Lithography Optical System with Decoupled Measurement Surface
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Solution Overview
Problem
Existing optical systems in lithography apparatuses face challenges in maintaining the accuracy of functional surfaces due to deformations caused by joining stresses, especially as the joining agent ages, which affect the precise positioning and orientation of movable elements.
Innovation Solution
The introduction of a decoupling device in the form of a constriction or using different materials for the functional element to decouple deformations between portions, preventing the transfer of stresses to the functional surface, thereby maintaining its integrity for accurate positioning and orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a functional element carrying the functional surface is connected to the optical element by a joining process, then the functional element can be securely attached to the movable element, but joining stresses (e.g., adhesive stresses) lead to undesired deformations of the functional surface especially when the joint ages
Solution Approach 1:
The functional element is divided into two portions: a first portion that is fastened to the movable element and a second portion that carries the functional surface. This segmentation allows the first portion to absorb joining stresses while the second portion remains stress-free and deformation-free, resolving the contradiction between secure attachment and surface precision.
Solution Approach 2:
The harmful effect (deformation) is extracted from the functional surface by isolating it in the second portion, which is decoupled from the joining process. The first portion takes on the role of bearing joining stresses, while the second portion is extracted from the stress path to maintain surface integrity.
2Strength
If the functional surface deforms due to joining stresses, then the joint provides secure connection, but the exact position of the mirror cannot be determined
Solution Approach 1:
By segmenting the functional element into two portions, the measurement reference (functional surface in the second portion) is separated from the connection interface (first portion). This ensures that positioning measurements are taken from a stable, deformation-free surface while the connection remains secure.
Solution Approach 2:
The first portion acts as an intermediary that absorbs joining stresses and protects the second portion (carrying the functional surface) from deformation. This mediator role allows secure connection without compromising measurement precision.
3Duration of action of moving object
If the joint ages or is subject to environmental changes (e.g., changes in humidity), then the joining agent undergoes changes, but this causes deformation of the functional surface affecting positioning accuracy
Solution Approach 1:
The functional element is segmented into a first portion exposed to environmental changes and aging, and a second portion protected from these effects. The segmentation creates a buffer zone where the first portion absorbs temporal and environmental stresses while the second portion maintains long-term dimensional stability.
Solution Approach 2:
The design provides beforehand cushioning by placing the first portion in the stress path of joining agents and environmental changes, protecting the second portion in advance. This preemptive protection ensures the functional surface remains stable throughout the joint's service life.
Data Source
AI summary
An optical system for lithography apparatus comprises a movable element and a functional element having a first and second portions. The optical element is designed as an optical element or as a reference structure. The first portion is fastened to the movable element by a joining mechanism along a fastening plane. The second portion comprises a functional surface. The functional element comprises a decoupling device for decoupling by deformation the first portion from the second portion. The decoupling device is formed by a narrowing of the functional element. The narrowing is located laterally outside a region of the functional surface. The functional surface is a measurement surface which is suitable for acquisition for the purposes of positioning and/or orientating the movable element.