In this work we study the structural properties and mechanical stress of silicon oxynitride (SiOxNy) 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 SiOxNy with very low mechanical stress, a necessary condition for the fabrication of mechanically stable thick films (up to ∼ 10 μm). Since this material (SiOxNy) 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 SiOxNy films deposition with the standard silicon based microelectronic processing technology makes this material promising for micro electro mechanical system (MEMS) fabrication. © 2002 Elsevier Science B.V. All rights reserved.