Materials Science Forum Vols. 556-557

Abstract: We report on the growth of 4H-SiC epitaxial layer on Si-face polished nominally on-axis 2” full wafer, using Hot-Wall CVD epitaxy. The polytype stability has been maintained over the larger part of the wafer, but 3C inclusions have not been possible to avoid. Special attention has given to the mechanism of generation and propagation of 3C polytype in 4H-SiC epilayer. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that all 3C inclusions were generated at the interface between the substrate and the epitaxial layer, and no 3C inclusions were initiated at later stages of the growth.

Abstract: A series of designed experiments have been conducted over a period of years in a multiwafer, planetary rotation, epitaxial reactor to quantify the effects of various epitaxial growth process parameters on the resulting SiC epitaxial layers. This paper summarizes the results obtained through statistically designed experiments varying process parameters and their resultant effect on the layer thickness, carrier concentration and the variability of these parameters wafer-to-wafer, and within a wafer.

Abstract: A fully-comprehensive three-dimensional simulation of a CVD epitaxial growth process has been undertaken and is reported here. Based on a previously developed simulation platform, which connects fluid dynamics and thermal temperature profiling with chemical species kinetics, a complete model of the reaction process in a low pressure hot-wall CVD reactor has been developed. Close agreement between the growth rate observed experimentally and simulated theoretically has been achieved. Such an approach should provide the researcher with sufficient insight into the expected growth rate in the reactor as well as any variations in growth across the hot zone.

Abstract: Vapor-Liquid-Solid was used for growing boron doped homoepitaxial SiC layers on 4HSiC( 0001) 8°off substrates. Si-based melts were fed by propane (5 sccm) in the temperature range 1450-1500°C. Two main approaches were studied to incorporate boron during growth : 1) adding elemental B in the initial melt, with two different compositions : Si90B10 and Si27Ge68B5; the growth was performed at 1500°C; 2) adding B2H6 (1 to 5 sccm) to the gas phase during growth with a melt composition of Si25Ge75; the growth was performed at 1450°C. In most cases, the growth time was limited by liquid loss due to wetting on the crucible walls. The longer growth duration (1h) was obtained when adding B2H6 to the gas phase. In the case of Si90B10 melt, the surface morphology exhibits large and parallel terraces whereas the step front is more undulated when adding Ge. Raman and photoluminescence characterizations performed on these layers confirmed the 4H polytype of the layers in addition to the presence of B which results in a strong B-N donor-acceptor band. Particle induced γ-ray emission was also used to detect B incorporation inside the grown layers.

Abstract: Gas phase etching of 4H SiC n+ substrates was performed utilizing chlorine containing etch chemistries in a hot wall CVD system. Carbon and silicon vapor were added to explore selective etching reactions on the wafer surface. The impact of the etch on the bare wafer surface as a function of temperature and etch chemistry is investigated. Selection of the etch chemistry and temperature are critical to ensure a smooth etched surface on which to begin epitaxial deposition. Etching also influences defect propagation from the substrate into the epitaxial layer. The results show etch chemistry reactions will influence the conversion of micropipes in the epi buffer layer.

Abstract: Crystal growth of 6H-SiC in two non-basal directions is reported. The two explored surfaces are the {1-103} plane, named qC-face, and the {1-10-3} plane, named qSi-face. The asgrown bulk surfaces exhibit a smooth structure with a small ridging effect originating from the miscut of the seed crystals. Layers, epitaxially grown on the chemically-mechanically polished qCface, nicely replicate the original crystal structure and show no sign of polytype mixing. Lowtemperature photoluminescence measurements collected on the epilayers exhibit near bandedge spectral characteristics indicative of good quality 6H-SiC.

Abstract: We detail a comprehensive approach to preparing epiwafers for bipolar SiC power devices which entails etching the substrate, growing a semi-sacrificial basal plane dislocation (BPD) conversion epilayer, polishing away a portion of that conversion epilayer to recover a smooth surface and then growing the device epilayers following specific methods to prevent the reintroduction of BPDs. With our best processing, we achieve a BPD density of < 10 cm-2 and an extended defect density of < 1.5 cm-2. Specifics of low BPD processing and particular concerns and metrics will be discussed in regard to process optimization and simplification.

Abstract: A vertical hot-wall type reactor, with a unique structure designed for controlling both gas flow behavior and thermal gradient (
T/mm) on the susceptor surface, was developed. The simulation results indicate that depending on the height of the epitaxy room (h), the
T/mm can be changed from a negative to a positive value. Preliminary epitaxial growth experiments resulted in a maximum growth rate of 51 μm/h, 4-inch area uniformity of σ/mean=1.7% for growth rate and σ/mean=21.5 % for doping concentration, and Z1/2 trap concentration of 9×1012 cm-3 at a growth rate of 43 μm/h.

Abstract: We have investigated the influence of in-situ H2 etching on the surface morphology of the 4H-SiC substrate prior to homoepitaxial growth. In this study, we varied the types of gas atmosphere during in-situ H2 etching; namely, hydrogen (H2) alone, hydrogen-propane (H2+C3H8), and hydrogen-silane (H2+SiH4). We found that in-situ H2 etching using H2 + SiH4 significantly improved the surface morphology of 4H-SiC substrate just after in-situ H2 etching. By adding SiH4, formation of bunched step structure during in-situ H2 etching could be significantly suppressed. In addition, H2 etching using H2 + SiH4 was able to remove scratches by etching a thinner layer than that using H2 alone. We also discussed the in-situ H2 etching mechanism under the additional SiH4 condition.

Abstract: Epitaxial layers have been grown on the (0001) C-face of 2- and 3-inch 4H-SiC wafers. Growth conditions like temperature, pressure, and C/Si ratio have been varied. In both systems smooth surface morphologies could be obtained. The main challenge of epitaxial growth on the Cface of 4H-SiC for electronic device applications seems to be the control of low doping concentration. High temperature and low pressure are the key parameters to reduce the nitrogen incorporation. The hot-wall CVD system used for these experiments allowed the application of higher temperatures and lower pressures than the cold-wall equipment. The lowest doping concentration of 2.5x1015 cm-3 has been achieved by hot-wall epitaxy using a temperature of 1625 °C, a system pressure of 50 hPa, a C/Si ratio of 1.4, and a growth rate of 6.5 2mh-1. Good doping homogeneity on 2-inch and 3-inch wafers could be achieved. For a doping level of ND-NA= 3×1015 cm-3 sigma is about 15%.