8 November 2012 EUV multilayer defect compensation (MDC) by absorber pattern modification: improved performance with deposited material and other progresses
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Abstract
According to the ITRS, mask defects are among the top technical challenges facing the introduction of extreme ultraviolet (EUV) lithography into production. Making a defect-free multilayer EUV mask blank is not possible today, and is unlikely to happen in the next few years. This means that EUV must work with masks having multilayer defects. The method presented here compensates effects of multilayer defects by modifying absorber patterns whose images they distort. It represents the patterns to be modified with level-set methods, providing more generality than binary pixels on a fixed grid. The level-set representation and fast model used to calculate fields at the mask have been published previously. The method has been applied with constraints to ensure that the pattern modifications are within the capability of available repair equipment, and has been shown to enlarge process windows. Although prior work focused on modifying absorber patterns, additional degrees of freedom to improve performance are available if modifications include deposition of different materials. Simulated images show potential benefits with deposited carbon. To apply the method, it is necessary to solve two sequential inverse problems. First, the defect buried in the multilayer must be modeled from available information about the top surface of the mask blank. Then the absorber modifications must be calculated from the desired image and properties of the modeled defect. Accuracy and speed of the computation meet requirements for using it to manufacture EUV masks.
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Linyong Pang, Masaki Satake, Ying Li, Peter Hu, Vikram Tolani, Danping Peng, Dongxue Chen, Bob Gleason, "EUV multilayer defect compensation (MDC) by absorber pattern modification: improved performance with deposited material and other progresses", Proc. SPIE 8522, Photomask Technology 2012, 85220J (8 November 2012); doi: 10.1117/12.977174; https://doi.org/10.1117/12.977174
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