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Initial Stage of SiC Crystal Growth by PVT Method

Emil Tymicki ¹, Krzysztof Grasza ^1,2, Ryszard Diduszko ¹, Rafał Bożek ³, Maciej Gała ¹

1. Institute of Electronic Materials Technology (ITME), Wólczyńska 133, Warszawa 01-919, Poland
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
3. Warsaw University, Faculty of Physics, Hoża 69, Warszawa 00-681, Poland

Abstract

Silicon carbide is a promising material for high power devices application due to its wide gap, high thermal conductivity and high breakdown field. The reduction of structural defects, such as micropipes, dislocations and mosaic structure is the main challenge the crystal growers have to deal with.

The silicon carbide single crystals were grown by the seeded physical vapour transport method (PVT) using graphite resistance heater. The crystals were grown on c-face (0001) of 6H-SiC seeds. The temperature measured on the back side of the crystal holder was in the range 2000-2300ºC. The growth atmosphere consisted of a mixture of argon and 5 vol. % of nitrogen. The total pressure was 100-300 mbar and was changed during the growth run. The SiC source was placed in a graphite crucible at temperature 50-200ºC higher than temperature of the seed. The initial source to seed distance varied in the range 10-50 mm. The growth proceeded under quasi- equilibrium conditions. Defects in the crystallization fronts and wafers cut from the crystals were studied by optical microscopy, atomic force microscopy combined with KOH etching and X-Ray diffraction.

In this work we pay special attention to the initialization of crystal growth. We observed that many nucleation sites appeared on the seed surface during the initial stage of the growth. Shortly, at the same places many separated flat faces on the crystallization front were generated. Formation of facets depends on the growth conditions and crucible geometry [1]. The number of facets is dependent on the shape of the crystallization front. The formation of many facets leads to decrease of structural quality of crystals due to degradation of regions where crystallization steps from independent site meet [2,3]. As a result we observed mosaic structure and increased number of micropipes and dislocations. An increased level of boron and nitrogen was found in parts of the crystal grown with faceted morphology. Therefore, it can be concluded that the optimal crystallization front is a little convex one, which permits the growth of crystals with single nucleation site and evolution of single facet on the crystallization front.

[1] K.Grasza, E. Tymicki, J. Kisielewski, Materials Science Forum 527-529 (2006) pp 87-90

[2] Xianxiang Li, Shouzhen Jiang, Xiaobo Hu, Jie Dong, Juan Li, Xiufang Chen, Li Wang, Xiangang Xu, Minhua Jiang Materials Science Forum Vols. 527-529 (2006) pp 95-98

[3] C.Basceni, I.Khlebnikov, Y.Khlemnikov, P.Muzykov, M.Sharma, G.Stratiy, M.Silan, and C.Balkas, Materials Science Forum 527-529 (2006) 39

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