Materials Science Forum Vols. 527-529

Abstract: In this work, the mechanism of the epitaxial growth of 4H SiC using CH3Cl as the carbon source gas was investigated. The experiments were conducted with a H2 carrier gas flow rate reduced in comparison to the standard conditions used for device-quality, full-wafer C3H8 growth. Low-H2 conditions have been found favorable for investigating the differences between the two gas systems. A non-linear trend of the growth rate dependence on CH3Cl flow was observed. This dependence was quantitatively different for C3H8 growth, which serves as an indication of different kinetics of CH3Cl and C3H8 precursor decomposition, as well as differences in Si droplet formation and dissociation. The maximum growth rate that we were able to achieve was by a factor of two higher for the CH3Cl precursor than for the C3H8 precursor at the same temperature and flow conditions. The growth on lower off-axis angle substrates produced surface morphology degradation similar for both CH3Cl and C3H8 precursor systems.

Abstract: Epitaxial growth of SiC films was performed on 4H SiC n+ substrates utilizing a chlorosilane/propane chemistry in both single wafer and batch CVD systems. Variations of the chlorosilane flow under fixed conditions of gas composition, temperature and pressure resulted in growth rates between 4 to 20 μm/hr. Fixing the chlorosilane flow rate to achieve a growth rate of approximately 4 μm/hr, the effects of temperature, pressure and gas composition on background dopant incorporation, epitaxial layer uniformity and epitaxial defect generation were investigated. Intentional n and p-type doping has been demonstrated over the carrier range 1×1018-1×1020/cm3. This paper presents the first reported of use of chlorosilane precursors to grow high quality undoped, n and p doped SiC epilayers.

Abstract: 4H-SiC epitaxial layers have been grown using trichlorosilane (TCS) as the silicon precursor source together with ethylene as the carbon precursor source. A higher C/Si ratio is necessary compared with the silane/ethylene system. This ratio has to be reduced especially at higher Si/H2 ratio because the step-bunching effect occurs. From the comparison with the process that uses silane as the silicon precursor, a 15% higher growth rate has been found using TCS (trichlorosilane) at the same Si/H2 ratio. Furthermore, in the TCS process, the presence of chlorine, that reduces the possibility of silicon droplet formation, allows to use a high Si/H2 ratio and then to reach high growth rates (16 *m/h). The obtained results on the growth rates, the surface roughness and the crystal quality are very promising.

Abstract: Thick epitaxial layers of 4H-SiC both n- and p-type were grown using horizontal Hot- Wall CVD (HWCVD). No large difference in the carrier lifetime was observed for the layers grown on n- and p-type substrates. The carrier lifetime usually increases with the increasing thickness of the epilayer. To investigate if the growth conditions and material properties are changing during the longer growth time a sample was prepared with uniformly varying epilayer thickness from 20μm on one side to 110μm on other side. Results of optical and electrical measurements, the variation in background impurities and other deep levels are discussed. Furthermore, the properties of thick layers grown on on-axis substrates are presented.

Abstract: A 4H-SiC epitaxial growth process has been developed in a horizontal hot-wall CVD reactor using a standard chemistry of silane-propane-hydrogen, producing repeatable growth rates up to 32 μm/h. The growth rate was studied as a function of pressure, silane flow rate, and growth time. The structural quality of the films was determined by X-ray diffraction. A 65 μm thick epitaxial layer was grown at the 32 μm/h rate, resulting in a smooth, specular film morphology with occasional carrot-like and triangular defects. The film proved to be of high structural quality with an X-ray rocking curve FWHM value of the (0004) peak of 11 arcseconds.

Abstract: Horizontal air-cooled low-pressure hot-wall CVD (LP-HWCVD) system is developed to get high quality 4H-SiC epilayers. Homoepitaxial growth of 4H-SiC on off-oriented Si-face (0001) 4H-SiC substrates purchased from Cree is performed at a typical temperature of 1500°C with a pressure of 40 Torr by using SiH4+C2H4+H2 gas system. The surface morphologies and structural and optical properties of 4H-SiC epilayers are characterized with Nomarski optical microscope, atomic force microscopy (AFM), x-ray diffraction, Raman scattering, and low temperature photoluminescence (LTPL). The background doping of 32 μm-thick sample has been reduced to 2-5×1015 cm-3. The FWHM of the rocking curve is 9-16 arcsec. Intentional N-doped and B-doped 4H-SiC epilayers are obtained by in-situ doping of NH3 and B2H6, respectively. Schottky barrier diodes with reverse blocking voltage of over 1000 V are achieved preliminarily.

Abstract: This paper presents SiC CVD epitaxy for MESFET fabrication in a horizontal hot-wall reactor with gas foil rotation. Excellent uniformity of < 2% for thickness and < 10% for doping has been routinely obtained for both 3x2-in. and 1x3-in. growth. The highly uniform epitaxy is maintained for the growth of a large range of doping concentrations (less than 5x1015 to greater than 1.5x1019 cm-3) and thicknesses (0.25 – 60 μm). MESFET buffer/channel structure has been characterized with SIMS measurement showing sharp interface transition. Pinch-off voltages are extracted from CV measurements over a full 2-in. wafer.

Abstract: The influence of the epitaxial layer growth parameters on the electrical characteristics of Schottky diodes has been studied in detail. Several diodes were manufactured on different epitaxial layers grown with different Si/H2 ratio and hence with different growth rates. From the electrical characterization a maximum silicon dilution ratio can be fixed at 0.04 %. This limit fixes also a maximum growth rate that can be obtained in the epitaxial growth, with this process, at about 8 μm/h. Several epitaxial layers have been grown, using this dilution ratio, with different temperatures (1550÷1650 °C). At 1600 °C the best compromise between the direct and the reverse characteristics has been found. With this process the yield decreases from 90% for a Schottky diode area of 0.25 mm2 to 61% for the 2 mm2 diodes. Optimizing the deposition process to reduce the defects introduced by the epitaxial process, yield of the order of 80% can be reached on 1 mm2 diodes.

Abstract: The epitaxial growth of SiC by a hot-wall CVD system using monomethylsilane (CH3SiH3) as a precursor is described. In the case of CH3SiH3 source only, an undoped homoepitaxial layer showed an n-type conduction around 1016-1017cm-3 on the Si face. To improve the quality of epilayers, the simultaneous supply of CH3SiH3 and C3H8 was carried out. The pit density of grown layers was reduced from 105 to 103cm-2, and a donor concentration as low as 1.6×1014cm-3 was achieved. An attempt to increase of the growth rate was also investigated.

Abstract: The initial homoepitaxial growth behavior on nearly on-axis 4H-SiC substrates was investigated. We have observed circular etch pits on the surface of on-axis substrate in the presence of source gases. However, there were no circular etch pits on the surface of off-axis substrates. In addition, the surface etched by H2 gas did not show circular etch pits even on nearly on-axis substrates. The shape of the circular etch pits was similar to spiral one. The initial growth behavior of epilayers was also investigated with various C/Si ratios of source gases (0.6

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