Conventional Metrology Research Articles

AB0533 Gender differences in spinal mobility reduction caused by ankylosing spondylitis in medium and long term assessed by a motion capture system.

BackgroundAnkylosing spondylitis (AS) is a chronic inflammatory disease which causes a reduction in the patient mobility. Several studies show that, at radiological level, structural damage is much higher in men....

Low-cost scheme for high-precision dual-wavelength laser metrology

A method capable of delivering relative optical path length metrology with nanometer precision is demonstrated. Unlike conventional dual-wavelength metrology, which employs heterodyne detection, the method developed in this work utilizes direct detection of interference fringes of two He-Ne lasers as well as a less precise stepper motor open-loop position control system to perform its measurement. Although the method may be applicable to a variety of circumstances, the specific application in which this metrology is essential is in an astrometric optical long baseline stellar interferometer dedicated to precise measurement of stellar positions. In our example application of this metrology to a narrow-angle astrometric interferometer, measurement of nanometer precision could be achieved without frequency-stabilized lasers, although the use of such lasers would extend the range of optical path length the metrology can accurately measure. Implementation of the method requires very little additional optics or electronics, thus minimizing the cost and effort of implementation. Furthermore, the optical path traversed by the metrology lasers is identical to that of the starlight or science beams, even down to using the same photodetectors, thereby minimizing the noncommon path between metrology and science channels.

In-plane displacement measurement in vortex metrology by synthetic network correlation fringes

Recently we proposed an alternative method of displacement analysis in vortex metrology, based on the application of the Fourier optics techniques, that is suitable for an intermediate range of displacement measurements ranging below the resolution of speckle photography and above that of the conventional vortex metrology. However, for smaller displacements, we introduce an approach to perform the Fourier analysis from vortex networks. In this work, we present an enhanced method for measuring uniform in-plane displacements, taking advantage of the capability of determining the subpixel locations of vortices and having the ability to track the homologous vortices onto a plane. It is shown that high-quality fringe systems can be synthesized and analyzed to accurately measure in an extended range of displacements and for highly decorrelated speckle patterns. Experimental results supporting the validity of the method are presented and discussed.

Applications of advanced metrology techniques for the characterization of extreme ultraviolet mask blank defects

Characterization of defects and their sources is essential for developing mitigation solutions to support the production of defect-free extreme ultraviolet (EUV) mask blanks. The characterization of sub-100-nm defects pose challenges to the conventional metrology techniques, such as atomic force microscopy and scanning electron microscopy, limiting mitigation of nanoscale defects. SEMATECH’s Mask Blank Development Center houses advanced metrology capabilities that include transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) to address these shortcomings. Scanning TEM was used to study the disruption of the Mo/Si multilayer of phase defects and to perform elemental analysis with energy dispersive x-ray spectroscopy that has supported projects including substrate smoothing activities, deposition simulation development, and defect printability studies. The Auger instrument was used to create elemental maps for defect identification and to characterize the ion beam deposition tool. Using advanced metrology, mitigation of small defects is being realized, yielding mask blanks with defect counts as low as eight defects at 50-nm sensitivity (Lasertec M7360 SiO 2 sphere equivalent) measured over the quality area of 132×132 mm 2 . The issues with the metrology of increasingly small EUV mask blank defects will be outlined, and comprehensive defect characterization results using TEM and AES will be presented.

Speckle decorrelation influence on measurements quality in vortex metrology

We study speckle decorrelation effects in connection with conventional vortex metrology techniques. Our proposal is based on processing speckled images recorded by using two different experimental set-ups. In both schemes two laterally displaced patterns are generated: one scheme allows for obtaining undecorrelated speckle distributions and the other for decorrelated ones. Vortex networks associated with speckle patterns are analyzed by employing the usual tools developed for vortex metrology. For each recorded image, a 2D pseudo-phase map is generated on the basis of the Reisz transform. Then the vortices are located, and parameterized in terms of their topological charge, eccentricity, vorticity and angles between the zero crossing lines from the real and the imaginary parts of the analytical signal. After tracking the homologous vortices onto the maps, the histograms corresponding to the coordinate displacements are analyzed. We show that histograms interpretation is prone to failure due to its high sensitivity to decorrelation. Experimental evidences are presented to support the restrictions imposed by decorrelation of actual speckles due to uniform in-plane displacements.

Assessment of spinal mobility in ankylosing spondylitis using a video-based motion capture system

This paper describes the use of a video-based motion capture system to assess spinal mobility in patients with ankylosing spondylitis (AS). The aim of the study is to assess reliability of the system comparing it with conventional metrology in order to define and analyze new measurements that reflect better spinal mobility. A motion capture system (UCOTrack) was used to measure spinal mobility in forty AS patients and twenty healthy subjects with a marker set defining 33 3D measurements, some already being used in conventional metrology. Radiographic studies were scored using the modified Stoke Ankylosing Spondylitis Spine Score index (mSASSS). Test–retest reliability studies were performed on the same day and over a two-week period. Motion capture shows very high reliability with Intraclass Correlation Coefficient values ranging from 0.89 to 0.99, low Standard Error of the Measurement (0.37–1.33 cm and 1.58°–6.54°), correlating very well with the Bath Ankylosing Spondylitis Metrology Index (BASMI) (p < 0.001) and, in some individual measures (cervical flexion, cervical lateral flexion, back inclination, shoulder–hip angle and spinal rotation), with mSASSS (p < 0.01). mSASSS also added significantly to the variance in multivariate linear regression analysis to certain measures (back inclination, cervical flexion and cervical lateral flexion). Quantitative results obtained with motion capture system using the protocol defined show to be highly reliable in patients with AS. This technique could be a useful tool for assessing the outcome of the disease and for monitoring the evolution of spinal mobility in AS patients.

Optical metrology for immersed diffractive multifocal ophthalmic intracorneal lenses

This paper deals with the optical characterization of diffractive multifocal Intra-Corneal Lenses (ICLs) that we have developed in order to correct presbyopia. These diffractive multifocal lenses are made of a very soft material (permeable to oxygen and nutrients), with a thickness smaller than 100 µm and require liquid immersion. As a consequence, most of the conventional metrology methods are unsuited for their characterization. We developed specific setups to measure diffractive efficiencies and Modulation Transfer Function (MTF) adapted to such components. Experimental results are in good agreement with Zemax® simulations. For the best of our knowledge, it is the first time that optical characterization is devoted to the ICLs. Furthermore, most of the IOL’s optical characterizations are focused on far vision MTF and don’t assess the near vision MTF, which we study in this paper.

Enabling Scatterometry as an In-Line Measurement Technique for 32 nm BEOL Application

Conventional metrology tools are unable to precisely monitor some interconnect attributes such as trench sidewall angle either due to limited capability or excessive cycle time. But these attributes have great impact on interconnect performance for 32 nm technology node and beyond. Scatterometry, a non-destructive metrology technique, is proposed to address the shortcomings of current metrology tools while also potentially providing additional measurement capabilities that enable more comprehensive characterization of interconnect attributes. Enabling scatterometry for back-end-of-line metrology at 32 nm technology node is challenged by the inherent complexity of a multilayer film structure. The research reported describes the implementation of scatterometry measurements to explore the advantages of this technique for the 32 nm technology node. The results obtained demonstrate the superiority of scatterometry techniques over conventional semiconductor metrology tools such as throughput, process control capability, precision, and accuracy. The total measurement uncertainty of scatterometry results with tunneling electron microscope and cross-sectional scanning electron microscope results for line height shows 1.92 and 6.46 nm, respectively, which compare favorably to the reference metrology tools. Scatterometry techniques also exhibited impressive potential to estimate end-of-the-line electrical parametric data. Finally, physical dimensions obtained from scatterometry measurements are shown to be comparable to TEM results from product wafers.

The operational evaluation of an inertial navigation technique for the provision of underwater metrology surveys

Early in 2008 Total through a regional operating company, Total Exploration Production Congo (TEPC), placed an operational survey contract with a vendor for the purposes of evaluating inertial technology, as applied to the offshore metrology survey application. This contract required the vendor to supply both conventional metrology survey services as well as inertial metrology survey services. The aim was to see if the inertial technology can be demonstrated to be:

Critical dimension scanning electron microscope local overlay measurement and its application for double patterning of complex shapes

We have developed a new local overlay measurement technique on actual device patterns using a critical dimension scanning electron microscope (CD-SEM), which can be applied to two-dimensional (2D) device structures such as a static random access memory contact hole array. CD-SEM overlay measurement can provide additional local overlay information at the site of device patterns, complementary to the optical overlay. The methodology includes the use of pattern symmetry to cancel out many process effects and reduce measurement uncertainty. CD-SEM overlay metrology was compared with conventional optical overlay metrology in terms of measurement uncertainty and overlay model analysis, and very good correlation was confirmed. The developed methodology was applied to local overlay measurement of double patterning contact hole layers of leading edge devices. The local overlay distribution was obtained across the device area, and spatial correlation of the overlay error vectors was examined over a large range of distances. The applications of CD-SEM overlay metrology were explored, and methodologies were introduced to examine both the overlay of double patterning contacts at the edge of an array and lithographic process-induced overlay shift of contacts. Finally, a hybrid optical CD-SEM overlay metrology was introduced in order to capture a high order, device weighted overlay response.

Acoustic Intensity Imaging Methods for in-situ Wave Propagation

In the paper the author has described the visualization methods in acoustic flow fields and show how these methods may assist scientists to gain understanding of complex acoustic energy flow in real-life field. A graphical method will be presented to determine the real acoustic wave distribution in the flow field. Visualization of research results, which is unavailable by conventional acoustics metrology, may be shown in the form of intensity streamlines in space, as a shape of floating acoustic wave and intensity isosurface in three-dimensional space. In traditional acoustic metrology, the analysis of acoustic fields concerns only the distribution of pressure levels (scalar variable), however in a real acoustic field both the scalar (acoustic pressure) and vector (the acoustic particle velocity) effects are closely related. Only when the acoustic field is described by both the potential and kinetic energies, we may understand the mechanisms of propagation, diffraction and scattering of acoustic waves on obstacles, as a form of energy image. This attribute of intensity method can also validate the results of CFD/CAA numerical modeling which is very important in any industry acoustic investigations.

High precision surface metrology using a phase retrieval method

At wavelength metrology offers a unique opportunity to characterize ultra high quality optics of diffraction limited performance. This technique is based on a coherent interaction of incident wave fields reflected from different surface positions. The mirror surface acts as a phase object which introduces a phase error in the outgoing wave fields. Resultant aberrated wavefront modulates the intensity near the focal plane. The modulated intensity profile can be used to retrieve the mirror shape profile using a numerical phase retrieval method which is developed in the present work. This at-wavelength metrology gives a precise shape information of a mirror having a figure error < 1nm which is extremely difficult to measure with conventional metrology tools.

Parametric boundary reconstruction algorithm for industrial CT metrology application

High-energy X-ray computed tomography (CT) systems have been recently used to produce high-resolution images in various nondestructive testing and evaluation (NDT/NDE) applications. The accuracy of the dimensional information extracted from CT images is rapidly approaching the accuracy achieved with a coordinate measuring machine (CMM), the conventional approach to acquire the metrology information directly. On the other hand, CT systems generate the sinogram which is transformed mathematically to the pixel-based images. The dimensional information of the scanned object is extracted later by performing edge detection on reconstructed CT images. The dimensional accuracy of this approach is limited by the grid size of the pixel-based representation of CT images since the edge detection is performed on the pixel grid. Moreover, reconstructed CT images usually display various artifacts due to the underlying physical process and resulting object boundaries from the edge detection fail to represent the true boundaries of the scanned object. In this paper, a novel algorithm to reconstruct the boundaries of an object with uniform material composition and uniform density is presented. There are three major benefits in the proposed approach. First, since the boundary parameters are reconstructed instead of image pixels, the complexity of the reconstruction algorithm is significantly reduced. The iterative approach, which can be computationally intensive, will be practical with the parametric boundary reconstruction. Second, the object of interest in metrology can be represented more directly and accurately by the boundary parameters instead of the image pixels. By eliminating the extra edge detection step, the overall dimensional accuracy and process time can be improved. Third, since the parametric reconstruction approach shares the boundary representation with other conventional metrology modalities such as CMM, boundary information from other modalities can be directly incorporated as prior knowledge to improve the convergence of an iterative approach. In this paper, the feasibility of parametric boundary reconstruction algorithm is demonstrated with both simple and complex simulated objects. Finally, the proposed algorithm is applied to the experimental industrial CT system data.

Thin film characterization by total reflection x-ray fluorescence

Sensitive and accurate characterization of films thinner than a few nm used in nanoelectronics represents a challenge for many conventional production metrology tools. With capabilities in the 10 10 at/cm 2, methods usually dedicated to contamination analysis appear promising, especially Total-reflection X-Ray Fluorescence (TXRF). This study shows that under usual configuration for contamination analysis, with incident angle smaller than the critical angle of the substrate, TXRF signal saturation occurs very rapidly for dense films (below 0.5 nm for HfO 2 films on Si wafers using a 9.67 keV excitation at 0.5°). Increasing the incident angle, the range of linear results can be extended, but on the other hand, the TXRF sensitivity is degraded because of a strong increase of the measurement dead time. On HfO 2 films grown on Si wafers, an incident angle of 0.32° corresponding to a dead time of 95% was used to achieve linear analysis up to 2 nm. Composition analysis by TXRF, and especially the detection of minor elements into thin films, requires the use of a specific incident angle to optimize sensitivity. Although quantitative analyses might require specific calibration, this work shows on Co–based films that the ratio between minor elements (W, P, Mo) and Co taking into account their relative sensitivity factors is a good direct reading of the composition.

Review of MEMS metrology solutions

This paper serves as a review of current solutions for MEMS metrology. This survey provides an extensive and in-depth review of the current tools and their fundamental limitations. Techniques that are reviewed include tools that are extensions of semiconductor tools, scaled down versions of conventional metrology tools and entirely novel methods for MEMS inspection.

Metrology for ITER assembly

The overall dimensions of the ITER Tokamak and the particular assembly sequence preclude the use of conventional optical metrology such as mechanical jigs and traditional dimensional control equipment used for the assembly of smaller, previous generation, fusion devices. This paper describes the state of the art of the capabilities of available metrology systems, with reference to the previous experience in fusion engineering and in other industries. Two complementary procedures of transferring datums from the primary datum network on the bioshield to the secondary datums inside the VV with the desired accuracy of about 0.1 mm is described, one method using the access directly through the ports and the other using transfer techniques, developed during the co-operation with ITER/EFDA. Another important task described is the development of a method for the rapid and easy measurement of the gaps between sectors, required for the production of the customised splice plates between them. The results from a practical, full-scale demonstration of the methodologies used, using the proposed equipment, is described. This work has demonstrated the feasibility of achieving the necessary accuracies for the successful construction of ITER.

Evaluation of producer’s and consumer’s risks in scatterometry and scanning electron microscopy metrology for inline critical dimension metrology

Measurement characteristics in scatterometry and critical dimension-scanning electron microscopy (CD-SEM) for lot acceptance sampling of inline CD metrology were investigated by using a statistical approach with Monte Carlo simulation. By operation characteristics curve analysis, producer's risk and consumer's risk arising from sampling were clarified. Single use of scatterometry involves a higher risk, such risk being particularly acute in the case of large intrachip CD variation because it is unable to sufficiently monitor intrachip CD variation including local CD error. Substituting scatterometry for conventional SEM metrology is accompanied with risks, resulting in the increase of unnecessary cost. The combined use of scatterometry and SEM metrology in which the sampling plan for SEM is controlled by scatterometry is a promising metrology from the viewpoint of the suppression of risks and cost. This is due to the effect that CD errors existing in the distribution tails are efficiently caught.

Differentiation of the surface topographies of pharmaceutical excipient compacts

The comparison of conventional surface metrology and area-scale fractal parameters to differentiate the surface topography of pharmaceutical excipient compacts and preliminary investigation of scale-based correlations with excipient properties were performed. The determination and selection of the most appropriate surface topography parameters is important in optimizing the design and quality of industrial processes and products. The surfaces of three types of excipient compacts (microcrystalline cellulose (MCC), spray dried lactose (SDL), and dibasic calcium phosphate dihydrate (DCPD)) were characterized with a non-contact optical surface profilometer. A statistical F-test matrix was used to rank and quantify the ability of conventional surface texture parameters: Sa, Sq, St, Ssk, Sku, and the fractal parameters: relative area, Asfc (complexity) and SRC (smooth–rough crossover), to differentiate the surfaces of the compacts. Based on this statistical analysis and area-scale plots generated from profilometer data, it was found that most of the conventional parameters were suitable for distinguishing the surfaces. The F-test applied to the relative areas as a function of scale also indicated the ranges of scales over which the differentiation was possible. MCC–SDL and DCPD–SDL material pairs were able to be differentiated between scales of 10 and 10,000 μm 2, however, MCC–DCPD pairs were only differentiable between 300 and 2000 μm 2. A new method was established for illustrating the scale-based correlations, using the product of the regression coefficient and the normalized slope. The correlations between the fractal parameters and the properties of the excipients, including brittle fracture and indentation hardness, gave plausible explanations for the similarities between certain excipients, supporting a phenomenological understanding of the behavior of excipient compacts and their surfaces.

Optical vortex metrology for nanometric speckle displacement measurement

As an alternative to correlation-based techniques widely used in conventional speckle metrology, we propose a new technique that makes use of phase singularities in the complex analytic signal of a speckle pattern as indicators of local speckle displacements. The complex analytic signal is generated by vortex filtering the speckle pattern. Experimental results are presented that demonstrate the validity and the performance of the proposed optical vortex metrology with nano-scale resolution.

Carbon nanotube tips for scanning probe microscopy: fabrication and high aspect ratio nanometrology

The atomic force microscope (AFM) is being adapted by industry as a tool for in line fabrication metrology. The last two decades have witnessed the evolution of the AFM into a versatile instrument, with many new scanning force techniques presently being developed. Consequently, the AFM has wide industrial applications from conventional surface roughness measurement of thin films to the characterization of magnetic domains as related to the information storage industry. There are a number of challenges that must be resolved in order to fully realize the potential of AFM as future nanoscale inspection tools for the information technology industry. Improvement in AFM tip technology is one of the most important factors for AFM to be fully adapted by industry. This paper reviews the development and application of carbon nanotube AFM tips, highlighting the progress from our lab. Many applications for carbon nanotube AFM tips have been demonstrated for scanning probe microscopy; however, herein we focus mainly on the measurement of high aspect ratio nanostructures. The structure of carbon nanotubes will be described in relationship to the application of the AFM tip. Fabrication techniques for carbon nanotube AFM probes will be highlighted, including an example detailing a high throughput large-scale production method. Data demonstrating the capability of carbon nanotube tips for imaging high aspect ratio features will be compared with conventional top-down SEM metrology. This review will also address some of the technical challenges that still remain for the full implementation of carbon nanotube AFM tip technology for industrial applications.