투명 디스플레이 패널 검사를 위한 선형빔 기반 간섭계 연구

Abstract

In this thesis, to inspect defects on display panels and to monitor the thickness and surface profile of the display panels such as AMOLED panels, IPS LCD panels and etc., line beam based optical imaging systems such as an optical coherence tomography (OCT) and a white light interferometry (WLI) were proposed and demonstrated. In addition, to inspect defects automatically, a novel pattern matching algorism was developed and applied optical imaging system by using Labview. As light sources for the imaging systems, wavelength swept lasers based on Fourier domain mode locking (FDML) and active mode locked wavelength swept (AMLWS) laser were proposed. OCT is based on a low coherence interferometry and can obtain the cross-section images with micro-resolution of the optical scattering media. These modalities can obtain a greater depth range than confocal without the need to physically scan the sample in the axial direction. In addition to inspection of defects, it is also important to measure thickness of thin layer for manufacture of display panels. To monitor the height of thin layers, WLI was introduced, which provides 3D visual inspection of a thin-film layer structure with nanometer level resolutions. The concepts and the operating principles of OCT and WLI were explained. OCT and WLI were united as an inspection imaging system to accomplish advantages of two inspection systems. In addition, in order to increase the imaging speed and to get rid of complexity of scanning optics in inspection system, a line beam based interferometer was devised and applied to the inspection system. Three different wavelength swept lasers that are the FDML laser, the AMLWS laser, tunable external cavity laser (T-ECL) were studied and analyzed to characterize the their properties including the swept speed of the lasing wavelength, the bandwidth and the center wavelength of the swept laser. Especially, the T-ECLs were utilized for microwave applications such as a photonic microwave filter and a photonic microwave generation. The optics design of the line beam based interferometer for OCT and WLI was introduced. The optics design of the line beam based interferometer is divided into two parts; one is an illumination optics design, and the other is an imaging optics design. In the illumination optics, the line beam was generated and illuminated into a sample by a cylindrical lens. Then the sample image was obtained through the imaging lens. Two optical designs are independent of each other, which give more freedom for the alignment. In terms of the system design, the imaging system operates three parts including a light source (the swept laser), the line camera, and the motorized linear stage. In order to operate and control the imaging system, the operating sequence of the system was designed carefully considering triggering signal treatment and the operating logic. According to the previous design of the imaging system, the line beam based interferometer for the SS-OCT and the WLI was configured. The AMLWS laser was used as the light source for the SS-OCT and the WLI. In order to improve signal to noise ratio (SNR), a k-domain linearization was performed and the method of the k-domain linearization was introduced. The axial resolution of the SS-OCT was measured to be 16 ?m while the uncertainty of the surface profile in the WLI was ±100 nm. The SS-OCT images of diverse samples including the mirror, the amplitude mask, the cover glass, and the AMOLED panel were achieved, which imply the capability of monitoring the thickness of the AMOLED panel during the fabrication process. In addition, the WLI was exploited to obtain a surface profile of the amplitude mask. Since the Fresnel reflection coefficients of the top and bottom boundaries and effective refractive index of a film layer in the display panel are confidential, the WLI could not be applied to the monitoring of the thickness of a film layer in display panels. However, from the results, it was noticed that the WLI has the capability of inspecting surface profiles of microelectronics devices. An important application of machine vision is the auto-detection of defects in an assembly line by using vision systems employing dedicated algorithms. The lighting alignment of the auto-detection system was optimized for the AMOLED panel to observe and monitor the RGB pixels clearly. By using pattern matching algorithm, entire pixels were detected and analyzed for the detection of the defects. The defects were artificially fabricated by using illuminating high power laser onto the AMOLED panel. The 14-defects with the size from 9 ?m to 17 ?m were automatically detected. Finally, an application of the wavelength swept laser based on the FDML method was introduced. A novel FBG strain sensor interrogation using a Raman-based FDML fiber laser was presented for high speed and long distance measurement. The Raman-based FDML fiber laser had a swept rate of the 30.8 kHz and a swept range of 37.2 nm. The long distance measurement of the proposed sensor system is realized by recycling a residual Raman pump after Raman amplification in the FDML laser for the output power enhancement of the sensing signal. By using the proposed Raman-based FDML fiber laser, the measured strain sensitivities in wavelength and time domains were estimated to be 0.81 pm/?strain and 0.19 ns/?strain, respectively. Using the proposed scheme, we can obtain typical response from the FBG sensor interrogation as a function of strain.