Reducing the overlay metrology sensitivity to perturbations of the measurement stack

Zhou, Yue; Park, DeNeil; Gutjahr, Karsten; Gottipati, Abhishek; Vuong, T. H. H.; Bae, Sung Yong; Stokes, Nicholas; Jiang, Aiqin; Hsu, Po Ya; O'Mahony, Mark; Donini, A.; Visser, Bart; Ruiter, Chris de; Grzela, Grzegorz; Laan, Hans van der; Jak, Martin; Izikson, Pavel; Morgan, Stephen P.

doi:10.1117/12.2257913

Cited by 2 publications

(2 citation statements)

References 1 publication

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“…This Z value is used for single-cell overlay calculation, which means it is a necessary factor. A smooth and radial shape is observed on the wafer, which is independent of the field coordinates [4] . Ideally, it's needed to measure one conventional target per field to calculate the z-value and use it not only for single-cell overlay calculation but also for process monitoring.…”

Section: Thickness Calibration Is Used For Single-cell Overlaymentioning

confidence: 84%

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Single-cell measurement by parallax effect for process control and target size reduction

Lee,

Jang,

Hong

et al. 2024

Metrology, Inspection, and Process Control XXXVIII

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As the cell size of memory devices continues to shrink, tighter On-Product Overlay (OPO) specifications toward a 1nm OPO budget are required. EUV (extreme ultraviolet lithography) production was adopted in 2019 and the next lithography development known as High NA EUV will fulfill market demand beyond 5nm and 3nm process nodes. High NA EUV requires shrinking the scribe line from 50µm to 40µm, which results in new requirements for the target size to be smaller than the current size µDBO (16x16µm) and AIM® (24x24µm) targets. The reduction in the scribe line is certainly beneficial to chipmakers for wafer real estate and yield. For metrology measurements in high-volume manufacturing (HVM), the main optical overlay (OVL) metrology usually uses imaging-based overlay (IBO) technology, while in other cases diffraction-based overlay (DBO) and scatterometry-based overlay (SCOL®) are used. All methods (IBO, DBO, and SCOL) face the same challenge of target size reduction. For instance, IBO targets require a restricted number of grating bars. Most importantly, the smaller the target size, the less kernel information affects measurement quality [1][2][3] . The spot size of DBO is larger than the target size, so it increases noise sources from the target's surroundings and affects the OVL accuracy. SCOL technology offers several advantages over IBO and DBO when measuring small targets since the spot size in SCOL is smaller and the spot navigation has a higher control mechanism. In this paper, we present a method called parallax to measure a single-cell overlay using pupil information. We will demonstrate three values: First, the target size can be reduced by up to half. Second, the measurement time is improved by saving navigation time from cell to cell. Third, the optical z-value for each point is reported along with OVL measurements. Additionally, the feasibility of single-cell OVL measurement and optical z-value is demonstrated as KPIs for process control.

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Section: Thickness Calibration Is Used For Single-cell Overlaymentioning

confidence: 84%

“…Grating imbalance (GI) is well known as stack variations in Figure 5. Stack variations are caused by chemical mechanical polishing (CMP) and thin fill deposition across wafers [4] . This GI can lead to overlay errors because different optical paths result in different signal intensities during OVL calculation.…”

Section: Grating Imbalance Due To Processmentioning

confidence: 99%

Single-cell measurement by parallax effect for process control and target size reduction

Lee,

Jang,

Hong

et al. 2024

Metrology, Inspection, and Process Control XXXVIII

View full text Add to dashboard Cite

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Selection of DBO measurement wavelength for bottom mark asymmetry based on FDTD method

Xu¹,

Wu²,

Dong³

et al. 2019

J. Semicond.

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A physical model for simulating overlay metrology employing diffraction based overlay (DBO) principles is built. It can help to optimize the metrology wavelength selection in DBO. Simulation result of DBO metrology with a model based on the finite-difference time-domain (FDTD) method is presented. A common case (bottom mark asymmetry) in which error signals are always induced in DBO measurement due to the process imperfection were discussed. The overlay sensitivity of the DBO measurement across the visible illumination spectrum has been performed and compared. After adjusting the model parameters compatible with the actual measurement conditions, the metrology wavelengths which provide the accuracy and robustness of DBO measurement can be optimized.

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Reducing the overlay metrology sensitivity to perturbations of the measurement stack

Cited by 2 publications

References 1 publication

Single-cell measurement by parallax effect for process control and target size reduction

Single-cell measurement by parallax effect for process control and target size reduction

Selection of DBO measurement wavelength for bottom mark asymmetry based on FDTD method

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