Growth and characterization of silicon carbide for MEMS pressure sensors

Silicon carbide is a promising material suitable for high-temperature microelectromechanical systems (MEMS). Growth of silicon carbide films on a variety of suitable substrates is the key to the development of SiC MEMS. The primary objectives of this thesis are (i) to explore the temperature and substrate issues connected with the growth of 3C-SiC films by atmospheric pressure chemical vapor deposition (APCVD), and (ii) to develop bulk-micromachined SiC piezoresistive pressure sensors using a proper combination of SiC film growth and microfabrication techniques.; Heteroepitaxial growth of 3C-SiC films on Si substrates was performed using a two-step growth process. Carbonization layers on Si(100) substrates produced using different times were characterized in hopes of elucidating the growth mode and a mechanism for the formation of voids.; The microstructure, surface morphology and growth rate of 3C-SiC films grown on Si substrates were characterized to study the effects of temperature and precursor concentration in film growth. An explanation for the formation of excess Si in SiC films at lower temperatures is proposed.; The nucleation, morphology and microstructure of SiC films deposited on SiO₂ and Si₃N₄ substrates at different temperatures were studied. Differences in nucleation and growth of SiC films were observed and reasons for their differences on these substrates at different temperature were explained based on thermodynamic and kinetic effects.; The deposition of SiC films on patterned substrates for MEMS applications was also studied. Selective epitaxial SiC growth using SiO₂ and Si₃N₄ masks, a lift-off patterning technique of thin SiC films, and the deposition of SiC films in high aspect ratio Si molds by APCVD were characterized.; SiC piezoresistive pressure sensors were designed and fabricated using bulk micromachining techniques. In one case, a pressure sensor using polycrystalline SiC films as piezoresistors and membranes was developed. The sensors had a gauge factor less than −3. A second type of pressure sensors using monocrystalline SiC piezoresistors, and monocrystalline Si membranes was developed using a modified wafer bonding technique. Monocrystalline SiC piezoresistors show a gauge factor of −18. The sensors were tested at temperatures up to 400°C. The improvement in sensor design to increase the sensitivity was addressed.