Method for manufacturing semiconductor device

1. A method for forming an element isolation film of a semiconductor device, comprising the steps of:

sequentially forming a pad oxide film, a pad nitride film and a mask oxide film on a semiconductor substrate on which a first region for forming a high voltage device and a second region for forming a low voltage device or a flash memory cell are defined;

etching the mask oxide film, the pad nitride film and the pad oxide film in the first region and the mask oxide film in the second region, and forming an oxide film for the high voltage device in the first region, wherein the oxide film for the high voltage device has a first thickness;

removing the residual pad nitride film in the second region, wherein the oxide film for the high voltage device has a second thickness;

performing a cleaning process to remove the residual pad oxide film in the second region and to partially remove the oxide film for the high voltage device in the first region, wherein the oxide film for the high voltage device has a third thickness; and,

forming a tunnel oxide film over the resulting structure,

wherein a gate oxide film for a high voltage device including the oxide film for the high voltage device and the tunnel oxide film is formed in the first region, and the tunnel oxide film for the low voltage device and cell is formed in the second region.

2. The method of claim 1 , wherein the cleaning process is performed with HF aqueous solution diluted by H 2 O at a ratio of 50:1 to 300:1.

3. The method of claim 2 , wherein the cleaning process is performed for 30 to 100 seconds.

4. The method of claim 1 , wherein the nitride film is removed with buffered oxide etchant and H 3 PO 4 .

5. The method of claim 4 , wherein the nitride film strip process is performed for 500 to 1200 seconds with the buffered oxide etchant, and for 5 to 10 minutes with the H 3 PO 4 .

6. The method of claim 1 , wherein the first thickness ranges from 350 to 700 Å, the second thickness ranges from 300 to 400 Å, and the third thickness ranges from 250 to 350 Å.

7. The method of claim 1 , wherein the step for etching the mask oxide film, the pad nitride film and the pad oxide film in the first region and the mask oxide film in the second region, and forming the oxide film for the high voltage device in the first region comprises the steps of:

forming a photoresist film pattern for opening the first region on the mask oxide film;

etching the mask oxide film in the first region and the photoresist film pattern;

etching the pad nitride film in the first region by using the mask oxide film in the second region as an etch mask;

etching the pad oxide film in the first region and the mask oxide film in the second region; and

forming the oxide film for the high voltage device in the first region according to an oxidation process.