Consequences of sputtering with molecular ions

Abstract

According to Sigmund’s linear cascade theory of sputtering, the yield for elemental collision partners is given by Y(E)=Cpt Sn(E/Ept), where Cpt and Ept are characteristic constants depending on projectile and target parameters and Sn is the reduced nuclear stopping. We show that under fairly general assumptions a similar relation holds for the physical sputtering yield of elemental targets bombarded by complex (molecular) ions. The characteristic constants must then be taken as the sum of those of the ion’s constituent particles. Complex ion yields (e.g., of CF+n≤3 on Si) are currently being compared with results for noble gas ions of approximately equal mass. ‘‘Chemical enhancement effects’’ are thus being ‘‘deduced’’ from Reactive Ion Beam Etching (RIBE) experiments. We show that with the proposed model description no such evidence can reliably be extracted from existing RIBE data. Finally, we present sputtering yield data for SO+ ions on Si (0.1–15 keV) at temperatures of 300, 700, and 1100 K to elucidate the above remarks and to show that chemical contributions can, at least partially, be isolated.