IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Thin Films Tuesday Sessions
       Session TF-TuP

Paper TF-TuP15
Inhomogeneous Optical Thin Films and Filters Based on SiN@sub x@:H Prepared by PECVD in Dual-mode Microwave/Radiofrequency Plasma

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Microstructure, Oxides, and Optical Properties Poster Session
Presenter: R. Vernhes, Ecole Polytechnique of Montreal, Canada
Authors: R. Vernhes, Ecole Polytechnique of Montreal, Canada
O. Zabeida, Ecole Polytechnique of Montreal, Canada
J.E. Klemberg-Sapieha, Ecole Polytechnique of Montreal, Canada
L. Martinu, Ecole Polytechnique of Montreal, Canada
Correspondent: Click to Email
Deposition of inhomogeneous thin films for optical applications offers great advantages in comparison to traditional multilayer structures. Particularly, optical losses and mechanical stresses due to interfaces are considerably reduced, as well as harmonics and side lobes are eliminated from transmission or reflection spectra. In the present work, we used plasma-enhanced chemical vapor deposition (PECVD) to grow amorphous hydrogenated silicon nitride (SiN@sub x@:H) films on glass and silicon substrates using silane and nitrogen. Control of the refractive index was performed by selectively varying the power of microwave and radiofrequency sources without any change in gas composition. In this way, the film properties are strictly controlled by the energetic interactions in the gas phase and at the exposed surface. The films were characterized by spectrophotometry, variable angle spectroscopic ellipsometry, Fourrier transform infrared spectroscopy, and elastic recoil detection in time-of-flight regime. We found that the radiofrequency mode permits one to obtain a higher refractive index, while the microwave mode leads to a lower refractive index. We demonstrated that this variation was related to a change in composition and density. Indeed, films deposited by radiofrequency mode contain larger quantities of Si-H groups and show a denser microstructure while films grown by microwave mode present a higher concentration of N-H groups with a porous microstructure. We proved that it is possible to pass continuously from one composition and structure to another by gradually adjusting the power of each source. This leads to a continuous variation of refractive index from 1.65 to 1.95. Using this refractive index interval, we demonstrate the fabrication of optical filters with an inhomogeneous refractive index depth profile. Optical and mechanical properties of such filters are discussed.