Lateral diffusion of In and formation of AuIn2 in Au-In thin films

Lateral diffusion of In in 20–100-nm-thick Au-In films has been studied in the 60–150 °C temperature range. Indium diffusion due to the chemical potential gradient occurs from In to Au-In with an AuIn2 phase being formed in the diffusion zone. The growth of the diffusion zone obeys a parabolic rate law with the growth rate strongly dependent on In concentration of the films. In order to understand these phenomena, the kinetics of the AuIn2 phase formation is analyzed considering In diffusion due to the chemical potential gradient with subsequent formation of AuIn2 at the diffusion front. As a result of this analysis, the diffusion coefficient of In in AuIn2 films is obtained as DIn=1.2×10−3 exp(−0.52 eV/kT) cm2/s. Grain boundary diffusion is thought to be the dominant mechanism. Additionally, a combined diffusion parameter δDg (δ is the grain boundary width) of 1.3×10−16 cm3/s (60 °C) is obtained.