Chinese Optics Letters, 2023, 21 (7): 071204, Published Online: Jul. 24, 2023   

Improving accuracy and sensitivity of diffraction-based overlay metrology

Author Affiliations
1 School of Microelectronics, Shanghai University, Shanghai 200072, China
2 Department of Precision Optics Engineering, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Figures & Tables

Fig. 1. (a) The microscopic picture of modern CPU chip[18] is on the left, and a close section of the two-layer structure is on the right. (b) Signal formation in DBO schematic diagram[19,20]; α is proportional to OVL Δl; β is the phase shift due to the optical path difference between the two diffracted beams, and its value is twice the distance difference between the bottom and top gratings.

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Fig. 2. Cross-sectional diagram of OVL mark (the bottom grating profile is parabolic).

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Fig. 3. Cross-sectional diagram of OVL mark (the bottom grating profile is linearly deformed).

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Fig. 4. Variation of error signal with slope w under different orders of diffracted light.

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Fig. 5. Cross-sectional diagram of OVL mark (both top and bottom grating profiles are linearly deformed).

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Fig. 6. Variation of error signal with amplitude ratio η under different orders of diffracted light. (a) The bottom and top gratings are tilted in the opposite direction (the absolute value of γ is greater than the absolute value of ε), ε = 0.005, γ = −0.01. (b) The bottom and top gratings are tilted in the same direction, ε = 0.005, γ = 0.01.

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Fig. 7. Variation of the absolute of function F (ε, γ) with the slope of the top grating ε and bottom grating γ. (a) n = 1; (b) n = 2.

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Fig. 8. Variation of 32η*F (ε, γ) (which is defined as F1) with respect to the amplitude ratio η for different orders of diffracted light (the bottom and top gratings are tilted in the same direction, ε = 0.005, γ = 0.01).

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Wenhe Yang, Nan Lin, Xin Wei, Yunyi Chen, Sikun Li, Yuxin Leng, Jianda Shao. Improving accuracy and sensitivity of diffraction-based overlay metrology[J]. Chinese Optics Letters, 2023, 21(7): 071204.

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