Suppression of surface topography development in ion‐milling of semiconductors

The occurrence and growth of hummocks on semiconductor surfaces rotated during ion bombardment have been studied. A simple geometrical is proposed which explains why such topographical features may be observed at incident angles of about 65° with respect to the surface normal, whereas they disappear or do not develop at angles of about 80°. It is argued that even microscopic surface undulations with dimensions of the order of 10 nm initiate hummock formation. Finally it is shown that a smooth surface, which can be produced by ion‐milling at grazing incidence, effectively prevents surface tropography development at any angle of incidence.