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17 November 2010 Investigation and prediction of image placement errors in extreme ultraviolet lithography masks
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According to the latest ITRS Roadmap, extreme ultraviolet lithography (EUVL) is expected to be one of the principal carriers for the IC production at sub-45 nm technology nodes. One of the most challenging tasks to fulfill EUVL is the fabrication of the EUVL mask in which the most important issue is the control of image placement errors. In this paper, the EUVL mask fabrication process was analyzed and image placement errors due to the fabrication process were investigated and predicted. A theoretical analysis was conducted to analytically benchmark the EUVL mask fabrication process. A line-and-space pattern (with pattern coverage of 50%) was employed in the theoretical analysis as an example. The theoretical deduction revealed that this 50% coverage pattern produces the same global response as a uniformly stressed thin film with half of the stress-thickness product of the patterned lines. Finite element (FE) models were established to simulate the EUVL mask fabrication process. In FE simulations, a new equivalent modeling technique was developed to predict the global distortions of the mask and the local distortions of the pattern features. Results indicate that for the EUVL mask with this line-and-space pattern (50% pattern coverage), the maximum image placement error is only about 10 nm, which is largely due to the application of a flat electrostatic chuck in both e-beam mounting and exposure chucking. Nonuniformities of either the mask or the electrostatic chuck will add to the final image placement errors of the EUVL mask.
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Liang Zheng "Investigation and prediction of image placement errors in extreme ultraviolet lithography masks", Proc. SPIE 7848, Holography, Diffractive Optics, and Applications IV, 78483H (17 November 2010);


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