Optical System Disturbance Localization via Test Beam Angles
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Solution Overview
Problem
Microlithography projection exposure apparatuses face challenges in identifying and isolating disturbances in optical systems, such as contamination and deformation of optical elements, which affect imaging quality due to complex interactions among multiple optical elements and fluctuations in radiation quality.
Innovation Solution
A method involving the use of test beams with varying angles of incidence to measure properties at specific measurement regions, allowing for the calculation of spatial diagnosis distributions that pinpoint disturbances by comparing measured values against idealized models, thereby identifying the nature and location of deviations in the optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple optical elements are used to achieve high imaging quality, then the imaging quality is improved, but the difficulty of detecting and measuring disturbances increases
Solution Approach 1:
The patent segments the optical system into multiple independently measurable components by introducing reference surfaces with known properties. Each reference surface is assigned a specific function in the measurement process, allowing disturbances to be isolated to particular segments (optical elements) rather than treating the entire system as a black box. This segmentation enables systematic identification of which specific optical element is causing imaging quality degradation.
Solution Approach 2:
The patent introduces reference surfaces as intermediary elements with well-defined optical properties. These reference surfaces act as mediators between the test beams and the optical elements being measured. By comparing the behavior of test beams at reference surfaces with known characteristics against actual measurements, the patent can indirectly identify disturbances in optical elements without directly measuring each one, thus solving the complexity problem.
2Manufacturing precision
If optical elements are positioned and manufactured with high precision, then the imaging quality is improved, but the device complexity increases
Solution Approach 1:
The patent enables the optical system to self-diagnose by incorporating reference surfaces that automatically reveal the presence and location of disturbances when test beams pass through the system. The system uses its own operational beams (test beams) to measure itself, eliminating the need for external complex measurement equipment. This self-service capability reduces overall device complexity while maintaining high manufacturing precision standards.
Solution Approach 2:
The patent changes the measurement parameter from direct physical measurement of each optical element to measurement of test beam properties (intensity, angle) at reference surfaces. By transforming the measurement approach from element-by-element physical inspection to beam property comparison, the patent simplifies the measurement system while maintaining the ability to detect high-precision positioning deviations.
3Productivity
If the optical system operates for extended duration, then productivity is improved, but reliability decreases due to degradation and contamination
Solution Approach 1:
The patent implements preliminary measurement actions at reference surfaces during normal operation to detect disturbances before they severely impact imaging quality. By continuously or periodically measuring test beam properties at reference surfaces with known characteristics, the system can identify degradation trends early and schedule maintenance proactively, thus maintaining reliability while extending operational duration.
Solution Approach 2:
The patent establishes a feedback mechanism where measurements at reference surfaces are continuously compared against expected values to identify disturbances. This feedback loop enables real-time monitoring of optical element performance, allowing for timely intervention to maintain imaging quality stability over extended operational periods. The feedback from reference surface measurements directly informs maintenance decisions.
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 method enables precise localization and identification of disturbances within the optical system, facilitating targeted corrections and maintenance, such as cleaning or reworking of optical elements, thereby maintaining imaging quality and extending the operational lifespan of the apparatus.
Implementation Method 1
passing a first plurality of test beams of a radiation through the optical system, so as to impinge on a first single measurement region in a measurement plane
Data Source
AI summary
First test beams (464a-d), after passing through an optical system on optical paths that differ in pairs, impinge on a first measurement region (461) at angles that differ in pairs with respect to the measurement plane. Second test beams (465a-d), after passing through the optical system on optical paths that differ in pairs, impinge on a second measurement region (462) at angles that differ in pairs, wherein the second region differs from the first. A value of a first measurement variable of the test beam at the first region is detected for each of the first test beams, and comparably for a second measurement variable at the second region for the second test beams. Impingement regions (467a-d) on reference surface(s) (466, 471) of the optical system are determined and a spatial diagnosis distribution of a property of the reference surface(s) for each test beam is calculated.