Ralf Sperling, Marcus Frank, Mario Berlinger, Bühler Alzenau GmbH, Leipzig, Germany
Closed-loop control represents a proven technical strategy for minimizing response time to fluctuations in process conditions and for maintaining stable production performance. In architectural, web, and automotive thin-film coating applications, automation solutions are continuously being developed to improve coater availability, product quality, and manufacturing yield.
Compared with conventional ex-situ measurements performed at the end of the coating line, in-situ measurements acquired near the respective deposition stations deliver feedback with a significant time advantage. This enables earlier identification of process deviations and more targeted process intervention. Furthermore, the approach supports the isolation and quantification of individual layer contributions within reverse-engineering fit-model calculations, thereby avoiding unnecessary readjustment of process parameters that are not the true root cause of the measured discrepancy.
In this contribution, a robust and modular broadband in-situ optical metrology system is presented for large-area coaters. The system measures spectra at up to five positions across a jumbo substrate using only one spectrometer and one light-source unit. Depending on the system configuration, transmission and reflectance spectra are acquired quasi-simultaneously over the wavelength range from 350 nm to 2500 nm. From these data sets, spectral absorption can be calculated, allowing the working point of reactive processes to be adjusted efficiently while the glass substrate is still in process inside of the coater.