Si-rich Silicon Nitride Films Research Articles

Influence of high-temperature thermal annealing on paramagnetic point defects in silicon-rich silicon nitride films formed in a single-wafer-type low-pressure chemical vapor deposition reactor

The influence of high-temperature thermal annealing on silicon dangling bonds called K centers in Si-rich silicon nitride films grown in a single-wafer-type low-pressure chemical vapor deposition reactor with the SiH2Cl2-NH3 system at 750 °C has been investigated by combining thermal desorption spectroscopy (TDS), Fourier transform infrared spectroscopy-attenuated total reflection, spectroscopic ellipsometry, and electron spin resonance. In the TDS analysis, H2 desorption from the nitride films was detected above about 600 °C. It is found that thermal annealing at 750 and 900 °C caused a slight decrease in the K center density and a change in the g value of K centers, which are considered to be caused by changes in the atomic structure of the nitride films. On the other hand, thermal annealing at 1050 °C resulted in a substantial decrease in the K center density and the generation of paramagnetic defects with unprecedented characteristics. The findings in this study are expected to provide important guidelines for the design of manufacturing processes of nonvolatile memories.

Effect of thermal and pulse laser annealing on photoluminescence of CVD silicon nitride films

The light-emitting properties of Si-rich silicon nitride films deposited on the Si (100) substrate by plasma-enhanced (PECVD) and low-pressure chemical vapor deposition (LPCVD) have been investigated. In spite of the similar stoichiometry (SiN1.1), nitride films fabricated by different techniques emit in different spectral ranges. Photoluminescence (PL) maxima lay in red (640 nm) and blue (470 nm) spectral range for the PECVD and LPCVD SiN1.1 films, respectively. It has been shown that equilibrium furnace annealing and laser annealing by ruby laser (694 nm, 70 ns) affect PL spectra of PECVD and LPCVD SiN1.1 in a different way. Furnace annealing at 600 °C results in a significant increase of the PL intensity of the PECVD film, while annealing of LPCVD films result only in PL quenching. It has been concluded that laser annealing is not appropriate for the PECVD film. The dominated red band in the PL spectrum of the PECVD film monotonically decreases with increasing an energy density of laser pulses from 0.45 to 1.4 J/cm2. Besides, the ablation of PECVD nitride films is observed after irradiation by laser pulses with an energy density of > 1 J/cm2. This effect is accompanied by an increase in blue emission attributed to the formation of a polysilicon layer under the nitride film. In contrast, the LPCVD film demonstrates the high stability to pulsed laser exposure. Besides, an increase in the PL intensity for LPCVD films is observed after irradiation by a double laser pulse (1.4 + 2 J/cm2) which has not been achieved by furnace annealing.

Modification of Light Emission in Si-Rich Silicon Nitride Films Versus Stoichiometry and Excitation Light Energy

Si-rich SiN x films with different stoichiometry were grown on Si substrate by plasma-enhanced chemical vapor deposition. The Si content was varied by changing the NH3/SiH4 gas flow ratio from 0.45 up to 1.0. Conventional furnace annealing at 1100°C for 30 min was applied to produce the Si quantum dots (QDs) in the SiN x films. Spectroscopic ellipsometry was used to determine the refractive index of the SiN x films that allowed estimating the film's stoichiometry. Fourier transform infrared spectroscopy has been also used to confirm the stoichiometry and microstructure. Photoluminescence (PL) spectra of Si-rich SiN x films are complex. A non-monotonous variation of the different PL peaks versus Si excess contents testifies to the competition of different radiative channels. The analysis of PL spectra, measured at the different excitation light energies and variable temperatures, has revealed that the PL bands with the peaks within the range 2.1–3.0 eV are related to the carrier recombination via radiative native defects in the SiN x host. Simultaneously, the PL bands with the peaks at 1.5–2.0 eV are caused by the exciton recombination in the Si QDs of different sizes. The way to control the SiN x emission is discussed.

Oxide-related defects in quantum dot containing Si-rich silicon nitride films

Silicon-rich silicon nitride thin films were deposited by co-sputtering silicon and silicon nitride and annealed at high temperatures to form precipitates of silicon nanocrystals within the nitride matrix. This process was chosen to replicate the typical fabrication used for silicon nitride based quantum dots. Photoluminescence (PL) spectra were observed from the silicon nitride samples after a high temperature anneal and the PL peak shifted with increasing Si concentration. However, the time resolved PL spectra exhibited a fast decay in the nanosecond range, indicating that the PL does not originate from a radiative transition due to quantum confinement in the silicon nanocrystals. The chemical composition and the structural properties of the thin films were studied using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and Raman spectroscopy. XPS and FTIR demonstrated that there was some oxygen incorporation in the as-deposited films, forming silicon oxynitride, which increased after high temperature annealing in N2 ambient. It is proposed that the PL originates from defect states related to the increased film oxidation after high temperature annealing and the shift in PL peak energies are due to transitions between the defect levels and the band edges of the nitride matrix.

Dielectric barrier characteristics of Si-rich silicon nitride films deposited by plasma enhanced atomic layer deposition

This work proposes a new method toward improving dielectric barrier characteristics through low dielectric permittivity (k) amorphous silicon nitride films (SiNx) deposited by plasma enhanced atomic layer deposition (PEALD). The dielectric constants of the atomic layer deposition (ALD) SiNx films were in the range of 4.25–4.71 and were relatively lower than that of SiNx deposited by plasma enhanced chemical vapor deposition (PECVD). The dielectric constants of the PEALD SiNx films were nearly identical to the values for PECVD silicon carbon nitride films (SiCN). Although the ALD SiNx films were low-k, they exhibited similar levels of film stress as PECVD SiNx, and the density of ALD SiNx film was higher than that of PECVD SiCN films. The ability to suppress copper (Cu) diffusion through 10-nm thick SiNx dielectric barriers in silicon dioxide/barrier/Cu/tantalum nitride structures on Si substrates was evaluated via Auger electron spectroscopy analysis. Although PEALD SiNx films possessed low dielectric constants (<5), their barrier property to Cu diffusion was nearly equivalent to that of PECVD SiNx. The PECVD SiCN films also exhibited low dielectric constants but showed weak barrier property. Therefore, the low-k ALD SiNx reported herein could be used as a thin film thickness dielectric barrier layer in future advanced technologies.

Light Emitting Properties of Si-Rich-Si3N4 Films Grown By PECVD Method

Bandgap engineering of Si-based materials through the control of the distribution of Si nanoclusters’ (Si-ncs) offered future applications of Si-based nanostructured materials in optoelectronics as low-cost, miniaturized, and CMOS-compatible, light-emitting and photovoltaic devices. In the past, most efforts were concentrated on the development of luminescent Si-ncs embedded in SiO2 host. However, its insulating nature remains a barrier for the production of future electrically pumped LEDs and efficient photovoltaic cells. This detrimental aspect can be coped with a medium of higher conductivity and lower band gap, for instance, Si nitride. Tunable room temperature visible light emission from Si-ncs embedded in Si nitride matrices has been recently demonstrated. Present work deals with the Si-rich Silicon nitride films were grown by PECVD technique on silicon substrates. The film stoichiometry was controlled via variation of NH3/SiH4 ratio from R=0.45 up to 1.0. Thermal treatment was performed at 1100°C for 30min in nitrogen flow to form Si-ncs. To control structural and light emitting properties of the films Raman scattering, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and photoluminescence (PL) methods were used. The evolution of PL spectra with the temperature of measurements from 20 to 300 K was studied also aiming at the determination of the types of optical transitions. The PL spectra were found to be complex and the shape and magnitude of PL spectra depends on silicon nitride stoichiometry. The increase of gas ratio from R=0.63 to R=1 results in the shift of PL peak position from 1.6 eV up to 2.7 eV. Analysis of the temperature dependence of PL spectra revealed the presence of several PL components with the maxima at 2.9-3.0 eV, 2.5-2.7 eV, 1.9-2.2 eV and 1.8-1.9 eV. The peak position of the former three PL components unchanged with the decrease of temperature of the measurements. This allows describing all these components to the defects of silicon nitride host. At the same time, PL band peaked at 1.8-1.9 eV showed high-energy shift with sample cooling and can be ascribed to the exciton recombination inside Si-ncs. The presence of these latter was confirmed by Raman scattering spectra and TEM images. The nature of light emitting defects in silicon nitride, the mechanism of photoluminescence and the way for the optimization of light emitting properties are discussed.

Structural and light emitting properties of silicon-rich silicon nitride films grown by plasma enhanced-chemical vapor deposition

Si-rich Silicon nitride films fabricated by plasma enhanced chemical vapor deposition (PECVD) on p-type silicon substrates were investigated by means of photoluminescence (PL) and X-ray diffraction (XRD) methods. The film stoichiometry was controlled via varying the NH3/SiH4 ratio (R) in the range R=0.56–1.0. Thermal annealing at 1100°C for 30min in the nitrogen flow was applied to form the Si nanocrystals (NCs) embedded in the films. XRD experiment has revealed also the formation of hexagonal silicon nitride NCs with the sizes of 26–30nm in the films grown with R=1. When R decreasing, the sizes of silicon nitride NCs decreases down to 2.8–3.0nm (R=0.63). In the films grown with R=0.56 the amorphous silicon nitride, amorphous Si and crystallized Si phases have been detected. PL study showed the non-monotonic behavior of PL intensity with the R decreasing. The highest PL intensity was detected for the films grown with R=0.63. PL spectra of all films were found to be complex containing a set of PL bands peaked at about 2.8–3.0, 2.5–2.7, 2.1–2.2 and 1.8–2.0eV. Temperature behavior of PL spectra was investigated in the range 20–300K that allowed analyzing the nature of each PL component. It was shown that the peak position of all PL bands varies with the SiNx stoichiometry and Si NC sizes, demonstrating a “red” shift with R decreasing. It was revealed that the former three PL bands did not change their peak positions versus temperature of measurement that permits to assign them to the carrier recombination via radiative defects in the silicon nitride matrix. The PL band at 1.8–2.0eV has demonstrated a “blue” spectral shift with cooling similar to the Si band gap shrinkage. Based on this behavior, the 1.8–2.0eV PL band has been attributed to exciton emission inside of Si NCs. The role of silicon nitride NCs in photoluminescence and its excitation is discussed.

Different charging behaviors between electrons and holes in Si nanocrystals embedded in SiNx matrix by the influence of near-interface oxide traps**Project supported by the National Basic Research Program of China (Grant No. 2010CB934402) and the National Natural Science Foundation of China (Grant No. 11374153).

Si-rich silicon nitride films are prepared by plasma-enhanced chemical vapor deposition method, followed by thermal annealing to form the Si nanocrystals (Si-NCs) embedded in SiNx floating gate MOS structures. The capacitance–voltage (C–V), current–voltage (I–V), and admittance–voltage (G–V) measurements are used to investigate the charging characteristics. It is found that the maximum flat band voltage shift (ΔVFB) due to full charged holes (∼ 6.2 V) is much larger than that due to full charged electrons (∼ 1 V). The charging displacement current peaks of electrons and holes can be also observed by the I–V measurements, respectively. From the G–V measurements we find that the hole injection is influenced by the oxide hole traps which are located near the SiO2/Si-substrate interface. Combining the results of C–V and G–V measurements, we find that the hole charging of the Si-NCs occurs via a two-step tunneling mechanism. The evolution of G–V peak originated from oxide traps exhibits the process of hole injection into these defects and transferring to the Si-NCs.

Effect of the stoichiometry of Si-rich silicon nitride thin films on their photoluminescence and structural properties

Si-rich Silicon nitride films were grown on silicon substrates by plasma enhanced chemical vapor deposition. The film stoichiometry was controlled via the variation of NH3/SiH4 ratio from 0.45 up to 1.0. Thermal annealing at 1100°C for 30min in the nitrogen flow was applied to form the Si nanocrystals in the films that have been investigated by means of photoluminescence and Raman scattering methods, as well as transmission electron microscopy. Several emission bands have been detected with the peak positions at: 2.8–3.0eV, 2.5–2.7eV, 2.10–2.25eV, and 1.75–1.98eV. The temperature dependences of photoluminescence spectra were studied with the aim to confirm the types of optical transitions and the nature of light emitting defects in silicon nitride. The former three bands were assigned to the defects in silicon nitride, whereas the last one (1.75–1.98eV) was attributed to the exciton recombination inside of Si nanocrystals. The photoluminescence mechanism is discussed.

Density improvement of Si quantum dots embedded in Si-rich silicon nitride films by light-filtering rapid thermal processing

Si-rich silicon nitride (SRSN) (SiNx, x ≈ 0.49) films were deposited on Si (100) and quartz substrates by magnetron co-sputtering. For comparison, two sets of identical samples were then treated in a nitrogen atmosphere by conventional rapid thermal processing (CRTP) and light-filtering rapid thermal processing (LRTP) at temperature in a range of 950–1,100 °C, respectively. Raman spectroscopy, grazing incident X-ray diffraction, transmission electron microscope, photoluminescence (PL) and Hall measurements were used to analyze the structure, luminescence, and conductivity of the films. Experimental results show that the samples treated with LRTP posses higher dot number density, crystalline volume fraction, PL intensity and conductivity than the CRTP samples. The quantum effects in rapid thermal processing have a negative influence on the formation and density of Si quantum dots (QDs) in SRSN films. The present work opens new strategy for the formation of high density Si QDs embedded in SRSN films.

Plasma-Enhanced Chemical Vapor Deposition of Si-Rich Silicon Nitride Films Optimized for Waveguide-Based Sensing Applications in the Visible Range

Plasma-Enhanced Chemical Vapor Deposition of Si-Rich Silicon Nitride Films Optimized for Waveguide-Based Sensing Applications in the Visible Range

Plasma-Enhanced Chemical Vapor Deposition of Si-Rich Silicon Nitride Films Optimized for Waveguide-Based Sensing Applications in the Visible Range

Hydrogenated amorphous silicon nitride (a-SiNx:H) films were deposited by plasma-enhanced chemical vapor deposition (PECVD), an attractive process for integrated optical device fabrication owing to the low temperatures involved (typically 200–400 °C). Two regimes of plasma radio frequency (380 kHz and 13.56 MHz) and a range of plasma powers were studied. Through physical and chemical analyses, we demonstrate the relationship between film optical properties and chemical composition. Films with refractive index close to that of stoichiometric Si3N4 and with very low absorption coefficients owing to the small number of Si–Si bonds, are obtained by low-frequency (LF) PECVD at low powers.

Photoluminescence of Si-rich silicon nitride: Defect-related states and silicon nanoclusters

The photoluminescence (PL) from defect-related states and Si nanoclusters was observed in the Si-rich silicon nitride films simultaneously. The weaker red-light emission of Si nanoclusters was obtained in the 1100°C annealed films with the 514.5nm excitation. Due to the quantum confinement effect, the PL peaks redshift with the increase of the excess Si concentration. Excited by the 325nm line, strong PL from N and Si dangling bond centers was observed in either the as-deposited films or the 1100°C annealed ones. The results demonstrate that the luminescence from defect-related states or Si nanoclusters is selected by the excitation energy.

Optical characterization of Si-rich silicon nitride films prepared by low pressure chemical vapor deposition

An investigation of the optical properties of Si-rich silicon nitride films prepared by low pressure chemical vapor deposition (LPCVD) from dichlorosilane (SiH 2Cl 2, DCS) and ammonia (NH 3) mixtures has been performed. From TEM analysis, it was found that the excess Si forms nanocrystals the size of which depends on the temperature. The real and the imaginary part of the refractive index of the films were calculated using spectroscopic ellipsometry by fitting the ellipsometric data in the range 1000–250 nm using the Tauc–Lorentz model. It was found that the optical constants of the films mainly depend on their chemical composition which can be controlled by the DCS/NH 3 flow ratio. Annealing at temperatures up to 1100 °C for 4 h does not considerably affect the refractive index of the films. Depending on their stoichiometry and the annealing conditions applied after growth, some of the films emitted light in the visible at room temperature. This was attributed to the quantum confinement of carriers in the Si nanocrystals contained in the films.

Light emission from silicon-rich nitride nanostructures

Light-emitting Si-rich silicon nitride (SRN) films were fabricated by plasma enhanced chemical vapor deposition followed by low temperature (500–900°C) annealing. The optical properties of SRN films were studied by micro-Raman and photoluminescence spectroscopy and indicate the presence of small Si clusters characterized by broad near-infrared emission, large absorption/emission Stokes shift, and nanosecond recombination. Our results are supported by first-principles simulations indicating that N atoms bonded to the surface of nanometer Si clusters play a crucial role in the emission mechanism of SRN films. Light emission from SRN systems can provide alternative routes towards the fabrication of optically active Si devices.

Ellipsometric investigation of nucleation sites for chemical vapor deposition of Si on SiO2 and Si3N4 surfaces

The nucleation of polycrystalline silicon by chemical vapor deposition on stoichiometric and silicon-rich silicon dioxide and silicon nitride films was studied using real time ellipsometry. The time of the appearance of the first stable Si nuclei, the incubation time (tinc), was found to vary with the Si content within a film type (oxide or nitride) and also tinc varied for different film types with the shortest tinc for Si-rich silicon nitride films. Differences between Si bound (to O or N) and free Si (bound to Si) were observed with free Si being more effective at promoting nucleation. Anion screening effects might also yield second order reactivity differences.

Bond density and physicochemical properties of a hydrogenated silicon nitride film

Hydrogenated silicon nitride films of 100–300 nm in thickness were prepared on GaAs and Si wafers by plasma enhanced chemical vapor deposition. The number of Si and N atoms in the film was measured by Rutherford backscattering. The number of H atoms was determined by an energy recoil detection (ERD) technique. A zero dose extrapolation method was employed to eliminate the effect of undesirable decrease in ERD count during ion-beam irradiation. The atomic density was determined by dividing the number of atoms by the film thickness obtained from ellipsometry. Infrared absorption cross sections of the SiH and NH bonds were obtained by using a correlation curve between IR band areas and the number of hydrogen atoms from ERD. The density of chemical bonds such as SiSi, SiN SiH and NH was obtained by equating the atomic density with the absorption cross-section of the bonds. Investigation of the refractive index of films with different chemical structures suggests that a concept of the bond refraction can explain a relatively high refractive index (1.8–2.3) and low density (2.1–2.7g/cm −3) of the Si-rich silicon nitride films, as compared with a stoichiometric compound Si 3N 4. The etch rate of the silicon nitride film in buffered oxide etchant solution showed a linear relation against the density of silicon atoms that were not bonded to hydrogen.

Properties of plasma-deposited Si-rich silicon nitride films in current enhancement injectors

Si-rich silicon nitride (SiNx:H) film deposited on top of thermal SiO2 has been found to give rise to current enhancement through the double-layer sandwich structure similar to the injector device based on Si-rich SiO2 [DiMaria et al., J. Appl. Phys. 51, 2722 (1980)]. In this paper, the properties of the SiNx:H film, deposited by the plasma-enhanced chemical vapor deposition technique and its injector structure, are reported. It has been found that the as-deposited film is amorphous, but subsequent annealing done at 900–1100 °C leads to the crystallization of the excess Si in the material. For injector structures made of moderately Si-rich films, the current enhancement effect does not depend strongly on the film composition and the subsequent heat treatment. For samples made of very Si-rich films, however, the post-metallization anneal step (at 400 °C) causes the as-deposited SiNx:H film to react strongly with the gate Al. This lowers the crystallization temperature of the excess Si very significantly, and also supresses the current enhancement in the corresponding injector structure. Possible mechanisms are discussed. The cyclability of the injector structure, in particular, charge trapping and degradation of the underlying SiO2 layer as a result of current injection, is also discussed.