Effect of Si target sputtering power on diffusion barrier properties of Ta–Si–N thin films

Abstract

Ta–Si–N thin films and Cu/Ta–Si–N thin films were deposited on p type Si(111) substrates by magnetron reactive sputtering. Then the films were characterised by four point probe sheet resistance measurement, AFM, SEM and XRD respectively. According to the XRD results, the authors found that the crystallisation of Ta nitrides in Ta–Si–N/Si thin films is suppressed effectively when fabricated by a high Si target sputtering power. As the Si target power varies, the failure temperature of Cu/Ta–Si–N/Si is changed. The sample fabricated by the Si target power of 200 W fails after 800°C rapid thermal annealing and it has the highest failure temperature. The investigation of failure mechanism shows that Cu atoms diffuse through grain boundaries or amorphous structure of the Ta–Si–N barrier, and react with Si to form Cu–Si phase. And it causes the failure of the barrier.     

Structural and optical properties of Cu–N codoped ZnO thin films deposited by magnetron cosputtering

ZnO films codoped by copper and nitrogen were prepared by magnetron cosputtering. The effects of this codoping on the structural and optical properties of ZnO films were systematically studied. The results show that Cu–N codoping didn’t affect the optimal orientation. Cu–N codoping can enlarge the grain size, enhance the crystallinity, reduce the stress and lead to denser and smoother surface. A significant red shift of absorption edge and gap-narrowing effect resulting from codoping were found in ZnO films. Cu-doping, N-doping, and oxygen vacancy are the main factors leading to property modification of the ZnO films. By Cu–N codoping, we can modulate the microstructure and optical properties of ZnO films in a wider range.     

Kinetics of reactive diffusion between Ta and Cu–9.3Sn–0.3Ti alloy

Tantalum is used as a diffusion barrier in the superconducting Nb₃Sn composite-wire manufactured by the bronze method. In order to examine the consumption behavior of the Ta barrier during annealing in the bronze method, the kinetics of the reactive diffusion between Ta and a bronze was experimentally observed using sandwich diffusion couples composed of Ta and a Cu–9.3Sn–0.3Ti alloy. The (Cu–Sn–Ti)/Ta/(Cu–Sn–Ti) diffusion couples were isothermally annealed at temperatures of T = 973–1053 K for various times up to t = 1462 h. Owing to annealing, Ta₉Sn is formed as a uniform layer at the initial (Cu–Sn–Ti)/Ta interface in the diffusion couple, and gradually grows mainly toward Ta. The mean thickness of the Ta₉Sn layer is proportional to a power function of the annealing time. However, the exponent of the power function is equal to unity at t < t _c but smaller than 0.5 at t > t _c. Thus, the transition of the rate-controlling process for the growth of Ta₉Sn occurs at t = t _c. The critical annealing time t _c takes values of 1.83 × 10⁶, 4.63 × 10⁵, and 5.98 × 10⁵ s at T = 973, 1023, and 1053 K, respectively. The growth of Ta₉Sn is controlled by the interface reaction at the migrating Ta₉Sn/Ta interface in the early stages with t < t _c but by the volume and boundary diffusion across the Ta₉Sn layer in the late stages with t > t _c. Due to the transition of the rate-controlling process, the growth rate is always much smaller for Ta₉Sn than for Nb₃Sn. As a result, Ta works as an effective barrier against the diffusion of Sn from the bronze to the Cu stabilizer in the superconducting Nb₃Sn composite-wire.     

Influence of quenching rate on microstructure and dimensional stability of Al–Cu–Mg–Si alloy

With the development of precision instrument in space industry fields, increasing attention has been devoted to improve the dimensional stability of structural materials. In this study, the influence of quenching rate on microstructure, residual stress and dimensional stability of Al–Cu–Mg–Si alloy was studied. The results showed that boil water quenching resulted in very low residual stress but unsatisfactory mechanical properties. In contrast, low residual stress and good mechanical property were achieved by quenching the sample into 80°C water. Residual stress has a significant influence on the thermal dimensional stability. The thermal dimensional stability of sample quenched in 80°C water is better than that of sample quenched in 20°C water due to lower residual stress in 80°C water-quenched sample.     

Physical–chemical and biological behavior of an amorphous calcium phosphate thin film produced by RF-magnetron sputtering

This work evaluates the thermal reactivity and the biological reactivity of an amorphous calcium phosphate thin film produced by radio frequency (RF) magnetron sputtering onto titanium substrates. The analyses showed that the sputtering conditions used in this work led to the deposition of an amorphous calcium phosphate. The thermal treatment of this amorphous coating in the presence of H₂O and CO₂ promoted the formation of a carbonated HA crystalline coating with the entrance of CO₃^2 ? ions into the hydroxyl HA lattice. When immersed in culture medium, the amorphous and carbonated coatings exhibited a remarkable instability. The presence of proteins increased the dissolution process, which was confirmed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses. Moreover, the carbonated HA coating induced precipitation independently of the presence of proteins under dynamic conditions. Despite this surface instability, this reactive calcium phosphate significantly improved the cellular behavior. The cell proliferation was higher on the Ticp than on the calcium phosphate coatings, but the two coatings increased cellular spreading and stress fiber formation. In this sense, the presence of reactive calcium phosphate coatings can stimulate cellular behavior.     

Effects of Si and Cu contents on grain size of Al–Si–Cu alloys

The influence of the silicon and copper contents on the grain size of high-purity Al–Si, Al–Cu, and Al–Si–Cu alloys was investigated. In the Al–Si alloys, a poisoning effect was observed and a poor correlation between the grain size and growth restriction factor was obtained. A possible cause of the poisoning effect in these alloys is the formation of a TiSi₂ monolayer on the particles acting as nucleation sites or another poisoning mechanism not associated with TiSi₂ phase formation. In the Al–Cu alloys, a good correlation between the grain size and growth restriction factor was found, whereas in the Al–Si–Cu alloys, the correlation between these two parameters was inferior.     

Structural and optical properties of sulfurized Cu2ZnSnS4 thin films from Cu–Zn–Sn alloy precursors

This study reports the preparation of Cu₂ZnSnS₄ (CZTS) thin films by magnetron sputtering deposition with a Cu–Zn–Sn ternary alloy target and sequential sulfurization. The effects of substrate temperatures on the structural, morphological, compositional as well as optical and electrical properties were characterized. The results showed the CZTS thin films prepared by sulfurization at substrate temperature of 570 °C yielded secondary phases along with CZTS compound. The relatively good properties of CZTS thin film were obtained after sulfurization at substrate temperature of 550 °C. This CZTS film showed compact structure with large grain size of 900 nm, direct optical band gap of 1.47 eV, optical absorption coefficient over 10⁴ cm^?1, resistivity of 4.05 Ω cm, carrier concentration of 8.22 × 10¹⁸ cm^?3, and mobility of 43.38 cm² V^?1 S^?1.     

Investigation on powder metallurgy Cr–Si–Ta–Al alloy target for high-resistance thin film resistors with low temperature coefficient of resistance

The sputtering target for high-resistance thin film resistors plays a decisive role in temperature coefficient of resistance (TCR). Silicon-rich chromium (Cr)–silicon (Si) target was designed and smelted for high-resistance thin film resistors with low TCR. Valve metal tantalum (Ta) and aluminum (Al) were introduced to the Cr–Si target to improve the performance of the target prepared. The measures for grain refining in smelting Cr–Si–Ta–Al target were taken to improve the performance of the prepared target. The mechanism and role of grain refinement were discussed in the paper. The phase structure of the prepared target was detected by X-ray diffraction (XRD). Rate of temperature drop was studied to reduce the internal stress of alloy target and conquer the easy cracking disadvantage of silicon-rich target. The electrical properties of sputtered thin film resistors were tested to evaluate the performance of the prepared target indirectly.     

Formation of Cu2SnS3 thin film by the heat treatment of electrodeposited SnS–Cu layers

Thin films of copper tin sulfide (Cu₂SnS₃) were obtained by sulfurizing a stack of thin layers of Cu and SnS in nitrogen atmosphere. The film stack was obtained by the sequential electrodeposition of SnS and Cu. The Cu₂SnS₃ film was characterized for structural, morphological, composition, optical, spectroscopic, and electrical properties. The optimum condition for the formation of Cu₂SnS₃ was developed after testing different sulfurization temperatures. The films were polycrystalline with monoclinic structure which was confirmed by Raman and transmission electron microscopy analysis. The interplanar spacings estimated from the high resolution transmission electron microscopy images are 2.74, 2.19, and 2.06 Å. The average crystallite size is 13 nm, and the band gap of the film is in the range of 1 eV. The surface chemical composition determined by X-ray photoelectron spectroscopy showed the Cu:Sn:S ratio as 1.9:1:2.85 which is close to the stoichiometric Cu₂SnS₃. The films are p-type, photosensitive, and the conductivity measured in dark was in the range of 4 × 10^?3 Ω^?1 cm^?1. The comprehensive characterization presented in this paper will update the knowledge on this material.     

Thermal evolution of morphological,optical, and photocatalytic properties of Au–Cu2O–CuO nanocomposite thin film

Plasmonic nanocomposite thin films find exciting applications in environmental remediation and photovoltaics. We report on thermal annealing driven development of morphology, structure and photocatalytic performance of Au–Cu₂O–CuO nanocomposite thin film. Nanocomposite thin film coatings of Au–Cu₂O–CuO, prepared by radio frequency (RF) magnetron co-sputtering, were annealed at different temperatures. Thermal annealing driven evolution of morphology of Au–Cu₂O–CuO nanocomposite was studied by field emission scanning electron microscopy (FESEM), which revealed significant growth in size of nanostructures from 10 nm to 69 nm upon annealing. X-ray diffraction (XRD) together with Raman studies confirmed the nanocomposite nature of Au–Cu₂O–CuO film. UV-visible diffuse reflectance spectroscopy (UV-vis-DRS) studies showed band gap variation from 2.44 eV to 1.8 eV upon annealing at 250 °C. Nanocomposite thin film annealed at 250 °C exhibited superior photocatalytic activity for organic pollutants [methylene blue (MB) and methyl orange (MO)] decomposition. The origins of thermal transformation of morphological, optical and photocatalytic behaviour of the Au–Cu₂O–CuO nanocomposite coating are discussed.

     

Effect of B content on thermal stability of nanocomposite Ti–B–N thin films

Abstract

Ti–B–N thin films with different B contents were deposited on Si (100) at room temperature, followed by vacuum annealed at 400, 600, 800 and 1000°C for 1 h respectively. Effect of boron content on thermal stability was investigated using X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and nanoindentation measurements. The results indicated that incorporation of B into TiN produced a nanocomposite structure, which had a positive effect on microstructure stability. A high B content resulted in an elevated recrystallisation temperature. The hardness stability was not consistent with that of microstructure, and depended on phase configuration and composition. The films with a high as deposited hardness showed high hardness stability. Excessive or lack of amorphous phase decreased hardness stability. The residual stress value was decreased with increasing annealing temperature owing to recovery of amorphous matrix, and crystallisation of amorphous phase made its direction transform from compression to tension.     

Structural and magnetic properties of Li–Al-substituted Ni–Zn–Cu ferrite powders prepared via chemical coprecipitation method

Li–Al substituted Ni–Zn–Cu ferrite powder specimens with the nominal composition Ni_0.25?2x Li _x Al _x Cu_0.15Zn_0.60Fe₂O₄ (x?=?0.00, 0.01, 0.02, 0.03, 0.04) were prepared via an improved chemical coprecipitation method. An X-ray diffractometer, a scanning electron microscope and a vibrating sample magnetometer were used to study their structural and magnetic properties. It is found that all the specimens exhibit typical single-phase spinel structures after annealing, and the saturation magnetization decreases with increase of x. The initial susceptibility first increases but then decreases, and obtains the maximum when x?=?0.02, which shows the proper content of Li–Al substitutions is favourable for the increase of initial susceptibility. It is also found that the Li–Al substitutions affect the grain growth slightly.     

Structural stability and non-catalytic nucleation inhibition effect of Si–Zr–B mould coating on undercooled superalloy melt

Abstract

The investment moulding technique was first adopted to prepare a SiO₂–ZrO₂–B₂O₃ (Si–Zr–B) substrate layer on the inner surface of the mould, by employing SiO₂ glass dust and ZrO₂ powder, SiO₂–ZrO₂ sol, and analytical grade H₃BO₃ as refractory material, binder, and softening agent, respectively. Then using sol–gel processing, seven layers of Si–Zr–B film of the same formula as the aforementioned Si–Zr–B substrate layer were compounded with the substrate layer step by step. After glassing treatment at 850°C for 60 min, this film transformed into a glass lined coating. It was shown from X-ray diffraction analysis that, after holding it at a temperature of 1500°C for 30 min, the amount of crystallinity in the Si–Zr–B coating was about 1–3% (vol.-%). Finally, the undercooling experiment showed that a large undercooling (up to 140 K) was achieved in a DD3 (Ni–Cr–Mo–Al–Ti–Co–W) single crystal superalloy melt in this coated mould. So it is concluded that a Si–Zr–B coating has got a good structural stability at high temperature and provides ideal non-catalytic nucleation inhibition for an undercooled superalloy.     

Growth and optical properties of Sn–Si nanocomposite thin films

The growth and optical properties of nanocomposite thin films comprising of nanocrystalline Sn and Si are reported. The nanocomposite films are produced by thermal annealing of bilayers of Sn and Si deposited on borosilicate glass substrates at various temperatures from 300 to 500 °C for 1 h in air. X-ray diffraction reveals that the as-deposited bilayers consist of nanocrystalline Sn films with a crystallite size of 30 nm, while the Si thin films are amorphous. There is onset of crystallinity in Si on annealing to 300 °C with the appearance of the (111) peak of the diamond cubic structure. The crystallite size of Si increases from 5 to 18 nm, whereas the Sn crystallite size decreases with increase in annealing temperature. Significantly, there is no evidence for any Sn–Si compound, and therefore it is concluded that the films are nanocomposites of Sn and Si. Measured spectral transmittance curves show that the films have high optical absorption in the as-deposited form which decreases on annealing to 300 °C. The films show almost 80 % transmission in the visible-near infrared region when the annealing temperature is increased to 500 °C. There is concomitant decrease in refractive index from 4.0, at 1750 nm, for the as-deposited film, to 1.88 for the film annealed at 500 °C. The optical band gap of the films increases on annealing (from 1.8 to ~2.9 eV at 500 °C). The Sn-Si nanocomposites have high refractive index, large band gap, and low optical absorption, and can therefore be used in many optical applications.     

Microstructure and solidification behavior of Cu–Ni–Si alloys

The microstructure and solidification behavior of Cu–Ni–Si alloys with four different Cu contents was studied systematically under near-equilibrium solidification conditions. The microstructures of these Cu–Ni–Si alloys were characterized by SEM and the phase composition was identified by XRD analysis. The phase transition during the solidification process was studied by DTA under an Ar atmosphere. The results show that the microstructure and solidification behavior is closely related to the composition of Cu–Ni–Si alloys. The microstructure of Cu–Ni–Si alloys with higher than 40% Cu content consists of primary phase α-Cu(Ni, Si) and eutectic phase (β₁-Ni₃Si + α-Cu(Ni,Si).When the Cu content is about 40%, only the eutectic phase (β₁-Ni₃Si + α-Cu(Ni,Si)) is present. DTA analysis shows there are three phase transitions during every cooling cycle of alloys with higher than 40% Cu content, but only one for 40% Cu content. Cu–Ni–Si alloy with 40% Cu solidifies by a eutectic reaction, but Cu–Ni–Si alloys with higher than 40% Cu content solidify as a hypoeutectic reaction.     

Al–O–N and Al–O–B–N thin films applied on Si–O–C fibers

Protective coatings (Al–O–N and Al–O–B–N) on Si–O–C fibers (Tyranno ZMI) were applied in order to enhance oxidation resistance under severe thermo-mechanical conditions in the 400–600 °C temperature range. The coating process consisted in three steps: (i) the transformation of the Si–O–C fiber surface into microporous carbon; (ii) the impregnation of these carbon microporous layers by an aluminium trichloride (AlCl₃) solution and then, (iii) a final heat treatment under ammonia. Processing parameters were studied in order to select the best conditions. Using these conditions, obtained results have shown that coatings were present around each fiber, with a controlled thickness, and that the mechanical properties of the fibers were preserved. Although, these coatings did not entirely stop the oxygen ingress, it has been shown that they strongly reduced the oxidation of the fiber.     

Density and viscosity of ternary Al–Cu–Si liquid alloys

Densities and viscosities of ternary Al–Cu–Si liquid alloys have been investigated over a wide temperature and composition range. Density was measured using electromagnetic levitation as a container-less technique, while viscosity was measured by means of a high-temperature oscillating cup viscometer. In this ternary system, binary interaction parameters as well as a third (ternary) interaction parameter need to be taken into account for the excess volume to describe the liquid densities. The temperature dependences of the viscosities are well described by the Arrhenius law. A maximum of the activation energy of viscous flow is found in that compositional range in which intermetallic phases exist in the solid state.     

The effects of electric field and gate bias pulse on the migration and stability of ionized oxygen vacancies in amorphous In–Ga–Zn–O thin film transistors

Abstract

Oxygen vacancies have been considered as the origin of threshold voltage instability under negative bias illumination stress in amorphous oxide thin film transistors. Here we report the results of first-principles molecular dynamics simulations for the drift motion of oxygen vacancies. We show that oxygen vacancies, which are initially ionized by trapping photoexcited hole carriers, can easily migrate under an external electric field. Thus, accumulated hole traps near the channel/dielectric interface cause negative shift of the threshold voltage, supporting the oxygen vacancy model. In addition, we find that ionized oxygen vacancies easily recover their neutral defect configurations by capturing electrons when the Fermi level increases. Our results are in good agreement with the experimental observation that applying a positive gate bias pulse of short duration eliminates hole traps and thus leads to the recovery of device stability from persistent photoconductivity.     

Growth of germanium–carbide thin film on crystal substrate

The formation of germanium-carbide in crystalline germanium substrate is studied using the perturbed γ–γ angular correlation (PAC) method. The growth of Ge–C micro-crystalline system in the host matrix was observed after annealing the sample above 450°C in vacuum. The Ge–C complexes have been detected at high dose carbon implantation in germanium (≥1 × 10¹⁵cm ⁻²). Information about the lattice locations of the carbon atoms in the host lattice can be obtained via the interaction between carbon atoms with unstable probe nucleus (¹¹¹In). Several carbon related complexes have been detected in this investigations which can be characterized by unique quadrupole interaction frequencies. The parameters of the hyperfine interactions drawn from the time spectra provide additional information about the formation of Ge–C system in germanium.