EUV Mirror Layering for Grazing Incidence Contamination
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Solution Overview
Problem
Microlithographic projection exposure apparatuses face challenges in achieving high reflectivities with low light losses and susceptibility to contamination, particularly in mirrors used under grazing incidence for EUV radiation.
Innovation Solution
The use of a mirror with a layer comprising a compound of an element from the second period combined with an element from the 4d transition group, such as molybdenum or ruthenium, along with a protective layer to enhance chemical resistance and optical properties, allowing for high reflectivity and reduced contamination risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mirrors are used under grazing incidence to achieve high reflectivity for EUV radiation, then optical performance is improved, but susceptibility to contamination increases
Solution Approach 1:
The mirror surface is segmented into multiple functional layers: a base layer (e.g., Mo, Ru, Rh, Pd) providing the primary reflective function, and an overlay layer (e.g., carbon, boron, nitrogen compound) providing contamination resistance. This segmentation allows each layer to specialize in one function, resolving the contradiction between reflectivity and contamination susceptibility.
Solution Approach 2:
The mirror uses composite material structures combining different elements and compounds in specific layer configurations. For example, a molybdenum base layer with a carbon overlay, or ruthenium with boron nitride coating. These composite structures integrate the high reflectivity properties of the base material with the chemical stability and contamination resistance of the overlay material.
2Object-affected harmful factors
If protective layers are added to reduce contamination, then chemical resistance is improved, but optical properties may deteriorate
Solution Approach 1:
The overlay layer is designed with specific local properties: extreme thinness (monolayer to few nanometers), specific material composition (carbon, boron, nitrogen compounds), and controlled morphology. These localized quality adjustments ensure the layer provides chemical protection while maintaining sufficient EUV radiation transmission and reflectivity.
Solution Approach 2:
The invention optimizes critical parameters of the overlay layer including thickness (controlling transmission vs. protection), material composition (affecting both chemical resistance and optical response), and surface morphology. By precisely controlling these parameters, the overlay provides contamination resistance while minimizing degradation of 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
This configuration achieves high reflectivity and low light losses while minimizing contamination, allowing for optimized optical performance and chemical stability, even under grazing incidence, by dividing tasks between layers to optimize both optical and chemical resistance properties.
Implementation Method 1
mirrors which are operated under grazing incidence and whose use is fundamentally desirable because of the comparatively high reflectivities which can be achieved
Implementation Method 2
the material of the layer arranged in each case underneath the protective layer in the direction of the optically effective surface has a lower absorption than the material of the protective layer
Data Source
AI summary
A mirror, in particular for a microlithographic projection exposure apparatus has an optically effective surface, wherein the mirror has a reflectivity of at least 0.5 for electromagnetic radiation which has a prescribed working wavelength and impinges on the optically effective surface at an angle of incidence based on the respective surface normal of at least 65°, wherein the mirror has at least one layer (160, 170, 320) which comprises a compound of an element of the second period and an element of the 4d transition group, wherein the mirror has a protective layer (430, 530, 630, 730) arranged on top in the direction of the optically effective surface, wherein the material of the layer (420, 510, 620, 705) arranged in each case underneath the protective layer in the direction of the optically effective surface has a lower absorption than the material of the protective layer (430, 530, 630, 730).