JPH0878546A - Nonvolatile semiconductor memory - Google Patents

Abstract

PURPOSE: To obtain an EEPROM having such structure and operation as fluctuation in the threshold voltage can be suppressed after writing and erasure without requiring any verify circuit. CONSTITUTION: In an EEPROM wherein a p-well 3 is formed on an n-well 2 formed on a p-type substrate 1 and a plurality of memory cells are arranged in the p-well 3, the memory cell comprises source-drain diffusion layers 4a, 4b formed in the p-well 3 add a floating gate 6 and a control gate laminated on a channel between the source and drain. A data is rewritten by delivering or receiving charges between the floating gate 6 and the p-well 33. A positive voltage is applied to the control gate 8 and 0V is applied between the source and drains 4a, 4b. A negative potential is applied to the p-well 3 to form a depletion region and then a negative potential is applied to the n-well 2 thus injecting carriers into the p-well 3. In the region of the p-well 3, energy is imparted to the carries to produce hot carriers which are then injected into the floating gate 6 thus writing a data.

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, and more particularly to a floating gate (charge storage layer) and a control gate.
The present invention relates to a non-volatile semiconductor memory device (EEPROM) using electrically rewritable memory cells in which memory cells are stacked.

[0002]

2. Description of the Related Art Conventionally, an N-type memory cell having a plurality of memory cells connected in series has been proposed as a highly-integrated EEPROM.
An AND cell type EEPROM is known. One memory cell has a stack gate structure in which a floating gate serving as a charge storage layer and a control gate are stacked on a semiconductor substrate via an insulating film, and a plurality of memory cells are adjacent to each other. Connected in series to share source / drain with N
Construct an AND cell. Such NAND cells are arranged in a matrix to form a memory cell array.

The drains on the one end side of the NAND cells arranged in the column direction of the cell array are commonly connected to the bit lines via the select gates, and the other end side is also a common source line via the select gates. It is connected to the source line. The gate electrode of the control gate of the memory cell and the gate electrode of the selection gate are commonly connected as a control gate line (word line) and a selection gate line in the row direction of the memory cell array.

The operation of this NAND cell type EEPROM is as follows. Data writing is sequentially performed from the memory cell farther from the bit line. In the case of n-channel, a high voltage Vpp (for example, 20V) is applied to the control gate of the selected memory cell, and the control gate of the non-selected memory cell on the bit line side is An intermediate potential Vm (for example, 10 V) is applied to the selection gate. 0 V (for example, “1”) or an intermediate potential Vm (for example, 8 V) is applied to the bit line depending on the data. At this time, the potential of the bit line is transmitted to the drain of the selected memory cell through the selected gate and unselected memory cells.

When there is data to be written ("1" data), a high electric field is applied between the gate and drain of the selected memory cell, and electrons are tunnel-injected from the substrate to the floating gate. As a result, the threshold value of the selected memory cell moves in the positive direction. When there is no data to be written (“0” data), the threshold value does not change.

Data erasing is either performed simultaneously on all the memory cells in the NAND type cell (batch erasing) or every byte unit (block erasing). That is, all (or all in the selected block) control gates are set to 0V (in the case of block erasing, Vpp (for example, 20V) is applied to the control gates and select gates of non-selected blocks), and non-selected The bit line and the source line are set in a floating state, and a high voltage (for example, 20V) is applied to the p well. As a result, in all (or all in the selected block) memory cells, electrons in the floating gate are emitted to the p-well, and the threshold value moves in the negative direction.

For data reading, the power supply voltage Vcc (for example, 5 V) is applied to the control gates of the selected gate and the unselected memory cells on the bit line side of the selected memory cell to turn them on, thereby controlling the selected memory cell. 0V to the gate
Is given. At this time, "0" or "1" is determined by detecting the current flowing on the bit line side. Such a conventional NAND type EEPROM has the following problems. That is, as shown in FIG. 21A, the threshold voltage after writing and erasing has a maximum variation of about 3V. First, the variation after writing will be described. As described above, the data reading is performed by detecting the current flowing through the bit line.
If the threshold value after writing is, for example, 0 V or less, this memory cell is not determined to be in the written state and a write error occurs.

On the other hand, when the threshold voltage is desired, the reading is normally performed, but when the threshold voltage is higher than Vcc, the non-selected cell is not turned on, and therefore the reading is not normally performed. Further, if the threshold value after writing is equal to or lower than the desired threshold value and is close to 0 V, a read error occurs. In this way, if the threshold values of all the memory cells do not fall within the desired threshold value range, the writing becomes NG.

The causes of this threshold variation are variations in the tunnel insulating film thickness and film quality, variations in the element region, the size of the bird's beak entering the element region from the element isolation region, variations in the height of the floating gate sidewall, and on the floating gate. Variations in the coupling ratio due to variations in the insulating film thickness, variations in the total surface area of the floating gate, and the like are considered. It is very difficult to solve all these variations in the current process technology.

Therefore, a NAND cell type EEPROM is generally used.
In M, a verify circuit, which is a circuit that detects a cell in which writing is insufficient and performs rewriting, has solved this problem. However, the repetition of detection and rewriting causes problems such as an increase in writing time, a complicated operation, and an increase in chip area.

On the other hand, the threshold value after erasing is 0V.
The following is sufficient, and all the memory cells are within this range, which can be solved by taking a margin and lengthening the erasing time to some extent. However, if the variation in the threshold value after erasing is large, it will be greatly reflected in the variation in the threshold value after writing.

In a so-called ETOX type memory cell (NOR type) in which hot electrons generated near the drain diffusion layer are used for writing data and F-N tunnel current is used from the floating gate to the source diffusion layer for erasing. It is very important to keep the threshold distribution within a certain range. As shown in FIG. 21B, ET
The threshold value after programming of the OX type memory cell is 6.5 V.
As described above, the threshold value after erasing needs to be within the range of 0.5V to 3.5V.

However, this type of memory cell has a problem of so-called over-erase, in which the threshold voltage after erasing becomes 0 V or less. That is, when a non-selected cell is over-erased, if a potential is applied to the bit line, a current will flow through the over-erased cell, and the data in the selected cell cannot be read. Therefore, it is extremely important to keep the threshold distribution on the erase side within a predetermined width.

[0014]

As described above, in the conventional NAND cell type EEPROM, the data cannot be correctly discriminated at the time of reading due to the threshold variation after writing and erasing, and in order to solve this problem. Therefore, there is a problem that the verify circuit is required, and therefore, the write time is increased, the write operation is complicated, and the chip area is increased.

Further, the NOR cell type EEPROM also has a problem of over-erase, and there is a problem that the data cannot be discriminated when the variation of the threshold value is not within the desired range.

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a structure and an operation which can reduce variations in threshold voltage after writing and erasing without requiring a verify circuit. It is to provide a nonvolatile semiconductor memory device having the same.

[0017]

In order to solve the above problems, the nonvolatile semiconductor memory device of the present invention employs the following configuration.

That is, the invention is characterized in that hot carriers accelerated in the depletion layer of the well are injected into the charge storage layer to perform writing and erasing.

The present invention also implements two write and erase operations.
Operation mode 1 in which the charge is exchanged between the charge storage layer and the well by utilizing FN tunnel current or hot carriers generated near the drain diffusion layer during writing and erasing. After completion of the above, hot carriers accelerated in the depletion layer region of the well are injected into the charge storage layer, and writing and erasing are performed in two stages of operation mode 2 in which the threshold value is adjusted by rewriting. And

The features of the present invention will be described in more detail as follows.

(1) In a nonvolatile semiconductor memory device in which a plurality of memory cells are formed in an array in a second conductivity type well formed in a first conductivity type semiconductor substrate, the memory cells are arranged in the second conductivity type well. The formed first conductivity type source and drain diffusion layers, the charge storage layer formed through a tunnel insulating film in a region sandwiched between the source and drain, and the gate insulating film formed over the charge storage layer. A rewritable memory cell that is formed of a control gate and that rewrites data by exchanging charges between the charge storage layer and the second conductivity type well. (1-1) A positive potential is applied to the control gate. By applying a voltage of 0 V to the source and drain, a potential is applied to the second conductivity type well to form a depletion region, and a potential is applied to the first conductivity type semiconductor substrate to inject carriers into the second conductivity type well to deplete it. Key in the area Rear and hot carriers by applying energy to, writing by injecting this hot carriers into the charge storage layer that.

(1-2) Having the means 1 for turning on the selected memory cell to generate hot carriers in the vicinity of the drain diffusion layer and injecting the hot carriers into the charge storage layer, after performing the means 1. , A positive potential is applied to the control gate, the source and drain are set to 0 V, a potential is applied to the second conductivity type well to form a depletion region, and a potential is applied to the first conductivity type semiconductor substrate to generate second carriers. A means for injecting into the conductivity type well, giving energy to carriers in the depletion region to form hot carriers, and injecting the hot carriers into the charge storage layer is provided.

(1-3) Data write operation in which the second conductivity type well is set to 0 V, a high potential is applied to the control gate, and carriers are injected from the second conductivity type well into the charge storage layer by the Fowler-Nordheim tunnel current. 1 and the write operation 1 is performed, a certain potential is applied to the control gate and a negative potential is applied to the well of the second conductivity type to deplete the semiconductor substrate of the first conductivity type or the second conductivity type. In conductivity type well or second
Carriers are injected from the diffusion layer of the first conductivity type formed in the region in contact with the conductivity type well, and energy is given to the carriers in the depletion region in the second conductivity type well to make them hot carriers. Injecting into the storage layer and rewriting.

(1-4) Data erasing operation in which the control gate is set to 0 V, a high potential is applied to the second conductivity type well, and carriers in the charge storage layer are emitted to the second conductivity type well by a Fowler-Nordheim tunnel current. 1 and after performing the erase operation 1, a certain potential is applied to the control gate and a negative potential is applied to the well of the second conductivity type to deplete the semiconductor substrate of the first conductivity type or the second substrate of the second conductivity type. Carriers are injected from the first conductivity type diffusion layer formed in the conductivity type well or in a region in contact with the second conductivity type well, and energy is applied to the carriers in the depletion region in the second conductivity type well to provide hot carriers. Then, the hot carriers are injected into the charge storage layer to rewrite.

(2) A first conductivity type well is formed in a second conductivity type well formed in a first conductivity type semiconductor substrate, and a plurality of memory cells are arrayed in the first conductivity type well. In the conductive semiconductor memory device, a memory cell is formed in a well of the first conductivity type, a source / drain diffusion layer of the second conductivity type, and a region sandwiched by the source / drain via a tunnel insulating film. A rewritable memory cell including a charge storage layer and a control gate formed on the charge storage layer via a gate insulating film, and rewriting data by exchanging charges between the charge storage layer and the first conductivity type well. And (2-1) applying a positive potential to the control gate,
The source and the drain are set to 0 V, a potential is applied to the first conductivity type well to form a depletion region, and the depletion region is formed in the second conductivity type well, or in the first conductivity type well or a region in contact with the first conductivity type well. A potential is applied to the second conductivity type diffusion layer to inject carriers into the first conductivity type well, energy is applied to the carriers in the depletion region to form hot carriers, and the hot carriers are injected into the charge storage layer for writing.

(2-2) The control gate is set to 0 V, a potential is applied to the second conductivity type well to form a depletion region, and the semiconductor substrate of the first conductivity type or the well of the second conductivity type or the second conductivity type is formed. A potential is applied to the first conductivity type diffusion layer formed in the region in contact with the well, carriers are injected into the first conductivity type well through the second conductivity type well, and energy is applied to the carriers in the depletion region to form hot carriers. , Injecting these hot carriers into the charge storage layer to erase them.

(2-3) Having the means 1 for turning on the selected memory cell to generate hot carriers in the vicinity of the drain diffusion layer and injecting the hot carriers into the charge storage layer, after performing the means 1, , A positive potential is applied to the control gate, the source and the drain are set to 0 V, and a potential is applied to the first conductivity type well to form a depletion region, and the second conductivity type well, the first conductivity type well, or the first conductivity type well is formed. A potential is applied to the second conductivity type diffusion layer formed in the region in contact with the conductivity type well to inject carriers into the first conductivity type well, and energy is applied to the carriers in the depletion region to form hot carriers. To have a means for injecting into the charge storage layer.

(2-4) Having the means 1 for turning on the selected memory cell to generate hot carriers in the vicinity of the drain diffusion layer and injecting the hot carriers into the charge storage layer, after performing the means 1. The control gate is set to 0 V, a potential is applied to the second conductivity type well to form a depletion region, and the semiconductor substrate of the first conductivity type, the second conductivity type well, or the second conductivity type well is formed.
A potential is applied to the first conductivity type diffusion layer formed in the region in contact with the conductivity type well, carriers are injected into the first conductivity type well through the second conductivity type well, and energy is applied to the carriers in the depletion region to make hot. As carriers, it must have means for injecting these hot carriers into the charge storage layer.

(2-5) Data writing operation in which the first conductivity type well is set to 0 V, a high potential is applied to the control gate, and carriers are injected from the first conductivity type well into the charge storage layer by the Fowler-Nordheim tunnel current. 1 and the write operation 1 is performed, then the control gate is set to 0 V, a potential is applied to the second conductivity type well to form a depletion region, and the first conductivity type semiconductor substrate or the second conductivity type well is formed. Alternatively, a potential is applied to the first conductivity type diffusion layer formed in the region in contact with the second conductivity type well, carriers are injected into the first conductivity type well through the second conductivity type well, and energy is applied to the carriers in the depletion region. A means for injecting these hot carriers into the charge storage layer is provided.

(2-6) Data writing operation in which the first conductivity type well is set to 0 V, a high potential is applied to the control gate, and carriers are injected from the first conductivity type well into the charge storage layer by the Fowler-Nordheim tunnel current. 1 and the write operation 1 is performed, a certain potential is applied to the control gate, and a negative potential is applied to the first conductivity type well to deplete it, thereby generating the second conductivity type well or the first conductivity type well. Carriers are injected from a second conductivity type diffusion layer formed in the well or in a region in contact with the first conductivity type well, and energy is applied to the carriers in the depletion region in the second conductivity well to form hot carriers,
Injecting these hot carriers into the charge storage layer and rewriting.

(2-7) Data erasing operation in which the control gate is set to 0 V, a high potential is applied to the first conductivity type well, and carriers in the charge storage layer are discharged to the first conductivity type well by a Fowler-Nordheim tunnel current. 1 and after performing the erase operation 1, a certain potential is applied to the control gate and a negative potential is applied to the first conductivity type well to deplete it, and the second conductivity type well,
Alternatively, carriers are injected from a second conductivity type diffusion layer formed in the first conductivity type well or in a region in contact with the first conductivity type well, and energy is applied to the carriers in the depletion region in the first conductivity type well. As hot carriers, injecting these hot carriers into the charge storage layer for rewriting.

(3) In a nonvolatile semiconductor memory device in which a plurality of memory cells are formed in an array in a second conductivity type well formed in a first conductivity type semiconductor substrate, the memory cells are arranged in the second conductivity type well. The formed first conductivity type source and drain diffusion layers, the charge storage layer formed through a tunnel insulating film in a region sandwiched between the source and drain, and the gate insulating film formed over the charge storage layer. A rewritable memory cell that is formed of a control gate and that rewrites data by exchanging charges between the charge storage layer and the second conductivity type well shares its source and drain with adjacent ones. The cells are connected in series to form a NAND cell, which has a memory cell array arranged in a matrix. The drain at one end of each NAND cell is arranged in the column direction through a select gate. It is connected to that bit line, each NAND
A control gate in a cell is a method of operating a nonvolatile semiconductor memory device in which NAND cells arranged in the row direction are continuously arranged to form a word line. The intermediate potential is applied to maintain the ON state, the bit line and the source line are set to 0 V, the potential higher than the intermediate potential is applied to the selected word line, and the negative potential is applied to the second conductivity type well to deplete. Then, a potential is applied to the first-conductivity-type semiconductor substrate or the first-conductivity-type diffusion layer formed in the second-conductivity-type well or in a region in contact with the second-conductivity-type well to inject carriers, Energy is applied to these carriers in the depletion region in the conductivity type well to make them hot carriers, and these hot carriers are injected into the charge storage layer for writing.

(3-2) In the NAND cell selected by the selection gate of each NAND cell, a positive intermediate potential is applied to the non-selected word line to turn it on, and the selected word line has a positive high potential. By applying a potential, carriers in the charge storage layer from the second conductivity type well are selected by the Fowler-Nordhei in the selected memory cell.
m has a data write operation 1 that is injected by a tunnel current, and after performing the write operation 1, a positive intermediate potential is applied to an unselected word line to keep the ON state, and the selected word line has an intermediate potential or more. At a high potential or less and a negative potential is applied to the second conductivity type well to deplete it.
Carriers are injected from a first-conductivity-type diffusion layer formed in the second-conductivity-type semiconductor substrate or in the second-conductivity-type well or in a region in contact with the second-conductivity-type well, so that depletion regions in the second-conductivity-type well are depleted. Energy is given to these carriers to make them hot carriers, and these hot carriers are injected into the charge storage layer for rewriting.

(3-3) Set a plurality of word lines within a predetermined range to 0
V has a data erase operation 1 in which a high potential is applied to the second conductivity type well and carriers in the charge storage layer of the memory cell in that range are discharged to the first conductivity type well by a Fowler-Nordheim tunnel current. After the erase operation 1 is performed, a certain potential is applied to the word line within the predetermined range, and a negative potential is applied to the second conductivity type well to deplete it, so that the first conductivity type semiconductor substrate or the first conductivity type semiconductor substrate is formed. Carrier is injected by applying a potential to a diffusion layer of the first conductivity type formed in the well of the second conductivity type or in a region in contact with the well of the second conductivity type, and energy is applied to the carrier in the depletion region in the well of the second conductivity type. As hot carriers, injecting these hot carriers into the charge storage layer for rewriting.

(4) A first conductivity type well is formed in a second conductivity type well formed in a first conductivity type semiconductor substrate, and a plurality of memory cells are formed in an array in the first conductivity type well. In the nonvolatile semiconductor memory device described above, the memory cell is formed in the first-conductivity-type well by the second-conductivity-type source and drain diffusion layers, and in the region sandwiched by these sources and drains via a tunnel insulating film. And a control gate formed on the charge storage layer via a gate insulating film. Data is rewritten by charge transfer between the charge storage layer and the first conductivity type well. The memory cells are connected in series in such a manner that their sources and drains are shared by adjacent ones to form a NAND cell, which has a memory cell array arranged in a matrix. The drain at one end of the D cell is connected to the bit line running in the column direction through the select gate, and the control gate in each NAND cell is continuously arranged for the NAND cells arranged in the row direction to form a word line. A method of operating a nonvolatile semiconductor memory device, comprising: (4-1) applying a positive intermediate potential to a non-selected word line to maintain an ON state,
A potential equal to or higher than the intermediate potential is applied to the selected word line, and a negative potential is applied to the first conductivity type well to deplete it.
Depletion in the first conductivity type well by applying a potential to the second conductivity type diffusion layer formed in the first conductivity type well or in a region in contact with the first conductivity type well Energy is applied to these carriers in a region to make them hot carriers, and these hot carriers are injected into the charge storage layer for writing.

(4-2) A word line within a predetermined range is set to 0 V, a potential is applied to the second conductivity type well to form a depletion region, and a semiconductor substrate of the first conductivity type or a well of the second conductivity type is formed. Alternatively, a potential is applied to the first conductivity type diffusion layer formed in the region in contact with the second conductivity type well, carriers are injected into the first conductivity type well through the second conductivity type well, and energy is applied to the carriers in the depletion region. Giving it as hot carriers, injecting these hot carriers into the charge storage layer to erase them.

(4-3) In the NAND cell selected by the selection gate of each NAND cell, a positive intermediate potential is applied to an unselected word line to turn it on, and a positive high voltage is applied to the selected word line. By applying a potential, carriers in the charge storage layer from the first conductivity type well are selected by the Fowler-Nordhei in the selected memory cell.
m has a data write operation 1 that is injected by a tunnel current, and after performing the write operation 1, a positive intermediate potential is applied to an unselected word line to keep the ON state, and the selected word line has an intermediate potential or more. At a high potential or less, and a negative potential is applied to the first conductivity type well to deplete it.
Depletion in the first conductivity type well by applying a potential to the second conductivity type diffusion layer formed in the first conductivity type well or in a region in contact with the first conductivity type well Energy is given to these carriers in the region to make them hot carriers, and these hot carriers are injected into the charge storage layer to rewrite.

(4-4) Set a plurality of word lines within a predetermined range to 0
V has a data erase operation 1 in which a high potential is applied to the first conductivity type well and carriers in the charge storage layer of the memory cell in the range are discharged to the first conductivity type well by a Fowler-Nordheim tunnel current. After performing the erase operation 1, a certain potential is applied to the word line within the predetermined range, a negative potential is applied to the first conductivity type well to deplete it, and the second conductivity type well,
Alternatively, a carrier is injected by applying a potential to a diffusion layer of the second conductivity type formed in the well of the first conductivity type or in a region in contact with the well of the first conductivity type, and the carriers are injected in the depletion region in the well of the first conductivity type. Energy is given to the charge storage layer as hot carriers, and these hot carriers are injected into the charge storage layer to rewrite.

(4-5) In the NAND cell selected by the selection gate of each NAND cell, a positive intermediate potential is applied to an unselected word line to turn it on, and a positive high voltage is applied to the selected word line. By applying a potential, carriers in the charge storage layer from the first conductivity type well are selected by the Fowler-Nordhei in the selected memory cell.
m has a data write operation 1 of injecting by a tunnel current, and after performing the write operation 1, the word line in a predetermined range is set to 0 V, a potential is applied to the second conductivity type well to form a depletion region, A potential is applied to the first conductivity type semiconductor substrate, or to the first conductivity type diffusion layer formed in the second conductivity type well or in a region in contact with the second conductivity type well, so that carriers are passed through the second conductivity type well Inject into conductivity type well,
Energy is applied to carriers in the depletion region to make them hot carriers, and these hot carriers are injected into the charge storage layer to be erased again.

(4-6) Set a plurality of word lines within a predetermined range to 0
V has a data erase operation 1 in which a high potential is applied to the first conductivity type well and carriers in the charge storage layer of the memory cell in the range are discharged to the first conductivity type well by a Fowler-Nordheim tunnel current. After performing the erasing operation 1, the word line in a predetermined range is set to 0 V, a potential is applied to the second conductivity type well to form a depletion region, and the first conductivity type semiconductor substrate is formed.
Alternatively, a potential is applied to the first conductivity type diffusion layer formed in the second conductivity type well or in a region in contact with the second conductivity type well, and carriers are injected into the first conductivity type well through the second conductivity type well, Energy is applied to carriers in the depletion region to make them hot carriers, and these hot carriers are injected into the charge storage layer to be erased again.

The following are preferred embodiments of the present invention.

(A) The hot carriers must include avalanche hot carriers generated by the carriers traveling in the depletion layer.

(B) When hot carriers are injected into the charge storage layer, the hot carriers are injected over the potential barrier of the tunnel insulating film, and F- through the potential barrier of the tunnel insulating film. What is done by N tunnel injection.

(C) When hot carriers are injected into the charge storage layer, the threshold voltage at the end of the write operation 1 is more negative than the desired threshold voltage than the desired threshold voltage. There are many hot carriers injected into the.

(D) When hot carriers are injected into the charge storage layer, the charge storage layer is more negative when the threshold voltage at the end of erase operation 1 is more positive than the desired threshold voltage. There are many hot carriers injected into the.

(E) When hot carriers are injected into the charge storage layer, the charge storage layer is more positive when the threshold voltage at the end of the write operation 1 is more negative than the desired threshold voltage. There are many hot carriers injected into the.

(F) When hot carriers are injected into the charge storage layer, the charge storage layer is more positive when the threshold voltage at the end of erase operation 1 is more negative than the desired threshold voltage. There are many hot carriers injected into the.

[0048]

According to the present invention, the spread of the threshold distribution is reduced by using hot carriers whose writing and erasing are accelerated in the depletion layer of the well. That is, at the time of writing, hot electrons accelerated by the depletion layer reach the vicinity of the interface between the tunnel insulating film and the well with a certain energy width, but the energy distribution and the electric field of the tunnel insulating film fall within a certain range. By adjusting the impurity concentration of the well, the spread of the depletion layer, the potential applied to the well, the potential applied to the control gate, etc., the electric field dependence of the tunnel insulating film for the hot electrons entering the charge storage layer. It can be held large. That is, the injection efficiency of the hot electrons in the charge storage layer largely depends on the amount of charges stored in the charge storage layer. The same applies to hot holes.

As a result, during writing, that is, when injecting electrons into the charge storage layer, it is difficult for electrons to enter when the amount of electrons stored in the charge storage layer is large, and it becomes easy for electrons to enter when the amount is large. Similarly, at the time of erasing, the injection of hot holes depends on the charges stored in the charge storage layer. This makes it possible to implement a writing / erasing method in which the spread of the threshold distribution after writing and erasing is small. The energy band diagram in this case is shown in FIG.

FIG. 1A shows a state of hot electron injection at the time of writing, and FIG. 1B shows a state of hot hole injection at the time of erasing.

However, in this case, in order to generate hot carriers, it is necessary to inject a large number of carriers from the diffusion layer, which may cause a problem of increased power consumption. In this case, as described below, an operation mode 1 using hot carriers generated in the FN tunnel current or the drain diffusion layer for writing and erasing, and an operation mode 2 using hot carriers accelerated in the depletion layer of the well. By the two-step writing / erasing, a writing / erasing method with low power consumption can be realized.

That is, at the time of writing, regardless of variations in the easiness of writing of the memory cells, the selected cells are uniformly written by FN tunnel injection for carrier injection at the same write voltage Vpp and write pulse width Tp. Two stages of operation mode 1 and operation mode 2 in which the threshold voltage is adjusted by selectively rewriting to the memory cell in which writing is insufficient by hot electron injection accelerated in the depletion layer of the well. By writing, it is possible to substantially reduce the variation in threshold value after writing. Energy band diagrams at this time are shown in FIGS.

In the operation mode 2, the threshold value may be adjusted by selectively re-erasing the overwritten memory cell by hot hole injection accelerated in the depletion layer of the well. it can. Energy band diagrams at this time are shown in FIGS.

Further, even at the time of erasing, the memory cells selected by the FN tunnel injection are made uniform at the same erase voltage Vpp and erase pulse width Tp regardless of the variation in the erasability of the memory cells. By the operation mode 1 to erase and hot electron injection accelerated in the depletion layer of the well,
By performing rewriting to the overerased memory cell selectively and performing two-step writing in the operation mode 2 for adjusting the threshold value, it is possible to substantially reduce the variation in the threshold value after the erasing. Figure 4 shows the energy band diagram at this time.
Shown in (a) and (b).

Further, in the above operation mode 2, it is possible to selectively re-erase an insufficiently erased memory cell by hot hole injection accelerated in the depletion layer of the well. The energy band diagram at this time is shown in FIGS.
Shown in

At the time of writing, the threshold voltage of the memory cell after the F-N tunnel injection varies as shown in FIG. 6A. First, however, by slightly weakening the F-N tunnel injection, Eliminate errors in the region near the threshold voltage Vcc. In this state, the electric field applied to the tunnel insulating film is small when the threshold voltage is high and is large when the threshold voltage is low, depending on the amount of charges accumulated in the charge accumulation layer.

Next, hot electrons generated in the well are easily injected into the charge storage layer when the electric field applied to the tunnel insulating film is large, and are difficult to be injected when the electric field is small. , Set the voltage applied to the well and the voltage applied to the word line. In this case, as compared with the case of using an FN tunnel current using a very high electric field, by using hot electron injection which can be injected in a low electric field, the tunnel insulating film of the tunnel insulating film determined by the charge amount of the charge storage layer is used. It is considered that the influence of the electric field on the injection amount becomes remarkable.

Therefore, in a memory cell having a high threshold value, the injection of hot electrons is unlikely to occur, so that the threshold value is less likely to change, and in a memory cell having a low threshold value, hot electron injection is likely to occur. Then, carriers are injected into the charge storage layer, and the threshold value moves in the positive direction. Therefore, variations in the threshold distribution can be substantially reduced. Further, as shown in FIG. 6B, by using hot hole injection, it is possible to selectively adjust the threshold value of an overwritten cell and suppress variations.

Further, at the time of erasing, the variation of the threshold distribution can be suppressed by the same method. That is, first, by slightly increasing the emission of the FN tunnel,
As shown in, the error in the region near the threshold voltage of 0 V is eliminated. In this state as well, the electric field applied to the tunnel insulating film is small when the threshold voltage is high and is large when the threshold voltage is low, depending on the amount of stored charges in the charge storage layer.

Next, hot electrons generated in the well are easily injected into the charge storage layer when the electric field applied to the tunnel insulating film is large, and are difficult to be injected when the electric field is small. , Set the voltage applied to the well and word line. This allows
Since the injection of hot electrons is less likely to occur in a memory cell with a high threshold value, the fluctuation of the threshold value is small, and the injection of hot electrons is likely to occur in a memory cell with a low threshold value. It is injected into the layer and the threshold shifts in the positive direction. Therefore, variations in the threshold distribution can be substantially reduced.

The same effect is obtained by applying the above operation to a NOR type memory cell, that is, by replacing the above FN writing with hot electrons near the drain diffusion layer used in the NOR type. Can be expected.

By this two-step writing and erasing method, the variation of the threshold voltage at the time of writing and erasing can be greatly reduced, and the NAND cell type EEPR can be obtained.
The operation of the OM memory cell can be improved. Further, in the NOR cell type EEPROM, the problem of overerasure can be solved.

[0063]

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

(Embodiment 1) In this embodiment, when a hot carrier accelerated in a depletion layer of a well is used for writing and erasing a memory cell, its operation will be described using a single memory cell.

FIG. 8 shows a sectional view of a single memory cell using an n-channel MOSFET and a timing chart during a write operation. The memory cell is configured as follows. That is, an n well (second conductivity type well) 2 and a p well (first conductivity type well) 3 are formed in a p type substrate (first conductivity type semiconductor substrate) 1 and each well 2, 3 is formed.
Depth, impurity concentration, and distribution are optimized to perform the operation of the present invention. N-type source / drain diffusion layers 4a and 4b are formed in the surface layer of the p-well 3, and a floating gate (charge storage layer) 6 is formed on the channel between the source / drain via a tunnel insulating film 5. A control gate 8 is formed on the gate insulating film 7.

For writing, a potential larger than a sufficient value for turning on the channel, for example, 13 V is applied to the control gate 8, and the source and drain are set to 0 V. Here, the p-well 3 is depleted at Vp1, the electrons injected into the depletion layer are sufficient to exceed the potential barrier of the tunnel insulating film 5, and the hot electrons injected into the floating gate 6 are included in the tunnel insulating film 5. A potential that depends on the electric field, for example, −8 V is applied. Then, a potential at which the pn junction is forward biased, for example, −8.5 V is applied to Vn, and electrons are injected from the n well 2 into the depletion layer of the p well 3.
The same potential as Vn is applied to Vp2.

Further, it is necessary to optimize the above potential according to the well profile and the like. That is, the hot electrons accelerated in the depletion layer are tunnel insulating film 5 and p well 3
Although it reaches the vicinity of the interface with a certain energy width, by adjusting the energy distribution and the electric field of the tunnel insulating film 5 to a certain range, that is, the impurity concentration of the p well 3, the depletion layer spread, and the p Potential applied to well 3,
By adjusting the potential or the like applied to the control gate 8, the hot electrons entering the floating gate 6 can have a large electric field dependency of the tunnel insulating film 5. That is,
The injection efficiency of the hot electrons in the floating gate 6 largely depends on the amount of charges accumulated in the floating gate 6.

According to this writing method, the spread of the threshold distribution is reduced by using hot electrons accelerated in the depletion layer of the p well 3.

Next, the erasing method will be described with reference to FIG. Use a hot hole when erasing. That is, the control gate 8 is set to 0V, and the source, drain, and Vp1 are made floating. In this state, for example, 17 V is applied to Vn. Part of the potential applied to Vn is used to deplete the p well 3, and the rest is the electric field of the tunnel insulating film 5. Since the depletion layer needs to be formed in the p-well 3, the concentration of the p-well 3 needs to be lower than the concentration of the n-well 2. In this state, a potential at which the pn junction is forward biased, for example, 17.5 V is applied to Vp2 to inject holes from the p-type substrate 1 into the n-well 2. Here, since the n well 2 is formed sufficiently thin, most holes are injected into the depletion layer of the p well 3. The holes injected into the depletion layer are accelerated by the electric field of the depletion layer and are injected into the floating gate 6 over the potential barrier of the tunnel insulating film 5, so that the memory cell is in an erased state.

Also in this case, the potential and the impurity profile of the well need to be optimized as in the case of writing.

According to this erasing method, the spread of the threshold distribution is reduced by using the hot holes accelerated in the depletion layer of the p well 3.

(Embodiment 2) In this embodiment, after writing and erasing a memory cell by an F-N tunnel current, the threshold voltage is adjusted by using hot carriers accelerated in the depletion layer of the p-well. The operation of the two-step write / erase method will be described using a single memory cell. The structure of the memory cell is exactly the same as that described in the first embodiment.

FIG. 10 shows a timing chart at the time of writing in this case. Since the normal FN tunnel current is used for the first step writing, the source 4a, the drain 4a, the wells 2 and 3 and the p substrate 1 are set to 0 V, and the control gate 8 is supplied with a high potential of 20 V, for example. Inject electrons into. In this state, the threshold value varies among the memory cells. Thereafter, as in the case of the first embodiment, holes are injected into the depletion layer of the p-well 3 to generate hot holes, which are then injected into the floating gate 6. At this time, if the threshold value after F-N implantation is a desired value or smaller than that, hot hole injection hardly occurs, and if it is larger than the desired value, hot hole injection occurs. It is necessary to adjust the potentials of 2 and 3 and the substrate 1.

By this two-step writing method, F
The threshold value after -N implantation can be kept within a desired range, and variations in threshold voltage are reduced. In addition, this method is not effective for those having a small threshold voltage, but raises the potential at the time of FN writing so that the threshold after FN tunnel writing becomes larger than a desired value in advance. By setting to 1, it is possible to reduce the variation of the lower threshold value.

Next, FIG. 11 shows a timing chart at the time of erasing. Since the FN tunnel current is used for the erasing in the first step, the source 4a and the drain 4b are floated, and a potential of 20 V is applied to the wells 2 and 3 and the substrate 1, so that electrons are injected from the floating gate 6 into the well 3. Pull out. In this state, the threshold values of the plurality of memory cells vary. After this, in the same manner as in Example 1, electrons are injected into the depletion layer of the p-well 3 to generate hot electrons, which are then injected into the floating gate 6. At this time, if the threshold value after F-N erasing is a desired value or larger, hot electron injection hardly occurs, and if it is smaller than the desired value, hot electron injection occurs. Therefore, it is necessary to adjust the potentials of the wells 2, 3, the substrate 1 and the control gate 8.

By this two-step erasing method, F-N
The threshold after injection can be kept within a desired range,
Variations in threshold voltage are reduced. In addition, this method is not effective for those having a large threshold voltage, but the potential during F-N writing is increased so that the threshold after F-N tunnel erasing becomes smaller than a desired value in advance. By setting to 1, it is possible to reduce the variation of the lower threshold value.

In order to realize this writing / erasing method, it is necessary to optimize the profiles of the wells 2 and 3 as in the first embodiment. The two-step write / erase method reduces the variation in threshold voltage.

(Embodiment 3) In this embodiment, after writing and erasing a memory cell by an F-N tunnel current, hot carriers accelerated in the depletion layer of the p-well 3 are used to increase the threshold voltage. The operation of the two-step write / erase method for adjustment will be described using a single memory cell.

FIG. 12 shows a timing chart at the time of writing in this case. Since the normal F-N tunnel current is used for the writing in the first step, the source 4a, the drain 4b, the wells 2 and 3 and the substrate 1 are set to 0 V, and the control gate 8 is supplied with a high potential of 20 V, for example, to the floating gate 6. Inject electrons. In this state, the threshold value varies among the memory cells. After this, Example 1
As in the case of, the electrons are injected into the depletion layer of the p-well 3 to generate hot electrons, which are then injected into the floating gate 6. At this time, if the threshold value after F-N injection is a desired value or larger than that, hot electron injection hardly occurs, and if it is smaller than the desired value, hot electron injection occurs. It is necessary to adjust the potentials of 2 and 3 and the substrate 1.

By this two-step writing method, F
The threshold value after -N implantation can be kept within a desired range, and variations in threshold voltage are reduced. In addition, this method is not effective for those having a large threshold voltage, but lowers the potential during FN writing so that the threshold after FN tunnel writing becomes smaller than a desired value in advance. By setting to 1, it is possible to substantially reduce the variation of the higher threshold.

Next, FIG. 13 shows a timing chart at the time of erasing. Since the FN tunnel current is used for the erasing in the first step, the source 4a and the drain 4b are floated, and a potential of, for example, 20 V is applied to the wells 2 and 3 and the substrate 1 so that electrons are injected from the floating gate 6 into the well 3. Pull out. In this state, the threshold values of the plurality of memory cells vary. Thereafter, as in the first embodiment, holes are injected into the depletion layer of the p-well 3 to generate hot holes, which are then injected into the floating gate 6. At this time, F
If the threshold value after -N erasing is a desired value or smaller, hot electron injection hardly occurs, and if it is larger than the desired value, hot electron injection occurs. 3. It is necessary to adjust the potentials of the substrate 1 and the control gate 8.

By this two-step erasing method, F-N
The threshold after injection can be kept within a desired range,
Variations in threshold voltage are reduced. In addition, this method is not effective for those having a small threshold voltage, but lowers the potential at the time of FN writing so that the threshold after FN tunnel erasing becomes larger than a desired value in advance. By setting to 1, it is possible to substantially reduce the variation of the higher threshold.

In order to realize this writing / erasing method, it is necessary to optimize the profiles of the wells 2 and 3 as in the first embodiment. The two-step write / erase method reduces the variation in threshold voltage.

(Embodiment 4) In this embodiment, as used in a NOR type memory cell, after writing and erasing the memory cell by hot electrons generated in the vicinity of the drain diffusion layer, the p-well is formed. The operation of the two-step write / erase method in which the threshold voltage is adjusted by using hot carriers accelerated in the depletion layer of No. 3 will be described using a single memory cell.

FIG. 14 shows a timing chart at the time of writing in this case. Since the hot electrons generated near the drain are used for the writing in the first step,
The source 4a, the wells 2 and 3 and the substrate 1 are set to 0V, and a potential of 10V is applied to the control gate 8 to turn them on.
A potential of, for example, 5 V is applied to the drain 4b to cause band-to-band tunneling near the drain diffusion layer, generate hot electrons, and inject electrons into the floating gate 6. In this state, the threshold value varies among the memory cells. Thereafter, as in the case of the first embodiment, holes are injected into the depletion layer of the p-well 3 to generate hot holes, which are then injected into the floating gate 6. At this time, 1
If the threshold value after step writing is a desired value or smaller than that, injection of hot holes hardly occurs, and if it is larger than the desired value, injection of hot electrons occurs so that the wells 2 and 3 and the substrate can be injected. The potential of 1 must be adjusted.

By this two-step writing method, the threshold value after writing can be kept within a desired range, and variations in threshold voltage can be reduced. In addition, this method is not effective for a device having a small threshold voltage, but the pulse width at the time of one-step writing is set longer so that the threshold value after one-step writing becomes larger than a desired value in advance. By doing so, it is possible to substantially reduce the variation of the lower threshold.

Erasing can be performed by the same method as that of the second embodiment to obtain a threshold distribution with small variations. This erase method reduces the problem of overerase.

(Embodiment 5) In this embodiment, a non-volatile semiconductor memory device (NAND type EEPROM) in which a plurality of memory cells in which the writing and erasing methods of Embodiments 1 to 3 of the present invention can be electrically rewritten are connected in series An example when applied to is shown.

FIG. 15 shows one NAND memory cell of a NAND type EEPROM using an n-channel MOSFET.
16A and 16B are plan views showing the cell portion, and
It is an A'and BB 'sectional drawing. FIG. 17 is an equivalent circuit of the memory cell array.

First, the structure of one NAND cell will be described. The p-type well 11 is formed on the n-type silicon substrate, or the n-type well is formed on the p-type silicon substrate and the p-type well 11 is formed therein.
In this embodiment, eight memory cells M1 to M8 and two select gate transistors S1 and S2 are formed in the element region divided by 1 in the element isolation region.

In this embodiment, L is formed in the element isolation region.
Although an example using OCOS is shown, generally, it may be an element isolation region and may be trench element isolation. Further, in this embodiment, the case where eight memory cells are used is shown, but the number of memory cells may be 16, or
It may be more than that. Moreover, the case where one selection transistor is provided on the source side and one on the drain side is shown.
Two or more may be provided on each of the source side and the drain side.

In each memory cell, the floating gate 14 of the first-layer polycrystalline silicon film is formed on the p-well 11 via the tunnel insulating film 13, and the second-layer polycrystalline film is formed on the floating gate 14 via the gate insulating film 15. The control gate 16 made of silicon is formed. Here, the tunnel insulating film 13
May be a thermal oxide film or an oxynitride film, and the gate insulating film 15 on the floating gate 14 is a thermal oxide film,
It may be an ONO film, an oxynitride film, or an HTO film. The floating gate 14 of each memory cell is a charge storage layer. The control gate 16 of each memory cell constitutes a word line WL (WL1 to WL8). The n-type diffusion layer 19 serving as the source and drain of each memory cell is connected in series so that eight memory cells are connected in series so as to be shared by adjacent memory cells.

In this embodiment, the selection gate transistors are connected to the source side and the drain side to form one NA.
An ND cell is configured. The gate electrodes SG1, SG2 and SG3, SG4 of the select gate transistor are obtained by simultaneously patterning the first layer and second layer polycrystalline silicon films forming the floating gate 14 and the control gate 16 of the memory cell, and SG1 and SG2 And SG3 and SG4 are in contact with each other at predetermined intervals in the word line direction.
The whole is covered with a CVD insulating film 17, and an Al wiring 18 is provided as a bit line BL that contacts the n-type diffusion layer which is the drain of the selection transistor S1 for the memory cell. The contact portion is overdoped with n-type impurities.

In the memory cell array of FIG. 17, 16 NAND cells having the above-mentioned configuration have eight bit lines BL1 to BL1.
8 is connected. Each word line WL1 ~
WL8, control line S for drain side select gates S1, S2
D1 and SD2 are derived from the array region via a D-type n-channel selection MOS transistor controlled by the control signal PRO, and the control lines SS1 and SS2 of the source side selection gates S3 and S4 are directly derived.

Next, the operation of the memory cell array of the NAND cell type EEPROM will be described. Below (Table 1)
Indicates that hot electron injection is used for writing and hot hole injection is used for erasing, and (Table 2) is a two-step writing method using F-N tunnel injection and hot hole injection for writing and F-N tunnel emission for erasing. When a two-step erase method using hot electron injection is used, (Table 3) shows a two-step write method using FN tunnel injection and hot electron injection for writing, and FN tunnel emission and hot electrons for erasing. The potential relationship of each part in each mode when the two-step erasing method using implantation is used is shown.

[0096]

[Table 1]

[Table 2]

[Table 3] In addition, in correspondence with (Table 1), (Table 2), and (Table 3), FIG.
8, 19 and 20 are timing charts showing potential relationships at the time of writing and erasing of the NAND cell type EEPROM memory cell when the operation method of the memory cell of the present invention is applied. Table 1 and FIG. 18 correspond to Example 1 and are examples of writing and erasing by injecting hot carriers. Table 2 and FIG. 19 correspond to Example 2 and are examples in which hot carriers are injected after F-N injection to perform writing and erasing. (Table 3) and FIG.
0 corresponds to Example 3, and is an example in which hot carriers are injected after F-N injection to perform writing and erasing.
Since these operations are substantially the same as those in the first to third embodiments, they are omitted here.

By using the programming and erasing method of this embodiment, programming of the NAND cell type EEPROM,
The threshold distribution after erasing is greatly improved.

The present invention is not limited to the above embodiments. In the embodiment, the double well structure in which the n well and the p well are formed on the p substrate is used, but the well does not necessarily have to be doubled, and the p well may be formed on the n substrate. Also, n-channel MOSF
When a p-channel MOSFET is used instead of ET, the conductivity types of the substrate and well may be reversed. In addition, various modifications can be made without departing from the scope of the present invention.

[0099]

As described above in detail, according to the present invention, the hot carriers accelerated in the depletion layer of the well are injected into the charge storage layer for writing and erasing, or the writing and erasing operations are performed. The operation mode 1 is divided into two stages and charges are exchanged between the charge storage layer and the well by utilizing the FN tunnel current at the time of writing and erasing, and the depletion layer of the well after the operation mode 1 is completed. By injecting hot carriers accelerated in the region into the charge storage layer and performing writing and erasing in two stages of the operation mode 2 in which the threshold value is adjusted by rewriting, the verify circuit is not required and the writing and erasing are performed. It is possible to realize a non-volatile semiconductor memory device having a structure and operation that can reduce variations in threshold voltage after erasing.

[Brief description of drawings]

FIG. 1 is a diagram showing a writing and erasing method according to the present invention.

FIG. 2 is a diagram showing a two-step writing method according to the present invention.

FIG. 3 is a diagram showing a two-step writing method according to the present invention.

FIG. 4 is a diagram showing a two-step erasing method according to the present invention.

FIG. 5 is a diagram showing a two-step erasing method according to the present invention.

FIG. 6 is a diagram showing improvement in threshold distribution by two-step writing.

FIG. 7 is a diagram showing improvement in threshold distribution by two-step erasing.

FIG. 8 is a diagram showing a timing chart at the time of writing in the first embodiment.

FIG. 9 is a diagram showing a timing chart at the time of erasing in the first embodiment.

FIG. 10 is a diagram showing a timing chart at the time of writing in the second embodiment.

FIG. 11 is a diagram showing a timing chart at the time of erasing in the second embodiment.

FIG. 12 is a diagram showing a timing chart at the time of writing in the third embodiment.

FIG. 13 is a diagram showing a timing chart at the time of erasing in the third embodiment.

FIG. 14 is a diagram showing a timing chart at the time of writing in the fourth embodiment.

FIG. 15 is a NAND cell type EEP according to a fifth embodiment.
FIG. 3 is a plan view showing a memory cell portion structure of a ROM.

16 is a cross-sectional view taken along the lines A-A 'and B-B' of FIG.

FIG. 17 is an equivalent circuit diagram of the memory cell array in the fifth embodiment.

FIG. 18 is a diagram showing a timing chart at the time of writing and erasing in the fifth embodiment.

FIG. 19 is a diagram showing a timing chart at the time of writing and erasing in the fifth embodiment.

FIG. 20 is a diagram showing a timing chart at the time of writing and erasing in the fifth embodiment.

FIG. 21 is a diagram for explaining a conventional problem, NA
FIG. 6 is a diagram showing distributions of threshold voltages of ND type and OR type memory cells.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... P-type semiconductor substrate (first conductivity type semiconductor substrate) 2 ... N well (second conductivity type well) 3 ... P well (first conductivity type well) 4a, 4b ... Source / drain diffusion layer 5 ... Tunnel insulating film 6 ... Floating gate (charge storage layer) 7 ... Gate insulating film 8 ... Control gate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 27/115

Claims (7)

[Claims] 1. A second substrate formed on a semiconductor substrate of a first conductivity type.
In a non-volatile semiconductor memory device in which a plurality of memory cells are formed in an array in a conductivity type well, the memory cell includes a first conductivity type source / drain diffusion layer formed in a second conductivity type well, and these source / drain. And a control gate formed on the charge storage layer via a gate insulating film. The charge storage layer and the second conductivity type well are formed on the charge storage layer. Data is rewritten by exchanging charges between the wells to form a depletion region by applying a potential to a well of the second conductivity type and a potential to a semiconductor substrate of the first conductivity type to transfer carriers to the second conductivity type. Injecting into the well, giving energy to carriers in the depletion region of the well to form hot carriers, and having means for injecting the hot carriers into the charge storage layer. Nonvolatile semiconductor memory device. 2. A second substrate formed on a semiconductor substrate of the first conductivity type.
In a nonvolatile semiconductor memory device in which a first conductivity type well is formed in a conductivity type well, and a plurality of memory cells are formed in an array in the first conductivity type well, the memory cell is formed in the first conductivity type well. A second conductive type source / drain diffusion layer, a charge storage layer formed through a tunnel insulating film in a region sandwiched between the source and drain, and a gate insulating film formed over the charge storage layer. And rewriting data by exchanging charges between the charge storage layer and the first-conductivity-type well to form a depletion region by applying a potential to the first-conductivity-type well. 2 conductivity type well, or in 1st conductivity type well or
A potential is applied to the second conductivity type diffusion layer formed in the region in contact with the conductivity type well to inject carriers into the first conductivity type well, and energy is applied to the carriers in the depletion region of the well to form hot carriers. A nonvolatile semiconductor memory device comprising means for injecting hot carriers into the charge storage layer. 3. A second conductive layer formed on a semiconductor substrate of the first conductivity type.
In a nonvolatile semiconductor memory device in which a first conductivity type well is formed in a conductivity type well, and a plurality of memory cells are formed in an array in the first conductivity type well, the memory cell is formed in the first conductivity type well. A second conductive type source / drain diffusion layer, a charge storage layer formed through a tunnel insulating film in a region sandwiched between the source and drain, and a gate insulating film formed over the charge storage layer. And rewriting data by exchanging charges between the charge storage layer and the first-conductivity-type well, and applying a potential to the second-conductivity-type well to deplete the first-conductivity-type well. A region is formed and a potential is applied to the first-conductivity-type semiconductor substrate or the first-conductivity-type diffusion layer formed in the second-conductivity-type well or in a region in contact with the second-conductivity-type well, so that carriers are secondarily supplied. Conductivity type A non-volatile semiconductor having means for injecting the carriers into the well of the first conductivity type through a fuel cell, applying energy to the carriers in the depletion region of the well to make them hot carriers, and injecting the hot carriers into the charge storage layer. Storage device. 4. A hot carrier is generated in the vicinity of the drain diffusion layer by turning on a selected memory cell before injecting the hot carrier into the charge storage layer, and the hot carrier is injected into the charge storage layer. 4. The nonvolatile semiconductor memory device according to claim 1, further comprising: 5. Before injecting hot carriers into the charge storage layer, carriers are injected from the second conductivity type well into the charge storage layer by a tunnel current, or carriers in the charge storage layer are injected into the second conductivity type. 2. The nonvolatile semiconductor memory device according to claim 1, further comprising means for emitting a tunnel current to the well. 6. Before performing a means for injecting hot carriers into the charge storage layer, carriers are injected from the first conductivity type well into the charge storage layer by a tunnel current, or carriers in the charge storage layer are subjected to the first conductivity. 4. The nonvolatile semiconductor memory device according to claim 2, further comprising means for emitting a tunnel current to the well. 7. The memory cells are connected in series in such a manner that their sources and drains are shared by adjacent ones to form a NAND cell, and the NAND cell has a memory cell array arranged in a matrix, The drain at one end of each NAND cell is connected to a bit line running in the column direction through a select gate, and the control gate in each NAND cell is continuously arranged for the NAND cells arranged in the row direction to form a word line. The non-volatile semiconductor memory device according to claim 1, wherein