A study of the oxidation of selected metal silicides

Abstract

In situ ellipsometry was used to investigate the oxidation behavior of a group of silicides, CoSi2, CrSi2, Ir3Si 5, Ru2Si3, and WSi2, on single-crystal silicon substrates. These observations were complemented by ex situ ellipsometric measurements on these silicides, as well as on Mn 11Si19, MoSi2, NiSi, NiSi2, and ReSi2. Refractive index measurements necessary for the oxide thickness calculations were made using ellipsometry on the bare silicide surfaces. Three regimes of oxidation behavior were identified: one group of silicides oxidized much faster than Si itself, CoSi2, CrSi2, NiSi, and NiSi2; another group was intermediate in oxidation rate between the fast group and Si at low temperature, typically comprising the refractory silicides MoSi2 and WSi2; the third group oxidized at about the same rate as Si and included the semiconducting silicides Ir3Si5, ReSi2, and Ru2Si3. The oxidation of Mn11Si 19 led to an oxide containing a small amount of Mn. The oxidation rates of the silicides scale with both the reported carrier concentrations and the measured absorption index. Thus, the electronic properties of the silicides are thought to be responsible for the oxidation behavior. Buffered HF etch rates of the oxides grown on silicides indicate that the oxides grown on the rapidly oxidizing silicides are less dense than the oxides on the intermediate and slowly oxidizing silicides.