Rapid Fabrication of Large-Area Periodic Structures by Multiple Exposure of Two-Beam Interference

Holographic lithography is a convenient, inexpensive technique to fabricate large-area, periodic biofunctional templates such as antireflection and superhydrophobic surfaces. As opposed to two-beam interference (TBI), which produces grating patterns, interference of three or more beams can create multifarious patterns of symmetry, which have broader range of functions. However, as the number of beams used increases, the configuration gets more complicated, and thus possibly incurs more errors of alignment. To avoid the issue, we employed the technique of multi-exposure of two-beam interference to fabricate two-dimensional periodic structures and quasi-periodic structures. The theoretical simulation of 2n-beam interference (n is a positive integer) and n exposures of TBI was compared to validate that patterns made by 2n-beam interference could also be made by n exposures of TBI. Structures with symmetry of different folds were demonstrated not only on the negative photoresist SU-8 based on an add-type fabrication approach but also directly on the surface of the infrared window material zinc sulfide (ZnS) through a subtract-type fabrication approach. A transmittance of more than 90% and a water contact angle of 145° were obtained by three exposures of two-beam interference, and a transmittance of 80% as well as a water contact angle of 126° by ablation of nine exposures of TBI on ZnS substrate.