Determination of PMMA etch rates using VASE modeling

Variable angle spectroscopic ellipsometry (VASE) was used to determine the thicknesses of polymethyl methacrylate (PMMA) on Si before and after etching with two different etchants (CF₄ + O₂ and Argon). Once a complete optical model for a base PMMA on Si sample was created, it was applied to all etched samples to determine thicknesses. Despite some minor changes to the optical behavior of PMMA caused by the Ar etching, our ability to fit to observed interference peaks remained unaffected. This technique allows for nanometer accurate thickness measurements, which is an improvement from current thickness measurement methods such as stylus profilometry.