Abstract: A metal barrier film which contains an additive element is formed on the side face and on the bottom of a trench formed in an insulating film; a seed film is formed over the metal barrier film; a plated layer (Cu film) is formed using the seed film as a seed so as to fill up the trench with a metal film; the metal barrier film and the metal film are annealed to thereby form therebetween an alloy layer which contains a metal composing the metal barrier film, the additive element, and a metal composing the metal film, and to thereby allow the additive element to diffuse into the metal film.