Materials Characterization in the Vacuum Ultraviolet with Variable Angle Spectroscopic Ellipsometry

The shift towards shorter wavelengths in the lithographic process has been the driving force for development of a commercial spectroscopic ellipsometer covering the vacuum ultraviolet (VUV) spectrum. Understanding the optical properties of thin films and substrate materials at short wavelengths (193 nm, 157 nm, and shorter) is necessary to develop the lithographic process. Lithography applications include optical coatings, photoresists, AR films, and masks. We present results for both single and multi-layer structures important to this industry. A complete description of the thin film optical properties can be used to track process changes or variations in sample structure. As an example, we compare the measured index for three oxynitrides that were subjected to different process conditions. In addition to lithography applications, VUV ellipsometry has many other potential applications. A variety of other materials have been characterized, often incorporating generalized ellipsometry to investigate anisotropic optical properties. The ordinary and extraordinary dielectric functions for bulk 4H SiC were measured over the wide spectral range from 0.73 to 8.5 eV.