Wafer-level AuSn and CuSn bonding for MEMS encapsulation

In this work we have studied AuSn and CuSn Solid-Liquid Interdiffusion (SLID) bonding that can be used for wafer-level encapsulation. SLID bonding of these metal structures takes place at temperatures around 300°C but show higher re-melting temperatures because of the solid-liquid intermetallic phase transformation. 6″ silicon wafers were bonded with 60 ßm wide, electroplated, AuSn and CuSn seal ring structures. Wafer bonding temperature was varied between 300°C and 450°C, the used bonding force was 3.5 kN under the ambient pressure less than 1×10
⁻³
mbar. The bonding quality was evaluated with different seal ring metal structures and bonding parameters.