Mirror Module CTE Matching for EUV Lithography Thermal Stability
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Solution Overview
Problem
In microlithographic projection exposure apparatuses, especially in the EUV range, mirror modules with unregulated mirrors face challenges in minimizing imaging errors due to thermal expansion differences between mirror and objective structures, leading to deformations and magnetostrictive effects that affect imaging quality.
Innovation Solution
A mirror module design with a mirror body and a supporting structure made from materials with coefficients of thermal expansion (CTE) differing by less than 0.5*10^-6K^-1, where the supporting structure is engineered to be highly rigid and decoupled from the mirror body to minimize thermal deformations, using materials like titanium dioxide-doped quartz glass and cordierite, and incorporating decoupling elements to reduce deformation transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If metallic coupling elements are used to connect the mirror to the objective structure, then the coefficient of thermal expansion is reduced, but magnetostrictive effects increase and worsen imaging quality
Solution Approach 1:
The patent changes the material parameter (CTE) of the coupling elements to match the mirror body material, reducing thermal expansion differences. This is achieved by selecting non-metallic materials with CTE values within 0.5×10^-6 K^-1 of the mirror body, thereby eliminating magnetostrictive effects while maintaining thermal stability
Solution Approach 2:
The patent employs composite material selection where the coupling elements are made from non-metallic materials (such as glass ceramics or polymers) that combine low CTE with non-magnetostrictive properties. This composite approach allows simultaneous optimization of thermal expansion matching and elimination of magnetic interference
2Object-generated harmful factors
If non-metallic coupling elements are used to connect the mirror to the objective structure, then magnetostrictive effects are reduced, but the coefficient of thermal expansion increases and worsens thermal stability
Solution Approach 1:
The patent carefully selects non-metallic materials whose CTE parameter is specifically engineered to be within 0.5×10^-6 K^-1 of the mirror body material. This precise parameter matching ensures that while magnetostrictive effects are eliminated, thermal expansion stability is maintained through careful material selection
3Manufacturing precision
If the supporting structure is made rigid to reduce deformation, then imaging accuracy is improved, but thermal expansion differences cause more stress and deformation at the connection point
Solution Approach 1:
The patent changes the CTE parameter of the supporting structure material to match the mirror body, reducing thermal expansion differences. This allows the rigid supporting structure to maintain its high stiffness and imaging accuracy while minimizing thermal stress accumulation at connection points
Solution Approach 2:
The patent applies local quality by ensuring the supporting structure has high overall rigidity for imaging accuracy, while the connection region uses materials with matched CTE to locally reduce thermal stress. This creates a gradient where stiffness is high where needed and thermal compatibility is high at connection points
4Ease of manufacture
If materials with different CTE are used for mirror body and supporting structure, then ease of manufacture is improved, but thermal deformations increase and worsen imaging quality
Solution Approach 1:
The patent imposes a specific parameter constraint (CTE difference < 0.5×10^-6 K^-1) that guides material selection. This parameter-based approach maintains manufacturing flexibility by allowing various material combinations as long as they meet the CTE matching criterion, while ensuring imaging quality through reduced thermal deformations
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 design significantly reduces thermally induced deformations and magnetostrictive effects, maintaining high imaging accuracy by keeping deformations below 0.1% and minimizing the impact of thermal expansion on the mirror surface, thereby enhancing the overall performance of the microlithographic projection exposure apparatus.
Implementation Method 1
the first material and the second material differ in terms of their coefficients of thermal expansion (CTE) by less than 0.5*10−6K−1 in a temperature range around an operating temperature
Data Source
AI summary
The disclosure relates to a mirror module, in particular for a microlithographic projection exposure apparatus, including a mirror, which has a mirror body and an optically effective surface. The mirror body has a first material, and a supporting structure for connecting the mirror body to an objective structure. The supporting structure has a second material. The first material and the second material differ in terms of their coefficients of thermal expansion by less than 0.5*10−6K−1 in a temperature range around an operating temperature which is reached by the mirror module during operation in the region of the connection of the mirror body to the supporting structure.