Method for fabrication semiconductor device having trench isolation structure

A method for fabricating a semiconductor device comprising:

• (1) selectively etching a semiconductor substrate to form a trench therein;
• (2) conducting a process at least once, said process comprising following substeps (a) and (b):
• (a) forming an electrically insulating film to have a film thickness where the trench is not fully buried, thereby leaving a space in the trench;
• and
• (b) conducting a heat treatment;
• (3) forming an electrically insulating film to fill the space;
• and
• (4) conducting a heat treatment.

A method of fabricating a semiconductor device comprising:

• performing a selective etching to form a trench in a semiconductor substrate by using a first insulating film formed on said semiconductor substrate as a mask, said trench having a first width;
• performing a first deposition to form a first high-density plasma insulating film in said trench, said first high-density plasma insulating film having a second width that is smaller than said first width to thereby leave a space in said trench;
• performing a first heat treatment on said second insulating film;
• performing a second deposition to form a second high-density plasma insulating film in said space;
• and
• performing a second heat treatment on said second high-density plasma insulating film.