Solution Growth of Self-Standing 6H-SiC Single Crystal Using Metal Solvent

Silicon carbide (SiC) crystal growth from ternary solutions Si-C-X where X is a transition metal was studied. In order to select the desirable transition element and to determine the solution composition, we have conducted the calculations of ternary phase diagrams by means of CALPHAD (CALculation of PHase Diagrams) method. Preliminary growth experiments without a seed crystal were also performed. Among various Si-based solutions, Si-C-Ti was one of the most effective solutions to increase crystal growth rate compared with Si-C. Optical microscopic observation of the obtained SiC etched by molten KOH showed no micropipe defects in the crystals. We have also performed the growth experiments with 6H-SiC seed crystal under temperature gradient. As a result, we have successfully obtained a 12mm×12mm self standing SiC crystal. Introduction At present, commercially available silicon carbide (SiC) wafers are produced by the Physical Vapor Transport (PVT) technique. Although a large number of attempts have been made on the reduction of structural defects, PVT crystals still exhibit remaining defects, such as micropipes and dislocations. Especially, micropipe is a primary defect degrading electronic devise performance and thought to be inevitable using PVT technique. Thus it is very important to establish new growth method of the low defect SiC bulk crystal. Solution growth technique is a promising answer to this problem. Growth from liquid phase has expected to improve the quality of the crystals because the growth proceeds under thermal equilibrium. In the case of SiC, although the congruent melt cannot be obtained, SiC can be precipitated from Si-C based solutions[1,2,3]. Si solvent (self flux) has only a small C solubility at moderate temperature, which reduces the SiC growth rate two orders of magnitude lower than that of PVT technique. On the other hand, ternary Si-C-X solution, where X is a carefully selected additive metal might exhibit a large C solubility at relatively low temperature. However lack of well-established ternary phase diagram, Si-C-X makes it difficult to select the desirable X element and to design the solution. In this study we report the solution growth of 6H-SiC from ternary Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 123-126 doi:10.4028/www.scientific. net/MSF.457-460.123 © 2004 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-11/03/20,15:23:08) Si-C-X solutions where X is a transition metal. In order to select the desirable transition element and to determine the solution composition, we have conducted the calculations of ternary phase diagrams. Experiment Ternary phase diagrams, Si-C-X where X is a transition metal, were calculated by CALPHAD (CALculation of PHase Diagrams) method. From the Si-C, Si-X and X-C binary phase diagrams, thermodynamic parameters imperative to calculate ternary phase diagrams were determined. Growth experiments without a seed crystal were performed in graphite resistive furnace in pure Ar atmosphere (Fig.1 (a)). Si-X mixtures were melted in the high purity graphite crucible, which acts as both container and C-source. The solution was kept at 1700°C for 1hour until the carbon solubility reached saturation. Then the solution was supercooled to 1300°C with cooling rate of 1 °C/min. After the growth procedure, the solidified metal was removed with HF: HNO3 (1:1) solution and residual crystals were picked up from the crucible. Optical microscopic observations of as-grown and etched crystal in molten KOH(450°C,5min.) were conducted. Growth of thick SiC layers on a seed 6H-SiC(0001) Si-face was conducted using Si-Ti solvent in the RF induction furnace in Ar atmosphere (Fig.1 (b)). The graphite crucible was charged with a solvent composing 77at%Si and 23at%Ti. The temperature gradient was applied in the vertical direction of crucible. The seed crystal grown PVT technique was mounted on a graphite rod and dipped into lower temperature area of the solution. Temperature gradient near the seed crystal was kept about 60°C/cm. The temperature at the seed crystal was varied from1600 to 1700°C. After 5 hours growth, the seed crystal was extracted from solution. The residual solvent was removed with HF: HNO3 (1:1) solution. Fig.1 Growth experiment sets-up: (a) without a seed crystal and (b) with a seed crystal Graphite crucible