Dynamic Monte Carlo simulation of surface composition change during sputter depth profiling

In the surface analysis methods such as X-ray photoelectron spectroscopy, Auger electron spectroscopy, or secondary-ion mass spectroscopy, sputtering processes are used for depth profiling. However, ion beam bombardment changes the surface composition and the surface structure, which deteriorates the accuracy of the surface analysis and the depth resolution. We studied the preferential sputtering in some materials consisting of two components with different mass ratio by using the dynamic Monte Carlo simulation. Dose dependence of the depth profile of composition is presented. By Ar sputtering, the surface compositions of Au_0.25Cu_0.75, Au_0.67Al_0.33, and Ni_0.5Cu_0.5 alloys changed to Au_0.28Cu_0.72, Au_0.76Al_0.24, and Ni_0.67Cu_0.33, respectively. These results agreed with the experimental data. In order to compare the effect of mass ratio on the preferential sputtering, B–C, Si–C, and W–C systems were investigated. In B–C system, preferential sputtering by 1 and 3 keV Ar ion was negligible. In W–C system, a significant preferential sputtering occurred. In Si–C system, carbon was enriched in the outermost surface layer at a fluence lower than 3×10¹⁶ ions/cm². At higher fluence, the partiality in concentration recovers because of the balance between the enrichment and the preferential sputtering.