Reactive pulse magnetron sputtered SiOxNy coatings on polymers

Amorphous SiO₂, Si₃N₄ and SiO_xN_y single layers have been deposited on silicon, glass and glycol modified polyethylene terephthalate substrates by reactive pulse magnetron sputtering. Apart from the expected correlation between refractive index, coating density and nitrogen content in the reactive gas mixture further results have been found regarding mechanical stress and the humidity barrier property of these thin films. The lowest compressive stress was observed in the coatings deposited with nitrogen contents of around 30% to 50% in the reactive gas mixture. The humidity barrier effect of the thin films already begins to increase significantly at low nitrogen contents of below 20% in the reactive gas. Additional investigations regarding chemical composition, coating adhesion and environmental stability complement this work with the main focus on optimizing these materials for optical multilayer systems on polymer substrates.     

Multilayer antireflective and protective coatings comprising amorphous diamond and amorphous hydrogenated germanium carbide for ZnS optical elements

To effectively protect and improve the transmittance of ZnS optical elements in the far infrared band, combined amorphous diamond (a-D) and amorphous hydrogenated germanium carbide (a-Ge_1−xC_x:H) films have been developed. The optical interference coatings were designed according to the layer optics theory. The a-D films, of which refractive index and film thickness were controlled by changing substrate bias and deposition time respectively, were deposited by filtered cathodic vacuum arc technology. The a-Ge_1−xC_x:H films were prepared by radio frequency sputtering technology. During this process their refractive index was modulated by changing the gas flow rate ratio and their film thickness was controlled by the flow rate ratio and deposition time. It has been shown that the combined films are superexcellent antireflective and protective coatings for ZnS optical elements.     

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.     

Influence of the target composition on reactively sputtered titanium oxide films

Titanium dioxide thin films have many interesting properties and are used in various applications. High refractive index of titania makes it attractive for the glass coating industry, where it is used in low-emissivity and antireflective coatings. Magnetron sputtering is the most common deposition technique for large area coatings and a high deposition rate is therefore of obvious interest. It has been shown previously that high rate can be achieved using substoichiometric targets. This work deals with reactive magnetron sputtering of titanium oxide films from TiO_x targets with different oxygen contents.The deposition rate and hysteresis behaviour are disclosed. Films were prepared at various oxygen flows and all films were deposited onto glass and silicon substrates with no external heating. The elemental compositions and structures of deposited films were evaluated by means of X-ray photoelectron spectroscopy, elastic recoil detection analysis and X-ray diffraction. All deposited films were X-ray amorphous. No significant effect of the target composition on the optical properties of coatings was observed. However, the residual atmosphere is shown to contribute to the oxidation of growing films.     

Chemical, optical, vibrational and luminescent properties of hydrogenated silicon-rich oxynitride films

X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Fourier transform infrared and room temperature photoluminescence spectroscopy has been used to investigate the chemical, optical, vibrational and luminescent properties of Plasma Enhanced Chemical Vapor Deposited SiO_xN_y/H (0.17≤x≤0.96; 0.07≤y≤0.27), hydrogenated silicon-rich oxynitride (SRON). The linear dependence of the refractive index of the SRON films on the O/Si ratio was established. The photoluminescence from the SRON films were attributed to the embedded amorphous silicon clusters in the films. The dependence of luminescence maximum values on the O/Si and O/N ratios has been explored. We postulate that at O/Si ratio of 0.18 and an O/N ratio of 2.0 (SiO_0.18N_0.09) the film underwent a transformation from silicon-rich oxynitride to a-Si/H film with oxygen and nitrogen impurities.     

Optical properties and structure of thin SiOx films

The optical properties of SiO_x films of variable composition obtained by reactive r.f. sputtering of silicon were investigated.The experimental results show that the films have a single-phase structure consisting of a continuous random network with a dominance of six-membered molecular rings of Si-(Si_yO_4-y tetrahedra, where 0⩽y⩽4, joined together by bridging oxygen atoms. The difference between the films investigated and those obtained by vacuum evaporation is determined by the dominance of four-membered rings in the evaporated films.Analysis of the IR spectra reveals that the shift in the absorption band with varying structure is connected with a variation in the central force constant.     

Protection of organic light-emitting diodes over 50 000 hours by Cat-CVD SiNx/SiOxNy stacked thin films

Silicon oxynitride (SiO_xN_y) films have been formed by adding proper amount of oxygen gas to usual forming condition of silicon nitride (SiN_x) films in catalytic chemical vapor deposition (Cat-CVD) method. The composition and refractive index of the film can be systematically controlled by changing oxygen flow rate. Organic light-emitting diodes (OLEDs) covered with SiN_x/SiO_xN_y stacked films have been completely protected from damage due to oxygen and moisture and their initial emission intensity is maintained over 1000 hours under 60 °C and 90% RH, which is equivalent to 50 000 hours in normal temperature and humidity conditions.     

Structure and tribological properties of reactively sputtered Zr-Si-N films

Zr-Si-N films were deposited on silicon and steel substrates by magnetron sputtering of a Zr-Si composite target in Ar-N₂ reactive mixtures. The silicon concentration in the films was adjusted in the 0-7.6 at.% range by varying the surface of Si chips located on the erosion zone of the target. The films were characterised by X-ray diffraction, electron probe microanalysis, atomic force microscopy and wear tests. The structure and the tribological properties of Zr-Si-N films were compared to those of ZrN coatings. Depending on the silicon concentration, the films were either nanocomposites (nc-ZrN/a-SiN_x) or amorphous. Introduction of silicon into the zirconium nitride coatings induced a change in the preferential orientation of the ZrN grains: [111] for ZrN films and [100] for Zr-Si-N ones. This texture modification was also observed for a ZrN film deposited on an amorphous SiN_x layer. Thus, within our deposition conditions, the occurrence of a-SiN_x enhanced the [100] preferred orientation. Friction and wear behaviour of the films were carried out against spheres of alumina or 100 Cr6 steel by using a ball-on-disc tribometer. The results showed that addition of silicon into ZrN-based coating induced a strong decrease in the friction coefficient and in the wear rate compared to those of ZrN films. These results were discussed as a function of the films structure and composition.     

Influence of deposition parameters on the optical and structural properties of TiO2 films produced by reactive d.c. plasmatron sputtering

We investigated the variations in the structure and optical properties of TiO₂ films produced by reactive d.c. plasmatron sputtering with the most important deposition parameters.Over a wide range, the phase composition (ratio of rutile to anatase) and the grain size of the TiO₂ films can be influenced in a controlled manner by variations in the substrate temperature and the oxygen partial pressure.Because of their high refractive index and low light-scattering losses, plasmatron-sputtered TiO₂ films are of great interest in the field of optical interference coatings, e.g. for dielectric multilayer stacks.     

Optische und mechanische Eigenschaften von RLVIP HfO2‐Schichten

Optical and mechanical properties of RLVIP HfO₂ films In this paper HfO₂‐films were deposited on unheated fused silica, borosilicate glass, and silicon wafer substrates by reactive low voltage ion plating (RLVIP). Optical film properties, i. e. refractive index and absorption as well as mechanical properties, particularly film stress, were investigated. Their dependence on deposition parameters, i. e. arc current and oxygen partial pressure was studied. The film refractive index was calculated from spectrophotometric measurements. The low absorption was determined by photothermal deflection spectrometry. Stress measurements were performed by bending disc method with uncoated and coated silicon wafer substrates.     

Absorbing TiOx thin film enabling laser welding of polyurethane membranes and polyamide fibers

We report on the optical properties of thin titanium suboxide (TiO_x) films for applications in laser transmission welding of polymers. Non-absorbing fibers were coated with TiO_x coatings by reactive magnetron sputtering. Plasma process parameters influencing the chemical composition and morphology of the deposited thin films were investigated in order to optimize their absorption properties. Optical absorption spectroscopy showed that the oxygen content of the TiO_x coatings is the main parameter influencing the optical absorbance. Overtreatment (high power plasma input) of the fiber surface leads to high surface roughness and loss of mechanical stability of the fiber. The study shows that thin substoichiometric TiO_x films enable the welding of very thin polyurethane membranes and polyamide fibers with improved adhesion properties.     

Substrate bias voltage influenced structural, electrical and optical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide (Ta₂O₅) films were formed on silicon (111) and quartz substrates by dc reactive magnetron sputtering of tantalum target in the presence of oxygen and argon gases mixture. The influence of substrate bias voltage on the chemical binding configuration, structural, electrical and optical properties was investigated. The unbiased films were amorphous in nature. As the substrate bias voltage increased to −50 V the films were transformed into polycrystalline. Further increase of substrate bias voltage to −200 V the crystallinity of the films increased. Electrical characteristics of Al/Ta₂O₅/Si structured films deposited at different substrate bias voltages in the range from 0 to −200 V were studied. The substrate bias voltage reduced the leakage current density and increased the dielectric constant. The optical transmittance of the films increased with the increase of substrate bias voltage. The unbiased films showed an optical band gap of 4.44 eV and the refractive index of 1.89. When the substrate bias voltage increased to −200 V the optical band gap and refractive index increased to 4.50 eV and 2.14, respectively due to the improvement in the crystallinity and packing density of the films. The crystallization due to the applied voltage was attributed to the interaction of the positive ions in plasma with the growing film.     

On the nitrogen and oxygen incorporation in plasma-enhanced chemical vapor deposition (PECVD) SiOxNy films

Silicon oxynitride films were deposited by plasma-enhanced chemical vapor deposition at low temperatures using nitrous oxide (N₂O) and silane (SiH₄) as gas precursors. The influence of the N₂O/SiH₄ flow ratio (varied from 0.25 up to 5) and the thickness of the films on the optical and structural properties of the material was analyzed. The films were characterized by ellipsometry, Fourier-transform infrared spectroscopy, Rutherford backscattering spectroscopy and optical absorption. Two distinct types of material were obtained, silicon dioxide-like oxynitrides SiO_2−xN_x and silicon-rich oxynitrides SiO_xN_y (x+y<2). The results demonstrate that in silicon dioxide-like material, the nitrogen concentration can be adequately controlled (within the range 0–15 at.%) with total hydrogen incorporation below 5 at.% and no appreciable SiH bonds. It is also shown that the composition remains uniform through the entire thickness of the films. Furthermore, a linear relation between the refractive index and the nitrogen concentration is observed, which makes this material very attractive for optoelectronic applications. On the other hand, silicon-rich material is similar to amorphous silicon, and presents an increasing concentration of SiH bonds, increasing refractive index and decreasing optical gap, which makes it promising for applications in light-emitting devices.     

Optical and structural properties of SiOx films from ion-assisted deposition

This study investigates the optical and structural properties of SiO_x (x ∼ 1) films prepared by an ion-assisted deposition (IAD) process. The films were prepared by evaporating silicon monoxide, with and without simultaneous Ar⁺ bombardment. The stoichiometry of each film was determined as measured by the infrared spectrometry and X-ray photoelectron spectrometry. The variation in the stoichiometry revealed that the oxygen content of the SiO_x thin films varied slightly under the different conditions of the Ar⁺ bombardment. The results of the X-ray diffraction and transmission electron microscopy (TEM) measurements illustrated that all of the films had amorphous structures. However, a different interfacial appearance between the film and the substrate was observed from the TEM image. The optical constants of the SiO_x thin films were determined by a spectroscopic ellipsometry. The extinction coefficient of all of the films approached zero in the infrared wavelength range from 2 to 7 μm, but the refractive index was varied by the IAD process. The variation of these refractive indices is mainly related to the packing density of the films.     

Optical waveguiding and birefringence properties of sputtered zinc oxide (ZnO) thin films on glass

Thin (≈1 μm), waveguiding and c-axis oriented ZnO films of good optical quality have been fabricated on corning glass substrates by r.f. magnetron reactive sputtering without substrate heating. The optical parameters of the films deposited in different O₂:Ar sputtering gas mixtures were found to vary. The extraordinary and ordinary refractive indices (n_e and n_o respectively) of the ZnO film grown in 60% O₂ and 40% Ar were found to be the highest (n_e=1.9876, n_o=1.9692) and closest to bulk single crystal values, and the birefringence of the film was ≈0.018. The films were annealed at 380 °C in air for 1 h, as a result of which the crystalline quality of the films was found to improve with increase in X-ray density and decrease in stress. While the refractive index decreased, the propagation loss was lowered substantially (3–5 dB/cm) as a result of annealing. The annealed zinc oxide film with minimum stress exhibited lowest loss (3 dB/cm) and highest birefringence (≈0.018). This indicated a correlation between propagation loss and stress.     

Influence of Relevant Gas Pressure on the Properties of Ionplated Ta2O5 Films. Einfluss relevanter Gasdrücke auf die Eigenschaften ionenplattierter Ta2O5 Schichten

Ta₂O₅ films were deposited onto unheated fused silica substrates (Suprasil®) by reactive low voltage ion plating (RLVIP). From these films of about 200 nm thickness the optical properties (refractive index n and the absorption coefficient k) and also the mechanical properties (density ρ and intrinsic stress σ) were investigated in dependence of the working gas pressure (Ar) and the reactive gas pressure (O₂). The experiments show a reasonable correlation between refractive index, density and intrinsic stress of the films. With low total pressure high refractive indices (up to n₅₅₀=2.25), high compressive film stress and high relative film density were found. However the film density, the refractive index and also the intrinsic stress decreased with films prepared under raising total gas pressure. The optical absorption depends on the amount of oxygen in the gas phase during deposition. By adding more oxygen to the Ar/O₂ gas mixture primarily the absorption could clearly be decreased.     

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.     

Ellipsometry on sputter-deposited tin oxide films: optical constants versus stoichiometry, hydrogen content, and amount of electrochemically intercalated lithium

Tin oxide thin films were deposited by reactive radio-frequency magnetron sputtering onto In(2)O(3):Sn-coated and bare glass substrates. Optical constants in the 3002500-nm wavelength range were determined by a combination of variable-angle spectroscopic ellipsometry and spectrophotometric transmittance measurements. Surface roughness was modeled from optical measurements and compared with atomic-force microscopy. The two techniques gave consistent results. The fit between experimental optical data and model results could be significantly improved when it was assumed that the refractive index of the Sn oxide varied across the film thickness. Varying the oxygen partial pressure during deposition made it possible to obtain films whose complex refractive index changed at the transition from SnO to SnO(2). An addition of hydrogen gas during sputtering led to lower optical constants in the full spectral range in connection with a blueshift of the bandgap. Electrochemical intercalation of lithium ions into the Sn oxide films raised their refractive index and enhanced their refractive-index gradient.     

Spectroscopic ellipsometry investigations of the optical properties of manganese doped bismuth vanadate thin films

The optical properties of Bi₂V_1−xMn_xO_5.5−x {x = 0.05, 0.1, 0.15 and 0.2 at.%} thin films fabricated by pulsed laser deposition on platinized silicon substrates were studied in UV-visible spectral region (1.51-4.17 eV) using spectroscopic ellipsometry. The optical constants and thicknesses of these films have been obtained by fitting the ellipsometric data (Ψ and Δ) using a multilayer four-phase model system and a relaxed Lorentz oscillator dispersion relation. The surface roughness and film thickness obtained by spectroscopic ellipsometry were found to be consistent with the results obtained by atomic force and scanning electron microscopy. The refractive index measured at 650 nm does not show any marginal increase with Mn content. Further, the extinction coefficient does not show much decrease with increasing Mn content. An increase in optical band gap energy from 2.52 to 2.77 eV with increasing Mn content from x = 0.05 to 0.15 was attributed to the increase in oxygen ion vacancy disorder.     

Effect of thermal treatments on the structure of MoNxOy thin films

MoN_xO_y films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure molybdenum target, varying the flow rate of reactive gases. X-ray diffraction (XRD) results revealed the occurrence of cubic MoN_x and hexagonal (δ-MoN) phases for the films with high nitrogen flow rates. The increase of oxygen content induces the decrease of the grain size of the molybdenum nitride crystallites. The thermal stability of a set of samples was studied in vacuum, for an annealing time of 1 h, for temperatures ranging from 500 to 800 °C in 100 °C steps. The results showed that pure molybdenum nitride films changed their structure from a meta-stable cubic MoN to hexagonal δ-MoN and cubic γ-Mo₂N-type structures with increasing annealing temperatures. The samples with molybdenum nitride films evidenced a good thermal stability, but those with molybdenum oxynitride coatings showed a tendency to detach with the increase of the annealing temperature.