In a copper plating process, a seed layer is uniformly deposited over a surface, including lining a high aspect ratio trench defined by that surface. A mask layer is provided using a process that fails to deposit in the trench. In one exemplary embodiment, the failure is due to the decrease in the isotropic flux of neutrals toward the bottom of the trench. Copper is subsequently electroplated. Because the seed layer is exposed only within the trench, copper deposits only therein. The self-aligned mask prevents plating outside of the trench. A chemical-mechanical planarization step removes the mask and the seed layer extending beyond the trench, leaving a copper structure within the trench. The structure may serve as a conductive line, an interconnect, or a capacitor plate.