Step Height Standards Research Articles

A Reflected-Light-Mode Multiwavelength Interferometer for Measurement of Step Height Standards.

The article is dedicated to measuring the thickness of step height standards using the author's version of the variable wavelength interferometer (VAWI) in the reflected-light mode, where the interference pattern is created by the combination of two Wollaston prisms. The element of novelty consists in replacing the traditional search for the coincidence of fringes in the object and background with a continuous measurement of their periods and phases relative to the zero-order fringe. The resulting system of sinusoids is then analyzed using two methods: the classical one and the second utilizing the criterion of uniform thickness. The theory is followed by simulation and experimental parts, providing insight to the metrological potential of the VAWI technology.

Precise lateral measurements of step height standards using Hamming area model

Since the ISO 5436 profile analysis presents the axial measurements of the step height/depth standards and does not present a direct method for the lateral measurements, a new method based on the Hamming area model for the lateral measurements of step height/depth standards is presented. The basic idea of the method is to mimic the experimental profile of the step height/depth by a combination of the Hamming window pass-band filter and the RMS model. The lateral position of the 50 % height/depth value of the mimicked Hamming height/depth is assigned. The areas up and down the assigned value are then computed and compared for the lateral measurements of the step height/depth standard. The method is applied for the lateral measurements of a groove structure of a transparent step depth standard. The results show that the total area included in the right line edge of the groove structure is greater than the total area included in the left line edge by 151.66 nm. The error in area measurement is computed to be 1.7 %. The proposed method can be applied to any step height/depth regardless of its height/depth, width, and sharpness of the line edges.

Self-elimination of phase noise in coherence scanning interferometry for nano-scale measurement

Coherence scanning interferometry (CSI) has been a powerful non-contact technique. In this work, a novel surface recovery algorithm based on phase noise self-correction is proposed for nano-scale measurements. Through spectrum analysis, the surface height is coarsely retrieved from the linear relationship between phase and angular wavenumber. Afterwards, the phase noise is modeled, and a correction array is designed to compensate the noises in surface height. A coefficient is defined to assess the accuracy of correction array, then the surface height is automatically corrected with the coefficient minimized. In the experiments, three step height standards are tested to prove the measurement accuracy, and additional comparisons with a commercial white light profiler and an AFM are provided as well to testify the measurement noise level. At last, a nano-scale grids matrix is measured, where the nano-topography is accurately recovered. All investigations have verified the effectiveness of the proposed method in nano-scale measurements.

Multi-mode interferometric measurement system based on wavelength modulation and active vibration resistance.

Optical interferometers are widely used in the measurement of micro- and nanoscale surface topography. However, their accuracy and resolution can be seriously affected by environmental noise. We present a multi-mode interferometric measurement system based on wavelength modulation and active vibration resistance. This supports two measurement modes: wavelength-scanning interferometry, which is suitable for structured surfaces, and wavelength-tuning interferometry, which is suitable for smooth continuous surfaces. In addition, the system can measure the optical path difference of the current position in real time, which is convenient for making system adjustments and improving the measurement accuracy. The proposed system was used to measure 1.806 µm and 43.2 nm step height standards. Under different degrees of vibration, the measured heights in the two modes agreed well with the calibrated values.

Effect analysis of surface metal layer on step height standard

In order to improve the measurement accuracy of the step height measuring instrument, a semiconductor process was used to prepare the step height standard for calibrating the instrument. Aiming at the problem of deviation in the white light interferometer measuring step height standard, the cause of the measurement deviation was theoretically analyzed, combining the optical theory and the principle of instrument. In addition, referring to the semiconductor sputtering process, a method of sputtering metal layer on the surface of the step structure was proposed, and a set of universal step height standards with a nominal value of [Formula: see text] nm were developed for the step height measuring instrument. Finally, the step height standards with the sputtered metal layer were compared and measured, using the white light interferometer and nanometer measuring machine (NMM). The measurement error of the white light interferometer can be effectively controlled within 1%, which is beneficial to verify the measurement capability of the step height measuring instrument.

Performance Analysis of Surface Reconstruction Algorithms in Vertical Scanning Interferometry Based on Coherence Envelope Detection.

Optical interferometry plays an important role in the topographical surface measurement and characterization in precision/ultra-precision manufacturing. An appropriate surface reconstruction algorithm is essential in obtaining accurate topography information from the digitized interferograms. However, the performance of a surface reconstruction algorithm in interferometric measurements is influenced by environmental disturbances and system noise. This paper presents a comparative analysis of three algorithms commonly used for coherence envelope detection in vertical scanning interferometry, including the centroid method, fast Fourier transform (FFT), and Hilbert transform (HT). Numerical analysis and experimental studies were carried out to evaluate the performance of different envelope detection algorithms in terms of measurement accuracy, speed, and noise resistance. Step height standards were measured using a developed interferometer and the step profiles were reconstructed by different algorithms. The results show that the centroid method has a higher measurement speed than the FFT and HT methods, but it can only provide acceptable measurement accuracy at a low noise level. The FFT and HT methods outperform the centroid method in terms of noise immunity and measurement accuracy. Even if the FFT and HT methods provide similar measurement accuracy, the HT method has a superior measurement speed compared to the FFT method.

Final report on supplementary comparison on step heights standards (APMP.L-S7)

Main textThis intercomparison is carried out for step height standards with nominal step sizes 8 nm, 18 nm, 88 nm and 10 µm using non-contact measurement methods, with four participating NMIs. Measurement observation from the pilot laboratory exhibit significant stability of step height standards. For each step height standard, the supplementary comparison reference value (SCRV) is determined using weighted mean, followed by calculation of En values for outlier identification. Further the outliers were excluded based upon the Birge Ratio consistency test. Measurement results from all the participating NIMs have been compiled in this report.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Step height standards based on self-assembly for 3D metrology of biological samples

Modern microscopes and profilometers such as the coherence scanning interferometer (CSI) approach sub-nm precision in height measurements. Transfer standards at all measured size scales are needed to guarantee traceability at any scale and utilize the full potential of these instruments, but transfer standards with similar characteristics upon reflection to those of the measured samples are preferred. This is currently not the case for samples featuring dimensions of less than 10 nm and for biosamples with different optical charasteristics to silicon, silica or metals. To address the need for 3D images of biosamples with traceable dimensions, we introduce a transfer standard with dimensions guaranteed by natural self-assembly and a material that is optically similar to that in typical biosamples. We test the functionality of these transfer standards by first calibrating them using an atomic force microscope (AFM) and then using them to calibrate a CSI. We investigate whether a good enough calibration accuracy can be reached to enable a useful calibration of the CSI system. The result is that the calibration uncertainty is only marginally increased due to the sample.

A robust surface recover algorithm based on random phase noise correction for white light interferometry

White light scanning interferometry is a very important technique for nanometrology. In this paper, a robust white light interference signal processing algorithm using random phase noise correction method is proposed. By analyzing the phase response of the correlgram mathematically, the phase noise is modelized by the combination of random noise and systematic deviation. The random noise can be corrected by assembling the least square result of phase information. As a result, the relationship between phase distribution and surface height is established in a more accurate way. The simulations show that the novel algorithm is capable of achieving robust measurements with standard deviation one tenth comparing to the scanning step length errors, and has an extremely high noise tolerance 14.25 nm with scanning step length 20 nm. In the experiments, a step height standard (VLSI, 182.7 ± 2.0 nm), a protected aluminum mirror and a drive shaft cover of aircraft engine were tested, where the repeatability error for the step height standard is 0.5 nm, the roughness repeatability of the mirror is only 0.03 nm, and the roughness repeatability of the cover is 5.14 nm, which proves the accuracy and robust of the algorithm.

Calibration method of curvature distortion in step height measurement by atomic force microscopy

Atomic force microscopy (AFM) is widely used to characterize the surface topography in nanomaterials and biology research since the high resolution in 3 dimensions. Height measurement is important in the investigation of graphene thickness. Due to some AFMs use tube scanner, the curved scanning distortion will cause height measurement error. Step height standards calibrated by metrological AFM are used to calibrate the Z axis of conventional AFMs. However, for step structure with large width, the method specified in ISO 5436 is not suitable. The distortion of the curvature scanning is discussed for different samples, and for large step width the influence is significant. So the substrate correction method is proposed to eliminate the scanning curvature and the comparison with several other fitting correction methods is also discussed.

Fiber optic white light interferometer for areal surface measurement

White light interferometers (WLI) are extremely powerful tools in the context of areal surface topography instrumentation. With lateral scanning mechanisms, larger objects with trans-scale structures are also measurable. However, the existing commercial WLIs are usually only applicable for off-line measurements in the laboratory. This paper presents a flexible WLI, in which the light source and the vertical scanning mechanism are separated from the interference probe using fiber-optic components. As a result, the interference probe is more compact, and portable for on-machine measurement. Meanwhile, a comprehensive algorithm that combines the improved gravity center method and phase-shifting technique is proposed for signal processing, which can balance computation time and noise robustness. The simulation results show the effectiveness by comparing with the traditional white light scanning interferometry methods. A 1000 nm step height standard was used as a test specimen to evaluate the proposed system and algorithm. The experimental data show that the measurement results are basically in good agreement with the calibrated value.

Atomic force microscope with an adjustable probe direction and piezoresistive cantilevers operated in tapping-mode / Im Tapping-Modus betriebenes Rasterkraftmikroskop mit einstellbarer Antastrichtung und piezoresistiven Cantilevern

Abstract This article presents a new tilting atomic force microscope (AFM) with an adjustable probe direction and piezoresistive cantilever operated in tapping-mode. The AFM is based on two rotational axes, which enable the adjustment of the probe direction to cover a complete hemisphere. The whole setup is integrated into a nano measuring machine (NMM-1) and the metrological traceability of the piezoresistive cantilever is warranted by in situ calibration on the NMM-1. To demonstrate the capabilities of the tilting AFM, measurements were conducted on a step height standard.

Rapid measurement of large step heights using a microscopic white-light spectral interferometer

A method for rapid measurement of large step heights is proposed. Owing to elimination of mechanical scanning processes, this method possesses a greatly reduced measurement time. The theory underlying the proposed method is described in detail. The single-shot spectral interferometric signal is recorded using a Linnik microscopic white-light spectral interferometer and phase information is retrieved using a windowed Fourier transform. The proposed method was used to measure a 10.083(±0.022) μm step height standard. The mean measured height and standard deviation obtained from ten measurements were 10.0827 μm and 2.1 nm, respectively, and the experimental results agreed well with the calibrated value.

Comparison of line width calibration using critical dimension atomic force microscopes between PTB and NIST

International comparisons between National Metrology Institutes are important to verify measurement results and the associated uncertainties. In this paper, we report a comparison of the line width calibration of a crystalline silicon line width standard, referred to as IVPS100-PTB standard, between the Physikalisch-Technische Bundesanstalt in Germany and the National Institute of Standards and Technology in the United States. Critical dimension atomic force microscopy was the measurement method used for this comparison. Both institutes applied generally the same but independently developed traceability pathways: the scaling factor of the atomic force microscope (AFM) scanner was calibrated by a set of step height and lateral standards certified by metrological AFMs, while the effective tip width was ultimately traceable to the lattice parameter of silicon via high resolution transmission electron microscopy. Good agreement has been achieved in the comparison: For two groups of line features with nominal critical dimensions (CDs) of 50 nm, 70 nm, 90 nm, 110 nm and 130 nm that were compared, the observed deviations of CD results were between −1.5 nm and 0.3 nm. The deviations are well within the associated measurement uncertainty.

Step-height standards based on the rapid formation of monolayer steps on the surface of layered crystals

Metrology is essential for nanotechnology, especially for structures and devices with feature sizes going down to nm. Scanning probe microscopes (SPMs) permits measurement of nanometer- and subnanometer-scale objects. Accuracy of size measurements performed using SPMs is largely defined by the accuracy of used calibration measures. In the present publication, we demonstrate that height standards of monolayer step (∼1 and ∼0.6nm) can be easily prepared by cleaving Bi2Se3 and ZnWO4 layered single crystals. It was shown that the conducting surface of Bi2Se3 crystals offers height standard appropriate for calibrating STMs and for testing conductive SPM probes. Our AFM study of the morphology of freshly cleaved (0001) Bi2Se3 surfaces proved that such surfaces remained atomically smooth during a period of at least half a year. The (010) surfaces of ZnWO4 crystals remained atomically smooth during one day, but already two days later an additional nanorelief of amplitude ∼0.3nm appeared on those surfaces. This relief, however, did not further grow in height, and it did not hamper the calibration. Simplicity and the possibility of rapid fabrication of the step-height standards, as well as their high stability, make these standards available for a great, permanently growing number of users involved in 3D printing activities.

Nano step height measurement using an optical method

This paper presents two optical methods for measuring nano step height standards and discusses the deviations in the measurements in detail. A white light interference (WLI) microscope and spinning disk confocal (SDCF) microscope were used in the experiments. The effect of illumination intensity and the standard’s surface reflectivity were studied and analyzed. The surface properties of the step height standard were ameliorated using secondary coating technology. The experimental results demonstrated that the secondary coating technology effectively improved the measurement accuracy of the SDCF microscope. The WLI microscope measured accurately both before and after a secondary coating was applied.

Non-contact on-machine measurement using a chromatic confocal probe for an ultra-precision turning machine

On-machine measurement (OMM) involves the interruption of the machining process and the subsequent measurement of the workpiece without its removal from the machining tool. Chromatic confocal sensing is a well-known measurement technique that is able to evaluate the position of a point on an object surface along the optical axis of the system with high accuracy. The present study integrates a chromatic confocal measurement probe with an ultra-precision diamond turning machine to achieve the non-contact OMM of machined components. The procedure for establishing the position of the rotary axis of the spindle based on dual standard spheres is first described in detail, and the relevant OMM procedure for machined components of different surface topographies is explained. Then, a 50-μm quartz step height standard is employed to investigate the linear measurement accuracy of the chromatic confocal probe. Finally, the measurement accuracy of the proposed OMM method is compared experimentally with that of the stylus method. The results show that the estimated form error value of the OMM method agrees well with the value obtained by the stylus method. The proposed OMM method feasibly achieves non-contact OMM with a nanometer-level accuracy for an ultra-precision turning machine and is capable of reconstructing the 3D surface topography of flat, spherical, and aspheric surfaces. After integrating the OMM method, the ultra-precision turning machine can realize the function of processing-measurement integration.

Manufacturing of new roughness standards for the linearity of the vertical axis – Feasibility study and optimization

In order to provide an alternative for the vertical axis calibration of stylus instruments which is usually performed based on step height standards, a new measurement standard geometry for the calibration of the linearity and research on its manufacturing is needed. For the manufacturing of these geometric measurement standards there is, according to the type of the measurement standard, a broad range of manufacturing processes that can be applied. New measurement standards for the roughness calibration were developed at the University of Kaiserslautern and an ultra-precision turning process was chosen for its manufacturing. The paper presents a feasibility study of the chosen manufacturing process. The aim of the investigations is to present the development of the standard and the qualification of the ultra-precision turning process for the manufacturing of calibration standards. An examination was performed in order to characterize the influences of different process parameters on the quality of the manufactured roughness standard.

High-resolution interferometic microscope for traceable dimensional nanometrology in Brazil

The double color interferometric microscope is developed for step height standards nanometrology traceable to meter definition via primary wavelength laser standards. The setup is based on two stabilized lasers to provide traceable measurements of highest possible resolution down to the physical limits of the optical instruments in sub-nanometer to micrometer range of the heights. The wavelength reference is He-Ne 633 nm stabilized laser, the secondary source is Blue-Green 488 nm grating laser diode. Accurate fringe portion is measured by modulated phase-shift technique combined with imaging interferometry and Fourier processing. Self calibrating methods are developed to correct systematic interferometric errors.

Multi-wavelength phase-shifting interferometry for micro-structures measurement based on color image processing in white light interference

Conventional multi-wavelength phase-shifting interferometry utilizes two or three monochromatic light sources, such as lasers, to realize the measurement of the surface topography with large discontinuity. In this paper, the white light source, with a single-chip CCD color camera, is used to accomplish multi-wavelength phase-shifting interferometry. In addition, we propose an algorithm which combines white light phase-shifting algorithm, equivalent wavelength method and fringe order method to achieve measuring and calibrating the micro-structures ranging from nanometer scale to micrometer scale. Finally, the proposed method is validated by a traceable step height standard.