A method of forming a copper metal line in a semiconductor device includes depositing an interlayer insulating layer on a semiconductor substrate having a lower metal line, forming a via contact hole and a metal line pattern in the semiconductor substrate, sequentially depositing a barrier metal film and a copper seed layer, forming a copper film on a surface of the semiconductor substrate, removing the copper film and the barrier metal film, other than the portion of a copper metal line to be formed, removing a native oxide film existing on a surface of the copper metal line of the semiconductor substrate, depositing a silicon layer on the semiconductor substrate, making the deposited silicon layer and copper metal react to each other to form a copper silicide layer, removing a remaining silicon layer without being reacted, and depositing an insulating anti-diffusion film over the semiconductor substrate.