Influence of ion mixing, ion beam‐induced roughness and temperature on the depth resolution of sputter depth profiling of metallic bilayer interfaces

To study the factors limiting the depth resolution of sputter depth profiling, we have examined the influence of ion mixing, ion beam‐induced roughness and temperature on the interface resolution of metallic bilayers consisting of Pt on top of Ni or Ti. We studied Pt/Ni and Pt/Ti interfaces because Ni and Ti have similar ballistic properties, including atomic mass and number, but the heat of mixing, ΔH_m of Pt/Ni and Pt/Ti are significantly different, ‐7 and ‐122 kJ g^‐1 at.^‐1, respectively. We observed that the measured interface width for Pt/Ti is ∼2.5 nm wider than that of Pt/Ni under identical experimental conditions, indicating the importance of the heat of mixing during ion mixing. Furthermore, for the given sputtering geometry we found that the interface widths were proportional to the square root of the Pt layer thickness. This thickness dependence was absent when the sample was rotated during sputtering, suggesting that the thickness dependence was largely due to roughness caused by unidirectional sputtering. We also investigated the influence of substrate temperature and found a small (0.7 nm) decrease in interface width at 150 K relative to that at 300 K, which may be due to reduced preferential sputtering and a smoother surface. Our studies show the importance of thermodynamic parameters in low‐energy ion mixing and support our earlier conclusion that diffusion in a thermal spike is a dominant mechanism in low‐energy ion mixing, just as it is at high energies in these systems.