Showing papers on "Oxide published in 1986"

Low Temperature Surface Cleaning of Silicon and Its Application to Silicon MBE

Abstract: A low temperature thermal cleaning method for Si molecular beam epitaxy (MBE) is proposed. This method consists of wet chemical treatment to eliminate carbon contaminants on Si substrates, thin oxide film formation to protect the clean Si surface from contamination during processing before MBE growth, and desorption of the thin oxide film under UHV. The passivative oxide can be removed at temperatures below 800°C. It is confirmed that Si epitaxial growth can take place on substrates cleaned by this method and that high quality Si layers with dislocations of fewer than 100/cm2 and high mobility comparable to good bulk materials are formed. Surface cleanliness, the nature of thin passivative oxide films, and cleaning processes are also studied by using such surface analytic methods as Auger electron spectroscopy, reflection high energy electron diffraction, and x‐ray photoelectron spectroscopy.

Preparation, characteristics and photovoltaic properties of cuprous oxide—a review

Abstract: The photovoltaic properties of cuprous oxide (Cu 2 O) are reviewed and discussed. The emphasis, however, is on reviewing the characteristics of Cu 2 O prepared by different techniques such as high-temperature thermal oxidation, low-temperature thermal oxidation, electro-deposition, anodic oxidation, chemical oxidation and reactive sputtering. It is shown that despite the economic prospects of efficient cells based on Cu 2 O, little is known about the photovoltaic properties of this material when it is fabricated by low-temperature techniques. The areas in which further research is needed because of the lack of information in the literature are pointed out.

Hydrolysis of titanium alkoxide and effects of hydrolytic polycondensation parameters

Abstract: Titanium alkoxides hydrolyse vigorously with water producing polycondensates whose equivalent oxide content varies from ∼ 70% to over 90%. This variation reflects the average molecular size and the nature of the terminal bonds. Hydrolysis conditions also affect the molecular and particle morphologies modifying the crystallization and sintering behaviour of oxide materials derived from polycondensates. It is also possible to form clear polymer solutions under excess water hydrolysis with the addition of certain acids. Investigations show that there is a window in the acid concentration which provides long-term solution stability. The gels formed from these clear solutions shrink in their liquor under certain conditions and the introduction of hydrogen peroxide into the liquor (surrounding the gel) causes vigorous gel shrinkage.

Investigations on hydrophilic and hydrophobic silicon (100) wafer surfaces by X-ray photoelectron and high-resolution electron energy loss-spectroscopy

Abstract: The paper reports on surface spectroscopy measurements of silicon single-crystal wafers which have been treated in order to obtain hydrophilic and hydrophobic surfaces, respectively. The wafers are characterized in terms of the oxidation behaviour in air (“native oxides”), their surface chemical composition and the chemical bonds involved. It is shown that the oxide on hydrophilic wafers mainly grows in the cleaning agent and consists of hydrated SiO2 through all stages of the growth. On a hydrophobic surface, however, the oxidation begins with the formation of a lower oxidation state which turns into SiO2 on storage in air. The thickness of the oxides on both surface types reaches 1.4–1.5 nm. Both the chemical shift in photoelectron spectroscopy and the frequency of the asymmetric Si-O-Si vibration in electron energy loss spectroscopy support the assumption of a reduced bonding angle of the oxygen bridge. Hydrophilicity is caused by singular and associated OH groups on the surface. Singular groups could be detected up to 700 K. There are hints that OH groups stabilize the oxide during heating. The hydrophobic state is mainly characterized by Si-H and Si-CH x groups on the surface, whereas Si-F exists only in minor quantities. Si-H groups were stable up to approximately 900 K in UHV. Si-CH x dehydrogenizes at temperatures between 500 and 700 K leaving SiC on the surface.

Oxidation Kinetics of Silicon Carbide Crystals and Ceramics: I, In Dry Oxygen

Abstract: The oxidation kinetics of several single-crystal and polvcrystalline silicon carbide materials and single-crystal silicon in dry oxygen over the temperature range 1200° to 1500°C were fitted to the linear-parabolic model of Deal and Grove. The lower oxidation rates of silicon carbide compared to silicon can be rationalized by additional consumption of oxidant in oxidizing carbon to carbon dioxide. The (000J) Si face of the silicon carbide platelets exhibited lower parabolic oxidation rates than the (0001) C face, by a factor of 10 at 1200°C. Apparent activation energies increased from a value of ∼120 kJ/mol below 1400°C to a value of ∼300 kJ/mol above this temperature. The (0001) Si face exhibited this high activation energy over the entire temperature range. The controlled nucleation thermally deposited material exhibited the highest oxidation rates of the polycrystalline materials followed by the hot-pressed and sintered α-silicon carbides. In general, the oxidation rates of the polycrystalline materials were bracketed by the oxidation rates of the basal planes of the single-crystal materials. Higher impurity concentrations and higher density of nucleation sites led to a greater susceptibility to crystallization of the scale which significantly complicated the oxidation behaviors observed. When crystallization of the oxide scale occurred in the form of a layer of spherulitic cristobalite crystals, a retardation of the oxidation rates was observed. An accelerated oxidation behavior was found when this coherent layer was superseded by the formation of fine mullite crystals.

Ion-based methods for optical thin film deposition

Abstract: The optical properties of the dielectric oxide films SiO2, Al2O3, TiO2, ZrO2, CeO2 and Ta2O5 produced by ion-based techniques have been reviewed. The influence of ion bombardment during deposition is discussed in some detail and the various production techniques are described. Recent results on the deposition and properties of diamond-like carbon films are also reviewed. Finally, some examples of the practical applications of high quality dielectric oxide films are given.

Localized Corrosion of Aluminum Alloys—A Review

Abstract: Localized corrosion, which usually appears as pitting, crevice corrosion (CC), or certain aspects of stress corrosion cracking (SCC), is a multi-step process. This review is organized by a consideration of the four steps involved in localized corrosion: (1) adsorption of the reactive anion on the oxide covered aluminum; (2) chemical reaction of the adsorbed anion with the aluminum ion in the aluminum oxide lattice or the precipitated aluminum hydroxide; (3) thinning of the oxide by dissolution; and (4) direct attack of the exposed metal by the anion, perhaps assisted by an anodic potential. The experimental work reported in the literature is evaluated within this framework.

A Relationship between Indigenous Impurity Elements and Protective Oxide Scale Adherence Characteristics

Abstract: A new and a radically different mechanism to account for the beneficial effects that small additions of elements such as yttrium have on the adherence of oxide scales is proposed. It has been long:known and has been reaffirmed here that indigenous impurities such as sulfur, known to be present at tramp levels (<100 ppm) within nickel and nickel-based alloys, can segregate to metal surfaces. However, here it has been disclosed that such sulfur segregation can also markedly affect the adherence of the protective oxide scale. In the absence of elements like yttrium, such segregation effects weaken the bond between the protective scale and the substrate metal. The role of the yttrium is to interact with such indigenous sulfur to form a refractory sulfide. This interaction lessens the amount of sulfur available to segregate to and concentrate at the critical scale-metal interface. Results reported here have focused on sulfur because sulfur has been long known to be a common tramp impurity in nickel and nickel-based alloys. However other elements, e.g., phosphorus, chlorine, etc., could very probably produce similar effects. The results of experiments involving Auger spectroscopy, optical, scanning electron microscopy, scanning electron microprobe, and scanning transmission electron microscopy techniques in conjunction with isothermal and cyclic oxidation testing which have led us to propose this mechanism are presented.

Production of ultrafine metal oxide aerosol particles by thermal decomposition of metal alkoxide vapors

Abstract: Ultrafine spherical titanium, silicon, and aluminium oxide particles were prepared by the thermal decomposition of their alkoxide vapors, produced by evaporation and subsequent heating. High-concentration ultrafine particles having geometric mean diameters ranging between 0.01 and 0.06 µm and a geometric standard deviation of about 1.4 were obtained by varying the temperatures of the evaporator containing the liquid alkoxides and the reactor furnace, and the flow rate of carrier gas. For furnace temperatures lower than 400^oC for TiO, and 1000^oC for SiO_2 and Al_2O_3, the particles obtained were found to be amorphous. The observed changes in the particle size distributions due to changes in operating conditions were compared with those predicted theoretically by solving the discrete-continuous aerosol general dynamic equation accounting for coagulation and generation of monomer by thermal decomposition. The effect of monomer number concentration on the size distribution of generated particles was found to be qualitatively explained.

Trap generation and occupation dynamics in SiO2 under charge injection stress

Abstract: The effect of enduring charge injection on the physical properties of the SiO2 layer of a metal‐oxide‐semiconductor structure is studied by means of a novel characterization method. It is based on the observation reported previously, that under charge injection conditions the density of occupied oxide traps reaches a value which is only a fraction of the total trap density. This trap occupation level is strongly dependent on the oxide electric field. The oxide trap density can be evaluated by measuring this field dependence, using a relatively small amount of charge injection. This method is used to distinguish between the process of trap generation and electron trapping in the generated traps, under conditions of continuous charge injection up to levels of more than 50 C/cm2. The trap generation rate is found to be proportional to the flux of the injected charge, and to increase exponentially with the oxide electric field. At high oxide field only a small fraction of the newly generated traps are occupie...

Substrate hole current and oxide breakdown

Abstract: It is known that when an n‐channel metal‐oxide‐semiconductor field‐effect transistor is biased with a high positive gate voltage, a hole current appears in the substrate cathode. Recent experiments indicate that the holes are generated within the oxide. We show that this hole generation mechanism is linked to oxide time‐dependent breakdown. When the hole fluence reaches a certain critical value, breakdown occurs. This is in agreement with a hole‐trapping‐induced breakdown model. For very thin oxides the hole generation rate can become so low that the substrate hole current is dominated by the tunneling of valence‐band electrons which is not expected to contribute to oxide breakdown. A different mechanism of hole generation such as hot‐hole tunneling from the anode may be responsible for oxide breakdown in the important case of low gate voltage (<6 V).

Generation of Interface States by Ionizing Radiation in Very Thin MOS Oxides

Abstract: The creation of interface states Dit by ionizing radiation is investigated in MOS capacitors as a function of oxide thickness in the range 6-50 nm A comparison of the thickness dependence in etchback and asgrown oxides supports the idea that the number of defects at the Si-SiO2 interface increases with oxidation time For relatively thin oxides (tox<12 nm), the rate of increase in Dit is significantly smaller than would be extrapolated from the behavior of thicker oxides for both oxide types This effect is probably caused by tunneling of trapped holes near the oxide interfaces

Oxidation of commercial purity titanium

Abstract: The oxidation kinetics of commercial purity Ti-A55 exposed to laboratory air in the 593-760 C temperature range were continuously monitored by thermogravimetric analysis. The oxide thickness was measured by microscopy, and the substrate contamination was estimated from microhardness measurements. The microhardness depth profiles were converted to oxygen composition profiles using calibration depth. The oxygen diffusion coefficient in alpha-Ti appears to be approximately concentration-independent in the 1-10 at. pct oxygen range. Diffusion coefficient for oxygen in TiO2 has been estimated as a function of temperature and is found to be about 50 times the value in alpha-Ti. The metallographically prepared cross sections of the oxidized specimens revealed a 'moving boundary' in the substrate, parallel to the oxide-metal interface. This boundary was associated with a specific oxygen level of 5.0 + or - 0.5 at. pct. It occurred at a distance from the oxide-metal interface which was correlatable with temperature and time of exposure. The diffusion coefficient corresponding to the composition of this moving boundary is in excellent agreement with the effective diffusion coefficient for the substrate contamination.

Internal Oxidation of Ag-In Alloys: Stress Relief and the Influence of Imposed Strain,

Abstract: The kinetics of internal oxidation of silver-indium alloys containing 3.5, 5.9, and 9.8 at.% In in air at temperatures 773 to 973 K were established by TGA with no load applied to the specimens. Silver nodules free of oxide particles were observed to form at the surface during internal oxidation. The volume of these silver nodules was comparable to the total volume increase caused by internal oxidation. The alloys were also creep tested during oxidation in air at creep rates varying from 10−7 to 5×10−5 s−1 at 773, 873, and 973 K. The parabolic rate constants kp for the internal oxidation of the solute were determined from the measured widths of the internal oxidation zones. A small increase in kp was observed with increased strain rate. The large volume change associated with internal oxide formation resulted in a stress gradient between the stress-free surface and the internal oxidation front which is under a high compressive stress. Stress relief occurred by transport of silver to the surface. A Nabarro-Herring creep type mechanism based on lattice diffusion of Ag cannot account for the high rate of silver transport to the surface. Pipe-diffusion controlled creep is proposed as the mechanism of stress accommodation by silver diffusion.

Adsorption characteristics of metal-EDTA complexes onto hydrous oxides

Abstract: The adsorption characteristics of a variety of metal-EDTA complexes onto hydrous oxides, principally aluminum oxide (γ-Al2O3), were examined in aqueous solution. Adsorption of these complexes increased with increasing proton concentration due to the formation of surface complexes between EDTA and the surface hydroxo groups, specifically the AlOH2+ surface groups. The pH-dependent adsorptive behavior and the magnitude of adsorption of the “free” EDTA species were similar to those of the metal complexes. The results also showed that the adsorption of “free” EDTA was exothermic, while the adsorption of Ni(II)-EDTA complexes was endothermic in the lower pH region (∼3.5) and exothermic at higher pH values (∼6.0). This implied that the surface preferred the NiHEDTA−1 species rather than the NiEDTA−2 species. Specific adsorption of the metal complexes was evidenced by the charge reversal exhibited by the γ-Al2O3 particles at the highest surface loadings. A quantitative model was formulated based on the pH-dependent speciation of the oxide surface, speciation of the metal complexes in solution, and ζ potential measurements. This model proved valid over a wide range of pH (3–10) and for both high (>50% coverage) and low (<10% coverage) surface loadings.

Spray-dried inorganic oxides from non-aqueous gels or solutions

Abstract: Inorganic metal oxides having high surface area and pore volume are prepared by spray drying. The admixture which is spray dried to yield the metal oxides is produced from reactants comprising at least one hydrolyzable metal compound, a sufficient amount of water to at least partially hydrolyze the metal compound and an organic solvent. The admixture is supplied as a plurality of droplets to a reaction zone operated under conditions of temperature and pressure below the critical temperature and pressure of the reactants but sufficient to produce a product comprising metal oxide powders and a gas comprising organic solvent vapors. The powders are separated from the gas in a known fashion and collected. Spray drying of non-aqueous systems unexpectedly produces metal oxides having properties generally intermediate conventionally produced oxides and aerogels.

Multilevel integrated circuits employing fused oxide layers

Abstract: A multilevel semiconductor integrated circuit is fabricated by providing a plurality of substrates having an epitaxial layer on one surface and a silicon oxide layer on the surface of the epitaxial layer. The substrates are sequentially stacked with the silicon oxide layers in contact and fused together. One substrate is retained as a support, and other substrates are removed by etching after the fusion of the silicon oxide layers, thereby leaving only the stacked epitaxial layers separated by silicon oxide. The stacked structure facilitates the vertical fabrication of CMOS transistor pairs sharing a common gate electrode in an epitaxial layer between the two transistors. Electrical isolation between the epitaxial layers is provided by the fused silicon oxide or by removing the silicon oxide and some of the silicon thereby forming a void between adjacent epitaxial layers. Circuit devices in the plurality of epitaxial layers are readily interconnected by forming conductive vias between the epitaxial layers.

Surface Characterization of Silicon Nitride and Silicon Carbide Powders

Abstract: The nature and composition of the surfaces of silicon nitride and silicon carbide powders were investigated using high voltage and high resolution transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). An amorphous oxide (or oxygen-rich) layer, approx. =3-5 nm thick, present on the powder surfaces forms strong bridges between particles. Both XPS and SIMS show that oxygen is the major impurity on the powder surfaces, but minor impurities such as chlorine, fluorine, carbon, iron and sodium are also revealed. The extent of the oxide layer was reduced substantially by washing the powder in anhydrous hydrofluoric acid or by treatment in an argon/hydrogen gas mixture at approx. =1300/sup 0/C. Surface treatment in the gas mixture did not cause further agglomeration of the powder.