A Fabry-Perot type anti-reflective coating for deep ultraviolet binary photomask application

In this paper, we demonstrated a novel anti-reflective coating structure for deep ultraviolet binary mask, which is based on three-layer Fabry-Perot structure. The anti-reflective coating structure is composed of the chrome/oxide/chrome stack. By adding different optimized structures, reflectance of less than 2% at both 248 nm and 193 nm have been achieved. The results are also agreed well with simulated ones. At the three-layer Fabry-Perot structure, the thickness of bottom chrome layer should be larger than 100 nm to provide suitable absorption. By controlling the thickness of the intermediate oxide layer, we can tune the minimum reflection regime to the desired exposure wavelength. The thickness of top chrome layer should be well controlled in order to optimize transmission light into Fabry-Perot structures. In general, the mask layer should have good electrical conductivity for e-beam writing in order to prevent writing errors due to charging effects. In the Fabry-Perot structure, the top metal layer can also prevent charge accumulation during e-beam writing.