Light-Coupling Masks for Lensless, Sub-Wavelength Optical Lithography

Light-coupling masks (LCMs) that are structured and make conformal contact with substrates provide high-contrast illumination of photoresists, constituting a new form of amplitude mask for light-based lithographies. LCMs allow pattern definition at high resolution and densities over large areas in conventional resists without the need for elaborate projection optics. Images of arbitrarily shaped structures having dimensions much smaller than that of the vacuum wavelength of the exposing light are formed in the resist in a 1:1 correspondence to their size in light-guiding portions of the mask. LCMs promise to extend the range of optical lithography and bring 100-nm-sized features on a 200-nm pitch within the reach of any laboratory.