Copper distribution in sputtered Al/Cu films

Abstract

The copper distribution in sputtered aluminum–copper films depends on copper concentration and deposition temperature. At high deposition rates the film temperature is high enough for diffusion to occur without external substrate heating. Targets containing 0.5%, 2%, and 4% copper were used to deposit films by dc magnetron sputtering. No segregation was found in the 0.5% Cu films at film deposition temperatures as high as 460°C. The 2% and 4% Cu films showed segregation, with the peak in the copper content located nearer the film–substrate interface. Auger and SEM data indicate that theta phase particles may form in this region during high rate deposition. These particles apparently redissolve slowly during 500°C postdeposition anneal. In contrast, 4% Cu films deposited by evaporation from a single source showed a similar as-deposited profile, but a more rapid redistribution of the Cu during anneal. The sputtered films are reported to be more resistant to hillock growth and corrosion than the evaporated films. At rates above 10 kÅ/min, and under conditions where film temperature rose toward a steady-state value, film melting or copper-rich whiskers up to several microns in length were observed on the 4% Cu alloy.