Real time control of the deposition of optical coatings by multiwavelength ellipsometry

Abstract

We review applications of fast feedback methods using multiwavelength ellipsometry to control growth of optical coatings. The growth control of multi-layer structures deposited by PECVD has been demonstrated both on absorbing substrates and on thick transparent substrates. The latter is achieved by using an incoherent reflection model and further incorporating it into the precalculation of target trajectories used by the control algorithm. In general, an accuracy better than 1% was easily obtained on both structures without any advanced fine tuning of process conditions and with the requirement of only rough information about the deposition rate of each layer.
The results of feedback methods given in this review demonstrate the application of ellipsometry as a powerful tool for real time control of complex optical coatings.