EUV Reflective Optical Element Multilayer Standing Wave Optimization
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Solution Overview
Problem
Existing reflective optical elements for EUV lithography have limited reflectivity due to material absorption and refractive index differences, which affects the overall performance of EUV lithography apparatuses.
Innovation Solution
A reflective optical element with a multilayer system that incorporates layers of different base materials with varying refractive indices, where a further material is used in layers at extreme field intensity points to enhance reflectivity, and a material with higher absorption is used at places of minimum field intensity to optimize reflectivity gains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a multilayer system with alternating layers of molybdenum and silicon is used, then good maximum reflectivity is achieved, but reflectivity is still limited by material absorption and refractive index differences
Solution Approach 1:
The patent applies local quality by replacing base materials with further materials at specific locations within the multilayer system where the standing wave has extreme field intensity. This localized material substitution optimizes reflectivity at critical positions without unnecessarily changing materials throughout the entire structure, thereby addressing the absorption limitation while maintaining the alternating layer architecture.
Solution Approach 2:
The patent changes material parameters (refractive index and absorption characteristics) at specific locations within the multilayer system. By selecting further materials with different optical parameters than the base molybdenum and silicon, the patent optimizes the standing wave interaction to achieve higher maximum reflectivity while compensating for material absorption losses.
2Illumination intensity
If material pairs with greater difference in real part of refractive index are used, then maximum reflectivity increases, but absorption increases leading to lower overall reflectivity
Solution Approach 1:
The patent resolves this contradiction by applying local quality - using further materials with greater refractive index differences only at specific locations where the standing wave has extreme field intensity, rather than throughout the entire multilayer system. This localized approach captures the reflectivity benefit while minimizing the absorption penalty.
Solution Approach 2:
The patent creates a functionally porous or heterogeneous structure by combining base materials and further materials in a non-uniform distribution. This allows the system to exploit the advantages of different material pairs at different locations, achieving optimal balance between reflectivity enhancement and absorption management.
3Adaptability or versatility
If multiple reflective optical elements are connected in series, then the optical system becomes more functional, but the cumulative absorption reduces overall light yield
Solution Approach 1:
The patent changes the optical parameters of individual reflective elements through selective material replacement, thereby increasing their reflectivity. This compensates for the cumulative absorption effect in series-connected elements, maintaining adequate light yield across the entire optical system while preserving its functional complexity.
Solution Approach 2:
The patent converts the harmful effect of material absorption into a benefit by strategically placing further materials at standing wave extrema. This transforms the absorption issue into an optimization opportunity, where the standing wave pattern itself guides the material placement to maximize reflectivity and compensate for cumulative losses.
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 proposed solution increases the maximum reflectivity of reflective optical elements at quasi-normal radiation incidence, leading to improved light yield in EUV lithography systems, even when multiple elements are connected in series.
Implementation Method 1
at which a standing wave of an electric field is formed upon reflection of a wavelength in the extreme ultraviolet wavelength range
Implementation Method 2
upon reflection of a wavelength in the extreme ultraviolet wavelength range
Implementation Method 3
layers of at least two different base materials with a different real part of the refractive index
Implementation Method 4
a standing wave of an electric field is formed upon reflection
Implementation Method 5
which at least partially replaces one of the at least two different base materials in the at least one layer at a place of extreme field intensity
Data Source
AI summary
This disclosure relates to a reflective optical element for a wavelength in the extreme ultraviolet wavelength range, comprising a substrate and a reflective coating designed as a multi-layer system. The multi-layer system has alternating layers of at least two different base materials different real parts of their refractive indexes in the extreme ultraviolet wavelength range. An electrical field standing wave is formed in the multilayer system by the reflection of extreme ultraviolet wavelength radiation. The multi-layer system has another material at least in a layer at a point of extreme field intensity, wherein the reflective optical element has a material as the other material at at least one point of minimal field intensity, which has greater absorption for the reflected wavelength than the at least partially replaced one.