Method for fabricating flash memory device

1. A method of fabricating a flash memory device comprising:

depositing a first oxide layer on a substrate;

depositing a first polysilicon layer on the first oxide layer;

forming a second oxide layer on a top surface and on grain boundaries of the first polysilicon layer;

removing the second oxide layer;

performing a heat treatment to make the first polysilicon layer have an embossed shape both on the top surface and on lateral faces of the grain boundaries;

depositing a dielectric layer on the top of the first polysilicon layer;

depositing a second polysilicon layer on the entire surface of the dielectric layer; and

removing some parts of the dielectric layer and the second polysilicon layer through a patterning process and an etching process.

2. The method as defined by claim 1 , wherein the second oxide layer is removed by HF vapor gas.

3. A method of fabricating a flash memory device comprising:

depositing a first oxide layer on a substrate;

depositing a first polysilicon layer on the first oxide layer;

forming a second oxide layer on the entire surface of the first polysilicon layer;

removing the second oxide layer;

performing a high-temperature vacuum heat treatment to make the first polysilicon layer have an embossed shape;

depositing a dielectric layer on the top of the first polysilicon layer;

depositing a second polysilicon layer on the entire surface of the dielectric layer; and

removing some parts of the dielectric layer and the second polysilicon layer through a patterning process and an etching process.

4. The method as defined by claim 3 , wherein the second oxide layer is formed on a top surface and grain boundaries of the first polysilicon layer.

5. The method as defined by claim 3 , wherein the second oxide layer is removed by HF.

6. The method as defined by claim 5 , wherein the HF vapor gas comprises HF and DIW and has a concentration of HF between 20% and 30%.

7. The method as defined by claim 3 , wherein the heat treatment is performed at a temperature between 600° C. and 700° C. at a pressure about 12 mT for 1 hour to 4 hours.

8. A method of fabricating a flash memory device comprising:

depositing a first oxide layer on a substrate;

depositing a first polysilicon layer on the first oxide layer,

forming a second oxide layer on the entire surface of the first polysilicon layer;

removing the second oxide layer with a mixture of HF and deionized water (DIW) having between 20% and 30% HF;

heating the first polysilicon layer to provide the first polysilicon layer with an embossed shape;

depositing a dielectric layer on the first polysilicon layer;

depositing a second polysilicon layer on the entire surface of the dielectric layer; and

removing some parts of the dielectric layer and the second polysilicon layer through a patterning process and an etching process.

9. The method as defined by claim 8 , wherein the second oxide layer is formed on the top surface and the grain boundaries of the first polysilicon layer.

10. The method as defined by claim 8 , wherein the heating is performed at a temperature between 600° C. and 700° C. at a pressure about 12 mT for 1 hour to 4 hours.

11. A method of fabricating a flash memory device comprising:

depositing a first oxide layer on a substrate;

depositing a first polysilicon layer on the first oxide layer;

forming a second oxide layer on the entire surface of the first polysilicon layer;

removing the second oxide layer;

heating the first polysilicon layer at a temperature between 600° C. and 700° C. at a pressure about 12 mT for 1 hour to 4 hours to provide the first polysilicon layer with an embossed shape;

depositing a dielectric layer on the top of the first polysilicon layer;

depositing a second polysilicon layer on the entire surface of the dielectric layer; and

removing some parts of the dielectric layer and the second polysilicon layer through a patterning process and an etching process.

12. The method as defined by claim 11 , wherein the second oxide layer is formed on the top surface and the grain boundaries of the first polysilicon layer.

13. The method as defined by claim 11 , wherein the second oxide layer is removed by HF.

14. The method as defined by claim 2 , wherein the HF vapor gas comprises a mixture of HF and deionized water (DIW).

15. The method as defined by claim 14 , wherein the HF vapor gas has a concentration of HF between 20% and 30%.

16. The method as defined by claim 1 , wherein the heat treatment is performed at a temperature between 600° C. and 700° C.

17. The method as defined by claim 16 , wherein the heat treatment is performed at a pressure of about 12 mT.

18. The method as defined by claim 16 , wherein the heat treatment is performed for a time of from 1 hour to 4 hours.