The 83rd JSAP Autumn Meeting 2022 Highlighted Presentations
October 24, 2022

Crystallinity improvement of 100-mm-diameter β-Ga2O3 epi-wafer

Success in further improving the quality of 100-mm-diameter βtype gallium oxide epi-wafers
This is expected to contribute significantly to the energy
conservation of power semiconductors for electric vehicles, etc.
Novel Crystal Technology, Inc.
Chia-Hung Lin, Kentaro Ema, Satoshi Masuya, Quang Tu Thieu, Ryoichi Sakaguchi, Kohei Sasaki, Akito Kuramata

Summary• On March 14, 2022, Novel Crystal Technology, Inc. announced that it successfully
improved the quality (reduction of killer defects) of 100-mm-diameter gallium oxide(Ga2O3) epi-wafers, which are expected to be the next generation of power
semiconductors, thereby facilitating the widespread deployment of Ga2O3 power
semiconductors for the requirement of 100 A-class power semiconductor markets. (Figure1).
• Ga2O3 power semiconductors can sustain an higher voltage and current compared withconventional silicon semiconductor, recently industrialized silicon carbide semiconductor
and gallium nitride semiconductor, and therefore are expected to be used for large-power
semiconductors required for electric vehicles and other applications.
• Ga2O3 semiconductors, an originated producing technology from Japan, are expected toenter the global market of power semiconductors in the next few years owing to apossibility of mass production with low cost and more energy conservation than otherconventional semiconductors.

Novel Crystal Technology, Inc. has been working on the commercial development of β-Ga2O3 Schottky
barrier diodes under the NEDO Strategic Energy Conservation Technology Innovation Program andcollaborated with the Saga University to develop a third-generation 100-mm-diameter Ga2O3 epi-wafer (*1).
In this development, the epi-wafer manufacturing technology has been improved, and defects (killerdefects*2) that inhibit the development of high-current Ga2O3 power semiconductors and degrade thebreakdown voltage characteristics, have been successfully reduced to one-tenth of the conventional level.
This achievement will facilitate the widespread deployment of Ga2O3 power semiconductors for therequirement of 100 A-class power semiconductors in markets for such as trains, industrial equipment, andelectric vehicles, etc. Ga2O3 semiconductors are expected to contribute to global energy conservation andcarbon neutrality in the future because of lower power losses compared with conventional semiconductors.
DetailReduction of "Killer Defects" Enables to obtain 100 A-class Large-power Devices
β-gallium oxide (β-Ga2O3) has paid attention as a new material that can realize low powerconsumption power semiconductors with a low cost. Power semiconductors are used in all types ofelectrical equipment, including home appliances, automobiles, trains, and industrial equipment, tocontrol voltage and current. Conventional power semiconductors have been fabricated usingsilicon (Si); however, power loss is generated during power control. Power semiconductors, suchsilicon carbide (SiC) and gallium nitride (GaN) have, therefore been developed to solve this issue,
however the use of Ga2O3 can further reduce the power loss and power consumption of electricalequipment.
Novel Crystal Technology, Inc. has already succeeded in developing epitaxial equipment with aproducing capability of Ga2O3 semiconductor epi-wafers up to 100 mm in diameter, which havebeen manufactured and commercially available. However, the epi-wafer produced using thisequipment has approximately 10 defects per cm2 (referred to as killer defects), which degrades thebreakdown voltage characteristics of devices, thereby rendering difficulty in producing large
devices and limiting the current flow to approximately 10 A.
To solve this problem, the company collaborated with the Saga University and discovered thatkiller defects were caused by a specific powder generated during the epitaxial growth. Therefore,
by improving the growth conditions, the company was able to obtain a third-generation 100-mmdiameter Ga2O3 epi-wafer with killer defects reduced to 0.7 defects/cm2, which is less than onetenth of the conventional level.
Figure 2 shows the electrical properties of Si, 4H-SiC, GaN, diamond, and β-Ga2O3semiconductors. Ga2O3 exhibits a Baliga’s Figure-of-Merits (BMOF) of 3,444, only second to thediamond semiconductor (referred to as "ideal semiconductor”). A large BMOF indicates that thehigh performance of power semiconductors, directly related to a "high breakdown voltage" and"low power loss", can be achieved.
Realization of low cost, high speed manufacturing, and energy conservation
Another huge advantage of Ga2O3 semiconductors is that bulk crystals can be made using aconsiderably faster manufacturing method than SiC and GaN semiconductors, which leads a
expective mass production resulting in a significant cost reduction (Figure 3). SiC and GaN bulk
crystals can be produced by evaporating raw materials (vapor phase growth method). However,this method has a slow growth rate of several hundred micrometers per hour and suffers a hugecost issue. In contrast, Ga2O3 semiconductor bulk crystals can be produced liquid raw materials(melt growth method); thus an overwhelmingly fast growth rate of several tens of millimeters perhour is possible for manufacturing semiconductor crystals. Furthermore, SiC and GaN
semiconductors are hard materials that causes difficult for processing, whereas Ga2O3 iscomparably soft and can be easily processing.
Novel Crystal Technology, Inc. has built a production line for commercializing the newdevelopment of third-generation 100-mm-diameter Ga2O3 epi-wafers and plans to begin

sales as soon as possible. Novel Crystal Technology, as a Japanese company, is currently theleading manufacturer of Ga2O3 epi-wafers in Japan and other countries, and it is expected toexpand its share of the power semiconductor market hereafter as continuously grow with thespread of electric vehicles.
Mr. Takekazu Masui as the chief of Novel Crystal Technology Sales Department explains theenergy-conservation effects by using Ga2O3 semiconductors in future: "We estimate that if Ga2O3
semiconductors are broadly used in battery chargers, air conditioners, electric vehicles, datacenters, smart grids, rail vehicles, etc., 10 million kW of electricity could be saved annually in 2050,
which is equivalent to 10 nuclear power units.”
Annotations*1 Epi-wafer
A semiconductor crystal film orientated on a single-crystal substrate. The quality of the crystal film is important because
the crystal film determines the performance of a semiconductor device.

*2 Killer defects
Generic term for defects that cause critical failure in semiconductor devices. Crystal imperfections, polishing scratcheson the wafer surface, and defects generated in the device process can result in killer defects. The density of the killer
defects must be reduced for manufacturing large (high-current) devices with high yields.

FiguresFigure 1. Third generation β-Ga2 O3 Schottky barrier diodes prototyped on 100-mm-diameter epi-wafers. Maximum chipsize of 10 mm × 10 mm .

Figure 2: Comparison of electrical properties of various semiconductor materials

Figure 3. Schematic of vapor phase growth and melt growth methods in the production of semiconductor crystals