Method for removing and/or redistributing material in the trenches and/or vias of integrated circuit interconnect structures by a gas cluster ion beam (GCIB) is described to improve the fabrication process and quality of metal interconnects in an integrated circuit. The process entails opening up an undesired `necked in` region at the entrance to the structure, re-depositing the barrier metal from thicker areas such as the neck or bottom of the structure to the side walls and/or removing some of the excess and undesired material on the bottom of the structure by sputtering. The GCIB process may be applied after the barrier metal deposition and before the copper seed layer/copper electroplating or the process may be applied after the formation of the copper seed layer and before electroplating. The method may extend the usability of the known interconnect deposition technologies to next generation integrated circuits and beyond.