EUV Mirror Mounting for Deformation Control
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Solution Overview
Problem
EUV projection exposure apparatuses face challenges in maintaining mechanical precision and minimizing deformations due to the high cost and weight of large-diameter mirror elements, which are exacerbated by thermal and actuation-induced stresses, and the difficulty in implementing precise alignment and mounting systems.
Innovation Solution
An optical arrangement with a mirror element supported at a single location, allowing the actuator to be free of forces in equilibrium, reducing heating and deformation risks, and utilizing a mounting force that compensates for weight forces without intersecting the optically effective reflection region, thereby minimizing structural space and deformation impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If mirror elements with large diameter are used to achieve large numerical aperture, then optical performance is improved, but manufacturing cost and weight increase significantly
Solution Approach 1:
The patent divides the mirror element into functionally independent segments: the mirror substrate (providing optical function) and the support frame (providing mechanical support). This segmentation allows the mirror substrate to be optimized for optical performance while the support frame is optimized for mechanical stability, enabling large diameter mirrors to be managed through modular construction and reduced overall weight.
Solution Approach 2:
The mirror substrate is nested within the support frame structure, with the reflection region positioned within the support frame's enclosed space. This nested arrangement allows the heavy support frame to provide structural stability while the actual optical element (mirror substrate) remains relatively lightweight, resolving the contradiction between large diameter requirements and weight constraints.
2Illumination intensity
If mirror elements with large diameter are used, then optical performance is improved, but manufacturing difficulty and cost increase
Solution Approach 1:
By segmenting the mirror element into substrate and frame components, each can be manufactured independently using optimized processes. The mirror substrate can be fabricated with precise optical surfaces using specialized techniques, while the support frame can be manufactured using standard mechanical fabrication methods, thereby reducing overall manufacturing difficulty and cost.
Solution Approach 2:
The support frame acts as an intermediary structure that simplifies manufacturing. Instead of manufacturing a single complex large-diameter mirror element, the frame provides a pre-fabricated mechanical structure that supports the mirror substrate, dividing the manufacturing task into simpler, more manageable steps.
3Measurement precision
If rigid mounting and actuation systems are used to maintain alignment precision, then positioning accuracy is improved, but deformations due to forces and moments increase
Solution Approach 1:
The mounting elements are positioned to act locally on the mirror substrate at specific points (edge regions) rather than distributing forces across the entire substrate. This localized mounting approach minimizes the area subjected to mounting forces, reducing overall deformation while maintaining positioning accuracy through precise local control.
Solution Approach 2:
The support frame serves as an intermediary between the rigid mounting/actuation system and the mirror substrate. It absorbs and distributes mounting forces and moments before they reach the substrate, reducing direct stress on the optical element while still enabling precise positioning through the actuation system.
4Measurement precision
If actuators are used to position and align mirror elements, then alignment precision is improved, but heating of the mirror element increases
Solution Approach 1:
The patent replaces direct mechanical actuation of the mirror substrate with electromagnetic actuators that interact with the support frame rather than directly with the substrate. This substitution reduces mechanical contact and associated heating of the optical element, while still achieving precise alignment through the support frame's movement.
5Stability of the object's composition
If multiple mounting elements are used to support mirror elements, then stability is improved, but alignment precision and mechanical precision decrease
Solution Approach 1:
The patent uses a small number of mounting elements positioned at specific local regions (edge areas) of the mirror substrate rather than distributing multiple mounting points across the entire surface. This localized mounting approach minimizes the cumulative effect of mounting forces on the substrate, reducing alignment errors while providing sufficient stability through strategic positioning.
Solution Approach 2:
The support frame acts as an intermediary that provides stable support for the mirror substrate using minimal mounting elements. The frame's rigid structure distributes and absorbs mounting forces, enabling stable support with fewer mounting points than would be required if mounting directly to the substrate, thereby preserving alignment precision.
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 solution reduces the risk of deformation and heating near the reflection region, allows for more compact and lightweight actuation, and facilitates easier thermal compensation, maintaining high mechanical precision with reduced structural requirements.
Implementation Method 1
the mounting element alone holds the mirror element at least approximately in an equilibrium position
Implementation Method 2
at least one actuator configured to move the mirror element in at least one degree of freedom
Implementation Method 3
a mirror element having a mirror substrate and a reflection region formed on a surface of the mirror substrate
Data Source
AI summary
An optical arrangement of a microlithographic projection exposure apparatus includes a mirror element having a mirror substrate, and a reflection region formed on a surface of the mirror substrate. The arrangement also includes at least one actuator configured to move the mirror element in at least one degree of freedom, and a mounting element, which acts on the mirror substrate. The mounting element alone holds the mirror element at least approximately in an equilibrium position, such that the at least one actuator is at least approximately free of forces in the equilibrium position.