Spectroscopic Ellipsometry Applications in Advanced Lithography Research

Abstract

Spectroscopic ellipsometry (SE) is an optical metrology technique widely used in the semiconductor industry. For lithography applications SE is routinely used for measurement of film thickness and refractive index of polymer photoresist and antireflective coatings. While this remains a primary use of SE, applications are now expanding into other areas of advanced lithography research. New applications include immersion lithography, phase‐shift photomasks, transparent pellicles, 193 and 157 nm lithography, stepper optical coatings, imprint lithography, and even real‐time monitoring of etch development rate in liquid ambients. Of recent interest are studies of immersion fluids where knowledge of the fluid refractive index and absorption are critical to their use in immersion lithography. Phase‐shift photomasks are also of interest as the thickness and index of the phase‐shift and absorber layers must be critically controlled for accurate intensity and phase transmission. Thin transparent pellicles to protect these masks must be also characterized for thickness and refractive index. Infrared ellipsometry is sensitive to chemical composition, film thickness, and how film chemistry changes with processing. Real‐time monitoring of polymer film thickness during etching in a liquid developer allows etch rate and endpoint determination with monolayer sensitivity. This work considers these emerging applications to survey the current status of spectroscopic ellipsometry as a characterization technique in advanced lithography applications.