IN-SITU OBSERVATION BY RBS OF OXYGEN GETTERING DURING CS SPUTTERING OF SI-BASED MATERIALS

In SIMS, Cs is commonly used as the bombarding species to enhance the yield of negative secondary ions. Using RBS we have studied the incorp oration of Cs in Si-bassd materials in order to understand the Cs buil d-up and surface modification during SIMS analysis. It is shown that C s at the surface acts as a getter for oxygen from the residual gas res ulting in the oxidation of the altered layer. Increasing the incident angle from normal incidence to 40 degrees suppresses the gettering and oxidation by the higher erosion rate. In SiGe-alloys the gettered oxy gen causes preferential oxidation of Si with respect to Ge, leading to the pile-up of Ge at the back of the oxide.