Method for manufacturing bonded SOI wafer

A method for manufacturing a bonded SOI wafer comprising:

• forming a silicon oxide film on a surface of at least one wafer of a bond wafer and a base wafer made of a silicon single crystal by a thermal oxidation treatment, implanting at least one gas ion of a hydrogen ion and a rare gas ion into the bond wafer from a surface thereof to form an ion-implanted layer, bonding the ion-implanted surface of the bond wafer to a surface of the base wafer through the silicon oxide film, and delaminating the bond wafer at the ion-implanted layer;
• wherein
• the thermal oxidation treatment includes at least one of a thermal oxidation during temperature-rising and a thermal oxidation during temperature-falling, and is performed by using a batch type heat treatment furnace, thereby forming the silicon oxide film in such a way that the oxide film buried in the delaminated bonded SOI wafer has a concentric oxide film thickness distribution, and
• the bonded SOI wafer after delaminating the bond wafer is subjected to a reducing heat treatment to make a film thickness range of the buried oxide film being smaller than a film thickness range before the reducing heat treatment.