Method for producing bonded wafer

A method for producing a bonded wafer, the method comprising:

• implanting ions of a light element such as hydrogen, helium or the like into a wafer for active layer at a predetermined depth position to form an ion implanted layer;
• bonding the wafer for active layer to a wafer for support substrate through an insulating film;
• exfoliating the wafer at the ion implanted layer at a heat temperature of between 400 and 600 degrees Celsius;
• a first heat treatment step, carried out at a first temperature, for conducting a sacrificial oxidation for reducing damage on a surface of an active layer exposed through the exfoliation;
• and
• a second heat treatment step, carried out at a second temperature, for raising a bonding strength, the second heat treatment step being continuously conducted after the first heat treatment step without removing an oxide film formed on the surface of the active layer,
• wherein the second temperature is higher than the first temperature;
• a cleaning step occurring after the second heat treatment step, and
• a planarization heat treatment step occurring after the cleaning step;
• wherein the first heat treatment step is a heat treatment in an oxygen atmosphere of not higher than 900° C.