Blazed Reflective EUV Filter for Spectral Purity Separation
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Solution Overview
Problem
Traditional EUV spectral purity filters (SPFs) suffer from limited efficiency, thermal degradation, limited spectral tunability, sensitivity to grating surface quality, EUV light attenuation, and handling durability issues, failing to achieve near 100% EUV transmission and effective OOB rejection.
Innovation Solution
A reflective SPF using a blazed diffraction grating on a grazing incidence mirror, configured to diffract EUV light into higher orders and confine OOB light to 0th order reflection, achieving near-complete EUV transmission and substantial OOB rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional absorption-based filters are used, then OOB light is blocked, but EUV transmission is limited to no more than about 50%
Solution Approach 1:
The patent replaces absorption-based filtering with a reflection-based blazed grating system. Instead of using materials that absorb OOB light (which limits EUV transmission to ≤50%), the invention uses diffraction and angular separation to redirect OOB light to a different spatial location while allowing EUV light to pass through with near 100% transmission efficiency.
Solution Approach 2:
The patent introduces spatial separation as an additional dimension for filtering. By using a blazed grating to diffract light at different angles based on wavelength, the system separates EUV and OOB light in the angular/spatial domain rather than relying solely on material absorption properties, enabling simultaneous high EUV transmission and OOB rejection.
2Loss of energy
If traditional reflective multilayer stacks are used, then OOB wavelengths are reflected, but EUV transmission is limited to no more than about 70%
Solution Approach 1:
The patent replaces traditional reflective multilayer stacks with a blazed grating on a grazing incidence mirror. Instead of relying on multiple thin layers that inherently limit transmission to ≤70%, the invention uses a single reflective surface with a blazed grating structure that achieves near 100% EUV transmission while maintaining effective OOB rejection through angular separation.
Solution Approach 2:
The patent changes the operational parameters by using grazing incidence geometry (incidence angles of 60-80 degrees) combined with a blazed grating structure. This parameter change enables the system to overcome the transmission limits of normal incidence multilayer stacks while maintaining spectral selectivity through diffraction-based angular separation.
3Object-affected harmful factors
If absorption-based filters are used, then OOB light is blocked, but thermal degradation occurs
Solution Approach 1:
The patent replaces absorption-based filtering with reflection-based diffraction. By using a blazed grating to redirect OOB light through angular separation rather than material absorption, the system eliminates the thermal degradation issues that plague absorption-based filters, significantly improving reliability and operational lifetime.
4Object-affected harmful factors
If traditional SPFs are used, then filtering is achieved, but handling durability and reliability are poor
Solution Approach 1:
The patent employs a composite structure combining a grazing incidence mirror with a blazed grating pattern. This composite design integrates the high reflectivity of the mirror substrate with the wavelength-selective diffraction properties of the blazed grating, creating a robust filter system that maintains both optical performance and mechanical durability.
Solution Approach 2:
The patent replaces fragile absorption-based filter materials with a durable reflective grating system. The blazed grating on a grazing incidence mirror provides mechanical robustness and handling durability while maintaining effective spectral filtering, overcoming the reliability issues of traditional SPFs.
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 reflective SPF provides enhanced spectral purity, durability, and reduced transmission loss, improving system throughput and extending operational life by using diffraction and dispersion principles instead of absorption, with near 100% EUV transmission and nearly zero OOB light reaching the imaging plane.
Implementation Method 1
a blazed diffraction grating having a predetermined grating pitch and blaze angle configured to simultaneously diffract incident EUV light into a higher-order diffraction angle
Implementation Method 2
confine out-of-band (OOB) light to a 0th order reflection angle to angularly separate the EUV light and the OOB light
Implementation Method 3
Traditional EUV SPFs operate on the principles of absorption and reflection. Reflection-based filters rely on Bragg reflection from precisely engineered multilayer stacks
Data Source
AI summary
A reflective spectral purity filter (SPF) for extreme ultraviolet (EUV) light includes a substrate having a reflective surface and an angle of incidence of at least 60 degrees, and a blazed diffraction grating formed on the substrate, the blazed diffraction grating having a grating pitch and blaze angle (fixed or variable) configured to simultaneously diffract incident EUV light into a higher-order diffraction angle and confine out-of-band (OOB) light to a 0th order reflection angle to angularly separate the EUV light and the OOB light. An imaging system including the reflective SPF, the imaging system having a field of view (FOV) configured to collect the spatially filtered EUV light and reject the OOB light based on angular separation of the lights.