A sequential Raman analysis of the growth of diamond films on silicon substrates in a microwave plasma assisted chemical
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A sequential Raman analysis of the growth of diamond films on silicon substrates in a microwave plasma assisted chemical vapor deposition reactor L. Fayette, B. Marcus, M. Mermoux, N. Rosman, L. Abello, and G. Lucazeau Laboratoire d’Electrochimie et de Physicochimie des Mat´eriaux et Interfaces (UMR 5631 INPG-CNRS, associ´e a` l’UJF), Domaine universitaire, BP 75.38402 Saint Martin D’Heres Cedex, France (Received 1 December 1996; accepted 21 April 1997)
A sequential analysis of the growth of diamond films on silicon substrates in a microwave plasma assisted chemical vapor deposition (CVD) reactor has been performed by Raman spectroscopy. The plasma was switched off during measurements, but the substrate heating was maintained to minimize thermoelastic stresses. The detectivity of the present experimental setup has been estimated to be about a few tens of mgycm2 . From such a technique, one expects to analyze different aspects of diamond growth on a non-diamond substrate. The evolution of the signals arising from the substrate shows that the scratching treatment used to increase the nucleation density induces an amorphization of the silicon surface. This surface is annealed during the first step of deposition. The evolution of the line shape of the spectra indicates that the non-diamond phases are mainly located in the grain boundaries. The variation of the integrated intensity of the Raman signals has been interpreted using a simple absorption model. A special emphasis was given to the evolution of internal stresses during deposition. It was verified that compressive stresses were generated when coalescence of crystals took place.
I. INTRODUCTION
As the applications of diamond films become more demanding, real time monitoring of the deposition process becomes increasingly important. In this regard, in situ techniques such as elastic scattering of light and reflectivity1 and spectroscopic ellipsometry2 have been developed, allowing different aspects of the growth process to be monitored in real time. Numerous analytic techniques have been used to study chemical vapor deposition (CVD) diamond films, and Raman spectroscopy has proven to be particularly valuable since it can distinguish among different forms of carbon, including diamond, diamond-like carbon, graphite, and disordered graphite.3–8 Furthermore, stress in the film is revealed by a shift of the diamond phonon frequency,9,10 and the film temperature can be assessed from the Raman shift or the ratio of the intensities of the Stokes and anti-Stokes lines.11,12 Up to now, most Raman studies were done at room temperature in an ex situ configuration, performed in general under a microscope to probe individual domains of the film. Nevertheless, many studies have shown that the Raman signature of diamond films may change with its thickness or the size of the probed area. These changes concern both the line shape and the position of the diamond line. This means that the incorporation of the non-diamond phases, the diam
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