Papers by Keyword: Bulk Crystal Growth

Abstract: A detailed knowledge of the growth front geometry during physical vapor transport (PVT) growth of SiC single crystals is beneficial to achieve high quality n+ SiC substrates for power device applications. In this report we show how mapping of resistivity in SiC wafers can shed light on local growth conditions, which are very difficult-to-study in situ. We consider both thermodynamic quantities (absolute temperature T and partial pressure p_N₂) and geometric characteristics of the growth surface relevant to growth kinetic parameters, namely atomic terrace width and atomic step velocity. Specifically, we show how an elevation map of the growth surface can be reconstructed from a spatially-resolved measurement of resistivity in a SiC wafer by integrating the spatial derivative of elevation with respect to the basal plane, which is assumed to be related to local resistivity through dependence of non-equilibrium nitrogen incorporation on the atomic step velocity.

Abstract: Photoluminescence (PL) signatures of 4H-SiC bare and epitaxial wafers from a surface inspection tool have been studied. Large variations in PL black or white dot densities were confirmed for comparable crystal quality and growth process conditions. Comparison with KOH etching results confirms that both PL black and white dots are tied to discrete threading dislocations. PL spectra results suggest dislocation decoration by donor-acceptor pairs.

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: Post-growth thermal processing at higher temperature generates more BPDs (basal plane dislocations). It is observed that dislocation visibility in surface inspection tool images varies significantly even at comparable dislocation densities. Combination of dislocation decoration and light absorbance from SiC matrix by point defects or dopants has been proposed as a working hypothesis to explain dislocation visibility variations.

Abstract: 200 mm diameter n-type 4H SiC wafers were produced from bulk crystals grown using a physical vapor transport (PVT) method. The configuration of the growth cell was modified to both allow for the growth of larger crystals with respect to the standard 150 mm process, and to induce a thermal environment necessary to increase the mass deposition rate. A 25% increase in deposition rate was achieved relative to the standard process. The resulting wafers exhibited resistivity uniformity comparable to commercial 150 mm product. Optical and x-ray techniques were used to evaluate wafer quality, and revealed surface and bulk crystal defect densities acceptable for epilayer growth.

Abstract: Continuous optimization of bulk 4H SiC PVT crystal growth processes has yielded an improvement in 150 mm wafer shape, as well as a marked reduction in stacking fault density. Mean wafer bow and warp decreased by 26% and 14%, respectively, while stacking faults were nearly eliminated from wafers produced using the refined process. These quality enhancements corresponded to an adjustment to key thermal parameters predicted to control intrinsic crystal stresses, and a reduction in crystal dome curvature.

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: p-type SiC crystals doped with aluminum and nitrogen were grown by the sublimation method. We found that Al and N co-doping is effective for stabilized growth of p-type 4H-SiC polytype. We studied the relationship of polytype of grown crystals and the condition of Al and N feeding during the crystal growth. p-type 4H-SiC with p~1 x 10¹⁸ cm^-3 are stably-obtained with this method.

Abstract: The nitrogen (N) and aluminum (Al) co-doped growth of n-type 4H-SiC bulk crystals were performed by sublimation method. In the co-doping growth, we achieved the lowest resistivity of 6.9mWcm, and we also confirmed phenomenon of stacking faults suppression in spite of high N concentration more than 8 x 10¹⁹cm^-3.

Abstract: We have developed RAF (Repeated a-face) growth method which is high quality bulk crystal growth technology [1, 2]. A block crystal more than 150 mm square size was produced by the RAF growth method. Since c-face growth crystal was produced on the seed obtained from the block crystal, high quality 150mm 4H-SiC wafer was achieved. This paper reports the results of the quality evaluation.