Surface smoothing effects with reactive cluster ion beams

Abstract

Surface smoothing effects of reactive cluster ion beams were studied and compared with those of Ar cluster ions. Si, SiC and W were irradiated with SF 6 cluster ion beams. As these materials show reactive sputtering, sputtering yields become one or two orders of magnitude higher than that of Ar cluster ions, which have only the physical sputtering effect. The Au surface was smoothed with SF 6 cluster ions at a normal incidence, however, the surface roughness of W was not improved with SF 6 cluster ions. The surface smoothing effect with reactive sputtering is weaker than that of physical sputtering. The angular distribution of Au sputtered with SF 6 cluster ion follows an under-cosine law, which is similar to that of Cu sputtered with Ar cluster ions. This under-cosine distribution of sputtered atoms is called the ‘lateral sputtering effect’. When W is irradiated with SF 6 cluster ions, volatile materials such as WF x are produced by a chemical reaction with F, and they are thermally evaporated. As a result, the angular distribution follows the cosine law. Therefore, the ‘lateral sputtering effect’ is responsible for the surface smoothing effect.