Abstract
In reduction photolithography, the stitching of stepper or scanner fields together is increasingly utilised to pattern devices used for optical or optoelectronics applications. Some of these devices can be up to 60 mm in size, whilst a typical scanner field is 25 by 33 mm. Using computer simulation we show the effect of individual projection lens aberrations at the stitching boundary for a 248 nm, 0.75NA, 4X reduction scanner. Depending on the magnitude and the aberration applied at a stitching point, shifts in position, changes in critical dimensions (CD) or changes in wall angles are observed. Of the lower-order aberrations, Coma has the greatest effect for placement errors, with Astigmatism having the greatest effect on CD and wall angle, though at defocus. Trifoil is also shown to have an effect on placement and wall angle. As way of a reference, rigorous electromagnetic field (emf) simulation was used to simulate aberration effects on a typical 1X contact aligner.
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