Asymmetric Support for EUV Optical Elements
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Solution Overview
Problem
Conventional optical element holding members fail to provide stable support for asymmetrical optical elements, leading to instability and reduced accuracy in projection exposure apparatuses, especially when using EUV light for manufacturing highly integrated semiconductor devices.
Innovation Solution
The optical apparatus includes an asymmetrical optical element with a holding member and at least three support members, where the weight of the optical element and holding member is distributed equally across the support members, with a balance weight optionally used to achieve optimal weight balance and stability, ensuring the center of mass or inertia axes align with the support positions for improved static and dynamic stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional optical element holding member supports an asymmetrical optical element at three points arranged at equal angular intervals, then the support structure is simple and easy to manufacture, but the optical element cannot be held stably and the apparatus accuracy deteriorates
Solution Approach 1:
The patent applies asymmetry by configuring the support members at unequal angular intervals around the optical element rather than at equal intervals. The angular intervals are specifically designed to distribute the optical element's weight equally among the three support members, creating an asymmetric support pattern that matches the asymmetric mass distribution of the optical element. This resolves the contradiction by sacrificing the simplicity of equal-interval support to achieve stable, vibration-resistant holding of asymmetric optical elements.
2Device complexity
If three support members are arranged at equal angular intervals to simplify the support structure, then the device complexity is reduced, but the optical element exhibits unpredictable behavior during alignment adjustment
Solution Approach 1:
The patent employs asymmetric angular positioning of support members to match the asymmetric mass distribution of the optical element. By calculating and setting specific unequal angular intervals, the support structure achieves balanced weight distribution across all support members, eliminating unpredictable movements during alignment adjustment while maintaining relatively simple three-point support geometry.
3Adaptability or versatility
If the optical element has asymmetrical shape with cutaway portions for light path, then the optical function is improved for EUV light, but the weight balance becomes poor and static stability deteriorates
Solution Approach 1:
The patent addresses the static stability problem of asymmetric optical elements by implementing an asymmetric support pattern. The support members are positioned at unequal angular intervals specifically calculated to distribute the element's weight equally, counterbalancing the asymmetric mass distribution caused by cutaway portions. This allows the optical element to maintain its necessary asymmetric shape for EUV light functionality while achieving stable, vibration-resistant support.
Solution Approach 2:
The patent applies counterweight principles by strategically positioning support members to compensate for the asymmetric mass distribution of the optical element. The unequal angular intervals are designed so that the combined center of gravity of the optical element and support structure aligns with the rotation axis, effectively counterbalancing the weight imbalance caused by cutaway portions and improving static stability.
4Device complexity
If conventional support members are used without weight balance consideration, then the device complexity is low, but environmental vibrations have significant impact on the optical apparatus
Solution Approach 1:
The patent reduces vibration sensitivity by implementing asymmetric angular positioning of support members. The unequal angular intervals are specifically designed to distribute the optical element's weight equally among support members, aligning the combined center of gravity with the rotation axis. This asymmetric configuration minimizes the impact of environmental vibrations on optical element position and attitude while maintaining relatively simple three-point support structure.
Data Source
AI summary
An optical system improved in weight balance and stability, comprising drive mechanisms that support, movable with respect to an outer ring, a virtual rigid body consisting of an inner ring, optical element in a shape asymmetrical with respect to the optical axis, and optical element holding members for holding the optical element and fixing it to the inner ring. The inner ring, the outer ring and drive mechanisms function as a parallel link mechanism. Balance weights are provided on the virtual rigid body such that the weight of the virtual rigid body acts uniformly on the drive mechanisms. Therefore, the optical element is not likely to vibrate when subjected to an external vibration or at adjusting. The optical system is suitable for use in an exposure system requiring high exposure accuracy.