Protective Scale Coating for EUV Optical Position Measurement
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Solution Overview
Problem
Existing optical position measuring devices in EUV lithography are susceptible to damage from high-energy electromagnetic radiation and hydrogen radicals, leading to material removal and contamination of mirror optics.
Innovation Solution
A scale design for optical position measuring devices comprising a carrier substrate, reflector layers, and a protective layer with tailored thicknesses and materials, applied via sputtering, to prevent erosion and maintain diffraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is applied to protect the scale from EUV radiation and hydrogen radicals, then resistance to radiation and radical erosion is improved, but diffraction efficiency deteriorates
Solution Approach 1:
The patent applies parameter changes by carefully controlling the thickness of the protective layer (specifically 50-200 nm range) to balance protection and optical performance. This thickness parameter is optimized to provide sufficient erosion resistance while maintaining acceptable diffraction efficiency for the measurement function
Solution Approach 2:
The patent uses composite materials by combining the protective layer with the underlying scale structure (carrier substrate, reflector layers, and spacer layer). This composite design allows the protective layer to provide radiation resistance while the underlying layers maintain the diffraction functionality, achieving both protection and measurement precision
2Reliability
If a thick protective layer is applied to prevent material erosion, then protection against hydrogen radicals is improved, but manufacturing precision deteriorates due to spin-coating variations
Solution Approach 1:
The patent replaces the mechanical spin-coating process with a chemical vapor deposition (CVD) process. This substitution eliminates the manufacturing variations inherent in spin-coating and provides superior thickness uniformity across the protective layer, while still achieving the required erosion protection
3Stability of the object's composition
If the protective layer thickness is increased to improve radiation resistance, then stability under EUV radiation is improved, but optical scanning performance deteriorates
Solution Approach 1:
The patent optimizes the protective layer thickness parameter within a specific range (50-200 nm) to balance radiation stability and optical scanning performance. This parameter optimization ensures the layer is thick enough to provide protection but thin enough to allow sufficient light transmission for accurate position measurement
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 scale effectively protects against EUV radiation and hydrogen radicals, preventing material loss and ensuring high diffraction efficiency for accurate position measurement.
Implementation Method 1
The protective layer consists of a material that prevents material erosion in the substrate and/or in the reflector layers and/or in the spacer layer caused by hydrogen radicals
Implementation Method 2
the intensity of the beams of radiation diffracted by the scale into the +/- 1st order
Implementation Method 3
applied using a sputtering process
Data Source
Figure 1a~1b
Figure 1a
Figure 2
AI summary
A scale for an optical position measuring device comprises a substrate, a first reflector layer arranged on the substrate, a transparent spacer layer arranged on the reflector layer, a structured second reflector layer arranged on the spacer layer, and a protective layer of defined thickness arranged on the upper surface of the scale above the second reflector layer. The protective layer is also arranged on the side surfaces of the scale (Figure 1a).