Ellipsometry as a sensor technology for the control of deposition processes

Ellipsometry is an indirect sensor used to characterize the optical properties of thin films. Previous research in the control of deposition processes using ellipsometry, however, has explicitly ignored the dynamics introduced by the sensor. This is because the dynamics of ellipsometry have not been widely available in a form useful for control, and because these dynamics turn out to be significantly more difficult to manage than those of the actual deposition processes. Thus, the typical approach to control has been to restrict oneself to problems where the ellipsometer dynamics are easily inverted and negligible for controller design. This study presents work on explicitly accounting for the dynamics of ellipsometry and their implications for control. In particular, a control oriented model is developed in contrast with alternatives from the literature. Formulations for the relevant control problems are then presented and discussed in light of these dynamics.