Degradation mechanisms of Ta and Ta–Si diffusion barriers during thermal stressing

Abstract

The degradation mechanisms of 10 nm thick Ta and Ta 73Si 27 diffusion barriers deposited between Cu and SiO 2 are compared by means of X-ray reflectometry, glancing angle X-ray diffraction, glow discharge optical emission spectroscopy depth profiling and transmission electron microscopy analysis. Annealing the samples at T an=600 °C for t an=1 h results in a diffusion of Ta atoms through the Cu capping layer to the sample surface, particularly in the case of the pure Ta barrier. During longer heat treatment ( t an>1 h), microstructural changes occur within both barrier types. Whereas the amorphous Ta–Si layer starts to crystallize into Ta 5Si 3, the initially grown metastable β-Ta of the pure Ta film transforms into the equilibrium α-Ta phase. Analyzing the diffusion rate of Cu atoms into the substrate, the Ta 73Si 27 barrier shows an enhanced thermal stability compared to the pure Ta film.