Microlithography Illumination Optics Intensity Control
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Solution Overview
Problem
Existing microlithography illumination optics struggle to independently control and monitor illumination intensity distribution across the object field without affecting the illumination angle distribution, leading to unwanted aberrations and inefficiencies, especially when using EUV sources.
Innovation Solution
The illumination optics divide the illumination light into sub-bundles assigned to different angles, which are superimposed in a separate plane from the object plane, allowing for independent adjustment and monitoring of intensity distribution without affecting the illumination angles, using a field intensity setting device and facet mirrors to achieve this.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the illumination optics control illumination intensity distribution across the object field, then the intensity distribution is adjusted, but the illumination angle distribution is affected causing unwanted aberrations
Solution Approach 1:
The illumination light is divided into multiple radiation sub-bundles, each assigned to different illumination angles. This segmentation allows independent control of intensity for each angle group without affecting the angular distribution, as each sub-bundle can be adjusted separately while maintaining the overall angle structure.
Solution Approach 2:
A superposition plane is introduced as a new spatial dimension, separated from the object plane. The radiation sub-bundles are superimposed in this separate plane, allowing intensity control to occur in one dimension (the superposition plane) without disturbing the illumination angle distribution in another dimension (the object field).
2Ease of operation
If a field intensity setting device is placed in the object plane to control intensity distribution, then intensity can be adjusted, but optical components are required between the object plane and superposition plane increasing device complexity
Solution Approach 1:
The field intensity setting device is extracted from the object plane and placed in the superposition plane. This relocation eliminates the need for additional optical components between the object plane and superposition plane, as the intensity control is performed directly in the superposition plane where the radiation sub-bundles are already superimposed.
3Volume of moving object
If the illumination optics size is reduced, then the system becomes more compact, but the ability to independently control intensity distribution without affecting angle distribution is compromised
Solution Approach 1:
By utilizing the superposition plane as a separate spatial dimension from the object plane, the system achieves independent control of intensity and angle distributions without requiring increased optical path length or larger component sizes. The separation of planes allows compact arrangement while maintaining functional independence.
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
This configuration enables virtually illumination-angle-independent intensity control, increased stability, and reduced impact from light source displacements, particularly beneficial for EUV plasma sources, by allowing the field intensity setting device to influence all superimposed sub-bundles equally, minimizing aberrations and ensuring consistent illumination.
Implementation Method 1
an optical assembly for guiding illumination light to an object field to be illuminated in an object plane
Implementation Method 2
and/or at least one diffractive element for dividing the illumination light radiation bundle into the radiation sub-bundles
Data Source
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AI summary
An illumination optics for microlithography comprises an optical assembly for guiding illumination light to an object field (19) to be illuminated in an object plane. According to a first aspect of the invention, the illumination optics (26) divides an illumination light radiation bundle (3) into a plurality of radiation sub-bundles (28 to 30) which are assigned to different illumination angles of the object field illumination. The illumination optics (26) is configured in such a way that at least some of the radiation sub-bundles (28 to 30) are superimposed in a superposition plane (16) which is spaced from the object plane and which is not imaged into the object plane in which superposition takes place. This superposition is such that edges (32) of the superimposed radiation sub-bundles (28 to 30) coincide at least partially. According to another aspect of the invention, a field intensity setting device (24) comprises a plurality of adjacent individual diaphragms (27) which at least attenuate illumination light (3) when exposed thereto. These individual diaphragms (27) are insertable into an illumination light radiation bundle (3) in a direction parallel to an object displacement direction (y). All individual diaphragms (27) of the field intensity setting device (24) are insertable into the illumination light radiation bundle (3) from one and the same side.