Infrared dielectric properties of low-stress silicon nitride
  Silicon nitride thin films play an important role in the realization of sensors, filters, and high-performance circuits. Estimates of the dielectric function in the far- and mid-infrared regime are derived from the observed transmittance spectra for a commonly employed low-stress silicon nitride formulation. The experimental, modeling, and numerical methods used to extract the dielectric parameters with an accuracy of approximately 4% are presented. 
Giuseppe Cataldo, James A. Beall, Hsiao-Mei Cho, Brendan McAndrew,   Michael D. Niemack, and Edward J. Wollack
astro-ph.IM cond-mat.mtrl-sci physics.optics