The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Heui Jae Pahk - One of the best experts on this subject based on the ideXlab platform.
-
Thickness Measurement of a Transparent Thin Film Using Phase Change in White-Light Phase-Shift Interferometry
2017Co-Authors: Heui Jae PahkAbstract:Measuring the thickness of thin films is strongly required in the display industry. In recent years, as the size of a pattern has become smaller, the substrate has become larger. Consequently, measuring the thickness of the thin film over a wide area with low spatial sampling size has become a key technique of manufacturing-yield management. Interferometry is a well-known metrology technique that offers low spatial sampling size and the ability to measure a wide area; however, there are some limitations in measuring the thickness of the thin film. This paper proposes a method to calculate the thickness of the thin film in the following two steps: first, pre-estimation of the thickness with the Phase at the peak position of the interferogram at the bottom surface of the thin film, using white-Light Phase-shift interferometry; second, accurate correction of the measurement by fitting the interferogram with the theoretical pattern through the estimated thickness. Feasibility and accuracy of the method has been verified by comparing measured values of photoresist pattern samples, manufactured with the halftone display process, to those measured by AFM. As a result, an area of 880 × 640 pixels could be measured in 3 seconds, with a measurement error of less than 12%.
-
Fringe-Order Determination Method in White-Light Phase-Shifting Interferometry for the Compensation of the Phase Delay and the Suppression of Excessive Phase Unwrapping
Journal of The Optical Society of Korea, 2013Co-Authors: Heui Jae PahkAbstract:White-Light Phase-shifting interferometry (WLPSI) is widely recognized as a standard method to measure shapes with high resolution over a long distance. In practical applications, WLPSI, however, is associated with some degree of ambiguity of its Phase, which occurs due to a Phase delay, which is the offset between the Phase of the fringes and the fringe envelope peak position. In this paper, a new algorithm is proposed for the determination of a fringe order suitable for samples in which the Phase delay mainly occurs due to noise, diffraction and a steep angle. The concepts of the decouple factor and the connectivity are introduced and a method for calculating the decouple factor and the connectivity is developed. With the Phase-unwrapping procedure which considers these values, it is demonstrated that our algorithm determines the correct fringe order. To verify the performance of the algorithm, a simulation was performed with the virtual step height under noise. Some specimens such as step height standard and a column spacer with a steep angle are also measured with a Mirau interference microscope, after which the algorithm is shown to be effective and robust.
-
New algorithm of white-Light Phase shifting interferometry pursing higher repeatability by using numerical Phase error correction schemes of pre-processor, main processor, and post-processor
Optics and Lasers in Engineering, 2008Co-Authors: Sung Won Yoon, Heui Jae PahkAbstract:Abstract White-Light Phase shifting interferometry (WLPSI) is frequently used for the precision measurement of 3D patterns in various fields. Phase error is one of the most dominant errors in WLPSI, and it is mainly generated by the scanner positioning error and mechanical vibrations. In this paper, Phase error detection method by image analysis is proposed, and the numerical correction method for minimizing the Phase error is also proposed. The image reconstruction method (IRM), iterative IRM (IIRM) as pre-processors, partial IRM (PIRM), least squares method (LSM) as a main processor, and surface compensation method (SCM) as a post-processor were developed for correcting Phase errors. The five methods are implemented and simulated, and the pros and cons of each method are explained. Mirau type interferometry and the Phase error generator using a PZT stage were used, and the measurements by WLPSI were done under various vibration conditions. The captured images were analyzed by the five correction methods, and the results were compared. Phase error was effectively minimized by the correction methods, and repeatability of 0.2 nm was obtained in the case of the specimen of 500 nm in height. Repeatability of 10 nm was obtained by conventional WLPSI algorithms for the same specimen.
-
New algorithm of white-Light Phase shifting interferometry pursing higher repeatability by using numerical Phase error correction schemes of pre-processor, main processor, and post-processor
Optics and Lasers in Engineering, 2008Co-Authors: Jung Hwan Kim, Woo Jung Ahn, Jeong-ho Lee, Sung Won Yoon, Heui Jae PahkAbstract:White-Light Phase shifting interferometry (WLPSI) is frequently used for the precision measurement of 3D patterns in various fields. Phase error is one of the most dominant errors in WLPSI, and it is mainly generated by the scanner positioning error and mechanical vibrations. In this paper, Phase error detection method by image analysis is proposed, and the numerical correction method for minimizing the Phase error is also proposed. The image reconstruction method (IRM), iterative IRM (IIRM) as pre-processors, partial IRM (PIRM), least squares method (LSM) as a main processor, and surface compensation method (SCM) as a post-processor were developed for correcting Phase errors. The five methods are implemented and simulated, and the pros and cons of each method are explained. Mirau type interferometry and the Phase error generator using a PZT stage were used, and the measurements by WLPSI were done under various vibration conditions. The captured images were analyzed by the five correction methods, and the results were compared. Phase error was effectively minimized by the correction methods, and repeatability of 0.2 nm was obtained in the case of the specimen of 500 nm in height. Repeatability of 10 nm was obtained by conventional WLPSI algorithms for the same specimen. © 2007 Elsevier Ltd. All rights reserved.
Huipeng Li - One of the best experts on this subject based on the ideXlab platform.
-
High-Stability Algorithm in White-Light Phase-Shifting Interferometry for Disturbance Suppression
IEEE Photonics Journal, 2018Co-Authors: Chunxi Zhang, Ningfang Song, Haowei Li, Huipeng LiAbstract:A hybrid algorithm, combining a “Gauss-type” envelope algorithm with the Carré algorithm, is proposed for disturbance suppression. For white-Light Phase-shifting interferometry (WLPSI), this novel algorithm provides suitable performance in suppressing noise caused by external conditions, such as mechanical vibrations, low-reflectivity surfaces, and poor-contrast interferograms. The algorithm is mathematically derived, and simulation testing is performed at the micro level to demonstrate that the algorithm can position the coherence peak correctly under challenging conditions. At the macro level, the algorithm is further verified on standard samples, with the repeatability of the step height being less than 0.32% in a favorable environment and 0.59% in a noisy environment. The repeatability of the roughness was 0.23% in a favorable environment and 0.65% in a noisy environment. Note that “repeatability” = “standard deviation” / “dean value”, reflecting the stability as a percentage. The simulated and experimental results prove that the proposed algorithm is highly precise and robust. This algorithm reduces the environmental dependence of the performance of WLPSI instrumentation and expands its range of application.
-
White Light Phase-stepping interferometry based on insensitive algorithm to periodic systematic error
AOPC 2015: Optical Test Measurement and Equipment, 2015Co-Authors: Ningfang Song, Jiao Li, Huipeng LiAbstract:Periodic systematic error caused by erroneous reference Phase adjustments and instabilities of interferometer has a great influence on precision of measurement micro-profile using white Light Phase-stepping interferometry. This paper presents a five-frame algorithm that is insensitive to periodic systematic error. This algorithm attempts to eliminate the periodic systematic error when calculating the Phase. Both theoretical and experimental results show that the proposed algorithm has good immunity to periodic systematic error and is able to accurately recover the 3D profile of a sample.
Pencho Marinov - One of the best experts on this subject based on the ideXlab platform.
-
Agomelatine treatment corrects impaired sleep-wake cycle and sleep architecture and increases MT_1 receptor as well as BDNF expression in the hippocampus during the subjective Light Phase of rats exposed to chronic constant Light
Psychopharmacology, 2019Co-Authors: Jana Tchekalarova, Lidia Kortenska, Natasha Ivanova, Milena Atanasova, Pencho MarinovAbstract:Rationale Exposure to chronic constant Light (CCL) has a detrimental impact on circadian rhythms of motor activity and sleep/wake cycles. Agomelatine is an atypical antidepressant showing a chronotropic activity. Objectives In this study, we explored the role of melatonin (MT) receptors and brain-derived neurotrophic factor (BDNF) in the brain in the mechanism underlying the effects of agomelatine on diurnal variations of motor activity, sleep/wake cycle, and sleep architecture in a rat model of CCL. Methods In Experiment #1 , home cage activity was monitored automatically with cameras for a period of 24 h. The diurnal rhythm of MT_1, MT_2 receptors, and BDNF expression in the hippocampus and frontal cortex (FC), was tested using the ELISA test. In Experiment #2 , rats were equipped with electroencephalographic (EEG) and electromyographic (EMG) electrodes and recordings were made under basal conditions (12:12 LD cycle + vehicle), LL + vehicle and LL + agomelatine (40 mg/kg/day for 21 days). Results The rats exposed to CCL showed an impaired diurnal rhythm of motor activity and sleep/wake cycle with reduced NREM sleep and delta power and increased REM sleep and theta power. The duration and number of episodes of the wake were diminished during the subjective dark Phase in this group. The circadian rhythm of MT_1 and MT_2 receptors and their expression did not change in the hippocampus and FC under CCL exposure, while the BDNF levels in the hippocampus decreased during the subjective Light Phase. Agomelatine restored the diurnal rhythm of motor activity, disturbed sleep/wake cycle, and sleep architecture, which effect was accompanied by an increase in MT_1 receptor and BDNF expression in the hippocampus at 10:00 in CCL rats. Conclusions These findings support the value of agomelatine as an antidepressant that can adjust circadian homeostasis of motor activity and sleep/wake cycle in a CCL model.
-
Agomelatine treatment corrects impaired sleep-wake cycle and sleep architecture and increases MT 1 receptor as well as BDNF expression in the hippocampus during the subjective Light Phase of rats exposed to chronic constant Light
Psychopharmacology, 2019Co-Authors: Jana Tchekalarova, Lidia Kortenska, Natasha Ivanova, Milena Atanasova, Pencho MarinovAbstract:Exposure to chronic constant Light (CCL) has a detrimental impact on circadian rhythms of motor activity and sleep/wake cycles. Agomelatine is an atypical antidepressant showing a chronotropic activity. In this study, we explored the role of melatonin (MT) receptors and brain-derived neurotrophic factor (BDNF) in the brain in the mechanism underlying the effects of agomelatine on diurnal variations of motor activity, sleep/wake cycle, and sleep architecture in a rat model of CCL. In Experiment #1, home cage activity was monitored automatically with cameras for a period of 24 h. The diurnal rhythm of MT1, MT2 receptors, and BDNF expression in the hippocampus and frontal cortex (FC), was tested using the ELISA test. In Experiment #2, rats were equipped with electroencephalographic (EEG) and electromyographic (EMG) electrodes and recordings were made under basal conditions (12:12 LD cycle + vehicle), LL + vehicle and LL + agomelatine (40 mg/kg/day for 21 days). The rats exposed to CCL showed an impaired diurnal rhythm of motor activity and sleep/wake cycle with reduced NREM sleep and delta power and increased REM sleep and theta power. The duration and number of episodes of the wake were diminished during the subjective dark Phase in this group. The circadian rhythm of MT1 and MT2 receptors and their expression did not change in the hippocampus and FC under CCL exposure, while the BDNF levels in the hippocampus decreased during the subjective Light Phase. Agomelatine restored the diurnal rhythm of motor activity, disturbed sleep/wake cycle, and sleep architecture, which effect was accompanied by an increase in MT1 receptor and BDNF expression in the hippocampus at 10:00 in CCL rats. These findings support the value of agomelatine as an antidepressant that can adjust circadian homeostasis of motor activity and sleep/wake cycle in a CCL model.
Martin Mauve - One of the best experts on this subject based on the ideXlab platform.
-
Learning Traffic Light Phase Schedules from Velocity Profiles in the Cloud
2012 5th International Conference on New Technologies Mobility and Security (NTMS), 2012Co-Authors: Markus Kerper, Christian Wewetzer, Andreas Sasse, Martin MauveAbstract:Traffic Lights strongly impact vehicle movement and fuel consumption in cities. If drivers were aware of the traffic Light Phase schedule, they could predict the traffic Light state at arrival time and could reduce fuel consumption. To acquire information like traffic Light Phase schedules, our vision is that drivers share their velocity profiles in a digital cloud, and in return benefit from smart algorithms evaluating the collected data. We present one such algorithm, Traffic Light State Estimation (TLSE), that operates on the velocity profiles to backward-estimate Phase schedules of traffic Light signal groups operating with fixed cycle length (representing about 80% of all traffic Lights in the US). We present simulation results showing that Phase schedule prediction on the base of TLSE is correct more than 90% of the time.
-
NTMS - Learning Traffic Light Phase Schedules from Velocity Profiles in the Cloud
2012 5th International Conference on New Technologies Mobility and Security (NTMS), 2012Co-Authors: Markus Kerper, Christian Wewetzer, Andreas Sasse, Martin MauveAbstract:Traffic Lights strongly impact vehicle movement and fuel consumption in cities. If drivers were aware of the traffic Light Phase schedule, they could predict the traffic Light state at arrival time and could reduce fuel consumption. To acquire information like traffic Light Phase schedules, our vision is that drivers share their velocity profiles in a digital cloud, and in return benefit from smart algorithms evaluating the collected data. We present one such algorithm, Traffic Light State Estimation (TLSE), that operates on the velocity profiles to backward-estimate Phase schedules of traffic Light signal groups operating with fixed cycle length (representing about 80% of all traffic Lights in the US). We present simulation results showing that Phase schedule prediction on the base of TLSE is correct more than 90% of the time.
M. Yano - One of the best experts on this subject based on the ideXlab platform.
-
Spatial Light Phase Modulator With Bidirectional Tilt–Piston Micromirror Array—Part I: Principle and Design
Journal of Microelectromechanical Systems, 2011Co-Authors: S. Yamashita, M. Mita, H. Fujita, T. Yamamoto, M. Kawai, Ryuichi Hirade, M. YanoAbstract:This paper proposes a novel structure of microelectromechanical-systems-based 1-D spatial Light Phase modulator (SLPM) that consists of a micromirror array on a silicon-on-insulator (SOI) wafer and indium tin oxide (ITO) electrodes on a glass plate. Each micromirror can exhibit bidirectional single-axis tilt, as well as up-and-down piston motions by combining the applied voltage on two ITO electrodes placed over the micromirror and the substrate of SOI (in the case that the substrate is energized, all micromirrors go down simultaneously). This device configuration enables SLPM to be fabricated by a simple process. Part I of this paper focuses on the principles and the design of the device. The optimum parameters of the device are derived to realize both tilt and piston motions, considering ways to reduce mirror warpage and crosstalk from the ITO electrode from the adjacent mirror. We simulate the dc and ac characteristics of the device and confirm that the designs that we optimized satisfy the target specifications to be widely used in optical communication systems.
-
Spatial Light Phase Modulator With Bidirectional Tilt–Piston Micromirror Array—Part II: Fabrication and Experiment
Journal of Microelectromechanical Systems, 2011Co-Authors: S. Yamashita, M. Mita, H. Fujita, T. Yamamoto, M. Kawai, M. YanoAbstract:In part I of this paper, we have proposed a novel structure of microelectromechanical-systems-based 1-D spatial Light Phase modulator (SLPM). We have discussed the design of the device and derived the optimum parameters to satisfy the target specifications. In part II, we focus on the fabrication process and experimental results of the device. We show that this device configuration allows us to use a simple fabrication process. We fabricated the device consisted of 24 micromirrors and realized the tilt and piston motions successfully. The measured dc (rotation angle and displacement on driving voltage) and ac (frequency response) characteristics matched well to the simulated data derived in part I. We also examined the distribution of the resonant frequencies over 24 micromirrors and verified that the variance was kept within 2%. As one of the applications of the device, we applied the device to optical beam shaping and succeeded in shaping the optical beam properly depending on the surface patterns of the SLPM. With these achievements, we show that the device can be adopted to a wide variety of applications in optical communication systems and optical signal processing.
-
Optical beam shaping by spatial Light Phase modulator with bidirectional tilt-piston micromirror array
2008 Conference on Lasers and Electro-Optics and 2008 Conference on Quantum Electronics and Laser Science, 2008Co-Authors: S. Yamashita, M. Mita, H. Fujita, T. Yamamoto, M. Kawai, M. YanoAbstract:We have succeeded in controlling the optical beam profile by MEMS spatial Light Phase modulator experimentally. The modulator proposed by our group has 1-D array of bidirectional tilt-piston micromirrors driven by electrostatic force.
-
Novel Spatial Light Phase Modulator with Bidirectional Tilt-Pistonmicromirror Array
TRANSDUCERS 2007 - 2007 International Solid-State Sensors Actuators and Microsystems Conference, 2007Co-Authors: S. Yamashita, M. Mita, H. Fujita, T. Yamamoto, M. Kawai, M. YanoAbstract:We have proposed a novel structure of one dimensional spatial Light Phase modulator (SLPM) that consists of a micromirror array on an SOI wafer and ITO (Indium Tin Oxide) electrodes on a glass plate. Each micromirror can exhibit bidirectional single-axis rotation, as well as up- and down- translation motion. We have fabricated the device, and confirmed its motion experimentally.