AbstractThis paper describes a contact degradation mechanism during window formation followed by selective tungsten chemical vapor deposition (W‐CVD). Contact resistances by using selective W‐CVD were increased as the overetching rate increased. Surface analysis made it clear that the Si surface at the bottom of contact was damaged and oxygen atoms from dielectrics were introduced during window etching. These damage and oxygen atoms break Si‐Si bonds and make Si‐O bonds after additional ion implantation. The Si‐O bonds degrade the valence‐band density of states of the Si surface. Such a damaged surface will not react with WF6.This inactivation is the reason for contact degradation. Controlling the Si surface state by using the chemical dry etching (CDE) technique solves t