Materials Science Forum Vols. 778-780

Abstract: The growth of 4H-SiC epilayers on 1.28^o off-cut substrates is reported in this study and comparison when using standard 4^o and 8^o off-cut substrates is added. Growth at high temperature is needed for the polytype stability, whereas low C/Si is requested to decrease both triangular defects density and roughness of the grown surface. An in-situ etching with Si rich ambient allows the growth of epilayers with specular surface. The formation of Si droplets can be observed on the grown surfaces when lowering the growth temperature and appears first for the high off-cut angle.

Abstract: The epitaxial growth of thick multi-layer 4H-SiC to fabricate very high-voltage C-face n-channel IGBTs is demonstrated using 3-inch diameter wafers. We employ an inverted-growth process, which enables the on-state voltage of resultant IGBTs to be reduced. Furthermore a long minority carrier lifetime (> 10 μs) and a low-resistance p⁺ epilayer can reduce the forward voltage drop of the IGBTs. The small forward voltage drop is demonstrated particularly at high temperatures by fabricating and characterizing simple pin diodes using the epi-wafer.

Abstract: Silicon carbide (SiC) power devices are expected to be useful in low-loss power conversion equipment in wide-ranging industrial areas. 4H-SiC Schottky barrier diodes (SBDs) and metal oxide semiconductor field-effect transistors (MOSFETs) have been launched on the commercial market, and many results obtaining outstanding performance of 4H-SiC switching devices have been reported [1-. Presently, SiC chip cost is a big problem preventing an increase in market penetration of such commercial devices. Therefore, 150 mm size wafers are urgently required reducing the cost per unit area for SiC epitaxial layers. Recently, some SiC wafer vendors announced that 150 mm SiC substrate would be released [4, and some groups have reported results of epitaxial growth on 150 mm SiC substrate [6-9].

Abstract: In this paper, we present a comparison of defects in 4H-SiC epilayers grown on 4^o off-axis (0001) and (000-1) substrates. It was confirmed using high sensitive surface observation and micro-Raman spectroscopy that the generation of epitaxial defects on (000-1) C-face substrates was less susceptible to substrate morphological defects such as pits than that on (0001) Si-face substrates and 'comet-like' defects on (000-1) C-faces were caused by the inclusion of 3C-SiC. Moreover, PL imaging observation showed that stacking fault densities decreased when increasing the growth temperature, and they increased when increasing the C/Si ratio, irrespective of the face polarity. The densities, however, were lower for C-faces at higher growth temperature and C/Si ratio. The present results indicated that C-faces were preferable to Si-faces to achieve smooth step-flow growth suppressing epitaxial defects and stacking faults, which were influenced by the substrate morphological defects and the fluctuation of C/Si ratio in the epitaxial growth.

Abstract: In this work, the generation of in-grown SFs, half-moon defects, and carrot defects in SiC epilayer is studied by using epitaxy-etch-epitaxy approach. It is found that under our growth conditions, most of these defects have a similar origin, and they nucleate at obstacles to step flow at the SiC substrate/epilayer interface. These obstacles may be micropipes, scratches, or foreign particles on the substrate surface.

Abstract: The defect evolution on 90 μm-thick heavily Al-doped 4H-SiC epilayers with Al doping level higher than 10²⁰ cm^-3 was studied by tracing back to initial growth stage to monitor major dislocations and their propagations in each growth stage. Results from X-ray topography and KOH etching demonstrate that all existing dislocations on the surface of 90 μm-thick epilayer can be identified as the defects originating from substrate. In other words, there seems no new dislocation generated after a long-term growth. Nevertheless, a high density of misfit dislocation was found appearing near the substrate/epilayer interface for epilayer with Al doping level of 3.5×10²⁰ cm^-3, while misfit dislocation cannot be seen on epilayer with Al doping level of 1.5×10²⁰ cm^-3.

Abstract: Silicon carbide (SiC) film on silicon (Si) was synthesized by chemical vapor deposition (CVD) with concurrent gas supply and alternative gas supply. The alternative gas supply method was very effective to improve the crystallinity of silicon carbide at the same experimental condition. The crystallinity was sensitive for source gas concentration and background pressure.

Abstract: The effect of process parameters such as growth temperature, C/Si ratio, etching time, and Si/H₂ ratio on dislocation density was investigated by performing KOH etching on 100 μm thick epitaxial layers grown on 4° off axis 4H-SiC substrates at various growth conditions by a chemical vapor deposition (CVD) process using a chloride-based chemistry to achieve growth rates exceeding 100 μm/h. We observe that the growth temperature and the growth rate have no significant influence on the dislocation density in the grown epitaxial layers. A low C/Si ratio increases the density of threading screw dislocations (TSD) markedly. The basal plane dislocation (BPD) density was reduced by using a proper in-situ etch prior to growth.

Abstract: Homo-epitaxial growth of 50 μm-thick 4H-SiC on 4° off-axis 100 mm substrates have been demostrated by using a commercial warm-wall multi-wafer planetary reactor (Aixtron 2800 G4). With optimized process, epitaxial layer with an average thickness of 48.146 μm and doping level of 8.39×10¹⁴/cm³ are obtained. The thickness uniformity with an edge exclusion of 5 mm are 1.30% (σ/mean) and 2.17% (max-min/max+min), and the doping level uniformity are 4.66% (σ/mean) and 6.95% (max-min/max+min), respectively. Surface roughness of the as-grown 50 μm-thick epitaxial layer has an RMS value of 0.606 nm with one step bunching on the 20×20 μm² areas. This initial effort on thick 4H-SiC homoepitaxial growth indicates that this comercial multi-wafer planetary reactor has the potential for mass production of SiC epiwafers for 5000 V and above power devices.

Abstract: A new growth method for considerably suppressing generation of carrot and triangle defects is presented. Based on the investigation for the surfaces before and after the epitaxial growth, it becomes clear that those defects were results from micrometer-scale SiC particles. For removing the particles, pre-flow of H₂ at high temperature before the growth was very effective. The density of those defects strongly depends on the condition of the pre-flow and especially decreased at Tp=1575°C and tp=180 sec.