The Materials Challenge in Diffraction-Unlimited Direct-Laser-Writing Optical Lithography

Using a novel photoresist (composed of pentaerythritol triacrylate and isopropyl thioxanthone) that favors stimulated emission depletion by a pi-pi* transition and using a two-color two-photon excitation scheme, 65-nm wide lines are achieved. This value is limited by parasitic two-photon absorption of the continuous-wave depletion beam. It is estimated that, without this process, line widths of 30 nm are in reach.