Research on New Optical Signal Modulation and Subdivision Technique for Precision Measurements

Abstract

In recent years modern scientific techniques such as optical measurement control and automation have prospered Furthermore with the booming development of the semiconductor industry in Taiwan high quality and multi-functional precision control as well as on-line measurement techniques have become relatively important To get more high quality and multi-functional measurement the system and signal analysis method are complicated Thus this study aims to develop novel signal modulation and subdivision technique analysis methods for modulated ellipsometer and multi-degree-of-freedom measurement In the future we expect the system proposed in this study to the application of on-line measures for the analysis of automatic processes as well as real-time monitoring At present single-point measurement multi-wavelength scanning and rotating optical components are expected to acquire sample characteristic curves which are then fitted to theoretical curves However the measurement steps take longer either by spectral scanning or by continuously rotating optical components with a motor In order to overcome these issues mentioned above we proposed a heterodyne signals analysis method to obtain the full range of ellipsometric parameters and thickness of the single-layer isotropic thin film by use of two-phase detection precisely and straightforwardly Also by combining the common-path interference polarization techniques with this signal analysis method the system can measure the ellipsometric parameters of amplitude ratio (Ψ) and phase difference (Δ) by phase detection The experimental results show that the average standard variation of measured ellipsometric parameters (Ψ and Δ) and the thickness measurement of silica thin film deposited on silicon substrate are 0 13° 0 94° and 0 55 nm respectively On the other hand although measuring and specifying static/quasi-static straightness is a well-established process in existing performance standards a standard test for characterizing dynamic straightness of single-axis linear positioning systems has not yet been developed In order to solve this issue we here present a novel triangular wave-based sequence signal analysis method with the advantages of simultaneously measuring linear displacements and vertical straightness errors of a linear moving air-bearing stage An active level-triggered method was adopted for analyzing sequential triangular-wave signals to obtain a steady subdivision signal The proposed system is similar to a linear encoder and can make online measurements of stage errors to analyze automatic processes and also be used for real-time monitoring The performance of the proposed method and its reliability has been verified by experiments The experiments show that the maximum error of measured rotation angle linear displacement and vertical straightness error is less than 0 058(degree) 0 239 μm and 0 188 μm respectively The maximum repeatability error on the measurement of the rotation angle linear displacement and vertical straightness error is less than ±0 264(degree) ±0 0215μm and ±0 0295 μm respectively

Date of Award	2020
Original language	English
Supervisor	Yu-Lung Lo (Supervisor)