Large-field electron optics: limitations and enhancements

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Abstract
The renewed interest in charged particle projection lithography has highlighted the need for particle optics to cover larger fields. Previous attempts to develop e-beam and ion beam projection systems for lithography have shown that particle optics can image 108 - 109 pixels in parallel at modest beam currents (< 10 uA). Competitive lithography tools for the high volume production of gigabit chips, however, will have to project more than 1011 pixels at beam currents up to 50 uA. This requirements can only be met through a significant advancement in the state-of-the-art. The field size of electron optics is limited by off-axis aberrations, prohibiting the simultaneous projection of such large numbers of pixels. Therefore, to date the most successful electron beam lithography approach has been that of the probe-forming scanning electron beam system. The sequential exposure of pixels allows (partial) dynamic correction of aberrations and image control `on the fly', but it also severely limits the throughput. Combining, however, the dynamic correction capability of probe- forming systems with the parallel projection of the pixels contained in fractions of a mask appears to be a promising approach to high throughput lithography. It has high potential of meeting the challenges of large field electron optics. This paper describes, how the field size of electron optics can be enlarged despite the limitations posed by off-axis aberrations and Coulomb interactions between beam electrons.

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