Forming a capacitor of a semiconductor device includes forming an interlayer dielectric having holes over a semiconductor substrate. A conductive layer is then formed on surfaces of the holes and on the upper surface of the interlayer dielectric. A silicon-containing conductive layer is formed by flowing a silicon source gas for the semiconductor substrate formed with the conductive layer, so that silicon atoms can penetrate into the conductive layer. The silicon-containing conductive layer prevents etchant from infiltrating the interlayer dielectric below the silicon-containing conductive layer.