RHEED and REM study of Si(111) surface degradation under Ar bombardment

The effect of 10 to 40 keV argon ion bombardment on Si(111) surfaces, at room temperature, has been investigated by RHEED and REM imaging using an electron microscope. Both RHEED intensity measurements and REM images show that the disorder of the first top-layers proceeds more slowly when increasing ion energy. The decrease of the specularly reflected beam intensity for increasing fluence can be fitted using a simple model in which the energy-dependent parameter is a «mean damaged area» per incident ion incoming on the surface. From 10 to 40 keV, this parameter varies from 4.7×10 −14 to 1.4×10 −14 cm 2 while the dose needed for the complete disordering of the surface, D c , varies from 5×10 13 to 1.8×10 14 ion/cm 2 . Damage energy depositions on the near-surface region were calculated and did not show a variation of more than 15% over the whole energy range. This variation cannot account for the more than 3-time variation of D c . A rough estimate of argon concentration in the first layers with increasing energy shows better agreement, and suggests that the RHEED intensity decrease is related to increasing distortions of the surface network due to argon entrapment Etude par microscopie electronique pour des ions Ar + de 10 a 40 keV. Les mesures d'intensites RHEED et les images obtenues en REM montrent que le desordre dans les premieres couches atomiques est d'autant plus faible que l'energie des ions incidents est elevee. La decroissance de l'intensite de l'onde electronique «speculaire» en cours de bombardement peut etre decrite en utilisant un modele simple dans lequel le parametre dependant de l'energie est une «aire moyenne endommagee» par ion frappant la surface. Discussion des resultats obtenus, par comparaison avec les resultats theoriques bases sur la theorie LSS