Rotatable Optical Element for Microlithography Aging
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Solution Overview
Problem
Current microlithography projection objectives face challenges in maintaining high accuracy and long service life due to photo-induced and environmental aging, requiring complex and costly solutions such as gas introduction, rotation of optical elements, and frequent replacement or correction.
Innovation Solution
The solution involves partially irradiating optical elements that are rotatably mounted along the optical axis, allowing undamaged areas to be used for imaging once damage exceeds a threshold, with different sectors or areas designed for compensation and mode switching, including protective measures and varying configurations for different materials and coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If optical elements are kept stationary in the projection objective, then the objective structure is simple and cost-effective, but photo-induced and environmental aging cause imaging errors that reduce service life
Solution Approach 1:
The patent makes the optical element dynamic by enabling rotation about the optical axis. The optical element can be rotated to different angular positions during operation, allowing previously irradiated and aged areas to be moved out of the ray path while fresh, undamaged areas are brought into the ray path, thereby maintaining imaging accuracy over extended periods
Solution Approach 2:
The patent implements periodic rotation of the optical element at predetermined intervals. This periodic action allows systematic access to different areas of the optical element, ensuring that no single area is continuously exposed to damaging radiation, thus extending the overall service life while maintaining reliability
2Reliability
If optical elements are rotated during exposure to compensate for aging, then imaging accuracy is maintained, but the device complexity and operational cost increase
Solution Approach 1:
The patent introduces rotational capability to the optical element mount, allowing the element to rotate about the optical axis. This dynamic feature enables the system to maintain imaging accuracy by periodically repositioning undamaged areas into the ray path, while the rotational mechanism itself remains relatively simple and integrated into the existing objective structure
Solution Approach 2:
The patent designs the optical element to serve multiple functions: it acts as both the primary optical component for imaging and as a rotatable element that can be repositioned to access different areas. This multi-functionality reduces the need for separate compensation mechanisms, thereby limiting the increase in device complexity
3Manufacturing precision
If optical elements are fully irradiated during imaging, then high imaging quality is achieved, but photo-induced degradation occurs rapidly reducing element lifespan
Solution Approach 1:
The patent effectively segments the optical element into multiple usable areas around the optical axis. By rotating the element, different segments or areas are brought into the ray path at different times, allowing the total usable life of the element to be extended beyond what would be possible with a single stationary area
Solution Approach 2:
The patent implements periodic rotation to systematically cycle through different areas of the optical element. This periodic repositioning ensures that no single area is continuously exposed to high-intensity imaging radiation, distributing the degradation load across multiple areas and extending the element's operational lifespan while maintaining imaging quality
Data Source
AI summary
An objective and a method for operating an objective, in particular a projection objective or an illumination objective for microlithography for imaging a reticle onto a wafer, with a plurality of optical elements that are arranged along a ray path, wherein at least one optical element of a first kind (1) is provided, which is irradiated only partially by a ray bundle, wherein the one or more optical element(s) of the first kind are rotatably mounted or positionable about the optical axis or an axis parallel thereto, wherein, for each optical element of the first kind at least two mounting positions are provided, and wherein the rotation angle between the two mounting positions is defined by the surface (7) irradiated by the ray bundle such that, in the various mounting positions, the surfaces irradiated by the ray path do not overlap.