RBS, AES and XPS analysis of ion beam induced nitridation of Si and SiGe alloys

Abstract

Nitridation of Si and SiGe alloys under normal incidence 12 keV N + 2 bombardment has been studied by in situ 1 MeV 4He RBS and by ex situ XPS and AES analysis. The in situ RBS measurements, which alternate with the sputtering/bombardment cycles, show the build-up of the nitrogen content in the silicon and Si .86Ge .14 sample with increasing N + 2 dose. For the silicon a stoichiometric ratio close to that of Si 3N 4 is found. In the case of the SiGe alloy a depletion of the Ge from the surface is noticed. Ex situ XPS measurements on the same samples indicate that nitrogen is bonded with silicon and germanium according to the Si 3N 4 and Ge 3N 4 phase. AES analysis of the steady state composition gives a depth profile with qualitative information on the chemical binding. Nitridation of a silicon sample with a buried Ge layer demonstrates that during the nitrogen build-up a large densification and even some swelling of the surface layer occurs. The transient region of nitridation before steady state is reached is explained by a two-phase model.