Frequency Comb Distance Measurement for Microlithography Optics
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Solution Overview
Problem
Highly productive projection exposure apparatuses for microlithography are sensitive to vibrations, leading to imaging aberrations due to deflections of optical components, and existing position measurement methods, such as capacitive sensors, can impair measurement accuracy and dynamic behavior.
Innovation Solution
A distance measurement system using a frequency comb generator to measure the distance between optical components and a reference element with high accuracy, optically and contactlessly, without affecting the dynamic behavior of the optical components, allowing for precise position determination in multiple degrees of freedom and monitoring of vibration behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dynamic sensors are positioned close to the optical component, then position measurement is enabled, but the dynamic behavior of the optical component deteriorates
Solution Approach 1:
The retroreflector serves as a mediator that carries the measurement function away from the optical component, allowing the sensor to measure position without being mechanically coupled to the optical component, thus preserving its dynamic behavior
Solution Approach 2:
The patent replaces direct mechanical attachment of sensors to the optical component with an optical measurement system using a retroreflector, eliminating the mechanical coupling that degrades dynamic performance
2Reliability
If optical components are continuously measured for position correction, then imaging aberrations are minimized, but measurement accuracy deteriorates due to thermal drift
Solution Approach 1:
The retroreflector acts as an intermediary measurement target that does not suffer from thermal drift, allowing continuous position measurement for correction while maintaining high measurement accuracy
Solution Approach 2:
The patent replaces direct sensing on the optical component with optical distance measurement using a retroreflector, enabling continuous measurement for aberration correction without thermal drift interference
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 solution enables accurate and non-invasive distance measurement of optical components, improving measurement accuracy while maintaining the dynamic behavior of the optical components, thus minimizing imaging aberrations caused by vibrations.
Implementation Method 1
The distance measurement system comprises a frequency comb generator, which is configured to generate electromagnetic radiation with a comb-shaped frequency spectrum
Implementation Method 2
The use of such a frequency comb generator makes it possible to carry out the distance measurement with a very high accuracy. Moreover, the measurement can be effected optically and thus contactlessly from a relatively large distance
Data Source
AI summary
A projection exposure apparatus (10) for microlithography has a plurality of optical components (M1-M6) forming an exposure beam path, as well as a distance measurement system (30, 130, 230) configured to measure a distance between at least one of the optical components and a reference element (40, 140, 240). The distance measurement system comprises a frequency comb generator (32, 132, 232), which is configured to generate electromagnetic radiation (36, 236) having a comb-shaped frequency spectrum.