8 August 1993 Vector diffraction analysis of phase-mask imaging in photoresist films
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Abstract
A vector diffraction analysis is applied to methods of image manipulation like phase masks or off-axis illumination. When such techniques eliminate the dc order altogether, as with alternating phase masks, it becomes possible to print a given intensity pitch with only half as large an NA as with a chrome mask. Some non-scalar imaging effects are therefore reduced. For example, in present lithographic practice the depth of focus with standard masks is often little larger than the thickness of the resist film, so it is no longer accurate to neglect defocus arising during multiple reflections within the resist. The angle dependence of the film stack then becomes significant, and small film perturbations give rise to swing-curve oscillations in pupil apodization and image shape as well as exposure dose. Specific film thicknesses can, for example, have a similar effect to stopping down the lens. Other thicknesses can enhance resolution of certain patterns. We treat these film effects by representing each layer in the process stack with pupil transfer functions. Like defocus, these pupil functions posses a symmetry that eliminates relative dephasing or apodization in the two-beam fringe pattern produced by an alternating phase mask. An alternating phase mask can produce stronger vector diffraction anomalies than a standard mask, despite being able to print a given pitch with half as large a lens NA.
© (1993) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Donis G. Flagello, Alan E. Rosenbluth, "Vector diffraction analysis of phase-mask imaging in photoresist films", Proc. SPIE 1927, Optical/Laser Microlithography, (8 August 1993); doi: 10.1117/12.150439; https://doi.org/10.1117/12.150439
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