Oxidation Of Si Surface Research Articles

Investigation of the initial stage of growth of HfO2 films on Si(100) grown by atomic-layer deposition using in situ medium energy ion scattering

The initial stage of growth of HfO2 films on p-type Si(100) grown by atomic-layer deposition (ALD) was investigated using in situ medium energy ion scattering (MEIS). The interaction between adsorbed HfCl4 molecules and the oxidized Si surface was examined as a function of growth cycles. The results clearly show that island-like growth occurs during the initial HfO2 growth and the islands are then merged into a continuous atomic layer with an increase in ALD cycles. The morphology of thicker HfO2 films remained essentially unchanged with growth cycles. Interfacial reactions between Hf and Si during the initial growth stage were minimal. As a result, the effect of insufficient nucleation density is a dominant factor in the initial stage of growth of hafnium oxide on the oxidized Si substrate, resulting in nonlinear growth behavior.

923 分子線散乱実験による表面反応過程の解析 : シリコン(100)表面の酸化過程(J14-3 量子・分子熱流体工学(3),J14 量子・分子熱流体工学,2005年度年次大会)

A molecular beam apparatus has been constructed to investigate the oxidation dynamics of Si(100) surface with O_3, which is a promising oxidizing species to reduce the thermal budget during SiO_2 film formation for gate oxide in semiconductor devices. With the surface exposed to the modulated molecular beam, time-resolved measurements of product molecules desorbing from the surface give us a clear understanding of the reaction dynamics. As the first step of our study, the active oxidation of Si(100) surface with O_2 was investigated employing molecular beam relaxation spectrometry to check the performance of the apparatus. The Fourier analysis of product waveforms indicated that the reaction can be described by the sequential two-step first-order reaction process. The activation energy of each step agreed with the values in literatures.

Investigation of Nanostructured Germanium/Silicon Dioxide Interfaces

The precipitation of Ge nanoclusters in SiO2 after implantation arises from their immiscibility and is technologically interesting due to their luminescence and potential use for non-volatile memory devices. Exploiting the same immiscibility, we have recently found that oxidation of germaniumimplanted Si surfaces can produce a pileup of Ge in front of the oxidation front and create an atomically sharp interface. In this paper, we examine the band structure and processing of such an interface. Based on ab initio band structure calculations, the band structure of the sharp interface seems to be more favorable for use in electronic devices than the usually diffuse interface in Si/SiO2. Furthermore, we propose an ab initio based Monte Carlo model to simulate such an oxidation of SiGe alloys. The model explains the formation of the sharp interface due to the repulsive interaction between O and Ge. In such cases, Ge is expelled from the oxide and O atoms do not enter the Ge region under the oxidation front, resulting in strong segregation. Furthermore, inclusion of Ge nanoparticles in the oxide is predicted for higher Ge concentrations, in agreement with experimental results.

Sexithiophene films on clean and oxidized Si(111) surfaces: Growth and electronic structure

The growth and the electronic properties of sexithiophene thin films on silicon surfaces have been studied by angle resolved ultraviolet photoelectron spectroscopy while morphology and crystalline order have been assessed by atomic force microscopy and x-ray diffraction. The influence of the surface modification of the substrate as well as of the growth temperature and the growth rate were investigated in ultrahigh vacuum through controlled multistep growth sequences ranging from (sub)monolayer coverage up to thick films. Depending on the preparation, two electronically distinct sexithiophene (6T) films could be produced, as revealed by their ionization potentials which differed by ∼0.7eV. The evolution of the electronic energy levels with film thickness is considered in terms of the concepts of interface dipole and band bending, with the latter being argued to be inappropriate. Irrespective of substrate or growth conditions the thick 6T films were found to all have the same work function of ∼0.4eV, which is related to near vertically oriented molecules on the films surface. Against general expectations 6T grown at a low rate on the reactive Si(111) substrate and those grown at high rates on the oxide surface produces films that are more uniform and crystalline than those grown at low rates on the passive oxidized Si surfaces. The latter promotes the formation of small three-dimensional crystallites and a much poorer morphology for planar devices.

Nonlinear optical spectroscopy of suboxides at oxidized Si(111) interfaces.

Native oxidation of the Si(111)(1 x 1)H surface causes the appearance and disappearance of second-harmonic generation (SHG) resonances related to specific bonding configurations of Si atoms at the interface. Resonances at 3.52 eV two-photon energy observed in p-polarized SHG spectra are indicative of a Si suboxide configuration present in a partially oxidized Si surface bilayer. Similar resonances are observed in spectra of thermally oxidized Si(111) and point to Si2+ suboxide states at the buried interface.

Real-time monitoring of oxidation processes on Si(001) surface using O2 gas under 1000 K by synchrotron radiation photoemission spectroscopy

Abstract The thermal oxidation of Si(0 0 1) surface under 1000 K in the O 2 pressure of 1 × 10 −4 Pa has been in situ investigated using real-time photoemission spectroscopy with high energy-resolution synchrotron radiation. Using a reaction kinetics model, we found that the oxidation at 1000 K progressed with a two dimensional island growth mechanism involving desorption of SiO molecules. Si 2+ species relating to the backbond oxidation at the topmost Si dimers appeared in conjunction with Si 1+ species at the initial oxidation stage at 1000 K. We clarified that the topmost Si atoms bonding to two oxygen atoms played an important role as an initial adsorbate. Since Si oxidation states with higher oxidation numbers, such as Si 4+ and Si 3+ , appeared at the early oxidation stages as well, we concluded that SiO 2 adsorbates constructed with the Si 4+ species were preferentially formed even in the oxide nucleus as well as the two dimensional islands on the Si(0 0 1) surface at 1000 K.

Oxidation of Si surface by a pulsed Nd : YAG laser

SiO2 thin films have been obtained by 1064 nm Nd : YAG laser oxidation of p-Si in the presence of O2. The thickness uniformity, dielectric and electrical properties of the layers have been studied. The effect of both the laser beam energy density and the substrate temperature on the oxide growth is also discussed. It was established that there exists an interval of laser beam energy density in which the oxidation occurs without surface melting. The oxidation process is controlled by the laser beam energy density rather than by the substrate temperature (673–748 K) and the higher laser power results in a thicker oxide. X-ray photoelectron spectroscopy (XPS) was used to provide information on the oxide composition. XPS results revealed that the as-grown oxide is a mixed layer of SiO2 and Si2O, which are distributed nonuniformly through the depth. MOS capacitors fabricated on the grown oxide exhibited typical capacitance–voltage, conductance–voltage characteristics. However, the density of interface states and oxide charge density were found to be higher than the typical values of thermally grown oxides. The quality of the oxide layers can be further improved by optimization of the process parameters and/or by post-processing of the grown films. It is concluded that the SiO2 films formed by the technique of Nd : YAG laser-enhanced oxidation at low temperature are potentially useful for device applications.

Polyaniline nanowires on Si surfaces fabricated with DNA templates.

It is essential to put individual, free-standing nanowires onto insulating substrates and integrate them to useful devices. Here we report a strategy for fabrication of conducting polymer nanowires on thermally oxidized Si surfaces by use of DNA as templates. The direct use of stretched and immobilized DNA strands as templates avoids the agglomeration of DNA caused by shielding of charges on DNA when polyaniline/DNA complexes formed in solution. Most importantly, the oriented DNA strands immobilized on the Si surface predetermine the position and the orientation of the nanowires. The approach described here is the first step toward uniting the programmable-assembly ability of DNA with the unique electronic properties of conducting polymers for high-density functional nanodevices. The conductivity of the nanowires is very sensitive to the proton doping-undoping process, suggesting that the nanowires hold great promise for sensitive chemical sensor applications.

Three-pairs of doublet bands assigned toSiH2scissoring modes observed inH2O-induced oxidation of Si(100) surfaces

Oxidation of Si(100) surfaces by H 2 O has been investigated on 2H+H 2 O/Si(100)-(2×1), H 2 O +Si(100)-(2×1), as well as H 2 O+H/Si(100)-(2×1) systems by infrared reflection absorption spectroscopy using CoSi 2 buried metal layer substrates (BML-IRRAS). Three pairs of doublet bands assigned to the scissoring modes of adjacent and isolated SiH 2 with zero, one, and two inserted back-bond oxygen atoms, respectively, have been reported. This report also has clearly shown the unique high sensitivity of BML-IRRAS for the perpendicular components in the fingerprint region, compared to the multiple internal reflection and the external transmission arrangements. Oxidation mechanisms have been proposed. In the 2H +H 2 O/Si(100)-(2×1) system, oxygen insertion into the back bond occurs easily. In the H 2 O+H/Si(100) system, however, the tunneling effect is important to reach the oxygen inserted state.

Formation of Ge nanoislands on pure and oxidized Si surfaces by MBE

The discussion deals with experimental data on the process of formation of self-organized Ge islands on an oxidized atomically pure Si(100) surface. Unlike the Stranski–Krastanow mechanism, which is characteristic of Ge growth on a pure silicon surface, the Volmer–Weber growth mechanism is observed on the oxidized silicon surface. The growth process is accompanied by a considerable change (up to 7%) in the surface unit cell of Ge relative to the parameters of Si. The generated nanoislands are less than 10 nm in base size and have a density of more than 2 × 1012 cm−2 for a Ge film not thicker than five monolayers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Competitive Etching and Oxidation of Vicinal Si(100) Surfaces

ABSTRACTExposure of a vicinal Si(100) surface to oxygen at around 550 C produces etching-mediated step recession. In addition, some oxide islands are formed which locally pin receding steps. We develop an atomistic lattice-gas model for this process which accounts for the interplay between oxygen surface chemistry (adsorption, diffusion, oxide formation, and etching via SiO desorption) and the silicon surface and step dynamics (anisotropic diffusion and aggregation of di-vacancies formed by etching, and ad-dimer attachment-detachment dynamics at steps incorporating anisotropic energetics). Kinetic Monte Carlo simulation of this model produces step morphologies retaining some qualitative but not quantitative features of their equilibrium structure (alternating rough SB steps and smooth SA steps), except for pinning which produces protruding “fingers”. These features are seen in Scanning Tunneling Microscopy studies.

熱延鋼板の内部酸化層が冷間圧延後の再結晶焼鈍時におけるＳｉ，Ｍｎ表面濃化挙動に及ぼす影響

By the heat treatment of a ultra low carbon hot-rolled steel containing 0.31mass%Si-1.02mass%Mn, not only readily oxidizable elements such as Si and Mn but also Fe were internally oxidized at the steel surface region. The scale of the steel acted as the source of oxygen for internal oxidation. The composition of the grain-boundary oxides differed from those in the grain, presumably due to the difference in oxygen potential ; oxides at the grain-boundary consisted mainly of Fe-Si-Mn-O, while oxides in the grain consisted mainly of Si-Mn-O. The internal oxidation layer remained after scale pickling and cold rolling. Fe containing grain-boundary oxides, arranged in layers by the cold rolling process, were considered to act as the oxidant of Si and Mn, which diffuse toward the steel surface in recrystallization annealing. By not only the low Si and Mn activity due to the depletion layer formed during the heat treatment, but also the redox reaction between the grain-boundary oxides and solute Si and Mn, the amounts of Si and Mn selective surface oxidation were remarkably decreased. The resultant suppression of the selective surface oxidation brought about improvement in the wettability by molten Zn of the annealed sheet steel surface.

Local Oxidation Induced by Inhomogeneous Stress on Blistered Si Surface

Surface stress can be utilized positively in modifying the surface reaction potential and increasing the surface reactivity. It will be a technique for two-dimensional patterning of surface chemical reactions by means of surface stress modulation. Blister is a local protrusion of solid surface induced by gas ion irradiation, and is considered to create local stress on surface layers. Si(100) substrate was irradiated with H+ (ion energy of 10 keV and fluence of 1×1022 ions/m2) at an angle of 30o to the surface normal. The blisters of several μm in diameter at the bottom were formed. After the ion irradiation, the substrate was oxidized. By means of scanning Auger microscopy, we observed that the rims of the blisters have higher oxygen intensities than the flat surfaces and the tops have lower than the flats. The stress distribution of the blister was calculated using finite element methods; the surface layers should be stretched laterally at the top of blisters and are compressed at the rim, relative to the flat surfaces. The O distribution clearly consists with the stress distribution of the surface. Our results demonstrate a patterned oxidation of Si surface applying its reactivity depending on the surface stress.

The atomic scale removal mechanism during chemomechanical polishing of Silicon: An atomic force microscopy study

ABSTRACTThe pressure dependence of the microwear of an oxidized Si surface under aqueous electrolyte solutions has been investigated using an atomic force microscope with a single crystal Si tip. The removal ratio of Si tip to SiO2 surface is found to be highly sensitive to the contact pressure. We present a microscopic removal mechanism which is determined by an interplay of the diffusion of H2O in Si and SiO2.

Thickness of surface thin oxide layers determined by impedance spectroscopy using silicon/oxide/electrolyte (SOE) structures

The differential capacitance of SiO2 ultra-thin layers on Si substrate is greatly sensitive to the space charge generated within the semiconductor. In the potential scan, the determination of the capacitance/voltage characteristics in MOS devices is hindered by the high value of the tunneling leakage current. In this work, the difficulty was overcome by careful measurement of the impedance diagrams using a semiconductor/oxide/electrolyte (SOE) structure, under zero current flow. Depending on the bias potential we obtained RC equivalent circuits corresponding either to the depletion layer or to the oxide dielectric film. A novel aspect of the work is that both R and C components were derived from the data processing.In a previous work the investigation was focussed on the depletion layer, and lead to values of the resistance term in the range of a few kΩ to a few MΩcm2, while the capacitance value was a few 10−2μFcm−2. These results were consistent with a theoretical treatment of the bias voltage dependence of the charge distribution near the flatband potential, and constitute a new technique for the determination of the fb potential versus a reference electrode.The present work is devoted to the electrical properties of the Si surface oxide layer. The leakage resistance term of the thermal oxide layer, a few nm thick, was found equal to several 108Ωcm2. But, the electric field within the semiconductor is not effective for the full charge of the oxide capacitance even when the polarization creates an accumulation layer. In accordance with the computed electric field within the semiconductor, the right value of the capacitance can be reached easily when the wafer is submitted to light radiation and provided the polarization of the substrate is such as to generate an inversion layer. This property leads to an accurate method for ultra-thin insulators characterization excluding tunnel leakage current.

FTIR-ATR evaluation of organic contaminant cleaning methods for SiO2 surfaces.

The effectiveness of cleaning organic contaminants from silicon dioxide (SiO2) surfaces was studied by conducting highly sensitive measurements using Fourier Transform Infrared Attenuated Total reflectance (FTIR-ATR) with a Si prism as the waveguide. To serve as an example, the surface of the prism was oxidized to an order of a few nanometers. The oxidized Si surface film was allowed to stand in the atmosphere and then wet-cleaned in a repeated manner; subsequently its thickness was measured by ellipsometry. Although, various wet-cleaning methods were tested, they only showed values of 0.1-0.2 nm larger than, but not equal to, the original thickness immediately after oxidation. FTIR-ATR measurements of the spectral change after exposure to air revealed that organic species, such as C-CH3 and -(CH2)n-, increased with time. Wet-cleaning the sample failed to remove the C-CH3 species, which indicates that they corresponded to the film thickness increment from the original.

Oxidation of Aqueous HF-treated Si(001) Surface Induced by Translational Kinetic Energy of O2 at Room Temperature

The oxidation induced by the translational kinetic energy of O2 on the Si(001) surface treated with HF solution were investigated by combining synchrotron radiation photoemission spectroscopy with the supersonic molecular beam techniques. The oxidation at room temperature did not progress up to 3600 L of O2 exposure with incident energy of 0.04 eV, whereas the oxidation states of up to Si4+ species were formed in the case of 3.0 eV. The oxide-layer thickness was estimated to be 0.26 nm at the final oxidation stages. We concluded that the Si atoms at the top layers were oxidized by the incident energy of 3.0 eV.

Thermally induced chemistry and electron-mediated processes of pyridine on (2×1) and modified Si( [formula omitted]) surfaces: evidence of electron-induced condensation oligomerization

The room-temperature (RT) adsorption and surface reactions of pyridine on Si(1 0 0)2 × 1 have been investigated by thermal desorption spectrometry, low-energy electron diffraction, and Auger electron spectroscopy. In addition to molecular desorption, evidence of dissociation into smaller fragments, including C 2H 2 and atomic hydrogen, was also found upon thermal desorption of pyridine chemisorbed on Si(1 0 0)2 × 1 at RT. Other possible surface processes such as hydrogen abstraction, fragmentation and dissociative desorption have also been identified on Si(1 0 0)2 × 1 surfaces modified by sputtering, and pre- and post-exposure of molecular oxygen and of atomic hydrogen. Evidence of condensation oligomerization of pyridine at RT has been found on Si(1 0 0)2 × 1 upon irradiated by low-energy electrons and on an oxidized Si surface even without electron mediation.

AFM fabrication of oxide patterns and immobilization of biomolecules on Si surface

A novel method of protein patterning based on anodic oxidation of Si surface by atomic force microscope (AFM) is presented. An oxide pattern is drawn on the Si surface by applying d.c. voltage between the Au-coated AFM tip and the Si substrate. The oxide patterns can be used as a template for patterning of biomolecules. Protocols for both positive and negative patterning of protein were established.

Nanoridge domains in α-phase W films

Two types of nanoridge domains oriented with each other with an angle ranging between 109° and 124° were measured by scanning tunneling microscopy on the α-W film sputter deposited on an oxidized Si surface. Each domain contains nanoridges with a period of 7.5±1.0 nm. No such domains were observed on the β-W film surface. We argued that due to the anisotropy of the W(110) surface, the impinging W atoms diffuse faster along the 〈111〉 directions on the surface to form the nanoridge structure. There are two equivalent 〈111〉 directions, which give rise to two orientational domains with an angle of ∼110°. An isotropic β-W(100) phase has no preferred diffusion direction for the impinging W atoms and therefore, no nanoridge domain structure was observed.