Ar N2 Discharges Research Articles

Measurement of the Ar(1sy) state densities by two OES methods in Ar–N2 discharges

In this work, results from two methods for the determination of the Ar(1sy) densities are compared in an Ar–N2 discharge. These methods involve measurements of optical emission spectroscopy (OES). The first method (band method) uses the bands belonging to the N2(C → B) second positive system, while the second method (branching fraction method) uses the line intensities corresponding to the Ar(2px → 1sy) transitions. These techniques were tested in the negative glow of dc discharge and the results show remarkable agreement.

Study of the excitation mechanisms of the second positive system in the negative glow of a N2–Ar discharge

In an Ar–N2 discharge, the high excitation transfer from Ar(3P2,0) to N2 produces an overpopulation of the high rotational levels of the bands of the second positive system (SPS), and so the spectra interpretation is not straightforward.This paper presents a fit function for the SPS bands measured in Ar–N2, which allows us to study the excitation process contributions to the N2(C) level.The procedure was tested in the negative glow of a pulsed Ar–N2 discharge at a pressure of 2.5 Torr, for different mixture concentrations. In this discharge, through the fitting, it was possible to calculate the variation of the N2(C) densities produced by different excitation processes as well as the variation of Ar metastable density.

Langmuir probe measurement and theoretical studies on inductively coupled plasma in Ar-N2 discharge

In this article we use the Langmuir probe and kinetic model to study the electron energy distribution function (EEDF), the electron temperature, and the electronic density in the radio-frequency inductively coupled plasma of Ar-N2 discharge. It has been found that, with the increase of the N2 flow, the EEDF varies from the bi-temperature distribution to the tri-temperature distribution; the electron temperature drops monotonically at low pressures (pp>1.3 Pa). In addition, due to the recombination of electrons and nitrogen molecular ions, the electron density drops substantially at high pressures when a small amount of N2 is added to the gas mixture. Although the theoretically obtained electron temperature is high than the experimentally measured one, the theoretical model presents good predictions of the influences of N2 ratio in Ar-N2 mixture on the electron temperature and EEDF.

A diagnostic method for real-time measurements of the density of nitrogen atoms in the postglow of an Ar–N2 discharge using a catalytic probe

We determined the density of neutral nitrogen atoms in an Ar–N2 postglow using a fiber-optics catalytic probe. The probe, which had a catalyst made of nitrided iron, was calibrated with a NO titration. The recombination coefficient for the heterogeneous recombination of N atoms on the nitrided iron surface was determined by comparing the probe signal with the NO titration. Within the limits of experimental error the coefficient was found to be independent of the catalyst temperature between 400 and 650K and had a value of 0.21±0.04. Real-time measurements of the N-atom density were performed at a nitrogen flow of 600SCCM (standard cubic centimeter per minute) for several discharge powers between 80 and 300W, and for argon flow rates between 200 and 3000SCCM. With increasing discharge power the N-atom density increased monotonously; with increasing Ar flow the N-atom density at first increased, reaching a broad maximum at about 1.8×1021m−3 for an Ar flow of 2000SCCM, after which the N-atom density decreased with any further increase of Ar flow.

Single-crystal Ti2AlN thin films

We have produced pure thin-film single-crystal Ti2AlN(0001), a member of the Mn+1AXn class of materials. The method used was UHV dc reactive magnetron sputtering from a 2Ti:Al compound target in a mixed Ar–N2 discharge onto (111) oriented MgO substrates. X-ray diffraction and transmission electron microscopy were used to establish the hexagonal crystal structure with c and a lattice parameters of 13.6 and 3.07Å, respectively. The hardness H, and elastic modulus E, as determined by nanoindentation measurements, were found to be 16.1±1GPa and 270±20GPa, respectively. A room-temperature resistivity for the films of 39μΩcm was obtained.

Influence of the target temperature on a reactive sputtering process

Reactive magnetron sputtering often presents an unstable sputtering mode preventing high rate deposition of stoichiometric ceramic films, the origin of which is mainly due to the avalanche-like target poisoning over a critical reactive gas partial pressure. In this paper, the effect of the target temperature is investigated for titanium targets sputtered in Ar–N2 or Ar–O2 reactive discharges. Paradoxically, raising the target temperature yields a stabilisation of the transition sputtering mode close to the elemental sputtering mode. With a discharge current modulated at low frequency, the stabilisation is complete for titanium sputtered in Ar–N2 discharges.

Enhanced deposition rate of high quality stoichiometric ceramic compounds reactively sputter deposited at low pressure by modulating the discharge current at low frequency

Low-frequency modulation of the discharge current constitutes an efficient means of achieving high rate deposition of stoichiometric ceramic compounds in spite of the so-called unstable sputtering conditions. The main trends of the process are reviewed in the case of titanium targets sputtered in reactive Ar–O2 or Ar–N2 discharges. The effect of the target temperature is also discussed in relation to the stabilisation propensity of a low-frequency modulated discharge.

Nanoindentation hardness, abrasive wear, and microstructure of TiN/NbN polycrystalline nanostructured multilayer films grown by reactive magnetron sputtering

TiN, NbN, and TiN/NbN polycrystalline nanostructured multilayer films were deposited on high-speed steel substrates by unbalanced reactive magnetron sputtering of Ti and Nb targets in Ar–N2 discharges. Two techniques were used for obtaining a series of multilayers with compositional modulation period, Λ, in the range 3.8–100 nm; rotation of a cylindrical substrate holder between two opposing cathodes or by positioning inclined cathodes above the substrate and using shutters. For the two setups, ions were accelerated from the discharge by a negative substrate bias Vs=120–150 V and Vs=100 V, respectively, with an ion-to-metal arrival rate ratio of ∼1. The nanoindentation hardness and abrasive wear resistance by dimple grinding test of the coatings were compared between the sample series and related to the microstructure, phase composition, and residual stress σres obtained by transmission electron microscopy, x-ray diffraction, and substrate curvature technique, respectively. All films exhibited a dense and columnar microstructure with 20–90 nm grain sizes. Nanoindentation test of the high-Vs series showed similar hardness for TiN/NbN nanostructured multilayers and homogeneous films in the range of 32–34 GPa. For the low-Vs series, mixed-phase hexagonal β-Nb2N/cubic δ-NbN films exhibited the highest hardness of 39 GPa, TiN had the lowest hardness with 26 GPa, and TiN/NbN multilayers had values in between. The absence of superlattice hardening in the polycrystalline TiN/NbN nanostructured multilayer is suggested to be due to microcracking at grain boundaries under the indentor tip. For both series, σres was lower for the multilayers than the corresponding homogeneous films. The low-Vs multilayers exhibited σres⩽1.6 GPa for Λ⩽16.6 nm, more than a factor of 2 smaller than for homogeneous TiN, NbN, and TiNbN-alloy films. High-Vs multilayers had σres∼4 GPa. The abrasive wear resistance of films between sample series showed a negative correlation with grain size. Films of the high-Vs series exhibited higher wear resistance compared to the corresponding films of the low-Vs series. Wear constants of high-Vs β-Nb2N films and TiN/NbN multilayers were as low as 28 and 40 μm3 mm−1 N−1, respectively.

Monolithic and multilayer Cr/CrN, Cr/Cr2N, and Cr2N/CrN coatings on hard and soft substrates

Using controlled low-energy ion bombardment, CrN and Cr2N films were reactively sputtered from a Cr target in a mixed Ar-N2 discharge. Various Cr-N based coating architectures were developed in this work to provide better substrate accommodation than is currently available using monolithic CrN or Cr2N, as well as to build in “load support” for the hard surface layers on more compliant substrates. A series of monolithic and multilayer structures were deposited at low temperatures (<200 °C) to examine the advantages and disadvantages of various coating architectures and ion energies on three substrates: A2 tool steel, 52100 stainless steel, and 2024-aluminum. The optimal operating point for deposition of stoichiometric CrN and Cr2N coatings was determined from analysis of the target state, and supported by in situ ellipsometric measurement of the optical properties of the films during growth. Films were characterized using X-ray, scanning electron microscopy and Rutherford backscattering spectroscopy. Their properties have been evaluated by microhardness, scratch adhesion, and pin-on-disk wear testing. Many of the multilayer coatings gave microhardness values in excess of 2000 HK, often having better adhesion than the single layer films. This was reflected in the wear performance of these films on both A2 and 2024-Al, where no measurable wear was observed in severe dry sliding wear over sliding distances of more than 9000 m against a WC ball. Thus, wear-resistant Cr-N film architectures can be used on some temperature- sensitive and/or compliant substrates to significantly enhance their surface properties.

Emission spectroscopy detection of N2 active species in plasma nitriding process

The present paper is a review of recent works related to the optical emission spectroscopy applied to the determination of ground state densities of N atoms in Ar-N2 flowing post-discharges. The effect of small quantities of H2 in the Ar-N2 discharge on N atom densities within the post-discharge has been analysed. The authors demonstrate that optical emission of Na impurity may be applied to the determination of the vibrational temperature of N2(X,v) states at the temperatures usual for nitriding of metals in Ar-N2 post-discharge. From the diagnostic of Ar-N2 post-discharges, it is clearly specified that nitriding of iron base alloys in a flowing post-discharge reactor is originating in N atoms, especially when a few H2 molecules are admixed into the Ar-N2 discharge. Finally, correlation between the N-atom density and the thickness of the iron nitrided layers when H2 is introduced into the Ar-N2 discharge are given.

Effect of negative bias voltage on the microstructures of AlN thin films fabricated by reactive r.f. magnetron sputtering

Aluminium nitride thin films have been fabricated on silicon wafers by reactive r.f. magnetron sputtering in mixed Ar-N2 discharge with variation of negative bias voltage. The effect of negative bias voltage on the microstructures of AlN thin films have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), stress measurement, Auger electron spectroscopy (AES), etc. While the negative bias voltage was varied in the range 0 to −45 V, highly c-axis oriented film can be fabricated at −30 V, and the grain size and compressive stress increase with the negative bias voltage. From the plasma analysis, the dominant positive chemical species is identified as N+2 ions. The above results can be understood considering that at the kinetic energy transfer and flux of N+2 ions increase with increasing negative bias voltage.

Low-temperature deposition of cubic BN:C films by unbalanced direct current magnetron sputtering of a B4C target

Controllable-unbalanced dc magnetron sputtering of a B4C target in mixed Ar–N2 discharges has been used to deposit BN:C thin films with carbon concentrations in the range of 5–21 at. % on Si(001) substrates. The variation of the nitrogen gas consumption with nitrogen partial pressure was used to determine the sorption capacity of the sputtering source and was then correlated to the film elemental composition. An additional axially symmetric magnetic field was used to vary the discharge plasma density near the substrate in a wide range. Hence, the ion flux Ji of primary Ar+ and N+2 ions accelerated to the substrate by an applied negative substrate bias could be varied while keeping the deposition flux Jn (the sum of film building species, B, C, and N atoms) near constant. BN:C films were grown at large ion-to-neutral flux ratios 3≤Ji/Jn≤24, ion energies Ei≤500 eV, and substrate temperatures 150≤Ts≤350 °C. The phase and elemental composition of as-deposited BN:C films were characterized by Fourier transform infrared spectroscopy and wavelength dispersive x-ray spectroscopy, respectively. Deposition of cubic phase c-BN:C containing 5–7 at. % of C is demonstrated under conditions of low energy (110 eV) ion bombardment, a high ion-to-atom arrival rate ratio (Ji/Jn∼24), and low growth temperatures (∼150 °C).

Influence of sputtering pressure on the microstructure evolution of AlN thin films prepared by reactive sputtering

Aluminum nitride (AlN) films have been deposited on Si (100) wafers by reactive r.f. magnetron sputtering in a mixed Ar-N2 discharge. It is important to control the preferred orientation and the texture morphology of the films with deposition parameters for the application of the surface acoustic-wave device. The change of preferred orientation and microstructure with sputtering pressure has been investigated using X-ray diffraction and transmission electron microscopy (TEM). It is found that highly c-axis oriented films are deposited at low pressures and the films with mixed (100) and (110) planes are deposited at high pressure. Through the cross-sectional TEM study, better aligned columns with smaller diameter are observed in the AlN films prepared at lower sputtering pressure. It is confirmed, by plan-view TEM micrographs, that an AlN film deposited at low pressure is composed of small and rounded grains, but the film prepared at high pressure is composed of elongated and open porous grains. The better microstructure of the AlN film prepared at low pressure must be attributed to the increased adatom mobility on the growing surface owing to the enhanced kinetic energy transfer and the longer mean free path of the gas molecule in the plasma. From the measurement of internal stress, it is found that the magnitude of compressive stress increases with the decrease of sputtering pressure mainly due to the enhanced kinetic energy transfer from the plasma to the film surface.

Influence of sputtering pressure on the microstructure evolution of AlN thin films prepared by reactive sputtering

Aluminum nitride (AlN) films have been deposited on Si (100) wafers by reactive r.f. magnetron sputtering in a mixed Ar-N2 discharge. It is important to control the preferred orientation and the texture morphology of the films with deposition parameters for the application of the surface acoustic-wave device. The change of preferred orientation and microstructure with sputtering pressure has been investigated using X-ray diffraction and transmission electron microscopy (TEM). It is found that highly c-axis oriented films are deposited at low pressures and the films with mixed (100) and (110) planes are deposited at high pressure. Through the cross-sectional TEM study, better aligned columns with smaller diameter are observed in the AlN films prepared at lower sputtering pressure. It is confirmed, by plan-view TEM micrographs, that an AlN film deposited at low pressure is composed of small and rounded grains, but the film prepared at high pressure is composed of elongated and open porous grains. The better microstructure of the AlN film prepared at low pressure must be attributed to the increased adatom mobility on the growing surface owing to the enhanced kinetic energy transfer and the longer mean free path of the gas molecule in the plasma. From the measurement of internal stress, it is found that the magnitude of compressive stress increases with the decrease of sputtering pressure mainly due to the enhanced kinetic energy transfer from the plasma to the film surface.

5294886 Antenna system for a magnetic resonance imaging tomography apparatus

310 stainless steel (SS)-nitrogen coatings with a nitrogen composition up to 40 at.% (14 wt.%) were deposited on steel substrates below 300 °C by d.c. reactive magnetron sputtering in mixed Ar-N2 discharges using amagnetic austenitic 310 SS targets. The chemical and structural characterization of the coatings is presented in relation to the deposition parameters, and some of their properties (internal stress, adhesion, microhardness etc.) are evaluated. The as-deposited coating structure is usually a metastable disordered supersaturated f.c.c. solid solution but, depending on the substrate temperature and nitrogen concentration, an amorphous-like structure is seen to occur.

Low-energy (∼100 eV) ion irradiation during growth of TiN deposited by reactive magnetron sputtering: Effects of ion flux on film microstructure

Cross-sectional transmission electron microscopy (XTEM) has been used to investigate the effects of variations in the low-energy ion irradiation flux during the growth of reactively sputter-deposited TiN. The films were deposited on steel substrates with a negative bias of 100 V at 350 °C in mixed Ar–N2 discharges at a pressure of 5 Pa (37 mTorr). The ion-to-Ti arrival rate ratio Jion /JTi at the substrate was varied between 0.3 and 7.1 through the use of a variable external magnetic field. Films grown with Jion /JTi ≲2 had a columnar morphology with a highly underdense microstructure. Increasing Jion /JTi ≳4 was sufficient to cause the growth of dense films with a more equiaxed grain structure due to renucleation. Further increases in Jion /JTi ≳7 resulted in increased TiN grain size and local heteroepitaxy between TiN and the martensitic phase of the substrate.

Resistivity changes and phase evolution in W-N films deposited in NeN2 and ArN2 discharges

Resistivity changes and phase evolution in W-N films deposited in NeN2 and ArN2 discharges

Resistivity changes and phase evolution in W–N films sputter deposited in Ne–N2 and Ar–N2 discharges

The effect of discharge N2 content and rare carrier gas type on the crystal structure and electrical resistivity of sputter deposited W–nitride films is reported here. A diode apparatus was used to sputter a W target in rf-excited Ne–N2 and Ar–N2 discharges spanning composition range from pure rare gas to pure N2. Postdeposition analysis included x-ray diffraction and four-point probe resistivity measurements. The results show that in Ar–N2 discharges, phase evolution proceeds with increasing discharge N2 content as follows: αW+βW→low-resistivity microcrystalline phase, a-W(N)→W2N1+x→high-resistivity phase, X.W–nitride. Ths use of Ne–N2 discharge accelerated the formation of the higher N content phases and suppressed the formation of a-W(N).