Phase structure characteristics of r.f. reactively sputtered zirconia thin film

Zirconia thin films were deposited by an r.f. magnetron reactive sputtering method. Three kinds of target (pure Zr metal and compounds of Y-ZrO₂ and Mg-ZrO₂) were employed. The phase characteristics of the three series of films deposited with various oxygen partial pressures and substrate temperatures were investigated. It is found that only monoclonic phase was formed in the sputtered thin films when using Zr target, and both tetragonal and monoclinic phases were formed when using the compound targets.     

Ta thin film resistors reactively sputtered onto substrates mounted on a rotating carousel

Ta thin film resistors have been reactively sputtered in 1.5×10^–5 Torr oxygen and 1.5×10^–5 Torr nitrogen simultaneously, using a d.c. diode system in which the anode is formed by a carousel. The substrates are mounted on this carousel and can be rotated through the discharge. For non-heat-treated films the resistivity increases and the TCR becomes more negative as the carousel rotation speed increases. These changes in electrical properties are attributed to the observed increase in the oxygen concentration and a simultaneous decrease in the nitrogen concentration in the films. The electrical properties are further perturbed by an elongation of the physical structure of the films as a result of carousel rotation. This elongation, which can produce an increased resistivity for a given TCR, is attributed to oblique incidence effects as the substrate rotates into, and out of the discharge. Changes produced in the electrical and structural properties of the films during heat-treatment at 500 C are shown to depend on carousel rotation speed: recrystallization and surface oxidation occur for films deposited onto a rotating carousel, whereas films deposited onto a stationary carousel undergo surface oxidation only, as indicated by the kinetics of the conductance change and the lack of structural changes as shown by transmission electron microscopy.     

Electrical studies of reactively sputtered Fe-doped VO2 thin films

Thin films of V_1−xFe_xO₂ (O<-x≤0.12) were prepared by r.f. reactive sputtering, and the resistivity of these films was measured from 25°C to 100°C. The semiconductor-metal transition temperature decreases as the iron content is increased at a rate of −6C°/at %Fe up to 1.4 %Fe. Beyond this concentration, the transition temperature then begins to increase slowly, remaining unchanged beyond 3% Fe. The apparent activation energy increases rapidly from 0.23 eV to a plateau of 0.33 eV, which then remains independent of the Fe concentration. This overall behavior is in contrast to previous reports and suggests that the iron has been incorporated into the VO₂ lattice in a fashion previously unobserved.     

Electrical and structural properties of NiCr thin film resistors reactively sputtered in O2

NiCr thin film resistors have been reactively sputtered using a d.c. diode system in which the anode is formed by a carousel. The substrates are mounted on this carousel and can be rotated through the discharge. For films deposited onto a stationary carousel (the substrates permanently fixed in the discharge), film resistivities range from 150 to 300 μΩ as the oxygen partial pressure is increased from the base pressure to 3 × 10^-5 torr. The TCR values range from 150 to 300 ppm/°C. For carousel rotation at 20 rev/min the corresponding resistivities may be increased by a factor as large as 20 without greatly affecting the TCR. Microprobe analysis indicates that the Ni/Cr concentration ratio is independent of the deposition conditions, but that for a given oxygen partial pressure the film density is less for films deposited onto a rotating carousel than for films deposited onto a stationary carousel. Transmission electron microscopy indicates that the crystallographic structure consists of a metallic phase and an oxide phase which do not change with carousel rotation, but that films deposited onto a stationary carousel have an island structure while those deposited onto a rotating carousel have a worm-like structure. The structural features of films deposited onto a rotating carousel may be due to oblique incidence effects. Measurements of film resistance at low temperatures indicate that conduction in the film may be considered to consist of a metallic conduction mechanism of positive TCR acting in conjunction with an oxide conduction mechanism of negative TCR, with the relative contribution of each mechanism being a function of the physical microstructure of the films. Heat treatment of films deposited onto a rotating carousel produces an increase in resistance which is attributed to oxidation of the film surface, while heat treatment of films deposited onto a stationary carousel produces a resistance decrease which is attributed to thermal annealing effects dominating surface oxidation effects.     

Structure and chemical bonds in reactively sputtered black Ti-C-N-O thin films

The evolution of the nanoscale structure and the chemical bonds formed in Ti-C-N-O films grown by reactive sputtering were studied as a function of the composition of the reactive atmosphere by increasing the partial pressure of an O₂ + N₂ gas mixture from 0 up to 0.4 Pa, while that of acetylene (carbon source) was constant. The amorphisation of the films observed by transmission electron microscopy was confirmed by micro-Raman spectroscopy, but it was not the only effect associated to the increase of the O₂ + N₂ partial pressure. The chemical environment of titanium and carbon, analysed by X-ray photoemission spectroscopy, also changes due to the higher affinity of Ti towards oxygen and nitrogen than to carbon. This gives rise to the appearance of amorphous carbon coexisting with poorly crystallized titanium oxynitride. The evolution of the films colour is explained on the basis of these structural changes.     

Physical and mechanical properties of reactively sputtered chromium boron nitride thin films

This paper reports on the first study of physical and mechanical properties of reactively sputtered chromium boron nitride coatings as a function of chemical composition, bias voltage and substrate temperature. Several sets of coatings were deposited by reactive unbalanced magnetron sputtering on Si(100) substrates. The chemical composition was deduced from X-ray photoelectron spectroscopy and Auger electron spectroscopy measurements, and was found to be influenced primarily by nitrogen flow rate. The phase composition was determined using X-ray diffraction in conjunction with spectroscopic ellipsometry. Atomic force microscopy was utilized to determine surface roughness and average surface grain size. Both surface roughness and surface grain size were largely independent of the nitrogen concentration and decreased with increasing bias voltage. The nanohardness and elastic modulus of each sample were measured by nanoindentation. The hardest films were produced using −150 V bias voltage and either very low (0.5-1 sccm) or very high (12-15 sccm) nitrogen flow rates.     

Facing target sputtered iron-silicide thin film

The FeSi_x thin films with the flatness to an atomic scale for mechanical and optical applications can be grown by a facing target sputtering method. Optical properties indicate the films contain nano-crystalline FeSi₂. The nano-indentation hardness of 10 GPa was obtained. An interesting point is that Young's modulus is larger than that of the carbon-based materials with the same hardness. This means that the FeSi_x is more elastic, which could be characteristic of the chemical bonding of the FeSi₂ with the large contribution of d-electrons. Furthermore, results of the Hall measurement at room temperature shows that the films have p-type conductivity, a carrier concentration of p = 2.49 × 10²⁰ cm^− 3 and a Hall mobility of μ = 6.42 cm² V^− 1 s^− 1.     

Nitrogen-doped tantalum thin film capacitors with improved temperature stability

The changes in capacitance, temperature coefficient of capacitance (t.c.c.) and dissipation factor (tan δ) of tantalum thin film capacitors subjected to heat treatment depend significantly on the nitrogen content of the Ta and the Ta₂O₅. If tantalum films deposited by reactive sputtering contain between 5 and 15 at.% nitrogen, the tan δ and t.c.c. of the finished capacitors can be reduced to constant values of 1.5 × 10^-3 and 135 ppm K^-1 respectively (test frequency 1 kHz) by heat treatment at temperatures between 250° and 350°C. However, if the nitrogen content is smaller or greater, or if β-Ta is used, both the t.c.c. and tan δ increase sharply with rising temperature and prolonged heat treatment.     

Conduction in thin films of r.f. reactively sputtered zinc sulphide

Experiments on d.c. electrical conduction in thin films of r.f. reactively sputtered zinc sulphide (thicknesses from 100 to 1000 Å) sandwiched between Al and Au are described. For an electric field between 10⁵ and 10⁶ V cm^-1, the plot of log J versus √V is linear; the thermal evolution of the current is described by log J ～T^-1/3. It is therefore assumed that the electrical conduction is due to the emission of electrons from defects into the conduction band of the zinc sulphide.     

Photocatalytic activity of reactively sputtered and directly sputtered titania coatings

It is well known that, depending on deposition conditions, the structure of titania coatings may be amorphous, anatase or rutile, or a mixture of phases, and that the anatase phase is the most promising photocatalyst for the degradation of organic pollutants. The formation of anatase depends on the energy delivered to the growing film, which in turn depends on the operating parameters chosen. In this study, titania coatings have been deposited onto glass substrates by pulsed magnetron sputtering both from metallic targets in reactive mode and directly from oxide powder targets. The as-deposited coatings were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400–700 °C and re-analysed. The photocatalytic activity of the coatings has been investigated through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. Further sets of coatings have been produced both from metallic and powder targets in which the titania is doped with tungsten. These coatings have also been analysed and the influence of the dopant element on photocatalytic activity has been investigated. It has been found that, after annealing, both sputtering processes produced photo-active surfaces and that activity increased with increasing tungsten content over the range tested. Furthermore, the activity of these coatings under exposure to fluorescent lamps was some 50–60% of that observed under exposure to UV lamps.     

Mechanical, microstructural and oxidation properties of reactively sputtered thin CrN coatings on steel

Thin (40 nm and 160 nm) CrN coatings were deposited on steel by reactive magnetron sputtering deposition, varying the N₂ flow. The coatings were characterized in the as-deposited condition and after annealing in air at 500 °C for 1 h, by X-Ray Diffraction, Transmission Electron Microscopy, Raman and Fourier Transform Infrared spectroscopies. Hardness was measured by nanoindentation. Coatings have a nanocrystalline microstructure with the phase shifting from Cr₂N to CrN, increasing grain size, thermal stability and resistance to oxidation with increasing N₂. Also intrinsic coating hardness is influenced by both N₂ flow during deposition and film thickness, as a result of changes in phase composition and microstructural properties.     

Noise and structural properties of reactively sputtered RuO2 thin films

Ruthenium dioxide thin films were reactively rf sputtered on SiO₂/Si substrates and annealed in the temperature range from 150 to 500 °C. The structural and morphological properties of the films were investigated using Raman spectroscopy, transmission electron microscopy and atomic force microscopy. The increase of grain size was improved with annealing temperature. After annealing at 500 °C, the roughening of the RuO₂/SiO₂ interface was observed. The electrical behaviour was analysed by resistivity, thermal coefficient of resistance and low frequency noise. Good correlation between structural and electrical properties of RuO₂ films was established.     

Dielectric properties of terbium fluoride thin film capacitors

The dielectric properties of thermally evaporated TbF₃ thin film capacitors (Al/TbF₃/Al) of various thicknesses were studied in the frequency range 0.5–30 kHz at various temperatures (300–443 K). The dielectric constant was found to increase with increasing film thickness. The large increase in capacitance towards the low frequency region indicates the possibility of an interfacial polarization mechanism prevailing in that region. The frequency-temperature dependence of tan δ reveals a loss peak which shifts to higher frequencies with increasing temperature. The dielectric relaxation phenomenon in these films was explained on the basis of dipolar reorientation. The activation energy was calculated for the relaxation process. Cole-Cole diagrams were drawn and used to determine the spreading factor β and the mean relaxation time τ_a.     

The microstructure of reactively sputtered Ti-N films

Ti-N films with nitrogen concentrations ranging from 0 to 52 at.% prepared by both d.c. magnetron and r.f. reactive sputtering are examined using transmission electron microscopy. The observed microstructures are correlated with physical properties of the films. In particular, the maximum in the microhardness and density and the minimum in the electrical resistivity are found to correspond to a fully dense structure. The sample prepared by magnetron sputtering has a very inhomogeneous and voided microstructure and a lower hardness than the r.f.-sputtered sample with a similar nitrogen content. A theory is proposed for the development of a lamellar microstructure in the films containing two phases.     

Properties of TiNxfilms reactively sputtered in an argon-nitrogen atmosphere

The dependence of the resistivity and temperature coefficient of resistivity (TCR) of TiN_x films on nitrogen pressure is described. The partial nitrogen pressure was varied from 10^?5 Torr to 2×10^?4 Torr. The maximum value of the resistivity (216 μΩ cm) and the lowest negative value of TCR (?33ppmK^?1) were obtained in the nitrogen pressure range (2?4)×10^?5 Torr. The minimum value of the resistivity (44 μΩ cm) and the highest positive value of the TCR (1160 ppm K^-1 were obtained in the nitrogen pressure range (4?10)×10^?5 Torr. The influence of aging temperature up to 573 K on the resistance changes are shown. X-ray diffraction analysis indicated the presence of oriented or non-oriented TiN in these films.     

Dielectric breakdown of reactively sputtered silicon nitride

Silicon nitride layers on silicon substrates were prepared by reactive sputtering of silicon in nitrogen under conditions which led to layers of maximum dielectric strenght. Dielectric breakdown and its dependence on temperature, pulse width and layer thickness were investigated. It is shown that conversion from thermal to electronic breakdown can be achieved at low temperatures and short pulse widths. This enables the thickness dependence of breakdown to be observed. From this dependence the mean free time of carriers was found to be 1.1×10^-15 sec.     

Oxidation of sputtered Zr thin film on Si substrate

Oxidation of sputtered Zr thin film on Si substrate has been investigated by varying oxidation times (5–60 min) at 500 °C. Fourier transform infrared spectroscopy indicated the existence of ZrO₂ by showing spectra of Zr–O. Vibration mode of Si–O and Zr–O–Si are also detected for all samples oxidized at different duration. This suggested the existence of SiO _x and Zr _x Si _y O _z compounds and they might be located at interfacial layers (ILs) between ZrO₂ and Si. Cross-sectional image of high resolution transmission electron microscopy taken from 60-min oxidized sample showed that both ZrO₂ and IL thickness is ~3.5 nm. Time-of-flight secondary-ion-mass spectroscopy suggested that Zr _x Si _y O _z may be formed after oxidized for 15 min. The proposed IL is consisted of a mixture of Zr _x Si _y O _z and SiO _x . A physical model has been established to explain the observation. Electrical characterization shows that capacitance–voltage curves have small hysteresis and their flatband voltages are shifted to a negative bias. Effective dielectric constant values of the investigated oxides are in the range of 4.22–5.29. Leakage current density–breakdown voltage characteristic shows that 5-min oxidized sample has the lowest dielectric breakdown voltage if compared with the other samples.