Transport number measurements during plasma anodization of Si, GaAs, and ZrSi2

Abstract

In contrast to the thermal oxidation of Si where molecular oxygen is the sole moving species, the plasma anodization involves the movements of anions (oxygen or its compounds) or cations (Si or its compounds) or both. A similar situation is observed during the plasma anodization of refractory metal silicides (ZrSi₂) or even GaAs. To get some insights on the mechanisms of plasma anodization, the transport number of cations t⁺ in oxides grown by anodization in oxygen plasma has been investigated using Xe atom markers. Rutherford backscattering techniques were used to determine the change in Xe marker position related to the change in oxide thickness. Results showed that t⁺≂0 for SiO₂ growth indicating oxide formation solely by oxygen ion movement while for GaAs oxide, the t⁺ value obtained (t⁺≠0) evidences cation and oxygen anion migration during the growth. For ZrSi₂ anodization, the position of the Xe markers remains unchanged during oxide formation yielding t⁺≂0, while the analysis of the backscattering spectra shows a Zr oxide enrichment in the near surface region of the oxide mixture. This suggests a relative movement of Zr cations with respect to Si cations. The implications of these findings on the microscopic transport mechanisms of ions under high electric field are presented.