Properties Of Copper Thin Films Research Articles

Surface morphology and electrical properties of copper thin films prepared by MOCVD

Thin copper films have been grown in a vertical MOCVD (Metal-Organic Chemical Vapor Deposition) reactor using bis(2,2,6,6-tetramethyl-3,5-heptanedionato) copper(II), Cu(thd)2, as precursor. Deposition has been carried out in a pure hydrogen atmosphere (pressure: 3, 20 mbar) at different substrate temperatures (350–750 ° C). The films have been investigated by profilometry, four-point resistivity measurements, ESCA, AES, XRD, AFM, and Normarsky microscopy. An unusual dependence of the film thickness with deposition time has been observed. Rapid growth occurred in the first minutes resulting in badly conducting films (thickness below 1000 A). Good electrical resistivities have been obtained above 2000 A. AFM has been used to gain information about the surface morphology of the films with different thicknesses. The grain size and surface roughness increased with increasing film thickness. Small grains grew in the beginning and the electrical properties have been governed by the highly Ohmic bridges between the individual grains.

Properties of thin copper films, condensed from a copper plasma with ion energies between 2 and 150 eV

A steady vacuum arc with a consumable anode, the anodic vacuum arc, was used to produce thin copper films of 1 μm thickness. This type of discharge is ignited in vacuum (10−3 Pa) and is characterized by a cold copper cathode operating in the spot mode and by copper vapor produced at a hot anode. This discharge generates a gas- and droplet-free copper vapor plasma which expands into the ambient vacuum and produces thin copper films at the surface of substrates. The degree of flux ionization (1%–30%) and the ion energy (2–150 eV) was manipulated by changing the geometric parameters of the arc discharge and by biasing the substrate relative to the vacuum vessel. The produced films are homogeneous and show bulk density. Their purity is ∼99.995%. The films show a strong [111] texture. The films exhibit a metastable state, which recrystallizes at room temperature within a few days. As a characteristic parameter describing the metastability the product of ion energy and degree of flux ionization, the mean ion energy per atom can be introduced. The final grain size decreases with increasing ion flux and ion energy and is determined by this recrystallization process. The surface topology is smoothed with increasing flux ionization. The surface roughness increases with higher ion energy due to an increase of the substrate temperature. The electrical resistivity of the copper films is ∼1.8 μΩ cm for ion energies below 25 eV (bulk value 1.67 μΩ cm). Towards higher ion energies the resistivity increases due to a higher dislocation density, lower grain size, and lower average distance of twin boundaries.

Relations between plasma properties and properties of thin copper films produced by an anodic vacuum arc

A steady vacuum arc with a consumable anode, the anodic vacuum arc, was used to produce thin copper films. This type of discharge is ignited in vacuum and is sustained by metal vapour produced at the anode. It generates a gas- and droplet-free metal vapour plasma which expands into the ambient vacuum and produces thin metallic films at the surface of substrates. The degree of flux ionization and the ion energy of the expanding plasma can be manipulated by a specific design of the electrodes. The films are homogeneous and show bulk density. Their purity is up to 99.98%. The influence of the degree of flux ionization and of the ion energy in the expanding plasma on the electrical resistivity, the mass density and the surface morphology are investigated.

Oxidation-induced changes in the electro-optical properties of thin copper films

The room temperature oxidation of vapour deposited copper films has been investigated as a function of film thickness and time by the sheet resistance and optical transmittance measurements. An increase of both sheet resistance and transmittance with a tendency to saturation has been observed. Time variation of the sheet resistance shows that the kinetics of oxidation could be described by a model whereby an initial logarithmic oxide growth changes to an inverse logarithmic one as time progresses; the thicker the film, the longer the change-over time. Absorption coefficients of oxidized films show that the resulting oxide is most probably Cu2O. Evaluation of the oxidized films for possible use as transparent electrode material shows the existence of an optimum thickness value.

An optical study of thermal effects in copper films

Changes in the structural and surface properties of copper thin films as a result of heating were studied optically. Variations in the reflectivity with temperature were investigated for samples of various thicknesses deposited on substrates at room temperature. The effects of using higher substrate temperatures during deposition were also studied. The results are explained on the basis of an increase in the grain size.

Electron transport properties of thin copper films. I.

The thickness dependence at 300 and 80 K of the electrical resistivity and its temperature coefficient, Hall coefficient, mobility, and thermoelectric power of as-deposited and annealed thin (< 1000 Å) evaporated polycrystalline copper films and films deposited at elevated temperatures have been studied. All transport parameters in carefully prepared and well-characterized films exhibit monotonically increasing size effects with decreasing film thickness. Both annealing and deposition at elevated temperatures cause considerable reduction of the ’’apparent’’ size effects in all the transport parameters of the room-temperature deposited films. A critical analysis of the observed size effects shows that the data in all cases depart markedly from the predictions of the Fuchs-Sondheimer theory (and also that of the Mayadas-Shatzkes theory which takes into account the grain boundary surface scattering). The departure from theory is different for each transport parameter. The annealing studies show that the enhanced size effects are due to the presence of a large concentration of structural defects in the films. The observed behavior may be understood by assuming the large concentration of point and/or line defects to decrease with film thickness and with annealing as well as deposition of films at elevated temperatures. The thermopower data suggest strongly that the large concentration of defects causes distortion of the Fermi surface and thereby a strong energy dependence of the mfp or relaxation time at the Fermi surface.

The effects of absorbed argon on the electrical properties of thin copper films

The electrical resistances of thin copper films formed by thermal evaporation in U.H.V. and in 10 -6 torr of “Specpure” argon have been measured. The results together with measured values of film thickness have been used to compute values of electronic mean free path and bulk resistivity using the Fuchs-Sonheimer relationship. It has been found that the presence of argon during film formation, although increasing the grain size of the films, produces a marked reduction in mean free path and in film conductivity. This is attributed to the incorporation of argon atoms in the film during its formation.

The effect of absorbed argon on the properties of thin copper films

A comparison has been made between the mean free paths of conduction electrons in copper films deposited in ultra-high vacuum and in a low-pressure atmosphere of argon. The effect of the argon is to decrease the mean free path and to increase the minimum thickness at which the film can be considered to be continuous.