Materials Science Forum Vols. 483-485

Abstract: II-VI has developed an Advanced PVT (APVT) process for the growth of nominally undoped (vanadium-free) semi-insulating 2” and 3” diameter 6H-SiC crystals with room temperature resistivity up to 1010 W·cm. The process utilizes high-purity SiC source and employs special measures aimed at the reduction of the impurity background. The APVT-grown material demonstrates concentrations of B and N reduced to about 2·1015cm-3. Wafer resistivity has been studied and correlated with Schottky barrier capacitance, yielding the density of deep compensating centers in 6H-SiC in the low 1015 cm-3 range for both ntype and p-type material. The nearly equal density of deep donors and deep acceptors ndicates that the centers responsible for the intrinsic compensation can be amphoteric. TheEPR density of spins from free carbon vacancies is about 1014 cm-3. It is also hypothesized that impurity-vacancy complexes can be present in the undoped material and participate in compensation.

Abstract: Planar defects have been found in nitrogen doped 2" 4H-SiC crystals grown on off-axis seeds. The doping level was 1×1019cm-3, which is below the critical one for the thermally activated cubic stacking fault formation in the 4H matrix. Planar defects in the doped region are nucleated on the whole seed surface outside the growth facet. They are coexisting 15R and 6H lamellas of unitcell height as revealed by means of luminescence and high resolution transmission electron microscopy. These inclusions are preferably formed at the rim of the growth facet, where polytype change occurs after switching off the nitrogen flow during growth.

Abstract: We present experimental results with regard to the evaluation of growth-induced polytype domains in 6H-SiC crystals grown by sublimation method and these domains are characterized by using the polarized optical microscopy and micro-Raman spectroscopy. The polytype domains of reverse triangular are generated by local variation of temperature along cdirection and spread-wing shapes normally occurred forming micropipes in many cases. These polytype domains may be generated due to the local variation of supersaturation and/or temperature at central position during crystal growth. In this work, we try to elucidate the origin and mechanism responsible for growth-induced polytype domains.

Abstract: SiC crystal boules with different shapes were prepared using sublimation physical vapor transport technique (PVT) and then their crystal quality was systematically investigated. The temperature distribution in the growth system and the crystal shape were controlled by modification of crucible and insulation felt design, which was successfully simulated using “Virtual Reactor” for flat structure design and concave structure design. The SiC polytype proved to be the n-type 6H-SiC from the typical absorption spectrum of SiC crystal. The defect density of SiC crystal boules with concave structure was slightly lower than that of flat structure and the crystal quality of SiC crystal boules with both flat structure and concave structure was significantly improved as the SiC crystal grows during the PVT methods.

Abstract: Growth, etching, and doping features of SiC-CVD in a horizontal hot-wall reactor were numerically analyzed using the improved heterogeneous model. The improved model was able to explain the growth and etching features accurately. In addition, we propose the surface flux, surface carbon and silicon concentration, and its ratio as the universal parameter of the SiC-CVD process. Concerning doping features, the improved model showed that nitrogen and aluminum doping incorporation could be explained by the site competition model, while taking into account the amount of surface silicon and surface carbon, respectively.

Abstract: The present production processes for epitaxial SiC do not allow the matching of productivity with the material quality requested by the microelectronics market. Here, to respond to such a demand, a combined experimental and multi-scale – multi-hierarchy modeling approach was adopted. Models allow to verify a priori the role of process operative parameters on the performance ones for both the final product and of the process itself, like growth rate uniformity, film stoichiometry and dopants incorporation, homogeneous nucleation of particulate, microdefects and film morphology. Specifically, in this work the developing of a lumped deposition mechanism is addressed

Abstract: The Hot-Wall CVD reactor was developed for the thick epitaxial SiC layers needed for high voltage power devices but its inherent better properties – better cracking efficiency of the precursor gases and better lateral and vertical temperature homogeneity – should also influence the growth of other materials such as the III-nitrides. We will give some examples of thick SiC layers grown on either off- or on-axis substrates with this technique. We will also show that high-quality III-nitride materials can be grown.

Abstract: The results of a new epitaxial process using an industrial 6x2” wafer reactor with the introduction of HCl during the growth have been reported. A complete reduction of silicon nucleation in the gas phase has been observed even for high silicon dilution parameters (Si/H2>0.05) and an increase of the growth rate until about 20 µm/h has been measured. No difference has been observed in terms of defects, doping uniformity (average maximum variation 8%) and thickness uniformity (average maximum variation 1.2 %) with respect to the standard process without HCl.

Abstract: Hydrogen chloride (HCl) was added to a standard SiC epitaxial growth process as an additive gas. A low-pressure, hot-wall CVD reactor, using silane and propane precursors and a hydrogen carrier gas, was used for these experiments. It is proposed that the addition of HCl suppresses Si cluster formation in the gas phase, and possibly also preferentially etches material of low crystalline quality. The exact mechanism of the growth using an HCl additive is still under investigation, however, higher growth rates could be obtained and the surfaces were improved when HCl was added to the flow. The film morphology was studied using SEM and AFM and the quality with LTPL analysis, which are reported.