Papers by Keyword: High Growth Rate

Abstract: Limitations in the very fast growth of 4H-SiC crystals are surveyed for a high-temperature gas source method. The evolution of macro-step bunching and void formation in crystal growth is investigated by changing the partial pressures of the source gases and crystal rotation speeds. The variation in macro-step formation depending on radial positions, where step-flow or spiral growth governs, of a grown crystal is also revealed. Based on the relation between growth conditions and macro-step bunching, a trade-off between growth rate enhancement and crystal quality and a method to improve such trade-off are discussed. Nitrogen at a high concentration under very high growth rates in the high-temperature gas source method is also investigated.

Abstract: The influence of chlorine has been investigated for high growth rates of 4H-SiC epilayers on 4o off-cut substrates. Samples were grown at a growth rate of approximately 50 and 100 μm/h and various Cl/Si ratios. The growth rate, net doping concentration and charge carrier lifetime have been studied as a function of Cl/Si ratio. This study shows some indications that a high Cl concentration in the growth cell leads to less availability of Si during the growth process.

Abstract: We report the development of over 100 μm/h growth rate process on 4-inch diameter wafers using chlorinated growth. The optimized growth process has shown extremely smooth epilayers completely free of surface step-bunching with very low surface defect density, high uniformity in thickness and doping and high run to run reproducibility in growth rate, controlled doping and defect density.

Abstract: Possibilities of very fast 4H-SiC crystal growth using a high-temperature gas source method are surveyed by computational simulation and experimental studies. The temperature range suitable to obtain high growth rates are investigated by simulating temperature dependences of growth rates for H₂+SiH₄+C₃H₈ and H₂ +SiH₄+C₃H₈+HCl gas systems. Simulation and experimental results demonstrate that an increase in source gas flow rates as well as gas-flow velocities enhance growth rates. High growth rates exceeding 1 mm/h are experimentally obtained using both gas systems. Single crystal growth on a 3-inch diameter seed crystal is also demonstrated.

Abstract: Our latest results of SiC bulk growth by High-Temperature Gas Source Method　are given in this paper. Based on Mullins-Sekerka instability, optimal growth conditions to preclude dendrite crystals, which are one of the pending issues for high-speed bulk growth, was studied. First, the simulation studies showed that high temperature gradient in a growing crystal is required for high-speed bulk growth without dendrite crystals. Second, high-speed bulk growth was demonstrated under high temperature gradient.

Abstract: A single wafer type 150 mm vertical 4H-SiC epitaxial reactor with high-speed wafer rotation was developed. The rotation of the wafer at high speed significantly enhances the growth rate, and high growth rates of 40–50 μm/h are possible on 4°off-cut 4H-SiC substrates. In addition, a low defect density and smooth surface without macro step bunching can be achieved. Excellent uniformity of thickness and doping concentration was obtained for a 150 mm wafer at a high growth rate of 50 μm/h.

Abstract: A review of recently achieved results with the chloride-based CVD on 8° and 4° off axis and nominally on-axis 4H-SiC wafers is done to clarify the epitaxial growth mechanisms on different off-angle substrates. The process conditions selected for each off-axis angle become even more difficult when running at growth rates of 100 µm/h or more. A fine-tuning of process parameters mainly temperature, C/Si ratio and in situ surface preparation is necessary for each off-angle. Some trends related to the surface properties and the effective C/Si ratio existing on the surface prior to and during the epitaxial growth can be observed.

Abstract: In this work we present the epitaxial growth of 4H-SiC on 100mm 4° off-axis substrates grown in a multi-wafer CVD planetary reactor. Highly uniform epitaxial layers having thickness and doping uniformities of 1.7% and 1.4% respectively were grown in the production reactor with optimized process conditions at 8µm/hr and 30µm/hr growth rates. Process optimizations resulted in epitaxial layers with surface roughness (RMS) of 0.32nm. Epitaxial layers with a thickness of 53µm grown with a 30µm/hr growth process had minimal degradation in surface roughness (RMS of 0.39nm).

Abstract: Ti film sputtered on flexible stainless steel substrate that rolled by 20-high Sendzimir Mill, was anodized in ethylene glycol bath in the presence of 0.5 wt.% NH4F and 3 vol.% H₂O at a high voltage of 60 V. High-aspect-ratio porous-nanotube arrays (PNTAs) of TiO2 with the tubes length of 6.2 µm were quickly prepared from Ti film, at the high growth rate of 20.7 nm·s^-1. Then the morphology and structure of PNTAs were characterized by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD), respectively. Finally, a DSSC with the photoanode of PNTAs exhibited a performance of J_sc = 2.40 mA·cm^-2, V_oc = 0.79V, FF = 0.57 and η = 1.08%.

Abstract: The effect of different C/Si ratio on the surface morphology has been studied to optimize the on-axis homoepitaxial growth conditions on 4H-SiC substrates to improve the surface roughness of epilayers. The overall surface roughness is found to decrease with decreasing C/Si ratio. An order of magnitude lower surface roughness has been observed using C/Si ratio = 0.8 without disturbing the polytype stability in the epilayer. A high growth rate of 10 µm/h was achieved without introducing 3C inclusions. The epilayers grown at higher growth rate with C/Si ratio = 1 also had improvements in the surface roughness. 100% 4H polytype was maintained in the epilayers grown with C/Si ratio in the range of 1.2 to 0.8 and with high growth rate of 10 µm/h.