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Ellipsometry Measurements

Ellipsometry is primarily interested in how p- and s- components change upon reflection or transmission in relation to each other. In this manner, the reference beam is part of the experiment. A known polarization is reflected or transmitted from the sample and the output polarization is measured. The change in polarization is the ellipsometry measurement, commonly written as:

[10]

A sample ellipsometry measurement is shown in Figure 6. The incident light is linear with both p- and s- components. The reflected light has undergone amplitude and phase changes for both p- and s- polarized light, and ellipsometry measures their changes.

Spectroscopic Ellipsometry Tutorial Ellipsometry Measurements model

Figure 6 Typical ellipsometry configuration, where linearly polarized light is reflected from the sample surface and the polarization change is measured to determine the sample response.

The primary tools for collecting ellipsometry data all include the following: light source, polarization generator, sample, polarization analyzer, and detector. The polarization generator and analyzer are constructed of optical components that manipulate the polarization: polarizers, compensators, and phase modulators. Common ellipsometer configurations include rotating analyzer (RAE), rotating polarizer (RPE), rotating compensator (RCE), and phase modulation (PME).

Spectroscopic Ellipsometry Tutorial Ellipsometry Measurements model

Figure 7 Rotating analyzer ellipsometer configuration uses a polarizer to define the incoming polarization and a rotating polarizer after the sample to analyze the outgoing light. The detector converts light to a voltage whose dependence yields the measurement of the reflected polarization.

The RAE configuration is shown in Figure 7. A light source produces unpolarized light which is then sent through a polarizer. The polarizer allows light of a preferred electric field orientation to pass. The polarizer axis is oriented between the p- and s- planes, such that both arrive at the sample surface. The linearly polarized light reflects from the sample surface, becomes elliptically polarized, and travels through a continuously rotating polarizer (referred to as the analyzer). The amount of light allowed to pass will depend on the polarizer orientation relative to the electric field “ellipse” coming from the sample. The detector converts light to electronic signal to determine the reflected polarization. This information is compared to the known input polarization to determine the polarization change caused by the sample reflection. This is the ellipsometry measurement of Psi and Delta.