Surface modification of polymethylmethacrylate (PMMA) films has been investigated with argon-oxygen mixture plasmas sustained with multiple low-inductance antenna units. PMMA films were exposed to argon-oxygen mixture (20%) plasmas on a water-cooled substrate holder. Average ion energies bombarding onto the PMMA films was estimated to be as low as 6 eV, which was evaluated from the gap between plasma potential and floating potential. The etching depth of PMMA surface increased linearly with increasing plasma-exposure time and the etching rate was 170 nm/min. Surface roughness of PMMA slightly increased from 0.3 nm to 1.4 nm with increasing exposure time. Hard X-ray photoelectron spectroscopy (HXPES) was carried out to examine chemical bonding states of the PMMA surface in deeper regions (about 54 nm) as compared with those observed in shallower regions (27 nm). (C) 2009 Elsevier B.V. All rights reserved.