Patent ID: 7273795

Claim:
A method for forming a trench element separation region on a surface of a semiconductor substrate, comprising the steps of: depositing a first insulation film onto the surface of the semiconductor substrate; depositing and patterning a second insulation film on the first insulation film to form a second insulation film pattern; dry etching the semiconductor substrate using the second insulation film pattern as an etching mask to form a trench; forming an oxide film on an inner wall of the trench by thermally oxidizing the semiconductor substrate using the second insulation film pattern as an oxidation mask; removing a modified layer formed on the surface of the second insulation film during the thermal oxidation step by using a neutral radical including fluorine; etching the surface of the second insulation film by a predetermined thickness after the modified layer is removed; depositing a filling insulation film over the whole surface of the trench to completely fill the trench after the surface of the second insulation film is etched; and chemically mechanical polishing the filling insulation film using the second insulation film as a polishing stopper to form a trench filling insulating material.