EUV Mirror Shape Correction via Thermally Deformable Layer
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Solution Overview
Problem
EUV mirrors in microlithographic projection exposure apparatuses face production-related geometric shape deviations that negatively impact imaging properties, and existing corrective measures are inadequate for achieving the required wavefront accuracy.
Innovation Solution
A method involving a thermally deformable layer system with a hysteresis profile in the layer thickness vs. temperature dependence, allowing for pre-mount correction of shape deviations by applying a temperature field, which induces deformations that are maintained even after cooling to operating temperature, using materials like Heusler alloys and shape-memory alloys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermal actuation is used to control mirror deformations during operation, then the geometric shape deviations can be corrected, but the device complexity increases and the corrective measures become complicated
Solution Approach 1:
The patent applies preliminary action by pre-configuring the optical element with a thermally deformable layer system during manufacturing, rather than adding complex correction mechanisms during operation. The layer system is designed in advance to enable controlled deformation through simple thermal actuation, thereby achieving shape correction without increasing operational device complexity
Solution Approach 2:
The patent utilizes parameter changes by exploiting the temperature-dependent properties of the thermally deformable layer system. By changing the temperature parameter, the optical element can transition between different geometric shapes, enabling correction of manufacturing deviations through simple thermal control rather than complex mechanical adjustment mechanisms
2Manufacturing precision
If existing corrective measures are applied to EUV mirrors, then some shape deviations can be addressed, but the wavefront accuracy required for high-precision microlithography is not sufficient
Solution Approach 1:
The patent applies composite materials by creating a multi-layer system comprising a substrate and a thermally deformable layer with specific material properties. This composite structure combines the structural integrity of the substrate with the controllable deformation characteristics of the thermally deformable layer, enabling precise wavefront control that meets the stringent accuracy requirements of EUV microlithography
Solution Approach 2:
The patent exploits phase transitions in the thermally deformable layer system, where controlled thermal energy input induces phase changes that result in predictable and reversible geometric deformations. This enables fine-tuning of the optical surface shape to achieve the required wavefront accuracy for high-precision imaging
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 approach enhances wavefront accuracy in optical systems by allowing for precise correction of shape errors before operation, maintaining the deformation during operation, and compensating for aberrations and surface deformations, even in systems with large substrate thicknesses.
Implementation Method 1
the thermally deformable layer has a phase transition, wherein this phase transition has a hysteresis profile in the temperature dependence of the layer thickness
Implementation Method 2
this phase transition has a hysteresis profile in the temperature dependence of the layer thickness of the thermally deformable layer such that any active deformation that is achieved by applying the temperature field to the optical element is maintained even if the relevant temperature required for the layer thickness change no longer prevails
Implementation Method 3
applying a temperature field to the optical element while at least regionally heating the thermally deformable layer to above a specified operating temperature of the optical system
Data Source
AI summary
A method for producing an optical element includes: providing a substrate (102), applying a layer system (103), wherein an optically effective surface (101) is formed and wherein the layer system has a layer (104) that is thermally deformable for manipulating the geometric shape of the optically effective surface, and applying a temperature field to the optical element while at least regionally heating the thermally deformable layer to above a specified operating temperature of the optical system. The thermally deformable layer is configured such that a deformation that is induced when the temperature field is applied is at least partially maintained after the optical element has cooled. Also disclosed is an optical element (400) that has an optically effective surface (401), a substrate (402), and a layer system (403) that has a reflection layer system (406), which includes a shape-memory alloy.