Rotating analyzer ellipsometer

Figure 1 A schematic diagram of the experimental set-up consisting of a rotating analyzer ellipsometer, an electrochemical cell with a copper substrate and a platinum electrode connected to a DC power supply. 

Fig. 2.15 Schematic diagram of a few possible configurations of automated ellipsometers. From the top to the bottom, a rotating analyzer ellipsometer (RAE), a rotating compensator ellipsometer (RCE), and a rotating analyzer with compensator ellipsometer (RACE)...

Figure 18-1. Geometry of standard null ellipsometer (a) and rotating analyzer ellipsometer (b). L, P, C, A, D and S represent the laser, polarizer, compensator, analyzer, detector and sample, respectively (after Jenkins, 1999).

D. E. Aspnes, Fourier transform detection system for rotating-analyzer ellipsometers. 

The ellipsometer used in this study is described elsewhere(3). It consists of a Xenon light source, a monochromator, a polarizer, a sample holder, a rotating analyzer and a photomultiplier detector (Figure 1). An electrochemical cell with two windows is mounted at the center. The windows, being 120° apart, provide a 60° angle of incidence for the ellipsometer. A copper substrate and a platinum electrode function as anode and cathode respectively. Both are connected to a DC power supply. The system is automated with a personal computer to collect all experimental data during the deposition. Data analysis is carried out by a Fortran program run on a personal computer. 

Fig. 2.14 Schematic diagram of a rotating analyzCT ellipsometer (RAE) and the Jones matrix representation for each comptment. The blue lines repiestait the trajectory of the electric field vector of the propagating light. The difference in the representations of the analyzer and polarizer is due to the angles a and ra being measured in opposite directions...

Up to date, diverse of ellipsometry has been developed, such as imaging ellipsometry [38-40], infrared spectroscopic ellipsometry [41-50], Mueller matrix ellipsometry [51-63], etc. Here, we wiU not make a full introduction about the developments of ellipsometry. As an example, a rotating-polarizer-analyzer ellipsometer (RPAE) will be introduced as follows. 

Example A rotating-polarizer-analyzer ellipsometer (RPAE)... 

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

Bllipsometric measurements were made with a Rudolf 437 ellipsometer equipped with a rotating analyzer detector and 488.0 nm (Ar+ laser) light. The... 

Figure 9.12 One type of ellipsometer, called a Null instrument. Polarizer and analyzer are rotated alternately until the null is found.

Several difl ereni types of cllipsometers arc available commercially. The earliest type was the null-type ellipsometer in which a circularly polarized incident beam was reflected off the sample surface onto an analyzer. The incident-beam polarization stale was chosen by a polarizer and compensator so that linearly polarized light was obtained after reflection. 1 he analyzer was then rotated until it was perpendicular to the polarization axis of the light coming from the sample as indicated by a minimum in the light iniciisiiy. Some instruments today still use the null principle, bui they are computer controlled and have charge-coupled-device (C (-I)f cameras as detectors. 

Common ellipsometers consist of a polarizer setting the polarization of the incident beam and an moveable analyzer (a linear polarizer and a quarter-wave plate, both on rotation stages and adjustable with respect to each other) to analyze the reflected beam [95]. 

As the null ellipsometer is rather tedious to operate, dynamic ellipsometers have been developed. An example is that the analyzer is rotating continuously in the PCSA cMifiguration. A Foirrier analysis of the intensity signal gives the eflipsometer angles A and T if the position of the compensator C and polarizer P are known. 

In 1990, Y. T. Kim et al. realized a real time spectrum measurement with the combination of RPE, prism spectrometer, and optical multichannel analyzer (OMA) [32]. It took 40 ms to finish the measurement of 128 sets of ellipsometry parameters over the whole spectrum. In 2003, this group developed a generalized ellipsometer with multichannel detecting using combination of RCE and OMA [33], The measurement time depends on the rotating frequency of compensation device, and it can take 150 sets of ellipsometry parameters in the energy range of 2 - 5 eV in 0.25 seconds. 

L. Y. Chen and D. W. Lynch, Scanning ellipsometer by rotating polarizer and analyzer,... 

Usually, for the quarter wave compensator, pc = exp j (71/2) = j. For the rotating ellipsometer, during continuous rotation of the analyzer, the Fourier coefficients, a and b, are monitored and converted to the ellipsometric parameters, T and A. 

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