U.S. patent application number 13/041579 was filed with the patent office on 2012-03-22 for nonvolatile semiconductor memory device.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Tomoki HIGASHI, Hitoshi IWAI, Shinichi OOSERA.
Application Number | 20120069660 13/041579 |
Document ID | / |
Family ID | 45817660 |
Filed Date | 2012-03-22 |
United States Patent
Application |
20120069660 |
Kind Code |
A1 |
IWAI; Hitoshi ; et
al. |
March 22, 2012 |
NONVOLATILE SEMICONDUCTOR MEMORY DEVICE
Abstract
A nonvolatile semiconductor memory device comprises a plurality
of memory blocks, each including a plurality of cell units and each
configured as a unit of execution of an erase operation. Each of
the cell units comprises a memory string, a first transistor, a
second transistor, and a diode. The first transistor has one end
connected to one end of the memory string. The second transistor is
provided between the other end of the memory string and a second
line. The diode is provided between the other end of the first
transistor and a first line. The diode comprises a second
semiconductor layer of a first conductivity type and a third
semiconductor layer of a second conductivity type.
Inventors: |
IWAI; Hitoshi;
(Kamakura-shi, JP) ; HIGASHI; Tomoki;
(Yokohama-shi, JP) ; OOSERA; Shinichi;
(Yokohama-shi, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
Tokyo
JP
|
Family ID: |
45817660 |
Appl. No.: |
13/041579 |
Filed: |
March 7, 2011 |
Current U.S.
Class: |
365/185.11 |
Current CPC
Class: |
G11C 16/14 20130101;
H01L 27/11582 20130101; G11C 16/0483 20130101; G11C 16/3427
20130101; G11C 16/10 20130101; H01L 27/1021 20130101; G11C 16/3418
20130101 |
Class at
Publication: |
365/185.11 |
International
Class: |
G11C 16/04 20060101
G11C016/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2010 |
JP |
2010-211326 |
Claims
1. A nonvolatile semiconductor memory device, comprising: a
plurality of memory blocks, each including a plurality of cell
units and each configured as a smallest unit of an erase operation;
a first line provided commonly to the plurality of memory blocks
and connected to one ends of the plurality of cell units; a second
line connected to the other ends of the plurality of cell units;
and a control circuit configured to control a voltage applied to
the plurality of memory blocks, each of the plurality of cell units
comprising: a memory string configured by a plurality of memory
transistors connected in series, the memory transistors being
electrically rewritable; a first transistor having one end
connected to one end of the memory string; a second transistor
provided between the other end of the memory string and the second
line; and a diode provided between the first transistor and the
first line and having a forward bias direction from a side of the
first transistor to a side of the first line, the memory string
comprising: a first semiconductor layer including a columnar
portion extending in a perpendicular direction with respect to a
substrate, the first semiconductor layer being configured to
function as a body of the memory transistors; a charge storage
layer formed to surround a side surface of the columnar portion and
configured to be capable of storing a charge; and a first
conductive layer formed commonly in the plurality of memory blocks
to surround the side surface of the columnar portion with the
charge storage layer interposed therebetween, the first conductive
layer being configured to function as a gate of the memory
transistors, and the diode comprising: a second semiconductor layer
of a first conductivity type, the second semiconductor layer
extending in the perpendicular direction with respect to the
substrate; and a third semiconductor layer of a second conductivity
type, the third semiconductor layer being in contact with an upper
surface of the second semiconductor layer and extending in the
perpendicular direction with respect to the substrate, the control
circuit being configured to perform the erase operation in a
selected one of the memory blocks by setting a voltage of the first
line higher than a voltage of a gate of the first transistor by a
first voltage to generate a GIDL current for raising a voltage of
the body of the memory transistors, and setting a voltage of the
gate of the memory transistors lower than the voltage of the body
of the memory transistors by a second voltage, and the control
circuit being configured to prohibit the erase operation in an
unselected one of the memory blocks by setting a voltage difference
between the voltage of the first line and the voltage of the gate
of the first transistor to a third voltage different from the first
voltage for prohibiting generation of the GIDL current.
2. The nonvolatile semiconductor memory device according to claim
1, wherein the control circuit is configured to perform the erase
operation in a selected one of the memory blocks by setting a
voltage of the second line higher than a voltage of a gate of the
second transistor by the first voltage to generate the GIDL current
for raising a voltage of the body of the memory transistors, and
setting a voltage of the gate of the memory transistors lower than
the voltage of the body of the memory transistors by the second
voltage, and the control circuit is configured to prohibit the
erase operation in an unselected one of the memory blocks by
setting a voltage difference between the voltage of the second line
and the voltage of the gate of the second transistor to the third
voltage for prohibiting generation of the GIDL current.
3. The nonvolatile semiconductor memory device according to claim
1, wherein the second line is divided on a memory block basis, and
wherein the control circuit is configured to prohibit the erase
operation in an unselected one of the memory blocks by setting the
second transistor to an on-state.
4. The nonvolatile semiconductor memory device according to claim
1, wherein the control circuit is configured to perform a write
operation for writing data to the memory transistors, by executing
a first processing setting the second transistor included in a
selected one of the cell units to an on-state, thereby a voltage of
the body of the memory transistors included in the selected one of
the cell units being set to not less than a voltage that may be
applied to the first line during the write operation, a second
processing setting the first transistor included in the selected
one of the cell units to an on-state after the first processing,
and a third processing setting the gate of the selected memory
transistors to a fourth voltage.
5. The nonvolatile semiconductor memory device according to claim
1, wherein the control circuit is configured to perform a read
operation for reading data from a selected memory transistor
included in a selected one of the cell units, by setting a voltage
of the second line higher than the voltage of the first line by a
fifth voltage, setting the first transistor and the second
transistor included in the selected one of the cell units to an
on-state, applying a sixth voltage to the gate of unselected memory
transistors included in the selected one of the cell units, and
applying a seventh voltage lower than the sixth voltage to the gate
of the selected memory transistors.
6. The nonvolatile semiconductor memory device according to claim
1, wherein the diode further comprises an ohmic contact layer
configured to be in contact with a lower surface of the second
semiconductor layer.
7. The nonvolatile semiconductor memory device according to claim
1, wherein the diode further comprises a fourth semiconductor layer
of the first conductivity type, the fourth semiconductor layer
being in contact with an upper surface of the third semiconductor
layer and extending in the perpendicular direction with respect to
the substrate.
8. The nonvolatile semiconductor memory device according to claim
1, wherein the first semiconductor layer includes a joining portion
configured to join lower ends of a pair of the columnar
portions.
9. The nonvolatile semiconductor memory device according to claim
1, wherein the first transistor comprises: a fifth semiconductor
layer extending in the perpendicular direction with respect to the
substrate and configured to function as a body of the first
transistor; a first gate insulating layer formed to surround a side
surface of the fifth semiconductor layer; and a second conductive
layer formed to surround the side surface of the fifth
semiconductor layer with the first gate insulating layer interposed
therebetween, the second conductive layer being configured to
function as the gate of the first transistor.
10. The nonvolatile semiconductor memory device according to claim
1, wherein the second transistor comprises: a sixth semiconductor
layer extending in the perpendicular direction with respect to the
substrate and configured to function as a body of the second
transistor; a second gate insulating layer formed to surround a
side surface of the sixth semiconductor layer; and a third
conductive layer formed to surround the side surface of the sixth
semiconductor layer with the second gate insulating layer
interposed therebetween, the third conductive layer being
configured to function as the gate of the second transistor.
11. The nonvolatile semiconductor memory device according to claim
8, wherein the memory string further comprises: a fourth conductive
layer formed to surround a side surface of the joining portion with
the charge storage layer interposed therebetween.
12. A nonvolatile semiconductor memory device, comprising: a
plurality of memory blocks, each configured as an arrangement of a
plurality of cell units and each configured as a unit of execution
of an erase operation, the erase operation being configured to
erase data retained in the cell units; a first line provided
commonly to the plurality of memory blocks and connected to one
ends of the plurality of cell units; a second line connected to the
other ends of the plurality of cell units; and a control circuit
configured to control a voltage applied to the plurality of memory
blocks, each of the plurality of cell units comprising: a memory
string configured by a plurality of memory transistors connected in
series, the memory transistors being electrically rewritable; a
first transistor having one end connected to one end of the memory
string; a second transistor provided between the other end of the
memory string and the second line; and a diode provided between the
first transistor and the first line and having a forward bias
direction from a side of the first line to a side of the first
transistor, the memory string comprising: a first semiconductor
layer including a columnar portion extending in a perpendicular
direction with respect to a substrate, the first semiconductor
layer being configured to function as a body of the memory
transistors; a charge storage layer formed to surround a side
surface of the columnar portion and configured to be capable of
storing a charge; and a first conductive layer formed commonly in
the plurality of memory blocks to surround the side surface of the
columnar portion with the charge storage layer interposed
therebetween, the first conductive layer being configured to
function as a gate of the memory transistors, and the diode
comprising: a second semiconductor layer of a first conductivity
type, the second semiconductor layer extending in the perpendicular
direction with respect to the substrate; and a third semiconductor
layer of a second conductivity type, the third semiconductor layer
being in contact with the second semiconductor layer and extending
in the perpendicular direction with respect to the substrate, the
control circuit being configured to perform the erase operation in
a selected one of the memory blocks by setting a voltage of the
second line higher than a voltage of a gate of the second
transistor by a first voltage to generate a GIDL current for
raising a voltage of the body of the memory transistors, and
setting a voltage of the gate of the memory transistors lower than
the voltage of the body of the memory transistors by a second
voltage, and the control circuit being configured to prohibit the
erase operation in an unselected one of the memory blocks by
setting a voltage difference between the voltage of the second line
and the voltage of the gate of the second transistor to a third
voltage different from the first voltage for prohibiting generation
of the GIDL current.
13. The nonvolatile semiconductor memory device according to claim
12, wherein the second line is divided on a memory block basis, and
wherein the control circuit is configured to prohibit the erase
operation in an unselected one of the memory blocks by setting the
second transistor to an on-state.
14. The nonvolatile semiconductor memory device according to claim
12, wherein the control circuit is configured to perform a write
operation for writing data to the memory transistors, by executing
a first processing setting the second transistor included in a
selected one of the cell units to an on-state, thereby a voltage of
the body of the memory transistors included in the selected one of
the cell units being set to not less than a voltage that may be
applied to the first line during the write operation, a second
processing setting the first transistor included in the selected
one of the cell units to an on-state after the first processing,
and a third processing setting the gate of the selected memory
transistors to a fourth voltage.
15. The nonvolatile semiconductor memory device according to claim
12, wherein the control circuit is configured to perform a read
operation for reading data from a selected memory transistor
included in a selected one of the cell units, by setting a voltage
of the second line higher than the voltage of the first line by a
fifth voltage, setting the first transistor and the second
transistor included in the selected one of the cell units to an
on-state, applying a sixth voltage to the gate of unselected memory
transistors included in the selected one of the cell units, and
applying a seventh voltage lower than the sixth voltage to the gate
of the selected memory transistors.
16. The nonvolatile semiconductor memory device according to claim
12, wherein the diode further comprises a fourth semiconductor
layer of the first conductivity type, the fourth semiconductor
layer being in contact with an upper surface of the third
semiconductor layer and extending in the perpendicular direction
with respect to the substrate.
17. The nonvolatile semiconductor memory device according to claim
12, wherein the first semiconductor layer has an upper portion
configured by a semiconductor of the second conductivity type.
18. The nonvolatile semiconductor memory device according to claim
12, wherein the first semiconductor layer includes a joining
portion configured to join lower ends of a pair of the columnar
portions.
19. The nonvolatile semiconductor memory device according to claim
12, wherein the first transistor comprises: a fifth semiconductor
layer extending in the perpendicular direction with respect to the
substrate and configured to function as a body of the first
transistor; a first gate insulating layer formed to surround a side
surface of the fifth semiconductor layer; and a second conductive
layer formed to surround the side surface of the fifth
semiconductor layer with the first gate insulating layer interposed
therebetween, the second conductive layer being configured to
function as the gate of the first transistor.
20. The nonvolatile semiconductor memory device according to claim
12, wherein the second transistor comprises: a sixth semiconductor
layer extending in the perpendicular direction with respect to the
substrate and configured to function as a body of the second
transistor; a second gate insulating layer formed to surround a
side surface of the sixth semiconductor layer; and a third
conductive layer formed to surround the side surface of the sixth
semiconductor layer with the second gate insulating layer
interposed therebetween, the third conductive layer being
configured to function as the gate of the second transistor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2010-211326, filed on Sep. 21, 2010, the entire contents of which
are incorporated herein by reference.
FIELD
[0002] Embodiments described in this specification relate to an
electrically data-rewritable nonvolatile semiconductor memory
device.
BACKGROUND
[0003] In recent years, many semiconductor memory devices having
memory cells disposed three-dimensionally are proposed in order to
increase the degree of integration of memory. For example, a
semiconductor memory device employing transistors of a circular
cylindrical type structure represents one such conventional
semiconductor memory device having memory cells disposed
three-dimensionally.
[0004] There is a risk that, when an erase operation is executed on
such an above-described semiconductor memory device, the erase
operation is not executed accurately due to the leak current
flowing into the memory cells from various wirings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a block diagram of a nonvolatile semiconductor
memory device in accordance with a first embodiment.
[0006] FIG. 2 is a schematic perspective view of the nonvolatile
semiconductor memory device in accordance with the first
embodiment.
[0007] FIG. 3 is a circuit diagram of a memory cell array 1 in
accordance with the first embodiment.
[0008] FIG. 4A is a cross-sectional view of the nonvolatile
semiconductor memory device in accordance with the first
embodiment.
[0009] FIG. 4B is a cross-sectional view of the nonvolatile
semiconductor memory device in accordance with the first
embodiment.
[0010] FIG. 5 is an enlarged view of FIG. 4A.
[0011] FIG. 6 is a schematic view of during a first erase operation
in the nonvolatile semiconductor memory device in accordance with
the first embodiment.
[0012] FIG. 7 is a timing chart of during the first erase operation
in the nonvolatile semiconductor memory device in accordance with
the first embodiment.
[0013] FIG. 8A is a schematic view of during a first write
operation in the nonvolatile semiconductor memory device in
accordance with the first embodiment.
[0014] FIG. 8B is a schematic view of during the first write
operation in the nonvolatile semiconductor memory device in
accordance with the first embodiment.
[0015] FIG. 9 is a timing chart of during the first write operation
in the nonvolatile semiconductor memory device in accordance with
the first embodiment.
[0016] FIG. 10 is a schematic view of during a first read operation
in the nonvolatile semiconductor memory device in accordance with
the first embodiment.
[0017] FIG. 11 is a timing chart of during the first read operation
in the nonvolatile semiconductor memory device in accordance with
the first embodiment.
[0018] FIG. 12 is a timing chart of during a second erase operation
in the nonvolatile semiconductor memory device in accordance with
the first embodiment.
[0019] FIG. 13 is a timing chart of during a second write operation
in the nonvolatile semiconductor memory device in accordance with
the first embodiment.
[0020] FIG. 14 is a timing chart of during a second read operation
in the nonvolatile semiconductor memory device in accordance with
the first embodiment.
[0021] FIG. 15 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the first embodiment.
[0022] FIG. 16 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the first embodiment.
[0023] FIG. 17 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the first embodiment.
[0024] FIG. 18 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the first embodiment.
[0025] FIG. 19 is a circuit diagram of a memory cell array 1 in
accordance with a second embodiment.
[0026] FIG. 20 is a cross-sectional view of a nonvolatile
semiconductor memory device in accordance with the second
embodiment.
[0027] FIG. 21 is a schematic view of during an erase operation in
the nonvolatile semiconductor memory device in accordance with the
second embodiment.
[0028] FIG. 22 is a timing chart of during the erase operation in
the nonvolatile semiconductor memory device in accordance with the
second embodiment.
[0029] FIG. 23A is a schematic view of during a write operation in
the nonvolatile semiconductor memory device in accordance with the
second embodiment.
[0030] FIG. 23B is a schematic view of during the write operation
in the nonvolatile semiconductor memory device in accordance with
the second embodiment.
[0031] FIG. 24 is a timing chart of during the write operation in
the nonvolatile semiconductor memory device in accordance with the
second embodiment.
[0032] FIG. 25 is a cross-sectional view of a nonvolatile
semiconductor memory device in accordance with a third
embodiment.
[0033] FIG. 26 is a cross-sectional view of a nonvolatile
semiconductor memory device in accordance with a fourth
embodiment.
[0034] FIG. 27 is a cross-sectional view of a nonvolatile
semiconductor memory device in accordance with a fifth
embodiment.
[0035] FIG. 28 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the fifth embodiment.
[0036] FIG. 29 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the fifth embodiment.
[0037] FIG. 30 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the fifth embodiment.
[0038] FIG. 31 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the fifth embodiment.
[0039] FIG. 32 is a cross-sectional view showing a manufacturing
process of the nonvolatile semiconductor memory device in
accordance with the fifth embodiment.
DETAILED DESCRIPTION
[0040] A nonvolatile semiconductor memory device in accordance with
an embodiment comprises a plurality of memory blocks, a first line,
a second line, and a control circuit. Each of the plurality of
memory blocks includes a plurality of cell units and is configured
as a smallest unit of an erase operation. The first line is
provided commonly to the plurality of memory blocks and is
connected to one ends of the plurality of cell units. The second
line is connected to the other ends of the plurality of cell units.
The control circuit is configured to control a voltage applied to
the plurality of memory blocks. Each of the plurality of cell units
comprises a memory string, a first transistor, a second transistor,
and a diode. The memory string is configured by a plurality of
memory transistors connected in series, the memory transistors
being electrically rewritable. The first transistor has one end
connected to one end of the memory string. The second transistor is
provided between the other end of the memory string and the second
line. The diode is provided between the first transistor and the
first line and has a forward bias direction from a side of the
first transistor to a side of the first line. The memory string
comprises a first semiconductor layer, a charge storage layer, and
a first conductive layer. The first semiconductor layer includes a
columnar portion extending in a perpendicular direction with
respect to a substrate and is configured to function as a body of
the memory transistors. The charge storage layer is formed to
surround a side surface of the columnar portion and is configured
to be capable of storing a charge. The first conductive layer is
formed commonly in the plurality of memory blocks to surround the
side surface of the columnar portion with the charge storage layer
interposed therebetween and is configured to function as a gate of
the memory transistors. The diode comprises a second semiconductor
layer and a third semiconductor layer. The second semiconductor
layer is configured as a first conductivity type extending in the
perpendicular direction with respect to the substrate. The third
semiconductor layer is configured as a second conductivity type
being in contact with an upper surface of the second semiconductor
layer and extending in the perpendicular direction with respect to
the substrate. The control circuit is configured to perform the
erase operation in a selected one of the memory blocks by setting a
voltage of the first line higher than a voltage of a gate of the
first transistor by a first voltage to generate a GIDL current for
raising a voltage of the body of the memory transistors, and
setting a voltage of the gate of the memory transistors lower than
the voltage of the body of the memory transistors by a second
voltage. On the other hand, the control circuit is configured to
prohibit the erase operation in an unselected one of the memory
blocks by setting a voltage difference between the voltage of the
first line and the voltage of the gate of the first transistor to a
third voltage different from the first voltage for prohibiting
generation of the GIDL current.
[0041] A nonvolatile semiconductor memory device in accordance with
another embodiment comprises a plurality of memory blocks, a first
line, a second line, and a control circuit. Each of the memory
blocks is configured as an arrangement of a plurality of cell units
and is configured as a smallest unit of an erase operation. The
first line is provided commonly to the plurality of memory blocks
and is connected to one ends of the plurality of cell units. The
second line is connected to the other ends of the plurality of cell
units. The control circuit is configured to control a voltage
applied to the plurality of memory blocks. Each of the plurality of
cell units comprises a memory string, a first transistor, a second
transistor, and a diode. The memory string is configured by a
plurality of memory transistors connected in series, the memory
transistors being electrically rewritable. The first transistor has
one end connected to one end of the memory string. The second
transistor is provided between the other end of the memory string
and the second line. The diode is provided between the first
transistor and the first line and has a forward bias direction from
aside of the first line to a side of the first transistor. The
memory string comprises a first semiconductor layer, a charge
storage layer, and a first conductive layer. The first
semiconductor layer includes a columnar portion extending in a
perpendicular direction with respect to a substrate and is
configured to function as a body of the memory transistors. The
charge storage layer is formed to surround a side surface of the
columnar portion and is configured to be capable of storing a
charge. The first conductive layer is formed commonly in the
plurality of memory blocks to surround the side surface of the
columnar portion with the charge storage layer interposed
therebetween and is configured to function as a gate of the memory
transistors. The diode comprises a second semiconductor layer and a
third semiconductor layer. The second semiconductor layer is
configured as a first conductivity type extending in the
perpendicular direction with respect to the substrate. The third
semiconductor layer is configured as a second conductivity type
being in contact with the second semiconductor layer and extending
in the perpendicular direction with respect to the substrate. The
control circuit is configured to perform the erase operation in a
selected one of the memory blocks by setting a voltage of the
second line higher than a voltage of a gate of the second
transistor by a first voltage to generate a GIDL current for
raising a voltage of the body of the memory transistors, and
setting a voltage of the gate of the memory transistors lower than
the voltage of the body of the memory transistors by a second
voltage. On the other hand, the control circuit is configured to
prohibit the erase operation in an unselected one of the memory
blocks by setting a voltage difference between the voltage of the
second line and the voltage of the gate of the second transistor to
a third voltage different from the first voltage for prohibiting
generation of the GIDL current.
[0042] Next, embodiments of a nonvolatile semiconductor memory
device are described with reference to the drawings.
First Embodiment
Configuration
[0043] First, a configuration of a nonvolatile semiconductor memory
device in accordance with a first embodiment is described with
reference to FIGS. 1 and 2. FIG. 1 is a block diagram of the
nonvolatile semiconductor memory device in accordance with the
first embodiment of the present invention, and FIG. 2 is a
schematic perspective view of the nonvolatile semiconductor memory
device in accordance with the first embodiment of the present
invention.
[0044] The nonvolatile semiconductor memory device in accordance
with the first embodiment includes a memory cell array 1 and a
control circuit 1A, as shown in FIG. 1.
[0045] The memory cell array 1 is configured by memory transistors
MTr1-MTr4 arranged in a three-dimensional matrix, each of the
memory transistors being configured to store data electrically, as
shown in FIG. 2. That is, the memory transistors MTr1-MTr4, in
addition to being arranged in a matrix in a horizontal direction,
are arranged also in a stacking direction (perpendicular direction
with respect to a substrate).
[0046] A plurality of the memory transistors MTr1-MTr4 aligned in
the stacking direction are connected in series to configure a
publicly known memory string MS (NAND string). Changing an amount
of charge stored in a charge storage layer of the memory
transistors MTr1-MTr4 causes a threshold voltage of the memory
transistors MTr1-MTr4 to change. Changing the threshold voltage
causes data retained in the memory transistors MTr1-MTr4 to be
rewritten. Connected respectively one each to the two ends of the
memory string MS are a drain side select transistor SDTr and a
source side select transistor SSTr which are turned on when the
memory string MS is selected. Moreover, the drain side select
transistor SDTr has its drain connected via a diode DI to a bit
line BL, and the source side select transistor SSTr has its source
connected to a source line SL. Note that specific circuit
configurations and stacking structure of the memory cell array 1
are described later.
[0047] The control circuit 1A is configured to control a voltage
applied to the memory cell array 1 (memory block BK to be described
later). The control circuit 1A comprises row decoders 2 and 3, a
sense amplifier 4, a column decoder 5, and a control signal
generating unit (high voltage generating unit) 6. The row decoders
2 and 3 decode downloaded block address signals and so on to
control the memory cell array 1. The sense amplifier 4 reads data
from the memory cell array 1. The column decoder 5 decodes a column
address signal to control the sense amplifier 4. The control signal
generating unit 6 boosts a reference voltage to generate a high
voltage required during write and erase, and, moreover, generates a
control signal to control the row decoders 2 and 3, the sense
amplifier 4, and the column decoder 5.
[0048] Next, a circuit configuration of the memory cell array 1 is
described with reference to FIG. 3. As shown in FIG. 3, the memory
cell array 1 includes a plurality of memory blocks BK_1, BK_2, . .
. , BK_n, a plurality of bit lines BL1, BL2, . . . , BLn, and a
plurality of source lines SL1, SL2, . . . , SLn. Note that memory
blocks are sometimes collectively referred to as memory block BK,
instead of specifying either one of BK_1, BK_2, . . . , BK_n. Bit
lines are sometimes collectively referred to as bit line BL,
instead of specifying either one of BL1, BL2, . . . , BLn. Source
lines are sometimes collectively referred to as source line SL,
instead of specifying either one of SL1, SL2, . . . , SLn.
[0049] Each of the memory blocks BK includes a plurality of cell
units MU and is configured as a smallest unit of an erase operation
for erasing data. Each of the bit lines BL is provided commonly to
the memory blocks BK_1, BK_2, . . . , BK_n. Each of the bit lines
BL is connected to drains of a plurality of the cell units MU. Each
of the source lines SL is provided divided on a memory block BK
basis. Each of the source lines SL is connected commonly to sources
of a plurality of cell units MU in one memory block BK.
[0050] In the example shown in FIG. 3, each one of the memory
blocks BK has the cell units MU provided in a matrix over k rows
and n columns. Each of the cell units MU includes the memory string
MS, the drain side select transistor SDTr, the source side select
transistor SSTr, and the diode DI. The memory string MS is
configured by the memory transistors MTr1-MTr4 connected in series.
The drain side select transistor SDTr is connected to a drain of
the memory string MS (drain of the memory transistor MTr4). The
source side select transistor SSTr is connected to a source of the
memory string MS (source of the memory transistor MTr1). Note that
the memory string MS may be configured by more than four memory
transistors.
[0051] As shown in FIG. 3, the memory transistors MTr1 arranged in
a matrix in the plurality of memory blocks BK have their gates
connected commonly to a word line WL1. Similarly, the memory
transistors MTr2-MTr4 have their gates commonly connected to word
lines WL2-WL4, respectively.
[0052] As shown in FIG. 3, the drain side select transistors SDTr
arranged in a line in a row direction in the memory block BK_1 have
their gates connected commonly to one drain side select gate line
SGD1,1 (or SGD1,2, . . . , SGD1,k). Similarly, the drain side
select transistors SDTr arranged in a line in the row direction in
the memory block BK_2 have their gates connected commonly to one
drain side select gate line SGD2,1 (or SGD2,2, . . . , SGD2,k). The
drain side select transistors SDTr arranged in a line in the row
direction in the memory block BK_n have their gates connected
commonly to one drain side select gate line SGDn,1 (or SGDn,2, . .
. , SGDn,k). Note that drain side select gate lines are sometimes
collectively referred to as drain side select gate lines SGD,
instead of specifying either one of SGD1,1, . . . , SGDn,k. The
drain side select gate lines SGD are each provided to extend in the
row direction and having a certain pitch in a column direction.
[0053] In addition, the drain side select transistors SDTr arranged
in a line in the column direction have their other ends connected
commonly via a respective diode DI to one bit line BL1 (or BL2, . .
. , BLn). The diode DI is provided to have a forward bias direction
from a side of the drain side select transistor SDTr to a side of
the bit line BL. The bit line BL is formed to extend in the column
direction straddling the memory blocks BK.
[0054] As shown in FIG. 3, the source side select transistors SSTr
arranged in a line in the row direction in the memory block BK_1
have their gates connected commonly to one source side select gate
line SGS1,1 (or SGS1,2, . . . , SGS1,k). Similarly, the source side
select transistors SSTr arranged in a line in the row direction in
the memory block BK_2 have their gates connected commonly to one
source side select gate line SGS2,1 (or SGS2,2, . . . , SGS2,k).
The source side select transistors SSTr arranged in a line in the
row direction in the memory block BK_n have their gates connected
commonly to one source side select gate line SGSn,1 (or SGSn,2, . .
. , SGSn,k). Note that source side select gate lines are sometimes
collectively referred to as source side select gate lines SGS,
instead of specifying either one of SGS1,1, . . . , SGSn,k. The
source side select gate lines SGS are each provided to extend in
the row direction and having a certain pitch in the column
direction.
[0055] In addition, all the source side select transistors SSTr in
the memory block BK_1 are connected commonly to one source line
SL1. Similarly, all the source side select transistors SSTr in the
memory block BK_2 are connected commonly to one source line SL2,
and all the source side select transistors SSTr in the memory block
BK_n are connected commonly to one source line SLn.
[0056] The above-described circuit configuration of the nonvolatile
semiconductor memory device is realized by a stacking structure
shown in FIGS. 4A and 4B. As shown in FIGS. 4A and 4B, the
nonvolatile semiconductor memory device in accordance with the
first embodiment includes a semiconductor substrate 10, and,
stacked sequentially on the semiconductor substrate 10, a source
side select transistor layer 20, a memory transistor layer 30, a
drain side select transistor layer 40, a diode layer 50, and a
wiring layer 60.
[0057] The semiconductor substrate 10 functions as the source line
SL. The source side select transistor layer 20 functions as the
source side select transistor SSTr. The memory transistor layer 30
functions as the memory string MS (memory transistors MTr1-MTr4).
The drain side select transistor layer 40 functions as the drain
side select transistor SDTr. The diode layer 50 functions as the
diode DI. The wiring layer 60 functions as the bit line BL and as
various other wirings.
[0058] The semiconductor substrate 10 includes a diffusion layer 11
in its upper surface, as shown in FIGS. 4A and 4B. The diffusion
layer 11 functions as the source line SL. The diffusion layer 11 is
divided on a memory block BK basis.
[0059] The source side select transistor layer 20 includes a source
side conductive layer 21 disposed on the semiconductor substrate 10
via an insulating layer, as shown in FIGS. 4A and 4B. The source
side conductive layer 21 functions as the gate of the source side
select transistor SSTr and as the source side select gate line SGS.
The source side conductive layer 21 is formed in stripes in each of
the memory blocks MB, the stripes extending in the row direction
and having a certain pitch in the column direction. The source side
conductive layer 21 is configured by polysilicon (poly-Si).
[0060] In addition, as shown in FIGS. 4A and 4B, the source side
select transistor layer 20 includes a source side hole 22. The
source side hole 22 is formed to penetrate the source side
conductive layer 21. The source side holes 22 are formed in a
matrix in the row direction and the column direction.
[0061] Moreover, as shown in FIGS. 4A and 4B, the source side
select transistor layer 20 includes a source side gate insulating
layer 23 and a source side columnar semiconductor layer 24. The
source side columnar semiconductor layer 24 functions as a body
(channel) of the source side select transistor SSTr.
[0062] The source side gate insulating layer 23 is formed with a
certain thickness on a side wall of the source side hole 22. The
source side columnar semiconductor layer 24 is formed to be in
contact with a side surface of the source side gate insulating
layer 23 and to fill the source side hole 22. The source side
columnar semiconductor layer 24 is formed in a column shape
extending in the stacking direction (perpendicular direction with
respect to the semiconductor substrate 10). The source side
columnar semiconductor layer 24 is formed on the diffusion layer
11. The source side gate insulating layer 23 is configured by
silicon oxide (SiO.sub.2). The source side columnar semiconductor
layer 24 is configured by polysilicon (poly-Si).
[0063] Expressing the above-described configuration of the source
side select transistor layer 20 in other words, the source side
conductive layer 21 is formed to surround the source side columnar
semiconductor layer 24 with the source side gate insulating layer
23 interposed therebetween.
[0064] The memory transistor layer 30 includes word line conductive
layers 31a-31d stacked sequentially on the source side select
transistor layer 20 with insulating layers interposed therebetween,
as shown in FIGS. 4A and 4B. The word line conductive layers
31a-31d function, respectively, as the gates of the memory
transistors MTr1-MTr4 and as the word lines WL1-WL4.
[0065] The word line conductive layers 31a-31d are formed to extend
two-dimensionally in the row direction and the column direction (in
a plate-like shape) over the plurality of memory blocks BK. The
word line conductive layers 31a-31d are configured by polysilicon
(poly-Si).
[0066] In addition, as shown in FIGS. 4A and 4B, the memory
transistor layer 30 includes a memory hole 32. The memory hole 32
is formed to penetrate the word line conductive layers 31a-31d. The
memory holes 32 are formed in a matrix in the row direction and the
column direction. The memory hole 32 is formed at a position
aligning with the source side hole 22.
[0067] Further, as shown in FIGS. 4A and 4B, the memory transistor
layer 30 includes a memory gate insulating layer 33 and a memory
columnar semiconductor layer 34. The memory columnar semiconductor
layer 34 functions as a body (channel) of the memory transistors
MTr1-MTr4.
[0068] The memory gate insulating layer 33 is formed with a certain
thickness on a side wall of the memory hole 32. The memory columnar
semiconductor layer 34 is formed to be in contact with a side
surface of the memory gate insulating layer 33 and to fill the
memory hole 32. The memory columnar semiconductor layer 34 is
formed in a column shape extending in the stacking direction. The
memory columnar semiconductor layer 34 is formed having its lower
surface in contact with an upper surface of the source side
columnar semiconductor layer 24.
[0069] A configuration of the memory gate insulating layer 33 is
now described in detail with reference to FIG. 5. FIG. 5 is an
enlarged view of FIG. 4A. The memory gate insulating layer 33
includes, from a side surface of the memory hole 32 side to a
memory columnar semiconductor layer 34 side, a block insulating
layer 33a, a charge storage layer 33b, and a tunnel insulating
layer 33c. The charge storage layer 33b is configured to be capable
of storing a charge.
[0070] As shown in FIG. 5, the block insulating layer 33a is formed
with a certain thickness on a side wall of the memory hole 32. The
charge storage layer 33b is formed with a certain thickness on a
side wall of the block insulating layer 33a. The tunnel insulating
layer 33c is formed with a certain thickness on a side wall of the
charge storage layer 33b. The block insulating layer 33a and the
tunnel insulating layer 33c are configured by silicon oxide
(SiO.sub.2). The charge storage layer 33b is configured by silicon
nitride (SiN). The memory columnar semiconductor layer 34 is
configured by polysilicon (poly-Si).
[0071] Expressing the above-described configuration of the memory
transistor layer 30 in other words, the word line conductive layers
31a-31d are formed to surround the memory columnar semiconductor
layer 34 with the memory gate insulating layer 33 interposed
therebetween.
[0072] The drain side select transistor layer 40 includes a drain
side conductive layer 41, as shown in FIGS. 4A and 4B. The drain
side conductive layer 41 functions as the gate of the drain side
select transistor SDTr and as the drain side select gate line
SGD.
[0073] The drain side conductive layer 41 is stacked on the memory
transistor layer 30 via an insulating layer. The drain side
conductive layer 41 is formed directly above the memory columnar
semiconductor layer 34. The drain side conductive layer 41 is
formed in stripes in each of the memory blocks BK, the stripes
extending in the row direction and having a certain pitch in the
column direction. The drain side conductive layer 41 is configured
by, for example, polysilicon (poly-Si).
[0074] In addition, as shown in FIGS. 4A and 4B, the drain side
select transistor layer 40 includes a drain side hole 42. The drain
side hole 42 is formed to penetrate the drain side conductive layer
41. The drain side holes 42 are formed in a matrix in the row
direction and the column direction. The drain side hole 42 is
formed at a position aligning with the memory hole 32.
[0075] Further, as shown in FIGS. 4A and 4B, the drain side select
transistor layer 40 includes a drain side gate insulating layer 43
and a drain side columnar semiconductor layer 44. The drain side
columnar semiconductor layer 44 functions as a body (channel) of
the drain side select transistor SDTr.
[0076] The drain side gate insulating layer 43 is formed with a
certain thickness on a side wall of the drain side hole 42. The
drain side columnar semiconductor layer 44 is formed to be in
contact with the drain side gate insulating layer 43 and to fill
the drain side hole 42. The drain side columnar semiconductor layer
44 is formed in a column shape to extend in the stacking direction.
The drain side columnar semiconductor layer 44 is formed having its
lower surface in contact with an upper surface of the memory
columnar semiconductor layer 34. The drain side gate insulating
layer 43 is configured by silicon oxide (SiO.sub.2). The drain side
columnar semiconductor layer 44 is configured by polysilicon
(poly-Si). Moreover, the drain side columnar semiconductor layer 44
has its lower portion 44a configured by an intrinsic semiconductor
and its upper portion 44b configured by an N+ type
semiconductor.
[0077] Expressing the above-described configuration of the drain
side select transistor layer 40 in other words, the drain side
conductive layer 41 is formed to surround the drain side columnar
semiconductor layer 44 with the drain side gate insulating layer 43
interposed therebetween.
[0078] The diode layer 50 includes an ohmic contact layer 51, a P
type semiconductor layer 52, and an N type semiconductor layer 53,
as shown in FIGS. 4A and 4B. The ohmic contact layer 51 causes
ohmic contact between the P type semiconductor layer 52 and the
drain side columnar semiconductor layer 44. The P type
semiconductor layer 52 and the N type semiconductor layer 53
function as the diode DI.
[0079] The ohmic contact layer 51 is formed in a column shape
extending in the stacking direction from an upper surface of the
drain side columnar semiconductor layer 44. The P type
semiconductor layer 52 is formed in a column shape extending in the
stacking direction from an upper surface of the ohmic contact layer
51. The N type semiconductor layer 53 is formed in a column shape
extending in the stacking direction from an upper surface of the P
type semiconductor layer 52. The P type semiconductor layer 52 is
configured by polysilicon doped with a P type impurity. The N type
semiconductor layer 53 is configured by polysilicon doped with an N
type impurity.
[0080] The wiring layer 60 includes a bit layer 61, as shown in
FIGS. 4A and 4B. The bit layer 61 functions as the bit line BL.
[0081] The bit layer 61 is formed to be in contact with an upper
surface of the N type semiconductor layer 53. The bit layer 61 is
formed to extend in the column direction and having a certain pitch
in the row direction. The bit layer 61 is configured by a metal
such as tungsten.
[0082] [First Erase Operation]
[0083] Next, a first erase operation in the nonvolatile
semiconductor memory device in accordance with the first embodiment
is described with reference to FIG. 6.
[0084] In the example shown in FIG. 6, memory block BK_1 is assumed
to be selected as object of the erase operation. On the other hand,
memory block BK_2, which shares bit lines BL with memory block
BK_1, is not an object of the erase operation, and erase of data
retained in memory block BK_2 is prohibited.
[0085] During the erase operation, a voltage Vera (for example,
about 17 V) is applied to bit line BL1. In selected memory block
BK_1, source line SL1 is applied with voltage Vera, and drain side
select gate lines SGD and source side select gate lines SGS are
applied with a voltage Vera-.DELTA.V that is smaller than voltage
Vera by .DELTA.V (for example, about 3 V). On the other hand, in
unselected memory block BK_2, source line SL2 is applied with 0 V,
and drain side select gate lines SGD and source side select gate
lines SGS are applied, respectively, with 0 V and a power supply
voltage Vdd (=1.2 V).
[0086] Specifically, as shown in FIG. 6, in selected memory block
BK_1, voltage Vera of bit line BL1 is higher than voltage
Vera-.DELTA.V of gates of drain side select transistors SDTr by an
the voltage .DELTA.V. In addition, voltage Vera of source line SL1
is higher than voltage Vera-.DELTA.V of gates of source side select
transistors SSTr by the voltage .DELTA.V. This causes a GIDL
current (refer to symbol "E11") to occur proximal to gates of
source side select transistors SSTr and drain side select
transistors SDTr in memory block BK_1. Moreover, in memory block
BK_1, holes caused by the GIDL current flow into the body of memory
transistors MTr1-MTr4, causing a voltage of the body of memory
transistors MTr1-MTr4 to rise.
[0087] Subsequently, a voltage of the gates of the memory
transistors MTr1-MTr4 is set to 0 V, in other words, is set lower
than the voltage of the body of memory transistors MTr1-MTr4. As a
result, a high voltage is applied to the charge storage layer of
memory transistors MTr1-MTr4, whereby the erase operation on memory
block BK_1 is executed.
[0088] On the other hand, in memory block BK_2, a voltage of gates
of the drain side select transistors SDTr is set to 0 V. That is, a
voltage Vera of bit line BL1 is set higher than a voltage (0 V) of
gates of the drain side select transistors SDTr by Vera. In
addition, source line SL2 is set to 0 V, a voltage of gates of the
source side select transistors SSTr is set to the power supply
voltage Vdd (for example, 1.2 V). That is, a voltage (Vdd) of gates
of the source side select transistors SSTr is set higher than a
voltage (0 V) of source line SL2 by Vera. As a result, occurrence
of the GIDL current is prohibited, and the source side select
transistors SSTr are turned on.
[0089] Now, gates of the memory transistors MTr1-MTr4 are connected
commonly between memory blocks BK_1 and BK_2 by the word lines
WL1-WL4. As a result, gates of memory transistors MTr1-MTr4 have
their voltage set to 0 V in memory block BK_2 as well as in memory
block BK_1.
[0090] However, in memory block BK_2, the voltage of the body of
memory transistors MTr1-MTr4 is not boosted by the GIDL current.
Moreover, in memory block BK_2, the source side select transistors
SSTr are turned on, hence, even if the voltage of the body of
memory transistors MTr1-MTr4 rises due to effects of leak current
and so on, that voltage is discharged to source line SL2 via those
turned-on source side select transistors SSTr (refer to symbol
"E12").
[0091] Furthermore, the first embodiment includes the diode DI.
This may suppress a current flowing from bit line BL1 into the body
of memory transistors MTr1-MTr4 in unselected memory block BK_2
(refer to symbol "E13").
[0092] As is clear from the above, in memory block BK_2, the
voltage of the body of memory transistors MTr1-MTr4 is retained at
low voltage. As a result, a high voltage is not applied to the
charge storage layer in those memory transistors MTr1-MTr4, hence,
the first embodiment may suppress incorrect erase in unselected
memory block BK_2.
[0093] A specific operation procedure when executing the
above-described erase operation is described with reference to a
timing chart in FIG. 7. First, at time t11 in FIG. 7, the voltage
of bit line BL1 and voltage of source line SL1 are raised to erase
voltage Vera (for example, 17V). Additionally, at time t11, the
voltage of source side select gate lines SGS1,1-SGS1,k and voltage
of drain side select gate lines SGD1,1-SGD1,k are raised to voltage
Vera-.DELTA.V (for example, 14V). This causes the GIDL current to
occur in memory block BK_1.
[0094] On the other hand, at time t11, the voltage of source line
SL2 is maintained at 0 V. Additionally, at time t11, the voltage of
source side select gate lines SGS2,1-SGS2,k is raised to the power
supply voltage Vdd, and the voltage of drain side select gate lines
SGD2,1-SGD2,k is maintained at 0 V. As a result, the GIDL current
does not occur in memory block BK_2, and the source side select
transistors SSTr are turned on.
[0095] Next, at time t12, the voltage of word lines WL1-WL4 is
lowered to 0 V. This causes data in the memory transistors
MTr1-MTr4 in memory block BK_1 to be erased, and data in the memory
transistors MTr1-MTr4 in memory block BK_2 to be retained (not
erased).
[0096] [First Write Operation]
[0097] Next, a first write operation in the nonvolatile
semiconductor memory device in accordance with the first embodiment
is described with reference to FIGS. 8A and 8B.
[0098] In FIGS. 8A and 8B, an example is described of the case in
which a cell unit MU (hereafter referred to as selected cell unit
sMU) in memory block BK_1 is selected as write target. Description
proceeds assuming write to be performed on memory transistor MTr3
(hereafter referred to as selected memory transistor sMTr3) in the
selected cell unit sMU.
[0099] Specifically, as shown in FIG. 8A, in the case of writing
"0" data to selected memory transistor sMTr3, the voltage of bit
line BL1 is set to 0 V. In contrast, in the case of retaining "1"
data in selected memory transistor sMTr3, the voltage of bit line
BL1 is set to the power supply voltage Vdd (=1.2 V). Source lines
SL1 and SL2 are set to the power supply voltage Vdd.
[0100] Then, the memory transistors MTr1-MTr4 included in memory
blocks BK_1 and BK_2 are applied with a pass voltage Vpass (for
example, 10 V) at their gates and turned on. The source side select
transistors SSTr are applied with a voltage Vdd+Vt at their gates
and turned on. This causes the voltage of the body of the memory
transistors MTr1-MTr4 included in memory blocks BK_1 and BK_2 to be
charged to the power supply voltage Vdd via source lines SL1 and
SL2 (refer to symbol "W11"). That is, the voltage of the body of
the memory transistors MTr1-MTr4 included in memory blocks BK_1 and
BK_2 is set to not less than the power supply voltage Vdd that may
be applied to bit line BL1 during the write operation. Moreover,
after a certain time, the source side select transistors SSTr are
turned off again.
[0101] Subsequently, as shown in FIG. 8B, the drain side select
transistors SDTr included in selected cell unit sMU are supplied
with voltage Vdd+Vt at their gates. In the case that 0 V is
supplied to bit line BL1 to write "0" data, the drain side select
transistors SDTr are turned on, whereby the voltage of the body of
the memory transistors MTr1-MTr4 included in selected cell unit sMU
are discharged to the same 0 V as bit line BL1 (refer to symbol
"W12"). On the other hand, in the case that the power supply
voltage Vdd is supplied to bit line BL1 to retain "1" data, the
drain side select transistors SDTr remain turned off, hence, the
body of the memory transistors MTr1-MTr4 included in selected cell
unit sMU is not discharged but set to a floating state, whereby its
potential is retained at the power supply voltage Vdd.
[0102] Then, a voltage of the gate of selected memory transistor
sMTr3 is set to a program voltage Vprg (=18 V). As a result, when
writing "0" data, the voltage of the body of selected memory
transistor sMTr3 is discharged to 0 V, hence, a high voltage is
applied to the charge storage layer of selected memory transistor
sMTr3, whereby the write operation on selected memory transistor
sMTr3 is executed. On the other hand, when retaining "1" data, the
body of selected memory transistor sMTr3 is set to the floating
state and its potential retained at the power supply voltage Vdd,
hence a high voltage is not applied to the charge storage layer of
selected memory transistor sMTr3, whereby the write operation on
selected memory transistor sMTr3 is not executed.
[0103] Now, gates of the memory transistors MTr1-MTr4 are connected
commonly by the word lines WL1-WL4 over a plurality of the cell
units MU. If the voltage of the gate of selected memory transistor
sMTr3 is set to the program voltage Vprg, the gates of memory
transistors MTr3 included in unselected cell units MU are also
applied with the program voltage Vprg. However, the voltage of the
body of memory transistors MTr1-MTr4 included in unselected cell
units MU is set to the floating state by the turned-off drain side
select transistors SDTr and source side select transistors SSTr. As
a result, a high voltage is not applied to the charge storage layer
of memory transistors MTr3 included in unselected cell units MU,
whereby the write operation is not executed on those memory
transistors.
[0104] A specific operation procedure when executing the
above-described write operation is described with reference to a
timing chart in FIG. 9. First, at time t21 in FIG. 9, the voltage
of source lines SL1 and SL2 is raised to the power supply voltage
Vdd, and the voltage of source side select gate lines SGS1,1-SGS1,k
and SGS2,1-SGS2,k is raised to voltage Vdd+Vt. Additionally, at
time t21, the voltage of word lines WL1-WL4 is raised to the pass
voltage Vpass. This causes the source side select transistors SSTr
in memory block BK_1 to be turned on, whereby the voltage of the
body of memory transistors MTr1-MTr4 attains the power supply
voltage Vdd. Further, at time t21, bit line 3L1 is lowered to 0 V
during a "0" data write, and is raised to the power supply voltage
Vdd during a "1" data retention.
[0105] Next, at time t22, the voltage of source side select gate
lines SGS1,1-SGS1,k and SGS2,1-SGS2,k is lowered to 0 V. This
causes the source side select transistors SSTr in memory block BK_1
to be turned off.
[0106] Subsequently, at time t23, the voltage of drain side select
gate line SGD1,2 is raised to voltage Vdd-Vt. This causes the drain
side select transistor SDTr in selected cell unit sMU only to be
turned on.
[0107] Next, at time t24, the voltage of word line WL3 is raised to
program voltage Vprog (for example, 18 V). This causes the write
operation on selected memory transistor sMTr3 to be executed.
[0108] [First Read Operation]
[0109] Next, a first read operation in the nonvolatile
semiconductor memory device in accordance with the first embodiment
is described with reference to FIG. 10. In the example shown in
FIG. 10, the read operation is executed on selected memory
transistor sMTr3.
[0110] Specifically, as shown in FIG. 10, bit line BL1 is set to 0
V. Source line SL1 is set to power supply voltage Vdd, and source
line SL2 is set to 0 V. The drain side select transistors SDTr and
source side select transistors SSTr included in selected cell unit
sMU is applied with voltage Vdd+Vt from the select gate lines
SGD1,2 and SGS1,2, and are turned on. Moreover, the gates of memory
transistors MTr1, MTr2, and MTr4 are applied with pass voltage
Vpass, and the gates of memory transistors MTr3 are applied with a
read voltage Vread (Vread<Vpass). As a result, in the case that
selected memory transistor sMTr3 is retaining "1" data, a current
flows from source line SL1 to bit line BL1 (refer to symbol "R1"),
whereby bit line BL1 is charged to power supply voltage Vdd. On the
other hand, in the case that selected memory transistor sMTr3 is
retaining "0" data (in the case that a threshold value is high), a
current does not flow from source line SL1 to bit line BL1 (refer
to symbol "R2"), whereby bit line BL1 is not charged but retains 0
V. Further, detection of the voltage of bit line BL1 is performed,
whereby the read operation on selected memory transistor sMTr3 is
executed.
[0111] A specific operation procedure when executing the
above-described read operation is described with reference to a
timing chart in FIG. 11. First, at time t31 in FIG. 11, the voltage
of source line SL1 is raised to the power supply voltage Vdd, and
the voltage of source side select gate line SGS1,2 and voltage of
drain side select gate line SGD1,2 are raised to voltage Vdd+Vt.
Additionally, at time t31, the voltage of word lines WL1, WL2, and
WL4 is raised to the pass voltage Vpass. This causes the memory
transistors MTr1,2,4, source side select transistors SSTr, and
drain side select transistors SDTr to be turned on.
[0112] Next, at time t32, the voltage of word line WL3 is raised to
the read voltage Vread. Subsequently, detection of the voltage of
bit line BL1 is performed, whereby the read operation on selected
memory transistor sMTr3 is executed.
[0113] [Second Erase Operation]
[0114] Next, a second erase operation in the nonvolatile
semiconductor memory device in accordance with the first embodiment
is described with reference to FIG. 12. As shown in FIG. 12, this
second erase operation differs from the first erase operation in
having source line SL2, drain side select gate lines SGD2,1-SGD2,k,
and source side select gate lines SGS2,1-SGS2,k raised to a voltage
V1 (=5 V) at time t11.
[0115] The above-described voltage V1 causes a voltage applied to
the gate insulating layer of source side select transistors SSTr
and drain side select transistors SDTr in unselected memory block
BK_2 during the above-described second erase operation to be lower
than that during the first erase operation. The second erase
operation therefore may suppress damage to the source side select
transistors SSTr and drain side select transistors SDTr even if
those transistors have a low breakdown voltage.
[0116] [Second Write Operation]
[0117] Next, a second write operation in the nonvolatile
semiconductor memory device in accordance with the first embodiment
is described with reference to FIG. 13. Now, as shown by the symbol
"W11" in FIG. 8A, the first write operation executes a charging
process for charging the body of memory transistors MTr1-MTr4 in
memory blocks BK_1 and BK_2 to the power supply voltage Vdd. In
contrast, the second write operation omits from the first write
operation this charging process of the body to the power supply
voltage Vdd. That is, as shown in FIG. 13, in the second write
operation, at time t21, the source side select gate lines
SGS1,1-SGS1,k and SGS2,1-SGS2,k are retained at 0 V. Even in such a
second write operation, prior to execution of the second write
operation, drain side select gate line SGD1,2 rises from 0 V to
Vdd+Vt, whereby the body of the cell unit MU connected to bit lines
BL applied with the power supply voltage Vdd are charged to the
power supply voltage Vdd to be set to the floating state, and a
similar write operation can be executed.
[0118] [Second Read Operation]
[0119] Next, a second read operation in the nonvolatile
semiconductor memory device in accordance with the first embodiment
is described with reference to FIG. 14. In the second read
operation, the voltage applied to gates of memory transistors
MTr1,2,4 in selected cell unit sMU and the voltage applied to the
gate of selected memory transistor sMTr3 differ from those of the
first read operation. That is, as shown in FIG. 14, at time t31,
the word line WL3 is retained at 0 V, and word lines WL1, WL2, and
WL4 are raised to read voltage Vread.
[0120] [Method of Manufacturing]
[0121] Next, a method of manufacturing the nonvolatile
semiconductor memory device in accordance with the first embodiment
is described with reference to FIGS. 15-18.
[0122] First, as shown in FIG. 15, the source side select
transistor layer 20, memory transistor layer 30, and drain side
select transistor layer 40 are formed. Now, an upper portion of the
drain side hole 42 is not filled but left as is.
[0123] Next, as shown in FIG. 16, the ohmic contact layer 51 is
deposited on an upper portion of the drain side columnar
semiconductor layer 44 in the drain side hole 42. Subsequently, as
shown in FIG. 17, the P type semiconductor layer 52 is deposited on
an upper portion of the ohmic contact layer 51 in the drain side
hole 42. Then, as shown in FIG. 18, the N type semiconductor layer
53 is deposited on an upper portion of the P type semiconductor
layer 52 in the drain side hole 42. The N type semiconductor layer
53 is formed, for example, by depositing polysilicon and then
implanting N+ ions in the polysilicon.
Second Embodiment
Configuration
[0124] Next, a circuit configuration of a memory cell array 1
included in a nonvolatile semiconductor memory device in accordance
with a second embodiment is described with reference to FIG. 19. As
shown in FIG. 19, the second embodiment differs from the first
embodiment in having the diode DI provided such that its forward
bias direction is from the bit line BL side to the drain side
select transistor SDTr side. Note that in the second embodiment,
identical symbols are assigned to configurations similar to those
of the first embodiment, and descriptions thereof are omitted.
[0125] The above-described circuit configuration of the nonvolatile
semiconductor memory device is realized by a stacking structure
shown in FIG. 20. FIG. 20 is a cross-sectional view of the
nonvolatile semiconductor memory device in accordance with the
second embodiment.
[0126] As shown in FIG. 20, a configuration of a diode 50a in the
second embodiment differs from that of the first embodiment. The
diode 50a includes an N type semiconductor layer 54 and a P type
semiconductor layer 55. The N type semiconductor layer 54 is formed
in a column shape to extend in the stacking direction from the
upper surface of the drain side columnar semiconductor layer 44.
The P type semiconductor layer 55 is formed in a column shape to
extend in the stacking direction from an upper surface of the N
type semiconductor layer 54. In addition, the P type semiconductor
layer 55 is formed to have its upper surface in contact with a
lower surface of the bit layer 61. The N type semiconductor layer
54 is configured by polysilicon doped with an N type impurity, and
the P type semiconductor layer 55 is configured by polysilicon
doped with a P type impurity.
[0127] [Erase Operation]
[0128] Next, an erase operation in the nonvolatile semiconductor
memory device in accordance with the second embodiment is described
with reference to FIG. 21.
[0129] As shown in FIG. 21, in the erase operation of the second
embodiment, it is only in the vicinity of gates of source side
select transistors SSTr in memory block BK_1 that the GIDL current
is generated (refer to symbol "E21"); in the vicinity of gates of
drain side select transistors SDTr in memory block BK_1, occurrence
of the GIDL current is prohibited. The erase operation in the
second embodiment differs in this regard from the erase operation
in the first embodiment. Furthermore, the second embodiment
includes a diode DI connected in a reverse direction to that of the
first embodiment. This may suppress the current flowing from
selected memory block BK_1 into bit line BL1 (refer to symbol
"E22"). Consequently, no leak current flows in memory block BK_2.
The above allows the erase operation in the second embodiment to
suppress incorrect erase in unselected memory block BK_2.
[0130] As shown in FIG. 22, in contrast to the first embodiment,
when executing the above-described erase operation, at time t11,
bit line BL1 is retained at 0 V, and drain side select gate lines
SGD2,1-SGD2,k and source side select gate lines SGS2,1-SGS2,k are
retained at 0 V.
[0131] [Write Operation]
[0132] Next, a write operation in the nonvolatile semiconductor
memory device in accordance with the second embodiment is described
with reference to FIGS. 23A and 23B.
[0133] In FIGS. 23A and 23B, an example is described assuming write
to be performed on memory transistor MTr3 in selected cell unit sMU
in memory block BK_1.
[0134] The write operation in the nonvolatile semiconductor memory
device in accordance with the second embodiment is similar to that
of the first embodiment in having the voltage applied to bit line
BL1 set to 0 V or the power supply voltage Vdd (=1.2 V). However,
as shown in FIG. 23A, prior to start of the write operation, it has
source line SL1 applied with a negative voltage -VSG, and differs
from the first embodiment in this respect.
[0135] Source side select transistors SSTr in memory block BK_1 are
applied with 0 V at their gates, whereby the body of cell units MU
in memory block BK_1 is once charged to the negative voltage
-VSG.
[0136] On the other hand, drain side select transistors SDTr in
memory block BK_1 are applied with -VSG from the start at their
gates, whereby, while the body of cell units MU in memory block
BK_1 is being charged to the negative voltage -VSG, the drain side
select transistors SDTr in memory block BK_1 are maintained turned
off.
[0137] Subsequently, in the write operation stage, as shown in FIG.
23B, source line SL1 has its potential raised from the negative
voltage -VSG to 0 V, and drain side select gate line SGD1,2
connected to selected cell unit sMU is applied with power supply
voltage Vdd. This causes a potential of the body of selected cell
unit sMU to become 0 V or the power supply voltage Vdd (floating
state) according to the potential applied to bit line BL1. In
addition, drain side select gate lines SGD1,1 and SGD1,3-1,k
connected to unselected cell units MU in selected memory block BK_1
are applied with 0 V, whereby the body of the unselected cell units
MU is charged to 0 V or the power supply voltage Vdd to be set to
the floating state. Hereafter, the write operation on selected
memory block BK_1 is executed in a similar manner to the first
embodiment.
[0138] Note that in unselected memory block BK_2, drain side select
gate lines SGD2,1-2,k are maintained at 0 V throughout, and source
side select gate lines SGS2,1-2,k and source line SL2 are
maintained at the power supply voltage Vdd throughout.
[0139] FIG. 24 shows a specific timing chart of the above-described
operation. First, at time t21 in FIG. 24, source line SL1 and drain
side select gate lines SGD1,1-SGD1,k are lowered to the negative
voltage -VSG. This causes source side select transistors SSTr in
memory block BK_1 to be turned on. Further, the voltage of the body
of memory transistors MTr1-MTr4 included in memory block BK_1 is
discharged to the same negative voltage -VSG as source line SL1.
Additionally, at time t21, word lines WL1-WL4 are raised to the
pass voltage Vpass.
[0140] Next, at time t22, source line SL1 and drain side select
gate lines SGD1,1-SGD1,k are raised to 0 V. Subsequently, at time
t23, drain side select gate line SGD1,2 is raised to voltage
Vdd+Vt. This causes the drain side select transistor SDTr included
in selected cell unit sMU to be turned on, whereby the voltage of
the body of memory transistors MTr1-MTr4 included in selected cell
unit sMU becomes 0 V or the power supply voltage Vdd (floating
state).
[0141] Then, at time t24, word line WL3 is raised to the program
voltage Vprog. This causes the write operation on selected memory
transistor sMTr3 to be executed.
[0142] [Read Operation]
[0143] A read operation in the nonvolatile semiconductor memory
device in accordance with the second embodiment is similar to that
of the first embodiment, and description thereof is thus
omitted.
Third Embodiment
Configuration
[0144] Next, a stacking structure of a nonvolatile semiconductor
memory device in accordance with a third embodiment is described
with reference to FIG. 25. Note that in the third embodiment,
identical symbols are assigned to configurations similar to those
of the first and second embodiments, and descriptions thereof are
omitted.
[0145] As shown in FIG. 25, the third embodiment includes a diode
layer 50b having a stacking structure substantially similar to that
of the first embodiment. The diode layer 50b further includes a P
type semiconductor layer 56 configured to extend in a column shape
in the stacking direction from the upper surface of the N type
semiconductor layer 53. This structure allows a bi-directional
diode to be formed as the diode DI.
Fourth Embodiment
Configuration
[0146] Next, a stacking structure of a nonvolatile semiconductor
memory device in accordance with a fourth embodiment is described
with reference to FIG. 26. Note that in the fourth embodiment,
identical symbols are assigned to configurations similar to those
of the first through third embodiments, and descriptions thereof
are omitted.
[0147] As shown in FIG. 26, the fourth embodiment includes a diode
layer 50c having a stacking structure substantially similar to that
of the second embodiment. The diode layer 50c further includes an N
type semiconductor layer 57 configured to extend in a column shape
in the stacking direction from the upper surface of the P type
semiconductor layer 55. This structure allows a bi-directional
diode to be formed as the diode DI.
Fifth Embodiment
[0148] Next, a stacking structure of a nonvolatile semiconductor
memory device in accordance with a fifth embodiment is described
with reference to FIG. 27. Note that in the fifth embodiment,
identical symbols are assigned to configurations similar to those
of the first embodiment, and descriptions thereof are omitted.
[0149] The nonvolatile semiconductor memory device in accordance
with the fifth embodiment differs greatly from the above-described
embodiments in including a U-shaped memory semiconductor layer 84
shown in FIG. 27 in place of the I-shaped memory columnar
semiconductor layer 34 of the above-described embodiments.
[0150] As shown in FIG. 27, the nonvolatile semiconductor memory
device in accordance with the fifth embodiment includes, stacked
sequentially on the semiconductor substrate 10, a back gate layer
70, a memory transistor layer 80, a select transistor layer 90, a
diode layer 100, and a wiring layer 110. The memory transistor
layer 80 functions as the memory transistors MTr. The select
transistor layer 90 functions as the drain side select transistor
SDTr and as the source side select transistor SSTr. The diode layer
100 functions as the diode DI. The wiring layer 110 functions as
the source line SL and as the bit line BL.
[0151] The back gate layer 70 includes a back gate conductive layer
71, as shown in FIG. 27. The back gate conductive layer 71 is
formed to extend two-dimensionally in the row direction and the
column direction parallel to the substrate 10. The back gate
conductive layer 71 is configured by polysilicon (poly-Si).
[0152] The back gate layer 70 includes a back gate hole 72, as
shown in FIG. 27. The back gate hole 72 is formed to dig out the
back gate conductive layer 71. The back gate hole 72 is formed in a
substantially rectangular shape having the column direction as a
long direction as viewed from an upper surface. The back gate holes
72 are formed in a matrix in the row direction and the column
direction.
[0153] The memory transistor layer 80 is formed in a layer above
the back gate layer 70, as shown in FIG. 27. The memory transistor
layer 80 includes word line conductive layers 81a-81d. Each of the
word line conductive layers 81a-81d functions as the word line WL
and as the gate of the memory transistor MTr.
[0154] The word line conductive layers 81a-81d are stacked
sandwiching interlayer insulating layers. The word line conductive
layers 81a-81d are formed extending with the row direction as a
long direction and having a certain pitch in the column direction.
The word line conductive layers 81a-81d are configured by
polysilicon (poly-Si).
[0155] The memory transistor layer 80 includes a memory hole 82, as
shown in FIG. 27. The memory hole 82 is formed to penetrate the
word line conductive layers 81a-81d and the interlayer insulating
layers. The memory hole 82 is formed to align with a near vicinity
of an end of the back gate hole 72 in the column direction.
[0156] Moreover, the back gate layer 70 and the memory transistor
layer 80 include a memory gate insulating layer 83 and a memory
semiconductor layer 84, as shown in FIG. 27. The memory
semiconductor layer 84 functions as a body of the memory
transistors MTr (memory string MS). The memory gate insulating
layer 83 includes a charge storage layer configured to store a
charge, similarly to the above-described embodiments.
[0157] The memory semiconductor layer 84 is formed to fill the back
gate hole 72 and the memory hole 82. The memory semiconductor layer
84 is formed in a U shape as viewed from the row direction. The
memory semiconductor layer 84 includes a pair of columnar portions
84a extending in the perpendicular direction with respect to the
substrate 10, and a joining portion 84b configured to join lower
ends of the pair of columnar portions 84a. The memory semiconductor
layer 84 is configured by polysilicon (poly-Si).
[0158] Expressing the above-described configuration of the back
gate layer 70 in other words, the back gate conductive layer 71 is
formed to surround the joining portion 84b with the memory gate
insulating layer 83 interposed therebetween. Moreover, expressing
the above-described configuration of the memory transistor layer 80
in other words, the word line conductive layers 81a-81d are formed
to surround the columnar portions 84a with the memory gate
insulating layer 83 interposed therebetween.
[0159] The select transistor layer 90 includes a source side
conductive layer 91a and a drain side conductive layer 91b, as
shown in FIG. 27. The source side conductive layer 91a functions as
the source side select gate line SGS and as the gate of the source
side select transistor SSTr. The drain side conductive layer 91b
functions as the drain side select gate line SGD and as the gate of
the drain side select transistor SDTr.
[0160] The source side conductive layer 91a is formed in a layer
above one of the columnar portions 84a configuring the memory
semiconductor layer 84. The drain side conductive layer 91b is in
the same layer as the source side conductive layer 91a and formed
in a layer above the other of the columnar portions 84a configuring
the memory semiconductor layer 84. The source side conductive layer
91a and the drain side conductive layer 91b are formed in stripes
extending in the row direction and having a certain pitch in the
column direction. The source side conductive layer 91a and the
drain side conductive layer 91b are configured by polysilicon
(poly-Si).
[0161] The select transistor layer 90 includes a source side hole
92a and a drain side hole 92b, as shown in FIG. 27. The source side
hole 92a is formed to penetrate the source side conductive layer
91a. The drain side hole 92b is formed to penetrate the drain side
conductive layer 91b. The source side hole 92a and the drain side
hole 92b are each formed at a position aligning with the memory
hole 82.
[0162] The select transistor layer 90 includes a source side gate
insulating layer 93a, a source side columnar semiconductor layer
94a, a drain side gate insulating layer 93b, and a drain side
columnar semiconductor layer 94b, as shown in FIG. 27. The source
side columnar semiconductor layer 94a functions as a body of the
source side select transistor SSTr. The drain side columnar
semiconductor layer 94b functions as a body of the drain side
select transistor SDTr.
[0163] The source side gate insulating layer 93a is formed with a
certain thickness on a side surface of the source side hole 92a.
The source side columnar semiconductor layer 94a is formed in a
column shape to extend in the perpendicular direction with respect
to the substrate 10 and to be in contact with a side surface of the
source side gate insulating layer 93a and one of upper surfaces of
the pair of columnar portions 84a. The source side gate insulating
layer 93a is configured by silicon oxide (SiO.sub.2). The source
side columnar semiconductor layer 94a is configured by polysilicon
(poly-Si). The source side columnar semiconductor layer 94a has a
lower portion 94aa configured by an intrinsic semiconductor and an
upper portion 94ab configured by an N+ type semiconductor.
[0164] The drain side gate insulating layer 93b is formed with a
certain thickness on a side surface of the drain side hole 92b. The
drain side columnar semiconductor layer 94b is formed in a column
shape to extend in the perpendicular direction with respect to the
substrate 10 and to be in contact with a side surface of the drain
side gate insulating layer 93b and the other of the upper surfaces
of the pair of columnar portions 84a. The drain side gate
insulating layer 93b is configured by silicon oxide (SiO.sub.2).
The drain side columnar semiconductor layer 94b is configured by
polysilicon (poly-Si). The drain side columnar semiconductor layer
94b has a lower portion 94ba configured by an intrinsic
semiconductor and an upper portion 94bb configured by an N+ type
semiconductor.
[0165] The diode layer 100 includes a source side ohmic contact
layer 101a, a source side N type semiconductor layer 102a, a drain
side ohmic contact layer 101b, a drain side P type semiconductor
layer 102b, and a drain side N type semiconductor layer 103b, as
shown in FIG. 27. The drain side P type semiconductor layer 102b
and drain side N type semiconductor layer 103b function as the
diode DI.
[0166] The source side ohmic contact layer 101a is formed in a
column shape extending in the stacking direction from an upper
surface of the source side columnar semiconductor layer 94a. The
source side N type semiconductor layer 102a is formed in a column
shape extending in the stacking direction from an upper surface of
the source side ohmic contact layer 101a. The source side N type
semiconductor layer 102a is configured by polysilicon including an
N type impurity.
[0167] The drain side ohmic contact layer 101b is formed in a
column shape extending in the stacking direction from an upper
surface of the drain side columnar semiconductor layer 94b. The
drain side P type semiconductor layer 102b is formed in a column
shape extending in the stacking direction from an upper surface of
the drain side ohmic contact layer 101b. The drain side N type
semiconductor layer 103b is formed in a column shape extending in
the stacking direction from an upper surface of the drain side P
type semiconductor layer 102b. The drain side P type semiconductor
layer 102b is configured by polysilicon including a P type
impurity, and the drain side N type semiconductor layer 103b is
configured by polysilicon including an N type impurity.
[0168] The wiring layer 110 includes a source layer 111, a plug
layer 112, and a bit layer 113. The source layer 111 functions as
the source line SL. The bit layer 113 functions as the bit line
BL.
[0169] The source layer 111 is formed to extend in the row
direction and to be in contact with an upper surface of the source
side N type semiconductor layer 102a. The bit layer 113 is formed
to extend in the column direction and to be in contact with an
upper surface of the drain side N type semiconductor layer 103b via
the plug layer 112. The source layer 111, the plug layer 112, and
The bit layer 113 are configured by a metal such as tungsten.
[0170] [Method of Manufacturing]
[0171] Next, a method of manufacturing the nonvolatile
semiconductor memory device in accordance with the fifth embodiment
is described with reference to FIGS. 28-32.
[0172] First, as shown in FIG. 28, the back gate layer 70, memory
transistor layer 80, and select transistor layer 90 are formed.
Now, an upper portion of the source side hole 92a and an upper
portion of the drain side hole 92b are not filled but left as
is.
[0173] Next, as shown in FIG. 29, the source side ohmic contact
layer 101a is deposited on an upper portion of the source side
columnar semiconductor layer 94a in the source side hole 92a. In
addition, the drain side ohmic contact layer 101b is deposited on
an upper portion of the drain side columnar semiconductor layer 94b
in the drain side hole 92b.
[0174] Subsequently, as shown in FIG. 30, a source side P type
semiconductor layer 104 is deposited on an upper portion of the
source side ohmic contact layer 101a in the source side hole 92a.
In addition, the drain side P type semiconductor layer 102b is
deposited on an upper portion of the drain side ohmic contact layer
101b in the drain side hole 92b. Next, as shown in FIG. 31, the
source side P type semiconductor layer 104 in the source side hole
92a is removed.
[0175] Subsequently, as shown in FIG. 32, the source side N type
semiconductor layer 102a is deposited on the upper surface of the
source side ohmic contact layer 101a in the source side hole 92a.
In addition, the drain side N type semiconductor layer 103b is
deposited on an upper surface of the drain side P type
semiconductor layer 102b in the drain side hole 92b. The source
side N type semiconductor layer 102a and drain side N type
semiconductor layer 103b are formed, for example, by depositing
polysilicon and then implanting N+ ions in the polysilicon.
Other Embodiments
[0176] While certain embodiments of the inventions 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 methods and systems described herein may be
embodied in a variety of other forms; furthermore, various
omissions, substitutions and changes in the form of the methods and
systems 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 inventions.
* * * * *