EUV Lithography Mirror Coating Thickness Optimization
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Solution Overview
Problem
EUV lithography mirrors have reflectivity issues due to manufacturing variances in coating thickness, leading to suboptimal reflectivity across different angular positions, as the layer thickness obtained does not exactly match the desired thickness, affecting the incidence angle and wavelength alignment necessary for high reflectivity.
Innovation Solution
An illumination system with a reflecting coating thickness optimized to minimize the impact of manufacturing errors, either by maximizing the mean reflectivity across angular positions or ensuring equal reflectivity at all positions, using a weighted mean value to account for different operational frequencies and error sensitivities of each position, and adjusting the thickness to minimize relative changes caused by manufacturing tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reflecting coating thickness is optimized for a specific angular position to maximize reflectivity, then the reflectivity at that position is improved, but the reflectivity at other angular positions deteriorates
Solution Approach 1:
The patent changes the parameter of coating thickness from being optimized for a single angular position to being optimized for multiple angular positions simultaneously. By selecting a thickness that maximizes the mean reflectivity across all operational angular positions, the system achieves acceptable reflectivity performance across the entire range of motion, rather than peak performance at only one position.
Solution Approach 2:
The reflecting coating is designed to serve multiple angular positions effectively, making it multi-functional. The coating thickness is chosen so that the optical surface can switch between different angular positions while maintaining satisfactory reflectivity at each position, enabling the illumination system to operate reliably across multiple configurations.
2Reliability
If the coating thickness is precisely controlled to maximize reflectivity, then the reflectivity performance is improved, but the manufacturing complexity and difficulty increase
Solution Approach 1:
The patent transforms the thickness optimization problem from maximizing reflectivity at a single precise thickness value to maximizing the mean reflectivity across a range of thickness values corresponding to multiple angular positions. This parameter change makes the system more robust to manufacturing variations, as the optimized thickness provides acceptable performance even with small deviations from the target value.
Solution Approach 2:
The patent anticipates manufacturing variations in coating thickness by pre-optimizing the thickness to maximize mean reflectivity across multiple angular positions. This creates a cushion against manufacturing errors, ensuring that even if the actual thickness deviates slightly from the intended value, the reflectivity performance remains acceptable across all operational positions.
3Reliability
If the reflecting coating thickness varies to account for manufacturing tolerances, then the consistency of reflectivity across positions is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent changes the optimization criterion from single-position maximum reflectivity to multi-position mean reflectivity. This parameter change results in a thickness value that provides more uniform performance across positions and is less sensitive to small manufacturing variations, thereby improving consistency without imposing stricter precision requirements.
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 reduces the sensitivity of reflectivity to manufacturing-dependent thickness variations, ensuring consistent and high reflectivity across various angular positions, thereby enhancing the performance and reliability of EUV lithography systems.
Implementation Method 1
a coating which reflects the illumination radiation from a light source
Implementation Method 2
at least one optical surface, preferably a plurality of optical surfaces, on which a coating which reflects the illumination radiation
Data Source
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AI summary
The invention relates to an illumination system for an optical arrangement, in particular for an EUV lithography apparatus, comprising: at least one optical element, which has at least one optical surface, preferably a plurality of optical surfaces, on which a coating which reflects the illumination radiation from a light source is applied, and an actuator device for aligning the at least one optical surface in at least two angular positions in the beam path of the light source. The coating either has a thickness (dopT1) at which a mean value (1/2 (R1 + R2)) formed from a thickness-dependent reflectivity (R1, R2) of the reflecting coating at the at least two angular positions is maximized or the reflecting coating has a thickness (dopT2) at which a maximum change (max(ΔR1/R1, ΔR2/R2)) in the reflectivity (R1, R2) caused by a thickness tolerance of the coating is minimized at the respective angular positions or else the reflecting coating (18) has a thickness (do2) at which the reflectivity (R1, R2) of the coating (18) has the same magnitude in the at least two angular positions. The invention also relates to an optical arrangement, in particular an EUV lithography apparatus, with such an illumination system, and also associated methods for thickness optimization of a reflecting coating or for applying said reflecting coating.