Silicon-Carbon Alloys Synthesized by Electron Cyclotron Resonance Chemical Vapor Deposition
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Silicon-Carbon Alloys Synthesized by Electron Cyclotron Resonance Chemical Vapor Deposition Mark B. Moran and Linda F. Johnson Research and Engineering, Code 4T4110D, Naval Air Warfare Center, China Lake, CA 93555 ABSTRACT Silicon-carbon alloys were deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using either halogenated or non-halogenated precursors for the Si and C sources. Halogenated precursors were chosen for initial experiments to try to reduce the H content and to improve the microstructure of the silicon carbide (SiCx) films. While a wide range of compositions has been deposited using the halogenated precursors, only a limited range has been deposited so far with the non-halogenated precursors. Electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared (FTIR) spectroscopy show that compositions ranging from near-stoichiometric SiCx to extremely C-rich can be deposited by controlling the deposition temperature, plasma power and C/Si ratio of the halogenated precursors. At the highest C/Si-precursor ratio, the deposited film is electrically conductive with a measured resistivity of 0.067Ω-cm, contains only 3-atomic-percent Si and should be considered a Si-doped carbon (C:Si) film. The excellent transparency, especially that of the C:Si films, allowed the assignment of FTIR absorption bands that are usually masked by graphitic inclusions and other impurities. A weak absorption band at 1180cm-1 was found to correlate with the electrical conductivity of the films and was attributed to the asymmetric “bond-and-a-half” Si...C stretch in a Si...C...C functional group where the pi electrons are distributed equally between the three atoms. Additional results show etching of the substrate by reactive Cl from the halogenated precursors can have a dramatic effect on the microstructure, porosity and moisture stability of the films. For experiments involving halogenated precursors, the C:Si films are much more stable than the near-stoichiometric SiCx because C:Si is deposited at lower plasma powers that do not etch the Si substrate. Finally, preliminary results show that near-stoichiometric SiCx films deposited using non-halogenated precursors are much more stable with respect to moisture incorporation than those deposited with halogenated precursors. INTRODUCTION A variety of high-temperature, high-power electronic devices including micro-electromechanical systems (MEMS) would benefit from the development of a process that could be used to deposit low-defect, microcrystalline SiC coatings. Shimkunas et al. used electron cyclotron resonance chemical vapor deposition (ECR-CVD) to deposit low-H-content, nearstoichiometric-SiC coatings up to 2-µm thick from mixtures of ethylene (C2H4), silane (SiH4) and Ar onto a Si substrate held at a temperature of 930°C using a plasma power of 500W [1]. Problems with temperature uniformity and bowing of the underlying Si substrate at the high deposition temperatures were cited as potential reasons for the presence of defects and the low b
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