Kamil Postava

Spectroscopic ellipsometry of epitaxial ZnO layer on sapphire substrate

Optical properties of epitaxial ZnO layers have been studied in the spectral region from 1.5 to 5.4 eV using four-zone null spectroscopic ellipsometry. An existing model dielectric function based on excitonic structure near direct band gap has been improved by including a high-energy absorption term. Surface layer, corresponding to the surface roughness, was found to be essential to fit the spectroellipsometric data obtained. Two kinds of samples have been studied: ZnO layers prepared on (0001) and (1120)-oriented sapphire substrates. The surfaces of the first ones were found to be more rough.

Linear and quadratic magneto-optical measurements of the spin reorientation in epitaxial Fe films on MgO

Abstract We have undertaken a detailed study by magneto-optical techniques of in-plane magnetization reversal behaviour in epitaxial Fe films grown by MBE on (10 0) oriented MgO substrate. We measure Mue5f8H loops for both orthogonal in-plane magnetization components Mt (component parallel to the magnetic field) and Mt (component perpendicular to the field) and for various orientations of the magnetic field with respect to the crystalline axis. These measurements show the classical four-fold cubic anisotropy for large Fe film thickness and confirm the appearance of weak uniaxial in-plane anisotropy superimposed for thinner films ( t = 20 A ). We have demonstrated the appearance of strong asymmetrical hysteresis loop for p-polarized incident light. We explain this behaviour as the mixing of transverse magnetization contribution to the longitudinal magnetization measurements on the basis of quadratic magneto-optical effects. The calculation of these effects based on eigenmode propagation in anisotropic layered media are developed by including the second-order magneto-optical terms in the permittivity tensor characteristic of a cubic crystal. The second-order reflection coefficients are discussed in the case of the normal incidence of the laser beam and for the magnetic field along the hard axis of the Fe film.

Doping effects on optical properties of epitaxial ZnO layers determined by spectroscopic ellipsometry

Optical properties of Al- and Ga-doped ZnO layers have been studied in the spectral range from 1.5 to 5.4 eV using a four-zone null spectroscopic ellipsometer and in the spectral range from 0.5 to 6.5 eV using near-normal incidence reflectivity measurements. The layers were prepared by RF magnetron sputtering onto (1 1 2 0) oriented single-crystal sapphire substrates. Al- and Ga-doping gives rise to a shift of the fundamental absorption edge from 3.4 to 3.7 eV. The model dielectric function (MDF) based on an excitonic structure derived by Tanguy [Phys. Rev. B 60 (1999) 10660] was completed by the Sellmeier and Drude terms. The Drude term describes a free-electron contribution originating from presence of the dopant. Spectroscopic ellipsometry and reflectometry are very sensitive to a surface roughness. The surface roughness was modeled by a surface layer of the Bruggeman effective medium and by diffraction theory.

Anisotropy of quadratic magneto-optic effects in reflection

Quadratic or second-order magneto-optic effects in reflection significantly effect in-plane magnetization measurements. While the magneto-optic effects linear in magnetization are independent of orientation of cubic crystal axes, the amplitude and sign of the quadratic effects change significantly under crystal rotation. Theoretical formulas for the magneto-optic effects have been derived using a permittivity tensor including terms quadratic in magnetization. A method for separation of the diagonal and off-diagonal quadratic magneto-optic tensor components (G11−G12) and 2G44 is proposed. The theory was completed by an experimental observation of the quadratic effect anisotropy in an epitaxial Fe layer prepared on a MgO substrate. The influence of the magnetization components on the magneto-optic vector magnetometry is discussed for an interface, a single layer, and exchange coupled bilayer system for a general magnetization direction including the quadratic magneto-optic effect anisotropy.

Spectroellipsometric characterization of materials for multilayer coatings

The optical functions of titanium dioxide (TiO2), tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2) have been determined in the spectral range from 1.5 to 5.4 eV (wavelength range from 230 to 840 nm). The ellipsometric spectra of 200 nm thick layers sputtered on a glass substrate were measured by a four-zone null spectroscopic ellipsometer. The data have been fitted by a Tauc–Lorentz model recently derived by Jellison and Modine for the optical functions of amorphous materials. The model dielectric function is based on a combination of the Tauc band edge and the Lorentz oscillator. The effects of the surface and interface layers and layer inhomogeneity on the measured data are discussed.

Magneto-optic polar Kerr and Faraday effects in magnetic superlattices

Magneto-optic (MO) effects in magnetic multilayers with periodic regions are discussed assuming normal incidence of polarized waves and polar magnetization (Faraday and polar Kerr effects). From the (4 × 4)-matrix formalism simplified analytical expressions linear in the off-diagonal permittivity tensor element are obtained with no loss in accuracy. The MO effects are expressed as weighted sums of contributions from individual layers. Approximate expressions are given for the case when the thickness of magnetic layers is much smaller than the radiation wavelength. The procedure is illustrated on superlattices consisting of symmetric sandwiches of ultrathin magnetic and non-magnetic metallic layers.

Optical characterization of TiN/SiO2(1000 nm)/Si system by spectroscopic ellipsometry and reflectometry

Titanium nitride (TiN) films are used as diffusion barrier layers in the semiconductor industry. There is a need for accurate data on optical properties, because film thickness are usually monitored by optical methods. There are further needs to characterize TiN/(interlayer dielectrics)/Si system simultaneously. Thus, TiN(35, 60, 90 and 105 nm)/SiO2(1000 nm)/Si samples were prepared using sputtering from a TiN target in argon and nitrogen atmosphere. Those samples were characterized using simultaneous fits of multiple angle of incidence spectroscopic ellipsometry and normal incidence spectroscopic reflectivity. TiN films partially transmit light that interferes in the thick thermal silicon oxide, which gives more detailed information on the optical properties of TiN. Consequently optical dielectric function of TiN as well as two thickness of TiN and SiO2 were successfully determined simultaneously.

Optical functions of low-k materials for interlayer dielectrics

The optical functions of low dielectric constant (low-k) materials have been determined using a high-precision four-zone null spectroscopic ellipsometer in the spectral range from 1.5 to 5.4 eV (230–840 nm wavelength region). The ellipsometric data were fitted simultaneously with near-normal incidence reflectivity spectra (ranging from 0.5 to 6.5 eV). A general method of simultaneous treatment of ellipsometric and reflectivity data is demonstrated on representative materials used in the semiconductor industry for interlayer dielectrics: (1) SiLK—organic dielectric resin from the Dow Chemical Company, (2) Nanoglass—nanoporous silica from the Honeywell Electronic Materials Company, and (3) tetra-ethyl-ortho-silicate (TEOS) (SiO2)—the standard dielectric material. The low-k materials (SiLK and Nanoglass) were prepared by a standard spin-coating process, while the SiO2 layer was prepared by thermal decomposition from TEOS onto single-crystal silicon wafers.The optical functions of low dielectric constant (low-k) materials have been determined using a high-precision four-zone null spectroscopic ellipsometer in the spectral range from 1.5 to 5.4 eV (230–840 nm wavelength region). The ellipsometric data were fitted simultaneously with near-normal incidence reflectivity spectra (ranging from 0.5 to 6.5 eV). A general method of simultaneous treatment of ellipsometric and reflectivity data is demonstrated on representative materials used in the semiconductor industry for interlayer dielectrics: (1) SiLK—organic dielectric resin from the Dow Chemical Company, (2) Nanoglass—nanoporous silica from the Honeywell Electronic Materials Company, and (3) tetra-ethyl-ortho-silicate (TEOS) (SiO2)—the standard dielectric material. The low-k materials (SiLK and Nanoglass) were prepared by a standard spin-coating process, while the SiO2 layer was prepared by thermal decomposition from TEOS onto single-crystal silicon wafers.

Magneto-optic polar Kerr and Faraday effects in periodic multilayers

Magnetooptic (MO) effects in magnetic multilayers with periodically stratified regions are analyzed for the case of normal light wave incidence and polar magnetization (Faraday and polar Kerr effects). From the universal 4 x 4-matrix formalism simplified analytical representations restricted to terms linear in the off-diagonal permittivity tensor elements are obtained with no loss in accuracy. The MO effects are expressed as weighted sums of contributions from individual layers. Approximate expressions useful for the evaluation of trends in MO effects are given for periodic multilayers consisting of blocks with ultrathin magnetic films. The procedure is illustrated on periodic systems built of symmetric units. Limits on the ultrathin approximation are discussed.

Estimation of the dielectric properties of low-k materials using optical spectroscopy

The dielectric function spectra of low dielectric constant (low-k) materials have been determined using spectroscopic ellipsometry, near-normal incidence spectroscopic reflectometry, and Fourier transform infrared transmission spectrometry over a wide spectral range from 0.03 to 5.4 eV (230 nm to 40.5 μm wavelength region). The electronic and ionic contributions to the overall static dielectric constant were determined for representative materials used in the semiconductor industry for interlayer dielectrics: (1) FLARE—organic spin-on polymer, (2) HOSP—spin-on hybrid organic-siloxane polymer from the Honeywell Electronic Materials Company, and (3) SiLK—organic dielectric resin from the Dow Chemical Company. The main contributions to the static dielectric constant of the low-k materials studied were found to be the electronic and ionic absorptions.