Optimization of double bottom antireflective coating for hyper numerical aperture lithography

In hyper numerical aperture lithography, the incident angle of imaging rays varies in a wide range. Conventional single bottom antireflective coatings (BARC) cannot control reflectivity (substrate reflectivity) at the resist-substrate interface. A novel dual BARC optimization method is developed by taking into account light source shape and mask diffraction for specific applications. A weighted average of the substrate reflectivity for the 0st order as well as a higher order is used when optimizing the dual BARC. BARC structures are optimized with the new method in the cases of binary mask, attenuated phase-shift mask and altering phase-shift mask. The results show that, the higher diffraction orders are captured by the objective lens (or larger the intensity of high orders is), more noteworthy the influence of mask is for BARC optimization. In some cases, such as imaging with altering phase-shift mask, it is indispensable to take the mask into account in BARC optimization.