Bonding wafers with sodium silicate solution

The temperature of wafer bonding can be reduced by using a thin intermediate layer of sodium silicate solution. This paper presents the results of our investigation on the bond quality, obtained by scanning acoustic 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 during annealing. The strength of the bond was measured by a tensile test. Eventually, a model for the bonding mechanism is proposed.