Ellipsometry is a well-known non-destructive optical method for determining film thickness and optical properties. It measures the change in the state of polarization of the light reflected off the film«s surface.
Fast ellipsometry methods, single or multi-wavelength, have been adopted for monitoring film growth in situ, allowing for the precise control of film deposition processes.
The advancement of spectroscopic ellipsometers has extended the analytical power of ellipsometry to complex multilayer coatings, where several optical parameters (refractive index, extinction coefficient, film thickness, roughness anisotropy, etc.) can be determined simultaneously.
Ellipsometry remains a macroanalysis technique, i.e., the sample size cannot be any smaller than a few millimeters. The development of imaging ellipsometry (Figure2), which combines the power of ellipsometry with microscopy, has overcome this limitation. The enhanced spatial resolution of imaging ellipsometers potentially expands ellipsometry into new areas of microanalysis, microelectronics, and bio analytics.
The unique imaging ellipsometer EP³ operates on the principle of classical null ellipsometry and real-time ellipsometric contrast imaging. The laser beam is elliptically polarized after it passes through a linear polarizer (P) and a quarter-wave plate (C). The elliptically polarized light is then reflected off the sample (S) onto an analyzer (A) and imaged onto a CCD camera through a long working distance objective.
In this PCSA configuration, the orientation of the angles of P and C is chosen in such a way that the elliptically polarized light is completely linear polarized after it is reflected off the sample. As shown in Figure3, the ellipsometric null condition is obtained when A "crossesÓ with respect to the polarization axis of the relected light, i.e., the state at which the absolute minimum of light flux is detected at the CCD camera.
The angles of P, C, and A that obtained the null condition are related to the optical properties of the sample. Reduction of the measured data with computerized optical modeling leads to a deduction of film thickness and the complex refractive indexes.