EUV Lithography Condensing Mirrors with Optical Eccentricity
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Solution Overview
Problem
Conventional extreme ultraviolet lithography (EUVL) exposure apparatus face challenges in optimizing the focal length of the condensing optical assembly and the distance between fly-eye mirrors to achieve optimal reflectivity and prevent physical interference with the wafer during exposure.
Innovation Solution
The use of a condensing optical system with optically eccentric reflecting mirrors, such as spherical or aspherical mirrors, allows for increased focal length and distance between incidence-side and emission-side fly-eye mirrors, reducing the angle of incidence and enhancing reflectivity while maintaining optimal illumination and preventing attenuation of illumination light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between incidence-side fly-eye mirror and emission-side fly-eye mirror is increased to reduce the angle of incidence of EUV light on the mirrors, then the reflectivity of the mirrors is improved, but the focal length of the condensing optical assembly must be increased which causes the assembly to be situated below the wafer level creating physical interference
Solution Approach 1:
The patent introduces a third dimension by placing the condensing optical assembly in a position above the wafer level rather than below it, allowing the system to accommodate increased mirror separation distance without physical interference. This spatial reconfiguration enables both improved reflectivity through reduced angle of incidence and proper positioning of the condensing assembly within the projection-optical system.
2Reliability
If the focal length of the condensing optical assembly is increased to improve the reflectivity of fly-eye mirrors, then the angle of incidence of EUV light on the mirrors is reduced, but the condensing optical assembly is forced below the wafer level causing physical interference with the scanning wafer
Solution Approach 1:
The patent resolves the conflict by repositioning the condensing optical assembly to a third dimension (above the wafer level) rather than allowing it to move below the wafer level. This spatial solution enables the assembly to have a long focal length for improved reflectivity while avoiding physical interference with the scanning wafer during exposure.
3Reliability
If the distance between fly-eye mirrors is increased to reduce angle of incidence, then EUV light reflectivity is improved, but the overall system size and complexity increases
Solution Approach 1:
The patent manages the increased system complexity by utilizing vertical space (third dimension) to position the condensing optical assembly above the wafer level. This allows the horizontal distance between fly-eye mirrors to be increased for improved reflectivity without proportionally increasing the overall system footprint, thereby controlling complexity while achieving the desired optical performance.
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 enables high-throughput exposure with improved reflectivity and resolution, preventing degradation of the image on the photosensitive substrate and allowing for the production of microdevices with detailed circuit patterns.
Implementation Method 1
a condensing optical system comprising two reflecting mirrors that guide the illumination light, reflected by the emission-side fly-eye optical system, to the surface of a mask for irradiation
Data Source
AI summary
Illumination systems are disclosed that illuminate a surface (M) for irradiation with illumination light emitted from a light source (5). An exemplary illumination system includes an incidence-side reflection-type fly-eye optical system (12) having multiple reflection-type partial optical systems arranged in rows, an emission-side reflection-type fly-eye optical system (14) having multiple reflection-type partial optical systems arranged in rows and corresponding to respective reflection-type partial optical systems of the incidence-side reflection-type fly-eye optical system (12), and a condensing optical system including two reflecting mirrors (18, 20) that guide illumination light, reflected by the emission-side reflection-type fly-eye optical system (14), to the surface (M). The center of curvature of at least one of the reflecting mirrors is optically eccentric with respect to a normal to the surface for irradiation at the center of the illuminated region.