Modeling of optical constants of materials comprising photolithographic masks in the VUV

The optical properties of materials comprising photolithographic masks are investigated at wavelengths covering the vacuum-ultra-violet (VUV) to the near-infra-red (NIR). Broadband reflectance (R) and transmittance (T) spectra from 130 to 1000-nm are obtained from a variety of single layer absorber and bi-layer absorber/anti-reflection coating (ARC) samples deposited on MgF2 and CaF2 substrates. These experimental data are analyzed using the Forouhi-Bloomer (F-B) dispersion equations, in conjunction with a least squares fitting algorithm, to infer the thickness and n and k spectra of the materials under investigation. Once determined, the optical properties of the component materials are used to calculate the optical density of the single layer absorbers at 157-nm. These preliminary calculations are performed to investigate the feasibility of extending the use of traditional mask materials to wavelengths below 193-nm. In addition, theoretical swing-curve and standing wave functions are predicted for a mask structure based on the CrOxNy/Cr material system.