US Patent 8008164 Wafer bonding method and wafer structure

A wafer bonding method includes providing a primary wafer and a plurality of secondary wafers, wherein the primary wafer is larger than the secondary wafers. An intermediate material layer is formed on at least one of a bonding surface of the primary wafer and bonding surfaces of the secondary wafers. The intermediate material layer has a thermal expansion coefficient greater than the thermal expansion coefficient of the primary wafer and the thermal expansion coefficient of the secondary wafers. The secondary wafers are bonded onto the primary wafer.