EUV Mirror Surface Roughness Reduction Using Thin Plate
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Solution Overview
Problem
Current techniques for producing optical surfaces for extreme-ultraviolet (EUV) and X-ray radiation systems are expensive and time-consuming due to the difficulty in achieving the required high smoothness and precision in curvature, particularly for non-planar and free-form surfaces, leading to scattering losses from high-spatial frequency roughness.
Innovation Solution
The method involves using a super-polished plane-parallel membrane or thin plate to cover a base substrate with a curved surface, where the thin plate is secured to conform to the target curvature and smooth over deviations at higher spatial frequencies, reducing surface roughness to achieve the desired smoothness without the need for extreme finishing methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional polishing and figuring techniques (IBF, MRF, CMP, CCOS) are used to achieve required surface smoothness and precision for EUV/X-ray optics, then the optical surface quality is improved, but the manufacturing cost and time consumption increase significantly
Solution Approach 1:
The invention applies preliminary action by pre-polishing the planar substrate to a very smooth surface (roughness < 1 nm RMS) before mounting. This preliminary surface preparation on the flat substrate eliminates the need for subsequent complex polishing of the curved optical surface, significantly reducing manufacturing time and cost while achieving the required surface quality for EUV/X-ray optics
Solution Approach 2:
The invention segments the manufacturing process into two independent stages: (1) polishing the planar substrate to high precision while flat, and (2) mounting the polished substrate to the curved holder to achieve the final optical shape. This segmentation allows each stage to be optimized independently, avoiding the complexity of polishing curved surfaces
2Manufacturing precision
If conventional polishing techniques are used to reduce high-spatial frequency roughness, then surface smoothness is improved, but the manufacturing cost and time consumption increase significantly
Solution Approach 1:
The invention performs the time-consuming high-spatial frequency roughness reduction on the planar substrate before mounting, when the surface is flat and accessible to standard polishing equipment. This preliminary action eliminates the need for subsequent time-consuming polishing of the curved optical surface, reducing total manufacturing time while achieving the required roughness specifications
3Manufacturing precision
If extreme finishing methods are used to achieve required surface smoothness on curved optical surfaces, then surface quality is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The invention inverts the conventional approach by polishing the substrate while it is flat (planar) rather than while it is curved. This inversion allows the use of simple, well-established flat surface polishing techniques instead of complex curved surface finishing methods, significantly simplifying manufacturing while achieving the same surface quality
Solution Approach 2:
The invention performs the difficult surface finishing operation preliminarily, while the substrate is still flat and accessible to standard polishing equipment. This preliminary action on the planar substrate eliminates the need for extreme finishing methods on the final curved optical surface, simplifying the manufacturing process
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 allows for cost-effective production of high-quality aspheric surfaces with reduced high-spatial frequency roughness, relaxing manufacturing requirements and enabling the use of ion beam finishing for error correction, thereby improving the efficiency and quality of EUV optics.
Implementation Method 1
the plate has a thickness thin enough to conform to the curvature of a target mirror surface and thick enough to attenuate deviations at high spatial frequencies
Data Source
AI summary
A method of making a mirror for use with extreme ultraviolet or x-ray radiation includes: i) providing a base substrate having a curved surface, wherein the curved surface deviates from a curvature of a target mirror surface at high spatial frequencies corresponding to spatial periods less than 2 mm; and ii) securing a first side of a thin plate to the curved surface of the base substrate to cover the curved surface, wherein the plate has a thickness thin enough to conform to the curvature of the target mirror surface and thick enough to attenuate deviations at the high spatial frequencies on a second side of the thin plate opposite the first side that are caused by the deviations on the curved surface of the base substrate. A mirror made by the method is also disclosed.