Symmetric and asymmetric collision effects on the formation of singly and doubly-charged ions in sputtering process

Measurements of Si2+ and Si+ ions sputtered due to bombardment of 3-5 keV Ar+ ions on silicon substrate have been performed for understanding exact charge-state formation mechanisms. Examination on the penetration depth dependence of incident particle on secondary ion formation has been performed. A closure look at the energetics of the secondary ions from their kinetic energy distributions suggests that Si+ ions are predominantly formed in the upper surface layer and Si2+ ions are produced due to target-target symmetric collision-induced Si 2p shell vacancy creation following the Auger electron emission. Furthermore, the increase in the oxygen-induced impurity in the silicon substrate enables us to explore the gradual transition from the dominating symmetric to asymmetric collision channel for production of Si2+ ions.