Materials Science Forum Vols. 556-557

Abstract: A simplified deposition model, involving both the description of the deposition and of the film morphology was adopted to quantitatively understand the experimental trends encountered in the epitaxial silicon carbide deposition in an industrial hot wall reactor. The attention was focused on the system involving chlorinated species because its really superior performances with respect the traditional silane/hydrocarbons process. The evolution of the crystalline structure (i.e., from poly to single) and of the surface roughness can be understood by simply comparing two characteristic times, like those inherent the surface diffusion and the matter supply to the surface.

Abstract: Epitaxial layers were grown in a horizontal hot-wall CVD reactor and intentionally doped with aluminium in a wide concentration range by varying the flow of aluminium into the reactor. The layers were grown on 4H and 6H SiC substrates on both Si and C face. Low temperature photoluminescence (LTPL) has been used to characterize the layers; 6H-SiC show differences in the structure of the Al bound-exciton (Al-BE) between the two faces, suggesting that the site preference is face dependent. From the LTPL spectra the Al concentration in the layers can be estimated.

Abstract: In this paper we present highly uniform SiC epitaxy in a horizontal hot-wall CVD reactor with wafer rotation. Epilayers with excellent thickness uniformity of better than 1% and doping uniformity better than 5% are obtained on 3-in, 4° off-axis substrates. The same growth conditions for uniform epitaxy also generate smooth surface morphology for the 4° epiwafers. Well controlled doping for both n- and p-type epilayers is obtained. Abrupt interface transition between n- and pdoped layers in a wide doping range is demonstrated. Tight process control for both thickness and doping is evidenced by the data collected from the epi operations. The average deviation from target is 2.5% for thickness and 6% for doping. PiN diodes fabricated on a standard 3-in, 4° epiwafer have shown impressive performance. More than half of the 1 mm2 devices block 1 kV (2.3 MV/cm) with a low leakage current of 1 μA.

Abstract: The growth of 3C-SiC polycrystal and 6H-SiC homoepitaxial layers from Metal-Si alloys is carried out as function of temperature and propane partial pressure. Based on the vapourliquid- solid mechanism, we present a new configuration for the growth of SiC which could allow first to simplify the liquid handling at high temperature and second to precisely control the crystal growth front. 3C-SiC crystals exhibiting well-faceted morphology are obtained at 1100-1200°C with outstanding deposition rates, varying from 1 to 1.5 mm/h in Ti-Si melt. At 1200-1300°C, thick homoepitaxial 6H-SiC layers were successfully obtained in Co-Si melts, with growth rates up to 200 ,m/h. Details on the experiments will be given and the potentialities of such process for the growth of bulk crystals will be discussed..

Abstract: Homoepitaxial growth of 4H-SiC p+/π/n- multi-epilayer on n+ substrate and in-situ doping of p+ and π-epilayer have been achieved in the LPCVD system with SiH4+C2H4+H2. The surface morphologies, homogeneities and doping concentrations of the n--single-epilayers and the p+/π/n- multi-epilayers were investigated by Nomarski, AFM, Raman and SIMS, respectively. AFM and Raman investigation showed that both single- and multi-epilayers have good surface morphologies and homogeneities, and the SIMS analyses indicated the boron concentration in p+ layer was at least 100 times higher than that in π layer. The UV photodetectors fabricated on 4H-SiC p+/π/n- multi-epilayers showed low dark current and high detectivity in the UV range.

Abstract: The authors attempted to grow a semi-insulating SiC epitaxial layer by in-situ vanadium doping. The homoepitaxial growth of the vanadium-doped 4H-SiC layer was performed by MOCVD using the organo-silicon precursor, bis-trimethylsilylmethane (BTMSM, [C7H20Si2]) and the metal-organic precursor, bis-cyclopentadienylvanadium (Verrocene, [C10H10V]). Vanadium doping effect on crystallinity of epilayer was very destructive. Vanadium-doped epilayers grown on normal condition had various surface or crystal defects such as micropipes, polytype inclusions. But this crystallinity degradation was overcome by high growth temperature. For the measurement of the resistivity of the highly resistive vanadium-doped 4H-SiC epilayers, the authors used the on-resistance technique. Based on the measurements of the on-resistance of the epilayers using the current-voltage technique, it is shown that the residual donor concentration of the epilayers was decreased with increasing partial pressure of verrocene. The resistivity of the vanadium-doped 4H-SiC epilayer was about 107 /cm.

Abstract: The lateral expansion of thin homoepitaxial cantilevers from mesas has been used to produce areas of on-axis 4H-SiC completely free of dislocations. Cantilever expansion is influenced by the geometric shape and crystallographic orientation of the pregrowth mesa. In order to form larger areas of defect free silicon carbide (SiC), progressive coalescence must occur when adjoining cantilevers merge. The progressive coalescence is largely dictated by the shape and orientation of the pregrowth mesa. We report on refinements to the pregrowth mesa geometry and orientation that allows rapid initiation of cantilever growth and promotes progressive coalescence of merging cantilevers. These modifications to the pregrowth mesa geometry permit larger areas of defect free 4H-SiC to be realized.

Abstract: A quadrupole mass spectrometer unit was utilized to accurately detect the chemical species present inside a SiC CVD reactor growth chamber before, during, and after epitaxial deposition. The in-situ mass spectrometer has been able to confirm the presence of silane (SiH4) and propane (C3H8) decomposition products (eg. Si and CH4) that were predicted from chemical modelling, and give insight into specific reaction kinetics. Additionally, the mass spectrometer has positively detected trace amounts of oxygen, which has helped to identify process weaknesses and possible sources of vacuum leaks.

Abstract: Real-time analysis of downstream nitrogen process-gas flows during 4H-SiC growth is reported. A Hiden Analytical HPR-20 quadrupole mass-spectrometer (QMS) was used to measure the process gas composition in the gas-stream of a hot-wall chemical vapor deposition (CVD) reactor. Using the 28 amu peak, it was found that the nitrogen partial pressure measured by the mass spectrometer directly correlates to the expected partial pressure of nitrogen in the process cell based on input flows. Two staircase doping samples were grown to track doping variations. The nitrogen mass flow was varied and corresponded to doping levels ranging from 1x1015 cm-3 to 8x1018 cm-3. Electron and nitrogen concentrations in the epilayers were measured by capacitancevoltage (CV) profiling and secondary ion mass spectrometry (SIMS), respectively. These efforts show real-time QMS monitoring is effective during growth for determining relative changes in nitrogen concentration in the gas flow, and thus, the level of nitrogen incorporation into the growing layer.

Abstract: Fast homoepitaxial growth of 4H-SiC has been carried out on off-axis (0001) substrates by horizontal hot-wall CVD at 1600οC. High growth rate up to 24 μm/h has been achieved with mirror-like surface in the C/Si ratio range of 1.0-2.0. The Z1/2 and EH6/7 concentrations can be kept as low as 7 × 1011 cm-3 and 3 × 1011 cm-3, although an unknown trap (UT1) is observed with the concentration in the 1011 cm-3 range. The photoluminescence spectra are dominated by strong free exciton peaks, and the L1 peak is not observed. The basal-plane dislocation (BPD) density has decreased with increase in growth rate, and it can be reduced to 22 cm-2 when epilayers are grown on Chemical Mechanically Polished (CMP) substrates at a growth rate of 24 μm/h.