Incorporation of Hydrogen and Oxygen into (t)a-C:H Thin Films Deposited using DECR plasma
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Incorporation of hydrogen and oxygen into (t)a-C:H thin films deposited using DECR plasma (*) Fabrice Piazza1, Dieter Grambole2, Folker Herrmann2, Gary Relihan3, Marie France Barthe4, Pierre Desgardin4 and André Golanski1 1
Centre National de la Recherche Scientifique (CNRS), Laboratoire PHASE, BP20, F-67037 Strasbourg, France 2 Forschungszentrum Rossendorf e.V., Institut für Ionenstrahlphysik und Materialforschung Postfach 51 01 19, 01314 Dresden, Germany 3 National Microelectronics Research Centre (NMRC), University College, Lee Maltings, Prospect Row, Cork, Ireland 4 Centre National de la Recherche Scientifique (CNRS), Laboratoire CERI, 3 A rue de la Férollerie, F-45071 Orléans, France ABSTRACT A distributed electron cyclotron resonance (DECR) plasma reactor powered by a microwave generator operating at 2.45 GHz (800 W) was used to deposit (t)a-C:H thin films at RT on Si substrates RF biased within the range 25≤|V0|≤600 V. C2H2 was used as precursor. The plasma pressure was varied within the range 0.1≤P≤1.5 mtorr. The films were analysed using spectroscopic ellipsometry (SE) and Fourier transform infrared (FTIR) spectroscopy. The hydrogen content NH and the density of the films were determined from nuclear reaction analysis (NRA) using the resonance at 6.385 MeV of the reaction: 15N + 1H → 12C + 4He + γ. Positron annihilation spectroscopy was used to detect the porosity. The evolutions of NH as a function of the substrate ion current density n+ and as a function of V0 show that the hydrogen incorporation results from the competition between chemisorption and deposited energy density related effects. The increase of the hydrogen incorporation leads to a decrease in the film density and a lower deposition rate. The porosity of the films deposited at low pressure (∼0.1 mTorr) with V0= −80 V has been detected. The comparison between results of SRIM-2000 simulations and the evolution of NH as a function of V0 shows that the porosity and the hydrogen content are not correlated. The absorption of oxygen and nitrogen for the low density films has been detected from the observation of the 3250-4000 cm-1 infrared (IR) band.
INTRODUCTION Hydrogen is known to be a fundamental constituent of the plasma deposited amorphous hydrogenated carbon (t)a-C:H films. The hydrogen content NH is usually close to 35 % and can reach ∼62 % [1]. Studies have shown that NH decreases when V0 increases [2]. Although the hydrogen incorporation mechanisms have been extensively studied, there are not fully understood. The goal of the present work is to shed more light on those mechanisms. The film structure and some of the physical properties such as the film hardness and the density are known to depend closely on the hydrogen content [3] and on the nature of the C-H bonds [4]. Little is known about the film porosity. In this study, the correlation between the film density, the deposition rate, the hydrogen content and the porosity is studied.
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EXPERIMENTAL DETAILS The (t)a-C:H films were grown at RT on Si substrates using a DECR plasm
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