A method includes forming an opening in a dielectric layer, depositing a seed layer in the opening, wherein first portions of the seed layer have a first concentration of impurities, exposing the first portions of the seed layer to a plasma, wherein after exposure to the plasma the first portions have a second concentration of impurities that is less than the first concentration of impurities, and filling the opening with a conductive material to form a conductive feature. In an embodiment, the seed layer includes tungsten, and the conductive material includes tungsten. In an embodiment, the impurities include boron.