Silicon Carbide and Diamond Materials Development for Micro- and Nano-Electromechanical Systems

Microelectromechanical systems (MEMS) are miniature integrated systems including both mechanical and electronic components, which are developed based on silicon integrated circuits technology. The current trend indicates two directions of MEMS technology: (1) a scaling downward to nanometer scale as nanoelectromechanical systems (NEMS); (2) a development of advanced materials that can outperform silicon. The goal of this work is to study and develop the material properties and process flows to realize the potential of silicon carbide (SiC) and diamond thin films for demanding MEMS and NEMS applications.
The SiC material development includes the deposition of polycrystalline 3C-SiC thin film, the study of the relationship between material structure and properties, and the development of an innovative process for achieving optimal combination of electrical, mechanical and metal contact properties for the design, fabrication and operation of MEMS. Polycrystalline 3C-SiC films are deposited by low pressure chemical vapor deposition using 1,3-disilabutane as the single precursor at 800◦C, and are in-situ n-type and p-type doped using ammonia and trimethylaluminum, respectively. Resistivity as low as 0.03 Ωcm is achieved by nitrogen doping. The effects of doping on the resistivity and film crystalline structure are studied. The temperature coefficient of resistivity (TCR) is also characterized and found to be negative and decrease in magnitude with temperature. Residual strain and strain gradient of nitrogen-doped films are characterized by microfabricated strain gauges and cantilever beam arrays. A bilayer deposition scheme consisting of films with different residual strains due to differing doping contents is developed in order to minimize the strain gradient without compromising the electrical resistivity of the film. Ohmic contacts to n-type doped polycrystalline SiC are formed at room temperature using nickel and platinum. Long-term thermally stable metal contacts to polycrystalline SiC at 300◦C in air are obtained on Pt covered Ni contacts.
The investigations on diamond thin films focused on microcrystalline and nanocrystaline diamond films, with emphasis on the relationship between microstructure, dopant incorporation and film residual strain. The diamond films are deposited by hot filament chemical vapor deposition using methane and are in-situ boron doped. The fabrication process flow including oxygen-based selective etching is established, and various micromechanical structures are fabricated.Both microcrystalline and nanocrystaline diamond films have compressive residual strain less than−0.05% and strain gradients smaller than ±5×10^−5μm−1 which are small enough to enable the realization of many MEMS devices. Through are active ion etching process, well-aligned diamond nanowires are fabricated. The formation of diamond nanowires is attributed to an in-situ formed micromasking process which provides a promising approach for the low-cost batch fabrication of diamond-based nanoscale devices.
Publication date: 
May 31, 2007
Publication type: 
Ph.D. Dissertation
Zhang, J. (2007). Silicon Carbide and Diamond Materials Development for Micro- and Nono-electromechanical Systems. (n.p.): University of California, Berkeley.

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