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Novel method to achieve CD modeling in the presence of higher diffraction orders
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Paper Abstract

The use of large numerical apertures in spectroscopic ellipsometer (SE) or reflectometer (SR) designs allows for smaller measurement targets, but it may introduce side effects like the propagation of high diffraction orders into the collection pupil. In the normal optical critical dimension (CD) measurement condition, the zeroth-order diffracted light is the only light illuminating the pupil. However, when the pitch of the measurement target is large enough, the high-order diffracted light can also enter the pupil and mix with the zeroth-order diffracted light. This contaminates the measurement and leads to inaccuracies in fitting the target's model to the data.

In this paper, we propose a method that retains good measurement results even when the collected spectrum includes contamination due to high-order diffraction. In this approach, we treat the high-order diffracted light contamination as the primary source of error in the measurement. We modify the maximum likelihood estimation using one of three different additional weighting schemes that lead to optimal measurement results. In general, we have found that not all the wavelengths in the affected wavelength zone have the same contamination impact

. The above concept was validated using a synthetic and an actual large pitch CD measurement, successfully demonstrating that the proposed method virtually eliminates the inaccuracy. These results show that this method effectively allows the user to use the full wavelength range of interest from 190-800nm, in spite of the fact that a significant fraction of this wavelength range includes the presence of higher diffraction orders. This method thus allows for accurate measurements of large pitch SRAM targets and enables yield improvement for N5 and newer logic devices.

Paper Details

Date Published: 26 March 2019
PDF: 6 pages
Proc. SPIE 10959, Metrology, Inspection, and Process Control for Microlithography XXXIII, 1095921 (26 March 2019); doi: 10.1117/12.2522826
Show Author Affiliations
Phillip R. Atkins, KLA Corp. (United States)
Liequan Lee, KLA Corp. (United States)
Shankar Krishnan, KLA Corp. (United States)
Chi-Fu Yen, Taiwan Semiconductor Manufacturing Co., Ltd. (Taiwan)
Shyh-Shii Pai, Taiwan Semiconductor Manufacturing Co., Ltd. (Taiwan)
Nick Weihan Chang, Taiwan Semiconductor Manufacturing Co., Ltd. (China)
Hsien-Hung Chang, Taiwan Semiconductor Manufacturing Co., Ltd. (China)
Li-Shiuan Tsai, Taiwan Semiconductor Manufacturing Co., Ltd. (China)
Sheng-Yang Tseng, Taiwan Semiconductor Manufacturing Co., Ltd. (China)
Jan-Hau Chang, Taiwan Semiconductor Manufacturing Co., Ltd. (China)
Yung-Hsiang Lin, Taiwan Semiconductor Manufacturing Co., Ltd. (China)
Chu-Han Chiu, KLA Corp. (United States)
Chun-Sheng Wu, KLA Corp. (United States)


Published in SPIE Proceedings Vol. 10959:
Metrology, Inspection, and Process Control for Microlithography XXXIII
Vladimir A. Ukraintsev; Ofer Adan, Editor(s)

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