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20 October 2006 Identification of subresolution assist features that are susceptible to imaging through process
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Abstract
Sub-resolution Assist Features (SRAFs) are powerful tools to enhance the focus margin of drawn patterns. SRAFs are sized so they do not print on the wafer, but the larger the SRAF, the more effective it becomes at enhancing through-focus stability. The size of an SRAF that will image on a wafer is highly dependent upon neighboring patterns and models of SRAF printability are, at present, unreliable. Conservative SRAF rules have been used to ensure that SRAFs never print on a pattern. More accurate models of SRAF printing should allow SRAF rules to be relaxed, resulting in more effective SRAF placement and broader focus margins. The process models that are used during Optical Proximity Correction have never been able to reliably predict which SRAFs will print on a pattern. This appears to be due to the fact that OPC process models are generally created using data that does not include subresolution patterns. In addition, the definition of a printing SRAF is not clear, as it can range from a photoresist film left on a wafer to a pattern that is transferred to the substrate during the etch process. This paper will demonstrate a model that identifies SRAFs which appear in photoresist and those which survive the etch step.
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Lawrence S. Melvin III, Martin Drapeau, and Jensheng Huang "Identification of subresolution assist features that are susceptible to imaging through process", Proc. SPIE 6349, Photomask Technology 2006, 63491Q (20 October 2006); https://doi.org/10.1117/12.692464
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