Characterization of polycrystalline silicon carbide films grown by atmospheric pressure chemical vapor deposition on pol
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Characterization of polycrystalline silicon carbide films grown by atmospheric pressure chemical vapor deposition on polycrystalline silicon Christian A. Zorman and Shuvo Roy Department of Electrical Engineering and Applied Physics, Case Western Reserve University, Cleveland, Ohio 44106
Chien-Hung Wu Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106
Aaron J. Fleischman and Mehran Mehregany Department of Electrical Engineering and Applied Physics, Case Western Reserve University, Cleveland, Ohio 44106 (Received 13 September 1996; accepted 22 May 1997)
X-ray diffraction, transmission electron microscopy, and Rutherford backscattering spectroscopy were used to characterize the microstructure of polycrystalline SiC films grown on as-deposited and annealed polysilicon substrates. For both substrate types, the texture of the SiC films resembles the polysilicon at the onset of SiC growth. During the high temperature deposition process, the as-deposited polysilicon recrystallizes without influencing the crystallinity of the overlying SiC. An investigation of the SiC/polysilicon interface reveals that a heteroepitaxial relationship exists between polysilicon and SiC grains. From this study, a method to control the orientation of highly textured polycrystalline SiC films has been developed.
I. INTRODUCTION
Polycrystalline silicon (polysilicon) is a dominant material in the fabrication of surface-micromachined microelectromechanical systems (MEMS).1 Polysilicon comprises the device structural layers and is typically deposited by low pressure chemical vapor deposition (LPCVD). However, the elastic modulus of Si decreases significantly above 600 ±C, making it unsuitable for high-temperature applications.2 In contrast to Si, SiC is noted for its mechanical hardness and electrical stability at temperatures above 600 ±C.3 Additionally, higher elastic modulus and yield strength values relative to Si make SiC an attractive candidate for the micromechanical components of high temperature MEMS devices. Historically, most research has focused on developing 6H-SiC as a semiconductor material for high temperature and high power electronics. But small wafer size (1.375 inch diameter) and the inability to grow heteroepitaxial 6H-SiC films on Si substrates has hindered the development of the 6H polytype for MEMS applications, which require large area substrates for highvolume, batch processing to reduce device unit cost to a level practical for commercial applications. Unlike 6H-SiC, 3C-SiC can be heteroepitaxially grown on Si substrates, which has generated interest in 3C-SiC as a high temperature MEMS material. Heteroepitaxy of 3C-SiC on (100) and (111) Si has been demonstrated using various deposition techniques,4–6 the most common 406
J. Mater. Res., Vol. 13, No. 2, Feb 1998
being atmospheric pressure chemical vapor deposition (APCVD). Bulk-micromachined 3C-SiC diaphragms and 3C-SiC coated Si fuel atomizers are examples of devices t
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