Arrival Ratio Research Articles

Control of film properties during filtered arc deposition

Titanium nitride films may be deposited by filtered arc deposition (FAD) onto heated substrates or by ion assisted arc deposition (IAAD) onto unheated substrates. The stress and microhardness of the deposited films are strongly dependent upon the bias applied to the substrate in FAD. In the case of FAD onto substrates heated to 400 °C, an increasingly negative substrate bias results in a decrease in film compressive stress from 10 to 2 GPa. In the case of nitrogen IAAD onto ambient temperature substrates, the film properties are influenced by the nature of the assisting ion beam, specifically the energy and the relative arrival ratio. The stress ranges from 1 to 7 GPa and the hardness from 26 to 38 GPa. Pronounced effects are also observed in the development of preferred orientation. When the assisting N ion energy is increased from 500 to 1200 eV the orientation changes from (111) to (220). The stress evolution of the arc deposited films may be qualitatively understood in terms of the generalised model for momentum transfer, modified to account for the increased energy of the condensing particles generated by the arc process.

Knock-on subplantation-induced formation of nanocrystalline c-BN with r.f. magnetron sputtering and r.f. argon ion plating

Boron nitride thin films were deposited by unbalanced r.f. magnetron sputtering from a hexagonal boron nitride (h-BN) target with r.f. argon ion plating at an argon gas pressure of 8 × 10−4 mbar. The content of cubic boron nitride (c-BN) is very high, as determined by infrared absorption spectroscopy (IR, 84% c-BN), factor analysis of Auger electron spectroscopy (AES, approximately 100% sp3) and X-ray reflectivity (approximately 100% sp3). Furthermore, the films were characterized by stress measurements and atomic force microscopy (AFM).The film-forming particles (fluxΦn) are mainly sputtered neutral boron and nitrogen atoms, and the plating particles (fluxΦi) are argon ions. The current density is about 2.25 mA cm−2, as determined from energy and mass analysis. The energy dependence due to r.f. substrate bias shows a maximum in the c-BN content at 137 eV at an arrival ratioΦi/Φn= 13 where AFM investigations show a minimum of the area roughness of 0.2 nm. Increasing the arrival ratio (to 20 and 66), the optimal c-BN formation is shifted to lower energies (87 eV and 62 eV respectively) which is in agreement with the subplantation model. Stress reduction experiments, such as UV-assisted deposition and post-annealing, are discussed.

Chemical shifts and optical properties of tin oxide films grown by a reactive ion assisted deposition

Highly oriented nonstoichiometric tin oxide thin films were grown by a reactive ion assisted deposition onto Si(100) and glass substrates at room temperature as a function of relative ion (O)/atom (Sn metal) arrival ratio, and concurrently the deposited ion energy per atom (eV/atom) were changed from 10 to 100 eV/atom. As-deposited tin oxide films show preferred orientation along the SnO2〈101〉 axis and the x-ray diffraction peak intensity appears maximum at an average energy of about 50 eV/atom. From quantitative Auger electron spectroscopy, characteristic transitional Auger peaks of Sn metal MNN transitions were shifted to lower kinetic energies by 4–6±1.0 eV as the Sn4+ component becomes dominant in the deposited tin oxide films and the position of O KL1,2L2,3 transition line was also shifted to lower kinetic energy by 1–2±1.0 eV as the composition of deposited tin oxide films were changed from SnO to SnO2, respectively. On the basis of a tin 3d core level and O 1s spectra analysis by x-ray photoelectron spectroscopy, the sizable chemical shift of different valencies between stannous tin (Sn2+:SnO) and stannic tin (Sn4+:SnO2) was 1.0±0.02 eV and that of O 1s was 0.87±0.02 eV, and those values show larger shifts than previously reported ones. The refractive index n of as-deposited tin oxide films was evaluated from an ellipsometer, and spectrophotometric transmittances were measured in the wavelength range of 200–800 nm. In the luminous range, the refractive index varied from n=2.36 to 2.04 as oxygen contents increased.

Formation of Fe—N films containing Fe 16N 2 phase by ion beam assisted deposition

Fe—N films were deposited on Si(100) and GaAs(100) substrates at room temperature by ion beam assisted deposition under various N Fe atomic arrival ratio, 0.09, 0.12, 0.15. The results of X-ray diffraction indicated that the film deposited at 0.12 of N Fe arrival ratio contained a considerable fraction of the Fe 16N 2 phase which had grown predominantly in the [001]orientation. For the larger N Fe arrival ratio, a martensite phase with 15 at.% nitrogen was obtained. It was found that a lower deposition temperature (<200 °C) was necessary for the formation of the Fe 16N 2 phase.

Mechanical and Tribological Properties of Chromium-Nitrogen Films Deposited by Ion Beam Assisted Deposition

AbstractMechanical and tribological properties of chromium-nitrogen films deposited by ion beam assisted deposition (IBAD) were investigated. The films were deposited reactively, i.e., via chromium evaporation with concurrent nitrogen ion beam bombardment, on stainless steel substrates at low deposition temperatures (&lt;200°C). Two primary deposition regimes, with differing Cr/N atom-to-ion arrival ratios, were investigated: approximately 0.8–1.0 and 2.5–3.0. Rutherford Backscattering Spectroscopic analysis showed the lower arrival ratio films to be essentially stoichiometric CrN, whereas films deposited at higher arrival ratios were Cr-rich with Cr/N ratios of about 3:1. Both films were fine grained polycrystalline (typically 5–20 nanometer crystal dimension). The stoichiometric films were approximately two times harder than the Cr-rich films., based on nanohardness indentation measurements, and possessed higher residual stress levels. Both film types substantially improved the wear resistance of stainless steel disks, based on the results of ball-ondisk wear tests against ruby balls. The best performance was obtained with Cr-rich films, which exhibited a very low wear rate and lower friction than either the stoichiometric film or the uncoated steel.

Optical and Structural Properties of Tantalum Pentoxide Thin Films by Ion Assisted Deposition Method with Radio Frrequency Ion Source.

Ion assisted deposition has been applied widely in present optical industry, to obtain more dense films, but it is often required to attain longer filament lifetime of the ion source particularly in the case of successively reactive oxidation processes under an additional oxygen gas inlet such as in oxide films for laser mirror application. It is the reason why radio frequency ion source is keenly interested at the present moment. Therefore we have investigated the optical and structural properties of Ta2O5 films as the functions of ion energy (300-750eV), substrate temperature (ambient or 300°C ), arrival ratio (0.2-0.8 atoms/ion), and providing the oxygen ions by RF ion source to bombardment. Typically, Ta2O5 thin films with refractive index larger than 2.25 and extinction coefficient less than 6×10-4 in visible region have been obtained under the conditions of oxygen ion energy of 500 eV, at the substrate temperature of 300°Cand with the arrival ratio of 0.4 atoms/ion. Their cross sections of the films are shown the amorphous-like, amorphous columnar, and polycrystalline columnar structures by SEM and XRD. Several results of surface roughness of these films by AFM and OP, and the packing densities of these films by spectrometer (OPM-V1) are also presented.

Engineered Nanocrystallites for Enhanced Performance of Ceramic Coatings by Ion Beam Assisted Deposition

AbstractTypical high-temperature thin-film deposition techniques are not suitable for certain substrates such as polymers and thermally-sensitive steels. In this work, ion beam assisted deposition (IBAD) was used to deposit ceramic and metallic films at temperatures below 150°C with nanocrystalline (&lt; 100Å diameter) grain size. Nanoindentation studies of these films have shown hardnesses 50 to 100% greater than larger-grained films and, in some cases, fracture toughness approaching that of Si3N4.By combining chromium evaporation with nitrogen beam bombardment, hard, adherent CrN films without any porosity have been produced at low temperatures with a N/Cr arrival ratio of about 1. The grain size is typically smaller than 100Å and hardness is typically higher than 25 GPa. For a N/Cr arrival ratio slightly less than 1, we observed possible grain boundary porosity. However, even with porosity, hardness is typically 20 to 24 GPa for grain sizes smaller than 100Å. For a N/Cr arrival ratio of 1/4 we deposited elemental Cr with a grain size of 300 to 500Å and a hardness greater than that of silicon (12 GPa). Using Ar ions and a N backfill, we produced elemental Cr containing a mixture of coarse (120 to 150Å) and fine (25 to 30Å) grains. For high-temperature deposition of CrN, the grain size increases (200 to 600Å) with a noticeable decrease in hardness. Mechanical properties of CrN are greatly influenced by impurities, as well as by surface conditioning of the substrate.TiN films having gold color and grain sizes from 50 to 1000Å have been produced at low temperatures. Nanoindentation measurements of hardness and fracture toughness indicate that impurity-free TiN (with grains smaller than 100Å) has a hardness higher than 25 GPa and a fracture toughness close to that of Si3N4, but with higher wear resistance. Mechanical properties of our TiN films are greatly influenced by impurities, particularly oxygen, although it does not influence the gold color of TiN.

Residual stress and adhesion in ion-assisted hafnia coatings on glass*

Thin film mechanical properties are strongly influenced by the features of the employed deposition technique. Ion beam-assisted evaporation permits good control of the parameters involved in the process and offers several advantages in processing coatings with expected performance. In this paper, the generation of residual stresses depending on the ion bombardment conditions and their effect on the adhesion behaviour of hafnium dioxide IBAD thin films were investigated. Stresses, which were tensile or compressive depending on the momentum parameter RE1/2 values, where R is the ion-to-atom arrival ratio and E is the ion energy, were measured with a mechanical profilometer by the curvature change of the sample before and after the deposition. The scratch test technique was used to evaluate the adhesion failure load (Lc) of the HfO2 thin films and is correlated with the stress present in the samples themselves. The analysed samples showed an increase in critical load as the momentum parameter value increased...

Synthesis and Mechanical Properties of Niobium Films by Ion Beam Assisted Deposition

AbstractMechanical properties of niobium thin films are studied by controlling the microstructure, texture and residual stress of the films using ion beam assisted deposition (IBAD). Niobium films were deposited onto (100) Si substrates and their microstructure, texture and residual stress were measured as a function of ion energy and R ratio (ion to atom arrival rate ratio). The grain sizes of these films ranged from 20 nm to 40 nm and no effect of ion bombardment was observed. All the films have strong (110) fiber texture, but the in-plane texture is a strong function of the incident angle, energy and flux of the ion beam. Results show that while the degree of the texture increases with increasing ion energy and flux, it is also a strong linear function of the product of the two. The residual stress of the films was measured by a scanninglaser reflection technique. As a function of normalized energy, the stress is tensile for En &lt; 30 eV/atom with a maximum of 400 MPa at about 15 eV/atom. It becomes compressive with increasing normalized energy and saturates at - 400 MPa for En &gt; 50 eV/atom. Both PVD (physical vapor deposition) and IBAD films have a hardness of about 6 GPa at shallow depth measured by nanoindentation. The different stress state may be responsible for the 15%difference on hardness observed between the PVD and IBAD films.

Surface Morphology of Nb Films by Ion Beam Assisted Deposition

AbstractNiobium films of thickness 50 nm to 1000 nm were deposited by ion beam assisted deposition (IBAD) using ion energies of 0, 500 and 1000 eV, and R ratios (ion-to-atom arrival rate ratio) of 0, 0.1, and 0.4 on (100) silicon and (0001) sapphire substrates. The films have columnar structures and the column width increases with normalized energy (En = E × R). The surface morphology depends on both the normalized energy of the ion beam, En, and the film thickness. All films have dome-like surface features that are oriented along the ion beam incident direction. The dimension of these features increases with normalized energy and film thickness. Surface roughness also increases with normalized energy and film thickness, with the root mean square (rms) roughness increasing from 1.6 nm for the PVD sample (100 nm thick) to 36.7 nm for the IBAD film (1000 eV, R = 0.4, 800 nm thick). The surface morphology of IBAD films is the result of a combination of channeling and shadowing effects.

Preparation and Characterization of Tin Oxide Films by Ion-Assisted Deposition

AbstractUndoped tin oxide films were grown on Si substrates by a reactive ion-assisted deposition technique in which oxygen ions were irradiated on depositing Sn particles. In order to investigate the oxidation from SnO to SnO2, the effects of initial oxygen contents and heat treatment on the final crystalline structure of tin oxide films were thoroughly examined. Oxygen to Sn metal ratio (No/Nsn) of as-deposited films were controlled from 1.1 to 1.9 by varying the relative arrival ratio (F) of oxygen ion to Sn particle from 0.025 to 0.1. Heat treatment was carried out in two different ways; one was post vacuum-annealing at 400 ∼ 600°C and the other was in-situ annealing 400 ∼ 500°C. Crystalline structure of as-deposited tin oxide films at room temperature was amorphous. After post-annealing at 400°C, only SnO phase was found below No/Nsn= 1.6 in x-ray diffraction and crystalline structure of the films comprising higher oxygen contents still appeared to be amorphous. Even though the films still showed SnO phase until Γ50 after 500°C post-annealing, however, mixed structures of SnO, SnO2, and intermediate Sn2O3/Sn3O4 were observed for the films Γ75 and Γ100 with higher oxygen contents. At 600°C annealing, perfect SnO2 phase was attained for the films having No/Nsn=1.9. On the other hand, pure polycrystalline SnO2 films could be obtained by in-situ annealing at low temperature. The values of No/Nsn and the chemical shifts with the variation of oxidation were carefully determined by the comparison of Sn MNN and O KLL Auger transitions. Surface microstructure of deposited films was also analyzed using a scanning electron microscopy (SEM) and an atomic force microscope (AFM).

On the mechanism of crystal growth orientation of ion beam assisted deposited thin films

The high number of degrees of freedom of the process parameters of ion beam assisted thin film deposition allows the formation of thin films with special features. Among these process parameters are ion energy, ion irradiation intensity, atom condensation rate and ion impact angle. By contrast to plasma deposition methods, these parameters are independent of each other and can be selected over a wide range. By carefully selecting the ratio I A of condensing atoms to impacting ions, the ion energy and the angle of ion incidence, films with a high degree of crystallographic orientation can be formed. To-date several mechanisms for the development of texture are discussed. Among them is the sputter theory which explains the growth of particular planes by sputtering and channeling. In a comparative study, this theory is applied to transition metal nitrides of group 4, 5 and 6 of the periodic system of elements. Based on results of structural measurements, the mechanisms which are involved in texture formation are discussed as a function of the process parameters arrival ratio I A , ion energy and ionic species. It turns out that it is not the ion energy deposited per atom but the momentum transfer per unit volume which correlates with the observed changes in preferred crystal orientation.

Effect of N+2 ion bombardment on the compositional change and residual stress of AlN film synthesized by ion beam assisted deposition

The compositional change and residual stress of aluminum nitride film synthesized by ion-assisted evaporation and sputtering are discussed in terms of ion bombardment. In the growth of AlN film, N+2 ion bombardment could increase the N incorporation probability and reduce oxygen impurities. The stoichiometric nitride was obtained at an arrival ratio of N/Al higher than 1.5. With increasing ion flux and energy the residual stress shows a tendency to shift from tensile to compressive stress. Except for the low region of ion flux and energy, the compressive stress shows a linear proportionality to the momentum parameter of incident ions defined as the product of ion flux and (ion energy)1/2 in the ion beam assisted deposition process. The temperature dependence of residual stress is also discussed.

Characterization of cubic boron nitride films prepared by ion beam assisted deposition

An attempt to prepare well-defined hexagonal (h-BN) and cubic (c-BN) boron nitride by the ion beam assisted deposition technique was undertaken. Ion beams with energies between 500 and 800 eV at a current density between 80 and 120 μA were used. The ion source was fed with a gas mixture of argon and nitrogen. Boron was evaporated from an electron beam evaporator. The ion to atom (I/A) arrival ratio was the most important parameter and was chosen to be between 0.5 and an upper limit given by the sputter loss. Depending on the conditions for the formation of the interface, the sputter loss exceeds the deposition at an I/A ratio between 1.0 and 1.3. The dependence of the stoichiometry and phase formation on I/A, the deposition rate and the operating gas was investigated. The microhardness, friction coefficient and tribological performance were determined for layers containing different fractions of the cubic and hexagonal phases. Stoichiometric films with c-BN contents of 70% were successfully deposited with the following parameters: I/A ratio, 1.2; N 2/Ar flux, 1.5; substrate temperature, above 350 °C; ion current density, higher than 100 μA cm −2; ion energy, 500 eV. The films with high contents of c-BN suffer from intrinsic compressive stress and poor adhesion. For this reason, the thickness of the films was limited to 300 nm. A microhardness of 10 000 N mm −2 was found. All films show friction coefficients below 0.1. The tribological behaviour changes as a function of the content of c-BN. High c-BN contents cause a rapid peel off; very low c-BN contents cause abrasive wear.

Ion-beam-assisted deposition of aluminium and aluminium alloy coatings for corrosion protection

Ion-beam-assisted deposition (IBAD) was used for depositing pure aluminium coatings on low carbon steel in order to study the corrosion properties as a function of the energy of the incident argon ions, the ion-to-atom arrival ratio and the angle of ion incidence. With theoretical considerations about the localized corrosion behaviour of substrate-coating systems it is possible to evaluate the porosity, the relative number of coating defects and their mean diameter. Their dependence on the process parameters gives an insight into the initial stages of film growth and shows that the energy deposition in the near-surface region is the most important factor for modifying coating defects and therefore the corrosion properties of the steel-aluminium system. The modification potential of each parameter of IBAD is studied in comparison to pure vapour deposition for the corrosion in acetate buffer. In chloride-containing aqueous solutions the depassivation behaviour of aluminium can be improved by use of alloying elements. Aluminium and magnesium were deposited on inert glass substrates; the magnesium concentration and the bombarding energy were varied. The resulting alloys have equilibrium potentials less noble than pure aluminium and increased passive regions. The passive region decreases with increasing magnesium concentration. From glancing-angle X-ray diffraction measurements it can be seen that structural changes influenced by the ion beam go parallel with changes in the localized corrosion behaviour.

Structure and magnetic properties of Fe–N films prepared by ion-beam-assisted deposition

Fe–N films were prepared by ion-beam-assisted deposition at different N/Fe atomic arrival ratios to the substrates. Films consisted of nitrogen-rich α-Fe and different phases of iron nitrides including ζ-Fe2N, ε-Fe2-3N, and γ′-Fe4N were formed. The phase composition of Fe–N films was found to depend sensitively on the N/Fe atomic arrival ratio and deposition temperature. The magnetic properties of the films mainly depends on phase composition. It was found that nitrogen-rich α-Fe films exhibited higher Ms than that of the pure iron film, and their Ms could be increased further by vacuum annealing at relatively low temperatures.

Structure and magnetic properties of FeN films deposited on heated substrates by ion-beam-assisted deposition

FeN films were prepared by ion-beam-assisted deposition at different temperatures. The composition, structure and magnetic properties of the films were investigated by Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and with vibrating sample magnetometer (VSM). The results of XRD indicated that the films consisted of α-Fe, γ-Fe 4N and ϵ-Fe 2–3N, or mixtures of these phases, according to different N/Fe atomic arrival ratios. It was observed that the film of α-Fe with supersaturated nitrogen exhibited a larger M s than that of bulk iron. However, its H c was too large to be used as soft magnetic film.

Low-temperature homoepitaxial growth of Si by electron cyclotron resonance plasma enhanced chemical vapor deposition

Epitaxial Si films have been deposited at low substrate temperatures of 400 and 500 °C, by plasma enhanced chemical vapor deposition using an electron cyclotron resonance source. Samples were analyzed using Rutherford backscatter spectrometry, cross-sectional transmission electron microscopy, and x-ray diffraction. The ion-to-adatom arrival ratio was found to be an important parameter in determining epitaxial film quality. This ratio was controlled by the SiH4 feed rate, microwave power level, and shape of the magnetic field in the substrate region. Incident ion energy and ion flux were monitored with a gridded energy analyzer located at the substrate location.

Control of composition and structure for molybdenum nitride films synthesized using ion beam assisted deposition

The purpose of the research described in this article was to synthesize molybdenum nitride films with well-defined structures and stoichiometries using ion beam assisted deposition (IBAD). Approximately 400 nm thick films were prepared by the evaporative deposition of molybdenum while simultaneously bombarding the growing film with low energy (250–1000 eV) nitrogen ions. The effects of ion-to-atom arrival rate ratio, ion angle of incidence, and ion energy on the film composition and phase constituents were examined. The film nitrogen to molybdenum stoichiometry increased linearly with increasing arrival rate ratio irrespective of the ion energy and varied significantly with changes in the ion angle of incidence. The latter was interpreted based on sputtering and reflection effects. The phase constituents were functions of all of the deposition parameters investigated. We propose that a single parameter, the effective energy density per deposited atom, can account for the effects of ion energy, mass, and angle of incidence. The effective energy density is approximately the ion energy divided by the ion range. The range incorporates the effects of ion mass and angle of incidence, as well as the energy. For low energy ions the energy density per depositing atom is proportional to E1/2, a dependence that it shares with other models that have been developed to account for phase formation during IBAD. The advantage of the energy density treatment is that it has a more obvious influence on the temperature in the growth zone, a factor controlling phase formation.

Outward transport of substrate atoms during dynamic ion mixing

The transport of deposited atoms and substrate atoms during dynamic ion mixing was investigated by Auger electron spectroscopy (AES). Mild steel substrates were treated by dynamic ion mixing, in which Ne, Ar or Kr ion implantation and Ti deposition were carried out simultaneously. Before the treatment, Ta markers were embedded in the surface region of the steel by Ta ion implantation in order to confirm the location of the original substrate surface. The distance of outward transport of Fe atoms (ΔFe) gradually exceeds that of the inward transport of Ti atoms (ΔTi) as the ion/atom arrival ratio (i.e. the ratio of impacting ions to condensing atoms) increases. The same Δ Fe Δ Ti ratio is attained with a lower ion/atom arrival ratio when the ion mass is larger and ion energy is lower, i.e. when the sputter yield of the ion implantation is larger. The outward transport of substrate atoms is thought to be caused by the reaction of the sputtered Fe atoms the depositing Ti atoms during the process.