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Optimisation advanced optical coatings technologies competitive manufacturing


A Plasma Impedance Monitor (PIM) has been installed along the RF feed-through of a RF PE-CVD reactor, used for plasma deposition of anti-scratch coatings onto plastic optical components. At the beginning of this project, the process suffered from scarce reproducibility in terms of coating properties (hardness, clearness, wear-resistance). Depositions carried out under same recipe have been compared in terms of PIM signals, and a database created on hard disk. A strong correlation has been evidenced between major differences in coating properties and appreciable differences in PIM signals. RF power generator, gas flows controller and PIM have been interfaced via PC, with software written in LabView (registered). A closed-loop control system has been established acting on input power (or on gas flows, in principle) and making PIM signals match some reference values. Reference values are chosen to be PIM signals as recorded from deposition processes giving excellent coating properties. In general, it is not possible to match all PIM signals (voltage V, current I and phase PHI) to corresponding references at the same time, and different matching strategies are available (match I, match V, match PHI, match V?I?cos(PHI)). Automatic matching of PIM signals with reference values appears to be a relatively fast operation (just a few seconds) and perfectly compatible with the process duration (deposition is divided in different steps at constant process parameters; each step lasts several minutes).