SiH4 N2 Research Articles

Hydrogen Balmer line broadening in Ar-N2-SiH4 DC glow discharge

Broadened hydrogen Balmer lines are observed in a DC glow discharge sustained in Ar–SiH4–N2 gas mixture. This broadening is due to the Doppler frequency shift. H atoms’ translational energy distribution is calculated in different positions between the two electrodes of the discharge along the interelectrode axis and in different gas mixtures. Three main components are observed at 0.6(±0.5) eV, 12(±3) eV, 62(±6) eV, 1(±1) eV, 28(±6) eV, and 105(±12) eV for Hα and Hβ, respectively. They correspond to hydrogen dissociation by electron impact producing H(n = 3, 4) atoms and dissociative recombination of the ion in the cathode fall or backscattered fast H atoms on the cathode surface. The density ratio nH2/nAr ranges from 44% to 13% or from 10% to 3% when a = nH/nH2 = 0.01 and 0.1, respectively, in function of the gas mixture. So, large hydrogen density could be due to hydrogen desorption from the wall and cathodes and/or to the gas recirculation within the reactor. A new low energy component is observed in the Hα line profile, when silane and nitrogen concentrations decrease and increase, respectively. It could also be due to the H atom desorbing from the reactor wall or NHx species dissociated by an electron impact within the reactor.

Room-temperature deposition of low H-content SiNx/SiNxOy thin films using a specially designed PECVD system

Low-temperature deposition of amorphous silicon nitride/oxynitride (a-SiNx/a-SiNxOy) is of significance for many industrial applications. In this work, low H-content a-SiNx/a-SiNxOy films were prepared at room temperature by a specially designed plasma enhanced chemical vapor deposition (PECVD) system using Ar-diluted SiH4 and pure N2 as the reactant gases. The plasmas for the deposition of a-SiNx/a-SiNxOy films were studied as a function of discharge power and working pressure. It was found that the density of N atoms in plasma plume was found to have significant impacts on the compositions and optical properties of a-SiNx/a-SiNxOy films and the correlations between the plasma discharge and the as-deposited films were explored. With the increase of N atoms in the plasma, the growth rate of a-SiNx/a-SiNxOy films was increased and the refractive index was gradually reduced, and thus the value of refractive index at 633 nm was tuned from 2.20 to 1.64 due to the increase of the atomic ratio of N to Si in the films. In addition, the O and H contents were increased with the increase of N density in the plasma and have contributions to the variation in the refractive index of a-SiNxOy films as well. The low-temperature deposition of a-SiNx/a-SiNxOy films with tunable refractive index exhibited a great potential in practical applications, especially in flexible electronics.

Structural and optical properties of nc-Si in SiOxNy matrix deposited by laser ablation for optoelectronic applications

In this work, we show the development of SiOxNy (silicon oxynitride) thin films using the laser ablation technique. Instead of commonly used precursor materials SiH4 and NH3 or N2, hereby, we report the deposition using crystalline silicon targets and N2 precursors. The experiment was carried out in such a way that we can eradicate the drawback of hydrogen concentration in the thin films (due to silane precursor) and finally, adequate deposition conditions were found which allowed obtaining the material with suitable optoelectronic properties. Numerous experiments varying the deposition pressure (0.4–6 Pa) were carried out making possible the formation of different kinds of the stoichiometry of the material. For one set of thin films (lower pressure), silicon rich silicon-oxynitride thin films (SRSON) were obtained, whereas, for the other half (higher pressure) it was oxygen-rich silicon oxynitride (ORSON) kind of stoichiometry. Fourier transform infrared spectroscopy (FTIR) shown the dominance of Si-N bonds for the samples deposited at lower pressure, whereas, for the samples deposited at higher pressure shift in the absorption bands towards Si-O bonds was observed. For the middle-pressure range ;(0.8–2 Pa) depending on the composition of SiOxNy thin films, a band gap variation from 2.08 eV to 4.36 eV was obtained. The same could be correlated with the Si, N and O ratios in the deposited thin films. From the XPS analysis, it was found that the Si content was found to be reduced, whereas, N content was found to be varying randomly as an effect of an increase in the pressure. Lately, it also shown an overall increase in the O concentration. For the same range of pressure value (0.8–2 Pa), Raman, X-ray diffraction (XRD) and HRTEM analysis illustrated the formation of crystalline silicon nanoparticles from the as-deposited thin films. Overall, confirmation of Si nanoparticles embedded in an amorphous matrix of SiOxNy can be established from these analyses. Photoluminescence (PL) spectra also demonstrated the visible emission which remarks the quality of material and its tendency for the optical applications. Intense and homogenous PL was observed for samples grown at 2 Pa. Using unique deposition method presented in this manuscript with a great control over the composition and hence, on the optoelectronic properties of Si related thin films can be used for the future optoelectronic applications.

IR Spectroscopic Study of Silicon Nitride Films Grown at a Low Substrate Temperature Using Very High Frequency Plasma-Enhanced Chemical Vapor Deposition

Hydrogenated amorphous silicon nitride (a-SiNx:H) films have been grown from a SiH4–N2 gas mixture through very high frequency (VHF) plasma-enhanced chemical vapor deposition (PECVD) at 50℃. The films are dense and transparent in the visible region. The peak frequency of the Si–N stretching mode in the IR absorption spectrum increases with increasing N–H bond density, which is similar to the behavior of a-SiNx:H films grown from SiH4–NH3 gas. During storage in a dry air atmosphere, the Si–O absorption increases. A large shift in the peak frequency of the Si–N stretching mode in the initial stage of oxidation, which is higher than the shift expected from the increase in the N–H bond density, is mainly caused by the change in the sum of electronegativity of nearest neighbors around the Si–N bond due to the increase in the Si–O bond density.

Effect of NH3-Free Silicon Nitride for Protection Layer of Magnetic Tunnel Junction on Magnetic Properties of Magnetoresistive Random Access Memory

The effects of plasma and precursors during low-temperature silicon nitride (LT-SiN) film deposition on the magnetic properties of a CoFeB alloy layer, which is one magnetic material in a magnetic tunnel junction (MTJ) in magnetoresistive random access memory (MRAM), were investigated. The NH3 plasma exposure was found to nitride the CoFeB alloy layer, resulting in degradation of the magnetic properties of the CoFeB alloy layer. To suppress this degradation, NH3-free LT-SiN films deposited using silane and nitrogen source gases with helium or argon dilution in a conventional plasma enhanced chemical vapor deposition (PECVD) apparatus were evaluated. The LT-SiN film deposited under conditions of a highly dilute helium flow in the SiH4–N2–He gas mixture exhibited high density, sufficient moisture-blocking ability, and low leakage current. On the other hand, the film deposited at the SiH4–N2–Ar gas mixture exhibited poor film qualities. It is revealed that helium gas has enhanced the generation of N2 radicals and the decomposition of silane gas during the deposition of the SiH4–N2–He gas mixture. Finally, we demonstrated that the electrical properties of 8-kbit MRAM arrays have been improved by using the optimized NH3-free LT-SiN film for the MTJ-protection layer.

Deposition of luminescent a-SiN x :H Films with SiH4–N2 gas mixture by VHF–PECVD using novel impedance matching method

Hydrogenated amorphous silicon nitride (a-SiN x :H) films are produced from a SiH4–N2 gas mixture by plasma enhanced chemical vapor deposition (PECVD) system with a newly developed impedance matching method at frequencies 13.6–150 MHz. An increase in the rf power from 35 to 350 mW/cm2 at the highest frequency of 150 MHz increases the optical bandgap (E opt) from 2.0 to 4.5 eV. Optical emission spectroscopy (OES) of the SiH4–N2 plasma shows that the emission intensity of SiH* (414 nm) is almost proportional to deposition rate. Films of a-SiN x :H deposited at 150 MHz and 210 mW/cm2 has an optical bandgap of E opt ≈ 4.1 eV and emits visible photoluminescence (PL) at room temperature (RT).

White electroluminescence from hydrogenated amorphous-SiNx thin films

White electroluminescence (EL) was observed from hydrogenated amorphous-SiNx-based light-emitting device. Silicon nitride thin films were deposited on the indium-tin-oxide (ITO)-coated glass substrate by plasma enhanced chemical vapor deposition method with a mixture of Ar-diluted 5% SiH4 and pure N2 gases, in the ratio 2 to 1. Measured x value of the film is 0.56, and the corresponding photoluminescence of a-SiN0.56:H thin film exhibited a red-infrared spectrum, centered at 630 nm. The layer structure of the EL device is ITO/a-SiN0.56:H (80 nm)/Al, with light emitting from the ITO layer, recognizable by the naked eye in the dark, under the 14 V forward bias conditions. White EL spectra from ∼400 to 750 nm, with a central peak at 560 nm, were observed in the hydrogenated amorphous silicon nitride EL device. A carrier transport mechanism was suggested, and the EL was attributed to the recombination of carriers through the luminescent states.

Rapid thermal annealing effects on the structural properties and density of defects in SiO2 and SiNx:H films deposited by electron cyclotron resonance

The effect of rapid thermal annealing processes on the properties of SiO2.0 and SiN1.55 films was studied. The films were deposited at room temperature from N2 and SiH4 gas mixtures, and N2, O2, and SiH4 gas mixtures, respectively, using the electron cyclotron resonance technique. The films were characterized by Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance spectroscopy. According to the FTIR characterization, the SiO2.0 films show continuous stress relaxation for annealing temperatures between 600 and 1000 °C. The properties of the films annealed at 900–1000 °C are comparable to those of thermally grown ones. The density of defects shows a minimum value for annealing temperatures around 300–400 °C, which is tentatively attributed to the passivation of the well-known E′ center Si dangling bonds due to the formation of Si–H bonds. A very low density of defects (5×1016 cm−3) is observed over the whole annealing temperature range. For the SiN1.55 films, the highest structural order is achieved for annealing temperatures of 900 °C. For higher temperatures, there is a significant release of H from N–H bonds without any subsequent Si–N bond healing, which results in degradation of the structural properties of the film. A minimum in the density of defects is observed for annealing temperatures of 600 °C. The behavior of the density of defects is governed by the presence of non-bonded H and Si–H bonds below the IR detection limit.

Remote plasma-enhanced CVD of silicon nitride films: effects of diluting nitrogen with argon. Part I: effect on nitrogen plasma parameters studied by emission spectroscopy

In a series of two papers we describe the effect of argon dilution of the nitrogen passed through the RF discharge region on the plasma composition, growth rate and some characteristics of silicon nitride films deposited by remove PECVD. In this part we report the results of an emission spectroscopic study of the plasma obtained in an SiH4–N2–Ar mixture. It is shown that argon in metastable electronic excited states plays an important role during the RPECVD of silicon nitride films by providing a high concentration of atomic nitrogen which is necessary for the promotion of film growth. In Part II the influence of argon dilution on the growth rate, composition and some properties of silicon nitride films deposited by capacitively and inductively coupled remote PECVD is discussed. © 1998 John Wiley & Sons, Ltd.

Remote plasma‐enhanced CVD of silicon nitride films: effects of diluting nitrogen with argon. Part I: effect on nitrogen plasma parameters studied by emission spectroscopy

In a series of two papers we describe the effect of argon dilution of the nitrogen passed through the RF discharge region on the plasma composition, growth rate and some characteristics of silicon nitride films deposited by remove PECVD. In this part we report the results of an emission spectroscopic study of the plasma obtained in an SiH4–N2–Ar mixture. It is shown that argon in metastable electronic excited states plays an important role during the RPECVD of silicon nitride films by providing a high concentration of atomic nitrogen which is necessary for the promotion of film growth. In Part II the influence of argon dilution on the growth rate, composition and some properties of silicon nitride films deposited by capacitively and inductively coupled remote PECVD is discussed. © 1998 John Wiley & Sons, Ltd.

Remote plasma-enhanced CVD of silicon nitride films: effects of diluting nitrogen with argon. Part II: effect of nitrogen plasma parameters on layer characteristics

In Part I we reported the results of an emission spectroscopic study of the plasma obtained in an SiH4–N2–Ar mixture. It was shown that argon in metastable electronic excited states provides a high concentration of atomic nitrogen. In this part we report the results of a study of the influence of argon dilution on the growth rate, composition and properties of silicon nitride films. The exact influence of nitrogen dilution with argon depends on the process parameters and on the method of coupling of the RF power, but it is found in general that a high concentration of atomic nitrogen leads to changes in the relative amounts of Si–Hj and N–Hi bonds and in the Si/N ratio of deposited films. In particular, it is shown that hydrogen incorporation can be reduced and improved stoichiometry can be obtained. © 1998 John Wiley & Sons, Ltd.

Low temperature deposition of SiNx:H using SiH4–N2 or SiH4–NH3 distributed electron cyclotron resonance microwave plasma

Silicon nitride films were deposited at floating temperature using distributed electron cyclotron resonance plasma enhanced chemical vapor deposition (DECR-PECVD) on Si and InP substrates. The deposition parameters studied included the nature of gases (SiH4–N2 or SiH4–NH3) and the gas phase composition (SiH4/N2 or SiH4/NH3). The experimental results establish that to obtain device quality Si3N4, it is desirable to use N2 instead of NH3 and a high diluted SiH4 gas phase. These process parameters yield to a high resistivity (1016 Ω cm) and a high critical field (4.5 MV/cm). These properties confirm that the DECR technique is well suited for processing III–V compound semiconductors. NH3 does not induce such promising characteristics in terms of electrical properties but silicon nitride deposited with this gas is particularly interesting for applications where no stress is required.

Properties of very low temperature plasma deposited silicon nitride films

Plasma enhanced deposition of silicon nitride films is shown to have less N–H bonds and provide better heat resistance using SiH4–N2 than SiH4–NH3–N2 plasmas at 100 °C. Properties of silicon nitride using SiH4–N2 plasma are studied versus various deposition parameters such as radio frequency power, silane flow ratio, and deposition pressure. The experimental data indicate that the deposition process at 100 °C has a N2-reaction-controlled mechanism.

Chemical composition of soft vacuum electron beam assisted chemical vapor deposition of silicon nitride/oxynitride films versus substrate temperature

Thin silicon nitride/oxynitride films were deposited on silicon substrates by a soft vacuum electron beam plasma assisted deposition in a triad gas feedstock mixture of silane, ammonia, and nitrogen. Fourier transform infrared spectra, x-ray photoelectron spectra, Auger electron spectra, and secondary ion mass spectra of these thin films were analyzed and compared to determine both the bulk chemical composition and the interfacial properties. Film composition varied from SiO2 to Si3N4 as the substrate temperature (Ts) varied from 50 to 450 °C. Between 150 and 350 °C a stable SiOxNyHz structure formed. The films deposited with NH4–SiH4–N2 mixtures contained large (20%–60%) amounts of N–H bonds, but no detectable Si–H bonds (<0.5%). The total hydrogen content of deposited films decreased by a factor of 10 (to 2%–3%) when only nitrogen and silane were used as source gases, in comparison with that obtained using the triad feedstock mixture.

Influence of Deposition Conditions on the Properties of Silicon Nitride Films Prepared by the ECR Plasma CVD Method

Properties such as the refractive index, etch rate and resistivity of silicon nitride films (SiN) prepared by an electron cyclotron resonance (ECR) plasma CVD method have been studied and correlated with their compositional and structural properties such as the N/Si ratio, bond configurations, spin density and film density. The microwave power, SiH4 flow rate under a constant flow rate of N2 gas and gas pressure during depositions, selected as the deposition parameters, were 50–500 W, 3–12 sccm and 4×10-4-4×10-3 Torr, respectively. The refractive index showed a unique correspondence to the N/Si ratio, but Si–H bonds had to be simultaneously taken into consideration in order to explain the dependency of the etch rate. The film density also had a strong influence on the film properties. The resistivity had a strong correlation with spin density, though it was also correlated with other properties such as the N/Si ratio. The compositional and structural properties of the films can be qualitatively explained by the optical emission spectra obtained from the ECR plasma of a SiH4–N2 mixture gas.

Effects of rf Power and Substrate Temperature on Properties of a-SiNx:H Films Prepared by Glow-Discharge of SiH4–N2–H2

Amorphous SiNx:H films were prepared by the rf glow-discharge of gaseous mixtures of SiH4–N2–H2 at various substrate temperatures and rf power densities. The nitrogen and hydrogen contents of the films were determined from the intensities of the IR absorption due to vibrations of Si–N bonds and Si–H bonds. The effects of these deposition parameters on the properties of the amorphous films are discussed on the basis of the variation of the composition and structure of the films.