Showing papers on "Silicon oxide published in 2000"

Self-Assembly Is Not the Only Reaction Possible between Alkyltrichlorosilanes and Surfaces: Monomolecular and Oligomeric Covalently Attached Layers of Dichloro- and Trichloroalkylsilanes on Silicon

Abstract: Silicon-supported alkylsiloxane layers were prepared by reaction of alkylmethyldichlorosilanes and alkyltrichlorosilanes with silicon wafers under two conditions: (1) in the vapor phase and (2) in toluene in the presence of ethyldiisopropylamine. Covalent attachment of di- and trichlorosilanes to the surface of silicon/silicon oxide through SiS−O−Si bonds occurs for the amine-catalyzed reactions. This sets apart this reaction from the self-assembly process that occurs in the reaction between certain trichlorosilanes and hydrated silica with no amine present. The thickness of the layers formed from dichloro- and trichlorosilanes (as assessed by ellipsometry) is on the order of the single molecule sizes and increases gradually with alkyl chain length. The thickness values are considerably smaller (by a factor of ∼0.75) than the length of the fully stretched alkyl chain, which argues for disordered structures of the monolayers. Dynamic advancing and receding contact angles for water, methylene iodide, and h...

Atomic Layer Deposition of Oxide Thin Films with Metal Alkoxides as Oxygen Sources

Abstract: A chemical approach to atomic layer deposition (ALD) of oxide thin films is reported here. Instead of using water or other compounds for an oxygen source, oxygen is obtained from a metal alkoxide, which serves as both an oxygen and a metal source when it reacts with another metal compound such as a metal chloride or a metal alkyl. These reactions generally enable deposition of oxides of many metals. With this approach, an alumina film has been deposited on silicon without creating an interfacial silicon oxide layer that otherwise forms easily. This finding adds to the other benefits of the ALD method, especially the atomic-level thickness control and excellent uniformity, and takes a major step toward the scientifically challenging and technologically important task of replacing silica as the gate dielectric in the future generations of metal oxide semiconductor field effect transistors.

Investigation of Humidity-Dependent Capillary Force

Abstract: Due to the strong capillary condensation, the adhesion force between a Si3N4 atomic force microscope (AFM) tip and silicon oxide was observed to first increase and then decrease with an increase of...

Thermal Probe Measurements of the Glass Transition Temperature for Ultrathin Polymer Films as a Function of Thickness

Abstract: The glass transition temperature of polystyrene and poly(methyl methacrylate) films on polar and nonpolar substrates was measured as a function of thickness using a thermal probe in contact with a polymer film. Using a technique called local thermal analysis, heat loss into the film was monitored as the temperature of the probe was ramped from ambient temperature to temperatures as high as 200 °C. The glass transition temperature was determined from a change in slope in the heat loss versus temperature plot. The Tg of polystyrene on silicon oxide decreased by as much as 25 °C below the bulk value for films 13 nm thick. The same trend in the glass transition temperature was observed for polystyrene films on silicon oxide treated with hexamethyldisilizane (HMDS). The Tg of poly(methyl methacrylate) on silicon oxide increased by up to 7 °C above the bulk value for films 18 nm thick. For poly(methyl methacrylate) on silicon oxide treated with HMDS, the Tg decreased by 10 °C below the bulk value for films 21 n...

Conversion of Some Siloxane Polymers to Silicon Oxide by UV/Ozone Photochemical Processes

Abstract: A variety of linear and cross-linked polysiloxanes are transformed into silicon oxide (SiOx) through the application of a recently developed room-temperature UV/ozone conversion process. Ozone and atomic oxygen, produced by exposure of atmospheric oxygen to ultraviolet radiation, remove organic portions of the polymers as volatile products and leave a thin silicon oxide surface film. The conversion rates differ for each polysiloxane studied and are related to differences in their chemical structures. X-ray photoelectron spectroscopy (XPS) measurements of atomic ratios indicate that UV/ozone treatment removes up to 89% of the carbon from the resultant surface film, leading to an overall stoichiometry close to that of SiO2. The binding energy of Si(2p) core level photoelectrons shifts from 101.5 eV for the polymer precursors to about 103.5 eV after UV exposure, consistent with the formation of silicon that is coordinated to four oxygen atoms. Ellipsometry measurements of apparent thickness changes during co...

Atomic beam deposition of lanthanum- and yttrium-based oxide thin films for gate dielectrics

Abstract: We report on the electrical and microstructural characteristics of La- and Y-based oxides grown on silicon substrates by ultrahigh vacuum atomic beam deposition, in order to examine their potential as alternate gate dielectrics for Si complementary metal oxide semiconductor technology. We have examined the issues of polycrystallinity and interfacial silicon oxide formation in these films and their effect on the leakage currents and the ability to deposit films with low electrical thickness. We observe that polycrystallinity in the films does not result in unacceptably high leakage currents. We show significant Si penetration in both types of films. We find that the interfacial SiO2 is much thicker at ∼1.5 nm for the Y-based oxide compared to the La-based oxide where the thickness is <0.5 nm. We also show that while the Y-based oxide films show excellent electrical properties, the La based films exhibit a large flat band voltage shift indicative of positive charge in the films.

Infrared spectroscopic analysis of the Si/SiO2 interface structure of thermally oxidized silicon

Abstract: The nature of the silicon oxide transition region in the vicinity of the Si/SiO2 interface is probed by infrared and x-ray photoelectron spectroscopies. The layer-by-layer composition of the interface is evaluated by uniformly thinning thermal oxide films from 31 A down to 6 A. We find that the thickness dependence of the frequencies of the transverse optical and longitudinal optical phonons of the oxide film cannot be reconciled by consideration of simple homogeneous processes such as image charge effects or stress near the interface. Rather, by applying the Bruggeman effective medium approximation, we show that film inhomogeneity in the form of substoichiometric silicon oxide species accounts for the observed spectral changes as the interface is approached. The presence of such substoichiometric oxide species is supported by the thickness dependence of the integrated Si suboxide signal in companion x-ray photoelectron spectra.

Method for densification of CVD carbon-doped silicon oxide films through UV irradiation

Abstract: Carbon-doped silicon oxide films (SiC x O y ) produced by CVD of an organosilane gas containing at least one silicon carbon bond, are rapidly densified by exposure to ultraviolet radiation. UV radiation exposure disrupts undesirable chemical bonds (such as Si—OH) present in the carbon-doped silicon oxide following deposition, replacing these bonds with more desirable chemical bonds characteristic of an ordered silicon oxide lattice. As a result of radiation exposure and the chemical bond replacement, gases such as water vapor are evolved and removed, producing a densified and stable carbon-doped silicon oxide film. Densification utilizing ultraviolet radiation is particularly useful because softness and fragility of freshly-deposited (SiC x O y ) films may preclude insertion and removal of coated substrates from conventional batch loaded thermal annealing chambers.

Synthesis of Large Areas of Highly Oriented, Very Long Silicon Nanowires

Abstract: Silicon is one of the most important electronic materials. Its nanoscale forms, such as nanocrystals, porous silicon, quantum wells, and nanowires, have stimulated great interest among scientists because of their peculiar physical properties, such as light emission, field emission, and quantum confinement effects. The progress made in the synthesis of silicon nanostructures and nanowires in recent years has attracted considerable attention. Today, large quantities of silicon nanowires can be produced by the laser ablation of metalor SiO2-containing silicon targets, [8] and a few properties, such as electric and thermal conductivity and optical properties, have also been studied. However, the experimental characterization and application of silicon nanowires, for example, the measurement of the elastic properties, the realization of efficient field emission of nanoscale silicon, and the fabrication of nanometer field effect transistors and planar displays, have been hampered so far because of the difficulty in growing oriented silicon nanowires. As a result, the production of highly oriented and very long silicon nanowires is a very important and challenging issue. In this communication, we report the successful synthesis of highly oriented, largescale, and very long silicon nanowires on flat silicon substrates by thermal evaporation of silicon monoxide (SiO). The growth mechanism and optical properties of the oriented silicon nanowires are also discussed. To the best of our knowledge, the synthesis of oriented silicon nanowires has not yet been reported. The equipment used for the present work is similar to that described previously. An alumina tube was mounted inside a tube furnace. The SiO powders (Gooodfellow, 99.95 %) were placed near the middle of the high-temperature zone of the furnace. The polished silicon (100) substrates about 5 mm in width and 50 mm in length were ultrasonically cleaned in acetone, ethanol, and deionized water for 20 min each, dipped in 20 % HF for 20 min, and finally rinsed in deionized water for 20 min before they were placed abreast at one end of the alumina tube. The tube had previously been evacuated to a base pressure of 10 torr by a mechanical pump before the starting materials were heated. The carrier gas of argon mixed with 5 % H2 admitted at the other end of the alumina tube flowed at 50 sccm (standard cubic centimeters per minute) at 400 torr. The temperature of the furnace was increased to 1300 C at 6 C/min and kept at this temperature for 7 h. The temperature of the silicon substrate surface where the oriented silicon nanowires grew was found to be approximately 930 C, which differed from that at the center due to the temperature gradient within the tube. The product was first directly examined by scanning electron microscopy (SEM, Philips XL 30 FEG). Microstructural characterization was carried out in a conventional Philips CM 20 transmission electron microscope (TEM) at 200 kV. The high-resolution transmission electron microscopy (HRTEM) study was performed in a Philips CM200 FEG transmission electron microscope, operated at 200 kV accelerating voltage at room temperature. The chemical compositions of the samples were determined by an energy dispersive X-ray (EDX) spectrometer attached to both the SEM and HRTEM instruments. Raman scattering spectra were measured with a Renishaw micro-Raman spectrometer at room temperature. Excitation was by means of the 514 nm line of an Ar laser, and the Raman signals were measured in a backscattering geometry with a spectral resolution of 1.0 cm. The deposited silicon nanowire product is light yellow in color. SEM images at different magnifications of a typical sample in Figures 1a, 1b, 1c, and 1d clearly show the large area of highly oriented nanowires on the surface of the silicon substrate. The low magnification SEM image (Fig. 1a) shows that the area of highly oriented silicon nanowires is about 2 mm ́ 3 mm and the lengths of individual nanowires are up to 1.5±2 mm. The thickness of the oriented nanowire product was about 10 lm, as estimated from the cross-sectional image (Fig. 1d) of the sample prepared by focused ion beam cutting. The highly oriented array of Si nanowires can also be observed from the cross-sectional image. The EDX results show that the nanowires are composed of silicon and oxygen. No metal was found in the sample. Such results are consistent with our previous theory that silicon nanowire growth is enhanced by silicon oxide instead of a metal particle catalyst. Because of local charging effects, the diameters observed from SEM images appear larger than the actual wire diameters. More information about the morphology of silicon nanowires is given by the following TEM characterization Small pieces of oriented silicon nanowire samples were peeled off from a silicon substrate and mounted on a folding grid for TEM and HRTEM observations. Figure 2 shows the typical morphology of silicon nanowires. As reported previously, these nanowires show a better orientation than those synthesized by laser ablation. Silicon nanowires as observed by TEM are quite clean, with very few particles attached to their surfaces, and are relatively homogeneous. Analysis of a number of nanowires shows that the diameters of these silicon nanowires vary from 18 to 46 nm, and the mean value is about 30 nm. The selected-area electron dif-

Nanopatterned Assembling of Colloidal Gold Nanoparticles on Silicon

Abstract: A quasi-one-dimensional (quasi-1D) Au nanocolloids array has been fabricated on silicon by combining the techniques of atomic force microscopy (AFM)-based nanooxidation and chemical assembling of colloidal nanoparticles. The silicon substrate, modified with an octadecyltrichlorosilane (OTS) monolayer, was first subjected to a localized chemical oxidation by using conductive AFM to form silicon oxide lines. After further modification of the oxidized region with an aminopropyltriethoxylsilane (APTES) monolayer via selective chemical adsorption, the substrate was exposed to a colloidal suspension of gold for deposition of gold nanoparticles. It is found that the Au nanoparticles can be selectively immobilized onto the AFM tip-defined amino-terminating regions of the silicon surface, forming quasi-1D gold nanoparticle arrays. The patterned structure is highly controllable and reproducible, which, we believe, will contribute to studies of nanodevices and mesoscopic phenomena.

Silicon Oxynitride Layers for Optical Waveguide Applications

Abstract: We report on the fabrication and characterization of silicon oxynitride (SiON) layers for applications as planar optical waveguides in the 1550 nm wavelength region. The optically guiding SiON waveguide core layer has a relatively high refractive index of 1500 and is sandwiched between two silicon oxide cladding layers with a lower refractive index of 1450. The SiON layer is deposited by plasma-enhanced chemical vapor deposition using silane, nitrous oxide, and ammonia as gaseous precursors. Waveguide bends with a radius of curvature as small as 1.5 mm can be realized because of the high refractive index difference achievable between core and cladding layers. This allows the fabrication of compact, relatively complex integrated optical waveguide devices, The deposition process and the characterization of the SiON films are discussed. The strengths of this high refractive index contrast planar waveguide technology are illustrated using the example of an optical add/drop filter for wavelength division multiplexing applications in the field of optical communication systems.

Detailed characterization of anodic bonding process between glass and thin-film coated silicon substrates

Abstract: Anodic bonding between Si-based and glass substrates has been characterized in detail. The effects of magnitude of the applied voltage, surface properties (coating of Si substrate), and surface cleanliness (pre-bonding cleaning procedure) on the time required for complete bonding were thoroughly studied. First, the generic bonding time versus applied voltage plot was found to be concave in shape (viewed from the origin). For bonding between p-type Si substrate and Corning 7740 glass pre-cleaned with acetone, the time required was cut down from 38 to 4 min if the applied voltage was increased from 200 to 500 V. Second, the bonding time required for five Si-based substrates in ascending order was determined to be Si (p-type), polysilicon, silicon nitride, silicon oxide and then Si (n-type). Third, the bonding between p-type Si substrate, pre-cleaned with H2SO4–H2O2 and HF, and Corning 7740 glass was completed within 1 min, which was much faster than that pre-cleaned with acetone (4 min). Finally, from bonding point of view, Corning 7740 glass was superior to Corning 7059 glass and Fisher slide due to its thermal coefficient of expansion matching with the underlying Si substrate and the presence of significant amount of sodium ions in the glass.

Yttrium silicate formation on silicon: Effect of silicon preoxidation and nitridation on interface reaction kinetics

Abstract: The effects of oxygen and nitrogen pretreatments on interface reaction kinetics during yttrium silicate formation on silicon are described. X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS) are used to determine chemical bonding and composition of films formed by oxidation of yttrium deposited on silicon. Capacitance–voltage testing is used to determine the quality of the dielectric and the electrical thickness. The effect of ultrathin silicon oxide, nitrided oxide, and nitrided silicon interfaces on metal oxidation kinetics is also described. When yttrium is deposited on clean silicon and oxidized, XPS and MEIS indicate significant mixing of the metal and the silicon, resulting in a film with Y–O–Si bonding and composition close to yttrium orthosilicate (Y2O3⋅SiO2). A thin (∼10 A) in situ preoxidation step is not sufficient to impede the metal/silicon reaction, whereas a nitrided silicon interface significantly reduces the silicon consumption rate, and the resulting film is c...

Swelling of a Polyelectrolyte Brush in Humid Air

Abstract: We present an experimental study on the swelling of polyelectrolyte brushes covalently attached to planar solid surfaces in contact with humid air. Monolayers of poly-N-methyl-[4-vinylpyridinium]iodide (MePVP) with film thicknesses of several hundred nanometers were used in this study. The MePVP brushes were attached to the surfaces of silicon wafers as well as to evaporated silicon oxide films on solid substrates by using self-assembled monolayers of an azo initiator and radical chain polymerization in situ. The film thicknesses of the surface-bound monolayers were measured by optical waveguide spectroscopy (OWS) as a function of the humidity of the environment. The MePVP brushes show strong increases in thickness as well as a strong decrease of the refractive index of the surface-attached layer due to water incorporation caused by the exposure to the humid environment.

Semiconductor device and its manufacture

Abstract: PROBLEM TO BE SOLVED: To adjust input/output capacitance of a semiconductor device meeting the maximum and minimum standards or a customer's request. SOLUTION: On the main surface of a semiconductor substrate 1, a thick silicon oxide film 2 which functions as an element isolation region is formed and a first electrode 6 is formed on the silicon oxide film 6 in a peripheral circuit region. The first electrode 6 is formed simultaneously with a gate electrode 4 of a MISFET Qs for memory cell selection. In addition, the first electrode 4, the substrate 1 which is a second electrode, and silicon oxide film 2 held between the electrode 6 and substrate 1 constitute a parallel plate capacitance element CA. Moreover, the first electrode 6 is connected electrically connected to a bonding pad BP of a third-layer wiring M3. The selection whether or not the electrode 6 is connected to the bonding section BP1 of the bonding pad BP is performed, by changing the pattern of the metal switch section BP2 of the bonding pad BP.

Focused ion beam induced deposition: fabrication of three-dimensional microstructures and Young's modulus of the deposited material

Abstract: In this work, some of the possibilities of focused ion beams for applications in microsystem technology are explored. Unlike most previous studies, the emphasis is on `additive' techniques, i.e. localized maskless deposition of metals and insulators. More precisely, we will show the possibility of fabricating small three-dimensional structures, using focused ion beam deposition of silicon oxide. Deposition examples will show that the technique is most promising for small post-processing steps or prototyping, because of its high degree of flexibility. Furthermore, an investigation into the mechanical properties of the deposited material is presented. More specifically, the Young's modulus of the deposited silicon oxide is determined.

Epitaxial growth of germanium dots on Si(001) surface covered by a very thin silicon oxide layer

Abstract: We show that germanium dots can be directly grown by molecular beam epitaxy (MBE) on a silicon (001) surface covered by a thin (1.2-nm-thick) thermal silicon oxide layer. We describe the experimental procedure, which induces the growth of a high density (1011/cm2) of nanometric germanium dots on silicon oxide. Germanium dots grown by MBE exhibit an epitaxial relationship with the underlying silicon substrate. We show that despite the presence of the thin silicon oxide layer, the silicon grown to embed the germanium dots is also single crystal in epitaxy with the silicon substrate. Nanometric size high-density crystalline inclusions in silicon oxide, seen in high-resolution transmission electron microscopy observations, are tentatively proposed as nucleation seeds for germanium dots and silicon lateral overgrowth on silicon oxide.

Chemical-mechanical polishing slurry

Abstract: A polishing slurry including an abrasive, deionized water, a pH controlling agent, and polyethylene imine, can control the removal rates of a silicon oxide layer and a silicon nitride layer which are simultaneously exposed during chemical mechanical polishing (CMP) of a conductive layer. A relative ratio of the removal rate of the silicon oxide layer to that of the silicon nitride layer can be controlled by controlling an amount of the choline derivative.

UV radiation source for densification of CVD carbon-doped silicon oxide films

Abstract: A UV radiation source is tunable to optimize the process of densifying a carbon-doped silicon oxide film. The composition and relative concentration of stimulated gases stimulated within an airtight bulb is controlled to produce radiation optimized for absorption by undesirable chemical bonds of the carbon-doped silicon oxide film, leading to disruption of these bonds and their replacement by more desirable stable chemical bonds. The energy of radiation emitted by the source is determined by the identity of excited chemical species, and the intensity of the radiation emitted by the source is determined by the concentration of the excited chemical species. By exciting a specific mixture of gases, radiation is emitted at a combination of energies and intensities calculated to disrupt populations of unstable bonds in the carbon-doped silicon oxide film while leaving desirable bonds in the film unaffected.

Electronic structure of silicon nanowires: A photoemission and x-ray absorption study

Abstract: Photoemission and x-ray absorption spectroscopy have been used to study silicon nanowires prepared by a laser ablation technique together with Si(100) and porous silicon. Si $2p$ and valence-band spectra show that the Si nanowires are essentially crystalline Si encapsulated by silicon oxide. HF etching removes the surface oxide but leaves the morphology intact. Si K-edge x-ray absorption near-edge structures show that the characteristic Si K-edge whiteline doublet in Si(100) smears out in the nanowires and blurs entirely in porous silicon and that the whiteline exhibits a small blueshift. This observation indicate a progressive degradation in long-range order going from bulk Si to nanowires to porous Si and a wider band gap for a fraction of the nanowires. The extended x-ray absorption fine structures show that despite an increased disorder relative to bulk Si, Si nanowire remains essentially crystalline, in good accord with recent transmission electron microscopy and x-ray powder diffraction studies.

Method for machining work by laser beam

Abstract: A method for machining a work so as to make a hole with a high aspect ratio in the work by laser machining. Silicon oxide protective films (2) are formed on both sides of a silicon substrate (1) and a laser beam is projected onto the silicon substrate (1) through the protective film (2) to make a hole. Alternatively, a circularly- or randomly-polarized laser beam is projected onto the silicon substrate (1). Thus, the aspect ratio of the hole is high, the hole is straight, and the machining accuracy is improved.

Reliability of ultrathin silicon dioxide under combined substrate hot-electron and constant voltage tunneling stress

Abstract: An experimental investigation of breakdown and defect generation under combined substrate hot-electron and tunneling electrical stress of silicon oxide ranging in thickness from 2.0 nm to 3.5 nm is reported. Using independent control of the gate current for a given substrate and gate bias, the time-to-breakdown of ultrathin silicon dioxide under substrate hot-electron stress is observed to be inversely proportional to the gate current density. The thickness dependence (2.0 nm to 3.5 nm) of substrate hot-electron reliability is reported and shown to be similar to constant voltage tunneling stress. The build-up of defects measured using stress-induced-leakage-current and charge-pumping for both tunneling and substrate hot-electron stress is reported. Based on these and previous results, a model is proposed to explain the time-to-breakdown behavior of ultrathin oxide under simultaneous tunneling and substrate hot-electron stress. The results and model provide a coherent understanding for describing the reliability of ultrathin SiO/sub 2/ under combined substrate hot-electron injection and constant voltage tunneling stress.

Advantage of radical oxidation for improving reliability of ultra-thin gate oxide

Abstract: This paper focuses attention on the advantage of oxygen radical oxidation by a microwave-excited high-density Kr/O/sub 2/ plasma for improving the disadvantages of conventional thermal oxidation processes using H/sub 2/O and/or O/sub 2/ molecules, and demonstrates that the Kr/O/sub 2/ plasma oxidation process can improve the thickness variation on shallow-trench isolation and integrity of silicon oxide not only on the [100] surface but also on the [111] surface compared to those of conventional thermal oxidation processes.

Semiconductor structure including a partially annealed layer and method of forming the same

Abstract: High quality epitaxial layers of compound semiconductor materials can be grown overlying large silicon wafers by first growing an accommodating buffer layer on a silicon wafer. The accommodating buffer layer is a layer of monocrystalline oxide spaced apart from the silicon wafer by an amorphous interface layer of silicon oxide. The amorphous interface layer dissipates strain and permits the growth of a high quality monocrystalline oxide accommodating buffer layer. The accommodating buffer layer is lattice matched to both the underlying silicon wafer and the overlying monocrystalline compound semiconductor layer. Any lattice mismatch between the accommodating buffer layer and the underlying silicon substrate is taken care of by the amorphous interface layer. To further relieve strain in the accommodating buffer layer, at least a portion of the accommodating buffer layer is exposed to a laser anneal process to cause the accommodating buffer layer to become amorphous, providing a true compliant substrate for subsequent layer growth.