Radial Filter Device for Asymmetric Pupil Illumination Correction
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Solution Overview
Problem
Existing illumination systems for lithographic applications face challenges in correcting complex asymmetries in the pupil illumination, as current filter technologies are limited to correcting only elliptical asymmetries and do not effectively address the angular spectrum or intensity asymmetries in the exit pupil.
Innovation Solution
A filter device comprising multiple radially arranged filter elements with adjustable insertion depth and orientation, capable of producing a shadow effect to correct asymmetries in the pupil illumination, while maintaining the pupil size and telecentricity, using a configuration of rod-like elements with partial transparency and sensors for precise intensity measurement and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a rod-like optical integrator is used to even the illumination of the field, then the illumination uniformity in the field plane is improved, but an asymmetric pupil illumination (ellipticity) occurs due to the rectangular cross section and differential reflection losses
Solution Approach 1:
The filter device divides the pupil plane into multiple radial segments, each with independently adjustable transmission characteristics. This segmentation allows differential attenuation of light in different angular regions of the pupil, enabling correction of the ellipticity caused by the rod integrator while preserving the overall illumination uniformity.
Solution Approach 2:
Different radial segments of the filter device are assigned different transmission properties tailored to the specific illumination asymmetry in each region. This local customization of filter characteristics enables precise correction of the asymmetric pupil illumination without affecting other regions, directly addressing the ellipticity problem.
2Shape
If adjustable symmetric pupil filters are used to correct ellipticity, then the angular distribution of illumination can be adjusted, but complex asymmetries in the pupil illumination cannot be corrected
Solution Approach 1:
The filter device incorporates dynamically adjustable elements that can be independently positioned and oriented in different radial segments. This dynamic adjustability transforms a static symmetric filter into a versatile system capable of adapting to various asymmetry patterns, including complex non-elliptical distortions, by reconfiguring the transmission characteristics in real-time.
Solution Approach 2:
The invention deliberately introduces asymmetric filter elements and configurations into the pupil plane to counterbalance the asymmetric illumination patterns. By employing asymmetric attenuation profiles in specific radial segments, the system can correct complex asymmetries that symmetric filters cannot address.
3Shape
If filter elements are introduced into the beam path to correct pupil asymmetry, then the asymmetry correction is achieved, but the pupil size and telecentricity may be affected
Solution Approach 1:
The filter device is designed to extract only the asymmetric components of the pupil illumination for correction, while leaving the symmetric parameters (pupil size and telecentricity) unaffected. This is achieved by implementing filters that selectively attenuate light in specific angular regions without introducing lateral displacement or overall intensity changes that would affect pupil geometry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The filter device enables precise correction of asymmetries in the pupil illumination, ensuring even illumination distribution and maintaining the desired pupil parameters, allowing for comprehensive calibration and adjustment of the illumination system without influencing other pupil properties.
Implementation Method 1
each of these filter elements projecting substantially in the radial direction into the beam path of a bundle of projecting rays which passes through the illumination system from the light source to the plane in which a structure-bearing mask such as a reticle is arranged and thus produces a shadow effect
Implementation Method 2
as a result of the plurality of total reflections of the light coupled into the rod-like optical integrator, a thorough mixture of the illumination light is achieved on its outside surfaces
Data Source
AI summary
The invention relates to a filter device for an illumination system, especially for the correction of the illumination of the illuminating pupil, including a light source, with the illumination system being passed through by a bundle of illuminating rays from the light source to an object plane, with the bundle of illuminating rays impinging upon the filter device, including at least one filter element which can be introduced into the beam path of the bundle of illuminating rays, with the filter element including an actuating device, so that the filter element can be brought with the help of the actuating device into the bundle of illuminating rays.