The Crack Opening Method in Silicon Wafer Bonding How Useful Is It

The crack opening method is widely used for the determination of the surface energy of two bonded wafers, which is associated with the energy required to separate bonded wafers. In the present paper the dependence of the measured surface energy of bonded silicon wafers on the time after insertion of a blade at various pressures, silanol group densities, and annealing temperatures is reported. At normal conditions (air pressure, room temperature, 30% humidity) a strong dependence of the effective surface energy on the insertion time is found for wafers which were annealed at 200, 400, and 900°C. For bonded wafers without subsequent annealing this phenomenon is not observed. Additional measurements under reduced pressure show that the debonding process appears to be related to the adsorption and chemical reaction of water molecules at sites of broken bonds at the opened surfaces. We conclude that a meaningful comparison of measured surface energies requires detailed information on the measurement conditions.