Fabrication of SiGe-On-Insulator by Improved Ge Condensation Technique

Abstract

Silicon germanium on insulator (SGOI) is a straightforward material for ultimate device scaling. This substrate combines two advantages: high carrier's velocity of the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 - x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x </sub> alloy and low parasitic capacitance due to the presence of a buried oxide. Several fabrication techniques for SGOI substrates, as SMOX, SMART-CUTtrade or liquid phase epitaxy have been proposed. Tezuka et al. present a new approach involving an epitaxial growth of low Ge contents SiGe alloy on SOI substrate followed by a high temperature oxidation. By selective oxidation of Silicon and diffusion of Germanium within the remaining SGOI layer, Ge content increases. A high Ge concentration SGOI layer is then obtained. Ge condensation technique is based on two competitive mechanisms: silicon oxidation involving Ge pill up at the oxide interface and Ge diffusion within the SiGe layer. Both take place during the high temperature oxidation. To favour Ge diffusion and carry out homogeneous SGOI profiles, we propose an improved Ge condensation technique with a multi-steps oxidation. Samples have been characterized by spectroscopic ellipsometry (SE), X ray reflection (XRR), X-ray fluorescence (XRF) and secondary ions mass spectroscopy (SIMS), transmission electronic microscopy (TEM) to assess the process quality for uniform SGOI fabrication with different Ge contents. Relaxation of SGOI layers has been observed either by atomic force microscopy or Raman spectroscopy. Influence of oxidation time has been studied and well defined oxidation recipes are proposed to obtain different Ge content SGOI substrates. Numerical simulations including the initial parameters, i.e., top SOI thickness, SiGe grown layer thickness and compositions have been studied by Athena software