Solar Wafer Micro-Crack Detection Using Oblique Infrared Illumination
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Solution Overview
Problem
Conventional high-speed imaging systems are limited in detecting micro-cracks in solar wafers due to insufficient image resolution and the complexity of detecting micro-cracks in multi-crystalline wafers, where cracks smaller than 36μm in width and random surface textures hinder effective detection.
Innovation Solution
An improved inspection method and apparatus using an oblique arrangement of infrared light and cameras to capture high-contrast images of solar wafers, where infrared light is directed at an acute angle to enhance image resolution and facilitate detection of micro-cracks, and image processing techniques are applied to superpose and analyze images for defect identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional high-speed imaging system with 12K line-scan camera is used, then the inspection speed can maintain one wafer per second, but the image resolution is insufficient to detect micro-cracks smaller than 36μm
Solution Approach 1:
The patent transforms the detection problem from a 2D surface inspection to a 3D cross-sectional inspection. By capturing images at an oblique angle (45 degrees) and processing them to show cross-sectional views, the system can detect micro-cracks based on their depth and shadow effects rather than relying solely on surface resolution. This dimensional transformation allows detection of cracks as narrow as 1μm that would be invisible in conventional top-down views.
2Measurement precision
If the image resolution is increased to detect narrower micro-cracks, then the detection precision improves, but the inspection speed decreases due to the large wafer surface area
Solution Approach 1:
The patent changes the lighting parameter from conventional perpendicular illumination to oblique illumination at 45 degrees. This parameter change creates shadow effects that amplify the visual contrast of micro-cracks, making them detectable at lower resolutions. The oblique angle transforms subtle surface variations into pronounced shadow patterns that image processing algorithms can easily identify, maintaining high detection precision without requiring increased resolution that would slow down inspection.
3Ease of operation
If conventional perpendicular illumination is used, then the imaging system is simple to operate, but micro-cracks are not prominent and difficult to detect
Solution Approach 1:
The patent modifies the illumination angle parameter from 0 degrees (perpendicular) to 45 degrees (oblique). This simple parameter change dramatically enhances micro-crack visibility by creating shadow effects along the crack edges. The oblique lighting causes cracks to appear as dark lines with enhanced contrast against the wafer background, making them easily detectable by image processing algorithms while maintaining operational simplicity.
Solution Approach 2:
The patent enhances the visual contrast of micro-cracks by using oblique illumination that creates shadow effects. The cracks appear as dark features with enhanced contrast in the processed images, transforming them from nearly invisible features to prominent detectable elements. This contrast enhancement is achieved through the interaction of oblique light with the crack geometry, creating optical effects that amplify visibility.
4Ease of manufacture
If multi-crystalline wafers are used to reduce cost, then the manufacturing cost decreases, but the random surface texture and crystal grain boundaries increase detection complexity
Solution Approach 1:
The patent uses oblique illumination at 45 degrees to create shadow effects that emphasize linear features like micro-cracks. This lighting parameter causes cracks to appear as distinct dark lines that contrast with the random grain patterns of multi-crystalline structures. The shadow effects create directional highlights and shadows that make linear crack features stand out from the isotropic grain boundary patterns, enabling detection algorithms to distinguish cracks from normal grain structure variations.
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 method and apparatus effectively increase the prominence of micro-cracks to facilitate detection, allowing for the identification of cracks as narrow as 1μm, independent of their actual width, and improve detection accuracy in multi-crystalline wafers by creating high-contrast images.
Implementation Method 1
due to silicon's band-gap energy level, solar wafers appear transparent when illuminated with light having a wavelength larger than 1127nm. Light having a wavelength of 1127nm is classified as near infrared (NIR) radiation. NIR is invisible to the human eye but is detectable by most commercial CCD or CMOS infrared cameras.
Implementation Method 2
An improved inspection method and apparatus using an oblique arrangement of infrared light and cameras to capture high-contrast images of solar wafers, where infrared light is directed at an acute angle to enhance image resolution and facilitate detection of micro-cracks
Data Source
AI summary
An inspection method comprises receiving light emanating from a first surface of a wafer substantially along a first axis for obtaining a first image of the first surface therefrom, the wafer having a crack formed therein and the first image containing at least one portion of the crack. The inspection method also comprises receiving light emanating from the first surface of the wafer substantially along a second axis for obtaining a second image of the first surface therefrom, the second image containing at least one second portion of the crack, the first surface extending substantially parallel a plane, and the orthographic projection of the first axis on the plane being substantially perpendicular the orthographic projection of the second axis on the plane. The inspection method further comprises constructing a third image from the at least one first portion of the crack and the least one second portion of the crack of the first and second images respectively. More specifically, the third image is substantially processable for inspecting the crack in the wafer.