When a natural oxide film is left at the interface between a metal silicide layer and a silicon nitride film, in various heating steps (steps involving heating of a semiconductor substrate, such as various insulation film and conductive film deposition steps) after deposition of the silicon nitride film, the metal silicide layer partially abnormally grows due to oxygen of the natural oxide film occurring on the metal silicide layer surface. A substantially non-bias (including low bias) plasma treatment is performed in a gas atmosphere containing an inert gas as a main component on the top surface of a metal silicide film of nickel silicide or the like over source/drain of a field-effect transistor forming an integrated circuit. Then, a silicon nitride film serving as an etching stop film of a contact process is deposited. As a result, without causing undesirable cutting of the metal silicide film, the natural oxide film over the top surface of the metal silicide film can be removed.