Facet Mirror Grid for Homogeneous Lithography Illumination
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Solution Overview
Problem
Current illumination optical assemblies for projection lithography face challenges in achieving homogeneous illumination of pupil sections, leading to inhomogeneities and gaps in the illuminated regions, which affect structure resolution and overall illumination quality.
Innovation Solution
The proposed illumination optical assembly employs a first facet mirror and a second facet mirror with specifically arranged second facets in a grid pattern, positioned at a distance from the pupil plane, to ensure that the entrance pupil is illuminated uniformly, with a grid constant optimized based on pupil distance and scan length, allowing for homogeneous illumination even when object points are illuminated by different light partial beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional illumination optical assemblies are used, then the structure is relatively simple, but the illumination homogeneity of pupil sections deteriorates with inhomogeneities and gaps
Solution Approach 1:
The second facet mirror is divided into multiple discrete facets arranged in a grid pattern, where each facet independently guides illumination light partial beams to specific regions of the object field. This segmentation enables precise control over illumination distribution across the pupil plane, eliminating gaps and inhomogeneities while maintaining manageable system complexity through modular facet design.
Solution Approach 2:
Different regions of the second facet mirror are designed with locally optimized facet characteristics, including varying facet sizes, orientations, and spacing patterns tailored to specific illumination requirements. This local quality approach ensures uniform illumination intensity across the entire pupil plane by compensating for position-dependent variations in light distribution.
2Illumination intensity
If the second facet mirror is positioned close to the pupil plane, then the device complexity is reduced, but the illumination homogeneity deteriorates due to gaps in illuminated regions
Solution Approach 1:
The solution transitions from a single-plane facet mirror configuration to a spatially distributed grid arrangement of facets at optimized distances from the pupil plane. By utilizing the third dimension (distance from pupil plane) and arranging facets in a two-dimensional grid pattern, the system achieves complete coverage of the pupil region without gaps, improving illumination homogeneity while maintaining reasonable device complexity.
3Illumination intensity
If different light partial beams illuminate different object points, then the device complexity is reduced, but the illumination homogeneity deteriorates during object field scanning
Solution Approach 1:
The second facets are pre-configured in a grid pattern with specifically calculated grid constants that anticipate the scanning motion of the object field. This preliminary arrangement ensures that as the object field scans through different positions, each object point receives consistent illumination from appropriate facets, maintaining homogeneous illumination quality throughout the scanning process without requiring real-time adjustments.
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 results in improved illumination homogeneity across the object field, reducing inhomogeneities and enhancing structure resolution during projection exposure, ensuring that the entire object field is illuminated with a consistent intensity distribution within predefined tolerance values.
Implementation Method 1
a first facet mirror (6), having first facets (21) for the reflective guidance of illumination light (3), and a second facet mirror (7) for the reflective guidance of the illumination light (3) reflected by the first facet mirror (6) towards an object field (8)
Data Source
AI summary
An illumination optical assembly for projection lithography serves for illuminating an object field, in which an object to be imaged is arrangeable. The object field has a scan length along an object displacement direction. The illumination optical assembly has two facet mirrors for the reflective guidance of illumination light towards the object field. Second facets of the second facet mirror serve for guiding a respective illumination light partial beam into the object field. The second facet mirror is a pupil distance from a pupil plane of the illumination optical assembly that is closest adjacent to the second facet mirror. The second facets are arranged in a grid, wherein at least one grid constant of the grid is predefined by the pupil distance and by the scan length. This results in an illumination optical assembly which achieves an illumination of predefined pupil sections that is relatively homogeneous.