Challenges in the inline characterization of conductive thin films

Although many ITO and other TCO coating processes are well established, increasing coating process speed, higher deposition rates and lower coating temperatures highly affect the layer uniformity, stoichiometry of the layer and crystallinity. All these parameters have a high impact on the conductivity and optical transparency of the layer – the two main properties of TCO films. Novel inline measurement technology is required to adapt to these challenges and to assure accurate and reliable measurements of the electrical and optical properties even at high production speed. Therefore, non-contact sensors have been developed for monitoring sheet resistances between 0.001 and 1000 Ohm/sq. Especially the stable measurement of high ohmic samples is challenging and requires specific adaption of the sensor concept. Examples of challenging inline measurements and non-destructive offline coating analysis are presented and discussed. A special focus is directed on the analysis, discussion and resolution of edge effect phenomena and other artifacts of the measurement.