Previous researches at the Plasma Physics Laboratory, National Institute of Physics at the University of the Philippines Diliman have shown that diamond and DLC thin films can be grown on silicon substrates with the Plasma Enhanced Chemical Vapor Deposition (PECVD) system via DC Glow discharge. The PECVD facility was developed for the deposition of diamond films as hard coatings for important industrial materials. The gas phase chemistry in low temperature (<300^oC) diamond and DLC chemical vapor deposition processes was investigated using optical emission spectroscopy (OES) to determine the effects of the different deposition parameters such as methane concentration, substrate temperature, plasma current and gas pressure in relation to diamond growth on silicon substrates. The OES data were analyzed to determine the important factors favorable for diamond deposition such as the mean electron temperature, Te, and the relative concentration levels of methane radicals (CH and CH+). The results indicated that the optimum deposition parameters for the low temperature diamond CVD system could be achieved by applying low methane concentration (1% to 3% methane in hydrogen), high substrate temperature (above 275^oC), low pressure (<20 mTorr) and high plasma current (above 30mA).Diamond films were attempted to be deposited on silicon substrates while gathering the OES data using varying methane concentrations (1%, 3%, 5% and 8 % methane in hydrogen) at fixed pressure (10 mTorr) and fixed plasma current (50 mA). X-ray Diffraction , Raman Spectroscopy and Scanning Electron Microscopy characterization of the deposited samples confirmed that diamond films were deposited at low methane concentrations (1% to 3%). Samples deposited using 5% methane resulted in DLC films while 8% methane concentration yielded graphitic carbon deposits. Film samples were also deposited using varying substrate temperatures (175^oC – 300^oC). Samples deposited at substrate temperature above 200^oC yielded diamond characteristics while films deposited at lower substrate temperatures resulted in DLC deposits.

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