A new robot-performance calibration system based on tracking multilaser trilateration has been developed. To realize 1 μm coordinate accuracy, a beam-deflecting tracking mechanism with both a ball-seated bearing and a spherically shaped cat’s eye retroreflector whose refractive index is 2.0 has been developed. The coordinate error and the repeatability of a commercial industrial robot have been verified by the system we developed in a two-dimensional plane.
The method as well as an appropriate instrumentation for measuring phase changes of reflected light is described. The phase changes on samples of Au, Al, Ag, and Cr evaporated films are measured for five wavelengths (lambda) from 442 to 633 nm, with respect to the phase change at the glass-air interface, where it should be zero. The measured results for the Au film are in fairly good agreement with values calculated by use of optical constants from a handbook or the complex refractive index measured by an ellipsometer. The phase changes for Al and Ag films are different from calculated values by ~5 degrees or a shift length of 4.4 nm at lambda = 633 nm, while those of the Cr film show large shifts as high as 16 degrees or a shift length of 9.8 nm at lambda = 442 nm.
A novel submicron dimension reference for calibrating electron-beam metrology systems has been developed. A fine rectangular-profile diffraction grating fabricated by laser interferometer lithography and anisotropic chemical etching of (1 10) crystalline silicon satisfies any conditions for submicron dimension reference. In this reference, pitch size of about 0.2 im is easily obtained by laser interferometer lithography with an accuracy, shown by optical diffraction measurement, of within 1 nm. This reference also satisfies several requirements for electron-beam metrology systems. It is stable and free from build-up of charge under electron-beam irradiation because it is fabricated from a conductive silicon single crystal. Also it generates high-contrast secondary electron signals due to high-aspect ratio grating profile.Evaluation of this reference by optical diffraction measurement and electron-beam CD measurements show high performance for submicron dimension calibration. In electron-beam CD measurements, the deviation of repeated measurements is under 5 nm within 3.
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