Projection Lens Aberration Fitting for Faster Field Correction
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Solution Overview
Problem
The measurement of aberrations in projection lenses for microlithographic projection exposure apparatuses is time-consuming, leading to reduced productivity due to interruptions in the exposure process, and existing methods do not accurately correct aberrations that form during the exposure operation.
Innovation Solution
A method involving a fit function with a polynomial dependence on spatial coordinates and rigid body sensitivities is used to extrapolate aberration measurements from a limited number of field points, allowing for accurate correction of aberrations using a manipulator system, reducing the need for additional interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If aberration measurement is performed at multiple field points to improve correction accuracy, then manufacturing precision is improved, but productivity deteriorates due to increased measurement time and exposure interruptions
Solution Approach 1:
The patent segments the field plane into a limited number of measured field points and uses polynomial functions to extrapolate aberration values to other field points. This segmentation allows measurement at only a few points while maintaining accuracy across the entire field through mathematical modeling, thus reducing measurement time without sacrificing correction accuracy.
Solution Approach 2:
The patent replaces the mechanical process of physically measuring aberrations at every field point with a mathematical substitution using polynomial functions. The polynomial model extrapolates aberration values from measured points to unmeasured points, substituting mechanical measurement with mathematical calculation to maintain accuracy while reducing measurement time.
2Productivity
If the number of measured field points is limited to maintain productivity, then productivity is improved, but measurement precision deteriorates
Solution Approach 1:
The patent uses polynomial functions to substitute for mechanical measurement at every field point. By fitting polynomial models to the limited measured data, the system extrapolates aberration values to all field points, maintaining measurement precision without requiring physical measurement at every point, thus preserving productivity.
Solution Approach 2:
The patent changes the approach from direct measurement at all field points to measurement at limited points combined with polynomial parameter fitting. The polynomial parameters are adjusted to match the measured aberration values, allowing the system to infer aberration characteristics at unmeasured points, thus maintaining precision while reducing measurement requirements.
3Manufacturing precision
If aberration measurement is performed frequently to correct aberrations forming during exposure, then manufacturing precision is improved, but loss of time increases due to repeated interruptions
Solution Approach 1:
The patent performs aberration measurement and correction calculation in advance during exposure interruptions, using the polynomial model to quickly determine required manipulator changes. By preparing correction data beforehand and using efficient extrapolation, the system minimizes the time needed for each interruption while maintaining continuous exposure progress.
Solution Approach 2:
The patent replaces time-consuming direct measurement and calculation with polynomial-based extrapolation. The polynomial model allows rapid calculation of aberration values and required manipulator changes without repeated physical measurement, reducing the time for each interruption while maintaining correction accuracy.
Data Source
AI summary
A method for evaluating measured values of projection lens (22) aberration(s) determined at plural field points in a field plane of the projection lens which has a plurality of optical elements (E1-E4) guiding exposure radiation and an optical element manipulator system (M1-M4) for carrying out a rigid body movement. The method includes: providing a fit function (62) having a polynomial function (64) that depends on the spatial coordinates defining a field plane and a rigid-body-sensitivities (70) term (66) for multiple locations in the field plane each describing a dependence of the aberration (63) on a degree of freedom of movement (68) at the relevant locations that is controllable by the manipulator system. The method further includes extrapolating the measured values (50) determined at the plural field points (52) to further field points (56) of the projection lens by fitting the fit function to the determined measured values.