Evaluation of single- and multilayered amorphous tantalum nitride thin films as diffusion barriers in copper metallization

Abstract

This study evaluates 40-nm-thick amorphous Ta2N (a-Ta2N) thin films with various compositions and metallurgical designs as diffusion barriers for copper metallization. Results based on sheet resistance measurements, x-ray diffraction analyses, and transmission and scanning electron microscopies consistently follow a sequence of coarsening copper grains, transforming a-Ta2N into a crystalline phase, and finally forming {111}-faceted pyramid Cu3Si precipitates and TaSi2. The degradation of the single-layered stoichiometric Ta2N (a-Ta67N33) barriers is primarily triggered by a premature crystallization of the amorphous barrier layers at temperatures as low as 450 °C. However, as adequately designed double-layered (20 nm Ta67N33/20 nm Ta62N38) amorphous barriers can be subjected to high-temperature annealing without crystallization, the effectiveness of the double-layered barriers can be significantly improved, elevating the degradation temperature by approximately 100 °C.