In-situ evaluation of interference fringe patterns to be generated by interference lithography

In the non-orthogonal Lloyd’s mirror interferometer based on the laser interference lithography, the pitch of interference fringe pattern is controlled by adjusting the angle between the exposure substrate and the collimated laser beam projected onto the substrate surface. However, It has been a time-consuming task to adjust the fringe pitch through the iterative process of pattern exposure and development. In this paper, a new method for the "in-situ" evaluation of the pitch of a interference fringe pattern is proposed. Two laser beams having different wavelengths are employed, and are aligned to be coaxial so that the two interference fringe patterns with different pitches can be generated; one interference fringe is employed for the pattern exposure in lithography process, while the other is employed for observing the fringe pitch. An optical system with an one-axis Lloyd’s mirror interferometer and an imaging system placed on the backside of the exposure substrate is developed, and some experiments are carried out to verify the feasibility of the proposed method.