Materials Science Forum Vols. 740-742

Abstract: A method was developed for growing SiC nanowires without depositing a metal catalyst on the targeted surfaces prior to the CVD growth. The proposed method utilizes in-situ vapor-phase catalyst delivery via sublimation of the catalyst from a metal source placed in the hot zone of the CVD reactor, followed by condensation of the catalyst-rich vapor on the bare substrate surface to form the catalyst nanoparticles. The vapor-phase catalyst delivery and the resulting nanowire density was found to be influenced by both the gas flow rate and the catalyst diffusion through the boundary layer above the catalyst source. The origin of undesirable bushes of nanowires and the role of the C/Si ratio were established.

Abstract: Numerical simulations are one way to obtain a better and more detailed understanding of the chemical vapor deposition process of silicon carbide. Although several attempts have been made in this area during the past ten years, there is still no general model valid for any range of process parameters and choice of precursors, that can be used to control the growth process, and to optimize growth equipment design. In this paper a first step towards such a model is taken. Here, mainly the hydrocarbon chemistry is studied by a detailed gas-phase reaction model, and comparison is made between C₃H₈ and CH₄ as carbon precursor. The results indicate that experimental differences, which previous models have been unable to predict, may be explained by the new model.

Abstract: Studies of threading dislocations with Burgers vector of c+a have been carried out using synchrotron white beam X-ray topography. The nucleation and propagation of pairs of opposite sign threading c+a dislocations is observed. Overgrowth of inclusions by growth steps leads to lattice closure failure and the stresses associated with this can be relaxed by the nucleation of opposite sign pairs of dislocations with Burgers vector c+a. Once these dislocations are nucleated they propagate along the c-axis growth direction, or can be deflected onto the basal plane by overgrowth of macrosteps. For the c+a dislocations, partial deflection can occasionally occur, e.g. the a-component deflects onto basal plane while the c-component continuously propagates along the growth direction. One factor controlling the details of these deflection processes is suggested to be related to the ratio between the height of the overgrowing macrostep and that of the surface spiral hillock associated with the threading growth dislocations with c-component of Burgers vector.

Abstract: Homoepitaxial layers with very good thickness and doping uniformity were grown on 4 inch 4˚ off-axis substrates in a 10x100mm planetary reactor. Process optimizations resulted in reduction of the size of the triangular defects. Aggressive pre-etching of the substrate prior to growth resulted in further suppression of the triangular defect concentration from 3-5cm^-2 to 0.5cm^-2 using the same growth processes. Even imperfect areas of the substrate with scratches show suppressed nucleation of triangular defects. JBS diodes with triangular defects show increased leakage depending on the size of the defects. This effect is more pronounced at higher voltages.

Abstract: Results of surface preparation on Si-face 4° off-cut 4H-SiC substrates are presented in this paper. The influences of two types of etchants, i.e. hydrogen chloride (HCl) and only hydrogen (H2), were investigated by Nomarski microscopy and AFM. The experiments were performed in a hot wall CVD reactor using a TaC coated susceptor. Four etching temperatures, including 1580 °C, 1600 °C, 1620 °C and 1640 °C, were studied. In-situ etching with only H2 as ambient atmosphere is found to be the optimal way for the SiC surface preparation. Using HCl at temperature higher than 1620 °C could degrade the substrates surface quality.

Abstract: we study the surface morphology of homoepitaxially grown 4H silicon carbide in terms of growth rate, miscut direction of the substrate and post growth argon thermal annealings. All the results indicate that the final surface morphology is the result of a competition between energetic reorganization and kinetic randomness. Because in all observed conditions energetic reorganization favors surface ondulations (“step bunching”), out-of-equilibrium conditions are one of the keys to favor the reduction of the surface roughness to values below ~0.5 nm. We theoretically support these results using kinetics superlattice Monte Carlo simulations (KslMC)

Abstract: The silicon carbide thin film formation process, completely performed at room temperature, was developed by argon plasma and a chemical vapor deposition using monomethylsilane gas. Silicon-carbon bonds were found to exist in the obtained film, the surface of which could remain specular after exposure to hydrogen chloride gas at 800 oC. The silicon dangling bonds formed at the silicon surface by the argon plasma are considered to react with the monomethylsilane molecules at room temperature to produce the amorphous silicon carbide film.

Abstract: We present our recent results on of 10 × 100 mm 4H-SiC epitaxy by a warm-wall planetary reactor at a growth rate of 10 μm/h. The epilayers grown by this high-throughput reactor show specular surfaces and good uniformities of thickness and doping. The intra-wafer and wafer-to-wafer thickness uniformities are 2.0% and 0.5%, respectively, while intra-wafer and wafer-to-wafer doping uniformities are 14.0% and 3.4%, respectively. The obtained surface RMS roughness is 0.2 nm. These results suggest that this 10 × 100 mm warm-wall planetary reactor provides very promising prospect on the mass production of 4H-SiC epilayers, which will further promote the development of SiC-based electronic devices.

Abstract: We have studied the defects on 4H-SiC substrates and epilayers by using molten KOH defect selective etching. It is found that adding Na₂O₂ into molten KOH at the etched temperature enables the revelation of dislocations on n⁺ and semi-insulating substrates, whereas purely molten KOH is sufficient to obtain good etched pattern on p⁺ substrates. Related statistical data on dislocation densities of n⁺, p⁺ and semi-insulating substrates are also presented. The morphological defects commonly observed on the epilayers are finally investigated and it is shown that some important structural features can be revealed by molten KOH method.

Abstract: Homoepitaxial 4H-SiC thin films were grown on (0 0 0 -1) C-face substrate by cold-wall chemical vapor deposition (CVD) using bis-trimethylsilylmethane (BTMSM, C7H20Si2) precursor. Because of the polarity difference of C-face and (0 0 0 1) Si-face, epitaxial growth conditions of C-face was quite different from those of Si-face. To improve the quality of C-face epitaxial films, effects of epitaxial growth conditions on surface morphology and crystallinity of epitaxial films were investigated.