3 March 2022
Gallium oxide film grown on 6-inch wafers by HVPE
A joint effort between Tokyo-based Taiyo Nippon Sanso Corp (TNSC), Tokyo University of Agriculture and Technology, Novel Crystal Technology Inc of Sayama, Saitama Prefecture, Japan has succeeded in growing gallium oxide film on a 6-inch wafer by halide vapor-phase epitaxy (HVPE).
Gallium oxide (β-Ga2O3) has an even wider bandgap than silicon carbide (SiC) and gallium nitride (GaN), so transistors and diodes made with β-Ga2O3 have excellent performance characteristics as power devices, namely high voltage resistance and high efficiency (low loss). In mid-2021, Novel Crystal Technology Inc developed a 4-inch β-Ga2O3 epitaxial wafer grown by HVPE, which it now manufactures and sells. The β-Ga2O3 substrate that forms the base of the epilayer growth differs from SiC and GaN in that it can be manufactured using the melt growth method, which enables rapid formation of bulk crystals. Therefore, β-Ga2O3 wafers can easily be obtained in large diameter and at low cost, which is useful for reducing the price of power devices.
However, while the HVPE system used in β-Ga2O3 film growth has the benefits of low material cost and high-purity film, the HVPE system has only been built for small-diameter (2- or 4-inch) wafers and for single-wafer manufacturing. So, to reduce the cost of growth, it was essential to build a batch-type mass-production system capable of producing large-diameter (6- or 8-inch) wafers by HVPE.
Taiyo Nippon Sanso began developing a mass-production β-Ga2O3 epi growth system for large-diameter wafers under the Strategic Innovation Program for Energy Conservation Technologies (‘Research and Development of Mass Production Epi Growth System Corresponding to Large Diameter Wafers for Next Generation Power Devices of Gallium Oxide’) of Japan’s New Energy and Industrial Technology Development Organization (NEDO). The program’s incubation research phase (fiscal 2019), saw the development of external supply technology for metal chloride (raw material for HVPE). The practical application development phase (fiscal 2020-2021) saw the development of a 6-inch single-wafer HVPE system and growth processes to establish the basic technology for a mass-production system, followed by its evaluation. Now that the growth of a β-Ga2O3 film on a 6-inch wafer has been achieved, it is expected that, if β-Ga2O3 power devices become widely adopted, power saving should be possible for industrial motor control inverters, residential solar power generation system inverters, and next-generation electric vehicles, as well as other applications.
Nippon Sanso developed the 6-inch single-wafer HVPE system, and achieved growth of a β-Ga2O3 film on a 6 inch test wafer using a sapphire substrate.
Moreover, the optimization of growth conditions and the adoption of a proprietary raw material nozzle construction enabled verification of β-Ga2O3 growth on the 6 inch test wafer as well as uniform film growth, and the achievement of a β-Ga2O3 film thickness distribution of less than ±10%. This result established the technology for growing films on large-diameter substrates along with hardware design technology, enabling the creation of a platform for a β-Ga2O3 growth system. This in turn paved the way for a significant advance in the development of a large-diameter batch-type mass-production system.
Nippon Sanso says that it will continue to develop mass-production systems for β-Ga2O3 growth under the NEDO project and, going forward, will develop high-quality β-Ga2O3 epi growth technology using 6-inch β-Ga2O3 wafers by evaluating the electrical characteristics and defects for β-Ga2O3 thin films. Moreover, after establishing β-Ga2O3 epiwafer mass-production technology, it aims to commercialize a mass-production system in fiscal 2024.β-Ga2O3 epiwafers manufactured using the HVPE system are expected to be used mainly for Schottky barrier diodes (SBDs) and field-effect transistors (FETs), for which the market is expected to grow to about ¥59bn (according to the report ‘2020 Current Status and Future Prospect of Next Generation Power Devices & Power Electronics Related Equipment Market’ from Fuji Keizai Co Ltd) by fiscal 2030. Looking ahead, we will contribute to the effort to save energy in next-generation electric vehicles etc., by realizing mass-production system, entering the β-Ga2O3 growth system market, and promoting the spread of Ga2O3 power devices.