Patent ID: 7067389

Claim:
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.