Embodiments in accordance with the present invention provide methods of forming a metal interconnect structure which avoid defects arising from copper migration. In accordance with particular embodiments, an electroplated copper feature is subjected to a brief thermal anneal prior to chemical mechanical polishing and subsequent formation of an overlying barrier layer. This thermal anneal intentionally provokes migration of the copper and resulting formation of hillocks or voids, which are then removed by a CMP step. The barrier layer may thus subsequently be formed over a defect-free surface, which has already experienced stress release along grain boundaries as a result of the thermal treatment.