Kazukuni Hara

Current-Voltage and Capacitance-Voltage Characteristics of Metal/Oxide/6H-Silicon Carbide Structure

Current-voltage ( I-V ) and capacitance-voltage ( C-V ) characteristics of metal/ SiO2/6H-SiC structure fabricated on the concave surface in (000)C-face 6H-SiC p/n double epitaxial wafers were studied. Breakdown field of thermally grown gate oxide and effective charge density at SiO2/6H-SiC interface on sloped surface of the metal/oxide/semiconductor (MOS) structure were measured for the first time to be 9.2 MV/cm and 2.2-2.5×1012 cm-2, respectively, for both p- and n-epilayers. Fabricated SiC CONCAVE-MOS field-effect-transistor (FET) including the concave MOS structure achieved FET operation with blocking voltage of 250 V. Temperature dependence of the threshold voltage was -27 mV/K, which is considerably larger than the ideal value of -1.6 mV/K, due to high interface state density.

Development of a 150 mm 4H-SiC epitaxial reactor with high-speed wafer rotation

A new type of 150 mm vertical 4H-SiC epitaxial reactor with high-speed wafer rotation has been developed. Multiple resistance heaters ensure uniform radial temperature distribution throughout a 150-mm-diameter wafer. Enhancement of the growth rates is realized by high-speed wafer rotation under a relatively high system pressure, and growth rates of 40?50 ?m/h are achieved on 4? off 4H-SiC substrates, maintaining a low defect density and a smooth surface without macrostep bunching. Excellent thickness and doping uniformities are simultaneously obtained for a 150-mm-diameter wafer at a high growth rate of 50 ?m/h.

Mechanism of nitrogen incorporation in sublimation growth of SiC

Abstract 6H-SiC crystals have been grown on the Si-face and the C-face of 6H-SiC seed crystals by sublimation growth, respectively, and their deep photoluminescence (PL) have been investigated in detail. The deep PL spectrum of undoped 6H-SiC crystal grown on the C-face consisted of multiple broad emissions. On the other hand, undoped 6H-SiC crystal grown on the Si-face showed a single weak emission peak. In the case of the nitrogen-doped 6H-SiC crystals grown on the C-face, the emissions decreased with increasing nitrogen doping concentration and that of the nitrogen-doped 4H-SiC crystals grown on the C-face also showed the same behavior. As a C-vacancy is easy to form during the sublimation growth on the C-face, we think that nitrogen occupies the C-vacancy during the doping growth and leads to a decrease in the C-vacancy concentration as reflected by the PL analysis. We speculated that the difference in the doping concentration of nitrogen in the C-face and the Si-face-grown SiC crystal is related to the presence of the C-vacancy during crystal growth.

4H-SiC Bulk Growth Using High-Temperature Gas Source Method

Our latest results of SiC bulk growth by High-Temperature Gas Source Method　are given in this paper. Based on Mullins-Sekerka instability, optimal growth conditions to preclude dendrite crystals, which are one of the pending issues for high-speed bulk growth, was studied. First, the simulation studies showed that high temperature gradient in a growing crystal is required for high-speed bulk growth without dendrite crystals. Second, high-speed bulk growth was demonstrated under high temperature gradient.

Analysis and Reduction of Stacking Faults in Fast Epitaxial Growth

We have developed a single-wafer vertical epitaxial reactor which realizes high-throughput production of 4H-SiC epitaxial layer (epilayer) with a high growth rate [1,2]. In this paper, in order to evaluate the crystalline defects which can affect the characteristics of devices, we investigated the formation of variety of in-grown stacking faults (SFs) in detail. Synchrotron X-ray topography, photoluminescence (PL) and transmission electron microscopy are employed to analyze the SFs and the origins of the SF formation are discussed. The result in reducing in-grown SFs in fast epitaxial growth is also shown.

150mm Silicon carbide selective embedded epitaxial growth technology by CVD

In this work, we have developed a selective embedded epitaxial growth process on 150-mm-diameter wafer by vertical type hot wall CVD reactor with the aim to realize the all-epitaxial 4H-SiC MOSFETs [1, 2, 3, 4, 5]. We found that at elevated temperature and adding HCl, the epitaxial growth rate at the bottom of trench is greatly enhanced compare to growth on the mesa top. And we obtain high growth rate 7.6μm/h at trench bottom on 150mm-diameter-wafer uniformly with high speed rotation (1000rpm).

3D Raman Spectroscopy Investigation of Defects in 4H-SiC Epilayer

In this report we were able to successfully identify and localize in 3D 3C and 6H foreign polytypes and stress in the embedded epilayer by high resolution 3D Raman spectroscopy, that were otherwise invisible under the microscope or SEM, in non-contact and non-destructive way. Stripe patterned deep trenches with aspect ratio about 2 (depth=3.0μm; width=1.5μm) were formed on 4H-SiC substrate by ICP. The epitaxial layer was embedded in these trenches by SiC CVD. Poly type defects and stress in the embedded epilayer were mapped by curve-fitting of spectra obtained from Raman measurement of the embedded SiC epilayer. The location of the foreign polytypes and the stress inside the stripe pattern allows speculating on the origin of the defects and correlating it to the manufacturing process.

Simulation Study of High-Speed Wafer Rotation Effects in a Vertical Reactor for 4H-SiC Epitaxial Growth on 150 mm Substrates

The effects of high-speed wafer rotation for 4H-SiC epitaxy in newly developed 150 mm vertical reactor is investigated by simulation analysis. The simulation model shows a good agreement with experimental results. It is revealed that a combination of high-speed wafer rotation as high as 1000 rpm and relatively high system pressure of 267 mbar is effective to reducing boundary layer thickness above the 4H-SiC wafer, and greatly enhances the epitaxial growth rates. The growth rate increase ~2 times using the combination of high-speed wafer rotation and relatively high system pressure.

Fast 4H-SiC Epitaxial Growth on 150 mm Diameter Area with High-Speed Wafer Rotation

A single wafer type 150 mm vertical 4H-SiC epitaxial reactor with high-speed wafer rotation was developed. The rotation of the wafer at high speed significantly enhances the growth rate, and high growth rates of 40–50 μm/h are possible on 4°off-cut 4H-SiC substrates. In addition, a low defect density and smooth surface without macro step bunching can be achieved. Excellent uniformity of thickness and doping concentration was obtained for a 150 mm wafer at a high growth rate of 50 μm/h.