A comparative analysis of oxidation rates for thin films of SiGeversusSi

TLDR: In this article, the role of Ge as a catalyst or inhibitor for the oxidation process in SiGe was evaluated and compared to previous reports and established models for Si oxidation. But the experimental results indicated that the presence of Ge in very thin films of SiGe does not lead to enhanced or retarded oxidation rates as compared to Si.

Abstract: In order to evaluate the role of Ge as a catalyst or inhibitor for the oxidation process in SiGe, oxidation rates for sub-100-nm films of SiGe are examined and compared to previous reports and established models for Si oxidation. Values for the Ge concentration in the pile-up layer at the oxidation interface are considered as well as the more traditional approach of considering the Ge content in the as-grown SiGe film. The experimental results presented here indicate that oxidation rates for SiGe closely match those of Si and provide evidence that the presence of Ge in very thin films of SiGe does not lead to enhanced or retarded oxidation rates as compared to Si. This comparative analysis is performed with a focus on oxidation of epitaxial thin films of Si1−xGex in dry O2 at 1 atm at 800, 850, 900, 950, and 1000 °C.

Figures

Figure 4.1: diffusion model

Figure 5.1: Gibbs energies for oxidation of Si, Ge, and Sn [6].

FIG. 6. (Color online) Oxidation rates for Si and SiGe vs the oxide thickness as measured by ellipsometry. Data from the present work is presented along with simulation results. The simulations used the Massoud (Ref. 7) model and published model parameters (Refs. 6 and 7) with the exception of the linear rate constant, B/A, which was determined from the data from the present work.

Figure 4.5: The standard error (as reported by the Leptos software) for XRD measurements of (a) Xpu and (b) zpu.

Figure 3.11: Transmition Electron Microscopy (TEM) image showing extended defects in the crystalline lattice of a thin film of SiGe on Si which has been subjected to oxidation at 1000 ◦C.

Figure 2.6: Diffusivity of Si and Ge in Si1−XGeX as a function of X and modeled following an Arrhenius relation, D = D0exp [−Ea/(kT )]. (a) Activation energies, Ea, for Si and Ge measured in eV. (b) Pre-exponential constant, D0, for Si and Ge measured in cm2/s. (c) Diffusivity of Si in Si1−XGeX for temperatures between 700 and 1100 ◦C. The data is as tabulated by Kube et al [16].

Full text

Nanostructuring and Ge redistribution in thin
films of Silicon-Germanium by thermal
oxidation
Ethan Schuyler Long
Thesis submitted in partial fulfillment
of the requirements for the degree of
Philosophiae Doctor
Department of Physics
University of Oslo
February 2013

© Ethan Schuyler Long, 2013
Series of dissertations submitted to the
Faculty of Mathematics and Natural Sciences, University of Oslo
No. 1340
ISSN 1501-7710
All rights reserved. No part of this publication may be
reproduced or transmitted, in any form or by any means, without permission.
Cover: Inger Sandved Anfinsen.
Printed in Norway: AIT Oslo AS.
Produced in co-operation with Akademika publishing.
The thesis is produced by Akademika publishing merely in connection with the
thesis defence. Kindly direct all inquiries regarding the thesis to the copyright
holder or the unit which grants the doctorate.

To Alexis, Francesca, Jason, Jared, Brandon,
Guy, Roberta, and Leland

Abstract
Despite the fact that germanium played a significant role in the advent of modern electronics,
silicon-germanium alloys have not been used or studied nearly as extensively as silicon. How-
ever, a recent resurgence in industrial and research interest in silicon-germanium ensures that
it will have an increasingly important role in nano- and opto-electronics. It is unavoidable that
a sound understanding of the oxidation of silicon-germanium will be required as processes are
developed for using the material in electronic applications. In fact, a profound appreciation for
the oxidation kinetics of silicon-germanium could itself create new applications for the material.
The present work investigates the use of thermal oxidation in nanostructuring of epitaxi-
ally grown silicon-germanium by examining the kinetics of oxidation and the redistribution of
germanium at the oxidation interface. This is done for oxidations in dry O
2
ambients with a
particular focus on the influence of temperature and crystalline orientation on the post-oxidation
germanium distribution. Physical characterization by x-ray diffraction and variable angle spec-
troscopic ellipsometry is used along with diffusion and oxidation modeling to derive a series of
relations to describe the germanium content and layer thicknesses for the multiple layers cre-
ated by oxidation. Both modeling and experimental results reveal that the germanium content at
the oxidation front is strongly dependent on the oxidation temperature and only weakly depen-
dent on the germanium content in the as-grown silicon-germanium layer. Evidence is presented
showing that a decrease, rather than an increase, in the germanium content at the oxidation front
may be achieved under certain conditions. The germanium content at the oxidation interface
is used to discuss the potential for germanium to act as a catalyst or inhibitor for oxidation of
silicon-germanium alloys. Taken together, germanium redistribution by thermal oxidation and
the empiric relations presented here may be used to design process recipes for fabrication of
nanostructures for nano- and opto-electronic applications.
v

Frequently asked questions

Q1. What have the authors contributed in "Nanostructuring and ge redistribution in thin films of silicon-germanium by thermal oxidation" ?

Despite the fact that germanium played a significant role in the advent of modern electronics, silicon-germanium alloys have not been used or studied nearly as extensively as silicon. Evidence is presented showing that a decrease, rather than an increase, in the germanium content at the oxidation front may be achieved under certain conditions. The germanium content at the oxidation interface is used to discuss the potential for germanium to act as a catalyst or inhibitor for oxidation of silicon-germanium alloys. 

Q2. What are the future works mentioned in the paper "Nanostructuring and ge redistribution in thin films of silicon-germanium by thermal oxidation" ?

Furthermore, the possibility to increase, maintain unaffected, or to decrease Ge induced oxidation rate enhancement or retardation will be subject to a number of factors, including point defect generation, bond strengths, steric hindrance, oxide strain, oxidant ambient, and the diffusivity of Si in SiGe.