Journal of Micro/Nanolithography, MEMS, and MOEMSSimulation of optical projection with polarization- dependent stray light to explore the difference between dry and immersion lithography
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When imaging at high incident angles to the resist, both the reflected light from the resist surface and the image forming process of the transmitted light into the resist are polarization dependent. The transmitted TM component and the reflected TE and TM components tend to induce stray light as a function of the incident angle. In this work, these components are analyzed and evaluated quantitatively. The polarization-dependent stray light (PDS) and the system stray light found in regular optical imaging systems are incorporated into a simulation program for diffracted intensity distribution to construct exposure-defocus (E-D) trees and windows to evaluate the exposure latitude and depth of focus (DOF) of typical circuit elements. The DOF of line-space pairs and contact holes with and without PDS are compared in the cases of two- and three-beam interference, first- and second-order beams, binary intensity masks, and phase shifting masks. Even though the 193-nm immersion system is shown to be better than 157- and 193-nm dry systems, using polarized illumination can improve DOF, particularly in low k1 situations, and in other situations when the stray-light-free image contrast is low.