Unwanted hillocks arising in copper layers due to formation of overlying
barrier layers may be significantly reduced by optimizing various process
parameters, alone or in combination. A first set of process parameters
may be controlled to pre-condition the processing chamber in which the
barrier layer is deposited. A second set of process parameters may be
controlled to minimize energy to which a copper layer is exposed during
removal of CuO prior to barrier deposition. A third set of process
parameters may be controlled to minimize the thermal budget after removal
of the copper oxide.