Materials Science Forum Vols. 600-603

Abstract: In this work the problem of growth rate decaying during growth is considered. A new design and growth profiles are suggested in order to reduce deviations of growth parameters during the process of growth.

Abstract: 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.

Abstract: II-VI is developing large-diameter SiC crystals to be used as lattice-matched, high thermal conductivity substrates for new generation GaN-based and SiC-based semiconductor devices. Large-diameter 6H SiC single crystals are grown at II-VI using our Advanced PVT sublimation growth process. Stable SI properties are achieved by compensation with vanadium, which results in high and spatially uniform resistivity, on the order of 1011 Ohm-cm. The quality of the presently grown 100 mm 6H SI substrates has been dramatically improved [1], and they are free of edge defects. Micropipe density in the 100 mm 6H SI substrates ranges from 2 to 8 cm-2 and dislocation density from 3·104 to 6·104 cm-2. X-ray rocking curves measured on as-sawn 100 mm 6H wafers showed edge-to-edge lattice curvature () between 0.1° and 0.3° and FWHM of the rocking curve between 50 and 100 arc-seconds

Abstract: The polytype structural variations of a set of SiC bulk wafers with different Nitrogen (N) doping levels, prepared by Physical Vapore Deposition (PVD), are studied. The initial growth conditions were used to produce 6H-polytype SiC, which has been approved for the undoped and lightly doped materials. However, when extreme high N-dopants were applied, the obtained wafer was found with 4H- and 15R-polytype features. Our experimental results of HR-TEM and Raman scattering have revealed clearly the polytype transformation, indicating that the inducement of N in the reactor leads to the polytype transformation of the resulted SiC crystal.

Abstract: An unusual contrast in SEM secondary electron imaging for PVT grown silicon carbide with vanadium doped was observed. An explanation in point of the compensation of different type of dopant was drawn. And the relationship between the doping properties of vanadium and orientation of SiC domains was investigated.

Abstract: A simulation study for high temperature chemical vapor deposition (HTCVD) of silicon carbide (SiC) is presented. Thermodynamic properties of the species were derived from the first-principles calculations in order to evaluate the activation energy (Ea) in the gas phase reaction. Pathways producing SiC2 and Si2C from SiCl4-C3H8-H2 system were proposed to investigate the effect of chlorinated species on HTCVD. A thermo-fluid analysis was carried out to estimate the partial pressures of the species. It was found that the main sublimed species of Si, SiC2, Si2C decreased in the SiCl4-C3H8-H2 system compared to the SiH4-C3H8-H2 system. This suggests that the growth rate would decrease in the atmosphere of chlorinated species at around 2500°C.

Abstract: This work focuses on computational analysis of SiC High Temperature Chemical Vapor Deposition (HTCVD) from silicon tetrachloride (SiCl4) and propane (C3H8) precursors supplied separately and diluted by argon and hydrogen, respectively. It is aimed at verification of the technological parameters providing complete precursor decomposition in the growth chamber, the optimal gas composition for SiC growth, and the required silicon-to-carbon ratio in the wafer region, as well as suppression of parasitic deposits at the reactor walls and inlet unit via the optimization of the reactor geometry and temperature distributions. As a result, a high growth rate and maximal yield are expected to be achieved due to minimal precursor losses.

Abstract: We have achieved the first successful growth of 2H-SiC single crystals using the C-Li-Si melt system. Li-Si melt, whose melting point is lower than 1000 oC, was chosen because the 2H-SiC polytype is more stable at lower temperatures than other polytypes such as 3C-, 4H-, and 6H-SiC. Many hexagonal-shaped crystals of approximately 100 m in diameter were observed via a scanning electron microscope (SEM). A high resolution transmission electron microscope (HR-TEM) lattice image of the grown crystals showed a periodical structure with A-B stacking along the <0001> direction. These results indicated that the Li-based flux was useful for growing bulk 2H-SiC single crystals.

Abstract: We investigated effects of Ti and Ge additions to Si solvent on the volume and the polytype of SiC precipitate in unseeded SiC solution growth. The Ti addition increased the amount of SiC precipitates. Compared to pure Si solvent, the amount of crystal grown in Si-30at%Ti at 1600 °C increased by 5 times. In addition, the Ti addition induced the precipitation of 6H-SiC. Further, the Ge addition to Si-Ti solvent promoted several polytype precipitations (4H and 6H). These results indicate the possibility of polytype control by solvent composition.

Abstract: A solution growth of 3C-SiC was performed on (111)Si-face or )111(C-face of 3C-SiC seed crystal at around 1700 °C by dipping method. The polytype of the crystal grown on the Si-face immediately changed to 6H-SiC. On the other hand, 3C-SiC stably grew on the C-face except for a small number of 6H-SiC precipitates. The polytype transition phenomenon can be explained by the difference of the chemical potential and the solution-crystal interfacial energy between 3C-SiC and 6H-SiC. To grow a larger 3C-SiC crystal, we carried out a long-term growth for 30 hours on the C-face. In the first 10 hours, the polytype of the grown crystal was 3C-SiC. In the next 10 hours, however, the polytype changed from 3C-SiC to 6H-SiC. According to our studies, 6H-SiC tends to grow on 6H-SiC at around 1700 °C, while both of 3C-SiC and 6H-SiC can grow on 3C-SiC at around the same temperature. In this case, 6H-SiC grows on 6H-SiC precipitates and then the dominant polytype changes to 6H-SiC after several 6H-SiC precipitations. To grow 3C-SiC crystal stably, it is necessary to surpress completely the polytype transition by the growth on C-face at lower growth temperatures.