1 April 2004 Initial assessment of the impact of a hard pellicle on imaging using a 193-nm step-and-scan system
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Abstract
Today there is little practical experience with hard pellicles (HP), which is why we are doing a series of lithographic exposures of reticles with a HP on a 193-nm step-and-scan system at IMEC. The goal of this work is to experimentally verify the (optical) effects of HPs (such as their contribution to distortion and aberrations), find and perform suitable scanner corrections for them if possible, and then compare critical dimension (CD) measurements from exposures with HP to the corresponding exposures without HP. In this way, we can assess the viability of the use of hard pellicles in semiconductor industry. The result of our work so far is that we have found no show-stoppers for the use of HPs in lithography (although there are a few restrictions on this statement): most of the expected optical effects are confirmed experimentally and can-to a large extent-be corrected. The CD measurement part of the work yielded no unpleasant surprises: we basically find identical results with and without HP. There are, however, a few restrictions to this largely positive evaluation. The first is the fact that the specs on the pellicle flatness are currently not met (yet), which means that the contribution of the pellicle nonflatness to distortion is still larger than the 1-nm spec that is allowed for. However, progress in improving the impact of nonflatness is still ongoing, so the current status is by no means the final one. The second restriction is that none of the work we have done on our 193-nm system can give a clear indication to what extent possible oxygen purging or contamination issues may turn out to be troublesome once HPs are applied on a genuine 157-nm system. However, we plan to investigate such 157-nm specific topics soon, as a 157-nm scanner has been available at IMEC since the Fall of 2003.
Peter De Bisschop, Michael K. Kocsis, Richard J. Bruls, Chris K. Van Peski, Adrew Grenville, "Initial assessment of the impact of a hard pellicle on imaging using a 193-nm step-and-scan system," Journal of Micro/Nanolithography, MEMS, and MOEMS 3(2), (1 April 2004). http://dx.doi.org/10.1117/1.1683279
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KEYWORDS
Pellicles

Reticles

Distortion

Scanners

Monochromatic aberrations

Semiconducting wafers

Projection systems

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