Fabrication of low-stray-light gratings by broad-beam scanning exposure in the direction perpendicular to the grating grooves.

Previous research on making low-stray-light gratings is mainly focused on process steps after the photoresist mask has been made. We propose to improve the quality of the photoresist mask directly in exposure. We present a broad-beam scanning exposure method along the grating vector (i.e., in the direction perpendicular to the grating grooves), utilizing a reference grating clamped below the substrate on the translation stage for phase and attitude locking. Scanning-exposed gratings with a size of 40  mm×40  mm are successfully made, which have straighter grooves and smoother surfaces, and their stray light levels around the first and second diffraction orders are decreased significantly.