EUV Mirror Contamination Monitoring via Remote Photoelectron Mapping
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Solution Overview
Problem
Existing surface contamination detection techniques for EUV technology, such as photoelectric emission detection, face challenges including invasive designs, space envelope constraints, unknown sensitivities, and high costs, particularly when integrating with EUV mask inspection systems.
Innovation Solution
A photoelectron emission mapping system that uses a photoelectron source and detector located outside the EUV beam path, allowing for non-invasive, real-time assessment of photoelectron intensity and spectrum from EUV masks and mirrors, with fiber optics introducing a time delay to enhance signal-to-noise ratios and integrate seamlessly with existing inspection systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrodes are positioned close to the test surface to maintain sensitivity, then photoelectric current detection sensitivity is improved, but the EUV beam path is interfered with and system design complexity increases
Solution Approach 1:
The patent positions the detector at a remote location (different spatial dimension) from the test surface, using electrostatic fields to guide photoelectrons across the vacuum chamber to the detector. This eliminates the need for close electrode positioning while maintaining detection sensitivity, as the electrostatic lens system can focus electrons from a distance without blocking the EUV beam path.
Solution Approach 2:
The patent introduces electrostatic fields and electrostatic lenses as intermediaries to transport photoelectrons from the test surface to the remote detector. These electromagnetic field mediators enable long-distance electron transport without requiring physical electrodes near the test surface, thus avoiding beam path interference while maintaining electron collection efficiency.
2Measurement precision
If a dedicated UV light source is used for photoemission detection, then contamination detection sensitivity is improved, but the system requires additional equipment and increases cost
Solution Approach 1:
The patent utilizes the existing EUV light source from the lithography system to generate photoelectrons for contamination detection, making the radiation source serve dual purposes: both the primary lithography function and the photoemission detection function. This eliminates the need for a separate UV light source while maintaining detection capability, as EUV photons are sufficiently energetic to photoemit electrons from contaminated surfaces.
Solution Approach 2:
The system uses its own operational EUV radiation to perform self-diagnosis of surface contamination. The lithography system's beam serves its primary purpose while simultaneously enabling contamination monitoring, allowing the system to monitor its own health without external assistance or additional radiation sources.
3Measurement precision
If gas is introduced into the vacuum system to minimize electron attachment, then photoelectron detection sensitivity is improved, but the vacuum system complexity and operational constraints increase
Solution Approach 1:
The patent maintains a high vacuum environment (inert to electron attachment) throughout the electron transport path, using electrostatic fields to guide photoelectrons without requiring protective gas atmospheres. The vacuum chamber design and electrostatic lens system enable electron transport while preserving the inert vacuum environment, eliminating the need for gas introduction and associated complexity.
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 provides a sensitive, non-destructive, and cost-effective method for detecting trace contaminants on EUV masks and mirrors, offering real-time contamination assessment without interfering with the EUV beam path or requiring additional radiation sources, thus addressing the limitations of existing techniques.
Implementation Method 1
A photoelectron emission mapping system uses an EUV light source and a photoelectron detector located outside the EUV beam path to assess contamination on EUV masks and mirrors
Implementation Method 2
scintillator-based detectors to enhance sensitivity and non-invasive detection
Data Source
AI summary
Photoelectron emission mapping systems for use with EUV (extreme ultraviolet) mask inspection and lithography systems are described. The mapping systems may be used to provide photoelectron emission maps for EUV photolithography masks and/or EUV mirrors. The systems use EUV photoelectron sources used for mask inspection or photolithography to impinge EUV light on the masks and/or mirrors. The EUV light generates photoelectron on the surfaces of the mask and/or mirrors and the photoelectrons are collected and analyzed by detectors placed away from optical spaces of the EUV chamber.