Deassociate the initial temporal phase deviation provided by photoelastic modulator for stroboscopic illumination polarization modulated ellipsometry

Abstract

In addition to operating the imaging ellipsometric measurements by four-specific temporal phases in the photoelastic modulated ellipsometry, we added the fifth one to solve the initial phase of the photoelastic modulator. This methodology has been developed to conquer the slow imaging processing of charge-coupled device camera for the stroboscopic illumination in the polarization modulated imaging ellipsometry. Without any calibration in its initial phase, we can perform the ellipsometric measurement by the measurements of intensity at five-specific temporal phases. The intensities of a full cycle for a point on SiO(2)∕Si thin film were measured and analyzed for verifying this algorithm. The five stroboscopic illuminations were performed to measure the two-dimensional distribution of the same SiO(2)∕Si thin film.

Photoelastic Modulated Imaging Ellipsometry

“…The frequency drift of PEMs and image recovery were taken more effort on calibration and measurement [22][23][24][25]. We adopted a simple approach by just changing the manner of light illumination from continuous mode to pulse mode, which coordinates with the reference signal of the PEM modulator, known as the stroboscopic illumination technique [14][15][16][17][18]. Stroboscopic effect is a result of temporal aliasing that occurs when continuous motion is represented by a series of short samples.…”

“…(20). The correction of phase shift x can also be achieved by the time shift delays of the pulses [15].…”

“…For single spot measurement, one can employ either lock-in amplifiers or the Fourier analysis technique to obtain the ellipsometric parameters in near real-time, but this approach is not applicable for a two-dimensional measurement, because the modulation frequency of the PEM is too high to compare it with the exposure times of the CCD camera. This deficiency was overcome by replacing the light source with an ultra-stable short pulse, known as the stroboscopic illumination technique, which was synchronized with the PEM modulation to freeze the intensity signal at specific times in the modulation cycles [14,15]. As a result, the ellipsometric images can be obtained in seconds by sequentially taking four images with single wavelength source.…”

The Development of Three-Intensity Measurement in PSA Ellipsometry and Photoelastic Modulation Ellipsometry

“…In this technique, one has to calibrate the initial phase for synchronizing the four specific phases to perform ellipsometric measurements. Again, with the help of symbolic computer program, Mathematica, Tsai [29] de-associated the initial phase by extra strobe measurement. This PEM stroboscopic imaging ellipsometry can measure a moving sample dynamically, such as the motion of dropping oil on SiO 2 film.…”