Surface Analysis of Ru Thin Films after Device Fabrication Processing Techniques*

Ruthenium is often used as an electrical contact material due to its resistance to oxidation at elevated temperatures. In addition, the most stable stoichiometry of ruthenium oxide under ambient conditions is RuO₂, which is an electrically conductive oxide. The goal of this study is to determine the stoichiometry and measured thickness of the surface oxide on Ru formed by typical semiconductor fabrication processing techniques such as reactive ion etch (RIE), plasma ashing processes, and annealing in various environments. The primary analysis techniques used for this study were angle-resolved XPS and AFM. The Ru thin films were deposited on SiO₂/Si(100) substrates. Analysis of the Ru-3d XPS spectrum of the as-grown Ru film indicated that the native oxide was in a 2+ state and was less than a nm thick. Annealing at atmospheric pressure results in the formation of RuO_2, with some higher order oxides and carbon also being detected. Performing a RIE or ashing process on the as-deposited Ru film resulted in the formation of a thinner RuO₂ film. The AFM data shows rounded clusters of material both before and after the different processing techniques.