A Technique for Estimating the Pitch of Interference Fringe Patterns for Pattern Exposure in a Non-Orthogonal One-Axis Lloyd’s Mirror Interferometer

Abstract

A technique to realize in-situ evaluation of the pitch of interference fringe patterns in a non-orthogonal Lloyd’s mirror interferometer is proposed. The proposed method employs two laser sources with different wavelengths. Two magnified collimated laser beams with different wavelengths are then projected onto a non-orthogonal Lloyd’s mirror interferometer to generate interference fringe patterns with different pitches. The interference fringe patterns with a pitch g₁ generated by a laser beam with a wavelength λ₁ sensitive to the photoresist layer are employed for the pattern exposure, while the ones generated by a laser beam with a wavelength λ₂ insensitive to the photoresist layer are employed to be observed by a microscopic optical system located at the back of the exposure substrate. This enables the estimation of the pitch of the interference fringe patterns with the pitch g₁ during the exposure process in optical interference lithography, contributing to accelerating the alignment of the angular position of the reflective mirror in the interferometer. A prototype optical setup consisting of a beam-collimating unit with two laser sources having wavelengths of 405 nm and 780 nm, a non-orthogonal one-axis Lloyd’s mirror interferometer unit, and a microscopic optical system is designed and developed, and experiments are conducted to demonstrate the feasibility of the proposed technique of estimating the pitch of interference fringe patterns for pattern exposure.