OPTICAL AND COMPOSITIONAL STUDY OF SILICON-OXIDE THIN-FILMS DEPOSITEDIN A DUAL-MODE (MICROWAVE RADIOFREQUENCY) PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION REACTOR/

This study is focused on the deposition and growth of amorphous silico n oxide optical thin films in a dual-mode (microwave/rf) reactor. The optical, chemical, and structural properties of a-SiOx:K films have be en studied as a function of different parameters (substrate temperatur e, microwave power, gas flow, dilution, addition of rf plasma) by in s itu UV-visible and in situ infrared (IR) ellipsometry, Fourier transfo rm IR transmission spectroscopy, nuclear analysis, and VUV absorption spectroscopy. We have shown that it is possible to increase the densit y of the films and decrease their hydrogen content by depositing at hi gher temperature (T greater than or equal to 200 degrees C) and/or usi ng a helium dilution and/or using the ion bombardment effect of the rf plasma. In situ IR ellipsometry has revealed water absorption on the as-deposited silicon oxide films, just after exposing them to the ambi ent atmosphere. The lower is the him density and the higher is the wat er absorption. UV absorption spectroscopy has evidenced an absorption peak at 6.3 eV, with an amplitude dependent on the hydrogen content. S ince the films are interesting for optical multilayers, we have also s tudied the effect of UV irradiation, showing the decrease of O-H group s (reduction of the hydrogen content) and a reoxydation of the silicon oxide films. The thermal stability studies reveal an effusion of H-2 and H2O molecules for temperatures above 300 degrees C. (C) 1998 Ameri can Institute of Physics.