Abstract

Studies of chemical sputtering of silicon by simultaneous exposure to Cl₂ and low-energy Ar⁺ ions, using mass spectroscopy and time-of-flight techniques, have shown that the main products are atomic Si and Cl and molcular SiCl and SiCl₂. The largest fractions of the time-of-flight distributions of these products have collision cascade-like distributions with a binding energy range characteristic for each of these four products. The model explaining these and some other observations ascribes a central role to Ar⁺ ion-induced amorphization and Ar⁺ ion-induced mixing of adsorbed Cl into the top atomic layers of the Si, which is accompanied by formation of molecular SiCl and SiCl₂ trapped in the bulk without further chemical binding to the surrounding bulk network. The largest part of the four main products is removed from the solid by physical sputtering. The chemical enhancement is ascribed to mainly two factors, first the formation of large amounts of trapped SiCl and SiCl₂ molecules with a low binding energy range and second a reduction in the binding energy of the Si in the binding network by the mixing with Cl. This was demonstrated, among other things, by the observation that for flux ratios of Cl₂ to Ar⁺ increasing from about 1 to about 100 the relative amount of SiCl and SiCl₂ with respect to Si is enhanced and the binding energies reduced (ref. ¹).

© 1987 Optical Society of America