Segmented Suppression Filter for Multi-Wavelength EUV Systems
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Solution Overview
Problem
Current suppression filters in EUV radiation systems struggle to effectively prevent the specular reflection of multiple wavelength lines, particularly when using lasers with output at two wavelengths, leading to inefficiencies in IR radiation suppression and reduced net output power.
Innovation Solution
A suppression filter with a profile defining two reflective surface levels separated by a specific distance, determined by minimizing the difference between the products of the wavelengths and approximate integer factors, is designed to prevent specular reflection of radiation at both wavelengths, allowing for the use of multiple CO2 output lines and increasing overall output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a suppression filter is designed to suppress one wavelength, then that wavelength is effectively blocked, but radiation at other wavelengths (particularly multiple CO2 output lines) is not suppressed and may be reflected into the beam path
Solution Approach 1:
The suppression filter is segmented into multiple reflective surface levels (first and second levels) with different separation distances, where each level is optimized to suppress a specific wavelength. This segmentation allows the single filter structure to handle multiple wavelength lines simultaneously, resolving the contradiction between suppressing one wavelength effectively and adapting to suppress multiple wavelengths.
Solution Approach 2:
Different regions of the suppression filter (different reflective surface levels) have locally optimized properties - specifically, different separation distances between reflective surfaces. The first reflective surface level has a first separation distance for suppressing the first wavelength, while the second reflective surface level has a second separation distance for suppressing the second wavelength. This local quality variation enables multi-wavelength suppression within a single filter component.
2Power
If laser output power is increased by utilizing multiple wavelength lines, then net output power increases, but laser radiation at these wavelengths is reflected from the fuel to the radiation collector, creating harmful radiation that reduces system efficiency
Solution Approach 1:
The suppression filter uses segmented reflective surface levels where each level targets a specific wavelength for suppression. This allows the system to maintain high laser output power at multiple wavelength lines while the segmented filter structure selectively blocks the reflected radiation at each wavelength, preventing it from reaching the radiation collector and converting harmful reflected radiation into beneficial EUV output.
Solution Approach 2:
The suppression filter converts the harmful reflected laser radiation into beneficial EUV radiation. By suppressing the reflected laser wavelengths at their respective levels, the filter redirects the energy that would otherwise be harmful into the desired EUV wavelength range, thus converting the harmful effect of multi-wavelength laser radiation into a beneficial outcome for increasing net output power.
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 solution effectively suppresses both primary and secondary IR wavelengths, enhancing the net output power by minimizing the fraction of power reflected into the zeroth order, thereby improving the efficiency of the EUV radiation system.
Implementation Method 1
a suppression filter with a profile defining two reflective surface levels separated by a specific distance, determined by minimizing the difference between the products of the wavelengths and approximate integer factors, is designed to prevent specular reflection of radiation at both wavelengths
Data Source
AI summary
Disclosed is a suppression filter having a profile defining at least two reflective surface levels, each reflected surface level being separated by a separation distance. The separation distance is such that the reflective suppression filter is operable to substantially prevent specular reflection of radiation at a first wavelength and at a second wavelength incident on said reflective suppression filter. Also disclosed is a radiation collector, radiation source and lithographic apparatus comprising such a suppression filter, and to a method of determining a separation distance between at least two reflective surface levels of a suppression filter.