Formation of Si nanocrystals utilizing a Au nanoscale island etching mask

Si nanocrystals were formed by using a Au nanoscale island etching mask. A high-resolution transmission electron microscopy image showed that the Si nanocrystals were created on a SiO_x layer, and the luminescence peak related to Si nanocrystals was observed in the cathodoluminescence spectrum. Capacitance-voltage measurements demonstrate a metal-insulator-semiconductor behavior with a flatband voltage shift for the Al/SiO₂/nanocrystalline Si/SiO₂/p-Si structures, indicative of the existence of the Si nanocrystals embedded into the SiO_x layer. These results indicate that Si nanocrystals embedded into the SiO_x layer can be formed by using a Au island etching mask.     

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.     

A model of the passivation of ultrathin SiO2 layer/Si substrate interfaces by atomic hydrogen from a thermalised plasma source

A theoretical model is developed to account for the kinetics of the decrease of the density of recombination active centres at the interface of SiO₂ layers with Si(111) substrates as a result of treatment by thermalised hydrogen plasma. The recombination active centres at the SiO₂/Si interface are ascribed to be the P_b centres. The model developed takes into account the kinetics of the incorporation of hydrogen atoms into the SiO₂ layer from the plasma source and their interaction with both passivated and unpassivated P_b centres. A special attention is given to ultrathin (∼2 nm) SiO₂ layers. A simplification of the general model to this important case allows one to obtain analytical solution for the density of unpassivated recombination active P_b centres as a function of the flow of hydrogen atoms from plasma, the initial density of P_b centres, and the treatment time. The model applicability is verified comparing the results of calculations with the experimentally measured values of the relative density of recombination active centres at the ultrathin SiO₂/Si(111) substrate interface upon passivation by atomic hydrogen from thermalised plasma source. A conformity of the model predictions to the experimental results is demonstrated.     

Structural roughness and interface strain properties in Si/SiO2/Poly-Si1−x Ge x tri-layer system with ultrathin oxide

We have explored the microstructure and local interface strain in the poly-Si_1-xGe_x/SiO₂/Si tri-layer system with ultrathin oxides. High-resolution transmission electron microscopy (HRTEM) and high-resolution X-ray diffraction rocking curves (HR-RC) and two-dimensional reciprocal space mapping (2D-RSM) were the main characterization tools. The poly-Si_1-xGe_x/SiO₂/Si structures have x=0, 0.2, and 0.35 for ultrathin oxides (2.0–3.0 nm). The result shows that for the adopted growth process, the poly grain size depends very strongly on the Ge concentration, and it increases with increasing Ge mole fraction. In turn, this increase of the grain size in the poly-Si_1-xGe_x/SiO₂/Si reduces the strain in the film, which then affects the interface strain at the lower SiO₂/Si interface. In addition, the presence of defects at the SiO₂/Si interface was found to be greater for samples with no local interface strain.     

The effect of He or Ar/O2 plasma treatment on Si surface prior to chemical vapor deposition of SiO2

The effect of O₂ plasma pretreatment on the SiO₂/Si interface property was studied using direct plasma varying the plasma power, He or Ar/O₂ ratio and the pretreatment time. The decrease of the pretreatment plasma power decreased the plasma damage and improved the interface property. The addition of He in O₂ glow discharge improved the electrical and the interface properties and there was an optimum He/O₂ ratio. The improvement of the interface property by Ar/O₂-plasma pretreatment was better than that by He/O₂, which is believed to be due to the lower oxidation rate of the Si surface. C–V analysis showed that the P_b center defect density was influenced by plasma pretreatment process parameters. To investigate the oxidation states near to and at the SiO₂/Si interface, X-ray photoelectron spectroscopy depth analysis was used and the gas phase in the glow discharge was investigated using optical emission spectroscopy analysis at various experimental conditions.     

Epitaxial Y2O3 film growth on an oxidized Si surface

The effects of the Si surface state on epitaxial growth of Y₂O₃ layers were investigated by various measurement methods. The characterization using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and high-resolution transmission electron microscopy (HRTEM) shows excellent film crystallinity when grown on an oxidized Si surface. The crystalline structure of the film was influenced by the interfacial mosaic structure, which depended on whether the Si surface contained adsorbed O or not. The thin SiO₂ layer of approximately 1.5 nm, provided favorable interfacial reaction sites for the nucleation of Y₂O₃, and still maintained the structural registry with the underlying Si substrate. In particular, the reaction between the Y and SiO₂ layer resulted in coherent finite growth, whereas the direct interaction between Y and Si was hindered by the nucleation of Y₂O₃. The high-quality epitaxial layer with the minimum channel yield (χ_min), lower than 3%, could be grown on the oxidized Si surface.     

The role of SiO2 buffer layer in the growth of highly textured LiNbO3 thin film upon SiO2/Si by pulsed laser deposition

Highly c-axis-oriented lithium niobate (LiNbO₃) thin films have been grown on Si with optimum thickness of the SiO₂ buffer layer by pulsed laser deposition technique. The amorphous SiO₂ buffer layer was formed on Si (100) wafer by thermal oxidation method. The crystallinity and c-axis orientation of LiNbO₃ films were strongly influenced by the thickness of amorphous SiO₂ buffer layers. The optimum thickness of the amorphous SiO₂ buffer layer was found to be about 230 nm for the growth of highly c-axis-oriented LiNbO₃ films. The achieved films have smooth surface and sharp interface. The prism coupler method indicates that the prepared LiNbO₃ films have great potential for optical waveguide device.     

Comparison study on the size and phase control of nanocrystalline TiO<Subscript>2</Subscript> in three Ti–Si oxide structures

Three types of Ti–Si binary oxides have been prepared by sol-gel processes. The effects of SiO₂ addition and annealing temperature on the grain size, phase transition, dispersion, and microstructure of nanocrystalline (nc) TiO₂ anatase in the three Ti–Si oxide structures have been comparatively investigated by X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy (HRTEM). The grain growth and anatase-rutile transformation (ART) of ncTiO₂ were found to depend not only on the SiO₂ content and annealing temperature, but also on the composite structure. Both the grain growth and the ART of ncTiO₂ proved to be significantly inhibited with increasing SiO₂ content for all of the Ti–Si samples, but the structure of intimately mixed Ti–Si binary oxide showed the best inhibiting ability under high-temperature annealing. This result might be attributed to variations in the large lattice strains in ncTiO₂, which were mainly induced by the substitution of Ti⁴⁺ by Si⁴⁺. Plausible mechanisms for the grain growth and ART of ncTiO₂ are proposed. To inhibit the grain growth of ncTiO₂, the addition of 10 and 30 mol% SiO₂ proved to be optimal for Ti–Si samples annealed at 773 K and 1273 K, respectively.     

Silicate formation at the interface of Pr-oxide as a high-K dielectric and Si(001) surfaces

The composition and chemical bonding of the first atoms across the interface between Si(001) and the dielectric determine the quality of dielectric gate stacks. An analysis of that hidden interface is a challenge as it requires both, high sensitivity and elemental and chemical state information. We used X-ray absorption spectroscopy in total electron yield and total fluorescence yield at the Si2p and the O1s edges to address that issue. We report on results of Pr₂O₃/Si(001) as prepared by both, epitaxial growth and metal organic chemical vapor deposition (MOCVD), and compare to the SiO₂/Si(001) system as a reference. We find evidence for the silicate formation at the interface as derived from the characteristic features at the Si2p and the O1s edges. The results are in line with model experiments in which films of increasing film thickness are deposited in situ on bare Si(001) surfaces.     

Atomic layer deposition of SiO2 from Tris(dimethylamino)silane and ozone by using temperature-controlled water vapor treatment

Atomic layer deposition of SiO₂ from tris(dimethylamino)silane (TDMAS) and ozone as precursors on Si(100) surfaces at near-room temperatures was studied by infrared absorption spectroscopy with a multiple internal reflection geometry. TDMAS can be adsorbed at OH sites on hydroxylated Si surfaces at room temperature. Ozone oxidation of the TDMAS-treated Si surface is effective in removing hydroaminocarbon adsorbates introduced during TDMAS adsorption at room temperature. After oxidation by ozone, treatment with H₂O vapor at a substrate temperature of around 160 °C causes regeneration of OH sites for TDMAS adsorption. Cycles involving TDMAS adsorption and ozonization at room temperature followed by H₂O treatment at 160 °C permit the buildup of layers of SiO₂. The amount of residual hydroaminocarbon at the interface between the growing SiO₂ film and the substrate can be reduced with the ozone treated Si surface as a starting surface.     

Low temperature diffusion of Au into Si in the Si(substrate)-Au(film) system

When the clean surface of a Si crystal is covered with an evaporated Au layer and heated in an oxidizing atmosphere at 100°–300°C, i.e. below the Si-Au eutectic point (370°C), Si atoms are ejected from the Si-Au interface and migrate through the Au film to its surface to appear as a SiO₂ layer. For an understanding of this low temperature ejection, an AES study of the Si-Au interface region has been undertaken. It is proposed that the Si at the interface is metallic and forms a metallic bonding with Au, the melting point of the interface being comparable with that of Si-Au eutectic. The metallic Si was identified from Si (LVV) Auger spectra of “vapor-quenched” metastable Si-Ag, Si-Au and Si-Cu alloys. The low temperature ejection is possible, therefore, from this metallic interface. To support this statement, low temperature ejection of Au atoms from the interface into the bulk of Si was also studied by photoconductivity measurements of the above specimen. The analysis of the photoresponse spectra of the ejected Au atoms inside the Si crystal suggests that the atoms diffuse interstitially with a diffusion coefficient of about 10^-9 cm² sec^-1 at 340°C.     

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.     

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.     

Depth redistribution of components of SiOx layers prepared by magnetron sputtering in the process of their decomposition

The process of thermal decomposition of SiO_x layers prepared by magnetron co-sputtering of Si and SiO₂ on Si and quartz substrates is studied by Auger and secondary ion mass spectroscopies. It is found that high temperature annealing of the layers causes a Si-depleted region near the layer/substrate interface. It is shown that the formation of this region does not depend on the type of substrate but depends on the content of excess Si and is observed at high content of excess Si. When the excess Si content decreases, the Si-depleted region at first smears and then disappears. The mechanism of SiO_x decomposition and possible reasons for the appearance of the Si-depleted region are discussed.     

Electric field induced interfacial reaction of Au-Ag bimetal film on SiO2 surface

Interface evolution of nanometer scale Au-Ag bimetal film on SiO₂ substrate surface during electromigration was investigated by angle resolved X-ray photoelectronspectroscopy (ARXPS). ARXPS spectra showed that a chemical reaction between Au-Ag filmand SiO₂ layer occurred at interface, which caused Au, Ag and Si having differentdistribution and chemical states across the film. This result as well as previousobservation by atomic force microscopy (AFM) demonstrate that electromigration of Au-Agbimetal film on SiO₂ surface is accompanied with strong interfacial chemicalreaction rather than a simple lateral physical diffusion process.     

Comparison of models for silicon etching in CF4 + O2 plasma

The plasma chemical etching (PCE) of Si in CF₄ + O₂ plasma is considered. The concentrations of plasma components are calculated using values extrapolated from experimental data. Resulting calculations of plasma components are used for the calculation of Si etching rates. The concentrations of the adsorbed layer and surface components, obtained from analysis of PCE of silicon, are used for the comparison of site-balance and adsorbed-layer models. It is found that adsorbed-layer model predicts higher concentration of SiO₂ molecules on the surface than site-balance model. The difference in SiO₂ concentration is important during ion-beam-assisted etching and reactive ion etching processes as the models predict different etching rates due to different sputtering yields of Si atoms and SiO₂ molecules.     

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.     

Valence number transition and silicate formation of cerium oxide films on Si(100)

Interface reactions of a Ce-oxide layer with Si(100) wafers have been characterized by X-ray photoelectron spectroscopy. The ratio of Ce atoms in Ce³⁺ states within the Ce-oxide layer has been found to decrease from 47% at as-deposited sample to 26% after annealing. From detailed reaction analysis of valence number transitions of Ce atoms and the creation of SiO₂ layer at the interface, the reacted Ce³⁺ atoms are converted into silicates and Ce⁴⁺ with a ratio of 2:1. The energy bandgap of Ce-silicate layer has been determined as 7.67 eV and the valence band offset with respect to Si(100) wafer has been extracted as 4.35 eV.     

Rapid monitoring of the charging properties of ion-doped MOS structures

A method for the analytical modeling of the high-frequency capacitance-voltage (C-V) characteristics of ion-doped MOS structures is proposed. The approach is based on the Gaussian approximation of the implanted dopant concentration profile and the exhaustion layer approximation (in the region of capacitance modulation). The theoretical C-V curves calculated by the proposed method were applied to monitoring the charging parameters of MOS structures. The new method is recommended for the rapid evaluation of the charging characteristics of a SiO₂/Si interface.     

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.