Effect of CO2 addition to Ar on gas cluster ion beam sputtering of a Si wafer: An in-situ XPS study

Abstract

Many recent studies showed mixing CO₂ with the Ar gas source improves the secondary ionization yield of an Ar gas cluster ion beam (GCIB) with enhanced depth resolution. However, the impact of CO₂ addition on the surface chemical structure remains unclear. In the present work, we studied the effect of CO₂ addition to Ar on the GCIB sputtering behavior of a Si wafer surface using an in-situ GCIB & X-ray photoelectron spectroscopy (XPS) combined system. During preferential sputtering with Ar GCIB, substoichiometric SiO_x (x < 2) forms, leaving unstable Si species on the surface. These species could interact with surface carbon impurities, leading to the formation of SiC. In addition, a slight distortion of Si lattice could increase its amorphous character. Mixing CO₂ with Ar significantly reduces these structural changes without specific carbon contamination.