A gas cluster ion beam process is used to reduce and/or even eliminate metal void formation in an interconnect structure. In one embodiment, gas cluster ion beam etching forms a chamfer opening in an interconnect dielectric material. In another embodiment, gas cluster ion beam etching reduces the overhang profile of a diffusion barrier or a multilayered stack of a diffusion barrier and a plating seed layer that is formed within an opening located in an interconnect dielectric material. In yet another embodiment, a gas cluster ion beam process deactivates a surface of an interconnect dielectric material that is located at upper corners of an opening that is formed therein. In this embodiment, the gas cluster ion beam process deposits a material that deactivates the upper corners of each opening that is formed into an interconnect dielectric material.