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20 October 2006 Accounting for lens aberrations in OPC model calibration
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Whenever an OPC calibration wafer is exposed, there will be an unavoidable and perhaps non-representative level of aberration at that part of the exposure field corresponding to where the calibration pattern is written on the mask. In practice these aberrations values will vary across both the field and from exposure tool to exposure tool. The OPC engineer is therefore faced with the question of whether the aberrations specific to this part of the reticle field and hence lens should be taken into account during model fitting. Methodologies have been developed to allow OPC model calibration when the aerial image is asymmetric either due to the test pattern or the aberrations in the lens that lead to this. This will be referred to as asymmetry aware model calibration. These methodologies allow asymmetric test structures to be added to the calibration set to allow greater pattern coverage and therefore allow for a better overall model fit. Asymmetric calibration structures tend also to be particularly sensitive to asymmetric lens aberrations such as Coma. The question becomes whether the calibration fit should include asymmetric structures and hence account for coma, or consider only symmetrical, coma-insensitive structures when doing a model fit. The paper will investigate, using actual model calibration measurement data the suitability of accounting for model coma in an actual OPC model calibration.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Laurent Depre, Christopher Cork, and Martin Drapeau "Accounting for lens aberrations in OPC model calibration", Proc. SPIE 6349, Photomask Technology 2006, 63494L (20 October 2006);


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