Influence of substrate bias on the composition of SiC thin films fabricated by PECVD and underlying mechanism

The influence of the substrate bias on the composition of SiC thin films synthesized by plasma-enhanced chemical vapor deposition was studied. Our results indicate that the ratio of Si to C in the thin films is almost stoichiometric at a bias of − 300 V, whereas excessive carbon is observed in the films if the bias is lower or higher. Very little oxygen can be detected in the film produced without biasing. The effects of the bias on the composition of the thin films can be attributed to the interaction between the positive ions in the plasma and the surface atoms. The underlying mechanism is also discussed.     

Structure and washing fastness of composite fluorocarbon/ZnO films prepared by RF sputtering

Composite fluorocarbon/ZnO films were deposited by RF sputtering, using polytetrafluoroethylene and Zn targets, on polyethylene terephthalate substrates. Argon and oxygen were used as working and reacting gases, respectively, with an oxygen:argon volume ratio of 3:1. The films were characterized by X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy and static contact angle measurements. It was found that the deposited films are made up of the four components -CF₃, -CF₂-, -CF- and -C-. The proportions of the four components varied with sputtering conditions. There was a large number of C=C double bonds on the surface of deposited films. The static contact angle of the deposited films was greater than 90°, indicating excellent hydrophobicity. The contact angle of films decreased after washing, and the washing fastness of the composite films were slightly inferior to those of the fluorocarbon films.     

Composite fluorocarbon/ZnO films prepared by R.F. magnetron sputtering of Zn and PTFE

In this paper, composite fluorocarbon/ZnO films were prepared by R.F. sputtering used polytetrafluoroethylene (PTFE) and Zn target on polyethylene terephthalate (PET) substrate. Argon was used as the working gas and oxygen used as reacting gas. The obtained films were characterized by means of SEM, XPS and UV-visible spectrophotometer. It was found, the surface morphology of composite fluorocarbon/ZnO films vary as the deposited time of ZnO. The growing mode of composite films is the deposition and expansion. The ultraviolet absorbance of composite fluorocarbon/ZnO films is equal to that of fluorocarbon films' when deposited time of ZnO is within 2 min, while distinctively increases when deposited time of ZnO exceeds 5 min, the absorbance value is larger than the ZnOs'. The composite films exhibit multi-enhanced ultraviolet absorption due to π-conjugated molecular structure, nanoparticle-pore reflection and the absorption effect of nanosized ZnO particles.     

Pulsed microwave plasma polymerization of silicon oxide ?lms: Application of efficient permeation barriers on polyethylene terephthalate

A microwave driven low pressure plasma reactor is developed based on a modi?ed Plasmaline antenna for plasma processing of polyethylene terephthalate (PET) foils and bottles. It allows for the treatment of thermolabile packaging materials, e.g. plasma sterilization and permeation barrier coating. Silicon oxide ?lms are deposited on PET foils as a permeation barrier coating. A pulsed hexamethyldisiloxane:oxygen plasma is ignited under various conditions and the oxygen permeation is investigated. A criterion for the homogeneous deposition of SiO_x coatings is described depending on the residence time of process gases. Additionally, the composition of the coatings is analyzed by means of Fourier transform infrared spectroscopy regarding carbon and hydrogen content. A strong relation between barrier properties and ?lm composition is found: good oxygen barriers are observed as carbon content is reduced and ?lms become inorganic, quartz-like. A residual permeation as low as J = 1.0 ± 0.3 cm³ m^− 2 day^− 1bar^− 1 for SiO_x coated PET foils is achieved. The dependencies of important plasma parameters, such as gas mixture, process pressure, power and pulse conditions on oxygen permeation through packaging foil are shown to optimize the coating process.     

Effect of negative pulsed high-voltage-bias on diamond-like carbon thin film preparation using capacitively coupled radio-frequency plasma chemical vapor deposition

Mechanical properties of diamond-like carbon films by an effective addition of negative pulsed high-voltage-bias have been investigated in capacitively coupled CH₄/Ar radio-frequency plasma. The results revealed that hardness and elastic modulus of the deposited film, estimated from nano-indentation load-displacement curve for about 1 μm-thick films, increase with the increase of the absolute value of high-voltage V_NPHV for V_NPHV < 5 kV and then saturate. Elastic recovery R got the highest value (> 90%) at V_NPHV = 5 kV.     

Development of anodic film on Mg alloy AZ91D

At constant applied current, the evolution of morphology, structure and composition of anodic film on Mg alloy AZ91D with anodizing time was investigated using SEM, EDX and XRD. The development of anodic film on the Mg alloy was similar to that on high-purity Mg except that, attributed to alloying effect, hunch-like resultants replaced volcano-like ones to become predominant initial products at transitional stage of anodization. The black cicatrices at the anode surface were related with the inhomogeneous activation and dissolution under strong polarization conditions. The evolution of micropores in shape, size and number was associated with anodizing mechanism. The main elements in anodizing products were Mg, O, Al and Si, indicating that both alloy substrate and electrolyte solution were involved in anodization. Anodic film developed early was mainly comprised of periclase MgO and forsterite Mg₂SiO₄. However, amorphous compounds became dominant with treatment time increasing. In anodizing products, the element Al existed primarily in the form of amorphous compound.     

Influence of ion-bombardment-energy on thin zirconium oxide films prepared by dual frequency oxygen plasma sputtering

Thin ZrO₂ films were prepared using dual frequency oxygen reactive plasma sputtering for wear-resistance coating of ceramics products. Influences of ion-bombardment-energy E_i were investigated for improvement of film characteristics. The results revealed that the deposition rate and the hardness of the prepared ZrO₂ thin films gradually increased with increasing E_i for E_i < 220-250 eV and then decreased, whereas the water-contact-angle on ZrO₂ thin films was about 90 °, having a good water-repellent nature.     

Structural characterization of amorphous hydrogenated-carbon nitride (aH-CNx) film deposited by CH4/N2 dielectric barrier discharge plasma: C, H solid state NMR, FTIR and elemental analysis

The chemical composition and bond structure of polymer like amorphous hydrogenated carbon nitride (aH-CN_x) thin films was studied by solid-state ¹³C and ¹H MAS NMR spectroscopy, FTIR spectroscopy and elemental analysis. The hydrogenated CN_x film was deposited on Si (100) substrate by CH₄/N₂ gas mixture dielectric barrier discharge (DBD) plasma. The broad ¹H signals obtained even at 33 kHz spinning speed with spinning side bands indicates the existence of a large proton proportion in the film. The ¹H and ¹³C signals are strongly broadened due to homo- and heteronuclear dipolar couplings and also due to amorphous nature of the deposited film. The local structure of the amorphous aH-CN_x film is dominated by C-C and C-N single bonds i.e. carbon is mainly in the sp³ hybridized state. The Fourier Transform infrared (FTIR) spectroscopy of the film indicates the typical regions for -C≡N, -(CO), -NH, vibrations together with overlapping NH and OH stretching bonds. CH₃ and C-N groups as well as species with CN conjugated double bonds are present in the deposited CN_x film. From elemental analysis it is obtained that the composition of the film is (in wt.%): C: 61.8, H: 8.4, N: 17.7.     

Spatial stress distribution and optical properties of GaN films grown on convex shape-patterned sapphire substrate by metalorganic chemical vapor deposition

μ-Raman and μ-photoluminescence methods have been employed to investigate microscopic spatial stress distribution and optical properties of GaN films grown on the convex shape-patterned sapphire substrate (CSPSS). By comparison of the μ-Raman and μ-PL spectra, we found that significantly large difference, Δσ_xx ∼0.46 GPa, in biaxial compressive stress between the flat trench and convex regions in the side facet of the GaN film, around ∼2 μm below the surface whereas on the GaN surface, little difference with large residual stress was observed in both regions compared to those from the side facet. Temperature dependent and time-resolved photoluminescence spectra have shown that the GaN film grown on the CSPSS has improved crystal purity through the reduction of intrinsic point defects.     

Coating of hydroxyapatite films on metal substrates by seeded hydrothermal deposition

Hydroxyapatite (HAP) was successfully coated on various metal substrates by a novel seeded hydrothermal deposition method. A nanoscale HAP seed layer was first formed by a short electrochemical synthesis. The seed layer promotes HAP crystal growth onto the surface during a subsequent hydrothermal crystallization step. The surface morphology and microstructure of the HAP coatings can be regulated by varying the reaction temperature, solution pH, calcium-to-phosphorus molar ratio in the starting solution, and hydrothermal deposition time. The new method has advantages over many other reported HAP deposition techniques in that it produces highly crystalline, crack-free, adherent films of uniform thickness. In all the films, the HAP crystals are preferentially oriented with the c-axis normal to the substrate. The as-developed HAP coatings are attractive for applications in the area of bioactive surface modification of metallic implants where the microstructure of the film is advantageous for promoting bone growth.     

X-ray photoelectron spectroscopy analysis of zirconium nitride-like films prepared on Si(100) substrates by ion beam assisted deposition

Thin zirconium nitride films were prepared on Si(100) substrates at room temperature by ion beam assisted deposition with a 2 keV nitrogen ion beam. Arrival rate ratios ARR(N/Zr) used were 0.19, 0.39, 0.92, and 1.86. The chemical composition and bonding structure of the films were analyzed with X-ray photoelectron spectroscopy (XPS). Deconvolution results for Zr 3d, Zr 3p_3/2, N 1s, O 1s, and C 1s XPS spectra indicated self-consistently the presence of metal Zr⁰, nitride ZrN, oxide ZrO₂, oxynitride Zr₂N₂O, and carbide ZrC phases, and the amounts of these compounds were influenced by ARR(N/Zr). The chemical composition ratio N/Zr in the film increased with increasing ARR(N/Zr) until ARR(N/Zr) reached 0.92, reflecting the high reactivity of nitrogen in the ion beam, and stayed almost constant for ARR(N/Zr) ≥ 1, the excess nitrogen being rejected from the growing film. A considerable incorporation of contaminant oxygen and carbon into the depositing film was attributed to the getter effect of zirconium.     

The influence of plasma power on the temperature-dependant conductivity and on the wet chemical etch rate of sputter-deposited alumina thin films

Aluminum oxide (Al₂O₃) thin films are synthesized by reactive d.c. magnetron sputter deposition on silicon substrates. The impact of varying plasma power P_p (i.e. 400 to 1000 W) and of thin film temperatures T up to 540 °C on the electrical performance are evaluated, as these dielectric layers with a thickness of 450 nm are targeted as potential candidates for high temperature sensor applications. From 150 °C to 500 °C, the current-voltage measurements show a leakage current behavior according to the Poole-Frenkel electron emission with an activation energy of 1.16 eV. At T > 500 °C, the conductivity increases above average, in respect to the extrapolated Poole-Frenkel behavior at T < 500 °C, most probably due to the migration of charged ions, such as Ar⁺, incorporated into the film during deposition. Basically, samples synthesized at higher plasma levels show an enhanced electrical insulation behavior. This result is supported by measurements applying optical ellipsometry as well as by the determination of the wet chemical etching behavior in phosphoric-based acid at different bath temperatures. At higher plasma power, the refractive index shows a slight tendency to increase, staying, however, below the value of single-crystalline Al₂O₃. In contrast, the etch rate decreases by a factor of 1.5 at samples deposited at 1000 W when lowering the temperature of the etchant from 90 °C to 60 °C. These results indicate an enhanced film density at higher P_p values as the microstructure of the Al₂O₃ films is X-ray amorphous independent of plasma power and post-deposition annealing temperatures up to 650 °C.     

Effect of plasma surface treatment on mechanical and corrosion protection properties of UV-curable sol-gel based GPTS-ZrO2 coatings on mild steel

Hybrid sol-gel based nanocomposite coatings derived from hydrolysis and condensation of a photopolymerizable silane precursor 3-Glycidoxypropyltrimethoxy silane in combination with zirconium-n-propoxide were deposited on mild steel substrates by a dip coating technique. In some cases, substrates were subjected to an atmospheric air-plasma surface pre-treatment prior to coating deposition. The coatings were subsequently densified by exposure to ultraviolet radiation followed by a thermal treatment at 250 °C. Characterization of the coatings with respect to thickness, water contact angle, pencil scratch hardness, adhesion and abrasion resistance was carried out. Corrosion testing was carried out on the coatings for a 1 h exposure to a 3.5% NaCl solution by electrochemical polarization and impedance measurements. The hybrid sol-gel coatings were found to improve the mechanical properties and corrosion resistance of mild steel. Plasma surface pre-treatment was found to improve the adhesion of coatings significantly and decreased the corrosion rate from 0.2652 mpy obtained for coatings without any surface pre-treatment to 0.0015 mpy, which was nearly 600 times lower than that of bare mild steel.     

Effects of plasma treatment on bioactivity of TiO2 coatings

In this work, nano-TiO₂ powders were deposited on titanium alloy substrates by atmospheric plasma spraying, followed by plasma immersion ion implantation (PIII) using hydrogen, oxygen and ammonia gases. The bioactivities of PIII-treated TiO₂ coatings were evaluated by the formation of apatite on their surface after soaked in simulated body fluids (SBF) for a period of time. As-sprayed TiO₂ coating is composed of rutile, anatase and TiO_2−x (most of them is Ti₃O₅). After immersion in SBF for two weeks, the hydrogen PIII-treated TiO₂ coating can induce bone-like apatite formation on its surface but apatite cannot be formed on the surface of as-sprayed and oxygen, ammonia PIII-treated TiO₂ coatings. The results obtained indicated that a hydrogenated surface plays a very important role to induce bioactivity of TiO₂ coatings.     

Characterization of titanium nitride films deposited by cathodic arc plasma technique on copper substrates

TiN films were deposited directly on Cu substrates by a cathodic arc plasma deposition technique. The films were then characterized by X-ray diffraction (XRD), grazing incidence X-ray diffraction (GID), (TEM), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The preferred orientation of the film changed from (200) to (111) with increasing film thickness. Analyses of both the XRD and GID results showed that in the highly (111) textured grains, the (111) plane was approximately parallel to the film surface, while in the (200) textured grains, the (200) plane was tilted away from the film surface. Small-elongated crystallites with a large aspect ratio and textured grains were found on the TiN surface. AES, which was employed to examine the concentration depth profile, showed no apparent interdiffusion between Cu and TiN during the growth of the film. XPS results showed that amorphous TiO₂, as well as titanium oxynitride, was present on the TiN surface. The spectra of Ti-2p, N-1s, O-1s and Cu-2p before and after the film being sputter etched through the entire film region were also discussed.     

High tunability of pulsed laser deposited Ba0.7Sr0.3TiO3 thin films on perovskite oxide electrode

Ferroelectric thin films such as BST, PZT and PLZT are extensively being studied for the fabrication of DRAMS since they have high dielectric constant. The large and reversible remnant polarization of these materials makes it attractive for nonvolatile ferroelectric RAM application. In this paper we report the characterization of Ba_0.7Sr_0.3TiO₃ (BST) thin films grown by pulsed laser ablation on oxide electrodes. The structural and electrical properties of the fabricated devices were studied. Growth of crystalline BST films was observed on La_0.5Sr_0.5CoO₃ (LSCO) thin film electrodes at relatively low substrate temperature compared to BST grown on PtSi substrates. Electrical characterization was carried out by fabricating PtSi/LSCO/BST/LSCO heterostructures. The leakage current of the heterostructure is studied and a band structure is modeled based on the transport properties of the heterostructure. The dielectric constant of the BST film is found to be 630 at 100 kHz with a loss tangent of 0.04. The capacitance voltage characteristics show high tunability for BST thin films.     

Controlling the growth of CVD carbon from methane on transition metal substrates

A hot-wall chemical vapor deposition (CVD) method was employed to grow crystalline graphitic carbon on transition metal substrates. Temperature dependence of the CVD carbon growth and the influence of methane concentration (carbon source) on the growth rate of carbon were systematically investigated. The effect of the substrate on the growth rate and carbon crystallinity was also investigated. These factors, temperature, methane concentration, and type of substrate, influenced the growth of CVD carbon. The carbon growth pattern appears to start with the most crystalline graphitic carbon being produced on the surface of the Fe and Ni and becomes more amorphous as the coating thickness increases.     

Influence of film structure on gas barrier properties of SiOxNy films

SiO_xN_y thin films were deposited on PET substrates by dc magnetron sputtering under various nitrogen gas flow ratios, and the influence of the nitrogen gas flow ratio on the gas barrier performance was examined on the basis of local structure of SiO_xN_y. The surface morphology of the films was evaluated by FE-SEM and AFM observations. The local structure of SiO_xN_y was determined by FT-IR analysis and measurement of refractive index. No obvious macro-defects, such as pinholes, were observed in the films and the surface morphology of all samples was similar. The film density increased with increasing nitrogen gas flow ratio during the deposition process. However, the gas barrier performance decreased with increasing nitrogen gas flow ratio. On the basis of FT-IR analysis, it was determined that the structure of the SiO_xN_y film was a random bonding model (RBM) structure and an increase in the nitrogen gas flow ratio caused an increase in hydrogen termination in the Si-O-N network. The degradation of gas barrier performance at a high nitrogen gas flow ratio is due to the discontinuous Si-O-N network caused by the hydrogen termination.     

Effects of Deposition Temperature on the Structure and Hardness of BN Films Prepared by a Gradient Temperature Method

采用温度梯度法,通过MW-ECR射频磁控溅射在硅片基底上制备了六方和立方混合的氮化硼薄膜。研究了薄膜的键结构,化学成分和力学性能。结果显示,对于氮化硼立方相的出现存在温度阈值,薄膜的硬度随沉积温度提高而提高。相对于传统薄膜制备方法,温度梯度方法具有更高的效率。