms, along the
bit line.
[0016] Yet another aspect of the present disclosure includes a
nonvolatile memory device. The device includes a semiconductor
substrate. The device also includes a device isolation layers
formed in parallel with each other in the semiconductor substrate,
defining an active region, string and ground selection lines in
parallel with each other, crossing over the active region,
pluralities of parallel word lines interposed between the string
and ground selection lines, crossing over the active region, a
first floating gate interposed between the word lines and the
active region, a first intergate insulating pattern interposed
between the word lines and the first floating gate, a first gate
insulation layer interposed between the first floating gate and the
active region, a second gate insulation layer interposed between
the first floating gate and the active region, a bit line
conductively connected to the active region adjacent to the
selection lines, intersecting the selection lines, wherein the
active region under the selection lines comprises a recessed
region, wherein the second gate insulation layer is conformably
provided along a profile of the recessed region, and wherein the
device isolation layers have a rugged bottom profile with shallower
and deeper bottoms along the bit line.
BRIEF DESCRIPTION OF THE FIGURES
[0017] The accompanying figures are included to provide a further
understanding of the disclosure, and are incorporated in and
constitute a part of this specification. The drawings illustrate
exemplary embodiments of the disclosure and, together with the
description, serve to explain principles of the present disclosure.
In the figures:
[0018] FIGS. 1 through 11 are perspective views illustrating
sequential processing steps of fabricating a NOR-type nonvolatile
memory device in accordance with an exemplary disclosed embodiment
of the invention;
[0019] FIG. 12 is a sectional view taken along line I-I' of FIG.
11;
[0020] FIG. 13 is a plane view illustrating the NOR-type
nonvolatile memory device in accordance with an exemplary disclosed
embodiment of the invention;
[0021] FIG. 14A is a plane view illustrating a NOR-type nonvolatile
memory device in accordance with another exemplary disclosed
embodiment of the invention;
[0022] FIG. 14B is a sectional view taken along line II-II' of FIG.
14A;
[0023] FIG. 15A is a plane view illustrating a NOR-type nonvolatile
memory device in accordance with yet another exemplary disclosed
embodiment of the invention;
[0024] FIG. 15B is a sectional view taken along line III-III' of
FIG. 15A;
[0025] FIGS. 16A, 17A, 18A, 19A, 20A, 21A, and 22A are plane views
illustrating sequential processing steps of fabricating a NAND-type
nonvolatile memory device in accordance with another exemplary
disclosed embodiment of the invention;
[0026] FIGS. 16B, 17B, 18B, 19B, 20B, 21B, and 22B are sectional
views taken along line IV-IV' of FIGS. 16A, 17A, 18A, 19A, 20A,
21A, and 22A, respectively; and
[0027] FIGS. 16C, 17C, 18C, 19C, 20C, 21C, and 22C are sectional
views taken along line V-V' of FIGS. 16A, 17A, 18A, 19A, 20A, 21A,
and 22A, respectively.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] Exemplary embodiments of the present invention will be
described below in more detail with reference to the accompanying
drawings. The present invention may, however, be embodied in
different forms and should not be constructed as limited to the
embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope of the invention to those skilled in
the art.
[0029] In the figures, the dimensions of layers and regions are
exaggerated for clarity of illustration. It will also be understood
that when a layer (or film) is referred to as being `on` another
layer or substrate, it can be directly on the other layer or
substrate, or intervening layers may also be present. Furthermore,
it will be understood that when a layer is referred to as being
`under` another layer, it can be directly under, and one or more
intervening layers may also be present. In addition, it will also
be understood that when a layer is referred to as being `between`
two layers, it can be the only layer between the two layers, or one
or more intervening layers may also be present. Like reference
numerals refer to like elements throughout.
[0030] FIGS. 1 through 11 are perspective views illustrating
sequential processing steps of fabricating a NOR-type nonvolatile
memory device in accordance with an exemplary disclosed
embodiment.
[0031] Referring to FIG. 1, a pad oxide layer (not shown) is
deposited entirely on a semiconductor substrate 1. Furthermore, a
first hard mask layer (not shown) is deposited on the pad oxide
layer. The first hard mask layer may comprise of silicon nitride,
silicon oxynitride, or/and photoresist. The semiconductor substrate
1 may comprise crystalline silicon, including a cell array region
and a peripheral circuit region. In an exemplary embodiment, the
semiconductor substrate 1 corresponds to a cell array region.
[0032] A first photoresist pattern (not shown) including openings
to confine recessed channel regions is formed on the first hard
mask layer. Furthermore, using the first photoresist pattern as an
etch mask, the first hard mask layer is selectively etched to form
a first hard mask pattern 5. That is, the first hard mask pattern 5
may be a photoresist pattern formed by means of a photolithography
process. In an exemplary embodiment, a chemical attachment process
is available to further shrink a width of the opening (i.e., a
first width W1) defined by the first hard mask pattern 5. In
detail, when a photoresist material is coated and thermally treated
after forming the first hard mask pattern 5, the photoresist
material is attached to the surface of the first hard mask pattern
5 and simultaneously shrunk down to form openings at spaces
provided by the first hard mask pattern 5 in widths smaller than
the first width W1. In addition, the hard mask pattern 5 itself may
be completed by means of photolithography, etching, and/or a
chemical attachment.
[0033] The semiconductor device of FIG. 1 also includes a pad oxide
pattern 3. Specifically, using the first hard mask pattern 5 as an
etch mask, the pad oxide layer is selectively etched to form the
pad oxide pattern 3. In addition, the semiconductor substrate 1
there under is etched to form recessed regions 7. These recessed
regions 7 have bottoms leveled lower than a surface 2 of the
semiconductor substrate 1 that has a first width W1 and a first
depth D1. The recessed regions 7 are provided for recessed channels
completed through the subsequent processing step.
[0034] In an exemplary embodiment, the recessed regions 7 may be
arranged in parallel with each other in plurality. Furthermore,
before forming trenches, the first photoresist pattern is formed on
the first hard mask layer that is flattened on the flat
semiconductor substrate 1. Because the first photoresist pattern is
formed before forming the trenches, a sufficient margin for DOF may
be included in the semiconductor device. Thereby, it is possible to
precisely form the recessed regions 7 in required depth and width
therefor.
[0035] Referring to FIG. 2, the semiconductor substrate 1 including
the recessed regions 7 is oxidized to form a passivation oxide
layer 9. This passivation oxide layer 9 is formed on the bottoms
and sidewalls of the recessed regions 7. In particular, during the
oxidation, the passivation oxide layer 9 is rounded, as shown by
the enclosed circle E, at corners where the bottoms of the recessed
regions 7 meet with the sidewalls thereof.
[0036] Referring to FIG. 3, the first hard mask pattern 5, is
removed from the top of the semiconductor substrate 1. The removal
of the first hard mask pattern 5 may be performed by using various
chemicals such as, for example, phosphoric acid. Furthermore,
during the removal of the first hard mask pattern 5, the
passivation oxide layer 9 and the pad oxide patterns 3 may protect
the semiconductor substrate 1 from being etched away.
[0037] After removing the first hard mask pattern 5, a second hard
mask layer is deposited all over the semiconductor substrate 1.
Beneficially, the second hard mask layer is formed in a thickness
of more than a half (1/2) the width W1 of the recessed region 7. In
addition, the second hard mask layer fills the recessed regions 7
and also has a flat surface. Furthermore, a second photoresist
pattern (not shown) is formed on the second hard mask layer.
Because the second photoresist pattern is settled on the second
hard mask layer having the flat surface, there is a sufficient
margin for DOF. This sufficient margin for DOF may allow for the
precise formation the second photoresist pattern.
[0038] Using the second photoresist pattern as an etch mask, the
second hard mask layer is patterned to form second hard mask
patterns 11. Specifically, the second hard mask patterns 11 are
formed parallel to each other and in plurality. Furthermore, the
second hard mask patterns intersect the recessed regions 7 and
define positions where a device isolation layer will be settled by
a subsequent processing step. Furthermore, the second hard mask
patterns 11 partially fill the recessed regions 7. The second hard
mask patterns 11 may comprise of various chemicals such as, for
example, silicon nitride or silicon oxynitride. Because the second
photoresist pattern is correctly formed, the second hard mask
patterns 11 can be formed accurately by using the second
photoresist pattern as the etch mask.
[0039] Referring to FIG. 4, using the second hard mask patterns 11
as an etch mask, the pad oxide patterns 3, the passivation oxide
layer 9, and the semiconductor substrate 1 are etched to form first
trenches 13 and second trenches 15. Specifically, the first
trenches 13 have a second depth D2. Furthermore, the second
trenches 15, which link with the first trenches, have a third depth
D3. In particular, the first trenches 13 are formed by grooving the
semiconductor substrate 1 under the pad oxide patterns 3, while the
second trenches 15 are formed by grooving the semiconductor
substrate 1 under the recessed regions 7. Therefore, the third
depth D3 corresponds to the sum of the first depth D1 in the
recessed regions 7 and the second depth D2 in the first trenches
13.
[0040] Next, referring to FIG. 5, an insulating material for a
device isolation layer is formed all over the semiconductor
substrate 1. Specifically, this insulating material is formed in a
thickness larger than 1/2 of the width of the first trenches 13.
Furthermore, the insulating material fills the first and second
trenches 13 and 15. The insulating material may be formed in a
single layer or a multi-level layer, containing materials such as,
for example, thermal oxide, silicon nitride, silicon oxynitride,
high-density plasma (HDP) oxide, or boron phosphorous silicate
glass (BPSG). In addition, the insulating material is flattened (or
planarized) to be leveled with the second hard mask patterns 11 to
form the device isolation layer 17. The planarization may be
carried out by processes such as, for example, chemical-mechanical
polishing (CMP) or etch-back process. Profiles on the bottoms of
the device isolation layer 17 are rugged by the first and second
trenches 13 and 15. The device isolation layer 17 confines active
regions in the cell array region. Furthermore, the formation of the
device isolation layer 17 exposes the second hard mask patterns
11
[0041] Referring to FIG. 6, the second hard mask patterns 11 are
removed from the semiconductor substrate 1. The removal of the
second hard mask patterns 11 may be performed by using a chemical
such as, for example, phosphoric acid. Upon removal of the second
hard mask patterns 11, the passivation oxide layer 9 is exposed on
the upper sidewalls of the device isolation layer 17, in the pad
oxide layers 3, and the recessed regions 7.
[0042] Referring to FIG. 7, the pad oxide patterns 3 and the
passivation oxide layers 9 are removed. The removal of the pad
oxide patterns 3 and the passivation oxide layer 9 may be performed
by chemicals such as, for example, fluoric acid. Furthermore, if
the device isolation layer 17 is made of a kind of oxide, the
oxides in the device isolation layer 17 are partially removed
simultaneously while removing the pad oxide patterns 3 and
passivation oxide layers 9. Removal of the pad oxide patterns 3 and
the passivation oxide layers 9 causes the surface 2 of the
semiconductor substrate 1 to be exposed. In addition, by removing
the passivation oxide layer 9, the semiconductor substrate 1 is
also partially exposed in the recessed regions 7. Although not
shown in FIG. 7, the passivation oxide layer 9 makes the exposed
lower corners of the recessed regions 7 rounded as shown by the
circle E in FIG. 2.
[0043] Referring to FIG. 8, an oxidation process is used to form a
gate insulating layer 19 on the exposed surface of the
semiconductor substrate 1. In particular, the gate insulating layer
19 is conformably formed along the profiles of the recessed regions
7. Because the corners of the recessed regions 7 are rounded, the
gate insulating layer 19 is also rounded at the corners of the
recessed regions 7. As a result, it prevents concentration of an
electric field thereon during an operation of the nonvolatile
memory device.
[0044] Referring to FIG. 9, a floating gate layer (not shown) is
deposited over the semiconductor substrate 1, filling the spaces
between the device isolation layers 17. In addition, a
planarization process on the floating gate layer is performed to
form floating gate patterns 21. Furthermore, the planarization
process exposes the upper surface of the device isolation layer 17.
Because the floating gate patterns 21 are self-aligned with the
device isolation layer 17, there may be no misalignment of the
floating gates. The lack of misalignment of the floating gates may
provide the semiconductor device with sufficient processing margin.
In an exemplary embodiment, the floating gate layer may comprise of
doped polysilicon. In addition, the planarization process may be
carried out through a CMP, an etch-back process, or any other such
process. Furthermore, in the planarization process, the device
isolation layer 17 functions as a planarization stopping layer.
[0045] After completing the planarization, referring to FIG. 10,
the exposed upper portion of the device isolation layer 17 may be
partially recessed. This recession may be done to level the height
of the device isolation layer 17 to a level lower than that of the
upper surface of the floating gate patterns. Such a recession may
extend an overlapping area between the floating gates and control
gates. This overlapping area between the floating gates and control
gates may enhance a coupling effect therethrough and also improve
program efficiency. The recessing process may be accomplished by
way of a dry or wet etching operation. After the recessing process,
an intergate insulating layer 23 is deposited over the
semiconductor substrate 1. The intergate insulating layer 23 may
comprise of silicon oxide, silicon nitride, silicon oxynitride,
hafnium oxide, tantalum oxide, and/or aluminum oxide. After the
deposition of the intergate insulating layer 23, a control gate
layer 25 is deposited on the intergate insulating layer 23. The
control gate layer 25 may comprise of doped polysilicon, tungsten,
tungsten silicide, and/or tungsten nitride.
[0046] FIG. 12 illustrates a section taken along line I-I' of FIG.
11. Referring to FIGS. 11 and 12, the control gate layer 25, the
intergate insulating layer 23, and the floating gate patterns are
selectively etched by using an etch mask with a photoresist pattern
(not shown) that overlaps with the recessed regions 7 and
intersects the device isolation layer 17. This selective etching
results in gate patterns 26 each of which comprises a word line WL
(or a control gate 25a), an intergate insulating pattern 23a under
the control gate 25a, and a floating gate 21a under the intergate
insulating pattern 23a. Furthermore, the floating gates 21a fill
the recessed regions 7. The width of the floating gate 21a is a
second width W2. The second width W2 of the floating gate may be
identical to or larger than the first width W1, that is the width
of the recessed region 7. In addition, although not shown, capping
patterns may be formed on the word lines 25a. Furthermore, spacers
may be also provided to cover sidewalls of the word lines 25a.
[0047] Referring to FIG. 11, the semiconductor substrate 1 may be
partially exposed by removing the device isolation layer 17 between
adjacent word lines 25a by using a mask pattern (not shown) as an
etch mask. Moreover, by using the word lines 25a as an ion
implantation mask, impurity ions are injected (or implanted) into
the semiconductor substrate 1 to form impurity regions 27.
[0048] The nonvolatile memory device shown in FIG. 11 or 12 may
correspond to the NOR-type nonvolatile memory device whose plane
view is shown in FIG. 13. That is, the nonvolatile memory device of
FIG. 11 may be a perspective taken from portion A of FIG. 13, while
FIG. 12 may be a section taken along line I-I' of FIG. 13. However,
some features shown in one figure may not be shown in the others.
For example, FIGS. 11 and 12 do not show bit line contact BLC and
bit line BL that are shown in FIG. 13. In FIGS. 11 and 12, the
impurity region 27 placed between the adjacent word lines 25a
corresponds to a common source line CSL shown in FIG. 13.
[0049] The structure of a NOR-type nonvolatile memory device
fabricated using the aforementioned processing method will now be
described with reference to FIGS. 11 and 13. The plurality of
device isolation layers 17 are arranged parallel to each other with
confining active regions in the semiconductor substrate 1. In
addition, the plurality of word lines (WL) 25a are arranged
parallel to each other such that they cross over the active regions
defined by the device isolation layer 17. One of the impurity
regions 27, which is disposed in the active region between one word
line and its adjacent word line, corresponds to a common drain
region (not shown). Another one of the impurity regions 27, which
is disposed in the active region between one word line and its
adjacent word line, corresponds to the common source line CSL.
[0050] Furthermore, as shown in FIG. 13, the bit line contacts BLC
are placed in the common drain regions. In addition, on the common
drain regions, the plural bit lines BL are disposed parallel to
each other to make contact with the bit line contacts BLC and to
intersect the word lines (WL) 25a. The bottom profiles of the
device isolation layer 17 are rugged by including shallower and
deeper bottoms 13 and 15 along the bit lines BL under the word
lines (WL) 25a. In an exemplary embodiment, the deeper bottoms 15
of the device isolation layer 17 are located around the recessed
regions 7. Because the deeper bottoms 15 of the device isolation
layer 17 accord depth to the recessed regions 7, they may prevent
leakage current from flowing towards adjacent cells through the
device isolation layer 17 during an operation of the NOR-type
nonvolatile memory device.
[0051] Thus, because the trenches for the device isolation layer
are formed after completing the recessed regions for channels, a
better margin of DOF may be provided than that provided by a
conventional method of semiconductor device fabrication.
Furthermore, the disclosed method may be used to form the recessed
regions with more precision than the conventional methods. Further,
because the floating gates are self-aligned with the device
isolation layer, the disclose method may prevent the issues arising
from misalignment of the floating gates. The amount of DOF margin
provided and the lack of misalignment occurring in the disclosed
method may increase the reliability of a NOR-type nonvolatile
memory device.
[0052] On the other hand, the NOR-type nonvolatile memory device
illustrated in FIGS. 11 through 13 may be modified as shown in
FIGS. 14A and 15A. Specifically, FIG. 14A is a plane view
illustrating a NOR-type nonvolatile memory device in accordance
with another exemplary disclosed embodiment. Furthermore, FIG. 14B
is a sectional view taken along line II-II' of FIG. 14A. Similarly,
FIG. 15A is a plane view illustrating a NOR-type nonvolatile memory
device in accordance with yet another exemplary disclosed
embodiment, and FIG. 15B is a sectional view taken along line
III-III' of FIG. 15A.
[0053] Referring to FIGS. 14A and 14B, a common source line contact
CSLC for applying a voltage to the common source line CSL is
disposed on the common source line CSL. Furthermore, the word lines
WL are concaved toward the common source line contact CSLC around
the common source line contact CSLC. In other words, the word lines
WL are adjacent to the common source line contact CSLC and equipped
with word line sidewalls 25b concaved toward the common source line
contact CSLC. This structural feature may assure a proper
processing margin by extending intervals among the word lines WL
when forming the common source line contact CSLC. Furthermore, in
the NOR-type nonvolatile memory device shown in FIGS. 14A and 14B,
the recessed regions 7 are also placed under the word lines WL
adjacent to the common source line contact CSLC. Moreover, the
recessed regions 7 under the word lines WL adjacent to the common
source line contact CSLC are also configured with sidewalls
concaved toward the common source line contact CSLC along the
concaved sidewalls 25b. Additionally, the deeper bottoms 15 are
present even under the device isolation layer 17 adjacent to the
common source line contact CSLC. To this end, some portions of
sidewalls of the deeper bottoms 15 are bended along the profiles.
Thereby, the sidewalls of the deeper bottoms 15 link with the
sidewalls of the recessed regions 7, as shown in the plane of FIG.
14A. Other structural features of the device illustrated in FIGS.
14A and 14B are the same as those of the NOR-type nonvolatile
memory device illustrated with reference to FIGS. 11 through
13.
[0054] A procedure for fabricating the NOR-type memory device with
the structure shown in FIGS. 14A and 14B is similar to that
aforementioned with reference to FIGS. 1 through 11, except for a
few differences. For example, the recessed regions 7 are formed
with sidewall profiles connected to the deeper bottoms 15 as shown
in FIG. 14A. Moreover, in order to complete the profiles of the
recessed regions 7 as shown in FIG. 14A, the hard mask patterns 5
need to have profiles corresponding to the recessed regions 7.
While the hard mask patterns may be formed using any manufacturing
process, the hard mask patterns 5 are beneficially formed by the
chemical attachment process.
[0055] On the other hand, referring to FIGS. 15A and 15B, while the
word lines WL are concaved toward the common source line contact
CSLC at the area adjacent to the common source line contact CSLC as
like FIG. 14A, there may be no recessed region in the active
regions under the word lines WL. In addition, the device isolation
layer 17 adjacent to the common source line contact CSLC does not
include the deeper bottoms 15 having bended sidewalls as shown in
FIG. 14A. In contrast, in the NOR-type nonvolatile memory device
shown in FIG. 15A, the deeper bottoms 15 link with the recessed
regions 7 in a line and are located only under linear portions of
the word lines WL. Thus, as illustrated in FIG. 15B, the device
isolation layer 17 adjacent to the common source line contact CSLC
is configured in rugged bottom profiles having the shallower and
deeper bottoms 13 and 15, respectively.
[0056] A procedure for fabricating the NOR-type memory device with
the structure shown in FIGS. 15A and 15B is similar to that
aforementioned with reference to FIGS. 1 through 11, except for a
few differences. For example, the recessed regions 7 are formed
with sidewall profiles with lines connected to the deeper bottoms
15. In order to complete the linear profiles of the recessed
regions 7 as shown in FIG. 14A, the hard mask patterns 5 (of FIG.
1) need to have profiles corresponding to the recessed regions 7.
The hard mask patterns 5 are beneficially formed by using a
photolithography process.
[0057] Yet another exemplary disclosed embodiment includes a
modification for a NAND-type memory device. FIGS. 16A, 17A, 18A,
19A, 20A, 21A, and 22A are plane views illustrating sequential
processing steps for fabricating an exemplary disclosed NAND-type
nonvolatile memory device. In addition, FIGS. 16B, 17B, 18B, 19B,
20B, 21B, and 22B are sectional views taken along line IV-IV' of
FIGS. 16A, 17A, 18A, 19A, 20A, 21A, and 22A, respectively.
Moreover, FIGS. 16C, 17C, 18C, 19C, 20C, 21C, and 22C are sectional
views taken along line V-V' of FIGS. 16A, 17A, 18A, 19A, 20A, 21A,
and 22A, respectively.
[0058] Referring to FIGS. 16A, 16B, and 16C, a pad oxide layer (not
shown) is deposited entirely on a semiconductor substrate 100. In
an exemplary embodiment, the semiconductor substrate 100 is
illustrated as corresponding to a cell array region. After the
deposition of the pad oxide layer, a first hard mask layer (not
shown) is deposited on the pad oxide layer. The first hard mask
layer may comprise silicon nitride or silicon oxynitride.
Furthermore, a first photoresist pattern (not shown) including
openings to confine a recessed channel region is arranged on the
first hard mask layer. Additionally, using the first photoresist
pattern for an etch mask, the first hard mask layer is selectively
etched to form a first hard mask pattern 104. Using the first hard
mask pattern 104 for an etch mask, the pad oxide layer is then
selectively etched to form a pad oxide pattern 102. In addition,
the semiconductor substrate 100 thereunder is etched to form
recessed regions 106 in the first width W1 and a first depth D1.
The recessed regions 106 are provided for recessed channels of
ground and string selection lines. Specifically, the recessed
regions 106 are arranged parallel to each other. Because the first
photoresist pattern is formed on the first hard mask layer having a
flat surface before forming the trenches, a sufficient margin for
DOF is provided for in the disclosed semiconductor device.
Therefore, it may be possible to precisely form the recessed
regions 106 with the required depth and width.
[0059] Referring to FIGS. 17A, 17B, and 17C, the semiconductor
substrate 100 including the recessed regions 106 is oxidized to
form passivation oxide layer 108 on the bottoms and sidewalls of
the recessed regions 106. During the oxidation, the passivation
oxide layer 108 is rounded as shown by the enclosed circle E, at
corners where the bottoms of the recessed regions 106 meet with the
sidewalls thereof. At this time, the first hard mask pattern 104 is
removed. The removal of the first hard mask pattern 104 may be
performed by using various chemicals such as, for example,
phosphoric acid. During the removal of the first hard mask pattern
104, the passivation oxide layer 108 and the pad oxide patterns 102
may protect the semiconductor substrate 100 from being etched away.
After removing the first hard mask pattern 104, second hard mask
patterns 110 are formed to define a device isolation layer. The
second hard mask patterns 110 are arranged parallel to each other
in plurality such that they intersect the recessed regions 106 and
expose the passivation oxide layers 108 and the pad oxide layers
102 at regions where the device isolation layer is provided in a
subsequent processing step.
[0060] Using the second hard mask patterns 110 as an etch mask, the
pad oxide patterns 102, the passivation oxide layers 108, and the
semiconductor substrate 100 thereunder, are etched to form first
trenches 112 in the second depth D2 and second trenches 114, which
link with the first trenches, in the third depth D3. Specifically,
the first trenches 112 are formed by grooving the semiconductor
substrate 100 under the pad oxide patterns 102, while the second
trenches 114 are formed by grooving the semiconductor substrate 100
under the recessed regions 106. Therefore, the third depth D3
corresponds to the sum of the first depth D1 in the recessed
regions 106 and the second depth D2 in the first trenches 112.
[0061] Next, referring to FIGS. 18A, 18B, and 18C, an insulating
material for a device isolation layer is formed over the
semiconductor substrate 100. This insulating material is deposited
with a thickness larger than 1/2 of the width of the first trenches
112 and fills the first and second trenches 112 and 114.
Furthermore, the insulating material may be formed in a single
layer or a multi-level layer. The insulating material may include a
number of materials. These materials may include, for example,
thermal oxide, silicon nitride, silicon oxynitride, high-density
plasma (HDP) oxide, or boron phosphorous silicate glass (BPSG).
[0062] Moreover, the insulating material is flattened (or
planarized) to be leveled with the second hard mask patterns 110,
to form the device isolation layer 116. In an exemplary embodiment,
the device isolation layer 116 confines active regions in the cell
array region. Furthermore, the device isolation layer 116 is formed
such that it exposes the second hard mask patterns 110. Moreover,
profiles on the bottoms of the device isolation layer 116 are
rugged by the first and second trenches 112 and 114,
respectively.
[0063] Referring to FIGS. 19A, 19B, and 19C, the second hard mask
patterns 110 are removed. The removal of the second hard mask
patterns 110 may be performed by using chemicals such as, for
example, phosphoric acid. By removal of the second hard mask
patterns 110, the upper sidewalls of the device isolation layer
116, the pad oxide patterns 102, and the passivation oxide layer
108 are exposed. In addition, the pad oxide patterns 102 and the
passivation oxide layers 108 are also removed. The removal of the
pad oxide patterns 102 and the passivation oxide layers 108 may be
performed by chemicals such as, for example, fluoric acid. The
removal of the pad oxide patterns 102 and the passivation oxide
layers 108 exposes surfaces of the semiconductor substrate 100.
[0064] Thereafter, an oxidation process forms a gate insulation
layer 118 on the exposed surfaces of the semiconductor substrate
100. Specifically, the gate insulation layer 118 is conformably
formed along the profiles of the recessed regions 106. Because the
corners of the recessed regions 106 are rounded, the gate
insulation layer 118 is also rounded at the corners of the recessed
regions 106. Next, a floating gate layer (not shown) is deposited
over the semiconductor substrate 100, filling spaces between the
device isolation layer 106. In addition, the floating gate layer is
flattened to form floating gate patterns 120 by through a
planarization process. This formation of floating gate patterns 120
exposes the upper surfaces of the device isolation layer 116.
[0065] Thereafter, referring to FIGS. 20A, 20B, and 20C, the upper
portion of the device isolation layer 116 is partially recessed.
Furthermore, an intergate insulating layer 122 is deposited over
the semiconductor substrate 100. Then, the intergate insulating
layer 122 is selectively etched away to partially expose the
floating gate patterns 120 and the device isolation layer 116.
These exposed floating gate patterns 120 form floating gates of
string and ground selection lines in the cell array of the
NAND-type nonvolatile memory device.
[0066] Next, referring to FIGS. 21A, 21B, and 21C, a control gate
layer 124 and a capping layer 126 are stacked over the
semiconductor substrate 100. Then, the capping and control gate
layers, the intergate insulating layer 122 and the floating gate
patterns 120 are etched to complete the ground and string selection
lines GSL and SSL, respectively, and the word line WL. Each of the
GSL, SSL, and WL includes a control gate 124, an intergate
insulating pattern 122a under the control gate 124, and a floating
gate 120a under the intergate insulating pattern 122a.
Specifically, in the ground and string selection lines GSL and SSL,
the intergate insulating pattern 122a is formed narrower in width
than the width of the selection lines themselves. This narrow width
of the intergate insulating pattern 122a makes the control gate 124
come in contact with the floating gate 120a. The contact between
the control gate 124 and the floating gate 120a may prevent an
increase of threshold voltage from a light programming of the
selection lines. Furthermore, the floating gates 120a of the
selection lines are formed to fill the recessed regions 106. In an
exemplary embodiment, the width of the floating gate, i.e., the
second width W2 may be equal to or larger than the width of the
recessed region 106, i.e., the first width W1. Alternatively, the
second width W2 may be smaller than the first width W1.
[0067] While the recessed regions 106 are not placed under the word
lines (WL) 124 in an exemplary embodiment, it can be understood by
those skilled in the art that they may also be formed under the
word lines.
[0068] Referring to FIGS. 22A, 22B, and 22C, using the lines WL,
SSL, and GSL as an ion implantation mask, impurity ions are
injected into the active regions to form impurity regions 132. The
impurity ions injected to form the impurity regions 132 vary
according to locations in kind and concentration. Then, spacers 130
are formed on sidewalls of the lines WL, SSL, and GSL.
Beneficially, the spacers 130 may be formed of at least a material
selected from silicon nitride, silicon oxide, and silicon
oxynitride. Furthermore, an interlevel insulation layer 134 is
deposited over the semiconductor substrate 100. In addition, a
common source line (CSL) 136 is formed on the semiconductor
substrate 100. This CSL 136 is in contact with the impurity regions
132 through the interlevel insulation layer 134 between adjacent
ground selection lines GSL. Moreover, bit line contacts (BLC) 138
are also formed on the semiconductor substrate 100. The BLC 138 is
in contact with the impurity regions 132 through the interlevel
insulation layer 134 between adjacent string selection lines SSL.
In addition, bit lines (BL) 140 are formed on the interlevel
insulation layer 134. In particular, the BL 140 are in contact with
the bit line contacts 138 and also intersect the lines WL, SSL, and
GSL.
[0069] As illustrated in FIGS. 22A, 22B, and 22C, in an exemplary
disclosed NAND-type nonvolatile memory device fabricated according
to the above-mentioned procedure, the plurality of device isolation
layers 116 are disposed in parallel with each other. These
plurality of device isolation layers 116 define the active regions
in the semiconductor memory device 100. In addition, the string and
ground selection lines SSL and GSL, respectively are arranged in
parallel with each other such that intersect the active regions
defined by the device isolation layers 116. Moreover, the plurality
of world lines WL are also arranged parallel with each other and
between the selection lines SSL and GSL.
[0070] Furthermore, as also illustrated in FIGS. 22A, 22B, and 22C,
the disclosed device includes impurity regions 132. These impurity
regions 132 are disposed between the adjacent ground selection
lines GSL and are connected to each other through the common source
line (CSL) 136. In addition, the bit line contacts (BLC) 138 are
placed on the impurity regions 132 between the adjacent string
selection lines SSL. These bit line contacts (BLC) 138 are in
contact with the bit lines (BL) 140 that intersect the lines WL,
SSL, and GSL. Here, the bottom profiles of the device isolation
layers 116 are rugged along the bit lines BL under the selection
lines SSL and GSL.
[0071] The disclosed NAN-type nonvolatile memory device may be used
in any component that uses semiconductor flash memory. Because the
trenches for the device isolation layer in the disclosed device are
formed after completing the recessed regions for channels, it may
make it easier to assure a sufficient margin of DOF. Furthermore,
by forming the trenches after completing the recessed channels, it
may be possible to form the recessed channels with more precision.
In addition, because the floating gates are self-aligned with the
device isolation layer, it may be possible to prevent or reduce
misalignment between the floating gates and the device isolation
layer. These features may help make the NAND-type nonvolatile
memory device more reliable.
[0072] The above-disclosed subject matter is to be considered
illustrative, and not restrictive, and the appended claims are
intended to cover all such modifications, enhancements, and other
embodiments, which fall within the true spirit and scope of the
present invention. Thus, to the maximum extent allowed by law, the
scope of the present disclosure is to be determined by the broadest
permissible interpretation of the following claims and their
equivalents, and shall not be restricted or limited by the
foregoing detailed description.
* * * * *