Blazed Diffraction Grating Made by Greyscale Lithography Using a Laser Writer

This study demonstrates a single-step fabrication of blazed gratings on silicon substrates using direct laser greyscale lithography and aluminum coating. Three key parameters were studied for process optimization, i.e., the exposure dose of the photoresist, the focusing method, and the laser scan writing mode. We have shown that a bijective correspondence between dose and thickness ranging from 0 to 127 mJ/cm2, defined across 100 levels, enabled us to obtain a linear photoresist thickness profile. The stitching artifacts were then eliminated using fine optical autofocus with overlap writing mode. Finally, the optimized grating (3.3 µm period, 12° blaze angle, 0.52 µm depth) exhibits a well-defined saw tooth profile, confirmed by atomic force and scanning electron microscopies. Optical characterization using Fourier-plane imaging shows a dominant −1st diffraction order, confirming successful blaze behavior, especially for 700 nm wavelength. This work establishes direct laser greyscale lithography as a viable, cost-effective, and fast method for fabricating high-quality blazed gratings.