Profiles of a high-aspect-ratio grating determined by spectroscopic scatterometry and atomic-force microscopy

The new and fast scatterometry method called optical diffraction microscopy is compared with atomic-force microscopy by use of cross-section scanning-electron microscope images as references. The sample is a high-aspect-ratio grating with a period of approximately 1000 nm. To allow the atomic-force microscope to track all parts of the grating profile, the grating is investigated at different tilt angles. The measured quantities of the profile include sidewall angle gamma (approximately 90 degrees), groove height h (approximately 2000 nm), and degree of filling f (approximately 40%). The two methods, which respond to quite different material properties, give consistent results within standard uncertainties of u(gamma)</=0.8 degrees , u(h)</=15 nm, and u(f)</=1%.