Surface morphology and sputtering yield of SiO2 with oblique-incidence gas cluster ion beam

The dependence of surface morphology and sputtering yield of SiO2 thin films on the incident angle of gas cluster ion beams (GCIBs) was studied. When the incident angles (θ) were either 0° or 30° ripples did not form on the surface of SiO2, and the sputtering depth increased linearly with increasing ion fluence. When θ = 45°, ripples formed in the direction perpendicular to that of the incident beam. The ripple pattern became shaper and wider with increasing θ–60°. When θ = 60°, the ripple wavelength and amplitude increased linearly with increasing ion fluence. However when θ = 80°, ripples formed in the direction parallel to that of the GCIB. When θ = 60°, the etching depth decreased with increasing ion fluence. This change in the sputtering rate can be associated with the change in the structure of the ripples.