The sputtering of oxides part i: a survey of the experimental results

Abstract

The sputtering behavior of oxides is now fairly well understood in 12 cases. Three categories can be recognized, with some oxides belonging to more than one category. The eight oxides Al₂O₃, MgO, Nb₂O₅, SiO₂, Ta₂O₅, TiO₂, UO₂, and ZrO₂ have sputtering coefficients as expected from Sigmund's theory of collisional sputtering, at least provided the surface binding energy can be identified with the heat of atomization. The four oxides MoO₃, SnO₂, V₂O₅, and WO₃ show high and (except possibly with SnO₂) temperature-dependent sputtering coefficients such that the inferred surface binding energics are significantly less than the heats of atomization. For example, V₂O₅ has S = 12.7 atoms/ion for 10-keV Kr, so that E_b is apparently 1.3 eV/atom as compared with 5.7 eV/atom for atomization. This is taken as evidence for thermal sputtering. The five oxides MoO₃, Nb₂O₅, TiO₂, V₂O₅, and WO₃ show preferential oxygen sputtering, such that they first amorphize, then lose oxygen, and finally crystallize as the phases MoO₂, NbO, Ti₂O₃, V₂O₃, and W₁₈O₄₉. A comparison between corresponding oxides and metals is also possible with the information available. The main result is that the ratio S _oxide/Smetal is normally greater than unity (Al₂O₃, MgO and TiO₂ are exceptions), whereas the ratio (S _oxide/S _metal) (mole fraction of metal in the oxide) is normally less than unity (V₂O₅ is an exception).