EUV Droplet Observation Optics With Central Reflection Blocking
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Solution Overview
Problem
Existing EUV light systems face challenges in accurately determining the position of material droplets due to interfering reflections from the optical unit, which overshadow the actual measurement signal, impairing accuracy and reliability.
Innovation Solution
An observation device with a light-blocking element is positioned between the optical unit and the sensor system to block interfering reflections, allowing the reflected light from the material droplet to reach the sensor while maintaining the integrity of the measurement signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a polarization-based filter mechanism is used to reduce interfering reflections, then the harmful reflections are partially filtered, but the brightness or intensity of the reflected light to be measured is reduced in an ultimately undesirable manner
Solution Approach 1:
The beam path is segmented into different regions: a central region where interfering reflections are blocked by the light-blocking element, and outer regions where the reflected light from the material droplet can pass through. This spatial segmentation allows selective blocking of harmful reflections while preserving the measurement signal.
Solution Approach 2:
The light-blocking element is designed with non-uniform properties: it has a central region with high light-blocking capability to eliminate interfering reflections, and outer regions with light-transmissive properties to allow the reflected measurement light to pass through. This local differentiation of properties resolves the contradiction between blocking reflections and preserving signal intensity.
2Measurement precision
If no light-blocking element is used, then the reflected light reaches the sensor system, but interfering reflections from the optical unit overshadow the actual measurement signal
Solution Approach 1:
The light-blocking element extracts and removes the interfering reflections from the beam path by blocking them in the central region, while allowing the desired reflected light from the material droplet to reach the sensor system through the outer regions. This extraction of harmful factors improves measurement precision without losing the measurement signal.
3Object-affected harmful factors
If a light-blocking element is placed in the central region of the beam path, then interfering reflections are blocked, but the reflected light must pass through or around the element
Solution Approach 1:
The light-blocking element is implemented as a thin, planar component with a simple geometric structure (central blocking region with light-transmissive outer regions). This thin-film approach blocks interfering reflections effectively while adding minimal complexity to the beam path configuration and maintaining a compact device structure.
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 precise, reliable, and efficient position determination of material droplets for EUV light generation by effectively eliminating interfering reflections, ensuring high light intensity and accuracy of the analysis.
Implementation Method 1
at least one light-blocking element arranged between the optical unit and the sensor system, as viewed along the beam path, for keeping away interfering reflections of the measurement laser beam
Implementation Method 2
an optical unit for focusing a measurement laser beam onto the material droplet and for directing light reflected by the material droplet along a predefined beam path
Implementation Method 3
a sensor system arranged at an end of the beam path for detecting the reflected light
Data Source
AI summary
An observation device for an extreme ultraviolet (EUV) light system for observing a material droplet for EUV light generation includes an optical unit for focusing a measurement laser beam onto the material droplet and for directing light reflected by the material droplet along a predefined beam path, a sensor system arranged at an end of the beam path for detecting the reflected light, and at least one light-blocking element arranged between the optical unit and the sensor system, as viewed along the beam path, for keeping away interfering reflections of the measurement laser beam, which emanate from the optical unit in a direction of the sensor system at least in a central region of the beam path, such that at least a part of the reflected light can reach the sensor system along the beam path in spite of the light-blocking element.