Materials Science Forum Vol. 924

Abstract: In this study, influence of both Si/H₂ ratio and C/Si ratio on growth rate uniformity and carrier concentration uniformity of n-type 4H-SiC epitaxial films grown by high speed wafer rotation vertical CVD tool was investigated. It was found that changes in radial profile of the growth rate and the carrier concentration obtained by varying Si/H₂ ratio showed quite similar behavior to those obtained by varying C/Si ratio. Such a similar trend would suggest that the distribution of local C/Si ratio near the wafer surface changes depending on total Si/H₂ ratio similarly to total C/Si ratio. Additionally, by using this relationship, both the growth rate uniformity of 49.2 μm/h ±1.78% (1.15% σ/mean) and carrier concentration uniformity of 1.08 ×10¹⁶cm^-3 ±6.15% (3.40% σ/mean) was achieved.

Abstract: We report on the results of a Design of Experiments (DOE) matrix of growth runs used to tune and improve the uniformity of thickness and doping across both 100 mm and 150 mm SiC epiwafers in our epitaxy reactor. Improvement of uniformity beyond the initial process recipe from the tool vendor is shown. Temperature measurement along an entire wafer platter indicate that there is a gas cold region extending into the growth zone that maybe the root cause of the non-uniformity.

Abstract: In order to develop a quick and practical cleaning process for the silicon carbide chemical vapor deposition reactor, the pyrolytic carbon-coated susceptor was used. The 30-μm-thick silicon carbide film was formed on the susceptor; the film was cleaning by chlorine trifluoride gas at 460 °C for 15 min. The remained fluorine was removed by the annealing at 900 °C in ambient hydrogen. The pyrolytic carbon surface did not suffer from any damage, because the pyrolytic carbon film surface morphology after the cleaning process was the same as that before the silicon carbide film deposition.

Abstract: Understanding the chemistry in CVD of SiC is important to be able to control, improve and scale up the process to become industrially competitive. A thorough understanding have so far been difficult to achieve due to the complex nature of the process. Through modeling tools, and a systematic approach when constructing the chemical models, new insights to the SiC CVD chemistry can be obtained. Using a general model that is independent on the choice of precursors and reactor configuration, and by coupling modeling results to experimental findings, we here show that SiCl₂ and SiH₂ previously suggested as the main silicon bearing growth species in the chlorinated and standard chemistries, respectively, does not contribute significantly to the SiC growth, and that the main active species are C₂H₂, CH₃, Si, and SiCl.

Abstract: High quality SiC Epilayers are essential for the development of high performance power devices. Killer defects such as triangular defects could cause leakage current paths within the high voltage SiC devices. This paper reports on the recent advances in 4H-SiC epitaxial growth toward high-throughput production in a commercial planetary reactor. The triangular defects are suppressed by the optimized pre-etching process, and the physics behind was investigated. The doping and thickness uniformities of the intra-wafer and wafer-to-wafer have also been improved.

Abstract: 4H-SiC homo-epitaxial films were grown using a high speed wafer rotation vertical CVD tool, and effects of wafer rotation speed during initial temperature ramping before epitaxial growth were investigated. Also, the effects of conditions during growth of the highly doped buffer layer on both surface and PL defect densities were investigated. It was found that the wafer rotation speed during the temperature ramping has a large influence on the surface defect density of the films. Especially, triangles generated from small pits were considerably reduced in the samples grown at a higher wafer rotation speed during the temperature ramping. The phenomena could be explained as a result of suppressed interfacial reaction between down-falls (DFs) and the wafer surface. Additionally, it was found that the density of basal plane dislocations (BPDs) on a drift layer is remarkably reduced by adjusting the C/Si ratio during growth of the buffer layer grown prior to the drift layer. By applying higher wafer rotation speed during the temperature ramping and optimizing the C/Si ratio for the growth of the buffer layer, a total defect density of 0.75 cm^-2 on the film, which includes DFs, triangles, DF-triangles, stacking faults (SFs) and BPDs, was achieved.

Abstract: The development of bipolar 4H-SiC devices for high blocking voltages requires the growth of high carrier lifetime epitaxial layers with low Z_1/2 concentrations. This paper shows a comprehensive investigation of the influence of epitaxial growth parameters (C/Si ratio and growth temperature) on Z_1/2 concentration and minority carrier lifetime. On the basis of a discovered exponential correlation of Z_1/2 with the C/Si ratio and growth temperature, a competitive low Z_1/2 concentration of 1.9∙10¹² cm^-3 could be achieved by lowering the growth temperature and switching to higher C/Si ratio. Thermodynamic considerations by an Arrhenius approach reveal a dependency of the formation enthalpy of Z_1/2 on the thermal process and process conditions of the epitaxial growth. Furthermore, the correlation between Z_1/2 and the effective minority carrier lifetime confirms the occurrence of a necessary second recombination mechanism beside the common recombination at deep levels by Shockley-Read-Hall for low Z_1/2 concentration.

Abstract: By mapping the source and HCl flow rates dependent growth rates, the evolving trend of a quasi-selective epitaxial growth (quasi-SEG) that growing very thin epilayer on mesa top and ensuring an extremely low risk of voids defect generation was firstly figured out on a 5-μm 4H-SiC trench. Then, basing on the acquired knowledge, a 25-μm 4H-SiC trench with an aspect ratio up to ~10 was completely filled in the quasi-SEG mode.

Abstract: Hot filament CVD (HFCVD) growth of undoped 4H-SiC epitaxial layers on 100 mm n-type 4^o-off 4H-SiC substrates is presented as an alternate growth method for the first time. High quality crystalline material with a low density of polytype inclusions has been demonstrated and characterized with optical micrographs, SEM imaging, micro-Raman measurements, and high resolution XRD. Typical growth rates are ~3 μm/hour. Double rocking omega scans revealed diffraction peaks with a FWHM of 23 arcsec.

Abstract: Stacking Faults (SFs) are the main defect of 3C-SiC material and in this work a detailed study of this typology of defect is presented. We studied the behavior of SFs with High Resolution XRD and STEM analysis. The homo-epitaxial growth was proposed as a solution for the reduction of SFs density in 3C-SiC material and the influence of the growth condition on the SFs density was studied. The knowledge of the mechanism of SFs reduction is crucial for the development of a high quality material for devices fabrication.