Influence of oxide density on O 2 diffusivity in thermally grown SiO 2 on Si and SiGe and on oxidation kinetics

Ultrathin compressively strained SiGe layers is one of the most promising materials for high mobility channels of p-type metal oxide semiconductor field effect transistors (pMOSEE,Ts). Fabrication of such layers by SiGe thermal oxidation processes need to be well controlled, which then require well-controlled oxidation kinetics and oxide properties for use in an industrial environment. In the present paper, we address oxidation kinetics of Si, Si0.9Ge0.1 and Si0.7Ge0.3 by means of dry furnace oxidation and dry rapid thermal oxidation (RTO). We showed in a previous paper that oxidation of SiGe by means of either dry furnace oxidation or dry RTO is limited by diffusion of the oxidizing species through the growing oxide and that the oxidation rate of SiGe is significantly higher than the one of Si. In the present paper we focus on the influence of the oxide density measured by Soft x-ray Reflectivity on oxidation kinetics. It is shown that the lower the density of the oxide is, the higher the oxidation rate is, in agreement with an oxidation regime that is governed by diffusion of O-2 through the growing oxide. Finally, we propose a model of O-2 diffusivity that depends on the oxide density through the modulation of the diffusion barrier. The modulation of the diffusion barrier is found to be linearly dependent on the oxide density.