The temperature of wafer bonding can be reduced by using a thin interm
ediate layer of sodium silicate solution. This paper presents the resu
lts of our investigation on the bond quality, obtained by scanning aco
ustic microscopy. Strong bonds were obtained at 150 degrees C between
oxide-covered silicon wafers. However, at temperatures higher than 200
degrees C, voids appeared at the interface and they did not vanish du
ring annealing. The strength of the bond was measured by a tensile tes
t. Eventually, a model for the bonding mechanism is proposed.