Application of 6H to 4H Polytype Conversion to Effective Reduction of Micropipes in 4H SiC Crystals


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Bulk crystals of 6H and 4H silicon carbide have been grown by PVT method. 6H-SiC were obtained in optimized near-to-equilibrium growth conditions in order to improve the crystal quality and to provide the 6H seeds for 6H to 4H-SiC conversion. In experiments of 6H to 4H polytype transformation a set of invariable growth conditions was applied: C-face seed, C-rich atmosphere, on-axis seed orientation, pre-heating of the source material, slightly convex crystallization front and optimized geometry of the growth system. Other growth parameters were varied to optimize the polytype conversion, e.g.: structural quality of the seed, intentionally added impurity (N and/or Sc), initial growth stage recipe, argon pressure and temperature gradient - resulting in variety of growth rates and temperatures of the seed. Special attention was paid to seed passivation and a scheme of temperature and inert gas pressure changes during growth. Crystals were characterized by KOH etching, X-ray diffraction, optical and AFM microscopy. A reproducible method of 75% efficient conversion was elaborated. A large central surface free of micropipes was observed with characteristic six symmetrical ridges as well as the increased concentration of nitrogen. The parasitic 15R-SiC polytype was nucleated on the vicinal part of the crystallization front of 6H-SiC and 4H-SiC crystals.



Materials Science Forum (Volumes 600-603)

Edited by:

Akira Suzuki, Hajime Okumura, Tsunenobu Kimoto, Takashi Fuyuki, Kenji Fukuda and Shin-ichi Nishizawa






K. Grasza and E. Tymicki, "Application of 6H to 4H Polytype Conversion to Effective Reduction of Micropipes in 4H SiC Crystals ", Materials Science Forum, Vols. 600-603, pp. 31-34, 2009

Online since:

September 2008




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