19 March 2015 Contour-based kernel modeling and verification for E-Beam lithography
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Abstract
In E-beam lithography, the double or multiple Gaussian kernels used to describe the electron scattering behavior have been discussed extensively for critical dimensions (CDs) larger than the e-beam blur size. However in e-beam direct write on wafer, CD dimensions are close to the beam blur size because of requirements in both resolution and throughput. This situation gives rise to a severe iso-dense CD bias. Hence the accuracy of the modeling kernel is required to achieve a larger common process window. In this paper we present contour-based kernel modeling and verification for e-beam lithography. The edge contours of CD-SEM images of the contact hole array pattern with duty ratio splits are used in this Gaussian kernel modeling study. A 2-step optimization sequence is proposed to improve the fitting efficiency and robustness. In the first step, roundness is the primary and the most effective index at the corner region which is sensitive to determine the beam blur size. The next step is to minimize the deviation of the through-pitch proximity effect by adjusting the ratio of the electron backscattering to the electron forward scattering. The more accurate cost index, edge placement error, is applied in the subsequent optimization step with constrained beam blur sizes extracted from the previous step. The optimum modeling kernel parameters can be obtained by the lowest cost deviation of the simulation contours and the CD-SEM extracted edge contours after optimization iterations. For early study of the proximity impact on future EBDW systems, the exposure experiment is performed on an EBM-8000 mask writer to build the modeling kernel. The prediction accuracy of the optimum modeling kernel on 60-nm features with different pattern densities is also verified experimentally to be within 1.5 nm.
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Jan-Wen You, Cheng-Hung Chen, Tsung-Chih Chien, Jaw-Jung Shin, Shy-Jay Lin, Burn J. Lin, "Contour-based kernel modeling and verification for E-Beam lithography", Proc. SPIE 9423, Alternative Lithographic Technologies VII, 94231D (19 March 2015); doi: 10.1117/12.2085099; https://doi.org/10.1117/12.2085099
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