STRUCTURE OF THE INTERFACIAL REGION BETWEEN POLYCARBONATE AND PLASMA-DEPOSITED SIN1.3 AND SIO2 OPTICAL COATINGS STUDIED BY ELLIPSOMETRY

Fabrication of optical films on plastic substrates presents a consider able challenge due to the necessity of controlling adhesion and the op tical properties of the interface. In the present work, the surface of polycarbonate (PC) substrates was pretreated in a microwave plasma in N-2 and He gases, and amorphous hydrogenated silicon nitride (SiN1.3) and dioxide (SiO2) films were deposited in a dual-mode microwave/radi ofrequency plasma. Using ex Situ variable angle spectroscopic ellipsom etry (VASE), spectrophotometry, and x-ray photoelectron spectroscopy, it was found that the plasma-treated PC contains a crosslinked surface layer which can extend to a depth of more than 50 nm, and which prese nts a refractive index increase of about 1%-2%. When PC is plasma trea ted and coated with SiN1.3 or SiO2, the interfacial region (interphase ) is structured: it comprises the crosslinked layer, and a less dense transition region between the polymer and the film. The interphase may extend up to 100 nm. Some of the results suggest that the plasma pret reatment stabilizes the surface, leading to a lower thickness of the i nterphase. The accuracy of ex situ VASE analysis is discussed and the importance of the interface structure on the design and mechanical pro perties of optical systems on plastic substrates is emphasized. (C) 19 98 American Vacuum Society. [S0734-2101(98)03306-5].