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

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.