Papers by Author: Yuan Li

Abstract: White light interference technique for topography measurement effectively avoids phase ambiguity in phase-shifting interferometry. The spatial frequency domain algorithm based on scanning white light interference technique has the advantage of insensitivity to noise and higher calculation accuracy compared with other methods. The white light interference sensor is constructed based on nano positioning and nano measuring machine (NMM), the calibrated step height standard of 100±3nm is measured. The spatial frequency domain algorithm is adopted for data processing, the repetitive test result of 97.9nm and standard deviation of 0.48nm are achieved. To verify the measuring ability of complex device, the number ‘242’ on ink box is measured and three-dimensional reconstruction is conducted. The high precision and traceable measurements of micro/nano scale step height standard and complex devices are realized by the white light interference system based on NMM with steady frequency laser interferometer built-in.

Abstract: The white-light interferometry (WLI) has been widely used in 3D topography measurement. This paper introduces a white light phase shifting method for interferometry with the combination of Hariharan phase shifting and WLI. A micro/nanolevel mechanic system was designed and built for the experiments. To verify system accuracy and feasibility, a 100nm step height standard was measured by the designed system and the metrological nanomeasurement machine (NMM). Results of 102.7nm and 102.5nm are obtained respectively. En value of 0.14 is calculated, demonstrating the reliability of result measured by the system. Based on classic nanoquantity traceability system, the measurement results can effectively traced back to the definition of nanometer magnitude, which can improve the accuracy of measurement.

Abstract: In a multiple probes scanning system for a high precision straightness measurement, the lateral setting error between probes is ignored generally due to the average effect in the range of the aperture of the probes. In this paper, we study a two displacement sensors scanning system. Firstly, the principle of two-point method which is based on the natural extension method is introduced. Then, the influence of the lateral setting error between two probes is analyzed quantificationally when the discrete Fourier transform algorithm is applied. It is shown that a relative evaluation error within the range of 1% can be obtained if the lateral setting error is smaller than 1.5% of the sampling interval as long as the spatial wavelength of the evaluated profile is longer than the probe interval. The effectiveness of the results of the quantitative analysis is confirmed by computer simulations.

Abstract: This paper develops one method to characterize nano dimension standards using Scanning White Light Interference Sensor (SWLIS) based on Nano Measurement Machine (NMM). The experimental results show the average value of SHS8-440 low step height standard is 44.15 nm and SHS8-100.0 high step height standard is 100.29 μm, with a standard deviation of 0.30 nm and 0.03 μm, respectively. Also, SWLIS is performed to measure and characterize step height standards, which cover most of the conventional step height standards produced by VLSI Standards Incorporated (VLSI). Additionally, atomic force microscope (AFM) is used as a beneficial supplement due to low lateral resolution of optical methods. The average value of TGZ1_PTB 1D grating from NT-MDT Company is 3000.2 nm with a standard deviation of 0.3 nm by AFM.

Abstract: Straightness error is the main profile error of guide rail. This paper studies a scanning six-probe system for measuring straightness of two guide rails. The system does not use angle sensors and consists of two probe-units, each having three displacement sensors. The two probe-units are moved by a scanning stage to scan the surface of two guide rails, then they are rotated 180 and scan guide rails again after the first scanning. The zero-differences of two probe-units before and after probe-units being rotated, as well as the straightness of the guide rails, can be accurately evaluated from the outputs of the displacement sensors in two scanning process. The effectiveness of this method is confirmed by computer simulation and experimental results in the case of two probe-units having different zero-differences before and after probe-units being rotated.

Abstract: Grating is a widely-used standard to calibrate the horizontal plane of almost all kinds of microscopes. A grating standard consisting of 1D grating and 2D grating was designed and fabricated by Shanghai Institute of Measurement and Testing Technology (SIMT). In this paper, a metrological large-range nano measuring machine integrated with atomic force microscope (AFM) and laser focus sensor (LFS) is used to calibrate this standard. In order to guarantee the measurement accuracy, cosine error, a significant error source which is caused by deviation angle between the scan direction and the perpendicular direction of the grating line, is analysed. Therefore, the scan direction should be determined accurately. For 1D grating, the scan direction is determined by two scanning profiles with deflection angle. Different beginning directions and deflection angles are analyzed to find the best beginning direction and deflection angle for fast and accurate scan direction determination. For 2D grating, the application of the same scan direction determination procedure is extended by using beginning direction and deflection angle which is opposite for 1D grating. Mean pitch is calculated through another profile which is scanned along the calculated scanning direction. Data from different probes are evaluated and the results demonstrate the method well.

Abstract: A multiple probes scanning system comprised of two displacement sensors and one angle sensor is studied for ultra-precise profile measurement. The least squares method is applied to reconstruct the measured profile with uncertainty estimation. The parameters that influence the uncertainty associated with the measured profile are investigated. In order to obtain the optimized uncertainty, the determination of the relative parameters has been discussed in two cases. The first one is that how to select suitable sensors when intervals between two displacement sensors are known. The second one is that how to select suitable intervals between two displacement sensors when the specifications of the sensors are known. The processes of the selection in two cases are illustrated respectively according to the actual situations of the measurement.