Showing papers on "Hydrofluoric acid published in 1989"

Reaction of water with hydrofluoric acid treated silicon(111) and (100) surfaces

Abstract: Si wafers with (100) or (111) oriented surfaces were treated in hydrofluoric acid (40% HF, 1 min) and then water rinsed for different times from 10 s to more than 50 h. Oxygen uptake and oxide formation were investigated by x‐ray photoelectron spectroscopy and high‐resolution electron energy‐loss spectroscopy. The initial state after the HF dip is characterized by a coverage with Si–hydride and small amounts of oxygen and fluorine. The interaction with the liquid phase of water was investigated up to the monolayer range. It shows distinct features: The first step is a rapid exchange of Si–F with H2 O to form Si–OH groups followed by a slow nucleophilic attack of OH− on surface Si–H to produce Si–OH. Growth law is logarithmic and extends to 3–5 h of water contact. The surface Si–OH act as nuclei for the attack of water on the polarized Si–SiOH backbonds. Interior Si–H and Si–OH groups develop. Further attack of OH− on interior Si–H yields Si–OH. Condensation of Si–OH forms Si–O–Si bridges and SiO2−x nuclei appear. Strain and altered surface topography lead to a changed rate of the logarithmic oxide growth. The oxide formation is accompanied by a slight corrosive attack of H2 O, leading to roughening of the surface.

Method and apparatus for purifying hydrogen fluoride.

Abstract: A method and apparatus for purifying hydrofluoric acid, comprising the steps of filtering the hydrofluoric acid to remove particulates (30), passing the filtered acid through a cation exchange material (14) and an anion exchange material (20) to remove ions therefrom, periodically monitoring (42) the acid that has passed through the cation exchange material for a level of cationic impurity representative of actual or impending ionic breakthrough in the cation exchange material, periodically monitoring (44, 46) the acid that has passed through the anion exchange material for a level of impurity representative of ionic breakthrough in the anion exchange material, interrupting the flow of acid at or prior to breakthrough and regenerating the anionic or cationic exchange material.

Application of Anhydrous Hydrogen Fluoride for the Structural Analysis of Polysaccharides

Abstract: Publisher Summary This chapter presents an overview of data regarding the application of hydrogen fluoride for the structural analysis of polysaccharides, primarily those of bacterial origin. The reactions of amylose, cellulose, inulin, starch, and xylans, and their constituent monosaccharides have been well studied. Before conducting the reaction, the hydrogen fluoride is often dried by distilling it from cobalt(III) trifluoride or filtering it through a layer of this salt. The use of hydrogen fluoride in establishing the monosaccharide composition of carbohydrates was studied for the first time in 1977. This reagent was shown to be applicable for the quantitative determination of monosaccharides in neutral and acidic plant polysaccharides (arabinogalactan from larch and whole cell-walls from tomato). A comparison of the recoveries of sugars from tomato suspension–culture cell walls after hydrolysis with 2 M trifluoroacetic acid, with and without previous solvolysis with hydrogen fluoride, showed a great increase in the recovery of D -glucose (from cellulose) after the solvolysis, but some decrease in the recovery of pentoses.

Monte Carlo studies of hydrogen fluoride clusters: cluster size distributions in hydrogen fluoride vapor

Abstract: An investigation into the structure and composition of hydrogen fluoride vapor is reported. Calculations are performed using a modified central force model potential developed by Klein and McDonald. Using a simulated annealing procedure, minimum energy structures for HF clusters are investigated ranging in size from n=2 to 7. Good agreement is found for the structural parameters obtained from the model potential and other theoretical and experimental information. The Monte Carlo method is used to determine the thermodynamic energy, entropy, and Gibbs free energy of the hydrogen fluoride clusters at 1 atm pressure and 100 and 273 K. A minimum in the Gibbs free energy change is found at n=4 implying that tetramers are very important in the vapor.

Method of reducing defects on semiconductor wafers

Abstract: A reduction in the number of impurities and defects on a semiconductor wafer is provided by cleaning the wafer in a hydrochloric acid, hydrofluoric acid, and water solution. This HCl:HF:H2 O solution removes silicon dioxide as well as metallic impurities from the wafer surface, thus preventing the formation of defects on the wafer and increasing the quality and yield of semiconductor devices.

Foamable fluoride compositions and method

Abstract: A foamable fluoride composition, for use in dental therapy, is provided that contains water, dental fluoride, foaming agent and acidifying agent. An illustrative composition comprises water, sodium fluoride, hydrofluoric acid, ethoxylated polyoxypropylene adduct of propylene glycol and phosphoric acid. The foamable fluoride composition, which is packaged in a nonmetallic, acid resistant, aerosol container in combination with an aerosol propellant, is dispensed into the trough of a dental tray as a dense, stable, non-flowable foam which is superimposed about and into engagement with the teeth to be treated to thereby effect fluoride uptake by the dental enamel. The fluoride foam provides substantially the same fluoride uptake as a fluoride gel but this result is achieved by the fluoride foam with substantially less fluoride in the tray than that which is present in a corresponding tray containing a like volume of fluoride gel.

Method for plating on titanium.

Abstract: A method for application of an adherent nickel plate to titanium includes steps of surface preparation, deposition of nickel from a plating solution, and a final treatment. The surface preparation steps include a hydrochloric acid dip, a nitric acid/hydrofluoric acid activation, treatment to slow the re-formation of an oxide layer, and deposition of a nickel strike. The treatment to reduce oxide formation may be accomplished without application of a current, in a solution of acetic and hydrofluoric acid, in which titanium alloy has been electrolytically dissolved. Alternatively, the treatment may be performed with the piece to be plated made anodic in a solution of acetic acid and hydrofluoric acid.

Preparation and Properties of Nitridotechnetic(VI) Acid. I. Observation of the E.S.R.-Spectrum of the [TcNF4]- Anion in Hydrofluoric Acid Solution

Abstract: Nitridotechnetic (VI) acid has been prepared by the hydrolysis of Cs2TcNCl5. Dissolution of this compound in concentrated HF gave an e.s.r. spectrum due to [TcNF4: g 1.895, g 1.990, A 0.03765 cm-1, A 0.01795 cm-1, Q 0.00052 cm-1 for Tcvi ; a, 0.0052 cm-l, ay 0.0010 cm-l, az , < 0.0002 cm-1 due to F-. A comparison of the 4dxy MO coefficient, β2, with those for [TcNCI4]- and [TcNBr4]-indicates that the Tc =N bond length is greater in [TcNF4]- than in [TcNCI4]- and [TcNBr4]-.

Infrared analysis of film growth on the silicon surface in room air

Abstract: Two infrared internal reflection spectroscopic techniques are used to analyze the composition of the film that grows on hydrophobic silicon at room temperature. A conventional internal reflection technique with a silicon internal reflectance element shows that the silicon surface adsorbs hydrocarbons from the atmosphere. A modified internal reflection technique showed <0.2 nm of SiO and SiO1.5 on the silicon surface one month after a hydrofluoric acid strip. Compared to the rate of contamination, the rate of silicon oxidation at room temperature is considered negligible.

Manufacture of high purity low arsenic anhydrous hydrogen fluoride

Abstract: A process for manufacturing high purity anhydrous hydrogen fluoride (HF) having low levels of arsenic impurity by contacting anhydrous hydrogen fluoride product, or an intermediate product obtained during the manufacture of HF, with hydrogen peroxide to oxidize the arsenic impurity in the presence of a catalyst which comprises a catalytic amount of a component selected from the group consisting of molybdenum, a molybdenum compound, vanadium, and a vanadium compound, and a phosphate compound. The volatile trivalent arsenic impurity in the anhydrous hydrogen fluoride is oxidized to a non-volatile pentavalent arsenic compound and the resultant mixture is distilled to recover high purity anhydrous hydrogen fluoride with reduced levels of arsenic impurity. In one embodiment, an oxidizing agent such as nitric acid or a nitrate salt is added to the reaction mixture to oxidize organic compounds.

Production of metal fluoride

Abstract: PROBLEM TO BE SOLVED: To obtain an anhydrous metal fluoride of a high purity, suppressed in oxide generated by a heat treatment at a high temperature, and having an extremely low concentration of transition metals, by dissolving a metal in a hydrofluoric acid solution containing a oxidizing agent while heating, then cooling to obtain a metal fluoride precipitate and performing the dehydration and drying. SOLUTION: This method for producing an anhydrous metal fluoride or a metal fluoride containing hydrated metal fluoride, is to add a metal consisting of Zr, Hf or La having a 6-7 nine purity in a hydrofluoric acid solution containing an oxidizing agent such as hydrogen peroxide water, nitric acid and a perchloric acid salt, heating the solution for dissolving the metal, cooling to obtain a metal fluoride precipitate, dehydrating and then vacuum drying. Especially ZnF2 , ZrF4 , HfF4 , LaF3 , YF3 and CdF2 are extremely easily prepared as the anhydrous metal fluoride as compared with the conventional method of dehydrating and drying by HF gas at a temp. of 300-600 deg.C to form the metal fluoride.

Atom probe studies of the composition of low-temperature oxides on (100) silicon and gallium arsenide surfaces

Abstract: Pulsed laser atom probe microanalysis has been used to investigate the stoichiometry of low‐temperature oxides on silicon and gallium arsenide. The composition of hydrophobic oxides grown on silicon after cleaning in hydrofluoric acid solutions is shown to tend to SiO as the oxide layer thickens. By contrast, hydrophilic oxides grown by low‐temperature chemical treatments have a layered structure, SiO2 /SiO/Si. Low‐temperature air‐grown and chemical oxides on GaAs have a composition (GaAs)2O3, and are covered by a layer of adsorbed water. This same composition is also approached by thermal oxides grown between 300 and 400 °C in a low partial pressure of oxygen.

Effects of Dipping in an Aqueous Hydrofluoric Acid Solution before Oxidation on Minority Carrier Lifetimes in p-Type Silicon Wafers

Abstract: A scanning photon microscope is successfully applied to measure ac surface photovoltages which correspond to apparent minority carrier lifetimes (τPCD) measured by the microwave-detected photoconductive decay (µ-PCD) method, using oxidized p-type silicon wafers pre-treated with or without dipping in an aqueous hydrofluoric acid (HF) solution. The dipping in HF solution causes a larger fixed oxide charge, resulting in a strongly inverted layer beneath the oxide. This situation gives longer τPCD than the bulk lifetime (τPV) by an ac photovoltaic method, while if the fixed oxide charge is small, τPCD gives an apparently smaller lifetime than τPV, implying that τPCD is influenced by the surface charge state or the surface potential. Hence, the process diagnosis by lifetime requires the measurements by both surface photovoltages and the µ-PCD method.

High-throughput, low-temperature process for depositing oxides

Abstract: The present invention relates to a low-pressure chemical vapor deposition (LPCVD) process for depositing silicon dioxide. In particular, the present invention describes a process involving a pre-cleaning step in which all impurities are removed from the substrate followed by a LPCVD step performed at temperatures of between 200° C. and 300° C. The process of the present invention is intended to replace higher temperature LPCVD and thermal processes for depositing silicon dioxide. More particularly, the present invention involves a process in which a substrate is washed using a predetermined cleaning process. The substrate is then exposed to a dilute hydrofluoric acid solution which removes native oxide and contaminants from the surface. Next, the substrate is rinsed with, for example, de-ionized water or ultra-clean water to remove any hydrofluoric acid or other residue from the previous process steps. A layer of material, for example, silicon dioxide, is then deposited using a low-pressure chemical vapor deposition process in which the gas flow comprises silane, oxygen and nitrogen at temperatures below 300° C. Oxide qualities approaching those of thermally grown oxides having been achieved.

Cleaning of semiconductor substrate

Abstract: PURPOSE:To lessen the deterioration of the roughnesses of the surfaces of wafers and to attain a supercleaning of the surfaces of the wafers by a method wherein a semiconductor substrate is brought into contact with an aqueous solution containing nitric acid and hydrofluoric acid and the surface etching rate of the solution is limited to a rate of 60nm/min or less to perform cleaning. CONSTITUTION:Heaters 2 are each provided on the sidewalls and the outer surface of the bottom surface of a container 1, a heating current, which is fed from a power supply 4 to the heaters 2, is controlled by a temperature control device 3 and the temperature of a cleaning fluid 5 in the container 1 is controlled. Si wafers 6 are mounted on a wafer carrier 7, are dipped into the fluid 5 and are cleaned. The fluid 5 consists of an aqueous solution containing nitric acid and hydrofluoric acid. The etching rate of the fluid is controlled at a rate of 60nm/min or less by changing the mixing ratio of the nitric acid and the fydrofluoric acid. Thereby, the deterioration of the roughnesses of the surfaces of the wafers 6 is reduced and a supercleaning of the surfaces of the wafers 6 is attained.

Polishing of titanium prosthetics (Part 6). The chemical polishing baths containing hydrofluoric acid and nitric acid

Abstract: Titanium was polished using several chemical polishing baths containing different ratios of hydrofluoric acid and nitric acid. The meltage, surface roughness, and surface texture of titanium samples after chemical polishing were affected by the ratio of hydrofluoric acid and nitric acid. Generally the meltage increased and surface roughness decreased when the mole concentration of hydrofluoric acid was high and that of nitric acid was low. For example the chemical polishing bath containing 5 mole hydrofluoric acid and 5 mole nitric acid improved the surface texture in one minute, but SEM observation revealed a partially rough surface caused by the excessive solution. The chemical polishing bath containing 1 mole hydrofluoric acid and 5 mole nitric acid did not improve the surface texture in a short time because of low solubility, but improved the surface texture gradually with the extension of the immersion time and a good surface texture was observed by SEM. The chemical polishing using the chemical polishing bath with low solubility and immersion of the prosthetics for a rather long time were considered useful procedures to obtain a smooth surface of titanium prosthetics while maintaining their accuracy.

Method for preventing contamination of semiconductor element by metal

Abstract: PURPOSE: To inhibit the deposition of a metal on the surface of a semiconductor element by adding a small amt. of a specified anionic surfactant to liq. chemicals for washing or etching the element. CONSTITUTION: When a semiconductor element is washed or etched with a treating soln. consisting of two or more among hydrofluoric acid, an aq. ammonium fluoride soln., an aq. hydrogen peroxide soln., an aq. ammonia soln., sulfuric acid, hydrochloric acid, nitric acid, alcohol and pure water, one or more kinds of anionic surfactants selected among C x F y COOH, C x F y SO 3 H, C x H y COOH and C x H y SO 3 H (x is 4-7 and y is 9-15) each having a normal chain or side chain alkyl group or salts of them are added to the treating soln. by 1-500ppm. This method is effective in washing or etching the semiconductor element by a wet process in the case where the element is more fined or highly integrated. COPYRIGHT: (C)1991,JPO&Japio

Production of fluorobenzene

Abstract: PURPOSE: To obtain the objective compound in high yield with excellent reproducibility by specifying temperature in diazotization and temperature increasing rate in thermal decomposition in diazotizing aniline with a nitrous acid imparting agent in hydrofluoric acid, then thermally decomposing the resultant diazonium salt and producing the subject compound. CONSTITUTION: Aniline is reacted and diazotized with a nitrous acid imparting agent in hydrofluoric acid at -40 to 10°C, preferably at -20 to -10°C temperature and the resultant diazonium salt is then heated at ≥1°C/min rate until the temperature attains 20°C and further at 0.1-0.5°C/min rate until the temperature exceeds 20°C and attains the refluxing temperature. Thereby, thermal decomposition is carried out to afford fluorobenzene useful as an intermediate for insecticides in high yield with excellent reproducibility and the separating operation of the fluorobenzene from by-products is facilitated to remarkably reduce the cost. COPYRIGHT: (C)1991,JPO&Japio

Method of reprocessing waste pickling liquors containing metal, nitric acid and hydrofluoric acid

Abstract: The rolling or annealing (heat treatment) scale adhering to the surface of austenitic, austenitic-ferritic and ferritic steels is removed in pickling baths containing nitric acid and hydrofluoric acid. The metals present in the pickling solutions are recovered by the waste pickling liquor being introduced into a dialysis cell bounded by permselective membranes and arranged between a pair of electrodes whose anode and cathode space contains sulphur.

Synthesis of 1,1-dichloro-1,2,2,2-tetrafluoroethane

Abstract: The invention relates to the selective manufacture of 1,1-dichloro-1,2,2,2-tetrafluoroethane by catalytic fluorination of 1,1,1-trichloro-2,2,2-trifluoroethane with anhydrous hydrofluoric acid. The reaction is carried out in the liquid phase at a temperature of between 70° and 170° C. and under a pressure of between 10 and 80 bars absolute, in the presence of an antimony-containing catalyst.

Hydrofluoric acid extraction by tbp and by amines: mechanism, species formed and unique properties at high acid to amine molar ratios

Abstract: Analysis of data concerning HF extraction by amines reveals a change in extraction mechanism when HF/amine molar ratio in organic phase (Z) reaches 2. Up to this point extraction is by ion-pair formation and after it by H-bonding. As a result, the two HF molecules initially extracted differ in nature from subsequent ones. The change in mechanism explains why seemingly unrelated properties such as water co-extraction dilution and diluent effects, selectivity and viscosity - all change when amine bifluoride composition is attained. Similar change in extraction of other mono-basic acids occurs at Z=1. The system with Z>2 for HF is equivalent to that with Z>1 for other mono-basic acids and to that of extraction by TBP. It therefore provides a model for extraction from concentrated aqueous solutions.

Characterization of hydrofluoric acid treated Y–Ba–Cu–O oxides

Abstract: Effects of hydrofluoric acid (HF) treatment on the properties of Y–Ba–Cu–O oxides were investigated. No obvious etching of bulk Y–Ba–Cu–O and no degradation of zero resistance temperature were observed even though the oxides were placed into 49% HF solution for up to 20 h. Surface passivation of Y–Ba–Cu–O due to HF immersion was verified by subsequent immersion of Y–Ba–Cu–O in water. A thin layer of amorphous fluoride formed on the surface of the Y–Ba–Cu–O during HF treatment, which limited further reaction between Y–Ba–Cu–O and HF, and later reaction with water. Thin film Y–Ba–Cu–O was passivated by HF vapors and showed no degradation in T c -zero after 30 min immersion in water. The properties of the surface layer of Y–Ba–Cu–O oxide after HF treatment are reported from Auger electron spectroscopy, x-ray diffraction, and scanning electron microscopy studies.

Silicon substrate processor

Abstract: PURPOSE:To inhibit the precipitation of a particulate silicon oxide by a reverse reaction from a reaction product, and to obtain a clean silicon substrate, which is hardly particulate-contaminated, by installing a cooler for keeping the temperature of an etchant containing hydrofluoric acid and a washing liquid at temperature lower than the boiling point of hydrofluoric acid. CONSTITUTION:An etchant 12 in an etching tank 13 is passed through a thermal equipment 20A and a filter 21 by a pump 19 and can be circulation-filtered while being kept at a temperature lower than the boiling point of hydrofluoric acid. The temperature of pure water supplied to a water washing tank 14 is also maintained at a temperature lower than the boiling point of hydrofluoric acid by a thermal equipment 20B, and fed to the water washing tank 14 form shower nozzles 15. For the purpose of etching an silicon oxide film is etched, an silicon substrate 1 is dipped into the etching tank 13, and the desired silicon oxide film is removed. The silicon substrate 1 is transferred into the water washing tank 14. Pure water is ejected from the shower nozzles 15 at that time, and the etchant and a reaction product remaining on the silicon substrate 1 are removed.

Ceramic fibers having improved surface properties/rupture strength

Abstract: Ceramic fibers based on silicon carbide, silicon nitride or silicon carbonitride are treated with hydrofluoric acid, e.g., with a 3% to 30% aqueous solution of HF, to strip surface impurities therefrom, to reduce critical surface defects and to enhance the rupture strength thereof.

Determination of impurities in titanium carbide and titanium nitride by inductively coupled plasma atomic emission spectrometry

Abstract: Inductively coupled plasma atomic emission spectrometry was applied to the determination of impurities (Al, Ca, Co, Cr, Fe, Mg, Mn, Mo, Na, Nb, Ni, Si, V, W and Zr) in titanium carbide (TiC) and titanium nitride (TiN). A 0.5-g amount of the powder sample was decomposed with 7.5 ml of nitric acid and 2.5 ml of hydrofluoric acid in a PTFE jar. The matrix effects on the background levels and the emission intensities of the elements were compensated for by using matrix-matched standard solutions for calibration. The results showed that the proposed method was useful for the analysis of TiC and TiN samples.

Method for etching gallium phosphide crystal and liquid etchant used therefor

Abstract: PURPOSE:To distinctly and stably expose a dislocation pit by using a liq mixture contg hydrofluoric acid and hydrogen peroxide to etch th gallium phosphide crystal having a (100) face CONSTITUTION:Hydrogen peroxide and hydrofluoric acid are mixed to prepare a liq etchant In this case, a 50wt% soln of hydrogen peroxide and a 30wt% soln of hydrofluoric acid are mixed in the volume ratio of about 1/4-4/1 The gallium phosphide having a (100) face is etched by using the obtained liq etchant As a result, the etched pit corresponding to dislocation can be exposed in the form of an inverted quadrangular pyramid, and can be accurately observed by a differential interference microscope, etc In addition, the etchant is appropriately kept at about 80 degC, phosphoric acid, nitric acid, etc, can be added to the etchant, or the etchant can be diluted with water