Study On Measurement Of Thin-Film Thickness With Fringe Scanning Method

With the rapid development of modern science and technology, the thin-film devices are more and more widely used in the field of communication technology, aerospace, and micro-mechanical electronics. The film thickness is an important indicator of the thin-film devices, which directly affect many optical properties of the thin-film devices, such as refractive index, reflectivity, resistance to injury, and so on. Uniform of film thickness is the basis of detecting film material performance, but also the important criterion for evaluating film properties, and merits of film department. It’s positive significance in controlling products quality that fast and accurately measuring film thickness during film device fabrication process. The lateral shearing interferometry is one of the many different testing thicknesses of thin-film methods, which has advantages of high accuracy, strong stability, non-contact measurement, and full filed testing. It is widely used in process detection of parts, aspheric surface shape testing, and aberration detection ect. Therefore, research on measurement of thin film thickness with lateral shearing fringe scanning method have a high level of academic significance in optimization of the thin-film device process, and provide a rich theoretical foundation and technical experience for further study based on interferometry method measuring thin-film thickness techniques.Introduce the thin-film thickness measurement methods. Discussion is made on the current commonly used optical measurement method of film thickness, summarized the advantages and disadvantages, measurement accuracy and range of the different measurement methods.Design and build a shearing interferometer thin-film measurement platform. Discussed on the measurement process of lateral shearing interferometer, do theoretical analysis of the measurement principle and accuracy of the fringe scanning method. Design measuring system, and discuss the experiment platform and measurement processes.Study on the key algorithm of lateral shearing theory. Complete the algorithm research and programming with fringe scanning method that including image preprocessing algorithm, Fast Fourier Transform,+1 level spectrum extracted, phase unwrapping. Simulate shearing interferogram using MATLAB tools, processing simulation pattern with fringe scanning program, and analysis of simulation results.This paper processing experimental collected interferogram, analysis of the treatment results. The result is 106.5nm with overall method. In order to verify the correctness of the algorithm, measures the same sample using ZYGO interferometer, and the result is 107.6nm. Basically the same with the result obtained by proposed method in this article. The experiment shows that this method achieves film thickness measurement, and has a good feasibility.