Materials Science Forum Vols. 717-720

Abstract: The LED technology started to developed many years ago with red light emitting diodes. To achieve the blue LED, novel growth technologies and process steps were explored, and made it possible to demonstrate efficient blue LED performance from nitrides. The efficiency was further developed and blue LEDs were commercially introduced in the 1990’s. The white LED became possible by the use of the blue LED and a phosphor that converts a part of the blue light to other colors in the visible range to combine into white light. However, even today there are limitations in the phosphor-based white LED technology, in particular for general lighting, and new solutions should be explored to speed the pace when white LEDs will be able to make substantial energy savings. In this paper we overview gallium nitride materials evolution and growth concepts for LEDs. We describe the fluorescent silicon carbide material prepared by a novel growth technology for a new type of white LED in general lighting with pure white light. This paper introduces an interesting research in fundamental growth and optical properties of light emitting silicon carbide.

Abstract: In this work we present the epitaxial growth of 4H-SiC on 100mm 4° off-axis substrates grown in a multi-wafer CVD planetary reactor. Highly uniform epitaxial layers having thickness and doping uniformities of 1.7% and 1.4% respectively were grown in the production reactor with optimized process conditions at 8µm/hr and 30µm/hr growth rates. Process optimizations resulted in epitaxial layers with surface roughness (RMS) of 0.32nm. Epitaxial layers with a thickness of 53µm grown with a 30µm/hr growth process had minimal degradation in surface roughness (RMS of 0.39nm).

Abstract: The chlorinated precursor is recently focused for high growth rate and high quality epitaxial layer. In the previous studies, the addition of chlorinated species from Si2Cl6 in the gas phase eliminated simultaneous Si nucleation which interferes with epitaxy. In this work, the characterization of epitaxial layers grown with chlorinated species is focused. High growth rate of 30 μm/h was achieved by using Si2(CH3)6 and Si2Cl6 as chlorinated precursors. We concluded that high growth rate was achieved by using HMDS and HCDS as the precursor of SiC at growth temperature of 1600 °C.

Abstract: 4H-SiC epitaxial growth on 2˚ off-axis substrates using trichlorosilane (TCS) is presented. Good surface morphology was obtained for epilayers with C/Si ratios of 0.6 and 0.8 at a growth temperature of 1600°C. The triangle defect density was reduced to a level below 5 cm^-2 at 1600°C and below 1 cm^-2 at 1625°C for a C/Si ratio of 0.8. Photoluminescence (PL) measurements were carried out with band-pass filters of 420 nm, 460 nm, and 480 nm to detect stacking faults. A stacking fault density of below 5 cm^-2 was achieved at 1600°C and 1625°C with a C/Si ratio of 0.8. The optimal conditions for TCS growth were a C/Si ratio of 0.8 and a growth temperature of 1600°C. The evaluation of stacking faults and etch pit density indicated that the use of 2˚ off-axis substrates and TCS is effective for reducing basal plane dislocations. Comparing these results to those using silane (SiH₄) with HCl added, it was demonstrated that TCS is much more suitable for obtaining high-quality epilayers on 2º off-axis substrates.

Abstract: A vertical 3×2〞low pressure chemical vapor deposition (LPCVD) system has been developed to realize fast epitaxial growth of 4H-SiC. The epitaxial growth process was optimized and it was found that the growth rate increases with increasing C/Si ratio and tends to saturate when C/Si ratio exceeded 1. Mirror-like thick 4H-SiC homoepitaxial layers are obtained at 1500 °C and C/Si ratio of 0.5 with a growth rate of 25 μm/h. The minimum RMS roughness is 0.20 nm and the FWHM of rocking curves of epilayers grown for 1 hour and 2 hours are 26.2 arcsec and 32.4 arcsec, respectively. These results indicate that high-quality thick 4H-SiC epilayers can be grown successfully on the off-orientation 4H-SiC substrates.

Abstract: Epitaxial growth of 4H-SiC on 8º off-axis substrates has been performed under different condition during the temperature ramp up in order to study the effect on the carrot defect. The study was done in a hot wall chemical vapor deposition reactor using the single molecule precursor methyltrichlorosilane (MTS). During the temperature ramp up, a small flow of HCl or C2H4 was added to the H2 ambient to study different surface etching conditions. The best result was obtained when HCl was added from 1175 to 1520 °C during the ramp up to growth temperature (1575 °C).

Abstract: A review of recently achieved results with the chloride-based CVD on 8° and 4° off axis and nominally on-axis 4H-SiC wafers is done to clarify the epitaxial growth mechanisms on different off-angle substrates. The process conditions selected for each off-axis angle become even more difficult when running at growth rates of 100 µm/h or more. A fine-tuning of process parameters mainly temperature, C/Si ratio and in situ surface preparation is necessary for each off-angle. Some trends related to the surface properties and the effective C/Si ratio existing on the surface prior to and during the epitaxial growth can be observed.

Abstract: SiC epitaxial films grown in an inverted chimney CVD reactor using silane-propane-hydrogen and dichlorosilane (DCS)-propane-hydrogen systems are compared for growth rates and doping concentrations at various growth pressures. Parasitic depositions in the gas injector tube using these precursor gases are also compared for precursor depletion. Virtual Reactor, a commercial software, is employed to predict growth rates and compare them to experimental results for the same growth conditions using DCS and silane gases.

Abstract: In-grown stacking faults (IGSFs) were studied in 4H-SiC homoepitaxial growth from a SiH₂Cl₂-C₃H₈-H₂ system. Most of the IGSFs, start from the epilayer/substrate interface, and exhibit photoluminescence emission peak at 2.58 eV (480 nm) indicating of 8H polytype. The growth parameters, including growth temperature, growth pressure, growth rate, hydrogen etching, et al., varied around the regular growth condition do not show a significant effect on the IGSF generation. Reactor furniture is identified to be a major reason of IGSF formation, especially when the insulation part of the furnace is not completely isolated from the growth zone. Dusting of insulation material is crucial in the formation of IGSFs. When using graphite felt as the insulation material, the IGSF density in the epilayer can be as high at ~10⁴ cm^-2. Improvement of the insulation material by using graphite foil reduces the density to 30-100 cm^-2. Further reduction of IGSF density to less than 10 cm^-2 is achieved by mild pretreatment of the substrate in molten KOH-NaOH eutectic.

Abstract: An optimized molten KOH-NaOH eutectic etching method is developed to reveal defects in highly n-doped SiC substrates and to pre-treat the substrate prior to epitaxial growth. Different from the conventional KOH etching method, by way of eutectic method, the basal plane dislocation (BPD) conversion in the subsequent epitaxial growth is independent of the etch pit size pre-generated on the substrate. Even with a short period (~3 minutes) of pretreatment which does not generate any visible etch pits or degradation of surface morphology on the substrate, an epilayer with low BPD density -2 is still achieved. This simple and non-destructive method shows high potential to be practically employed as one of the basic pretreatment steps to the substrates in SiC epitaxial growth in order to achieve very low or free BPD density.