Nano-Structured Amorphous Carbon Films Synthesised Using Decr Plasma
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NANO-STRUCTURED AMORPHOUS CARBON FILMS SYNTHESISED USING DECR PLASMA André Golanski1, Dieter Grambole 3, Jean Hommet 2, Folker Herrmann 3, Philippe Kern 1, Liam McDonnell 4, Fabrice Piazza 1 and Jean-Paul Stoquert 1 1
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Centre National de la Recherche Scientifique (CNRS), Laboratoire PHASE, B.P.20, F-67037 Strasbourg, France. Centre National de la Recherche Scientifique (CNRS), Laboratoire IPCMS B.P. 20, F-67037 Strasbourg, France Forschungszentrum Rossendorf e.V., Institut für Ionenstrahlphysik und Materialforschung Postfach 51 01 19, 01314 Dresden, Germany Centre for Surface and Interface Analysis, Dept. of Applied Physics and Instrumentation, Cork Institute of Technology Rossa Av., Cork, Ireland
ABSTRACT A Distributed Electron Cyclotron Resonance plasma reactor powered by a microwave generator operating at 2.45 GHz was used to deposit ta-C:H (Diamond-Like Carbon, DLC) thin films at RT. A graphite sputtering target immersed in an argon plasma was used as carbon source. The Ar plasma density was about 5x1010 cm-3. Single crystal Si substrates were RF biased to a negative voltage of -80 V. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), nuclear reaction analysis (NRA) using the resonance at 6.385 MeV of the reaction: 15N + 1H 12C + 4+H HODVWLFUHFRLOGHWHFWLRQ analysis (ERDA) and Rutherford backscattering (RBS) were used to investigate the early phase of the growth. The morphology of the films grown at low pressure (0.3 mTorr) is shown to be dominated by stress-mediated nucleation leading to formation of basket-like clusters of circular hillocks 20 nm high surrounded by a planar, mostly sp2 bonded film ~8 nm thick. With increasing plasma pressure the spatial frequency of the hillocks becomes random and the growth is dominated by the Stranski-Krastanov mode. The XPS data taken at decreasing emergence angles show that the structure of the hillocks is dominated by sp3 bonded carbon. The XPS argon signal disappears at 10° emergence angle indicating that integration of argon occurs mainly within the sp2 bonded regions. The NRA and ERDA analysis show that the amount of integrated hydrogen decreases with increasing substrate current density. RBS data indicate that increasing bias enhances argon integration. INTRODUCTION In the plasma deposition process where a negatively biased substrate is immersed in a carbonrich plasma, the nucleation and growth are controlled by the flux and energy of the incoming species (charged and neutral). The results of the competition between integration of the incoming species and sputtering erosion depends on the precursor gas, ion energy and dose rate. Addition of argon to a carbon rich precursor such as acetylene is known to reduce the growth rate but momentum transfer being a forward-peaking process, argon bombardment may lead to a densification of the film and stress generation. Stress may in turn lead to transformation of sp2 sites to sp3 sites. Despite considerable experimental study over the last decade [1-6 and ref. therein] the effects of energy
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