Fundamentals and applications of spectroscopic ellipsometry

Abstract

Recebido em 1/8/01; aceito em 8/11/01 This paper describes the use of ellipsometry as a precise and accurate technique for characterizing substrates and overlayers. A brief historical development of ellipsometry and the basic principles necessary to understand how an ellipsometer works are presented. There are many examples of studies performed in addressing materials science issues, and several are presented here: measurements of thickness, optical properties, and modeling of surface roughness. These selected results obtained in our laboratory for substrates, Si/SiO 2 interfaces, and polymers provide evidence that ellipsometry can play a critical role in characterizing different types of materials.Keywords: ellipsometry; polarization; films. BRIEF HISTORICAL OVERVIEWEllipsometry (reflection ellipsometry) measures the changes in the state of polarization of light upon reflection from a surface. The fact that changes are measured rather than the absolute intensity of light renders ellipsometry sensitive to submonolayer surface coverage. As a non-invasive and non-destructive tool, ellipsometry requires only a low-power light source and, consequently, it does not affect most processes, which renders ellipsometry a convenient tool for in situ studies 1,2 . P. Drude 3 was the first to build an ellipsometer even before Rothen has coined the word 'ellipsometry ' in 1945 4 . The equipment built by Drude is surprisingly very similar to many types of instruments in use today. Except for sparse papers, this technique received little attention for several decades after Drude, but in the 1970's and 1980's, ellipsometry became widely utilized, and relevant technical papers [5][6][7] and a classical book 8 were produced during this period. In 1991, Azzam compiled a considerable number of papers on ellipsometry 9 . As a search of the literature indicates, the number of papers on experimental improvement of ellipsometers has been decreasing in the last years, because many of the problems that existed before the advance of computers have been solved, including measurement speeds and spectral range. Most of the equipment used today is automated with wide band light sources, scanning monochromators, optical multichannel analyzers, and interfaces with acquisition and analysis software. Early studies on ellipsometry were performed using single wavelength equipment, usually a wide band visible light source with a filter, and later lasers. However, spectroscopic ellipsometers are commonly used nowadays in different research fields. BASIC CONCEPTSA description of ellipsometry as an optical technique would not be complete without mentioning J.C. Maxwell (1831-1879). Maxwell's theory predicts that light is a wave represented by two mutually perpendicular vectors: E, the amplitude of the electric field strength, and B, the amplitude of the magnetic field strength, and both E and B are also perpendicular to the direction of propagation, z. The electromagnetic wave is described by its amplitude and frequency in complex form:where E ...

Investigation of Gold Nanolayer Properties Using X-Ray Reflectometry and Spectroscopic Ellipsometry Methods

“…The SE is non-invasive and non-destructive technique which measures the changes in the state of polarization of light upon reflection from a surface [6]. The polarization change is represented as an amplitude ratio Ψ , and the phase difference ∆.…”

Surface Characterization of Absorbing Polymer Films Deposited on Transparent Glasses

“…Ellipsometry measures the changes in phase (Δ) and amplitude (Ψ) between the p and s components of polarized light, thus expressed as the complex reflection coefficient, [8][9][10][11][12]. The reflectance (R p and R s ) and phase difference (δ rs and δ rp ) for the s-and pcomponents of light as a function of θ 0 (angle of incidence) can be calculated for a glass substrate with a defined index of refraction.…”

“…The reflectance (R p and R s ) and phase difference (δ rs and δ rp ) for the s-and pcomponents of light as a function of θ 0 (angle of incidence) can be calculated for a glass substrate with a defined index of refraction. Figure 1 shows how the reflectance (a) and phase shift (b) vary with the angle of incidence for a glass with n = 1.50 at an air/glass interface, and calculated by using the Fresnel coefficients for the p and s components of the reflected light for a single interface between medium 0 (ambient) and medium 1 (substrate) [8][9][10][11][12]. In Figure 1a, it can be noticed that R s increases monotonically with θ 0 , and R p is close to zero at θ B , that is in this case 56.3 .…”

“…However, accurate interferometry requires film optical properties; profilometry is dubious for most polymer films because they are usually soft, and AFM works well for ultra-thin polymer films that have appropriate steps [7]. Spectroscopic ellipsometry (SE) emerges as an alternative technique that can be used to obtain thickness (L), refractive index (n) and extinction coefficient (k) of overlayers on substrates including transparent glasses [8][9][10][11][12].…”

“…The advantage of SE over other techniques for analysis of surfaces and interfaces is that SE is a nondestructive and noninvasive technique, no special requirements on the sample preparation is necessary, and measurements can be made in minutes [8,9]. However, data analysis requires the establishment of an optical model.…”