Contact features for semiconductor devices and methods of forming same

The invention relates to a contact feature of a semiconductor device and a method of forming the same. A method includes forming a dielectric layer over an epitaxial source/drain region, forming an opening in the dielectric layer. The opening exposes a portion of the epitaxial source/drain region. A barrier layer is formed on sidewalls and a bottom of the opening. An oxidation process is performed on sidewalls and a bottom of the opening. An oxidation process converts a portion of the barrier layer into an oxidation barrier layer and a portion of the dielectric layer adjacent the oxidation barrier layer into a liner layer. And removing the oxidation barrier layer. The opening is filled with a conductive material from bottom to top, the conductive material being in physical contact with the liner layer.