Kazuhiko Kusunoki

High-Speed Growth of 4H-SiC Single Crystal Using Si-Cr Based Melt

In this study, we have investigated the rate-limiting process of 4H-SiC solution growth using Si-Cr based melt, and have tried high-speed growth. It is revealed that the rate-limiting process of SiC growth under our experimental condition is interface kinetics, which can be controlled by such factors as temperature and supersaturation of carbon. By enhancing the interface kinetics, SiC crystal has been grown at a high rate of 2 mm/h. The FWHM values of X-ray rocking curves and threading dislocation density of the grown crystals are almost the same as those of seed crystal. Possibility of high-speed and high-quality growth of 4H-SiC has been indicated.

Solution growth of SiC crystal with high growth rate using accelerated crucible rotation technique

We performed solution growth of SiC single crystals from Si-Ti-C ternary solution using the accelerated crucible rotation technique (ACRT). It was confirmed that the growth rate exceeding 200 μm/hr was achievable by several ACRT conditions. This high growth rate might be due to the enhancement of the carbon transport from the graphite crucible to the growth interface using the ACRT. Moreover, the incorporation of inclusions of the Si-Ti solvent in the grown crystal was significantly suppressed by using the ACRT. It was thought that the intensive convection near the growth interface resulted in not only the marked increase of SiC growth rate but also the superior homogeneity in the surface morphology. It was concluded that faster stable growth can be accomplished in the SiC solution growth using the ACRT.

Crystalline Quality Evaluation of 6H-SiC Bulk Crystals Grown from Si-Ti-C Ternary Solution

The growth of 6H-SiC crystal from Si-Ti-C ternary solution was conducted under the temperature gradient and the crystalline quality evaluations of the grown crystals were carried out. 6H-SiC(0001) on-axis pvt-grown crystal was used as a seed crystal. Micropipes in the seed crystal were terminated during the solution growth and 28mm28mm self-standing micropipe-free SiC crystals were obtained. The quality of the grown crystals was investigated by SIMS, high-resolution x-ray diffraction and molten KOH etching. The content of residual impurities in the SiC were very low. The X-ray -rocking curves of the solution grown SiC showed single peak with high peak intensity ,while that of the seed crystal showed several peaks due to the misoriented domains. Moreover, it was found that the number of etch-pit in the grown crystal is much less than that in the seed crystal and it decreases with the increase of the growth thickness. These results indicate that the crystalline quality of grown crystal was significantly improved during the solution growth.

Solution Growth of Self-Standing 6H-SiC Single Crystal Using Metal Solvent

Silicon carbide (SiC) crystal growth from ternary solutions Si-C-X where X is a transition metal was studied. In order to select the desirable transition element and to determine the solution composition, we have conducted the calculations of ternary phase diagrams by means of CALPHAD (CALculation of PHase Diagrams) method. Preliminary growth experiments without a seed crystal were also performed. Among various Si-based solutions, Si-C-Ti was one of the most effective solutions to increase crystal growth rate compared with Si-C. Optical microscopic observation of the obtained SiC etched by molten KOH showed no micropipe defects in the crystals. We have also performed the growth experiments with 6H-SiC seed crystal under temperature gradient. As a result, we have successfully obtained a 12mm×12mm self standing SiC crystal. Introduction At present, commercially available silicon carbide (SiC) wafers are produced by the Physical Vapor Transport (PVT) technique. Although a large number of attempts have been made on the reduction of structural defects, PVT crystals still exhibit remaining defects, such as micropipes and dislocations. Especially, micropipe is a primary defect degrading electronic devise performance and thought to be inevitable using PVT technique. Thus it is very important to establish new growth method of the low defect SiC bulk crystal. Solution growth technique is a promising answer to this problem. Growth from liquid phase has expected to improve the quality of the crystals because the growth proceeds under thermal equilibrium. In the case of SiC, although the congruent melt cannot be obtained, SiC can be precipitated from Si-C based solutions[1,2,3]. Si solvent (self flux) has only a small C solubility at moderate temperature, which reduces the SiC growth rate two orders of magnitude lower than that of PVT technique. On the other hand, ternary Si-C-X solution, where X is a carefully selected additive metal might exhibit a large C solubility at relatively low temperature. However lack of well-established ternary phase diagram, Si-C-X makes it difficult to select the desirable X element and to design the solution. In this study we report the solution growth of 6H-SiC from ternary Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 123-126 doi:10.4028/www.scientific.net/MSF.457-460.123

Crystallinity Evaluation of 4H-SiC Single Crystal Grown by Solution Growth Technique Using Si-Ti-C Solution

Crystallinity of 4H-SiC bulk crystal obtained by solution growth technique was characterized mainly by KOH etching of the off-ground and serially ground specimen. Marked reduction of basal plane dislocation, threading edge and screw dislocations during the growth of on-axis crystal was confirmed. Cross-sectional TEM observation revealed the rapid reduction behavior of threading dislocations microscopically. AFM observation of as-grown morphology showed that screw dislocation dipoles is related to the reduction of threading screw dislocations and single domain formation, which is essential for establishing the high crystallinity.

Solution Growth and Crystallinity Characterization of Bulk 6H-SiC

The stable long time growth with the use of Si -C-Ti ternary solution was realizedu3000by improving the thermal condition during the growth. We have succeeded in obtaining a maximum 10 mm thick bulk 6H-SiC crystal, which is the largest bulk crystal ever obtained by the solution growth technique. The obtained crystal was free of cracks and exhibited a homogeneous light green color. The crystallinity of the grown crystal was characterized by X-ray rocking curve measurements using (0006) reflection and by the molten KOH etching. The mapping of the full width at half maximum (FWHM) revealed the average FWHM around 30 arc seconds and the minimal FWHM under 16 arc seconds. The etch pit density (EPD) was typically in the range between 104 and 105 cm-2, which was comparable to that of the crystal seed.

Solution Growth of Single Crystalline 6H-SiC from Si-Ti-C Ternary Solution

Solution growth of 6H-SiC single crystal from Si-Ti-C ternary solution using the accelerated crucible rotation technique (ACRT) was performed. The SiC growth rate exceeding 200 μm/hr was achieved in several ACRT conditions. Such a high growth rate can be ascribed to the enhancement of the carbon transport from the graphite crucible to the growth interface due to the use of the ACRT. The incorporation of inclusions of Si-Ti solvent in the grown SiC crystal was also significantly suppressed by using the ACRT. The intensive convection near the growth interface induced by the ACRT resulted in not only the marked increase of SiC growth rate but also the superior homogeneity in the surface morphology. It was concluded that faster stable growth could be accomplished in the SiC solution growth using the ACRT. The obtained SiC self-standing crystal exhibited homogeneous green colour without cracks and inclusions. We investigated the crystalline quality of the grown SiC crystal by means of X-ray diffraction. The, ω-scan rocking curves of (0006) reflection measured by X-ray diffraction provided the FWHM of 15-20 arc-second showing the excellent crystallinity of the solution grown 6H-SiC single crystal.

Real-time observation of the interface between SiC and a liquid alloy and its application to the dissolution behavior of SiC at 1573 K

Real-time observation of the high temperature interface between silicon carbide (SiC) and liquid alloy is indispensable to optimize the conditions for producing high quality SiC crystals by the solution growth method. In this work, real-time observation of the interface was established by using the interference observation to measure the height profile of the interface. The temperature dependence of the refractive index of 4H-SiC was measured up to 1773u2009K. The height measurement was then carried out for the SiC/alloy interface at 1573u2009K. From interference observation, bunched step heights of less than 10u2009nm were measured. The developed technique was applied for the real-time observation of dissolution behavior of SiC into molten Fe-Si alloy at 1573u2009K. The dissolution kinetics was discussed in terms of carbon mass transfer in the solution and interfacial reaction.

Liquid phase epitaxy of 4H-SiC layers on on-axis PVT grown substrates

We performed liquid phase epitaxial growth of SiC layers on on-axis 4H-SiC substrates using Si solvent. It was found that the polytype controllability of the epilayer significantly depends on the growth process conditions. By optimizing them, polytype mixing in the epilayers can be completely suppressed. It is shown that the density of basal plane dislocations in the epilayers is much less than in the substrates due to on-axis growth. SIMS analysis showed that the concentrations of trace impurity elements (B,Al,Ti,V,Cr,Fe,Ni,P) in the epilayers are under lower detection limit. The only impurity is nitrogen resulting in an n-type layer. Carrier concentrations Nd-Na ranging from high 1016 to low 1017cm-3 are achievable.

Top-seeded solution growth of 3 inch diameter 4H-SiC bulk crystal using metal solvents

We performed top-seeded solution growth of 4H-SiC for obtaining longer length crystal. Si-Cr and Si-Ti melts were used as solvents. Meniscus formation technique was applied to the present study. Special attention was paid to improve the process stability during long-term growth. One of major technological problems in the solution growth is that the precipitation of polycrystalline SiC which hiders the stable single crystal growth. Another problem is the fluctuation of supersaturation at the growth interface during the growth. Through the optimization of growth process conditions, we have successfully grown 4H-SiC single crystals up to 14 mm long with three-inch-diameter, and evaluated their crystalline quality.