JPH05174589A - Nonvolatile semiconductor memory - Google Patents

Abstract

PURPOSE:To provide a NAND cell type EEPROM in which a block can be erased at a high speed. CONSTITUTION:The nonvolatile semiconductor memory comprises a memory cell array in which memory cells having p-type wells formed on an n-type substrate and each having a floating gate and a control gate are arranged in a matrix in such a manner to be electrically rewritable by communicating charge between the floating gate and the well and that a plurality of the cells are connected in series to form a NAND cell to connect a bit line through a selective gate. The memory also comprises data erasing means for applying a ground potential to all control gates in selected plurality of NAND cell blocks 201, 202 and an erasing potential to all control gates in non-selected blocks 203-20n, all selected gates in all the blocks 201-20n and the wells, and means for varying the number of the NAND cell blocks to be selectively erased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonvolatile semiconductor memory device (EEPROM) using an electrically rewritable memory cell having a floating gate and a control gate, and more particularly to an N-type semiconductor memory device.
EEPRO having a memory cell array of AND cell configuration
Regarding M.

[0002]

2. Description of the Related Art As an EEPROM which can be highly integrated, a NAND type EEPROM in which a plurality of memory cells are connected in series is known. One memory cell has a FETMOS structure in which a floating gate and a control gate are laminated on a substrate through an insulating film, and a plurality of memory cells adjacent to each other are connected in series so that their sources and drains are shared. To form a NAND cell. The drain on one end side of the NAND cell is connected to the bit line via the select gate, and the source on the other end side is also connected to the common source line via the select gate. An EEPROM is constructed by arranging a plurality of such memory cells in a matrix. The memory cell array is usually formed in a p-type well formed in an n-type semiconductor substrate.

The operation of this NAND type EEPROM is as follows. Data writing is performed in order from the memory cell farther from the bit line. Explaining the case of the n-channel, a boosted write potential Vpp (about 20 V) is applied to the control gate of the selected memory cell, and the control gate and the select gate of the non-selected memory cell on the bit line side from this are applied. Is applied with an intermediate potential VppM (= about 10V), and 0V (for example, "1") is applied to the bit line according to the data.
Alternatively, an intermediate potential (for example, “0”) is applied. At this time,
The potential of the bit line is transferred to the non-selected memory cell and transmitted to the drain of the selected memory cell. When the data is "1", a high electric field is applied between the floating gate and the drain of the selected memory cell, electrons are tunnel-injected from the drain to the floating gate, and the threshold value moves in the positive direction. When the data is "0", there is no threshold change.

Data erasing has two types of modes: chip erasing and block erasing. Chip erasing is simultaneously performed on all memory cells in the NAND cell. That is, all control gates and select gates are set to Vpp, and the erase potential VppE (= 20) boosted to the p-type well and the n-type substrate.
V) is applied. As a result, in all the memory cells, electrons in the floating gate are emitted to the well, and the threshold value moves in the negative direction.

On the other hand, in the block erase, all control gates in the selected NAND cell block are supplied with the ground potential, all control gates in the non-selected NAND cell block, and all the control gates in all the NAND cell blocks. An erase potential is applied to the p-type well in which the select gate and the memory cell are formed. As a result, in the selected block, electrons in the floating gate are emitted to the well, and erase is performed in block units.

For example, a 4M bit NAND type EEPROM
In, the memory cell is divided into 32 kbits × 128 blocks. The erasing time (the time for applying a high voltage to the p-type well) is about 10 ms, and the erasing time is the same both when erasing by 4 M bits at a time by chip erasing and when erasing only one block (32 k bits).

Therefore, for example, when erasing a block of 1 Mbit, 32 blocks are erased, so 32 × 10 =
It requires an erase time of 320 ms. When erasing a large number of blocks as described above, there is a problem that the erase time is significantly increased as compared with the chip erase.

For data reading, the control gate of the selected memory cell is set to 0V, and the control gates and selection gates of the memory cells in the other selected blocks are set to the power supply potential Vcc.
(= 5V), and it is performed by detecting whether or not a current flows in the selected memory cell.

[0009]

As described above, the conventional N
The AND-type EEPROM has a problem that when erasing a block in a large area, the erasing time is significantly longer than that in the chip erasing. The present invention has been made in view of such a point, and N which enables high-speed block erasing
It is an object to provide an AND cell type EEPROM.

[0010]

The essence of the present invention is to erase not a single NAND cell block but a plurality of NAND cell blocks at the same time as a block erasing method.

That is, according to the present invention (claim 1), a memory cell having a charge storage layer and a control gate is arranged in a matrix on a semiconductor substrate, and electric rewriting is made possible by exchanging charges between the charge storage layer and the substrate. The semiconductor memory device is characterized in that the memory cell is divided into a plurality of blocks to be erased in block units, and means for varying the number of blocks to be erased is provided.

According to the present invention (claim 2), a second conductivity type well is formed in the first conductivity type semiconductor substrate, and memory cells having a charge storage layer and a control gate are arranged in a matrix in the second conductivity type well. Electrically rewriting is made possible by exchanging charges between a charge storage layer and a second conductivity type well, and a plurality of memory cells are connected in series to form a NAND cell and a bit line via a select gate. In a nonvolatile semiconductor memory device including a memory cell array connected to, all control gates in a plurality of selected NAND cell blocks are set to ground potential, and all control gates in a non-selected NAND cell block are Data erasing means for applying an erasing potential to a second conductivity type well in which all selection gates and memory cells in all NAND cell blocks are formed, and selective erasing And having a means for variably setting the number of NAND cell block to.

[0013]

According to the present invention, a plurality of NAND cells are selected, a ground potential is applied to all control gates in the selected NANAD cell block, and all control gates in the non-selected NAND cell block are By applying an erase high voltage to the second conductivity type well in which all select gates and memory cells in all NAND cell blocks are formed, a plurality of NAND cell blocks can be simultaneously erased. Therefore, the blocks can be erased at a higher speed than in the case where the blocks are erased one by one. For example, erasing two blocks at a time can achieve about twice as high speed as erasing one block at a time.

By changing the number of blocks to be selected, one block can be erased or chip can be erased. For this reason, versatility with respect to various OSs (operating systems) is increased.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the N according to the first embodiment of the present invention.
It is a block diagram showing a schematic structure of an AND cell type EEPROM. In the figure, the control circuit unit for controlling the data writing and reading operations is omitted, and only the portion related to the data erasing is shown. The memory cell array 5 includes a p-type well 4 formed on an n-type silicon substrate as described later in detail.
Is formed inside. A block selection circuit 7 for erasing a block is provided for the memory cell array 5. A control gate / select gate control circuit 6 is provided in order to apply an erase potential given from the erase potential control circuit 2 to the control gate and the select gate in each NAND cell block according to the output of the block select circuit 7. ..

The erase potential is generated by the erase potential boosting circuit 1. The erase potential obtained from the erase potential boosting circuit 1 is applied to the control gate and select gate of each NAND cell via the erase potential control circuit 2 and the control gate / select gate control circuit 6. The erase potential from the erase potential control circuit 2 is also applied to the p-type well 4. The potential of the n-type substrate is controlled by the substrate potential control circuit 3. The bit line control circuit 8 operates at the time of writing and reading data, and is disconnected from the memory cell array 5 at the time of erasing data.

2A and 2B are a plan view and an equivalent circuit of one NAND cell portion of the memory cell of the embodiment, and FIG.
(A) and (b) are respectively AA 'and B- in FIG. 2 (a).
It is a B'sectional view. A p-type well 4 is formed in the memory cell array region of the n-type silicon substrate 9, and an NA is formed in a region defined by the element isolation insulating film 12 of the p-type well 4.
An ND cell is formed.

Explaining one NAND cell, in this embodiment, eight memory cells M _{1 to} M ₈ form a NAND cell. Each memory cell has a thin gate insulating film 13 formed on the p-type well 4 by thermal oxidation.
Floating gate 14 made of the first-layer polycrystalline silicon film through
(14 _{1 to} 14 ₈ ) are formed, and the interlayer insulating film 1 is formed thereon.
Control gate 1 of the second layer polycrystalline silicon film via
6 (16 _{1 to} 16 ₈ ) are laminated and formed. The floating gate 14 is a charge storage layer.

The control gate 16 of each memory cell is continuously arranged as a control gate line CG (CG1 to CG8) for the NAND cells arranged in the lateral direction, and this normally becomes a word line. The n-type layer 11 which is the source / drain diffusion layer of the memory cell is shared by adjacent ones, and eight memory cells M1 to M8 are connected in series. These 8
Select gates S1 and S2 are provided on the drain side and the source side of each memory transistor. The gate insulating film of these select gates is usually formed to be thicker than the memory cell portion, and has a two-layer gate electrode 14 formed thereon.
₉ , 16 ₉ and 14 ₁₀ , 16 ₁₀ are formed. These two layers of gate electrodes are in contact with each other at a predetermined interval and are continuously arranged in the direction of the control gate line CG to form select gate lines SG1 and SG2.

The CVD insulating film 17 is formed on the substrate on which the elements are formed.
And the bit line 18 is arranged on this. The bit line 18 is in contact with the drain diffusion layer of one select gate S1. The source diffusion layer of the other select gate S2 usually has a plurality of NAs as a common source line.
It is arranged commonly to the ND cells. Figure 4 shows such an NA
The equivalent circuit of a memory cell array in which ND cells are arranged in a matrix is shown.

An outline of block erasing in this embodiment will be described with reference to FIG. The memory cell array as shown in FIG. 5, a plurality of NAND cell block 20 (20 ₁ to
20 _n ). Assuming that the first cell block 20 ₁ and the second NAND cell block 20 _{2 from the top} are selected in the erase mode, the erase potential VppE (= 20V) is respectively applied to the p-type well and the n-type substrate in which the memory cell array is formed. Is applied and N selected at the same time
0V is applied to all the control gates in the AND cell blocks 20 ₁ and 20 ₂ . And the selected NAND
The erase potential VppE is applied to all the select gates in the cell block and the non-selected NAND cell block and all the control gates in the non-selected NAND cell block. All bit lines are floating.

As a result, the electrons of the floating gates of all the memory cells in the selected NAND cell blocks 20 ₁ and 20 ₂ are discharged to the p-type wells, and the blocks 20 ₁ and 20 2
The data of ₂ will be erased. The specific configuration and operation of each unit of FIG. 1 for performing the block erase as described above will be described in detail below.

FIG. 6 shows a specific configuration of the block selection circuit 7 and the control gate / selection gate control circuit 6 of FIG. 1 for one NAND cell block 20i. In the block selection circuit 7, a NAND gate G1 which takes the logic of the row decoder enable signal RDENB and the address signal ai is a basic circuit, and the node N1 becomes "H" level in the selected block.

The signal at the node N1 is input to the control gate / select gate control circuit 6 via the transfer gate 71 or via the inverter I2 and the transfer gate 72. In this embodiment, the transfer gates 71 and 72 are formed by connecting a PMOS transistor and an NMOS transistor in parallel, and are controlled by the erase control signals ERASE and / ERASE so that either one becomes conductive. That is, at the time of erasing data, the control signal ERASE is at the "H" level, the transfer gate 72 is turned on at this time, and the signal of the node N1 is inverted by the inverter I2 and transmitted to the node N2. That is, in the erase mode, the node N2 of the selected block becomes "L" level. Further, the node N1 of the block selection circuit 7 is connected to the NAN via another transfer gate 73 which is controlled by the control signal READ which becomes "H" level during reading.
It is connected to the source side select gate of the D cell block.

The control gate / selection gate control circuit 6 includes:
Boosted potential VppE obtained from boosted potential control circuit 2 in FIG.
It has a common drive circuit 61 for applying (= 20 V) to each control gate. The drive circuit 61 includes PMOS load transistors Qp1 and Qp2 and an NMOS driver transistor QN.
It is composed of 1 and QN2. The signal of the node N2 is directly input to the gate of one driver transistor QN1 and inverted by the inverter I1 and input to the gate of the other driver transistor QN2. This allows
Complementary outputs are obtained in the drive circuit 61. This drive circuit 6
One of the outputs, ie, the drain output of the driver transistor QN2, is at the "L" level for the selected block in the erase mode, which is the NAND cell block 20.
to the control gate line CG of the control signal CD (CD1 to CD8
) Is used as a control signal for the transfer gates 62 _{1 to} 62 ₈ . Thus, the transfer gate 62 ₁ to 62 ₈ for the selected block is turned off.

The control signal CD is the erase potential V in the erase mode.
ppE. Each of the control gate lines CG has a discharge N
MOS transistors QN8, ..., QN10, ..., QN14,
…, QN16 is provided. The other output of the drive circuit 61, that is, the drain output of the driver transistor QN1 is
It enters into the gate of these discharge transistors as a control signal.

Therefore, in the erase mode selected block in which the output of the block selection circuit 7, that is, the node N2 is at "L" level, the drain output of one driver transistor QN1 of the drive circuit 61 is at "H" level and the other is since the drain output of the driver transistor QN2 is at "L" level, PMOS transistor is "H" level of the transfer gate 62 ₁ to 62 _8, the NMOS transistor becomes all off enters the "L" level. At this time, the discharge transistors QN8, ..., QN10, ..., QN14, ..., QN16 provided on each control gate line CG are turned on, and the control gates of the selected block are all set to 0V. The unselected block, since the node N2 is at "H" level, the output of the drive circuit 61 is reversed to the selected block, the transfer gate 62 ₁ to 62 ₈ is turned on the control signal CD is the control gate lines Given to CG.

In the control gate / select gate control circuit 6, C ² for controlling the select gate line SG1 on the drain side is provided. M
A selection gate drive circuit 63 having an OS inverter configuration is provided. As a power source of the drive circuit 63, a control signal VMSG having an intermediate potential during writing and having the same value as the external power source potential Vcc is used. This drive circuit 6
3 PMOS side clock signal ERASEH is V in erase mode
This signal has the same high potential as ppE. Also, the drain,
Control signals are applied to the select gate lines SG1 and SG2 of both sources.
NMOS transistors QN12 and Q controlled by ERASEH
A control signal VppSG having the same potential as the boosted potential VppE is provided through N17 at the time of erasing. Therefore, in the erase mode, the NMOS transistors QN12 and QN17 are turned on and the control signal VppSG is applied to the select gate lines SG1 and SG2 regardless of the selected block or the non-selected block.

Strictly speaking, select gate lines SG1 and SG2
Is given to the NMOS transistors QN12, QN17
Is VppE-Vth. NAND at the same time as the p-type well in which the memory cell array is formed
A well control signal Vwell which is the erase potential VppE in the erase mode is applied to the common source of the cells.

Here, in this embodiment, a block is selected by an address input to the NAND gate G1 of the block selection circuit 7. 4Mbit NAND type EEPR
Considering OM as an example, the memory cell is divided into 128 blocks, and addresses A12 (A12) to A
It is selected by 7 addresses of 18 (A18).

FIG. 7 shows the configuration of the address buffer section.
Here, a description will be added by setting the chip erase and the block erase for every two blocks. As shown in (b), (A1
2 to A18), the CERASE signal is input, and (a)
As shown in (A12), a BERASE signal is also input to this (A12). When chip erase, CERASE signal is H
Then, both Ai and / Ai of all the addresses become H, the 128 block selecting circuits described above are in the selected state, and the outputs of the NAND gate G1 are all "L".

Even when the block is erased, the BERASE signal is high.
Then, in the address buffer circuit where the BERASE signal is input (A12), both A12 and / A12 are H.
Becomes The remaining Ai and / Ai are selected by a block address signal from the outside of the chip, and as a result, two blocks are selected. That is, unlike the conventional example in which the BERASE signal is not input to the address buffer, it is possible to select two blocks instead of setting only one block in a selected state according to a block address signal input from the outside. ..

Thus, according to this embodiment, (A12)
H of both A12 and / A12 of the address buffer
As a result, the unit of block erasing seen from the outside of the chip is double that of the conventional one. Therefore, the speed of block erasing can be increased as compared with the conventional example in which a plurality of blocks are erased one block at a time. As a matter of course, if (A13) has the same structure as (A12), 4 blocks are selected, and if (A14) has the same structure, 8 blocks are simultaneously selected.

Note that the above-mentioned erasure for each of a plurality of blocks is
It is also possible to set it as a wiring option when the chip is manufactured. The simplest method is to set a plurality of address buffers in the same shape as in (A12) of FIG. 7 and set one of the inputs of the 3-input NOR circuit to the BE of block erase.
Wiring may be performed by selecting whether to input the RASE signal or Vss.

Further, as shown in FIG. 8, the block size can be changed by blowing the fuse 80. When the fuse 80 is cut, the BERASE signal becomes "H".
At the same time, both A12 and / A12 are multiple-selected. Further, as shown in FIG. 9, the block size can be changed by using a bonding option. If the bonding pad 90 is connected to Vcc, A12 and / A12 are multi-selected when the BERASE signal is "H". Also, instead of fuses and bonding options, EEPRO
A method of storing the information of M is also conceivable.

Next, a second embodiment of the present invention will be described. In the first embodiment, the block erase size is variable depending on the shape of the address buffer, but the user himself cannot set the block erase size. However, according to the second embodiment described below, the user himself / herself can select the block erase size according to the situation. In this embodiment, a case will be described in which erasing has three types of erasing modes: chip erasing, erasing every block, erasing every block.

Normally, the chip operates by receiving a command signal from the CPU side, but in this embodiment, it is assumed that the chip has three kinds of commands corresponding to the erase mode. FIG. 10 shows an address buffer in this embodiment.
As shown in (c), the CERASE signal is input to (A12 to A18), and the BERASE2 signal is also input to (A13) as shown in (b). In addition, (A1
In 2), instead of BERASE2 in the configuration of (A13), the BERASE1 signal and BERASE2 are input via the OR gate.

In this embodiment, when the chip erasing command is first fetched, the signal CERASE becomes "H" and A12
Ai and / Ai signals of all addresses from ~ A17 become H,
All blocks are selected and the chips are erased at once. When the erase command for every two blocks is input, the BERASE1 signal goes high. Both A12 and / A12 are H, and two blocks are in the selected state. Further, when the erase command for every four blocks is input, the BERASE2 signal becomes H, and all of A12, / A12, A13, and / A13 become H, and as a result, four blocks are selected.

With this, it becomes possible to change the block erase size by having several kinds of block erase commands. Also in this embodiment, as described in the first embodiment, the wiring option,
The degree of freedom of block erasing can be increased by using a fuse, an EEPROM or the like.

The present invention is not limited to the above-described embodiments, but various modifications can be carried out without departing from the scope of the invention. In the embodiment, the NAND type EEPROM has been described as an example, but the invention can be similarly applied to various nonvolatile memories.

[0042]

As described above, according to the present invention, since a plurality of NAND cell blocks can be erased at the same time, a high speed block erase mode can be achieved. Further, by changing the number of blocks to be selected, one block can be erased or chip can be erased, and versatility for various OSs can be improved.

[Brief description of drawings]

FIG. 1 is a NAND cell type EEPR according to a first embodiment.
The figure which shows the schematic structure of OM,

FIG. 2 is a layout and an equivalent circuit diagram of a NAND cell in the first embodiment,

3 is a sectional view taken along line AA ′ and BB ′ of FIG.

FIG. 4 is an equivalent circuit diagram of the memory cell array in the first embodiment,

FIG. 5 is a diagram for explaining an outline of a block erase operation in the first embodiment,

FIG. 6 is a diagram showing the configurations of a block selection circuit and a gate control circuit unit in the first embodiment;

FIG. 7 is a diagram showing a configuration of an address buffer unit in the first embodiment,

FIG. 8 is a diagram showing a modification of the address buffer unit of the first embodiment,

FIG. 9 is a diagram showing another modification of the address buffer unit of the first embodiment,

FIG. 10 is a diagram showing a configuration of an address buffer unit in the second embodiment.

[Explanation of symbols]

 1 ... Erase potential booster circuit, 2 ... Erase potential control circuit, 3 ... Substrate potential control circuit, 4 ... P-type well, 5 ... Memory cell array, 6 ... Control gate / select gate control circuit, 7 ... Block selection circuit, 8 ... Bit line control circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location H01L 29/792 H01L 29/78 371 (72) Inventor Hideko Ohira Toshiba Komukai Toshiba, Kawasaki City, Kanagawa Prefecture No. 1 in the Town, Toshiba Research Institute, Inc. (72) Inventor Kazunori Ouchi No. 1, Komukai Toshiba Town, Kawasaki City, Kanagawa Prefecture No. 1 in the Toshiba Research Institute, Ltd.

Claims (4)

[Claims] 1. A non-volatile semiconductor memory device in which memory cells having a charge storage layer and a control gate are arranged in a matrix on a semiconductor substrate, and electric rewriting is possible by exchanging charges between the charge storage layer and the substrate. A nonvolatile semiconductor memory device, characterized in that a cell is divided into a plurality of blocks and is configured to be erasable in block units, and means for varying the number of blocks to be erased is provided. 2. A second conductivity type well is formed in a first conductivity type semiconductor substrate, and memory cells having a charge storage layer and a control gate are arranged in a matrix in the second conductivity type well, and the charge storage layer and the second conductivity type are formed. A memory cell array in which a plurality of memory cells are connected in series to form a NAND cell and are connected to a bit line through a select gate In the nonvolatile semiconductor memory device, all the control gates in the selected plurality of NAND cell blocks are set to the ground potential, all the control gates in the non-selected NAND cell blocks, and all the control gates in all the NAND cell blocks. Second selection gate and memory cell are formed
Data erasing means for applying an erasing potential to the conductivity type well,
And a unit for variably setting the number of NAND cell blocks to be selectively erased. 3. The NAND cell block is divided into a plurality of blocks that can be independently erased, and a plurality of the blocks are simultaneously selected and erased by multiple selection of address signals that select the blocks. The nonvolatile semiconductor memory device according to claim 2. 4. A means for variably setting the number of NAND cell blocks to be selectively erased, the bonding or wiring is changed, or the fuse is blown to change the number of addresses to be multi-selected. The nonvolatile semiconductor memory device described.