An insulating film having a concave portion is formed on a semiconductor substrate. The inner surface of the concave portion and the upper surface of the insulating film are covered with an auxiliary film made of Cu alloy containing a first metal element other than Cu. A conductive member containing Cu as a main composition is deposited on the auxiliary film, the conductive member being embedded in the concave portion. Heat treatment is performed in an atmosphere containing P compound, Si compound or B compound. With this method, a content of element other than Cu in the conductive member can be reduced and a resistivity can be lowered.
