Methodology for generating exposure tool specification for alternating phase shift mask application for 70 nm node

Abstract

An enhanced methodology of generating exposure tool specification, specifically lens specification, using alternating phase shift mask (AltPSM) features as anchor structures is introduced in this paper. The use of AltPSM as a resolution enhancement technique requires a unique set of exposure tool requirement on lens and body functionality. The lens aberration level requirement and sensitivity of certain type of Zernike term need to be identified for optimization of the lens for AltPSM application. The NA/Sigma scaling of AltPSM with current level of aberration is discussed briefly. We also extend the response surface CD model to a quadratic model that includes cross talk among Zernike terms. New definition of CD aberration sensitivity based on the quadratic model allows the sensitivity term to include the crosstalk effect. Specifications for aberration levels were established by Monte Carlo CD simulation, taking into account the inherent correlation between Zernike coefficients that we determine from analysis of the pupil Power Spectral Density. Difference on the phasemap behavior and final calculated specification are compared for the correlated and uncorrelated Zernike case. Finally we briefly discuss the flare effect on trim mask exposure and the issues in AltPSM EMF simulation in a high NA regime. Similar treatment for image placement indicated it is as critical as CD for 70nm mode AltPSM application.