Method of forming a trench isolation for semiconductor device with lateral projections above substrate

A fabrication method of a semiconductor device having a trench type element isolation structure, comprising:

• a first step of forming a first oxide film on a semiconductor substrate;
• a second step of forming an easily oxidizable film on said first oxide film;
• a third step of forming an anti-oxidation insulating film on said easily oxidizable film;
• a fourth step of patterning said anti-oxidation insulating film;
• a fifth step of etching said easily oxidizable film, said first oxide film and said semiconductor substrate using said patterned anti-oxidation insulating film as a mask to thereby form a trench in said easily oxidizable film, said first oxide film and said semiconductor substrate;
• a sixth step of oxidizing an exposed portion of said easily oxidizable film, which is exposed from a side surface of said trench, to thereby form a second oxide film, and oxidizing an exposed portion of said semiconductor substrate, which is exposed from bottom and side surfaces of said trench, to thereby form a third oxide film;
• a seventh step of forming a fourth oxide film on said anti-oxidation insulating film in such a manner that said trench is buried by said fourth oxide film;
• an eighth step of polishing said fourth oxide film to thereby expose said anti-oxidation insulating film;
• and
• a ninth step of removing said anti-oxidization film, said easily oxidizable film and said first oxide film to thereby form an element isolation oxide film containing at least said second to fourth oxide films.