Interferometer Tilt for Roll-to-Roll Metrology
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Solution Overview
Problem
Current in-line metrology systems for roll-to-roll processing face challenges such as flexible substrates fluttering, roller runout, and curvature, leading to focus variations and vibration issues, which limit their ability to perform precise real-time measurements of surface roughness and defects in flexible electronic circuits.
Innovation Solution
The system tilts the interferometer along the substrate travel direction to reduce fringe width within the camera's field of view, allowing for real-time measurement by shifting the measurement field of view to track the best fringes, and uses a reference surface conforming to the roller's curvature to minimize focus errors and accommodate web flutter and roller runout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional interferometric inspection tools are used for laboratory-bench work, then measurement precision can reach nanometer level, but the measurement area is limited to less than 1 square mm and measurement time spans several seconds
Solution Approach 1:
The patent divides the large field-of-view measurement into multiple smaller measurement zones that can be sequentially scanned across the substrate. Each zone is measured with high precision interferometry, and the results are stitched together to form a complete map of the entire substrate surface, achieving both nanometer precision and large area coverage
Solution Approach 2:
The patent employs dynamic measurement techniques where the interferometer and substrate move relative to each other during measurement. This allows continuous real-time measurement of the moving web substrate in roll-to-roll processing, transforming static laboratory measurement into dynamic in-line measurement without sacrificing precision
2Productivity
If machine-vision-based in-line methods are used, then measurement speed can keep up with production, but lateral resolution is limited to about 100 μm and roughness measurement capability is lost
Solution Approach 1:
The patent replaces traditional machine-vision optical systems with interferometric measurement technology. This substitution enables the system to achieve nanometer-scale vertical resolution for roughness measurement while maintaining real-time measurement capability through synchronized motion control between the interferometer and the moving substrate
3Measurement precision
If the substrate is kept in continuous contact with the measurement system, then focus stability can be maintained despite web flutter, but substrate damage may occur due to contact during motion
Solution Approach 1:
The patent introduces a curved reference surface that conforms to the roller curvature as an intermediary between the interferometer and the moving substrate. This reference surface remains stationary while the substrate moves, providing a stable reference for interferometric measurement without requiring physical contact with the substrate itself, thus maintaining focus stability while eliminating contact damage risk
4Ease of operation
If the measurement system is focused on the top of the roller, then roller runout causes the optical image to go in and out of focus, but avoiding this requires complex focus adjustment mechanisms
Solution Approach 1:
The patent uses a curved reference surface that matches the roller's curvature. This curved reference remains stationary relative to the interferometer while accommodating the roller's rotation and runout, maintaining consistent focus across the measurement field without requiring complex focus adjustment mechanisms to compensate for roller imperfections
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 enables immediate identification of substrate defects and their locations, allowing for real-time quality control during roll-to-roll processing, reducing measurement errors and maintaining high precision even at high web speeds, and is more cost-effective by minimizing the need for vacuum-compatible components.
Implementation Method 1
3D optical metrology is particularly suited for in-situ roll-to-roll measurement of the height and slope of such defects in real time during the deposition process
Data Source
AI summary
A substrate is tested with an interferometer in-line in a roll-to-roll processing operation to detect defects and exclude them from further processing. A tilt is introduced in the illumination path of the interferometer to allow detection of best fringes in a selected measurement field of view (FOV) that is smaller than the camera FOV in the direction transverse to the fringes. At each acquisition frame, the measurement FOV is shifted to track the best-fringe position within the camera field of view based on irradiance acquired at the previous step. As a result, the system is able to accommodate substrate flutter and roller runout and maintain focus on the substrate that allows precise identification of defects and their isolation for subsequent processing.