In accordance with some embodiments, a method for forming a semiconductor device structure is provided. The method includes forming a dielectric layer on a semiconductor substrate. The dielectric layer has at least one first trench in the dielectric layer. The method also includes forming a seed layer on a sidewall and a bottom surface of the first trench. The method further includes forming a first conductive layer on the seed layer. The method includes performing a thermal treatment process to melt and transform the seed layer and the first conductive layer into a second conductive layer. The method also includes forming a third conductive layer on the second conductive layer to fill the first trench.