Design optimization of a non-orthogonal two-axis Lloyd's mirror interferometer for fabrication of large-area two-dimensional scale gratings

An optimized beam expansion assembly is newly designed for a non-orthogonal two-axis Lloyd's mirror interferometer to fabricate large-area two-dimensional (2D) diffraction scale gratings in a small-scale manufacturing facility or a research laboratory. Theoretical calculations are at first carried out to quantitatively estimate the influences of the coherence length and the Gaussian light intensity distribution of a collimated laser beam, which is projected onto a mirror-substrate assembly for the generation of interference fringe fields on a substrate. Design optimization of the interferometer is then carried out in such a way that a beam shaper, which contributes to obtain a flat-top light intensity distribution in the collimated laser beam and is expected to reduce the amplitude deviation of the developed pattern structures as well as the pattern exposure time, is integrated into the beam expansion assembly. The feasibility of the newly developed beam expansion assembly is demonstrated through fabricating a 100 mm × 100 mm 2D scale grating having pattern structures with uniform amplitude of approximately 500 nm and a short period of 1 μm.