Metrology Target Design for Lithographic Overlay Error Compensation
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Solution Overview
Problem
Current lithographic processes face challenges in accurately measuring and minimizing overlay errors, which are critical for ensuring the precision and quality of integrated circuits during manufacturing, as existing metrology targets are not optimized to account for optical aberrations in lithographic systems.
Innovation Solution
A method for designing metrology targets that involves determining the sensitivity of parameters to various optical aberrations and optimizing the target design to minimize overlay errors by using the optical system's aberrations, specifically employing Zernike polynomials to simulate and calculate the impact of aberrations on the target design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing metrology targets are used without optimization, then the manufacturing process can proceed, but overlay error measurements are inaccurate due to unaccounted optical aberrations
Solution Approach 1:
The patent applies preliminary action by determining the sensitivity of metrology target parameters to optical aberrations before actual manufacturing. The method calculates sensitivity values for different Zernike polynomials representing various aberrations, and uses these pre-determined sensitivities to optimize the target design in advance, ensuring accurate overlay measurements from the outset.
Solution Approach 2:
The patent implements parameter changes by modifying the metrology target design parameters based on calculated sensitivities to optical aberrations. The optimization process adjusts target geometry parameters (such as grating dimensions, spacing, and patterns) to compensate for expected aberration effects, thereby improving measurement accuracy despite the presence of optical system imperfections.
2Measurement precision
If metrology targets are optimized to account for optical aberrations, then overlay error measurement accuracy improves, but the design complexity increases
Solution Approach 1:
The patent manages design complexity by systematically varying target parameters based on sensitivity calculations. Rather than creating entirely complex new designs, the method optimizes existing target geometry parameters (dimensions, spacing, patterns) according to calculated sensitivity values, achieving improved accuracy through controlled parameter adjustments.
Solution Approach 2:
The patent uses a modeling and simulation approach where virtual copies of metrology targets are created and tested against various aberration scenarios. The sensitivity analysis is performed on simulated target models exposed to simulated optical systems with known aberrations, allowing optimization without requiring physical prototypes or complex manual design iterations.
Data Source
AI summary
A method of metrology target design is described. The method includes determining a sensitivity of a parameter for a metrology target design to an optical aberration, determining the parameter for a product design exposed using an optical system of a lithographic apparatus, and determining an impact on the parameter of the metrology target design based on the parameter for the product design and the product of the sensitivity and one or more of the respective aberrations of the optical system.