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12 pages, 4440 KiB

Open AccessArticle

Defocus Effect Correction for Back Focal Plane Ellipsometry for Antivibration Measurement of Thin Films

by Jian Wang, Jun Yang, Lihua Peng, Dawei Tang, Feng Gao, Rong Chen and Liping Zhou

Appl. Sci. 2023, 13(3), 1738; https://doi.org/10.3390/app13031738 - 29 Jan 2023

Cited by 2 | Viewed by 1463

Back focal plane (BFP) ellipsometry, which acquires the ellipsometric parameters of reflected light at different incident and azimuthal angles through a high-NA objective lens, has recently shown great potential in industrial film measurement. In on-line metrology cases for film manufacturing, the film [...] Read more.

Back focal plane (BFP) ellipsometry, which acquires the ellipsometric parameters of reflected light at different incident and azimuthal angles through a high-NA objective lens, has recently shown great potential in industrial film measurement. In on-line metrology cases for film manufacturing, the film vibration, which is caused by equipment vibrations or environmental disturbances, results in defocus blur and distortion of the received BFP images. Thus, subsequently extracted ellipsometric spectra and film parameters significantly deviate from the ground truth values. This paper proposes a cost-effective method for correcting vibration-induced BFP ellipsometric spectral errors. The method relies on an initial incident angle calibration of BFP radii at different defocus positions. Then, corresponding ellipsometric spectral errors are corrected by inserting a calibrated Jones compensation matrix into a system model. During measurement, the defocus position of the vibrational film is first determined. Then, BFP ellipsometric spectral errors, including incident angle mapping distortion and ellipsometric parameter variations, are corrected for a bias-free film analysis using the previous calibration results. Experimental results showed that this method significantly improved measurement accuracy without vibrational defocus compensation, from over 30 nm down to less than 1 nm. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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15 pages, 7901 KiB

Open AccessArticle

Single-Shot Three-Dimensional Reconstruction Using Grid Pattern-Based Structured-Light Vision Method

by Bin Liu, Fan Yang, Yixuan Huang, Ye Zhang and Guanhao Wu

Appl. Sci. 2022, 12(20), 10602; https://doi.org/10.3390/app122010602 - 20 Oct 2022

Cited by 7 | Viewed by 1749

Abstract

Structured-light vision methods are widely employed for three-dimensional reconstruction. As a typical structured light pattern, grid pattern is extensively applied in single-shot three-dimensional reconstruction. The uniqueness of the grid feature retrieval is critical to the reconstruction. Most methods using grid pattern utilize the [...] Read more.

Structured-light vision methods are widely employed for three-dimensional reconstruction. As a typical structured light pattern, grid pattern is extensively applied in single-shot three-dimensional reconstruction. The uniqueness of the grid feature retrieval is critical to the reconstruction. Most methods using grid pattern utilize the epipolar constraint to retrieve the correspondence. However, the low calibration accuracy of the camera–projector stereo system may impact the correspondence retrieval. An approach using grid pattern-based structured-light vision method is proposed. The grid pattern-based structured-light model was combined with the camera model and the multiple light plane equations. An effective extraction method of the grid stripe features was investigated. The system calibration strategy, based on coplanar constraint, is presented. The experimental setup consisted of a camera and an LED projector. Experiments were carried out to verify the accuracy of the proposed method. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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6 pages, 1276 KiB

Open AccessCommunication

Simple and Efficient Non-Contact Method for Measuring the Surface of a Large Aspheric Mirror

by Jie Li, Jie Yang and Lin Chen

Appl. Sci. 2022, 12(19), 9666; https://doi.org/10.3390/app12199666 - 26 Sep 2022

Viewed by 1022

Abstract

A non-contact measurement method for measuring large aspheric surfaces with a laser tracker is proposed. Using an air-bearing probe eliminates the need to contact the optical surface and improves measurement efficiency and accuracy. Using this method, we measured the surface of an aspheric [...] Read more.

A non-contact measurement method for measuring large aspheric surfaces with a laser tracker is proposed. Using an air-bearing probe eliminates the need to contact the optical surface and improves measurement efficiency and accuracy. Using this method, we measured the surface of an aspheric mirror 3 m in diameter and 13.6 m in the radius of curvature. The preliminary experimental result indicates that the error of surface measurement is 0.8 μm (RMS). Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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14 pages, 1250 KiB

Open AccessArticle

Measurement Precision of a Planar Nanopositioning Machine with a Range of Motion of Ø100 mm

by Jaqueline Stauffenberg, Ingo Ortlepp, Johannes Belkner, Denis Dontsov, Enrico Langlotz, Steffen Hesse, Ivo Rangelow and Eberhard Manske

Appl. Sci. 2022, 12(15), 7843; https://doi.org/10.3390/app12157843 - 04 Aug 2022

Cited by 4 | Viewed by 1456

Abstract

This work deals with various investigations into the accuracy of a newly developed planar nanopositioning machine. This machine, called Nanofabrication Machine 100 (NFM-100), has a positioning range of 100 mm in diameter. To determine the precision, various movement scenarios are performed with the [...] Read more.

This work deals with various investigations into the accuracy of a newly developed planar nanopositioning machine. This machine, called Nanofabrication Machine 100 (NFM-100), has a positioning range of 100 mm in diameter. To determine the precision, various movement scenarios are performed with the machine table, and the trajectory deviation from the set trajectory is determined. In particular, the focus is on high velocities of up to 20 mm/s. Even at high speeds in the range of several millimetres per second, this machine can impress with its performance and only has a deviation in the nanometre range. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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11 pages, 3802 KiB

Open AccessArticle

Accuracy Improvement of a Miniature Laser Diode Interferometer by Compensating Nonlinear Errors and Active Stabilizing Laser Diode Wavelengths

by Yindi Cai, Yang Liu, Chang Li and Zhixiang Wen

Appl. Sci. 2022, 12(12), 6064; https://doi.org/10.3390/app12126064 - 15 Jun 2022

Cited by 1 | Viewed by 1253

Abstract

A miniature laser diode interferometer (MLDI), which can be embedded in precision machines or measurement equipment as an on-line measurement sensor, is designed. A compact laser diode (LD) is adopted as the laser source of the MLDI. The measurement accuracy of the MLDI [...] Read more.

A miniature laser diode interferometer (MLDI), which can be embedded in precision machines or measurement equipment as an on-line measurement sensor, is designed. A compact laser diode (LD) is adopted as the laser source of the MLDI. The measurement accuracy of the MLDI is affected by the nonlinear errors induced by the installation errors and manufacturing errors of the optical elements and the stability and accuracy of the LD wavelength. An arithmetic is applied to eliminate the nonlinear errors, and an error sensitivity analysis is conducted to enhance the understanding of which error components are more important or influence the measurement accuracy of the MLDI. An active wavelength stabilizer based on a compact laser wavelength meter is proposed to improve the stability of the LD wavelength. A group of experiments are carried out to verify the effectiveness of the proposed methods and the capabilities of the MLDI. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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14 pages, 5544 KiB

Open AccessArticle

A Second Harmonic Wave Angle Sensor with a Collimated Beam of Femtosecond Laser

by Wijayanti Dwi Astuti, Kuangyi Li, Ryo Sato, Hiraku Matsukuma, Yuki Shimizu and Wei Gao

Appl. Sci. 2022, 12(10), 5211; https://doi.org/10.3390/app12105211 - 21 May 2022

Cited by 4 | Viewed by 1612

Abstract

An optical angle sensor based on the collimated mode-locked femtosecond laser (Fs) beam, in which the angle measurement is carried out by observing the second harmonic wave generated by irradiating the Fs beam towards MgO:LiNbO₃ crystal, is proposed. The angle detection is [...] Read more.

An optical angle sensor based on the collimated mode-locked femtosecond laser (Fs) beam, in which the angle measurement is carried out by observing the second harmonic wave generated by irradiating the Fs beam towards MgO:LiNbO₃ crystal, is proposed. The angle detection is demonstrated by identifying the second harmonic generation (SHG) spectrum peaks against the angular position of the rotating stage-mounted MgO:LiNbO₃ crystal that represents the measurement object. The MgO:LiNbO₃ with a length of 2 mm, a cut-off angle of 47°, a diameter of 5 mm, and 5% of MgO:LN, is rotated within the phase-matching angle over a wavelength range from 1480 nm to 1640 nm. Angle measurement is also carried out by placing the crystal at different positions along the laser beam propagation direction to confirm the feasibility of the angle sensor where the measurement range, measurement sensitivity, and resolution of the proposed method are also evaluated. The result shows that the proposed angle sensor can overcome the working distance limitation of conventional angle sensors and has no specific material target requirement. Since the configuration of the proposed angle sensor is not limited by the specification of the measurement target, it is expected to have wide potential applications, especially in the manufacturing process and inspection process. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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10 pages, 2326 KiB

Open AccessArticle

A Differential Phase-Modulated Interferometer with Rotational Error Compensation for Precision Displacement Measurement

by Liping Yan, Yucen Yan, Benyong Chen and Yingtian Lou

Appl. Sci. 2022, 12(10), 5002; https://doi.org/10.3390/app12105002 - 16 May 2022

Cited by 2 | Viewed by 1384

Abstract

In this paper, a differential phase-modulated interferometer (DPMI) is proposed to compensate for the rotational error for precision displacement measurement. In DPMI, a reference interferometer sharing the same reference arm with the measurement interferometer is constructed. Using the two interferometers to differentially measure [...] Read more.

In this paper, a differential phase-modulated interferometer (DPMI) is proposed to compensate for the rotational error for precision displacement measurement. In DPMI, a reference interferometer sharing the same reference arm with the measurement interferometer is constructed. Using the two interferometers to differentially measure the displacement, the unbalanced environmental disturbance on the measurement can be minimized. An integrated 2 × 2 array photodetector (APD) is adopted in DPMI. Based on APD with differential wavefront sensing (DWS) technology, the rotation angle can be detected and compensated. Therefore, precision displacement without rotational error and unbalanced environmental disturbance can be achieved. Three confirmatory experiments were performed, and the experimental results show that the maximum displacement drift is reduced from 902.9 nm to 16.3 nm in 100 min stability test, the standard deviations between the pitch and yaw angles obtained by DPMI and Renishaw interferometer are 1.68 × 10⁻⁵° and 1.86 × 10⁻⁵°, respectively, and the maximum deviation between the measurement result of DPMI and the stage positioning before and after angle compensation is reduced from 5.207 μm to about 0.719 μm. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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17 pages, 5308 KiB

Open AccessArticle

Influence of Surface Tilt Angle on a Chromatic Confocal Probe with a Femtosecond Laser

by Ryo Sato, Yuki Shimizu, Hiraku Matsukuma and Wei Gao

Appl. Sci. 2022, 12(9), 4736; https://doi.org/10.3390/app12094736 - 08 May 2022

Cited by 3 | Viewed by 1665

Abstract

This paper presents an intentional investigation of the effect of the object tilt angle on the tracking local minimum method (TL method), which is the one for detecting the measurement target position of the object optical axis, in a chromatic confocal probe employing [...] Read more.

This paper presents an intentional investigation of the effect of the object tilt angle on the tracking local minimum method (TL method), which is the one for detecting the measurement target position of the object optical axis, in a chromatic confocal probe employing a differential dual-fiber-detector optical system with a mode-locked femtosecond laser as the light source. The effect of the object tilt angle on dual-detector confocal probes, and even chromatic confocal probes, has not been investigated in detail so far, although the effect of object tilt angle on scanning confocal probes has been studied. At first, to examine the influence of the object tilt angle on the TL method, a theoretical model is established, and numerical simulations are performed based on the established theoretical equation. Then, the effect of aberrations in confocal optics on the confocal response curve is investigated in experiments. Finally, investigations on the effect of the object tilt angle on the TL method are demonstrated in experiments. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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17 pages, 5808 KiB

Open AccessArticle

Focused and TSOM Images Two-Input Deep-Learning Method for Through-Focus Scanning Measuring

by Zhange Zhang, Jiajun Ren, Renju Peng and Yufu Qu

Appl. Sci. 2022, 12(7), 3430; https://doi.org/10.3390/app12073430 - 28 Mar 2022

Cited by 3 | Viewed by 1865

Abstract

Through-focus scanning optical microscopy (TSOM) is one of the recommended measurement methods in semiconductor manufacturing industry in recent years because of its rapid and nondestructive properties. As a computational imaging method, TSOM takes full advantage of the information from defocused images rather than [...] Read more.

Through-focus scanning optical microscopy (TSOM) is one of the recommended measurement methods in semiconductor manufacturing industry in recent years because of its rapid and nondestructive properties. As a computational imaging method, TSOM takes full advantage of the information from defocused images rather than only concentrating on focused images. In order to improve the accuracy of TSOM in nanoscale dimensional measurement, this paper proposes a two-input deep-learning TSOM method based on Convolutional Neural Network (CNN). The TSOM image and the focused image are taken as the two inputs of the network. The TSOM image is processed by three columns convolutional channels and the focused image is processed by a single convolution channel for feature extraction. Then, the features extracted from the two kinds of images are merged and mapped to the measuring parameters for output. Our method makes effective use of the image information collected by TSOM system, for which the measurement process is fast and convenient with high accuracy. The MSE of the method can reach 5.18 nm² in the measurement of gold lines with a linewidth range of 247–1010 nm and the measuring accuracy is much higher than other deep-learning TSOM methods. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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11 pages, 2312 KiB

Open AccessArticle

Optical Coherence Tomography for 3D Weld Seam Localization in Absorber-Free Laser Transmission Welding

by Frederik Maiwald, Clemens Roider, Michael Schmidt and Stefan Hierl

Appl. Sci. 2022, 12(5), 2718; https://doi.org/10.3390/app12052718 - 05 Mar 2022

Cited by 1 | Viewed by 2428

Abstract

Quality and reliability are of the utmost importance for manufacturing in the optical and medical industries. Absorber-free laser transmission welding enables the precise joining of identical polymers without additives or adhesives and is well-suited to meet the demands of the aforementioned industries. To [...] Read more.

Quality and reliability are of the utmost importance for manufacturing in the optical and medical industries. Absorber-free laser transmission welding enables the precise joining of identical polymers without additives or adhesives and is well-suited to meet the demands of the aforementioned industries. To attain sufficient absorption of laser energy without absorbent additives, thulium fiber lasers, which emit in the polymers’ intrinsic absorption spectrum, are used. Focusing the laser beam with a high numerical aperture provides significant intensity gradients inside the workpiece and enables selective fusing of the internal joining zone without affecting the surface of the device. Because seam size and position are crucial, the high-quality requirements demand internal weld seam monitoring. In this work, we propose a novel method to determine weld seam location and size using optical coherence tomography. Changes in optical material properties because of melting and re-solidification during welding allow for weld seam differentiation from the injection-molded base material. Automatic processing of the optical coherence tomography data enables the identification and measurement of the weld seam geometry. The results from our technique are consistent with microscopic images of microtome sections and demonstrate that weld seam localization in polyamide 6 is possible with an accuracy better than a tenth of a millimeter. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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14 pages, 6155 KiB

Open AccessArticle

Lithography Hotspot Detection Method Based on Transfer Learning Using Pre-Trained Deep Convolutional Neural Network

by Lufeng Liao, Sikun Li, Yongqiang Che, Weijie Shi and Xiangzhao Wang

Appl. Sci. 2022, 12(4), 2192; https://doi.org/10.3390/app12042192 - 19 Feb 2022

Cited by 2 | Viewed by 3262

Abstract

As the designed feature size of integrated circuits (ICs) continues to shrink, the lithographic printability of the design has become one of the important issues in IC design and manufacturing. There are patterns that cause lithography hotspots in the IC layout. Hotspot detection [...] Read more.

As the designed feature size of integrated circuits (ICs) continues to shrink, the lithographic printability of the design has become one of the important issues in IC design and manufacturing. There are patterns that cause lithography hotspots in the IC layout. Hotspot detection affects the turn-around time and the yield of IC manufacturing. The precision and F1 score of available machine-learning-based hotspot-detection methods are still insufficient. In this paper, a lithography hotspot detection method based on transfer learning using pre-trained deep convolutional neural network is proposed. The proposed method uses the VGG13 network trained with the ImageNet dataset as the pre-trained model. In order to obtain a model suitable for hotspot detection, the pre-trained model is trained with some down-sampled layout pattern data and takes cross entropy as the loss function. ICCAD 2012 benchmark suite is used for model training and model verification. The proposed method performs well in accuracy, recall, precision, and F1 score. There is significant improvement in the precision and F1 score. The results show that updating the weights of partial convolutional layers has little effect on the results of this method. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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Review

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21 pages, 8345 KiB

Open AccessReview

Optical Accelerometers for Detecting Low-Frequency Micro-Vibrations

by Ying-Jun Lei, Rui-Jun Li, Lian-Sheng Zhang, Peng-Hao Hu and Qiang-Xian Huang

Appl. Sci. 2022, 12(8), 3994; https://doi.org/10.3390/app12083994 - 14 Apr 2022

Cited by 8 | Viewed by 3817

Abstract

Optical accelerometers are high-precision inertial sensors that use optical measurement technology to achieve high-precision and electromagnetic interference-resistant acceleration measurements. With the intensive research and development of optical accelerometers in recent years, their applications in inertial navigation, structural health monitoring, precision vibration isolation systems, [...] Read more.

Optical accelerometers are high-precision inertial sensors that use optical measurement technology to achieve high-precision and electromagnetic interference-resistant acceleration measurements. With the intensive research and development of optical accelerometers in recent years, their applications in inertial navigation, structural health monitoring, precision vibration isolation systems, wind turbine fault monitoring, earthquake monitoring, and other low-frequency vibration detection have flourished. Optical accelerometers have various schemes; however, their characteristics vary considerably due to different optical modulation schemes. This study aims to address the lack of systematic evaluation of currently available low-frequency optical accelerometers. Optical accelerometers can be classified into four categories in accordance with their optical modulation schemes: optical path-, optical intensity-, optical phase-, and optical wave-length-modulated accelerometers. The typical performance, advantages and disadvantages, and possible application scenarios of various optical accelerometers are summarized. This study also presents the current status and trends of low-frequency optical accelerometers in consideration of the growing demand for high-precision, low-frequency acceleration measurements. Full article

(This article belongs to the Special Issue State-of-the-Art of Optical Micro/Nano-Metrology and Instrumentation)

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