In-situ control of chemical vapor deposition for fiber coating

Chemical vapor deposition (CVD) is a widely used process for the application of thin films. In this case, CVD is being used to apply a thin-film interface coating (LaAl11O18) to single-crystal.. monofilament sapphire fibers for the production of ceramic matrix composites. Traditionally, CVD fiber coating has been hampered by problems such as poor coating uniformity, thickness, and chemistry control. To attempt to rectify these problems, a fully-instrumented CVD processing apparatus has been constructed. In addition to more standard sensors such as thermocouples, pressure transducers, and how meters, sensors capable of monitoring the coating and gas phase properties of interest have been used. Specifically, a quadrupole mass spectrometer and Raman spectrometer are being used to monitor both the gas phase reactants and the coating quality. A fuzzy-logic controller has been developed to control the O-2 flow rate, based on in situ temperature measurements. Mass spectrometer data and corresponding improved temperature control for a deposition are presented. Raman spectra which were taken off-line are also presented. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.