U.S. patent application number 14/204623 was filed with the patent office on 2015-07-16 for semiconductor memory device and method for manufacturing same.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. The applicant listed for this patent is Kabushiki Kaisha Toshiba. Invention is credited to Tatsuya Kato, Tatsuya Okamoto, Wataru SAKAMOTO, Ryota Suzuki.
Application Number | 20150200199 14/204623 |
Document ID | / |
Family ID | 53522001 |
Filed Date | 2015-07-16 |
United States Patent
Application |
20150200199 |
Kind Code |
A1 |
SAKAMOTO; Wataru ; et
al. |
July 16, 2015 |
SEMICONDUCTOR MEMORY DEVICE AND METHOD FOR MANUFACTURING SAME
Abstract
According to one embodiment, a semiconductor memory device
includes a substrate, a semiconductor pillar provided on the
substrate to extend in a vertical direction, a plurality of first
electrode films provided sideward of the semiconductor pillar to
extend in a first direction. The plurality of first electrode films
are disposed to be separated from each other along the vertical
direction. The semiconductor memory device further includes a
plurality of second electrode films provided between the
semiconductor pillar and the first electrode films. The plurality
of second electrode films are disposed to be separated from each
other along the vertical direction. The semiconductor memory device
further includes a first insulating film provided between the
semiconductor pillar and the second electrode films, and a second
insulating film provided between the second electrode film and the
first electrode film.
Inventors: |
SAKAMOTO; Wataru; (Mie-ken,
JP) ; Suzuki; Ryota; (Mie-ken, JP) ; Okamoto;
Tatsuya; (Mie-ken, JP) ; Kato; Tatsuya;
(Mie-ken, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Toshiba |
Minato-ku |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Toshiba
Minato-ku
JP
|
Family ID: |
53522001 |
Appl. No.: |
14/204623 |
Filed: |
March 11, 2014 |
Current U.S.
Class: |
257/329 ;
438/268 |
Current CPC
Class: |
G11C 16/0408 20130101;
H01L 29/66825 20130101; H01L 29/0649 20130101; G11C 16/0483
20130101; H01L 27/11519 20130101; H01L 29/7926 20130101; H01L
27/11556 20130101; H01L 23/528 20130101; H01L 27/11582
20130101 |
International
Class: |
H01L 27/115 20060101
H01L027/115; H01L 21/311 20060101 H01L021/311 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 2014 |
JP |
2014-003793 |
Claims
1. A semiconductor memory device, comprising: a substrate; a
semiconductor pillar provided on the substrate to extend in a
vertical direction; a plurality of first electrode films provided
sideward of the semiconductor pillar to extend in a first
direction, the plurality of first electrode films being disposed to
be separated from each other along the vertical direction; a
plurality of second electrode films provided between the
semiconductor pillar and the first electrode films, the plurality
of second electrode films being disposed to be separated from each
other along the vertical direction; a first insulating film
provided between the semiconductor pillar and the second electrode
films; and a second insulating film provided between the second
electrode film and the first electrode film.
2. The device according to claim 1, wherein an equivalent oxide
thickness of the first insulating film is thicker than an
equivalent oxide thickness of the second insulating film, and a
dielectric constant of the first insulating film is lower than a
dielectric constant of the second insulating film.
3. The device according to claim 2, wherein the second insulating
film includes: a first layer provided on the first electrode film
side to cover an upper surface and a lower surface of the first
electrode film; and a second layer provided on the second electrode
film side to cover an upper surface and a lower surface of the
second electrode film.
4. The device according to claim 1, wherein an equivalent oxide
thickness of the second insulating film is thicker than an
equivalent oxide thickness of the first insulating film, and a
dielectric constant of the second insulating film is lower than a
dielectric constant of the first insulating film.
5. The device according to claim 4, wherein the first insulating
film is disposed along a side surface of the semiconductor
pillar.
6. The device according to claim 1, wherein a plurality of the
semiconductor pillars are provided, the plurality of semiconductor
pillars is arranged in a matrix configuration along the first
direction and a second direction intersecting the first direction
as viewed from above, the first electrode film is not disposed
between the semiconductor pillars arranged along the first
direction, and when the semiconductor pillars arranged along the
second direction are organized into sets every two
mutually-adjacent semiconductor pillars and when two of the first
electrode films are positioned between the sets, the first
electrode films are not disposed between the two semiconductor
pillars belonging to each set.
7. The device according to claim 6, wherein the two semiconductor
pillars belonging to the set are formed as one body.
8. The device according to claim 6, wherein a length in the first
direction of an end portion of the second electrode film on the
semiconductor pillar side is shorter than a length in the first
direction of an end portion of the second electrode film on the
first electrode film side.
9. The device according to claim 6, wherein an air gap is made in
at least one location between the semiconductor pillars, between
the first electrode films adjacent to each other in the vertical
direction, and/or between the second electrode films adjacent to
each other in the vertical direction.
10. The device according to claim 1, wherein the second electrode
films are provided around the semiconductor pillar as viewed from
above, and the first electrode films are provided around the second
electrode films as viewed from above.
11. The device according to claim 1, wherein the second insulating
film is not disposed between the first electrode film and the
second electrode film for the uppermost level or for a plurality of
levels including the uppermost level, and the first electrode film
is connected to the second electrode film for the uppermost level
or for the plurality of levels including the uppermost level.
12. The device according to claim 1, wherein the second insulating
film is divided along the vertical direction for each of the first
electrode films.
13. The device according to claim 1, further comprising: a cell
source line provided between the substrate and the semiconductor
pillar to be connected to a lower end of the semiconductor pillar;
a bit line provided on the semiconductor pillar to be connected to
an upper end of the semiconductor pillar; a third insulating film
provided between the substrate and the cell source line; a source
region and a drain region formed to be separated from each other in
a region of the substrate distal to a region directly under the
semiconductor pillar; a fourth insulating film provided in a region
directly above a region of the substrate between the source region
and the drain region; and a gate electrode provided on the fourth
insulating film.
14. A method for manufacturing a semiconductor memory device,
comprising: forming a stacked body on a substrate by alternately
stacking an insulating film and a first film; making a first trench
in the stacked body to extend in a first direction; making a first
recess by causing an exposed surface of the first film at an inner
surface of the first trench to recede; forming a first insulating
layer on the inner surface of the first trench; forming a first
conductive film on the first insulating layer; removing a part of
the first conductive film and a part of the first insulating layer
located outside the first recess by etching and remaining another
part of the first conductive film and another part of the first
insulating layer located inside the first recess; forming a first
insulating film on the inner surface of the first trench; forming a
semiconductor film on the first insulating film; making a second
trench in the stacked body between the first trenches to extend in
the first direction; making a second recess by removing the first
film via the second trench; forming a second insulating layer on an
inner surface of the second recess; forming a second conductive
film inside the second recess; and dividing the semiconductor film
and the first conductive film along the first direction, an
equivalent oxide thickness of a second insulating film made of the
first insulating layer and the second insulating layer being
thinner than an equivalent oxide thickness of the first insulating
film, a dielectric constant of the second insulating film being
higher than a dielectric constant of the first insulating film.
15. The method according to claim 14, further comprising filling an
inter-layer insulating film into the first trench after the forming
of the semiconductor film and prior to the making of the second
trench, the making of the first trench including: forming a first
mask on the stacked body in a line-and-space configuration
extending in the first direction; and performing anisotropic
etching using the first mask, the dividing of the semiconductor
film and the first conductive film along the first direction
including: forming a second mask on the first mask in a
line-and-space configuration extending in a second direction
intersecting the first direction; making a through-hole by
selectively removing the inter-layer insulating film and the
semiconductor film by performing anisotropic etching using the
second mask and the first mask; and performing isotropic etching of
the first conductive film via the through-hole.
16. The method according to claim 14, further comprising forming a
second film on a back surface of the first recess after the making
of the first recess and prior to the forming of the first
insulating layer, the second film being made of a material
different from a material of the first film, the making of the
second recess including removing the first film using the second
film as a stopper.
17. A method for manufacturing a semiconductor memory device,
comprising: forming a stacked body on a substrate by alternately
stacking an insulating film and a first conductive film; making a
first trench in the stacked body to extend in a first direction;
forming a first insulating film on an inner surface of the first
trench; forming a semiconductor film on the first insulating film;
making a second trench in the stacked body between the first
trenches to extend in the first direction; making a recess by
causing an exposed surface of the first conductive film at an inner
surface of the second trench to recede; forming a second insulating
film on an inner surface of the recess, an equivalent oxide
thickness of the second insulating film being thicker than an
equivalent oxide thickness of the first insulating film, a
dielectric constant of the second insulating film being lower than
a dielectric constant of the first insulating film; forming a
second conductive film inside the recess; and dividing the
semiconductor film and the first conductive film along the first
direction.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2014-003793, filed on
Jan. 10, 2014; the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments described herein relate generally to a
semiconductor memory device and a method for manufacturing the
same.
BACKGROUND
[0003] Although conventionally the planar structure of NAND flash
memory has been shrunk to increase the bit density and reduce the
bit cost, such shrink is approaching a limit. Therefore, in recent
years, technology has been proposed to stack the memory cells in
the vertical direction. The data retention characteristics of the
memory cells are problematic in such a stacked memory device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a perspective view showing a semiconductor memory
device according to a first embodiment;
[0005] FIG. 2 is a cross-sectional view showing the semiconductor
memory device according to the first embodiment;
[0006] FIG. 3 is a cross-sectional view showing region A shown in
FIG. 2;
[0007] FIG. 4 is a cross-sectional view along line B-B' shown in
FIG. 2;
[0008] FIG. 5A to FIG. 17B are plan views and cross-sectional views
showing a method for manufacturing the semiconductor memory device
according to the first embodiment;
[0009] FIG. 18 is a cross-sectional view showing a semiconductor
memory device according to a modification of the first
embodiment;
[0010] FIG. 19 is a cross-sectional view showing a semiconductor
memory device according to a second embodiment;
[0011] FIG. 20A to FIG. 30C are plan views and cross-sectional
views showing a method for manufacturing the semiconductor memory
device according to the second embodiment;
[0012] FIG. 31 is a cross-sectional view showing a semiconductor
memory device according to a first modification of the second
embodiment;
[0013] FIG. 32 is a cross-sectional view showing a semiconductor
memory device according to a second modification of the second
embodiment;
[0014] FIG. 33 is a cross-sectional view showing a semiconductor
memory device according to a third modification of the second
embodiment;
[0015] FIG. 34 is a cross-sectional view showing a semiconductor
memory device according to a third embodiment;
[0016] FIGS. 35A to 37C are plan views and cross-sectional views
showing the method for manufacturing the semiconductor memory
device according to the third embodiment;
[0017] FIGS. 38A to 38C are cross-sectional views showing a
semiconductor memory device according to a modification of the
third embodiment;
[0018] FIGS. 39A to 39C are cross-sectional views showing a method
for manufacturing the semiconductor memory device according to the
modification of the third embodiment;
[0019] FIG. 40 is a cross-sectional view showing a semiconductor
memory device according to a forth embodiment;
[0020] FIG. 41 is a cross-sectional view showing region E shown in
FIG. 40;
[0021] FIG. 42A is a cross-sectional view showing a method for
manufacturing the semiconductor memory device according to the
forth embodiment; and FIG. 42B is a plan view;
[0022] FIG. 43 and FIG. 44 are cross-sectional views showing a
semiconductor memory device according to a fifth embodiment;
[0023] FIG. 45 to FIG. 53 are cross-sectional views showing a
method for manufacturing the semiconductor memory device according
to the fifth embodiment;
[0024] FIG. 54 is a cross-sectional view showing a semiconductor
memory device according to a modification of the fifth embodiment;
and
[0025] FIG. 55 to FIG. 57 are cross-sectional views showing the
method for manufacturing the semiconductor memory device according
to the modification of the fifth embodiment.
DETAILED DESCRIPTION
[0026] In general, according to one embodiment, a semiconductor
memory device includes a substrate, a semiconductor pillar provided
on the substrate to extend in a vertical direction, a plurality of
first electrode films provided sideward of the semiconductor pillar
to extend in a first direction. The plurality of first electrode
films are disposed to be separated from each other along the
vertical direction. The semiconductor memory device further
includes a plurality of second electrode films provided between the
semiconductor pillar and the first electrode films. The plurality
of second electrode films are disposed to be separated from each
other along the vertical direction. The semiconductor memory device
further includes a first insulating film provided between the
semiconductor pillar and the second electrode films, and a second
insulating film provided between the second electrode film and the
first electrode film.
First Embodiment
[0027] Embodiments of the invention will now be described with
reference to the drawings.
[0028] First, a first embodiment will be described.
[0029] FIG. 1 is a perspective view showing a semiconductor memory
device according to the embodiment.
[0030] FIG. 2 is a cross-sectional view showing the semiconductor
memory device according to the embodiment.
[0031] FIG. 3 is a cross-sectional view showing region A shown in
FIG. 2.
[0032] FIG. 4 is a cross-sectional view along line B-B' shown in
FIG. 2.
[0033] As shown in FIG. 1 and FIG. 2, a silicon substrate 10 is
provided in the semiconductor memory device 1 according to the
embodiment. A memory cell region Rm and a peripheral circuit region
Rc are set in the silicon substrate 10. Hereinbelow, an XYZ
orthogonal coordinate system is employed in the specification for
convenience of description. Two mutually-orthogonal directions
parallel to an upper surface 10a of the silicon substrate 10 are
taken as an X-direction and a Y-direction; and a direction
perpendicular to the upper surface 10a is taken as a
Z-direction.
[0034] In the memory cell region Rm, an insulating film 11 (a third
insulating film) that is made of, for example, silicon oxide, a
conductive layer 12 that is made of, for example, polysilicon, an
interconnect layer 13 that is made of, for example, tungsten, and a
conductive layer 14 that is made of, for example, polysilicon are
stacked in this order on the silicon substrate 10. A cell source
line 15 is formed of the conductive layer 12, the interconnect
layer 13, and the conductive layer 14. An insulating film 17 that
is made of, for example, silicon oxide is provided on the cell
source line 15. Multiple silicon pillars 20 that extend in the
Z-direction are provided on the cell source line 15. The silicon
pillars 20 are made of, for example, polysilicon; and the lower
ends of the silicon pillars 20 pierce the insulating film 17 to be
connected to the cell source line 15. The silicon pillars 20 are
arranged in a matrix configuration along the X-direction and the
Y-direction as viewed from the Z-direction and have a common
connection with a single cell source line 15.
[0035] Multiple control gate electrode films (the first electrode
films) 21 are provided sideward of the silicon pillar 20 to be
separated from each other along the Z-direction. Each of the
control gate electrode films 21 is made of, for example, tungsten
and extends in the Y-direction. Therefore, the control gate
electrode films 21 are not disposed between the silicon pillars 20
arranged along the Y-direction. Also, in the X-direction, two of
the silicon pillars 20 are arranged alternately with two of the
control gate electrode films 21. In other words, when the silicon
pillars 20 arranged along the X-direction are organized into
multiple sets 22 every two mutually-adjacent silicon pillars 20 and
when two of the control gate electrode films 21 are arranged to be
positioned between the sets 22, the control gate electrode films 21
are not disposed between the two silicon pillars 20 belonging to
each set 22.
[0036] An inter-layer insulating film 23 is provided between the
silicon pillars 20. An inter-layer insulating film 24 that is made
of, for example, silicon oxide is provided between the control gate
electrode films 21, below the control gate electrode film 21 of the
lowermost layer, and above the control gate electrode film 21 of
the uppermost layer. A hard mask 26 is provided on a stacked body
25 that is made of the multiple control gate electrode films 21,
the inter-layer insulating film 23, and the inter-layer insulating
film 24.
[0037] The silicon pillar 20 is drawn out onto the hard mask 26 to
be a single body with an interconnect 27 extending in the
X-direction. Thereby, the silicon pillars 20 that are arranged
along the X-direction are connected to a common interconnect 27. A
via 28 is provided on the interconnect 27; and a bit line 29 that
extends in the X-direction is provided on the via 28. The bit line
29 is connected to the interconnect 27 by the via 28. Thus, each of
the silicon pillars 20 is connected between the bit line 29 and the
cell source line 15. In other words, the semiconductor memory
device 1 is an I-shaped pillar type stacked memory device.
[0038] The Y-direction end portion of the stacked body 25 is
patterned into a stairstep configuration; and at the end portion of
the stairstep configuration, the multiple control gate electrode
films 21 that have the same position in the Z-direction are bundled
together. A via 38 is provided on the end portion of the bundled
control gate electrode films 21. A word line 39 that extends in the
Y-direction is provided on the via 38. In the Z-direction, the
position of the word line 39 is the same as the position of the bit
line 29. The word line 39 is connected to the control gate
electrode film 21 by the via 38.
[0039] As shown in FIG. 3 and FIG. 4, floating gate electrode films
31 (second electrode films) that are made of, for example,
polysilicon are provided between the silicon pillars 20 and the
control gate electrode films 21. Because the floating gate
electrode films 31 are provided at each intersection between the
silicon pillars 20 and the control gate electrode films 21, the
floating gate electrode films 31 are arranged in a matrix
configuration to be separated from each other along the Y-direction
and the Z-direction. When viewed from the Z-direction, the
configuration of the floating gate electrode film 31 is a fan-like
shape that is wider on the control gate electrode film 21 side.
Therefore, a length L1 in the Y-direction of the end portion of the
floating gate electrode film 31 on the silicon pillar 20 side is
shorter than a length L2 in the Y-direction of the end portion of
the floating gate electrode film 31 on the control gate electrode
film 21 side.
[0040] A tunneling insulating film 33 that is made of, for example,
silicon oxide is provided between the silicon pillar 20 and the
floating gate electrode films 31. The tunneling insulating film 33
is provided at each silicon pillar 20; and the configuration of the
tunneling insulating film 33 is a band configuration that extends
in the Z-direction and has the X-direction as the thickness
direction and the Y-direction as the width direction.
[0041] On the other hand, a blocking insulating film 34 is provided
between the floating gate electrode film 31 and the control gate
electrode film 21. The blocking insulating film 34 is, for example,
a three-layer film in which a silicon nitride layer 35, a silicon
oxide layer 36, and a silicon nitride layer 37 are stacked in this
order from the floating gate electrode film 31 side toward the
control gate electrode film 21 side. The silicon nitride layer 35
is formed around the floating gate electrode film 31 to cover an
upper surface 31a and a lower surface 31b of the floating gate
electrode film 31. The silicon oxide layer 36 and the silicon
nitride layer 37 are formed around the control gate electrode film
21 to cover an upper surface 21a and a lower surface 21b of the
control gate electrode film 21.
[0042] Although the tunneling insulating film 33 normally is
insulative, the tunneling insulating film 33 is a film in which a
tunneling current flows when a voltage within the range of the
drive voltage of the semiconductor memory device 1 is applied. The
blocking insulating film 34 is a film in which a current
substantially does not flow even when a voltage within the range of
the drive voltage of the semiconductor memory device 1 is applied.
The equivalent oxide thickness (EOT) of the tunneling insulating
film 33 is thicker than the equivalent oxide thickness of the
blocking insulating film 34; and the dielectric constant of the
tunneling insulating film 33 is lower than the dielectric constant
of the blocking insulating film.
[0043] In the peripheral circuit region Rc as shown in FIG. 2, a
source region 40s and a drain region 40d are formed in the silicon
substrate 10 to be separated from each other. The region between
the source region 40s and the drain region 40d is a channel region
40c. A gate insulating film 41 (a fourth insulating film) that is
made of, for example, silicon oxide is provided on the silicon
substrate 10 in the region directly above the channel region 40c;
and a conductive layer 42 that is made of, for example, polysilicon
and an interconnect layer 43 that is made of, for example, tungsten
are stacked in this order on the gate insulating film 41. A gate
electrode 45 is formed of the conductive layer 42 and the
interconnect layer 43. A transistor 46 includes the source region
40s, the drain region 40d, the channel region 40c, the gate
insulating film 41, and the gate electrode 45. The transistor 46 is
included in the peripheral circuit.
[0044] As described below, the insulating film 11 that is in the
memory cell region Rm and the gate insulating film 41 that is in
the peripheral circuit region Rc are formed by dividing the same
silicon oxide film; the conductive layer 12 that is in the memory
cell region Rm and the conductive layer 42 that is in the
peripheral circuit region Rc are formed by dividing the same
polysilicon layer; and the interconnect layer 13 that is in the
memory cell region Rm and the interconnect layer 43 that is in the
peripheral circuit region Rc are formed by dividing the same
tungsten layer.
[0045] A method for manufacturing the semiconductor memory device
according to the embodiment will now be described.
[0046] FIG. 5A to FIG. 17B are plan views and cross-sectional views
showing the method for manufacturing the semiconductor memory
device according to the embodiment.
[0047] Only the memory cell region Rm is shown in FIG. 5A to FIG.
17B.
[0048] First, as shown in FIG. 1 and FIG. 2, the channel region
40c, the source region 40s, and the drain region 40d are formed in
the upper layer portion of the silicon substrate 10 in the
peripheral circuit region Rc. Then, a silicon oxide film is formed
on the silicon substrate 10 in both the memory cell region Rm and
the peripheral circuit region Rc. Therefore, in the peripheral
circuit region Rc, a relatively thin silicon oxide film is formed
in the low breakdown voltage transistor (LV Tr) region; and a
relatively thick silicon oxide film is formed in the high breakdown
voltage transistor (HV Tr) region. Also, a relatively thick silicon
oxide film is formed in the memory cell region Rm.
[0049] Then, a polysilicon layer is formed on the entire surface.
STI (Shallow Trench Isolation) is formed in the upper layer portion
of the silicon substrate 10 in the peripheral circuit region Rc
using an appropriate mask (not shown). Then, a tungsten layer is
formed. Then, a polysilicon layer and a silicon oxide film are
formed only in the memory cell region Rm. Then, these layers are
patterned by RIE (Reactive Ion Etching).
[0050] Thereby, the insulating film 11, the conductive layer 12,
the interconnect layer 13, the conductive layer 14, and the
insulating film 17 are formed for each block in the memory cell
region Rm. The cell source line 15 is formed of the stacked body
made of the conductive layer 12, the interconnect layer 13, and the
conductive layer 14. Erasing is possible by block unit by forming
the cell source line 15 to be divided for each block. On the other
hand, the gate insulating film 41, the conductive layer 42, and the
interconnect layer 43 are formed in the peripheral circuit region
Rc. The gate electrode 45 is formed of the stacked body made of the
conductive layer 42 and the interconnect layer 43. Thereby, the
transistor 46 is formed in the peripheral circuit region Rc.
[0051] Then, as shown in FIGS. 5A and 5B, a silicon oxide film 51
and a silicon nitride film 52 are stacked alternately on the
insulating film 17 (referring to FIG. 2) in the memory cell region
Rm. Thereby, the stacked body 25 is formed. At this time, because
the gate length (the total thickness of the control gate electrode
film 21 and the blocking insulating film provided around the
control gate electrode film 21) on the electrode side is longer
than the gate length (the total thickness of the floating gate
electrode film 31 and the blocking insulating film provided around
the floating gate electrode film 31) on the channel side, the film
thickness ratio of the silicon oxide film 51 and the silicon
nitride film 52 that are stacked is adjusted according to the film
thickness of the blocking films filled from both sides. FIG. 5A is
a cross-sectional view; and FIG. 5B is a top view. This is similar
for the following drawings as well.
[0052] Continuing as shown in FIGS. 6A and 6B, the hard mask 26
that is made of, for example, silicon nitride is formed on the
stacked body 25. Then, the hard mask 26 is patterned; and
anisotropic etching such as RIE, etc., of the stacked body 25 is
performed using the patterned hard mask 26 as a mask. Thereby,
multiple trenches 53 are made in the stacked body 25 to extend in
the Y-direction. The trenches 53 pierce the stacked body 25.
[0053] Then, as shown in FIGS. 7A and 7B, the silicon nitride films
52 are recessed by performing wet etching via the trench 53.
Thereby, the exposed surfaces of the silicon nitride films 52
recede at the inner surface of the trench 53 to make recesses 54
that extend in the Y-direction. Then, oxidation treatment is
performed by SPA, etc. Thereby, the exposed surfaces of the silicon
nitride films 52 at the inner surface of the trench 53 are covered
with a thin silicon oxide layer 50.
[0054] Continuing as shown in FIGS. 8A and 8B, the silicon nitride
layer 35 is formed on the entire surface. Then, a polysilicon film
55 is formed on the entire surface. The silicon nitride layer 35
and the polysilicon film 55 also are formed on the inner surface of
the trench 53 to enter the recesses 54.
[0055] Then, as shown in FIGS. 9A and 9B, by performing anisotropic
etching such as RIE, etc., along the trench 53, the polysilicon
film 55 and the silicon nitride layer 35 are selectively removed to
remain inside the recesses 54; and the polysilicon films 55 that
remain inside the recesses 54 adjacent to each other in the
Z-direction are separated from each other. Similarly, the silicon
nitride layers 35 that remain inside the recesses 54 adjacent to
each other in the Z-direction also are separated from each
other.
[0056] Continuing as shown in FIGS. 10A and 10B, the tunneling
insulating film 33, a polysilicon film 56, and an insulating film
57 are deposited in this order.
[0057] Then, as shown in FIGS. 11A and 11B, trenches 58 are made in
the stacked body 25 and the stacked body stacked above the stacked
body 25 to extend in the Y-direction between the trenches 53.
Thereby, the trenches 53 and the trenches 58 are arranged
alternately along the X-direction.
[0058] Continuing as shown in FIGS. 12A and 12B, the silicon
nitride films 52 are recessed by performing wet etching using hot
phosphoric acid via the trench 58. The recessing is stopped by the
silicon oxide layer 50 that is exposed at the back surfaces of
recesses 59. Thereby, the silicon nitride films 52 are removed; and
the recesses 59 are made in the inner surface of the trench 58 to
extend in the Y-direction. At this time, the silicon nitride layer
35 is not damaged because the silicon nitride layer 35 is protected
by the silicon oxide layer 50.
[0059] Then, as shown in FIGS. 13A and 13B, the silicon oxide layer
50 that is exposed at the back surfaces of the recesses 59 is
removed. Thereby, the silicon nitride layers 35 are exposed at the
back surfaces of the recesses 59. Then, the silicon oxide layer 36
and the silicon nitride layer 37 are formed on the inner surface of
the trench 58. As a result, as shown in FIG. 3, the blocking
insulating film 34 is formed of the silicon nitride layer 35, the
silicon oxide layer 36, and the silicon nitride layer 37. Then, a
tungsten film 61 is formed on the entire surface by, for example,
CVD (Chemical Vapor Deposition). The silicon oxide layer 36, the
silicon nitride layer 37, and the tungsten film 61 also enter the
recesses 59 via the trench 58.
[0060] Continuing as shown in FIGS. 14A and 14B, the tungsten film
61 is selectively removed by performing anisotropic etching such as
RIE, etc. Thereby, the tungsten film 61 is caused to remain inside
the recesses 59; and the tungsten films 61 that remain inside the
recesses 59 adjacent to each other in the Z-direction are separated
from each other. As a result, the control gate electrode films 21
that are made of the tungsten films 61 are formed inside the
recesses 59. Subsequently, the inter-layer insulating film 24 is
filled into the trench 58; and the upper surface of the inter-layer
insulating film 24 is planarized. FIG. 14B is a cross-sectional
view along line B-B' shown in FIG. 14A.
[0061] Then, as shown in FIGS. 15A to 15C, a hard mask 62 is formed
in which openings 62a are arranged in a matrix configuration along
the X-direction and the Y-direction. The configuration of each of
the openings 62a is a rectangle with the X-direction as the
longitudinal direction; and the openings 62a are arranged
intermittently along the Y-direction in the region directly above
the polysilicon films 56 and the insulating film 57 between the
polysilicon films 56 but are not disposed in the region directly
above the inter-layer insulating film 24. Then, the polysilicon
film 56 and the insulating film 57 are divided along the
Y-direction by performing anisotropic etching such as RIE, etc.,
using the hard mask 62 and the hard mask 26 as a mask. Thereby, a
through-hole 63 is made in the polysilicon film 56 and the
insulating film 57 in the region directly under the opening 62a;
the portion of the polysilicon film 56 that is formed on the hard
mask 26 becomes the interconnect 27; and the portion of the
polysilicon film 56 that is divided by the through-hole 63 becomes
the silicon pillar 20. FIG. 15B is a plan view along line C-C'
shown in FIG. 15A; and FIG. 15C is a cross-sectional view along
line B-B' shown in FIG. 15A.
[0062] Continuing as shown in FIG. 16, the tunneling insulating
film 33 and the polysilicon films 55 are selectively removed by
performing isotropic etching such as CDE (Chemical Dry Etching),
wet etching, etc., via the through-hole 63. Thereby, the tunneling
insulating film 33 and the polysilicon films 55 are divided along
the Y-direction. The insulating film 57 also is removed. As a
result, the floating gate electrode films 31 are formed of the
polysilicon films 55. At this time, because the polysilicon films
55 are etched from the silicon pillar 20 side, the length L1 in the
Y-direction of the end portion of the floating gate electrode film
31 on the silicon pillar 20 side is shorter than the length L2 in
the Y-direction of the end portion of the floating gate electrode
film 31 on the control gate electrode film 21 side. On the other
hand, at this time, the inter-layer insulating film 24 remains
without being removed.
[0063] Then, as shown in FIGS. 17A and 17B, the inter-layer
insulating film 23 is deposited on the entire surface. The
inter-layer insulating film 23 is filled also inside the
through-hole 63. The silicon oxide film 51 also becomes a portion
of the inter-layer insulating film 23.
[0064] Continuing as shown in FIG. 1 and FIG. 2, the vias 28, the
vias 38, the bit lines 29, and the word lines 39 are formed. Thus,
the semiconductor memory device 1 according to the embodiment is
manufactured.
[0065] Effects of the embodiment will now be described.
[0066] In the embodiment, the floating gate electrode films 31 that
are made of polysilicon are provided as charge storage units.
Therefore, the data retention characteristics of the memory cells
are good; and the erasing operation is fast because the charge that
is stored in the floating gate electrode films 31 can be erased by
moving electrons instead of holes. The data retention
characteristics are even better because the floating gate electrode
films 31 are separated from each other.
[0067] In the embodiment, because the blocking insulating film 34
is a three-layer film made of the silicon nitride layer 35, the
silicon oxide layer 36, and the silicon nitride layer 37, the
coupling ratio can be ensured while suppressing the leakage
current. Also, the silicon nitride layer 35 is formed from the
silicon pillar 20 side in the process shown in FIGS. 8A and 8B; and
the silicon oxide layer 36 and the silicon nitride layer 37 are
formed from the control gate electrode film 21 side in the process
shown in FIGS. 13A and 13B.
[0068] Thus, by dividing the three-layer film of the blocking
insulating film 34 into two and forming the three-layer film from
both sides, compared to the case of forming from only one side, the
thickness of the blocking insulating film 34 can be distributed on
the two X-direction sides of the floating gate electrode film 31;
and the thickness in the Z-direction as an entirety can be reduced.
Thereby, the height in the Z-direction of the recesses 54
(referring to FIGS. 8A and 8B) and the recesses 59 (referring to
FIGS. 13A and 13B) can be reduced; the bit density of the memory
cells in the Z-direction can be increased; and the aspect ratio can
be reduced.
[0069] In the embodiment, the blocking insulating film 34 is
divided for each of the control gate electrode films 21 along the
Z-direction. Thereby, the electrons that are stored in the floating
gate electrode film 31 can be prevented from propagating through
the blocking insulating film 34 and leaking. As a result, the data
retention characteristics of the memory cells are good.
[0070] In the embodiment, as shown in FIG. 4, the configuration of
the floating gate electrode film 31 is a fan-like shape that is
wider on the control gate electrode film 21 side. Thereby, the IPD
capacitance between the floating gate electrode film 31 and the
control gate electrode film 21 can be large; and the coupling ratio
can be large.
[0071] Although an example is illustrated in the embodiment in
which the blocking insulating film 34 is a three-layer film, this
is not limited thereto. The layers of the blocking insulating film
34 are not limited to the silicon oxide layer (the SiO.sub.2 layer)
and the silicon nitride layers (the Si.sub.3N.sub.4 layers) and may
be a high dielectric constant layer such as, for example, an
Al.sub.2O.sub.3 layer, a MgO layer, a SrO layer, a SiN layer, a BaO
layer, a TiO layer, a Ta.sub.2O.sub.5 layer, a BaTiO.sub.3 layer, a
BaZrO layer, a ZrO.sub.2 layer, a Y.sub.2O.sub.3 layer, a ZrSiO
layer, a HfAlO layer, a HfSiO layer, a La.sub.2O.sub.3 layer, a
LaAlO layer, etc.
[0072] Although an example is illustrated in the embodiment in
which the floating gate electrode film 31 is formed of polysilicon,
the floating gate electrode film 31 is not limited thereto and may
be formed of, for example, a metal silicide or a metal.
[0073] Although an example is illustrated in the embodiment in
which the control gate electrode film 21 is formed of tungsten, the
control gate electrode film 21 is not limited thereto and may be
formed of, for example, a metal silicide by filling a polysilicon
film and subsequently siliciding the polysilicon film.
[0074] In the process shown in FIGS. 5A and 5B, the silicon nitride
films 52 of the lowermost layer and the uppermost layer may be
formed to be thicker than the other silicon nitride films 52.
Thereby, the film thicknesses of the selection gate electrode films
that are formed below and above the control gate electrode films 21
can be thicker than those of the control gate electrode films 21.
As a result, a selection transistor that has a gate length longer
than that of the memory cell transistor can be formed.
[0075] Several layers of the control gate electrode films 21
provided at the upper portion of the stacked body 25 may be shorted
to each other to be used as the selection gate electrode film; and
several layers of the control gate electrode films 21 provided at
the lower portion of the stacked body 25 may be shorted to each
other to be used as the selection gate electrode film. Thereby, a
selection transistor that has a gate length longer than that of the
memory cell transistor can be formed.
Modification of First Embodiment
[0076] A modification of the embodiment will now be described.
[0077] FIG. 18 is a cross-sectional view showing a semiconductor
memory device according to the modification.
[0078] In the semiconductor memory device is according to the
modification as shown in FIG. 18, one wide silicon pillar 65 is
provided between two floating gate electrode films 31 adjacent to
each other in the X-direction. In other words, the inter-layer
insulating film 24 is not provided between the two silicon pillars
20 belonging to each of the sets 22; and the two silicon pillars 20
are formed as one body.
[0079] In the semiconductor memory device is according to the
modification, the two X-direction side portions of the wide silicon
pillar 65 are used as distinct channels. Otherwise, the
configuration, the manufacturing method, and the effects of the
modification are similar to those of the first embodiment described
above.
Second Embodiment
[0080] A second embodiment will now be described.
[0081] FIG. 19 is a cross-sectional view showing a semiconductor
memory device according to the embodiment.
[0082] As shown in FIG. 19, the semiconductor memory device 2
according to the embodiment differs from the semiconductor memory
device 1 (referring to FIG. 1 to FIG. 4) according to the first
embodiment described above in that the disposition of the tunneling
insulating film 33 and the blocking insulating film 34 is
reversed.
[0083] In other words, in the semiconductor memory device 2, the
blocking insulating film 34 is disposed between the silicon pillar
20 and the floating gate electrode films 31; and the tunneling
insulating film 33 is disposed between the floating gate electrode
films 31 and the control gate electrode films 21.
[0084] Therefore, the components included in the memory cell are
arranged in the order of silicon pillar 20-blocking insulating film
34-floating gate electrode film 31-tunneling insulating film
33-control gate electrode film 21.
[0085] More specifically, in the semiconductor memory device 2,
silicon oxide films 71 are arranged to be separated from each other
along the Z-direction; and the floating gate electrode films 31 and
the control gate electrode films 21 are provided in the spaces
between the mutually-adjacent silicon oxide films 71. Also, the
tunneling insulating film 33 is disposed to cover the upper surface
and the lower surface of the control gate electrode film 21 and the
side surface of the control gate electrode film 21 on the floating
gate electrode film 31 side. On the other hand, the blocking
insulating film 34 is disposed linearly along the side surface of
the silicon pillar 20.
[0086] Similarly to the first embodiment, the blocking insulating
film 34 may be a multilayered film, e.g., a three-layer film.
However, the blocking insulating film 34 is not subdivided between
the silicon pillar 20 side and the control gate electrode film 21
side; and the entire blocking insulating film 34 is disposed on the
silicon pillar 20 side.
[0087] In the semiconductor memory device 2, the lower end portions
of the two silicon pillars 20 belonging to the set 22 are connected
to each other; and the cell source line 15 is not provided. A
source line (not shown) is provided above the stacked body. In
other words, the semiconductor memory device 2 is a U-shaped pillar
type stacked memory device. Otherwise, the configuration of the
embodiment is similar to that of the first embodiment described
above.
[0088] The basic operations and the read-out method of the
semiconductor memory device 2 are similar to those of a normal NAND
flash memory; and the polarity of the voltage applied between the
silicon pillar 20 and the control gate electrode film 21 in the
programming operation and the erasing operation are the reverse of
those of a normal NAND flash memory. Thereby, the charge is caused
to move into and out of the silicon pillar 20 from the control gate
electrode film 21.
[0089] A method for manufacturing the semiconductor memory device
according to the embodiment will now be described.
[0090] FIG. 20A to FIG. 30C are plan views and cross-sectional
views showing the method for manufacturing the semiconductor memory
device according to the embodiment.
[0091] First, as shown in FIGS. 20A and 20B, the insulating film 17
that is made of silicon oxide is formed on the silicon substrate 10
(referring to FIG. 2); and subsequently, a stacked body 73 is
formed by alternately stacking the silicon oxide film 71 and a
polysilicon film 72. The polysilicon film 72 may be doped with
boron (B), may be doped with phosphorus (P), or may not be doped.
FIG. 20A is a cross-sectional view; and FIG. 20B is a top view.
This is similar for the following drawings as well.
[0092] Then, as shown in FIGS. 21A and 21B, multiple trenches 75
are made in the stacked body 73 to extend in the Y-direction by
forming a hard mask (not shown) on the stacked body 73, patterning
by lithography, and performing anisotropic etching such as RIE,
etc., using the patterned hard mask as a mask. The trenches 75
pierce the stacked body 73 in the Z-direction but do not pierce the
insulating film 17.
[0093] Continuing as shown in FIGS. 22A and 22B, on the inner
surface of the trench 75, the blocking insulating film 34 is
formed; and subsequently, a polysilicon film 77 is formed. The
blocking insulating film 34 and the polysilicon film 77 are formed
on the side surface of the trench 75 and on the bottom surface of
the trench 75 to be folded back into a U-shaped as viewed from the
Y-direction. Accordingly, the relationship between the width of the
trench 75 and the film thicknesses of the blocking insulating film
34 and the polysilicon film 77 is set such that such folding back
is possible. Then, the inter-layer insulating film 24 is filled
into the trench 75 by depositing silicon oxide.
[0094] Then, as shown in FIGS. 23A and 23B, trenches 78 are made in
the portion of the stacked body 73 between the trenches 75 to
extend in the Y-direction by forming a hard mask (not shown) on the
stacked body 73, patterning by lithography, and performing
anisotropic etching such as RIE, etc., using the patterned hard
mask as a mask. The trenches 75 and the trenches 78 are arranged
alternately along the X-direction.
[0095] Continuing as shown in FIGS. 24A and 24B, wet etching is
performed using, for example, TMY (choline aqueous solution).
Thereby, the polysilicon films 72 are etched isotropically via the
trench 78; and the exposed surfaces of the polysilicon films 72 at
the inner surface of the trench 78 are caused to recede. Thereby,
recesses 79 are made at the inner surface of the trench 78.
[0096] Then, as shown in FIGS. 25A and 25B, the tunneling
insulating film 33 is formed by depositing silicon oxide on the
inner surface of the trench 78. At this time, the tunneling
insulating film 33 is formed also on the inner surfaces of the
recesses 79 to contact the polysilicon films 72. The tunneling
insulating film 33 may be formed by thermal oxidation of the
exposed surfaces of the polysilicon films 72.
[0097] Continuing as shown in FIGS. 26A and 26B, a tungsten film 81
is formed inside the trench 78 by, for example, depositing tungsten
by CVD. At this time, the tungsten film 81 is filled also into the
recesses 79.
[0098] Then, as shown in FIGS. 27A and 27B, the portion of the
tungsten film 81 that is not filled into the recesses 79 is removed
by etching the tungsten film 81. Thereby, the tungsten films 81
that remain inside the recesses 79 are separated from each other
between the recesses 79 to become the control gate electrode films
21. Then, the inter-layer insulating film 24 is filled into the
trench 78; and the upper surface of the inter-layer insulating film
24 is planarized. Instead of tungsten, silicon may be deposited in
the process shown in FIGS. 26A and 26B; and the silicon may be
silicided in this process. Thereby, the control gate electrode
films 21 are formed of a metal silicide.
[0099] Continuing as shown in FIGS. 28A to 28C, through-holes 82
are made in the trench 75 by selectively removing the inter-layer
insulating film 24, the polysilicon film 77, and the blocking
insulating film 34 by performing anisotropic etching using an
appropriate mask. The polysilicon film 77 is divided periodically
along the Y-direction by the through-holes 82 to become the silicon
pillars 20. FIG. 28A is a cross-sectional view; FIG. 28B is a
cross-sectional view along line C-C' shown in FIG. 28A; and FIG.
28C is a cross-sectional view along line B-B' shown in FIG. 28A.
This is similar for FIGS. 29A to 29C and FIGS. 30A to 30C.
[0100] Then, as shown in FIGS. 29A to 29C, the blocking insulating
film 34, the polysilicon films 72, and the tunneling insulating
film 33 are further removed via the through-holes 82 to be divided
along the Y-direction by performing isotropic etching such as CDE,
wet etching, etc. Thereby, the polysilicon films 72 that are
divided along the Y-direction become the floating gate electrode
films 31. At this time, the configuration of the floating gate
electrode film 31 becomes a fan-like shape that is wider on the
control gate electrode film 21 side according to the conditions of
the isotropic etching.
[0101] Continuing as shown in FIGS. 30A to 30C, the inter-layer
insulating film 24 is filled into the through-holes 82 by, for
example, depositing silicon oxide and planarizing the upper surface
of the silicon oxide. Then, the vias 28, the vias 38, the source
lines, the bit lines 29, and the word lines 39 (referring to FIG. 1
and FIG. 2) are formed by normal methods. Thus, the semiconductor
memory device 2 according to the embodiment is manufactured.
[0102] Effects of the embodiment will now be described.
[0103] In the programming operation and the erasing operation of a
NAND memory device, it is necessary for the current to flow in the
tunneling insulating film and for the current to not flow easily in
the blocking insulating film. To this end, it is necessary for the
physical film thickness of the blocking insulating film to be
thicker than the physical film thickness of the tunneling
insulating film. Accordingly, if the blocking insulating film 34 is
to be formed to extend around into the gaps between the silicon
oxide films 71, it is necessary to set the spacing between the
silicon oxide films 71 to be long in the Z-direction, which
obstructs higher integration of the memory cells in the
Z-direction. Further, the aspect ratio of the trenches 75 and 78
undesirably increases; and patterning becomes difficult.
[0104] If the spacing of the silicon oxide films 71 nevertheless is
set to be short, the thickness of the control gate electrode film
21, which is covered with the blocking insulating film 34 at the
upper surface and the lower surface of the control gate electrode
film 21, becomes shorter than the spacing of the silicon oxide
films 71. Accordingly, the interconnect resistance of the control
gate electrode film 21 increases; the gate length of the memory
cell transistor becomes short; and the characteristics of the
memory cell transistor undesirably degrade due to the short channel
effect.
[0105] Conversely, in the embodiment, the blocking insulating film
34 is formed on the inner surface of the trench 75 in the process
shown in FIGS. 22A and 22B. Thus, by forming the blocking
insulating film 34 at an early stage, it is no longer necessary for
the blocking insulating film 34 to extend around into the gaps
between the silicon oxide films 71; and the spacing of the silicon
oxide films 71 can be shorter. As shown in FIG. 19, in the
embodiment, although the tunneling insulating film 33 extends
around into the gaps between the silicon oxide films 71, there are
few problems because the tunneling insulating film 33 is thinner
than the blocking insulating film 34 as described above. Thus,
according to the embodiment, the bit density of the memory cells in
the Z-direction can be increased after ensuring the thickness of
the control gate electrode film 21; and the aspect ratio can be
reduced. Otherwise, the effects of the embodiment are similar to
those of the first embodiment described above.
First Modification of Second Embodiment
[0106] A first modification of the embodiment will now be
described.
[0107] FIG. 31 is a cross-sectional view showing a semiconductor
memory device according to the modification. In the semiconductor
memory device 2a according to the modification as shown in FIG. 31,
a charge storage film 85 that is made of an insulative charge
storage material is provided instead of the floating gate electrode
film 31 that is made of a conductive material. The charge storage
film 85 is formed of, for example, silicon nitride. Accordingly,
the memory cell of the semiconductor memory device 2a has a MONOS
structure. Otherwise, the configuration, the manufacturing method,
the operations, and the effects of the modification are similar to
those of the second embodiment described above.
Second Modification of Second Embodiment
[0108] A second modification of the embodiment will now be
described.
[0109] FIG. 32 is a cross-sectional view showing a semiconductor
memory device according to the modification.
[0110] In the semiconductor memory device 2b according to the
modification as shown in FIG. 32, the cell source line 15 is
provided; and the lower end of the silicon pillar 20 is connected
to the cell source line 15. In other words, the semiconductor
memory device 2b is an I-shaped pillar type stacked memory
device.
[0111] To connect the lower end of the silicon pillar 20 to the
cell source line 15 when manufacturing the semiconductor memory
device 2b according to the modification, it is necessary for the
portion of the blocking insulating film 34 formed on the bottom
surface of the trench 75 to be removed by etching in the process
shown in FIGS. 22A and 22B. However, the etching does not damage
the tunneling insulating film 33 because the tunneling insulating
film 33 is not yet formed at this time. Otherwise, the
configuration, the manufacturing method, the operations, and the
effects of the modification are similar to those of the second
embodiment described above.
Third Modification of Second Embodiment
[0112] A third modification of the embodiment will now be
described.
[0113] FIG. 33 is a cross-sectional view showing a semiconductor
memory device according to the modification.
[0114] As shown in FIG. 33, the modification is an example in which
the first modification and the second modification described above
are combined. Namely, in the semiconductor memory device 2c
according to the modification, the charge storage film 85 that is
made of an insulative charge storage material is provided; and the
lower end of the silicon pillar 20 is connected to the cell source
line 15. Accordingly, the semiconductor memory device 2c has a
MONOS structure and is the I-shaped pillar type. Otherwise, the
configuration, the manufacturing method, the operations, and the
effects of the modification are similar to those of the second
embodiment and the first and second modifications of the second
embodiment described above.
Third Embodiment
[0115] A third embodiment will now be described.
[0116] FIG. 34 is a cross-sectional view showing a semiconductor
memory device according to the embodiment.
[0117] Compared to the semiconductor memory device 2 (referring to
FIG. 19) according to the second embodiment described above, in the
semiconductor memory device 3 according to the embodiment as shown
in FIG. 34, an air gap 86 is made between the silicon pillars 20,
the control gate electrode films 21, the floating gate electrode
films 31, the tunneling insulating films 33, and the blocking
insulating films 34. More specifically, the air gap 86 is made
between the control gate electrode films 21 adjacent to each other
in the Z-direction, between the floating gate electrode films 31
adjacent to each other in the Z-direction, between the silicon
pillars 20 adjacent to each other in the Y-direction, between the
blocking insulating films 34, between the floating gate electrode
films 31, between the tunneling insulating films 33, and between
the two silicon pillars 20 adjacent to each other in the
X-direction and belonging to the same set 22.
[0118] A method for manufacturing the semiconductor memory device
according to the embodiment will now be described.
[0119] FIGS. 35A and 35B to FIGS. 37A to 37C are plan views and
cross-sectional views showing the method for manufacturing the
semiconductor memory device according to the embodiment.
[0120] FIG. 35A is a cross-sectional view; and FIG. 35B is a plan
view. FIG. 36A is a cross-sectional view; FIG. 36B is a
cross-sectional view along line C-C' shown in FIG. 36A; and FIG.
36C is a cross-sectional view along line B-B' shown in FIG. 36A.
This is similar for FIGS. 37A to 37C.
[0121] First, as shown in FIGS. 35A and 35B, a stacked body is
formed by forming the insulating film 17 made of silicon oxide on
the silicon substrate 10 (referring to FIG. 2) and subsequently
stacking a silicon nitride film 87 alternately with the polysilicon
film 72.
[0122] Then, the processes shown in FIGS. 21A and 21B to FIGS. 29A
to 29C are implemented. However, in the processes shown in FIGS.
24A and 24B and FIGS. 27A and 27B, a silicon nitride film 88 is
filled instead of the inter-layer insulating film 24 made of
silicon oxide.
[0123] Thereby, as shown in FIGS. 36A to 36C, an intermediate
structural body that is similar to the intermediate structural body
shown in FIGS. 29A to 29C is made. However, in the intermediate
structural body of the embodiment, the silicon nitride films 87 are
provided instead of the silicon oxide films 71; and the silicon
nitride film 88 is provided instead of the inter-layer insulating
film 24.
[0124] Then, as shown in FIGS. 37A to 37C, the silicon nitride
films 87 and the silicon nitride film 88 are removed by, for
example, wet etching. Thereby, the air gap 86 is made in the space
where the silicon nitride films 87 and the silicon nitride film 88
were disposed. Thus, the semiconductor memory device 3 according to
the embodiment is manufactured.
[0125] According to the embodiment, because the air gap 86 is made
between the silicon pillars 20, the control gate electrode films
21, the floating gate electrode films 31, the tunneling insulating
films 33, and the blocking insulating films 34, the proximity
effect can be suppressed; and the breakdown voltage can be
increased.
[0126] Otherwise, the configuration, the manufacturing method, the
operations, and the effects of the embodiment are similar to those
of the second embodiment described above.
[0127] It is possible for the air gap to be made only between the
silicon pillars 20 by alternately stacking the silicon oxide film
71 and the polysilicon film 72 instead of the silicon nitride film
87 and the polysilicon film 72 in the process shown in FIGS. 35A
and 35B.
Modification of Third Embodiment
[0128] A modification of the embodiment will now be described.
[0129] FIGS. 38A to 38C are cross-sectional views showing a
semiconductor memory device according to the modification.
[0130] FIG. 38A is a cross-sectional view; FIG. 38B is a
cross-sectional view along line C-C' shown in FIG. 38A; and FIG.
38C is a cross-sectional view along line B-B' shown in FIG.
38A.
[0131] FIG. 38A is a cross-sectional view along line D-D' shown in
FIG. 38C. This is similar for FIGS. 39A to 39C described below.
[0132] As shown in FIGS. 38A to 38C, the semiconductor memory
device 3a according to the modification differs from the
semiconductor memory device 3 (referring to FIG. 34) according to
the third embodiment described above in that a reinforcing member
89 is formed in multiple regions by causing the silicon nitride
films 87 and 88 to partially remain. The reinforcing member 89
extends in the Z-direction and is disposed intermittently along the
Y-direction inside the semiconductor memory device 3a.
[0133] FIGS. 39A to 39C are cross-sectional views showing a method
for manufacturing the semiconductor memory device according to the
modification.
[0134] In the modification as shown in FIGS. 39A to 39C, the
through-holes 82 are not made in the region where the reinforcing
member 89 is to be formed. Thereby, in the process shown in FIGS.
37A to 37C, the silicon nitride films 87 and 88 remain locally to
become the reinforcing member 89 when performing wet etching of the
silicon nitride films 87 and 88 via the through-holes 82.
[0135] According to the modification, by providing the reinforcing
member 89, the mechanical strength of the semiconductor memory
device 3a can be ensured; and collapse can be prevented. Otherwise,
the configuration, the manufacturing method, the operations, and
the effects of the modification are similar to those of the third
embodiment described above.
Fourth Embodiment
[0136] A fourth embodiment will now be described.
[0137] FIG. 40 is a cross-sectional view showing a semiconductor
memory device according to the embodiment.
[0138] FIG. 41 is a cross-sectional view showing region E shown in
FIG. 40.
[0139] As shown in FIG. 40 and FIG. 41, the semiconductor memory
device 4 according to the embodiment differs from the semiconductor
memory device 1 (referring to FIG. 1 to FIG. 4) according to the
first embodiment described above in that the blocking insulating
film 34 is not disposed between a control gate electrode film 21u
of the uppermost level and a floating gate electrode film 31u of
the uppermost level; and the control gate electrode film 21u of the
uppermost level is connected to the floating gate electrode film
31u of the uppermost level.
[0140] The semiconductor memory device according to the embodiment
will now be described.
[0141] FIG. 42A is a cross-sectional view showing a method for
manufacturing the semiconductor memory device according to the
embodiment; and FIG. 42B is a plan view.
[0142] First, the processes shown in FIGS. 5A and 5B to FIGS. 12A
and 12B are implemented.
[0143] Then, as shown in FIGS. 42A and 42B, the silicon oxide layer
36 and the silicon nitride layer 37 are formed on the inner surface
of the trench 58. Then, a resist material 90 is filled into the
trench 58; and a recess 59u of the uppermost level is exposed by
the upper surface of the resist material 90 being recessed. Then,
the portions of the silicon nitride layer 37, the silicon oxide
layer 36, and the silicon nitride layer 35 that are exposed from
the resist material 90 are removed by, for example, wet etching.
Thereby, the polysilicon film 55 is exposed at the back surface of
the recess 59u of the uppermost level. Then, the resist material 90
is removed.
[0144] Continuing as shown in FIGS. 13A and 13B, the tungsten film
61 is formed on the inner surface of the trench 58. At this time,
the tungsten film 61 contacts the polysilicon film 55 inside the
recess 59u of the uppermost level. The subsequent processes are
similar to those of the first embodiment described above.
[0145] According to the embodiment, the control gate electrode film
21u of the uppermost level and the floating gate electrode film 31u
of the uppermost level can be electrically integrated to be used as
the selection gate electrode film by causing the control gate
electrode film 21u to connect the floating gate electrode film 31u.
Thereby, a selection gate transistor can be formed in which the
threshold does not fluctuate because charge is not stored.
[0146] Otherwise, the configuration, the manufacturing method, the
operations, and the effects of the embodiment are similar to those
of the first embodiment described above.
Fifth Embodiment
[0147] A fifth embodiment will now be described.
[0148] FIG. 43 and FIG. 44 are cross-sectional views showing a
semiconductor memory device according to the embodiment.
[0149] In the semiconductor memory device 5 according to the
embodiment as shown in FIG. 43 and FIG. 44, the multiple silicon
pillars 20 are provided and arranged in a matrix configuration
along the X-direction and the Y-direction. Each of the silicon
pillars 20 has a circular columnar configuration extending in the
Z-direction. The tunneling insulating films 33, the floating gate
electrode films 31, and the blocking insulating film 34 are
provided in circular ring configurations around each of the silicon
pillars 20 in order from the inside, i.e., the silicon pillar 20
side. In other words, the floating gate electrode films 31 are
provided around the silicon pillar 20 as viewed from the
Z-direction.
[0150] The tunneling insulating films 33 and the floating gate
electrode films 31 are divided in the Z-direction. The silicon
oxide films 51 are provided between the stacked bodies having the
circular ring configurations made of the tunneling insulating film
33 and the floating gate electrode film 31 in the Z-direction. In
the floating gate electrode film 31, a polysilicon layer 91 is
disposed on the inner side; and a metal silicide layer 92 is
disposed on the outer side. The metal silicide layer 92 is formed
of a metal silicide but may be formed of a metal.
[0151] In the blocking insulating film 34, a silicon oxide layer 93
is disposed on the inner side; and high dielectric constant layers
94 are disposed on the outer side. The high dielectric constant
layers 94 are made of a material having a higher dielectric
constant than silicon oxide, for example, hafnium (Hf), aluminum
oxide (AlO), titanium nitride (TiN), tantalum nitride (TaN), or
tantalum oxide (TaO). The silicon oxide layer 93 is provided
continuously in a tubular configuration in the Z-direction.
However, the diameter of the tube fluctuates periodically such that
the diameter of the portions corresponding to the floating gate
electrode films 31 is relatively small and the diameter of the
portions corresponding to the silicon oxide films 51 is relatively
large. Therefore, the silicon oxide layer 93 has a circular tubular
bellows-like configuration. The high dielectric constant layers 94
are disposed inside recesses 93a at the outer surface of the
circular tubular bellows-like configuration made of the silicon
oxide layer and are divided for each of the recesses 93a. The
configuration of the blocking insulating film 34 is not limited to
the two-layer structure made of the silicon oxide layer 93 and the
high dielectric constant layers 94. For example, the configuration
may be a combination of any layer of a silicon oxide layer (a
SiO.sub.2 layer), a silicon nitride layer (a Si.sub.3N.sub.4
layer), an Al.sub.2O.sub.3 layer, a MgO layer, a SrO layer, a SiN
layer, a BaO layer, a TiO layer, a Ta.sub.2O.sub.5 layer, a
BaTiO.sub.3 layer, a BaZrO layer, a ZrO.sub.2 layer, a
Y.sub.2O.sub.3 layer, a ZrSiO layer, a HfAlO layer, a HfSiO layer,
a La.sub.2O.sub.3 layer, a LaAlO layer, etc.
[0152] In the semiconductor memory device 5, the multiple control
gate electrode films 21 are provided to be arranged in a matrix
configuration along the X-direction and the Z-direction. The
control gate electrode films 21 have band configurations extending
in the Y-direction. The control gate electrode film 21 is a
conductive film, e.g., a two-layer film made of a titanium nitride
layer (TiN) and a tungsten layer (W), a two-layer film made of a
tungsten nitride layer (WN) and a tungsten layer (W), or a
two-layer film made of a tantalum nitride layer (TaN) and a
tungsten layer (W). However, the configuration of the control gate
electrode film 21 is not limited thereto; and, for example, a metal
silicide layer formed by siliciding a polysilicon film may be
used.
[0153] The structural body that is made of the silicon pillar 20,
the tunneling insulating film 33, the floating gate electrode films
31, and the blocking insulating film 34 pierces the control gate
electrode films 21. The control gate electrode films 21 are
disposed in the recesses 93a. In other words, the control gate
electrode films 21 are provided around the floating gate electrode
films 31 as viewed from the Z-direction. The inter-layer insulating
film 24 is provided between the structural bodies made of the
silicon pillar 20, the tunneling insulating film 33, the floating
gate electrode films 31, the blocking insulating film 34, and the
control gate electrode films 21.
[0154] A method for manufacturing the semiconductor memory device
according to the embodiment will now be described.
[0155] FIG. 45 to FIG. 53 are cross-sectional views showing the
method for manufacturing the semiconductor memory device according
to the embodiment.
[0156] First, similarly to the first embodiment described above,
the insulating film 11, the cell source line 15, and the insulating
film 17 (referring to FIG. 1 and FIG. 2) are formed on the silicon
substrate 10.
[0157] Then, as shown in FIG. 45, the stacked body 60 is formed by
alternately stacking the silicon oxide film 51 and the silicon
nitride film 52.
[0158] Continuing, multiple memory holes 95 are made in the stacked
body 60. The memory holes 95 extend in the Z-direction and pierce
the stacked body 60 and the insulating film 17 (referring to FIG.
2) to reach the cell source line 15.
[0159] Then, as shown in FIG. 46, the exposed surfaces of the
silicon nitride films 52 at the inner surface of the memory hole 95
are caused to recede by performing wet etching. Thereby, recesses
96 having annular configurations are made in the inner surface of
the memory hole 95.
[0160] Continuing as shown in FIG. 47, the polysilicon layers 91
are filled into the recess 96 by depositing polysilicon and
selectively removing the polysilicon by performing isotropic
etching. Then, the tunneling insulating films 33 are formed by
oxidizing the exposed surfaces of the polysilicon layers 91.
[0161] Then, as shown in FIG. 48, the silicon pillar 20 is formed
by filling polysilicon into the memory hole 95. The silicon pillar
20 is connected to the cell source line 15 (referring to FIG.
2).
[0162] Continuing as shown in FIG. 49, a trench 97 is made in the
portion of the stacked body 60 between the memory holes 95. The
trench 97 spreads in the Y-direction and the Z-direction, and
pierces the stacked body 60 in the Z-direction but does not pierce
the insulating film 17 (referring to FIG. 2).
[0163] Then, as shown in FIG. 50, the silicon nitride films 52 are
removed by performing wet etching via the trench 97. Thereby,
recesses 98 are made at the inner surface of the trench 97. The
polysilicon layers 91 are exposed at the back surfaces of the
recesses 98.
[0164] Continuing as shown in FIG. 51, the exposed surfaces of the
polysilicon layers 91 inside the recesses 98 are silicided by
siliciding via the trench 97 and the recesses 98. Thereby, the
metal silicide layers 92 are formed. The floating gate electrode
film 31 includes the polysilicon layer 91 and the metal silicide
layer 92.
[0165] Then, as shown in FIG. 52, the silicon oxide layer 93 is
formed on the inner surface of the trench 97. Then, the high
dielectric constant layer 94 is formed on the silicon oxide layer
93. The silicon oxide layer 93 and the high dielectric constant
layer 94 have circular tubular bellows-like configurations
reflecting the recesses 98.
[0166] Continuing as shown in FIG. 53, a conductive film 99 is
formed on the high dielectric constant layer 94 by depositing a
conductive material by, for example, CVD. The conductive film 99
also is filled into the recesses 98 but is formed such that the
trench 97 is not filled.
[0167] Then, as shown in FIG. 43 and FIG. 44, the conductive film
99 and the high dielectric constant layer 94 are recessed by
performing isotropic etching such that the conductive film 99 and
the high dielectric constant layer 94 remain only inside the
recesses 93a of the silicon oxide layer 93. Thereby, the conductive
films 99 that remain inside the recesses 93a become the control
gate electrode films 21. Also, the blocking insulating film 34 is
formed of the silicon oxide layer 93 and the remaining portion of
the high dielectric constant layer 94. Thus, the semiconductor
memory device 5 according to the embodiment is manufactured.
[0168] Effects of the embodiment will now be described.
[0169] According to the embodiment, memory cells having good
controllability can be realized because the control gate electrode
films 21 are provided around the floating gate electrode films 31
and the silicon pillar 20.
[0170] The programming characteristics are good because the
floating gate electrode films 31 are formed of conductors. Also,
because the floating gate electrode films 31 are separated from
each other, the movement of the charge is suppressed; and the data
retention characteristics are high. The erasing characteristics are
good because the erasing operations can be implemented by FN
erasing or assisted erasing from the floating gate electrode films
31.
[0171] In the embodiment, it is unnecessary to remove the tunneling
insulating film 33 formed on the bottom surface of the memory hole
95 by etching because the silicon pillar 20 is connected to the
cell source line 15 (referring to FIG. 2) because the tunneling
insulating film 33 is formed in the process shown in FIG. 47 prior
to forming the silicon pillar 20 in the process shown in FIG. 48.
Therefore, the tunneling insulating films that are formed on the
side surface of the memory hole 95 are not damaged by the
etching.
[0172] Otherwise, the configuration, the manufacturing method, the
operations, and the effects of the embodiment are similar to those
of the first embodiment described above. Although an I-shaped
pillar type device is illustrated in the embodiment, a U-shaped
pillar type device may be used similarly to the first modification
of the second embodiment described above.
Modification of Fifth Embodiment
[0173] A modification of the fifth embodiment will now be
described.
[0174] FIG. 54 is a cross-sectional view showing a semiconductor
memory device according to the modification.
[0175] As shown in FIG. 54, the modification is an example in which
the fourth embodiment and the fifth embodiment described above are
combined. Namely, the semiconductor memory device 5a according to
the modification differs from the semiconductor memory device 5
(referring to FIG. 43) according to the fifth embodiment described
above in that the blocking insulating film 34 is not disposed
between the control gate electrode film 21u of the uppermost level
and the floating gate electrode film 31u of the uppermost level;
and the control gate electrode film 21u of the uppermost level is
connected to the floating gate electrode film 31u of the uppermost
level. However, the level at which the control gate electrode film
21 is connected to the floating gate electrode film 31 is not
limited to the uppermost level and may be multiple levels including
the uppermost level.
[0176] A method for manufacturing the semiconductor memory device
according to the modification will now be described.
[0177] FIG. 55 to FIG. 57 are cross-sectional views showing the
method for manufacturing the semiconductor memory device according
to the modification.
[0178] First, the processes shown in FIG. 45 to FIG. 52 are
implemented.
[0179] Then, as shown in FIG. 55, the resist material 90 is filled
into the trench 97 and recessed from the upper surface side by
exposing. Thereby, the recess 93a of the uppermost level is exposed
from the resist material 90. Although the recesses 93a of multiple
levels including the uppermost level may be exposed at this time,
in the description hereinbelow, an example is described in which
only the recess 93a of the uppermost level is exposed.
[0180] Continuing as shown in FIG. 56, the portions of the high
dielectric constant layer 94 and the silicon oxide layer 93 exposed
from the resist material 90 are removed by performing isotropic
etching such as, for example, wet etching, etc. Thereby, the metal
silicide layer 92 is exposed at the back surface of the recess 93a
of the uppermost level.
[0181] Then, as shown in FIG. 57, the resist material 90 is
removed.
[0182] Continuing, the process shown in FIG. 53 is implemented.
Thus, the semiconductor memory device 5a according to the
modification can be manufactured.
[0183] According to the modification, similarly to the fourth
embodiment described above, the control gate electrode film 21u and
the floating gate electrode film 31u of the uppermost level can be
electrically integrated to be used as the selection gate electrode
film. As a result, a selection gate transistor can be formed in
which the threshold does not fluctuate. Otherwise, the
configuration, the manufacturing method, the operations, and the
effects of the modification are similar to those of the fifth
embodiment described above.
[0184] According to the embodiments described above, a
semiconductor memory device having good data retention
characteristics and a method for manufacturing the semiconductor
memory device can be realized.
[0185] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
invention. Additionally, the embodiments described above can be
combined mutually.
* * * * *