Embodiments of the invention generally provide methods of filling contact
level features formed in a semiconductor device by depositing a barrier
layer over the contact feature and then filing the layer using an PVD,
CVD, ALD, electrochemical plating process (ECP) and/or electroless
deposition processes. In one embodiment, the barrier layer has a
catalytically active surface that will allow the electroless deposition
of a metal on the barrier layer. In one aspect, the electrolessly
deposited metal is copper or a copper alloy. In one aspect, the contact
level feature is filled with a copper alloy by use of an electroless
deposition process. In another aspect, a copper alloy is used to from a
thin conductive copper layer that is used to subsequently fill features
with a copper containing material by use of an ECP, PVD, CVD, and/or ALD
deposition process. In one embodiment, a portion of the barrier layer is
purposely allowed to react with traces of residual oxide at the silicon
junction of the contact level feature to form a low resistance
connection.