Reflective Optical Element Deformation Reduction Layer
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Solution Overview
Problem
Reflective optical elements in EUV microlithographic systems experience thermal deformation and imaging impairments due to radiation absorption, which is difficult to address with solutions from VUV systems, as they increase system complexity and have limited optically effective surfaces for deformation compensation.
Innovation Solution
A reflective optical element with a deformation reduction layer having a material with a negative coefficient of thermal expansion, paired with a reflection layer system, to compensate for thermal expansion and reduce deformation, thereby minimizing thermal deformations and imaging impairments with reduced structural complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional devices are used for rigid-body movements and/or temperature changes to compensate for thermal deformation, then thermal deformation compensation is achieved, but system complexity increases
Solution Approach 1:
The patent applies thermal expansion principles by incorporating a deformation reduction layer with negative thermal expansion coefficient that compensates for the thermal expansion of the reflection layer system. This passive compensation mechanism eliminates the need for active rigid-body movement devices or temperature control systems, thereby reducing system complexity while maintaining thermal deformation compensation.
Solution Approach 2:
The patent uses composite material structure consisting of the reflection layer system (with positive thermal expansion) and the deformation reduction layer (with negative thermal expansion). This composite structure enables passive thermal deformation compensation through material property combination, avoiding the need for complex active compensation devices.
2Loss of energy
If the number of optical elements is kept small to avoid light losses, then light transmission is improved, but the number of surfaces for active deformation compensation is limited
Solution Approach 1:
The patent incorporates a deformation reduction layer with negative thermal expansion coefficient that passively compensates for thermal deformation of the reflection layer system. This approach maintains the minimal number of optical surfaces required for EUV operation while providing adequate deformation compensation capability.
Solution Approach 2:
The deformation reduction layer provides self-service thermal compensation by automatically counteracting thermal expansion of the reflection layer system through its negative thermal expansion property. This eliminates the need for additional active compensation mechanisms, thereby maintaining light transmission while ensuring deformation compensation capability.
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 solution effectively reduces thermal deformations by compensating for volume changes in the reflective optical element, maintaining imaging quality and simplifying the system by avoiding the need for active deformation compensation, especially in EUV systems with small illumination poles.
Implementation Method 1
a deformation reduction layer (15) which, upon the optically effective surface (11) being irradiated with electromagnetic radiation, reduces a maximum deformation level of the reflection layer system (14) in comparison with an analogous construction without the deformation reduction layer
Implementation Method 2
The inventors have recognized that the maximum deformation level can be reduced by virtue of the fact that, in the case of the reflective optical element according to the invention, a deformation reduction layer is taken into account or incorporated from the outset and has the effect that an undesired thermally governed deformation of the reflective optical element toward the vacuum as far as possible does not actually occur in the first place
Data Source
AI summary
A reflective optical element for a microlithographic projection exposure apparatus, a mask inspection apparatus or the like. The reflective optical element has an optically effective surface, an element substrate (12, 32, 42, 52), a reflection layer system (14, 34, 44, 54) and at least one deformation reduction layer (15, 35, 45, 55, 58). When the optically effective surface (11, 31, 41, 51) is irradiated with electromagnetic radiation, a maximum deformation level of the reflection layer system is reduced in comparison with a deformation level of an analogously constructed reflective optical element without the deformation reduction layer.