Showing papers on "Thin film published in 1985"

Perpendicular magnetic anisotropy in Pd/Co thin film layered structures

Abstract: This letter presents the results of magnetic studies of thin film, periodic, Pd/Co layered structures with ultrathin cobalt (4–13 A). We show that films with Co thicknesses less than 8 A are easy to magnetize along a direction normal to the film surface. The best films have a saturation magnetization of about 500 emu/cm3 and a coercivity of 550 Oe, and thus they are candidates for a vertical magnetic recording medium. We attribute the perpendicular magnetic easy axis in these films to surface anisotropy at Pd/Co interfaces and strain in thin Co layers.

The drainage of thin liquid films between solid surfaces

Abstract: We present measurements of the thickness as a function of time of liquid films as they are squeezed between molecularly smooth mica surfaces. Three Newtonian, nonpolar liquids have been studied: octamethylcyclotetrasiloxane, n‐tetradecane, and n‐hexadecane. The film thicknesses are determined with an accuracy of 0.2 nm as they drain from ∼1 μm to a few molecular layers. Results are in excellent agreement with the Reynolds theory of lubrication for film thicknesses above 50 nm. For thinner films the drainage is slower than the theoretical prediction, which can be accounted for by assuming that the liquid within about two molecular layers of each solid surface does not undergo shear. In very thin films the continuum Reynolds theory breaks down, as drainage occurs in a series of abrupt steps whose size matches the thickness of molecular layers in the liquid. The presence of trace amounts of water has a dramatic effect on the drainage of a nonpolar liquid between hydrophilic surfaces, causing film rupture whi...

Group III Impurity Doped Zinc Oxide Thin Films Prepared by RF Magnetron Sputtering

Abstract: The detailed study of electrical properties in group III impurity doped ZnO thin films prepared by rf magnetron sputtering is described. The resistivity is lowered by doping of B, Al, Ga and In into ZnO films. The characteristic features of ZnO films doped with group III elements except for B are their high carrier concentration and low mobility. Variation of the mobility with the impurity content is roughly governed by the ionized impurity scattering. It is shown that the doped ZnO films exhibit the resistivity dependence on film thickness below 300 nm.

Optical properties of semiconducting iron disilicide thin films

Abstract: Iron disilicide thin films were prepared by furnace reaction of ion beam sputtered iron layers with single‐crystal silicon wafers and with low‐pressure chemical vapor deposition (LPCVD) polycrystalline silicon thin films. X‐ray diffraction indicates the films are single‐phase, orthorhombic, β‐FeSi2. Impurity levels are below the detection limit of Auger spectroscopy. Normal incidence spectral transmittance and reflectance data indicate a minimum, direct energy gap of 0.87 eV. The apparent thermal activation energy of the resistivity in the intrinsic regime is about half of this minimum optical gap. With such a direct band gap, the material may be suitable for the development of both light‐sensitive and light‐emitting thin‐film devices within the silicon microelectronics technology.

Transient thermoreflectance from thin metal films (A)

Abstract: This report describes the first demonstration of thermal diffusivity measurements using picosecond transient thermoreflectance (TTR). Although previously reported methods of measuring thermal transport properties of thin films require precise knowledge of the thermal properties of the substrate, this technique allows measurements on films as thin as 100 nm without any evidence of substrate interaction. The TTR measurement is modeled with a one‐dimensional heat flow equation using a two‐parameter fitting routine to determine the thermal diffusivity. The validity of our approach is confirmed by the TTR measured thermal diffusivity of single crystal nickel. We have also measured the thermal diffusivity of sputtered and evaporated single element metal films. Preliminary results from TTR measurements on compositionally modulated structures are also presented.

Electrical breakdown in thin gate and tunneling oxides

Abstract: The breakdown of thin oxides (7.9-32 nm) subjected to high-field current injection is investigated in this study. The physical mechanism of breakdown is found to be localized field enhancement at the cathode interface due to hole trapping. The source of this hole trapping is believed to be impact ionization in the SiO 2 . A quantitative model for oxide breakdown based on impact ionization and hole trapping at the cathode is presented and shown to agree well with the experimental J - t and time-to-breakdown, (t BD ) results. We observe that log t BD varies linearly with 1/ E rather than with E as commonly assumed. The field acceleration factor, i.e., the slope of the log t BD versus 1/ E plot, is approximately 140 decades per centimeter per megavolt for the 7.9 nm oxide, with approximately 25 percent of this coming from the field dependence of the impact ionization coefficient and the remainder from the Fowler-Nordheim current dependence on 1/ E . Based on this model, oxide wearout performance might be improved by process changes that reduce interface hole trapping, such as radiation-hard processing, in addition to the reduction of particulate contamination and crystal defects.

Organic fluorescent dyes trapped in silica and silica-titania thin films by the sol-gel method. Photophysical, film and cage properties

Abstract: The sol-gel process is utilized to solve the notorious problem of incorporating an organic dye in an inorganic oxide thin film. Fluorescent thin films are prepared by this low temperature process with the aid of a surface active agent, with good homogeneity and reproducability. A variety of organic fluorescent molecules are embeded either in silica or in silica-titania films. The dye molecules are not leached out by water. Absorption and emission spectra, enhanced photostability, longer lifetimes and energy transfers between the trapped dye molecules are described and discussed in terms of the effects of molecule matrix-isolation on these properties. Potential uses of the special thin films are numerous, e.g., as laser or solar light guides.

Detection of thermal waves through optical reflectance

Abstract: We show that thermal wave detection and analysis can be performed, in a noncontact and highly sensitive manner, through the dependence of sample optical reflectance on temperature. Applications to the study of microelectronic materials are illustrated by an example of measuring the thickness of thin metal films.

Metastable phase formation in titanium‐silicon thin films

Abstract: The formation of TiSi2 thin films on silicon substrates has been investigated with several transmission electron microscope techniques. For films formed either by reacting titanium with a silicon substrate or by sintering a codeposited (Ti+Si) mixture, electron diffraction patterns show that a metastable phase—TiSi2 (C49 or ZrSi2 structure)—forms prior to the equilibrium phase—TiSi2 (C54 structure). High‐resolution images indicate that the metastable TiSi2‐silicon interface is atomically sharp, with no ‘‘glassy membrane’’ layer present. The annealing temperature required to transform the metastable TiSi2 to the low resistivity, equilibrium TiSi2 increases as the thin‐film impurity content increases. Previous studies of TiSi2 formation are discussed in light of these results.

The electronic and electrochemical properties of poly(isothianaphthene)

Abstract: The physical and electronic properties of poly(isothianaphthene) PITN, are reported, including initial characterization, electrochemical cyclic voltammetry, spectroscopy, and transport properties. PITN has the smallest energy gap of any known conjugated organic polymer, Eg≂1 eV. This novel conjugated polymer exhibits reversible chemical and electrochemical p‐type doping with an associated high contrast color change. After doping, thin films of PITN have very low optical density in the visible portion of the spectrum. Thus, PITN is the first example of a transparent highly conducting polymer (σ∼50 Ω−1 cm−1).

An applied science perspective of Langmuir-Blodgett films

Abstract: Langmuir-Blodgett (LB) films are prepared by transferring floating organic monolayers onto solid substrates. A combination of innovative chemistry and a carefully engineered instrument (a Langmuir trough) can result in high quality monomolecular assemblies displaying a high degree of structural order. The technique was first reported about fifty years ago and since then, LB films have been widely used as model systems in fundamental research. However, it is only during the past decade that the extensive applied potential has been recognised. Their precise thickness, coupled with the degree of control over the molecular architecture, has now firmly established a role for these layers in thin film technology. Following a historical introduction, this review describes the preparation and characterization of LB films and summarizes their importance in basic science. Particular emphasis is then placed on their potential applications, especially in fields related to electronics. The article concludes w...

Theory of photopyroelectric spectroscopy of solids

Abstract: Light absorption by a solid material and conversion of part, or all, of the optical energy into heat due to nonradiative deexcitation processes within the solid can give rise to an electrical signal in a pyroelectric thin film in contact with the sample. This effect forms the basis of a new spectroscopic technique for the study of condensed phase matter. A one‐dimensional theory is presented, which describes the dependence of the pyroelectric signal on the optical, thermal, and geometric parameters of the solid/pyroelectric system. Specifically, the theory examines the conditions under which the photopyroelectric signal exhibits a linear dependence on the optical absorption coefficient of the solid. Thus a theoretical basis for the technique of photopyroelectric spectroscopy is established. Qualitative comparisons between predictions of the theory and preliminary experimental observations are used to test the applicability of the theory to experimental configurations of practical interest.

High-temperature SiO2 decomposition at the SiO2/Si interface.

Abstract: The high-temperature decomposition of thin (\ensuremath{\sim}100\AA{}) Si${\mathrm{O}}_{2}$ layers on Si(001) under ultrahighvacuum annealing conditions has been studied by means of ion scattering and microscopy techniques. Si${\mathrm{O}}_{2}$ is removed from the Si surface by the formation and lateral growth of holes in the oxide, exposing regions of atomically clean Si, while the surrounding oxide retains its initial thickness. Surface diffusion of Si inside the holes supplies Si for reaction with Si${\mathrm{O}}_{2}$ at the periphery, so that a volatile product (presumably SiO) can be formed.

Strong magnetic dichroism predicted in the M4,5 x-ray absorption spectra of magnetic rare-earth materials.

Abstract: A theory is presented which predicts an anomalously large magnetic dichroism in the ${M}_{4,5}$ x-ray absorption-edge structure of rare earths in magnetically ordered materials. Polarized synchrotron radiation can therefore be used to determine accurately the magnitude, the orientation, and the temperature and magnetic field dependence of the local rare-earth magnetic moment in a large variety of magnetically ordered materials and thin films.

Secondary grain growth in thin films of semiconductors: Theoretical aspects

Abstract: Secondary grain growth in thin films can lead to grain sizes much greater than the film thickness. Surface energy anisotropy often provides an important fraction of the driving force for secondary grain growth, especially in the early stages of growth. Surface‐energy‐driven secondary grain growth leads to the development of large grains with restricted crystallographic textures. A model is presented for growth of secondary grains into a uniform matrix of columnar normal grains. The model indicates that secondary grain growth rates should increase with grain boundary energy, surface energy anisotropy, grain boundary mobility, and temperature. While final secondary grain sizes will decrease with film thickness, their growth rates will increase. The final secondary grain sizes and orientations will be strongly affected by grain sizes and orientations in the initial film. The models presented here provide analytical tools for experimental study of secondary grain growth in thin films. They will be used in for...

A simple technique for the determination of mechanical strain in thin films with applications to polysilicon

Abstract: Free standing, doubly supported micromechanical beams which are fabricated from films with built‐in compressive strain fields buckle at critical geometries. Experimental determination of the onset of buckling for known geometries leads to a direct measurement of the strain level in the films. This idea is supported by appropriate theory for experimental structures which form clamped, doubly supported beams with constant cross section and varying lengths. Application to low pressure chemical vapor deposition polysilicon leads to the conclusion that strain fields of 0.2% reduce to 0.05% during annealing.

Metalorganic chemical vapor deposition of III‐V semiconductors

Abstract: The metalorganic chemical vapor deposition (MOCVD) of epitaxial III‐V semiconductor alloys on III‐V substrates is reviewed in detail. The emphasis is placed on both practical and theoretical knowledge of the equipment and deposition process. The chemistry of the source alkyls and the dynamics of the transport process are discussed. The growth of the GaAs and AlxGa1−xAs systems are treated as prototypical examples (and the most studied) of the III‐V materials. Latter sections review InP, Ga1−xInxAs, and related alloys. Finally, the antimonide and the other systems are reviewed. Electronic and optical devices fabricated from MOCVD‐grown materials are used as examples of the capabilities of the growth technique.

Chemical Vapor Deposition of Ruthenium and Ruthenium Dioxide Films

Abstract: The preparation of Ru and RuO/sub 2/ thin films by organometallic chemical vapor deposition and an investigation of the films' properties are reported. Ru is of interest for metallization in integrated circuit fabrication because its thermodynamically stable oxide, RuO/sub 2/, also exhibits metallic conductivity. As a result, oxidation during processing of Ru is a less critical concern than in current metallization technology. Taking advantage of the benefits of chemical vapor deposition, such as conformal coverage and low temperature, damage-free deposition, we have deposited Ru, RuO/sub 2/, and Ru/RuO/sub 2/ by pyrolysis of three organoruthenium complexes. Films of a given phase composition were deposited under a wide variety of conditions and exhibited large variations in electrical resistivity and carbon content. The best Ru film, produced from Ru/sub 3/(CO)/sub 12/ at 300/sup 0/C in vacuum, had a resistivity of 16.9 ..mu cap omega..-cm and exhibited excellent adhesion to Si and SiO/sub 2/ substrates. The best RuO/sub 2/ film, produced from Ru(C/sub 5/H/sub 5/)/sub 2/ at 575/sup 0/C in O/sub 2/, had a resistivity of 89.9 ..mu cap omega..-cm and similarly exhibited excellent adhesion. Rutherford backscattering studies show tha Ru and RuO/sub 2/ films are effective diffusion barriers between Al and Si upmore » to annealing temperatures of about 550/sup 0/ and 600/sup 0/C (1/2 h exposure), respectively. Thus, they are significantly better than the currently used W films, which are only effective to about 500/sup 0/C.« less

Epitaxial Growth and Characterization of β ‐ SiC Thin Films

Abstract: Crack‐free monocrystalline films having very smooth final surfaces may be reproducibly grown at 1600 K and 760 torr on (100) Si substrates using and and if the Si is initially reacted with the alone. This initial step produces a buffer layer which reduces the mismatches in expansion coefficients and lattice parameters and thus allows the subsequent growth of the film to a thickness exceeding 5 μm. It is necessary to heat the Si wafers from room temperature to the reaction temperature in a and environment rather than preheating the substrates to the reaction temperature. An off‐axis orientation of the Si in excess of approximately 3° results in a very rough final growth surface on the film.

Growth of diamond thin films by electron assisted chemical vapor deposition

Abstract: Diamond thin films have been formed by the newly proposed electron assisted chemical vapor deposition on SiC with a high growth rate (3∼5 μm/h). The obtained films have good crystallinity in the sense of electron and x‐ray diffraction. Vicker’s hardness of the films is about 9000 kg/mm2. The influence of the electron bombardment on the initial island density on the substrate surface and on the decomposition of the reactant gases (CH4 and H2) is discussed relating to the growth process of the films.

High-density electronic processing package--structure and fabrication

Abstract: A high-density electronic package module is disclosed which comprises a stack of semiconductor chips having integrated circuitry on each chip. To permit the emplacement of thin film circuitry on the access ends, each access plane is etched to cut back the semiconductor material then covered with passivation material, and thereafter lapped to uncover the ends of electrical leads on the chips.

Thermal diffusivity measurement of thin films by means of an ac calorimetric method

Abstract: A new method to measure thermal diffusivity of a thin sample was developed using a light‐irradiated ac calorimetric technique. The experimental conditions and the fundamental equations for the measurement are discussed. In principle, this method can be applied no matter how thin a sample may be. This method was tested for samples of nickel, silicon, stainless steel, and alumina in the range from 50 to 300 μm in thickness. The measured thermal diffusivities coincide satisfactorily with the values reported for bulk materials. It is concluded that this method is useful in the measurement for thin materials with a variety of thermal diffusivities, and the sample mounting is easy in comparison with other methods.

Dependence of thin-film microstructure on deposition rate by means of a computer simulation

Abstract: A computer simulation is employed to demonstrate, in a two‐dimensional growth model, that a vapor‐deposited thin film of low adatom mobility undergoes a sudden change from a porous columnar microstructure to a densely packed film if the substrate temperature is increased to a certain value. The temperature where this structural transition occurs is shown to be related to the lower boundary temperature of the empirical structure‐zone model. The dependence of the transition temperature and range on the vapor deposition rate is discussed.

Thermal nitridation of Si and SiO 2 for VLSI

Abstract: This paper presents an extensive review of our work on thermal nitridation of Si and SiO 2 . High-quality ultrathin films of silicon nitride and nitrided-oxide (nitroxide) have been thermally grown in ammonia atmosphere in a cold-wall RF-heated reactor and in a lamp-heated system. The growth kinetics and their dependence on processing time and temperature have been studied from very short to long nitridation times. The kinetics of thermal nitridation of SiO 2 in ammonia ambient have also been studied. In nitroxide, nitrogen-rich layers are formed at the surface and interface at a very early stage of the nitridation. Then the nitridation reaction mainly goes on in the bulk region with the surface and near interface nitrogen content remaining fairly constant. Our results also indicate the formation of an oxygen-rich layer at the interface underneath the nitrogen-rich layer whose thickness increases slowly with nitridation time. The nitride and nitroxide films were analyzed using Auger electron spectroscopy, grazing angle Rutherford backscattering, and etch rate measurements. MIS devices were fabricated using these films as gate insulators and were electrically characterized using I - V, C - V , time-dependent breakdown, trapping, and dielectric breakdown techniques. Breakdown, conduction, and C-V measurements on metal-insulator semiconductor (MIS) structures fabricated with these films show that very thin thermal silicon nitride and nitroxide films can be used as gate dielectrics for future highly scaled-down VLSI devices. The electrical characterization results also indicate extremely low trapping in the nitride films. The reliability of ultrathin nitride was observed to be far superior to SiO 2 and nitroxide due to its much less trapping. Studies show that the interface transition from nitride to silicon is almost abrupt and the morphology and roughness of the interface are comparable to the SiO 2 -Si interfaces.

Optical Properties of Thin Films and the Berreman Effect

Abstract: The measurement of reflection and transmission of normally incident light to obtain the optical constants of a material is a usual tool in solid-state spectroscopy. If the material under investigation is a thin film, the interaction of the electromagnetic field with the sample can be enhanced by oblique incidence. If the light is p-polarized, structures in the reflection and transmission spectra are observed at the frequencies of transverse (TO) and longitudinal (LO) resonances. The LO structure — called the Berreman effect — is generated by the surface charges due to the normal component of the electric field. We discuss this effect for three cases: a free film, a film with a metallic back and a substrate with thin films on both sides. The dependence of the effect on the energy-loss function Im {−1/ɛ} and on the film thickness is discussed. For idealized systems simple formulae are derived and a characteristic parameter, called the Berreman thickness, is obtained. Films of this thickness show a maximum effect. Intuitive arguments are given to explain the effect. Examples for the application of the Berreman effect to characterize very thin films are discussed.

Magnetic recording medium

Abstract: PURPOSE:To obtain a high-density magnetic recording medium by forming a magnetic thin film of iron oxide contg. rhenium on a base body. CONSTITUTION:A gamma-Fe3O4 thin film contg. Re or a thin film of an intermediate composition between FE3O4 and gamma-Fe3O4 contg. Re can be obtained by oxidizing an Fe3O4 thin film contg. Re on a base body. The oxidation is prectically carried out in the atmosphere, and the oxidation temp., in this case, in preferably regulated to <=400 deg.C. The content of Re in the iron oxide continuous film is preferably regulated to 1.0-10.0atom% when expressed in terms of Re/FE (atom%). An aluminum base body coated with an Al alloy or alumite or vitreous base body can be exemplified as the hard base body, and a base body consisting of a synthetic resin having excellent resistance to heat such as polyimide, polyester, polyvinyl chloride, polycarbonate, and ''Teflon'' can be exemplified as the flexible base body.

Effects of oxygen content on the optical properties of tantalum oxide films deposited by ion-beam sputtering.

Abstract: Ion-beam sputter deposition of tantalum oxide films was investigated for possible optical coating applications. Optical properties of such films were found to be a sensitive function of oxygen-to-argon ratio in the ion beam. Refractive index and absorption coefficient were determined in the 250–2000-nm wavelength range by spectrophotometric transmissivity. The different bonding states of the tantalum atoms were revealed by x-ray photoelectron spectroscopy. The visible wavelength refractive index was found to be 2.18 and optical band gap 4.3 eV, so long as the films did not contain inclusions of metallic tantalum. Films with an admixture of oxygen deficient suboxide components had a low-energy tail of increasing magnitude in the absorption spectrum.

Determination of the nonlinear optical susceptibility χ(2) of surface layers by sum and difference frequency generation in reflection and transmission

Abstract: The theoretical investigation of sum and difference frequency generation in thin surface layers with rotational symmetry leads to formulas which connect the generated light intensities to the surface second order nonlinear susceptibility tensor. A maximum of seven tensor components can be determined in the case of lowest symmetry. Measurements in transmission should be especially useful since they allow easy variation of both polarization and angle of incidence. On the other hand, large signal enhancements are expected for total internal reflection geometries. A consistent set of χ(2) tensor components for a thin layer of rhodamine-6G adsorbed on fused silica is found based on data from reflection and transmission measurements.