AVS 46th International Symposium
    Manufacturing Science and Technology Group Wednesday Sessions
       Session MS-WeM

Paper MS-WeM4
Real Time Control of Plasma Deposited Optical Filters by Multiwavelength Ellipsometry

Wednesday, October 27, 1999, 9:20 am, Room 611

Session: Metrology I
Presenter: T. Heitz, CNRS-Ecole Polytechnique France
Authors: T. Heitz, CNRS-Ecole Polytechnique France
P. Bulkin, CNRS-Ecole Polytechnique France
A. Hofrichter, CNRS-Ecole Polytechnique France
F. Chataignere, CNRS-Ecole Polytechnique France
B. Drevillon, CNRS-Ecole Polytechnique France
Correspondent: Click to Email
Multilayer and gradient coatings allow the integration of advanced functionnalities. But due to their complexity, in-situ probes are necessary to control the process and obtain a good reproducibility. Our optical filters (Fabry-Perot, anti-reflective or heat-reflecting coatings) consist of SiO@sub x@N@sub y@ multilayers and/or graded index profile structures deposited at room temperature in an IDECR reactor on glass, PMMA or polycarbonate. Due to its thickness sensitivity, multiwavelength UV-visible phase-modulated ellipsometry was chosen to monitor the growth process. The control strategy is based on minimising the sum of the distances between the measured point and the theoretical end point of the optical trajectory at 4 wavelengths. This strategy is proved to be very efficient and independent of the deposition rate. As substrates are thick and transparent, the theoretical trajectories have been calculated using the incoherent reflection model which takes into account backreflection. Moreover, to model possible anisotropy effects, optical calculations have been developed based on a non-diagonal dielectric matrix for the susbtrate. In order to build a closed-loop automation system, efficient algorithms have been developed to determine in real time the optical properties and the current deposition rate. Using 4-wavelength optical data, 1 sec step acquisition and appropriated dispersion laws, the refractive index and the current thickness can be calculated which allows to correct in real time the gas flow values. The high quality of the filters deposited using the ellipsometric monitoring system is demonstrated by comparing experimental and theoretical transmission/reflection curves in terms of peak positions and bandwidth.