Anomalous surface damage in ion bombarded silicon from channelling-backscattering measurements

The surface disorder created by 1 MeV He+ bombardment of Si has been studied for random and aligned ⟨111⟩ bombardment at 40 K and 300 K. For the aligned beam it is found that the surface disorder is much larger than can be predicted by bulk damage production and that the disorder production rate is only weakly dependent on temperature and alignment. The observations suggest a component of beam induced annealing present at 40 K. The energy dependence of the surface disorder production is reasonably well explained by a surface atom recoil model in which the initial surface oxide atoms can be recoiled to create damage. When the damage production caused by low dose heavy ion bombardments is increased using MeV He+ beams, the surface damage caused by the analysing beam may form a large part of the total damage, unless care is taken to minimise the analysing beam dose.