Mechanical properties of PECVD silicon oxide films suitable for integrated optics applications

Silicon oxide films are deposited on silicon wafers by PECVD from SiH4 and N2O at different values of the deposition parameters. The refractive index is found to vary with gas flow ratio (R), making these films suitable for a silicon-based integrated optics technology. The films are submitted to annealing processes on inert atmosphere in order to facilitate the impurity effusion, thus reducing the light transmission losses. However, relying upon deposition conditions, this process significantly changes the film stress and often affects the film integrity. In this work a study of the evolution of mechanical stress under different annealing conditions is carried out for silicon oxide PECVD- films. All as-deposited samples exhibit compressive stress. During thermal cycles up to 300 degree(s)C a different behavior of the mechanical stress is obtained depending on the deposition parameters. For R at about 20 a significant stress hysteresis is observed at low deposition temperatures. For R at about 5 no hysteresis is observed at any deposition temperature. After a subsequent RTA a drastic and opposite variation of the stress is observed for the two kind of films and a very stable material from the mechanical point of view, is obtained. An insight into the physical causes of these behaviors is presented.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.