Heat Transfer Modeling of a New Crystal Growth Process

Modeling and simulation were used to evaluate a new reactor concept for SiC bulk growth. In this reactor, we succeed to fulfill thermal conditions for CVD deposition from tetramethylsilane dilute in argon and subsequent sublimation and condensation on a seed. Heat transfer modeling allowed to visualize the influence of gas flow in the reactor and temperature distribution on the seed and in the SiC deposition area. The results have been compared with experimental results. Introduction The common processes for the growth of SiC single crystals are the seeded sublimation growth technique called the Modified-Lely method [1][2] and more recently the High Temperature Chemical Vapor Deposition technique (HTCVD) [3]. The first one is a semiclosed technique where a polycrystalline powder is the source material. The second one is a pure chemical vapor deposition technique where siliconand carbon-containing gaseous species are the precursors. A hybrid technique involving CVD and sublimation is proposed. The source material is a polycrystalline plate continuously fed by a CVD technique on one face. On the other face, sublimation takes place and there is a transport of reactive gaseous species towards the seed. The objective of this paper is to evaluate the impact of the gas flow on this new open crucible and to demonstrate that it is possible to fulfill the constraints associated with CVD and sublimation. Fluid mechanics, heat transfer modeling and numerical simulation were used to quantify, interpret and visualize this new process concept. More details concerning the experimental validation are presented at this conference [4,5]. Experimental Setup In order to implement such a process, a crucible has been designed (Fig.1). Three graphite pieces compose this crucible : a) The heating element, b) the sublimation chamber and c) the HTCVD chamber. The first reaction area is the sublimation zone (1), which contains a SiC seed at the top and a plate of sintered SiC powder as the source material at the bottom. The second one is the HTCVD area (2) which permits the continuous feeding of the source from silicon and carbon gaseous precursors. This crucible is indirectly heated as the power dissipation mainly located in the heating element [4]. Both reaction zones are thus mainly heated by radiation and convection phenomena. Temperatures, pressure and gas flow rates are the controlled parameters during the process. Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 103-106 doi:10.4028/www.scientific.net/MSF.433-436.103 © 2003 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-12/03/20,10:56:39) Figure 1 : Crucible setup. (1) Sublimation zone, (2) HTCVD zone. Pyrometric measurements Numerical simulation The electromagnetic, flow and temperature fields are analyzed by finite volume methods using CFD-ACE software. The different phenomena occurring in the reactor are described by the equations of mass conservation, electromagnetic and energy balance. Fluid dynamics in porous media and chemical reactivity are not shown in this study.