5 April 2012 Quality indicators of image-based overlay
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Abstract
A new method for indicating the image quality of overlay measurement is proposed in this paper. Due to the constraint of the overlay control tolerance, the overlay metrology requirement has become very stringent. Current indicators such as the total measurement uncertainty (TMU) are insufficient to guarantee a good overlay measurement. This paper describes two quality indicators, the contrast index (CI) and the asymmetry index (AI). The CI is a crucial quality indicator that affects the overlay accuracy greatly. The AI, based on an imaging process with modified cross-correlation operation, shows alignment mark robustness in both the x and the y directions. For determination of the best recipe, the box-in-box overlay marks are measured to obtain the images with different conditions. The conventional TMU indicators are used first to sieve out the better choices. Then the CI and AI can help to judge whether the overlay results are reliable and can be applied to monitoring of process variations.
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Yen-Liang Chen, Yen-Liang Chen, Jacky Huang, Jacky Huang, Rita Lee, Rita Lee, Chen-Ming Wang, Chen-Ming Wang, Chih-Ming Ke, Chih-Ming Ke, Tsai-Sheng Gau, Tsai-Sheng Gau, } "Quality indicators of image-based overlay", Proc. SPIE 8324, Metrology, Inspection, and Process Control for Microlithography XXVI, 83241C (5 April 2012); doi: 10.1117/12.917995; https://doi.org/10.1117/12.917995
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