National Institute of Advanced Industrial Science and Technology (AIST, President: Hiroyuki Yoshikawa) and Japan Atomic Energy Research Institute (JAERI, President: Toshio Okazaki) developed silicon carbide (SiC) based transistors which achieved a world record electron channel mobility, making them faster and more efficient.
Due to the superior material properties of SiC, it is widely expected to be used in ultra-low loss power devices in electrical power networks, motorcars/trains, and appliances. It is also a promising candidate for radiation-hard devices used in artificial satellites and nuclear power plants because of its high radiation resistance compared to conventional silicon (Si) based devices. SiC has many different crystal structures (polytypes) such as cubic, hexagonal, and rhombohedral structures. Although cubic SiC (3C-SiC) has the best electric properties of all polytypes, high quality 3C-SiC wafers have been difficult to grow. Hence, progress in the crystal growth of 3C-SiC has been regarded a key issue. In addition, fabricating SiC-based electronic devices requires the development of a means to selectively dope impurities as well as form SiC insulating layers.
In July 2002, AIST and JAERI started cooperative research on overcoming the problems mentioned above. Under this cooperation, AIST covered the technology for growing high-quality epitaxial layers of 3C-SiC. The task of JAERI was the development of transistor fabrication process technologies. As a result, AIST has succeeded in using the chemical vapor deposition (CVD) technique for growing high quality p-type 3C-SiC epilayers on 3C-SiC substrates supplied from HOYA Advanced Semiconductor Technologies Co.,Ltd.. JAERI, on the other hand, has developed the ability to form n-type regions in a p-type epilayer by hot-implantation of phosphorus ions, in addition to the formation of an insulating oxide film by pyrogenic oxidation. Consequently JAERI and AIST have together succeeded in fabricating the world’s best n-channel 3C-SiC Metal-Oxide-Semiconductor Field-Effect-Transistors (MOSFETs) with an electron channel mobility of 230cm2/Vs.
After further development of these devices, we fully expect them to be a suitable replacement for Si power devices. Due to their superior performance, larger reductions in wasted energy are expected. The application of SiC devices in the space and nuclear power plants is also expected to result in the realization of higher radiation resistant devices and longer satellite lifetimes. To ensure both of the above plans are fulfilled, further investigations are necessary to improve the crystal quality of 3C-SiC epilayers, and in doing so, the SiC MOSFET channel mobility. R&D into controlling the threshold voltage and increasing the reliability of oxide layers for 3C-SiC MOSFETs is also indispensable.