Wavelength-scanning polarization-modulation ellipsometry: some practical considerations

Study of the new ellipsometric measurement method using integrated analyzer in parallel mode

A new type of ellipsometer using an integrated analyzer composed of 12 sub-analyzers with different azimuth angles was constructed and studied. By using a two-dimensional CCD array camera to measure the light intensity emerging in parallel from each sub-analyzer with the azimuth angles uniformly distributed in the range of about 180 degrees , the ellipsometric parameters were extracted within the data acquisition time less than 1 second. The ellipsometric parameters for the polished bulk Si sample were measured to show good agreement with the results measured by using another two ellipsometric methods. The new method having the merits of high speed and reliability in the optical data measurement can be potentially used in the fields where the in situ data acquisition with high precision is the key issue as required.

Polarization modulation imaging ellipsometer

The polarization modulation technique was successfully combined with parallel synchronous detection using a switching light source and a CCD camera to realize full-frame measurement of ellipsometric parameters. The detected thickness of a monolayer film of n-octadecylsiloxane agreed well with theoretical and reported experimental values. The thickness resolution for imaging and the temporal noise in parallel thickness measurements were smaller than +/-0.1 nm and smaller than +/-0.02 nm, respectively.

Two-modulator generalized ellipsometry: theory

A new ellipsometer is described that uses two photoelastic modulator-polarizer pairs, where the photoelastic modulators are operating at differing resonant frequencies. The time-dependent intensity of the light beam is extremely complicated but can be analyzed so that all elements of the sample Mueller matrix are obtained. For a given configuration, nine of the Mueller matrix elements can be measured at any one time; the other seven elements are accessible when the azimuthal angles of the photoelastic modulators are changed. The single-configuration measurement is often sufficient to characterize a number of real situations completely, such as film growth in a vacuum environment, anisotropic samples, and simple depolarization.

Theoretical simulation of a polarization modulator based on mechanical rotation of a polarizing element

The properties of three alternative designs for a polarization modulator of potential use for the measurement of vibrational circular dichroism (VCD) are evaluated and compared by use of Mueller calculus. The analysis shows that the combination of a fixed polarizer plus either a photoelastic modulator or a rotating quarter-wave plate possesses nearly the same capability for generation of time-varying, circularly polarized light. However, a modulator composed of a rotating polarizer plus a fixed birefringent plate entails considerable theoretical and experimental difficulties for use in the measurement of VCD spectra. While VCD spectra obtained with the rotating devices can be calibrated in the same manner as spectra obtained with a photoelastic modulator, Mueller analysis shows that the form of the resultant calibration signal will have a different shape. The relevant expressions for VCD and linear dichroism as well as the calibration signals are presented, and consequences for practical realization of these experiments are discussed.

Polarimetry of transmission gratings

We have investigated the polarizing properties of gold wire gratings in the resonance domain. The partial polarizing properties of 1-μm period gratings in the near IR are then used to orient the wire structure of transmission grating facets parallel to each other by means of an alignment polarimeter technique. The absolute alignment accuracy for these gratings is limited by the influence of the support structure on the orientation of the polarization ellipse. If the polarizing properties of this perturbative component are known, the accuracy can be enhanced by treating the polarization by means of the Mueller calculus.

Azimuthal alignments in ellipsometry: a high-precision method using a polarization modulator

An original (to the best of our knowledge) method to achieve azimuthal alignments of all polarizing components in ellipsometry is presented. It is an accurate nulling method, and it is easy to implement and can be used with any isotropic reflecting layer. It also allows one to check the eventual presence of surface anisotropy. The ferrofluid modulator used in this setup is briefly described. Measurements made for three reflecting surfaces (fused silica, silicon, and germanium) are presented.

Two-channel polarization modulation ellipsometer

A new wavelength-scanning two-channel polarization modulation ellipsometer is described, where a photo-elastic modulator is used and the analyzed light is separated into orthogonally polarized beams using a Wollaston prism. Both beams are detected using phototubes whose bias voltage is dynamically controlled for constant dc. The dc from each phototube is measured with a digital voltmeter, and the fundamental and second harmonic of the phototube current are measured using individual lock-in amplifiers. All three of the associated ellipsometric parameters (N = cos2psi, S = sin2psi sindelta, and C = sin2psi, cosDelta) can be determined simultaneously in a single scan. The versatility of the instrument is demonstrated by the determination of the optical functions of Si from 238 to 652 nm (5.3-1.9 eV).

High-speed retardation modulation ellipsometer

Construction and performance of a high-speed retardation modulation ellipsometer are described. An ADP four-crystal electrooptic modulator is used for the retardation modulation and a high-speed digitizer for the simultaneous detection of the transmitted light intensity and the modulation voltage. The ellipsometer can acquire the necessary data for determining a data point (Psi, Delta) in 4 microsec and repeat the data acquisition for fifty data points at intervals of 4 microsec-160 msec. In such conditions, precision represented in terms of an average of root mean squares is 0.05 degrees in Psi and 0.15 degrees in Delta when a BaK1 standard optical glass is used as a sample at the present stage. An example is given of the application to rapid growth of anodic films on a semiconductor GaAs wafer.