A method comprises forming a source/drain contact over a source/drain region; forming an etch stop layer over the source/drain contact and an interlayer dielectric (ILD) layer over the etch stop layer; performing a first etching process to form a via opening extending through the ILD layer and a recess in the etch stop layer; oxidizing a sidewall of the recess in the etch stop layer; after oxidizing the sidewall of the recess in the etch stop layer, performing a second etching process to extend the via opening down to the source/drain contact; and after performing the second etching process, forming a source/drain via in the via opening.