Light-Coupling Masks: An Alternative, Lensless Approach to High-Resolution Optical Contact Lithography

We describe an approach to optical lithography using light-scattering contact masks with protruding elements that couple light into a photoresist. This method differs from conventional contact lithography in two important ways. First, because portions of the light-coupling mask (LCM) are made from a polymer, intimate contact with the resist occurs over large areas without additional load. This contact is readily reversible, and causes no observable damage or contamination of the LCM or substrate. Second, the structure formed by the protruding parts of the LCM in contact
with the resist can define local optical modes that impart directionality to the light propagating through the LCM and amplify its intensity. We provide an experimental realization and theoretical description of the method, demonstrating its use for the formation of 100-nm features with light having a wavelength of 256~nm.