Centimeter-scale subwavelength photolithography using metal-coated elastomeric photomasks with modulated light intensity at the oblique sidewalls

By coating polydimethylsiloxane (PDMS) relief structures with a layer of opaque metal such as gold, the incident light is strictly allowed to pass through the nanoscopic apertures at the sidewalls of PDMS reliefs to expose underlying photoresist at nanoscale regions, thus producing subwavelength nanopatterns covering centimeter-scale areas. It was found that the sidewalls were a little oblique, which was the key to form the nanoscale apertures. Two-sided and one-sided subwavelength apertures can be constructed by employing vertical and oblique metal evaporation directions, respectively. Consequently, two-line and one-line subwavelength nanopatterns with programmable feature shapes, sizes, and periodicities could be produced using the obtained photomasks. The smallest aperture size and line width of 80 nm were achieved. In contrast to the generation of raised positive photoresist nanopatterns in phase shifting photolithography, the recessed positive photoresist nanopatterns produced in this study provide a convenient route to transfer the resist nanopatterns to metal nanopatterns. This nanolithography methodology possesses the distinctive advantages of simplicity, low cost, high throughput, and nanoscale feature size and shape controllability, making it a potent nanofabrication technique to enable functional nanostructures for various potential applications.