KR100199380B1 - Flash eeprom cell - Google Patents

Abstract

The present invention provides a flash EPIROM cell capable of increasing the overall channel width by bending a boundary between a channel region and a field region of a cell up and down between a stack channel and a select channel, thereby making the select channel wider than the conventional one. It is about.

Description

Flash Ipyrom Cell

1 is a layout for explaining a conventional flash Y pyrom cell.

2 is a cross-sectional view of the state taken along the line A-A of FIG.

3 is a cross-sectional view of the line B-B of FIG.

4 is a layout for explaining a flash Y pyrom cell according to the present invention.

5 is a cross-sectional view taken along the line C-C of FIG.

* Explanation of symbols for main parts of the drawings

1 silicon substrate 2 tunnel oxide film

3: interlayer insulation only 4: floating gate

5: control gates 6 and 7: source and drain regions

8 gate oxide film 9 select gate

10 and 11: source and drain lines 12: channel

13: field area

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to flash easy pyrom cells, and more particularly, to a flash easy pyrom cell having a virtual ground split gate structure.

In general, flash Y pyrom cells are electrically programmable and erased, and are classified into stacked structures and split gate structures.

FIG. 1 is a layout diagram for explaining a flash Y pyrom cell having a virtual ground split gate structure, and FIG.

As shown in FIG. 1 and FIG. 2, a tunnel oxide film 2, a floating gate 4, an interlayer insulating film 3 and a control gate 5 are sequentially formed on the silicon substrate 1. Further, after the source and drain regions 6 and 7 are formed in the silicon substrate 1, the gate oxide film 8 and the select gate 9 are sequentially formed on the entire structure. The channel 12 of each cell is formed in the transverse direction as shown in FIG. The drain line and source element lines 11 and 10 are arranged in the longitudinal direction and the remaining portion becomes the field region 13. The select gate 9 is positioned on the channel 12 in the horizontal direction, the control gate 5 is disposed on both sides of the drain line 11 in the longitudinal direction, and the floating gate 4 is disposed only under the control gate 5. .

In a flash Y pyrom cell having such a virtual ground split gate structure, hot electrons are generated between a stack channel formed under a floating gate and a select channel formed under a select gate. When the hot electrons are stored in the floating gate, the threshold voltage rises to become OFF-cell, while the hot electrons from the floating gate enter the drain region through the Fowler-Nordheim tunneling. When discharged, the threshold voltage is lowered to become an on-cell.

The program, erase and read operations of the flash Y pyrom cell having the above-described characteristics will be described in detail as follows.

A. Program Operation

During programming, a voltage of about 13V on the control gate, about 2V on the select gate, about 5V on the drain region, and 0V on the source region applies a high electric field between the select channel below the select gate and the stack channel below the floating gate. Is formed. As the electrons move from the source region to the drain region by the electric field, hot electrons are generated. Since the potential of the floating gate is released by the voltage applied to the control gate, hot electrons move to the floating gate. When electrons are stored in the floating gate, a certain level of voltage is applied to the control gate by electric field screening. When applied, the channel is not inverted. In other words, the threshold voltage is increased. The cell having the increased threshold voltage is recognized as off-cell by the peripheral circuit because a low current flows when read.

B. Erase

During erasing, if a voltage of about -12V is applied to the control gate and about 5V to the drain region, a potential difference of 10V or more is generated between the floating gate and the source region, so that the electrons of the floating gate are called Fowler-Nordheim tunneling (Fowler-Nordheim). Is emitted to the drain region through the tunnel oxide film. Then, when the threshold voltage of the cell decreases and reads again, a high current flows and is recognized as an on-cell by the peripheral circuit.

C. Read Action

When reading, if a voltage of about 4V is applied to the control gate, about 5V to the select gate, about 0V to the drain region, and about 2V to the source region, the channel under the floating gate may or may not be formed depending on the amount of charge in the floating gate. As a result, the value of the flowing current changes, and thus the periphery circuit recognizes the on or off cell.

In the operation of the flash Y pyrom cells as described above, the current flowing through each cell has a decisive effect on the sensing speed, that is, the access time, and the larger the current value, the less the possibility of malfunction of the sense amplifier. However, as described above, since a stack channel and a select channel are connected to one cell in series, it is difficult to increase a current value flowing through the cell.

Accordingly, the present invention provides a flash Y pyrom which bends the boundary of the channel region and the field region up and down between the stack channel and the select channel to increase the overall channel width by widening the pole of the select channel more than the conventional one. The purpose is to provide a cell.

Flash IPIROM cell according to the present invention for achieving the above object has a floating gate, a control gate, a select gate, a drain region, a source region and a field region and is applied to the floating gate, control gate mill select gate In a flash EPIROM cell in which a stack channel and a select channel are formed according to a voltage, and which can be electrically programmed and erased, the field region is formed so that the width of the select channel is larger than the width of the stack channel. It is done.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

4 is a layout for explaining a flash Y pyrom cell according to the present invention.

As shown in the drawing, the channel 12 including the stack channel and the select channel is formed in the horizontal direction, and the drain lines and the source lines 11 and 10 are disposed in the vertical direction. Except for 12, 11 and 10, the remaining portion becomes the field region 13. In order to increase the channel 12 width, the present invention maintains the width of the field region adjacent to the stack channel as before but the width of the field region adjacent to the select channel is smaller than that. Therefore, the width of the select channel becomes larger than the width of the stack channel.

On the other hand, the select gate 9, the control gate 5 and the floating gate 4 are arranged as before.

FIG. 3 is a cross-sectional view of the first line BB of FIG. 1, and FIG. 5 is a cross-sectional view of the fourth line CC of FIG. 4, as shown in the drawing. Since the width is much smaller than that of the prior art, the width of the channel is thus large. For example, assuming that the width of the field region adjacent to the conventional select channel is α, the width of the field region adjacent to the select channel of the present invention is α-K.

As described above, according to the present invention, the following effects can be obtained.

First, by increasing the width of the select channel while maintaining the cell size, the cell precursor is increased to speed up the read operation and consequently reduce the access time.

Second, a malfunction of the sense amplifier can be prevented by increasing the sensing current.

Third, there is an excellent effect of increasing the density of the cell error by increasing the cell current without increasing the cell size.

Claims (2)

A floating gate, a control gate, a select gate, a drain region, a source region, and a field region are provided, and a stack channel and a select channel are formed according to voltages applied to the floating gate, the control gate, and the select gate. An erasable flash epyrom cell, wherein the width of the select channel is larger than the width of the stack channel. 2. The flash Y pyrom cell of claim 1, wherein a width of the field oxide film adjacent to the select channel is smaller than a width of the field oxide film adjacent to the stack channel.