Papers by Keyword: Homoepitaxy

Abstract: The effect of increasing Buffer Layer (BL) thickness on crystal defectivity has been investigated in 4° off-axis 4H-SiC homoepitaxy on 200mm substrates coming from different suppliers. The results, based on optical microscopy and scatter light methods, show a slight increase in morphological defects in the case of a thicker BL with respect to the standard thickness for both suppliers.

Abstract: During 4H silicon carbide (4H-SiC) homoepitaxy and post-growth processes, the development of stress relaxation has been observed, in which interfacial dislocations (IDs) are formed at the epilayer/substrate interface, relaxing the misfit strain induced by the nitrogen doping concentration difference between the epilayer and substrate. It is widely believed that an interfacial dislocation is created by the glide of a mobile segment of a basal plane dislocation (BPD) in the substrate or epilayer towards the interface, leaving a trailing edge component right at the interface. However, direct observation of such mechanisms has not been made in SiC before. In this work, we present an in situ study of the stress relaxation process, in which a specimen cut from a commercial 4H-SiC homoepitaxial wafer undergoes the stress relaxation process during a high-temperature heat treatment while sequential synchrotron white beam X-ray topographs were recorded simultaneously. Based on the dynamic observation of this process, it can be concluded that thermal stress plays a role in the relaxation process while the increased misfit strain at elevated temperature most likely drives the formation of an interfacial dislocation.

Abstract: Efforts to develop 150 mm 4H SiC bare wafer and epitaxial substrates for power electronic device applications have resulted in quality improvements, such that key metrics match or outperform 100 mm substrates. Total dislocation densities and threading screw dislocation densities measured for 150 mm wafers were ~4100 cm^-2 and ~100 cm^-2, respectively, compared with values of ~5900 cm^-2 and ~300 cm^-2 measured for 100 mm wafers. While median basal plane dislocation counts in 150 mm samples exceed those of the smaller platform, a nearly 45% reduction was realized, resulting in a median density of ~3900 cm^-2. Epilayers grown on 150 mm substrates likewise exhibit quality metrics that are comparable to 100 mm samples, with median thickness and doping sigma/mean values of 1.1% and 4.4%, respectively.

Abstract: Doping incorporation and good uniformity along the wafer it is a mandatory for application in high voltage electronic devices. In this work the effect of the Hydrogen (H) flux position inside the reaction chamber on homo-epitaxial 4H-SiC growth process has been studied. Capacitance-Voltage and FT-IR analyses show as the different position of the gas injector affect the doping and thickness uniformity and profile. On the other hand, By Candela and AFM analyses no morphological or surface influence by Hydrogen flux position has been observed.

Abstract: In this paper, we will describe a detailed experimental study on the behavior of Ge incorporation into 4H-SiC during its homoepitaxial growth by CVD. Addition of GeH₄ precursor to the standard chemical system SiH₄ + C₃H₈ was investigated as a function of various growth parameters. Its effect on surface morphology, layer quality and purity was followed. All these results will allow proposing an exhaustive picture of Ge incorporation mechanism into 4H-SiC with the possible benefits of such impurity incorporation in the silicon carbide lattice.

Abstract: Step-bunching and triangular defects are significant problems in achieving higher growth rate 4H-SiC epilayers in a horizontal hot wall CVD reactor using a standard non-chlorinated chemistry of silane-propane-hydrogen on 4°off-axis substrates. In this work, the impact of growth pressure on generation of step-bunching and triangular defects and the correlations between the surface roughness and the formation of defects were investigated. It has been found that the impact of growth pressure on concentration of the triangle defects and surface roughness is obviously different. An overall reduction of defects was observed with decreasing growth pressure while the surface roughness increased. The increased adatom surface mobility in low pressure range and minimization of surface free energy are the main reasons for the phenomenon above. High Resolution X-Ray Diffraction (HRXRD) indicated that the structural quality of 4H-SiC epilayers performed at low pressure was higher than that obtained at high pressure.

Abstract: We report the demonstration of a GaN-based planar metal-semiconductor-metal (MSM) ultraviolet photodetector (PD). The MSM PD with semitransparent interdigitated Schottky electrodes is fabricated on low-defect-density GaN homoepitaxial layer grown on bulk GaN substrate by metal-organic chemical vapor deposition. The dislocation density of the GaN homo-epilayer characterized by cathodoluminescence mapping technique is ~5×10⁶ cm⁻². The PD exhibits a low dark current density of ~4.1×10⁻¹⁰ A/cm² and a high UV-to-visible rejection ratio up to 5 orders of magnitude at room temperature under 10 V bias. Even at a high temperature of 425 K, the dark current of the PD at 10 V is still <1×10⁻⁹ A/cm² with a reasonable UV-to-visible rejection ratio more than 3×10⁴, indicating that such kind of PDs are suitable for high temperature operation.

Abstract: We have investigated key factors for controlling the polytype and surface morphology of 4H-SiC homoepitaxial growth on less than 4^o off-axis substrates. In addition, we characterized the crystal quality and surface quality of the epitaxial layer of an entire 3-inch vicinal off angled substrate. The results suggested that the control of surface free energy, control of the vicinal off angle itself, and high temperature growth, is highly important in controlling the surface morphology and polytype stability of the epitaxial layer grown on a vicinal off angled substrate. We also obtained a high-quality epitaxial layer grown on a 3-inch vicinal off angle substrate, which was comparable to those on 4^o off-axis substrates.

Abstract: This paper presents the results obtained after chemical vapor deposition of SiC with the addition of GeH₄ gas to the classical SiH₄+C₃H₈ precursor system. Epitaxial growth was performed either on 8°off-axis or on-axis 4H-SiC substrate in the temperature range 1500-1600°C. In the off-axis case, the layer quality (surface morphology and defect density) does not change though accompanied with Ge droplets accumulation at the surface. The Ge incorporation level was found to increase with temperature in the 10¹⁷ 10¹⁸ cm^-3 ranges. It was observed that adding GeH₄ leads to the increase of the n type doping level by a factor from 2 to 5 depending on the C/Si ratio. In the on-axis case, GeH₄ was only added to the gas phase before starting the SiC growth. It was found that there is a conditions window (temperature and GeH₄ flux) for which 3C-SiC twin free layers can be grown. Adding this foreign element before SiC growth clearly modifies SiC nucleation on on-axis substrate.

Abstract: In this paper we present a concept on the defect generation and annihilation during the homoepitaxial growth step of cubic silicon carbide by sublimation epitaxy on templates grown by chemical vapor deposition on silicon substrates. Several structural defects like stacking faults, twins and star defects show opposite evolution from the template layer into the sublimation grown material. While single planar defects tend to annihilate with increasing layer thickness, the defect clusters assigned to the star defects are enlarging. These issues contribute to a balance of how to achieve the best possible quality on thick layers.