Reproducible Reliable AuSi Eutectic Wafer Bond Process With High Yield

The AuSi eutectic bond process is a well known and important technique in the field of single chip packaging. When it comes to low-cost and hermetic sealed packages for MEMS/NEMS sensors and actuators this technology has its decisive merits. The AuSi bonding is a low-temperature process with an electric conductive alloy. To achieve a reliable bonding with 100% yield is quite difficult, especially for large areas. In our institute we made several analyses with different process parameters and surface properties variations. The results show that the surface condition of the silicon side of the wafer pair as well as the process parameters are very important factors in relation to the yield of the eutectic bond. We also did investigations on the thickness of the gold layer. Unlike conventional AuSi wafer bonding technologies [1] our technique does not need several μm thick gold layers. We were able to achieve 100% bond yield with 1500nm and even 150nm thin gold layers. Another result we found was that a good bonding process is not only depending on the value of applied temperature and time, there is also an important influence because of the heat flow and applied pressure. In the presentation we would like to introduce our results and experience, plus we will present the coherences of parameter variations for achieving 100% yield.