Prism System Polarizing Beam Splitter Ghost Reflections
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Solution Overview
Problem
Current lithographic apparatuses face challenges in accurately measuring parameters such as critical dimensions and overlay errors due to issues with ghost reflections and chromatic aberrations in scatterometers, which affect the precision of radiation beam analysis.
Innovation Solution
A prism system incorporating a polarizing beam splitter (PBS) surface and a quarter-wave plate (QWP) is used to separate incoming radiation beams into polarized sub-beams with different polarization information, ensuring they travel the same optical path and achieving a predetermined polarization extinction ratio, thereby minimizing ghost reflections and chromatic aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a scatterometer is used to measure substrate parameters, then measurement capability is provided, but ghost reflections and chromatic aberrations reduce measurement precision
Solution Approach 1:
The patent converts the harmful ghost reflections into beneficial signals by using a polarizing beam splitter to separate polarized components. The ghost reflections that would normally interfere with measurements are redirected to a specific detector, allowing the system to distinguish between genuine substrate signals and artifact signals, thereby converting a harmful interference into a useful diagnostic tool for improving measurement precision
Solution Approach 2:
The patent introduces a polarizing beam splitter as an intermediary optical element between the radiation source and the substrate. This intermediary device separates the radiation beam into polarized components and redirects ghost reflections to specific detectors, acting as a mediator that filters and organizes the optical paths to eliminate chromatic aberrations and improve measurement accuracy
2Measurement precision
If beam splitting is implemented to analyze polarized components, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent merges multiple optical functions into a single integrated prism system. The polarizing beam splitter, quarter-wave plate, and beam directing surfaces are combined in one compact optical assembly, allowing the system to achieve precise polarized beam separation and ghost reflection management without requiring multiple separate components, thus improving measurement accuracy while controlling device complexity
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 configuration enhances the precision of radiation beam analysis by reducing ghost reflections and chromatic aberrations, allowing for more accurate measurement of substrate parameters like critical dimensions and overlay errors.
Implementation Method 1
A polarizing beam splitter (PBS) surface configured to generate first and second sub-beams having corresponding first and second polarization information from a received beam
Implementation Method 2
A second optical element of the pair includes a quarter-wave plate
Data Source
AI summary
According to one embodiment, a prism system is provided. The prism system includes a polarizing beam splitter (PBS) surface. The PBS surface is configured to generate first and second sub-beams having corresponding first and second polarization information from a received beam, the second polarization information being different than the first polarization information. A first optical path of the first sub-beam within the prism system has substantially same length as a second optical path of the second sub-beam within the prism system. Additionally or alternatively, the first sub-beam achieves a predetermined polarization extinction ratio.