Patent ID: 7811878

Claim:
A method for manufacturing an SOI substrate comprising a step of partially forming a mask oxide film ( 23 ) on the surface of a silicon substrate ( 12 ), a step of implanting oxide ions ( 16 ) into the surface of the substrate ( 12 ) through the mask oxide film ( 23 ), and a step of annealing the substrate ( 12 ) to form a buried oxide film ( 13 ) inside the substrate ( 12 ), further comprising between the step of implanting the oxygen ions ( 16 ) and the step of annealing the substrate ( 12 ): a step of etching the mask oxide film ( 23 ) so as to become a predetermined thickness; and a step of forming a buffer film ( 42 ) on a predetermined-width boundary area contacting with the side of the mask oxide film ( 23 ) on a silicon substrate surface ( 12 a ) serving as the SOI area and on the side of the mask oxide film ( 23 ).