25 June 1999 Electron optical analysis of SCALPEL writing strategy
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Abstract
In SCALPEL, the maximum projected area of the electron optical sub-field, though large by electron optical standards, is limited by aberrations of the projection optics. The effective exposure region can be increased by electronically scanning the illumination off-axis, in a direction orthogonal to the mechanical motion of the mask and wafer stages. Even though the aberrations associated with the scan are minimized by applying dynamic corrections, the residual aberrations may still increase with increasing off-axis scan distance. Thus the image quality may very during dose accumulation in each pixel. Our previous simulation method has been extended to consider the writing strategy, including scanning the sub-field over a pixel, and eliminating the mask struts and the non-patterned regions at the wafer plane. We have examined two variations of writing strategy, for a column with demagnification m: (1) The case where the mask stage velocity is exactly m times the wafer stage velocity, k and (2) The case where the mask stage velocity is increased so that the mask and wafer patterns remain in synchronism with each other, after removing the unpatterned areas of the mask from the image. In case (1), an additional deflection is required to eliminate the struts and skirts in the mask from the printed image. This deflection increases with time, as the mask and wafer patterns get progressively out of synchronism. Case (2) eliminates this effect. We compare these two cases, and show that case (2) provides significantly improved fabrication pattern quality.
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Xieqing Zhu, Xieqing Zhu, Eric Munro, Eric Munro, Haoning Liu, Haoning Liu, John A. Rouse, John A. Rouse, Warren K. Waskiewicz, Warren K. Waskiewicz, } "Electron optical analysis of SCALPEL writing strategy", Proc. SPIE 3676, Emerging Lithographic Technologies III, (25 June 1999); doi: 10.1117/12.351092; https://doi.org/10.1117/12.351092
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