Thermal Stability of Au-Sn/Near Noble Metal Barrier Metallization Systems

Abstract
We studied the reaction barrier characteriatics and thermal stability of evaporated Pd, Pt and Rh films when used with Au-Sn (30 wt% Sn). Sn in Au-Sn diffused preferentially into a barrier metal uniformly for all three metals. The diffusion coefficient was sufficiently small for Pt and Rh. Rh showed the samllest diffusion coefficient between 200°C and 400°C with the highest activation energy, 1.95 eV, below the melting point of Au-Sn (280°C). This result demonstrates the usefulness of Pt, and especially Rh, in highly stable metallization systems applicable to flip-chip integration.