Comparison of diamond-like carbon film deposition by electron cyclotron resonance with benzene and methane
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Comparison of diamond-like carbon film deposition by electron cyclotron resonance with benzene and methane P. S. Andry, P. W. Pastel, and W. J. Varhue Department of Electrical Engineering, University of Vermont, Burlington, Vermont 05405-0156 (Received 14 October 1993; accepted 29 September 1995)
A comparative study of the deposition of diamond-like carbon films using methane or benzene in a microwave electron cyclotron resonance plasma-enhanced chemical vapor deposition system has been performed. Process variables studied were reactor pressure, applied radio frequency substrate bias, and microwave power. The plasma stream was characterized using optical emission spectroscopy and mass spectrometry. Film properties studied included optical energy gap, total hydrogen content, integrated C-H stretch absorption, index of refraction, and Raman spectra. The use of a high CyH ratio reactant such as benzene was found to be advantageous over methane in that higher deposition rates were possible and the resultant films exhibit diamond-like properties without the application of large substrate biases. Another result of this investigation was further confirmation that hard carbon films contain a significant quantity of nonbonded hydrogen [A. Grill and V. Patel, Appl. Phys. Lett. 60 (17), 2089 (1992)]. I. INTRODUCTION
Amorphous carbon thin films produced by vapor phase deposition techniques have several properties similar to diamond. These properties include mechanical hardness, chemical inertness, good electrical insulation, and good infrared transmission.2,3 Diamond-like carbon (DLC) thin films are well suited for applications such as tribological coatings,4 integrated circuit passivation coatings,5 and infrared optical coatings.6 Microwave electron cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition is an attractive technique for DLC film deposition because it combines a high production rate of plasma species, low substrate temperature, and independent control of ion energy in a process which is compatible with semiconductor device fabrication.7,8 A number of studies of DLC deposition in microwave ECR systems have been performed; in these works methane, methane-hydrogen mixtures, or acetylene were used as the source gas.9–11 The addition of an independent RF-biased substrate stage to the microwave ECR system has been shown to be useful in modifying DLC film properties.12 In the present work a systematic study of the effects of substrate bias and pressure on DLC film properties deposited from benzene and methane has been done. Wild et al.13 and Wagner et al.14 showed that the chemistry in an RF discharge was sensitive to the specific hydrocarbon used, but that the properties of the deposited film were insensitive to the process gas. They concluded that ionic species were accelerated across the plasma sheath and dissociated by impact fragmentation, thus producing the precursors to film growth. However, more recently, Matsukura et al.15 proposed a model in which CHn
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