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FTIR monitoring of industrial scale CVD processes


Haseth, J.A. de ; American Institute of Physics -AIP-, New York:
Fourier transform spectroscopy. Eleventh international conference
Woodbury, N.Y.: AIP, 1998 (AIP Conference Proceedings 430)
ISBN: 1-56396-746-4
International Conference on Fourier Transform Spectroscopy (ICOFTS) <11, 1997, Athens/Ga.>
Fraunhofer IWS ()
CVD; IR-Diagnostik; Optik; Spektroskopie

Chemical vapour deposition (CVD) as well as infiltration (CVI) processes are key technologies in many industrial sectors, including extensive use in micro electronics, surface protection of components, for energy efficient optical coatings on glass for buildings and for manufacturing fibre reinforced ceramic composite materials. Gaseous precursors containing the elements to be deposited are pyrolysed at the heated substrate or, alternatively, by exciting the molecules with laser photons or by a plasma. Although the techniques are used on a technological scale, the underlying chemistry is not completely understood. The goal of the presentation is to improve CVD process control by a multipurpose, knowledge based feedback system for monitoring the CVD/CVI process with in-situ FTIR spectroscopic data as input information. In the presentation, three commonly used, and distinctly different, types of industrial CVD/CVI processes are taken as test cases: (i) a thermal high capacity CVI batch p rocess for manufacturing carbon fibre reinforced SiC composites for high temperature applications, (ii) a continuously driven CVD thermal process for coating float glass for energy protection, and (iii) a laser stimulated CVD process for continuously coating bundles of thin ceramic fibres (i) The CVI process operates near 1000oC, in the low pressure region and with CH3SiCl3 (MTS) as a SiC precursor. Using FTIR emission spectroscopy, several gaseous species have been detected including MTS, SiCl2, (SiCl3)n=1,2, SiCl4, HSiCl3, CH4, CH3Cl and HCl which, consequently, can be monitored simultaneously. (ii) The CVD process operates at atmospheric pressure. A model reactor has been developed for studying the concentration dependence of FTIR emission spectra. The measured spectra are compared with calculated spectra which have been derived by optical modelling of a multilayer based optical model. (iii) Based on an industrial 6kW cw-CO2- laser, a laser driven process currently runs in a prototy pe coater. Layers of graphitisised carbon and several ceramic materials (SiC, TiCxNy, TiB2, BN, etc.) have been deposited on carbon fibres and on SiC fibres. Depending on the selected precursor, the chemistry of the laser driven CVD process is characterised by photothermal reaction paths, typically in the temperature region 1300oC -2500oC and photolytical paths. The FTIR measurements have been carried out by rapid extraction of the gaseous reaction products and measurements in an optimised volume gas cell. As an example, the deposition of SiC layers from MTS results in the detection of HCl, HSiCl3, H2SiCl2, SiCl2, CH4, CO and C2H2.