XPS Investigation of Monatomic and Cluster Argon Ion Sputtering of Tantalum Pentoxide

In recent years, gas cluster ion beams (GCIB) have become the cutting edge of ion beam technology to sputter etch organic materials in surface analysis. However, little is currently known on the ability of argon cluster ions (Arn+) to etch metal oxides and other technologically important inorganic compounds and no depth profiles have previously been reported. In this work, XPS depth profiles through a certified (European standard BCR-261T) 30 nm thick Ta2O5 layer grown on Ta foil using monatomic Ar+ and Ar1000+ cluster ions have been performed at different incident energies. The preferential sputtering of oxygen induced using 6 keV Ar1000+ ions is lower relative to 3 keV and 500 eV Ar+ ions. The depth profiling etch rate and depth resolution is substantially better for the monatomic beam compared to the cluster beam. Ar+ ions exhibit a steady state O/Ta ratio through the bulk oxide but Ar1000+ ions show a gradual decrease in the O/Ta ratio as a function of depth. Higher residual O concentrations are observed on the Ta bulk metal for the Ar1000+ profiles compared to the Ar+ profiles