Wafer-level Au–Au bonding in the 350–450 °C temperature range

Metal thermocompression bonding is a hermetic wafer-level packaging technology that facilitates vertical integration and shrinks the area used for device sealing. In this paper, Au–Au bonding at 350, 400 and 450 °C has been investigated, bonding wafers with 1 µm Au on top of 200 nm TiW. Test Si laminates with device sealing frames of 100, 200, and 400 µm in width were realized. Bond strengths measured by pull tests ranged from 8 to 102 MPa and showed that the bond strength increased with higher bonding temperatures and decreased with increasing frame width. Effects of eutectic reactions, grain growth in the Au film and stress relaxation causing buckles in the TiW film were most pronounced at 450 °C and negligible at 350 °C. Bond temperature below the Au–Si eutectic temperature 363 °C is recommended.