Dimensional Metrology Research Articles

Characterization of 1D Grating Standard for National Laboratory Comparison Using Scanning Electron Microscope

Nanometrology, which is dimensional metrology on the nanometer scale, is rapidly gaining importance. In Nanometrology, length standard traceable measurements are required to certify the values obtained from measurements. Standard Reference Material (SRM) is a sample for calibrating the magnification scale of a Scanning Electron Microscope (SEM). The standard are produced by recording a precision, laser-generated, interference pattern using photosensitive materials and other processing steps. This fabrication technique provides an accurate measure of the period of the line-space. Some of the critical quality attributes of a pitch standard are (1) the fundamental pitch distance, (2) the uniformity of the pitch, (3) the quality of the line edge roughness, (4) the imaging contrast that it produces, (5) the accuracy of the certified pitch value, and (6) the traceability of the certified pitch value to an internationally recognized standard. In this paper, we describe characterization of 1D grating standard with nominal 700 nm and 300 nm using SEM and its measurement uncertainty. The measurements were performed at 10 differents measurement position at each nominal. Total number of pitch at all measurement position in each nominal was 180. An image was taken at each measurement position. The average pitch of them represents the pitch value of the specimens. The results shows measured pitch for nominal 700 nm is 700.3 nm and 300 nm is 293.6 nm with measurement uncertainty for nominal 700 nm is 5.5 nm nominal 300 nm is 4.4 nm.

Development of a new hybrid approach combining AFM and SEM for the nanoparticle dimensional metrology.

At this time, there is no instrument capable of measuring a nano-object along the three spatial dimensions with a controlled uncertainty. The combination of several instruments is thus necessary to metrologically characterize the dimensional properties of a nano-object. This paper proposes a new approach of hybrid metrology taking advantage of the complementary nature of atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques for measuring the main characteristic parameters of nanoparticle (NP) dimensions in 3D. The NP area equivalent, the minimal and the maximal Feret diameters are determined by SEM and the NP height is measured by AFM. In this context, a kind of new NP repositioning system consisting of a lithographed silicon substrate has been specifically developed. This device makes it possible to combine AFM and SEM size measurements performed exactly on the same set of NPs. In order to establish the proof-of-concept of this approach and assess the performance of both instruments, measurements were carried out on several samples of spherical silica NP populations ranging from 5 to 110 nm. The spherical nature of silica NPs imposes naturally the equality between their height and their lateral diameters. However, discrepancies between AFM and SEM measurements have been observed, showing significant deviation from sphericity as a function of the nanoparticle size.

Analysis and Realization of Sampling Strategy in Coordinate Metrology

The stringent customer demands and competitive market emphasize the importance of efficient and effective inspection in industrial metrology. Therefore, the implementation of an appropriate sampling strategy, i.e., the number of points and their distribution, has become very important in the inspection process using a coordinate measuring machine. Moreover, the quality of inspection results has frequently been influenced by sampling plan as well as workpiece size and surface characteristics. It has been an indispensable problem in the present-day measurement processes. Thus, this paper investigates various sample sizes and different point distribution algorithms that can be employed in the evaluation of form error. The effect of specimen size and surface quality on the sampling strategy has also been investigated. Furthermore, this work employs a fuzzy based Technique for Order Performance by Similarity to Ideal Solution approach to realize the best sampling strategy. The results have demonstrated the significance of robust optimization techniques as well as the importance of a suitable sampling strategy in coordinate metrology. This study has also established that Poisson point distribution achieved the best accuracy and the Grid point distribution had taken the least measurement time.

Electron Reflectometry for Measuring Nanostructures on Opaque Substrates.

Here, we present a method for measuring dimensions of nanostructures using specular reflection of electrons from an electronically opaque surface. Development of this method has been motivated by measurement needs of the semiconductor industry1-4, and it can also be more broadly applicable to any periodic, pseudo-periodic or statistically stationary nanostructures or nanopattern on an opaque substrate. In prior work5,6, it was demonstrated through the presentation of proof of concept experiments and simulated examples that Reflective Small Angle Electron Scattering (RSAES) can meet certain dimensional metrology requirements of the semiconductor industry. In RSAES, an entire reflected scattering pattern is measured, with the scattered electrons being of primary interest. Later, in the process of further simulating RSAES, it was serendipitously discovered that dimensional measurement using reflected electrons might be greatly simplified by Electron Reflectometry (ER), whereby the intensity of the specularly reflected electron beam is measured and the scattered beams ignored.7 This innovation may allow faster and cheaper development and deployment or at the very least provide an alternate pathway to exploit the phenomenon of reflected electrons for dimensional measurement. Here we discuss how ER complements existing dimensional measurement techniques, show simulated applications with an emphasis an defect detection and line-width measurements.

Optimization of acoustic coupling for bottom actuated scattering based subsurface scanning probe microscopy.

The characterization of buried nanoscale structures nondestructively is an important challenge in a number of applications, such as defect detection and metrology in the semiconductor industry. A promising technique is Subsurface Scanning Probe Microscopy (SSPM), which combines ultrasound with Atomic Force Microscopy (AFM). Initially, SSPM was used to measure the viscoelastic contrast between a subsurface feature and its surrounding medium. However, by increasing the ultrasonic frequency to >1 GHz, it has been shown that SSPM can also measure acoustic impedance based contrasts. At these frequencies, it becomes difficult to reliably couple the sound into the sample such that the AFM is able to pick up the scattered sound field. The cause is the existence of strong acoustic resonances in the sample, the transducer, and the coupling layer-the liquid layer used to couple the sound energy from the transducer into the sample-in combination with the nonlinearity of the tip-sample interaction. Thus, it is essential to control and measure the thickness of the coupling layer with nanometer accuracy. Here, we present the design of a mechanical clamp to ensure a stable acoustic coupling. Moreover, an acoustic method is presented to measure the coupling layer thickness in real-time. Stable coupling layers with thicknesses of 700 ± 2 nm were achieved over periods of 2-4 h. Measurements of the downmixed AFM signals showed stable signal intensities for >1 h. The clamp and monitoring method introduced here makes scattering based SSPM practical, robust, and reliable and enables measurement periods of hours.

Methodology to evaluate the uncertainty associated with nanoparticle dimensional measurements by SEM

The scanning electron microscopy (SEM) technique is widely used for the characterizing of nanoparticle (NP) size, but very few papers deal with NP dimensional metrology. This article reports on a methodology with which to evaluate the uncertainty budget associated with the measurement of the mean diameter of a standard silica NP population by SEM. In this context, the effects of potential error sources have been evaluated though a metrological qualification of the instrument. The measuring method, consisting of determining the area equivalent diameter taken at middle height (Deq-FWHM), has been tested on a reference silica NP with an indicative certification value given by SEM/TEM (number-based modal diameter). Because agglomeration phenomena can cause measurements errors, semi-automatic homemade software has been employed to build the diameter distribution histogram, selecting only isolated particles. Finally, an uncertainty budget, including the main experimental components, has been established for the mean diameter measurement of this silica NP population. The main contributors to this uncertainty budget are the resolution linked to the dimension of the electron beam diameter at the focal plane, the calibration uncertainty on reference NPs, and the measurement repeatability.

Introductory notes for the Acta IMEKO Special Section on the ‘2018 IEEE International Workshop on Metrology for Industry 4.0 & IoT’

Introductory notes for the Acta IMEKO Special Section on the ‘2018 IEEE International Workshop on Metrology for Industry 4.0 & IoT’

Standardizing Innovation Management: An Opportunity for SMEs in the Aerospace Industry

In a globalized marketplace, the competition in the aerospace industry has increased significantly. Producers can choose between many suppliers. These suppliers have to comply with more requirements and technical specifications, as well as take on greater responsibilities that originally fell on producers. In this context, business opportunities for small and medium-sized enterprises (SMEs) are limited, but still suppliers must try to leverage the maximum strategic advantage of the few that present. Adopting research, development and innovation (R+D+i) practices has proven to bring great benefits to companies and allows them to gain significant competitive advantages. However, the process of designing, implementing and testing R+D+i-related processes is not straightforward, nor it has been addressed in the recent research on SMEs. In this paper, a case study of a Spanish innovative small company providing industrial metrology and quality services is analyzed. Thanks to an internal decision-making process, an R+D+i management system based on the UNE 166.002:2014 standard is eventually adopted. A pilot project is closely followed up to test the robustness of the system implementation. The R+D+i management system has allowed the company to streamline its innovation activities, establish objectives to better allocate essential resources, organize high performing innovation units within the organization structure, increase the clients’ confidence, improve the company’s competitiveness, carry out technological surveillance, and get more patented technology, among many others. Adoption steps taken by this SME are generalizable to other SMEs from other industries and show how an R+D+i management system can be chosen, designed, implemented and tested in the context of Industry 4.0 (I4.0).

Plastic deformation and material transfer on steel gage blocks during low force mechanical probing

Contact probing of gaging surfaces is used throughout dimensional metrology. Probe tips such as ruby, sapphire, or diamond are commonly employed as styli for universal length measuring machines (ULMs) and coordinate measuring machines (CMMs) due to the hardness, durability, and wear resistance. Gaging surfaces of gage blocks are precision ground or lapped, with very low surface roughness to enable wringing. Damage or contamination of these surfaces can prevent wringing and lead to measurement error. Experimental investigations using a horizontal ULM and CMM have revealed that even at low force settings (≤0.16 N), probe materials such as ruby and sapphire can cause plastic deformation to hardened carbon chrome steel (such as AISI 52,100) gage block surfaces at the microscale, likely attributed to fretting-associated wear. Under some conditions, permanent transfer of material from the probe stylus to the gaging surface is possible. Results demonstrate irreversible changes and damage to gaging surfaces with repeated probe contact on a ULM and CMM. Optical microscopy, optical profilometry, and scanning electron microscopy (SEM) provide a semi-quantitative assessment of microscale plastic deformation and material transfer. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Raman techniques confirm chemical constituency of reference materials used (gage blocks and probes) and also identify makeup of deposits on gaging surfaces following probe contact.

Effect of scan substrates on accuracy of 7 intraoral digital impression systems using human maxilla model.

This study aimed to determine how the accuracy of digital impressions was affected by four common dental substrates using seven prevalent IOS systems to scan the complete arch of a human maxilla. The Department of Oral Rehabilitation at the Medical University of South Carolina. A single cadaver maxilla. Seven digital intraoral impression systems were used to scan a freshly harvested human maxilla. The maxilla contained several teeth restored with amalgam and composite, as well as unrestored teeth characterized by enamel. Also, three teeth were prepared for full coverage restorations to expose natural dentin. An industrial grade metrology software program that allowed 3D overlay and dimensional computation compared deviations of the complete arch and its substrates on the test model from the reference model. Substrates were significantly different from each other when considering scan data as a whole, as well as when comparing IOS devices individually. Only PlanScan failed to reveal trueness differences between the different substrates, while only Emerald revealed precision differences between the substrates. Substrate type does impact the overall accuracy of intraoral scans with dentin being the most accurate and enamel being the least accurate. The four substrates scanned impacted the trueness of all IOS devices.

Measurement uncertainty in laboratory medicine: the bridge between medical and industrial metrology

Abstract Uncertainty is an inseparable part of all types of measurements, that is, in metrology a measurement without uncertainty is not possible. Calculation of uncertainty increases the awareness of the certainty of measurement results. Reporting measurement uncertainty is mandatory in almost all industrial sectors but not in laboratory medicine. Test results without analytical uncertainty increases the diagnostic uncertainty, causing errors that could seriously affect patients health. To improve diagnostic certainty, we should calculate and upon request report measurement uncertainty to laboratory users (ISO 15189). In this mini-review, we summarized the theoretical perspective of uncertainty concept, its relation to Six Sigma and finally compared it with Total Error Method.

EVALUATION OF VISION-BASED LOCALIZATION AND MAPPING TECHNIQUES IN A SUBSEA METROLOGY SCENARIO

Abstract. Metrology is fundamental in all the applications that require to qualify, verify and validate measured data according to standards or, in other words, to assess their compliance with predefined tolerances. At sea, metrology is commonly associated with the process of measuring underwater structures, mainly pipeline elements widely used in offshore industry. Subsea operations are very expensive; optimizing time and money resources are the core factors driving innovation in the subsea metrology industry. In this study, the authors investigate the use of state-of-art vision-based algorithms, i.e. ORB-SLAM2 and Visual Odometry, as a navigation tool to assist and control a Remotely Operated Vehicle (ROV) while performing subsea metrology operations. In particular, the manuscript will focus on methods for assessing the accuracy of both trajectory and tie points provided by the tested approaches and evaluating whether the preliminary real time reconstruction meets the tolerances defined in typical subsea metrology scenarios.

Verifying the measurement accuracy for X-ray cone-beam CT scans of objects smaller than 5 mm diameter

Dimensional metrology has become an important and well-established application of industrial X-ray computed tomography (CT). Currently there is an increasing need to use CT-based metrology for objects scanned at very high resolution (< 1 μm voxel size). In order to validate the measurement accuracy of a CT scanner, calibrated length standards are required that match the range of field-of-view (FOV) sizes offered by the scanner. While there are now many lengths standards available for FOV diameters of 50 mm and above [1], so far there are few or no standards that are suitable for a small FOV diameter, and at the same time meet the requirements of guideline VDI/VDE 2617/2630 [2], dealing with CT-based metrology. In order to fit a FOV diameter of less than 5 mm, a length standard was designed in accordance with that guideline, manufactured from a support material and ruby spheres, and tactile measurements were performed with a ZEISS F25 coordinate measurement machine. CT metrology was performed using a ZEISS METROTOM 800, and the results are compared.

2D Contour Reconstruction for Industrial Computed Tomography using Crease Cluster

One task of industrial computed tomography in dimensional metrology is to provide surface models of examined objects. Currently, in the standard approach polygonal surface meshes from reconstructed tomograms are extracted. Precise surface meshes require a high resolution tomogram, leading to time-consuming reconstruction algorithms. In order to overcome this problem, we propose a method to approximate the contour by a point cloud of folds, which resemble the most characteristic parts of the object. These creases are reconstructed from filtered projection images directly in Cartesian space. This cloud of creases will serve as a basis for the creation of meshes. Initial results of a 2D phantom study indicate that the method reaches reconstruction accuracies comparable to standard methods while the number of necessary projections is reduced significantly, leading to a notable decrease in scan time.

Development of Reference Samples to Study the Effects of Systematic Errors of Industrial X-ray Computed Tomography

X-ray computed tomography (XCT) has been increasingly used for dimensional metrology. However, the impact of systematic errors has not been well studied. Typical systematic errors of XCT includes scattering, beam hardening, cone beam errors etc. The impact of these systematic errors on dimensional metrology is an on-going research topic. At the United Kingdom’s National Physical Laboratory a set of reference samples have been developed to study the impact of these systematic effects, especially when measuring metal components. The samples developed include the stair case reference sample, the additive manufacturing (AM) reference sample and the large industry reference sample. The paper discusses the establishment of reference data for XCT using traceable measurement instruments and the applications of these samples in investigating the impact of systematic effects.

CT machine geometry changes under thermal load

Computed tomography systems are increasingly used for dimensional metrology. Accurate CT machine geometry and temperatures close to 20 °C are crucial for dimensional measurements. Usually, considerable thermal loads are imposed onto CT systems by the X-ray source and the detector that dissipate heat in the order of 100 W. Because temperature variations and gradients induce deformations on the machine geometry, it is crucial to characterise and control such influences. Here, a homebuilt water cooling system for a flat-panel X-ray detector was characterised for heat dissipation into the CT system, positional and angular drift, and pixel grey value stability.

CT Measurement Realization Process: The Need for Advanced Correction Methods

Computed tomography use as a dimensional metrology technique has increased steadily, despite the fact that the uncertainty has been rarely determined and expressed in measurements of production parts. This perception may be attributed in part to a limited way of employing the uncertainty concept. From this perspective, the conceptual integration of the product (and measurement) realization process with the uncertainty approach is first emphazised in this paper. The reasoning behind it is to employ different methods for uncertainty evaluation in a rational sense, where the accuracy required to the uncertainty evaluation process drives the method selection. For critical measurement cases, which can be identified in the proposed concept, the need for advanced correction methods, using master part reference measurements for point-based compensation, is presented, tested and justified for GD&T characteristics.

Simulation-based sensitivity analysis of geometrical misalignments in X-ray computed tomography systems for dimensional metrology – detector angular misalignments

Nowadays, X-ray computed tomography (XCT) represents a viable solution for metrological investigations of industrial components characterized by external as well as internal geometries. However, the traceability of measurements is still difficult to be established because of a great number of influence factors, often difficult to be identified and assessed. The XCT system geometry represents one of the most critical aspects, as any deviation from the ideal alignment conditions may generate errors in measurement results. Many efforts have been made to find methods able to characterise the actual geometry of the system, but work is still needed to obtain faster and easier solutions. This work is part of a study that aims at investigating the magnitude of dimensional measurement errors caused by geometrical misalignments that can affect an XCT system, with the purpose of developing a faster and easier solution by focusing on the most critical factors. Results of a simulation-based investigation on the influence of detector angular misalignments are presented. The center-to-center distances of spheres belonging to a newly designed ball plate are evaluated, starting from angular misalignments already investigated experimentally in literature.

Proposition and experimental evaluation of a point-based compensation approach to reduce systematic errors in CT measurements

Industrial applications of computed tomography (CT) for dimensional metrology have increased steadily over the last few years, despite the fact that the measurement uncertainty has rarely been evaluated and reported. Despite being an important prerequisite of any scientific or industrial measurement, the complex CT measurement chain and the numerous influencing quantities involved in the measurement process mean that the problem of evaluating the uncertainty and tracing the dimensional measurement results back to the unit of length remains an unsolved issue. In this paper, the use of master part reference measurements for later point-based compensation of CT datasets is proposed to correct known systematic effects and reduce the measurement uncertainty down to the level of the CT measurement process repeatability, for part features that can be accessed and calibrated using a reference coordinate measuring system (R-CMS). The point-based compensation approach is described, experimentally tested using a prismatic part and is discussed for several geometrical tolerance verification cases.

Physical-chemical measurement method development for self-assembled, core-shell nanoparticles

Improvements in dimensional metrology and innovations in physical-chemical characterization of functionalized nanoparticles are critically important for the realization of enhanced performance and benefits of nanomaterials. Toward this goal, we propose a multi-technique measurement approach, in which correlated atomic force microscopy, dynamic light scattering, high performance liquid chromatography and mass spectroscopy measurements are used to assess molecular and structural properties of self-assembled polyplex nanoparticles with a core-shell structure. In this approach, measurement methods are first validated with a model system consisting of gold nanoparticles functionalized with synthetic polycationic branched polyethylenimine macromolecules. Shell thickness is measured by atomic force microscopy and dynamic light scattering, and the polyelectrolyte uptake determined by chromatographic separation and mass spectrometric analysis. Statistical correlation between size, structure and stability provide a basis for extending the methods to more complex self-assembly of nucleic acids and macromolecules via a condensation reaction. From these size and analytical chemical measurements, we obtain a comprehensive spatial description of these assemblies, obtain a detailed interpretation of the core-shell evolution, and identify regions of the parameter space where stable, discrete particle formation occurs.