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

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 similar to 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 similar to 1.2 while further reducing the Eoc difference between Cu and Co to similar 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. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.073206jes] All rights reserved.