Real-time monitoring by multiwavelength ellipsometry of the growth of silicon alloy multilayers and gradient index structures

Real time monitoring and control, by multiwavelength phase modulated ellipsometry of the growth of plasma deposited optical structures is presented. The transparent layers consists of SiO2 SiNx and oxynitrides. We present an efficient method for the estimation of the optical parameters based on a sliding window containing the last acquired measurements. This method is used to monitor the deposition of multilayer coatings with homogenous deposition conditions, and is also used in feedback control of such coatings. The sliding window method is further developed to follow slowly time-varying parameters such as the deposition rate. A preliminary study of a fast novel method based on the same principle for real time monitoring of refractive index gradients is described. As an example, the real time monitoring of the growth of a linear gradient index is demonstrated.