Reactive sputter deposition of indium tin oxide films onto polymeric webs using optical emission spectroscopy and mass spectroscopy as process monitoring and control

Abstract

Reactive sputter deposition of indium tin oxide (ITO) from an alloy target is an extremely sensitive process. The quality of the deposited ITO films is dependent upon the ability to maintain a certain partial pressure of oxygen in the sputter zone during the deposition process. Minor instabilities within the glow discharge plasma caused by contaminants outgassing from the substrate, low pump throughput, target poisoning 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. These instabilities can lead to an uncontrollable transition between the metallic and fully reactive modes of the target that can force the process away from the desirable operating point. It has been shown previously that a plasma emission controlled circuit can be implemented to help with the control of the deposition of oxide films in this transition region. In this work we have configured a plasma emission monitor (PEM) with a residual gas analyzer (RGA) into a closed loop feedback circuit for the deposition of ITO onto moving flexible substrates. It was found that the stabilization of the operating point was achieved by controlling the admission of the reactive gas into the process zone using the chosen emission line of interest as the input signal. Furthermore, the operating point was determined without the continuous calibration of the PEM by choosing the RGA baseline as the normalizing signal. The result of these experiments are discussed and compared to the traditional method of producing an ITO coating using a constant pressure control process.