Inhibition of Galvanic Corrosion of Wnc Barrier Metal for Reliable Cu Cmp

This paper discusses chemical and galvanic corrosion of tungsten nitride carbide (WNC) barrier metal. Chemical corrosion occurs due to the oxidation of W in the WNC film by H2O2, which is used as oxidizer in CMP slurries, followed by the dissolution of the oxide complex. Galvanic corrosion takes place due to the high potential difference between Cu and WNC established in the presence of H2O2 based slurries during the CMP process. Use of HNO3 as the oxidizing agent instead of H2O2 reduces chemical and galvanic corrosion of WNC. In order to protect Cu against corrosion in such model slurries organic acids are used as additives. Malic acid containing HNO3 based corrosion inhibiting model slurry is further tested on an experimental CMP tool for wafer level tests that showed promising Cu and WNC compatibility.