Rapid search of the optimum placement of assist feature to improve the aerial image gradient in iso-line structure

Jianliang Li; Qiliang Yan; Lawrence S. Melvin III

doi:10.1117/12.712167

27 March 2007 Rapid search of the optimum placement of assist feature to improve the aerial image gradient in iso-line structure

Jianliang Li, Qiliang Yan, Lawrence S. Melvin III

Author Affiliations +

Proceedings Volume 6520, Optical Microlithography XX; 65204A (2007) https://doi.org/10.1117/12.712167
Event: SPIE Advanced Lithography, 2007, San Jose, California, United States

Abstract

In modern photolithography, the dose latitude, Normalized Image Log Slope (NILS), and hence the image quality are closely related to the gradient of the aerial image intensity at the evaluation point. The placement of sub-resolution assist feature (SRAF) in isolated lines helps improve the aerial image quality by increasing the gradient. Traditionally, it is simple and straightforward to calculate the effect of the SRAF placement on the gradient at a certain evaluation point. The gradients before and after the SRAF placement are computed separately. The difference between these two gradients indicates the magnitude of the effect. However, this simple methodology is only convenient when the location of the SRAF placement is known. In addition, this methodology is not adaptable to searching for the optimum placement, as many potential placements need to be evaluated. In this report, an innovative and rapid solution for SRAF placement is presented. The methodology output indicates the optimal location for the SRAF placement to increase the gradient of the aerial image is about 210 nm from the drawn edge of the iso-line and is independent of the iso-line structure for an annular illumination system. The results are verified by measuring the gradient difference with an independent tool.

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Jianliang Li, Qiliang Yan, and Lawrence S. Melvin III "Rapid search of the optimum placement of assist feature to improve the aerial image gradient in iso-line structure", Proc. SPIE 6520, Optical Microlithography XX, 65204A (27 March 2007); https://doi.org/10.1117/12.712167

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