THE CRACK OPENING METHOD IN SILICON-WAFER BONDING - HOW USEFUL IS IT

The crack opening method is widely used for the determination of the s urface energy of two bonded wafers, which is associated with the energ y required to separate bonded wafers. In the present paper the depende nce of the measured surface energy of bonded silicon wafers on the tim e after insertion of a blade at various pressures, silanol group densi ties, and annealing temperatures is reported. At normal conditions (ai r pressure, room temperature, 30% humidity) a strong dependence of the effective surface energy on the insertion time is found for wafers wh ich were annealed at 200, 400, and 900 degrees C. For bonded wafers wi thout subsequent annealing this phenomenon is not observed. Additional measurements under reduced pressure show that the debonding process a ppears 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 de tailed information on the measurement conditions.