Methods of forming a semiconductor device include forming an insulation layer on a semiconductor structure, forming an opening in the insulation layer, the opening having a sidewall defined by one side of the insulation layer, forming a first metal layer in the opening, at least partially exposing the sidewall of the opening by performing a wet-etching process on the first metal layer, and selectively forming a second metal layer on the etched first metal layer. An average grain size of the first metal layer is smaller than an average grain size of the second metal layer. Related semiconductor devices are also disclosed.