Method for forming isolation film for semiconductor devices

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

• successively forming a pad oxide film and a pad nitride film on a silicon substrate having an active region and a field region;
• etching the pad nitride film, the pad oxide film and the silicon substrate to form a trench in the active region of the substrate;
• forming a sidewall oxide film on the surface of the trench;
• removing the pad nitride film;
• forming a linear nitride film on the sidewall oxide film and the pad oxide film;
• subjecting the linear nitride film to CMP such that a portion of the pad oxide film on the field region of the substrate is exposed;
• removing the exposed pad oxide film to expose the field region of the substrate;
• oxidizing the exposed field region of the substrate to form an oxide film to the same depth as the bottom of the trench;
• removing the linear nitride film;
• removing the sidewall oxide film to expose the active region of the substrate;
• and
• forming a silicon epitaxial layer serving as an active layer on the exposed active region of the substrate to the same height as the oxide film.