Projection Objective Min-Max Aberration Optimization
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Solution Overview
Problem
Existing methods for adjusting projection objectives in microlithography machines struggle to accurately minimize aberrations across various field points, leading to suboptimal image-forming properties, particularly when dealing with multiple lithographic processes.
Innovation Solution
The implementation of min-max optimization techniques to adjust parameters at various field points, focusing on minimizing the maximum aberration value, which is more effective than traditional least square optimization, especially when using Zernike coefficients to describe wave aberrations and lithographically important variables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If least square optimization is used to minimize aberrations, then the average root-mean-square deviation is reduced, but the maximum aberration at critical field points remains suboptimal
Solution Approach 1:
The patent changes the optimization parameter from minimizing average root-mean-square deviation to minimizing the maximum absolute value of aberration parameters at critical field points. This parameter transformation shifts the optimization focus from statistical average to worst-case performance, directly addressing the contradiction between average precision and maximum precision.
Solution Approach 2:
Instead of optimizing for the average case (least square), the patent inverts the approach by optimizing for the worst-case scenario (min-max). This inversion prioritizes the most critical field points with maximum aberrations, ensuring that the worst performance is improved rather than just the average.
2Manufacturing precision
If optimization focuses on average aberration reduction, then overall image quality improves, but image-forming properties for specific lithographic processes remain suboptimal
Solution Approach 1:
The patent applies local quality by identifying and optimizing specific critical field points that are most important for different lithographic processes. Rather than uniform optimization across all field points, the method selectively targets local areas (field points) that have the greatest impact on process-specific performance, thereby improving both overall quality and process adaptability.
Solution Approach 2:
The patent introduces dynamic adaptability by allowing the selection of different critical field points and aberration parameters depending on the specific lithographic process requirements. The optimization criteria can be dynamically adjusted to match different process needs, making the system versatile across multiple applications.
3Ease of operation
If traditional adjustment methods are used, then the adjustment process is simple, but the adjustment precision and image-forming quality are insufficient
Solution Approach 1:
The patent implements self-service by using measured aberration data to automatically determine the critical field points and optimize the adjustment parameters. The system uses the projection objective's own measurement data to guide the optimization process, eliminating the need for external complex measurement equipment while achieving high precision adjustment.
Data Source
AI summary
A projection objective having a number of adjustable optical elements is optimized with respect to a number of aberrations by specifying a set of parameters describing imaging properties of the objective, each parameter in the set having an absolute value at each of a plurality of field points in an image plane of the projection objective. At least one of the optical elements is adjusted such that for each of the parameters in the set, the field maximum of its absolute value is minimized.