Angular displacement mechanisms are widely used in X-ray diffraction and the nrad resolution is essential for high resolution X-ray diffractor. A multi-pass differential interferometer is designed to improve the resolution of the angel to ~ 10 nrad by increasing the optical pass length. For common interferometer based on Michelson interferometry, nonlinearity is caused by phase mixing due to the imperfect of polarization optical components in both homodyne and heterodyne interferometers. In this angular measurement interferometer, the laser beam of the reference path and measuring path are separated to eliminate the mixture and to reduce the nonlinearity. The four-pass design of the reference and measuring beam improve the resolution. The performance of the interferometer can be used measure the small angle generated by compact piezo driven flexure hinge stage.
Heterodyne interferometer is a nanometer measurement system that uses the laser wavelength as the working reference for length measurement. Under ideal conditions, the laser wavelength is the wavelength λ<sub>0</sub> of the light wave in the vacuum, but in practical applications, the laser wavelength will change with the influence of the air refractive index and the refractive index of air is greatly affected by the environment. This will have a great influence on the measurement results of the high-precision and high-resolution nano-displacement measurement system. Therefore, it is necessary to correct the air refractive index to compensate the laser wavelength. In this paper, the air refractive index in the initial measurement is obtained by using the Edlen empirical formula. Then the relationship between the current air refractive index and the initial air refractive index is obtained by using the wavelength compensation unit to achieve the automatic real-time compensation of the wavelength. The wavelength compensation component is mainly composed of an interference mirror and a fixed length etalon. Through the measurement of air refractive index and the experiment of compensation, the feasibility of the method is confirmed. The relative error after wavelength compensation is less than 0.03% relative to the relative error before compensation.
This paper presents the control and non-linear calibration of large-scale two-dimensional nanometer displacement stage. The stage consists of a monolithic compliant mechanism, which using flexible hinge superimposed branch as a transmission part, driven by three piezoelectric actuators, To certify excellent performance of the stage, a micro-displacement measurement system which based on the measurement principle of a laser interferometer was setted up, then comparison of several stage parameters accomplished between before and after calibration. Based on the measurement of optical path and composition of dual-frequency laser interferometer, a experimental study on nano-positiong stage was carried out. The non-linear calibration method which based on newton-steffensen accelerated iteration are described; The accuracy of the calibration method was verified through experiments. Experiments show that: before calibration, the maximum nonlinearity error of x-axis and y-axis were 4.012μm and 2.875μm. after calibration, the maximum non-linearity of the x-axis is 8 nm and the maximum nonlinearity error of the y-axis is 10 nm, Meanwhile, a mathematical model is established to calculate the coupled displacement and yaw angle, The actual coupled displacement and yaw angle of X/Y were limited to 380nm and 1.4μrad.
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 surface topography of micro-structures would significantly affect the products quality and industrial performance of micro-nano devices <sup></sup>. 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.
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.
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.
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.
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.
The nonlinearity of the interferometer is an essential error in nanoscale measurements influenced by anisotropic gain and nonorthogonality of imperfect polarization components. In this paper, polarization error and the corresponding nonlinearity correction method are studied. The paper is divided into two parts, in the first part, main research focuses on the polarization mixing effect of multi-pass interferometer, besides this, polarization beam splitter and retardation plate are also analyzed, then a final synthetic evaluation is obtained through Jones matrix. In the second part, a harmonic separation method of interferometer signals is researched, the method first decomposes signals into Fourier series, then uses least square fitting to estimate coefficients of main terms of series. In the correction process, the primary phase angle is obtained through coefficients of base series and trigonometric formulas; the finer phase angle is obtained through coefficients of harmonics and Taylor expansion. Experimental results demonstrate that the nonlinearity of homodyne interferometer is significantly reduced in nanometer measurements.