Spatial Filter for High Harmonic Illumination Source
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Solution Overview
Problem
Current techniques for filtering pump laser radiation from high harmonic generation sources are inadequate, particularly as ultra-thin metallic filters become damaged with increasing laser power, leading to measurement errors and inaccuracies in lithographic processes.
Innovation Solution
An illumination source apparatus and method that spatially separates pump radiation and high harmonic radiation beyond the focal plane using a tiled aperture geometry with a central region devoid of sub-beams, allowing for effective filtration of pump radiation using a spatial filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ultra-thin metallic filters are used to filter pump radiation, then measurement precision is improved, but reliability deteriorates as the filters become damaged with increasing laser power
Solution Approach 1:
The harmful pump radiation is extracted and removed from the beam path before reaching the detector. The spatial filter extracts the pump radiation component from the combined beam, separating it from the high harmonic radiation. This prevents the pump radiation from damaging the detector and degrading measurements, while maintaining measurement precision through clean spectral separation.
Solution Approach 2:
A spatial filter serves as an intermediary element between the pump radiation source and the detector. This mediator selectively removes pump radiation while allowing high harmonic radiation to pass through to the detector, protecting the detection system from damage while maintaining measurement accuracy.
2Productivity
If laser power is increased to improve signal strength, then productivity is improved, but object-generated harmful factors worsen due to filter damage
Solution Approach 1:
The spatial arrangement of the tiled aperture geometry converts the potentially harmful overlap between pump and harmonic beams into a beneficial spatial separation. By positioning the aperture such that pump radiation and high harmonic radiation pass through different regions, the system transforms what could be a damaging interaction into an opportunity for clean spectral separation without filter damage.
3Measurement precision
If spatial filtering is implemented to remove pump radiation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The aperture is segmented into multiple tiled sections, each receiving and processing different portions of the beam. This segmentation allows the spatial filter to selectively block pump radiation in specific regions while transmitting high harmonic radiation, achieving precise spectral separation through a modular, manageable structure rather than a single complex filter element.
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 enables efficient separation and filtration of pump radiation, preventing measurement errors and maintaining the integrity of high harmonic radiation for accurate metrology in lithographic processes, even with higher laser powers.
Implementation Method 1
a pump radiation source operable to emit a beam of pump radiation having a profile comprising no pump radiation in a central region of the beam, for exciting the high harmonic generation medium so as to generate high harmonic radiation
Implementation Method 2
a spatial filter located beyond a focal plane of said beam of pump radiation, operable to block said pump radiation; wherein said pump radiation and the generated high harmonic radiation are spatially separated beyond the focal plane of said beam of pump radiation
Data Source
AI summary
Disclosed is an illumination source apparatus comprising a high harmonic generation medium, a pump radiation source and a spatial filter. The pump radiation source emits a beam of pump radiation having a profile comprising no pump radiation in a central region of the beam and excites the high harmonic generation medium so as to generate high harmonic radiation. The pump radiation and the generated high harmonic radiation are spatially separated beyond the focal plane of the beam of pump radiation. The spatial filter is located beyond a focal plane of the beam of pump radiation, and blocks the pump radiation. Also disclosed is a method of generating high harmonic measurement radiation optimized for filtration of pump radiation therefrom.