Optical Measurement Pupil Stop Array for Lithography Simulation
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Solution Overview
Problem
Current methods for simulating illumination and imaging properties in optical production systems are limited in accuracy, particularly in reducing illumination angle-dependent artifacts and accounting for 3-D mask effects during lithography, especially in EUV lithography.
Innovation Solution
A simulation method that utilizes multiple pupil stops with varying shapes and orientations, combined with a displacement drive and actuator system, to record measurement aerial images at multiple positions, allowing for precise selection of pupil stops and defocus values, and modeling illumination direction-dependent mask spectra to optimize the simulation of aerial images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single pupil stop is used for measurement, then the device complexity is reduced, but the measurement precision and accuracy of simulating illumination settings deteriorates
Solution Approach 1:
The patent divides the illumination measurement into multiple segments by using a plurality of pupil stops, each representing different illumination settings (e.g., dipole, quadrupole, annular). Each pupil stop captures a specific angular range, and the results are combined to achieve comprehensive and accurate simulation of complex illumination settings, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The patent introduces an additional dimensional approach by specifying multiple measurement positions for each pupil stop (e.g., central position and offset positions). This multi-position measurement strategy adds a spatial dimension to the data collection, enabling more accurate reconstruction of the complex mask transfer function and aerial image simulation without requiring an overly complex single-position system.
2Measurement precision
If multiple measurement positions are used for each pupil stop, then the measurement precision improves, but the loss of time increases
Solution Approach 1:
The patent implements preliminary action by pre-specifying the measurement positions (central and offset positions) and pre-configuring the pupil stops before actual measurement begins. The measurement plan is prepared in advance with all positions and parameters defined, allowing the system to efficiently execute the measurements without real-time decision-making, thus reducing the overall time loss while maintaining high measurement precision.
Solution Approach 2:
The patent employs periodic action by systematically measuring at multiple predefined positions (central position followed by offset positions) in a regular sequence. This periodic measurement pattern allows for efficient data collection across different spatial locations, improving the accuracy of the mask transfer function reconstruction while maintaining a structured and time-efficient measurement process.
3Adaptability or versatility
If conventional illumination settings are used, then the ease of operation is maintained, but the adaptability to different illumination configurations decreases
Solution Approach 1:
The patent implements universality by designing a measurement system that can handle multiple illumination settings (dipole, quadrupole, annular, and custom configurations) using a unified approach with standardized pupil stops and measurement positions. The system provides a universal framework that adapts to different illumination types without requiring fundamentally different measurement procedures, thus maintaining ease of operation while significantly improving adaptability.
Solution Approach 2:
The patent utilizes parameter changes by allowing flexible configuration of pupil stop parameters (shape, size, position, orientation) and measurement parameters (defocus values, pixel sizes) to adapt to different illumination settings. This parameter-based approach enables the system to accommodate various illumination configurations by simply adjusting parameters rather than changing the fundamental measurement methodology, preserving ease of operation while enhancing versatility.
Data Source
AI summary
When simulating illumination and imaging properties of an optical production system when illuminating and imaging an object by use of an optical measurement system of a metrology system, the optical measurement system having an illumination optical unit for illuminating the object and a pupil stop, in particular a displaceable pupil stop, and having an imaging optical unit for imaging the object into an image plane is initially provided. When simulating the properties of the optical production system with the optical measurement system, a plurality of pupil stops are initially provided. Measurement aerial images are then recorded by use of the plurality of pupil stops. A complex mask transfer function is reconstructed from the recorded measurement aerial images and a 3-D aerial image is determined from this function and the illumination setting of the optical production system. This yields an improved simulation method.