Chemical structure and physical properties of diamond-like amorphous carbon films prepared by magnetron sputtering
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D. B. Bogy Computer Mechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, California 94720 (Received 19 April 1990; accepted 17 July 1990) Thin films of amorphous carbon (a-C) and amorphous hydrogenated carbon (a-C • H) were prepared using magnetron sputtering of a graphite target. The chemical structures of the films were characterized using electron energy loss spectroscopy (EELS) and Raman spectroscopy. The mass density, hardness, residual stress, optical band gap, and electrical resistivity were determined, and their relation to the film's chemical structure are discussed. It was found that the graphitic component increases with increasing sputtering power density. This is accompanied by a decrease in the electrical resistivity, optical band gap, mass density, and hardness. Increasing the hydrogen content in the sputtering gas mixture results in decreasing hardness (14 GPa to 3 GPa) and mass density, and increasing optical band gap and electrical resistivity. The variation in the physical properties and chemical structures of these films can be explained in terms of the changes in the volume of sp2-bonded clusters in the a-C films and changes in the termination of the graphitic clusters and sp3-bonded networks by hydrogen in the a-C :H films.
I. INTRODUCTION
There has been a growing interest in the useful and unique properties of diamond-like amorphous carbon thin films. These properties include high hardness and wear resistivity, chemical inertness, high electrical resistance and lack of magnetic response, optical transparency in the infrared region, and an optical band gap up to a few eV. Amorphous carbon thin films, thus, have potential applications as protective coatings for magnetic and optical disks, wear-resistant coatings for abrasive applications, and also as semiconducting materials.1"6 These films can be produced by ion beam sputtering, magnetron sputtering, and plasma-assisted chemical vapor deposition. Of interest to the computer industry are sputtering techniques using parallel-plate electrodes. These techniques have the advantages of low cost, process simplicity, good process control, and coating homogeneity, and are used routinely for thin film deposition of magnetic media in the production of computer hard disks. The physical properties of sputtered a-C films change with changes in the deposition parameters. It is important to understand the relation of the chemical structure of a-C thin films to the physical properties in order to define useful deposition parameters. DiamondOn sabbatical leave from IBM Research Division, Almaden Research Center, San Jose, California 95120.
like amorphous carbon films are metastable phases formed when carbon particles are condensed on a subtrate.7 A number of investigations have been performed to identify the microstructure of amorphous carbon films using a variety of techniques such as Raman spectroscopy,8"14 EELS,915"18 nuclear magnetic resonance,1719'20 optical measurements,9'21"23 transmission electron microscopy
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