Sputtering and depth-distribution phenomena in KCl, Al2O3, and TiO2

Abstract

If a solid is bombarded with an inert gas, the thickness removed by sputtering is proportional to (S) (μA min/cm2), where S is the sputtering coefficient. We have used this effect first to evaluate S for Kr–Al2O3, O2–Al2O3, Kr–TiO2, and O2–TiO2 in the region 2–10 keV. With Al2O3, pieces of free anodic oxide were bombarded until perforated, while with TiO2 the changes in the interference colors of anodized Ti were noted. Knowing the values of S, we have then obtained depth distributions for 10-keV Kr in KCl, Al2O3, and TiO2 at doses of 1–50 μA min/cm2, the amount of Kr remaining in the targets being determined by radioactivity measurements. Rm, the median range, was 105 Å with KCl, and thus within a factor-of-2 agreement of other range data for crystalline materials; with Al2O3 and TiO2, however, Rm was only 11–18 Å, and thus a factor of 4–6 lower than expected on the basis of low-dose data for anodic oxides. In the case of Al2O3, the low values of Rm were explicitly shown to be due in part to a dose effect, such that Rm is at least a factor of 2.3 lower for doses over 1 μA min/cm2, and similar behavior can probably be assumed also for TiO2. In addition, however, gas sputtering or surface roughening may possibly play a role with Al2O3 and TiO2.