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In General, OLED, LCD, TSP Glass TFT Pattern consists of multi-layer of electrodes separated by a thin insulating film and layers are very close to each other. The inspection of electrode pattern and defect in multilayered devices by using visible light (550nm around) image is too much difficult to define its critical shape among layers, because of deep depth range in conventional optics of moderate numerical aperture (NA). To increase image contrast between materials and layers, this study uses UV wavelength that has larger selective differences of reflectance than visible light. Newly developed optical system and image analysis units are focused to the proper inspection wavelength at the specific UV range to clearly define a top electrode layer and reduce image processing time. To detect defects on the electrode, the resolution of the optical system should be much higher than the spatial frequency of the electrode size. After considering system requirements, two types of different magnification systems (1.2X and 3X) are developed. Direct side illumination is available in 1.2X system which has large back focal length, however, 3X system needs on axis illumination. Line beam illumination from the multi-point LED source (custom made) is used to increase the light efficiency and decrease noise(4). Illumination beam passing through the common objective lens (in front of imaging optics) and illumination optics (including cylinder lens) can realized uniform intensity of one dimensional Fourier plane on the surface of target electrode. Electric units for high speed data processing and transfer and image processing algorithm are also developed. For processing large capacity image data (8 GB) synchronized with moving sensors in real time, embedded system with hardware optimizing design and FPGA module camera are adopted. Final image shows good selective contrast and resolution between layers even in the high depth condition followed by required NA for the target resolution. This inspection system can be used in inspection of PCB Pattern, LCD, OLED and Mobile Glass including many other film and glass.
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