Influence of thickness on H2 gas sensor properties in polycrystalline SnO x films prepared by ion-beam sputtering

Amorphous SnO _x films were deposited on sintered alumina substrates by ion-beam sputtering. They were annealed at 500° C for 2 h in air and polycrystalline films with thickness varying from about 1 to 700 nm were prepared. Film-sensor properties against 0.47% H₂ gas were measured as a function of thickness and the operating temperature for 150 to 350° C. The film thickness exhibiting a sensitivity maximum increased gradually with temperature. The optimum thickness shifted from 7 nm at 150° C to 175 nm at 350° C. Highly sensitive films lay in a narrow thickness range of 60 to 180 nm and films thinner or thicker than this were relatively insensitive at 300 and 350°C. A model was proposed to interpret the sensitivity behaviour in terms of thickness and grain-boundary effect.     

Thickness dependence of electrical properties in thin films of undoped indium oxide prepared by ion-beam sputtering

Preparation and electrical characterization of undoped indium oxide films were examined as a function of thickness and annealing. Thin films ranging from 1.1 to 113 nm thickness were deposited on glass substrates by ion-beam sputtering. Low-angle X-ray diffraction analysis in multi-layered films showed the possibility that physically continuous and almost flat films were formed even in the thinnest 1.1 nm films. Room temperature resistivity of as-deposited films decreased sharply by more than five orders of magnitude as the thickness increased from 1.1 to 5.2 nm. The 2.4 nm thick films, in its as-deposited state, showed a gradual resistivity modulation with the change of atmosphere between air and argon gas at room temperature. Annealing at 300° C for 5 h in air increased the resistivity drastically; the room temperature resistivity of 24.3 nm thick films changed from 2.2×10^–3 cm (as-deposited) to higher than 10⁵ cm (annealed).     

Thickness effect on grain growth and precipitate coarsening of a copper-silver thin film in an advanced metallization process

Annealing of Cu(Ag)/SiO₂/Si films was carried out to investigate the relationship between grain growth and precipitate coarsening. Ag in copper was selected as an immiscible dopant for diffusion and precipitation. Annealing effects were characterized in terms of resistivity, morphology, preferred orientation, grain growth, precipitation, and diffusional characteristics. The lowest observed resistivity was 2.06 cm in a 900 nm thick film annealed at 500 °C. The resistivity decrease was attributed to Ag precipitation and grain growth. A transition thickness exists at below 220 nm in the grain growth and the precipitate coarsening of the Cu(Ag) films. A relationship was established between grain growth and precipitate coarsening above the transition thickness that fits well to the experimental data. The grain size in the Cu(Ag) film can thus be predicted from the Ag precipitate size by using this relationship.     

Preparation and characterization of radio-frequency-sputtered Ba2Si2TiO8 thin films

Radio-frequency-sputtered barium titanium silicate (BST, Ba₂Si₂TiO₈) thin films were grown on crystalline Si (100) substrates and were characterized using wavelength-dispersive spectrometry (WDS), X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM), and diagonal techniques for dielectric properties. The chemical compositions of the films increasingly deviated from stoichiometry with film thickness. At the initial stage of deposition the grain configuration is dependent on the Si substrate texture. XRD analysis indicates that the BST films deposited at an optimum substrate temperature of 845 °C were strongly c-axis oriented, and that the film orientation is manipulated by substrate temperature and supersaturation. The corresponding film-growth rate in the direction normal to the film surface at 845 °C was 1.95 nm min^–1 at the initial stage, and decreased with sputtering time. The as-deposited films have a room-temperature bulk resistivity of 1.8 ×10⁷ m in the direction of thickness and an isotropic surface resistivity of 1.5×10³ m. The high-frequency relative dielectric constant, 0.05 at frequencies higher than 9 MHz, is lower than that of many typical piezoelectric materials. The high-frequency impedance character is typical of piezoelectric materials, giving a minimum impedance frequency of 9.0 MHz and a serial resonant frequency at about 9.5 MHz.     

Metalorganic chemical vapor deposition of SrRuO3 thin film and its characterization

Synthesis of conducting oxide strontium ruthenate is carried out in a hot-wall tubular reactor, using Sr(C₁₁H₁₉O₂)₂/Ru(C₅H₅)₂/O₂ reaction system. Owing to a large difference in depositing efficiency between strontium and ruthenium precursors, the stoichiometric ratio of thin film is controlled in one cycle of two consecutive depositions at different temperatures. Thin films of SrRuO₃ single phase are synthesized in the subsequent 700°C annealing. Thin films of SrRuO₃ with extra ruthenium oxide can also be prepared by adjusting the molar ratio of RuO₂ and SrO layers. The deposition sequence of ruthenium oxide first, strontium oxide later is preferred. If the deposition sequence is reverse, the thin film is plagued with unreacted oxides even when the annealing temperature is raised to 800°C. The relative ease of preparing SrRuO₃ thin films, when RuO₂ is under SrO, is attributed to evaporation of ruthenium oxide in O₂ and diffusion in its open columnar microstructure. The sheet resistivity of thin film decreases with the ruthenium content. The room temperature resistivity of SrRuO₃ film of Ru/(Sr + Ru) = 0.5 is around 910 ohm-cm. The room-temperature resistivity of Ru/(Ru + Sr) = 0.53 decreases to 470 ohm-cm. The root mean square surface roughness of 700°C synthesized SrRuO₃ thin film is 22 nm, in a 2 × 2 m² area of film thickness 280 nm.     

Film thickness dependence of critical current density for YBa2Cu3O7 films post-annealed at a low oxygen partial pressure

The variation of critical current density at 77 K as a function of film thickness was studied for YBa₂Cu₃O₇ films on (100) LaAlO₃ substrates. Film thicknesses were in the range 0.2–1.6m. The films were deposited by co-evaporation and post-annealed under conditions which have previously resulted in high-quality films (750°C and an oxygen partial pressure of 29 Pa). The critical current density at 77 K exceeds 1 MA cm^–2 for the thinner films, and decreases with increasing film thickness in excess of about 0.4m. The decrease is in rough agreement with a switch fromc-axis toa-axis growth at about this critical thickness. A good anticorrelation was found between room temperature resistivity and critical current density at 77 K. The results are compared to those obtained before by post-annealing at 850°C in 1 atm of oxygen.     

Ru thin film grown on TaN by plasma enhanced atomic layer deposition

Ru thin films were sequentially deposited onto TaN (5 nm) by plasma enhanced atomic layer deposition using Ru(EtCp)₂ and NH₃ as precursors. The effect of growth temperature on the electrical resistivity and morphology of the Ru films were studied. It was found that the Ru films can achieve a low resistivity of 14 µΩ cm and a low root-mean-square roughness at a growth temperature of 270 °C. The thickness of the underlying TaN film was found to affect the Ru film growth. The oxidation of the very thin TaN film was correlated with the island growth of Ru. Ex and in-situ X-ray diffraction was employed to verify the copper diffusion barrier properties of a Ru (3 nm)/TaN (5 nm) bi-layer structure.     

Deposition of WNxCy thin films for diffusion barrier application using the dimethylhydrazido (2) tungsten complex (CH3CN)Cl4W(NNMe2)

Tungsten nitride carbide (WN_xC_y) thin films were deposited by chemical vapor deposition using the dimethylhydrazido (2⁻) tungsten complex (CH₃CN)Cl₄W(NNMe₂) (1) in benzonitrile with H₂ as a co-reactant in the temperature range 300 to 700 °C. Films were characterized using X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy and four-point probe to determine film crystallinity, composition, atomic bonding, and electrical resistivity, respectively. The lowest temperature at which growth was observed from 1 was 300 °C. For deposition between 300 and 650 °C, AES measurements indicated the presence of W, C, N, and O in the deposited film. The films deposited below 550 °C were amorphous, while those deposited at and above 550 °C were nano-crystalline (average grain size < 70 Å). The films exhibited their lowest resistivity of 840 µΩ-cm for deposition at 300 °C. WN_xC_y films were tested for diffusion barrier quality by sputter coating the film with Cu, annealing the Cu/WN_xC_y/Si stack in vacuum, and performing AES depth profile and XRD measurement to detect evidence of copper diffusion. Films deposited at 350 and 400 °C (50 and 60 nm thickness, respectively) were able to prevent bulk Cu transport after vacuum annealing at 500 °C for 30 min.     

Development of phases and texture in sol-gel derived lead zirconate titanate thin films prepared by three-step heat-treatment process

Lead zirconate titanate (PZT) films were fabricated by the addition of 10 mol% excess Pb to the starting solution which was spin-coated onto Pt/Ti/SiO₂/Si substrates. The effect of film thickness on texture was investigated, and it is clear that the (100) texture gradually increases and the (111) texture decreases with increasing film thickness. A Pt _x Pb intermetallic metastable phase was observed by X-ray diffraction, and it is found that the position of this peak shifted from 38.30° 2 (d : 0.2348 nm) to 37.10° 2 (d : 0.4213 nm) with increasing firing temperature from 350°C to 550°C. The (111) preferred orientation in the PZT film was promoted by the metastable Pt _x Pb phase. The formation of the (100) texture of perovskite phase in the multilayer films was mainly attributed to the effects of both substrates and crystal growth rates which depend on the crystal orientation.     

Effect of high temperature annealing on the electrical performance of titanium/platinum thin films

In this study, the influence of post deposition annealing steps (PDA) on the electrical resistivity of evaporated titanium/platinum thin films on thermally oxidised silicon is investigated. Varying parameters are the impact of thermal loading with maximum temperatures up to T_PDA = 700 °C and the platinum top layer thickness ranging from 24 nm to 105 nm. The titanium based adhesive film thickness is fixed to 10 nm. Up to post deposition annealing temperatures of T_PDA = 450 °C, the film resistivity is linearly correlated with the reciprocal value of the platinum film thickness according to the size effect. Modifications in the intrinsic film stress strongly influence the electrical material parameter in this temperature regime. At T_PDA > 600 °C, diffusion of titanium into the platinum top layer and its plastic deformation dominate the electrical behaviour, both causing an increase in film resistivity above average.     

A batch process to deposit amorphous metallic Mo–Si–N films

A process for depositing amorphous electrically conducting Mo–Si–N films in a batch-type reactive sputtering system has been developed. Each elemental constituent in the film is individually adjustable: molybdenum and silicon through the electrical power applied to the separate targets, and nitrogen through the gas flow rate. Argon is used for the tuning of the intrinsic stress. The amorphous structure of a Mo₃₁Si₁₈N₄₅ film is confirmed by cross-sectional transmission electron microscopy and electron diffraction. The structure remains unchanged up to at least 700 °C for 1 min of annealing in an argon ambient. In the process, the room-temperature resistivity decreases from an initial value of about 1.1 to about 1.0 m cm with no change in the film thickness. After 1100 °C for one minute, grains nucleate and the film resistivity falls by two-thirds. The intrinsic stress in Mo–Si–N films is significantly more uniform throughout the film area than in polycrystalline molybdenum films. These results hold promise for applications of Mo–Si–N films in micromechanical devices. Self-supported beams and membranes have been successfully delaminated from their silicon substrates; molybdenum-rich films are more ductile than silicon-rich films.     

In-situ electrical characterization of ultrathin TiN films grown by reactive dc magnetron sputtering on SiO2

Ultrathin TiN films were grown by reactive dc magnetron sputtering on thermally oxidized Si (100) substrates. The electrical resistance of the films was monitored in-situ during growth in order to determine the minimum thickness of a continuous film. The coalescence thickness has a minimum of 1 nm at a growth temperature of 400 °C after which it increases with growth temperature. The minimum thickness of a continuous film decreases with increasing growth temperature from 2.9 nm at room temperature to 2.2 nm at 650 °C. In-situ resistivity measurements show that films grown at 500 °C and above are resistant to oxidation indicating high density. X-ray photoelectron spectroscopy and X-ray diffraction measurements show that the TiN grain stoichiometry and grain size increases with increasing growth temperature.     

Stability of nano-thick transparent conducting oxide films for use in a moist environment

The stability of nano-thick transparent conducting oxide thin films in a high humidity environment was investigated. The stability of ITO and impurity-doped ZnO thin films prepared with a thickness in the range from approximately 20 to 100 nm on glass substrates at a temperature below 200 °C by a pulsed laser deposition was evaluated in air at a relative humidity of 90% and a temperature of 60 °C. The resistivity of all Al- and Ga-doped ZnO thin films tested was found to increase markedly with test time, whereas that of ITO remained relatively stable; the stability (resistivity increase) of the doped ZnO thin films was considerably affected by film thickness but was relatively independent of the deposition substrate temperature. In particular, doped ZnO thin films with a thickness below approximately 50 nm were very unstable under the test conditions. The resistivity increase of doped ZnO films is mainly attributed to the grain boundary scattering resulting from the adsorption of oxygen on the grain boundary.     

Properties of indium oxide/tin oxide multilayered films prepared by ion-beam sputtering

The preparation and characterization of indium oxide (InO _x )/tin oxide (SnO _y ) multilayered films deposited by ion-beam sputtering are described and compared with indium tin oxide (ITO) films. The structure and the optoelectrical properties of the films are studied in relation to the layered structures and the post-deposition annealing. Low-angle X-ray diffraction analysis showed that most films retained the regular layered structures even after annealing at 500° C for 16 h. As an example, we obtained a resistivity of 6×10^–4 cm and a transparency of about 85% in the visible range at a thickness of 110 nm in a multilayered film of InO _x (2.0 nm)/SnO _y (0.2 nm)×50 pairs when annealed at 300° C for 0.5 h in air. Hall coefficient measurements showed that this film had a mobility of 17 cm² V^–1 sec^–1 and a carrier concentration (electron density) of 5×10²⁰ cm^–3.     

Study on electroplated copper thin film and its interfacial reactions in the EPCu/IMPCu/IMPTaN/SiO2/Si multilayer structure

Electroplated Cu film on a thin seed layer of IMP deposited Cu has been investigated in the EPCu (1 m)/IMPCu (150 nm)/TaN (25 nm)/SiO₂(500 nm)/Si multi-layer structure. The characteristics of Electroplated-Cu films before and after annealing were investigated by means of sheet resistance, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Rutherford Backscattering Spectroscopy (RBS). Annealing at temperatures of higher than 750°C resulted in slightly higher sheet resistance, larger grain sizes and rougher surface. SEM micrograph showed that the agglomeration of EP-Cu film occurred only at annealing temperatures higher than 850°C. During annealing, the EP-Cu grain grew normally and their sizes increased to about five times larger than the thickness of the EP-Cu film but the (111) preferred orientation was maintained up to 950°C. Furthermore, the interfacial reactions between Cu layer and IMP-TaN diffusion barrier were also detected at annealing temperatures of higher than 750°C.     

Hydroxyapatite films on silicon single crystals by a solution technique: texture,supersaturation and pH dependence

Thick films of hydroxyapatite (HA) were deposited on silicon single crystal wafers placed in close proximity to a plate of apatite- and wollastonite-containing glass and dipped into a simulated physiological solution at 36°C. Amorphous calcium phosphate phase present in the glass leached into the solution, causing supersaturation of Ca²⁺ and PO₄ ^3- ions. Spherical cap-like islands of calcium phosphate nucleated on Si crystals and grew in size with time. The thickness of the film grown on Si (111) in a solution having a composition similar to that of human blood plasma, and maintained at pH of 7.2, reached 7.1 m in 336 h, compared with a thickness of 12.7 m when the ion concentrations of the solution were doubled. HA films grown on Si (111) showed strong (102) texture. In contrast, hardly any HA film could be grown on Si (100). With increasing pH value of the solution the Ca/P ratio of the film increased. At a pH of 7.2 the as-grown and annealed (at 800°C for 3 h in argon) films had Ca/P ratios of 1.10 and 1.72, respectively. The Vickers hardness and the adhesion strength of the film increased upon annealing. Our results suggest that the driving force for formation of apatite films arises from the lowering of free energy of the supersaturated solution by deposition of ions (Ca, P, O, H) in certain crystallographic arrangements on suitable substrates with low interface energies.     

Localization of carriers of Y-doped CaCuO2 films prepared by an organometallic-chemical-vapour-deposition method

Y-doped CaCuO₂ films have been formed on SrTiO₃(1 0 0) substrates in the range 730–790 °C. The lattice constants of c=0.3180 0.3183 nm were estimated from the X-ray diffraction (XRD) of c-axis-oriented Y-doped CaCuO₂ films. The values of the c-axis were shorter than those of the undoped CaCuO₂ film. Although the resistivity of a Y-doped CaCuO₂ film is significantly lower in comparison with that of an undoped CaCuO₂ film, no superconductivity was found in these Y-doped CaCu₂ films at temperatures higher than 12 K.     

Effects of molybdenum, silver dopants and a titanium substrate layer on copper film metallization

Annealing of 100 nm-thick Cu, Cu(Mo) and Cu(Ag) films was carried out to investigate the effect of dopant atoms on the films. Molybdenum (Mo) and silver (Ag) were selected as immiscible dopants for out-diffusion studies. A thermally grown SiO₂ layer and a sputtered Ti layer were used as substrates. The dopant and substrate effects were characterized in terms of surface morphology, resistivity, preferred orientation, and diffusional characteristics. The lowest observed resistivity was 2.32 · cm in the Cu(Ag) film, which was lower than that in a pure Cu film of the same thickness. Ag addition enhanced the surface morphology and thermal stability of the Cu(Ag) films. The highest thermal stability was obtained in the case of a Cu(Mo)/Ti film which maintained film integrity to 800°C. A Ti substrate enhanced Cu(111) texture growth. A highly oriented Cu(111)-texture was obtained in the Cu(Mo)/Ti films. Cu diffusion through the Ti layer was limited in the (111)-textured Cu(Mo)/Ti films, which showed good potential as a diffusion barrier.     

Chemical solution deposition of thin TiO2-anatase films for dielectric applications

Thin films of TiO₂ have been prepared using chemical solution deposition on 6 n-type Si(1 0 0) wafers. Thin film thickness in the range from 70 to 210 nm could be achieved via control of the number of deposition sequences. The final annealing temperature of 700 °C resulted in an anatase phase structure with fine elongated grains and smooth surface topography. The capacity of the thin films is shown to depend on thickness, and could be interpreted assuming a series capacity with an SiO₂ interfacial layer. The resulting dielectric constant of the TiO₂ thin film has been calculated to be 23. The leakage current behavior and the break-down field also depend on film thickness. It is shown that thinner films are higher break-down fields.     

Electrical resistivity of Ti-Zn mixed oxide thin films deposited by atomic layer deposition

Ti-Zn mixed oxide thin films, with thickness less than 50 nm, were grown with atomic layer deposition (ALD) technique at low temperature (90 °C) varying the composition. ALD is a powerful chemical technique to deposit thin films with thickness of few atomic layers. ALD oxide material growth is achieved by dosing sequentially the metal precursor and the oxidizing agent. Thanks to ALD nature of layer by layer growth it was possible to realize mixed metal, Ti and Zn, oxide thin films with controlled composition, simply by changing the number of cycles of each metal oxide layer. Structural and electrical properties of the prepared thin films were studied as a function of their composition. Synchrotron radiation X-ray diffraction technique was used to follow thin film crystallization during sample annealing, performed in situ. It was observed that the onset temperature of crystallization raises with Ti content, and sample structure was Zn₂TiO4 phase. Electrical resistivity measurements were performed on crystalline samples, annealed at 600 °C, revealing an increase in resistivity with Ti content.