Method for forming gate oxide of semiconductor device

1. A method for forming a gate oxide of a semiconductor device, comprising the steps of:

defining a first region where a gate oxide having a first thickness will be formed, a second region where a gate oxide having a second thickness will be formed and a third region where a gate oxide having a third thickness will be formed on a semiconductor substrate;

forming a first oxide film on the semiconductor substrate and forming a second oxide film on the first oxide film;

blocking the first region and selectively removing portions of the second oxide film and the first oxide film, which are formed on the second region and the third region;

forming a third oxide film on the semiconductor substrate;

blocking the first region and the second region and selectively removing a portion of the third oxide film, which is formed on the third region; and

forming a fourth oxide film on the semiconductor substrate and then forming a nitride film thereon,

wherein a gate oxide-having a triple structure of the first oxide film/second oxide film/nitride film is formed in the first region, a gate oxide having a double structure of the third oxide film/nitride film is formed in the second region and a gate oxide having a double structure of the fourth oxide film/nitride film is formed in the third region.

2. The method of claim 1 , wherein the first oxide film is formed through wet oxidation and the third and fourth oxide films are formed through thermal oxidation.

3. The method of claim 1 , wherein the thickness ratio of the first oxide film to the second oxide film is 1:20.

4. The method of claim 3 , wherein the first oxide film formed by a thickness in the range of 40 to 220 Å and the second oxide film is formed by a thickness in the range of 200 to 1100 Å.

5. The method of claim 1 , wherein the first oxide film is formed in the ambient of H 2 /O 2 at a temperature in the range of 800 to 900° C. through wet oxidation.

6. The method of claim 1 , wherein the second oxide film corresponds to a TEOS oxide formed through LP-CVD.

7. The method of claim 1 , wherein the second oxide film is formed at a low temperature in the range of 600 to 650° C.

8. The method of claim 1 , wherein the portions of the first and second oxide films, which are formed on the second region and the third region, are removed through an etch process using 1:20 BOE.

9. The method of claim 1 , wherein the third oxide film is formed by a thickness in the range of 100 to 150 Å.

10. The method of claim 1 , wherein the third oxide film is formed in the ambient of H 2 /O 2 at a high temperature in the range of 800 to 900° C. such that the second oxide film is heat treated to be hardened while the third oxide film is formed.

11. The method of claim 1 , wherein the portion of the second oxide film, which is formed on the third region, is removed through an etch process using 1:20 BOE.

12. The method of claim 1 , wherein the fourth oxide film is formed by a thickness in the range of 15 to 20 Å on the third region in the ambient of H 2 /O 2 at a temperature in the range of 650 to 700° C.

13. The method of claim 1 , wherein the nitride film is formed through plasma nitridation.

14. The method of claim 12 , wherein the plasma nitridation is performed at a temperature in the range of 400 to 450° C. using remote plasma.