PECVD-SiOxNy films for large area self-sustained grids applications

In this work we study the structural properties and mechanical stress of silicon oxynitride (SiO_xN_y) films obtained by plasma enhanced chemical vapor deposition (PECVD) technique at low temperatures (320 °C) and report the feasibility of using this material for the fabrication of large area self-sustained grids. The films were obtained at different deposition conditions, varying the gas flow ratio between the precursor gases (N₂O and SiH₄) and maintaining all the other deposition parameters constant. The films were characterized by ellipsometry, by Fourier transform infrared (FT-IR) spectroscopy and by optically levered laser technique to measure the total mechanical stress. The results demonstrate that for appropriated deposition conditions, it is possible to obtain SiO_xN_y with very low mechanical stress, a necessary condition for the fabrication of mechanically stable thick films (up to 10 μm). Since this material (SiO_xN_y) is very resistant to KOH wet chemical etching it can be utilized to fabricate, by silicon substrate bulk micromachining, very large self-sustained grids and membranes, with areas up to 1 cm² and with thickness in the 2–6 μm range. These results allied with the compatibility of the PECVD SiO_xN_y films deposition with the standard silicon based microelectronic processing technology makes this material promising for micro electro mechanical system (MEMS) fabrication.