Site: Kyoto University
Semiconductor Science and Engineering Laboratory
Department of Electronic Science and Engineering
Yoshidahonmachi, Sakyo
Kyoto 606-8501, Japan
Tel.: (07) 57 53 5340
Fax: (07) 57 51 1576
http://matsunami.kuee.kyoto-u.ac.jp/
Date Visited: 9 June 1998
TTEC Attendees:
V. Dmitriev (report author)
R. C. Clarke
H. Morishita
M. S. Shur
U. Varshney
Hosts:
Dr. Hiroyuki Matsunami, Professor
Dr. Tsunenobu Kimoto, Associate Professor
Dr. Jun Suda, Research Associate
INTRODUCTION
The research team headed by Prof. Matsunami has made great contributions in the development and understanding of SiC growth techniques. The laboratory has developed blue LEDs based on SiC epitaxial p-n structures. Currently, silicon carbide activity is focused on SiC bulk and epitaxial growth and high power device development. Kyoto University researchers have developed a world-recognized epitaxial technique for the growth of high quality CVD SiC material, namely step-controlled epitaxy. They have performed detailed investigations on the growth mechanisms and surface morphology of SiC grown by step-controlled epitaxy. High voltage (1750 V) Schottky barriers on Ti/4H-SiC were demonstrated using CVD-grown SiC material. Al and B ion implantation in SiC is under investigation (1070 V mesa p-n diodes have been fabricated). The laboratory is involved in the MITI-funded Combustion Control Systems Project. Recently, a new project on GaN growth on sapphire and SiC substrate has begun.
STATUS OF ACTIVITIES AND COMMENTS
Professor Matsunami described aspects of the work in the laboratory. The research team includes 3 professors, 3 PhDs, 9 graduate students, and 6 undergraduate students. The laboratory is focusing on the following research topics:
- growth and characterization of SiC
- development of SiC power devices
- ultra-thin insulators for Si MOS devices
- growth and characterization of GaN
- III-V photonic devices on Si substrates
The laboratory is equipped with the following growth and processing machines (a laboratory tour was provided):
- setup for bulk SiC growth by sublimation
- CVD growth machine for SiC epitaxy
- device processing: evaporators, RIE equipment, oxidation equipment, photolithography, and rapid thermal annealing
- SiC MBE growth machine
- GaN MBE growth machine
The laboratory is working in close cooperation with the Kyoto University Venture Business Laboratory (KUVBL). The KUVBL was founded in 1997 with the financial support of the Japanese government in order to promote research on "An Atomic and Molecular Approach for the Development of Advanced Electronic Materials" and to imbue younger researchers with the "venture" spirit. The KUVBL has state-of-the-art characterization equipment including XPS, AFM, STM, X-ray diffractometers, and a Hall measurement station.
QUESTIONS AND ANSWERS
Q.
How is high temperature electronics defined in Japan? What materials and products are included in that definition? What role does the Japanese government play in supporting education, basic research, applied research, and product development in high temperature electronics?
A.
Definition: electronics involving devices that can operate at high temperatures
materials: SiC, GaN, partly Si and their devices.
education: no special support
basic research: almost no support
applied research: For 6 years in the Kansai area, MITI has supported a local project on SiC to realize a monitoring system for the control of combustion
Q.
Is your organization involved in any government high temperature and/or high power electronics program?
A.
MITI provides sub-support for high temperature electronics through the Ion Engineering Research Laboratory. The Ministry of Education has promoted research in conductivity control both in-situ and in ion-implantation high power electronics through its program "Control of Widegap Semiconductors and Application to Energy Electronics."
Q.
Does the company view materials and/or devices for high temperature and/or high power electronics based on SiC and group III nitrides as products to sell? What "roadmap" do you see for high temperature, high power electronics (similar to the famous "roadmap" for Si MOSFET technology)?
A.
High power SiC electronic devices can be sold on a commercial basis. Roadmap would be as follows: the first 5 years would be spent on basic research.
Q.
What high temperature and/or high power component/system is your organization targeting for development and introduction over the following time scale:
A.
1-5 years - SiC Schottky devices
5-10 years- SiC switching devices (MOSFET, IGBT etc.)
>10 years
Q.
In meeting these applications areas, what gaps exist in the current technology base in SiC and group III nitrides? What are the major issues to be overcome in the following general areas?
A.
material growth, wafer quality
device fabrication, MOS interface, acceptor implantation
packaging
reliability, oxide reliability
systems integration and performance testing.
Q.
What temperature range would you consider for high temperature electronic operations?
A.
250-350oC
Q.
What power level would you consider for high-temperature devices?
A.
100-1000 W
1-10 Kw
Q.
In your organization, what percentage of the overall investment in wide bandgap semiconductor electronics is directed at the development of:
A.
material growth45%
device manufacturing processes40%
device design and modeling5%
packaging0%
device testing10%
Q.
What wide bandgap semiconductor material has the best potential for high temperature and/or high power electronics? What semiconductor material for high temperature electronics do you expect to dominate the market?
A.
SiC
Q.
What are the most important material characteristics for substrate material for wide bandgap electronics?
A.
defect density
cost
size
Q.
What are the most important material characteristics for epitaxial material for high temperature and high power electronics?
A.
defect density
electrical properties
growth rate
Q.
What are the main issues in manufacturing materials for high temperature electronics?
A.
high quality substrate
Q.
Does the university grow substrate and/or epitaxial material for high temperature electronics? What methods are used? What technology has the best prospect for production of bulk and epitaxial materials for high temperature electronics? Does the university buy substrate and/or epitaxial material for high temperature electronics?
A.
grow substrate for some purpose: seeded sublimation
grow epitaxial material: CVD
buy substrates, but not epitaxial material
Q.
What device building blocks (ohmic contacts, Schottky barriers, p-n junctions, device isolations, etc.) do you consider to be bottlenecks for high temperature devices fabricated in SiC and group III nitride materials?
A.
oxide reliability for SiC
Q.
What is the relative importance of unipolar devices (MOSFETs, MESFETs, SITs, etc.) compared to bipolar devices (BJTs, HBTs, etc.) for devices fabricated in SiC and group III nitrides? What is the role of super switching in high temperature, high power devices? What are specific issues in developing high temperature sensors?
A.
depends on the kind of application
super switching?
Q.
Are the key material parameters for SiC and group III nitrides known well enough for the design of high temperature, high power electronics?
A.
no
Q.
What are U.S. strengths in R&D for high temperature electronics?
A.
support from various financial sources
SUMMARY
This research group is leading in SiC technology. The continuing need in basic materials research, including research and development on micropipe-free substrates, doping, and surface preparation techniques, was emphasized several times during the discussion. New methods for bulk SiC growth should be considered. Commercialization of SiC devices, probably power Schottky diodes together with Si IGBT power switches and high frequency/high power devices for microwave application, is expected in 5 years. Those power devices will be used in the early stages; then later power electric systems will need SiC devices. Prof. Matsunami sees the largest market for SiC high temperature devices in the automotive industry in the future when mature technologies for SiC devices have been established, but he is concerned about the cost of SiC materials and devices.
REFERENCES
A 3C-SiC/Si 6-inch-diameter epitaxial wafer fabricated by HOYA Company was demonstrated.
Itoh, A., and H. Matsunami. 1997. Single crystal growth of SiC and electronic devices. Critical Reviews in Solid State and Materials Sciences. 22:111-197.
Lab tour and KUVBL tour.
Matsunami, H., and T. Kimoto. 1997. Step-controlled epitaxial growth of SiC: high quality homoepitaxy. Materials Science and Engineering. R20:125-166.