Ellipsometry Techniques and Its Advanced Applications …
549
2 Instrumentation and Measurements
Instrumentation of ellipsometry and its methodology of measurements are equally
important for proper and precise characterization of a specimen. Therefore, optical
elements as an integral part of instrumentation and the classifications of ellipsometry
measurements are briefly discussed in the following sections.
2.1 Optical Elements
Optical elements are the main components of an optical instrument which are
employed to detect or change the polarization state of light [3, 15]. For instance, an
ellipsometry setup includes various optical elements viz. polarizers, compensators,
retarders, modulators, etc. which are briefly introduced in the following sections.
2.1.1 Polarizer
A polarizer is an optical filter, utilized to pass a specific polarization state from
unpolarized or partially polarized light [3, 15]. Generally, a polarizer is placed in
front of the light source. However, while placing the polarizer in front of the light
detector, the polarization state of transmitted light is determined from the intensity
of light measured by the detector. In such cases, polarizer is termed as analyzer. A
polarizer (or analyzer) is generally made from a CaCO 3 (calcite) crystal.
2.1.2 Compensator
It is essentially a birefringent crystal which is used before a polarizer or analyzer
to separate the horizontal and vertical component of a 45° oriented linear polarized
light along with compensator thickness-dependent phase difference between both
the components [3, 15]. Thus, a compensator (or retarder) can convert 45° oriented
linear polarized light into a circular polarized light.
2.1.3 Modulator
Modulator is a stress-operated compensator which works on the principle of photoelasticity [3, 15]. In fact, it is a cemented structure of quartz crystal and fused quartz
which transfers the resonant electric field-induced periodic stress from quartz crystal
to fused quartz and thus, 45° oriented linear polarized light is separated into the
horizontal and vertically polarized light with a variable phase difference depending
upon amplitude and frequency of applied voltages and wavelength of incident light.
549
2 Instrumentation and Measurements
Instrumentation of ellipsometry and its methodology of measurements are equally
important for proper and precise characterization of a specimen. Therefore, optical
elements as an integral part of instrumentation and the classifications of ellipsometry
measurements are briefly discussed in the following sections.
2.1 Optical Elements
Optical elements are the main components of an optical instrument which are
employed to detect or change the polarization state of light [3, 15]. For instance, an
ellipsometry setup includes various optical elements viz. polarizers, compensators,
retarders, modulators, etc. which are briefly introduced in the following sections.
2.1.1 Polarizer
A polarizer is an optical filter, utilized to pass a specific polarization state from
unpolarized or partially polarized light [3, 15]. Generally, a polarizer is placed in
front of the light source. However, while placing the polarizer in front of the light
detector, the polarization state of transmitted light is determined from the intensity
of light measured by the detector. In such cases, polarizer is termed as analyzer. A
polarizer (or analyzer) is generally made from a CaCO 3 (calcite) crystal.
2.1.2 Compensator
It is essentially a birefringent crystal which is used before a polarizer or analyzer
to separate the horizontal and vertical component of a 45° oriented linear polarized
light along with compensator thickness-dependent phase difference between both
the components [3, 15]. Thus, a compensator (or retarder) can convert 45° oriented
linear polarized light into a circular polarized light.
2.1.3 Modulator
Modulator is a stress-operated compensator which works on the principle of photoelasticity [3, 15]. In fact, it is a cemented structure of quartz crystal and fused quartz
which transfers the resonant electric field-induced periodic stress from quartz crystal
to fused quartz and thus, 45° oriented linear polarized light is separated into the
horizontal and vertically polarized light with a variable phase difference depending
upon amplitude and frequency of applied voltages and wavelength of incident light.