EUV Projection Optics With Compact Mirror Area and High NA
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Solution Overview
Problem
Existing EUV projection exposure apparatuses face challenges in achieving a balance between maintaining high image-side numerical aperture and overall transmission while minimizing the overall mirror surface area, which affects production costs and installation space.
Innovation Solution
The development of an imaging EUV optical unit with a mirror surface area less than 1.5 m², an image-side numerical aperture greater than 0.3, and overall transmission greater than 10%, utilizing a specific configuration of mirrors with polishing overrun edges and optimized mirror surfaces to enhance usability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the overall mirror surface area is reduced to less than 1.5 m², then production costs and installation space are reduced, but the ability to maintain high image-side numerical aperture and overall transmission becomes more difficult
Solution Approach 1:
The optical system is divided into multiple mirrors (first mirror, second mirror, third mirror, fourth mirror) with specific functions. Each mirror is optimized for its particular role in the beam path, allowing the system to achieve high numerical aperture and transmission efficiency without requiring a single large mirror surface. The segmentation enables distributed optical functions that collectively satisfy the performance requirements while keeping the total mirror area below 1.5 m².
Solution Approach 2:
Each mirror in the system is designed with specific local properties optimized for its position and function. The first mirror has specific curvature and coating properties for initial beam direction, while subsequent mirrors are optimized for their respective roles in focusing and directing the EUV beam. This local optimization allows each mirror to contribute maximally to the overall system performance without requiring excessive surface area.
2Ease of operation
If the number of mirrors is increased to guide EUV light through the imaging beam path, then the imaging capability is improved, but the overall transmission is reduced due to multiple reflection surfaces
Solution Approach 1:
The system optimizes critical parameters including the angle of incidence for each mirror, the curvature radius, and the coating properties to maximize transmission. By carefully selecting and optimizing these parameters, the system achieves high overall transmission (>10%) despite using multiple mirrors. The parameter optimization ensures that each reflection contributes minimally to energy loss while maintaining the necessary imaging functionality.
3Measurement precision
If the image-side numerical aperture is increased to greater than 0.3, then the imaging resolution is improved, but the mirror surface area and system complexity increase
Solution Approach 1:
The optical system uses a combination of spherical and aspherical mirror surfaces with specific curvatures to achieve the desired numerical aperture. The dynamic design allows the system to focus light effectively while maintaining a compact mirror surface area. The aspherical surfaces enable better control over the beam path and focus properties, achieving high resolution without proportionally increasing the total mirror area.
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 configuration reduces production costs and installation space while maintaining high imaging performance, with improved wavefront aberration and polarisation rotation, suitable for use in projection exposure apparatuses for lithography.
Implementation Method 1
a plurality of mirrors for guiding EUV imaging light at a wavelength of shorter than 30 nm along an imaging beam path from the object field towards the image field
Data Source
AI summary
An imaging EUV optical unit serves for imaging an object field into an image field. The imaging optical unit has a plurality of mirrors for guiding EUV imaging light at a wavelength of shorter than 30 nm along an imaging beam path. The imaging EUV optical unit has an image-side numerical aperture of at least 0.3. An overall transmission of the plurality of mirrors is greater than 10%. An overall mirror surface, which represents the sum of all used mirror surfaces of the plurality of mirrors, is less than 1.5 m2. This design can yield an imaging EUV optical unit with improved usability for an EUV projection exposure apparatus.