Wafer bonding of gallium arsenide on sapphire

Three-inch (100) gallium arsenide wafers were bonded to <(1(1)over bar 02)> sapphire in a micro-cleanroom at room temperature under hydrophilic or hydrophobic surface conditions. Subsequent heating up to 500 degrees C increased the bond energy of the GaAs-on-sapphire (GOS) wafer pair close to the fracture energy of the bulk material. The bond energy was measured as a function of the temperature. Since the thermal expansion coefficients of GaAs and sapphire are close to each other, the bonded wafer pair is stable against thermal treatment and quenching in liquid nitrogen. During heating in different gas atmospheres, macroscopic interface bubbles and microscopic imperfections were formed within the bonding interface, which were analysed by transmission electron microscopy (TEM). These interface bubbles can be prevented by hydrophobic bonding in a hydrogen atmosphere.