Papers by Author: Sven Andersson

Abstract: The growth of 3C-SiC on hexagonal polytype is addressed and a brief review is given for various growth techniques. The Chemical Vapor Deposition is shown as a suitable technique to grow single domain 3C epilayers on 4H-SiC substrate and a 12.5 µm thick layer is demonstrated; even thicker layers have been obtained. Various characterization techniques including optical microscopy, X-ray techniques and photoluminescence are compared for the evaluation of the crystal quality and purity of the layers.

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: This study has been focused on 3C-SiC epitaxial growth on 4H-SiC (0001) on-axis substrates using the standard CVD chemistry. Several growth parameters were investigated, including growth temperature, in-situ etching process and C/Si ratio. High quality single domain 3C epilayers could be obtained around 1350 °C, with propane present during pre-growth etching and when the C/Si ratio was equal to 1. The best grown layer is 100% 3C-SiC and single domain. The net n-type background doping is around 2x10¹⁶ cm^-3. The surface roughness of the layers from AFM analysis is in the 3 to 8 nm range on a 50x50 μm2 area.

Abstract: A chloride-based chemical-vapor-deposition (CVD) process has been successfully used to grow very high quality 3C-SiC epitaxial layers on on-axis α-SiC substrates. An accurate process parameters study was performed testing the effect of temperature, in situ surface preparation, precursor ratios, nitrogen addition, and substrate polytype and polarity. The 3C layers deposited showed to be largely single-domain material of very high purity and of excellent electrical characteristics. A growth rate of up to 10 µm/h and a low background doping enable deposition of epitaxial layers suitable for MOSFET devices.

Abstract: The epitaxial growth at 100 µm/h on on-axis 4H-SiC substrates is demonstrated in this study. Chloride-based CVD, which has been shown to be a reliable process to grow SiC epitaxial layers at rates above 100 µm/h on off-cut substrates, was combined with silane in-situ etching. A proper tuning of C/Si and Cl/Si ratios and the combination of different chlorinated precursors resulted in the homoepitaxial growth of 4H-SiC on Si-face substrates at high rates. Methyltrichlorosilane, added with silane, ethylene and hydrogen chloride were employed as precursors to perform epitaxial growths resulting in very low background doping concentration and high quality material, which could be employed for power devices structure on basal-plane-dislocation-free epitaxial layers.

Abstract: A chloride-based CVD process has been studied in concentrated growth conditions. A systematic study of different carrier flows and pressures has been done in order to get good quality epilayers on 8° off and on-axis substrates while using very low carrier flows. Hydrogen chloride (HCl) was added to the standard gas mixture to keep a high growth rate and to get homo-polytypic growth on on-axis substrates. The carrier flow was reduced down to one order of magnitude less than under typical growth condition. By lowering the process pressure it was possible to reduce precursor depletion along the susceptor which improved the thickness uniformity to below 2% variation (σ/mean) over a 2” diameter wafer.

Abstract: Growth of thick epitaxial SiC layers needed for high power devices is presented for horizontal hot-wall CVD (HWCVD) reactors. We demonstrate thickness of epilayer of 100 μm and more with good morphology, low-doping with no doping variation through the whole thick layer and reasonable carrier lifetime which mainly depends on the substrate quality. Typical epidefects are described and their density can dramatically be reduced when choosing correctly the growth conditions as well as the polishing of the surface prior to the growth. The control of the doping and thickness uniformities as well as the run-to-run reproducibility is also presented. Various characterization techniques such as optical microscopy, AFM, reflectance, CV, PL and minority carrier lifetime have been used. Results of high-voltage SiC Schottky power devices are presented.