Correlation between outward diffusion of additives and oxidation of Cu(3.9at.%Ti) and Cu(2.3at.%Ta) thin films

Abstract

Thin film reaction of transition metals with germaniumThin films of pure Cu and Cu alloys ͑with 3.9 at. % Ti or 2.3 at. % Ta͒ are deposited on SiO 2 /Si substrates by magnetron sputtering. Upon annealing at 700°C in vacuum for 30 min, Ti in the Cu͑3.9 at. % Ti͒ films will mostly diffuse to the free surface, but the majority of Ta in the Cu͑2.3 at. % Ta͒ film remains within the Cu layer. The outward diffusion of Ti or Ta strongly influences the oxidation of Cu in air. The degree of Cu oxidation was determined by glancing incident angle x-ray diffraction and the normalized sheet resistance. Oxidation test shows that the Cu͑3.9 at. % Ti͒ films exhibit a superior oxidation resistance when oxidized at 200°C in air, especially for the Cu͑3.9 at. % Ti͒ film which has been preannealed at 700°C in vacuum. But the Cu͑2.3 at. % Ta͒ film with the same preannealing treatment only slightly improves the oxidation resistance, in comparison with the pure Cu film. The correlation between outward diffusion of additives and oxidation of Cu in the Cu͑3.9 at. % Ti͒ and Cu͑2.3 at. % Ta͒ thin films is discussed.