Materials Science Forum Vols. 615-617

Abstract: In this paper we present results on the growth of low-doped thick epitaxial layers on 4° off-oriented 4H-SiC using a commercially available hot-wall multi-wafer CVD system. For the first time we show results of a low-doped full-loaded 73” run on 4° off-oriented substrates with a layer thickness of more than 70 µm. The target doping concentration of 1.2×1015 cm-3 is suitable for blocking voltages > 6 kV. Results on doping, thickness and wafer-to-wafer homogeneities are shown. The surface quality of the grown layers was characterized by AFM. The density of different types of dislocations was determined by Defect Selective Etching.

Abstract: CVD growth of epitaxial layers with a mirror like surface grown on 75 mm diameter 4° off-axis 4H SiC substrates is demonstrated. The effect of the C/Si ratio, temperature and temperature ramp up conditions is studied in detail. A low C/Si ratio of 0.4 and a temperature of 1530 °C is the best combination to avoid step bunching and triangular defects on the epitaxial layers. Using a low growth rate (about 3 µm/h) 6 μm thick, n-type doped epilayers were grown on 75 mm diameter wafers resulting in an RMS value of 0.7 nm and good reproducibility. 20 μm thick epitaxial layers with a background doping in the low 1014 cm-3 were grown with a mirror-like, defect-free surface. Preliminary results when using higher Si/H2 ratio (up to 0.4 %) and HCl addition are also presented: growth rate of 28 μm/h is achieved while keeping a smooth morphology.

Abstract: The co-doping of nitrogen and aluminum has been studied in the sublimation epitaxy growth process. It is shown that the doping may be tuned from n-type to p-type by effect of substrate doping, growth face and volume of the growth crucible. The co-doped layers show a nearly ideal I V characteristic and luminescence at room temperature.

Abstract: Some aspects of the chloride-based CVD growth process have been investigated by using both the approach to add HCl to the standard precursors or/and by using the single molecule precursor methyltrichlorosilane (MTS). The efficiency of the process for different precursors, the growth rate stability and the effect that the Cl/Si-ratio has on the growth have been studied. MTS is showed to be the most efficient precursor; the growth can be hindered by to much chlorine in the gas mixture. The Cl/Si-ratio is also found to be a process parameter that affects the amount of incorporated nitrogen in the epilayers.

Abstract: Homoepitaxial growth of 4H-SiC on on-axis Si-face substrates is reported using hydrogen chloride together with silane and ethylene. In this study, the main process parameters, such as temperature, Cl/Si ratio, C/Si ratio, Si/H2 ratio and ramp up conditions, were studied in detail to understand their effects on the growth mechanisms. Two different optimal epitaxial growth conditions were found. Silicon rich conditions and a high Cl/Si ratio were the key parameters to grow thick homoepitaxial layers with a very low background doping concentration and a growth rate higher than 20 μm/h.

Abstract: Chlorinated silicon precursor SiCl4 was investigated as a source of additional chlorine instead of or in combination with HCl during the low temperature (13000C) halo-carbon epitaxial growth. No Si cluster cloud was visible inside the hot-wall susceptor indicating negligible homogeneous gas-phase nucleation. The growth rate was significantly enhanced compared to the SiH4-case, but was relatively close to the SiH4+HCl case. Similar to the SiH4+HCl growth, the increase of the growth rate caused by suppressed cluster formation was less significant than expected. The depletion of the growth species by vigorous polycrystalline deposition upstream of the hot zone, which was earlier reported for the SiH4+HCl growth, was also significant in the SiCl4-based growth. Closer to the growth zone, carbon species also get incorporated in the polycrystalline deposits.

Abstract: A method to improve the uniformity of epitaxial wafers grown in planetary rotation reactors through analysis of intentionally stalled wafer measurements is described. A set of basis functions that are completely uniform when rotated in the reactor environment are described and used to construct a nearest uniformity producing profile (NUPP). The methodology for use of stalled wafer profiles and comparison to the NUUP allows easy identification of the changes in process parameters necessary for more uniform epitaxial growth. Although described here as applied to SiC epitaxial growth, this method is applicable to all planetary rotation reactors which are utilized for SiC and III-V semiconductor epitaxial growth.

Abstract: Epitaxial layers were grown on 4° off-axis 4H-SiC substrates by hot-wall chemical vapor deposition. The reduced off-cut angle resulted in lower basal plane dislocation (BPD) densities. The dependence of BPD reduction on growth conditions was investigated using ultraviolet photoluminescence (UVPL) imaging. With this method, it was found that the dislocations were converting to threading edge dislocations throughout the thickness of the film. A high (≥ 97%) conversion efficiency was found for all films grown with this orientation. A conversion of 100% was achieved for several films without pre-growth treatments or growth interrupts.

Abstract: The influence of substrate surface scratches on the quality of CVD grown 4H-SiC homo-epitaxial layers has been studied using a combination of post-growth Monochromatic Synchrotron X-ray Topography (MSXT) and KOH etching. MSXT observations suggest that the scratches on the substrate surface act as dislocation nucleation centers during the growth. When the scratch is along the off-cut direction, only TED-TED pairs are generated. As the inclination of the scratch to the off-cut direction increases, an increasing number of TED-BPD pairs are generated. A model is presented for a possible mechanism for the nucleation of dislocations at scratches.

Abstract: We have carried out detailed investigations on the influence of the growth conditions and the wafer off angle on the surface morphology of low off angle homoepitaxial growth. We found triangular features to be also serious problems on a 4 degree off 4H-SiC Si-face epitaxial layer surface. The control of the C/Si ratio by controlling the SiH4 flow rate is effective in suppressing the triangular features on 4 degree off Si-face homoepitaxial layer. As regards epitaxial growth on a vicinal off-axis substrate, the small off angle difference of a tenth part of a degree has an influence on the surface morphology of the epitaxial layer. This tendency depends on the face polarity and a C-face can be obtained that has a specular surface with a lower vicinal off angle than a Si-face. By controlling this off angle, a specular surface morphology without a bunched step structure could be obtained on a vicinal off angle 4H-SiC Si-face.