Scatterometry measurement of sub-0.1 μm linewidth gratings

Abstract

The effort discussed here addresses the use of shorter incident wavelengths for characterizing sub-0.1 μm linewidths and the corresponding influence on scatterometry measurement sensitivity to linewidth variations. A sensitivity metric, based on the variance statistic, was developed using well-characterized, large-pitch (0.80 μm) photoresist grating structures on Si illuminated at 633 and 442 nm. The same metric was applied to short-pitch (0.20 μm), etched gratings on InP, with the result that appreciable scatterometry sensitivity was measured, even at the 633 nm incident wavelength. Modeling was used to estimate scatterometry sensitivity at three wavelengths for photoresist critical dimensions of 100 and 70 nm on Si. A significant increase in sensitivity was not found until the incident wavelength was reduced to 325 nm. We are presently investigating techniques to improve measurement sensitivity for short-pitch structures using the 633 nm incident wavelength.