Single-angle-of-incidence single-element rotating-polarizer (Single SERP) ellipsometer for film-substrate systems

Abstract

The single-element rotating-polarizer ellipsometer is where a rotating polarizer is inserted into the incident beam and the reflected-signal intensity is detected using a photodetector. The polarizer is either rotated mechanically or electromagnetically. The angle of incidence of the beam is adjusted to detect the angles where the detector signal is dc. The ellipsometric function of the film-substrate system under measurement is of a unity magnitude at those detected angle(s). The number of required measurements (such angles of incidence) is related (directly proportional) to the number of system parameters to be determined: film thickness is one parameter, film optical constant is two parameters, and substrate optical constant is two parameters. The more parameters to be determined, the more the number of measurements required. This creates film-thickness bands, which number and width depend on the system physical properties and the wavelength used for measurement, and where a continuum exists above a certain film-thickness value. Accordingly, full characterization of film-substrate systems is limited to systems with large film thicknesses for the required multiple angles of incidence to exist. In this paper, we use only one detected angle of incidence to fully characterize the film-substrate system. This allows for film-substrate systems with much smaller film thicknesses to be fully characterized. A fast genetic algorithm is used to heuristically obtain all the system parameters: film thickness and optical constants of the film and the substrate, or any subset thereof.

Single-instrument morphology: single-element polarizer (SEP) ellipsometers, reflecsometers, elliptometers, and reflectometers

“…The same instrument with a different DRM would lead to a different ellipsometer, in some cases totally different. For example, combining any experimental technique with the proper heuristic DRM would change a multiple-angle-of-incidence ellipsometer to a single-angle-of-incidence one [16,17]. Therefore, the selection of the DRM is important, and is crucial for some applications; using the ellipsometer in real-time applications, such as a component in a control loop for example.…”

“…We introduced this concept in Reference [16]. There is synergy between these two parts, and the total energy involved is directly related to that synergy.…”

“…The detector signal is given by; In Eq. 11, the term I includes a detector constant and the intensity of the incident beam [16], where P is the polarizer azimuth and the amplitudes of the two signal components are the p and s reflectances, respectively. Equation 11 holds for all modes of operation.…”