Shape-Memory Alloy Bearing for Lithography Optical Clamping
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Solution Overview
Problem
In lithography apparatuses, the existing optical systems face challenges in maintaining a stable clamping force without inducing stress-induced changes in optical elements, particularly due to high surface pressure and frictional forces during the movement and acceleration of optical components.
Innovation Solution
An optical system utilizing a shape-memory alloy with pseudo-elastic deformation to increase the contact area between optical elements and their holding devices, reducing surface pressure and enhancing heat transfer while maintaining a constant clamping force, thereby preventing stress-induced changes in optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the contact face between the optical element and the holding device is made as small as possible for adjustment purposes, then the adjustability is improved, but the surface pressure increases leading to stress-induced changes in optical properties
Solution Approach 1:
The patent applies parameter changes by utilizing the phase transition characteristics of shape-memory alloys. The bearing portion is made from a shape-memory alloy that can transform between austenite and martensite phases, allowing the contact face area to be dynamically adjusted. During adjustment, the alloy is heated to transform to austenite, increasing the contact face area to reduce surface pressure. During operation, it transforms to martensite, reducing the contact face area for precise positioning. This resolves the contradiction by making the contact face area a variable parameter rather than a fixed geometric constraint.
Solution Approach 2:
The patent directly applies phase transitions of shape-memory alloys to resolve the technical contradiction. The bearing portion utilizes the reversible phase transition between austenite (high-temperature phase with larger contact area) and martensite (low-temperature phase with smaller contact area). By controlling the phase state through temperature or stress, the system can switch between adjustment mode (larger contact area, lower surface pressure) and operation mode (smaller contact area, precise positioning), thereby eliminating the need to choose between adjustability and surface pressure constraints.
2Ease of operation
If a punctiform or linear contact is used between the optical element and the holding device, then the adjustability is improved, but the Hertzian stress increases causing stress-induced changes in optical properties
Solution Approach 1:
The patent changes the parameter of contact geometry by using a shape-memory alloy bearing portion that can dynamically alter its contact face area. Instead of a fixed punctiform or linear contact, the contact area becomes a variable parameter controlled by the phase state of the alloy. During adjustment operations, the alloy transforms to austenite, increasing the contact area to distribute Hertzian stress. During normal operation, it transforms to martensite, reducing the contact area for precise positioning while maintaining acceptable stress levels through the material's pseudo-elastic properties.
Solution Approach 2:
The patent employs composite material properties by utilizing shape-memory alloys, which combine the characteristics of elastic materials with phase transition capabilities. The bearing portion made from shape-memory alloy exhibits both elastic deformation behavior and reversible phase transitions, creating a composite-like functionality within a single material system. This allows the bearing portion to adapt its mechanical properties and contact geometry dynamically, resolving the contradiction between adjustability and Hertzian stress by providing both compliance during adjustment and stability during operation.
3Stress or pressure
If a large contact face is used between the optical element and the holding device, then the surface pressure is reduced preventing stress-induced changes, but the adjustability deteriorates
Solution Approach 1:
The patent applies dynamics by making the contact face area a dynamic variable rather than a static geometric feature. The shape-memory alloy bearing portion can dynamically change its contact area with respect to the optical element based on operational requirements. During adjustment phases, the alloy transforms to austenite, increasing the contact area to reduce surface pressure and prevent stress-induced changes. During operation phases, it transforms to martensite, reducing the contact area to enable precise positioning and adjustment. This dynamic adaptation resolves the contradiction by allowing the system to have both large and small contact areas at different times.
4Stability of the object's composition
If a constant clamping force is applied to the optical element, then the position stability is improved, but the frictional force increases potentially causing movement during acceleration
Solution Approach 1:
The patent applies parameter changes by utilizing the phase transition characteristics of shape-memory alloys to dynamically adjust the clamping force. The bearing portion made from shape-memory alloy can transform between austenite and martensite phases, changing its mechanical properties including stiffness and friction characteristics. During acceleration phases, the alloy can transform to a phase with lower friction coefficients, reducing the frictional force that would otherwise oppose acceleration forces. During normal operation, it maintains sufficient clamping force for position stability. This resolves the contradiction by making the frictional force a variable parameter rather than a constant determined solely by the clamping force.
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 achieves stress-reduced and improved clamping with a larger contact area, reducing Hertzian stress and enhancing heat transfer, thus maintaining the optical properties of the elements and ensuring stable operation during acceleration and movement.
Implementation Method 1
at least one of the components includes a bearing portion which contacts the optical element and which has a shape-memory alloy. In particular, in the pseudo-elastic deformation of the bearing portion, a contact face between the optical element and at least one of the components increases
Implementation Method 2
Moreover, the surface enlargement also improves the heat transfer between the optical element and the bearing portion
Data Source
AI summary
An optical system for a lithography apparatus, having a first component, a second component, and an optical element, which is held between the first component and the second component with force-fit engagement and for this purpose is subjected to a clamping force. At least one of the components includes a bearing portion which contacts the optical element and which has a shape-memory alloy.