Hydrogen Incorporation in MPCVD Nanocrystalline Diamond Films During the Deposition Process
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1203-J17-33
Hydrogen Incorporation in MPCVD Nanocrystalline Diamond During the Deposition Process Dominique Ballutaud1, Marie-Amandine Pinault1, François Jomard1, Alain Lusson1 et Samuel Saada2 1 CNRS-GEMaC, 1 place Aristide Briand 92195 Meudon cedex, France 2 CEA, LIST, Diamond Sensor Laboratory, 91191 Gif-sur-Yvette, France
ABSTRACT Hydrogen incorporation is studied in two Microwave Plasma CVD nanocrystalline diamond films deposited with prolongated bias or not during the growth step. The hydrogen content and bonding forms are analysed by Secondary Ion Mass Spectrometry, Raman and Fourier Transformer Infrared Spectroscopy. Our results show a high hydrogen concentration up to 3.1021 cm-1, as expected in nanocrystalline diamond, and in good agreement with the sp2 phase rate measured by Raman spectroscopy . The FTIR spectra exhibit two sharp peaks at 2850 and 2920 cm-1 and show that a fraction of hydrogen is bonded to sp3 CH2 groups. Hydrogen desorption experiments are performed to analyse the local structure modification of the diamond films.
INTRODUCTION High intrinsic hydrogen concentrations - up to 1021 cm−3 for nanocrystalline diamond (NCD) - are found in diamond grown by microwave plasma chemical vapour deposition (MP CVD)[1]. The presence of disordered hydrogenated sp2 carbon in grain boundaries, a high density of dislocations which may trap hydrogen, together with the presence of H2* dimers, are supposed to explain this high hydrogen concentration [2–4]. Bulk hydrogen is stable in crystalline diamond up to 950 °C [5]. The NCD films structure and the related properties depend on the growth conditions, on the grain size but also the crystalline quality of the diamond phase [6]. In this work, we study the effects of a prolongated bias applied during the growth step on the hydrogen concentration and bonding forms in the diamond films. Hydrogen concentration is measured by secondary ion mass spectrometry (SIMS) and the local structure of the diamond films is analysed par Raman and Fourier Transformed Infra-red Spectroscopy (FTIR). Out-diffusion of bulk hydrogen is performed by thermal annealing under ultra-high vacuum and the local structure modifications are analysed. EXPERIMENTAL The MPCVD reactor used for the NCD film deposition was described previously [7]. Two different deposition processes were used : the sample A was grown with a methane concentration of 10%, with a bias enhanced nucleation; the sample B was grown with the same
methane concentration and same parameters, but with a bias voltage of –307 V applied during all the growth step and a biasing current of 58 mA. Figure 1 show the SEM micrographs of the sample [7]. For sample A, the size of the grain is about 9 nm. Sample B exhibits a different particular morphology with clustering of the nanograins at the top of the film. The films have the same thickness of 200 nm. The hydrogen concentration profiles were analysed with a CAMECA IMS 4f secondary ion mass spectrometer with Cs+ primary ion beam. Quantifications of hydrogen were achieved by using C
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