Novel Time-modulated Chemical Vapor Deposition Process for Growing Diamond Films
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W. Ahmed Department of Chemistry and Materials, Manchester Metropolitan University, Manchester, United Kingdom
J. Gracioa) Department of Mechanical Engineering, University of Aveiro, 3810 Aveiro, Portugal (Received 12 December 2001; accepted 25 March 2002)
Smooth polycrystalline diamond films were deposited onto silicon substrates using a newly developed time-modulated chemical vapor deposition (TMCVD) process. The distinctive feature of the TMCVD process involves pulsing the hydrocarbon gas, methane, at different flow rates for varying durations into the vacuum reactor during the chemical vapor deposition (CVD) process. Generally, CVD diamond films display nonuniformity in the crystal sizes and surface roughness along the film growth profile. The TMCVD method was specifically developed to (i) deposit smooth films, (ii) control film microstructure and morphology, and (iii) improve film reliability. We show that the TMCVD process produces diamond films with improved surface smoothness as compared to films of similar thickness produced by conventional CVD method under similar conditions. Surprisingly perhaps, the TMCVD method gave growth rates much higher than the conventional CVD method without reducing the film quality as revealed by the SEM micrographs and micro-Raman spectra. Diamond is a unique engineering material, due to its superior combination of physical, optical, and chemical properties.1 As a result, the material has many potential uses in numerous industrial and consumer applications.2,3 For example, diamond coatings are employed to yield significant benefits in applications such as cutting tools (drills, hand hacksaws, razor blades), optical lenses (ophthalmic lenses, aerospace screens), biomedical components (implants), microelectronics (integrated circuits), engineering (piston rings, cylinder liners), and thermal management systems. The difficulty in depositing truly superior diamond films is nearly as extreme as its unique properties. Researchers throughout the world have employed a range of thin film coating technologies to deposit diamond onto a range of substrate materials.4 –6 However, the most successful method of deposition is chemical vapor deposition (CVD), because it yields films with high degree of sp3 bonding. It is generally accepted that the morphology, crystal size, crystal orientation, film quality, surface roughness, and coating adhesion, are critical in determining the suitability of the coating being used for a particular application. It is
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 7, Jul 2002
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essential to be able to design the coating to suit the specific application. Therefore, it is necessary to control film microstructure, morphology, surface roughness, etc., to produce films that will display superior properties for new applications. Generally, CVD methods produce films that display rough surfaces, which become pronounced with the increase in film thickness.
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