Method of manufacturing a semiconductor device using a trench isolation technique

A method of manufacturing a semiconductor device comprising:

• a first step of depositing an etching stopper film on a semiconductor substrate having a plurality of element formation regions in which respective MOS transistors are to be formed and a trench isolation region for separating said individual element formation regions;
• a second step of performing etching using a mask with an opening corresponding to said isolation region so as to partially remove said etching stopper film and said semiconductor substrate from said isolation region and thereby form a trench having a specified depth in said semiconductor substrate;
• a third step of depositing, on the substrate formed with said trench, an underlying insulating film;
• a fourth step of depositing, on the substrate with said underlying insulating film deposited thereon, a film for filling made of a material with excellent step coverage;
• a fifth step of etching back said film for filling so as to form a buried layer in a position at least lower than an upper edge of said trench;
• a sixth step of depositing, on the substrate with said buried layer formed therein, an insulating film for isolation;
• a seventh step of substantially planarizing a surface of the substrate by removing said insulating film for isolation till at least a surface of said etching stopper film becomes exposed, while leaving said insulating film for isolation in said trench, so as to form isolation;
• and
• an eighth step of forming MOS transistors each having a gate insulating film, a gate electrode, and source/drain regions in said respective element formation regions.