Influence of polarization on the optimization of dual BARC structures for hyper-numerical aperture ArF immersion lithography

Abstract

Hyper-numerical aperture (NA) immersion lithography has created new challenges for ArF bottom antireflective coating (BARC). The reflectivity control over a wider range of incident angles of the incoming imaging rays is most important in order to reduce stand wave effect and get a good profile of lithography pattern. The conventional single-layer BARC structure will be not suitable for Hyper-NA immersion lithography. The dual BARC structures will possibly be used in hyper-NA ArF lithography at 45-nm node. The optimization of dual-BARC parameters will depend on the angle of incidence and the polarization of the light in the BARC. Here we discuss the influence of polarization on optimization of dual BARC structure through simulations. A computational code is developed that performs optimizations of dual- BARC parameters for both TE and TM polarized light. In the code, the reflectivity vs. angle plot is integrated, and over a given range of BARC optical constants, the best BARC parameters, which are relative to the minimum value of the reflectivity-angle integral (RAI), are obtained. Using the optimized BARC parameters, we calculate the maximum reflectance in the corresponding region of incident angle of NA being 1.0, 1.2 to 1.4. It is found that the maximum reflectance tends to increase if the NA increases. Comparison of the results for the TE and TM polarized light shows that the reflectance of the former tends to be significantly larger than that of the latter, especially for hyper-NA lithography. It means that it is more difficult to control substrate reflectivity for TE polarized light than for TM polarized light.