Low Temperature Deposition of Diamond Thin Films Using Electron Cyclotron Resonance Plasmas
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ABSTRACT We have used an electron cyclotron resonance enhanced plasma system to deposit films from methyl alcohol at a pressure of 1.00 Torr. Depositions occurred on silicon substrates at temperatures from 550 - 750 *C. Film morphology was examined using SEM. Structural characterization was conducted using Raman spectroscopy and x-ray diffraction. Based on these analyses, certain trends in film quality as a function of deposition temperature were determined.
INTRODUCTION Research on chemical vapor deposition (CVD) of diamond in recent years has been driven by the desire to exploit diamond's many exemplary attributes. Along with diamond's extreme hardness, it is also a low friction material with excellent chemical inertness, making it a prime candidate for wear-resistant coatings. Diamond is also an attractive optical coating material because of its excellent infrared transmission characteristics and relatively low dielectric constant. Deposition of diamond thin films has been well established in many different gas activation systems (e.g., hot filament, R.F. and microwave plasma, DC plasma jet, and oxy-acetylene flame). Typical gas phase compositions for diamond growth have been widely surveyed in the carbonhydrogen-oxygen (C/HIO) system and have been used to determine the well-known Bachmanntriangle.[1] Although there is still debate concerning the specific roles of different monomer species in the growth process, certain aspects of diamond deposition are widely accepted. Hydrogen is critical in preferentially removing non-diamond-bonded carbon which is codeposited along with diamond. It also serves to stabilize the forming diamond surface by occupying dangling bond sites. Oxygen plays a similar role to hydrogen in preferentially etching graphitic carbon, either alone in its atomic state or as part of an OH molecule. At the same time, oxygen acts to effectively reduce the amount of gas phase carbon available for deposition by forming CO, which is very thermally stable. It has been reported that oxygen addition to a diamond CVD system resulted in higher growth rates and better structural quality of deposited films, as well as facilitating deposition at lower substrate temperatures. [2-6] Despite general success in the development of diamond CVD, there are still many obstacles to the general application of diamond films. The barrier to nucleation of diamond on non-diamond substrates is a common problem. The most successful results have been obtained using carbideforming materials with relatively high melting points such as silicon and molybdenum. Even on these materials, results are significantly improved by using pre-deposition treatments such as scratching of the growth surface with diamond grit or "seeding" with diamond particles. [7] Another problem in diamond deposition is thermal expansion mismatch between the deposited diamond film and the substrate material. The resulting stress due to this mismatch can result in cracking and delamination of the film. Disregarding thermal mismatch, the typical substrate tem
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