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Line-edge roughness (LER) characterization is vital in the semiconductor industry to this day. This paper presents an EKEI (enhanced knife edge interferometry)-based system for photomask LER characterization. From the given EKEI-based system, the LER on the photomask pattern can be characterized. In this paper, the Fresnel (F) number-based geometrical optical model was developed for the LER-induced edge diffraction fringe simulation. The LER here was defined by three times the standard deviation of the edge profile on the photomask. Periodic rectangular functions were employed to characterize LER effects on the diffraction fringe patterns in simulation. The simulation-generated fringe pattern was then analyzed by cross-correlation. From the simulation result, the fringe pattern will get attenuated when adding the LER onto the line edge profile. Once the LER value increases, some of the high-order fringes vanish. A negative correlation between the similarity and the LER value was discovered. From the F number-based simulation model, the real photomask decorated with different LER values was designed and fabricated. After the photomask writing process, we used the EKEI system to scan the LER-programmed pattern for photomask LER characterization. By using the cross-correlation, the same trend was found in the experiment and simulation results. The fringe pattern from the edge was attenuated while the LER was added to the edge. The geometrical-based simulation and analysis model for photomask LER characterization was validated. From the simulation results, the fringe pattern from the edge was attenuated when adding LER on the edge. The experiment results show good agreement with the simulation ones. In sum, the proposed EKEI-based system has great potential to be utilized for on-machine photomask LER characterization and those defect inspection. The F number-based geometrical optical model also has the potential for diffraction-free pattern design and analysis.
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Line-edge-roughness characterization of photomask patterns and lithography-printed patterns
This paper presents the line-edge-roughness (LER) characterization of the photomask patterns and the lithography-printed patterns by enhanced knife edge interferometry (EKEI) that measures the interferometric fringe patterns occurring when the light is incident on the patterned edge. The LER is defined as a geometric deviation of a feature edge from an ideal sharp edge. The Fresnel number-based computational model was developed to simulate the fringe patterns according to the LER conditions. Based on the computational model, the photomask patterns containing LER features were designed and fabricated. Also, the patterns were printed on the glass wafer by photolithography. The interferometric fringe patterns of those two groups of patterns were measured and compared with the simulation results. By using the cross-correlation method, the LER effects on the fringe patterns were characterized. The simulation and experimental results showed good agreement. It showed that the amplitude of the fringe pattern decreases as the LER increases in both cases: photomask patterns and printed wafer patterns. As a result, the EKEI and its analysis methods showed the potential to be used in photomask design and pattern metrology, and inspection for advancing semiconductor manufacturing processes.
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- Award ID(s):
- 2124999
- PAR ID:
- 10552498
- Publisher / Repository:
- Precision Engineering
- Date Published:
- Journal Name:
- Precision Engineering
- Volume:
- 88
- Issue:
- C
- ISSN:
- 0141-6359
- Page Range / eLocation ID:
- 235 to 240
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.precisioneng.2024.02.006
