Cobalt Polishing with Reduced Galvanic Corrosion at Copper/Cobalt Interface Using Hydrogen Peroxide as an Oxidizer in Colloidal Silica-Based Slurries

Abstract

A colloidal silica-based slurry with H2O2 (1 wt%) as the oxidizer and arginine (0.5 wt%) as the complexing agent was found to polish cobalt (Co) with superior performance (better post-polish surface quality and no pit formation) at pH 10 compared to pH 6 and 8. At pH 10, there is no measurable dissolution of Co and an open circuit potential (Eoc) difference of ∼20 mV between Cu and Co, suggestive of reduced galvanic corrosion. Our results also suggest that, during polishing, the Co film surface was covered with a passive film, possibly of Co(III) oxides. Addition of 5 mM BTA to this slurry inhibited Cu dissolution rates and yielded a Co/Cu removal rate ratio of ∼1.2 while further reducing the Eoc difference between Cu and Co to ∼10 mV, both very desirable attributes. The roles of H2O2, arginine, and silica abrasives as well as the pH on the Co material removal process are discussed and a removal mechanism is proposed.