Spectral interferometric technique to measure the ellipsometric phase of a thin-film structure

Abstract

A two-step white-light spectral interferometric technique is used to retrieve the ellipsometric phase of a thin-film structure from the spectral interferograms recorded in a polarimetry configuration with a birefringent crystal. In the first step, the phase difference between p-and s-polarized waves propagating in the crystal alone is retrieved. In the second step, the additional phase change that the polarized waves undergo on reflection from the thin-film structure is retrieved. The new method is used in determining the thin-film thickness from ellipsometric phase measured for SiO 2 thin film on a Si substrate in a range from 550 to 900 nm. The thicknesses of three different samples obtained are compared with those resulting from polarimetric measurements and good agreement is confirmed. c 2009 Optical Society of America OCIS codes: 120.3180, 120.5050, 120.5410, 120.5700, 240.0310. Ellipsometry and interferometry are widely used techniques for the analysis of surfaces and thin films. Various ellipsometry types are employed to determine the thickness and the optical properties of thin film. Ellipsometric measurements performed at a single wavelength and a fixed angle of incidence are used to determine the amplitude and phase changes of p-and spolarized components to provide the film thickness and optical constants [1]. Measurements by spectroscopic ellipsometry provide the results over a wide wavelength range with greater precision and accuracy [2]. The use of white-light interferometry [3] was extended into the spectral domain [4,5] where the phase of the reflected wave, which changes as a function of wavelength and layer thickness [6,7], is inscribed in the recorded interferogram (channeled spectrum). There are also available single-wavelength interferometric ellipsometers [8] that employ Michelson or Mach-Zehnder interferometer. In this Letter, a two-step white-light spectral interferometric technique for measuring ellipsometric phase of a thinfilm sample is presented. The technique, which is a modification of the technique originally employed for surface plasmon resonance sensing [9], utilizes a polarimetry configuration with a birefringent crystal that allows to obtain the channeled spectrum. Two such spectra, one including reflection of p-and s-polarized waves from the thin-film sample and the other one without the reflection, are used to retrieve the ellipsometric phase. Moreover, in the same polarimetric configuration, the ratio between the reflectances of both polarization states is measured. Let us consider a simple experimental setup as shown in Fig. 1 proposed for measuring the wavelength dependence of ellipsometric phase of a thin-film structure. The collimated beam from a white-light source passes through a polarizer oriented 45• with respect to the plane of incidence so that both p-and s-polarized components are generated. Next, the beam passes through the birefringent crystal whose optical axis is perpendicular to the plane of incidence and the phase delays φ p,s (λ) for the p-and s-polarize...

Maxima of the spectral reflectance ratio of polarized waves used to measure the thickness of a nonabsorbing thin film

“…This is demonstrated in determining the thicknesses of a SiO 2 thin film prepared by thermal oxidation on a Si wafer. The results are compared with those obtained by the algebraic fitting method [11], and very good agreement is confirmed. …”

“…The procedure for the measurement of the reflectance ratio R p (λ)/R s (λ), which corresponds to tan 2 Ψ(λ), where Ψ(λ) is the ellipsometric angle, consists of three steps: first, with the source blocked, the background spectrum I bkg (λ) is measured; second, with the analyzer oriented perpendicularly to the plane of the incidence, the reflection spectrum I s (λ) for s polarization is measured; and third, with the analyzer oriented parallel to the plane of the incidence, the reflection spectrum I p (λ) for p polarization is measured. The reflectance ratio R p (λ)/R s (λ) of the structure is given by [11] …”

“…To use a cheaper instrumentation compared to expensive spectral reflectometers and ellipsometers, we propose measurement methods allowing one to characterize thin films employing only the wavelengths of the maxima and minima in the spectral reflectances [7] or the maxima in the ratio between the spectral reflectances of p-and s-polarized components measured at oblique incidence of light. The ratio between the spectral reflectances of the two polarization states can be measured in a simple polarimetry configuration [11] using the procedure with only two orientations of an analyzer.…”

Surface Plasmon Resonance Based Sensing of Aqueous Solutions Using Spectral Interferometry

“…1). The reflectance ratio R p (λ)/R s (λ) measurement consists of three steps [5]. First, with the source blocked, the background spectrum I bkg (λ) is measured; second, with the analyzer oriented perpendicularly to the plane of the incidence, the reflection spectrum I s (λ) for s-polarization is measured; and third, with the analyzer oriented parallel to the plane of the incidence, the reflection spectrum I p (λ) for p-polarization is measured.…”

“…Spectral reflectance and spectral phase change measurements rank among often used techniques in the last year [5,6]. There are several techniques, based on the fringe analysis in the spatial, temporal and spectral domain, which are able to retrieve the phase changes caused by the SPR effect according to experimental conditions [1,3,5].…”