Photometric ellipsometer

The infrared ellipsometer is a combination of a Fourier-transform spectrometer (FTS) with a photometric ellipsometer. One of the two polarizers (the analyzer) is moved step by step in four or more azimuths, because the spectrum must be constant during the scan of the FTS. From these spectra, the tanf and cosd spectra are calculated. In this instance only A is determined in the range 0-180°, with severely reduced accuracy in the neighborhood of 0° and 180°. This problem can be overcome by using a retarder (compensator) with a phase shift of approximately 90° for a second measurement -cosd and sind are thereby measured independently with the full A information [4.315]. 

Various types of ellipsometers have been developed. Classically nulling method has been adopted, and recently the photometric ellipsometers have been used. 

A typical photometric ellipsometer is a rotating analyzer apparatus. When the analyzer rotates, the light intensity is modulated. 

To overcome this difficulty, several methods are proposed for obtaining the three unknowns without assumptions. First, one has to measure reflectance, R, in addition to F and A. " During the oxide film formation, the reflectance change, AR, is measured with the changes of F and A. Since lo in Eq. (18) corresponds to the reflection intensity from the sample surface, the photometric ellipsometer can easily be modified to the simultaneous measurement of reflectance. For the nulling ellipsometer, however, it is difficult to simultaneously measure the reflectance with F and A. From the three parameters of F, A, and R, one can calculate the three unknowns, h, and d with help of computer program. 

A further type of fast automatic ellipsometer for electrochemical investigations has been described [933] and an experimental approach to observe fast transients with ellipsometry was reported [934]. In the photometric mode, the intensity of the reflected light is measured as a function of the position of polarizer and sometimes compensator in the incoming beam for further details and an overview, see [934]. A general overview of instrumental developments has been provided [935]. 

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