Abstract:We present a white-light spectral interferometric technique for measuring the absolute spectral optical path difference (OPD) between the beams in a slightly dispersive Michelson interferometer with a thin-film structure as a mirror. We record two spectral interferograms to obtain the spectral interference signal and retrieve from it the spectral phase, which includes the effect of a cube beam splitter and the phase change on reflection from the thin-film structure. Knowing the effective thickness and dispersion of the beam splitter made of BK7 optical glass, we use a simple procedure to determine both the absolute spectral phase difference and OPD. The spectral OPD is measured for a uniform SiO 2 thin film on a silicon wafer and is fitted to the theoretical spectral OPD to obtain the thin-film thickness. The theoretical spectral OPD is determined provided that the optical constants of the thin-film structure are known. We measure also the nonlinear-like spectral phase and fit it to the theoretical values in order to obtain the thin-film thickness.

We report on processing the spectral interference signals by a new method based on a windowed Fourier transform applied in the wavelength domain. First, the numerical simulations are performed to demonstrate high precision of the phase retrieval from the spectral signal. Second, the feasibility of the method is confirmed in processing experimental data from a dispersive Michelson interferometer comprising a cube beamsplitter made of BK7 glass. From the retrieved spectral phase difference, the effective thickness of the beamsplitter is determined precisely.

A new method for a precise measurement of the oscillatory part of phase change on reflection (interferometric phase) from a thin-film structure is presented. The method, which is based on phase retrieval from the spectral interferograms recorded at the output of a slightly dispersive Michelson interferometer, is combined with reflectometry. The interferometric phase of the thin-film structure is measured precisely using a reference sample of known phase change on reflection. The spectral reflectance of the thin-film structure is also measured in the interferometer. The feasibility of the method is confirmed in processing the experimental data for SiO 2 thin film on a silicon wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. We confirm very good agreement between the thicknesses obtained from the interferometric phase and reflectance measurements.

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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...

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