REACTIVE SPUTTER-DEPOSITION OF INDIUM TIN OXIDE-FILMS ONTO POLYMERIC WEBS USING OPTICAL-EMISSION SPECTROSCOPY AND MASS-SPECTROSCOPY AS PROCESS MONITORING AND CONTROL

Reactive sputter deposition of indium tin oxide (ITO) from an alloy ta rget is an extremely sensitive process. The quality of the deposited I TO films is dependent upon the ability to maintain a certain partial p ressure of oxygen in the sputter zone during the deposition process. M inor instabilities within the glow discharge plasma caused by contamin ants outgassing from the substrate, low pump throughput, target poison ing due to the buildup of insulating layers on the target surface, or target arcing, can result in significant changes in the stoichiometry of the deposited layer, thus producing an inferior conducting film. Th ese instabilities can lead to an uncontrollable transition between the metallic and fully reactive modes of the target that can force the pr ocess away from the desirable operating point. It has been shown previ ously that a plasma emission controlled circuit can be implemented to help with the control of the deposition of oxide films in this transit ion region. In this work we have configured a plasma emission monitor (PEM) with a residual gas analyzer (RGA) into a closed loop feedback c ircuit for the deposition of ITO onto moving flexible substrates. It w as found that the stabilization of the operating point was achieved by controlling the admission of the reactive gas into the process zone u sing the chosen emission line of interest as the input signal. Further more, the operating point was determined without the continuous calibr ation of the PEM by choosing the RGA baseline as the normalizing signa l. The result of these experiments are discussed and compared to the t raditional method of producing an ITO coating using a constant pressur e control process. (C) 1997 Elsevier Science S.A.