Spirothiopyran based photoresists for large area sub-diffraction nanopatterning

Optical interference lithography is an attractive technique to cheaply and rapidly pattern 3D features in polymer photoresists. However, both resolution and feature size obtained are limited by diffraction. In the past few years, STED microscopy inspired lithography schemes using reversibly saturable switching systems have shown the ability to direct-write features well below the diffraction limit using light. However, the high laser intensity required for saturation limits their use to serial writing.
Here, we show that combining the reversibly saturable photoisomerization of spirothiopyran with the Michael addition chemistry can be used to formulate low intensity threshold photoresists suitable for writing with sub-diffraction resolutions over large areas. NMR studies confirm an exponential decrease in the ‘writing’ yield with low saturation depletion intensity. Photokinetic simulations demonstrate the ability to fabricate patterns with nanoscale resolution over range spanning hundreds of microns using a simple 2W laser, which are experimentally corroborated by interference lithography using a spirothiopyran-PEG copolymer. These experiments demonstrate the viability of a spirothiopyran based photoresist to become a prime candidate material for large area 3D nanofabrication.