Surface morphology of PMMA surfaces bombarded with size‐selected gas cluster ion beams

The surface morphology and sputtering rate of polymethylmethacrylate (PMMA) samples bombarded with size‐selected Ar cluster ion beam (1000–16 000 atoms/cluster) was investigated. The incident cluster ion size was selected before irradiation by using the time‐of‐flight (TOF) method. The sputtering rates decreased with increasing incident cluster size at constant total energy. The average surface roughness values measured by AFM after 25 nm etching with 20 keV Ar 1000 + and Ar 16 000 + were 4.0 ± 0.4 and 0.78 ± 0.09 nm, respectively. Thus, small clusters would be effective for high‐speed etching, and large clusters would be suitable for low‐damage etching.