Showing papers on "Ellipsometry published in 1989"

The structure of self-assembled monolayers of alkylsiloxanes on silicon: a comparison of results from ellipsometry and low-angle x-ray reflectivity

Abstract: The thicknesses of C10-C18 alkylsiloxane monolayers on silicon-silicon dioxide substrates have been measured with ellipsometry and low-angle X-ray reflection. Although, for any given sample, thicknesses measured by the two methods agree to within experimental error, ellipsometric measurements are systematically larger by approximately 2 {angstrom}. This difference may result from variations in the sensitivity of the two techniques to the structure of the interface between silicon dioxide and the alkylsiloxane monolayer. The x-ray reflectivity measurements provide evidence that these organic monolayers do not build up as island structures and demonstrate that the approximate area projected by each alkyl group in the plane of the monolayer is {approximately} 21 {plus minus}3 {angstrom}{sup 2}. Preliminary studies indicate that this technique can be used to follow the changes in the structure of a monolayer which result from chemical transformations. The influence of damage that is induced by x-ray radiation on these measurements is discussed.

Ion-assisted deposition of mixed Tio2-Sio2 films

Abstract: Mixed thin films of TiO2 and SiO2 were produced by coevaporation from separate electron‐beam sources and simultaneous bombardment of the growing film with oxygen ions. The optical properties of the films were determined during growth by in situ ellipsometry and the surface composition of the deposited films studied by in situ ion scattering spectroscopy, ex situ x‐ray photoelectron spectroscopy, and energy filtered electron diffraction. The correlation between the optical and surface characterization is presented. There is evidence of local variations in the relative concentrations of TiO2 and SiO2. The position of the Si 2p binding energy depends on the TiO2 content in the film, indicating the possible formation of an intimate mixture.

Thin‐film deposition by a new laser ablation and plasma hybrid technique

Abstract: We have developed a new laser ablation and plasma hybrid technique for depositing thin diamond‐like carbon (DLC) films on Si〈100〉 substrates at room temperature and at 110 °C with improved optical and mechanical properties. The technique involves coupling of laser energy (λ=0.308 μm, pulse duration=40 ns, and power 125 MW/cm2) to a graphite target and superimposing capacitively stored energy (2–3 J at 3 kV) to the laser ablated spot. The laser‐ and plasma‐deposited diamond‐like carbon films were analyzed by spectroscopic ellipsometry and microhardness measurements. These films showed considerable improvements in both uniformity and homogeneity. Optical properties and hardness of the films deposited by this technique closely match the DLC films. We discuss possible causes of improvements in the above properties of these films.

In situ ellipsometry of thin‐film deposition: Implications for amorphous and microcrystalline Si growth

Abstract: Real‐time ellipsometric characterization of the nucleation of hydrogenated amorphous silicon (a‐Si:H) prepared by plasma‐enhanced chemical vapor deposition (PECVD) on smooth, dense metal, and crystalline Si substrates is reviewed. The experimental results for photoelectronic quality a‐Si:H from pure SiH4 on Mo and Cr are consistent with the Volmer–Weber nucleation mode, with a separation of 40–50 A between nucleation centers. For c‐Si substrates, a new interpretation suggests that nucleation occurs on the same scale, but the geometry in the first monolayer is disklike. A well‐defined lobe and cusp in the data can be ascribed to surface smoothening by diffusion that results upon coalescence of these structures. For films from a pure SiH4 plasma, the rates of coalescence and relaxation of substrate‐induced surface roughness on thick films are consistent with a diffusion length of ∼80 A for the adsorbed precursors. For films prepared from a SiH4‐depleted plasma, the average surface diffusion length is reduce...

In situ investigation of the optoelectronic properties of transparent conducting oxide/amorphous silicon interfaces

Abstract: Transparent conducting oxide (TCO)/hydrogenated amorphous silicon (a‐Si:H) interfaces are investigated combining kinetic ellipsometry and Kelvin probe measurements. It is shown that the correlation between both in situ techniques allows a detailed description of the optoelectronic behavior of these interfaces. The Schottky barrier at the TCO/a/Si:H interfaces, as revealed by Kelvin probe measurements, is correlated with the chemical reduction of the TCO surface during the early stage of a:Si:H growth, as evidenced by kinetic ellipsometry. In particular, indium tin oxide (ITO) and SnO2 are found to be reduced by the silane plasma at 250 °C. On the countrary, ZnO is found highly resistant upon plasma reduction. The influence of the substrate temperature during a‐Si:H deposition is analyzed. Finally, the technical consequences of this study are outlined.

Ellipsometric studies of polyaniline growth and redox cycling

Abstract: Ellipsometry has been used to characterise the growth of polyaniline films on platinum and gold electrodes by potential cycling. Analysis of the time evolution of the ellipsometric parameters allowed continuous monitoring of the growth process, and subsequent measurements of the changes in optical properties during oxidation and reduction of the PANI film were related to the electrochemical behaviour. Spectroscopic ellipsometry has been used to evaluate n and k values of the film for differing degrees of oxidation. Frequency-resolved transmission measurements have been used to show that the periodic electrical and optical responses of the polyaniline film are directly related.

A real time ellipsometry study of the growth of amorphous silicon on transparent conducting oxides

Abstract: In situ fast kinetic ellipsometry is used to investigate the early stage of the growth of hydrogenated amorphous silicon (a‐Si:H) on tin‐doped indium oxide (ITO), tin oxide (TO), and zinc oxide substrates. Transparent conducting oxide (TCO) substrates obtained from various sources and deposited by different techniques are studied. A wide range of deposition parameters of a‐Si:H films is considered. For a comparison with growth of amorphous silicon from silane, the ellipsometry data on pure hydrogen plasma degradation of TCO surfaces are also presented. In case of ITO and TO films, a two‐step deposition is observed: the first step is dominated by the reduction of TCO and formation of metallic In or Sn (≊10 s time scale) and the second step is the subsequent growth of a‐Si:H on the reduced substrates. In contrast, ZnO does not show any reduction. The substrate temperature during a‐Si:H deposition is found to have the most important influence on the chemical reduction of the substrates. Variations of other d...

Measurements and Modeling of Thin Silicon Dioxide Films on Silicon

Abstract: : The ellipsometric measurement of refractive indices for films less than 50 nm thick is of dubious quality due to the significance of the size of random errors relative to the accuracy required to extract reliable index values from the measurements. In this study the various errors are quantitatively assessed as a function of the film thickness, and then compared with experimental data obtained from differently prepared silicon dioxide films on silicon. The new results confirm previous work that shows higher refractive indices for thinner films. Transmission electron microscopy results confirm the results and graded and discreet layer models are compared.

The dielectric function of AlSb from 1.4 to 5.8 eV determined by spectroscopic ellipsometry

Abstract: We have prepared AlSb substrates for optical measurements by chemomechanical polishing and etching. The quality of the surface was investigated with optical and electron microscopy and by Raman scattering and ellipsometry. We have measured the pseudodielectric function 〈e〉(ω) of AlSb in the 1.4–5.8 eV photon‐energy region with a spectroscopic ellipsometer. A peak value of 〈e2〉=24.6 at 4 eV was reached. We list the refractive index, the reflectivity, and the absorption coefficient, and obtain the critical point parameters at 300 K. Finally, we fit the index of refraction of AlSb at low photon energies with a semiempirical model.

Surface‐roughness and grain‐boundary effects on the optical properties of low‐pressure chemical‐vapor‐deposited silicon thin films by spectroscopic ellipsometry

Abstract: The optical properties of polycrystalline silicon thin films prepared by low‐pressure chemical vapor deposition were studied by spectroscopic ellipsometry. The surface roughness and the microstructure of the films were investigated by combining the theory of Ohlidal and Lukes with the Bruggeman effective‐medium approximation. Furthermore, a line‐shape analysis of the dielectric function, as well as a method to describe the dielectric function, was used to discuss the effect of the surface roughness and that of the crystallite size and grain boundaries in these materials. The results of this analysis show that the parameters that mainly control the growth mode in these materials, at a temperature of 630 °C, are the silane pressure and the growth rate. The different surface morphologies and the growth of a native oxide on the material surface seem to be associated with the growth mode of the film. The effect of surface roughness on the measured data must be taken into account even at energies as low as 2 eV, while the presence of a native oxide overlayer influences the measured data at higher energies. A reasonable agreement with recent electron microscopy studies on these materials was found.

Infrared spectroscopic ellipsometry using a Fourier transform infrared spectrometer: some applications in thin-film characterization

Abstract: The prototype of an infrared spectroscopic ellipsometer using a Fourier transform PC‐based infrared spectrometer is described. Several applications in thin‐film characterization are given, particularly in the case of bulk substrate, thick‐layered materials, and determination of the dielectric function of layered materials such as silicon oxide and silicon nitride. The sensitivity and possible improvements of this technique are discussed.

Spectroscopic ellipsometry with synchrotron radiation

Abstract: The design, construction, and performance of an automatic photometric ellipsometer with rotating analyzer for the VUV region (5–30 eV) is described. The use of a synchrotron radiation source and triple‐reflection polarizers makes this new spectral region accessible to spectroscopic ellipsometry. New dielectric function data are presented for InP(110), YBa2Cu3O7, and epitaxial CaF2/Si(111).

In situ study of the thermal decomposition of B2H6 by combining spectroscopic ellipsometry and Kelvin probe measurements

Abstract: In amorphous silicon (a‐Si:H) p‐i‐n solar cells preparation, B2H6 is added to the SiH4 discharge in order to deposit the p layer. However, chemical vapor deposition (CVD) of the (B2H6,SiH4) mixture, in the absence of plasma excitation, can contribute to poor p/i interface characteristics. The thermal decomposition of B2H6 at 250 °C is studied in situ by combining spectroscopic ellipsometry and Kelvin‐probe measurements. The advantage of correlating both techniques is underlined. Both diagnostics provide complementary information. Spectroscopic ellipsometry is highly sensitive upon film deposition and surface morphology modifications. On the other hand, Kelvin‐probe measurements may be directly related to Fermi‐level shifts. The thermal decompositon of (B2H6,H2) and (B2H6,SiH4) mixtures is evidenced, even at low total pressure (30 mTorr). The boron incorporation is found to be little affected by the diluent gas. In contrast, the CVD consequences strongly increase as a function of the gas pressure. The surf...

Molecular sieving by electropolymerized porphyrin films only a few monolayers thick

Abstract: Polymeric films can be formed on smooth Pt electrodes by oxidative polymerization of cobalt tetrakis(o-aminophenyl)porphyrin, (Co(o-NH{sub 2})TPP). Although the films are extremely thin, as few as two monomolecular layers of porphyrin sites, they exhibit permeabilities to molecular monomers that fall in a regular order of permeant molecular volume. The molecular sieving property is taken as evidence that membrane transport, rather than pinhole transport, is the predominant transport mechanism in these films. The permeability data are supported by film thickness measurements by electrochemical reactivity, surface profilometry, transmission spectrophotometry, ellipsometry, and X-ray photoelectron spectroscopy.

Properties of carbon films deposited by pulsed laser vaporization from pyrolytic graphite

Abstract: Amorphous carbon films have been deposited on silicon 〈111〉 and quartz substrates by pulsed ruby laser vaporization from pyrolytic graphite. Depositions have been carried out at different substrate temperatures, and the properties of the deposited carbon films have been studied using IR and UV–VIS transmission, ellipsometry, and laser-Raman spectroscopies. Chemical and electrical resistivity measurements have also been performed. It is shown that the film properties depend critically on the substrate temperature and that at the substrate temperature of 50 °C films with substantial proportion of sp 3 hybridized orbitals are obtained.

The plasma oxidation of titanium thin films to form dielectric layers

Abstract: A remote indicatively coupled radio frequency plasma has been used to oxidize titanium thin films evaporated onto silicon substartes. The substrate was heated during oxidation to temperatures between 200 and 500 °C using a resistively heated furance. Titanium dioxide layers were formed of thicknesses from 53 to 150 nm. The crystal structure was shown to be rutile by x‐ray diffraction for oxidation temperatures of 500 °C. These samples were also seen to have a thin interfacial silicon dioxide layer. Measurements on 1‐mm Al dot capacitors showed the leakage current of a 53‐nm film oxidized at 500 °C to be below 10−8 A at a 2‐V bias. Good capacitance‐voltage characteristics were observed for high oxidation temperatures, with a dielectric constant of between 15 and 22 for the TiO2/SiO2 layers. The refractive index of the layers was measured by ellipsometry to be 2.5–2.6. Plasma oxidation thus provides a low‐temperature method of forming titanium dixoide thin films.

In Situ Ellipsometry to Monitor Swelling and Dissolution of Thin Polymer Films

Abstract: An situ rotating-analyzer ellipsometer has been designed for monitoring swelling and dissolution of thin polymer films. Equipment details, procedures, precision and accuracy, and data interpretation are discussed. For polymer/solvent systems, the precision and accuracy depend on the particular optical parameters of the system. The usefulness of ellipsometry for distinguishing between swelling and dissolution, measuring swelling and dissolution rates, differentiating diffusion mechanisms, and determining equilibrium swelling compositions is demonstrated

In situ studies of the growth of hydrogenated amorphous silicon

Abstract: In situ studies of the growth of a-Si:H are reviewed. The ability of kinetic ellipsometry, with submonolayer resolution, to study interfaces of physical systems involving reactive processes is illustrated. The influence of the substrate on the growth of the film, even after a long term deposition, is emphasized. Further, it is shown that the correlation of spectroscopic ellipsometry with in situ Kelvin probe measurements can lead to a detailed description of the optoelectronic behaviour of conducting substrates/a-Si:H interfaces.

Spectroscopic ellipsometry and transmission electron microscopy study of annealed high‐dose oxygen implanted silicon

Abstract: The first results are presented of a comparative study of separation by implanted oxygen structures using spectroscopic ellipsometry (SE) and transmission electron microscopy. The strength of SE to measure the layer thicknesses of multilayer structures nondestructively is illustrated. Some limitations of the technique are also indicated.

Simultaneous determination of refractive index, its dispersion and depth-profile of magnesium oxide thin film by spectroscopic ellipsometry.

Abstract: A new method of using the spectroscopic ellipsometry technique to determine (a) the true (or bulk) refractive index of the film material, (b) the dispersion of the above refractive index with wavelength, (c) the thickness of the film, and (d) the distribution of the voids in the film is presented.

Ellipsometric method for the measurement of temperature and optical constants of incandescent transition metals.

Abstract: The development of a unique noncontact temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomitant with radiance brightness. Simultaneous determinations of dielectric constants and refractive indices allow changes in the physical and chemical state of a heated surface to be monitored. The results of optical property measurements at 633 nm as functions of temperature between 1000 and 2500 K for eight transition metals including Hf, Ir, Mo, Nb, Pd, Pt, Ta, and V are presented together with preliminary results of oxidation studies on iridium.

Making van der Waals Films on Fibers

Abstract: The liquid layer coating a solid fiber drawn at constant velocity V0 out of a bath of liquid is all the thicker since V0 is large. We discuss in this letter the limit of very low capillary numbers: if the liquid wets the fiber, the thickness e of the liquid layer should not depend any longer on V0 below a critical value of the velocity (V0 < 0) and should be equal to a2/3 b1/3, where a is a microscopic length related to the wetting interactions (which are supposed to be van der Waals ones) and b is the radius of the fiber. This thickness is in the 100 A range. Then, a new experiment is presented: it consists of making such very thin films of dodecane on polymeric fibers and measuring their average thicknesses by gas chromatrography titrations. The results are promising: this technique could be an interesting alternative for detecting or measuring very thin films on curved surfaces for which more usual methods like ellipsometry are not suited.

A combined ellipsometric and in situ infrared (SNIFTIRS) study of poly(benzo-[c]-thiophene) films

Abstract: Films of poly(benzo[c]thiophene)[poly(isothianaphthene)] have been grown from a solution of the monomer in acetonitrile by two methods. First, anionic polymerisation onto a platinum electrode in the presence of tetrafluoroborate affords a stable polymer (type I film). Secondly, oxidative polymerisation with Br2 as an electrochemically generated intermediate gives a rather different material (type II film). Films of type I are found by ellipsometry to be relatively dense, containing very little solvent in the neutral form. On switching from the neutral to the oxidised form, the film swells as solvent and counter anions are absorbed. Type II films are found to have a much more open form and estimates from ellipsometry and coulometry are consistent with a factor of four greater solvent content. Potential cycling of these films appears to have little effect on their thickness. The in situ i.r. measurements, carried out on a type I film, are consistent with absorption of solvent in the oxidised form, but the spectra are dominated by the development of a strong electronic absorption centred above 4000 cm–1 that shifts towards lower frequency at higher potentials. This electronic band is accompanied by the appearance of strong absorption bands between 1000 and 1400 cm–1 associated with the five-membered S-containing ring and correlating with the shift in electronic absorption maximum. The enhanced vibrational peaks are due to ‘amplitude-mode’ effects arising from the coupling of the quinonoid vibrations to the mobile charge defect. The evolution of the i.r. spectra with potential can then be associated with the changing character of the charge carriers.