Platinum Diffusion Barrier Breakdown in a-Si/Au Eutectic Wafer Bonding

Eutectic bonding in semiconductor fabrication requires a large degree of control over the stoichiometry and precision film thickness of the bonding materials. To reduce the migration of the bonding layers, diffusion barriers are typically utilized. Here, we demonstrate that a widely utilized diffusion barrier, Pt, does not prevent migration of Si in Si/Au eutectic bonding. We observe that this barrier breaks down at approximately 375°C, above the Au-Si eutectic temperature (363°C), and encourages consumption of the silicon substrate leading to uncontrolled stoichiometry variations and creation of microvoids. This failure results in reductions of bond strength and hermeticity. As an alternative, silicon dioxide is observed to prevent the silicon diffusion and subsequent substrate loss.