Cluster Size Dependence of Etching by Reactive Gas Cluster Ion Beams

Mass-selected reactive gas cluster ion beams (GCIB) were formed using a permanent magnetic filter. Irradiations of CO(2) GCIB on amorphous carbon films and irradiations of SF(6) and SF(6)/Ar mixed GCIB on Si surfaces were performed to study the cluster size dependence on etching yields by reactive GCIB. The reactive sputtering yield of carbon by CO(2) GCIB was almost ten times higher than that by Ar GCIB. In the case of (CO(2))(20000) GCIB with energy of 20 keV (1 eV/atom), it showed the high sputtering yield of 200 atoms/ion, however, there was little crater formation on the carbon surface. It is thought that very soft etching without crater formation would take place in this condition. In the case of SF(6) GCIB on Si, the etching depth of Si showed maximum value when the fraction of SF6 to Ar was around 50%. As the etching yield was higher than pure SF(6) GCIB, there was a strong ion assisted etching effects in the case of Ar/SF(6) mixed cluster ion irradiations.