Nanometer gap measurement and verification via the chirped-Talbot effect

Abstract

Electron beam and optical proximity effect reduction for nanolithography: New results J.We describe a noncontact, optical method of measuring, with nanometer-level sensitivity, the gap between two planar objects in close proximity, such as a substrate and either a proximity-lithography mask or an imprint template. Interference fringes from a chirped-checkerboard mark on one object are observed using a nonexposing wavelength with long-working-distance, oblique-incidence microscopes. The gap is determined from the spatial frequency and phase of the fringes. We verify the gap measurement using a variation of the Talbot effect with the chirped-checkerboard mark. The two forms of gap measurement are complementary since one is suited to measuring and setting gap prior to exposure, and the other is ideal for confirmation of the gap that existed during exposure.

Dynamic alignment control for fluid-immersion lithographies using interferometric-spatial-phase imaging

“…3,4 ACKNOWLEDGMENTS Many thanks to Molecular Imprints, Inc. for their sponsorship, and to Jim Dailey for his invaluable assistance. FIG.…”

High-resolution proximity lithography for nano-optical components

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Nanometer-precision pattern registration for scanning-probe lithographies using interferometric-spatial-phase imaging

“…Previous articles 8,9 described an interferometric gap detection method, called transverse chirp gapping ͑TCG͒, in which fringes produced by interference from chirped-period checkerboard marks are viewed by the oblique-incidence ISPI microscopes, in the same field of view as the ISPI alignment marks, and provide subnanometer gap detectivity. TCG marks are designed to operate in a range from contact up to 50 m. In the present application, a new type of gapsensitive mark is required for use with gaps Ͼ50 m. The design of this long-range interferometric gap ͑LRIG͒ detec-a͒ Electronic mail: euclid@nano.mit.edu tion mark employs gratings with similar periods, p 1 and p 2 , akin to the ISPI alignment mark design; the primary difference lies in the arrangement of the gratings.…”