The role of Ni buffer layer between InSn solder and Cu metallization for hermetic wafer bonding

In order to achieve low temperature hermetic sealing for MEMS and IC packaging, wafer-wafer bonding using In/Sn and Cu metallization system was investigated. We found that in order to get high bonding yield, a thin buffer layer between solder and Cu metallization is necessary except suitable bonding parameters. In this paper, diffusion phenomena between solders and metallization were studied, the conception of buffer layer for wafer eutectic wafer bonding was introduced, the effect of Ni thickness on the bonding and hermetic properties were reported.