Papers by Keyword: Copper Films

Abstract: The article considers the possibility of applying the eddy current method of non-destructive testing for measuring the electrical conductivity of new material - thin metal films. Copper films of various thickness obtained by physical vapour deposition were used as the measurement object. The deposition method and the hardware and software complex for measuring the electrical conductivity of the film were briefly described. A calibration curve that makes it possible to restore the values of the electrical conductivity of the material by the signal value of the eddy current probe was presented. The test results of films with different characteristics were given, and the distribution of the electrical conductivity of the films depending on the batch was shown. Based on different values of the electrical conductivity in a batch, the difference in deposition quality of various films was found.

Abstract: An affordable 6-cm diameter magnetron sputtering source was designed and constructed using a neodymium cylindrical permanent magnet inner stud and an outer ring magnet. Both magnets were set in isolation from a water-cooled disk behind the target. In this work, our magnetron sputtering source was employed to deposit copper thin films by changing the outer magnet ring. The outer magnate ring diameter sizes were 29 mm (I.D.)/39 mm (O.D.) and 30 mm (I.D.)/50 mm (O.D.). At the same applied bias voltage, the discharge current of the magnetron with a big outer magnet was higher than that of one with a small outer magnet. According to XRD pattern and AFM image of copper films, the degree of (111) and (200) orientations and surface roughness were increased in the case of films grown by magnetron with bigger outer magnet. The cross-sectional and plane-view SEM images showed that the grain size and film thickness were increased in the case of films grown by magnetron with bigger outer magnet. These results should be because the radial motion of secondary electron emitted from sputtering in front of target surface was increased with a bigger magnet.

Abstract: Metallic copper ultra-thin layers were synthesized by modified PE CVD method from low-sized volatile metal complexes consisting of small (2- to 5atomic) ligand molecules. To characterize the deposited copper layers the X-ray photoelectron (XPS), infrared (FTIR) and UV-vis spectroscopy, SEM, XRD analyses were used. The layers were found to be nanocrystalline and have a nanoscale grain structure with parameters depending on the experimental conditions. It was revealed that plasma activation decreases mean size of copper grains and increases its stability on the air. The microstructure of the layers was examined by scanning electron microscopy (SEM) and diffraction of synchrotron radiation (DSR) methods, and chemical composition with a predominant content of copper in the metallic state Cu0.

Abstract: The molecular dynamics simulations are performed with single-crystal copper thin films under uniaxial tensile and cyclic loading to investigate temperature effects on the mechanical responses. With the changes of sample temperatures in uniaxial extension, the variation characteristics of maximum stress, the Young’s modulus, the maximal potential energy, the atomic structure of the emerging dislocation, and activation volume and activation free energy at the maximum stress point make us identify and explain the critical temperature for the transition of deformation mechanism in a temperature range from 293 to 460 K. Under cyclic loading, with raising temperature, the number of cycles to failure of copper films increases under different manners in different temperature range, which can be explained by our constructing model based on the evolutionary features of dislocation. Thus, the mechanisms of the strange temperature dependence of tensile and cyclic deformation have been explained. When the temperature is above 370 K, the rate controlling mechanism is dislocation climbing during uniaxial loading, and the number of cycles to failure goes up quickly with temperature; when below 370 K, the mechanism of uniaxial tensility is mainly characterized by the overcoming of Peierls–Nabarro barrier and a few localized pinnings, the number of cycles rises slowly; and when about 370 K, the mechanism in single-axial tension is pipe diffusion, the number of cycles increases at middle speed.

Abstract: Using a fatigue testing method by which fatigue cracks can be initiated and propagated in a film adhered to cover a circular through-hole in a base plate subjected to cyclic loads, annealed copper films of 100m thickness with different crystal grain sizes were fatigued. The fatigue crack propagation in the film with large grains was often decelerated, so the crack propagation rate of the film with the large grain was lower than that of the film with the small grain. When the crack propagation was decelerated, the crack opening displacement obtained from the film with large grain size was smaller than that obtained from the film with small grain size. The relationship between the fatigue crack propagation rate and the stress intensity factor estimated from the crack opening displacement was identical for the cracks in the film with the large grain and the small grain.

Abstract: Influence of the electrodepositing parameters e.g. applied electric current as variable on texture formation and on mechanical properties of copper thin films was studied. Experiment was done for copper deposition from sulphate bath under galvanostatic and pulse current. It was found that copper layers exhibits different texture depending on applied current conditions during electrodepositing process. Pulse and direct current conditions leads to different texture of electrodeposited copper. Texture of electrodeposited copper coatings and mechanical properties could be correlated. It was found that, texture indexes although are not complex information about texture could be used for analysis of such correlation in technological process.

Abstract: Electrodeposition and other methods are employed to obtain metallic films and coatings. Copper coatings are most extensively used in circuit board industry and often as a base to further formation of other metallic films. Electrodeposited copper films (thin layers) are widely used in electronic and automotive industry so its electrical and mechanical properties and its thickness are important. Several methods are used for thickness determination of thin films and coatings for example mechanical, magnetic and ball crater with light microscopy methods. They are destructive and not precise enough. The X-ray fluorescence, absorption and diffraction are more frequently used due to better precision. Although they are complex and expensive, they pronounce an important feature like non-destructive character. For particular cases geometrical conditions and mathematical calculation procedure must be elaborated. An application of X-ray diffraction in grazing incidence angle for thickness determination is described in this article. The method is based on absorption principles of X-ray beam. The absorption is proportional to thickness of the coating and to incidence and to the diffraction angle which. Geometrical conditions were obtained experimentally and suitable mathematical calculations were introduced. The elaborated methodical approach was applied to thickness determination of copper coatings electrodeposited on a brass substrate.

Abstract: Stress-assisted atomic migration occurs in thin films due to thermal stress development, followed by hillock and void formation on a film surface. Relation between thermal stresses and hillock formation was investigated on copper films with and without passivation layer. Copper films with a thickness of 10, 50 and 100 nm on oxidized silicon wafer were prepared for investigating thermal stress and hillock formation. In-situ thermal stress observation by X-ray measurement revealed that compressive stresses develop in an early stage of heating followed by a sudden decrease in the temperature region between 100 and 200 deg. In a cooling stage, stresses in a film linearly changed with decreasing temperature to form a tensile residual stress state. Surface morphology is observed by optical microscope and SEM after the heat cycle as well as at elevated temperatures in a vacuum chamber. Dome-like swells were formed on an AlN passivation layer. Almost of all of the swells on 100 nm thick film collapsed after the heat treatment up to 350 deg whereas the swells on 10 nm thick film had no collapse excepting a few case. Comparing with the film without passivation, the swell is considered to be the result of atomic migration of copper film to form hillocks in the interface between copper film and AlN passivation film during heating. Atoms are considered to migrate reversibly into the copper film in the cooling stage, resulting to make vacant hall in the swell of AlN film and then collapse due to tensile stress development.

Abstract: Fatigue tests of nanometer-thick Cu films as deposited and annealed in vacuum were conducted under constant load ranges at room temperature. Fatigue strengths of the Cu films, which is defined as the critical load range being able to cause crack initiation within 106 cycles, are determined. The experimental results show that fatigue strength increases with decreasing film thickness. Fatigue cracking behaviors were characterized by electron microscope. It is also found that fatigue cracking resistance is dependent on film thickness and increases with decreasing film thickness. Size effects on fatigue properties of the nanometer-thick Cu films are discussed.

Abstract: Sputtered Cu films containing various insoluble substances, such as Cu(W2.3), Cu(Mo2.0), Cu(Nb0.4), Cu(C2.1) and Cu(W0.4C0.7), are examined in this study. These films are prepared by magnetron sputtering, followed by thermal annealing. The crystal structure, microstructure, SIMS depth-profiles, leakage current, and resistivity of the films are investigated. Good thermal stability of these Cu films is confirmed with focused ion beam, X-ray diffractometry, SIMS, and electrical property measurements. After annealing at 400°C, obvious drops in resistivity, to ~3.8 μ-cm, are seen for Cu(W) film, which is lower than the other films. An evaluation of the leakage current characteristic from the SiO2/Si metal-oxide-semiconductor (MOS) structure also demonstrates that Cu with dilute tungsten is more stable than the other films studied. These results further indicate that the Cu(W) film has more thermal stability than the Cu(Mo), Cu(Nb), Cu(C), Cu(WC) and pure Cu films. Therefore, the film is suitable for the future barrierless metallization.