SiC Thin Films by Chemical Conversion of Single Crystal Si
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SiC THIN FILMS BY CHEMICAL CONVERSION OF SINGLE CRYSTAL Si Chien C. Chiu, Chi Kong Kwok, and Seshu B. Desu Department of MaterialsScience and Engineering Virginia Polytechnic Institute and State University Blacksburg, VA 24061 ABSTRACT:
The reaction of (100)Si with C2 H2 in a hot wall CVD reactor has been studied using a X-ray photolectron spectroscopy, and a scanning electron microscopy. The growth of the SiC films was observed through the behavior of Si2p peaks and their plasmons. Smooth surface morphology with a monolayer of SiC was obtained at 9500C for 7 minutes and defects were observed for longer reaction times at this temperature. For higher reaction temperatures (e.g. 10000C), defects were observed for reaction times as short as 10 seconds. The formation of defects was correlated to the out-diffusion of Si in the carborization process. INTRODUCTION: Growth of single crystal /3-silicon carbide (SiC) on a (100)Si substrates by Chemical Vapor Deposition (CVD) is generally carried out at high temperatures. In growing SiC single crystals by a one step process, some problems were encountered which are related to the large mismatch (20%) in lattice constants, and the differences in thermal expansion coefficients between the deposited SiC film and the underlying Si substrate (8%) [1]. Therefore, the resulting SiC films often exhibit poor morphology. In addition, peeling of SiC film from the Si substrate is ofetn observed after the deposition. Furthermore, in depositing SiC films etching problems were reported for Cl-based precursor systems (e.g. CH 2CI-SiH 4- H2 and CH3SiCI3) because of the formation of Cl and CH 3 radicals [2]. Growth of a buffer layer has been proved to be a necessary step in obtaining good quality SiC films on Si substrates [3]. This buffer layer is generally grown at relatively low temperatures, after which the substrate is raised to higher temperatures for carrying out the bulk growth of SiC films. The buffer layer is grown by either reacting Si substrate with a hydrocarbon gas or by sputtering SiC onto the Si substrate [4]. Table I shows various hydrocarbon gases and the reaction parameters that are used for the conversion of Si surfaces to SiC layers. Note that the reactions had been carried out in high vacuum and cold-wall systems which are not compatible with the low pressure chemical vapor deposition (LPCVD) processes which are often carried out in hot wall reactors to increase the throughput. Therefore, in this work the reaction between acetylene (C2H2 ) and (100)Si substrate was studied to obtain the optimum parameters to grow buffer layer in a conventional horizontal hot wall CVD reactor in a low pressure. Emphasis will be given for the formation of surface defects during the reaction of C2H2 with Si substrates. EXPERIMENTAL PROCEDURE:
Single-crystal (100)Si substrates were used in this study. Before introducing the substrates into the reaction chamber, the organic contamination on the surface of Si substrate was first washed out by using acetone and then by dipping into methanol. F
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