Electromigration in sputtered copper films on polyimide

Electromigration damage (EMD) is one of the major causes for the failures of interconnects. In this study, the electromigration of Cu on polyimide is investigated. An empirical formula is used to evaluate the EMD of Cu film. The activation energy (Q) obtained is significantly less than those of lattice and grain boundary diffusion. This suggests that the electromigration in copper proceeds via an interfacial diffusion path. The geometry of the metallization also affects the activation energy. Any abrupt change in the interconnect direction and metal width causes current crowding and should be avoided. The current exponents (n), calculated from EMD data, are 3.58 and 3.35 for straight and zig-zag Cu films, respectively.     

Electrical resistivity and microstructures of sputtered CuxMo6S8 films

The resistivity of superconducting Cu_xMo₆S₈ films prepared by sputtering was measured between 10 and 300 K. Using a scanning electron microscope, the microstructures of the films with different preparation conditions were examined. The broadly varying values of the measured resistivities were explained on the basis of the particular microstructures of the films.     

Effects of hydrogen atmosphere on pulsed-DC sputtered nanocrystalline Si:H films

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared by a pulsed-DC magnetron sputtering method under an atmosphere of hydrogen/argon mixture. The effects of hydrogen concentration on the structural and electrical properties of the films were systematically investigated using grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, and conductivity measurement. A threshold hydrogen concentration of about 70% was found necessary before any crystallinity was detectable. The deposition rate decreased monotonically with increasing hydrogen concentration, while the conductivity varied with crystallite size. The abnormally low conductivity level of these nc-Si:H films was due to the extraordinarily high defect density, which was attributed both to the enhanced ion bombardment from the pulsed-DC plasma and to the oxygen contamination from the target.     

Barrier layer effect of titanium-tungsten on the electromigration in sputtered copper films on polyimide

Titanium-tungsten is employed as the diffusion barrier in a Cu/barrier/polyimide/Si system. The electromigration damage (EMD) of Cu with a TiW barrier is investigated utilizing an empirical formula. Two activation energies are obtained suggesting a surface electromigration mechanism at low temperature (140–190 °C) and a combined migration mechanism at high temperature (190–230 °C). The presence of the TiW barrier layer improves the high temperature electromigration resistance. The effects of the TiW barrier on the microstructure and electrical properties of Cu metallization are discussed.     

Photocurrent enhancement of d.c. sputtered copper oxide thin films

Copper oxide (CuO) thin films with photocurrent as high as 25 μA/cm² were deposited on conductive glass substrates using d.c. reactive sputtering. This was the highest reported photocurrent for sputteredp- type copper oxide measured in the electrolyte KI. The photocurrent drastically increased up to 25 (μA/cm² as the sputtering pressure and the substrate temperature were increased up to 8.5 mbar and 192°C, respectively. All the synthesized films contained single phase of CuO in this range of pressure and substrate temperature. Variation of the photocurrent, photovoltage, structure and absorbance with deposition conditions were studied in detail.     

The effects of incident angle on C-axis orientation in sputtered Co-Cr films

The effects of the incident angle of the sputtered atoms on the crystallographic orientation in the Co-Cr films have been investigated in detail. Specimen films 1000 - 2000 Å thick were prepared by the Facing Targets Sputtering (FTS) system. The specially designed mask was used for collecting only the sputtered particles with the quasi-coherent incidence to the substrate. When the films are prepared at relatively low argon gas pressures, the effect of incident angle is not so apparent and the well c-axis oriented films can be obtained for the incident angle below 45°. This result indicate that the surface diffusion may be dominant over the incident angle for attaining the desired crystallographic orientation in the films when they are prepared at low working gas pressures. Owing to the unique target/substrate layout, the plasma-free FTS system with low working gas pressures may have much larger flexibilities for preparing the well c-axis oriented Co-Cr films as compared with the conventional sputtering systems or the vacuum evaporation one.     

Effects of the loadings and type of copper powder on the electrical resistivity of copper powder-polymer paint films

Conductive behaviour in copper powder-filled paint films was subdivided into three regions, I, II, and III, with copper loading. Paint films were insulators in Region I. In Region II, resistivity decreased linearly in proportion to the cube root of the volume concentration, V, of the copper powders, reaching a minimum value at a certain V, which is the critical volume concentration, V _c, of copper powders. V _c, increased linearly in proportion to the bulk density of branched copper powders. This suggests that conductivity in the region is dependent upon the packing state of the copper particles. V _c, and resistivity at V _c, decreased with decrease in the grain size of isotropic branched and spherical copper powders, although they increased for flake copper powders. In Region III, resistivity increased with increase in copper loading. The increase in resistivity was due to the decrease in the apparent density of dry paint films.     

Effect of sputtering power on the physical properties of dc magnetron sputtered copper oxide thin films

Cuprous oxide films were deposited on glass substrates using dc magnetron sputtering technique by sputtering of pure copper target in a mixture of argon and oxygen atmosphere under various sputtering powers in the range 0.38–1.50 W cm⁻². The influence of sputtering power on the structural, electrical and optical properties was systematically studied. The films were polycrystalline in nature with cubic structure. The films formed at sputtering powers ≤0.76 W cm⁻² exhibited mixed phase of Cu₂O and CuO while those formed at 1.08 W cm⁻² were single phase Cu₂O. The single-phase Cu₂O films formed at a sputtering power of 1.08 W cm⁻² showed electrical resistivity of 46 Ω cm, Hall mobility of 5.7 cm² V⁻¹ s⁻¹ and optical band gap of 2.04 eV.     

Elasticity and resistivity study on the electromigration effects observed in aluminum–silicon–copper alloy thin films

The early electromigration (EM) processes in the Al–Si(Cu) thin films several tens of nanometers thick deposited on Si reed substrates were investigated by means of the simultaneous anelasticity and electrical resistivity measurements below 360 K. The grain growth, the shortening of a and the probable lengthening of a take place during the EM tests at the current density of 10⁸ A/m², where a and a denote the atomic plane spacing normal to and the one parallel to the film surface, respectively. The activation energy, E_GB, for the grain growth is found to be as low as 0.32 eV, possibly suggesting that E_GB in very thin nanometer-thick films is much lower than that found in thin micrometer-thick films. The increase in the Young’s modulus of the Al–Si(Cu) thin films takes place during the EM tests, suggesting that the grain growth is responsible for it. The decrease in Q⁻¹ observed at 330 and 360 K may be explained by a decrease in the grain boundary regions too. The increase in Q⁻¹ found during the EM tests at 300 K is possibly associated with an increase in a certain anelastic process in the grain boundary regions.     

Magnetron sputtered tungsten oxide films activated by dip-coated platinum for ppm-level hydrogen detection

Platinum-activated tungsten oxide (Pt-WO₃) films are prepared for hydrogen (H₂) sensing applications. In this study, WO₃ films were fabricated by reactive magnetron sputtering and Pt clusters were deposited on them by dip-coating. The microstructure, chemical composition and phase structure of Pt-WO₃ films were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction, respectively. It was observed that a reconditioning period is required after a rest period of the sensor for obtaining a stable signal. A thermal treatment at 450 °C for 24 h is proposed to solve this problem.     

The effects of aluminium composition on the mechanical properties of reactivity sputtered TiAlN films

TiAlN films were deposited on tool materials through an r.f. bias reactive sputtering process. The effects of the aluminium composition in the films on the hardness, oxidation resistance and wear properties were studied. The results indicated that both the aluminium composition and cutting speed had substantial effects on wear resistance. The oxide phases formed at elevated cutting temperatures, especially alumina, had important effects on the cutting performance. An optimum improvement of nine times in wear resistance compared to uncoated tools, was observed. © 1998 Chapman & Hall     

Electrical resistivity and lattice parameters of sputtered iridium alloys

Films of iridium and Ir-Cr, Ir-Mo, Ir-W, Ir-Re and Ir-Pt alloys were prepared by r.f. sputtering on Al₂O₃ substrates. Because an asymmetric target arrangement was used for the iridium and alloying elements the sputtered films had a defined compositional gradient. Resistance probes, 1 × 5 mm in area, with well-defined alloy composition were cut out of the film using a computer-controlled laser. The electrical resistivity of the alloys was measured between 4 and 684 K. The temperature coefficient of the resistivity at 283 K varies with the composition from 400 to 1500 ppm K^-1. The increase in resistivity with impurities is 2.04, 3.65, 3.02, 2.70 and 1.33 μΩ cm at.%^-1 for chromium, molybdenum, tungsten, rhenium and platinum respectively. The linear size factor (1/a₀) (da/dc)_{c = 0} is -7.0%, +3.0%, +3.0%, +0.1% and +2.0% for chromium, molybdenum, tungsten, rhenium and platinum respectively.     

Electrical studies on sputtered CuCl thin films

CuCl is a wide-direct band gap semiconductor, lattice matched to Si and it possesses excellent ultra violet (UV) emission properties. It is thus a promising candidate for the next generation Si based UV optoelectronics. CuCl films were deposited using RF magnetron sputtering technique. X-ray diffraction analysis reveals that the grains are strongly <111> oriented. Triangular crystallites of CuCl were observed in the AFM surface topograph. Au–CuCl–Si–Au structures were fabricated and field dependent electrical studies were carried out in the electric field range of 1.25 × 10⁶ to 2.5 × 10⁷ V/m. I–V characteristics show that ohmic conduction prevails in low electric fields up to 2.5 × 10⁶ V/m. In the higher field range, from 2.5 × 10⁶ to 2.5 × 10⁷ V/m, the conduction mechanism was Schottky emission controlled. There was no trap related charge transport observed at higher electric fields. Preliminary electrical studies are reported in this article.     

Electrical resistivity, structure and composition of d.c. sputtered WNx films

WN_x films have been deposited by reactive d.c. diode sputtering in an Ar-N₂ gas mixture on Si substrates. The electrical resistivity, structure, microstructure and composition of the films were investigated. The parameters were the total and partial pressures, the discharge current and the negative bias voltage applied to the substrate. We have found that good W₂N films are obtainable with a dense structure and a resistivity of near 200 μΩ cm, but either the resistivity or the composition and structure suffer great variations with the discharge parameters. Depending on the nitrogen partial pressure and the bias voltage, the deposited layers are W₂N films, W₂N-W mixtures or W films.     

The effect of oxygen and hydrogen contamination on the electrical resistivity of rare earth metal films

The effect of air and hydrogen contamination on the electrical resistivity of Er, Ho, Dy, Tb, Gd and Yb films was studied. The resistivity of the films increases almost discontinuously as soon as air is admitted into the vacuum chamber. After this sudden increase, the change becomes slow and the resistivity attains a constant value for thicker films (> 200 Å). For very thin films (<100 Å) the resistivity increases rapidly after the initial jump and very soon attains a very high value owing to the complete oxidation of the film. When hydrogen is admitted into the system, the resistivity of the films increases as for air contamination, but after a few minutes the resistivity starts to decrease except for Yb films. The increase in the resistivity for Er, Ho, Dy, Tb and Gd films is due to the interstitial solution of hydrogen in these metals (α phase); however, the decrease in ? after the initial increase is due to the formation of high conductivity f.c.c. dihydride. In the case of Yb the resistivity does not decrease because YbH₂ has a higher resistivity than pure Yb. For thin erbium films (about 200 Å) at a hydrogen pressure of several torrs the resistivity rises again after reaching a minimum value. This increase is thought to be due to the interstitial solution of hydrogen in the metallic conductor ErH₂. The investigation supports an earlier suggestion of the authors that the dihydride phase present in rare earth metal films (except Yb and Eu) made in ordinary vacuum may decrease the resistivity of these films below their bulk value.     

Segregation in sputtered Co-Cr films

The segregation growth process in sputtered Co-Cr films is investigated by examining the effect of substrate temperature on the segregated microstructure and magnetic properties. In sputtered Co-25at%Cr films, segregation occurs below 560°C, and both the saturation magnetization and the perpendicular anisotropy constant show a maximum around a substrate temperature of 300°C, where a specific microstructure, called a CP (chrysanthemum-like pattern) structure, is observed. The results suggest that the CP structure becomes observable in the highly segregated state and generates high perpendicular anisotropy. A new segregation growth model is derived from the results of the CP structure observations. Using this model, it is possible to explain the continuous transition of the magnetization mode between the continuous and the particulate modes.     

The effects of annealing temperature on characteristics of UBMS sputtered CNx films for protective coatings

The carbon nitride (CNx) films have been prepared by unbalanced magnetron sputtering (UBMS) at room temperature. The deposited CNx films have been post-annealed at temperatures ranging from 300 °C to 700 °C in increments of 200 °C using rapid thermal annealing (RTA) equipment in vacuum ambient. We investigated the effects of rapid thermal annealing on the structural, surface, and physical properties of CNx films for application of protective coatings. As the result, the increasing annealing temperature led to a decline in physical properties of CNx films such as hardness, elastic modulus, adhesion, frication coefficient, and surface roughness, however it is attributed to the improvement of the residual stress in the film. These results are related to the ordering of sp² bonded clustering and the increase of disordered graphite domain by the desorption of N contents in the films, Specially, high annealing temperature over 700 °C is attributed to the graphitization of film.