The resistivity of damascene copper is measured at pitch ranging down to 40 nm and copper cross-sectional area as low as 140 nm2. Metallization by copper reflow is demonstrated at 28 nm pitch with patterning by directed self-assembly (DSA). Extremely low line-edge-roughness (LER) is attained by surface reconstruction of a single crystal silicon mask. Variation of LER is found to have no impact on resistivity. A resistivity benefit is found for wires with nearly bamboo grain structure, offering the promise of improved performance beyond the 7 nm node if grain size can be controlled.