Optimized wavelength selection for diffraction-based overlay measurement by minimum asymmetry factor variation with finite-difference time-domain simulation

Hsieh, Hung-Chih; Cheng, Jui-Ming; Yeh, Yun-Chi

doi:10.1364/ao.449500

Cited by 8 publications

(8 citation statements)

References 19 publications

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“…Other parameters were set as follows. The empirical normal and uniform distribution parameters are determined according to the existing studies as separately presented in tables 4 and 5 [13,15,16]. The iterative convergence threshold τ of CDF-GSA is set as 0.01.…”

Section: Experiments Designmentioning

confidence: 99%

“…Then, a correction method was developed to improve the OVL metrology accuracy, taking different illumination wavelengths and polarization states under asymmetric conditions into account. Hsieh et al investigated the defect feature combination of the SWA and the top rounded angle [16]. Through introducing asymmetric factors, measurement wavelength is optimized to improve OVL metrology accuracy.…”

Section: Introductionmentioning

confidence: 99%

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Neural network driven sensitivity analysis of diffraction-based overlay metrology performance to target defect features

Wang,

Meng,

Zhang

et al. 2024

Meas. Sci. Technol.

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Overlay (OVL) is one significant performance indicator for the lithography process control in semiconductor manufacturing. The accuracy of the OVL metrology is extremely critical for guarantee the lithography quality. Currently, diffraction-based overlay (DBO) is one of the mainstream OVL metrology techniques. Unfortunately, the accuracy of the DBO metrology is largely affected by the defect features of the overlay target. Therefore, there is a strong need to investigate the impacts of these target defects on the DBO metrology performance. However, efficiently investigating the statistical and interactive impacts of various DBO target defects remains challenging. This study aims to address this issue through proposing an intelligent sensitivity analysis approach. A cumulative distribution based Global Sensitivity Analysis (GSA) method is utilized to assess the nonlinear influences of multiple defects in the OVL target on the DBO inaccuracy. The scenarios with both known and unknow distributions of the OVL target defects are considered. For the former, a neural network driven forward model is constructed for fast calculating the optical diffraction responses to accelerate the GSA process. For the latter, another neural network based inverse model are built for efficiently estimating the distribution of the target defects. Finally, a series of simulation experiments are conduct for typical DBO targets with multiple common defect features. The results demonstrate the effectiveness and robustness of the proposed approach as well as give valuable insights into the DBO defect analysis. Our study provides a strong tool to assist the practitioners in achieving intelligent and efficient DBO analysis and thus in enhancing OVL metrology performance.

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Section: Experiments Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Neural network driven sensitivity analysis of diffraction-based overlay metrology performance to target defect features

Wang,

Meng,

Zhang

et al. 2024

Meas. Sci. Technol.

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show abstract

“…Their findings indicate that ensuring the linewidth of the bottom overlay mark matches the pitch of the top overlay mark effectively reduces the overlay error. Hung-Chih Hsieh proposed an innovative method for wavelength selection in overlay metrology that eliminates the need for wafers [25]. A calculation model was developed to account for the presence of asymmetric overlay marks, which revealed that additional diffraction intensities contribute to the overlay error.…”

Section: Introductionmentioning

confidence: 99%

Adaptive Weighted Error-Correction Method Based on the Error Distribution Characteristics of Multi-Channel Alignment

Song,

Wang,

et al. 2024

Sensors

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As process nodes of advanced integrated circuits continue to decrease below 10 nm, the requirement for overlay accuracy is becoming stricter. The alignment sensor measures the position of the alignment mark relative to the wafer; thus, sub-nanometer alignment position accuracy is vital. The Phase Grating Alignment (PGA) method is widely used due to its high precision and stability. However, the alignment error caused by the mark asymmetry is the key obstacle preventing PGA technology from achieving sub-nanometer alignment accuracy. This error can be corrected using many methods, such as process verification and multi-channel weighted methods based on multi-diffraction, multi-wavelength and multi-polarization state alignment sensors. However, the mark asymmetry is unpredictable, complex and difficult to obtain in advance. In this case, the fixed-weight method cannot effectively reduce the alignment error. Therefore, an adaptive weighted method based on the error distribution characteristic of a multi-channel is proposed. Firstly, the simulation result proves that the error distribution characteristic of the multi-alignment result has a strong correlation with the mark asymmetry. Secondly, a concrete method of constructing weight values based on error distribution is described. We assume that the relationship between the weight value of each channel and the deviations of all channels’ results is second-order linear. Finally, without other prior process correction in the simulation experiment, the residual error’s Root Mean Square (RMS) of fixed weighted method is 14.0 nm, while the RMS of the adaptive weighted method is 0.01 nm, when dealing with five typical types of mark asymmetry. The adaptive weighted method exhibits a more stable error correction effect under unpredictable and complicated mark asymmetry.

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“…DBO is traditionally performed by measuring the interference signal of the ±1st diffraction order light that is diffracted by the top and bottom structures to obtain the value of overlay [22]. The accuracy of the overlay could be influenced by the asymmetry of the overlay target [13,23].…”

Section: Introductionmentioning

confidence: 99%

Mitigating the Impact of Asymmetric Deformation on Advanced Metrology for Photolithography

Yang,

Yao,

Cao

et al. 2024

Applied Sciences

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Controlling overlay in lithography is crucial for improving the yield of integrated circuit manufacturing. The process disturbances can cause undesirable morphology changes of overlay targets (such as asymmetric grating), which can significantly impact the accuracy of overlay metrology. It is essential to decouple the overlay target asymmetry from the wafer deformation, ensuring that the overlay metrology is free from the influence of process-induced asymmetry (e.g., grating asymmetry and grating imbalance). Herein, we use an asymmetric grating as a model and show that using high-diffraction-order light can mitigate the impact of asymmetric grating through the rigorous coupled-wave analysis (RCWA) method. In addition, we demonstrate the diffraction efficiency as a function of the diffraction order, wavelength, and pitch, which has guiding significance for improving the measurement accuracy of diffraction-based overlay (DBO) metrology.

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Optimized wavelength selection for diffraction-based overlay measurement by minimum asymmetry factor variation with finite-difference time-domain simulation

Cited by 8 publications

References 19 publications

Neural network driven sensitivity analysis of diffraction-based overlay metrology performance to target defect features

Neural network driven sensitivity analysis of diffraction-based overlay metrology performance to target defect features

Adaptive Weighted Error-Correction Method Based on the Error Distribution Characteristics of Multi-Channel Alignment

Mitigating the Impact of Asymmetric Deformation on Advanced Metrology for Photolithography

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