Combined substrate polishing and biasing during hot-filament chemical vapor deposition of diamond on copper
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Q.H. Fan Department of Physics, University of Aveiro, 3810 Aveiro, Portugal (Received 18 June 1999; accepted 6 December 1999)
Diamond deposition on copper is problematic mainly due to the poor affinity between copper and carbon. Therefore, it becomes necessary to pretreat the substrate surfaces prior to diamond deposition. Several surface pretreatments have been investigated, such as polishing using various abrasives and substrate biasing. In this study, we report new results relating diamond nucleation on copper substrates to a combination of surface polishing and biasing pretreatments. The results show that the combined pretreatments give a higher nucleation density than the two individual treatments. It was found that an increase of 70% in the nucleation density was observed when the surfaces were polished with diamond paste and then negatively biased. Copper surfaces polished with diamond powder and then biased displayed the highest nucleation density obtained. Raman spectroscopy revealed that after negatively biasing the substrate for 30 min, broad D- and G-bands of microcrystalline graphite were present, which completely disappeared with subsequent diamond growth, leaving behind a good-quality diamond film.
Diamond synthesis via chemical vapor deposition (CVD) on metallic substrates such as copper is a difficult task due to the noncarbon affinity of copper, which results in poor adhesion, lower nucleation density, and film cracking.1–3 One way of improving the nucleation density is to pretreat the substrates using polishing and biasing methods. Polishing materials such as diamond powder, diamond paste, alumina (Al2O3), and silicon carbide paper (SiC) have been used to prepare substrates for subsequent diamond deposition.4 The bias-enhanced nucleation (BEN) process used involved negatively biasing the substrate, with respect to the filament, in order to further enhance the diamond nucleation density.5 A hot-filament CVD (HFCVD) system, which has been described elsewhere,6 was used for carrying our diamond depositions; the process conditions are shown in Table I. The polycrystalline foil copper substrates (>99.9% purity) used in this investigation were of 5 × 5 mm dimen-
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 3, Mar 2000
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sion and 0.5 mm thick. Copper substrates were polished with (i) 3-m diamond powder, (ii) 3-m diamond paste, (iii) 3-m Al2O3 paste, and (iv) SiC paper (2400 grid). The copper surfaces were ultrasonically cleaned with acetone prior to any pretreatment. Bias pretreatments were conducted on a diamond-coated molybdenum substrate holder. Before conducting bias pretreatment, the filament was pre-carburised for 15 min under standard CVD growth conditions except at 3% CH4 concentration. The as-deposited films were analyzed in order to study film crystallinity, morphology, quality, and phase purity by scanning electron microscopy (SEM) (Cambridge Stereoscan-250) and Raman Spectros
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