Fabry-Perot-type antireflective coating for deep-ultraviolet binary photomask applications

We demonstrate an antireflective coating structure, which is based on the three-layer metal interference called the Fabry-Perot structure, for a deep-ultraviolet binary mask. The antireflective coating structure is composed of a metal–oxide–metal stack. By addition of different optimized structures, reflectances of less than 1.5% at both 248 and 193 nm have been achieved. At the three-layer Fabry–Perot structure, the bottom chrome layer provides suitable absorption. By controlling the thickness of the intermediate silicon oxide layer, we can tune the minimum-reflection regime to the desired exposure wavelength. The top metal layer can prevent charge accumulation during e-beam writing.