A COMPARATIVE-STUDY OF HILLOCK FORMATION IN ALUMINUM FILMS

Studies were conducted to evaluate the performance of a variety of alu minum alloys with respect to hillock formation. Specifically, the effe cts of film composition, deposition temperature, and underlayer on hil lock formation were investigated. The film compositions included pure Al, Al with 1.5 wt.% Cu (or AlCu), AlCu with 0.2 wt.% W, and AlCu with 0.4 wt.% W. These films were sputter deposited at 300 degrees C and 4 50 degrees C on either oxide- or Ti-W-coated Si substrates. Following deposition, the films were annealed in air for 20 min at 450 degrees C . For all film compositions, the deposition temperature had the most s ignificant effect on the hillock density. For a given deposition tempe rature, the addition of Cu to pure Al drastically reduced the hillock density, but the addition of W to AlCu increased the hillock density, The effect of the underlayer on the hillock density was negligible. Cr oss-sections of the hillocks showed that they were solid from the bott om interface to the top surface, and no voids were found near the hill ocks. The grain size did not have a significant effect on the hillock density. However, a correlation between increasing (111) film texture and decreasing hillock density was observed.