Physico-chemical, structural and physical properties of hydrogenated silicon oxinitride films elaborated by pulsed radiofrequency discharge

Films prepared by radiofrequency pulsed plasma enhanced chemical vapor deposition from a mixture of silane (SiH₄) and nitrous oxide (N₂O) were studied. Variation of operating conditions (flow rate, deposition temperature ...) resulted in films with chemical compositions changing from hydrogenated silicon oxynitride (SiO_xN_y:H) to silicon oxide (SiO_x:H). Infrared and Rutherford backscattering spectroscopy studies of the as-deposited films revealed different SiO_x arrangements disturbed by Si-N bonds and H-Si ≡ Si_(3 − x)O_x clusters depending on the substrate temperature and the N₂O/SiH₄ ratio. For films obtained using low N₂O/SiH₄ rations and annealed at temperature higher than 1273 K, Raman spectroscopy and microscopy analyses revealed the presence of silicon nanocrystals embedded in a matrix containing Si, O, and N. Spectroscopic ellipsometry revealed the presence of silicon nanocrystals along with two other amorphous phases (SiO_xN_y and SiO₂) in annealed samples. The electrical characteristics of annealed films obtained from capacitance-voltage measurements indicated a stable charge trapping in ultra-thin SiO_xN_y layers. These preliminary results suggest that Si-nc containing silicon oxynitride layers can be potential candidates to be used in the floating gate fabrication of memory devices.     

Formation of gold nanoparticles in silicon suboxide films prepared by plasma enhanced chemical vapour deposition

Nanostructured materials fabricated by dispersing metal particles on the dielectric surface have potential application in the field of nanotechnology. Interfacial metal particles/dielectric matrix interaction is important in manipulating the structural and optical properties of metal/dielectric films. In this work, a thin layer of gold (Au) was sputtered onto the surface of silicon oxide, SiO_x (0.38 < x < 0.68) films which was deposited at different N₂O/SiH₄ flow rate ratios of 5 to 40 using plasma enhanced chemical vapor deposition (PECVD) technique prior to the annealing process at 800 °C. FTIR spectra demonstrate the intensity and full-width at half-maximum (FWHM) of Si-O-Si stretching peaks are significantly dependent on the N₂O/SiH₄ flow-rate ratio, η. The films deposited at low and high N₂O/SiH₄ flow rate ratios are dominated by the oxygen and silicon contents respectively. The size and concentration of Au particles distributed on the surface of SiO_x films are dependent on the N₂O/SiH₄ flow-rate ratio. High concentrations of Au nanoparticles are distributed evenly on the surface of the film deposited at N₂O/SiH₄ flow-rate ratio of 30. Crystallinity and crystallite sizes of Au are enhanced after the thermal annealing process. Appearance of surface plasma resonance (SPR) absorption peaks at 524 nm for all samples are observed as a result of the formation of Au particles. The annealing process has improved SPR peaks for all the as-deposited films. The energy gap of the as-deposited Au/SiO_x films are in the range of 3.58 to 4.38 eV. This energy gap increases after the thermal annealing process except for the film deposited at η = 5.     

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.     

Multi-phase structured silicon carbon nitride thin films prepared by hot-wire chemical vapour deposition

In this work, Silicon Carbon Nitride (Si-C-N) thin films were deposited by Hot Wire Chemical Vapour Deposition (HWCVD) technique from a gas mixture of silane (SiH₄), methane (CH₄) and nitrogen (N₂). Six sets of Si-C-N thin films were produced and studied. The component gas flow rate ratio (SiH₄:CH₄:N₂) was kept constant for all film samples. The total gas flow-rate (SiH₄ + CH₄ + N₂) was changed for each set of films resulting in different total gas pressure which represented the deposition pressure for each of these films ranging from 40 to 100 Pa. The effects of deposition pressure on the chemical bonding, elemental composition and optical properties of the Si-C-N were studied using Fourier transform infrared (FTIR) spectroscopy, Auger Electron Spectroscopy (AES) and optical transmission spectroscopy respectively. This work shows that the films are silicon rich and multi-phase in structure showing significant presence of hydrogenated amorphous silicon (a-Si:H) phase, amorphous silicon carbide (a-SiC), and amorphous silicon nitride (a-SiN) phases with Si-C being the most dominant. Below 85 Pa, carbon content is low, and the films are more a-Si:H like. At 85 Pa and above, the films become more Si-C like as carbon content is much higher and carbon incorporation influences the optical properties of the films. The properties clearly indicated that the films underwent a transition between two dominant phases and were dependent on pressure.     

Preparation and photoluminescence of nanocrystalline Si-rich silicon oxide films by PECVD

Nanocrystalline Si-rich silicon oxide films were deposited using plasma enhanced chemical vapor deposition technique with the mixture of silane (SiH₄), nitrous oxide (N₂O) and hydrogen (H₂) as gas source on quartz glass substrate at the substrate temperature of 300 °C. The effect of the ratio N₂O/SiH₄ on the oxidation, microstructures and photoluminescence (PL) of the as-deposited Si-rich silicon oxide films was investigated with FTIR, XRD and HRTEM. The results reveal that with the increasing ratio of N₂O/SiH₄, more amounts of oxygen are incorporated in the as-deposited films and more nanosized silicon particles are embedded in the films, forming nanocrystalline Si-rich silicon oxide films. The quantum confinement effect or the cooperation of quantum confinement and luminescence center results in the nanocrystalline Si-rich silicon oxide films of higher PL intensity.     

Effects of cetyltrimethylammonium bromide on redox deposition and rectification properties of silicon oxide thin film

Silicon oxide (SiO_x) thin film was deposited onto fluorine-doped tin oxide (FTO) and silicon wafer substrate by the reduction of an aqueous solution containing ammonium hexafluorosilicate, dimethylamine borane and cetyltrimethylammonium bromide (CTAB). Characterization of the films by X-ray photoelectron spectroscopic depth profile and infrared spectroscopy proved that the addition of CTAB into the film enhanced the aggregation of silica particles and the growth rate. The SiO_x films (resistivity: 3.2 × 10⁸ Ω cm) remarkably improved the rectification properties of FTO/SiO_x/poly(3,4-ethylenedioxythiophene) derivative diodes. A rectification mechanism based on conduction of electron and ions was investigated.     

Deposition of silicon nitride thin films by hot-wire CVD at 100 °C and 250 °C

Silicon nitride thin films for use as passivation layers in solar cells and organic electronics or as gate dielectrics in thin-film transistors were deposited by the Hot-wire chemical vapor deposition technique at a high deposition rate (1-3 ?/s) and at low substrate temperature. Films were deposited using NH₃/SiH₄ flow rate ratios between 1 and 70 and substrate temperatures of 100 °C and 250 °C. For NH₃/SiH₄ ratios between 40 and 70, highly transparent (T ~ 90%), dense films (2.56-2.74 g/cm³) with good dielectric properties and refractive index between 1.93 and 2.08 were deposited on glass substrates. Etch rates in BHF of 2.7 ?/s and < 0.5 ?/s were obtained for films deposited at 100 °C and 250 °C, respectively. Films deposited at both substrate temperatures showed electrical conductivity ~ 10^− 14 Ω^− 1 cm^− 1 and breakdown fields > 10 MV cm^− 1.     

Influence of process steps on the performance of microcrystalline silicon thin film transistors

Bottom gate microcrystalline silicon thin film transistors (μc-Si TFT) have been realized with two types of films: μc-Si(1) and μc-Si(2) with crystalline fraction of 80% and close to 100% respectively. On these TFTs we applied two types of passivation (SiN_x and resist). μc-Si TFTs with resist as a passivation layer present a low leakage current of about 2.10^− 12 A for V_G = − 10 and V_D = 0.1V an ON to OFF current ratio of 10⁶, a threshold voltage of 7 V, a linear mobility of 0.1 cm²/V s, and a sub-threshold voltage of 0.9 V/dec. Microcrystalline silicon TFTs with SiN_x as a passivation present a new phenomenon: a parasitic current for negative gate voltage (− 15 V) causes a bump and changes the shape of the sub-threshold region. This excess current can be explained by and oxygen contamination at the back interface.     

Thermal annealing effects on the interface state density of metal-oxide-semiconductor capacitors with electron cyclotron resonance plasma enhanced chemical vapor deposition Silicon dioxide

Silicon dioxide films (SiO₂), deposited at room temperature by electron cyclotron resonance (ECR) plasma reactor from a gas phase combination of O₂, SiH₄ and He, present excellent structural and electrical properties. However, when fabricating field effect devices it is also crucial to minimize the defect density at the semiconductor/insulator interface. We show that the interface state density, investigated in Al/SiO₂/Si MOS capacitors, can be substantially reduced performing post-deposition annealing. In particular we studied the effects of annealing temperature and time in different gas ambient: vacuum, nitrogen and forming gas (5% H₂ + N₂). We found that interface state passivation mainly occurs when thermal annealing is performed after Al-contact deposition and that it is quite insensitive to the annealing atmosphere. The present results clearly suggest that the hydrogen passivation mechanism is driven by the H-containing species present in the film and a possible mechanism to explain the results is proposed.     

Interfacial layer growth of ZrO2 films on silicon

In this work, the interfacial layer growth for both as-deposited and annealed ZrO₂ thin films on silicon is analyzed in detail by the high-resolution cross-sectional transmission electron microscope and spectroscopic ellipsometry. For as-deposited ZrO₂/SiO₂/Si, the thickness of a SiO₂-like layer at the silicon interface was found to depend on the oxygen partial pressure during deposition. At oxygen partial pressure ratio of above 50% the interfacial silicon oxide thickness increased through oxygen diffusion through the ZrO₂ film and silicon consumption at the interface. At oxygen partial pressure ratio in the range 7-50%, the visible growth of interfacial silicon oxide layer was not present. The interfacial layer for ZrO₂/Si with optimal partial pressure (15%) during annealing at 600 °C was found to be the two-layer structure composed of the ZrSi_xO_y overlayer and the SiO_x downlayer. The formation of the interfacial layer is well accounted for diffusion mechanisms involving Si indiffusion and grain-boundary diffusion.     

Formation of gas barrier films by Cat-CVD method using organic silicon compounds

Silicon nitride (SiN_x) and silicon oxynitride (SiO_xN_y) films have been formed by catalytic chemical vapor deposition (Cat-CVD) method using hexamethyldisilazane (HMDS). Addition of NH₃ gas and increase in gas pressure can prevent carbonization of tungsten (W) catalyzer. These SiO_xN_y films have high gas barrier ability compare to the case of SiO_xN_y films using SiH₄ and thus are expected for novel sealing films.     

Metal-oxide-semiconductor characteristics of thermally grown nitrided SiO2 thin film on 4H-SiC in various N2O ambient

Metal-oxide-semiconductor characteristics of thermally grown nitrided SiO₂ (9-11.5 nm) on n-type 4H-SiC at 1175 °C in various N₂O ambient (1, 10, and 50% N₂O mixed with 99, 90, and 50% of high purity N₂ gas, respectively) have been investigated. The chemical composition of oxide-semiconductor interface has been evaluated by X-ray photoelectron spectroscopy. The interfacial layer consists of either silicon oxynitride, silicon nitride, and/or silicon oxide phases that may be segregated or mixed in a single layer. Depending on the percentage of N₂O being used, the stoichiometry may vary accordingly. The lowest leakage current density is recorded for thin film oxide grown in10% N₂O and it is limited to an applied electric field of not more than 7 MV/cm. This is attributed to the lowest density value of deep oxide trap in this sample if compared with others. The highest dielectric breakdown field has been obtained for thin film oxide grown in 50% N₂O as this sample is having the lowest interface trap density and negative effective oxide charge. The origin of these charges is explained in the text.     

Design of porous silicon/PECVD SiOx antireflection coatings for silicon solar cells

The meso-porous silicon (PS) has become an interesting material owing to its potential applications in many fields, including optoelectronics and photovoltaics. PS layers were grown on the front surface of the n⁺ emitter of n⁺-p mono-crystalline Silicon junction. The thickness and the porosity of the PS layer were determined by an ellipsometer, as a function of time duration of anodization, and the variation law of the PS growth kinetics is established. Single layers PS antireflection coating (ARC) achieved around 9% of effective reflectivity in the wavelength range between 400 and 1000 nm on junction n⁺-p solar cells. To reduce the reflectivity and improve the stability and passivation properties of PS ARC, silicon oxide layers were deposited by PECVD on PS ARC. SiO_x layers of thickness of 105 nm combined with PS layer led to 3.8% effective reflectivity. V_oc measurements were carried out on all the samples by suns-V_oc method and showed an improvement of the quality of the passivation brought by the oxide layer. Using the experimental reflectivity results and taking into account the passivation quality of the samples, the PC1D simulations predict an enhancement of the photogenerated current exceeding 44%.     

Amorphous Si1−xCx:H films prepared by hot-wire CVD using SiH3CH3 and SiH4 mixture gas and its application to window layer for silicon thin film solar cells

B-doped hydrogenated amorphous silicon carbon (a-Si_1−xC_x:H) films have been prepared by hot-wire CVD (HWCVD) using SiH₃CH₃ as the carbon source gas. The optical bandgap energy and dark conductivity of the film are about 1.94 eV and 2 × 10^− 9 S/cm, respectively. Using this film as a window layer, we have demonstrated the fabrication of solar cells having a structure of the textured SnO₂(Asahi-U)/a-Si_1−xC_x:H(p)/a-Si_1−xC_x:H(buffer)/a-Si:H(i)/μc-Si:H(n)/Al. The conversion efficiency of the cell is found to be 7.0%.     

High rate growth highly crystallized microcrystalline silicon films using SiH4/H2 high-density microwave plasma

The plasma parameter for fast deposition of highly crystallized microcrystalline silicon (μc-Si) films with low defect density is presented using the high-density and low-temperature microwave plasma (MWP) of a SiH₄-H₂ mixture. A very high deposition rate of ∼ 65 Å/s has been achieved at SiH₄ concentration of 67% diluted in H₂ with high Raman crystallinity I_c / I_α > 3 and low defect density of 1-2 × 10¹⁶ cm^− 3 by adjusting the plasma condition. Contrary to the conventional rf plasma, the defect density of the μc-Si films strongly depend on substrate temperature T_s and it increased with increasing T_s despite T_s below 300 °C, suggesting that the real surface temperature at the growing surface was higher than the monitored value. The sufficient supply of deposition precursors such as SiH₃ at the growth surface under an appropriate ion bombardment was effective for the fast deposition of highly crystallized μc-Si films as well as the suppression of the incubation and transition layers at the initial growth stage.     

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.     

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.     

Growth of silicon carbide thin films by hot-wire chemical vapor deposition from SiH4/CH4/H2

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH₄/CH₄/H₂ and their structural properties were investigated by X-ray diffraction, Fourier transform infrared absorption and Raman scattering spectroscopies. At 2 Torr, Si-crystallite-embedded amorphous SiC (a-Si_1 − xC_x:H) grew at filament temperatures (T_f) below 1600 °C and nanocrystalline cubic SiC (nc-3C-SiC:H) grew above T_f = 1700 °C. On the other hand, At 4 Torr, a-Si_1 − xC_x:H grew at T_f = 1400 °C and nc-3C-SiC grew above T_f = 1600 °C. When the intakes of Si and C atoms into the film per unit time are almost the same and H radicals with a high density are generated, which takes place at high T_f, nc-3C-SiC grows. On the other hand, at low T_f the intake of Si atoms is larger than that of C atoms and, consequently, Si-rich a-Si_1 − xC_x:H or Si-crystallite-embedded a-Si_1 − xC_x:H grow.     

Structural, optical and electrical properties of high-k ZrO2 dielectrics on Si prepared by plasma assisted pulsed laser deposition

ZrO₂ films were grown on p-type Si(100) using plasma assisted pulsed laser deposition and the electrical characteristics of the ZrO₂ dielectrics incorporated in metal oxide silicon (MOS) capacitors were studied in combination with their structural and optical properties. The ZrO₂ dielectric layers are of polycrystalline structure with a monoclinic phase and show good interfacial properties without obvious SiO_x interface. The electrical performance of the capacitors exhibits typical MOS-type capacitance-voltage (C-V) and leakage current density-voltage (J-V) characteristics. Thermal annealing of the ZrO₂ dielectrics results in an improvement in C-V and J-V characteristics and a reduction in C-V hysteresis without obvious introduction of leakage paths for the fabricated MOS capacitors. The dielectric constant was calculated to be 15.4 and the leakage current density was measured to be 6.7 × 10^− 6 A/cm² at a gate voltage of + 1.0 V for 900 °C annealed ZrO₂ dielectric layers with an equivalent oxide thickness of 5.2 nm.     

Low refractive index silicon oxide coatings at room temperature using atmospheric-pressure very high-frequency plasma

Low refractive index silicon oxide films were deposited using atmospheric-pressure He/SiH₄/CO₂ plasma excited by a 150-MHz very high-frequency power. Significant increase in deposition rate at room temperature could prevent the formation of dense SiO₂ network, decreasing refractive index of the resulting film effectively. As a result, a silicon oxide film with the lowest refractive index, n = 1.24 at 632.8 nm, was obtained with a very high deposition rate of 235 nm/s. The reflectance and transmittance spectra showed that the low refractive index film functioned as a quarter-wave anti-reflection coating of a glass substrate.