Ellipsometers

An ellipsometer is an optical instrument used to measure the change in polarization of light upon reflection from or transmission through a sample. This change in polarization is dependent on the optical properties of the material, specifically its refractive index and extinction coefficient, as well as the thickness of thin films present on the sample's surface. Ellipsometry is a non-destructive technique, meaning it does not damage the sample being analyzed.

The fundamental principle behind ellipsometry involves analyzing how a polarized light beam's state of polarization changes as it interacts with a sample. Typically, light is polarized into two perpendicular components, often referred to as 's' and 'p' components. After interacting with the sample, the relative amplitude and phase difference between these components are altered. An ellipsometer measures these changes, which are commonly expressed as the ellipsometric parameters psi (Ψ) and delta (Δ).

By fitting the measured Ψ and Δ values to an optical model that describes the sample's structure (e.g., substrate, film layers, and their optical properties), one can determine unknown parameters such as film thickness, refractive index, and extinction coefficient. This makes ellipsometry a powerful tool for characterizing thin films, semiconductors, dielectrics, and various other materials used in industries like microelectronics, optics, and materials science. Different types of ellipsometers exist, including rotating analyzer ellipsometers (RAE) and rotating retarder ellipsometers, differing in how they modulate the polarization state. Spectroscopic ellipsometry analyzes the ellipsometric parameters over a range of wavelengths, providing more comprehensive material characterization.