Sputtering yields of compounds using argon ions

M P Seah (1) , T S Nunney (2)

1 Analytical Science Division
2 Thermo Fisher Scientific

An analysis is made of published sputtering yield data for compounds using argon primary ions at normal incidence to evaluate the validity of simple predictive equations. These are sputtering yields at dynamical equilibrium. First, two archetypal compounds are analysed: GaAs with constituent elements of similar atomic number and weak preferential sputtering, and Ta 2 O 5 with constituent elements of widely separate atomic number and strong preferential sputtering. The agreements of the sputtering yields predicted by the semi-empirical linear cascade theory are excellent when the appropriate parameters are interpolated, rather than using an average atomic number. The effect of preferential sputtering is included within the framework of the simple pair-bond theory. The average ratios of the data to the initial predictions for GaAs and Ta 2 O 5 are 1.01 ± 0.06 and 1.00 ± 0.07, respectively. Extension of this analysis to a range of oxides shows that the heat of reaction of the oxidation process needs inclusion. It is here that the effect of preferential sputtering can lead to an expansion of the uncertainties. SiO 2 is often used as a reference material and so the published yield data are analysed in detail. These show an extremely broad scatter and so new experimental data are measured. These new results are in the upper range of previous data and correlate with the semiempirical theory with a scatter of only 9%. These correlations show that the semi-empirical linear cascade theory is excellent for predicting the energy dependence of the yield and can be excellent for absolute yields where the compound heat of formation is low. D I. Introduction The sputtering of materials using inert gas primary ions, particularly argon, is a routine part of surface and thin film analysis for compositional depth profiling using Auger electron spectroscopy (AES) or X-ray photoelectron spectroscopy (XPS) [ 1, 2 ]. Other inert gases are also used to improve the depth resolution, or to ensure that spectral peaks from the inert gas are well separated from the spectral peaks required to identify the materials being profiled, or to reduce the effects of preferential sputtering. Nevertheless, argon is still the ion of first choice for compositional depth profiling using AES or XPS by most analysts. Recently, we have analysed extensive data for the sputtering yields of elemental solids in order to develop the semi-empirical theory of sputtering yields for bombardment by argon [ 3 ], neon, and xenon [ 4, 5 ]. That theory provides a very good description to the absolute yields for the energy range 250 to 10000 eV and, for the elemental solids analysed, the scatter between the prediction at normal incidence and the experimental data for Ar + is 9%. A figure of 9% is better than the current laboratory-to-laboratory reproducibility of sputtering yield measurements. Similar scatters are

Mots clés: Argon ions; GaAs; SiO 2; Sputtering yields; Ta 2 O 5 PACS:34.35.+a; 68.49.Sf; 68.55.jd; 79.20.Rf; 79.60.Dp; 81.70.Jb.; 81.70.Jb

M P Seah, T S Nunney. Sputtering yields of compounds using argon ions. Journal of Physics D: Applied Physics, 2010, 43 (25), pp.253001. ⟨10.1088/0022-3727/43/25/253001⟩. ⟨hal-00569630⟩