Spatial Optical Pulse Filtering for Noise and Spectral Control
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Solution Overview
Problem
Existing metrology tools face challenges in generating high-quality broadband radiation sources for accurate and robust measurements in lithographic and metrology applications, particularly in lithographic apparatus and metrology devices, due to limitations in noise reduction and spectral control.
Innovation Solution
An optical filter apparatus comprising an optical divergence device and a spatial filter that spatially distributes optical pulses based on pulse energy, using a deflectable mirror to apply spatial filtering, and an optical delay arrangement to enhance broadband radiation generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If broadband radiation sources are used for metrology applications, then measurement robustness and accuracy are improved, but noise reduction and spectral control remain insufficient
Solution Approach 1:
The patent segments the broadband radiation source into discrete spectral components using a dispersive element (prism or grating) that separates different wavelengths spatially. This allows individual spectral components to be selectively filtered and controlled, transforming the inherently noisy broadband source into a controlled multi-line source with improved signal-to-noise ratio while maintaining measurement accuracy.
Solution Approach 2:
The patent applies local quality by introducing a spatially varying filter (such as a tunable optical filter or acousto-optic modulator) that can selectively attenuate or enhance specific spectral components at specific spatial locations. This enables differential control of spectral content to optimize both noise reduction and measurement accuracy for different metrology applications.
2Adaptability or versatility
If existing radiation sources are used, then broadband coverage is achieved, but spectral control and noise reduction are limited
Solution Approach 1:
The patent employs dynamic spectral control elements such as tunable optical filters, acousto-optic modulators, or electro-optic modulators that can dynamically adjust the spectral content in real-time. This allows the system to adapt the spectral characteristics of the broadband source for different metrology applications without requiring multiple fixed sources, thereby maintaining versatility while improving spectral control.
Solution Approach 2:
The patent incorporates feedback mechanisms where the spectral content is monitored and controlled elements are adjusted based on the measured spectrum. This closed-loop control enables automatic optimization of spectral distribution to achieve desired noise reduction and measurement accuracy while maintaining broadband coverage.
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 provides improved broadband radiation sources with enhanced noise reduction and spectral control, enabling more accurate measurements and improved performance in lithographic and metrology applications.
Implementation Method 1
a deflectable mirror configured to receive and subsequently reflect the optical pulses; said deflectable mirror being further configured to deflect upon every reflection of each of the optical pulses, the magnitude of said deflection being dependent on a pulse energy of each of the optical pulses
Data Source
AI summary
An optical filter apparatus including an optical divergence device, operable to receive optical pulses and spatially distribute the optical pulses over an optical plane in dependence with a pulse energy of each of the optical pulses; and a spatial filter, located at the optical plane, operable to apply spatial filtering to the optical pulses based on a location of each of the optical pulses at the optical plane resulting from the spatial distributing.