Showing papers on "Hydrofluoric acid published in 1991"

Fluorine‐containing species on the hydrofluoric acid etched silicon single‐crystal surface

Abstract: The chemical structure and property of fluorine‐containing species on the hydrofluoric acid (HF) etched Si surface was examined by use of x‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The fluorine content on the surface was found to increase with increase of HF concentration. A silicon surface etched by 50% HF has fluorine of 2.6×1014 atoms/cm2 as Si–F. Most of the Si–F bondings are rapidly hydrolyzed to Si–OH by rinsing the wafer in water. Thus prepared Si–OH groups are found to be useful as active sites for chemical modification of the bare silicon single‐crystal surface. The Si–F was observed not to influence the oxidation rate of HF etched silicon surface.

Reduction of foreign particulate matter on semiconductor wafers

Abstract: A substantial reduction in the foreign particulate matter contamination on surfaces, such as the surfaces of semiconductor wafers, is achieved by treating the surfaces with a solution comprising a strong acid and a very small amount of a fluorine-containing compound. A preferred method employs a solution containing sulfuric acid, hydrogen peroxide and a very small amount of hydrofluoric acid, which is effective in reducing foreign particulate matter contamination, without significant etching, of the surface being treated.

Process for treating semiconductor substrates

Abstract: Semiconductor substrates are treated in a treating solution consisting of hydrofluoric acid, hydrogen peroxide and a purified water or in a treating solution consisting of hydrofluoric acid, ammonium fluoride, hydrogen peroxide and a purified water, wherein the treating solution preferably has a hydrofluoric acid concentration of 0.1 to 10 wt % and a hydrogen peroxide concentration of 0.1 to 15 wt %. A process for treating semiconductor substrates is provided according to this invention, which allows less inclusion of metallic impurities from the treating solution and has excellent ability of removing metallic impurities with a very small amount of microparticles deposited on the substrate. The number of microparticles deposited on the semiconductor substrates can be reduced to about 1/10 the level in the conventional process.

Milling solution and method

Abstract: A substantially nitrate-free solution for milling products of refractory metals, especially titanium, which milling solution comprises: (a) about 20-100 g/l hydrofluoric acid; (b) a hydrogen inhibitor selected from the group comprising of: about 55-650 g/l of sodium chlorate, about 180-650 g/l of ammonium peroxysulfate, and at least about 10 g/l of hydrogen peroxide; and (c) a balance of water and impurities. A method for chemically milling, etching and/or pickling metal products, such as titanium alloy forgings, with the aforementioned solution is also disclosed.

Synthesis of Fluorine-Containing Ferroelectric Liquid Crystals

Abstract: Ferroelectric liquid crystals having a fluorine atom at an asymmetric carbon were synthesized by means of a new method without hydrofluoric acid. An amino acid, L-isoleucine, is converted to (R,S)-α-fluorinated chiral carboxylic acid. Biphenyl and triphenyl type liquid crystals are easily synthesized using this fluorinated carboxylic acid, which show a large spontaneous polarization of 200 nC/cm2 for the biphenyl type and 300 nC/cm2 for the triphenyl type. The electro-optic properties of the mixtures consisting of the chiral compound and various non-chiral smectic C (SmC) compounds are also described.

Chemical etch rates in HF solutions as a function of thickness of thermal SiO2 and buried SiO2 formed by oxygen implantation

Abstract: A comparative study of chemical etch rates in diluted HF or a mixture of HF, H2O, and HNO3 (P etch) was performed on conventional thermal silicon oxides (1050–1120 °C; O2 pressure ≊1.1 atm; one type with addition of 0.02% C2H3Cl3) and buried oxide layers. The latter were formed by single or multiple implanting n‐ and p‐type (100) Si maintained at ≊600 °C with 150–200‐keV O+ ions to a dose of ≊1.8×1018 cm−2, and subsequent annealing at 1250–1325 °C. The multi‐implanted samples had three implants of a dose of 0.5–0.8×1018 O+ ions cm−2 each, separated by anneals but no final anneal. One of the thermal oxides was additionally irradiated with As+ ions to a dose of 1014 cm−2. Accurate mechanical thickness measurements revealed variations in etch rate between the different oxides, which provide direct evidence for a structural and/or stoichiometrical difference between thermal and buried oxides. The data indicate that the buried oxide is in a densified state as compared to thermal oxide. Also O+ and As+ irradiation‐induced bond strain was clearly observed in buried oxide and thermally grown oxide, respectively. Additionally, plots of the etch rate as a function of oxide thickness reveal detailed information on structural variations of the oxide layers as a function of thickness. This is in contrast with the generally assumed homogeneity of most of these layers.

An infrared study of thin‐film formation on Si and Ge surfaces treated with aqueous NH4F and HF

Abstract: The surface chemistry of Si and Ge after treatment with hydrofluoric acid buffered with ammonium fluoride (BHF) was studied using surface infrared spectroscopy. For each of these materials, the BHF not only dissolved the native oxide, but also deposited a thin inorganic film comprised of ammonium salts (NH4F and NH4F.HF). Through one or more complex reactions with the substrate, these salts slowly disappear as the thermodynamically very stable hexafluorometallate compounds [(NH4)2SiF6 and (NH4)2GeF6] form. The NH4F.HF disappearance correlates directly with the hexafluorometallate formation. Though the original fluoride and bifluoride salts are quite soluble in alcohols as well as in aqueous solutions, the hexafluorometallates are completely insoluble in alcohols, and can only be removed by thorough water rinse.

Wet chemical etching technique for optical fibers

Abstract: A wet chemical etching technique is disclosed for forming a lensed optical fiber (20) In particular, the fiber is placed in a mixture comprising buffered hydrofluoric acid (eg, HF and NH₄F) and a treating agent comprising acetic acid or citric acid The relative concentrations of the constituents are adjusted so that a double conical lens (22,24) is formed which requires no further operations (such as fire polishing) to provide coupling efficiencies of about 80% with a standard deviation of less than ±2% (FIG 2)

Liquid etchant composition for thin film resistor element

Abstract: A resistor material having at least chromium, silicon and oxygen, Cr.SiO2, contained in electronic integrated circuits, particularly in the case of an aluminum layer being on the material, is etched with a liquid etchant composition containing 1.92 to 2.64 mol/l of hydrochloric acid, 0.26 to 0.77 mol/l of phosphoric acid, 5 to 10 mol/l hydrofluoric acid and 3.2 to 5.4 mol/l of ammonium fluoride.

Method for testing electrical properties of silicon single crystal

Abstract: The evaluation of the oxide film dielectric breakdown voltage of a silicon semiconductor single crystal is caried out by cutting a wafer out of the single crystal rod, etching the surface of the wafer with the mixed solution of hydrofluoric acid and nitric acid thereby relieving the wafer of strain, then etching the surface of the wafer with the mixed solution of K₂Cr₂O₇, hydrofluoric acid, and water therby inducing occurrence of pits and scale-like patterns on the surface, determining the density of the scale-like patterns, and computing the oxide film dielectric breakdown voltage by making use of the correlating between the density of scale-like patterns and the oxide film dielectric breakdown voltage. This fact established the method of this invention to be capable of effecting an evaluation equivalent to the evaluation of the oxide film dielectric breakdown voltage of a PW wafer prepared from the single crystal rod.

Purification of graphite

Abstract: This invention discloses a process to purify high-carbon graphite. A mixed acid agent of hydrochloric acid, nitric acid (or sulfuric acid) and hydrofluoric acid is used for the wet treatment of medium-or low-carbon raw material for 2-4 days at ordinary temp (0-65 deg.C) to remove impurities. If more 3- and 4-valence metallic ions exist, EDTA salts have to be added.

Potentiometric determination of proton activities in solutions containing hydrofluoric acid using thermally oxidized iridium electrodes

Abstract: A robust sensor based on iridium oxide is shown to be suitable for use in determining proton activities in solutions containing hydrofluoric acid. Fabricated by a thermal growth process, the low-impedance sensor possesses analytical utility for regulating acidity levels in etching media and pickling-baths. The thermally oxidized electrodes function satisfactorily in hydrofluoric acid solutions with concentrations up to 28 mol dm–3 and show responses comparable to electrodes prepared by the more involved method of reactive sputtering.

Method for cleansing polycrystalline silicon

Abstract: PURPOSE:To readily remove silicon oxide films and impurities from a highly pure polycrystalline silicon by cleansing the silicon with an aqueous cleansing solution comprising hydrofluoric acid, hydrogen peroxide and water with minimized deterioration and discoloration of the solution. CONSTITUTION:A hydrofluoric acid aqueous solution having a concentration of 50wt.%, a hydrogen peroxide aqueous solution having a concentration of 31wt.% and water are mixed in a volumetric ratio of 1:0.03-4:1-10. The cleansing solution is heated to >=35 deg.C, and highly pure polycrystalline silicon is cleansed with the hated cleansing solution for 1-10min to provide the polycrystalline silicon containing <=0.5 weight ppb of Fe, <=0.05 weight ppb of Cu, <=0.05 weight ppb of Ni and <=0.2 weight ppb of Cr as impurities.

Manufacture of solar cell

Abstract: PURPOSE:To form an excellent P/N junction provided with a substrate with a surface free from damage by a method wherein the substrate on which an oxide film has been formed is subjected to a hydrogen passivation treatment, the oxide film is removed, and the substrate is subjected to a low temperature plasma treatment CONSTITUTION:Both the front and the rear of a P-type crystal silicon substrate are etched with alkali and cleansed, Al paste is printed on the rear and burned at a temperature of 700 degC or so for 15 minutes to form an Al electrode 2, and Ag paste is printed thereon and burned at a temperature of 600 degC or so for 15 minutes to form an Ag electrode used for final soldering In succession, the substrate 1 is subjected to a hydrogen passivation treatment with hydrogen plasma After a passivation treatment is finished, the oxide film 4 formed on the surface of the substrate is removed with hydrofluoric acid or a mixed solution of hydrofluoric acid and nitric acid By this setup, the surface oxide layer damaged by hydrogen plasma is removed, and the excellent semiconductor surface is exposed Then, through a low temperature plasma method, an N-type silicon layer 5 of conductivity type opposite to that of the semiconductor substrate 1 is formed in film on the surface of the substrate 1 which has been etched to form a P/N junction Lastly, a surface electrode 6 is printed on the deposited N-type silicon layer 5 with Ag paste and burned

Process for the production of phosphoric acid and hydrogen fluoride from phosphate rock and fluosilicic acid

Abstract: Fluosilicic acid is reacted with phosphate rock in order to produce wet process phosphoric acid and calcium fluoride which is later reacted with sulfuric acid to produce hydrogen fluoride and calcium sulfate. The hydrogen fluoride is then stripped from the phosphoric acid and recovered as either anhydrous hydrogen fluoride or concentrated hydrofluoric acid or reacted aluminum trihydrate to produce aluminum fluoride; with sodium carbonate to produce sodium fluoride/bifluoride; or with ammonia to produce ammonium fluoride/bifluoride.

Liquid acid alkylation catalyst and isoparaffin:olefin alkylation process

Abstract: This invention provides an isoparaffin-olefin alkylation catalyst composition comprising hydrofluoric acid, an additive, and a superacid promoter. The additive is present in concentration sufficient to effect deactivation of the hydrofluoric acid for isoparaffin-olefin alkylation such that the catalytic properties of said admixture of the hydrofluoric acid and the additive, in the absence of superacid promoter are characterized by the conversion of a mixed isoparaffin-olefin stream to product containing more than about 0.1 weight percent of alkyl halide.

Cleaning method of semiconductor wafer

Abstract: PURPOSE:To enhance the removal property of heavy metal contamination regardless of the ionization tendency of a metal and to contrive to make thin the film thickness of a natural oxide film, which if formed by cleaning, by a method wherein a semiconductor wafer is dipped in a mixed chemical of a hydrofluoric acid, a hydrochloric acid and water or a mixed chemical of a hydrofluoric acid, a hydrochloric acid, hydrogen peroxide and water at normal temperatures. CONSTITUTION:A semiconductor wafer is dipped in a mixed chemical of a hydrofluoric acid, a hydrochloric acid and water or a mixed chemical of a hydrofluoric acid, a hydrochloric acid, hydrogen peroxide and water at normal temperatures. For example, a mixed chemical, in which the mixing ratio of a hydrofluoric acid : a hydrochloric acid : water is set at 1:10:100, is produced and is used at normal temperatures or a mixed chemical, in which the mixing ratio of a hydrofluoric acid : a hydrochloric acid : hydrogen peroxide : water is set at 1:10:20:100, is produced and is used at normal temperatures.

Water-repellent treatment of glass

Abstract: PURPOSE:To improve environmental resistance performances simply and inexpensively by forming a SiO2 film on the surface of glass by immersion in a specific solution, making unevenness on the prepared surface and coating the surface with a water repellent layer. CONSTITUTION:1 L of a saturated aqueous solution of 0.5-3.0mol/L hydrosi1 icofluoric acid with silicon oxide is mixed with 2.0X10 mol boric acid to give a treating solution. Then glass is immersed in the treating solution and treated at 10-80 deg.C to form a SiO2 film having >=0.03mum on the surface of glass. Then the glass having formed the film is etched with <=0.1wt.% solution of hydrofluoric acid for <=60 minutes and fine unevenness is formed on the surface of the formed film to give glass having unevenness. Then the glass is coated with a water repellent such as a polyfluoroalkyl group-containing silane compound and baked by heating to carry out water-repellent treatment of glass.

Cleaning method for silicon substrate surface

Abstract: PURPOSE:To clean surfaces and prevent undesired oxide film etching, by using hydrofluoric acid wherein HF weight is less than or equal to 0.2% of the total weight, making solution temperature higher than or equal to 50 deg.C, and dissolving and eliminating a natural oxide film on an Si substrate by dipping. CONSTITUTION:An Si substrate 1 having an oxide film pattern 8 is dipped in H2O2 based washing solution 3; the surface is covered with a thin natural oxide film 4; rinsing is performed with pure water; contamination of fine particles, organic materials, etc., is eliminated. The substrate is dipped, for a specified period, in high temperature low concentration hydrofluoric acid 10, wherein HF weight is less than or equal to 0.2% of the total weight and the temperature is higher than or equal to 50 deg.C. While the etching amount of the oxide film pattern 8 is restricted to about 10Angstrom , the natural oxide film 4 is eliminated, and a clean Si surface 6 exhibiting hydrophobic nature is obtained. On account of high temperature treatment, rinsing effect is high. Since the amount of HF may be little, contamination also is little when HF stock solution is added to the pure water 9. The substrate 1 is rinsed with pure water at a high temperature, pulled out in N2 at a high temperature, and easily dried, thereby preventing water mark and natural oxidation.

Production of highly pure metal fluoride

Abstract: PURPOSE:To produce a metal fluoride having a low vapor pressure in high purity. CONSTITUTION:A process for producing a highly pure metal fluoride, characterized by wet-purifying the metal in a solution state, preparing fluoride precipitates with a fluorinating agent, dehydrating and drying the precipitates, calcining the dried fluoride in a calcination step, subjecting the calcined product to an acid-dissolving step and subsequently preparing the metal fluoride in a dehydration treatment step. The high purification by the wet purification step, the removal of organic reagent residues by the wet purification step and the removal of oxide impurities by the dissolution treatment in the respective solutions of hydrofluoric acid, hydrochloric acid and nitric acid give the highly pure fluoride reduced in all of transition metal impurities, carbon impurities, and oxygen impurities.

Amorphous alloy catalyst for exhaust gas cleaning

Abstract: PURPOSE:To provide a catalyst functioning even at a low temp., highly active, and easily regenerated by subjecting an Ni- and/or Co-base amorphous alloy containing specific amounts of Nb and/or Ta and platinum metal to activating treatment by means of immersion in hydrofluoric acid. CONSTITUTION:This amorphous alloy catalyst for exhaust gas cleaning is obtained by applying hydrofluoric acid treatment to an amorphous alloy having a composition consisting of, by atom, 20-70% Nb and/or Ta, 0.5-20% of one or more elements among Ru, Pd, Rh, Pt, and Ir, and the balance Ni and/or Co. Although the concentration of the platinum group elements is extremely low, this catalyst produces high catalytic activity and can clean exhaust gases even at a temp. in the vicinity of ordinary temp. The amount of the platinum group elements is regulated to a value in the above range because the addition of the platinum group elements in large quantities causes not only increase in costs but also reduction in the action of dissolving unnecessary elements at the time of hydrofluoric acid treatment and, as a result, the surface concentration of the platinum group elements as well as the increase in surface area by means of hydrofluoric acid treatment are made difficult.

Processing solution for semiconductor substrate and method for processing

Abstract: PURPOSE:To obtain a semiconductor device with high quality and a high yield which has little collection of metallic impurities from processing solution and little adhesion of fine particles by specifying a hydrofluoric acid concentration and a hydrogen peroxide concentration within a specific range. CONSTITUTION:Processing solution of a semiconductor substrate contains 0.5 to 15wt.% hydrogen peroxide and a hydrofluoric acid concentration is 0.1 to 10wt.%. While a semiconductor substrate surface is oxidized very thinly by adding hydrogen peroxide into dilute hydrofluoric acid (DHF), its naturally oxidized film can be removed. Therefore deposition of Cu, etc., which has been a problem in conventional DHF can be prevented as well as adhesion of fine particles is decreased. In addition since thickness of the naturally oxidized film is considerably thinner than that with a conventional mixture such as sulfuric acid-hydrogen peroxide (SPM), hydrochloric acid-hydrogen peroxide (HPM) or ammonia-hydrogen peroxide (APM), collection of easily oxidized metal such as Al and Fe is also reduced.

Cleaning method of semiconductor substrate

Abstract: PURPOSE:To reduce leak current between element isolation regions and in the periphery of the element isolation regions, by performing HCl+H2O2 system washing subsequent to HNO3+HF system washing after plasma etching of a silicon oxide film, a silicon nitride film, etc., in an element isolation process. CONSTITUTION:After plasma etching of a silicon nitride film 3 and a CVD oxide film 4, a silicon substrate 1 is etched by using nitric acid + hydrofluoric acid (HNO3:HF:H2O=43:1:70), and subsequently washed by using hydrochloric acid + hydrogen peroxide water (HCl:H2O2:H2O=1:1:5). Hence etching damage introduced into a semiconductor substrate 1 is eliminated by the nitric acid + hydrofluoric acid system washing, and metal elements are effectively eliminated by hydrochloric acid + hydrogen peroxide system washing, so that leak current after an element isolation film is formed can be reduced.

Microscopically worked surface treatment agent containing little particulates

Abstract: PURPOSE:To develop buffered fluoric acid containing small number of particles. CONSTITUTION:At least a kind, selected from the group of surfactant consisting of specific aliphatic carboxylic acid, aliphatic carboxylic acid salt, aliphatic amine and aliphatic alcohol, is added to the mixed solution consisting of hydrofluoric acid, a hydrofluoric ammonium solution and water.

Chromating method of zinc-based plated steel sheet

Abstract: A chromating liquid for forming a chromate film on a Zn or Zn-alloy plated steel sheet, is prepared by adding and mixing a silane coupling agent in a molar ratio of from 0.05 to 0.3 relative to Cr 6+ contained in an aqueous chromating liquid which contains 1-30 g/l of Cr 6+ and 1-30 g/l of Cr 3+ at a weight ratio of Cr 6+ /Cr 3+ ranging from 0.1 to 2.0; and further contains 1-59 g/l of hydrofluoric acid and 1-59 g/l of phosphoric acid at total of hydrofluoric acid and phosphoric acid ranging from 2 to 60 g/l and at a weight ratio of (fluoride ions+phosphate ions)/Cr 3+ ranging from 0.5 to 3.5. and, further said chromating liquid is applied on a surface of the zinc-based plated steel sheet and is then dried, thereby forming the chromate film having a coating amount of from 10 to 150 mg/m 2 in terms of the chromium.