Reactive Gas Flow Ratio Research Articles

Characterization of cosputtered (TiZrHfY)Nx films

Medium-entropy TiZrHfY alloy films and corresponding nitride (TiZrHfY)Nx films were fabricated through cosputtering. The Ti0.24Zr0.23Hf0.27Y0.26 film had the form of a hexagonal close-packed (HCP) solid solution with a mixing enthalpy of 9.09 kJ/mol, mixing entropy of 11.50 J/mol·K (1.38 R), atomic size difference of 7.72 %, and valence electron concentration of 3.73. Moreover, this film had a hardness of 6.0 GPa and an elastic modulus of 106 GPa. (TiZrHfY)Nx films with various stoichiometric ratios (x) were fabricated by adjusting the reactive gas flow ratio fN2 [N2/(N2 + Ar)] in the range 0.1–0.7. Adding N to the TiZrHfY matrix resulted in a change of phase from an HCP structure to a face-centered cubic phase. The (Ti0.23Zr0.18Hf0.24Y0.35)N0.71 film (with fN2 = 0.2) exhibited the most favorable mechanical properties, having a hardness of 19.1 GPa and an elastic modulus of 244 GPa. Moreover, the film had the highest critical loads (LC3 = 46.6 N) among the films analyzed in the scratch test. The anticorrosive properties of the TiZrHfY and (TiZrHfY)Nx films were evaluated using potentiodynamic polarization curves, obtained in 3.5 wt% NaCl aqueous solution. High polarization resistance of 1.1 × 106 Ω·cm2 was obtained for the (Ti0.23Zr0.18Hf0.24Y0.35)N0.71 film, which was 145 times higher than that of the bare SUS420 substrate. The (Ti0.23Zr0.18Hf0.24Y0.35)N0.71 film had the most favorable mechanical and anticorrosive properties of the surveyed (TiZrHfY)Nx films.

Revisitation of reactive direct current magnetron sputtering discharge: Investigation of Mg–CF4, Mg–O2, and Ti–O2 discharges by probe measurements

The reactive direct current (DC) magnetron sputtering discharges of Mg–CF4, Mg–O2, and Ti–O2 were investigated using probe measurements as a function of reactive gas flow ratio. The emission spectroscopy, which was conducted before the probe measurements, demonstrates that all the three DC discharges transit from nonreactive to reactive discharge mode with increasing reactive gas flow ratio. The probe measurements show that the plasma potentials of the Mg–O2 and Ti–O2 DC discharges slightly increase or remain almost constant with increasing reactive gas flow ratio, whereas that of the Mg–CF4 DC discharge drastically decreases at the mode transition. For the same change in reactive gas flow ratio, the discharge voltage of the Mg–CF4 DC discharge slightly increases and that of the Mg–O2 DC discharge drastically increases at the mode transition, whereas that of the Ti–O2 DC discharge slightly decreases at the mode transition. The changes in the cathode sheath potential difference at the mode transition differ between the Mg–CF4 and Ti–O2 DC discharges and the Mg–O2 DC discharge because of the difference in the probability of secondary electron emission at the cathode surface; furthermore, the changes in the anode sheath potential difference at the mode transition differ between the Mg–CF4 DC discharge and the Mg–O2 and Ti–O2 DC discharges because of the difference in the probability of negative-ion formation in the plasma bulk. The most informative results obtained in this study were the differences in the potential differences at the cathode and anode sheaths among the Mg–CF4, Mg–O2, and Ti–O2 DC discharges. They well demonstrated the effects of the change in secondary-emitted species at the cathode surface and the change in reactive gas concentration in the plasma on the potential configuration.

Effects of the Nitrogen Flow Ratio and Substrate Bias on the Mechanical Properties of W–N and W–Si–N Films

The reactive gas flow ratio and substrate bias voltage are crucial sputtering parameters for fabricating transition metal nitride films. In this study, W–N films were prepared using sputtering with nitrogen flow ratios (f) of 0.1–0.5. W–N and W–Si–N films were then prepared using an f level of 0.4 and substrate bias varying from 0 to −150 V by using sputtering and co-sputtering, respectively. The variations in phase structures, bonding characteristics, mechanical properties, and wear resistance of the W–N and W–Si–N films were investigated. The W–N films prepared with nitrogen flow ratios of 0.1–0.2, 0.3, and 0.4–0.5 displayed crystalline W, amorphous W–N, and crystalline W2N, respectively. The W–N films prepared using a nitrogen flow ratio of 0.4 and substrate bias voltages of −50 and −100 V exhibited favorable mechanical properties and high wear resistance. The mechanical properties of the amorphous W–Si–N films were not related to the magnitude of the substrate bias.

Manipulation of nanostructured carbon films as field emitters in an electric-and-magnetic-field-assisted chemical vapor deposition process

To enhance the field emission performance and understand the emission essence of carbon materials, carbon films with different morphology and phase composition were fabricated by regulating the reactive gas flow ratio in a hot filament chemical vapor deposition system with the assistance of electric field and magnetic field. The characterization of carbon film quality and measurement of their field emission performance indicated that carbon nanostructures, including nanoclusters, nanopillars and nanotips, which were determined by the methane concentration in the process, were formed under the assistance of electric field. Further magnetic field assistance could lead to the formation of finer nanostructures with higher crystallinity. Field emission performance was highly dependent on the morphology and phase composition of the carbon films. Among all the samples, carbon nanotips, deposited in high methane concentration with the co-assistance of magnetic and electric field, possessed the best field emission performance, with the lowest turn-on field of 6.5 V·μm−1 (J = 10 μA·cm−2). Besides, a comparative study on the fitting degree of several conduction mechanisms revealed that the essence of field emission was the combination of several emission mechanisms, which was also dependent on the morphology and phase composition of these carbon films.

Inductively-coupled plasma-enhanced chemical vapour deposition of hydrogenated amorphous silicon carbide thin films for MEMS

In this study, the impact of various deposition parameters such as the reactive gas flow ratio, plasma power, substrate temperature and chamber back pressure of ICP-CVD deposited a-SiC:H thin films is investigated and the influence on important MEMS-related properties like residual stress, Young’s modulus, hardness, mass density and refractive index is evaluated. Basically, tailoring of the as-deposited a-SiC:H characteristics is possible to a great extent with residual stress values ranging from −16 up to −808MPa, Young’s modulus values between 36 and 209GPa or deposition of layers with hardness values ranging from 5.3 to 27.2GPa is feasible. Especially the mechanical parameters are strongly linked to both the SiC bond density and the amount of incorporated hydrogen obtained from Fourier transform infrared spectroscopy analyses.

Spectroscopic Ellipsometry Studies of n-i-p Hydrogenated Amorphous Silicon Based Photovoltaic Devices.

Optimization of thin film photovoltaics (PV) relies on characterizing the optoelectronic and structural properties of each layer and correlating these properties with device performance. Growth evolution diagrams have been used to guide production of materials with good optoelectronic properties in the full hydrogenated amorphous silicon (a-Si:H) PV device configuration. The nucleation and evolution of crystallites forming from the amorphous phase were studied using in situ near-infrared to ultraviolet spectroscopic ellipsometry during growth of films prepared as a function of hydrogen to reactive gas flow ratio R = [H2]/[SiH4]. In conjunction with higher photon energy measurements, the presence and relative absorption strength of silicon-hydrogen infrared modes were measured by infrared extended ellipsometry measurements to gain insight into chemical bonding. Structural and optical models have been developed for the back reflector (BR) structure consisting of sputtered undoped zinc oxide (ZnO) on top of silver (Ag) coated glass substrates. Characterization of the free-carrier absorption properties in Ag and the ZnO + Ag interface as well as phonon modes in ZnO were also studied by spectroscopic ellipsometry. Measurements ranging from 0.04 to 5 eV were used to extract layer thicknesses, composition, and optical response in the form of complex dielectric function spectra (ε = ε1 + iε2) for Ag, ZnO, the ZnO + Ag interface, and undoped a-Si:H layer in a substrate n-i-p a-Si:H based PV device structure.

Phase formation and microstructure evolution of reactively r.f. magnetron sputtered Cr–Zr oxynitride thin films

Thin films in the system Cr–Zr–O–N were deposited by reactive r.f. magnetron sputtering at a substrate temperature of 500°C in various argon–oxygen–nitrogen plasmas. The depositions were realized by an experimental combinatorial approach: five substrates were placed linearly in front of a circular segmented target consisting of a metallic Cr and Zr half plate. Consequently, the coated samples exhibit different elemental compositions (with respect to their position in relation to the target half plates, i.e. from Cr-rich to Zr-rich) and constitutions. Additionally to the impact of the Cr/Zr concentration ratio (mainly determined by the sample position in relation to the target) the influence of reactive gases, i.e. oxygen and nitrogen, on phase formation, microstructure evolution, hardness and Young's modulus was investigated. For this purpose, the O2 and N2 gas flows were varied systematically, while the total gas pressure was kept constant for all depositions. The coatings were characterized by electron probe micro analysis (EPMA), X-ray diffraction (XRD) and microindentation. In dependence of the sample position and the reactive gas flow ratio coatings with various phases were grown: i) coatings with a high Cr/(Cr+Zr) concentration ratio (i.e. grown at the Cr-rich side of the target) exhibited a single-phase solid solution corundum structure with up to 1.9at.% nitrogen incorporation, (Cr,Zr)2(O,N)3. ii) coatings with similar Cr and Zr concentration (i.e. grown at the center positions of the target) exhibited a single-phase solid solution cubic ZrO2 structure with approximately 2at.% nitrogen incorporation, c-(Zr,Cr)(O,N)2. iii) coatings with a higher Zr concentration (i.e. grown at the Zr-rich side of the target) grew in mixed-phase monoclinic and tetragonal structure, incorporating up to 2.3at.% nitrogen, m+t-(Zr,Cr)(O,N)2.These coating structures developed over a wide range of oxygen and nitrogen gas flow settings and substrate positions. It indicates that oxygen determines the microstructure evolution under the chosen experimental conditions, and only little nitrogen contents can be incorporated into these oxide structures. For high nitrogen gas flows (i.e. N2/(N2+O2)>0.75) this situation changed significantly, and only coatings with face-centered-cubic CrN structures were grown. These contained up to 11.4at.% oxygen and were clearly understoichiometric in the non-metal sites. All deposited coatings exhibited hardness values between 15GPa and 27GPa, indicating their suitability as protective coatings.

Effect of reactive gases flow ratios on the microstructure and electrical resistivity of Ta–N–O thin films by reactive co-sputtering

A combination of the beneficial properties of tantalum oxide and tantalum nitride may result in a new and functional tantalum oxynitride (Ta–O–N). In this paper, Ta–O–N thin films were fabricated by using reactive magnetron sputtering at different reactive gas ratios. The ratio of reactive gases to total flow gases was controlled from 6% to 30%. The microstructure, composition, chemical bonding, morphology and resistivity of the Ta–O–N thin films were characterized. Increasing reactive gas flow ratio will result in the increase of the O/(O + N) ratio in Ta–O–N from 0.22 to 0.79. All films were quasi-amorphous structures in this study. The higher reactive gas flow ratio led to more disorder or amorphous microstructure with a broader diffraction peak. The position of the highest intensity peak about 36° shifts downward with increasing O/(O + N) ratio because of the sufficient Ta–O phase formation. The FTIR absorption bands at 500–800 cm − 1 corresponding to Ta–O–Ta and Ta–O stretching vibration modes were observed . A weak absorption band at 800–1000 cm − 1 was the tantalum suboxides. The resistivity increased from 288 μΩcm (conducting) to 11,540 Ωcm (semiconducting–insulating) with increasing O/(O + N) ratio. The oxygen content dominates the microstructure formation and resistivity of the Ta–O–N system compared to nitrogen.

Microstructure, stress and mechanical properties of arc-evaporated Cr–C–N coatings

The relationships between coating microstructure and properties in the Cr–C–N system have been investigated as a function of composition and post-deposition annealing. Coatings of varying compositions were grown using arc-evaporation, by varying the reactive gas flow ratio fR=f(C2H4)/f(N2) from 0 to 0.2, and were found to consist primarily of the cubic δ-Cr(C,N) phase. Changes in both the unstressed lattice parameter, ao, and X-ray diffraction background intensity indicate that both the carbon concentration within the δ-phase and amorphous/crystalline content increases with fR. Increasing fR also decreases the magnitude of the compressive biaxial residual stress, from approximately 6 to 1 GPa, while increasing both the inhomogeneous stress and thermal stability. The elastic modulus and hardness of as-deposited coatings were determined from nanoindentation to be 320 and 23 GPa, respectively, for moderate carbon concentrations (fR≤0.05). Concurrent variations in microstructure and hardness with post-deposition annealing indicate that the as-deposited hardness is significantly enhanced by the microstructure, primarily by lattice defects and related stresses (microstresses) rather than average stresses (macrostresses).

Investigation of Si-doped diamond-like carbon films synthesized by plasma immersion ion processing

Silicon (Si)-doped diamond-like carbon (DLC) was prepared on Si(100) and polymethyl metha_crylate (PMMA) substrates using a C2H2–SiH4–Ar plasma immersion ion processing (PIIP) method. The chemical composition of the films was varied by adjusting the reactive gas-flow ratio of SiH4 to C2H2 during PIIP depositions. The influence of the Si dopant on the bonding structure, stress, and properties of the DLC films was investigated by using ion beam analysis techniques, Raman shift, ultraviolet/visible spectroscopy, and by analyzing the measured properties. The incorporation of Si up to 17.3 at. % produced a reduction in film stress and increased the density and optical band gap. The Si-doped DLC films also exhibited increased sp3 bonding and higher hardness (25–28 GPa). Further increase in Si dopant, to above 22 at. %, caused a transformation from DLC to amorphous silicon carbide (a-SiC) that showed high hydrogen capacity, low hardness, and low stress. Pin-on-disk tribological tests of Si-doped DLC on PMMA showed greatly improved wear and friction properties related to the uncoated PMMA.

Different pulse techniques for stationary reactive sputtering with double ring magnetron

Abstract Double Ring Magnetron (DRM) sources are suitable for stationary uniform coating of large substrates with metals, alloys and insulating layers. DRM sources are characterized by two concentric discharges on electrically insulated targets. Therefore, different pulse techniques in the frequency range between 10 and 100 kHz can be applied: (i) a voltage with alternating polarity between the inner and outer target (bipolar mode); (ii) a pulsed d.c. voltage for both of the targets (unipolar mode). Process parameters like energetic ion flux towards the substrate and thermal load as well as layer properties like mechanical stress and hardness are influenced by the pulse technique and the pulse parameters. Pulsed reactive sputtering allows a high rate deposition even of insulating compounds. Furthermore, unique materials such as compounds with multiple gas constituents (e.g. ternary compounds) or layers with changing composition (gradient layers) can be deposited. It will be shown that by adjusting the reactive gas flow ratio of oxygen and nitrogen, oxynitride layers with a defined composition and refractive index can be deposited. Gradient layers have been produced by changing the reactive gas flow ratio during deposition, including the appropriate adaptations of the reactive working point.

Selective deposition of tungsten by chemical vapour deposition from SiH 4 reduction of WF 6

Tungsten films were deposited on tungsten-patterned wafers by the selective chemical vapour deposition (CVD) process from SiH 4-reduction of WF 6 in a cold-wall reduced pressure CVD reactor. The experimental conditions such as reactive gas flow ratio, temperature, total pressure etc. providing good selective deposition were investigated (in terms of voids and homogeneity of the coatings in each plug) and particularly the pretreatment of wafers by different sorts of plasma. The tungsten deposition rate and dependence of the selectivity loss on the SiO 2 film were checked using a scanning electron microscopy technique, vs. the different parameters. These results show the importance of the plasma pretreatment and of the first reactive gas introduced for the selectivity. A temperature window for optimum selectivity was established and an apparent activation energy was measured. From all these results, an interesting correlation could be made between the selectivity loss and the rate-controlling mechanism. Finally the flexibility of this process is demonstrated by the feasibility of selective tungsten deposition on aluminium-patterned wafers. The conditions for tungsten and for aluminium are very different; in particular, the electrical results obtained on aluminium show a high sensitivity to the pretreatment carried out before deposition.

Tin, Tic and Ti(C, N) film characterization and its relationship to tribological behaviour

AbstractScanning electron microscopy observations, energy dispersive spectroscopy, x‐ray diffraction and x‐ray photoelectron spectroscopy analyses have been employed to study the composition and the microstructure of titanium carbonitride coatings deposited by a reactive ion‐plating industrial system. Both TiN and Ti(C, N) coatings show a very fine and dense microstructure and consist of a NaCl‐type single phase with a marked preferred orientation. X‐ray photoelectron spectroscopy analysis of the characteristic Ti, C and N lines establishes the extent of Ti(C, N) compound formation and the dependence of composition on the reactive gas flow ratio. Depth profiles obtained by XPS analyses after cycles of Ar+ sputtering indicate chemical uniformity of the films. Microhardness measurements taken on coated HSS specimens show that Ti(C, N) are significantly harder than TiN and TiC films deposited under the same conditions. Ti(C, N) coatings have a lower coefficient of friction and a higher wear resistance than TiN coatings, irrespective of the mating material.