in a method of manufacturing a semiconductor device , a semiconductor substrate including an insulating layer is provided . a groove is formed on the insulating layer . an additive - containing barrier layer is formed on the insulating layer . a metal seed layer and a metal layer are formed on the barrier layer . then , the metal layer is subjected to a first heat treatment at a first temperature that is capable of promoting grain growth of the metal seed layer and the metal layer . the barrier layer , the metal seed layer and the metal layer are partially removed so that a conductive layer including the metal seed layer and the metal layer is formed in the groove . finally , the conductive layer is subjected to a second heat treatment at a second temperature that is higher than the first temperature and allows an additive element in the barrier layer to diffuse into the metal layer .