12 May 2004 The impact of mask topography on CD control
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Past work on mask topography has documented the effects of the topography on the aerial image intensity and on the responses of CD through defocus and image placement. Device performance, however, is limited by the statistical CD variation in the poly lines that form the logic and memory gates. We have developed a tool that combines fast, rigorous EMF calculations with Monte Carlo simulation to investigate the impact of mask topography on CD control. We have applied it to study the effects of mask topography on through-pitch CD control in 6% EAPSM, AAPSM, and CPL reticles at 90-nm half-pitch design rules. The effects of the topography can be understood by examining the coefficients of the Fourier expansion of the near-field radiation pattern. The magnitude of the 3D effects is not correlated with the amount of mask topography but with the specific details of the Fourier coefficients that pass through the pupil. The topography mainly distributes the energy more evenly and introduces additional phase information. The best imaging results at tight pitch are obtained when the difference between the magnitudes of the two main Fourier coefficients that pass through the pupil is small and their phase difference is close to π. At larger pitches more diffracted orders will pass through the pupil, and the extra phase information from the additional orders will couple with aberrations in a reticle-dependent way and complicate overall RET choice.
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Jonathan L. Cobb, Jonathan L. Cobb, Bernard J. Roman, Bernard J. Roman, Vladimir Ivin, Vladimir Ivin, M. Sarychev, M. Sarychev, } "The impact of mask topography on CD control", Proc. SPIE 5754, Optical Microlithography XVIII, (12 May 2004); doi: 10.1117/12.601175; https://doi.org/10.1117/12.601175


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