Transparent Substrate Defect Inspection via Holographic Reconstruction
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Solution Overview
Problem
Current defect detection technologies for transparent substrates, such as glass, are inadequate for high-resolution, wide-field imaging and are time-consuming, especially for micro bubble defects, due to limitations in pixel resolution and field of view, leading to inefficiencies in production processes and increased costs.
Innovation Solution
The method involves an optical system that performs diffraction on the object wave passing through a transparent substrate, interferes it with a reference wave to form holograms, and uses numerical reconstruction to obtain defect complex images, including amplitude and phase, which are then analyzed and classified to create a database for defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If traditional machine vision with camera is used to obtain reflection or penetration pattern of glass substrate, then the detection process can be automated, but the camera cannot effectively focus on transparent substrate leading to loss of focus and inability to obtain complete complex image information
Solution Approach 1:
The patent introduces a reference wave as an intermediary to interfere with the object wave passing through the transparent substrate. This interference pattern (hologram) captures both amplitude and phase information, enabling the camera to effectively 'focus' on transparent substrates without manual adjustment. The reference wave acts as a mediator that makes the invisible phase information visible through interference fringes.
Solution Approach 2:
The patent replaces the mechanical focusing mechanism (manual or automatic focus adjustment of camera lenses) with an optical interference-based wavefront recording system. Instead of mechanically adjusting the camera to focus on transparent substrates, the system uses digital holography to capture complete complex image information including phase data, eliminating the focusing problem entirely.
2Area of stationary object
If wide-field optical imaging system with mechanical scanning and image stitching is used, then the field of view can be expanded, but the detection process becomes time-consuming
Solution Approach 1:
The patent segments the wide-field detection task into multiple localized holographic measurements taken at different positions across the substrate. Each local hologram captures complex image information (amplitude and phase) of a specific region. By combining these segmented measurements through numerical reconstruction, the system achieves wide-field coverage without mechanical scanning, significantly reducing detection time.
Solution Approach 2:
The patent replaces the mechanical scanning system with a stationary optical setup that captures holographic information. Instead of mechanically moving the camera or sample to scan the field of view, the system uses digital holography to capture complete optical field information in a single shot at each position, then uses computational methods to reconstruct and combine the images, eliminating mechanical movement and reducing detection time.
3Device complexity
If traditional defect detection methods performing only edge detection are used, then the detection algorithm is simple, but micro bubble defects cannot be effectively detected
Solution Approach 1:
The patent extends the detection capability from simple intensity (edge detection) to complex image information including phase, analogous to extending from grayscale to full color information. The phase information acts as an additional 'dimension' of image data that provides contrast for transparent defects like micro bubbles, which are invisible in traditional intensity-only images. This allows effective detection of micro bubble defects without significantly increasing algorithmic 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 approach enhances the resolution and field of view for defect detection, reducing detection time and improving yield by capturing complete complex image information, including micro bubble defects, and is applicable to various transparent substrates like glass and sapphire.
Implementation Method 1
providing an optical system for performing a diffraction process of object wave passing through a transparent substrate to create optical diffraction field
Implementation Method 2
interfering and wavefront recording for the diffracted object wave and a reference wave to form at least one hologram for wavefront recording
Data Source
AI summary
A method for defect inspection of a transparent substrate comprises (a) providing an optical system for performing a diffraction process of object wave passing through a transparent substrate, (b) interfering and wavefront recording for the diffracted object wave and a reference wave to reconstruct the defect complex images (including amplitude and phase) of the transparent substrate, (c) characteristics analyzing, features classifying and sieving for the defect complex images of the transparent substrate, and (d) creating defect complex images database based-on the defect complex images for comparison and detection of the defect complex images of the transparent substrate.