Piezoelectric Mirror Arrangement for Lithography Wavefront Correction
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Solution Overview
Problem
Lithography exposure systems face challenges in maintaining precise optical properties over time due to factors like mirror surface deviations, aging, and environmental influences, which affect the quality of imaging and the accuracy of structure positioning, especially at high numerical apertures and short wavelengths.
Innovation Solution
A mirror arrangement with multiple adjacently arranged mirror elements, each featuring a multilayer structure including a piezoelectric layer and electrode arrangement, allowing for independent control of layer thickness and reflection properties to correct wavefront errors and maintain optical quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the image-side numerical aperture is enlarged to increase resolution capability, then the resolution capability is improved, but the depth of focus range is reduced
Solution Approach 1:
The patent implements dynamic focus adjustment by making the focus plane position variable through a manipulator system. The focus plane can be moved axially relative to the projection objective to maintain the desired depth of focus range while operating at high numerical apertures. This dynamic adjustment compensates for the reduced depth of focus caused by enlarged NA.
2Measurement precision
If shorter wavelengths are used to increase resolution capability, then the resolution capability is improved, but the range of depth of focus is reduced
Solution Approach 1:
The manipulator system enables dynamic adjustment of the focus plane position, allowing the system to compensate for the reduced depth of focus that occurs when using shorter wavelengths. By making the focus plane position variable, the system maintains adequate depth of focus range even when operating at wavelengths that provide higher resolution capability.
3Ease of manufacture
If mirror surface shape deviates from specified shape, then manufacturing is simplified, but wavefront quality and imaging precision deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where the actual mirror surface shape is measured and compared to the specified shape. The measured deviations are used to generate correction signals that drive manipulators to adjust the mirror surface, thereby compensating for manufacturing errors and maintaining high wavefront quality.
Solution Approach 2:
The system performs self-correction by automatically measuring its own mirror surface deviations and adjusting the mirror positions to compensate for these deviations. This self-service capability allows the system to maintain high imaging precision without requiring extremely tight manufacturing tolerances.
4Manufacturing precision
If multiple exposure steps are used to generate fine structures, then finer structures can be produced, but lateral image positioning accuracy requirements are increased
Solution Approach 1:
The patent uses feedback from measured mirror surface shapes and wavefront errors to adjust mirror positions, ensuring high lateral image positioning accuracy. This feedback mechanism compensates for positioning errors that would otherwise accumulate across multiple exposure steps, enabling the production of fine structures with the required precision.
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
The solution enables improved wavefront correction and maintains precise optical properties, reducing aberrations and ensuring high superimposition accuracy across the mirror surface, even under changing conditions.
Implementation Method 1
Each multilayer arrangement includes a piezoelectric layer having a layer thickness which can be controlled by an electric field generated by an associated electrode arrangement
Data Source
AI summary
Mirror elements (2a, 2b) include a substrate (4a, 4b) and a multilayer arrangement (5a, 5b). The multilayer arrangement includes a reflective layer system (6a, 6b) having a radiation entrance surface (7a, 7b) and a piezoelectric layer (8a, 8b) arranged between the radiation entrance surface and the substrate. Each mirror element includes an electrode arrangement (9a, 9b, 9c) associated with the piezoelectric layer. A layer thickness (tp) of the piezoelectric layer is controlled by the electric field generated. An interconnection arrangement (10) electrically interconnects adjacent electrodes of adjacent electrode arrangements. According to one formulation, the interconnection arrangement generates an electric field in a gap region (11) between the adjacent electrodes. According to another, an electric resistance (Ri) of the interconnection arrangement in the gap region is greater than an electric resistance (Rw) of the adjacent electrodes and less than an electric resistance (Rl) of the piezoelectric layers of adjacent electrode arrangements.