Ab initio comparative study of C54 and C49 TiSi2 surfaces

A theoretical comparison of C54 and C49 TiSi₂ surfaces is presented, using ab initio plane-wave ultrasoft pseudopotential method based on generalized gradient approximation (GGA). The different surface energies of TiSi₂ have not only been calculated out, but the preferential formation of C49 phase in solid-state reaction could be explained by smaller surface energies and Poisson's ratio of C49 TiSi₂ as well. As for polar C54 TiSi₂(1 0 0) and C49 TiSi₂(0 1 0) surfaces, the Si termination surfaces are more stable.     

Influence of N2 flow ratio on the properties of hafnium nitride thin films prepared by DC magnetron sputtering

Hafnium nitride (Hf-N) thin films were deposited on fused silica at different N₂ flow ratio (N₂/N₂ + Ar) using a reactive DC magnetron sputtering system. A gradual evolution in the composition of the films from Hf₃N₂, HfN, to higher nitrides was found through X-ray diffraction (XRD). Films of Hf₃N₂ and HfN show positive temperature coefficients of resistivity, while higher nitride has a negative one. Highly oriented growth of (0 0 1) Hf₃N₂ and NaCl-structure (1 0 0) HfN films were fabricated on fused silica substrate at relatively lower temperature of 300 °C. The electrical resistivity values of both as-deposited and post-deposition annealed films were measured by a four-point probe method. The obtained minimum resistivity of as-deposited film is 20 μΩ cm, and this result shows potential application of HfN films as electrode materials in electronic devices.     

Effect of oxygen content and deposition temperature on the characteristics of thin silver films deposited by magnetron sputtering

Thin silver films were prepared by direct current magnetron sputtering in a single-ended in-line sputter system at various substrate temperatures and in O₂ contents in sputter gas, and their electrical, optical, structural and morphological properties together with the compositional properties were investigated. When deposited at room temperature, the electrical and optical properties of Ag films deteriorated with addition of O₂ to sputter gas. Deposition of Ag films in O₂ added sputter gas promoted the formation of Ag crystallites with (2 0 0) plane parallel to the substrate surface. The electrical resistivity and optical reflection of Ag films deposited above 100 °C were not affected by the sputtering plasma containing oxygen. X-ray photoelectron spectroscopic analysis showed that Ag films deposited above 100 °C in O₂ added sputter gas did not possess surplus oxygen in the film, and that the oxidation states of these films were almost identical to that of Ag films deposited in pure Ar gas.     

Spectroscopic ellipsometry study of the dielectric response of Au-In and Ag-Sn thin-film couples

Optical properties and phase composition of In-Au and Sn-Ag ultra-thin films grown by sequential evaporating and co-depositing of metals in a vacuum were investigated combining X-ray diffraction and spectroscopic ellipsometry methods. The atomic concentration ratios of bilayer and co-deposited samples were the same, i.e. In(Sn):Au(Ag) = 1:2. The XRD patterns indicated creation of AuIn, AuIn₂, Au₃In₂, Au₉In₄ and Ag₃Sn intermetallic compounds at room temperature. The effective complex dielectric functions of the composite layers, , were determined from ellipsometric quantities Ψ and Δ measured in a photon energy range of 0.6-6.5 eV. The free-carrier parameters (unscreened plasma frequency and free-carrier damping) and optical resistivity were evaluated using a semiclassical Drude-Lorentz model of the effective dielectric function. There was noticed a distinct influence of phase composition and surface morphology on the optical constants and conductivity of the samples: ρ_op changed from approximately 15 μΩ cm to 37 μΩ cm for Ag-Sn structures, composed of β-Sn and Ag₃Sn phases, and from 21 μΩ cm to 83 μΩ cm for Au-In multiphase system. Lower resistivity demonstrated diffusive layers formed after deposition of an In(Sn) thin film on the noble metal underlayer.     

Investigation of p-type behavior in Ag-doped ZnO thin films by E-beam evaporation

Ag-doped ZnO (ZnO:Ag) thin films were grown on glass substrates by E-beam evaporation technique. The structural, electrical and optical properties of the films were investigated as a function of annealing temperature. The films were subjected to post annealing at different temperatures in the range of 350-650 °C in an air ambient. All the as grown and annealed films at temperature of 350 °C showed p-type conduction. The films lost p-type conduction after post annealing treatment temperature of above 350 °C, suggesting a narrow post annealing temperature window for the fabrication of p-type ZnO:Ag films. ZnO:Ag film annealed at 350 °C revealed lowest resistivity of 7.25 × 10⁻² Ω cm with hole concentration and mobility of 5.09 × 10¹⁹ cm⁻³ and 1.69 cm²/V s, respectively. Observation of a free-to-neutral-acceptor (e,A^o) and donor-acceptor-pair (DAP) emissions in the low temperature photoluminescence measurement confirms p-type conduction in the ZnO:Ag films.     

Transparent and conducting Zn-Sn-O thin films prepared by combinatorial approach

Zn-Sn-O (ZTO) films with continuous compositional gradient of Sn 16-89 at.% were prepared by co-sputtering of two targets of ZnO and SnO₂ in a combinatorial method. The resistivities of the ZTO films were severely dependent on oxygen content in sputtering gas and Zn/Sn ratio. Except for the films with Sn 16 at.%, all the as-prepared films were amorphous and maintaining the stable amorphous states up to the annealing temperature of 450 °C. Annealing at 650 °C resulted in crystallization for all the composition, in which ZnO, Zn₂SnO₄, ZnSnO₃, and SnO₂ peaks were appeared successively with increasing Sn content. Above Sn 54 at.%, the ZTO films were deduced to have a local structure mixed with ZnSnO₃ and SnO₂ phases which were more conductive and stable in thermal oxidation than ZnO and Zn₂SnO₄ phases. The lowest resistivity of 1.9 × 10⁻³ Ω cm was obtained for the films with Sn 89 at.% when annealed at 450 °C in a vacuum. The carrier concentrations of the amorphous ZTO films that contained Sn contents higher than 36 at.% and annealed at 450 °C in a vacuum were proportional to the Sn contents, while the Hall mobilities were insensitive to Sn contents and leveling in the range of 23-26 cm²/V s.     

Photoconductivity of thin organic films

Thin organic films were deposited on silicon oxide surfaces with golden interdigitated electrodes (interelectrode gap was 2 μm), and the film resistivities were measured in dark and under white light illumination. The compounds selected for the measurements include molecules widely used in solar cell applications, such as polythiophene (PHT), fullerene (C₆₀), pyrelene tetracarboxylic diimide (PTCDI) and copper phthalocyanine (CuPc), as well as molecules potentially interesting for photovoltaic applications, e.g. porphyrin-fullerene dyads. The films were deposited using thermal evaporation (e.g. for C₆₀ and CuPc films), spin coating for PHT, and Langmuir-Schaeffer for the layer-by-layer deposition of porphyrin-fullerene dyads. The most conducting materials in the series are films of PHT and CuPc with resistivities 1.2 × 10³ Ω m and 3 × 10⁴ Ω m, respectively. Under light illumination resistivity of all films decreases, with the strongest light effect observed for PTCDI, for which resistivity decreases by 100 times, from 3.2 × 10⁸ Ω m in dark to 3.1 × 10⁶ Ω m under the light.     

Effect of annealing temperature on the decomposition of reactively sputtered Ag2Cu2O3 films

Ag₂Cu₂O₃ films were deposited on glass substrates by reactive sputtering of a composite silver-copper target. The deposited films were annealed in air at 100, 200 and 300 °C. The structure of the films was studied using X-ray diffraction (XRD), their surface morphology was characterised using scanning electron microscopy (SEM) and their electrical resistivity at room temperature was measured using the four point probe method. The 100 °C annealing did not modify either the film structure or the film morphology. On the other hand, Ag₂Cu₂O₃ films were partially decomposed into Ag and CuO after a 200 °C annealing. The decomposition was complete for a 300 °C annealing. The evolution of the film surface morphology as a function of the annealing temperature was discussed in connection to the evolution of the molar volume of the phases constituting the films.     

Two routes to polycrystalline CoSi2 thin films by co-sputtering Co and Si

Two processes for the fabrication of polycrystalline CoSi₂ thin films based on the codeposition of Co and Si by sputtering were studied and compared. The first process involved “annealing after deposition”, where Co and Si are codeposited at ambient temperature and then crystallized by annealing. This process yielded randomly oriented plate-like CoSi₂ grains with a grain size that is governed by the nanostructure of the as-deposited film. Polycrystalline CoSi₂ thin films were obtained at a process temperature of 170 °C, which was much lower than the annealing temperature of 500 °C needed for Co/Si bilayers. The second process involved “heating during deposition”, where Co and Si are codeposited on heated substrates. This process yielded CoSi₂ grains with a columnar structure, and the grain size and degree of (1 1 1) orientation are temperature dependent. The sheet resistance of the resulting films was determined by the preparation temperature regardless of the deposition process used, i.e. “annealing after deposition” or “heating during deposition”. Temperatures of 500 °C and higher were needed to achieve CoSi₂ resistivity of 40 μΩ cm or lower for both processes.     

Microstructure of epitaxial SrRuO3 thin films on MgO substrates

SrRuO₃ thin films have been grown on singular (1 0 0) MgO substrates using pulsed laser deposition (PLD) in 30 Pa oxygen ambient and at a temperature of 400-700 °C. Ex situ reflection high-energy electron diffraction (RHEED) as well as X-ray diffraction (XRD) θ/2θ scan indicated that the films deposited above 650 °C were well crystallized though they had a rough surface as shown by atom force microscopy (AFM). XRD Φ scans revealed that these films were composed of all three different types of orientation domains, which was further confirmed by the RHEED patterns. The heteroepitaxial relationship between SrRuO₃ and MgO was found to be [1 1 0] SRO//[1 0 0] MgO and 45°-rotated cube-on-cube [0 0 1] SRO//[1 0 0] MgO. These domain structures and surface morphology are similar to that of ever-reported SrRuO₃ thin films deposited on the (0 0 1) LaAlO₃ substrates, and different from those deposited on (0 0 1) SrTiO₃ substrates that have an atomically flat surface and are composed of only the [1 1 0]-type domains. The reason for this difference was ascribed to the effect of lattice mismatch across the film/substrate interface. The room temperature resistivity of SrRuO₃ films fabricated at 700 °C was 300 μΩ cm. Therefore, epitaxial SrRuO₃ films on MgO substrate could serve as a promising candidate of electrode materials for the fabrication of ferroelectric or dielectric films.     

Microstructure and magnetic properties of FePt:Ag nanocomposite films on SiO2/Si(1 0 0)

FePt:Ag nanocomposite films were prepared by pulsed filtered vacuum arc deposition system and subsequent rapid thermal annealing on SiO₂/Si(1 0 0) substrates. The microstructure and magnetic properties were investigated. A strong dependence of coercivity and ordering of the face-central tetragonal structure on both Ag concentration and annealing temperature was observed. With Ag concentration of 22% in atomic ratio, the coercivity got to 6.0 kOe with a grain size of 6.7 nm when annealing temperature was 400 °C.     

Characterization of AgInS2 thin films prepared by vacuum evaporation

We characterized AgInS₂ thin films prepared by vacuum evaporation. In the case of thin films annealed at 400 °C, diffraction peaks were observed only for the chalcopyrite AgInS₂ phase. The chemical composition of the thin films annealed at 400 °C was 26.5 at% Ag, 23.8 at% In, and 49.7 at% S. PL spectra of the AgInS₂ thin films at 10.7 K showed peaks at 1.70, 1.80, and 1.83 eV. The PL peak at1.80 eV was attributed to sulfur deficiency.     

Thermal stability of Ag films in air prepared by thermal evaporation

The thermal stability of silver films in air has been studied. Pure Ag films, 250 nm in thickness, were prepared on glass substrates by thermal evaporation process, and subsequently annealed in air for 1 h at temperatures between 200 and 400 °C. The structure and morphology of the samples were investigated by X-ray diffraction, Raman spectra and atomic force microscopy. It is found that the crystallization enhances for the annealed films, and film surface becomes oxidized when annealing temperature is higher than 350 °C. The electrical and optical properties of the films were studied by van der Pauw method and spectrophotometer, respectively. Reflectance drops sharply as Ag films are annealed at temperatures above 250 °C. Film annealed at 250 °C has the maximum surface roughness and the minimum reflectance at 600 nm optical wavelength. Film annealed at 200 °C has the minimum resistivity, and resistivity increases with the increasing of the annealing temperature when temperature is above 200 °C. The results show that both oxidization on film surface and agglomeration of silver film result in infinite of electrical resistivity as the annealing temperature is above 350 °C.     

High-performance copper alloy films for barrierless metallization

In this study, we observe useful properties of V_1.1- and V_0.8N_0.4-bearing copper (Cu) films deposited on barrierless silicon (Si) substrates by a cosputtering process. The Cu_98.8(V_0.8N_0.4), or Cu(VN_x) for brevity, films exhibit low resistivity (2.9 μΩ cm) and minimal leakage current after annealing at temperatures up to 700 °C for 1 h; no detectable reaction occurs at the Cu/Si interface. These observations confirm the high thermal stability of Cu(VN_x) films. Furthermore, since these films have good adhesion features, they can be used for barrierless Cu metallization.     

Atom beam sputtered Mo2C films as a diffusion barrier for copper metallization

The saddle field fast atom beam sputtered (ABS) 50 nm thick molybdenum carbide (Mo₂C) films as a diffusion barrier for copper metallization were investigated. To study the diffusion barrier properties of Mo₂C films, the as-deposited and annealed samples were characterized using four probes, X-ray diffraction, field enhanced scanning electron microscopy, energy dispersive X-ray analysis, atomic force microscopy and Rutherford back scattering techniques. The amorphous structure of the barrier films along with presence of carbon atoms at the molybdenum carbide-silicon interface is understood to reduce effective grain boundaries and responsible for increased thermal stability of Cu/Mo₂C/Si structure. The lowest resistivity of the as-deposited molybdenum carbide barrier films was ∼29 μΩ cm. The low carbon containing molybdenum carbide was found thermally stable up to 700 °C, therefore can potentially be used as a diffusion barrier for copper metallization.     

Effect of composition and deposition temperature on the characteristics of Ga doped ZnO thin films

ZnO films doped with Ga (GZO) of varying composition were prepared on Corning glass substrate by radio frequency magnetron sputtering at various deposition temperatures of room temperature, 150, 250 and 400 °C, and their temperature dependent photoelectric and structural properties were correlated with Ga composition. With increasing deposition temperature, the Ga content, at which the lowest electrical resistivity and the best crystallinity were observed, decreased. Films with optimal electrical resistivity of 2-3 × 10⁻⁴ Ω cm and with good crystallinity were obtained in the substrate temperature range from 150 to 250 °C, and the corresponding C_Ga/(C_Ga + C_Zn) atomic ratio was about 0.049. GZO films grown at room temperature had coarse columnar structure and low optical transmittance, while films deposited at 400 °C yielded the highest figure of merit (FOM) due to very low optical absorption despite rather moderate electrical resistivity slightly higher than 4 × 10⁻⁴ Ω cm. The optimum Ga content at which the maximum figure of merit was obtained decreased with increasing deposition temperature.     

Preparation and characterization of C54 TiSi2 nanoislands on Si (1 1 1) by laser deposition of TiO2

We present the preparation of C54 TiSi₂ nanoislands on Si (1 1 1) with a method of the pulsed laser deposition of titanium oxide thin films. The TiO₂ thin films with nominal thicknesses of 1 nm on Si (1 1 1) were annealed at 850 °C for about 4 h in situ. The X-ray diffraction patterns and the X-ray photoelectron spectra indicate that the nanoislands are in C54 TiSi₂ phase. The characterization using a scanning tunneling microscope shows that the nanoislands with triangular, polygonal and rod-like shapes on Si (1 1 1) exhibit the Volmer-Weber growth mode. The sizes of the polygonal islands distribute in two separated ranges. For the small islands, they have a narrow lateral size distribution centered at 4 nm and a height range in 0.6-3.6 nm, while for the large islands, their lateral sizes are in the range of 12-40 nm and the heights in the range of 4-9 nm. The sizes of the well-shaped triangular islands are intermediate with the lateral sizes in range of 5-20 nm and the heights of 2-3.5 nm. The rod-like islands are about 50-200 nm in length, 5 nm in height and about 15-20 nm in width. The origination of the various shapes of the nanoislands is attributed to the symmetry of Si (1 1 1) substrate and the lattice mismatch between the C54 TiSi₂ and the Si (1 1 1) surface.     

Influence of deposition temperature on the crystallinity of Al-doped ZnO thin films at glass substrates prepared by RF magnetron sputtering method

Al-doped ZnO (AZO) transparent conducting films were successfully prepared on glass substrates by RF magnetron sputtering method under different substrate temperatures. The microstructural, electrical and optical properties of AZO films were investigated in a wide temperature range from room temperature up to 350 °C by X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), High-Resolution Transmission Electron Microscopy (HRTEM), Hall measurement, and UV–visible meter. The nature of AZO films is polycrystalline thin films with hexagonal wurtzite structure and a preferred orientation along c-axis. The crystallinity and surface morphologies of the films are strongly dependent on the growth temperature, which in turn exerts a great effect on microstructural, electrical and optical properties of the AZO films. The atomic arrangement of AZO film having an wurtzite structure was indeed identified by the HRTEM as well as the Selected Area Electron Diffraction (SAED). The defect density of AZO film was investigated by HRTEM. The film deposited at 100 °C exhibited the relatively well crystallinity and the lowest resistivity of 3.6 × 10⁻⁴ Ω cm. The average transmission of AZO films in the visible range is all over 85%. More importantly, the low-resistance and high-transmittance AZO film was also prepared at a low temperature of 100 °C.     

Rapid thermal annealing of ITO films

Tin-doped indium oxide (ITO) films with 200 nm thickness were deposited on glass substrates by DC magnetron sputtering at room temperature. And they were annealed by rapid thermal annealing (RTA) method in vacuum ambient at different temperature for 60 s. The effect of annealing temperature on the structural, electrical and optical properties of ITO films was investigated. As the RTA temperature increases, the resistivity of ITO films decreases dramatically, and the transmittance in the visible region increases obviously. The ITO film annealed at 600 °C by RTA in vacuum shows a resistivity of 1.6 × 10⁻⁴ Ω cm and a transmittance of 92%.     

Characterization of SnO2 obtained from the thermal oxidation of vacuum evaporated Sn thin films

Tin oxide has been prepared by thermal oxidation of evaporated tin thin films onto pyrex glass substrates. Films oxidation was achieved in air at a temperature of 600 °C with varied duration from 20min to 3 h. Structural, optical and electrical properties of the films were characterized by means of X-ray diffraction, UV–vis spectroscopy and electrical resistivity measurements respectively. The X-ray analysis revealed the transformation of Sn into SnO₂ with preferential orientation along (101) plans. No intermediate phases such as SnO and Sn₃O₄ were evidenced. It was also found that the SnO₂ crystallites orientation changed with the annealing time due to the strain energy effect. Both band gap energy and electrical resistivity decrease with annealing time due to the crystalline quality improvement and films densification. We have noticed that oxidation at 600 °C for 3 h leads to transparent and conductive films with suitable properties for photovoltaic applications.