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1 November 2007Automatic residue removal for high-NA extreme illumination
An epidemic for smaller node has been that, as the device architecture shrinks, lithography process requires
high Numerical Aperture (NA), and extreme illumination system. This, in turn, creates many lithography problems such
as low lithography process margin (Depth of Focus, Exposure Latitude), unstable Critical Dimension (CD) uniformity
and restricted guideline for device design rule and so on. Especially for high NA, extreme illumination such as
immersion illumination systems, above all the related problems, restricted design rule due to forbidden pitch is critical
and crucial issue. This forbidden pitch is composed of numerous optical effects but majority of these forbidden pitch
compose of photo resist residue and these residue must be removed to relieve some room for already tight design rule.
In this study, we propose automated algorithm to remove photo resist residue due to high NA and extreme
illumination condition. This algorithm automatically self assembles assist patterns based on the original design layout,
therefore insuring the safety and simplicity of the generated assist pattern to the original design and removes any resist
residue created by extreme illumination condition. Also we tested our automated algorithm on full chip FLASH
memory device and showed the residue removal effect by using commercial verification tools as well as on actual test
wafer.