Off-plane Double Bend Research Articles

The reversible wettability of Ti containing amorphous carbon films by UV irradiation

The Ti-containing amorphous carbon (a-C:Ti) deposited by the off-plane double bend (OPDB) Filtered Cathodic Vacuum Arc (FCVA) technique has been shown to exhibit very good mechanical properties such as low stress and ultra-high hardness and electrochemical properties. Further studies reveal that a-C:Ti films have a hydrophobic surface (contact angle with water >90°). This is mainly due to the formation of Ti–O bond when the samples are exposed to the ambient air. In this paper, we show that with ultraviolet (UV) laser treatment, the contact angle of a-C:Ti films with water could be reduced to be as low as 36.2°, forming a hydrophilic surface. After storing the film in ambient air for 3 h, the contact angle increased to 80° and the film recovered back to the original hydrophobic condition. We attributed this to the absorption of hydroxyl groups on the surface by the photocatalysis reactions of TiO 2. This behavior makes the film a good potential candidate for self-clean coatings.

Fabrication of diamond-like amorphous carbon cantilever resonators

Amorphous carbon (a-C) films were deposited by an off-plane double bend filtered cathodic vacuum arc technique fitted with a plasma immersion ion implantation system. High resolution XPS measurements showed these films have an sp3 content of about 60%. Laser-surface acoustic wave measurements have shown such films to have a Young’s modulus and density of 310GPa and 2.33g∕cm3. 1.2μm thick a-C films were grown and subsequently patterned into 150μm×50μm cantilevers using standard photolithography. Residual stress measurements were obtained from the curvature of bend of the cantilever. An accurate knowledge of the microstructural properties will in turn give accurate modeling results. Simulation results showed that such free-standing cantilevers fabricated with amorphous carbon films have resonant frequency much higher than standard polysilicon cantilevers. As such, free-standing diamond-like amorphous carbon cantilevers had been fabricated. The resonant frequency of these cantilevers was measured by laser vibrometer to be ∼108MHz, in very good agreement with simulation results.

X-ray reflectivity, photoelectron and nanoindentation studies of tetrahedral amorphous carbon (ta-C) films synthesized by double bend cathodic arc

Tetrahedral amorphous carbon (ta-C) films have been prepared with floating potential (no substrate bias voltage) on Si substrates by an off-plane double bend filtered vacuum cathodic arc (FCVA) system. The influences of arc current on mass density, chemical bonding and nanomechanical response have been studied for coatings. Based on X-ray reflectivity spectra, the maximum density of FCVA films is 3.27 g/cm 3. The hardness measurements performed as a function of indentation depth for 75-nm-thick films have a maximum hardness of 37.5 GPa and stress values up to 13 GPa. The sp 3 content in the ta-C films as determined by analysis of the C 1s core level spectra had a value of approximately 80% with standard deviation value 1.2% on 6-cm diameter Si waver. Therefore, these coatings have both structural and thickness uniformity, which can be used for large area coating applications (i.e. flat panel display units).

Properties of amorphous ZrO x thin films deposited by filtered cathodic vacuum arc

The deposition of amorphous zirconium oxide thin films by off-plane double bend filtered cathodic vacuum arc (FCVA) is reported for the first time. The ZrO x growth is at room temperature and X-ray diffraction (XRD) showed an amorphous film was deposited. Atomic force microscopy (AFM) confirmed that the film morphology is very smooth. The surface microstructure and interface properties of ZrO x thin films were investigated using monochromatic high-resolution X-ray photoelectron spectroscopy (XPS). From depth profile, it was deduced that the bulk of the film was ∼ZrO 1.9 and at the interface, O–Zr–Si types of bonds were observed to be present. Such amorphous films were observed to have a high optical bandgap of 5.2 eV and high refractive index of ∼2.0.

Comprehensive study of ZnO films prepared by filtered cathodic vacuum arc at room temperature

Room temperature deposition of high crystal quality zinc oxide (ZnO) films was realized by the filtered cathodic vacuum arc (FCVA) technique. Detrimental macroparticles in the plasma as byproducts of arcing process are removed with an off-plane double bend magnetic filter. The influence of oxygen pressure on the structural, electrical and optical properties of ZnO films were investigated in detail. The crystal structure of ZnO is hexagonal with highly c-axis orientation. Intrinsic stress decreases with an increase of chamber pressure, and near stress-free film was obtained at 1×10−3 Torr. Films with optical transmittance above 90% in the visible range and resistivity as low as 4.1×10−3 Ω cm were prepared at pressure of 5×10−4 Torr. Energetic zinc particles in the cathodic plasma and low substrate temperature enhance the probability of formation of zinc interstitials in the ZnO films. The observation of strong ultraviolet photoluminescence and weak deep level emission at room temperature manifest the high crystal quality of the ZnO films prepared by FCVA. Enlargement of the band gap is observed in the absorption and photoluminescence spectra, the band gap shifts towards lower energy with an increase of oxygen pressure. This phenomenon is attributed to the Burstein–Moss effect.

Deposition pressure dependence of internal stress in TiN films deposited by filtered cathodic vacuum arc

TiN films were deposited by an off-plane double bend filtered cathodic vacuum arc technique. The composition, structure, and surface morphology of the films were characterized by x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy, respectively. Internal stress was determined by a substrate bending method. The influence of the deposition pressure on the composition, structure, and internal stress of the films was studied systematically. At a deposition pressure of 1×10−5 Torr, the films are composed of single α-TiN0.30 phase with fairly low internal stress, and the atomic ratio of N to Ti is 0.32. As the deposition pressure increases to 5×10−5 Torr, the N/Ti ratio increases to 0.56, and the films are composed of a mixture of hexagonal α-TiN0.30 and cubic TiN0.90. The formation of TiN0.90 phase and the mismatch of these two kinds of phases contribute to a dramatic increase of internal stress in the films. The increase of deposition pressure to 2×10−4 Torr results in the formation of stoichiometric TiN films with single TiN phase, which corresponds to slightly lower internal stress. However, a further increase of deposition pressure results in a continuous increase in the N/Ti ratio and the formation of overstoichiometric films. The incorporation of excess N atoms in the films accounts for the further increase of internal stress.

Studies of copper vacuum arc plasma through an off-plane double-bend filtering duct

A novel off-plane double-bend (OPDB) magnetic filter, designed to remove unwanted macroparticles effectively from the plasma beam of a cathodic vacuum arc, was used in our filtered vacuum arc system to deposit copper thin film as an interconnect material for deep submicron IC applications. A filter with high plasma transmission efficiency is essential for a high deposition rate, which is key to the commercialisation of the technology. Hence, an investigation has been carried out to study the copper arc plasma under varying magnetic field and duct bias. The ion throughput was determined by measuring the ion saturation output current using a copper disc probe. To study further the copper ion motion in the OPDB filter, a modified drift model was applied, which took into account radial electric fields generated by the potential difference between the duct wall and torus centre. Relatively good agreement between the experimental and simulation results were obtained.

Development of texture in TiN films deposited by filtered cathodic vacuum arc

X-ray diffraction was used to characterize the texture in TiN films deposited by an off-plane double bend filtered cathodic vacuum arc technique. The influence of deposition pressure, substrate bias, and deposition temperature on the texture of the films was studied systematically. The texture develops from a random orientation to a mixed (1 1 1) and (2 2 0) preferred orientation with increasing deposition pressure. As substrate bias is increased, the texture evolves from a (2 0 0) preferred orientation to a mixed (1 1 1) and (2 2 0) preferred orientation at a substrate bias of −100 V. However, further increase of substrate bias changes the texture back to the (2 0 0) preferred orientation again. The deposition temperature has no significant effect on the development of the film texture. Comparing the texture with the internal stress and surface roughness, it is observed directly that the texture in the TiN films is controlled by the internal stress and surface roughness.

Structure and mechanical properties of tungsten carbide films deposited by off-plane double bend filtered cathodic vacuum arc

High quality nanocrystalline tungsten carbide films were deposited by a filtered cathodic vacuum arc technique at room temperatures. X-ray diffraction and atomic force microscopy were used to characterize the crystalline structure and surface morphology of the films. Substrate bending methods and nanoindenter were used to measure internal stress, hardness, and Young’s modulus of the films. The film structure evolves from a single hexagonal α-W2C phase to a mixture phase, which is composed of a hexagonal α-W2C, a cubic WC1−x, and a cubic W phase, as the substrate bias, which is always negative, is increased to 200 V. As the substrate bias is further increased, the film structure changes gradually to a single α-W2C phase again. The variation trends of internal stress, hardness, and Young’s modulus with the substrate bias are similar. They increase with substrate bias, reaching a maximum of 7.2, 26, and 270 GPa, respectively, at a substrate bias of 200 V, then decrease with further increase of substrate bias.

Structural characteristics and mechanical properties of aluminium oxide thin films prepared by off-plane filtered cathodic vacuum arc system

Transparent and smooth alumina thin films have been deposited on Si (1 0 0) and quartz substrates at low temperature by an off-plane double bend filtered cathodic vacuum arc (FCVA) system, which is slightly different from traditional vacuum arc system. The films were analysed using X-ray diffraction and X-ray photoemission spectroscopy to investigate the crystalline and chemical characteristics of these thin films. The films displayed a very smooth surface morphology, which were verified from AFM and SEM. The compressive stress, hardness and Young's modulus of aluminium oxide thin films deposited under varying oxygen partial pressure were investigated, and compared with that by other technologies. Friction coefficient of stoichiometric film against steel and DLC balls were analysed by tribometer (pin-on-disk), respectively. The deposited stoichiometric aluminium oxide thin films possess good optical properties. The results show that the alumina thin films prepared by FCVA technology have potential applications as wear-resistance coatings and optical coatings.

Microstructural and surface properties of cobalt containing amorphous carbon thin film deposited by a filtered cathodic vacuum arc

Cobalt containing tetrahedral amorphous carbon (ta-C:Co) films were deposited on silicon wafers at room temperature under various bias conditions by an off-plane double bend filtered cathodic vacuum arc technique. The microstructural and surface properties of the ta-C:Co films were systematically studied by XPS, Raman, and surface energy measurements via contact angle measurements. Incorporation of Co increases the contact angle sharply to 107.5° as compared to the value for pure ta-C of ∼80°. XPS measurements showed that an increase in negative substrate bias affects both the sp3 content as well as the Co oxidation state on the sample surface. Correlation between XPS and surface energy measurements showed that two different mechanisms might cause the overall decrease in surface free energy of the films.

On the properties of nanocomposite amorphous carbon films prepared by off-plane double bend filtered cathodic vacuum arc

It is known to deposit hard thin films, such as tetrahedral amorphous carbon (ta-C), using a filtered cathode vacuum arc (FCVA). These ta-C films have interesting and useful properties because of the high sp 3 fraction of carbon atoms (up to 87%) in the film. However, the high internal stress in the films can limit their applications as the film may flake away from the substrate. In order to reduce the internal stress of the ta-C films and in an attempt to improve adhesion of thick films of this type, growth modifications such as incorporating metal into the ta-C films have been carried out. Nanocomposite amorphous carbon films were deposited by FCVA technique using metal–carbon composite target. Atomic force microscopy, Raman, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of the films. Nanoindenter and surface profilometer were used to determine the hardness, Young's modulus, and internal stress. The same metal composition targets for different elements results in different metal composition in the corresponding nanocomposite amorphous carbon films. We attribute this observation to the dynamic balance deposition effect of the FCVA deposition process. The influence of the type of metallic elements and its composition in the films on the structural, mechanical properties, surface energy and field emission (FE) performance was studied. The incorporation of metal into the films results in the decrease of sp 3 fraction, internal stress in the films, but the hardness and Young's modulus remains at high level. The surface energy of the films increases with incorporating Ni atoms, but decreases after incorporating Fe and Al atoms into the films. After heat-treatment, the incorporation of metal into ta-C films can greatly improve the FE performance.

Electrical properties of TiN films deposited by filtered cathodic vacuum arc

High quality TiN films were deposited by an off-plane double bend filtered cathodic vacuum arc technique. The influence of deposition pressure, substrate bias, and deposition temperature on the structure and electrical resistivity of TiN films were systematically studied. As the deposition pressure is increased, the film structure evolves from hexagonal α-TiN0.30 to cubic TiN, and the electrical resistivity decreases drastically at the pressure below 2×10−4 Torr, then increases slightly with the further increase of deposition pressure. With the increase of substrate bias, the electrical resistivity decreases drastically, reaching the minimum of 45 μΩ cm at a substrate bias of −100 V, then increases greatly, which results from the variation of N content in TiN films with increasing substrate bias. The increase in the deposition temperature results in a significant decrease in the defect density and a slight increase in the grain size, which accounts for a linear decrease in the electrical resistivity. Our results indicate that the main factors that affect the electrical resistivity of TiN films are the N content, phase structure, and defect density in the films. The grain size plays only a minor role in the electrical resistivity of TiN films.

Substrate bias dependence of Raman spectra for TiN films deposited by filtered cathodic vacuum arc

Raman spectroscopy was used to characterize TiN films deposited by using an off-plane double bend filtered cathodic vacuum arc technique. The influence of substrate bias on the Raman spectra was systematically studied. Four peaks at 235, 320, 440, and 570 cm−1, related to transverse acoustic (TA), longitudinal acoustic (LA), second-order acoustic (2A), and transverse optical (TO) modes of TiN, respectively, were observed in the Raman spectra of TiN films. The intensity of all four peaks and the area fraction as well as the full width at half maximum (FWHM) of the TO peak increase drastically with increasing substrate bias, reaching a maximum at −100 V, and then decrease greatly. However, the area fraction of TA, LA, and 2A peaks, the FWHM of TA and 2A peaks, as well as the frequency of all four peaks decrease rapidly with increasing substrate bias to −100 V, and then increase greatly. At a bias above −200 V, only a slight change in the Raman spectra of TiN films were observed. The change in the N/Ti ratio is the main reason for the evolution in the Raman spectra of TiN films with increasing substrate bias. The internal stress and the crystal size play only a minor role in the Raman spectra of TiN films in the present study.

Substrate bias dependence of the structure and internal stress of TiN films deposited by the filtered cathodic vacuum arc

TiN films were deposited by an off-plane double bend filtered cathodic vacuum arc technique. Atomic force microscopy and x-ray diffraction were used to study the surface morphology and crystal structure. Substrate bending methods were used to determine the internal stress in the films. The influence of substrate bias on the structure and internal stress were systematically studied. As substrate bias is increased to −100 V, the surface roughness decreases to the minimum, the preferred orientation changes gradually from (200) to (111), and the internal stress increases greatly to the maximum. Further increase of substrate bias results in the drastic increase of surface roughness and the gradual decrease of internal stress. The preferred orientation changes gradually from (111) to (200). Except for the atomic peening, the change in the structure and preferred orientation also contributes to the variation of internal stress in the films with substrate bias.

Influence of deposition temperature on the structure and internal stress of TiN films deposited by filtered cathodic vacuum arc

TiN films were deposited by an off-plane double bend filtered cathodic vacuum arc technique. Atomic force microscopy and x-ray diffraction (XRD) were used to study the surface morphology and crystal structure of TiN films. Substrate bending methods were used to measure the internal stress. The influence of deposition temperature on the surface morphology, crystal structure, and internal stress were systematically studied. The surface roughness, grain size and the intensity of the XRD peak increase linearly with increasing deposition temperature. The crystallographic orientation develops from (111) preferred orientation to (200) preferred orientation as the deposition temperature is increased. The increase of deposition temperature from 50 to 450 °C results in a linear decrease of internal stress from 9.88 to 4.30 GPa. The enhancement of the mobility of atoms in the films and the variation of crystallographic orientation with increasing deposition temperature contribute to the decrease of internal stress in the films.

Carbon arc plasma transport through different off-plane double bend filters

An off-plane double bend (OPDB) magnetic filter is used to remove macroparticles from the plasma beam of cathodic vacuum arcs, making it suitable for the preparation of high quality thin films. A filter with high plasma transmission efficiency is desirable and essential for high deposition rate, which is the key to the commercialization of the technology. Hence, an investigation has been carried out to study the carbon arc plasma transport under varying arc current and magnetic field conditions. The plasma efficiency tests were carried out on different sizes of off-plane double bend (OPDB) filters by measuring the ion saturation output current and ion density using a copper plate and Langmuir probes, respectively. It was found that in our FCVA systems, there exists an optimum arc current operation for obtaining the maximum plasma efficiency. This seems to be as an important factor for future filter design.

Filtered cathodic vacuum arc deposition of thin film copper

A major obstacle for metallization application of filtered cathodic vacuum arc (FCVA) is the presence of micro-particles. By using an off-plane double bend magnetic filter, metallic films can be deposited with relevant deposition rates and free of micro-particles. Clean copper thin films with low electrical resistivity were deposited by filtered cathodic vacuum arc techniques at room temperature. All the copper films have a polycrystalline structure and preferably oriented to (111). When the substrate bias is applied, the (111) orientation of Cu film is further enhanced. The internal stress of the films is strongly dependent on the substrate bias. When the bias increases from 0 to −600 V, the internal stress of the film changes from tensile to compressive. At the bias of −300 V, a stress-free Cu film can be obtained.

Influence of substrate bias on the structure and mechanical properties of ta-C:W films deposited by filtered cathodic vacuum arc

Tungsten containing tetrahedral amorphous carbon (ta-C:W) films were deposited by an off-plane double bend filtered cathodic vacuum arc technique from a composite target. Raman spectroscopy and atomic force microscopy (AFM) were used to characterize the film structure and surface morphology. Substrate bending method and nanoindenter were used to determine the internal stress, hardness, and Young's modulus. The influence of substrate bias on the surface morphology, structure, and mechanical properties was systematically studied. All the deposited films were very smooth. The internal stress, hardness and Young's modulus for the deposited films increase with increasing substrate bias, reaching the maximum at a substrate bias of −80 V, then decrease drastically with increasing substrate bias to −200 V. Further increase of substrate bias results in the slight decrease of internal stress, hardness and Young's modulus. The correlation between the structure and the mechanical properties of the deposited films was established.

Influence of substrate bias on the microstructure and internal stress in Cu films deposited by filtered cathodic vacuum arc

Copper films were deposited by a novel off-plane double bend filtered cathodic vacuum arc technique at ambient temperatures. X-ray diffraction (XRD) and atomic force microscopy (AFM) are used to characterize the film’s structure and surface morphology. The substrate bending method was used to study the internal stress. The influence of substrate bias on the surface morphology, grain size, crystalline structure, and internal stress was systematically studied. XRD results indicate that all the deposited Cu films exhibit face-centered cubic-type (fcc) crystallite structure with (111) preferred orientation growth. The increase of substrate bias results in the improvement of (111) preferred orientation. At the substrate bias of 0 V, the deposited films are composed of nano-sized columnar grains, which contribute to the tensile stress in the deposited films. The grain size and surface roughness increase gradually with increasing substrate bias up to −200 V. Further increase of substrate bias results in the drastic decrease of grain size and surface roughness due to self-sputtering. The internal stress in the deposited films is also strongly dependent on the substrate bias. The increase of substrate bias results in the decrease of tensile stress in the deposited films, and the transition of tensile to compressive stress at the substrate bias of −300 V. Further increase of substrate bias results in the linear increase of compressive stress in the deposited films. At the substrate bias of −300 V, dense and stress-free Cu films can be obtained.