Far Pupil Reflective Imaging Optical System for EUV Exposure
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Solution Overview
Problem
Existing reflective imaging optical systems for EUV exposure apparatus face challenges in increasing numerical aperture while minimizing light loss and aberration, particularly in systems with a large number of mirrors, which affects the throughput and resolving power.
Innovation Solution
A reflective imaging optical system of the far pupil type is designed with eight mirrors, where the first to third mirrors are arranged on the side of the optical axis, and specific conditions regarding the distance between the entrance pupil and the object plane, the distance between the object and image planes, and the angle of incidence are met to achieve a large numerical aperture and corrected aberration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of mirrors is increased to correct aberration and increase numerical aperture, then the resolving power is improved, but the light loss increases and throughput decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the distances between mirrors and the angle of incidence to optimize the optical path. By adjusting these parameters within specific ranges, the system achieves high resolving power with only eight mirrors, minimizing light loss while correcting aberration effectively.
Solution Approach 2:
The patent employs a far pupil type configuration where the entrance pupil is positioned on the opposite side of the optical system from the object plane. This dimensional arrangement allows for effective aberration correction and high numerical aperture with a reduced number of mirrors, thereby reducing light loss compared to conventional near pupil configurations.
2Measurement precision
If the numerical aperture is increased to improve resolving power, then the image quality is improved, but the system complexity increases
Solution Approach 1:
The far pupil type configuration repositions the entrance pupil to the opposite side of the optical system, creating a different spatial arrangement that enables high numerical aperture with fewer optical elements. This dimensional change reduces system complexity while maintaining or improving resolving power.
Solution Approach 2:
By optimizing specific parameters such as the distance between the entrance pupil and object plane (PD), the distance between object and image planes (TT), and the angle of incidence (R), the system achieves high numerical aperture with a simplified eight-mirror configuration, reducing overall system complexity.
3Reliability
If the distance between entrance pupil and object plane is adjusted to meet specific conditions, then the aberration is corrected, but the system design constraints increase
Solution Approach 1:
The patent establishes specific parameter ranges for PD (distance between entrance pupil and object plane), TT (distance between object and image planes), and R (angle of incidence). By controlling these parameters within defined ranges, the system achieves effective aberration correction while the constraints are managed through systematic design rather than arbitrary limitations.
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 allows for high-resolution projection exposure with a large resolving power, reducing light loss and aberration, enabling the production of highly accurate devices using EUV light with improved throughput.
Implementation Method 1
a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, a fourth reflecting mirror, a fifth reflecting mirror, a sixth reflecting mirror, a seventh reflecting mirror and an eighth reflecting mirror which are arranged in an order of reflection from the first plane toward the second plane
Data Source
AI summary
An reflective imaging optical system of the far pupil type, which is applicable to an exposure apparatus using for example the EUV light, forms on a second plane an image of a predetermined area on a first plane and is provided with first to eighth reflecting mirrors arranged in an order of reflection from the first plane toward the second plane. An entrance pupil of reflective imaging optical system is positioned on a side opposite to the reflective imaging optical system with the first plane intervening therebetween; and the following condition is fulfilled provided that PD represents a distance along an optical axis between the entrance pupil and the first plane, TT represents a distance along the optical axis between the first plane and the second plane, and R represents an angle of incidence of a main light beam coming into the first plane: −14.3<(PD/TT)/R<−2.5.