Low temperature Si homoepitaxy by a reactive CVD with a SiH 4 /F 2 mixture.
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1153-A09-02
Low temperature Si homoepitaxy by a reactive CVD with a SiH4/F2 mixture.
Akihisa Minowa1 and Michio Kondo1,2 1
Tokyo Institute of Technology, Department of Innovative and Engineered Materials, 4259 Nagatsuta-cho, Midori-ku, Yokohama-shi, Kanagawa-ken, 226-8502, Japan 2
Advanced Industrial Science and Technology, Research Center for Photovoltaics, Central 2, 1-1-1 Umezono, Tsukuba-shi, Ibaraki-ken, 305-8568, Japan
ABSTRACT The technique for the preparation of single crystalline Si thin films termed “a reactive chemical vapor deposition (CVD)” is proposed, in which SiH4 decomposes spontaneously by gas phase reactions with F2 at low temperature and reduced pressure. Thus this technique provided us a variety of the films from “amorphous” to “single crystalline” in a wide range of the preparation conditions by a choice of the external parameters for the reactions. The technique was successfully applied for the homoepitaxial growth of single crystalline Si thin films. The films exhibited rather high deposition rates over 1 nm/sec.
INTRODUCTION Single crystalline Si thin films on insulating substrates (SOI) have a variety of potential applications such as high mobility thin film transistor (TFT) and high efficiency and low cost solar cells. As an insulator, boro-silicate glass is a promising material because of the low cost and almost identical CTE (Coefficient of thermal expansion) to silicon. The SOI, however, is limited to a thin layer of the order of 0.1 micron and therefore it is necessary to develop an epitaxial growth technology to form active layers thicker than several microns at temperatures lower than a glass softening temperature. Si molecular beam epitaxy (Si MBE) technology has been widely used for low temperature epitaxy with good crystal quality. However, the conventional Si MBE has several disadvantages for large area devices and up scaling due to the limitation of volume of silicon solid source. Another disadvantage is a trade-off between deposition temperature and deposition rate. The lower the temperature is, the lower the maximum deposition rate for good crystallinity. [1, 2] We have attempted to establish a Reactive CVD technique for single crystalline Si thin films using silane and fluorine gas mixture where the advantage is the high quality epitaxy at low temperatures and at high deposition rate because of the exothermic reaction between source gases. [3, 4] The purpose of this study is to develop a deposition technique of single crystalline Si thin films by a Reactive CVD method at temperatures less than 600°C utilizing gas-phase reaction (SiH4, F2). We investigated how the deposition condition affects a variety of the Si films directly.
EXPERIMENTAL DETAILS The Reactive CVD apparatus is schematically shown in Fig.1. It consists of two chambers, i.e., the exchange chamber and the growth chamber based on a gas source MBE system where the back ground pressure is less than 1.0 × 10-8Torr. A substrate holder was heated by carbon heater and the maximum temperature is 1000°C. A gas no
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