Novel Functional Materials Team
Research Objectives
Wide-gap semiconductor materials such as SiC and GaN and their power devices are attracting attention as one of the key components for achieving carbon neutrality by 2050, and are beginning to be implemented in society. Our team is conducting research and development of thin-film growth technology, which is the key to use these wide-gap semiconductor materials as power devices, and through this development, we will promote further performance and functionality of wide-gap semiconductor devices. We also support external research and development by providing the materials we have developed to external parties.
Technology
Focused Research
Key Research (1) 4H-SiC Thick Film Growth Technology Development
SiC is expected to be used for low-loss and intelligent power distribution systems to achieve carbon neutrality by 2050. In this research, we are developing materials for ultra-high voltage devices such as SiC-IGBTs and SiC-thyristors through two approaches: the development of high-speed thick film growth technology on standard 4H-SiC off-wafer and low off-angle epitaxial growth technology to solve problems caused by the use of off-wafer.
(1)-a High-speed thick film growth technology
In this research, we are developing technology to form epitaxial layers with a thickness of over 200 μm on 4-inch and 6-inch diameter 4H-SiC wafers in order to realize ultra-high voltage devices with a voltage of over 20 kV. We have achieved film thickness and density uniformity equivalent to that of 1kV-class wafers, and are working to further improve the quality.
(1)-b SiC low off-angle epi growth technology
Various polymorphs of SiC are stable. Therefore, in order to stabilize one type of polymorphism during epi growth, step flow growth has been implemented to take over the polymorphism of the substrate by applying an off-angle to the substrate. However, this step-flow growth method has the problems of (1) degradation of device characteristics due to the inheritance of substrate basal plane dislocations during epi growth and (2) reduction of effective area during thick film growth.
(1) Priority Research (2): Trench backfill growth technology for spallation device fabrication
Superjunction (SJ) structure with PN column structure has already been put to practical use in Si under the name of CoolMOS as a technology that exceeds the theoretical limit of unipolar devices determined by material properties. In order to apply this structure to SiC, we are developing a new PN column structure fabrication technology using trench backfilling growth. growth technology that is under development.
Priority Research (3) Wide-gap semiconductor heteroepitaxy technology
It is known that semiconductor heterojunctions can exhibit material properties that are not possible with a single material alone. For example, in a GaN-based HEMT structure, a two-dimensional electron gas is formed at the interface due to the lattice distortion caused by the GaN-AlGaN heterojunction, and a similar two-dimensional electron gas is theoretically predicted to be formed in a 3C-SiC-4H-SiC heterojunction. If realized, the heterojunction is expected to operate at higher speeds than GaN-HEMTs. In this study, we are developing an epitaxial growth technique of high-grade 3C-SiC crystals on a 4H-SiC substrate for the formation of a two-dimensional electron gas in a heterojunction of 3C-SiC and 4H-SiC, and are developing a high electron mobility transistor using this material.
Priority Research (4) Diamond Ion Implantation Technology
Iammonds are expected to be the next generation of semiconductors for power devices. Ion implantation is an indispensable technology for the device process, and ion implantation technology has been established for SiC as well as for Si. On the other hand, the control of irradiation damage, which is the fate of ion implantation, is still in its infancy in diamond, and once the implantation amount exceeds a certain level, the material becomes graphite, which is the most stable material under ambient pressure, and does not revert back to diamond. Although a certain degree of conductivity control has been achieved for the p-type by ion implantation of boron, it has not yet been applied to device processes.
Major papers, etc.
- ”Study of spiral growth on 4H-silicon carbide on-axis substrates”, K. Masumoto , K. Kojima, and H. Okumura, J. Crustal Growth 475, 251 (2017).
- “Investigation of Factors Influencing the Occurrence of 3C-Inclusions for the Thick Growth of on-Axis C-Face 4H-SiC Epitaxial Layers”, K. Masumoto , K Kojima and H. Yamaguchi, Materials 13, 4818 (2020).
- US10741648 (Semiconductor device and manufacturing method thereof)
- Patent No. 6760604, [Semiconductor device and its manufacturing method].
- “Fast-filling of 4H-SiC trenches at 10 μm/h by enhancing partial pressures of source species in chemical vapor deposition processes” S.Y. Ji, R. Kosugi, K. Kojima, K. Adachi, Y. Kawada, K. Mochizuki, Y. Yonezawa, S. Yoshida, and H. Okumura et al., J. Cryst. Growth, 546,12580 (2020).
- “A study of CVD growth parameters to fill 50-μm-deep 4H-SiC trench”, S.Y. Ji, R. Kosugi, K. Kojima, K. Adachi, Y. Kawada, K. Mochizuki, A. Nagata, Y. Matsukawa, Y. Yonezawa, S. Yoshida, and H. Okumura, Mater. Sci. Forum 963, 131 (2019) .
- “An empirical growth window concerning the input ratio of HCl/SiH4 gases in filling 4H-SiC trench by CVD”, S. Y. Ji, R. Kosugi, K. Kojima, K. Mochizuki, S. Saito, A. Nagata, Y. Matsukawa, Y. Yonezawa, S. Yoshida, and H. Okumura, Appl. Phys. Express, 10, 055505 (2017).
- “Growth of vanadium doped semi-insulating 4H-SiC epilayer with ultrahigh resistivity”，K. Kojima, S. Sato, T. Ohshima, S. Kuroki, J. Appl, Phys.,131, 245107 (2022).
- “High-mobility 2D electron gas in carbon-face 3C-SiC/4H-SiC heterostructure with single-domain 3C-SiC layer”, H. Sazawa and H. Yamaguchi, Appl. Phys. Lett. 120, 212102 (2022).
- “Electrical properties of a B doped layer in diamond formed by hot B implantation and high-temperature annealing” N. Tsubouchi, M. Ogura, N. Mizuochi, and H. Watanabe, Diamond Relat. Mater., 18, 128 (2009).
Others
The group is taking advantage of its epitaxial thin film fabrication technology, mainly SiC, to provide special SiC epitaxial wafers and small-diameter epi wafers that are difficult to obtain in the market, and to provide data on the temperature dependence of conductivity characteristics of 4H-SiC at various carrier concentrations.
