REAL-TIME CONTROL OF THE GROWTH OF SILICON ALLOY MULTILAYERS BY MULTIWAVELENGTH ELLIPSOMETRY

Real time control, by multiwavelenglh phase modulated ellipsometry (PM E), of the growth of plasma deposited optical structures is presented here. The transparent multilayers consist of SiO2 and SiNx alloys. Var ious on-line methods are compared. The best results are obtained with a feedback method based on comparison between the real time PME measur ements and pre-computed target trajectories. It can provide the high p recision required to deposit high performance optical coatings. In par ticular, an overall accuracy better than 1% is obtained on a 15-layer quaterwave filter, designed at 670 nm. This real time procedure, which is not limited to transparent materials or plasma processes, appears a useful tool for process control.