Polarizing assist features for high-NA optical lithography

Frederick T. Chen

doi:10.1117/12.467249

27 December 2002 Polarizing Assist Features for High-NA Optical Lithography

Frederick T. Chen

Proceedings Volume 4889, 22nd Annual BACUS Symposium on Photomask Technology; (2002) https://doi.org/10.1117/12.467249
Event: Photomask Technology 2002, 2002, Monterey, CA, United States

Abstract

Optical lithography continues to be extended with shorter exposure wavelength and higher numerical aperture tools. Strong resolution enhancement techniques such as alternating aperture phase-shifting utilize 2-beam imaging to achieve effective spatial frequency doubling, high DOF, and ultralow k1. For these techniques, unpolarized light exposure latitude worsens significantly for tighter pitches and smaller linewidths. In addition, the mask error factor begins to become polarization-dependent. Due to vector interference effects, TE-polarized light (electric field polarized parallel to line) provides better imaging than TM-polarized light (electric field perpendicular to line). Suppression of TM-polarized light will therefore enable aggressive subwavelength imaging. In this paper, we apply rigorous electromagnetic simulations to evaluate the typical dimensions of photomask features in order for them to exhibit TM polarization suppression. Subwavelength absorbing features with high aspect ratio are one possible way of achieving adequate polarization selectivity on a photomask. TE polarization selectivity for darkfield binary and alternating aperture strong phase-shifting masks can also be achieved with the use of smaller spaces and/or thicker absorbers. Throughput is traded off against polarization selectivity since there is also significant absorption of TE-polarized light by the polarizing features. Polarization-selective imaging solutions based on thick Cr photomask blanks are presented.

Citation Download Citation

Frederick T. Chen "Polarizing Assist Features for High-NA Optical Lithography", Proc. SPIE 4889, 22nd Annual BACUS Symposium on Photomask Technology, (27 December 2002); https://doi.org/10.1117/12.467249

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KEYWORDS

Polarization

Photomasks

Optical lithography

Phase shifts

Absorption

Chromium

Resolution enhancement technologies

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