Increasing Substrate Bias Voltage Research Articles

Structures and mechanical properties of diamond like carbon films prepared by closed-field unbalanced magnetron sputtering

Diamond like carbon (DLC) films were synthesized by closed-field unbalanced magnetron sputtering (CFUBM) using carbon targets in Ar and Ar/C2H2 atmosphere. The deposition rate, structure and mechanical properties of these films were studied as a function of applied bias voltage on the substrate during deposition. The film structures were investigated using Raman spectroscopy. The hardness and elastic modulus were measured by nano-indentation tests and the friction coefficient of DLC films was measured by a ball-on-disc type wear tester. Raman analysis showed that sp3/sp2 ratio in DLC films changed with increasing substrate bias voltage. Hydrogenated DLC films deposited at the bias of −200 V exhibited a maximum hardness of 28 GPa and a relatively low friction coefficient of about 0.1.

Effect of substrate temperature and bias voltage on DC magnetron sputtered Fe–N thin films

Iron nitride films were deposited by DC magnetron sputtering using an Ar/N2 gas mixture at various substrate temperatures and substrate bias voltages. Using X-ray photoelectron spectroscopy (XPS), the composition of the films was analyzed. The structure, roughness, surface morphology, and magnetization of the films were investigated using X-ray diffraction (XRD), grazing incidence X-ray scattering (GIXS), atomic force microscopy (AFM), and superconducting quantum interference device (SQUIDS). Attempts have been made to correlate the phase structure, roughness, morphology and magnetization with the substrate bias voltage and substrate temperature. It was found that films deposited at different substrate temperature exhibited different structure, growth mechanism and magnetization. With the increase of the substrate temperature, the coercivity of the films has the tendency to increase. Except for roughness and coercivity of the iron nitride thin films, substrate bias voltage had little influence on the structure and saturation magnetization of the films. Films deposited at different substrate bias voltage will exhibit different coercivity. With the increase of substrate bias voltage, the coercivity of Fe-N films decreased.

Influence of Substrate Bias Pretreatment on Growth of Diamond Films By HFCVD

In the hot filament CVD (HFCVD) process, the nucleation process is enhanced by ion bombardment of the negatively biased substrate. To achieve ion bombardment at voltages as low as possible, a hybrid HFCVD technique was developed utilising a dual plasma arrangement. The I-V measurements of the plasma formed between the substrate and the filaments showed that the saturation of the total current depends on the process duration and substrate bias. A low nucleation bias voltage, i.e. ≤ 100 V, results in poor nucleation and non-continuous film formation. An increase in substrate bias voltage up to 120 V results in homogeneous nucleation and subsequent deposition of diamond films consisting mainly of large rectangle-like crystals. Further increase in nucleation voltage to ≥ 140 V leads to the formation of films with increased density of grains, which show edges with streak and cracking features indicating a twinning growth. During nucleation, the total current on the substrate has a tendency to increase with time, except for the sample nucleated at 100 V. The time constant, defined as the point when the total current starts to increase, is reduced with increase in substrate bias. It is proposed that this effect is related to the increased density of diamond nucleation sites.

Synthesis and mechanical properties of amorphous carbon films by closed-field unbalanced magnetron sputtering

Amorphous hydrogen-free carbon (a-C) films were synthesized by closed-field unbalanced magnetron sputtering (CFUBM). The deposition rate, structure, and mechanical properties of these films were studied as a function of applied bias voltage on substrate during deposition. The film structures were investigated in Raman spectroscopy, and surface roughness was analyzed by atomic force microscopy (AFM). The hardness and elastic modulus were evaluated by nanoindentation test. Raman analysis showed that sp 3/sp 2 ratio in a-C films increased with increasing substrate bias voltage. a-C films deposited at a bias of −100 V exhibited a maximum hardness of 25 GPa.

The properties of (Ti,Al)N coatings deposited by inductively coupled plasma assisted d.c. magnetron sputtering

(Ti,Al)N coatings were deposited on M2 high speed steel substrates by inductively coupled plasma (ICP) assisted d.c. magnetron sputtering, and the structure and mechanical properties such as hardness, Young's modulus, wear resistance and adhesion strength were investigated. A TiAl alloy target (Ti/Al — 50:50 at.%) was sputtered in an Ar and N 2 atmosphere with 400 W for d.c. magnetron power as well as 400 W for ICP power at 80 mtorr of working pressure. Both the hardness and adhesion strength of the coating were found to increase with increasing substrate bias voltage. The hardness value was higher than 6500 HK 0.01 at the bias voltage higher than –50 V. The Young's modulus of the coating had a maximum value of approximately 450 GPa at −50 V. The wear properties of coatings also improved with the application of the substrate bias voltage. It was found that the grain size decreased (<100 nm), and the columnar structure, which was observed in the absence of bias, disappeared when a bias voltage was applied. The high hardness and good wear property was attributed to the microstructure change from a columnar structure with facet shaped grains to a denser one with small and round shaped grains.

Formation and Properties of Carbon Nitride Thin Films by Pulsed Nd:YAG Laser Deposition

Carbon nitride thin films were synthesized on Si(100) substrates by pulsed Nd:YAG laser deposition. Several spectral lines originating from the neutral and ionic species, such as carbon atoms, carbon ions, carbon molecules and carbon nitride molecules were identified in the plasma plume. The surface morphology of the carbon nitride thin films reveals numerous droplets on the films out of which several are spiral shaped. The N/C composition ratio is increased from 0.18 to 0.25 with increasing substrate bias voltage. Fourier transform infrared spectroscope absorption spectra show two characteristic bands: a broad band composed of the graphite G-band and disordered D-band of carbon, and another associated with the CN triple bond. Raman spectra have also been used to characterize the films.

Properties of zirconium oxide thin films deposited by pulsed reactive magnetron sputtering

Abstract Zirconium oxide thin films were deposited by direct current (d.c.) reactive magnetron sputtering on glass slide, silicon wafer and stainless steel substrates. The thickness of the thin films was between 200 nm and 3 μm. The target power density controlled deposition process was used. The process parameters investigated were the target power, the sputtering gas pressure and the substrate bias voltage and their influence was studied on the film properties such as O/Zr ratio, density, nanohardness, intrinsic stress, crystallographic structure and surface roughness. The deposition rate increased as a function of the target power, the sputtering gas pressure and the substrate bias voltage. The nature of the residual stress changed from compressive to tensile as the sputtering gas pressure was increased. The nanohardness of the thin films increased with decreasing sputtering gas pressure and with increasing substrate bias voltage. The thin films were colourless and transparent when fully oxidised to monoclinic structure, black when rich in metal. These black substoichiometric thin films with the O/Zr ratio of 1.6 had a tetragonal structure. Black thin films represented low nanohardness and strongly increased surface roughness.

Investigation of titanium nitride films deposited at room temperature by energetic cluster impact

Energetic cluster impact (ECI) deposition was applied to grow titanium nitride films on silicon (100) substrate at room temperature. Proton elastic scattering (PES), X-ray diffraction (XRD) and atomic force microscopy (AFM) were employed to characterize the composition, structure and morphology of TiN x films, respectively. The PES results reveal that the films are N-deficient and there exists a certain amount of oxygen impurity in the films. It is found from the XRD results that the structure of TiN x films is sensitive to experimental conditions such as nitrogen gas partial pressure, sputtering current and substrate bias voltage and that TiN x films are (220) preferred orientation within some range of experimental conditions. The AFM observation indicates that the films become more uniform and compact with increasing substrate bias voltage. The root mean square roughness also decreases with increasing bias voltage. Some interpretation for the above results are also given in this paper.

Effects of DC Bias on the Thermal Stability of DC In-Line Sputtered CoCrTa/Cr Thin Film Media

AbstractThe effects of DC bias on the thermal stability and magnetic anisotropy of CoCrTa/Cr thin film media fabricated by using a DC in-line sputtering machine is presented in this paper. In sputtering, a negative DC bias voltage, varying from 0 to 400 V, was applied for the CoCrTa layer. The coercivity was observed to increase almost linearly from 1800 to 2300 Oe for negative bias voltage from 0 to 400V. The thermal stability of these media was studied by measuring the time decay of remanent magnetization under various reverse magnetic fields. The maximum value of the magnetic viscosity coefficient, which happens around remanent coercivity of each samples, decreases with increasing substrate bias voltage. This implies an improvement in the thermal stability of the CoCrTa/Cr thin film media. The magnetic anisotropy constants were measured using both a torque magnetometer and a vibrating sample magnetometer. The magnetic anisotropy measured using torque magnetometer decreases, while that measured using the method of the law of approach to saturation was found to be almost constant, with increasing bias voltage. The activation volumes decreased with increasing bias voltage. The magnetic hardness coefficient determined using the law of approach to saturation, indicating the number of in-depth defects in the CoCrTa layer, increased with increasing bias voltage. The internal stress in these films measured using X-ray diffractometer also supported the existence of in-depth defects. The pinning of the rotation of magnetization by these defects in the magnetic grains maybe responsible for the improvement of thermal stability.

Effect of substrate bias voltage on the properties of arc ion-plated TiN films onto high speed steels

The effect of substrate bias voltage on the properties of arc ion-plated TiN films onto high speed steels has been investigated. The high density structure with a large crystallite size grew at the high bias voltage. TiN films deposited by higher bias exhibited strong preferential (111) orientation from XRD. The internal stress of TiN films increased at first with increasing substrate bias voltage; however, it decreased as the bias voltage increased over 100 V. The coating adhesion measured by the scratch tester increased with increasing bias voltage, and this is coupled with a cohesion of films. Cutting performance of TiN coated drills, which increased markedly with increasing substrate bias, has been studied in relation to the physical and chemical properties of deposited films.

Rayleigh mode in amorphous hydrogenated carbon films.

Brillouin-scattering experiments are performed on amorphous hydrogenated carbon (a-C:H) films grown by plasma deposition on silicon substrates at various bias voltages (-50 to -1400 V) and annealed after deposition at a bias of -400 V between 100 and 1100 \ifmmode^\circ\else\textdegree\fi{}C. Scattering from Rayleigh surface phonons is observed. The results show that the Reyleigh mode frequencies are between those of diamond and graphite. With increasing substrate bias voltage the Rayleigh mode frequency first increases to a maximum value at -200 V and then decreases monotonically. Upon annealing, the Rayleigh phonon frequency decreases drastically for temperatures above 500 \ifmmode^\circ\else\textdegree\fi{}C with minor changes below 400 \ifmmode^\circ\else\textdegree\fi{}C. These results correspond to the results of the ${\mathit{sp}}^{3}$-to-${\mathit{sp}}^{2}$ bonding ratio, indicating that the frequency variation of the Rayleigh phonon is due to phase transformations of a-C:H. The coupling between the relaxation mechanism and the phonon also confirms the phase transitions. Based on the hydrogen concentration, the ${\mathit{sp}}^{3}$-to-${\mathit{sp}}^{2}$ bonding ratio, and the phonon frequency, the correlated densities and elastic constants of annealed a-C:H films are calculated.

The study of mechanical properties of a-C:H films by Brillouin scattering and ultralow load indentation

In this study diamondlike a-C:H films have been prepared by different methods: In our first experiment a-C:H films were deposited by plasma decomposition of methane at different bias voltages. In the second experiment a-C:H films with high hardness were implanted with 400-keV C+ ions and different doses between 1013 and 1017 ions/cm2 . Subsequently, the following mechanical properties of the films were measured: The shear modulus μ by the frequency of the surface phonon (Rayleigh wave), the stiffness S by an ultralow load indentation of diamond. The Young’s modulus and the Poisson’s ratio were calculated from μ and S. The internal stress σ was determined with the bending beam method. From the Young’s modulus E and the internal stress σ, the average strain ε of the films has been calculated. From the behavior of ε it was concluded that a phase transition from amorphous diamondlike to amorphous graphitelike a-C:H films occurred with increasing substrate bias voltage.

Preparation of permalloy films using facing‐type targets and a high‐rate and low‐temperature sputtering method

AbstractPermalloys are promising as candidates for a thin‐film head and as a material for the soft substrate magnetic layer using normal magnetic memory media. Permalloy films prepared using facing‐type targets and a high‐rate and low‐temperature sputtering process are examined. As a result in the facing‐type target sputtering method, it is desirable to use double targets with a structure consisting of a small satellite target positioned eccentrically inside the mother target.The morphology and magnetic properties of sputtered films depend strongly on the substrate bias voltage. To obtain a good magnetic film, a substrate bias voltage in the range of ‐120 to ‐150 V and/or a substrate temperature of 350 C is needed. In particular, with the application of bias voltage, in addition to being stress free at low substrate temperature, a thermally stable film is also obtained. It is observed that adhesion of the film to the substrate can be improved by sputter‐cleaning of the substrate before deposition. Perpendicular anisotropy of the films decreases significantly and the magnetic properties of the films improve with increasing substrate bias voltage and substrate temperature. This is probably attributable to the change in film morphology.