Polishing of Sidewall Surfaces Using a Gas Cluster Ion Beam

The polishing of silicon sidewalls at an average surface roughness of 0.3 nm is demonstrated for the first time by SF6 gas cluster irradiation at an incident angle of 82 degrees from the sidewalls. A new phenomenon for surface smoothing occurs on material surfaces irradiated by reactive gas clusters at incident angles above 60 degrees from the surface normal. A characteristic of this smoothing phenomenon is that the surface roughness decreases as the chemical reactivity between the material and gas clusters increases, whereas the surface roughness shows an opposite tendency for conventional gas cluster ion beam smoothing at angles below 60 degrees.