Method of forming and operating trench split gate non-volatile flash memory cell structure

• US 6,580,641 B2
• Filed: 10/31/2002
• Issued: 06/17/2003
• Est. Priority Date: 04/24/2001
• Status: Expired due to Fees

• Current Assignee: Ememory Technology Inc.
• Original Assignee: Ememory Technology Inc.
• Inventors: Kin, Ya-Chin, Chen, Fu-Yuan, Hsu, Ching-Hsiang, Wu, Meng-Yi, Lee, Kung-Hong, Yang, Ching-Song, Chou, Hsin-Fen
• Primary Examiner(s): Tran, M.
• Application Number:
  US10/065,590
• Publication Number:
  US 20030086296A1
• Time in Patent Office: 229 Days
• Field of Search: 365/185.18, 365/185.33
• US Class Current: 365/185.18
• CPC Class Codes: G11C 16/0433 comprising cells containing a single floating gate transistor and one or more separate select transistors
• CPC Class Codes: H01L 29/42328 with at least one additional gate other than the floating gate and the control gate, e.g. program gate, erase gate or select gate
• CPC Class Codes: H01L 29/42336 with one gate at least partly formed in a trench
• CPC Class Codes: H01L 29/66825 with a floating gate H01L29/6684 takes precedence
• CPC Class Codes: H10B 41/23 with source and drain on different levels, e.g. with sloping channels
• CPC Class Codes: H10B 69/00 Erasable-and-programmable ROM [EPROM] devices not provided for in groups H10B41/00 - H10B63/00, e.g. ultraviolet erasable-and-programmable ROM [UVEPROM] devices

Abstract

A method of forming and operating a trench split-gate non-volatile flash memory cell structure. The auxiliary gate of the structure is formed inside a trench on one side of the gate and the source terminal is underneath the auxiliary gate, thereby reducing overall area occupation of the auxiliary gate and the source terminal relative to the cell and increasing packing density. By enclosing the common source terminal inside a deep N-well layer, source resistance for reading data from the cell is reduced and the process of etching out a contact opening is simplified. The structure also ensures the injection of most hot electrons into the floating gate, thereby increasing execution speed.

Claims

1. A trench split-gate non-volatile flash memory cell structure, comprising:

a P-type substrate;

a deep N-well layer above the p-type substrate;

a shallow P-well layer above the deep N-well layer;

a source region inside the deep N-well layer;

a trench auxiliary gate region inside the deep N-well layer and the shallow P-well layer above the source region;

a gate region above the shallow P-well layer on one side of the auxiliary gate region; and

a drain region inside the shallow P-well layer on one side of the gate region.

2. The flash memory cell structure of claim 1, wherein the trench auxiliary gate further comprises:

a polysilicon layer; and

an oxide layer at the bottom of and on each side of the polysilicon layer.

3. The flash memory cell structure of claim 1, wherein the structure further includes a metal silicide layer over the exposed surface of the drain region and the trench auxiliary gate region.

4. The flash memory cell structure of claim 1, wherein the gate includes:

a first polysilicon layer;

a second polysilicon layer above the first polysilicon layer; and

an isolation layer between the first polysilicon layer and the second polysilicon layer and on the sidewalls of the first polysilicon layer.

5. The flash memory cell structure of claim 4, wherein the isolation layer includes an oxide-nitride-oxide layer of silicon.

6. The flash memory cell structure of claim 4, wherein the isolation layer includes an oxide-nitride layer of silicon.

7. The flash memory cell structure of claim 4, wherein the isolation layer includes a nitride layer of silicon.

8. A method of operating a trench split-gate non-volatile flash memory cell, wherein a word line voltage, a source voltage, an auxiliary gate voltage and a bit line voltage are applied to the gate region, the source region, the trench auxiliary gate region and the drain region of the flash memory cell respectively, the bottom section of the flash memory cell comprises three layers including, from top to bottom, a shallow P-well layer, a deep N-well layer and a P-type substrate such that the source region is inside the deep N-well layer, and the trench auxiliary gate region is above the source region inside the shallow P-well layer and the deep N-well layer, the operating method comprising the steps of:

applying a high voltage to the word line, applying a voltage lower than the word line voltage to the bit line, applying a voltage lower than both the word line voltage and the bit line voltage to the source terminal and applying a voltage lower than both the word line voltage and the bit line voltage to the auxiliary gate to program data into the flash memory cell;

applying a low voltage to the word line, applying a voltage higher than the word line voltage to the bit line, applying a voltage higher than the word line voltage but lower than the bit line voltage to the source terminal and applying a voltage higher than the word line voltage but lower than the bit line voltage to the auxiliary gate to erase data from the flash memory cell; and

applying a high voltage to the word line, applying a voltage lower than the word line voltage to the source terminal, applying a voltage higher than the source terminal voltage to the bit line and applying a voltage higher than the source terminal voltage to the auxiliary gate to read data from the flash memory cell.

9. The operating method of claim 8, wherein the ranges applied to the word line, the source terminal, the bit line and the auxiliary gate for programming data into the flash memory cell are 8V˜

16V, 0V, 4V˜

10V and 1V˜

5V respectively.

10. The operating method of claim 8, wherein the ranges applied to the word line, the source terminal, the bit line and the auxiliary gate for erasing data from the flash memory cell are −

8V˜

−

16V, 0V, 0V˜

5V and 0V respectively.

11. The operating method of claim 8, wherein the ranges applied to the word line, the source terminal, the bit line and the auxiliary gate for reading data from the flash memory cell are 5V˜

10V, 0V, 1V˜

5V and 1V˜

5V respectively.