High-Temperature Mechanical Integrity of Cu-Sn SLID Wafer-Level Bonds

Abstract

Wafer-level Cu-Sn SLID (Solid-Liquid Interdiffusion)-bonded devices have been evaluated at high temperature. The bonding process was performed at 553 K (280°C) and the mechanical integrity of the bonded samples was investigated at elevated temperatures. The die shear strength of Cu-Sn systems shows a constant behavior (42 MPa) for shear tests performed from room temperature [RT-298 K (25°C)] to 573 K ( to 300°C). This confirms experimentally the high-temperature stability of Cu-Sn SLID bonding predicted from phase diagrams. The fractography of sheared samples indicates brittle-fracture mode for all samples shear tested from RT to 573 K (300°C). The two dominating failure modes are Adhesive fracture between the Ti-W adhesion layer and the Si, and interface fracture at the original bond interface. This indicates that the bonding material itself is stronger than the observed shear strength values, and since these interfaces can be improved with process optimization even stronger bonds can be achieved. The presented work offers fundamental evidence of the Cu-Sn SLID bonding process for operating microelectronics and MEMS at high temperature.