Computer-Generated Hologram for Multi-Zone Mirror Testing
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Solution Overview
Problem
The existing methods for testing large mirrors, particularly those under grazing incidence, face challenges with the limitations of computer-generated holograms (CGHs) in terms of size, accuracy, and complexity, leading to increased testing time and difficulty in distinguishing between manufacturing errors and mirror errors.
Innovation Solution
A test appliance and method utilizing a single computer-generated hologram (CGH) with multiple use functionalities, allowing for interferometric testing of different mirror regions without changing the CGH position, by providing distinct test waves for various mirror portions, facilitating efficient testing of large concave or grazing incidence mirrors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If multiple CGHs are used for different mirror positions, then the required CGH dimensions are reduced, but the testing time is lengthened and the complexity of combining measurement results increases
Solution Approach 1:
The patent applies a single CGH that can test multiple mirror positions and regions by incorporating multiple zone plates with different focal lengths and orientations. This multi-functional CGH eliminates the need to physically exchange multiple CGHs, thereby reducing testing time while maintaining manageable CGH dimensions
Solution Approach 2:
The patent merges multiple testing functionalities into a single CGH structure by combining multiple zone plates that correspond to different mirror positions. This consolidation allows simultaneous or sequential testing of multiple regions without requiring separate CGHs, reducing both time loss and the complexity of combining results
2Area of moving object
If multiple CGHs are used for different mirror positions, then the required CGH dimensions are reduced, but the difficulty of distinguishing manufacturing errors from mirror errors increases
Solution Approach 1:
The patent uses a reference wave that is common to all interferograms as an intermediary for error identification. By comparing multiple interferograms (each corresponding to different mirror regions but using the same reference wave), systematic errors from CGH manufacturing can be distinguished from actual mirror errors through differential analysis
Solution Approach 2:
The patent implements a feedback mechanism where measurement results from different mirror regions are systematically combined and analyzed. The interferograms are processed to identify consistent patterns that indicate CGH manufacturing errors versus region-specific mirror errors, enabling accurate error attribution
3Productivity
If a single CGH is used for multiple mirror positions, then the testing process is simplified and time is reduced, but the CGH complexity increases
Solution Approach 1:
The patent segments the single CGH into multiple functional zones, each containing a zone plate optimized for a specific mirror position or region. This segmentation allows the complex CGH to be systematically designed and manufactured by treating each zone as a separate functional element that can be independently optimized
Solution Approach 2:
The patent varies key parameters of the zone plates within the single CGH, including focal lengths, orientations, and positions, to optimize performance for different mirror regions. These parameter changes enable the single CGH to adapt to multiple testing scenarios without requiring physical exchange of components
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 approach reduces testing time and improves accuracy by eliminating the need for CGH interchange and adjustment, enabling reliable testing of large mirror surfaces with reduced complexity and increased precision.
Implementation Method 1
a first test wave for testing a first portion of the mirror by interferometric superposition with a reference wave in a first position of the mirror and at least a second test wave for testing a second portion of the mirror by interferometric superposition with a reference wave in a second position of the mirror
Implementation Method 2
the computer-generated hologram is designed in such a way that, during operation of the appliance, it provides a first test wave for testing a first portion of the mirror by interferometric superposition with a reference wave
Data Source
AI summary
A test appliance and a method for testing a mirror, e.g., a mirror of a microlithographic projection exposure apparatus. The test appliance has a computer-generated hologram (CGH), and a test can be carried out on at least a portion of the mirror by way of an interferometric superposition of a test wave that is directed onto the mirror by this computer-generated hologram and a reference wave. Here, the computer-generated hologram (CGH) (120, 320) is designed in such a way that, during operation of the appliance, it provides a first test wave for testing a first portion of the mirror (101, 301) by interferometric superposition with a reference wave in a first position of the mirror (101, 301) and at least a second test wave for testing a second portion of the mirror (101, 301) by interferometric superposition with a reference wave in a second position of the mirror (101, 301).