high depth-of-field nanostructures by rotational near-field photolithography

Rotational near-field photolithography uses one or an array of plasmonic lenses to directly pattern features on a rotating substrate that is coated with a very sensitive photoresist. critical for this method is its limited etching depth. we investigate and demonstrate that the depth-of-field of the so-obtained nanopatterns is determined by both the refractive index and the thickness of the air/photoresist multi-dielectric layer. using the transfer-matrix theory, the bounded air/photoresist dielectric layer refracts the light at the interface, which causes the constructive interference of surface plasmon polaritons (spps) to be confined. the wavelength of the spps decreases with increasing photoresist thickness. both the simulation and experiment indicate that high depth-of-field nanostructures can be obtained by optimizing the resonance wavelength of spps due to the response of the system. combining this with high-speed rotational near-field photolithography technology, we find that nanostructures with four times the depth-of-field compared with the previous off-resonance system can be obtained using organic photoresists with this optimization.