Optimization of topside antireflective coatings for hyper numerical aperture lithography

In hyper numerical aperture (NA) lithography, the incident angle of imaging rays varies in a wide range. Conventional topside antireflective coatings (TARC) optimization methods, minimize the reflectivity only for normal incident light, but are insufficient to suppress the reflectivity in the whole incident angles range of the incoming imaging rays for hyper-NA lithography. A novel TARC optimization method is developed, and the average reflectivity at the resist/TARC/air (or immersion fluid) interface is calculated over the whole range of incident angles that NA determines. Optimal design of TARC structure is carried out to minimize the reflectivity. The results show that, with this method, the thin-film interference effects which cause remarkable line width fluctuation can be reduced, the swing curve effect is controlled, the transmittance of TARC and the ratio of transmittance of TE to that of TM waves are increased, so that the scanner throughput and image contrast, can be improved.