Nitride (SiNx) insulators have been deposited by low temperature (20°C) electron cyclotron resonance (ECR) plasma on Si substrates. Characterization by Fourier transform infra-red (FTIR) spectrometry analyses reveal the presence of Si-N, Si-H and N-H bonds in the silicon nitride films. The refractive indexes between 1.77 and 2.9 and the thickness between 300 nm and 460 nm were measured by ellipsometry. With these thickness values, the deposition rates of 13 to 16 nm/min, the BHF etch rates of 0.7 to 454 nm/min, and the KOH etch rates lower than 1 nm/min were determined. The nitrides, which presented high resistance to BHF and KOH etchings, were used to fabricate suspended membranes on Si substrates. Scanning Electron Microscopy (SEM) inspections were used to investigate the SiNx resistance to KOH etchings. The results indicated that formed SiNx films are suitable membranes for micro-electro-mechanical systems (MEMS).3 119124Diniz, J.A., Doi, I., Swart, J.W., (2003) Mater. Charact., 50 (2-3), p. 135Moshkalyov, S.A., Diniz, J.A., Swart, J.W., Tatsch, P.J., Machida, M., (1997) J. Vac. Sci. Technol., B15, p. 2682Madou, M.M., (2002) "Fundamentals of Microfabrication - The Science of Miniaturization", Second Edition, , CRC PressNeli, R.R., (2001), Master Thesis, FEEC/UNICAMP