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Showing papers on "Hydrofluoric acid published in 2006"


Journal ArticleDOI
TL;DR: A new procedure for fabricating fused-silica emitters for electrospray ionization-mass spectrometry (ESI-MS) in which the end of a bare fused- silica capillary is immersed into aqueous hydrofluoric acid, and water is pumped through the capillary to prevent etching of the interior.
Abstract: We have developed a new procedure for fabricating fused-silica emitters for electrospray ionization-mass spectrometry (ESI-MS) in which the end of a bare fused-silica capillary is immersed into aqueous hydrofluoric acid, and water is pumped through the capillary to prevent etching of the interior Surface tension causes the etchant to climb the capillary exterior, and the etch rate in the resulting meniscus decreases as a function of distance from the bulk solution Etching continues until the silica touching the hydrofluoric acid reservoir is completely removed, essentially stopping the etch process The resulting emitters have no internal taper, making them much less prone to clogging compared to, eg, pulled emitters The high aspect ratios and extremely thin walls at the orifice facilitate very low flow rate operation; stable ESI-MS signals were obtained for model analytes from 5-μm-diameter emitters at a flow rate of 5 nL/min with a high degree of interemitter reproducibility In extensive evaluatio

238 citations


Journal ArticleDOI
15 May 2006
TL;DR: It was found that HF under controlled conditions significantly etched inward into the interior of the existing pore structure in the clay mineral due to its high content of silica, leaving a framework possessing a larger BET surface area.
Abstract: This work was a study of the chemical modification of diatomaceous earth (DE) using hydrofluoric acid (HF) solution. Under the experimental conditions investigated, it was found that HF under controlled conditions significantly etched inward into the interior of the existing pore structure in the clay mineral due to its high content of silica, leaving a framework possessing a larger BET surface area (ca. 10 m2 g−1) in comparison with that (ca. 4 m2 g−1) of its precursor (i.e., DE). Further, the results indicated that the HF concentration is a more determining factor in creating more open pores than other process parameters (temperature, holding time, and solid/liquid ratio). This observation was also in close agreement with the examinations by the silicon analysis, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The adsorption kinetics and the adsorption isotherm of methylene blue onto the resulting clay adsorbent can be well described by a pseudo-second-order reaction model and the Freundlich model, respectively.

115 citations


Journal ArticleDOI
TL;DR: Silicon nanoparticles ranging from 2 to 16 nm were synthesized by a facile wet chemical route, in which SiO amorphous powder was annealed at 1000 °C, etched in hydrofluoric acid, and surface modifi...
Abstract: Silicon nanoparticles ranging from 2 to 16 nm were synthesized by a facile wet chemical route, in which SiO amorphous powder was annealed at 1000 °C, etched in hydrofluoric acid, and surface modifi...

106 citations


Patent
Michael J. Fuller1
06 Dec 2006
TL;DR: In this paper, the authors describe a mixture of aqueous liquid, a fluoride source, and an effective amount of an alkane sulfonic acid to adjust pH of the fluid where the acid may be an unbranched, a branched or a cyclic alkyl residue.
Abstract: Acidizing methods for subterranean formations formed of predominantly siliceous material as well as acidizing compositions. Some methods include injecting into a predominantly siliceous subterranean formation, an aqueous acidic mixture formed by blending an aqueous liquid, a fluoride source, and an effective amount of an alkane sulfonic acid, preferably methane sulfonic acid, to adjust the pH of the fluid where the alkane sulfonic acid where the alkane group may be an unbranched, a branched or a cyclic alkyl residue. Hydrofluoric acid (HF) may not be added to the fluid in some embodiments as the fluoride source, such as the case for an HF free fluid, and, in some instances, hydrochloric acid is not added to the fluid to adjust pH. Also described are compositions containing an aqueous acidic mixture formed by blending an aqueous liquid, a fluoride source, and an effective amount of an alkane sulfonic acid to adjust pH.

42 citations


Patent
29 Mar 2006
TL;DR: An etching solution for a metal hard mask is described in this paper, which comprises a mixture of a dilute HF (hydrofluoric acid) and a silicon containing precursor.
Abstract: An etching solution for a metal hard mask. The etching solution comprises a mixture of a dilute HF (hydrofluoric acid) and a silicon containing precursor. The etching solution also comprises a surfactant agent, a carboxylic acid, and a copper corrosion inhibitor. The etching solution is selectively toward etching the metal hard mask material (e.g., Titanium) while suppressing Tungsten, Copper, oxide dielectric material, and carbon doped oxide.

37 citations


Journal ArticleDOI
TL;DR: In this paper, the results of x-ray photoelectron spectroscopy indicated that the carbon content of the selectively etched HfO2 surface was extremely low compared with the preetched surface contaminated by adventitious hydrocarbon in atmosphere.
Abstract: Inductively coupled hydrogen-added fluorocarbon (CF4∕Ar∕H2 and C4F8∕Ar∕H2) plasmas were used to etch HfO2, which is a promising high-dielectric-constant material for the gate of complementary metal-oxide-semiconductor devices. The etch rates of HfO2 and Si were drastically changed depending on the additive-H2 flow rate in C4F8∕Ar∕H2 plasmas. The highly selective etching of HfO2 over Si was done in the condition with an additive-H2 flow rate, where the Si surface was covered with the fluorocarbon polymer. The results of x-ray photoelectron spectroscopy indicated that the carbon content of the selectively etched HfO2 surface was extremely low compared with the preetched surface contaminated by adventitious hydrocarbon in atmosphere. In the gas phase of the C4F8∕Ar∕H2 plasmas, Hf hydrocarbide molecules such as metal-organic compounds and Hf hydrofluoride were detected by a quadrupole mass analyzer. These findings indicate that the fluorine species, carbon, and hydrogen can work to etch HfO2 and that the carbon species also plays an important role in selective etching of HfO2 over Si.

27 citations


Journal ArticleDOI
TL;DR: In this paper, a simple synthesis route to aluminum fluoride, AlF 3, from aqueous phase is reported, where Al 2 O 3 is dissolved in aqueously hydrofluoric acid, HF, and re-precipitated as Al F 3 ǫ · 3H 2 O, with high specific surface areas between 120 and 60m 2 /g depending on treatment temperatures.

26 citations


Patent
07 Apr 2006
TL;DR: In this article, a method for regenerating cerium-based abrasives usually abandoned due to a substantial fall in a grinding speed is proposed, which is made into slurry re-dispersed with water.
Abstract: PROBLEM TO BE SOLVED: To provide a method for regenerating cerium-based abrasive usually abandoned due to a substantial fall in a grinding speed. SOLUTION: The used cerium-based abrasive is made into slurry re-dispersed with water. The re-dispersed slurry is treated with acid. The obtained acid-treated slurry is subjected to solid-liquid separation. The obtained cake is dried and cracked, or preferably, the dried cake is baked and cracked. By performing these steps, the cerium-based abrasive is regenerated. As an acid, one or combination of two or more of hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid can be used. COPYRIGHT: (C)2008,JPO&INPIT

26 citations


Journal ArticleDOI
TL;DR: In this article, the etch rate and oxidation mechanisms of copper were studied in mono-, di-, and triorganic acids, and a similar electrochemical behavior of copper was observed in all cases, except in the case of oxalic acid.
Abstract: The interactions of organic acids with copper were characterized with electrochemical and atomic force microscopy methods in order to develop efficient cleaning formula for wet copper processing. The etch rate and oxidation mechanisms of copper were studied in mono-, di-, and triorganic acids. A similar electrochemical behavior of copper was observed in all cases, except in the case of oxalic acid, which shows passivating properties. The interactions of organic acids with diluted hydrofluoric acid result in significant reduction in copper dissolution rate.

25 citations


Journal ArticleDOI
TL;DR: In this paper, an increased etch rate for implanted oxide with boron, phosphorus, arsenic, and argon was characterized for aqueous and vapor hydrofluoric acid (HF).
Abstract: Increased etch rate for implanted oxide with boron, phosphorus, arsenic, and argon is characterized for aqueous and vapor hydrofluoric acid (HF). Destruction by implantation of Si-O bonds makes oxide more reactive to HF. Water being reaction product and catalyst for oxide etching, its amount controls the reaction kinetic. In aqueous solution selectivity of four between implanted and unimplanted oxide is reached but increases up to 200 in vapor HF. In the case of HF etching under vapor phase the generated water increases the etch rate. This technique opens many process possibilities such as etch stop layer development, etching of buried trenches, definition of MEMS anchors, etc. (c) 2006 The Electrochemical Society.

23 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discussed about the modelling of equilibrium reactions that could take place, like complexation of iron and chromium, in the pickling of stainless steels.
Abstract: Mixtures of hydrofluoric and nitric acids are used in the pickling of stainless steels, in order to remove oxide scale, generating pickling waste liquors with high HF concentration. Species appearing in this mixed acid solution are fluoride-metal complexes with high stabilization constants. This work discusses about the modelling of equilibrium reactions that could take place, like complexation of iron and chromium. As observed in the literature, 31 species could be present in pickling liquor with 25 equilibrium reactions. Activity coefficients are calculated using Bromley's methodology that depends on cation–anion interaction parameter B. New parameters at 25°C have been calculated, using Nelder and Mead Simplex Algorithm. The new model shows that FeF3, CrF2+ and Ni2+ are the main metallic forms in the solution and undissociated hydrofluoric acid has a high relative concentration, while free fluoride practically does not exist in solution. In neutralization processes, free fluoride is released from undisocciated hydrofluoric acid. Therefore, high fluoride complexes are formed, which could precipitate instead of metal hydroxides.

Patent
12 May 2006
TL;DR: In this paper, a method for measuring a silicon concentration in a phosphoric acid solution under recirculation and use as an etching solution in a semiconductor substrate processing system in operation is presented.
Abstract: Disclosed is equipment for measuring a silicon concentration in a phosphoric acid solution under use as an etching solution during operation of a semiconductor substrate processing system. The equipment is provided with at least a reaction tank and a concentration-measuring tank. The reaction tank includes a reaction unit for adding hydrofluoric acid to a predetermined constant amount of the phosphoric acid solution drawn out of the semiconductor substrate processing system to form a silicon fluoride compound and then causing the silicon fluoride compound to evaporate. The concentration-measuring tank comprises a hydrolysis unit for bubbling the silicon fluoride compound, which has evaporated from the reaction tank, through deionized water to hydrolyze the silicon fluoride compound and a measurement unit for determining a change rate of silicon concentration in the deionized water subsequent to the bubbling. Also disclosed is a method for measuring a silicon concentration in a phosphoric acid solution under recirculation and use as an etching solution in a semiconductor substrate processing system in operation.

Journal ArticleDOI
TL;DR: In this paper, the pore size and surface modification of a nanofiltration membrane were analyzed and attributed to a complex process of active layer modification, as confirmed by retention tests with known size neutral molecules and scanning probe microscopy.

Patent
05 Jul 2006
TL;DR: In this article, a corrosion resisting magnesium alloy micro-arc oxidation electrolyte and its microarc oxidation method is described. But the electrolyte is not free of Cr6+ and thus brings little pollution to the environment.
Abstract: This invention relates to a corrosion resisting magnesium alloy micro-arc oxidation electrolyte and its micro-arc oxidation method. The electrolyte contains 5~25g/L phytic acid or its alkali metal salt, 5~40g/L hydrofluoric acid or its ammonium salt, 15~70g/L phosphoric acid or its ammonium salt, 5~60g/L boracic acid or its ammonium salt (and/or fluoboric acid or its ammonium salt). The process includes following steps: a) preprocessing, including grinding, degreasing and pickling. b) micro-arc oxidation. Hydrofluoric acid, phosphoric acid and boracic acid/fluoboric acid or their ammonium salts are added into phytic acid (or its alkali metal salt) solution, which is subsequently adjusted to a pH value of 6~10 with one or several species among ammonia, hexamethylene tetramine and diethylene triamine and then oxidized. c) Postprocessing. The micro-arc oxidation electrolyte adopted in this invention is free of Cr6+ and thus brings little pollution to the environment. The films obtained are smooth on the surface with only small-scale pores and have ceramic appearances. The oxidized samples without any postprocessing undergo a 5% NaCl neutral salt spray test and evaluated 8-class according to Criteria ASTM B537-70.

Patent
20 Jan 2006
TL;DR: In this paper, a manufacturing method of a silicon substrate wherein the unevenness of a submicron order is formed on its surface has been proposed in order to provide an excellent mass productivity.
Abstract: PROBLEM TO BE SOLVED: To provide a manufacturing method of a silicon substrate wherein the unevenness of a submicron order is formed on its surface having the unevenness of a micron order in excellent mass productivity. SOLUTION: The manufacturing method of a silicon substrate for solar batteries has a process for preparing the silicon substrate having on its surface a formed texture comprising the unevenness whose difference of altitude is 1-20 μm, a process (a) for etching the substrate by the mixed aqueous solution of an oxidant with hydrofluoric acid after subjecting the substrate having the texture to an electroless plating using metal particles, and a process (b) for etching the substrate by the mixed aqueous solution of an oxidant with hydrofluoric acid which contains metal ions. COPYRIGHT: (C)2007,JPO&INPIT

Journal ArticleDOI
TL;DR: In this article, the solubility of β-FeF3·3H2O has been measured in solutions with different concentrations of nitric acid (0 to 7 m) and hydrofluoric acid (1 to 6 m) at the temperatures of (30, 40, and 50) °C.
Abstract: The solubility of β-FeF3·3H2O has been measured in solutions with different concentrations of nitric acid (0 to 7 m) and hydrofluoric acid (1 to 6 m) at the temperatures of (30, 40, and 50) °C. The total iron concentration at equilibrium was measured with inductively coupled plasma (ICP) spectroscopy. The solubility was evaluated in terms of the stepwise complexation of iron by fluoride ions at different ionic strength and temperature. The solubility of β-FeF3·3H2O increases with decreasing concentration of HF and HNO3 and increasing temperature.

Patent
25 Oct 2006
TL;DR: In this paper, a method for synthesizing AlPO4 or SAPO molecular sieves using ionic liquid as reaction medium, adding in amine as auxiliary template, blending at 70-100 deg.C for 1-30 min; adding in precursor compounds of P, Al and Si and hydrofluoric acid to prepare precursor mixture of molecular sieve.
Abstract: The invention is a method for preparing AlPO4 or SAPO molecular sieve, using ionic liquid as reaction medium, adding in amine as auxiliary template. And it can be used to synthesize molecular sieves of various structures, comprising the steps of: A) using halogen 1-alkyl-3- methylimidazole ionic liquid as reaction medium and amine as auxiliary template, blending at 70-100 deg.C for 1-30 min; B) adding in precursor compounds of P, Al and Si and hydrofluoric acid to prepare precursor mixture of molecular sieve, crystallizing at 150-300 deg.C for 0.5-3 h, where the molar ratio of Al2O3 to P2O5 to SiO2 to HF to amine to halogen 1-alkyl -3-methylimidazole ionic liquid = 1:(1.7-3.8):(0-1):(0.05-0.2):(0.5-3):(10-40); and C) cooling to room temperature, filtering, washing and drying, so as to obtain a solid-AlPO4 or SAPO molecular sieve.

Patent
23 Aug 2006
TL;DR: In this paper, acid corrosion solution for preparing polycrystalline silicon pile surface and its usage is disclosed. But the solution is compounded with oxidant and hydrofluoric acid and through mixing, and the oxidant is nitrate or nitrite.
Abstract: The present invention discloses acid corrosion solution for preparing polycrystalline silicon pile surface and its usage. The solution is compounded with oxidant and hydrofluoric acid and through mixing, and the oxidant is nitrate or nitrite. During use, the cut polycrystalline silicon chip is set inside the corrosion solution for corrosion at the temperature of -10 to +25 deg.c for 0.5-20 min to eliminate damage surface caused by wire electrode cutting, with the acid corrosion time and temperature being dependent on the solution concentration. The present invention is suitable for both intermittent production and continuous production, and has easy treatment of the produced waste acid.

Journal ArticleDOI
TL;DR: In this article, the growth of beta-FeF3 • 3H(2)O has been investigated in mixtures of 3 mol kg(-1) hydrofluoric acid and 3mol kg(1) nitric acid at 30, 40 and 50 degrees C.

Journal ArticleDOI
TL;DR: In this article, the effect of hydrofluoric acid on the cathodic reduction of molybdate ions is studied and it is shown that the mechanism of this process is determined by the acid concentration.
Abstract: The effect of hydrofluoric acid on the cathodic reduction of molybdate ions is studied. It is shown that the mechanism of this process is determined by the acid concentration: in a concentration range below 25 g/l the intermediate products of molybdate-ion reduction, namely, black or colored deposits containing molybdenum with the average valence of 3.6–4 are formed on the cathode. For the concentration above 50 g/l, molybdate ions are completely reduced and form at the cathode dense light metallic coatings with a thickness of 3–5 μm and good adhesion to the substrate. The addition of hydrofluoric acid prevents polymerization of molybdate ions.

Journal ArticleDOI
TL;DR: Anisotropic etching of silicon is achieved in the presence of ultra-violet exposure in a solution containing hydrofluoric/nitric/acetic acids (HNA) as mentioned in this paper.
Abstract: Anisotropic etching of silicon is achieved in the presence of ultra-violet exposure in a solution containing hydrofluoric/nitric/acetic acids (HNA). The HNA solution is typically used for polishing silicon and etching polysilicon due to its isotropic etching property. In the technique proposed in this paper which is called UV-HNA, the etching of silicon is enhanced in the direction determined by UV exposure. A mixture of HF/HNO 3 /CH 3 COOH with a relative composition of 1:15:5 seems suitable for revealing 〈111〉 planes with an etch rate of 10 μ m/h at 35 °C. The bottom of the etched craters is hillock-free and etch rates as high as 60 μ m/h can be achieved using higher concentration of HF acid in HNA solution. In the latter case the etching is more isotropic and mask undercut is observed. Also membranes with a depth of 400 μ m are fabricated on n -type Si 〈100〉 with a thickness of 500 μ m by means of standard 34 wt% solution of KOH at temperature of 60 °C. Problems encountered during the experiment, and their solutions are discussed and results of these experiments are reported.

Patent
24 May 2006
TL;DR: In this paper, a semiconductor cleaning liquid composition containing phosphonic acid, and a relevant method of cleaning is presented. But the method is not suitable for the use of semiconductor wafer processing.
Abstract: [PROBLEMS] To provide a semiconductor cleaning liquid composition containing phosphonic acid, and provide a relevant method of cleaning. [MEANS FOR SOLVING PROBLEMS] A composition that in the operation of semiconductor wafer processing, is used for cleaning performed to remove residues; and a relevant method of cleaning. The composition comprises at least one fluorocompound (a) selected from among hydrofluoric acid, ammonium hydrogen fluoride and ammonium fluoride, phosphonic acid (b), formic acid (c), at least one organic amine (d) and water (e). Further, as an optional component of the composition, there may be added at least one member selected from the group consisting of at least one organic solvent (f), ascorbic acid (g), at least one surfactant (h) and mercapto-having at least one anticorrosive agent (i).

Journal ArticleDOI
H. Sakly, R. Mlika, H. Chaabane1, Lotfi Beji, H. Ben Ouada 
TL;DR: In this article, the electrochemical response of a field effect capacitor composed by a porous silicon (PS)/silicon dioxide (SiO2) structure as transducer's surface and ptert-butylcalix[6]arene molecules as a recognizing agent towards nickel ions was studied.

Patent
29 Dec 2006
TL;DR: A wet-etch formulation that is proven to etch copper is defined in this paper, which includes a mixture of a strong inorganic acid, such as sulfuric acid or hydrofluoric acid, and an oxidizing agent such as hydrogen peroxide.
Abstract: A composition comprising an aqueous solution of: a wet-etch formulation that is proven to etch copper; and a wetting agent Exemplary wet-etch formulations include a mixture of a strong inorganic acid, such as sulfuric acid or hydrofluoric acid, and an oxidizing agent such as hydrogen peroxide, and further include ammonium persulfate Exemplary wetting agents include organic acids such as citric acid, acetic acid, oxalic acid, or formic acid Processes of using the compositions for wet-etching, or chemical mechanical polishing, or fabricating thick copper inductors, are further provided

Patent
25 May 2006
TL;DR: In this paper, the surface of the polycrystalline silicon is roughened and a surface area is increased to obtain a capacitor having a large electrostatic capacity even by a shrunk cell area.
Abstract: PROBLEM TO BE SOLVED: To obtain a capacitor having a large electrostatic capacity even by a shrunk cell area. SOLUTION: In a manufacturing process for a memory cell, a polycrystalline silicon as a lower electrode is washed with an etchant containing hydrofluoric acid and an oxidizing agent, and the surface of the polycrystalline silicon is roughened and a surface area is increased. COPYRIGHT: (C)2006,JPO&NCIPI

Journal ArticleDOI
TL;DR: In this paper, the surface oxidation and corrosion behavior of furan-resin-derived carbons in nitric, sulfuric and hydrofluoric acids were investigated by the relative weight changes and X-ray pohotoelectron spectroscopy (XPS).

Patent
21 Dec 2006
TL;DR: In this paper, the authors proposed a solution to remove metal titanium, titanium oxide, titanium nitride, metal copper, and copper oxide attached to a shield without damaging aluminum or stainless steel, which is a shield base material of a CVD or sputtering apparatus.
Abstract: Metal titanium, titanium oxide, titanium nitride, metal copper, copper oxide, and the like attached to a shield are removed without damaging aluminum or stainless steel, which is a shield base material of a CVD or sputtering apparatus. SOLUTION: 0.1 to 10% by weight of at least one fluorine compound selected from the group consisting of sodium fluoride, potassium fluoride, lithium fluoride and ammonium fluoride, and phosphoric acid and / or phosphate 1 to 50% by weight, 0.5% to 35% by weight of hydrogen peroxide, and 5% by weight or less of hydrofluoric acid, the balance being water, and the weight ratio of hydrogen peroxide to the amount of fluorine in the fluorine component in the system A semiconductor formed by adhering at least one of deposits made of titanium metal, titanium oxide, titanium nitride, metal copper, and copper oxide using a composition for cleaning a semiconductor manufacturing apparatus in which (hydrogen peroxide / fluorine) is 4 or more Clean the production equipment. [Selection figure] None

Journal ArticleDOI
TL;DR: In this article, the authors used hydrofluoric acid (HF) as a catalyst in sol-gel method to prepare nanoporous silica thin film with ultra-low dielectric constant (k ).
Abstract: In this paper, hydrofluoric acid (HF) was used as catalyst in sol–gel method to prepare nanoporous silica thin film with ultra-low dielectric constant ( k ). The introduction of HF not only produced the Si–F bonds, which has the lower polarizability deriving from the least electronegative of fluorine ion, but also adjusted the speed of sol–gel reaction. The microstructure morphologies of the films catalyzed using HCl and HF were compared by FE-SEM. The results of N 2 adsorption and desorption further confirmed the FE-SEM morphologies and indicated that the suited introduction of HF as catalyst increased the porosity and reduced the pore size distribution (about 10 nm). The differences among samples, which were catalyzed with different acids and different dosage, were also investigated by FTIR. All these results indicated that the film deposited using HF as catalyst exhibited better structural and dielectric properties, which appear to be a promising low- k material for IMD application.

Patent
11 Oct 2006
TL;DR: In this paper, a handling method of acid washing liquor was proposed, in particular to handle acid washing liquids containing nitric acid, hydrofluoric acid, fluosilicic acid, manganese ion, iron ion and so on.
Abstract: The invention relates to a handling method of acid washing liquor, in particular to a handling method of acid washing liquor containing nitric acid, hydrofluoric acid, fluosilicic acid, manganese ion, iron ion and so on. The method comprises the following steps: firstly, adding said acid washing liquor into retort, adding sodium carbonate or natrium hydroxydatum for neutralization until PH value reaches to 3-3.5; secondly, adding calcium carbonate to react with hydrofluoric acid to get calcium fluoride precipitation, react with fluosilicic acid to get calcium silicofluoride precipitation; thirdly, adding sodium carbonate until PH value reaches to 7.5-8, to react with manganese ion, iron ion to get their oxides precipitation; fourthly, filtering, filter residue are oxides of manganese and iron, calcium fluoride and calcium silicofluoride, and concentrating and crystallizing filter liquor to get the product of sodium nitrate. The invention makes full use of valuable ingredient, with no secondary pollution, secondary pollution, low cost and high-purity material finished product.

Patent
29 Sep 2006
TL;DR: In this paper, a process for the production of high-silica fluorosilicic acid is described, which can reduce the cost for the silicon tetrafluoride production and can also reduce the quantities of waste products produced in the process.
Abstract: Disclosed is a process for production of silicon tetrafluoride which can reduce the cost for the silicon tetrafluoride production and can also reduce the quantities of waste products produced in the process. Also disclosed is an apparatus for use for the process. The method comprises the steps of: (a) a high-silica fluorosilicic acid production step in which a raw material (1) containing silicon dioxide is reacted with a mixed solution containing hydrofluoric acid and hydrofluosilicic acid to yield an aqueous high-silica fluorosilicic acid solution: (c) a silicon tetrafluoride production step in which the aqueous high-silica fluorosilicic acid solution is reacted with sulfuric acid to yield silicon tetrafluoride; and (d) a sulfuric acid production step in which a sulfuric acid fraction containing hydrogen fluoride which is a by-product in the silicon tetrafluoride production step (c) is subjected to water vapor distillation to yield sulfuric acid. The process is characterized in that the sulfuric acid produced in the step (d) is reused in the step (c).