Modeling Analysis of Free-Spreading Sublimation Growth of SiC Crystals
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Modeling Analysis of Free-Spreading Sublimation Growth of SiC Crystals M. V. Bogdanov1, S. E. Demina1, S. Yu. Karpov1, A. V. Kulik1, D. Kh. Ofengeim1, M. S. Ramm1, E. N. Mokhov2, A. D. Roenkov2, Yu. A. Vodakov2, Yu. A. Makarov3, and H. Helava4 1 Soft-Impact Ltd., P.O. Box 33, 194156 St.Petersburg, Russia 2 Crystal Growth Science and Technology Laboratory, St.Petersburg, Russia 3 STR, Inc., P.O.Box 70604, Richmond, VA 23255-0604, U.S.A 4 The Fox Group, Inc. 1154 Stealth St., Livermore, CA 94550, U.S.A. ABSTRACT Recently, an advanced technique for growing free-spreading SiC bulk crystals by sublimation has been demonstrated. This method was used to grow 6H- and 4H-SiC boules free of polycrystalline deposits on the crystal periphery, up to 35 mm in diameter with the micropipe density less than 20 cm-2 and the dislocation density about 102-103 cm-2. In this paper, we report on the numerical modeling of free-spreading crystal growth. We consider the global heat transfer in an inductively heated growth system, species transport in the growth cell and in the powder charge, and thermoelastic stress, focusing on the crystallization front dynamics, poly-SiC deposition, and powder source evolution. Special attention was given to the validation of the simulations. The computed thermal field and evolution of the powder and crystal shape were found to agree qualitatively with observations. INTRODUCTION A new advanced technique for growing low-defect free-spreading SiC bulk crystals by sublimation has recently been suggested [1,2]. In this method, high crystal quality is achieved by (i) considerable lateral spreading of the growing crystal so that threading dislocations originating from the seed are localized in the near-axis zone of the crystal while the peripheral areas are grown dislocation-free, and (ii) preventing the growing crystal from the mechanical contact with the crucible and parasitic deposits on its side walls and lid. The negative effect of the mechanical contact is illustrated in Figure 1 presenting a photograph of a vertical cross-section of a boule grown under non-optimal conditions. Poly-SiC deposition occurring on the side crucible walls gives rise to an extensive generation of threading dislocations and micropipes on the periphery of the crystal. Lateral crystal enlargement avoiding the contact of the crystal with the walls requires a careful temperature profiling in the growth crucible. In this paper, we discuss numerical modeling as a tool providing a better insight into the growth mechanisms and growth condition optimization. With the software tool “Virtual Reactor” [3], we have simulated the global heat transfer in the growth system, species transport in the growth cell accounting for poly-SiC deposition, heat and mass transport in the SiC powder, and thermoelastic stress in the growing crystal. To validate the simulations, we employ the temporal variation of the crystal shape and properties of the powder source. Comparison of the computations with experimental data has demonstrated good
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