Papers by Keyword: XRT

Abstract: Commercially available 4H-SiC substrate quality has improved over time, and this has extensively reduced defect concentration in the active epitaxial layer, during epi growth conditions at the interface. The objective of this work is to investigate bulk crystal quality for the purpose of future vertical power device fabrication in exfoliated, non-epitaxial, undoped material layers. Mathematical estimations on the device yield fraction, that is immune to bipolar degradation for the suggested future process were calculated based on XRT measurements to detect BPD and TSD densities on donor substrates. The full wafer BPD density maps of on-axis semi-insulating wafer substrates from two vendors were compared.

Abstract: X-ray topography (XRT) presents itself as an attractive non-destructive method to replace industry-standard destructive KOH etching used to measure dislocation density. However, a production-line-compatible XRT has to employ a low scan speed in order to work well with automated image analysis, which makes it impractical for a high-volume manufacturing to scan an entire wafer. We introduce the “radial band” approach to sampling the entire wafer’s area with a single-pass 16 mm tall scan band. Such a band spans the entire range of radii and thus captures the typically strong radial dependence of dislocation density over the entire range, while mostly ignoring the typically weak angular dependence of dislocation density and averaging the inevitable noise over the 16 mm band height. The XRT scan time savings for this approach are roughly 15-fold and 20-fold for 150mm and 200mm wafers respectively.

Abstract: Thick (> 25 µm) 4H n+ epitaxial layer growth was performed on 4H n+ substrates utilizing chlorine containing etch chemistries in a hot wall CVD system. Optimization of the n+ epitaxial layer growth was achieved by varying C/Si ratio and N2 flow. Desired epitaxial layers have doping levels > 5x1018 cm-3, epitaxial surface roughness <10 nm on a 20x20 µm area and overall micropipe density reduction. To confirm the conversion of micropipes into closed core screw dislocations, microscopic examination of the epitaxial and wafer surfaces was carried out after KOH etching. Grazing incidence x-ray topography (XRT) as well as cross sectional XRT and microscopy were also performed. The cross sectional evaluation showed that the dissociation of the micropipes occurs very close to the epitaxy/wafer interface.