Method of forming an isolation film in a semiconductor device

A method of forming an isolation film in semiconductor devices, comprising the steps of:

• forming a mask pattern on a silicon substrate in a memory cell region and a peripheral circuit region and then etching an exposed portion of the silicon substrate by a given depth to form a shallow trench;
• implanting an inert ion into the surface of the trench in the peripheral circuit region;
• performing a rapid thermal oxidization process in order to an anti-diffusion layer is formed at the bottom of the trench
• implementing an oxidization process so that an oxide film is grown on the surfaces of the trenches in the memory cell region and the peripheral circuit region, wherein the depth of the trench in the peripheral circuit region is increased due to excessive oxidization at the portion in which the ion is implanted;
• and
• forming an oxide film on the entire structure so that the trench is buried and planarizing the surface of the oxide film.