Fabrication of double-grooved gratings using coplanar multibeam holographic lithography with a phase mask

Submicrometer double-grooved gratings feature unique optical properties and diverse potential applications, most of which have been fabricated by electron beam lithography up till now. On the other hand, holographic lithography based on a phase mask [near-field holography (NFH)] has the advantages of high throughput, low cost, and a compact setup in terms of a short optical path. Distinguished from conventional NFH based on double-beam interference, multibeam NFH based on multibeam interference is studied to form groove profiles of double-grooved gratings in this study. The formation principle of double-grooved gratings is attributed to the multibeam interference of the transmitted beams behind the phase mask. Within such multibeam interference, every two of diffracted beams interfere and form several sets of latent subgrating patterns. The formation of double-grooved gratings can be understood as the superimposition of different portions of subgrating patterns. We also demonstrated the potential and challenges of several key factors in tailoring the symmetric and asymmetric double-grooved structures, including the incidence angles, the efficiency distribution of phase masks, exposure-development conditions, and the spacing between the mask and substrate. Symmetric and asymmetric double-grooved gratings with periods of 666.7, 950, and 1000 nm were fabricated by coplanar three-beam NFH at normal incidence, and coplanar four-beam NFH at oblique incidence and near normal incidence. The experimental results of the evolution of the grating profiles of double-grooved gratings are in relatively good agreement with the simulation. This study provides an alternative cost-effective fabrication method for the mass production of double-grooved gratings. Moreover, this study also enriches the diversity of groove profiles of diffraction grating by NFH.