Effect of NH3 flow rate on growth, structure and luminescence of amorphous silicon nitride films by electron cyclotron resonance plasma

In this paper, hydrogenated amorphous silicon nitride (a-SiN_x:H) films have been deposited using an electron cyclotron resonance chemical vapor deposition system. The effect of NH₃ flow rate R on the deposition rate, structure and luminescence were studied using various techniques such as optical emission spectroscopy, Fourier Transform Infrared absorption (FTIR), X-ray photoelectron spectroscopy (XPS) and fluoro-spectroscopy, respectively. Optical emission behavior of SiH₄ + NH₃ plasma shows that atomic Si radical concentration determines the film deposition rate. Structural transition of a-SiN_x film from Si-rich one to near-stoichiometric/N-rich one with R was revealed by FTIR and the two phase separation of a-Si and a-Si₃N₄ was also convinced in Si-rich SiN_x films by XPS. Either photo- or electroluminescence for all the SiN_x films with R > 3 sccm shows a strong light emission in visible light wavelength range. As R < 6 sccm, recombination of electrons and holes in a-Si quantum dots is the main mechanism of photo/electroluminescence for Si-rich SiN_x films, however, for photoluminescence, gap states' luminescence is also in competition; as R > 6 sccm, light emission of the SiN_x film originates from defect states in its band gap.     

Characterization of SiNx:H films deposited by rapid thermal chemical vapor deposition

Hydrogenated silicon nitride films were deposited with NH₃, SiH₄ and N₂ gas mixture at 700 °C by rapid thermal chemical vapor deposition (RTCVD) system. The NH₃/N₂ flow ratio and deposition pressure are found to influence the film properties. The stress of SiN_x:H films deposited by RTCVD is tensile, which can reach ~ 1.5 GPa in our study. The stress of SiN_x:H films is dependent on the deposition parameters, which can be associated with chemical configuration of the film. It is suggested that the presence of hydrogen atoms will relax the Si-N network, which results in the decrease of tensile stress of the SiN_x:H film.     

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.     

Characteristics of SiOx thin films deposited by atmospheric pressure chemical vapor deposition as a function of HMDS/O2 flow rate

SiO₂-like thin films were deposited using a modified dielectric barrier discharge with a gas mixture of hexamethyldisilazane (HMDS)/O₂/He/Ar and their film characteristics were investigated as functions of the HMDS and O₂ flow rates. As the HMDS flow rate was increased, higher amounts of Si-(CH₃)_x bonds and lower amounts of Si-OH bonds were observed in the deposited SiO_x, due to the increase in the amount of the less dissociated HMDS, which also caused an increase of the surface roughness. The addition and increase of the oxygen flow to HMDS/He/Ar brought the stoichiometry of SiO_x close to SiO₂ and decreased the surface roughness by decreasing the amount of Si-(CH₃)_x bonds through the increased decomposition and oxidation of HMDS, even though the deposition rate was decreased. However, when the O₂ flow rate was higher than a certain threshold, the surface roughness increased again, possibly due to the decrease in the extent of HMDS dissociation caused by the decreased plasma density at the higher oxygen flow rate. By using an optimized gas mixture of HMDS (150 sccm)/O₂ (14 slm)/He (5 slm)/Ar (3 slm), SiO₂-like thin films with a very low impurity level and having a smooth surface could be obtained with a deposition rate of approximately 42.7 nm/min.     

Structure and mechanical properties of ZrO2 films deposited by gas flow sputtering

ZrO₂ films were deposited by reactive gas flow sputtering (GFS) where voltage is applied to a cyindrical hollow-cathode target from a DC source, the discharge being produced at relatively high sputtering pressure. In this system, secondary electrons form a major component of the total current flow and lead to heating of the substrate which in turn has an effect on the properties of deposited films. The present experiments were carried out under the following conditions: Ar gas flow rate of 200 sccm, O₂ flow rate FO₂ in the range between 0.003 and 1 sccm, and sputtering power (P_S) in the range of 50-800 W. The reults showed that the crystal structure of the films deposited for P_S below 200 W was monoclinic but for P_S above 400 W, the films included tetragonal cystals of stable structure formed at high temperature by the electron bombardment. The films were formed with grains of 20-100 nm in diameter in a porous structure. The mechanical properties of the films were determined by a nanoindentation technique. Martens hardness (H_M) of the porous films was found to be in the range between 220 and 330 MPa which is substantially less than that of films typically deposited by rf magnetron sputtering.     

Microstructure and mechanical properties of CrAlN/SiNx nanostructure multilayered coatings

Multilayered CrAlN and SiN_x films were deposited periodically by radio frequency reactive magnetron sputtering. In the CrAlN/SiN_x multilayered coatings, the thickness of CrAlN layer was fixed at 4 nm, while that of SiN_x layer was adjusted from 4 nm to 0.3 nm. The dependence of the SiN_x layer thickness on the preferred orientation, crystalline behavior and mechanical properties of multilayered coatings were discussed with the aid of XRD patterns and HRTEM. It was demonstrated that amorphous SiN_x layer transformed to a crystallized one when the thickness decreased from 4 nm to 0.3 nm. The crystalline SiN_x layer grew epitaxially, formed the coherent interface with the CrAlN layer, and the columnar structure was exhibited. The critical layer thickness for the transition from amorphous SiN_x to a crystallized one was found to be around 0.4 nm, and maximum hardness of 33 GPa was revealed.     

Influence of the argon flow rate on the arsenic fraction of a-GaxAs1−x sputtered at high substrate temperature

The experimental study of the chemical composition of amorphous gallium arsenide (a-Ga_xAs_1−x) versus argon flow rate, Q, by rf sputtering, shows that the As fraction of sputtered films is controlled by the argon flow rate. At the substrate temperature, T_s=500 °C, the films are stoichiometric when deposited under the argon flow rate between 8 and 22 sccm. These observations indicate that at low argon flow rate the As fraction of films is governed only by the preferential re-sputtering of As during the film growth. In addition, a correlation between the deposition rate R, and chemical composition x was deduced from these results.     

Atmospheric pressure PECVD of SiO2 thin film at a low temperature using HMDS/O2/He/Ar

SiO₂-like thin films were deposited at a low temperature (< 50 °C) by a remote-type, atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) using a pin-to-plate-type, dielectric barrier discharge with gas mixtures containing hexamethyldisilazane (HMDS)/O₂/He/Ar. The film characteristics were investigated according to the HMDS and O₂ flow rates. To obtain a more SiO₂-like thin film, an adequate combination of HMDS and oxygen flow rates was required to remove the -(CH₃)_x bonding in the HMDS and to oxidize the Si in HMDS effectively. At the optimized flow rates, the surface roughness of the SiO₂-like thin film was also the lowest. By using HMDS (50 sccm) and O₂ (500 sccm) flow rates in the gas mixture of HMDS/O₂/He (2 slm)/Ar (600 sccm), SiO₂-like thin films with a low impurity (< 6.35% C) were obtained at a deposition rate of approximately 10.7 nm/min.     

Annealing optimization of silicon nitride film for solar cell application

Hydrogenated films of silicon nitride (SiNx:H) is commonly used as an antireflection coating as well as passivation layer in crystalline silicon solar cell. SiNx:H films deposited at different conditions in Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor were investigated by varying annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in silicon solar cells. By varying the gases ratio (R = NH₃/SiH₄ + NH₃) during deposition, the SiNx:H films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, the silicon wafer with SiNx:H film deposited at 450 °C showed the best effective minority carrier lifetime. The film deposited with the gases ratio of 0.57 shows the best peak of carrier lifetime at the annealing temperature of 800 °C. The single crystalline silicon solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrates (125 mm × 125 mm) were found to have the conversion efficiencies as high as 17.05 %. Low cost and high efficiency single crystalline silicon solar cells fabrication sequence employed in this study has also been reported in this paper.     

Perovskite oxynitride LaTiOxNy thin films: Dielectric characterization in low and high frequencies

Lanthanum titanium oxynitride (LaTiO_xN_y) thin films are studied with respect to their dielectric properties in low and high frequencies. Thin films are deposited by radio frequency magnetron sputtering on different substrates. Effects of nitrogen content and crystalline quality on dielectric properties are investigated. In low-frequency range, textured LaTiO_xN_y thin films deposited on conductive single crystal Nb-STO show a dielectric constant ε′ ≈ 140 with low losses tanδ = 0.012 at 100 kHz. For the LaTiO_xN_y polycrystalline films deposited on conductive silicon substrates with platinum (Pt/Ti/SiO₂/Si), the tunability reached up to 57% for a weak electric field of 50 kV/cm. In high-frequency range, epitaxial LaTiO_xN_y films deposited on MgO substrate present a high dielectric constant with low losses (ε′ ≈ 170, tanδ = 0.011, 12 GHz).     

Effect of N2O/SiH4 flow ratios on properties of amorphous silicon oxide thin films deposited by inductively-coupled plasma chemical vapor deposition with application to silicon surface passivation

Silicon oxide (SiO_x) thin films have been deposited at a substrate temperature of 300 °C by inductively-coupled plasma chemical vapor deposition (ICP-CVD) using N₂O/SiH₄ plasma. The effect of N₂O/SiH₄ flow ratios on SiO_x film properties and silicon surface passivation were investigated. Initially, the deposition rate increased up to the N₂O/SiH₄ flow ratio of 2/1, and then decreased with the further increase in N₂O/SiH₄ flow ratio. Silicon oxide films with refractive indices of 1.47-2.64 and high optical band-gap values (>3.3 eV) were obtained by varying the nitrous oxide to silane gas ratios. The measured density of the interface states for films was found to have minimum value of 4.3 × 10¹¹ eV⁻¹ cm⁻². The simultaneous highest τ_eff and lowest density of interface states indicated that the formation of hydrogen bonds at the SiO_x/c-Si interface played an important role in surface passivation of p-type silicon.     

Effects of argon and oxygen flow rate on water vapor barrier properties of silicon oxide coatings deposited on polyethylene terephthalate by plasma enhanced chemical vapor deposition

Plasma polymer coatings were deposited from hexamethyldisiloxane on polyethylene terephthalate (PET) substrates while varying the operating conditions, such as the Ar and O₂ flow rates, at a fixed radio frequency power of 300 W. The water vapor transmission rate (WVTR) of the untreated PET was 54.56 g/m²/day and was decreased after depositing the silicon oxide (SiO_x) coatings. The minimum WVTR, 0.47 g/m²/day, was observed at Ar and O₂ flow rates of 4 and 20 sccm, respectively, with a coating thickness of 415.44 nm. The intensity of the peaks for the Si-O-Si bending at 800-820 cm^− 1 and Si-O-Si stretching at 1000-1150 cm^− 1 varied depending on the Ar and O₂ flow rates. The contact angle of the SiO_x coated PET increased as the Ar flow rate was increased from 2 to 8 sccm at a fixed O₂ flow rate of 20 sccm. It decreased gradually as the oxygen flow rate increased from 12 to 28 sccm at a fixed Ar carrier gas flow rate. The examination by atomic force microscopy revealed a correlation of the SiO_x morphology and the water vapor barrier performance with the Ar and O₂ flow rates. The roughness of the deposited coatings increased when either the O₂ or Ar flow rate was increased.     

Effects of oxygen addition on electrochromic properties in low temperature plasma-enhanced chemical vapor deposition-synthesized MoOxCy thin films for flexible electrochromic devices

Electrochromic organomolybdenum oxide (MoO_xC_y) films are deposited onto 60 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates by low temperature plasma-enhanced chemical vapor deposition (PECVD) using a precursor of molybdenum carbonyl vapor, which is carried by argon gas, mixed with oxygen gas and synthesized by radio frequency power at room temperature (23 °C). The MoO_xC_y films with modified surface morphology and compositions of varying oxygen contents are proven to offer noteworthy electrochromic performance. Porous surface of the MoO_xC_y film (398 nm thick) provides Li⁺ ion diffusion coefficient value of 1.7 × 10^− 10 cm²/s for Li⁺ de-intercalation at a potential scan rate of 2 mV/s. High x/y value at high surface composition of oxygen to carbon in the MoO_xC_y film offers light modulation with transmittance variation of up to 63% and coloration efficiency of 36 cm²/C at a wavelength of 800 nm for 200 cycles of Li⁺ intercalation and de-intercalation. PECVD-synthesized MoO_xC_y thin films show promising electrochromic properties for applications in flexible electrochromic devices.     

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.     

Formation of NiSi2/SiNX compound nanocrystal for nonvolatile memory application

In this paper, the NiSi₂/SiN_X compound NCs (CNCs) structure is studied to further improve the retention. To introduce the nitride based traps, NiSi₂ was also sputtered in the mixture gas of Ar (50 sccm) and NH₃ (10 sccm) at room temperature, and the NiSi₂/SiN_X CNCs can be easily formed after rapid thermal annealing. In addition, standard memory devices with single and double NiSi₂ nanocrystal were also prepared for comparison. By XPS analyses, the nanocrystals fabricated in the ambiance of NH₃ can be confirmed to be composited of NiSi₂ and SiN_X compound. According to memory characteristics results, better retention characteristic of device with single-layer NiSi₂/SiN_X compound nanocrystal NVMs can be observed after 10⁴ s, raises from 50% to 72% in comparison with the control sample, even better than the double-layer NiSi₂ nanocrystal, 58%. Indeed, the formation of NiSi₂/SiN_X CNCs can improve the retention characteristics remarkably due to the additional tunnel barrier and deep traps in the nitride.     

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.     

Effect of grain size on mechanical properties in CrAlN/SiNx multilayer coatings

Both CrAlN and SiN_x coatings were deposited sequentially by RF magnetron sputtering. During sputtering, thickness of SiN_x layer was set to be 1 nm, while that of CrAlN layer was controlled to be 4, 20, 40, 100, and 200 nm. According to XRD results, it was revealed that grain size of the CrAlN coatings increased from 3.6 nm to 24.2 nm with the increasing thickness. From HRTEM images, the variation on grain size was attributed to the amorphous SiN_x layer, which significantly retarded the continuous growth of CrAlN layer. Hardness of the CrAlN/SiN_x coatings with various bilayer thicknesses was measured by nanoindentation. The relationship between grain size and hardness could be interpreted by the Hall-Petch equation, and an improved hardness around 32 GPa was achieved.     

Structural and mechanical properties of multi-element (AlCrMoTaTiZr)Nx coatings by reactive magnetron sputtering

(AlCrMoTaTiZr)N_x high-entropy films were deposited on silicon wafer and cemented carbide substrates from a single alloy target by reactive RF magnetron sputtering under a mixed atmosphere of Ar and N₂. The effect of nitrogen flow ratio R_N on chemical composition, morphology, microstructure, and mechanical properties of the (AlCrMoTaTiZr)N_x films was investigated. Nitrogen-free alloy film had an amorphous structure, while nitride films with at least 37 at.% N exhibited a simple NaCl-type FCC (face-centered cubic) structure. Mixed structures occurred in films with lower nitrogen contents. Films with the FCC structure were thermally stable without phase decomposition at 1000 °C after 10 h. The (AlCrMoTaTiZr)N film deposited at R_N = 40% exhibited the highest hardness of 40.2 GPa which attains the superhard grade. The main strengthening mechanisms for this film were grain-size and solid-solution strengthening. A residual compressive stress of 1.04 GPa was small to account for the observed hardness. The nitride film was wear resistant, with a wear rate of 2.8 × 10^− 6 mm³/N m against a loaded 100Cr6 steel ball in the sliding wear test. These high-entropy films have potential in hard coating applications.     

Deposition of zirconium oxynitride films by reactive cathodic arc evaporation and investigation of physical properties

The area of metal oxynitrides is poorly explored, and understanding of the fundamental mechanism that explains structural, mechanical, electrical, and optical properties is still insufficient. Therefore, the purpose of the present investigation is to analyze structural, electrical, and optical properties of ZrN_xO_y films deposited by reactive cathodic arc evaporation.Depending on the oxygen flow, cubic ZrN:O, monoclinic ZrO₂:N, and tetragonal ZrO₂:N phases films were prepared. The sheet resistance and the optical transmittance very much depend on the oxygen flow. Optical transparent ZrN_xO_y films with transmittance of 86% at 650 nm, the sheet resistance 1.1 · 10³ Ω/sq, and the figure of merit 2 · 10^− 4 Ω^− 1 are deposited with the 60 sccm oxygen flow.