Backside Metallization of Ag–Sn–Ag Multilayer Thin Films and Die Attach for Semiconductor Applications

Abstract

Backside metallization, which offers the advantages of a thin die-attach layer, excellent ohmic contacts, good thermal dissipation, and electrical conduction, is a reliable die-attach method for high-temperature semiconductor devices. Optimized Ag–Sn–Ag thin film structures have been deposited as a backside metal layer and their mechanical and electrical characteristics evaluated as a replacement for conventional Au-based backside metal. The results confirmed that the Ag/Sn/Ag sandwich structure provided more reliable properties than the Sn/Ag and Ag/Sn structures. After the die-bonding process using the Ag/Sn/Ag backside metal, Cu6Sn5, Cu3Sn, and Ag3Sn intermetallic compounds were observed at the interface between the Si chip and Cu-plated Alloy 42 lead frame. The shear strength of the Ag/Sn/Ag backside metal was superior to that of conventional Au-12Ge backside metal, and its electrical characteristics met the requirement specifications of a commercial discrete semiconductor package.