Materials Science Forum Vols. 527-529

Abstract: The long term performance of today’s SiC based bipolar power devices suffer strongly from stacking fault formation caused by slip of basal plane dislocations, the latter often originating from the n-type doped SiC substrate wafer. In this paper, using sequentially p-type / n-type / p-type doped SiC crystals, we address the question, whether basal plane dislocation generation and annihilation behaves differently in n-type and p-type SiC. We have found that basal plane dislocations are absent or at least appear significantly less pronounced in p-type doped SiC, which may become of great importance for the stacking fault problem in SiC.

Abstract: SiC single crystal ingots grown by sublimation physical vapor transport (PVT) technique were prepared and then the SiC crystal quality with varying crucible design employing a guide tube and tantalum foil was systematically investigated. The growth rate of 2-inch SiC crystal grown by these crucible designs was about 0.3 mm/hr. The n-type and p-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC were successfully fabricated. The doping concentration level of below ~1017/cm3 was extracted from the absorption spectrum and Hall measurement. The densities of micropipes and inclusions in SiC crystal boules grown using the graphite/Ta foil double layer guide tube were significantly decreased. Finally we improved crystal quality through the introduction of new crucible design.

Abstract: Silicon carbide crystals were grown from the vapor. Improvement of the quality of the central part of the crystal was achieved by optimization of the geometry of the source material. Active thermal interaction of the source material and the crystallization front made possible an effective programming of the shape and morphology of the crystal. Termination of micropipes on microfacets formed on the crystallization front during growth was observed.

Abstract: We examined the influence of thermal treatment of high-purity SiC powder on 6H-SiC crystal growth. The doping concentration was decreased by increasing either thermal treatment temperature or time. It was also found that the defects such as micropipes and planar cavities were generated under relatively long treatment time (13 hours), because SiC powders were significantly graphitized. A 6H-SiC crystal grown by using SiC source treated at 2100oC for 6 hours revealed the best result with relatively low micropipes. For the effects of thermal treated sources on the improvement of crystallinity, it could be explained that both the amount of alpha phase transformed from high-purity beta-SiC powder and the elimination of porous powders in SiC powder had an influence on the removal of silicon droplets, resulting in higher Si vapor pressure at the initial growth stage.

Abstract: 6H-SiC ingots were grown with different growth interfaces at different rates via the sublimation method. A model for the step flow growth mechanism is proposed to interpret the occurrence of 15R-SiC inclusions in the 6H-SiC single crystal. The results show that the 15R-SiC occurs more easily on the convex and the concave interface than on the slight convex interface and 15R-SiC inclusion also occurs when the growth rate of 6H-SiC exceeds the critical rate of 300 %m/h with the slight convex interface at the seed temperature 2250°C.

Abstract: Because of the formation of DPB (Double Positioning Boundary) when starting from a hexagonal <0001> seed, DPB-free 3C-SiC single crystals have never been reported up to now. In a recent work we showed that, using adapted nucleation conditions, one could grow thick 3C-SiC single crystal almost free of DPB [1]. In this work we present the results of a multi-scale investigation of such crystals. Using birefringence microscopy, EBSD and HR-TEM, we find evidence of a continuous improvement of the crystal quality with increasing thickness in the most defected area, at the sample periphery. On the contrary, in the large DPB-free area, the SF density remains rather constant from the interface to the surface. The LTPL spectra collected at 5K on the upper part of samples present a nice resolution of multiple bound exciton features (up to m=5) which clearly shows the high (electronic) quality of our 3C-SiC material.

Abstract: The effects of H2 addition to the growth ambient during physical vapor transport (PVT) growth of 6H and 4H SiC were investigated using SIMS, DLTS and Hall effect measurements. Using this hybrid physical-chemical vapor transport (HPVT) approach, boules were grown using Ar-H2 and He-H2 mixtures with H2 concentrations up to 50 at%. Thermodynamic modeling suggests that addition of H2 improves the carbon transport in HPVT compared to standard PVT. This should lead to a substantial decrease in the concentration of residual N donors and the concentration of electron traps. This is confirmed by the experimental results. As expected, the source transport rate increased as H2 was added to the growth environment due to increased C transport. The background nitrogen concentration and the free electron density decreased significantly with increasing H2 concentration. The formation of electron traps (activation energies of 0.4 eV, 0.6-0.65 eV, 0.7 eV, 0.9 eV and 1 eV) was also strongly suppressed. These changes were observed for H2 concentrations as low as 4 at%. The decreased N concentration improves the ability to produce high resistivity SiC material, and for H2 concentrations as high as 10-25%, the very first wafers cut from the seed end of the boules have a resistivity exceeding 106
cm.

Abstract: High temperature chemical vapor deposition (HTCVD) simulations of silicon carbide (SiC) were demonstrated with experimental results. A vertical cylindrical reactor was used in an RF inductive heating furnace and the temperature was more than 2200
. SiH4 and C3H8 were used as source gases and H2 as carrier gas. A gas phase reaction model from the literature was used on the condition that the gas phase reaction is a quasi-equilibrium state. It was found that the major species were Si, Si2C, SiC2 and C2H2 in the gas phase reaction model as well as in the thermodynamic equilibrium calculation. Sublimation etching was considered in the surface reaction rates by modifying partial pressures of species with equilibrium vapor pressures. CFD-ACE+ and MALT2 software packages were used in the present calculation. The sticking coefficients were determined by fitting the calculated growth rates to the experimental ones. The simulated growth rate in a different reactor is in good agreement with the experimental value, using the same sticking coefficients. The present simulation could be useful to design a new reactor and to find optimum conditions.

Abstract: The growth of SiC crystals or epilayers from the liquid phase has already been reported for many years. Even if the resulting material can be of very high structural quality and the possibility to close micropipes was demonstrated, handling the liquid phase still is a challenge. Moreover, it is highly difficult to stabilize the C dissolution front and then to stabilize the growth front over a long growth time. Based on the Vapour-Liquid-Solid mechanism, we present a new configuration for the growth of SiC single crystal which should allow first to simplify the liquid handling at high temperature and second to precisely control the crystal growth front. The process consists in a modified top seeded solution growth method, in which the liquid is held under electromagnetic levitation and fed from the gas phase. In a Co-Si solution fed from a propane flow at 1350°C, thick epitaxial layers of 4H-SiC have been grown at 28 0m/h. The potentiality of this new process will be discussed in the paper.

Abstract: We carried out the growth of single crystalline silicon carbide (SiC) from Si-C-X (X= Co, Fe) ternary solutions. These ternary solutions are expected to show large carbon solubility compared with Si solvent (self-flux) by means of CALPHAD (CALculation of PHAse Diagrams) method. We investigated the growth rate and the polytype of the grown crystal from the ternary solutions. Then we found that the growth rate from the ternary solutions is much larger than that from the self-flux. The growth rate from Si-C-Co (Si-C-Fe) system was about 6mm/hr (12mm/hr) while that from the self-flux was only 2mm/hr. The grown crystal from the ternary solutions is classified into 6H that takes over the seed polytype.