A study of texture in diamond films as functions of methane concentration during chemical vapor deposition and post-grow
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We have studied effects of hydrogen on texture in diamond films grown by hot filament assisted chemical vapor deposition by utilizing x-ray diffraction (XRD). We present results for the relative intensities of the XRD peaks originating from the (111), (220), and (400) crystallographic planes as functions of CH 4 /H 2 makeup during growth and post-growth H2 treatment of the films. The texture of the films can be controlled by varying composition of the CH 4 /H 2 mixture during growth and also by subjecting films to hydrogen treatment. The complementary characterization of these films by XRD, Raman spectroscopy, and positron annihilation techniques exemplifies a correlation among film texture, diamond content, and density of the microvoids in the films.
I. INTRODUCTION Low-pressure chemical vapor deposition, using hydrocarbon/hydrogen mixtures, is known to produce diamond films with exceptional properties.1'2 Hence, there continues to be an increasing interest in understanding how the growth and properties of diamond films can be controlled. The low-pressure deposition and properties of such films have been reviewed recently in several articles.3'4 A significant progress has already been made in understanding the growth of polycrystalline and homoepitaxial single-crystal diamond films. Recent studies have also examined means to obtain highly textured diamond films.5"12 We describe briefly relevant features from selected investigations. Geis5 developed a technique in which fine diamond seed crystals were attached to a substrate such that most seeds had {111} texture. Additional growth resulted in (111) textured polycrystalline diamond films.5 For films grown by microwave plasma CVD, Kobashi et al.6 observed morphological modifications upon changes in the makeup of the CH 4 /H 2 mixture and film thickness. They also observed an increase in the degree of the (110) orientation between deposition times of 7 and 21 h. However, these authors had some difficulty in evaluating intensity ratios from their XRD data because of abnormally broad tails in the (111) diffraction bands. A study by Wild et al. focused on an examination of texture in relatively thick (~15 to 175 /mm) films.7 These authors observed a pronounced 110 fiber texture; the crystals formed at the beginning of the film growth were randomly oriented and a preferential orientation of the {110} planes developed with 1764 http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 7, Jul 1995 Downloaded: 20 Mar 2015
increasing thickness of the film. Sprang et al. utilized pulsed supersonic beams as gas inlet into a hot-filament reactor to control the texture of the films.8 Baik and Eun9 have presented results showing that the texture formation in diamond films follows the van der Drift evolutionary selection rule 10 ; texture is formed by competition between growing grains in the direction perpendicular to the substrate plane; the higher the growth rate is in that direction, the higher the probability of survival of that grain. Stoner et al. have grown oriented di
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