Spectral Purity Filter for EUV Lithography
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Solution Overview
Problem
Current EUV lithographic apparatuses face issues with contamination and secondary radiation, which degrade image quality and cause heating problems due to the production of particles and non-EUV secondary electromagnetic radiation, such as 10.6 μm radiation from CO2 lasers, that are not effectively filtered out.
Innovation Solution
A spectral purity filter is designed with a body transmissive to EUV radiation and a reflective layer for non-EUV secondary radiation, utilizing materials like zirconium and molybdenum, and optionally an anti-diffusion layer to prevent material diffusion, ensuring high transmissivity for EUV radiation and significant deflection of secondary radiation, thereby improving spectral purity and reducing heat load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a laser produced plasma source is used to generate EUV radiation, then EUV radiation is produced, but secondary radiation (such as 10.6 μm radiation from CO2 lasers) and contamination particles are also produced
Solution Approach 1:
The patent extracts and removes harmful secondary radiation and contamination particles from the radiation beam using a spectral purity filter and contamination trap, separating the desired EUV radiation from unwanted byproducts
Solution Approach 2:
The patent introduces intermediary components (spectral purity filter with reflective layer, contamination trap) that mediate between the plasma source and the collector, filtering out harmful elements while allowing EUV radiation to pass
2Reliability
If a spectral purity filter is used to remove secondary radiation, then spectral purity is improved, but heat load on the filter increases
Solution Approach 1:
The patent converts the harmful secondary radiation into a beneficial filtering mechanism by using a reflective layer that reflects non-EUV radiation away from the filter body, thereby reducing heat load while maintaining spectral purity
Solution Approach 2:
The patent segments the filter into distinct functional layers (transparent EUV-transmissive layer and reflective non-EUV-reflective layer), with each layer handling specific radiation types to optimize performance and heat management
3Illumination intensity
If materials with high EUV transmissivity are used for the filter body, then EUV radiation transmission is improved, but material diffusion between layers may occur
Solution Approach 1:
The patent applies preliminary protective measures by depositing barrier layers (such as silicon oxide or silicon nitride) on the EUV-transmissive material before assembling the filter, preventing material diffusion in advance
Solution Approach 2:
The patent uses composite material structures combining EUV-transmissive materials with barrier layers and reflective layers, creating a multi-material system that prevents diffusion while maintaining optical properties
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 spectral purity filter effectively transmits EUV radiation while deflecting non-EUV secondary radiation, enhancing image quality and reducing thermal issues, with optimized materials like zirconium and molybdenum providing high transmissivity and reflectivity, respectively, and extending the filter's operational lifetime by managing heat effectively.
Implementation Method 1
a body of material transmissive of EUV radiation
Implementation Method 2
a layer of material reflective to the non-EUV secondary radiation
Data Source
AI summary
A spectral purity filter is configured to transmit extreme ultraviolet (EUV) radiation and deflect or absorb non-EUV secondary radiation. In an embodiment, the spectral purity filter includes a body of material highly transmissive of EUV radiation and a layer of material highly reflective of non-EUV secondary radiation located on a radiation incident side of the body. In an embodiment, the spectral purity filter includes a body of material highly transmissive of EUV radiation and a layer of high emissivity material on an end of the body.