Modeling of substrate bias effect on the compositional variations in sputter-deposited TiB_2+x diffusion barrier thin films

Sputter-deposited titanium boride diffusion barrier layers have been found to be boron enriched when r.f. substrate bias was applied. In the present experiments titanium boride was deposited by co-sputtering from Ti and B pure targets in Ar discharge and the voltage of r.f. self-bias was in the range of 100-250 V. Films deposited were found by Auger electron spectroscopy to be B enriched with increasing bias voltage at constant Ti and B sputtering rates. A model of the sputter-deposition conditions was developed to predict the composition and the thickness of the growing film. The model explains the experimental results indicating that B enrichment is mainly a result of differential resputtering of the components from the growing film by energetic Ar ions captured from the r.f discharge.