Yushu Shi

Analysis method of microstructure surface topography based on wavelet filter

The surface topography of micro-structures would significantly affect the products quality and industrial performance of micro-nano devices [1]. In recent years, the application of micro-structures in Micro Electro Mechanical Systems (MEMS) and integrated circuit is more and more widely. How to reflect the 3D surface topography of these micro structures accurately and measure the surface’s parameters precisely as well as quickly are becoming a hot research area of precision measurement. White-light interference microcopy technology is one of the most widely used non-contacting measurement methods at present, which has the advantages of nondestructive, fast measurement and high accuracy, has been widely applied in surface topography measurement of micro structures. In this paper, an analysis method of microstructure surface topography algorithm based on wavelet filter to analyze white interference signals is proposed, this method utilizes R/G/B three channels color information which is significantly superior to traditional black and white imaging process method. The experimental results shows that this method has good accuracy and repeatability in 3D surface measurement.

Calibration of industrial CT using two forest-balls

A small forest-ball was manufactured and calibrated using CMM F25. An industrial CT called Metrotom1500 was calibrated by the small forest-ball and another big forest-ball produced by Carl Zeiss. These two forest-balls were separately measured at two different magnifications of the industrial CT, and the measurement results could meet the maximum permissible error of Metrotom1500.

Long range metrological atomic force microscope with versatile measuring head

A long range metrological atomic force microscope (AFM) has been developed at NIM. It aims to realize a maximum measurement volume of 50mm×50mm×2mm with an uncertainty of a few tens of nanometers in the whole range. In compliance with Abbe Principle, the instrument is designed as a sample-scanning type. The sample is moved by a 6-DOF piezostage in combination with a hybrid slide-air bearing stage for long scanning range. Homodyne interferometers with four passes attached to a metrological frame measure relative displacement between the probe and sample thus the instrument is directly traceable to the SI. An AFM head is developed as the measuring head for the instrument. Considering accuracy and dynamic performance of the instrument, it is designed to be capable of scanning perpendicularly in a range of 5μm×5μm×5μm with a 3-DOF piezostage. Optical beam deflection method is used and a minimum of components are mounted on the moving part. A novel design is devised so that the photodetector is only sensitive to the deflection of cantilever, but not the displacement of the head. Moving manner of the head varies with scanning range and mode of the instrument. Results of different measurements are demonstrated, showing the excellent performance of the instrument.

Atomic Force Microscope Scanning Head with 3-Dimensional Orthogonal Scanning to eliminate the curved coupling

An atomic force microscopy (AFM) scanning head is designed with the probe orthogonal scanning mode for metrological AFM to eliminate the curvature distortion. The AFM probe is driven by piezostage and the scanning trajectory of the probe in 3 directions are orthogonal to reduce the cross coupling. A new optical lever amplification optical path is developed to eliminate the coupling error. The tracing lens and probe tip are moved as an integrated part. The AFM is operated at contacting mode. The step approach process of the probe tip is tested to the sample surface and the noise of the AFM head is analyzed. The response of the probe demonstrates a 0.5 nm resolution of the probe head in the z direction. Finally, the planar scanning performance of the scanning head is demonstrated compared with tube scanning AFM.

Active coherent control of nanoscale light confinement: Modulation of plasmonic modes and position of hotspots for surface-enhanced Raman scattering detection

Multistep plasmonic nanostructures can induce the deep modulation of electromagnetic-field interactions on the nanoscale for positioning hotspots, and this generation of enhanced fields is important in many optical applications. In this article, a new strategy is proposed for fabricating a plasmonic doublestacked nanocone (DSC) nanostructure. In the DSC structure, a tunable plasmonic hybrid mode proceeds from the strong coupling of the plasmonic resonance of a fundamental cavity mode with a localized surface plasmon gap mode. In the nanostructure, the far-field response is deeply modulated and the hottest spots can be effectively positioned on the top surface of the DSC nanostructure. A controllable and cost-effective mask-reconfiguration technique for manufacturing the multiscale nanostructure is developed, which guarantees the generation of the introduced crucial stage on the DSC nanostructure. To evaluate the features of the plasmonic resonance, the DSC nanostructure is used as a surface-enhanced Raman scattering (SERS) substrate for detecting 4-mercaptopyridine molecules under specific excitation conditions. Its good performance, with an average measured SERS enhancement factor as high as 108, demonstrates its strong plasmonic-mode hybridization and extreme field enhancement.

Novel dual-probes atomic force microscope for line width measurements

Dual-probe Atomic Force Microscope (AFM) can effectively eliminate the influence of the probe size on measurement of the line width, and realize true three-dimensional measurement. Novel dual-probe AFM consists of probe system, scanning system, alignment system and displacement measurement system. As displacement measurement system, the interferometers are added to the novel dual-probes AFM. In order to simplify the dual-probe AFM structure, self-sensing tuning fork probe is used. Measurement method has two steps: the first step is to align two probes and obtain the reference point; the second step is to scan two sides of measured line by two probes separately, and calculate the line width value according to the reference point. In the alignment of two probes, the alignment method is improved by using the edge alignment and the feedback scanning alignment.

The research progress of metrological 248nm deep ultraviolent microscope inspection device

In lithography process, the precision of wafer pattern to a large extent depends on the geometric dimensioning and tolerance of photomasks when accuracy of lithography aligner is certain. Since the minimum linewidth (Critical Dimension) of the aligner exposing shrinks to a few tens of nanometers in size, one-tenth of tolerance errors in fabrication may lead to microchip function failure, so it is very important to calibrate these errors of photomasks. Among different error measurement instruments, deep ultraviolent (DUV) microscope because of its high resolution, as well as its advantages compared to scanning probe microscope restrained by measuring range and scanning electron microscope restrained by vacuum environment, makes itself the most suitable apparatus. But currently there is very few DUV microscope adopting 248nm optical system, means it can attain 80nm resolution; furthermore, there is almost no DUV microscope possessing traceable calibration capability. For these reason, the National Institute of Metrology, China is developing a metrological 248nm DUV microscope mainly consists of DUV microscopic components, PZT and air supporting stages as well as interferometer calibration framework. In DUV microscopic component, the Köhler high aperture transmit condenser, DUV splitting optical elements and PMT pinhole scanning elements are built. In PZT and air supporting stages, a novel PZT actuating flexural hinge stage nested separate X, Y direction kinematics and a friction wheel driving long range air supporting stage are researched. In interferometer framework, a heterodyne multi-pass interferometer measures XY axis translation and Z axis rotation through Zerodur mirror mounted on stage. It is expected the apparatus has the capability to calibrate one dimensional linewidths and two dimensional pitches ranging from 200nm to 50μm with expanded uncertainty below 20nm.

Characterization of Akiyama probe applied to dual-probes atomic force microscope

The measurement of nano-scale line-width has always been important and difficult in the field of nanometer measurements, while the rapid development of integrated circuit greatly raises the demand again. As one kind of scanning probe microscope (SPM), atomic force microscope (AFM) can realize quasi three-dimensional measurement, which is widely used in nanometer scale line-width measurement. Our team researched a dual-probes atomic force microscope, which can eliminate the prevalent effect of probe width on measurement results. In dual-probes AFM system, a novel head are newly designed. A kind of self-sensing and self-exciting probes which is Nanosensors cooperation’s patented probe—Akiyama probe, is used in this novel head. The Akiyama probe applied to dual-probe atomic force microscope is one of the most important issues. The characterization of Akiyama probe would affect performance and accuracy of the whole system. The fundamental features of the Akiyama probe are electrically and optically characterized in “approach-withdraw” experiments. Further investigations include the frequency response of an Akiyama probe to small mechanical vibrations externally applied to the tip and the effective loading force yielding between the tip and the sample during the periodic contact. We hope that the characterization of the Akiyama probe described in this paper will guide application for dual-probe atomic force microscope.

Control and measuring system of a two-dimensional scanning nanopositioning stage based on LabVIEW

A control and measuring system of two-dimensional nanopositioning stage is designed for the multiple selection and combinations control based on LabVIEW. The signal generator of the system can not only generate the commonly used control signals such as sine, square, triangle and sawtooth waves, but also generate special signals such as trapezoidal wave and step wave with DAQ data acquisition card. The step wave can be triggered by the other signals for the strict timing corresponding relation between X-Y control signals. Finally, the performance of the control system of two-dimensional nanopositioning stage is conducted by the heterodyne interferometer. The results show that the operation of the system is stable and reliable and the noise peak - valley value is superior to 2nm while the stage moving with 6nm step. The system can apply to the field requiring the precise control to the positioning stage in nano-measurement and metrology.

The assessment of industrial CT's probing error

Similar to traditional CMM, probing error of industrial CT is used for assessing the 3D measurement error of the machine in a very small measurement volume. A research on the assessment of probing error of industrial CT is conducted here. Lots of assessment tests are carried out on the industrial CT Metrotom1500 in the National institute of metrology, using standard balls with different size and materials. The test results demonstrate that probing error of industrial CT can be affected seriously by the measurement strategy and standard balls. According to some further analysis about the test results, the assessment strategy of industrial CT’s probing error is concluded preliminary, which can ensure the comparability of the assessment results in different industrial CT system.