Single Crystalline 4H-SiC MEMS Devices with N-P-N Epitaxial Structure
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Single Crystalline 4H-SiC MEMS Devices with N-P-N Epitaxial Structure Feng Zhao1, Allen Lim1, Zhibang Chen1, Chih-Fang Huang2 1
Micro/Nanoelectronics and Energy Laboratory, Electrical Engineering, School of Engineering
and Computer Science, Washington State University, Vancouver, WA 98686 USA 2
Department of Electrical Engineering, National Tsing Hua University, 30013 Hsinchu, Taiwan,
R.O.C. ABSTRACT In this paper, single crystal 4H-SiC MEMS devices with n-p-n epitaxial structure was fabricated. A dopant-selective photoelectrochemical etching technique was applied to etch the sacrificial p-type SiC layer to release n-type SiC suspended structures on n-type SiC substrate. The selective etching was achieved by applying a bias which employs the different flat-band potentials of n-SiC and p-SiC in KOH solution. Such MEMS devices have the potential to fully exploit the superior properties of single crystal SiC for harsh environment operation, as well as mature epitaxial growth and device fabrication of 4H-SiC. The n-p-n structure, together with the previously reported p-n structure, extends the capability of monolithic integration between MEMS with electronic devices and circuits on SiC platform. INTRODUCTION SiC has been identified as a desirable semiconductor material platform for MEMS operated in harsh environments, such as high temperature and extreme pressure, shock, chemical, radiation, biological and corrosion attacks, etc. This is due to the excellent intrinsic material properties of SiC including large bandgap energy, mechanical robustness, chemical resistance, radiation hardness and biocompatibility. Efforts have been taken to develop SiC MEMS devices. One group of such devices is made of single crystalline SiC (such as 3C-polytype [1]) or polycrystalline [2] SiC deposited on Si or silicon-on-insulator (SOI) substrate [3]. The fabrication of these devices uses the standard surface micromachining technique by etching the sacrificial Si or SiO2 layer to release the free-standing SiC MEMS structures. Another group of devices is made of homoepitaxial single crystalline SiC film grown on single crystalline SiC substrate, such as 4H-SiC and 6H-SiC polytypes. Without Si or SOI substrate, these devices are more promising to fully exploit the potential of SiC material for harsh environment [4]. The lower interfacial defect density between SiC film and substrate, and high quality material by homoepitaxial growth provide potential to further improve the resonant characteristics. However, due to the excellent chemical inertness, it is challenging to undercut single crystalline 4H-SiC and 6H-SiC to release suspended structures. Isotropic etching can only be done by molten KOH at >600ºC, which is not applicable for MEMS fabrication. In recent years, potential solutions have been developed. Bulk micromachining by etching from the backside of SiC substrate and through the wafer by inductively coupled plasma (ICP) [5], deep reactive ion etching (DRIE) [6, 7], ultrasonic drilling [8], and laser milling [9] were reported. Til
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