In-situ monitoring of optical coatings on architectural glass and comparison of the accuracy of the layer thicknesses attainable with ellipsometry and photometry

For the deposition of optical coatings on architectural glass, spectroscopic ellipsometry and spectral photometry have been applied. For the purpose of achieving a high competitiveness of manufacturing plants, high deposition rates as well as low scrap quanitities are important. The first can be obtained by using the mid-frequency (MF) sputtering technique developed in the beginning of the nineties for the deposition of highly isolating materials. The latter can be improved by using an effective plasma control and a monitor of the optical film properties. In order to obtain constant layer properties, not only the MF but also the directcurrent (DC) sputter process has to be stabilized within a relatively narrow process window, which necessitates a suitable plasma control as well as optical monitoring. Spectroscopic ellipsometry as well as spectral photometry are used for monitoring the optical properties of SnO2-based low-e-coatings on architectural glass. It is estimated that spectroscopic ellipsometry is distinctly more sensitive for monitoring the thicknesses of low-e coatings than spectral photometry.