EUV Mirror Stress Compensation via Boron-Lanthanum Layers
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Solution Overview
Problem
Existing methods for producing mirrors for extreme ultraviolet (EUV) radiation face challenges in managing intrinsic compressive stresses, which can lead to deformation and loss of precision in optical elements.
Innovation Solution
A method involving a stress-compensating layer sequence made of alternating boron or boron-based materials and lanthanum or lanthanum-based materials, followed by a temperature treatment to generate tensile stress, which is then used to counteract the compressive stress in a reflective layer sequence, ensuring reduced overall stress and maintaining optical precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reflective layer sequence is applied to a substrate, then the mirror achieves high reflectivity for EUV radiation, but intrinsic compressive stresses cause deformation and loss of precision
Solution Approach 1:
The mirror structure is segmented into multiple functional layers: a stress-compensating layer sequence with alternating first and second layers, and a reflective layer sequence with alternating third and fourth layers. This segmentation allows independent optimization of stress management and reflectivity functions.
Solution Approach 2:
The patent applies heat treatment to change the physical state and stress parameters of the stress-compensating layer sequence. By heating to specific temperatures, the compressive stress is converted into tensile stress, transforming the mechanical properties of the material to achieve stress compensation.
2Strength
If the compressive stress in the layer sequence is increased to improve coating adhesion, then layer bonding is enhanced, but substrate bending and deformation increase
Solution Approach 1:
The stress-compensating layer sequence generates tensile stress that acts as a counterweight to the compressive stress in the reflective layer sequence. This counterbalancing stress system prevents substrate bending while maintaining layer bonding integrity.
Solution Approach 2:
The stress-compensating layer sequence is applied and heat-treated before the reflective layer sequence to pre-establish the stress balance. This preliminary action ensures that when the reflective layers are deposited, the substrate is already in a stress-compensated state, preventing deformation.
3Stress or pressure
If heat treatment is applied to generate tensile stress, then compressive stress is reduced, but additional processing time and temperature control requirements are introduced
Solution Approach 1:
The heat treatment process utilizes phase transitions and thermal activation to transform the stress state of the stress-compensating layer sequence from compressive to tensile. This phase transition approach efficiently achieves stress compensation through controlled thermal processing.
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 method effectively reduces mechanical stresses in EUV mirrors, preventing substrate bending and maintaining high reflectivity and precision, particularly in the 6 nm to 15 nm wavelength range, thus enhancing the performance and reliability of EUV mirrors.
Implementation Method 1
In a subsequent step, a heat treatment is carried out in a temperature range between 100 °C and 800 °C, preferably between 400 °C and 800 °C. This heat treatment reduces the compressive stress in the stress-compensating layer sequence and generates a tensile stress.
Implementation Method 2
This heat treatment reduces the compressive stress in the stress-compensating layer sequence and generates a tensile stress
Implementation Method 3
Mirror for reflecting EUV radiation with tension compensation and method for producing the same
Implementation Method 4
thin-film systems, which typically contain a periodic sequence of numerous layer pairs
Data Source
Figure 1
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Figure 3A~3D
AI summary
A mirror (5) for reflecting EUV radiation is described, comprising a stress-compensating layer sequence (2) arranged on a substrate (1), the layer sequence having alternating first layers (2a) and second layers (2b), wherein the first layers (2a) comprise boron, a boron nitride, a boron carbide, or a boron oxide, and the second layers (2b) comprise lanthanum, a lanthanum nitride, a lanthanum carbide, or a lanthanum oxide, and wherein the stress-compensating layer sequence (2) is subject to tensile stress. A reflective layer sequence (3) is arranged above the stress-compensating layer sequence (2), comprising alternating third layers (3a) and fourth layers (3b), and wherein the reflective layer sequence (3) is subject to compressive stress. Furthermore, a method for fabricating the EUV mirror (5) is described.