Materials Science Forum Vols. 527-529

Abstract: In this work, we have developed an innovative epitaxial growth process named the “Migration Enhanced Embedded Epitaxial” (ME3) growth process. It was found that at elevated growth temperatures, the epitaxial growth at the bottom of the trenches is greatly enhanced compared to growth on the sidewalls. This is attributed to the large surface diffusion length of reactant species mainly due to the higher growth temperature. In addition, it was found that this high temperature ME3 growth process is not influenced by the crystal-orientation. Similar growth behavior was observed for stripe-trench structures aligned either along the [11-20] or [1-100] directions. No difference was observed in the electrical performance of the pn diodes fabricated on either oriented stripe geometry. The ME3 process can also be used as an alternative to ion-implantation technology for selective doping process.

Abstract: Hot-wall chemical vapor deposition has been used to epitaxially grow SiC layers on porous n-type 4H-SiC substrates. The growth was carried out at different speeds on porous layers of two different thicknesses. The quality of the SiC films was evaluated by X-ray diffraction and photoluminescence techniques. Based on the measurements, both the growth speed and the thickness of the porous layer buried underneath the epilayers do not appear to influence the structural integrity of the films. The intensity of the near bandedge low temperature photoluminescence appears stronger by a factor of two in films grown on porous layers.

Abstract: We have previously reported on the selective growth of 4H-SiC epitaxial layers on a 4HSiC substrates in a chemical vapor deposition (CVD) reactor using TaC mask. It was shown that pn junctions fabricated using selectively grown n-layers on trench etched p-substrates have properties similar to the mesa etched pn junction diodes, indicating good interface properties. In this paper, we present more systematic studies on the selective growth and in-situ selective etching of 4H-SiC using a TaC mask. The morphological evolution during selective epitaxy as a function of crystallographic orientation was analyzed. Anisotropy in surface morphology along <11-20> and <1-100> has been observed. Cross sectional SEM viewgraphs show lateral overgrowth on the TaC mask, and the extent of lateral overgrowth varied with the stripe orientation. It was found that the “growth window” for selective growth was a function of the surface area covered by the TaC mask as well as the window opening to mask width ratios. Experiments with various window widths to mask width ratios have been carried out to investigate the selective growth process using this mask.

Abstract: We demonstrate high-speed and high-quality 6H-SiC homoepitaxial growth on a 1°-off c-plane SiC substrate by a closed-space sublimation method. By optimizing the size of single-crystal source materials in the growth system, a high-quality 6H-SiC epilayer with an X-ray diffraction rocking curve (0006) full-width at the half maximum (FWHM) of 38 arcsec was obtained. We also carried out doping of nitrogen and boron during the growth of the SiC epilayer. A strong donor-acceptor pair (DAP) emission at a peak wavelength of 570 nm under excitation by a 395 nm nitride-based light-emitting diode (LED) was observed. The 6H-SiC with DAP emission is promising for use as a phosphor in a nitride-based LED, because high-quality nitride layers can be grown on the SiC substrates with small off-oriented angles.

Abstract: A sublimation epitaxial method, referred to as the Closed Space Technique (CST) was adopted to produce thick SiC epitaxial layers for power device applications. We aimed to systematically investigate the dependence of SiC epilayer quality and growth rate during the sublimation growth using the CST method on various process parameters such as the growth temperature and working pressure. The etched surface of a SiC epitaxial layer grown with low growth rate (30 μm/h) exhibited a low etch pit density (EPD) of ~2000 /cm2 and a low micropipe density (MPD) of 2 /cm2. The etched surface of a SiC epitaxial layer grown with a high growth rate (above 100 μm/h) contained a high EPD of ~3500 /cm2 and a high MPD of ~500 /cm2, which indicates that high growth rate aids the formation of dislocations and micropipes in the epitaxial layer.

Abstract: The vapour-Liquid-Solid mechanism was used for growing epitaxial SiC layers on onaxis 6H-SiC and 4H-SiC substrates. By feeding Al70Si30 melts with propane, homoepitaxial growth was demonstrated down to 1100°C on both polytypes. At this temperature, the surface morphology is rough and non uniform with spiral growth forming large hillocks at the places where screw dislocations emerge from the substrate. Raman spectroscopy confirms the absence of the 3C-SiC polytype and shows the high Al doping of the layers. This growth temperature of 1100°C is the lowest one ever reported for growing homoepitaxial layers on low tilt angle SiC substrates. Increasing the temperature to 1200°C eliminates these hillocks but creates other morphological features due to fast substrate etching at this high temperature before growth starts.

Abstract: Al-Si and Ge-Si systems were studied for selective epitaxial growth (SEG) of 4H-SiC by the Vapour-Liquid-Solid mechanism. Al-Si and Ge-Si bilayers stackings were deposited on 8° off, Si face, 4H-SiC substrates. After patterning of the layers, the samples were heated up to 1000°C and 1220°C, respectively, for Al-Si and Ge-Si stackings in order to melt the layers. Propane was introduced either during the initial heating ramp, before melting of the alloy, or after reaching the temperature plateau. It was found that introduction of propane before melting was a key parameter in order to improve the homogeneity of the deposit. In both cases, SEG of SiC was achieved. However, the best results were obtained with Ge-Si system giving smooth and uniform ∼100 nm thick epitaxial deposits on all the pattern sizes and shapes. Ge incorporation in the SiC was found to be rather limited but homogeneous in the layer.

Abstract: Cross-sectional transmission electron microscopy (TEM) was used to investigate the extended defects in 3C-SiC films deposited on atomically flat 4H-SiC mesas. The nominal layer thickness was 10 μm and was considerably larger than the critical thickness determined by either the Matthews and Blakeslee or People and Bean models. Threading dislocation densities determined by KOH etching are far below densities typical of relaxed heteroepitaxial layers, down to as low as 104cm-2 densities found in 4H-SiC. Misfit dislocations with Burgers vectors of <11 2 0> were observed in planes parallel to the 3C/4H SiC interface. These defects were interpreted as due to nucleation of dislocation half loops at mesa edges and glide along the 3C/4H interface.

Abstract: We report on growth of 3C-SiC by sublimation process in vacuum with the aim to ultimately select conditions for single polytype growth of bulk crystals. The 3C polytype occurrence, growth mechanism and structure evolution have been in the focus of the study. To gain understanding of the initial formation of the cubic polytype, growth was performed on various substrates, such as 6H- and 4H-SiC (on-axis and vicinal), as well as freestanding 3C-SiC wafers. The growth configuration used allowed a high growth rate, e.g. up to 200 (m/h, respectively very thick layers. The grown material was studied by means of optical microscopy, AFM and HRTEM. 6H-SiC (0001) Si-face substrates may be a good choice if the 3C nucleation is well controlled, which can be achieved by selecting the initial temperature ramp up and substrate orientation. These growth conditions limit the number of nucleation centers and decrease the defective boundaries.

Abstract: Using the Vapor-Liquid-Solid mechanism in Ge-Si melts we have grown 3C-SiC layers on top of <0001>-oriented, Si face, 6H-SiC substrates. The surface morphology was free of spiral growth but highly step bunched. The 3C-SiC polytype was identified by micro- Raman spectroscopy and confirmed by low temperature photoluminescence. Electron backscattering diffraction mapping showed that the upper side of the layers is single-domain, i.e. that the 3C-SiC material displays only one in-plane orientation. Cross-sectional and planeview TEM investigations allowed detection of double positioning boundaries but only confined at the substrate/epilayer interface. The main additional defects found were stacking faults (SF) with a density of ~ 4.103 cm-1. Forming at the interface, they propagate through the epitaxial layer.