EUV Lens Surface Shape Characterization via Orthogonal Polarization Interferometry
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In microlithography, interferometric measurements of EUV projection lenses face challenges due to polarization-induced phase components that corrupt surface shape determination, making accurate compensation complex and error-prone.
Innovation Solution
The method involves characterizing the surface shape of optical elements using interferogram measurements with electromagnetic radiation having linear or circular input polarizations that differ, specifically using orthogonal polarizations to reduce polarization-induced phase components by averaging interferogram phases, thereby isolating the actual surface shape phase component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometric measurement is performed with a single polarization state, then measurement simplicity is maintained, but polarization-induced phase components corrupt the surface shape determination accuracy
Solution Approach 1:
The measurement process is segmented into multiple interferogram measurements performed with different input polarization states (e.g., orthogonal linear polarizations). Each measurement captures phase information with different polarization-induced phase components, allowing subsequent separation and extraction of the true surface shape phase component through computational processing.
Solution Approach 2:
The method employs feedback through iterative computational processing of multiple interferogram phases. The measured phases from different polarization states are processed to identify and eliminate polarization-induced phase components, with the result feeding back into refined surface shape determination.
2Measurement precision
If polarization compensation methods are applied, then surface shape measurement accuracy is improved, but the complexity and error-proneness of the measurement process increases
Solution Approach 1:
The patent replaces complex mechanical or optical polarization compensation systems with a computational approach. Instead of using additional optical elements or mechanical adjustments to compensate for polarization effects, the invention uses mathematical processing of interferogram data from multiple polarization states to eliminate polarization-induced phase components.
Solution Approach 2:
The method changes the parameter of input polarization state across multiple measurements. By systematically varying the input polarization (e.g., using orthogonal linear polarizations or circular polarizations), the measurement process captures different polarization-induced phase components, enabling their subsequent identification and removal through parameter-based differentiation.
3Measurement precision
If multiple interferogram measurements with different polarizations are performed, then polarization-induced phase components are reduced, but measurement time increases
Solution Approach 1:
The measurement process employs periodic action by performing interferogram measurements in a systematic sequence with different input polarization states. This periodic variation of polarization states allows efficient capture of polarization-dependent phase information, which is then processed to extract the true surface shape while minimizing redundant measurements.
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 significantly reduces polarization-induced phase components, enhancing the accuracy of surface shape determination in EUV projection lenses by differentiating and averaging interferogram phases from measurements with orthogonal input polarizations, thus improving the reliability of figure determination.
Implementation Method 1
a test wave reflected at the optical element is caused to be superimposed with a reference wave not reflected at the optical element
Implementation Method 2
interferogram measurements with electromagnetic radiation having linear or circular input polarizations that differ, specifically using orthogonal polarizations to reduce polarization-induced phase components
Data Source
AI summary
A method and a device for characterizing the surface shape of an optical element. In the method, in at least one interferogram measurement carried out by an interferometric test arrangement, a test wave reflected at the optical element is caused to be superimposed with a reference wave not reflected at the optical element. In this case, the figure of the optical element is determined on the basis of at least two interferogram measurements using electromagnetic radiation having in each case linear input polarization or in each case circular input polarization, wherein the input polarizations for the two interferogram measurements differ from one another.