INFLUENCE OF THERMAL ANNEALING ON THE ULTRAVIOLET STABILITY OF A-SIC-H THIN-FILMS DEPOSITED FROM LIQUID ORGANOSILANES

The photoluminescence (PL) of a-SiC:H thin films, deposited in a plasm a enhanced chemical vapor deposition process from liquid organosilane sources degrades under ultraviolet (UV) exposure (325 nm). UV illumina tion reduces the PL intensity of as-grown films usually to one-half of the initial intensity. The W-induced decay of the PL follows a stretc hed exponential time dependence. Annealing of the films at about 400 d egrees C in nitrogen atmosphere increases both the UV stable and the u nstable part of the FL, by a factor 1.5 to 3 dependent on the starting material. We have investigated the annealing behaviour for different starting materials. Best results with respect to reproducible UV-stabl e PL are obtained for hexamethyldisilazane. Infrared absorption spectr a indicate that the UV exposure is accompanied by photo-oxidation, whi le annealing in inert gas atmosphere results in a decrease of hydrogen -related vibrations. We discuss the structural changes in the a-SiC:H thin films caused by UV illumination and by thermal annealing on the b asis of the spectroscopic investigations. (C) 1998 Elsevier Science B. V. All rights reserved.