Metrological Scanning Research Articles

Investigation of SiO2 thin films on Si substrates for use as standards for laser-acoustic measuring devices

Abstract We report on an investigation of the suitability of SiO2 thin films for use as calibration standards for the measurement of elastic modulus by laser-acoustic measuring devices. Film thicknesses for a range of thin film standards, originally developed for the calibration of ellipsometers, were obtained by X-ray reflectometry, ellipsometry, and metrological scanning force microscopy. Using the calibrated values of film thickness, a laser-acoustic method was used to obtain the elastic moduli of the thin films. Nanoindentation of the films, performed at two different laboratories was used to provide an independent measure of the elastic modulus values. The modulus values determined by nanoindentation and the laser-acoustic method were found to agree within 4.6 %, which was within the calculated uncertainty of the measurements performed. As a result of their high homogeneity with respect to film thickness and elastic modulus, their low surface roughness and the good laser-acoustic signal quality, the thin films investigated appear to hold promise as standards for laser-acoustic measuring devices.

Characterization of a nano line width reference material based on metrological scanning electron microscope

The line width (often synonymously used for critical dimension, CD) is a crucial parameter in integrated circuits. To accurately control CD values in manufacturing, a reasonable CD reference material is required to calibrate the corresponding instruments. We develop a new reference material with nominal CDs of 160 nm, 80 nm, and 40 nm. The line features are investigated based on the metrological scanning electron microscope which is developed by the National Institute of Metrology (NIM) in China. Also, we propose a new characterization method for the precise measurement of CD values. After filtering and leveling the intensity profiles, the line features are characterized by the combination model of the Gaussian and Lorentz functions. The left and right edges of CD are automatically extracted with the profile decomposition and k-means algorithm. Then the width of the two edges at the half intensity position is regarded as the standard CD value. Finally, the measurement results are evaluated in terms of the sample, instrument, algorithm, and repeatability. The experiments indicate efficiency of the proposed method which can be easily applied in practice to accurately characterize CDs.

Non-equidistant scanning path generation for the evaluation of surface curvature in metrological scanning probe microscopes

In this paper, we present a novel geometry information-based adaptive step (non-equidistance) scanning path generation method for metrological scanning probe microscopes. This method reduces the total amount of required data and enables faster surface scanning speed for large industrial workpieces while preserving adequate geometric information for performance evaluation after surface reconstruction. The grid points are generated iteratively while gaining knowledge of the surface geometry step by step. We focus on the curvature properties and then propose a metric for the curvature information based on the triangulated surface geometry. With certain convergence criteria on the curvature measure variation, the proposed methods promise better surface reconstruction completeness and performance evaluation correctness. Simulations on the algorithm are performed on a typical parametric surface. A brief comparison to height-based scanning algorithm is performed to show the adaptability of the novel method on curvature evaluation. Experimental verifications are conducted to show the efficiency of the proposed algorithm.

Local geometric error corrections for a metrological scanning probe microscope

A local geometric error correction method is developed for a metrological scanning probe microscope. The method corrects geometric errors in stage displacements using the interferometric measurements of angular position and known geometric offsets. Local and global error correction methods are considered and general scaling dependences on the number of measured steps or points are derived and compared. For the local method, the total uncertainty scales the same or decreases with a sufficient number of measurement steps compared with the global method. Implementation of the local geometric error correction method is demonstrated on measurements of a three-dimensional height standard artefact. The applied error correction method reduces the contribution of geometric errors to the uncertainty budget by two orders of magnitude. The presented approach can be extended to any scanning technique where a measurement translation mechanism can be identified and accurately quantified by relating the measured values with a measurand.

计量型扫描电子显微镜成像的微纳米级振动

计量型扫描电子显微镜成像的微纳米级振动

Gwyscan: a library to support non-equidistant scanning probe microscope measurements

We present a software library and related methodology for enabling easy integration of adaptive step (non-equidistant) scanning techniques into metrological scanning probe microscopes or scanning probe microscopes where individual x, y position data are recorded during measurements. Scanning with adaptive steps can reduce the amount of data collected in SPM measurements thereby leading to faster data acquisition, a smaller amount of data collection required for a specific analytical task and less sensitivity to mechanical and thermal drift. Implementation of adaptive scanning routines into a custom built microscope is not normally an easy task: regular data are much easier to handle for previewing (e.g. levelling) and storage. We present an environment to make implementation of adaptive scanning easier for an instrument developer, specifically taking into account data acquisition approaches that are used in high accuracy microscopes as those developed by National Metrology Institutes. This includes a library with algorithms written in C and LabVIEW for handling data storage, regular mesh preview generation and planning the scan path on basis of different assumptions. A set of modules for Gwyddion open source software for handling these data and for their further analysis is presented. Using this combination of data acquisition and processing tools one can implement adaptive scanning in a relatively easy way into an instrument that was previously measuring on a regular grid. The performance of the presented approach is shown and general non-equidistant data processing steps are discussed.

Traceable Quantitative Raman Microscopy and X-ray Fluorescence Analysis as Nondestructive Methods for the Characterization of Cu(In,Ga)Se2 Absorber Films.

The traceability of measured quantities is an essential condition when linking process control parameters to guaranteed physical properties of a product. Using Raman spectroscopy as an analytical tool for monitoring the production of Cu(In1-xGax)Se2 thin-film solar cells, proper calibration with regard to chemical composition and lateral dimensions is a key prerequisite. This study shows how the multiple requirements of calibration in Raman microscopy might be addressed. The surface elemental composition as well as the integral elemental composition of the samples is traced back by reference-free X-ray fluorescence analysis. Reference Raman spectra are then generated for the relevant Cu(In1-xGax)Se2 related compounds. The lateral dimensions are calibrated with the help of a novel dimensional standard whose regular structures have been traced back to the International System of Units by metrological scanning force microscopy. On this basis, an approach for the quantitative determination of surface coverage values from lateral Raman mappings is developed together with a complete uncertainty budget. Raman and X-ray spectrometry have here been proven as complementary nondestructive methods combining surface sensitivity and in-depth information on elemental and species distribution for the reliable quality control of Cu(In1-xGax)Se2 absorbers and Cu(In1-xGax)3Se5 surface layer formation.

A Traceable Metrological Method with Nanometer Scale Resolution for Micro-Structure

Micro-structure dimension metrology is a grand challenge to current metrological methods and tools. In this paper, a retraceable metrological scanning electron microscopy (M-SEM) system with precision stage and laser interferometer is presented in detail. The double stages structure is used to realize both sample positioning in 50mm×50mm range and accuracy imaging in several tens of micron scale. In order to acquiring metrological scanning image, the control system based on digital signal processing (DSP) is constructed. Furthermore, this paper focuses on demonstrating a metrological SEM image edge detection algorithm which is the essential part of the metrological SEM system to realize the traceable metrology of line width.

Micron and Nanometer Measuring Methods Based on Metrological Scanning Electron Microscope

Micron and nanometer dimensional metrology is an important part of integrated circuits manufacturing system and nanofabrication research work. Semiconductor device feature size has shrunk from the micron to dozen of nanometers. How to watch the micro structure clearly, identify its edge, and measure its dimension accurately are the major issues that need to be research. In this paper, a metrological scanning electron microscope (M-SEM) system with precision stage and laser interferometer is presented. Furthermore, this paper focuses on demonstrating a metrological SEM image edge detection algorithm which is the essential part of the metrological SEM system to realize the measurement of line width. The procedure of the algorithm is that SEM image is first analyzed by noise type according to the histogram characteristics. Then the image noise is reduced by specific filters. Furthermore, a specific interesting object image region is selected and pixel gray level values of the region are obtained by line scan. SEM image edges are determined by the characteristic of the pixel information in two possible cases. This algorithm preserves the edge details of the original image and detects the image edge automatically in an easy and fast way.

Multifunctional nanoanalytics and long-range scanning probe microscope using a nanopositioning and nanomeasuring machine

An interferometer-based metrological scanning probe microscope (SPM) is successfully integrated into our nanopositioning and nanomeasuring machine (NPM machine) for high-precision measurements with nanometre uncertainty over a range of 25 mm × 25 mm × 5 mm. Both devices were developed at the Institute of Process Measurement and Sensor Technology of Ilmenau University of Technology, Germany. Outstanding results were achieved for different measurement tasks. With the NPM machine, truly long-range and long-term measurements are possible. Due to the tip wear, an automatic SPM cantilever replacement is preferable. Such a tip replacement is also required for the integration of multifunctional nanoanalytics. For example, for Kelvin probe force microscopy (KPFM), the measurement of topography and surface potential with different SPM tips is necessary. For this purpose, an electromagnetic tip changer was designed. The tip changer comprises three SPM probes. In order to retrieve the previous tip positions, additional fiducial marks were developed. The repeatability of relocation is less than 10 nm. The automatic tip changer and fiducial marks are integrated into a sample holder. The tip changer in combination with fiducial marks allows scanning distances three times longer (with the same type of SPM probes) and multifunctional nanoanalytics (with different SPM probes with special properties). Sample KPFM measurements are demonstrated. The developed tip changer, including special fiducial marks, improves the performance and functionality of the NPM machine crucially.

Investigation into sources of random uncertainties in the NanoScan-3Di metrological scanning probe microscope

The construction and operation principle of the metrological NanoScan-3Di scanning probe microscope (SPM) are briefly described. This device is a combination of a commercial NanoScan-3D SPM and a three-coordinate heterodyne laser interferometer. The metrological characteristics and main sources of random uncertainties of this measurement complex have been analyzed. The experiments have demonstrated high reproducibility and low noise level when measuring linear displacements on the nanometer-length scale.

Large-scale shape measurement by a combined method based on three instruments

The accuracy of optical three-dimensional metrology scanning decreases as the size of the parts for inspection increase to several tens of meters because of accumulated errors. A combined method that includes coordinate and surface metrology is proposed. The method features the use of a laser tracker, photogrammetric system, and a hand-held scanner that identifies fiducials. Each instrument provides a distinct measurement density of point data and ranges which are complementary to each other. The laser tracker is used to position and orient the scanner within a large volume, thus, to ensure accurate measurement, the data captured in the respective sensors' coordinate system is aligned to a common global coordinate system. Close-range photogrammetry is used to improve the speed with which fiducials are measured. The measurements obtained, using the photogrammetric system and laser tracker, are combined to produce highly accurate measurements of part surfaces. The performance, of the combined measurement systems, is verified by measuring calibrated lengths. Results show that the proposed technique enables quick measurement and yields submillimeter accuracy in measuring the absolute distance up to the laser tracker range. Error accumulation is therefore avoided.

Metrological scanning probe microscope based on a quartz tuning fork detector

We give an overview of the design of a metrological scanning probe microscope (mSPM) currently under development at the National Measurement Institute Australia (NMIA) and report on preliminary results on the implementation of key components. The mSPM is being developed as part of the nanometrology program at NMIA and will provide the link in the traceability chain between dimensional measurements made at the nanometer scale and the realization of the International System of Units (SI) meter at NMIA. The instrument is based on a quartz tuning fork (QTF) detector and will provide a measurement volume of 100 μm×100 μm×25 μm with a target uncertainty of 1 nm for the position measurement. Characterization results of the nanopositioning stage and the QTF detector are presented along with an outline of the method for tip mounting on the QTFs. Initial imaging results are also presented.

Novel control scheme for a high-speed metrological scanning probe microscope

Some time ago, an interferometer-based metrological scanning probe microscope (SPM) was developed at the Institute of Process Measurement and Sensor Technology of the Ilmenau University of Technology, Germany. The specialty of this SPM is the combined deflection detection system that comprises an interferometer and a beam deflection. Due to this system it is possible to simultaneously measure the displacement, bending and torsion of the probe (cantilever). The SPM is integrated into a nanopositioning and nanomeasuring machine (NPM machine) and allows measurements with a resolution of 0.1 nm over a range of 25 mm × 25 mm × 5 mm. Excellent results were achieved for measurements of calibrated step height and lateral standards and these results are comparable to the calibration values from the Physikalisch-Technische Bundesanstalt (PTB) (Dorozhovets N et al 2007 Proc. SPIE 6616 661624–1–7). The disadvantage was a low attainable scanning speed and accordingly large expenditure of time. Control dynamics and scanning speed are limited because of the high masses of the stage and corner mirror of the machine. For the vertical axis an additional high-speed piezoelectric drive is integrated in the SPM in order to increase the measuring dynamics. The movement of the piezoelectric drive is controlled and traceable measured by the interferometer. Hence, nonlinearity and hysteresis in the actuator do not affect the measurement. The outcome of this is an improvement of the bending control of the cantilever and much higher scan speeds of up to 200 µm s−1.

Uncertainty modeling in nanoscale scanning probe microscopy measurements of fullerene C60

Nanoscale dimensional measurements are very often focused on small objects formed by only a few atomic layers in one or more dimensions. The classical convolution approach to tip–sample artifacts cannot be, on its own, sufficient for these specimens due to their quantum-mechanical nature. With growing resolution of specialized metrology scanning probe microscopes and increasing requirements of exact measurements in nanoscale range, it is necessary to make a transition from the classical picture to a quantum approach on the field of uncertainty analysis. In this paper, sources of uncertainty connected with tip–sample relaxation at the atomic level are discussed. Results of density functional theory modeling (using the tight-binding approximation software FIREBALL) of AFM scans on fullerenes are presented. In our approach we model the tip apex and the sample as systems of individual atoms. As interatomic forces act on the sample and the tip of the microscope, the atoms of both relax in order to reach equilibrium positions. This leads to changes in those quantities that are finally interpreted as the ‘atomic force microscope (AFM) tip position’ and influences the resultant dimensional measurements. The results from modeling are compared to the experimental results found in the literature.

Bilateral comparison of 25 nm pitch nanometric lateral scales for metrological scanning probe microscopes

One-dimensional (1D) and two-dimensional (2D) gratings are some of the most important transfer standards for the calibration of nanometrological instruments. National Metrology Institutes (NMIs) demonstrate their calibration capability through international comparisons among themselves and provide pitch calibration services for their customers. In the past, international comparisons were performed three times for gratings with large pitches such as 4000 nm, 1000 nm, 700 nm and 300 nm. Additionally, a bilateral comparison was conducted for 100 nm and 50 nm between the Japanese National Metrology Institute (NMIJ) and the German National Metrology Institute (PTB). The industry, however, requires calibration services for increasingly smaller pitches. In a previous study, NMIJ developed a nanometric lateral scale, a special 1D grating with 25 nm pitch consisting of Si/SiO2 multilayer thin-film structures, and calibrated the pitch of this scale by using the NMIJ's atomic force microscope equipped with differential laser interferometers (DLI-AFM). In this paper, we will report results of an informal bilateral comparison for the nanometric lateral scale between NMIJ and PTB.

Construction and evaluation of a traceable metrological scanning tunnelling microscope

Scanning tunnelling microscopy enables for imaging of conductive surfaces with a resolution down to the atomic level. However, virtually all commercial scanning tunnelling microscopes use piezo tube scanners and capacitance gauges what limits the operating range to typically less than 100 μm in the scanning axes and 10 μm in probing direction. Traceability of measured dimensions to the length unit metre can only be ensured by frequent calibration with the help of standards for pitch and step height. To improve the metrological characteristics of the measurement technique scanning tunnelling microscopy and to broaden its field of application, a directly traceable long range metrological scanning tunnelling microscope was set-up using a laser-interferometrically controlled nanopositioning unit with an operating range of 25 · 25 · 5 mm 3 as scanner and a passive tunnelling current measuring probing system as a null indicator. Line scan repeatability of 5 nm has been achieved at 1 nm vertical resolution.

Traceable Nanometrology Realized by Means of Nanopositioning and Nanomeasuring Machine

The today’s nanometrology limits the accuracy of the precision engineering. These limits are based on the meter definition as redefined in 1983. It is proposed to define precision mechatronics as the science and engineering of high level precision systems and machines. The paper describes a precision mechatronic machine. This device represents a long range positioning machine having a resolution of 0.1 nm over the range of 25 mm x 25 mm x 5 mm. The integration of several optical and tactile nanoprobes makes the 3D-nanopositioning suitable for various tasks. New developed nanoprobes (optical focus probe, nanoindenter, metrological scanning force microscope) and results of measurement will be presented.

Nanoscaling of Microdomain Spacings in Thin Films of Cylinder-Forming Block Copolymers

We present first quantitative measurements of the characteristic lateral dimensions in thin films of cylinder-forming block copolymers. Using a metrological scanning force microscope and tailor-made image analysis, we map out lateral distances with subnanometer accuracy. Microdomain spacings change in a systematic way as a function of the film thickness and as a function the lateral cylinder bending. We show that in very thin films the unit cell is stretched perpendicular to the plane of the film resulting in lateral distances smaller than those in bulk. The changes are distinct, although small, and can be rationalized within the framework of the strong segregation theory of block copolymers.

Investigation of SiO2 thin films on Si substrates for use as standards for laser-acoustic measuring devices

Abstract We report on an investigation of the suitability of SiO2 thin films for use as calibration standards for the measurement of elastic modulus by laser-acoustic measuring devices. Film thicknesses for a range of thin film standards, originally developed for the calibration of ellipsometers, were obtained by X-ray reflectometry, ellipsometry, and metrological scanning force microscopy. Using the calibrated values of film thickness, a laser-acoustic method was used to obtain the elastic moduli of the thin films. Nanoindentation of the films, performed at two different laboratories was used to provide an independent measure of the elastic modulus values. The modulus values determined by nanoindentation and the laser-acoustic method were found to agree within 4.6%, which was within the calculated uncertainty of the measurements performed. As a result of their high homogeneity with respect to film thickness and elastic modulus, their low surface roughness and the good laser-acoustic signal quality, the thin films investigated appear to hold promise as standards for laser-acoustic measuring devices.