A semiconductor substrate is inserted into a heat treatment apparatus at a low temperature ranging from room temperature to about 50.degree. C., and organic substances included in a metal on the semiconductor substrate are released without carbonization in an annealing process before CMP. Further, organic substances capable of preventing the corrosion of the metal are decomposed, and the organic substances themselves and chlorine, sulfuric acid, and ammonia which are included in the organic substances are diffused out of the metal film by setting the heat treatment apparatus at a rate of temperature rise of 15.degree. C./min or less until a prescribed heat treatment temperature is reached.