2023.6

About Instruments Today No. 235

People

Seeing the Wood for the Trees: Chair Professor Hong Hocheng Dedicate Himself to Education and Governing NTHU

Claire Lin

Automated Optical Inspection

Special Issue Introduction of “Automated Optical Inspection”

Liang-Chia Chen

Design of Thicknesses and Refractive Indices Measurement System for Multilayer Transparent Samples

Wen-Yu Shih, Chien-Sheng Liu

The representative measurement methods, including ellipsometry, interferometry, and confocal methods, can measure the thickness and refractive index of a transparent sample. However, all methods are limited by thickness range and do not consider that one layer may be nonparallel to each other. In order to improve the deficiencies of these techniques, this study proposes a novel optical inspection method based on the fundamental theorem of geometrical optics. Through a simple optical structure, it can measure not only the thicknesses and refractive indices of multilayer transparent samples, but also the inclination angles of nonparallel layer simultaneously.

Polarization Interferometry for the Measurement of Refractive Index and Roll Angular Displacement

Yue-Jhe Tsai, Shu-Han Chang, Ching-Tse Hsu, Chia-Yu Chiang, Wei-Yi Sung, Ju-Yi Lee

Interferometry is widely used in precision machining and measurement of optical components, and is crucial to scientific research and engineering field. This paper proposes a new type of polarization interferometer, which uses phase detection of polarization interferometry with a quarter wave plate and polarization camera to quickly obtain the change of phases and calculate changes in specific physical parameters. In addition to introducing the working principle of polarization interferometry, several experiments and theoretical inference were performed to evaluate the feasibility and performance of the proposed technique. This technology can be widely applied to the measurement of the refractive index of transparent objects and the measurement of the roll angular. The proposed technique offers relevant measurement results and system resolution demonstrated in this article.

Development and Application of Five-degree-of-freedom Measurement System

Cheng-Hung Wei, Kuang-Chao Fan, Chao-Ching Ho

Due to the manufacturing and assembly errors of any motion axis, there are six degrees of freedom geometric errors. The traditional method of measuring geometric errors of precision machines is to measure each item one by one, which is not only time-consuming but also expensive. In this paper, we introduce a self-developed five-degree-of-freedom measurement system. By combining well-designed optical components, five geometric errors of moving targets can be measured simultaneously, and only a single-beam laser for displacement detection is required, including positioning errors, straightness errors in both horizontal and vertical directions, and angular errors in both deflection and pitch. This multi-degree-of-freedom error measurement system uses a 60 MHz frequency modulated light with high speed and high accuracy, and can perform real-time measurements over long distances. The geometric error of each axis of motion has six degrees of freedom due to component manufacturing and assembly errors. The traditional method of measuring geometric errors of precision machines is to measure each item one by one, which is not only time consuming but also expensive. In this paper, we introduce a self-developed five-degree-of-freedom measurement system. By combining well-designed optical components, five geometric errors of moving targets can be measured simultaneously, and only a single-beam laser for displacement detection is required, including positioning errors, straightness errors in both horizontal and vertical directions, and angular errors in both deflection and pitch. This multidegree-of-freedom error measurement system uses 60 MHz frequency modulated light with high speed and high accuracy, and can perform long-distance real-time measurements with an accuracy of ±1 μm for straightness error, ±1 arc-sec for angular error, and 0.01 μm for positioning error with a resolution of better than 2 ppm. The system also has a simple and easy-to-use structure. The system has the advantages of simple structure, easy installation, and low cost, and its feasibility was verified on an optical inspection machine. The system also has the advantages of simple structure, easy installation and low cost, and its feasibility was verified on an optical inspection machine.

An Automatic Inspection System Development Based on Photoluminescence for CIGS Thin Film Solar Panels

Chih-Hao Lin, Ming-Fu Chen, Po-Jui Chen, Ho-Lin Tsay, Chun-Chieh Lien

Solar cells are the important fundamental components for photovoltaic energy conversion. Photovoltaic conversion efficiency and manufacturing cost for solar cells are the most critical factors. Copper Indium Gallium Selenide (CIGS) thin-film solar cells can save lots of raw materials and have flexible properties, a wide absorption spectrum range and more than 18% photovoltaic conversion efficiency. Thus CIGS thin-film solar cells are considered to have good development potential. Developed automatic optical inspection system based on photoluminescence (PL) for CIGS thin film solar panels includes a PL spectra measuring subsystem and a PL optical inspection subsystem. And the system is integrated with the production line system to provide full inspection for CIGS solar panels. The system measures CIGS thin film solar panels with a length of 1220 mm and a width of 620 mm for PL spectra, PL images, and data processing. The system can load solar panels in and out and measure PL spectra or acquire PL images within a takt time of 60 seconds. At the same time as loading out the solar panel, the measured data are processed and transferred to the machine learning system to predict the photovoltaic conversion efficiency. Stability and accuracy of the system were validated in the mass production phase. The in-line full inspection service for solar panel production line was built as well. The system helps not only for filtering out the NG products but also for real-time adjusting the manufacturing process and equipment by the comprehensive analysis results.

Machine Vision and Deep Learning Based Scribe Defect Detection for LCD

You-Cheng Lin, Chun-Hsiang Huang, Yu-Chun Luo, Chao-Ching Ho

In recent years, the demand for information and communication products has increased, leading to a thriving TFT-LCD panel industry. However, the process of inspecting TFT-LCD panels still heavily relies on manual visual inspection, which can often be subjective and unreliable. Therefore, replacing manual inspection with automated optical inspection (AOI) is an important issue. Since different materials with varying surface characteristics require different illumination methods, unstable illumination can affect the overall stability of the defect detection process. In this study, we developed a real-time automatic optical inspection system for TFT-LCD panels. The system uses images to identify whether the material is abnormal after the TFT-LCD substrate is cut, preventing poorly cut TFT-LCD panels from entering the back-end process, which can result in panel breakage or damage to the back-end machinery. The system helps to improve process yields and reduce equipment damage. The results show that the deep learning image prediction speed is 38% more efficient than the traditional method, and the prediction accuracy reached 100%.

Novel Scatterometry Technique for Critical Dimension Metrology of High-aspect-ratio Microstructures

Wei-Hsin Chein, Fu-Sheng Yang, Zi-Ying Fu, Liang-Chia Chen

In this study, we proposed a novel optical critical dimension (OCD) metrology system for nondestructive inspection of high-aspect-ratio (HAR) microstructures used in advanced packaging processes. The proposed system involves the integration of spectral reflectometry and scatterometry techniques, and incorporates the high spatial coherence of a broadband laser source for optimal beam shaping. The proposed technique significantly enhances the measurement light efficiency and enables single-structure measurements, addressing the limitations of existing optical metrology techniques that rely on average information from multiple structures. With the proposed modelbased measurement scheme for solving an inverse problem, experimental tests demonstrate that multiple CDs of a RDL structure with a fine nominal linewidth and spacing of 1 μm and an aspect ratio of 3:1 can be accurately measured.

Column

Predicting the Surface Morphology of Laser Powder Bed Fusion Parts After Laser Polishing: Numerical and Experimental Study

Dac–Phuc Pham, Hong–Chuong Tran

Laser Powder Bed Fusion (LPBF) process can produce parts with complex structures by using the thermal energy of laser beam to melt specific area of metal powder layers in a layer-by-layer manner. The surface roughness of the as-built parts is one of the major requirements to determine the quality of final products. Laser Polishing employed laser radiation to melt a thin layer of metal to achieve a better surface quality. Accordingly, this technology demonstrated its strong potential in replacing mechanical polishing because of no additional cost for tooling is required. Accurately predicting the surface topology after applying laser polishing will create a foundation for optimizing the processing conditions for Laser Polishing. For solving this issue, in this work, an integrated computational framework including surface generation model, ray-tracing model, heat transfer simulation low pass filter was developed to predict the surface morphology of LPBF processed part after applying laser polishing. It is observed that by using the proposed simulation model, the predicted and measured results of mean roughness (𝑅𝑎), mean roughness depth (𝑅𝑧) and correlation length (cl) are in good agreement with error less than 10%.