Analysis of the Sublimation Growth Process of Silicon Carbide Bulk Crystals
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E. SCHMITT * and A. WINNACKER * • Materials Science Department 6, University of Erlangen-Ntimberg, Martensstr. 7, ** Fluid Mechanics Institute, University of Erlangen-Ntirnberg, Cauerstr. 4, Applied Physics Institute, University Erlangen-Nrmberg, Staudtstr. 7, D-91058 Erlangen, Germany ABSTRACT Experimental and numerical analysis have been performed on the sublimation growth process of SiC bulk crystals. Crystallographic, electrical and optical properties of the grown silicon carbide (SIC) crystals have been evaluated by various characterization techniques. Numerical models for the global simulation of SiC bulk growth including heat and mass transfer and chemical processes are applied and experimentally verified. INTRODUCTION The present quality of SiC bulk crystals is far from satisfying all the needs of future SiC device applications in high power and high temperature electronics and blue/uv emitting nitridebased IIl-V optoelectronis. On the one hand SiC substrates are still very defective. Although remarkable progress has been made recently in defect reduction [1], SiC wafers contain still a high number of defects like micropipes, precipitates, dislocations and inhomogeneities (stress and dopant distribution) [2-4]. On the other hand important aspects with regard to economic manufacturing of SiC substrates by the sublimation process has to be improved considerably to achieve higher growth rates and longer crystals with an increase of wafer diameter from 1.25 inch to 4 inch. Research and development activies in these directions require basic understanding of the SiC bulk growth process and defect generation mechanisms. Despite the technological and commercial relevance of SiC there exist a surprisingly small number of experimental studies which are devoted to the quantitative evaluation of the relation of boundary conditions of SiC bulk growth, e.g. temperature field, system pressure etc., and crystal quality in growth geometries relevant for the preparation of SiC substrates with diameter d > 1 inch and length I > 10 mm [5,6]. For considerable smaller crystal geometries or epitxial growth several authors have presented basic experimental studies [7-10]. Numerical modelling which has already shown to be an effective tool for the anaysis of the growth of semiconductors from the melt and its optimization [11] is only at the beginning and marginaly used [1], partly because of the abscence of relevant physical models. In this paper first results on experimental and numerical analysis of the SiC bulk growth process are introduced. The status of SiC growth activities at the Materials Science Department of the University of Erlangen-Ntirnberg is reviewed. EXPERIMENT SiC crystals habe been prepared in both vertical (seed located at the bottom of the graphite container) and inverted (seed at the top) configurations by physical vapor transport according to the modified Lely technique (for details see e.g. Ziegler et al. [12] and Tairov [13]). SiC growth runs has been perfomed both in resistively and inductively heated furn
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