Investigation of silicon carbide physical vapor transport growth on the C-terminated face of 6H seeds
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Investigation of silicon carbide physical vapor transport growth on the C-terminated face of 6H seeds
D. Schulz, J. Doerschel, K. Irmscher, H.-J. Rost, D. Siche, J. Wollweber Institut für Kristallzüchtung, Max-Born-Str. 2, D-12489 Berlin, GERMANY Phone: +49 30 6392 2844 Fax: +49 30 6392 3003 e-mail: [email protected] ABSTRACT Sublimation growth of 6H-SiC has been studied with respect to surface morphology, growth temperature, supersaturation and growth rate. Growth was performed on the C-terminated face of 6H seeds mainly and for comparison also the Si-terminated face was used. Step bunching is observed dependent on different parameters and is strongly influenced by the seed orientation. The growth rate of 4H on the C-face is found to be higher than the rate of 6H grown on the Siface.
INTRODUCTION Bulk crystal growth of the 4H polytype is exclusively achieved on the (0001) face, whereas 6H-SiC growth is performed on the (0001) face [1]. Usually, for crystal growth of one polytype seeds of the same polytype are used. The polytype stability for growth on the C-terminated face is lower compared to the other face, due to its lower surface energy. There have been only a few attempts dealing with the sublimation growth on 6H(0001) seeds and the results are not consistent. Kanaya et al. concluded from a detailed study that 4H crystal growth on C-terminated 6H seeds is favored at lower temperature, higher source-seed temperature difference and lower argon pressure as compared to 6H crystals [2]. Koga et al. investigated the polytype stability on both polar faces of 6H seeds by varying the temperature and the pressure reduction rate [3]. In contrast to [2] 4H crystals were only obtained on the Cterminated face at high temperatures. The probability of polytype changes is high during the seeding sequence of the sublimation growth process. This is owing to the growth conditions at this stage which are away from equilibrium. Therefore, the early stages of crystal growth has been investigated with reference to the surface morphology. Some aspects of 4H crystal growth will be discussed.
EXPERIMENTAL The seeds were wafers prepared from 6H crystals. To determine the surface polarity wet oxidation has been performed. In addition, by removing the oxide layer also the thickness of the surface damage layer is decreased. The damage layer is generated during wafering, e.g. grinding and polishing. Two different types of sublimation growth experiments have been done. Firstly, thin layers were grown by using a modified growth sequence. After the growth temperature and growth pressure had been reached the process was interrupted by backfilling with inert gas and H1.8.1
decreasing the temperature simultaneously. Tests were done with an additional nitrogen gas flow. It could be shown, that growth stops almost immediately because the increase in nitrogen concentration at the surface could not be detected. Therefore also the growth morphology can be kept by the procedure described above. Dependent on the growth conditions layers from 10
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