Metrology Methods Research Articles

Precise wavefront characterization of x-ray optical elements using a laboratory source.

Improvements in x-ray optics critically depend on the measurement of their optical performance. The knowledge of wavefront aberrations, for example, can be used to improve the fabrication of optical elements or to design phase correctors to compensate for these errors. At present, the characterization of such optics is made using intense x-ray sources, such as synchrotrons. However, the limited access to these facilities can substantially slow down the development process. Improvements in the brightness of lab-based x-ray micro-sources in combination with the development of new metrology methods, particularly ptychographic x-ray speckle tracking, enable characterization of x-ray optics in the lab with a precision and sensitivity not possible before. Here, we present a laboratory setup that utilizes a commercially available x-ray source and can be used to characterize different types of x-ray optics. The setup is used in our laboratory on a routine basis to characterize multilayer Laue lenses of high numerical aperture and other optical elements. This typically includes measurements of the wavefront distortions, optimum operating photon energy, and focal length of the lens. To check the sensitivity and accuracy of this laboratory setup, we compared the results to those obtained at the synchrotron and saw no significant difference. To illustrate the feedback of measurements on performance, we demonstrated the correction of the phase errors of a particular multilayer Laue lens using a 3D printed compound refractive phase plate.

Toward a New Mathematical Definition of Datums in Standards to Support Advanced Manufacturing.

Recent advances in the digitization of manufacturing have prompted ASME and International Organization for Standardization (ISO) standards committees to reexamine the definition of datums. Any new definition of datums considered by the standards committees should cover all datum feature types used in design and support both traditional metrological methods and new digital measurement techniques. This is a challenging task that requires some careful compromise. This paper describes and analyzes various alternatives considered by the standards committees. Among them is a new mathematical definition of datums based on constrained least-squares fitting. It seems to provide the best compromise and has the potential to support advanced manufacturing that is increasingly dependent on digital technologies.

Integrated interferometry for in-process monitoring of critical dimension in vertical NAND flash memory dry etch

Integrated interferometry installed on top of dry etch equipment was developed for the in-process measurement of critical dimension (CD) in vertical NAND flash memory dry etch forming word-line steps, also known as word-line processes. The etching process sequentially consists of mask trimming and mold etching (multilayered structure of Si3N4 and SiO2). In-process real-time CD measurements can be made in a trimming step that etches the photoresist (PR) to form a vertical mask shape. The measurement principle is based on the analysis of the interference fringe signal of light reflection to a single point in the center of the wafer. To check the measurement accuracy of the interferometer, the CD measured with interferometry was compared with an in-line SEM (scanning electron microscope). The correlation coefficient between the interferometric measurements measured during the mask trimming step and the in-line SEM measured after the completed process was 86%. On the other hand, when the mask trimming and the mold etching steps including Si3N4 over etching were added, the total measurement results showed that the correlation coefficient was 95%. This is because the CD value was derived based on the phenomenon that the PR thickness change measured by interferometry in the trimming step was a linear relationship with the change in the lateral PR amount, so the lateral PR amount was weakly etched in the mold etching step after the trimming step, which eventually affected the final formed CD. This metrology method can be simply applied to dry etching equipment in real production lines.

Solving optimal carrier frequencies of a CGH null compensator through a double-constrained searching method based on iterative ray-tracings.

Interferometry based on a computer-generated hologram (CGH) null compensator is a general method for high-precision metrology of aspherics. Because the most commonly used CGHs are the Ronchi type with only two quantization steps, tilt and defocus carrier frequencies must always be introduced to separate the disturbing diffraction orders (DDOs). Determining the amount of carrier frequencies is a pivotal but difficult issue in the CGH design process. Previous studies have only drawn qualitative conclusions or obtained some approximate results under specific conditions. This paper proposes a double-constrained searching method based on iterative ray-tracings, which can directly and accurately give the optimal combination of tilt and defocus carrier frequencies, as long as the aspheric under test is a concave one and has an analytical expression. The optimal carrier frequencies solved by the proposed method will minimize the line density of the CGH on the premise of separating all DDOs, which will reduce the cost and difficulty of fabrication as much as possible. The proposed method is almost error-free and holds a clear advantage over the previous methods in terms of versatility. Several typical design examples are presented to verify the feasibility and versatility of the proposed method. Its accuracy is also verified through making comparisons of the ray-tracing results between another method and Zemax models based on these examples.

Measurements of virial coefficients of Helium, Argon and Nitrogen for the needs of static expansion method

<p>Generally, there are three primary methods in vacuum metrology: mercury manometer, static expansion method, and continuous expansion method. For the pressure below 10 Pa, the idea of the primary standard is that the gas is measured precisely at a pressure as high as possible, and then the gas is expanded to the bigger volumes; this allows to calculate the expanded pressure. An important parameter that needs to be taken care of in primary vacuum calibration methods is the compressibility factor of the working gas. The influence of virial coefficients on the realization of primary standards in vacuum metrology, especially in the realization of the static expansion method is very important. In this paper we will present the measured data for virial coefficients of three gases Helium, Argon and Nitrogen measured at room temperature and a pressure range from 3 kPa to 130 kPa. The dominating term due to real gas properties arises from the second virial coefficient. The influence of higher orders of virial coefficients drops rapidly with lower pressure, particularly for gas pressures values lower than one atmosphere. Hence, in our calculation, the series of real gas was used for the first and second virial coefficients but not for higher-order virial coefficients.</p>

X-ray wavefront sensing and optics metrology using a microfocus x-ray grating interferometer with electromagnetic phase stepping

A metrology method of x-ray optical elements based on an electromagnetic phase stepping x-ray grating interferometer with high slope accuracy is presented in this study. The device consists of an x-ray tube, a phase grating G1 for modulating the incoming wavefront, and an absorption grating G2 as a transmission mask to produce a broader moiré pattern for the x-ray camera. The focal spot of the microfocus x-ray source is shifted by a magnetic field from a solenoid coil. Electromagnetic phase stepping analysis is used to obtain a pixel-wise map of the wavefront phase distortion to replace the traditional precision mechanical scanning system, improving stability, speed, accuracy, and flexibility. The x-ray grating interferometer can be used as a feedback tool for evaluating the quality of optical elements and detecting defects caused by the x-ray beam or the x-ray optical elements in ordinary laboratories and mirror-processing centers without the need of scheduling synchrotron beam time.

Analysis of Heavy Vehicle Research Status about Knowledge Structure and Research Hotspots Based on CiteSpace

Heavy vehicle is an important carrier of cargo transportation and is always the research focus of the automotive and environment field. In this paper, the scientific metrological analysis method is used to systematically summarize the research topics and current situation of heavy vehicles. From 2000 to 2019, 1047 articles and 7259 references were investigated. The subject and subject of heavy vehicle research are determined. This paper makes an in-depth study on the phenomenon of citation burst. The research results of this paper not only provide practitioners with a deeper understanding of heavy vehicles, but also help researchers carry out relevant in-depth research.

Characterization of the Interaction of Metalworking Fluids with Grinding Wheels

The thermal load that occurs during grinding can be reduced with the aid of an optimized metalworking fluid (MWF) supply. In previous work, mainly the free jet was considered for the determination of the conditions required for an optimized MWF supply. An investigation of the interaction area between the MWF and the grinding wheel has not yet been carried out due to the lack of suitable measurement techniques. In the presented work, both the free jet and the interaction area are analyzed with the aid of new metrological analysis and evaluation methods based on high-speed records (shadowgraphy and shadogram imaging velocimetry) in order to assess the free jet geometry and velocities, as well as the velocity distribution and the MWF amount in the interaction area. Using this approach, the following main results were derived: (1) The free jet velocity remains approximately constant in a defined free jet cross-section even at high distances from the nozzle outlet. (2) The velocity distribution in the interaction area is mainly influenced by the flow rate. (3) A new image parameter (black pixel fraction) was derived for the evaluation of the MWF supply to the contact zone.

Toward realization of high-throughput hyperspectral imaging technique for semiconductor device metrology

Background: High-throughput three-dimensional metrology techniques for monitoring in-wafer uniformity (IWU) and in-cell uniformity (ICU) are critical for enhancing the yield of modern semiconductor manufacturing processes. However, owing to physical limitations, current metrology methods are not capable of enabling such measurements. For example, the optical critical dimension technique is not suitable for ICU measurement, because of its large spot size. In addition, it is excessively slow for IWU measurement. Aim: To overcome the aforementioned limitation, we demonstrate a line-scan hyperspectral imaging (LHSI) system, which combines spectroscopy and imaging techniques to provide sufficient information for spectral and spatial resolution, as well as high throughput. Approach: The proposed LHSI system has a 5-μm spatial resolution together with 0.25-nm spectral resolution in the broad-wavelength region covering 350 to 1100 nm. Results: The system enables the simultaneous collection of massive amounts of spectral and spatial information with an extremely large field of view of 13 × 0.6 mm2. Additionally, throughput improvement by a factor of 103 to 104 can be achieved when compared with standard ellipsometry and reflectometry tools. Conclusions: Owing to its high throughput and high spatial and spectral resolutions, the proposed LHSI system has considerable potential to be adopted for high-throughput ICU and IWU measurements of various semiconductor devices used in high-volume manufacturing.

Phase derivative estimation in digital holographic interferometry using a deep learning approach.

In digital holographic interferometry, reliable estimation of phase derivatives from the complex interference field signal is an important challenge since these are directly related to the displacement derivatives of a deformed object. In this paper, we propose an approach based on deep learning for direct estimation of phase derivatives in digital holographic interferometry. Using a Y-Net model, our proposed approach allows for simultaneous estimation of phase derivatives along the vertical and horizontal dimensions. The robustness of the proposed approach for phase derivative extraction under both additive white Gaussian noise and speckle noise is shown via numerical simulations. Subsequently, we demonstrate the practical utility of the method for deformation metrology using experimental data obtained from digital holographic interferometry.

Fabrication of poly(AA)-chitosan nanoparticles graft copolymer via microwave irradiation system for enhancing water solubility and antimicrobial properties

PurposeThis paper aims to study previously prepared and fully characterized chitosan nanoparticles (CNPs) as a starting substrate and microwave initiation technique for grafting acrylic acid (AA). This was done to see the influence of both CNPs with respect to well-dispersed nanosized particles, large surface areas, biodegradability, biocompatibility and reactivity and microwave initiation technique with respect to reduction in organic solvents, toxic chemical initiator and exposer time on exploiting the graft yield % and enhancing water solubility and antibacterial properties.Design/methodology/approachFor evaluating the best accurate standard metrological method for calculating the graft yield %, the grafting parameters were stated in terms of graft yield percent and measured gravimetrically (based on dry weight method) and titrimetrically (based on carboxyl content). Microwave power, AA and CNPs concentrations and reaction duration were shown to be the most important parameters influencing the grafting process.FindingsThe optimum reaction conditions were obtained when CNPs 1.5 g, AA 150 bows, microwave irradiation power 500 W and reaction duration 120 s were used. Various analytical methods were used to characterize CNPs and poly(AA)–CNPs graft copolymers. According to the findings, Fourier transform infrared spectroscopy examination determines the attachment of carboxyl groups to CNPs chains. The thermogravimetric analysis revealed that the copolymers were more thermally stable than CNPs counterparts. Furthermore, the resulting copolymers were shown to have greater water solubility biodegradability resistance and antibacterial properties than CNPs counterpart. Finally, a preliminary mechanism demonstrating all occasions that occur during the polymerization reaction has been proposed.Originality/valueThe advancement addressed here is undertaken using previously prepared and fully characterized CNPs as a green bio-nanocompatible polymer and microwave initiation technique as green and efficient tool with respect to reduction in organic solvents toxic chemical initiator and exposer time for grafting AA.

CPU and GPU real-time filtering methods for dense surface metrology using general matrix to matrix multiplications

Filtering is a required task in surface metrology for the identification of the components relevant for automated quality control. The calculation of real-time features about the surface is crucial to determining the mechanical and physical properties of the inspected product. The computation efficiency of the filtering operations is a major challenge in surface metrology, as current sensors provide massive volumes of data at very high acquisition rates. To overcome the challenges, this work presents different real-time filtering solutions comparing the performance on the CPU and on the GPU, using modern hardware. The proposed framework is focused on filtering techniques that can be expressed using a finite impulse response (FIR) kernel that includes the Gaussian kernel, the most common filtering technique recommended by ISO and ASME standards. This research work proposes variations of the double FIFO and double circular filters. The filters are transformed into a series of general matrix to matrix multiplications, which can be run extremely efficiently on different architectures. The proposed filtering approach provides superior performance compared with previous works. Additionally, tests are carried out to quantify the performance of the GPU in terms of data transfer and computation capabilities in order to diminish the penalty imposed by data transfer from main memory to the GPU in real-time operations. Based on the results, an efficient batch filtering technique is proposed that can be run on the GPU faster than the CPU even for small profile and kernel sizes, offloading this task from the host CPU for optimal system and application response.

Metrological approach to the assessment of the criteria of speed and strength training of middle school students in physical education lessons in athletics

Evaluation of the results of pedagogical control is the main factor for obtaining information about the state of physical fitness and effectiveness of educational work in physical education lessons. Obtaining an objective assessment of the level of development of speed and strength qualities of middle school students helps to improve the management of the educational process, making adjustments in the planning of physical education and forecasting academic achievement. The main metrological requirements for the development of evaluation criteria for the manifestation of speed and strength training of students include: 1) the correct choice of control, tests and their compliance with statistical criteria of reliability, objectivity and informativeness; 2) compliance of methods and means of control with the objectives of the study; 3) the adequacy of methods of statistical processing of test results. The purpose of the study is aimed at developing assessment criteria for speed and strength training of middle school students in physical education classes in athletics. The research methodology is aimed at substantiating the results of pedagogical control, development of quantitative and qualitative criteria of speed and strength training of middle school students of general secondary schools. The scientific novelty is to develop quantitative and qualitative criteria for assessing the speed and strength of middle school students, to determine the impact of the process of physical education on the dynamics of their changes in the results of phased control. The use of metrological tools and methods for assessing the speed and strength of middle school students allows the implementation of individual and differential approach to each student in the process of physical education.

Novel alignment method for optical 3D gear metrology of spur gears with a plain borehole

In 3D optical metrology, novel approaches to characterise the geometrical quality of gears require a custom gear alignment process to produce reliable results. This study proposes a novel scan alignment method known as subsequent gear alignment (SGA). It emphasises on the proper alignment of the gear hole and follows the alignment of gears in real-world applications. Therefore, the SGA method increases the usability of the previously developed and published methods. The scanned data were first processed with both the commercial global alignment and SGA methods and then evaluated to obtain standard geometrical parameters. These were compared with those obtained by the tactile method, and the SGA method offered improved results over the global alignment method.

Comprehensive Areal Geometric Quality Characterisation of Injection Moulded Thermoplastic Gears.

Injection moulding is currently the most widely employed production method for polymer gears. Current standardised gear metrology methods, which are based on metal gear inspection procedures, do not provide the key information regarding the geometric stability of injection moulded gears and are insufficient for a thorough gear inspection. The study developed novel areal quality parameters, along with a so-called moulding runout quality parameter, with a focus on the injection moulding method. The developed parameters were validated on twenty-nine gear samples, produced in the same moulding tool using various processing parameters. The gears were measured using a high-precision structured-light 3D scanner. The influence of injection moulding process parameters on the introduced novel quality parameters was investigated. The developed moulding runout quality parameter proved to be effective in evaluating the shrinkage that can occur in the injection moulding process. The novel moulding runout parameter returned an average value of −21.8 μm in comparison to 29.4 μm exhibited by the standard parameter on all the gears, where the negative value points directly to mould shrinkages. The rate of cooling was determined to be the most influential factor for the shrinkage of the gear. The developed areal parameters demonstrated to be advantageous in characterising the deviations on the teeth more comprehensively.

НАБЛИЖЕНИЙ МЕТОД ЕКСПЕРТНИХ ОЦІНОК ЕФЕКТИВНОСТІ ЗАСТОСУВАННЯ ПОЛІМЕРНИХ КОМПОЗИЦІЙНИХ МАТЕРІАЛІВ У КОНСТРУКЦІЯХ ЦИВІЛЬНИХ ЛІТАКІВ НА ОСНОВНИХ ЕТАПАХ ЖИТТЄВОГО ЦИКЛУ

In connection with the growing use of polymer composite materials all over the world and in domestic aircraft construction in civil aircraft of the transport category, the analysis of forecasting methods of their application at the main stages of the life cycle of this class of structures becomes an urgent problem.Efficiency, as the ratio between the achieved result and the resources spent on its achievement, can be interpreted as the ratio between the total quality indicators of the created object and the total costs.However, quality indicators are such metrological characteristics, the quantitative measurement of which in most cases is difficult or almost impossible. In this regard, the qualimetric quality indicators acquire the qualimetric form of qualitative characteristics. Qualimetric characteristics make it possible to operate during their analysis by a productive method of expert assessments of criteria for the implementation of any object, including composite structures of aircraft aggregates. As a criterion for predicting the effective volume of use of composite structures, an analogue of D.L. quality at the stages of their life cycle. The numerical values of each level of the stages of the life cycle are assessed by an expert according to the proposed five-level general identification tables with the subsequent summation of the criterion indicators by stages of the life cycle, making it possible to determine both the efficiency of using composites at individual stages and its integral value for all main stages. The relative value of the efficiency criterion can be represented in monetary terms by multiplying it by an equivalent established on the basis of metrological (qualimetric) methods and means of assessing the results of a particular production.

Comparison of EUV Photomask Metrology Between CD-AFM and TEM

Accurate metrology of extreme ultraviolet (EUV) photomask is a crucial task. In this paper, two different methods for reference EUV photomask metrology are compared. One is the critical dimension atomic force microscopy (CD-AFM). In the measurements, the contribution of its AFM tip geometry is usually the dominant error source, as measured AFM images are the dilated results of measured structures by the AFM tip geometry. To solve this problem, a bottom-up approach has been applied in calibrating the (effective) AFM tip geometry where the result is traceably calibrated to the lattice constant of silicon crystals. The other is transmission electron microscopy (TEM). For achieving measurement traceability, structure features are measured in pairs in TEM images; thus the distance between the structure pair calibrated by a metrological AFM in prior can be applied to determine the magnification of the TEM image. In this study, selected photomask structures are calibrated by the CD-AFM, and then sample prepared and measured by high-resolution TEM nearly at the same location. The results are then compared. Of six feature groups compared, the results agree well within the measurement uncertainty, indicating excellent performance of the developed methodology. This research supports the development of a photomask standard, which is applied as a “reference ruler” with improved low measurement uncertainty in photomask fabs.

Robust phase unwrapping algorithm based on Zernike polynomial fitting and Swin-Transformer network

Phase unwrapping plays an important role in optical phase measurements. In particular, phase unwrapping under heavy noise conditions remains an open issue. In this paper, a deep learning-based method is proposed to conduct the phase unwrapping task by combining Zernike polynomial fitting and a Swin-Transformer network. In this proposed method, phase unwrapping is regarded as a regression problem, and the Swin-Transformer network is used to map the relationship between the wrapped phase data and the Zernike polynomial coefficients. Because of the self-attention mechanism of the transformer network, the fitting coefficients can be estimated accurately even under extremely harsh noise conditions. Simulation and experimental results are presented to demonstrate the outperformance of the proposed method over the other two polynomial fitting-based methods. This is a promising phase unwrapping method in optical metrology, especially in electronic speckle pattern interferometry.

Development and evaluation of three-dimensional metrology of nanopatterns using electron microscopy

The semiconductor industry continuously moves toward smaller features and more complex, three-dimensional (3D) structures to enable next-generation devices. Thus there is a high need for 3D metrology techniques that would provide feedback to the advancing nanoscale fabrication processes. We introduce an approach for evaluating, calibrating, and developing new metrology of nanopatterns through comparing the new metrology data to 3D ground truth data, obtained by accurate scanning transmission electron microscopy (STEM) tomography 3D characterization. We demonstrate this approach by evaluating 3D height maps of sub-20-nm patterns obtained using multi-secondary electron detector scanning electron microscopy (multi-perspective SEM) and photometric stereo algorithm. We demonstrate the importance of full 3D characterization, including cross-sectional structure, height fluctuations, and line edge roughness to truly probe the pattern’s average structures and their 3D variations. Although STEM tomography is a high-resolution and accurate method, it is considered demanding in terms of sample preparation and cannot be used as an efficient in-line metrology method. However, we show that it can be used as a reliable 3D characterization technique to obtain the necessary 3D data for the development of new 3D metrology tools and demonstrate this approach by evaluating the accessible, in-line, multi-perspective SEM.

Metrological Traceability of High Polarization Extinction Ratio (PER) Based on Precision Coaxial Rotating Polarization-Maintaining Fiber

This article proposes a metrological traceability method for polarization extinction ratio (PER) ranging from 0 up to 70 dB, while the common method is limited to 50 dB. A precision alignment coupling point is designed and manufactured using two polarization-maintaining fibers (PMFs). By rotating one of the PMFs to change the axis-alignment angle and to control the distribution of light energy in the fast and slow axis, a traceability chain from the PER to the rotation angle is established. With extremely low-stress clamping of the PMF, 5-D precision adjustment of the fiber position, and precision coaxial rotation in the order of arc seconds, accurate and controllable generation of any PER in the range of 0–70 dB can be achieved. A high PER traceability system is designed and built, which is successfully used in the traceability of PER to the angle of circumference. The expanded uncertainty ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k = 2$ </tex-math></inline-formula> ) in the ranges of 0–30 dB, 30–50 dB, and 50–70 dB is 0.01, 0.06, and 1.20 dB, respectively. Controlled generation of high PER (50–70 dB) with metrological traceability is realized for the first time as far as we know.