Plasmons in double interfaces system of Si3N4/SiO2/Si irradiated by Co

The first level plasmons of Si in the pure Si state, in the SiO₂ state and in the Si₃N₄ state (corresponding to bonding energy 116.95, 122.0 and 127.0 eV) were investigated directly with X-ray photoelectron spectroscopy before and after ⁶⁰Co radiation. The experimental results demonstrate that there existed two interfaces, one consisted of plasmons of Si in the Si₃N₄ and SiO₂ states, while another was made of plasmons of Si in the pure Si state and in the SiO₂ state. When the Si₃N₄-SiO₂-Si samples were irradiated by ⁶⁰Co, the interface at Si₃N₄/SiO₂ was extended and at the same time the center of this interface moved towards the surface of Si₃N₄. The concentration of plasmon for silicon in the SiO₂ state is decreased at the SiO₂-Si interface, and the effects of radiation bias field on plasmons in the SiO₂-Si interface are observable. Finally, the mechanism of experimental results is analyzed by the quantum effect of plasmon excited by the photoelectron.     

Interface states in MNOS systems

The quasistatic C-V technique can be used under certain conditions to obtain the energy distribution of the interface states located in the silicon band gap of an MNOS system. An increase of the SiO₂ thickness leads to a considerable decrease in the interface state density around the mid-gap. It is shown that, for the thin oxide MNOS capacitors we measured, the Si₃N₄SiO₂ interface dominates over the SiSiO₂ interface in producing interface states with a high density.     

Structure of double interfaces system of Si3N4/SiO2/Si irradiated by γ-rays

The interfacial structures of double interfaces system of Si₃N₄/SiO₂/Si were examined using X-ray photoelectron spectroscopy (XPS) before and after ⁶⁰Co radiation. The experimental results demonstrate that there existed two interfaces, one consisted of Si₃N₄ and SiO₂, while another was made of Si and SiO₂, the interface between SiO₂ and Si was extended towards the interface of the Si₃N₄/SiO₂ meanwhile the center of the former interface was removed in the direction of the latter interface by ⁶⁰Co. The concentration of silicon in the Si₃N₄ state (BE 101.8 eV) was decreased with the variation of radiation dosage as well as bias field within the SiO₂-Si interface, remarkably. The mechanism for the experimental results is analyzed.     

Liquid-phase bonding of silicon nitride ceramics using Y2O3–Al2O3–SiO2–TiO2 mixtures

Hot-pressure sintered β-Si₃N₄ ceramic was bonded to itself using Y₂O₃–Al₂O₃–SiO₂–TiO₂ mixtures. Reactive behavior at interface between Si₃N₄ and Y₂O₃–Al₂O₃–SiO₂–TiO₂ mixtures during silicon nitride ceramic joining was studied by means of scanning electron microscopy (SEM), electron probe microanalyses (EPMA), X-ray diffraction (XRD) and auger electron spectroscopy (AES). The joint strength under different bonding conditions was measured by four-point bending tests. The results of EPMA, AES and XRD analyses show that the liquid glass solder reacts with silicon nitride at interface, forming the Si₃N₄/Y–Si–Al–Ti–O–N glass/TiN/Y–Si–Al–O glass gradient interface. From the results of four-point bending tests, it is known that with increase of bonding temperature and holding time, the joint strength increased reaching a peak, and then decreased. The maximum joint strength of 200 MPa measured by the four-point bending tests is obtained for silicon nitride bonded at 1823 K for 30 min.     

Profiling of deep traps in silicon oxide–nitride–oxide structures

Thermally stimulated exoelectron emission has been applied for high-resolution depth profiling of traps in amorphous SiO₂/Si₃N₄/SiO₂ (ONO) dielectric stacks used in silicon–oxide–nitride–oxide–silicon (SONOS) memory devices. It is shown that maximum density of traps responsible for charge storage in ONO structures is at the interface between top silicon oxide and silicon nitride in ONO.     

Auger electron spectroscopy and electron energy loss spectroscopy studies of the formation of silicon nitride by implanting low energy nitrogen ions into silicon

Thin (d ? 10 nm) films of almost stoichiometric silicon nitride were prepared by implanting nitrogen ions with energies below 5 keV into silicon with subsequent thermal annealing. A combination of Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS) was used to determine the chemical composition and to investigate the chemical bonding states of the thin films. The spectra are in good agreement with those obtained for Si₃N₄ produced by chemical vapour deposition. The use of AES and electron ELS allowed the stepwise formation of the SiN bonds to be investigated for the first time, and hence further information about the electronic structure of Si₃N₄ was obtained. Depth-concentration profiles for nitrogen are presented.     

Thickness dependence of high-k materials on the characteristics of MAHONOS structured charge trap flash memory

The electrical characteristics of tunnel barrier engineered charge trap flash (TBE-CTF) memory of MAHONOS (Metal/Al₂O₃/HfO₂/SiO₂/Si₃N₄/SiO₂/Si) structure were investigated. The stack of SiO₂/Si₃N₄/SiO₂ films were used as engineered tunnel barrier, HfO₂ and Al₂O₃ films were used as charge trap layer and blocking oxide layer, respectively. For comparison, the electrical characteristics of MONOS (Metal/SiO₂/Si₃N₄/SiO₂/Si), MONONOS (Metal/SiO₂/Si₃N₄/SiO₂/Si₃N₄/SiO₂/Si), and MAHOS (Metal/Al₂O₃/HfO₂/SiO₂/Si) were also evaluated. The energy band diagram was designed by using the quantum-mechanical tunnel model (QM) and then the CTF memory devices were fabricated. As a result, the optimized thickness combination of MAHONOS structure was confirmed. The tunnel barrier engineered MAHONOS CTF memory showed a considerable enhancement of program/erase (P/E) speeds, retention time and endurance characteristics.     

Formation mechanism of 21R AlN-polytypoids in aluminothermic reduction and nitridation process

Synthesis of 21R AlN polytypoids was investigated using Al and ultrafine SiO₂ powder in a flowing nitrogen atmosphere by means of thermal gravity (TG), differential scanning calorimeter (DSC), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) linked with energy dispersive spectrometer (EDS). The results showed that the formation mechanism of AlN polytypoids was different from that in reaction sintering process using Si₃N₄, AlN, Al₂O₃ and other sintering additive as raw materials. It was suggested that firstly Al reduce SiO₂ into Si and is also nitrided into AlN, then AlN, Al₂O₃ and SiO₂ dissolve into silicon liquid until the AlN polytypoids precipitate in saturated liquid in a flowing nitrogen atmosphere at lower than 1700 °C.     

Influence of dopant concentration and type of substrate on the local organization of low-pressure chemical vapour deposition in situ boron doped silicon films from silane and boron trichloride

The deposition of in situ boron doped silicon films from boron trichloride BCl₃ and silane SiH₄ in a conventional low-pressure chemical vapour deposition reactor has been studied for high boron doping levels and two kinds of substrates (SiO₂ and Si₃N₄). On the basis of transmission electron microscopy and X-ray photoelectron spectroscopy results, these films appear to be highly sensitive to the local electronic environment of both substrate and deposited atoms. Indeed, beyond a critical doping level, this material becomes more and more amorphous, due to the occurrence of a particular organization of boron atoms in the silicon matrix. This behaviour results in a lowering of the well-known boron enhancement effect for deposition rate and crystalline fraction.     

The formation of amorphous and crystalline condensates from the vapour phase

An electron microprobe technique is described for determining the thickness of SiO₂ and Si₃N₄ in wafers and devices. The technique is based on the measurement of oxygen and silicon X-ray intensities at 2.5 kV and 10 kV through the nitride overlay. At the lower accelerating voltage, both intensities decrease with increasing nitride thickness owing to absorption and silicon distribution in depth. The SiO₂ thickness, however, is obtained by measuring the oxygen X-ray intensity at the higher voltage (10 kV), because at this voltage the oxygen intensity is not dependent on the nitride thickness.Empirical relationships expressing Si₃N₄ thickness in terms of Si and O X-ray intensities and SiO₂ thickness are derived.     

The deposition of group III nitrides on silicon substrates

The reaction between silicon substrates and ammonia present in the systems GaCl (AlCl₃)-NH₃-H₂ (He) during the vapour phase epitaxy of Group III nitrides has been investigated. Silicon was treated with an NH₃-HCl-H₂ mixture at a constant temperature in the range873–1273 K. Using electron spectroscopy for chemical analysis measurements layers of Si₃N₄ and Si₃N₄-SiO₂ were detected at the silicon surface. Reflection high energy electron diffraction tests indicated the amorphous nature of this passivating layer which was found partially or completely to prevent epitaxial deposition of the Group III nitrides. The deposits of GaN on Si(111) and Si(100) were either polycrystalline or textured and an amorphous Si₃N₄-SiO₂ interface was found.     

Core and valence electron excitations of amorphous silicon oxide and silicon nitride studied by low energy electron loss spectroscopy

Valence and core electron excitations were measured for thermal SiO₂ films and chemical-vapour-deposited Si₃N₄ films using low energy electron loss spectroscopy (ELS). A reasonable interpretation of the spectra can be obtained using electron energy level diagrams derived from optical and X-ray experiments and from theoretical calculations using literature values. The electron levels of these amorphous materials can then be described by localized molecular states. The ELS spectra show the formation of basic [SiO₄] and [SiN₄] tetrahedra and the existence of Si-Si bonds in mixed tetrahedra, suggesting a deviation from ideal stoichiometry and the presence of broken Si-O and Si-N bonds. Auger spectra have also been measured for elemental silicon, for SiO₂ and for Si₃N₄ and are discussed in terms of chemical shifts and line shape.     

Preparation and interface modification of Si_3N_(4f)/SiO_2 composites

In order to modify the interface, SiON coating was introduced on the surface of silicon nitride fiber by perhydropolysilazane conversion method. Si₃N_4f/SiO₂ and Si₃N_4f/SiON_c/SiO₂ composites were prepared by sol-gel method to explore the influence of SiON coating on the mechanical properties of composites. The results show that with the protection of SiON coating, Si₃N₄ fiber enjoys a strength increase of up to 24.1% and Si₃N_4f/SiON_c/SiO₂ composites have a tensile strength of 170.5 MPa and a modulus of 26.9 GPa, respectively. After 1000 °C annealing in air for 1 h, Si₃N_4f/SiON_c/SiO₂ composites retain 65.0% of their original strength and show a better toughness than Si₃N_4f/SiO₂ composites. The improvement of mechanical properties is attributing to the healing effect of SiON coating as well as its intermediate coefficient of thermal expansion between Si₃N₄ fiber and SiO₂ matrix.     

Nitrogen ion induced nitridation of Si(111) surface: Energy and fluence dependence

We present the surface modification of Si(111) into silicon nitride by exposure to energetic N₂⁺ ions. In-situ UHV experiments have been performed to optimize the energy and fluence of the N₂⁺ ions to form silicon nitride at room temperature (RT) and characterized in-situ by X-ray photoelectron spectroscopy. We have used N₂⁺ ion beams in the energy range of 0.2–5.0 keV of different fluence to induce surface reactions, which lead to the formation of Si_xN_y on the Si(111) surface. The XPS core level spectra of Si(2p) and N(1s) have been deconvoluted into different oxidation states to extract qualitative information, while survey scans have been used for quantifying of the silicon nitride formation, valence band spectra show that as the N₂⁺ ion fluence increases, there is an increase in the band gap. The secondary electron emission spectra region of photoemission is used to evaluate the change in the work function during the nitridation process. The results show that surface nitridation initially increases rapidly with ion fluence and then saturates.     

Investigations of gold surface state energy levels at the silicon-silicon dioxide interface by the MOS capacitance-voltage measurement technique

The influence of gold in the Si/SiO₂ system has been studied both theoretically and experimentally. The gold is found to introduce two regions of shallow acceptor surface state energy levels in the silicon band gap at the SiSiO₂ interface: one at 0.09 eV from the valence band edge and the other at 0.13 eV from the conduction band edge. It is tentatively postulated that both the surface state energy levels are due to gold atoms in substitutional sites.The two deep normal bulk gold energy levels in silicon do not seem to occur at the SiSiO₂ interface.Finally a model of gold diffusion is suggested, and gold is found to diffuse through the bulk silicon by a complex interstitial and substitutional mechanism.     

Applying RF current harmonics for end-point detection during etching multi-layered substrates and cleaning discharge chambers with NF3 discharge

The present paper reports the results of studying the characteristics of the etching process of multi-layered materials (Si₃N₄/SiO₂/Si and SiO₂/Si) and of cleaning technological chambers covered with silicon nitride films (Si₃N₄) in a NF₃ RF capacitive discharge. The process of chamber cleaning was monitored with a mass spectrometer. The gas pressure, RF voltage amplitude, current-voltage phase shift, ohmic current as well as the second harmonic of the RF current were also recorded. The opportunity of using these parameters for end-point detection of etching and plasma cleaning is discussed. It is found that the second harmonic of the RF current may be successfully used for end-point detection of multi-layered materials etching and to monitor the cleaning process of technological chambers. The cleaning of chambers of complicated design may possess a double-stage pattern.     

Electron energy-loss spectroscopy investigation of Y2O3 films on Si (001) substrate

Electron energy -loss spectroscopy has been used to investigate the interface between a Y₂O₃ film and the silicon substrate. The chemical composition of the interface layer is revealed to be nearly pure amorphous SiO₂. Yttrium silicates are found at the Y₂O₃/SiO₂ interface region. The formation of the interfacial yttrium silicates has been interpreted by the direct chemical reaction between the deposited Y₂O₃ film and the SiO₂ interface layer. The Si L₂₃ and O K edges of yttrium silicates (Y₂SiO₅ and Y₂Si₂O₇) have been calculated by the first-principle full multiple - scattering method. The theoretical results are consistent with the experimental spectra, which confirms the formation of yttrium silicates.     

Silicon-rich oxynitride hosts for 1.5 μm Er emission fabricated by reactive and standard RF magnetron sputtering

This study compares the erbium emission from different Si-rich silicon oxynitrides matrices fabricated by magnetron sputtering. The Er-doped layers were grown by two different sputtering configurations: (i) standard co-sputtering of three confocal targets (Er₂O₃, Si₃N₄ and SiO₂) under Ar plasma, and (ii) reactive co-sputtering under Ar + N₂ plasma of either three (Er₂O₃, pure Si and SiO₂) or two targets (Er₂O₃ and pure Si). The last reactive configuration was found to offer the best Er³⁺ PL intensity at 1.5 μm. This highest PL intensity was found comparable to the corresponding emission from Er-doped silicon-rich silicon oxide.     

Investigation of electronic structure of Si nanocrystals and their interface with host matrix in P-doped SiO2:Si and Al2O3:Si nanocomposites

The system of the nanoinclusions of Si in the SiO₂ and Al₂O₃ matrix (SiO₂:Si, Al₂O₃:Si) attracts great attention due to its ability of the luminescence in visible and near-IR range of spectrum. The influence of the P ion alloying on the electronic structure of nanocomposites was investigated. The P ion doping and post-annealed at T = 1000 °C (2 h) results in the enhancement of the photoluminescence (PL) peak connected with the Si nanocrystals. The electronic structure was investigated by X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy losses spectroscopy (HREELS) methods. Ion surface modification and annealing forms the special nanostructure with Si nanocrystals in SiO₂ and Al₂O₃ matrix having high density of interfaces with special atomic structure and various degree of oxidation of Si atoms on the boundaries. HREELS investigations show that the P ion doping increases the probability of interband transitions in SiO₂:Si and Al₂O₃:Si composites.     

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.