Microstructure of vacuum-deposited tin thin films

Tin thin films of equal thickness were vacuum deposited on NaCl substrates at different deposition rates both in high vacuum (2×10^–5 Torr) and poor vacuum (1×10^–3 Torr). These films were examined by electron microscopy and the grain size and density in the films were determined. It was found that both in poor and high vacuum, as the deposition rate was increased the grain size decreased and grain density increased. However, the deposition rate must be increased by an order of magnitude in order to observe large changes in the grain size and density. It was also observed that the films prepared in poor vacuum, especially at low deposition rates, consist of islands with jagged edges. These observations have been interpreted on the basis of nucleation theory and the effect of adsorbed/chemisorbed gases on island growth in these films.     

Quantitative secondary neutral mass spectroscopy of thin films

A secondary ion mass spectrometer, having a liquid metal primary ion beam capable of focusing down to below 100 nm, has been adapted so that it can operate in conventional secondary ion or secondary neutral analysis mode. An electron beam is used to ionize the neutral species in the secondary neutral mass spectroscopy (SNMS) mode. Optimum operating conditions are reported including the use of an energy filter, which is shown to reduce background signals significantly. Typical results for various types of thin film coatings are reported including semiconductor materials, multilayer structures, metal oxides and metal alloys. A comparison of the SNMS data with that obtained in the secondary ion mass spectroscopy mode shows that the new technique provides more reliable quantitative data.     

Structural control of vacuum-deposited thin films by the use of a Langmuir-Blodgett multilayer

An amphiphilic diacetylene of heptacosa-10,12-diynoic acid (14-8C) was vacuum deposited on a commercially available glass plate and on 10-layer LB films of both arachidic acid (C₂₀C) and 14-8C at various substrate temperatures (T_s). At a T_s of 22°C, 14-8C molecules on the glass substrate were oriented randomly with respect to the substrate, whereas those on 14-8C LB film at the same T_s were all oriented perpendicularly. At the higher T_s of 50°C, 14-8C molecules were randomly oriented even on the LB film because of the disordering of molecules in LB films.

In the process of structural characterization we have succeeded for the first time in the direct observation of lattice images of LB films by use of a liquid-helium- cooled cryo-electron microscope.     

Microstructure determined anisotropy in the properties of vacuum-deposited AgBr thin films

Thin porous AgBr films were prepared by physical vapor deposition under high vacuum conditions. By varying only one basic parameter of the deposition technique – the vapor incidence angle, films with different microstructures could be obtained. The presence of microstructural inhomogeneity and anisotropy in the microhardness and dark ionic conductivity of the films was revealed.     

Semiconducting behaviour of thin bismuth films vacuum-deposited at different substrate temperatures

Thin bismuth films (thickness 25 nm) have been vacuum-deposited onto glass substrates at different substrate temperatures in a vacuum of 2×10^–5 torr. The resistance of the films has been measured as a function of temperaturein situ during and after annealing. It is found that the resistance of all the annealed films decreases with increasing temperature thus showing a semiconducting type of behaviour. The films do not show a resistivity minimum observed in thicker films [1]. The absence of a resistivity minimum is attributed to the thinness of the films and consequent larger energy band gap and smaller grain size.     

Theoretical analysis of the Hall effect in thin polycrystalline metallic films

In polycrystalline films where three types of scattering processes (background, grainboundaries and external surfaces scatterings) are taking place at the same time an effective relaxation time is defined in the light of a three-dimensional model of grain-boundaries. Analytical expressions for the Hall coefficient and conductivity in thin polycrystalline metallic films subjected to a transverse magnetic field are then derived by using the Boltzmann transport equation. Previously published data can be theoretically interpreted in terms of the proposed model.     

Quantitative measurements of the mass distribution in thin films during electrotransport experiments

A method is described which allows a thin metallic film strip to be scanned transversally with an electron beam. Thus a strip 780μm long is divided into about 390 individual parts. The mass of each of these “slices” can be evaluated electronically. Such a series of individual determinations, made with a modified scanning electron microscope, gives the mass distribution along the strip.     

Mechanical testing of thin metallic films

Mechanical properties of thin-film metallizations used as interconnects in VLSI devices can be studied by different techniques. The present investigation centers about mechanical testing of aluminum films of submicron dimensions. Free-standing films were subjected to bulge and uniaxial testing, while films adherent to the silicon substrate were tested in an apparatus that employed cantilever specimens. It measured the deflection as a function of a variable load. The results of these in situ tests can be compared with stress-strain curves of free-standing films of identical composition. Because of the very high sensitivity required of the equipment, various experimental problems tend to arise, which are discussed in detail.     

Related structural,electrical and photoelectrical properties of vacuum-deposited GaP thin films

GaP thin films with thicknesses from 0.1 to 0.6 μm were prepared by the thermal evaporation of the compound GaP onto quartz substrates at temperatures from ambient temperature to 740 °C. The properties of the films depended strongly on substrate temperature and deposition rate. With increasing substrate temperature the film structure changed from amorphous to textured polycrystalline with a strong [100] texture. The temperature of the amorphous-to-crystalline transition depended on deposition rate and was found to be 360 and 400 °C for deposition rates of 2 and 10 Å s^-1 respectively. At these temperatures the electrical resistivity of the films fell sharply from 10⁸ Ω cm to a minimum value of $\text{5 × 10}{}^4\text{Ω}\text{cm}$, after which it increased again with increasing temperature. The amorphous films exhibited a moderate photosensitivity with a maximum value near the temperature of the structural transition; above this temperature the films lost their photosensitivity completely. The spectral dependence of the photoconductivity was measured and an attempt was made to interpret the observed spectra.     

Electrical conductivity of thin metallic manganese films

Thin metallic Mn films of various thicknesses were thermally vapour-deposited on glass substrates at room temperature in a high vacuum. The electrical conductivity of these Mn films was measured in situ as a function of film thickness and annealing temperature. The experimental results indicate that the electrical resistivity decreases as the film thickness and annealing temperature increase. The calculated values of the activation energy for electric conduction decrease as the film thickness increases. The mean free path and mobility for charge carriers, and the electrical resistivity of infinitely thick films, were calculated as a function of temperature; they are in good agreement with the theoretical relationships.     

Properties of vacuum-deposited polyimide films

Vacuum-deposited polyimide (PI) thin films have been prepared by co-deposition of precursor pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) followed by thermal treatment. The dependency of the optical and electrical properties, chemical resistivity and mechanical stability on the composition (ODA:PMDA) and the degree of imidization of the PI layers have been investigated and discussed. The experimental results have yielded possibilities to microstructure the vacuum-deposited PI films by excimer laser irradiation or reactive ion etching in gas mixture CF₄/O₂.     

Structure and electrical properties of vacuum-deposited antimony telluride thin films on an amorphous substrate

Sb₂Te₃ thin films, 50–109 nm thick, have been prepared by vacuum evaporation on to quartz substrates. Electrical properties of as-deposited and annealed films show that the activation energy is thickness dependent. Optical measurements indicate that there is an indirect transition having an energy of 1.9 eV. Transmission electron micrographs show the fine grains of the deposit.     

The electrical conductivity of inhomogeneous thin metallic films

This paper reports the following results: (i) an explicit for the electrical conductivity of a thin metal film where the electron mean free path is not constant through its thickness, and (ii) calculations showing how in this case an illusory fit to the Fuchs-Sondheimer result can be obtained with a dependence of the specularity parameter on thickness or angle. A survey of experimental results is also presented.