T. Martini et al., THE CRACK OPENING METHOD IN SILICON-WAFER BONDING - HOW USEFUL IS IT, Journal of the Electrochemical Society, 144(1), 1997, pp. 354-357
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.