Showing papers on "Silicon dioxide published in 1996"

Covalent Attachment of Synthetic DNA to Self-Assembled Monolayer Films

Abstract: The covalent attachment of thiol-modified DNA oligomers; to self-assembled monolayer silane films on fused silica and oxidized silicon substrates is described. A heterobifunctional crosslinking molecule bearing both thiol- and amino-reactive moieties was used to tether a DNA oligomer (modified at its terminus with a thiol group) to an aminosilane film formed on silica surfaces. A variety of aminosilanes, crosslinkers and treatment conditions have been tested to identify optimal conditions for DNA immobilization using this approach. The DNA films which result have been characterized using UV spectroscopy, water contact angle measurement, radiolabeling and hybridization methods.

Fluorescence interference-contrast microscopy on oxidized silicon using a monomolecular dye layer

Abstract: A silicon chip is covered by a monomolecular film of a fluorescence dye with silicon dioxide used as a spacer. The fluorescence depends on the distance of the dye from the silicon. The modulation of the intensity is described quantitatively by an optical theory which accounts for interference of the exciting light and of the emitted light. The effect is used to obtain a microscopic picture of the surface profile with a precision of a few Angstroms. The perspectives for an application in wet systems such as neuron-silicon junctions and lipid membranes on silicon are pointed out.

Pharmaceutical excipient having improved compressibility

Abstract: A microcrystalline cellulose-based excipient having improved compressibility, whether utilized in direct compression, dry granulation or wet granulation formulations, is disclosed. The excipient is an agglomerate of microcrystalline cellulose particles and from about 0.1% to about 20% silicon dioxide particles, by weight of the microcrystalline cellulose, wherein the microcrystalline cellulose and silicon dioxide are in intimate association with each other. The silicon dioxide utilized in the novel excipient has a particle size from about 1 nanometer to about 100 microns. Most preferably, the silicon dioxide is a grade of colloidal silicon dioxide.

Organic insulating films of nanometer thicknesses

Abstract: It is demonstrated that monolayers of organic molecules (long chain hydrocarbons) as thin as 1.9 nm, deposited by the self‐assembly technique on silicon, form high performance electrically insulating barriers. Their properties are compared with those of silicon dioxide. Leakage current densities through the organic monolayers of the order of 10−8–10−7A/cm2 have been obtained. These values are 4–5 decades lower than those for silicon dioxide of equivalent thickness. Larger tunneling barriers for organic monolayers than for silicon dioxide explain these results.

Purification, recovery, and laser-driven fluorination of silicon from dissolved and particulate silica for the measurement of natural stable isotope abundances.

Abstract: A procedure for the purification, recovery, and determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and dissolved silicic acid is reported. Purification involves the reaction of acid molybdate with dissolved silicon in natural waters or that produced by the dissolution of particulate silica by hydrofluoric acid. The resulting silicomolybdic acid is then quantitatively precipitated by reaction with triethylamine hydrochloride. The silicon is recovered as silicon dioxide through stepwise combustion of the dried precipitate. Fluorination of the product for isotopic analysis is accomplished by laser heating under pure fluorine generated by the decomposition of a fluorine-based salt. The resulting silicon tetrafluoride is separated from hydrogen fluoride and other fluorination byproducts cryogenically using a variable-temperature cold trap. Yields for silicon recovery are 99.9% for precipitation and greater than 95% for the purification/fluorination procedure. Reprod...

Light Emission from Nanometer-Sized Silicon Particles Fabricated by the Laser Ablation Method

Abstract: Luminescent nanometer-sized silicon particles are fabricated by laser ablation of a silicon target in helium gas. The formation of products is found to be governed by the dynamics of the laser-ablated silicon particles in the gas. The products deposited on silicon substrates exhibit light emission with a peak at 1.6 eV in the air, while 2.1 eV after annealing for 20 min at 800°C in oxygen gas. Applying the laser ablation technique, we demonstrate a novel technique for fabricating silicon particles embedded in a silicon dioxide film. The particles also exhibit visible light emission.

Explanation for the polarity dependence of breakdown in ultrathin silicon dioxide films

Abstract: The polarity dependence observed for destructive breakdown of ultrathin silicon dioxide films is shown to be directly correlated to the oxide degradation caused by hot‐electron‐induced defect production. The probability of defect generation is also demonstrated to depend on the Fermi level position at the anode/oxide interface. The specific anode interface, whether substrate/oxide or gate/oxide, is shown to have no direct relationship to the degradation rate.

The fabrication and characterization of EEPROM arrays on glass using a low-temperature poly-Si TFT process

Abstract: The fabrication and optimization of poly-Si thin-film transistors and memory devices on glass substrates at temperatures of 200/spl deg/C-400/spl deg/C is described, and the device characteristics and stability are discussed. The devices were formed using PECVD amorphous silicon, silicon dioxide, and silicon nitride films, and the crystallization of the amorphous silicon was achieved with an excimer laser. The performance of 16/spl times/16 EEPROM arrays with integrated drive circuits formed using this technology is presented.

Kinetics of residual stress evolution in evaporated silicon dioxide films exposed to room air

Abstract: Deposition of silicon dioxide thin films on silicon, germanium, and glass substrates has been accomplished by electron gun evaporation under various experimental conditions. The level of compressive residual stresses in evaporated SiO2 films determined just after deposition of films on Si or Ge substrates and the mass density of silica were found to be dependent on the substrate temperature and oxygen partial pressure in the evaporation chamber. Moreover, the intensity of compressive residual stresses decreased linearly as the logarithm of the exposure time of films to room air (aging time) was increased. After a compressive–tensile stress transition observed at a given aging time for films with relatively low densities, the intensity of tensile stresses continued to increase progressively with increasing aging time. The relative variation of residual stresses in SiO2 films was dependent on the mass density of the deposited material. Since the intensity of the absorption band of Si–OH radicals in the infrared spectra of SiO2 films exposed to room air increased with increasing aging time, the evolution of residual stresses was attributed to the effect of the hydration of silica by water vapor contained in room air. A reaction mechanism involving the physical adsorption of water vapor molecules on the SiO2 surface and reaction between adspecies and Si–O–Si species is proposed and discussed to interpret the logarithmic kinetics of residual stress evolution in evaporated SiO2 films exposed to room air.

Influence of nitrogen profile on electrical characteristics of furnace- or rapid thermally nitrided silicon dioxide films

Abstract: Thin silicon dioxide films nitrided in N2O by rapid thermal processing (RTP) or in a classical furnace were investigated by x‐ray photoelectron spectroscopy, secondary ion mass spectroscopy, and electrical measurements on metal‐oxide‐semiconductor capacitors. Differences between the two nitridation processes were observed and explained. In lightly nitrided films, nitrogen occupies two configurations. Nitrogen is bound to three silicon atoms with at least one in the substrate or all three in the oxide. In RTP‐nitrided films, both of these species are confined to within 1.5 nm of the Si/SiO2 interface. In furnace‐nitrided films, the first species is also located close to the interface whereas the second one fills most of the regrown oxide thickness. In furnace‐grown films, which are more heavily nitrided, a third structure due to Si2=N–O is observed throughout the layer. The electrical characteristics are well correlated with the amount of nitrogen at the interface that is bound to Si atoms in the substrate.

Plasma etch with trifluoroacetic acid and derivatives

Abstract: The present invention is directed to the etching of a material selected from the group consisting of silicon dioxide, silicon nitride, boronphosphorus silicate glass, fluorosilicate glass, siliconoxynitride, tungsten, tungsten silicide and mixtures thereof under plasma etch conditions, particularly for cleaning operations to remove silicon dioxide or silicon nitride from the walls and other surfaces within a reaction chamber of a plasma-enhanced chemical vapor deposition reactor. The etching chemicals used in the etch process are trifluoroacetic acid and it derivatives, such as; trifluoroacetic anhydride, trifluoromethyl ester of trifluoroacetic acid and trifluoroacetic acid amide and mixtures thereof.

Silicon dioxide chemical vapor deposition using silane and hydrogen peroxide

Abstract: SiH4 and H2O2 have been successfully used for the deposition of silicon dioxide for shallow trench isolation. With this chemistry, it is possible to fill up trenches without voids up to an aspect ratio 2.3:1. The very good gap filling is due to the presence of SiOH groups in the oxide film. To obtain a density close to that of thermal oxide, the film must be annealed at high temperature. The electrical characteristics are equivalent to those obtained using thermal silicon dioxide.

Comparative study of the elastic properties of silicate glass films grown by plasma enhanced chemical vapor deposition

Abstract: The Brillouin light scattering technique has been used to study the elastic properties of a number of silicon dioxide films deposited by plasma‐enhanced chemical vapor deposition on Si substrates. In addition to stoichiometric undoped glass films produced from either silane or tetraethylorthosilicate, we have also studied nonstoichiometric Si‐rich films and P‐doped films. The phase velocity of both the surface Rayleigh mode and the longitudinal bulk wave in the film material has been measured and the two independent elastic constants c11 and c44 have been evaluated. The derived values of the Young modulus and the Poisson ratio show appreciable deviations from the values we measured on thermally grown oxide. Moreover, the evolution of the stress during thermal cycles has been analyzed using the substrate curvature method. This permitted us to estimate the thermal expansion coefficient of the films and to distinguish between the intrinsic and thermal components of the stress.

Using neutral metastable argon atoms and contamination lithography to form nanostructures in silicon, silicon dioxide, and gold

Abstract: This letter describes the fabrication of ∼80 nm structures in silicon, silicon dioxide, and gold substrates by exposing the substrates to a beam of metastable argon atoms in the presence of dilute vapors of trimethylpentaphenyltrisiloxane, the dominant constituent of diffusion pump oil used in these experiments. The atoms release their internal energy upon contacting the siloxanes physisorbed on the surface of the substrate, and this release causes the formation of a carbon‐based resist. The atomic beam was patterned by a silicon nitride membrane, and the pattern formed in the resist material was transferred to the substrates by chemical etching. Simultaneous exposure of large areas (44 cm2) was also demonstrated.

TEOS‐based PECVD of silicon dioxide for VLSI applications

Abstract: Silicon dioxide films deposited from tetraethylorthosilicate (TEOS) using plasma-enhanced chemical vapour deposition (PECVD) are reviewed. The effect of the presence of oxygen on the film deposition rate and mechanism and the physical properties of the films, particularly the step coverage properties (conformality), are discussed in detail. Structural characterisation of the films has been carried out via etch rate measurements, infrared transmission spectroscopy, X-ray photoelectron spectroscopy (XPS) and Auger and secondary ion mass spectroscopy (SIMS) analysis. Electrical properties, i.e. resistivity, breakdown strength, fixed oxide charge density, interface state density and trapping behaviour, have been evaluated using metal-oxide-semiconductor (MOS) structures fabricated using the deposited oxides. Films deposited by microwave plasma-enhanced decomposition of TEOS in the presence of oxygen have been found to be comparable with standard silane-based low-pressure chemical vapour deposition (LPCVD) and PECVD oxides. It has been shown that films deposited on thin native oxides grown by either in situ plasma oxidation or low-temperature thermal oxidation exhibit excellent electrical properties.

Aging of photochemical vapor deposited silicon oxide thin films

Abstract: Further development of the microelectronic technology requires the growing of stable and passivated dielectric thin films. Photochemical processes are very promising methods to obtain silicon dioxide films for microelectronic purposes. In this article, the aging of silicon oxide films obtained by ArF laser chemical vapor deposition at low temperature is studied. The evolution of the properties of films has been followed up using infrared spectroscopy and ellipsometry, and compared with aging of thermally oxidized silica films. The role of moisture in film aging is also clarified by comparing films exposed to humid and to dry atmospheres. Si–OH groups are incorporated into the film in a specific local bonding environment and relaxation in the film structure takes place while new Si–O groups can be created. Moreover, the dependence of the stability of film properties on the processing parameters is analyzed.

Optical and mechanical properties of reactively sputtered silicon dioxide films

Abstract: The reactive sputtering method, using an mixture, was applied to deposit silicon dioxide film. Both x-ray photoemission spectroscopy (XPS) and infrared absorption spectroscopy were employed to evaluate the structure of films sputtered at various oxygen percentages. The optical and mechanical properties of films on glass substrates were investigated. Films prepared at a higher oxygen content have a higher density and a higher refractive index.

Study of plasma - surface interactions: chemical dry etching and high-density plasma etching

Abstract: We report results of the characterization of the plasma - surface interactions of silicon and silicon dioxide in fluorocarbon discharges using real-time ellipsometry and post-plasma multi-technique surface analysis for chemical dry etching (CDE) and high-density plasma etching (HDPE). We show that changes of the gas composition in CDE causes major changes in silicon surface chemistry and etching behaviour. For low-pressure HDPE we investigate the influence of power deposition into the discharge and bias voltage and bias power at the wafer on the surface chemical changes of silicon and .

CO2 laser‐assisted removal of submicron particles from solid surfaces

Abstract: A CO2 laser‐based system was used to provoke the vapor‐assisted removal of contaminating particles from different kinds of surfaces. Particles of alumina, silicon carbide, boron carbide, and cerium dioxide, with a size as small as 0.1 μm, have been efficiently removed from silicon, gold, and silicon dioxide surfaces. The dependence of the cleaning efficiency on the laser fluence was investigated; a threshold was found at 0.65 J/cm2 and the efficiency was highest for a fluence ranging from 2.9 to 3.2 J/cm2 for silicon, and 3.2 J/cm2 for gold and silicon dioxide surfaces. The amount of the water vapor which condenses at the surface was also found to play a major role, the best results being obtained with a condensed thickness calculated to be 6 μm. The zeta potential value of the contaminant particles with respect to that of the surface greatly influences the cleaning process.

Micronucleus formation in V79 cells treated with respirable silica dispersed in medium and in simulated pulmonary surfactant.

Abstract: Chinese hamster lung fibroblasts (V79 cells) were challenged with respirable silica particles using an in vitro genotoxicity assay. Two particle sizes of crystalline quartz and a non-crystalline silica were assayed for induction of micronuclei (MN) in V79 cells. Some of the silica dusts used were pretreated with simulated pulmonary surfactant to model in vivo exposure conditions. The results showed that both crystalline and non-crystalline silica dispered in medium (MEM) induced MN formation in a dose-dependent manner. Crystalline silica was more active in this assay than non-crystalline silica on a mass basis. The results also show that the frequency of micronucleated cells in cultures treated with surfactant-coated silica was not significantly different from that of the non-treated control cultures. These results seem to indicate that silica can cause chromosomal aberrations and/ or aneuploidies in V79 cells; however, pretreatment of silica particles with simulated pulmonary surfactant reduces or delays genotoxicity in this assay.

Visible luminescences from thermally grown silicon dioxide thin films

Abstract: We introduce visible photoluminescences (PL) of violet (432 nm) and yellow (561 nm) at room temperature from thermally treated silicon dioxide thin films. These luminescences were very strong with a near infinite degradation time. At an oxide layer thickness less than 200 nm, these luminescences were not seen, even with high temperature annealing at about 1000 °C. As a result of photoluminescence, x‐ray photoelectron spectroscopy, Fourier transform infrared, and high‐resolution transmission electron microscopy measurements, we conclude that the violet PL originates from the nanocrystalline silicon formed in the silicon oxide film by the thermal strain effect between the silicon substrate and the silicon dioxide film, while the yellow PL originates from the radiative decay of self‐trapped excitons that are confined to oxygen sufficient structures.

Matting agent based on aggregated silica

Abstract: The invention relates to an aggregated silica gel which has been produced from silica gel particles having a particle size of 1 to 20 ν, a surface of 200 to 1000 m2/g and a specific pore volume of 0.4 to 2.5 ml/g and a binding agent selected from synthetic or natural phyllosilicate, pyrogenic silicon dioxide and organic polymers soluble in water or dispersible in water. Aggregation takes place by spray-drying a suspension having 1 to 25 % solids. The product is suitable as a matting agent for coatings, as an antiblocking agent for polymer films and as a beer clarifying agent.

Method of making a solar cell having improved anti-reflection passivation layer

Abstract: A silicon solar cell has increased efficiency by providing an anti-reflection and passivation layer comprising a layer of silicon dioxide thermally grown on a surface of a silicon body and a layer of titanium dioxide deposited on the layer of silicon oxide. In fabricating the composite anti-reflection passivation layer, a layer of aluminum is first deposited on a surface of the thermally grown silicon oxide. After annealing the aluminum layer, the aluminum is removed from the silicon dioxide layer, and the layer of titanium dioxide is then deposited on the surface of the silicon dioxide from which the aluminum was removed. A layer of magnesium fluoride can be deposited on the surface of the titanium dioxide.

Method of etching silicon dioxide

Abstract: A layer of silicon dioxide is formed conformably over a substrate having a surface with non-planar topography. The layer of silicon dioxide is then implanted with a species that affects the etch rate of the silicon dioxide when etched in an HF based etchant. The implant energy, dose, and direction are chosen such that only a selected portion of the layer of silicon dioxide is implanted with the implant species. The layer of silicon dioxide is then etched in an HF based etchant. The HF etchant etches both doped and undoped silicon dioxide, but the implanted silicon dioxide is removed at a faster rate or slower rate, depending on the implant species, than the unimplanted silicon dioxide. This allows the formation of specialized silicon dioxide structures due to the selectivity of the etch as between the implanted and unimplanted portions of the layer of silicon dioxide, without any damage to silicon.