Collector Mirror Rotation Using Reflectivity Maps for EUV Emission
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Solution Overview
Problem
Existing projection exposure apparatuses face challenges in maintaining optimal imaging quality due to non-uniform emission of electromagnetic radiation from collector mirrors, which are affected by degradation and contamination, leading to reduced throughput and system performance.
Innovation Solution
A method utilizing a reflectivity map of the collector mirror, combined with a Sagnac Interferometer and sensors, to optimize the rotational position of the collector mirror, ensuring uniform emission of EUV-light by recalculating light paths and adapting the mirror's position to maximize system power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the collector mirror is used continuously for EUV light collection, then the system operates continuously with high productivity, but the coating degrades and reflectivity decreases over time
Solution Approach 1:
The patent implements a rotatable collector mirror that can change its rotational position dynamically. The mirror is rotated to different angular positions (e.g., 0°, 45°, 90°, 135°) to bring different surface areas into the light path. This dynamic repositioning allows the system to continue operating at high productivity while using different portions of the mirror surface, effectively distributing the degradation across the entire mirror surface rather than concentrating it in one area.
2Power
If different areas of the collector mirror are used to compensate for degradation, then the system power can be optimized, but the complexity of controlling mirror rotation increases
Solution Approach 1:
The patent incorporates a feedback control system that includes sensors (such as photodetectors or cameras) to detect the actual rotational position of the collector mirror. This feedback information is fed back to a control unit that compares the actual position with the desired position and makes real-time adjustments to correct any deviations. This ensures precise and reliable mirror positioning while optimizing system power, despite the added complexity of the control mechanism.
3Productivity
If the collector mirror is rotated to optimize light emission, then throughput increases, but the precision of mirror positioning must be maintained to avoid light path misalignment
Solution Approach 1:
The patent introduces intermediary components such as precision bearings, gears, or belt drives between the motor and the collector mirror. These intermediary mechanisms serve as precision transmission elements that can convert the motor's rotation into accurate, controlled angular positions of the mirror. They provide mechanical advantage and precision positioning capabilities, ensuring that the mirror can be rotated to the correct angles (0°, 45°, 90°, 135°) with high accuracy while maintaining the throughput benefits of rotation.
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 system performance by optimizing EUV-light emission, increasing throughput by up to 5% and extending the service life of the apparatus by correcting reflectivity issues without laborious surface scans.
Implementation Method 1
a Sagnac Interferometer to optimize the rotational position of the collector mirror
Implementation Method 2
The collector mirror, like other mirrors used in the apparatus too, also comprises at least one layer system, for example a molybdenum-silicon multi-ply layer, which allows high-precision working of the surface and/or a high reflectivity in the desired spectral range
Implementation Method 3
a plasma that emits electromagnetic radiation in the desired short-wave frequency ranges is generated by means of laser irradiation of tin droplets
Data Source
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AI summary
The invention relates to a method for optimization the emission of electromagnetic radiation (16) of an illumination system (2) of a projection exposure apparatus (1), the illumination system (2) comprising a rotatable collector mirror (31) to optimize the emission, whereas the method is characterized in that the optimization is based on a reflectivity map of the collector mirror (31). Furthermore, the invention relates to an illumination system (2) comprising a source with a rotatable collector mirror (31), whereas the illumination system (2) is characterized in that the collector mirror (31) is designed in such a way, that the collector mirror (31) can be positioned in an arbitrary angle between 0° and 360° around its longitudinal axis.