Sims depth profiling analysis of Cu/Ta/SiO2 interfacial diffusion at different annealing temperature

Abstract

The interfacial reactions of Cu (60nm)/ Ta(35nm)/ SiO2/ Si and Cu (500nm)/ Ta(35nm)/ SiO2/ Si have been investigated in the 350°C ∼ 700 °C temperature range. We have found that the thickness of Cu top layer is one of the key factors to influence Ta barrier performance in the Cu/barrier/SiO2/Si system. SIMS depth profile spectra were obtained by using O2 + primary ion beam with 12.5keV high voltage and a 5.0keV extraction field of the secondary ions. In the thinner (60nm) Cu system, Si has not penetrated the whole 35nm Ta layer after annealing at 600°C for 30 min under high vacuum. This indicated Ta still functions as a diffusion barrier between Cu and Si at 600°C, though Ta5Si3 formed at 500°C as shown by XRD results. As a good diffusion barrier material for Cu metallization, 35nm Ta layer prevent Cu and Si inter diffusion at 650°C for at least 30 min. In the thicker Cu (500nm) system, top Cu layer changes its structural from small grain to big grain during annealing. This could suppress the grain boundary diffusion of Cu to Ta and SiO2. 35nm Ta layer still functions as diffusion barrier between Cu and SiO2 at the annealing temperature of 700°C.