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Overview: Spectroscopic ellipsometry has been widely used in materials science, microelectronics, physical chemistry and biomedicine due to the advantages of non-destructive, non-interference, fast speed and high accuracy. Many researchers have improved system models to correct the effect by artifacts of spectroscopic ellipsometry system, including those artifacts of polarizer due to its optical activity, leakage and stress birefringence, artifact of wave plate compensator, the correction to finite numerical aperture and the finite spectral bandwidth, as well as those artifacts by focusing lens due to the optical activity and stress birefringence. Additionally, we considered in this paper the influence of polarization degree of the light source and polarization sensitivity of spectrometer, and find that these artifacts need to be corrected for ultra-high accuracy measurement. Furthermore, we presented here a method to measure the polarization correlation coefficients simultaneously for light source and spectrometer. Theoretically, the polarization correlation coefficients of the light source can be measured by a spectrometer with known polarization characteristics, and the polarization correlation coefficients of the spectrometer can be measured by a light source with known polarization state. However, these measurement methods rely on additional characterized light sources and spectrometers, which can be troublesome often.
In this article, we analyzed the effect of polarization parameters of light source and spectrometer on spectroscopic ellipsometry via a correction model; and proposed a method for measuring the polarization correlation coefficients of light source subsystem and spectrometer subsystem simultaneously and mutually. This is done by adding polarizers or combination of polarizers and wave plates between light source and spectrometer subsystem. For illustration of the measurement method, we demonstrated the feasibility by measuring the polarization correlation coefficients of the light source and spectrometer in our laboratory. The measurement results show that the degree of polarization of our light source has a relatively large variation over 400 nm~800 nm range, and a sharp spike in 425 nm~460 nm is found. Since this band coincident with the combination band of a deuterium lamp and a halogen lamp, this may indicate a large polarization dependent reflectivity of the beam combiner. The polarization correlation coefficient of the spectrometer is below 0.05, which shows that the spectrometer may take polarization insensitive design to reduce the polarization dependence of reflective gratings.
Structural schematic diagram of spectroscopic ellipsometry measurement system
Schematic diagram of polarization correlation coefficients measurement setup for light source subsystem and spectrometer subsystem, where P, A are polarizers and C is a wave plate. (a) Schematic diagram of (A1, A2, P1, P2) measurement setup; (b) Schematic diagram of P3 measurement setup; (c) Schematic diagram of A3 measurement setup
Experimental device for measuring polarization correlation coefficient of light source and spectrometer
Measurement results of polarization correlation coefficients of light source subsystem and spectrometer subsystem