Polycrystalline diamond films etched by Ar+ beam bombardment were investigated by scanning electron microscopy and Raman spectroscopy. In an ion sputtering apparatus, an etching rate of 14 mu m C-1 was obtained when 10 kV-accelerated Ar+ ions penetrated with an angle of 15-30 degrees from the normal. A number of cavities were created on the surface treated at low incidence angle. In contrast, micro-prominence was seen under the condition of high incidence angle. The degree of surface roughness on etched films was also changed with the incidence angle of the beam. A relatively smooth surface appeared after the treatment with an incidence angle of greater than or equal to 15 degrees. Raman spectroscopy revealed that the physical etching of diamond is effective in obtaining high quality surface of polycrystalline diamond films.