Papers by Keyword: Epitaxial Layer

Abstract: A non-destructive technique to image the dislocations and other extended defects in SiC epitaxial layers has been developed. Basal plane dislocations (BPDs) and threading dislocations (TDs) are imaged. Photoluminescence from the dislocations is excited with the 364 and/or 351 nm lines of an argon ion laser and near-infrared light is collected. A computer controlled probe station takes multiple images and the mm-sized images are stitched together to form whole-wafer maps. The technique is applied to a set of four n+ wafers from the same boule with 50 um n- epitaxial layers. The epitaxy was grown with Cree’s low-BPD process. BPDs form as either single, isolated dislocations or as clusters encircling micropipes. The concentration of TDs is on the order 104/cm2 and the local concentration varies more than an order of magnitude. The advantages of mapping dislocations by UV-PL imaging compared to other techniques are discussed.

Abstract: The advantage of room-temperature photoluminescence (PL) mapping was demonstrated for nondestructive detection of stacking faults (SFs) in off-oriented 4H-SiC epitaxial and bulk wafers. In mapping of the SF-related emission at 2.9 eV on the wafers, the SFs in the surface region appeared as a bar-shaped pattern with the long side perpendicular to the off-cut direction. The use of 266 nm light excitation is essential to detect the SF pattern in the bulk wafers because of its shallow penetration depth. The dark lines crossing the bar-shaped patterns in the epitaxial wafers are ascribable to the basal plane dislocation located close to the SF-planes.

Abstract: This work presents results on the growth of thick epitaxial layers on 4° off-oriented 4HSiC in a commercially available hot-wall CVD system. Results on background doping level, homogeneity of thickness and doping, and run-to-run reproducibility will be shown. Defect structures we observed on 4° off-oriented substrates only are discussed. AFM measurements are presented to show the degree of step-bunching. 6.5 kV PiN-diodes with an active device area of 5.7 mm2 were fabricated and electrically characterized. In spite of the surface defects and stepbunching, up to 50% of the devices per wafer fulfilled our strict yield criteria even at 6.5 kV. Up to the onset of avalanche, the devices exhibited extremely low leakage currents. These results turn the cheaper 4° off-oriented substrates into a promising choice for producing higher volumes of highvoltage SiC power devices at reasonable costs.

Abstract: The rapid market development for SiC-devices during the last years can be attributed particularly to the success in supplying high-quality SiC wafers and corresponding epitaxial layers. The device quality could be enhanced and the costs were reduced by enlarging the wafer size as well as by a significant progress in epitaxial growth of active layers by using multi-wafer CVD systems. In this paper we want to give an overview of CVD multi-wafer systems used for SiC growth in the past and today. We present recent results of SiC homoepitaxial growth using our multi-wafer hot-wall CVD system. This equipment exhibits a capacity of 5×3” wafers per run and can be upgraded to a 7×3” or 5×4” setup. By optimizing the process conditions epitaxial layers with excellent crystal quality, purity and homogeneity of doping and thickness have been grown. Issues like reproducibility, drift of parameters and system stability over several runs will be discussed.

Abstract: Radiation hardness of silicon detectors based on thin epitaxial layer for the LHC upgrade was studied. No type inversion was observed after irradiation by 24 GeV protons in the fluence range (1.5–10)⋅1015 cm–2 due to overcompensating donor generation. After long-term annealing highly irradiated devices show decrease of effective doping concentration and then undergo type inversion. All mentioned means that thin epitaxial devices might be used for innermost layers of vertex detectors and need moderate cooling during beam off time. Properly chosen scenario might help to restore their working characteristics.

Abstract: In this paper we present recent results of epitaxial growth of 4H-SiC on 3” (0001) 8° and 4° off-oriented wafers using a multi-wafer hot-wall CVD system. This equipment exhibits a capacity of 5x3” or 7x2” wafers per run. By optimizing the process conditions epitaxial layers with excellent crystal quality, purity and homogeneity in doping and thickness were grown. The intra-wafer as well as the wafer-to-wafer homogeneity will be illustrated by doping and thickness mappings of a full-loaded run. Surface morphology of epitaxial layers on 8° and 4° off-oriented wafers was investigated by atomic force microscopy.

Abstract: We report an experimental investigation of the residual (n-type) and intentional (p-type) doping level of <11-20> epitaxial layers grown on a-cut 4H-SiC substrates. Using SIMS, C(V) measurements, low temperature photoluminescence and Hall effect investigations, we show that nitrogen incorporates 3 times more than usually found for <0001> surfaces. Conversely, aluminum incorporates 8 times less. Altogether, this is in excellent agreement with previous results from stepcontrolled epitaxy.