Influence of N2 flow rate on the mechanical properties of SiNx films deposited by microwave electron cyclotron resonance magnetron sputtering

Hydrogen-free amorphous silicon nitride (SiN_x) films were deposited at room temperature by microwave electron cyclotron resonance plasma-enhanced unbalance magnetron sputtering. Varying the N₂ flow rate, SiN_x films with different properties were obtained. Characterization by Fourier-transform infrared spectrometry revealed the presence of Si-N and Si-O bonds in the films. Growth rates from 1.0 to 4.8 nm/min were determined by surface profiler. Optical emission spectroscopy showed the N element in plasma mainly existed as N⁺ species and N₂⁺ species with 2 and 20 sccm N₂ flow rate, respectively. With these results, the chemical composition and the mechanical properties of SiN_x films strongly depended on the state of N element in plasma, which in turn was controlled by N₂ flow rate. Finally, the film deposited with 2 sccm N₂ flow rate showed no visible marks after immersed in etchant [6.7% Ce(NH₄)₂(NO₃)₆ and 93.3% H₂O by weight] for 22 h and wear test for 20 min, respectively.     

Hard BCxNy thin films grown by dual ion beam sputtering

Boron carbonitride thin films were deposited by sputtering of a B₄C target with Ar-N₂ ion assistance. BC_xN_y films were grown onto Si (001) at room temperature. The chemical composition and the type of bonding were determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The hardness of the films was measured with a nanoindenter. The chemical analysis of the samples indicates the formation of two different compounds, a ternary BC_xN_y and a binary carbonitride CN_x. All the films showed high hardness, in the range 16-33 GPa, which clearly increases as the BC_xN_y content in the sample increases. In this study the highest hardness (i.e. 33 GPa) was obtained when the BC_xN_y content in the sample was 50%. The average composition of this BC_xN_y was estimated by XPS as 20 at.% carbon and 12 at.% nitrogen.     

Time and energy resolved ion mass spectroscopy studies of the ion flux during high power pulsed magnetron sputtering of Cr in Ar and Ar/N2 atmospheres

Mass spectroscopy was used to analyze the energy and composition of the ion flux during high power pulsed magnetron sputtering (HIPIMS/HPPMS) of a Cr target in an industrial deposition system. The ion energy distribution functions were recorded in the time-averaged and time-resolved mode for Ar⁺, Ar²⁺, Cr⁺, Cr²⁺, N₂⁺ and N⁺ ions. In the metallic mode the dependence on pulse energy (equivalent of peak target current) was studied. In the case of reactive sputtering in an Ar/N₂ atmosphere, variations in ion flux composition were investigated for varying N₂-to-Ar flow ratio at constant pressure and HIPIMS power settings. The number of doubly charged Cr ions is found to increase linearly with increasing pulse energy. An intense flux of energetic N⁺ ions was observed during deposition in the reactive mode. The time evolution of ion flux composition is analyzed in detail and related to the film growth process. The ionization of working gas mixture is hampered during the most energetic phase of discharge by a high flux of sputter-ejected species entering the plasma, causing both gas rarefaction and quenching of the electron energy distribution function. It is suggested that the properties (composition and energy) of the ion flux incident on the substrate can be intentionally adjusted not only by varying the pulse energy (discharge peak current), but also by taking advantage of the observed time variations in the composition of ion flux.     

Synthesis and tribological properties of WSex films prepared by magnetron sputtering

WSe_x films with variable Se/W ratio were deposited by non-reactive r.f. magnetron sputtering from WSe₂ target changing the applied d.c. pulsed bias conditions and substrate temperature. The structural and chemical properties were measured by cross-sectional scanning electron microscopy (X-SEM), energy dispersive analysis (EDX), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The tribological properties were measured in ambient air (RH = 30–40%) and dry nitrogen by means of a reciprocating ball-on-disk tribometer. A clear correlation was found between the Se/W ratio and the measured friction coefficient displaying values below 0.1 (in ambient air) and 0.03 (in dry N₂) for ratios Se/W ≥ 0.6 as determined by electron probe microanalysis (EPMA). The results demonstrated that notable tribological results could be obtained even in ambient air (friction ≤ 0.07 and wear rate ≈10⁻⁷ mm³ Nm⁻¹) by controlling the film microstructure and chemical composition. By incorporating carbon, wear and chemical resistance can be gained by formation of non-stoichiometric carbides and/or alloying into the defective WSe_x hexagonal structure. The existence of a WSe₂ rich interfacial layer (either on the ball scar or embedded in the film track) was evidenced by Raman in low friction conditions. The improvement in tribological performance is therefore obtained by means of layered WSe_x, the formation of gradient composition from metallic W (hard) to WSe₂ (lubricant) and carbon incorporation.     

Optical and electrical properties of 2 wt.% Al2O3-doped ZnO films and characteristics of Al-doped ZnO thin-film transistors with ultra-thin gate insulators

Al-doped ZnO (AZO) thin films have been prepared on the c-Si oriented direction of (100) and glass substrates, by radio frequency magnetron sputtering from ZnO-2 wt.% Al₂O₃ ceramic targets. The effects of the working pressure on the optical and electrical properties of the films have been studied. The optical properties, measured by the ultraviolet-visible system, show that the transmittance and optical bandgap energy are influenced by the working pressure. The Hall resistivity, mobility, and carrier concentration were obtained by a Hall measurement system and these parameters were also influenced by the working pressure. The AZO thin-film transistors (TFTs) were fabricated on highly doped c-Si substrates. The TFT structures were made up AZO as the active layer and SiO_xN_y/SiN_x/SiO_x as the gate layer with 20 nm and 35 nm thickness, respectively. The ultra-thin TFTs had an on/off current ratio of 10⁴ and a field-effect mobility of 0.17 cm²/V·s. These results show that it is possible to fabricate an AZO TFT that can be operated with an ultra-thin gate dielectric.     

Effects of methane flow rate on the optical properties and chemical bonding of germanium carbon films deposited by reactive sputtering

Amorphous hydrogenated germanium carbon (a-Ge_1−xC_x:H) films were prepared by radio frequency (RF) reactive magnetron sputtering of a pure Ge (111) target in a CH₄ + H₂+Ar mixture and their composition, optical properties, chemical bonding were investigated as a function of gas flow rate ratio of CH₄/(Ar + H₂). The results showed that the deposition rate first increased and then decreased as gas flow rate ratio of CH₄/(Ar + H₂) was increased from 0.125 to 0.625. And the optical gap of the a-Ge_1−xC_x:H films increased from 1.1 to 1.58 eV accompanied with the increase in the carbon content and the decrease in the relative content of Ge–C bonds of the films as the CH₄ flow rate ratio was increased, while refractive index of the films decreased and the absorption edge shifted to high energy. Through the analysis of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, it was found that the formation of Ge–C bonds in the films was promoted by low CH₄ flow rate which is connected with relatively high H₂ concentration and Ge content. Especially in low CH₄ concentration, the formation of sp²-hybridised C–C bonds was suppressed considerably both due to the etching effect on weak bonds of H and the fact that chemical bonding for germanium can be only sp³ hybridization.     

Effect of the oxygen fraction on the structure and optical properties of HfOxNy thin films

The main purpose of this work was to prepare hafnium oxynitride (HfO_xN_y) thin films. HfO_xN_y thin films were deposited by radio frequency reactive magnetron sputtering from a pure Hf target onto Quartz and ZnS substrates at room temperature. The depositions were carried out under an oxygen-nitrogen-argon atmosphere by varying the flow rate of the reactive gases (oxygen/nitrogen ratio). The variation of the flow rate of the reactive gases changed the structure and properties of the films. Glancing incidence X-ray diffraction (GIXRD) was used to study the structural changes of as-deposited films; a new crystalline hafnium oxynitride phase was formed in a region of oxygen/nitrogen ratio. Cross-section of the films observed by SEM revealed that the films grew with a columnar-type structure, and surface observation with AFM showed values of surface roughness changed with the flow rate of the reactive gases, higher oxygen fraction had lower surface roughness than lower oxygen fraction. Visible spectra, infrared spectra, refractive index, absorption coefficient also changed with the variation of the oxygen fraction.     

Reactively sputtered GaAsxN1−x thin films

Thin films of GaAs_xN_1−x alloys were deposited by reactive rf magnetron sputtering of GaAs target with a mixture of argon and nitrogen as the sputtering gas. Growth rate was found to decrease from ∼ 7 μm/h to ∼ 2 μm/h as the nitrogen content increased from 0% to 40%. XRD and TEM studies of the films reveal the presence of hexagonal GaN with a significant increase of the lattice parameters in a narrow range of composition of the sputtering gas (5-10% nitrogen), which is attributed to the incorporation of arsenic. The limited availability of nitrogen in the sputtering atmosphere is found to encourage the incorporation of arsenic in the alloy films. Optical absorption coefficient spectra of the films were obtained from reflection and transmission data. The effect of arsenic incorporation is seen in the optical absorption spectra of the films, which show a continuous shift of the absorption edge to lower energies with respect to that of gallium nitride.     

Mechanisms of reactive sputtering of indium I: Growth of InN in mixed Ar-N2 discharges

Optical absorption and emission spectroscopies were used for in situ investigations of process occuring in the plasma and at the electrode-gas interfaces which control the reactive sputter etching of indium targets and the reactive deposition of InN films in mixed Ar-N₂ glow discharges. The sputtering parameters used were a d.c. target voltage of -2.5 kV, a total sputtering pressure P of 30–70 m Torr (4–9.3 Pa), N₂ mol.% C_N2 values of 0–100 and a target-to-substrate separation d of 3–6 cm. Under these conditions no indication of complete nitride formation at the target surface or of sputter ejection of InN molecular species was obtained. Increasing C_N2 at a constant value of P caused a decrease of the target sputtering rate R. This decrease was due primarily to a decrease in the ion current i_T, which was caused by thermalization of low energy electrons in the plasma through excitation of vibrational modes in molecular N₂. Atomic absorption provided a real-time monitor of R over the entire range of sputtering parameters. The optical emission intensity from sputtered indium atoms in the cathode glow was found to increase with C_N2 (even though R decreased) because of enhanced excitation through collisions with N₂ metastable species.The nitrogen concentration in the deposited films, as determined by X-ray photoelectron spectroscopy and X-ray diffraction, was found to depend strongly on C_N2, P_N2 and d. The dependence on d was caused by the position of the growing film surface with respect to the negative glow region where most of the atomic nitrogen was formed through the reaction N₂⁺ + N₂ → N₂ + N⁺ + N In discharges with short mean free paths this is the primary mechanism of nitrogen incorporation since indium does not chemisorb N₂, only atomic nitrogen. InN films grown on glass substrates at about 80°C were found to be polycrystalline n-type semiconductors with a room temperature resistivity of 40 mΩ cm, a carrier concentration of about 5×10¹⁸ cm^-3 and an electron mobility of approximately 20 cm² V^-1 s^-1. The refractive index at a wavelength of 1 μm and the room temperature direct band gap were found to be 2.85 and 1.7 eV respectively.     

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.     

Thin film encapsulation of DSSCs on plastic substrate

Aluminum oxynitride (AlO_xN_y) films were deposited on polyethylene naphthalate (PEN) substrates using a reactive radio frequency (RF) magnetron sputtering system by varying the nitrogen flow rate. Experimental results show that the AlO_xN_y films deposited on PEN substrate exhibit a pebble-like surface morphology. The deposition rate decreases slightly upon increasing the nitrogen flow rate. The surface roughness of the deposited AlO_xN_y films also decreases upon increasing the nitrogen flow rate. The AlO_xN_y film deposited at a nitrogen flow rate of 15 sccm exhibited the lowest water vapor transmission rate of 0.02 g/m²·day. Meanwhile, the passivation of AlO_xN_y films can effectively improve the long-term stability of plastic DSSC. Their power conversion efficiency can sustain 50% of the initial values even after 300 h.     

Synthesis of Al-Cr-O-N thin films in corundum and f.c.c. structure by reactive r.f. magnetron sputtering

Advanced PVD coatings for metal cutting applications must exhibit a multifunctional property profile including high hardness, chemical inertness and high temperature stability. Recently, ternary Al-Cr-O thin films with mechanical properties similar or superior to conventional aluminium oxide thin films have been suggested as potential materials meeting such demands. These coatings can be deposited at moderate temperatures in PVD processes. In this work, new quaternary Al-Cr-O-N coatings are suggested as alternative for offering thin film materials of high strength, hardness and even toughness. A combinatorial approach to the synthesis of Al-Cr-O-N thin films by means of reactive r.f. magnetron sputtering is presented. A thorough phase analysis of deposited coatings covering a wide range of elemental compositions revealed a well-defined phase transition from a corundum-type α-(Al_1 − x,Cr_x)_2 + δ(O_1 − y,N_y)₃ structure to a CrN-type f.c.c.-(Al_1 − x,Cr_x)_1 + θ(O_1 − y,N_y) structure as a function of the Al/Cr ratio and the nitrogen gas flow ratio. Detailed results on the coatings composition, constitution and microstructure are discussed compared to ternary Al-Cr-O thin films deposited by reactive r.f. magnetron sputtering under nearly identical conditions.     

Photoelectrochemical and optical properties of N-doped TiO2 thin films prepared by oxidation of sputtered TiNx films

Nitrogen-doped titanium dioxide thin films with visible light photoresponse were prepared by oxidation of sputtered TiN_x films, whose nitrogen contents can be easily changed by controlling the volume ratio of N₂/(Ar + N₂) during reactive direct current (DC) magnetron sputtering process. The reference TiO₂ sample was also deposited by the same method under Ar/O₂ gas mixture. The as-prepared films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoemission spectroscopy, UV-vis spectrophotometry and photoelecrochemical measurements. The formation of anatase type TiO₂ is confirmed by XRD. SEM measurement indicates a rough surface morphology with sharp, protruding modules after annealing treatment. Optical properties reveal an extended tailing of the absorption edge toward the visible region due to nitrogen presence. The band gap of the N-doped sample is reduced from 3.36 eV to 3.12 eV compared with the undoped one. All the N-doped samples show red shift in photoresponse towards visible region and improved photocurrent density under visible irradiance is observed for the N-doped samples.     

Structural and magnetic properties of Co-N thin films synthesized by direct current magnetron sputtering

Influence of nitrogen fractions [N_f = N₂/(N₂ + Ar)] and sputtering powers (P_s) on the structural and magnetic properties of Co-N thin films synthesized by direct current magnetron sputtering have been studied. With increasing N_f from 0 to 20%, a series of phases from β-Co, β-Co (N), Co₄N to Co₃N were obtained. However, when N_f was fixed at 10%, only Co₄N phase with different Co contents in the films was prepared, whose values of saturation magnetism (M_s) increased from 12.9 ± 8.2 Am²/kg to 103.9 ± 6.1 Am²/kg with the increase of P_s. Interstitial nitrogen caused the decrease of coercivity from 24.12 kAm^− 1 (for β-Co film) to 2.71 kAm^− 1. However, the addition of interstitial nitrogen was not observed to increase the M_s of β-Co.     

Nitrogen doping of SiC thin films deposited by RF magnetron sputtering

Silicon carbide thin films (Si _x C _y ) were deposited in a RF (13.56 MHz) magnetron sputtering system using a sintered SiC target (99.5% purity). In situ doping was achieved by introducing nitrogen into the electric discharge during the growth process of the films. The N₂/Ar flow ratio was adjusted by varying the N₂ flow rate and maintaining constant the Ar flow rate. The structure, composition and bonds formed in the nitrogen-doped Si _x C _y thin films were investigated by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), Raman spectroscopy and Fourier transform infrared spectrometry (FTIR) techniques. RBS results indicate that the carbon content in the film decreases as the N₂/Ar flow ratio increases. Raman spectra clearly reveal that the deposited nitrogen-doped SiC films are amorphous and exhibited C–C bonds corresponding to D and G bands. After thermal annealing, the films present structural modifications that were identified by XRD, Raman and FTIR analyses.     

Reactively sputtered N-doped titanium oxide films as visible-light photocatalyst

Nitrogen-doped titanium oxide (TiO_xN_y) films were prepared by reactive magnetron sputtering of a titanium metal target in gas mixtures of argon, oxygen and nitrogen. Two types of nitrogen species are formed in the films following the fraction of N₂ (F_N2) in the reactive atmosphere. One is substitutional nitrogen in anatase titania phase and the other is nitrogen in TiN phase. In a large range of F_N2 from 0 to 0.57, TiO_xN_y films in anatase structure with about 1.0–1.4 at.% substitutional nitrogen are produced and the films exhibit red shifts to ∼ 500 nm from the absorption edge of ∼ 380 nm of undoped TiO₂. The nitrogen is readily doped in the films by energetic nitrogen ions in the plasma and the films exhibited photocatalytic properties under visible light. When excess nitrogen is supplied as the F_N2 above 0.75, the resulting film contains 20.8 at.% of nitrogen with formation of TiN that makes the film opaque and destroys the photocatalytic activity largely.     

Preparation of ZrNxOy films by magnetron sputtering using air as a reactive gas

Zirconium oxynitride (ZrN_xO_y) thin films were prepared by d.c. magnetron sputtering using air as a reactive gas. Replacing conventionally used N₂/O₂ with air as a reactive gas allows the process to perform at high base pressures (low vacuum), which could drastically reduce the processing time. The color of the obtained films changed from light golden and dark golden for low air/Ar flow ratios, to dark violet and bright cyan for high air/Ar ratios. X-ray diffraction patterns show that the films transformed from ZrN and Zr₂ON₂ mixed phases to a Zr₂ON₂ phase, and then an m-ZrO₂ phase. The thickness of the films decreased slightly with increasing the air/Ar flow ratio. ZrN_xO_y films possessed a mixture of Zr-N-O, Zr-N and Zr-O chemical binding states determined from X-ray photoelectron spectroscopy. ZrN_xO_y films with mainly a Zr₂ON₂ phase exhibited the band gap of 1.96-2.26 eV, while the m-ZrO₂ films with slight nitrogen incorporation had a band gap of 2.32 eV, evaluated from transmittance spectra. By varying the air/Ar ratio during deposition, the nitrogen/oxygen content of the films could be controlled and hence, the color, crystal structure, atomic composition, and band gap of the films could be tailored.     

Correlation between the composition, structure and properties of dual ion beam deposited SiNx films

Silicon nitride (SiN_x) films were prepared by dual ion beam deposition at room temperature. An assisted N₂⁺ ion beam (current I_b=0-45 mA) was directed to bombard the substrate surface to control the N content x, which saturated at x≈1.36 when I_b?25 mA. The presence of SiN bonds was indicated by the appearance of a Si 2p photoelectron peak at 101.9 eV and an infrared absorption peak at 850 cm⁻¹. As x increases from 0 to 1.36, the hardness, elastic modulus and compressive stress increase from 12.2 to 21.5 GPa, 191 to 256 GPa and 0.52 to 1.4 GPa and the friction coefficient against stainless steel ball decreases from 0.65 to 0.37. The optical band gap increases remarkably with a concomitant drop in electrical conductivity (σ_RT) by more than 10⁷ times. Ion bombardment induces defects and trap states in the mid-gap, such that the transport mechanism is dominated by hopping of charge carriers through the trap states. Consequently, the activation energy of electrical conductivity is much lower than the optical band gap.     

Effect of nitrogen flow ratio on structure and properties of zirconium nitride films on Si(100) prepared by ion beam sputtering

In this study, zirconium nitride thin films were deposited on Si substrates by ion beam sputtering (IBS). Influence of N₂/(N₂+Ar) on the structural and physical properties of the films has been investigated with respect to the atomic ratio between nitrogen and zirconium. It was found that the thickness of layers decreased by increasing the F(N₂). Moreover, crystalline plane peaks such as (111), (200) and (220) with (111) preferred orientation were observed due to strain energy which associate with (111) orientation in ZrN. Also, the fluctuation in nitrogen flow ratio results in colour and electrical resistivity of films.