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Axel Zibold, Ulrich Stroeßner, Andrew Ridley, Carl Zeiss SMS GmbH, Germany
Vicky Philipsen, Joost Bekaert, Live van Look, IMEC, Belgium

ABSTRACT

Immersion lithography offers the semiconductor industry an opportunity to extend the current ArF processes to smaller half-pitch nodes before switching to a shorter exposure wavelength. The transition to immersion will require increased attention to the photomask along with new effects influencing the aerial image formation as the numerical apertures (NA) of scanners move up to at least 0.93 and beyond. Feature sizes on the photomask become comparable to, or even smaller than, the wavelength and begin to act like wire grid and/or other types of polarizers, which can lead to potentially serious polarization effects.

In addition to mask-polarization effects, high-NA imaging can cause additional polarization effects due to the high angle of incidence of light entering the photoresist through the scanner lens. These so-called “vector effects” cause contrast loss when light polarized in the TM polarization direction is used to illuminate the photomask.

In this paper polarization effects of different photomask features are examined by comparing measurement results using linear polarized illumination parallel and perpendicular to various line and space patterns and nonpolarized illumination. These polarization effects are examined using a Carl Zeiss AIMS™ fab 193i scanner emulator and are cross-checked using rigorous aerial image simulation.