Selective epitaxial growth of silicon-germanium by a tubular hot-wall low pressure chemical vapor deposition system
Abstract
The goal of this study is to obtain fundamental process-property relationships for the SiGe epitaxial growth and from such knowledge to assemble a tubular hot-wall low pressure chemical vapor deposition system capable of producing selective epitaxial SiGe films. This is the very first report of such an attempt by any research group to produce epitaxial SiGe films using this type of reactor configuration. This reactor is proposed to be a low cost alternative for producing epitaxial SiGe films. The study consists of three milestones. First of all, thermodynamic analyses of the reaction system were conducted through which a fundamental understanding of the process was gained. The amount of oxygen that the system can tolerate for SiO$\sb{2(s)}$- and GeO$\sb{2(s)}$-free film growth was examined. Also the optimal chlorine concentration to achieve growth selectivity was investigated. Secondly, process improvements were implemented through such an understanding. Three major improvements proved to be essential for the success of the project: a two-step hydrogen bake to eliminate the germanium outgassing problem, selective growth of a Si buffer layer to obtain a clean surface for epitaxial SiGe growth, and use of a small flow of dichlorosilane for the suppression of oxide formation during the temperature ramp down period prior to the SiGe growth. Growth results from this system are presented and discussed in the context of several aspects such as growth selectivity, film thickness uniformity, system contamination level, electrical properties, and defect density. Finally, modeling and simulations of this system are presented on relating processing conditions to the film growth rate. The model is shown to be capable of simulating other microelectronic processes as well. Relevant to this subject, a study of the oxide regrowth on SiGe surfaces after a chemical clean was done. This was to understand different aspects of the passivation of Si and SiGe surfaces. This study incorporated several surface sensitive techniques like ellipsometry, contact angle measurements, atomic force microscopy, and x-ray photoelectron spectroscopy to monitor the change of the SiGe surface upon oxide regrowth after a chemical clean. Such information is indeed important for the fabrication of SiGe-based circuitry.
Degree
Ph.D.
Advisors
Takoudis, Purdue University.
Subject Area
Chemical engineering|Electrical engineering
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