Laser interferometry is a typical representative of the highest level in the field of geometric metrology, and its accuracy can reach sub-nanometer while taking the light wavelength as a measuring scale. In this paper, we present a precisely controlled transmission structure to realize the conversion between angular and linear displacement, therefore the angular displacement can be obtained based on the high-precision linear displacement measured by the laser interferometric system. By comparing the measured angular values with the reference values, the maximum error of angular displacement measurement in this system is ± 5 arcsec, which is from the calibration certification of the National Institute of Metrology. The reference values are obtained by measuring the angular polygon with a photoelectric autocollimator, and an angular displacement measurement error of ±1 arcsec is achieved based on laser interferometric system in this paper after correcting with a series of conversion coefficients between linear and angular displacement.
In this context, the present research work aims at studying and developing an innovative approach for automated sampling path model for large simple regularly conical workpiece, which could provide designers easily and rapidly taken. Therefore, our attention is focused on 3D geometric relationships between neighboring end points of edge features of workpiece. An algorithm is proposed to guide the scanner device and move it along the main direction of the plane containing the projection of the next critical end point with the use of geometric properties of previously extracted end points. Thus, an appropriate 3D circular-arc scanning path is on-line automatically yielded step by step by an orderly collection of local connected end points. Finally, a series of experiment on typical conical workpieces are carried out to demonstrate the automated path planning technique and the final sampling quality.
Nowadays, 3D geometric dimensional measurements of step height are performed on many types of samples using different instruments, such as AFM, optical microscopy, et.al. For step height measurements generally, the traceability of the z-axis is very importance. In this paper, displacement metrology in the vertical direction or z-axis is first determined, thus having a known and specific relationship between the physical edge on the sample and the location of the detected edge in the image. By consider of the location of the step, a step height is calculated by requirement of fitting to upper and lower surfaces. An algorithm is introduced to fit the upper and lower terraces. Then, we locate the edge and determine the step height by the data extrapolation of those fits. In order to reduce the uncertainty budget for step height measurements, 50nm, 100nm, 200nm, 500nm and 1000nm step height are respectively tested, and dominant sources are also discussed.
Laser interference system has been extensively applied in high-precision geometric metrology benefit from the advantages of high accuracy, high resolution and stability in linear displacement measurement. In this paper, we present a novel and compact mechanical structure to realize the conversion between angular and linear displacement, so that the slight angular displacement can be enlarged and obtained by using the characteristics of high-precision linear displacement measurement of laser interference system. A series of experiments are carried out on this device, the conversion ratio of angular and linear displacement we achieved is 5.76 arcsec/ μm, which is determined by the transmission ratio of the worm gear pair and the pitch of the ball screw. By comparing the measured angular values with 23 reference values distributed on the whole circumference, the maximum original error of angular displacement measurement in this system without correction or compensation is ± 25 arcsec and the resolution is 0.6 arcsec.
Nowadays, with 3D topographic features increasingly complicated and complex, scanning probe microscopes have widely been used of nano-scale dimensional measurement in the semiconductor manufacturing and space industry, which can create three-dimensional data over almost all solids in a wide range of ambient. Although scanning probe microscopes readily achieve nanometer level resolution images of measured surfaces, there are several aspects of their behavior that can cause them to yield large measurement errors. In this paper, according to possible traceability pathways for calibration of lateral axes and z axis, both pitch and step height measurements are respectively performed and axis error self-correction model is proposed. The influence of thermal stability on drift error is also discussed. Experimental results show that our method will be helpful for a fast performance evaluation test for scanning probe microscope.
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