Showing papers on "Ellipsometry published in 1988"

Adsorption of ordered zirconium phosphonate multilayer films on silicon and gold surfaces

Abstract: Multilayer films of zirconium 1,10-decanediylbis(phosphonate) have been prepared on silicon and gold substrates and characterized by ellipsometry, XPS, and electrochemical measurements. The deposition technique requires first covalent attachment or adsorption of a phosphonic acid anchoring agent; HO(CH/sub 3/)/sub 2/Si(CH/sub 2/)/sub 3/PO/sub 3/H/sub 2/ (I) and (-S(CH/sub 2/)/sub 4/PO/sub 3/H/sub 2/)/sub 2/ (II) were used with Si and Au, respectively. The functionalized substrates are exposed alternately to aqueous ZrOCl/sub 2/ and 1,10-decanediylbis(phosphonic acid) solutions to yield multilayer films. Ellipsometry shows an increase in film thickness, on Si, of 17 A/layer, which corresponds to the layer spacing in bulk Zr(O/sub 3/PC/sub 10/H/sub 20/PO/sub 3/). Variable take-off angle X-ray photoelectron spectra from four-layer films have attenuated Si peaks but strong Zr and P peaks when the detector is 70/sup 0/ off the surface normal, implying that the films on Si are continuous. Electrochemical comparison of bare and functionalized Au shows facile electron transfer between Au or Au-II electrodes and 1 mM aqueous Fe(CN)/sub 6//sup 3 -/ but nearly complete blocking of electron transfer at Au-II electrodes immersed once each in ZrOCl/sub 2/ and 1,10-decanediylbis(phosphonic acid) solutions.

Investigation of the void structure in amorphous germanium thin films as a function of low-energy ion bombardment

Abstract: Amorphous germanium thin films were prepared by electron‐beam evaporation with low‐energy Ar ion assist. The ion energy and ion/atom arrival rate ratio were varied from 15 to 110 eV and between 0% and 25%, respectively. The low‐density ‘‘void’’ network structure was observed by transmission electron microscopy and characterized by spectroscopic ellipsometry. The void content of the films was shown to depend strongly on the ion/atom arrival rate ratio and to a lesser extent on the incident ion energy. A more quantitative description of thin‐film evolution and important factors which affect it are discussed.

Structure and properties of sputtered carbon overcoats on rigid magnetic media disks

Abstract: Sputtered carbon overcoats on commercial rigid disks with thin‐film magnetic media are studied using transmission electron analysis (microscopy, microdiffraction, and energy‐loss spectroscopy), Raman spectroscopy, Auger spectroscopy, ellipsometry, x‐ray diffraction, and microhardness testing. Data from transmission electron analysis, Raman spectroscopy, and ellipsometry suggest that the carbon overcoats are composed of small graphite crystallites (≤2 nm), randomly oriented, with a small percentage (0%–5%) of fourfold coordinated carbon bonds. Auger spectroscopy and transmission electron energy‐loss spectroscopy indicate the presence of a small amount of oxygen. Auger spectroscopy also shows some surface nitrogen. The optical constants, n=2.1 and k=0.78, exhibit a small wavelength dependence. In addition, the extinction coefficient k shows a dependence upon film thickness. X‐ray diffraction and microhardness testing did not yield any information concerning the carbon overcoats. There was no indication of d...

Ellipsometric analysis for surface roughness and texture

Abstract: A 2-D symmetric model is incorporated into the calculation of the ellipsometric parameters Psi and Delta for surface roughness and texture characterization based on the effective medium theory. The least-squares fits of the experimental data at a 5-microm IR wavelength for rough fused silica samples at multiple angles of incidence give the standard deviations of Psi and Delta of about twice the instrumental errors. The effective thickness and the depolarization factor obtained by ellipsometry agree with the roughness and average height-to-halfwidth ratio of voids obtained by stylus profilometry. The surface texture can be characterized by the fit depolarization factors set. The excellent agreement between theory and experiments indicates that ellipsometry can be a promising nondestructive technique for rough-surface evaluation.

Calibration method for rotating-analyzer ellipsometers

Abstract: In operating a rotating-analyzer ellipsometer one must know the plane of incidence accurately. We present a new calibration method, phase calibration, which is complementary to residue calibration Phase calibration is shown to be superior to the residue method for Δ 5π/6;.

Growth dynamics of aluminum nitride and aluminum oxide thin films synthesized by ion‐assisted deposition

Abstract: Some aspects of the dynamics of thin‐film synthesis of aluminum nitride and aluminum oxide produced by ion‐assisted deposition have been deduced from in situ measurements by ellipsometry, photometry, and ion scattering spectroscopy. Measurements obtained during the etching of aluminum films by nitrogen and oxygen ion beams have established the thickness of the synthesized layer and the rate of compound formation. Some of these measurements have been compared with a theoretical model which predicts the time evolution of the synthesized surface layer as well as the steady‐state layer thickness. The breakdown voltage and variation of capacitance with applied voltage of aluminum oxide films prepared by ion‐assisted deposition are also presented. Furthermore, the optical properties of ion‐assisted AlN and Al2O3 in the visible region are given.

Adsorpton at the liquid surface studied by means of specular reflection of neutrons

Abstract: Etude de l'adsorption d'une couche monomoleculaire d'arachidate de butyle a l'interface air-liquide

Line shape of the optical dielectric function

Abstract: A systematic study of the optical dielectric function by spectroscopic ellipsometry and electroreflectance has shown that the proper functional form for the Green’s function for an electron‐hole pair in GaAs or CdTe is primarily Gaussian, not Lorentzian as is commonly assumed, although it is primarily Lorentzian for Hg1−xCdxTe. The Lorentzian part of the broadening is shown to measure the alloy, impurity, and defect scattering.

Stress measurements in sol-gel films

Abstract: Thin solid films of a wide variety of materials have received increased attention during the past decade. These films have been instrumental in the growth of numerous technologies. Until recently, “thin films” have primarily described layers of metallic or dielectric materials deposited onto substrates by evaporation, electron beam or ion beam techniques. Advances in sol-gel technology have extended film research to include “glassy” materials of either crystalline, or amorphous nature. Sol-gel films can be tailor-made to accommodate a diverse range of applications due primarily to flexibility in chemical make up which determines the respective film's structure. One important characteristic of such films is their inherent residual stress. This inherent stress, and the stress the film introduces to the substrate as it is deposited, can result in a complex stress profile. While “thin” in the case of sol-gel films generally means <1 μm in thickness, large (10–100s of nm of retardance) inherent stress per unit thickness can severely limit a film's performance and subsequent application. We describe our efforts to quantify the residual stress in silica-based sol-gel films as a function of several processing parameters.

Characterization of dielectric-coated, metal mirrors using surface plasmon spectroscopy.

Abstract: The surface plasmon spectroscopy (SPS) technique is used in the characterization of dielectric-coated metal mirrors. Experiments performed on a MgF2-coated aluminum mirror indicate good agreement between SPS and ellipsometry techniques for the determination of coating thickness. In addition, the optical constants of aluminum obtained from the same experiment agree well with values presented in the literature. Advantages of SPS are that it is a simple procedure providing a high degree of accuracy, and only a single measurement is required to yield both the film thickness and the complex permittivity of the substrate.

Ellipsometric and optical reflectivity studies of reactively sputtered NbN thin films

Abstract: The optical parameters of NbN thin films reactively sputtered mainly at room temperature are investigated by in situ ellipsometry using a He‐Ne laser source. Systematic correlations between the ellipsometric parameters and the film properties are observed. In particular, the Tc film shows an approximately linear relation with the parameter ψ over the wide range of 7–17 K. Optical reflectivity measurements are carried out in the wavelength range of 0.2–2.5 μm for these films. Each spectrum is well fitted by the curve calculated using the Drude model with a screened plasma frequency of 25 000–30 000 cm−1. The Tc film also shows a stronger correlation with the damping constant of plasma excitation than with the reflectivity. This is considered to be a universal degradation curve for this system, similar to those observed in high ‐Tc A15 compounds. The relation of Tc to ψ is found to be equivalent to this correlation.

Ellipsometry study of two-dimensional phase transitions

Abstract: The structure of a monolayer of pentadecanoic acid at a water-air interface has been studied through its gas, liquid, and condensed phases by use of a very sensitive ellipsometry technique. The results clearly show the presence of two coexistence regions on the isotherm and a nonuniform film at full coverage.

Investigation of frictional transfer films of PTFE by infrared emission spectroscopy and phase-locked ellipsometry

Abstract: When a PTFE sheet was rubbed lightly and unidirectionally over a smooth surface of stainless steel an essentially monomolecular transfer film was formed. By special ellipsometric and emission infrared spectroscopic techniques it was possible to show that the film was 10–15 A thick and birefringent. From the intensity differences of infrared bands obtained with a polarizer passing radiation polarized in mutually perpendicular planes, it was possible to deduce transfer film orientation with the direction of rubbing. After standing in air for several weeks the transfer film increased in thickness by as much as threefold. At the same time both the index of refraction and the absorption index decreased. Examination of the surfaces by optical and electron microscopies showed that the films had become porous and flaky. These observations were consistent with previous tribological measurements. The coefficients of friction and were decreased with the formation of the transfer film but increased again as the film ...

Infrared ellipsometry study of the vibrational properties and the growth of hydrogenated amorphous silicon ultrathin films

Abstract: The first experimental study of hydrogenated amorphous silicon (a‐Si:H) ultrathin films (df <500 A) deposited on glass substrates using infrared spectroscopic phase‐modulated ellipsometry is presented. The high sensitivity of this new technique is emphasized. In particular, SiH and SiH2 stretching bonds are identified on 50‐A‐thick samples. It is shown that the structure of a‐Si:H in the early stage of the growth (df <100 A) may differ considerably from that of bulk materials: Hydrogen–silicon bonds are not observed in the first few seconds of the growth and the imaginary part of the dielectric function of the film is found to increase with df. These behaviors are attributed to an interaction of the growing film with the substrate.

Attenuated Total Reflection FT-IR Spectroscopy to Measure Interfacial Reaction Kinetics at Silica Surfaces

Abstract: Attenuated total reflection (ATR) FT-IR spectroscopy has been adapted to measure the rates of chemical modification reactions at silica surfaces. In this method, a silicon ATR crystal is oxidized at 1000°C under dry O2 to produce a silicon dioxide layer on the crystal surface, the thickness of which can be measured using ellipsometry. The oxidized silicon layer is then used as a model silica surface in measurements of the rates of chemical modification. A flow cell is filled with a solution of a surface active reagent. ATR infrared spectra are obtained at regular time intervals, where confinement of the intensity to the interface by total internal reflection provides a measure of local changes in concentration of species which adsorb or bind to the surface. The effect of the silicon dioxide layer on the sensitivity of measuring absorbance at the silica-solution interface is investigated. A model reaction study is carried out to determine the binding kinetics diphenylchlorosilane to silica from carbon tetrachloride solution. The technique yields both in situ kinetic and structural information about the reaction of this reagent with silica surfaces.

Optical sol-gel coatings : ellipsometry of film formation

Abstract: A method was developed to image an area of a drying, steady-state film during dip-coating using ellipsometry, thereby obtaining the film's thickness and refractive index as a function of position. Measurements on TiO 2 and SiO2 alcohol-based sols indicate that the film approaches a volume fraction Φ ∼ 0.2 in the wet state and suggests that the film resists densifying further for kinetic reasons. In dense films, as the final drying front passes, the film undergoes a rapid collapse owing to capillary forces ; porous films formed from relatively large SiO2 aggregates appear to collapse more slowly in the final stage due to smaller capillary forces. The thickness profiles are consistent with thinning by a combination of evaporation and gravitational draining.

Variable angle spectroscopic ellipsometry - Application to GaAs-AlGaAs multilayer homogeneity characterization

Abstract: Variable angle spectroscopic ellipsometry has been applied to a GaAs‐AlGaAs multilayer structure to obtain a three‐dimensional characterization using repetitive measurements at several spots on the same sample. The reproducibility of the layer thickness measurements is of order 10 A, while the lateral dimension is limited by beam diameter, presently of order 1 mm. Thus, the three‐dimensional result mainly gives the sample homogeneity. In the present case we used three spots to scan the homogeneity over 1 in. of a wafer, which had molecular‐beam epitaxially grown layers. The thickness of the AlGaAs, GaAs, and oxide layers and the Al concentration x varied by 1% or less from edge to edge. This result was confirmed by two methods of data analysis. No evidence of an interfacial layer was observed on top of the AlGaAs.

Ellipsometric and Rutherford backscattering characterization of low-energy hydrogen-, helium-, neon-, and argon-bombarded silicon

Abstract: Ellipsometry and Rutherford backscattering/channeling were used to study silicon surfaces modified by low‐energy hydrogen, helium, neon, and argon ion bombardment. Ellipsometry was found to be a very sensitive technique for characterization of these samples, able in some cases to simultaneously distinguish the ion identity, incident energy, and total dose experienced by the material. A comparison of the ellipsometric results for the different cases indicates qualitative differences in the physical modifications induced in the silicon surface region under bombardment by different ions. Comparison of the ellipsometric results with Rutherford backscattering/channeling data yielded estimates of the complex refractive index of the silicon layer modified by hydrogen and helium bombardment, showing a general decrease in the refractive index and an increase in the optical extinction coefficient upon bombardment. It was possible to explain these changes, at least qualitatively, by using the Bruggeman effective medium approximation to estimate the volume composition of this layer subject to certain simplifying assumptions. One result of this was the development of the exact solution for the three‐component Bruggeman analysis; these equations are derived in the Appendix.

Optical properties and structure of microcrystalline hydrogenated silicon prepared by radio‐frequency magnetron sputtering

Abstract: We have studied the optical properties of hydrogenated microcrystalline silicon films prepared by rf magnetron sputtering. Spectroscopic ellipsometry (SE) has been used to measure the dielectric spectra in the 1.66–5.6‐eV range. Films produced with substrate temperature higher than 200 °C and hydrogen partial pressure ratio equal to 0.5 exhibited a microcrystalline structure. Distinct differences were observed between such films as amorphous and microcrystalline films in their dielectric function spectra and other optical quantities. An energy shift and a broadening of the E1 and E2 transitions for the microcrystalline samples were calculated from the analysis of SE data. It was observed that the rf power and the substrate temperature were the primary factors controlling the microcrystallite formation. A strong density dependence of microcrystallinity was observed, for all the optical parameters investigated. The effect of the hydrogen concentration and the hydrogen‐bonding configuration on the optical pr...