Tiltable Facet Mirror Reflectivity in Lithography
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Solution Overview
Problem
Illumination optical systems face challenges in maintaining consistent light throughput due to the influence of illumination tilt positions on the reflection characteristics of tiltable facets, leading to variations in energy distribution across the illumination field.
Innovation Solution
The system employs a design where facets are assigned to specific tilt positions using conic section portions on the second facet mirror, ensuring consistent angles of incidence and reflection, independent of tilt position, using a multilayer or broadband reflection coating to maintain a predetermined degree of reflection within a tolerance range, allowing for efficient illumination across various angles of incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If facets are made tiltable between various illumination tilt positions, then the illumination field can be illuminated from different angles, but the light throughput and total transmission of the illumination optical system become dependent on the illumination tilt position
Solution Approach 1:
The patent applies parameter changes by optimizing the angle of incidence for each facet at different illumination tilt positions. The facets are designed with specific angles of incidence that are predetermined to ensure consistent light throughput across multiple tilt positions. This parameter optimization allows the system to maintain constant light throughput while adapting to different illumination angles, directly resolving the contradiction between versatility and energy loss.
2Loss of energy
If facets are optimized for specific angles of incidence, then reflection efficiency is maximized for those angles, but the system becomes sensitive to variations in illumination tilt position
Solution Approach 1:
The patent segments the illumination optical system into multiple facets, each optimized for specific angles of incidence. By dividing the mirror surface into discrete facets with predetermined angles, the system can maintain high reflection efficiency for each facet while the collection of facets provides adaptability across multiple tilt positions. This segmentation allows the system to achieve both high reflection efficiency and versatility simultaneously.
3Loss of energy
If the illumination optical system is designed with constant light throughput independent of tilt position, then energy distribution remains stable, but the system complexity increases due to multiple facets with predetermined angles
Solution Approach 1:
The patent employs dynamics by making facets tiltable between various illumination tilt positions. This dynamic capability allows the system to adapt to different illumination angles while maintaining constant light throughput. The tiltable facets provide the necessary flexibility to achieve energy distribution stability without requiring a completely static and complex multi-facet configuration, thus reducing overall system complexity while maintaining 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 approach ensures consistent energy distribution and high reflection efficiency across different illumination tilt positions, reducing the need for extensive optimization and enhancing the production of microstructured or nanostructured components, such as semiconductor chips, with precise and complex structures.
Implementation Method 1
The reflection coating can be configured as a single-layer coating, a two-layer coating or a multilayer coating. The reflection coating may, for example, have five layers, ten layers, twenty layers, thirty layers or still more layers.
Data Source
AI summary
An illumination optical system for projection lithography for the illumination of an illumination field has a facet mirror. An optical system, which follows the illumination optical system, has an object field which can be arranged in the illumination field of the illuminate optical system. The facet mirror has a plurality of facets to reflectively guide part bundles of a bundle of illumination light. Reflection faces of the facets are tiltable in each case. In a first illumination tilt position, the tiltable facets guide the part bundle impinging on them along a first object field illumination channel to the illumination field. In a different illumination tilt position, the tiltable facets guide the part bundle impinging on them along a different object field illumination channel to the illumination field. The reflection faces of the tiltable facets are configured so that the part bundle in the at least two illumination tilt positions is reflected with a degree of reflection R coinciding within a tolerance range of +/â10%. The result is an illumination optical system which avoids an undesired influence of the illumination tilt position of the tiltable facets on the illumination light throughput of the illumination optical system.