EUV Imaging Optical System Atmospheric Transition Stability
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Solution Overview
Problem
Conventional optical systems for EUV exposure apparatuses face significant optical characteristic fluctuations when transitioning between air and vacuum atmospheres, leading to precision issues in alignment and focus detection due to refractive index changes, which is exacerbated by the need for complex and costly adjustments in vacuum chambers.
Innovation Solution
The implementation of an imaging optical system with a first and second imaging optical system, where the first system moves in one direction along the optical axis and the second in the opposite direction, minimizing the overall position change of the final imaging plane, thereby reducing optical characteristic fluctuations. This system includes specific lens configurations and arrangements to maintain optical stability across atmospheric changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical system is arranged in the vacuum atmosphere for EUV exposure, then the EUV light attenuation is prevented, but the optical characteristic fluctuates due to refractive index change
Solution Approach 1:
The patent changes the physical state parameter of the atmosphere from vacuum to air for the detection optical system. By arranging the alignment detection system and focus position detection system in the air atmosphere rather than vacuum, the refractive index remains stable, preventing optical characteristic fluctuations and maintaining imaging position precision while still allowing EUV light to pass through the vacuum chamber via viewing windows.
2Manufacturing precision
If the optical system is arranged in the air atmosphere via viewing window, then the optical characteristic stability is improved, but the device complexity increases
Solution Approach 1:
The patent segments the detection system into two parts: the EUV light path remains in vacuum while the detection optical systems (alignment detection and focus position detection) are placed in the air atmosphere. This is achieved by introducing viewing windows that separate the vacuum chamber from the air atmosphere, allowing each subsystem to operate in its optimal environment without requiring complete system redesign.
Solution Approach 2:
The viewing window acts as an intermediary element between the vacuum chamber and the air atmosphere. It allows EUV light to pass through while enabling the detection optical systems to operate in the air atmosphere, thus mediating between the conflicting requirements of vacuum environment for EUV light and air environment for optical stability.
3Manufacturing precision
If the imaging position change is reduced to small value, then the optical stability is improved, but the adjustment complexity in vacuum increases
Solution Approach 1:
The patent extracts the detection optical systems from the vacuum environment and places them in the air atmosphere. By taking out the alignment detection system and focus position detection system from the vacuum chamber, the need for complex vacuum-compatible adjustment mechanisms is eliminated, while the imaging position stability is maintained through the stable refractive index of air.
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 effectively reduces the imaging position change to a small value, maintaining optical stability and precision in both air and vacuum environments, enabling high-precision detection systems for EUV exposure apparatuses without the need for extensive vacuum chamber adjustments.
Implementation Method 1
When it is assumed that for the light having a wavelength of 820 nm, the refractive index of the vacuum atmosphere is 1.00000, and the refractive index of the air atmosphere is 1.00027. This variation of the refractive index influences the optical characteristic of the optical system
Data Source
AI summary
An imaging optical system for imaging a pattern of an object plane onto an image plane includes a first imaging optical system for imaging at a first imaging position, the first imaging optical system having a magnification α in a vacuum atmosphere, and a second imaging optical system for imaging at a second imaging position, the second imaging optical system having a magnification β in the vacuum atmosphere, wherein when an environment in which the imaging optical system is placed changes from the vacuum atmosphere to an air atmosphere or vise versa, a direction of the first imaging position that moves along an optical axis is opposite to a direction of the second imaging position that moves along the optical axis.