The present invention relates to methods and systems for the metallization of semiconductor devices. One aspect of the present invention is a method of depositing a copper layer onto a barrier layer so as to produce a substantially oxygen free interface therebetween. In one embodiment, the method includes providing a substantially oxide free surface of the barrier layer. The method also includes depositing an amount of atomic layer deposition (ALD) copper on the oxide free surface of the barrier layer effective to prevent oxidation of the barrier layer. The method further includes depositing a gapfill copper layer over the ALD copper. Another aspect of the present invention is a system for depositing a copper layer onto barrier layer so as to produce a substantially oxygen-free interface therebetween. In one embodiment, the integrated system includes at least one barrier deposition module. The system also includes an ALD copper deposition module configured to deposit copper by atomic layer deposition. The system further includes a copper gapfill module and at least one transfer module coupled to the at least one barrier deposition module and to the ALD copper deposition module. The transfer module is configured so that the substrate can be transferred between the modules substantially without exposure to an oxide-forming environment.