Phase formation and redistribution of Xe implanted in the Ni-Si system after fast melting and solidification

The behaviour of Xe implanted at the Ni-Si interface and irradiated with Nd-laser pulses is studied in details and compared with Xe implantation into NiSi₂ and into pure Si. Ion beam mixing followed by laser irradiation is able to form good quality epitaxial NiSi₂ layer on Si.An inward segregation of Xe is observed with retention of Xe at a depth of 30 nm inside pure silicon. Implantation of Xe into NiSi₂ or pure Si causes broadening and loss of Xe, as generally observed for implantation into pure materials. The different behaviour of Xe at the Si/NiSi₂ interface must thus be ascribed to peculiar characteristics of the interface itself.     

Epitaxial growth of uniform NiSi2 layers with atomically flat silicide/Si interface by solid-phase reaction in Ni-P/Si(1 0 0) systems

As metal-oxide-semiconductor field-effect transistor (MOSFET) devices are shrunk to the nanometer scale, flat shallow metal/Si electrical contacts must be formed in the source/drain region. This work demonstrates a method for the formation of epitaxial NiSi₂ layers by a solid-phase reaction in Ni-P(8 nm)/Si(1 0 0) samples. The results show that the sheet resistance remained low when the samples were annealed at temperatures from 400 to 700 °C. P atoms can be regarded as diffusion barriers against the supply of Ni to the Si substrate, which caused the formation of Si-rich silicide (NiSi₂) at low temperature. Furthermore, elemental P formed a stable capping layer with O, Ni and Si during the annealing process. A uniform NiSi₂ layer with an atomically flat interface was formed by annealing at 700 °C because of the formation of a Si-Ni-P-O capping layer and a reduction in the total interface area.     

Silicidation in Ni/Si thin film system investigated by X-ray diffraction and Auger electron spectroscopy

Silicide formation induced by thermal annealing in Ni/Si thin film system has been investigated using glancing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES). Silicide formation takes place at 870 K with Ni₂Si, NiSi and NiSi₂ phases co-existing with Ni. Complete conversion of intermediate silicide phases to the final NiSi₂ phase takes place at 1170 K. Atomic force microscopy measurements have revealed the coalescence of pillar-like structures to ridge-like structures upon silicidation. A comparison of the experimental results in terms of the evolution of various silicide phases is presented.     

Experimental and simulation investigations of the peculiarities of relativistic electron beam scattering at a small angle of incidence on a thin flat target

The refraction angles θ _d of electron beams passing through aluminum and thin flat copper foils and reflection angles θ _r are measured. A microtron with 7.4 MeV particles is used as a source of electrons. The angle between the particle trajectory and the target surface α is varied in the range 5°–30°. The dependences of the refraction and reflection angles on the α angle and foil thickness δ are measured. A dosimetric film is used to make pictures of cross sections of the electron beam scattered by a thin 50 μm copper foil. Image processing allows the spatial distributions of refracted and reflected particles to be obtained. The processes of relativistic electron scattering at a small angle of incidence on a flat target are simulated by the Monte Carlo method. The results of simulation are compared with experimental data. Particle scattering at a bimetallic target consisting of 200-μm aluminum and 70-μm lead layers are simulated. A dependence of the spatial-energy distributions on the order of metal layers placed along electron trajectories is found.     

Ultrasoft X-ray spectroscopy investigation of the model system Si-SiO2

SiO₂ surface films with different thicknesses (ranging from 20 to 630 Å), grown on a crystal silicon substrate, have been investigated by the method of reflection and scattering of ultrashoft X-rays. It is shown on the basis of a simultaneous analysis of the SiL _{2, 3} reflection spectra and the scattering indicatrix that the critical angle θ_c for total external reflection for SiO₂ at λ = 57 Å lies in the range 4.5 °–°. The angular dependence of the thickness of the surface layer that forms the specular reflection is obtained. It is shown that the surface layer, whose thickness corresponds to the penetration depth of the radiation into the material with glancing angle close to the critical value θ_c, plays a large role in the formation of the anomalous scattering peak (Yoneda peak).     

Angle-dependent infrared absorption spectroscopy at electrode/electrolyte interfaces

Angle-dependent internal reflection spectroscopy is performed in the attenuated total reflection setup for an electrochemical cell with a Fourier transform infrared spectrometer. The working electrode is a thin Pt film evaporated onto a hemispherical Si prism. The refractive index of the Pt film obtained from the experiment is found to differ from the value for bulk material. The difference is ascribed to the surface corrugation of the Pt surface and the film thickness in the nanometer range. The function of reflection intensity versus angle of incidence changes significantly when a resonant absorption occurs in the electrolyte medium. The angle-dependent absorption band intensity of CO adsorbed on the Pt film under potential control reveals changes in magnitude and an inversion of the band for different angles of incidence. This behaviour is explained by the excitation of resonant surface plasmon waves at the Pt/electrolyte interface and by multiple reflections occurring at the interfaces. A simulation for the three-layer system Si/Pt/electrolyte agrees with the experimental results.     

Investigation of the electronic properties of Au nanoclusters in SiO<Subscript>2</Subscript> by combined scanning tunneling/atomic force microscopy

The tunneling of electrons through Au nanoc lusters formed by pulsed laser deposition in a SiO₂ thin film on a Si substrate has been investigated by combined scanning/atomic force microscopy (STM/AFM). Conducting Pt-coated Si cantilevers were used. The feedback was maintained via the AFM channel, and the current-voltage (I-V) characteristics of the tunnel contact between the AFM probe and the n ⁺-Si substrate through a =4-nm-thick SiO₂ film with Au nanoclusters =2 nm in diameter were measured simultaneously. The current image of the structure contained areas of increased current (tunnel-current channels) 2–15 nm in size, related to tunneling of electrons through Au nanoclusters in SiO₂. The I-V characteristics recorded in the tunnel-current channels exhibit specific features related to the Coulomb blockade of electron tunneling through Au nanoclusters.     

Fast electro-optical response of a cell with a homeoplanar layer of a nematic liquid crystal

The refraction of light, i.e., the turn of an extraordinary ray in the liquid crystal layer similar to total internal reflection at an interface between two media, has been studied in a cell with the homeoplanar orientation of the director. The rise, τ_on, and decay, τ_off, times of optical responses have been obtained for various angles of incidence of light on a liquid crystal layer subjected to an electric field. The times τ_on and τ_off of optical responses for the angles of incidence much larger than the angle of total internal reflection are 1–2 ms, which is three orders of magnitude smaller than the relaxation time of an optical response in the case of normal incidence of the ray.     

Structural and electrical characterization of the nickel silicide films formed at 850 °C by rapid thermal annealing of the Ni/Si(1 0 0) films

Nickel di-silicide formation induced by RTA process at 850 °C for 60 s in the Ni/Si(1 0 0) systems are investigated as a function of the initial Ni film thickness of 7-89 nm using XRD, RBS, SEM, X-SEM and AFM. Based on the XRD and RBS data, in the silicide films of 400-105 nm, NiSi and NiSi₂ silicide phases co-exist, indicating that Ni overlayer is completely transformed to NiSi and NiSi₂ silicide phases. SEM reveals that these films consist of large grains for co-existence of NiSi₂ and NiSi phases, separated from one another by holes, reflecting that NiSi₂ grows as islands in NiSi matrix. These films have low sheet resistance, ranging from 1.89 to 5.44 Ω/□ and good thermal stability. For thicknesses ≤ 80 nm RBS yields more Si-rich silicide phases compared to thicker films, whereas SEM reveals that Si-enriched silicide islands with visible holes grow in Si matrix. As the film thickness decreases from 400 to 35 nm, AFM reveals a ridge-like structure showing a general trend of decreasing average diameter and mean roughness values, while sheet resistance measurements exhibit a dramatic increase ranging from 1.89 to 53.73 Ω/□. This dramatic sheet resistance increase is generated by substantial grain boundary grooving, followed by island formation, resulting in a significant phase transformation from NiSi₂-rich to Si-rich silicide phases.     

Electronic structure of FeSi<Subscript>2</Subscript>

The electronic structure of volume and film iron disilicides with crystal structure of the type of α leboit and fluorite was calculated using the linearized augmented plane-wave formalism. Joint and local partial densities of electronic states, x-ray emission spectra in different series of all inequivalent atoms of these phases, and photoelectron spectra for different excitation energies were obtained. γ-FeSi₂ was found to be, unlike α-FeSi₂, an unstable phase in both the volume and film realizations. X-ray L _2,3 emission spectra of silicon in the iron group disilicides NiSi₂, CoSi₂, and FeSi₂ were compared. NiSi₂, CoSi₂, and α-FeSi₂ exhibit transformation of the maximum in the near-Fermi region of the Si L _2,3 spectra as one crosses over from a bulk to a film sample. This transformation is closely connected with phase stability and may serve as a criterion of thermodynamic stability of the iron-group transition-metal disilicides.     

Anomalous X-ray scattering and channeling inside hollow microcapillary structures

XANES L _2,3 spectra and the reflection spectra of silicon, obtained in the case of the grazing incidence of radiation onto channel walls of microchannel plates, are studied. The channeling of secondary long-wavelength X-ray radiation was observed due to anomalous scattering in the vicinity of L edges of silicon absorption. The spectral composition of the secondary radiation at the microchannel output remains unchanged. The surfacebound propagation of X-ray fluorescence excited inside microchannels is observed for angles of incidence of less than θ ≈ θ_c/2.     

Oxidation process of SiGe on SOI substrates

The oxidation of SiGe film epitaxial grown on top of SOI wafers has been studied. These SiGe/SOI samples were oxidized at 700, 900, 1100 °C. Germanium atoms were rejected from SiGe film to SOI layer. A new Si_1−xGe_x (x is minimal) layer formed at SiGe/Si interface. As the germanium atoms diffused, the new Si_1−xGe_x (x is minimal) layer moved to Si/SiO₂ interface. Propagation of threading dislocation in SiGe film to SOI substrate was hindered by the new SiGe/Si interface. Strain in SOI substrate transferred from SiGe film was released through dislocation nucleation and propagation inner. The relaxation of SiGe film could be described as: strain relaxed through strain equalization and transfer process between SiGe film and SOI substrates. Raman spectroscopy was used to characterize the strain of SiGe film. Microstructure of SiGe/SOI was observed by transmission electron microscope (TEM).     

Backscattering of Relativistic Electrons Incident on a Planar Foil at a Small Angle to Its Surface

Photographs of cross sections of an electron beam backscattered from a thin tungsten target have been obtained on a dosimetric film. The procession of images makes it possible to obtain the spatial distribution of backscattered particles. The angles of back reflection θ_br of electron beams from foils have been measured. A 7.4-MeV microtron has been used as a source of electrons. The experiments have been performed with a tungsten foil 386 mg/cm² (200 μm) thick and a tantalum foil 1328 mg/cm² (800 μm) thick. Particles have been injected at an angle of α = 10° to the foil surface. The Monte Carlo simulation of the scattering of relativistic electrons incident on a planar target at small angles to its surface has been performed. The spatial and energy distributions of backscattered particle fluxes both transmitted through the target and reflected from it have been calculated. The dependences of fluxes on the direction of injection of particles and on the material and thickness of the target have been considered.     

Formation of iron and iron silicides on silicon and iron surfaces. Role of the deposition rate and volumetric effects

A thin iron film deposited at the rate of 10³ nm/sec on the Si(001) surface and a sandwich structure silicon/iron/Si(111) are studied by Surface Magneto-Optic Kerr Effect, High Resolution Electron Microscopy and X-ray Photoelectron Microscopy methods. The phases present in the structures are identified. Both structures are non-uniform. The ultra-fast-deposited film is magnetically hard (H _c=45 Oe), it contains the silicide Fe₅Si₃. The XPS line shift by +0.55 eV with respect to the pure iron 2p 3/2 level is attributed to Fe₅Si₃. The cross-section image of the sandwich structure shows the presence of enhanced-intermixing channels crossing the Si-rich layer. Iron atoms are the main diffusion species both at the Fe/Si(111) and Si/Fe interfaces. The nature of the volume defect and internal stresses in the transforming iron silicides and their effects on material intermixing and film growth process are discussed.     

Theoretical and experimental determination of the initial stage of plastic relaxation of misfit stresses in a (111) substrate-film islands heterosystem

A model for determining the critical thickness of a film h _c is developed to introduce misfit dislocations in the slip planes of a film and a substrate parallel to the interphase boundary (111). Experimental values h _c that agree with calculated values are determined for the Ge/Si(111) and Si₃N₄/Ge(111) heterosystems. The two-level epitaxial growth of Ge on Si is attained in the regime of combining the step-layer and 2D island growth mechanisms.     

A spectroscopic prism coupler for measuring the refractive indices and thicknesses of dielectric films

A spectroscopic prism coupler is created for measuring refractive indices n_f and thicknesses H_f of dielectric films. The operating principle of the device is based on the simultaneous resonance excitation of several waveguide modes in a film by a focused TE or TM polarized light beam in the geometry of frustrated total internal reflection. Calculations of n_f and H_f are performed using measured angular positions θ_m of dark m-lines in the cross section of the specularly reflected beam. Using obtained angles θ_m, we can calculate effective refractive indices β_m of modes. By solving a set of nonlinear dispersion equations for the modes of a planar waveguide, we can calculate refractive index n_f and thickness H_f of a film. The proposed prism coupler has no moving parts and allows us to measure the optical parameters of films 0.5–10 μm thick in the 400–1100 nm range of wavelengths. The device can also be used as a spectroscopic refractometer for measuring the refractive indices of bulk media. The device is used to measure refractive index and thickness of a SiO film and the refractive index of TF4 glass.     

Fermi Level Unpinning and Schottky Barrier Modification by Ti, Sc and V Incorporation at NiSi2/Si Interface

A new method is proposed to modify the Schottky barrier height （SBH） for nickel silicide/Si contact. Chemical and electrical properties for NiSi2/Si interface with titanium, scandium and vanadium incorporation are investigated by first-principles calculations. The metal/semiconductor interface states within the gap region are greatly decreased, which is related to the diminutions of junction leakage when Ti-cap is experimentally used in nickel silicide/Si contact process. It leads to an unpinning metal/semiconductor interface. The SBH obeys the Schottky-Mort theory. Compared to Ti substitution, the SBH for electrons is reduced for scandium and increases for vanadium.     

Physics of fluctuation processes in downscaled silicon MOSFETs

Physical mechanics of fluctuation processes in advanced submicron and decananometer MOSFETs (metal-oxide-semiconductor field-effect transistors) including the ultra-thin film SOI (siliconon-insulator) devices using strained silicon films are reviewed. The review is substantially based on the results obtained by the authors. It is shown that the following drastic changes occur in the nature and parameters of noise in such devices as a result of their downscaling when the gate oxide thickness and the channel length and width are decreased, the SOI substrates are used, the silicon film thickness is reduced, the film doping level is varied, the strained silicon films are employed, etc. Firstly, the Lorentzian components can appear in the current noise spectra. Those components are due to (i) electron tunneling from the valence band through the gate oxide in the SOI MOSFETs of a sufficiently thin gate oxide (LKE-Lorentzians); (ii) Nyquist fluctuations generated in the source and drain regions near the back Si/SiO₂ interface in the SOI MOSFETs (BGI Lorentzians); (iii) electron exchange between the channel and some single trap in the gate oxide of the transistors with sufficiently small length and width of the channel (RTS Lorentzians). Secondly, the 1/f-noise level can increase due to (i) the appearance of recombination processes near the Si/SiO₂ interface activated by the currents of electron tunneling from the valence band; (ii) an increase in the trap density in the gate oxide of the devices fabricated on the biaxially tensile-strained silicon films; (iii) the contribution of the 1/f fluctuations of the current flowing through the gate oxide as a result of electron tunneling from the conduction band. At the same time, the 1/f-noise level may decrease due to a decrease in the trap density in the gate oxide of the transistors fabricated on the uniaxially tensile-strained silicon films. Moreover, a 1/f ^1.7 component may appear in the noise spectra for the transistors of a sufficiently thin gate oxide, whose component is due to charge fluctuations on the defects located near the interface between the gate polysilicon and the gate oxide.     

Si-W/Si/SiO2/Si(100)的横截面电子显微镜研究

本文用横截面电子显微镜法分析了Si-W/Si/SiO₂/Si(100)在440—1000℃退火后的晶化过程,以及各个界面的变化情况.发现Si-W合金膜中,WSi₂并未优先在表面、界面处形成晶核.当退火温度不高于700℃时,反应在合金膜内发生,表面、界面起伏和缓.退火温度高达800—1000℃时,界面、表面出现原子扩散,造成剧烈的界面起伏;表面则出现小的热沟槽,Si/SiO₂界面也出现高分辨电子显微镜才能观察到的起伏.表面、界面的原子迁移的动力来源于晶界与表面、界面张力.由于SiO₂中Si—O键很稳定,不易发生Si和O在界面处的互扩散,所以Si/SiO₂界面起伏很小. 关键词：     

Sr/Si(100)表面TiSi2纳米岛的扫描隧道显微镜研究

为了解半导体衬底与氧化物之间存在的相互作用,以及量子尺寸效应对不同再构体的影响,制备了1—2个原子层厚的TiSi₂/Si(100)纳米岛,并使用扫描隧道显微镜(STM)表征手段详细地研究了TiSi₂ /Si(100)纳米岛的电子和几何特性. 结果发现:这些纳米岛表面显示出明显的金属性;其空态STM图像具有典型的偏压依赖性:在高偏压下STM 图像由三聚物形成的单胞构成,并在低偏压下STM 图像显示为密堆积的图案,这些不同的图案反映出不同能量位的态密度有明显差异. 关键词： 2纳米岛')" href="#">TiSi₂纳米岛 Sr/Si(100)表面 扫描隧道显微镜