EUV Illumination System Collector Mirror Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current illumination systems for EUV projection exposure face challenges in efficiently transferring EUV illumination light into the object field, as the constriction and focus areas are often intertwined, limiting design freedom and complicating the production of collector imaging optics.
Innovation Solution
The solution separates the constriction and focus effects, allowing for independent placement of the first downstream focus area, and employs free-form collector mirrors with specific edge contours and geometric designs, including ring and ellipsoidal mirrors, to enhance the illumination system's efficiency and design flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the constriction area is arranged at the focus area of the collector, then the imaging effect is achieved, but the design freedom is limited and the production of collector imaging optics is complicated
Solution Approach 1:
The patent segments the optical system into two independent functional areas: a constriction area for beam compression and a focus area for imaging. This segmentation allows each area to be optimized independently, with the constriction area handling beam manipulation and the focus area handling image formation, thereby simplifying the production of collector optics while maintaining design freedom.
Solution Approach 2:
The patent extracts the constriction function from the focus area, creating a separate constriction area downstream of the radiation source. By taking out the beam constricting effect from the imaging location, the system allows independent optimization of both functions, simplifying collector optics production while enhancing design versatility.
2Device complexity
If the downstream focus area is arranged in the area of the pupil facet mirror, then the design is simplified, but the intermediate image is eliminated
Solution Approach 1:
The patent extracts the downstream focus area from the traditional intermediate image location and places it directly in the pupil facet mirror area. This extraction eliminates the need for a separate intermediate image plane, thereby simplifying the overall illumination system design while maintaining all necessary imaging functions.
3Ease of manufacture
If separate collector mirrors are used, then the production is simplified, but the mirror surfaces require free-form designs
Solution Approach 1:
The patent divides the collector into multiple separate collector mirrors rather than using a single complex mirror. This segmentation allows each mirror to have a simpler free-form surface geometry that is easier to manufacture, while the collective arrangement of multiple mirrors achieves the overall optical function.
Solution Approach 2:
The patent employs free-form surface geometries for the separate collector mirrors, utilizing curved and non-spherical surfaces optimized for their specific positions and functions. These free-form designs, while complex in geometry, are easier to manufacture individually compared to a single large complex mirror, as each can be produced using specialized forming techniques.
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 enables efficient guidance of EUV illumination light, simplifies the design of the illumination system, and increases the number of design degrees of freedom by separating imaging properties, leading to improved performance in EUV projection exposure systems.
Implementation Method 1
Separate collector mirrors simplify the production of collector imaging optics with a constricting effect and one that is not imaging at the location of the constriction. The collector mirrors can have mirror surfaces that are designed as free-form surfaces.
Implementation Method 2
Ellipsoidal mirror surfaces according to claim 7 can be manufactured with comparatively little effort.
Implementation Method 3
A spherical optic according to claim 8 increases the solid angle range around the radiation source that can be detected by the collector.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to an illumination system (30) having an illumination optical unit (4), which leads EUV illumination light (14) collected by a collector (31) to an object field (5). The illumination optical unit has a field facet mirror (17) and a pupil facet mirror (20). Pupil facets (34) belong to a transmission optical unit, which images the field facets (32) into the object field (5) in a superposed manner. The collector (31) images a radiation source region (3) into a downstream intermediate focus region (25). The downstream intermediate focus region produces the first image of the radiation source region (3) in the downstream beam path. A constriction region (37) not coinciding with the downstream focus region (25) lies between the collector (31) and a first component (17) of the illumination optical unit (4). In the constriction region, a cross-section of an entire bundle of the EUV illumination light (14) is reduced in relation to the cross-section on the field facet mirror (17) by at least a factor (2). The result is an illumination system that ensures efficient transfer of the EUV illumination light into the illumination field.