Titanium and cobalt silicides have long been used as gate electrode materials for very large-scale integrations (VLSI) circuits. As scaling has pushed the industry to quarter micron technologies and below, cobalt has become the material of choice for forming silicides, since it can maintain its low resistivity on much narrower line widths. Oxidation of the cobalt film is a concern during silicide processing, as the cobalt oxide will not be removed during the cobalt etch step. To protect against the oxidation of the cobalt layer during the silicidation process, the reaction is conducted underneath a titanium nitride (TiN) capping layer. Variations in the TiN capping layer thickness were investigated to determine the affect on oxygen sensitivity of the cobalt silicide process. A strong correlation was found to the thickness of the TiN-capping layer, to the oxygen concentration required to oxidize cobalt during the silicidation process.