EUV Pupil Facet Reflectivity Gradient Correction
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Solution Overview
Problem
Illumination optical systems for projection lithography face challenges in achieving a desired combination of high light throughput and uniform illumination, with existing systems struggling to correct illumination intensity gradients effectively.
Innovation Solution
The use of selectively reflecting and broadband reflecting pupil facets with varying reflective coatings allows for independent correction of illumination light intensity distribution across the field, enabling fine adjustments and uniformity through tailored reflectivity distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional uniform reflective coatings are used on pupil facets, then the system structure is simple, but illumination intensity gradient cannot be corrected
Solution Approach 1:
The patent applies local quality by dividing the pupil facet surface into multiple coating areas with different reflectivities. Specifically, the pupil facet is segmented into a first coating area with a first reflectivity and a second coating area with a second reflectivity, where the reflectivities differ to compensate for local illumination intensity variations. This allows each region of the pupil facet to have tailored optical properties that collectively achieve uniform illumination across the illumination field.
Solution Approach 2:
The patent segments the reflective coating on the pupil facet into distinct coating areas with different reflectivity characteristics. By dividing the otherwise uniform coating into multiple zones (first coating area, second coating area, and potentially third coating area), the system can independently control the reflectivity in each zone to correct the illumination intensity gradient without requiring complete system redesign.
2Illumination intensity
If broadband reflective coating is applied to reduce angle dependency, then illumination uniformity improves, but light throughput may be reduced
Solution Approach 1:
The patent employs parameter changes by utilizing broadband reflective coatings on certain pupil facets to modify the angular response characteristics. The broadband coating is specifically designed to maintain high reflectivity across a wide range of incident angles, thereby reducing angle dependency and improving illumination uniformity. Meanwhile, the selective application of broadband versus wavelength-specific coatings allows optimization of light throughput by matching coating properties to the specific illumination requirements of different pupil facet regions.
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 enhances illumination conditions by correcting intensity gradients and reducing angle dependency, achieving optimized illumination for high numerical aperture imaging systems, particularly in EUV and DUV ranges, and enabling the production of complex semiconductor structures with precise uniformity.
Implementation Method 1
the selectively reflecting pupil facet has a reflective coating for the illumination light, wherein a first coating area on a first part of the selectively reflecting pupil facet has a first reflectivity, a second coating area on a second part of the selectively reflecting pupil facet has a second reflectivity
Implementation Method 2
the broadband pupil facets have a broadband reflective coating for the illumination light
Data Source
AI summary
An illumination optical system for projection lithography includes a pupil facet mirror having pupil facets. For at least some of the pupil facets which are designed as selectively reflecting pupil facets, the selectively reflecting pupil facet has a reflective coating for the illumination light, wherein a first coating area on a first part of the selectively reflecting pupil facet has a first reflectivity, a second coating area on a second part of the selectively reflecting pupil facet has a second reflectivity, the first coating area is different from the second coating area, and the first reflectivity is different from the second reflectivity. In combination or as an alternative, for at least some of the pupil facets which are designed as broadbands reflecting pupil facets, the broadband reflecting facets have a broadband reflective coating for the illumination light.