Presence Of Native Oxide Research Articles

Ab initio study of the mechanism of carbonization of {111} Si-substrate at high temperature

In this study, the CVD process of carbonization of {111} silicone surface is simulated employing ab initio metadynamics at the temperature of 1423 K. The entire chain of reactions is discovered, including the formation of an initial SiC crystallite seed with three carbon atoms, in the presence of native oxide. The characterization of all mechanisms includes transition states (TSs) and intermediate products. The forward free energy barriers were measured when possible. Carbonization always begins with alkylated surface products and progresses through loss of hydrogen. Only when all hydrogen atoms are lost, the carbon is accommodated in the crystal volume. Oxygen atoms of the native oxide may stay trapped in the SiC phase or in a buffer Si–C–O phase, forming a glass layer there. The native oxygen expresses certain mobility at the surface of the material. Occasionally TSs with hypervalent carbon and silicon atoms occur. The rate-determining reaction in the CVD synthesis of SiC has a free energy barrier of 173 kJ/mol.

Thermal Instability of Gold Thin Films

The disintegration of a continuous metallic thin film leads to the formation of isolated islands, which can be used for the preparation of plasmonic structures. The transformation mechanism is driven by a thermally accelerated diffusion that leads to the minimalization of surface free energy in the system. In this paper, we report the results of our study on the disintegration of gold thin film and the formation of nanoislands on silicon substrates, both pure and with native silicon dioxide film. To study the processes leading to the formation of gold nanostructures and to investigate the effect of the oxide layer on silicon diffusion, metallic film with a thickness of 3 nm was deposited by molecular beam epitaxy (MBE) technique on both pure and oxidized silicon substrates. Transformation of the thin film was observed by low-energy electron microscopy (LEEM) and a scanning electron microscope (SEM), while the nanostructures formed were observed by atomic force microscope (AFM) method. Structural investigations were performed by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) methods. Our experiments confirmed a strong correlation between the formation of nanoislands and the presence of native oxide on silicon substrates.

Printable Liquid Metal Microparticle Ink for Ultrastretchable Electronics.

Liquid metal confined in the elastomer represents an ideal platform for stretchable electronics with ultimate deformability. To enable facile and scalable patterning of conductive features, bulk liquid metal is typically dispersed into fine particles to formulate printable inks. The presence of native oxide or organic ligands stabilizing these liquid metal particles unfortunately inhibits their direct coalescence to recover the metallic conductivity and liquid-state deformability. Here, we report a chemical sintering process that converts printed liquid metal microparticles into a highly deformable conductor. The process involves the removal of surface passivating oxide by a short exposure to acid fume and subsequent selective wetting of liquid metal microparticles onto copper nanoplates present in the ink formulation. The chemical reaction provides the basis for a facile and scalable procedure to print conductive features over a large area with exceptional conductivity (>104 S cm-1) and ultrahigh stretchability (∼1000% strain). Their practical suitability is demonstrated by the fabrication of an ultrastretchable ribbon cable and an epidermal heater.

Effect of native oxide on the crystal orientation contrast in SEM micrographs obtained at hundreds, tens and units of eV

This paper aims to elucidate the effect of native air-formed oxide on the crystallographic contrast between differently oriented copper grains in scanning electron microscope images obtained at energies from 0 eV up to 1 keV. The contrast between the Cu grains is strongly affected by the presence of native oxide. The crystallographic orientation contrast between the grains without covering the native oxide layer is relatively weak at hundreds of eV, negligible at tens of eV, and dramatically increases at energies below 10 eV. At extremely low landing energies, say below ~ 1 eV, the surface potential differences caused by work function variations between the differently oriented Cu grains affect the primary electrons, which enables us to obtain the micrographs with high crystallographic contrast. This contrast becomes surprisingly visible even if the grains are covered by a several nm thick native oxide layer. The presence of the native air-formed oxide layer on the Cu surface is inconsiderable for the contrast formation at energies close to the mirror conditions (< 1 eV). The surface potential differences originating in the substrate can affect the incident electrons through the native oxide film situated on the Cu surface. Scanning low-energy electron microscopy is a powerful tool for mapping local work function differences with a spatial resolution slightly better than 30 nm due to high sensitivity to local electrical potentials.

Surface passivation dictated site-selective growth of aligned carbon nanotubes.

Surface defects play a significant role in the nucleation and growth of metal particles. Site-selective nucleation of metal catalyst particles, and the subsequent growth of nanostructures, could thus be accomplished by defect engineering. This paper demonstrates the switching of growth sites of vertically aligned multiwall carbon nanotubes (MW-CNTs) by manipulation of surface passivation of the substrate and discusses the possible mechanism behind this selectivity. A complementary growth pattern of CNTs is observed for pre-treatment of identically patterned SiO2/Si substrates under a reducing and non-reducing atmosphere. Variation in the number density of oxygen vacancies on the silicon dioxide surface and the presence of native oxide on the silicon face are believed to dictate the observed selectivity. The CNT architectures mimic the substrate pattern meticulously, exhibiting sharp edges, illustrating a high degree of site selectivity. The chemical state of the substrate surface and catalyst particles has been studied using Auger electron spectroscopy. Electron microscopy and Raman spectroscopy were employed to characterize the synthesized CNTs. The Hermans orientation factor was calculated to quantify the degree of alignment of the MWCNTs. Such facile control over the growth site of aligned carbon nanotubes on a substrate is a desirable aspect of synthesis for easy integration with existing silicon fabrication technology.

The Role of the Substrate on Photophysical Properties of Highly Ordered 15R-SiC Thin Films

We report on the structural optimization and photophysical properties of in situ RF-sputtered single crystalline 15R-SiC thin films deposited on various substrates (ZrO2, MgO, SiC, and Si). The role of the substrates on the structural, electronic, and photodynamic behavior of the grown films have been demonstrated using x-ray diffraction, photoluminescence (PL) and time-resolved photoluminescence spectroscopy. The appropriate bonding order and the presence of native oxide on the surface of the grown samples are confirmed by x-ray photoelectron spectroscopy measurement. A deep-blue PL emission has been observed corresponding to the Si-centered defects occurring in the native oxide. Deconvolution of the PL spectra manifested two decay mechanisms corresponding to the radiative recombination. The PL intensity and carrier lifetime were found to be substrate- dependent which may be ascribed to the variation in the trap-density of the films grown on different substrates.

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy, transmission electron microscopy, X-ray absorption spectroscopy and X-ray photoelectron spectroscopy.

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High-resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)- and (100)-oriented planes which stabilizes against further oxidation of the particles. X-ray absorption spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) measurements at the O 1s-edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milled for different times. XANES results reveal the presence of the +4 (SiO2) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2p XPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub-oxide, +1 (Si2O), +2 (SiO) and +3 (Si2O3), states are present. The analysis of the change in the sub-oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.

Tin etching from metallic and oxidized scandium thin films

Abstract

Application of extra‐low impact energy SIMS and data reduction algorithm to USJ profiling

Secondary ion mass spectrometry analysis of ultra‐shallow (sub‐200 eV) B implants is complicated by the presence of native oxide on the surface of Si. Knowledge of the type of oxide present on the surface as well as accurate oxide thickness is very important for correct data reduction in extra‐low energy depth profiling. Sputter rate (SR) variation approach based on the accurate SR measurement in Si and SiO2 can be successfully applied to B implants done through thermal oxides of various thicknesses. Lowest profiling energy should be used to achieve the least profile distortion in the case of de‐channeled B implants: the rule of half of the implant energy used for profiling energy is confirmed. Profiling energy that is equal to the implant energy can be used if implantation is done through native oxide or into the stripped Si. If no thermal oxide is present on the surface, the most consistent result will be obtained when implants are done into the pre‐stripped Si thus eliminating uncontrollable and variable native oxide‐related issues. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Improvement in Film Quality of Epitaxial Graphene on SiC(111)/Si(111) by SiH4 Pretreatment

The epitaxy of graphene on 3C-SiC/Si (GOS) has attracted much attention owing to its viability to fuse graphene with Si-based technologies. It is known that the surface condition of the 3C-SiC thin film before graphitization plays a decisive role in determining the quality of the GOS film. We have investigated the effect of the pretreatment of the 3C-SiC thin film in vacuo at a SiH4 partial pressure of 6.7 ×10-4 Pa on the subsequent formation of graphene. As a result, it is revealed that the SiH4 pretreatment restores the defects on the SiC surface, such as the Si vacancy and point defects formed by the presence of native oxides, and improves the quality of graphene. The effect is found to be highest when the substrate temperature is 1173 K.

Interface barriers at the interfaces of polar GaAs(111) faces with Al2O3

Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces.

Oxide mediated liquid–solid growth of high aspect ratio aligned gold silicide nanowires onSi(110) substrates

Silicon nanowires grown using the vapor–liquid–solid method are promising candidates fornanoelectronics applications. The nanowires grow from an Au–Si catalyst during siliconchemical vapor deposition. In this paper, the effect of temperature, oxide at the interfaceand substrate orientation on the nucleation and growth kinetics during formation ofnanogold silicide structures is explained using an oxide mediated liquid–solidgrowth mechanism. Using real time in situ high temperature transmission electronmicroscopy (with 40 ms time resolution), we show the formation of high aspect ratio (≈15.0) aligned gold silicide nanorods in the presence of native oxide at the interface during in situannealing of gold thin films on Si(110) substrates. Steps observed in the growth rate andreal time electron diffraction show the existence of liquid Au–Si nano-alloy structures onthe surface besides the un-reacted gold nanostructures. These results might enable us toengineer the growth of nanowires and similar structures with an Au–Si alloy as a catalyst.

Structural phase transitions in Au thin films on Si (1 1 0): An in situ temperature dependent transmission electron microscopy study

We present a review on the formation of gold silicide nanostructures using in situ temperature dependent transmission electron microscopy (TEM) measurements. Thin Au films of two thicknesses (2.0 nm and 5.0 nm) were deposited on Si (1 1 0) substrate under ultra-high vacuum (UHV) conditions in a molecular beam epitaxy (MBE) system. Also a 2.0 nm thick Au film was deposited under high vacuum condition (with the native oxide at the interface of Au and Si) using thermal evaporation. In situ TEM measurements (for planar samples) were made at various temperatures (from room temperature, RT to 950 °C). We show that, in the presence of native oxide (UHV-MBE) at the interface, high aspect ratio (≈15.0) aligned gold silicide nanorods were observed. For the films that were grown with UHV conditions, a small aspect ratio (∼1.38) nanogold silicide was observed. For 5.0 nm thick gold thin film, thicker and lesser aspect ratio silicides were observed. Selected area diffraction pattern taken at RT after the sample for the case of 5.0 nm Au on Si (1 1 0)-MBE was annealed at 475 °C show the signature of gold silicide formation.

Atomic Layer Deposition of HfO2 Thin Films on Si and GaAs Substrates

ABSTRACTThe atomic layer deposition of HfO2 thin films is studied on Si(100) and GaAs(100) surfaces. The films are grown using tetrakis(dimethylamido)hafnium (TDMAH) and H2O precursors at a deposition temperature of 275°C. The Si surfaces used include a H-terminated surface and an OH-rich chemical oxide. GaAs substrates are subjected to two different pre-deposition treatments involving an HF and a NH4OH wet chemical etch that has been shown to remove most of the Ga and As native oxides. Spectroscopic ellipsometry (SE) confirms linear growth rates of 1.05±0.05 Å/cycle for all surfaces. Rutherford backscattering spectrometry (RBS) shows that steady-state growth of 2.6×1014 Hf/cm2/cycle is reached after 10 ALD cycles for the HF-etched GaAs surface. X-ray photoelectron spectroscopy (XPS) indicates the presence of native oxides on both GaAs starting surfaces after 10 cycles due to postdeposition surface oxidation. However, the presence of the native oxide is not detected for thicker 15 and 20 cycle samples indicating passivation of the surface and suppression of the interfacial layer formation.

Enhancement of TiSi2 Formation during Rapid Thermal Annealing in N 2 by the Presence of Native Oxide

Ti/Si and systems are annealed by rapid thermal annealing (RTA) in ambient, and the formation of silicide and nitride is studied and compared. The sheet resistance of system is slightly higher than that of Ti/Si system because of native oxide (1.9 nm) at the Ti/Si interface. The only impurity detected by Auger electron spectroscopy at the Ti/Si interface is oxygen in the system, but no impurities are detected in the Ti/Si system. After RTA in ambient at 715°C for 10 s, it is interesting to find that the results of sheet resistance measurement for two systems are reversed. This suggests that the formation of Ti silicide in the system is easier than in the Ti/Si system whereas the formation of Ti nitride in the system is more difficult than in the Ti/Si system. X-ray measurement shows that the annealed systems have a higher intensity peak of and lower intensity peak of TiN as compared to those of the annealed Ti/Si systems. The AES study also supports the easier formation of in the system, where it is found that the diffusion of N from the ambient into Ti film is more difficult in the case of the system, such that the diffusion of Si toward the surface is easier. A difference is clearly observed in N and O diffusion through the TiN film and in the interface position. When the RTA time was varied from 10 s to 20 s and 30 s, X-ray diffraction shows the same results described above except that the to phase transformation occurs, and the resulting silicide phase is a mixture of C49 and By contrast, the TiN phase has no phase transformation but the intensity is more and more intense. The sheet resistance of the annealed system has lower values than those of the annealed Ti/Si system as the RTA increases. interface analysis is characterized by cross-sectional transmission electron microscopy. © 2001 The Electrochemical Society. All rights reserved.

The effect of native oxide on thin gate oxide integrity

We have studied the effect of native oxide on thin gate oxide integrity. Much improved leakage current of gate oxide can be obtained by in situ desorbing the native oxide using HF-vapor treated and H/sub 2/ baked processes. Furthermore, an extremely sharp interface between oxide and Si is obtained, and good oxide reliability is achieved even under a high current density stress of 11 A/cm/sup 2/ and a large charge injection of 7.9/spl times/10/sup 4/ C/cm/sup 2/. The presence of native oxide will increase the interface roughness, gate oxide leakage current and stress-induced hole traps.

On the adhesion of In0.2Ga0.8Sb to quartz ampoule during synthesis

In0.2Ga0.8Sb has been synthesized and polycrystals have been grown by the vertical Bridgman technique. Sticking of ingot to the quartz ampoule and ampoule cracking have been found to be major problems. The presence of native oxides on the surface of the starting material impedes the formation of homogeneous compounds due to which the structural quality of the ingots is poor. Worst sticking is observed with improper homogeneization and when excess of pure indium is present on the surface of the crystal. Several procedures have been adopted to avoid sticking and cracking. The most efficient way of solving this problem is to employ a high-temperature baking in dynamic vacuum prior to synthesis by placing the ampoule in a region of the furnace with a temperature gradient. The post-baking cooling rate is also extremely critical to avoid cracking. The polycrystalline alloy thus formed by adopting the pre-synthesis baking cycle shows better homogeneity and structural quality.

Interface engineering in silicon semiconductor processing using a vacuum cluster tool

Some general aspects of clustered processing will be discussed: the surface adsorption of background impurities and the nucleation of Chemical Vapor Deposition films on silicon and silicon dioxide surfaces. Three applications of HF vapor etching clustered with hot wall batch type LPCVD and Oxidation reactors will be presented. In stacked Nitride / Oxide films for capacitor dielectrics, the presence of native oxide on the silicon surface strongly influences the nucleation and properties of the nitride film. In poly-emitter and poly-contact structures, the amount of interfacial oxide directly influences the performance of the device. For poly-gate structures, control of the silicon / silicon oxide interface morphology and control of particle and metallic contamination is vital.

The optical response above the band gap of light emitting porous silicon, as investigated by photoacoustic spectroscopy

Photoacoustic Spectroscopy (PAS) has been performed on Porous Silicon Layers (PSL) obtained by chemical and electrochemical etching of crystalline Silicon. In the investigated energy range (2.0eV-4.7eV) the samples behave as optically opaque and show strong light scattering properties so to prevent the application of standard reflectivityftrasmission techniques. PAS proves suitable in studying porous media, providing evidence that PSLs retain the original cristallinity. The presence of native oxides on PSLs has been revealed by PAS.

Very thin CoSi2 films by Co sputtering

The structure, resistivity, and thermal stability of CoSi2 films ranging in thickness from ∼11 to 52 nm were investigated. Both the bulk and the surface components of the resistivity were extracted. The films exhibited good thermal stability. The thermal stability and the silicidation temperature which gave the minimum film sheet resistance were found to increase with the sputtered film thickness. The sheet resistance was independent of the ramp-up rate (3–20 °C/s), prolonged exposure of the Co film to air, and the presence of native oxides on the Si surface prior to Co deposition.