Research On Improving The Precision Of Ellipsometry-Measured Optical Parameters Of Thin Films

With the development of film materials and techniques, it is very important to obtain thickness and optical constant of thin films accurately and rapidly. But for some films, which are very thin or have strong absorption properties, many common measurements can't get these data. Ellipsometry can not only solve the problem easily but also has many extra advantages comparing with other methods, and it plays a very important part in measuring optical parameters of thin films. Specially, with the rapid development of the technique on nanometer, more and more nano-thin films produce and need to measure, so ellipsometry is given particular attention to and widely used in many fields.Ellipsometry is famous for its essentially nondestructive character and remarkable sensitivity to minute interfacial effects. But it has a basic problem which is how to effectively avoid false solutions, find accurate ones and improve the precision of optical parameters of thin films. The problem seriously affects elliposmotric further application, so it is necessary and has important scientific meaning to solve the difficulty.The main contents of the dissertation are: effectively selecting patterns, selecting better inversion algorithm, and improving the precision of ellipsometry-measured parameters. They are respectively analyzed and discussed in order to finally get high precise results. First, it is systematically discussed that the method and its meaning of effectively selecting patterns, and the key to selecting incident angles and sensitive zones of ellipsometry-measured parameters. Second, comparing with many inversion algorithms, Simulated-Annealing algorithm is adopted. For the defects of the algorithm in the past documents, a new method which involves two kind ofmeasuring Gaussian deviation is developed and gets good results after some research. The new method makes Simulated-Annealing algorithm perfected. Third, improving the precision of ellipsometry-measured parameters is the most important. Multiple angles of incidence method is described, but it is found that false solutions would be gotten if incident angle is incorrectly chosen. So the dissertation mainly discusses two aspects: statistics error and system error, presents a multi-times measurement, and introduces the method of internal and external reflection ellipsometry. A new procedure, the combination of the method of internal and external reflection and the Simulated-Annealing algorithm, is presented and gets good results after much simulation calculation and laboratory tests for many absorbing films patterns. The method can easily and effective avoid false solutions and get accurate and steady values. It is one of the effective and feasible methods to improve precision of films' parameters comparing with multiple angles of incidence. Of course, it will be better to synthesize the above three kinds of method: the method of internal and external reflection, the Simulated-Annealing algorithm, and multi-times measurement.