Optimized overlay metrology based on polarization eigenstate of Mueller matrix.

Area of Science:

• Semiconductor manufacturing
• Optical metrology
• Lithography quality control

Background:

• Overlay metrology is crucial for semiconductor lithography quality.
• Empirical diffraction-based overlay (DBO) methods are widely used but face challenges in indicator selection.
• Selecting indicators with linearity, sensitivity, and robustness is a key difficulty.

Purpose of the Study:

• To propose a new overlay indicator based on the polarization eigenstate of the retardance Mueller matrix.
• To analyze the general property requirements and optimization mechanisms for overlay indicator selection.
• To provide a theoretical basis and practical tool for DBO indicator design.

Main Methods:

• Development of a novel overlay indicator using ellipsometry-based metrology.
• Theoretical analysis of indicator properties and optimization.
• Validation through simulations and experimental testing on double-layer-grating targets.

Main Results:

• The proposed polarization eigenstate indicator demonstrates superior accuracy and robustness compared to existing Mueller matrix indicators.
• Effectiveness validated by both simulations and experiments.
• The method is suitable for typical double-layer-grating overlay targets.

Conclusions:

• The novel polarization eigenstate indicator offers improved performance for overlay metrology.
• This work provides a theoretical foundation for designing DBO indicators.
• The proposed method represents a potentially valuable new tool for industrial overlay metrology practices.