Development of Absolute Self-Calibration Systems for Displacement and Profile Measuring Instruments with Subnanometric Accuracy

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The purpose of this study is to establish absolute self-calibration systems for displacement and profile measuring instruments with subnanometricaccuracy. It is necessary to frequently calibrate the linearity error ofsuch instruments in situ. In this study, we first proposed a new self-calibration method. This method can obtain the linearity error by using only the measurement data, without using any calibration references and extra devices. In this method, the derivative of the calibration curve is measured from the difference of two measurement data obtained before and after a small shift of the sample in the sensing direction. The calibration curve can then be evaluated by the integration of the derivative. The feasibility and accuracy of this method was investigated by computer simulations and calibration experiments of several kinds of instruments. It was verified that the calibration error of this method is less than twice of the resolution of the calibrated instruments. Next, th … More e absolute calibration was performed by including the calibration of mean sensitivity. For this purpose, a specially designed compact laser interferometer, was set in the sample holder. The shift amount between the two measurements in the self-calibration method was controlled to be several times of the wavelength of the interferometer laser source. As a result, the mean sensitivity can be calibrated in an accuracy that is determined by the stability of the wavelength. The effectiveness of the absolute calibration method was confirmed by an experiment of calibrating an interferometer microscope. In addition, the self-calibration method has been compared with the external monitoring method, which had been proposed in a research project of improving the accuracy of STM/AFM.The results of the two method achieved a good agreement, and this proved the reliability of the self-calibration method. Finally, a theory of a new autonomous method, which can detect the wavefront error due to the reference mirror and optical path distortion in a interferometer, has also been established. This method uses two surfaces and four interferograms obtained at different positions of a specimen. Less