Dr. Zhi Li Profile

Dr. Zhi Li

at Physikalisch-Technische Bundesanstalt

SPIE Involvement:

Author

Publications (13)

Proceedings Article | 26 June 2017 Paper

Broadband interferometric characterisation of nano-positioning stages with sub-10 pm resolution

Zhi Li, Uwe Brand, Helmut Wolff, Ludger Koenders, Andrew Yacoot, Prabowo Puranto

Proceedings Volume 10329, 1032944 (2017) https://doi.org/10.1117/12.2270262

KEYWORDS: Mirrors, Nanolithography, Beam splitters, Signal processing, Calibration, Interferometry, Data acquisition, Interferometers, Homodyne detection, Laser interferometry, Sensor calibration, Modulation, Digital signal processing

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Proceedings Article | 7 June 2017 Paper

A multi-functional MEMS-SPM for quantitative characterization of nano-objects

Zhi Li, Sai Gao, Uwe Brand, Karla Hiller, Nicole Wollschläger, Xianghui Zhang

Proceedings Volume 10246, 102460J (2017) https://doi.org/10.1117/12.2265680

KEYWORDS: Scanning probe microscopy, Head, Transducers, Graphene, Prototyping, Silicon, Sensing systems, Microelectromechanical systems, Calibration, Atomic force microscopy, Metrology, Actuators, Microscopes, Microscopy, Atomic force microscope, Microfabrication

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Proceedings Article | 21 May 2015 Paper

Smart sensors and calibration standards for high precision metrology

Uwe Brand, Sai Gao, Lutz Doering, Zhi Li, Min Xu, Sebastian Buetefisch, Erwin Peiner, Joachim Fruehauf, Karla Hiller

Proceedings Volume 9517, 95170V (2015) https://doi.org/10.1117/12.2179455

KEYWORDS: Silicon, Standards development, Calibration, Microelectromechanical systems, Sensors, Microtechnology, Metrology, Atomic force microscopy, Sensor calibration, Bridges

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Proceedings Article | 1 May 2014 Paper

A dual-styli micro-machined system for precise determination of the thickness of free-standing thin films

Zhi Li, Sai Gao, Helmut Wolff, Uwe Brand, Ludger Koenders

Proceedings Volume 9132, 91321G (2014) https://doi.org/10.1117/12.2052415

KEYWORDS: Microelectromechanical systems, Silicon, Transducers, Interferometers, Thin films, Microfabrication, Glasses, Sensors, Calibration, Sapphire

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Proceedings Article | 14 May 2010 Paper

An optical microform calibration system for ball-shaped hardness indenters

Zhi Li, Sai Gao, Konrad Herrmann

Proceedings Volume 7718, 77181C (2010) https://doi.org/10.1117/12.854800

KEYWORDS: Calibration, Confocal microscopy, Microscopes, Objectives, Spherical lenses, Optical testing, Optical calibration, Sensors, Polarizers, Image resolution

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Proceedings Article | 14 May 2010 Paper

A micro-SPM head array for large-scale topography measurement

S. Gao, Z. Li, K. Herrmann

Proceedings Volume 7718, 77181L (2010) https://doi.org/10.1117/12.854397

KEYWORDS: Head, Scanning probe microscopy, Actuators, Microelectromechanical systems, Metrology, Atomic force microscopy, Interferometers, Calibration, Sensing systems, Scanning probe microscopes

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Proceedings Article | 23 September 2009 Paper

A 193nm optical CD metrology tool for the 32nm node

Z. Li, F. Pilarski, D. Bergmann, B. Bodermann

Proceedings Volume 7488, 74881J (2009) https://doi.org/10.1117/12.829629

KEYWORDS: Microscopes, Critical dimension metrology, Deep ultraviolet, Objectives, Photomasks, Excimer lasers, Diffusers, Multimode fibers, Metrology, Imaging systems

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Proceedings Article | 25 April 2008 Paper

Determination of in-plane displacement of MEMS by means of an AFM sensor

S. Gao, Z. Li, K. Herrmann

Proceedings Volume 6993, 69930J (2008) https://doi.org/10.1117/12.780407

KEYWORDS: Microelectromechanical systems, Atomic force microscopy, Sensors, Actuators, Scanning probe microscopy, Inspection, Confocal microscopy, Performance modeling, Calibration, Finite element methods

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Proceedings Article | 25 April 2008 Paper

In-situ imaging of interlayer nanodeformation with improved differential confocal microscopy

Z. Li, S. Gao, K. Herrmann

Proceedings Volume 6995, 699516 (2008) https://doi.org/10.1117/12.780267

KEYWORDS: Confocal microscopy, Sensors, Microscopes, Finite element methods, Light sources, Prototyping, Inspection, Reflection, Mathematical modeling, Beam splitters

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Nanoindentation testing has proved to be an effective tool to determine the mechanical properties of small volumes of materials applied in various micro-systems, including hardness, indentation modulus, creep and so on. Nowadays, with the help of advanced numerical methods, especially the finite element analysis (FEA) technique, further mechanical properties of the material under test (e.g. tensile strength, etc.) can be interpreted from the typical indentation curve. However, the reliability and accuracy of these analytical models have to be well tested. Recently, the deformed topography of the interlayer surface within the tip-film-substrate system has been proposed to be the reference for the evaluation of FEA and other mathematic models for indentation testing. Here an in-situ interlayer deformation imaging system based on differential confocal microscopy is therefore developed, which has the capability to measure in-situ the real-time topography deformation within a layered specimen during nanoindentation testing. By means of linear regression and interpolation of the linear region of the standard confocal microscopy, differential confocal microscopy (DCM) can achieve a very high resolution for topography measurements. However, the actual capability and measurement uncertainty of DCM would be subject to those common-mode error sources like surface heterogeneity, intensity fluctuation of the light source, etc. In this paper an improved DCM is proposed, which introduces an additional point detector to the conventional DCM, creating dual confocal signals with slight relative axial shifting. The real topography of the surface under test can then be easily deconvoluted from the dual differential signals, whilst the common-mode errors within the measurement are eliminated. A prototype was developed and applied for measuring a step-height composed of two different materials and for in-situ inspection of the interlayer deformation during nanoindentation testing. Preliminary experimental results verify the feasibility and accuracy of the proposed method.

Proceedings Article | 27 April 2006 Paper

An optical differential probe for measurement of MEMS topography

Z. Li, K. Herrmann, F. Pohlenz

Proceedings Volume 6188, 61880D (2006) https://doi.org/10.1117/12.662985

KEYWORDS: Microelectromechanical systems, Confocal microscopy, Actuators, Interferometers, Microscopes, Sensors, Measurement devices, Prototyping, Objectives, Thin films

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Proceedings Article | 18 October 2002 Paper

In-situ optical probe interferometer for measuring displacement of nanoindenter: a configuration

Zhi Li, Konrad Herrmann, Frank Pohlenz

Proceedings Volume 4902, (2002) https://doi.org/10.1117/12.467681

KEYWORDS: Interferometers, Calibration, Opto mechatronics, Digital Light Processing, Picosecond phenomena, Microelectronics, Sensing systems, Interferometry

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Proceedings Article | 18 October 2002 Paper

Surface profiling method for large aspheres: diffraction image-forming approach

Zhi Li, Yang Zhao, Dacheng Li

Proceedings Volume 4902, (2002) https://doi.org/10.1117/12.467512

KEYWORDS: Diffraction, Fourier transforms, Prototyping, Profiling, Aspheric lenses, Image resolution, Synchrotron radiation, Charge-coupled devices, Optical components, Optical alignment

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Proceedings Article | 18 October 2002 Paper

Correction of nonlinearity in single-frequency interferometry

Zhi Li, Konrad Herrmann, Frank Pohlenz

Proceedings Volume 4902, (2002) https://doi.org/10.1117/12.467682

KEYWORDS: Interferometers, Interferometry, Data modeling, Digital Light Processing, Opto mechatronics, Picosecond phenomena, Lithium, Calibration, Neural networks

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Single-frequency interferometer with bidirectional fringe counting is frequently used in accurate length measurements due to its high resolution, stability and compact hardware. Meanwhile, in order to obtain nanometric path length resolution, corrections have to be introduced to the phase quadrature signals of a real interferometer due to its systematic deviations such as phase quadrature error, dc bias, unequal gains, etc. Conventional approaches to correct nonlinearity in a single frequency interferometer are generally based on ellipse fitting proposed by Heydemann, i.e. fitting an ellipse to instantaneous phase quadrature signals as the interferometer path length is varying. Consequently, when interferometer path length variation is far larger than light wavelength, the highest correction accuracy could be obtained by the largest number of data points. In some cases like nanoindentation instruments in particular, however, the path length variation of an interferometer cannot be large enough to produce a closed Lissajou figure. Simulation and experimental results show that the accuracy of conventional calibration techniques drops quickly as the range of the optical path length variation reduces. A new approach to correct nonlinearity in single-frequency interferometry was introduced, which was based on the concept of model reference control technique. Firstly, a Neural Network (NN) model was created and trained to predict the instantaneous phase of an ideal interferometer. And then the NN model was used as a reference model due to such characteristic that its outputs would be quite different from those obtained by conventional instantaneous phase computation methods when the input data were not on an ideal Lissajou figure. Better correction results could be achieved through minimizing the phase error between the NN model outputs and the conventional computation results. Theoretical derivation and analysis of the new approach are detailed in this paper. Simulation and experimental results show that this new

Showing 5 of 13 publications

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