EUV Projection Mirror Dimensional Constraints for High Reflectivity
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Solution Overview
Problem
Existing projection optical units for EUV projection lithography face challenges in optimizing reflection coatings for very short EUV illumination light wavelengths due to dimensional relationships not being satisfied for individual mirrors, limiting reflectivity and efficiency.
Innovation Solution
The use of NI and GI mirrors with specific dimensional relationships and orientations, where the mirror dimensions satisfy certain étendue and angle of incidence bandwidth conditions, allowing for reflection coatings with high reflectivity (>60% for NI mirrors and >75% for GI mirrors) at EUV wavelengths of 6.7 nm, enabling efficient imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional mirror dimensions are used in projection optical units for EUV lithography, then the optical system can be compact and easier to manufacture, but the reflection coatings cannot achieve sufficient reflectivity (>60% for NI mirrors and >75% for GI mirrors) at very short EUV wavelengths (6.7 nm)
Solution Approach 1:
The patent applies parameter changes by establishing specific dimensional relationships for mirrors (Dx ≥ 4·LLWx/IWPVmax for NI mirrors and Dy ≥ 4·LLWy/(IWPVmax·cos(α)) for GI mirrors) that directly link mirror dimensions to optical performance parameters. This ensures sufficient reflectivity at very short EUV wavelengths while maintaining manufacturability through quantifiable design criteria.
2Reliability
If mirror dimensions are increased to satisfy the dimensional relationships (Dx ≥ 4·LLWx/IWPVmax and Dy ≥ 4·LLWy/(IWPVmax·cos(α))), then high reflectivity can be achieved at very short EUV wavelengths, but the optical system becomes larger and more complex
Solution Approach 1:
The patent resolves the dimensionality conflict by introducing the angle of incidence bandwidth (IWPVmax) as a critical parameter that links mirror dimensions to optical performance. The dimensional relationships Dx ≥ 4·LLWx/IWPVmax and Dy ≥ 4·LLWy/(IWPVmax·cos(α)) enable compact mirror designs that achieve high reflectivity by optimizing the relationship between physical dimensions and angular acceptance bandwidth.
3Ease of operation
If the angle of incidence bandwidth (IWPVmax) is increased to allow more flexible mirror positioning, then the mirror dimension requirements become less stringent, but the angle of incidence control becomes less precise
Solution Approach 1:
The patent maintains angle of incidence precision by establishing quantitative relationships between IWPVmax and mirror dimensions. The formulas Dx ≥ 4·LLWx/IWPVmax and Dy ≥ 4·LLWy/(IWPVmax·cos(α)) ensure that even with increased positioning flexibility, the angular precision required for high reflectivity is maintained through proportional scaling of mirror dimensions.
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 optimized projection optical unit achieves high reflectivity for EUV wavelengths, ensuring efficient imaging and coating optimization, even for very short EUV illumination light, by adhering to specific mirror dimension and angle of incidence bandwidth criteria.
Implementation Method 1
a plurality of mirrors for imaging an object field into an image field with illumination light
Data Source
AI summary
A projection optical unit for EUV projection lithography has a plurality of mirrors for imaging an object field into an image field with illumination light. At least one of the mirrors is an NI mirror and at least one of the mirrors is a GI mirror. A mirror dimension Dx of the at least one NI mirror in a plane of extent (xz) perpendicular to a plane of incidence (yz) satisfies the following relationship:4 LLWx/IWPVmax<Dx. A mirror dimension Dy of the at least one GI mirror in the plane of incidence (yz) satisfies the following relationship:4 LLWy/(IWPVmax cos(a))<Dy.