High Substrate Bias Research Articles

Growth and visible photoluminescence of highly oriented (1 0 0) zinc oxide film synthesized on silicon by plasma immersion ion implantation

High-quality (1 0 0) ZnO films with smooth surface topography have been synthesized on Si substrate by plasma immersion ion implantation. The materials exhibit compressive stress because of room temperature growth. After annealing at different temperatures, various visible photoluminescence bands are observed. The optical phenomenon as well as the transition mechanism which may involve defects such as [Zn I], [V Zn], and [ O i −] induced by the high substrate bias are discussed in this paper.

The effect of graded interface thickness on the life of Pb coating ion plated on SUS 17-4PH steel substrate

Low-speed spacecraft mechanisms like solar array drives and pay load steering mechanisms use high precision gears of SUS 17-4PH material. In order to have the lowest overall weight of the mechanisms, simplest design with solid lubricated bearings and gears are preferred against complicated design with fluid lubrication involving hermetic sealing for retaining the fluid lubricant against evaporation. The operating speed of these mechanisms is in the range of 1–15 revolutions per day. Hence to optimally meet the above requirements like the need for the tribo-component to function for many years unattended and exposed to the vacuum of space, solid lubrication of these gears with thin films of Pb ion-plated (Pb-IP) is widely adopted. The long life requirement of these mechanisms with low jitter depends on the friction, wear and endurance life of the lubricant coating. The latest upgraded design of such mechanisms, with requirements of high torque and more than 15 years of orbital life, needs to be supported with appropriate enhancement/improvement of the tribological aspects of the solid lubricant coatings. In regard to the present study of ion-plated Pb coating on SUS 17-4PH steel, a newly developed Pb-IP coating processed with higher substrate bias has shown an increase in the coating life cycles while testing in a ball-on-disk tester in vacuum of 10 −6 Pa. The cross-sectional examination of the graded interfaces by SEM–EDS showed an increase in thickness of the graded interface for the new Pb-IP coating compared to that of the conventional Pb-IP coating.

Optical and electrical properties of amorphous carbon films deposited using filtered cathodic vacuum arc with pulse biasing

Passive devices using metal containing amorphous (a-C) films have been successfully fabricated. However, difficulties in the etching of these films as well as their inferior inertness compared to pure a-C films led us to study the electrical and optical properties of pure a-C films. The films were deposited using a filtered cathodic vacuum arc system (FCVA) in conjunction with high substrate pulse biasing. It is possible to control the sp 2 content and hence the properties, by varying the substrate pulse bias voltage. In this study, the a-C films were prepared by varying the high substrate bias between 3 and 11 kV using a Plasma immersion ion implantation (PI 3) system. Characterization of these samples gives us an indication about the suitability of the films for integrated passive devices and other applications. Four-point probe measurement has been carried out to study the resistivity of the films deposited on quartz and SiO 2. The resistivity decreases with increasing pulse bias voltage, which is likely attributed to the sp 2 fraction in the film as well as the substrates’ resistivity. The sp 2 content in the films is estimated using XPS and Raman spectroscopy. Optical properties of the films are characterized using spectroscopic phase-modulated ellipsometry. The band gap decreases from 2.3 to 1.49 with increasing bias voltage.

Mechanical properties and thermomechanical stability of diamond-like carbon films synthesized by pulsed vacuum arc plasma deposition

The higher sp 3 bonding fraction hydrogen-free diamond-like carbon (DLC) films were deposited on Si(1 0 0) and Cr17Ni14Cu4 stainless steel substrates by pulsed vacuum arc plasma deposition as a function of bias substrate voltage. The results show that the sp 3 content increases slightly with higher substrate bias and the effective microhardness only increases slightly. The wear resistance of the as-deposited DLC films decreases with increasing substrate bias. The effective hardness of the annealed DLC films diminishes by approximately 20% and the wear resistance decreases after annealing at 400 °C due to local adhesion decreases, even though the wear resistance of the annealed DLC films is still much better than that of the Cr17Ni14Cu4 substrate. The thermomechanical stability of hydrogen-free DLC films synthesized by pulsed vacuum arc plasma deposition is better than the DLC films containing hydrogen synthesized by PECVD.

Haemocompatibility of hydrogenated amorphous carbon (a-C:H) films synthesized by plasma immersion ion implantation-deposition

Diamond-like-carbon has attracted much attention recently as a potential biomaterial in blood contacting biomedical devices. However, previous reports in this area have not adequately addressed the biocompatibility and acceptability of the materials in blood contacting applications. In this study, hydrogenated amorphous carbon (a-C:H) films were fabricated on silicon wafers (1 0 0) using plasma immersion ion implantation-deposition. A series of a-C:H films with different structures and chemical bonds were fabricated under different substrate voltages. The results indicate that film graphitization is promoted at higher substrate bias. The film deposited at a lower substrate bias of −75 V possesses better blood compatibility than the films at higher bias and stainless steel. Our results suggest two possible paths to improve the blood compatibility, suppression of the endogenic clotting system and reduction of platelet activation.

Synthesis and optical characterization of amorphous carbon nitride thin films by hot filament assisted RF plasma CVD

Carbon nitride thin films were synthesized by hot filament assisted radio frequency plasma chemical vapour deposition using methane and nitrogen gas mixture on silicon and glass substrates. The films were deposited at different substrate bias and at different substrate temperatures. At higher substrate bias (>−120 V) there was no deposition on the substrate, but complete etching of the deposited layer was observed. X-ray diffraction studies indicated the films were amorphous. The Fourier transform infrared spectra showed that the films produced exhibited high transmittance with the presence of the C–N stretching band at 1260 cm −1. For the films deposited at a lower substrate temperature C=N peaks were also present. Raman spectroscopic study indicated the presence of D and G peaks whose relative height varied with substrate temperature. The transmittance versus wavelength measurement in the UV–VIS–NIR region showed the high transmittance in the NIR region. The optical band gap of the films was calculated to be 2.0 eV and the refractive index varied within 1.6–1.7 for the wavelength range 800–1800 nm.

The influence of thermal annealing on residual stresses and mechanical properties of arc-evaporated TiC xN 1−x[formula omitted] thin films

We report the stress relaxation behavior of arc-evaporated TiC x N 1− x thin films during isothermal annealing between 350 and 900°C. Films with x= 0, 0.15, and 0.45, each having an initial compressive intrinsic stress σ int = −5.4 GPa, were deposited by varying the substrate bias V s and the gas composition. Annealing above the deposition temperature leads to a steep decrease in the magnitude of σ int to a saturation stress value, which is a function of the annealing temperature. The corresponding apparent activation energies for stress relaxation are E a =2.4 , 2.9, and 3.1 eV, for x= 0, 0.15, and 0.45, respectively. TiC 0.45N 0.55 films with a lower initial stress σ int = −3 GPa, obtained using a high substrate bias, show a higher activation energy E a =4.2 eV. In all the films, stress relaxation is accompanied by a decrease in defect density indicated by the decreased width of X-ray diffraction peaks and decreased strain contrast in transmission electron micrographs. Correlation of these results with film hardness and microstructure measurements indicates that the stress relaxation is a result of point-defect annihilation taking place both during short-lived metal-ion surface collision cascades during deposition, and during post-deposition annealing by thermally activated processes. The difference in E a for the films of the same composition deposited at different V s suggests the existence of different types of point-defect configurations and recombination mechanisms.

Self-consistent three-dimensional model of dust particle transport and formation of Coulomb crystals in plasma processing reactors

Dust particle transport in low-temperature plasmas has received considerable attention due to the desire to minimize contamination of wafers during plasma processing of microelectronic devices and for their use to study nonideal plasmas. Dust particles in radio frequency discharges form Coulomb crystals and display collective behavior under select conditions. In this article, we discuss results from a self-consistent three-dimensional model for dust particle transport in plasma processing reactors. The consequences of varying the bias voltage of the capacitively coupled discharge, plasma density, particle diameter, and the number of particles on the propensity for Coulomb crystal formation in argon plasmas will be discussed. We found that a single one-layer lattice spontaneously breaks up into separate lattices as the substrate bias is increased due to a redistribution of plasma forces. At high substrate biases, a void occurs in the plasma crystal which tends to close upon addition of electronegative gases such as O2 and Cl2 to argon. The interparticle spacing in the lattice depends on the number of particles in the lattice due to gravitational compressive forces; and on the plasma density due to the change in shielding length.

From plasma immersion ion implantation to deposition: a historical perspective on principles and trends

Plasma immersion techniques of surface modification are known under a myriad of names. The family of techniques reaches from pure plasma ion implantation, to ion implantation and deposition hybrid modes, to modes that are essentially plasma film deposition with substrate bias. In the most general sense, all plasma immersion techniques have in common that the surface of a substrate (target) is exposed to plasma and that relatively high substrate bias is applied. The bias is usually pulsed. In this review, the roots of immersion techniques are explored, some going back to the 1800s, followed by a discussion of the groundbreaking works of Adler and Conrad in the 1980s. In the 1990s, plasma immersion techniques matured in theoretical understanding, scaling, and the range of applications. First commercial facilities are now operational. Various immersion concepts are compiled and explained in this review. While gas (often nitrogen) ion implantation dominated the early years, film-forming immersion techniques and semiconductor processing gained importance. In the 1980s and 1990s we have seen exponential growth of the field but signs of slowdown are clear since 1998. Nevertheless, plasma immersion techniques have found, and will continue to have, an important place among surface modification techniques.

Crystalline silicon films grown by pulsed dc magnetron sputtering

Pulsed dc magnetron sputtering is used as a novel method for the deposition of crystalline silicon films on glass substrates. Hydrogen-free polycrystalline Si-films are deposited with high deposition rates at temperatures of 400–450 °C and pulse frequencies f in the range 0–250 kHz. Strong preferential (1 0 0) orientation of the crystallites is observed with increasing f. High frequency and similarly high negative substrate bias cause an increase of the Ar content and an enhancement of structural disorder. Measurements of the transient floating potential suggest that the observed structural effects are related to bombardment of the growing film by Ar + ions of high energy.

Effect of gradient a-SiCx interlayer on adhesion of DLC films

Diamond-like carbon films were prepared on radio-frequency (RF) biased substrates of silicon wafer and Corning 7059 glass at low temperature substrate by electron cyclotron resonance microwave plasma chemical vapor deposition using CH4–H2 and CH4–Ar as reactant gases. The effects of a-SiCx interlayer prepared by RF-PECVD on the adhesion and failure mode of DLC films were investigated. In CH4–H2 system with the a-SiCx interlayer and RF bias applied to −90 V, the adherence of DLC films was improved significantly and the critical load was increased from 2 N without RF bias to 80 N. The failure mode transferred from spalling failure at lower substrate bias to conformal cracking at higher substrate bias. In CH4–Ar system with a-SiCx interlayer, the critical load was increased to 20 N at RF bias −90 V and the spalling failure mode was revealed. Comparing the DLC films obtained in the two system coated with a-SiCx interlayer and RF bias applied to −90 V, the one deposited in CH4–H2 system exhibited less damage which demonstrates that the films obtained has a better adherence behavior.

Tribological properties and adhesive strength of DLC coatings prepared under different substrate bias voltages

An investigation has been carried out to study the effect of high substrate bias voltages on the morphological, mechanical, adhesive and tribological properties of diamond-like carbon (DLC) films. The morphological study shows that the film has a tendency to be rougher, when it is prepared with increased substrate bias voltages. Relatively lower hardness and poor wear resistance (the coefficient of friction remains almost same) are characteristics of the films that are prepared with higher substrate bias voltages. Improved adhesion is observed for the films that are prepared under high substrate bias voltage, and is due to the formation of increased intermixed layer thickness.

Investigations of surface reactions during C2F6 plasma etching of SiO2 with equipment and feature scale models

During fluorocarbon plasma etching of SiO2, a polymer passivation layer is generally deposited on the surface of the wafer. The polymer layer regulates the etch by limiting the availability of activation energy and reactants, and providing the fuel for removal of oxygen. To investigate these processes, a surface reaction mechanism for fluorocarbon plasma etching of SiO2 has been developed. The mechanism describes the polymerization process as resulting from neutral sticking, ion sputtering, F atom etching, and low-energy ion assisted deposition. The etch mechanism is a multistep passivation process which results in consumption of both the polymer and the wafer. The surface mechanism was incorporated into an equipment scale simulator to investigate the properties of SiO2 etching in an inductively coupled C2F6 discharge, and predicts that the SiO2 etch rate saturates at high substrate biases due to the depletion of passivation. Experimental results for SiO2 etch rates and selectivity of SiO2 over Si as a function of substrate bias were well reproduced. The blanket reaction mechanism was also employed in a feature scale simulator to investigate high aspect ratio (HAR) trench topography. Results from the feature scale model showed that strong sidewall passivation leads to tapered profiles in HAR SiO2 etching. The incident ion energy and the ratio of the passivating neutral to ion fluxes largely determine the degree of the taper or bowing. Profile control can be obtained by regulating this ratio, with one such method being argon dilution.

Sputter deposition of 45% Ni-55% Fe for high moment top pole applications

We present the properties of dc magnetron sputter-deposited 45% Ni-55% Fe. Optimal magnetic properties obtained in 1.4 μm films were: 4πMs∼16.4 kG, Hce∼3.7 Oe, Hch∼0.8 Oe, Hk∼9.6 Oe, at a deposition rate of 29 Å/s. A linear designed experiment revealed that: higher gas pressure significantly lowers both Hce and Hk; higher (rf) substrate bias increases α90 and Hch, while decreasing Hk; and higher substrate magnetic field worsens Hch and α90. Augmentation of the experimental matrix and analysis of higher order terms implied that a combination of intermediate pressure and small bias provides optimal magnetic properties. From x-ray diffraction, the 45–55 NiFe is fcc, with lattice parameter 3.578–3.584 Å, in fair agreement with the bulk value of ∼3.585 Å. Grain sizes in the range 150–180 Å were estimated. Analysis of the (111): (200) peak intensity ratio showed that higher substrate bias or lower pressure both significantly enhance the (111) texture. Correlation was observed between the magnetics and the crystalline texture; less [111] texture gives lower coercivity. Data on 2000 Å films for seedlayer applications are also presented.

Collimated deposition of hard bias magnetic films via long-throw techniques

We present an optimization of long-throw sputter-deposited Cr/CoCrPt films, specifically for (lifted-off) hard bias applications in an AMR/GMR head. Deposition was carried out in the target-to-substrate (T/S) range of 7–9 in., with pressure down to 0.25 mTorr. On increasing the T/S by 1 in., a 5% reduction in coercivity was observed, and shown to be only partially explained by the deposition rate reduction. On the other hand, lower gas pressure during the CoCrPt deposition significantly increased the coercivity. Higher target power and higher substrate bias also increased the coercivity. All the observed T/S, pressure, target power, and bias dependencies suggest enhanced coercivity is associated with higher CoCrPt adatom mobility. X-ray diffraction data showed the relative intensity of the (0002) to the (1010) peak to be decreased both with higher CoCrPt deposition power or substrate bias; more in-plane c-axis texture could explain the increased coercivity. A sputter etch of the wafer before Cr deposition increased the coercivity by about 300 Oe. A combination of these techniques may be used to compensate for the deterioration in magnetic properties due to the long-throw. Optimal properties of 1790 Oe coercivity and 3.5 memu/cm2 Mrt were achieved.

Cavitation-resistant TiNi films deposited by using cathodic arc plasma ion plating

TiNi intermetallic compound with superelasticity and corrosion resistance could have potential use in resisting sliding wear, rolling fatigue, corrosion, or erosion environments. TiNi is, however, expensive. A thin film coating of TiNi may enable low-cost materials such as plain steel to be used in the above applications. Thus, a study on the uses of TiNi coating is necessary. A cathodic arc plasma (CAP) ion plating process was used to deposit TiNi films onto plain steel using Ti 50Ni 50 target material. The substrate's bias voltage was changed to optimize the properties of the deposited film. Experimental results show that the deposited films have approximately the stoichiometry of Ti 40Ni 60. The nickel-rich composition may be caused by the ease of scattering of the titanium atoms or the thermalization of the background gas atoms during their flight to the substrate. Due to the higher migration ability of the surface adatoms, the films deposited at high substrate bias voltage possess a higher crystallinity. The major phase in such films is TiNi-B2. TiNi 3 and TiNi-B19′ coexist as the minor phases. Cavitation resistance of the specimen in freshwater was significantly increased to a 3-fold value in comparison with the uncoated plain steel. These promising results suggest that CAP ion plating is suitable for preparing cavitation-resistant TiNi films, if high substrate bias voltage is employed. The highly aggressive electrolyte develops a perfect Galvanic cell around the pits and the electrolyte accelerates the electrochemical dissolution of the anodically polarized substrate.

Sheath expansion in a drifting, nonuniform plasma

A model is proposed for the sheath expansion into a nonuniform plasma with substantial drift velocity. We refer in particular to the streaming metal plasma produced by a vacuum arc discharge; this kind of plasma is characterized by its spatial nonuniformity and high ion drift velocity. It is shown that for a nonuniform plasma and high substrate bias voltage (>10 kV), the sheath thickness is significantly smaller than in a uniform plasma. High drift velocity also leads to a decrease in sheath thickness. For plasma immersion ion implantation carried out in a nonuniform plasma, the increase in ion implantation current with increasing voltage is different from that of a uniform plasma where the ion current is constant with voltage. This effect was found to be quantitative agreement with experiment. The decrease in sheath thickness with increasing plasma drift velocity can explain qualitatively the experimentally observed existence of a stable high-voltage sheath for a relatively long time.

Magnetic and microstructural characterization of FeTaN high saturation materials for recording heads

Magnetically soft FeTaN high saturation materials have been deposited on both sloping and planar surfaces by RF reactive sputtering with an appropriate high substrate bias. A perpendicular anisotropy component accompanying degrading soft magnetic properties is observed under low substrate bias. This undesirable perpendicular anisotropy in the FeTaN films arises from the magnetoelastic anisotropy due to in-plane compressive stress and positive magnetostriction constant and from the magnetocrystalline anisotropy due to out-of-plane [200] easy axes. This is supported by X-ray pole figures, temperature-dependent VSM measurements, and synchrotron radiation X-ray stress measurements. The absence of microshape perpendicular anisotropy is supported by SQUID measurements and high resolution TEM images. This work has identified the processing parameters and microstructures that are critical for successfully incorporating high saturation magnetic materials in recording heads.

Stoichiometry of unbalanced magnetron sputtered Al–Mg alloy coatings

Abstract Numerous Al–Mg coatings were prepared by unbalanced magnetron sputtering with a range of substrate bias voltages. The coatings were deposited from circular planar targets, composed of sequential sectors of Al and Mg, bonded to a directly cooled copper backing plate. The chemical composition of the coatings was found to be significantly affected by preferential resputtering of Mg due to ion bombardment. X-ray diffraction indicated that all coatings were extremely fibre textured. Some dramatic changes in d -spacing of the coating were observed for only small increments in the bias voltage. This indicates a transition in crystal structure induced by preferential resputtering. Extremely high amounts of argon were also detected in the coatings which contained a Mg-rich cph structured phase. Very little argon was detected in any of the Al-rich fcc coatings, even with high substrate bias voltages (−200 V). The burial of argon in the cph structured Al–Mg coatings is not purely an ion implantation phenomenon, but is controlled by microstructural entrapment or alloying effects. It is concluded that ion-assisted deposition of Al–Mg alloy coatings should be treated with some caution, because of these difficulties with the control of stoichiometry.

Structure and hardness studies of CNx/TiN nanocomposite coatings

Crystalline CNx/TiN multilayer composite coatings have been synthesized using an opposed cathode unbalanced magnetron sputtering system. Electron microscopy studies showed that the CNx/TiN coatings were fully crystalline and dense at small bilayer thicknesses. An amorphous phase was formed when the CNx layer thickness exceeded 4–5 nm. Two new d spacings extracted by Fourier transform of digitized images of the crystalline CNx region cannot be matched by known compounds formed by the detected elements. This provides limited evidence for the possible formation of a new carbon–nitrogen compound. Nanoindentation hardness about 45–55 GPa was reproducibly achieved for coatings produced under low nitrogen partial pressure and high substrate bias (−150 to −250 V). TiN (111) preferred orientation was strongly correlated to the high coating hardness.