A low‐energy, high‐brightness, broad beam Cu ion source is used to study the effects of self‐ion energyEion the deposition of epitaxial Cu films in ultrahigh vacuum. Atomically flat Ge(001) and Si(001) substrates are verified byinsituscanning tunneling microscopy (STM) prior to deposition of 300 nm Cu films withEiranging from 20 to 100 eV. Film microstructure, texture, and morphology are characterized using x‐ray diffraction &ohgr;‐rocking curves, pole figure analyses, and STM. Primary ion deposition produces significant improvements in both the surface morphology and mosaic spread of the films: AtEi>37 eV the surface roughness decreases by nearly a factor of 2 relative to evaporated Cu films, and atEi&bartil;35 eV the mosaic spread of Cu films grown on Si substrates is only &bartil;2°, nearly a factor of 2 smaller than that of evaporated Cu. During deposition withEi&bartil;25 eV on Ge substrates, the film coherently relaxes the 10% misfit strain by formation of a tilt boundary which is fourfold symmetric toward ⟨111⟩. The films have essentially bulk resistivity with &rgr;=1.9±0.1 &mgr;&OHgr; cm at room temperature but the residual resistance at 10 K, &rgr;0, shows a broad maximum as a function ofEi, e.g., atEi&bartil;30 eV, &rgr;0=0.5 &mgr;&OHgr; cm. ©1996 American Institute of Physics.