Abstract: A semiconductor device manufacturing process for forming a contact plug includes sequentially depositing a titanium or tantalum contact layer (30), a titanium nitride barrier layer (40), and a tungsten seed layer (50) in a contact opening (24). The contact hole (24) is then filled up from a bottom surface of the contact opening by electroplating a copper layer (60) so that no voids are formed in the contact opening (24). Any excess metal is removed with a CMP process to form the contact plugs (70), where the CMP process may also used to thin or remove one or more of the contact/seed/barrier layers (30, 40, 50).