Polycrystalline copper was physically sputtered by helium ion irradiation with changing the ion fluence and the incident angle. After that, flatness of the surface was examined. For normal incidence, small bubbles and pores were formed at the surface. The average size and areal density increased with the increase of helium ion fluence. By the increase of the incident angle, the copper surface gradually became flat. However, in the case of shallow bombardment with an angle of 67.5°, the surface had a different morphology compared to the other cases. One possible reason may be formations of blisters. In the present experiment, helium ion, which easily produces blisters, was employed. If the ion species such as argon ion and reactive ion is employed, the surface roughness may decrease with increase of incident angle.