Al-Ge Diffusion Bonding for Hermetic Sealing Application

Abstract

The high-temperature requirement of Al-Ge eutectic bonding stands as a major obstacle to its wider acceptance for hermetic sealing application in the microelectromechanical systems packaging industry, in particular for temperature-sensitive devices. It has been demonstrated that a reduction in bonding temperature is feasible without compromising the hermeticity. The change in the mode of bonding from eutectic to solid-state diffusion did not have a dramatic impact on the bonding quality. However, this resulted in a substantial increase in bonding time. The shear strength also deteriorated as a result of the decrease in thickness of the reaction interface. However, the shear strength still complied with military standards. It has been confirmed that a hermetic seal could still be achieved without any solidification occurring at the interface. This is feasible since the interdiffusion coefficients of Al in (Ge) phase and Ge in (Al) phase are closer and are comparable to diffusion between solid-solution phases of identical metals such as in Au-Au, Cu-Cu, and Si-Si bonding, which are generally used for such hermetic sealing application. An appropriate stacking mechanism for Al-Ge diffusion bonding is identified to overcome the limitations with respect to surface topography.