The role of epitaxy in Au-Si eutectic bonding

Abstract

The properties of thick gold layers deposited on Si (100) wafer surfaces and annealed at 415°C are of crucial importance in the Au-Si eutectic bonding process. The presence of a thick, homogeneous silicon dioxide surface layer degrades considerably the adherence of the chip (Si wafer) to its substrate. We have shown that the presence of this oxide layer is associated with an underlying polycrystalline Au film. In contrast, for good chip-to-substrate bonding, the absence of this oxide is correlated to phase separation between Au and Si atoms, and epitaxy on Si (100) surface. The physical origin of these observations is discussed and a non-destructive method to determine the quality of the bonding is suggested.