The ion energy distributions and ion flux composition from a high power impulse magnetron sputtering discharge

The energy distribution of sputtered and ionized metal atoms as well as ions from the sputtering gas is reported for a high power impulse magnetron sputtering (HIPIMS) discharge. High power pulses were applied to a conventional planar circular magnetron Ti target. The peak power on the target surface was 1-2 kW/cm² with a duty factor of about 0.5%. Time resolved, and time averaged ion energy distributions were recorded with an energy resolving quadrupole mass spectrometer. The ion energy distributions recorded for the HIPIMS discharge are broader with maximum detected energy of 100 eV and contain a larger fraction of highly energetic ions (about 50% with E_i > 20 eV) as compared to a conventional direct current magnetron sputtering discharge. The composition of the ion flux was also determined, and reveals a high metal fraction. During the most intense moment of the discharge, the ionic flux consisted of approximately 50% Ti¹⁺, 24% Ti²⁺, 23% Ar¹⁺, and 3% Ar²⁺ ions.     

In-situ analysis of positive and negative energetic ions generated during Sn-doped In2O3 deposition by reactive sputtering

Using a quadrupole mass spectrometer combined with an energy analyser, we have investigated the in-situ energy distribution of highly energetic ions generated during reactive sputtering of In-Sn alloy (IT) targets and non-reactive sputtering of Sn-doped In₂O₃ (ITO) ceramic targets. Ar⁺, In⁺, O⁺, O⁻, O₂⁻, InO⁻ and InO₂⁻ ions with kinetic energies greater than 40 eV were clearly observed. Upon increasing the O₂ flow ratio for reactive sputtering, the surface of the IT target changes from metal (metal mode) to oxide (oxide mode) via a state of mixed metal and oxide (transition region). O⁻ ions with the kinetic energy corresponding to cathode voltage are generated at the oxide layer, which expands upon the target surface with increasing O₂ flow ratio in the metal mode and the transition region. In contrast, the flux of 60-eV Ar⁺ ions decreases with increasing O₂ flow ratio. The presence of 125- and 200-eV In⁺ ions is attributed to the dissociation of InSnO₂⁻ and InO₂⁻ with the kinetic energy corresponding to cathode voltage, respectively, while the presence of 40- and 150-eV O⁺ ions is attributed to the dissociation of InO₂⁻ and O₂⁻ with the kinetic energy corresponding to cathode voltage, respectively.     

Ion sputtering rates of C, CrxCy, and Cr at different Ar ion incidence angles

To study the ion sputtering of a layered structure with different layer densities and ion sputtering yields a trilayer structure of C-graphite(46 nm)/Cr_xC_y(60 nm)/Cr(69 nm) was sputter deposited onto smooth silicon substrates. The ion sputtering rates of amorphous carbon, amorphous Cr_xC_y and polycrystalline Cr were determined by means of Auger electron spectroscopy depth profiling as a function of the angle of incidence of two symmetrically inclined 1 keV Ar⁺ ion beams in the range between 22° and 82°. The sputtering rates were calculated from the known thicknesses of the layers and the sputtering times necessary to remove the individual layers. It was found that the sputtering rates of C-graphite, Cr_xC_y carbide and Cr were strongly angle dependent. The experimental sputtering yields were in agreement with the theoretical results obtained by calculation of the transport of ions in solids, but the sputtering yields of C-graphite measured at ion incidence angles larger than 29° were smaller than the simulated ones.     

Novel TiAlCN/VCN nanoscale multilayer PVD coatings deposited by the combined high-power impulse magnetron sputtering/unbalanced magnetron sputtering (HIPIMS/UBM) technology

A new TiAlCN/VCN coating combining high hardness, low friction coefficient and chemical inertness has been developed for dry machining of “Sticky” (Al-, Ti- and Ni-based) alloys as well as advanced Metal-Matrix-Composite (MMC) materials used in aerospace and automotive industries. Excellent performance was achieved due to the synergy between V and C as main coating elements and the nanoscale multilayer structure of the coating. TiAlCN/VCN was deposited by the combined High-Power Impulse Magnetron Sputtering/Unbalanced Magnetron sputtering (HIPIMS/UBM) technology. Macroparticle free V⁺ ion flux generated by HIPIMS discharge was used to sputter clean the substrates prior to the coating deposition. A 0.4 μm thick TiAlN base layer followed by 3 μm thick TiAlCN/VCN nanoscale multilayer coating was deposited by unbalanced magnetron sputtering. The sputtering was carried out in a mixed CH₄, N₂ and Ar atmosphere. In dry milling of Al7010-T7651 alloy, TiAlCN/VCN nanoscale multilayer PVD coating outperformed state of the art Diamond Like Carbon (DLC, Cr/WC/a-CH) coating by factor of 4. In drilling Al-alloy enforced MMC materials, cemented carbide drills coated with TiAlCN/VCN produced 130 holes compared to 1-2 holes with uncoated drills.     

In-situ analyses on the reactive sputtering process to deposit Al-doped ZnO films using an Al-Zn alloy target

The kinetic energies of generated ions were investigated during the reactive sputtering process to deposit Al-doped ZnO (AZO) films using an Al-Zn alloy target. The sputtering system was equipped with specially designed double feedback system to stabilise the reactive sputtering processes and analysis was performed with a quadrupole mass spectrometer combined with an energy analyser. Negative ions O⁻, O₂⁻, AlO⁻ and AlO₂⁻ with high kinetic energies corresponding to cathode voltage are generated at the partially oxidised target surface, after which some of the ions undergo subsequent charge exchange and/or dissociation. Positive ions O⁺, Ar⁺, Zn⁺ and Al⁺ with lower kinetic energies (around 10 eV) are generated by charge exchange of sputtered neutral O, Ar, Zn and Al atoms, respectively. As the target surface oxidises, cathode voltage decrease, the flux of high-energy negative ions increases and the electrical properties of the AZO degrade by ion bombardment as well as the AZO films that are deposited by conventional magnetron sputtering using an AZO target.     

Surface morphology analysis of natural single crystal diamond chips bombarded with Ar ion beam

We have studied the surface morphology of natural single crystal diamond chips machined by 0.5-3.0 keV Ar⁺ ion beam irradiation at ion incidence angles of 0°, 30°, 45°, 60°, and 80° with ion doses from 3.4 × 10¹⁸ ions/cm² to 6.8 × 10¹⁸ ions/cm². The surface of diamond chips machined with 0.5 and 1.0 keV Ar⁺ ion beam, at angles of ion incidence from 0° to 45° can be made smooth. Results show that the machined surface at ion dose of 6.8 × 10¹⁸ ions/cm² and beam energy of 0.5 and 1.0 keV become ultra-smooth (surface roughness SR = 0.1 nm rms) compared with unprocessed surface (SR = 0.15-2.1 nm rms). Results also confirm the ripple formation on diamond surface at ion incidence angles of 60°-80° by 0.5-3.0 keV Ar⁺ ion beam. Therefore, the technique of smoothing by choosing ion beam irradiation parameter can be applicable to nano-finishing of diamond tools without ripple formation. This technique can also be applicable in mass production if the diamond surface is mechanically pre-finished.     

Formation of CoNx ultra-thin films during direct-current nitrogen ion sputtering in ultrahigh vacuum

This study reports the formation of ultra-thin cobalt nitride (CoN_x) films on a Co/ZnO(002) crystal by low-energy ion sputtering of nitrogen in an ultrahigh vacuum system. The CoN_x film formed during ion bombardment in which the nitrogen plasma (N⁺) results in both sputtering and implantation in the formation process of CoN_x, especially for the Co adsorbed layers. Auger electron spectroscopy analysis shows that the composition ratio x as a function of sputtering time was highly related to the N⁺ ion energy that was varied from 0.5 to 2 keV. The composition ratio x of CoN_x films is inversely proportional to the ion energy. Low-energy ion sputtering is possible to fabricate ultra-thin CoN_x films and to adjust their chemical compositions.     

Development of a compact angle-resolved secondary ion mass spectrometer for Ar sputtering

A compact angle-resolved secondary ion mass spectrometer with a special geometrical configuration, composing of a differentially pumped micro-beam ion gun, a tiltable sample stage and a time-of-flight (TOF) mass spectrometer, was newly developed. This system enables the measurement of angular distribution (AD) of secondary ions, which are ejected by oblique Ar⁺ sputtering, by a simple tilt operation of the sample stage for ejection angles ranging from 0° to 60° with keeping the ion incidence angle constant 62°±2° from the normal to the surface. Using this system, AD of secondary ions from an HfN film by 3 keV Ar⁺-ion bombardment was measured at room temperature. Since the yield of HfN⁺ dimer ions was almost independent of Hf⁺ and N⁺ monomer ions, it was concluded that the HfN⁺ dimer ions were generated via the “as such” direct emission process.     

The phase and microstructure of CrAlN films deposited by pulsed dc magnetron sputtering with synchronous and asynchronous bipolar pulses

CrAlN films have been deposited from a Cr target and an Al target using pulsed dc magnetron sputtering. The Cr and Al targets were pulsed in asynchronous and synchronous pulsing modes at different pulsing frequencies and duty cycles. The ion energy distributions of the plasma were characterized by a Hiden mass spectrometer. The pulsed plasma contains a wide range of energetic ions. The ion energies depend on the pulsing parameters and the pulsing mode of the two targets. The ion energy and ion flux increased as the pulsing frequency was increased. The plasma exhibited higher ion energies and ion fluxes in the synchronous pulsing mode than those in the asynchronous pulsing mode for the same pulsing frequency and duty cycle. A decrease in the N content and an increase in the Al/(Cr + Al) ratio were observed as the pulsing frequency was increased in both pulsing modes. When the pulsing frequency was increased to 350 kHz, the films deposited in the asynchronous pulsing mode exhibited a NaCl cubic structure, whereas a mixture of the cubic and hexagonal phases was formed in the films deposited in the synchronous pulsing mode. The hardness of the films increased with an increase in the pulsing frequency in the asynchronous pulsing mode. In contrast, a decrease in the hardness was found in the synchronously deposited films as the pulsing frequency was increased due to the formation of hexagonal AlN phase and the stress relaxation in the films.     

Hysteresis-free reactive high power impulse magnetron sputtering

High power impulse magnetron sputtering (HIPIMS) of an Al target in Ar/O₂ mixtures has been studied. The use of HIPIMS is shown to drastically influence the process characteristics compared to conventional sputtering. Under suitable conditions, oxide formation on the target as the reactive gas flow is increased is suppressed, and the hysteresis effect commonly observed as the gas flow is varied during conventional sputtering can be reduced, or even completely eliminated, using HIPIMS. Consequently, stoichiometric alumina can be deposited under stable process conditions at high rates. Possible explanations for this behavior as well as a model qualitatively describing the process are presented.     

Reactive deposition of Al-N coatings in Ar/N2 atmospheres using pulsed-DC or high power impulse magnetron sputtering discharges

In this paper, the metal to ceramic transition of the Al-N₂ system was investigated using classical reactive pulsed-DC magnetron sputtering and HIgh Power Impulse Magnetron Sputtering (HIPIMS) at a constant average current of 3 A. Optical emission spectroscopy measurements revealed more ionised aluminium species in the HIPIMS discharge compared to pulsed-DC sputtering. It also showed excited N⁰ and ionised N⁺ species in reactive Ar/N₂ HIPIMS discharges. The corresponding evolution of the consumed nitrogen flow as a function of the N₂ partial pressure revealed that a higher amount of reactive gas is needed to achieve stoichiometric AlN with HIPIMS. Electron probe micro-analysis and X-ray diffraction measurements confirmed that a partially poisoned aluminium target is enough to allow the deposition of stoichiometric hcp-AlN thin films via HIPIMS. To go further in the comparison of both processes, two stoichiometric hexagonal aluminium nitride thin films have been deposited. High power impulse magnetron sputtered hcp-AlN exhibits a higher nano-hardness (18 GPa) than that of the coating realised with conventional pulsed-DC sputtering (8 GPa).     

Deposition rate characteristics for steady state high power impulse magnetron sputtering (HIPIMS) discharges generated with a modulated pulsed power (MPP) generator

High power impulse magnetron sputtering (HIPIMS) pulses have been of great interest over the last decade. With such sputtering techniques a substantial amount of target material can be ionized and used for the engineering of surfaces and coatings. Depending on voltage, system configuration and target material, such discharges can be either transient or reach steady state currents during the pulse. The used HIPIMS power supply was a constant voltage supplies. Similarly, HIPIMS pulses with multiple steady state current phases can be generated using a modulated pulsed power (MPP) generator. A typical pulse consists of an ignition, low current and high current phase. The contribution of these phases to the deposition rate is presented. The ionization rate of single charge chromium ions has been found to increase linearly with increasing peak current density. An increase in deposition rate with lower magnetic field strength at the target surface can be attributed to a higher sputter yield due to a higher cathode voltage due to increasing system impedance in HIPIMS case, weaker trapping of deposition flux and to enhanced ion flux towards the substrate.     

Radiation-induced luminescence from TiO2 by 10 keV O, N and Ar ion irradiation

Radiation-induced luminescence (RIL) produced by 10 keV O⁺, N⁺ and Ar⁺ irradiation at room temperature has been used to study energy transfer in titanium dioxide (TiO₂) targets. RIL spectra in the UV-visible region show numerous atomic lines and three bands. Two visible bands by crystalline defects and an UV band at 3.9 eV originating from radiation transitions between the Ti³⁺ 3d and O²⁻ 2 s states in the TiO₂ crystal are observed. The experimental results suggest that the excitations were not mainly produced by transitions from the ground state to excited states but by cascade radiations from higher excited states.     

Mitigating the geometrical limitations of conventional sputtering by controlling the ion-to-neutral ratio during high power pulsed magnetron sputtering

High power pulsed magnetron sputtering has been used to grow thin chromium layers on substrates facing and orthogonal to the target. It is demonstrated that at low peak target current density, j_T < 0.6 A/cm² corresponding to a low ion-to-neutral flux ratio, films grown on substrates facing the target exhibit in-plane alignment. This is due to the rectangular shape of the target that yields an asymmetry in the off-normal flux of sputtered species. With increasing j_T the biaxial alignment degrades, as the major portion of the incoming flux (ions) can be effectively steered by the electric field of the substrate to remove asymmetry imposed by geometrical restrictions. Eventually, at j_T = 1.7 A/cm² a fiber texture is obtained. For films grown on substrates orthogonal to the target, the large column tilt characteristic for growth at low j_T, decreases with increasing ion content in the flux and almost disappears at the highest value of j_T. The latter indicates that material flux to the substrate is highly ionized so that deposition takes place along substrate normal despite the high nominal inclination angle. Thus, in the limit of high j_T the artifacts of conventional physical vapor deposition, resulting from the line-of-sight deposition, are effectively eliminated and the film growth proceeds more or less unaffected by the substrate orientation. Samples mounted orthogonally thus possess a similar texture, morphology, and topography as those facing the target.     

Electron energy loss spectroscopy study of the effect of low-energy Ar-ion bombardment on the surface structure and composition of Pt80Co20 (1 1 1) alloy

Electron energy loss spectroscopy has been employed for investigation of the effect of 600 eV Ar⁺-ion irradiation in the dose range 7×10¹⁶-4×10¹⁷ ions/cm² on the atomic structure and surface composition of alloy Pt₈₀Co₂₀(1 1 1). A method of the layer-by-layer reconstruction of the lattice interplanar distance changes based on the analysis of the plasmon spectra excitation was proposed. The ion bombardment was shown to result in a non-monotonic variation of the lattice interplanar distance due to formation of the stable defects, with the topmost layer being in the state of compression. Using the ionization energy loss spectra, a layer-by-layer concentration profile of the alloy components was reconstructed for different doses of ion irradiation of the surface. The Ar⁺-ion bombardment of the alloy was found to result in the preferential sputtering of Co and in the enrichment of the near-surface region by Pt atoms with formation of an altered layer, which is characterized by a non-monotonic concentration profile dependent on the irradiation dose. The results obtained are discussed in the framework of the models of preferential sputtering and radiation-induced segregation.     

Structural and mechanical properties of ZrN films prepared by ion beam sputtering with varying N2/Ar ratio and substrate temperature

Zirconium nitride (ZrN) films were deposited by ion beam sputtering technique on stainless steel 304 substrates using a mix of (Ar+N₂) gas. In this paper, the effects of N₂/(N₂+Ar) flow ratio (F(N₂)) and substrate temperature on the microstructure and microscopic properties of the deposited films were investigated. The phase and the morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively; moreover, the composition depth profile of ZrN was obtained using secondary ion mass spectroscopy (SIMS). In a wide range of F(N₂) (10-54%), the intensity of (1 1 1) peak increased which was the preferred orientation, while for F(N₂) more than 54% the ZrN peak intensity was decreased and the amorphous structure was formed at 95%. The XRD patterns presented a texture change due to the processing temperature, which was varied within the range 200-550 °C. At 400 °C, the (1 1 1) crystalline plane intensity was higher than the other ones, leading to the presence of a preference for this orientation. Good planarity of the deposited films was confirmed by SEM, it did not reveal any undulations, fractures, or cracking. The Vickers micro-hardness tester with a load of 25 g was used to measure the hardness of the films. The results showed that the structural and mechanical properties were strongly influenced by nitrogen ratio and substrate temperature.     

Modulated pulse power sputtered chromium coatings

Cr coatings were deposited using continuous dc magnetron sputtering (dcMS) and modulated pulse power sputtering (MPP) techniques in a closed field unbalanced magnetron sputtering system at equivalent average target powers. It was found that MPP sputtering exhibited higher deposition rates than in dcMS when the average target power density was above 14 W cm^− 2 for the Cr coating depositions. Plasma diagnostics confirmed a significant increase in the numbers of both target material (Cr) and gas (Ar) ions in the MPP plasma as compared to the dc plasma. The substrate peak current densities measured in the MPP depositions (104-324 mA cm^− 2) have been increased by over a factor of 50 to those in the dcMS conditions (2-5.5 mA cm^− 2). The enhanced ion flux bombardment from the highly ionized MPP plasma led to the formation of denser microstructure and finer grain size in the MPP Cr coatings than in the dcMS Cr coatings. In addition, MPP sputtered Cr coatings exhibited improved hardness and adhesion.     

Secondary ion emission from Ti and Si targets induced by medium energy Ar ion bombardment - Experiment and computer simulation

The paper presents experimental results of secondary ion energy distributions obtained for Ti and Si targets bombarded by 20-30 keV monoisotope Ar⁺ ion beam. The influence of the extraction voltages between target and a slit of the electrostatic energy analyzer entrance on the energy distributions of secondary ions was investigated. After optimization of the secondary ion extraction system, the mass spectra of secondary ions were also measured. The investigations were done using recently built experimental system. Experimental data are compared with the computer simulation results obtained using TRQR and SATVAL codes.     

An investigation of the Ar+ ion-enhanced reaction of CCl4 on Si(100) by secondary ion mass spectrometry

The Ar⁺ ion-enhanced reaction of carbon tetrachloride (CCl₄) on Si(100) at room temperature is investigated at primary ion energies of 2 and 9 keV using the secondary ion mass spectrometry (SIMS) technique. Static SIMS shows that CCl₄ reacts with Si at room temperature. This surface reaction is enhanced by simultaneous sputtering with an Ar⁺ ion beam, the reaction rate being higher at 9 keV than at 2 keV. Possible products of surface reaction are discussed.     

Silicide formation by Ar+ ion bombardment of Pd/Si

Palladium films, 45 nm thick, evaporated on to Si(111) were irradiated to various doses with 78 keV Ar⁺ ions to promote silicide formation. Rutherford backscattering spectroscopy (RBS) shows that intermixing has occurred across the Pd/Si interface at room temperature. The mixing behaviour is increased with dose which coincides well with the theoretical model of cascade mixing. The absence of deep RBS tails for palladium and the small area of this for silicon spectra indicate that short-range mixing occurs. From the calculated damage profiles computed with TRIM code, the dominant diffusion species is found to be silicon atoms in the Pd/Si system. It is also found that the initial compound formed by Ar⁺ irradiation is Pd₂Si which increases with dose. At a dose of 1×10¹⁶ Ar⁺ cm^–2, a 48 nm thickness of Pd₂Si was formed by ion-beam mixing at room temperature.