Showing papers on "Hydrofluoric acid published in 1998"

PECVD silicon carbide as a chemically resistant material for micromachined transducers

Abstract: Plasma enhanced chemical vapor deposited (PECVD) amorphous hydrogenated silicon carbide is a material with many potential applications for micromachined transducers. Specifically, its resistance to etching in a broad range of media such as sulfuric acid/peroxide, hydrofluoric acid and potassium hydroxide make it an excellent choice for use as an encapsulating material for media compatible transducers. This etch resistance also makes it useful as a masking material for intermediate processing steps. Despite this wet chemical resistance, it can be patterned easily in fluorine-based plasmas. A series of trials were undertaken in an attempt to correlate stress, resistivity and wet etch resistance with the following deposition parameters: pressure, CH4 flow rate, low frequency power, low frequency cycle time, high frequency power, and high frequency cycle time. Work to date has demonstrated a CMOS compatible, insulating thin film with a low stress (

Selection of activated carbon for the selective hydrogenolysis of CCl2F2 (CFC-12) into CH2F2 (HFC-32) over palladium-supported catalysts

Abstract: In this study, a selection of the support for palladium in the hydrogenolysis of CCl 2 F 2 into CH 2 F 2 has been made. Activated carbon has been selected because of its inertness against HF and HCl, co-products formed under reaction conditions. Different types of activated carbon have been applied in the investigation. These include peat-based, coconut-shell based, and synthetic carbons, which are either steam or chemically activated. The carbons have been purified by different methods, such as washing with aqueous sodium hydroxide and aqueous hydrochloric acid or boiling in concentrated hydrochloric acid or nitric acid or by immersing the carbon in concentrated hydrofluoric acid. A peat-based, steam-activated carbon resulted in the optimal performance for the palladium catalyst. Before impregnation with the palladium precursor, it is necessary to purify this support by a washing procedure to remove impurities present in this carbon. This procedure consists of washing with aqueous sodium hydroxide, aqueous hydrochloric acid, and water. For characterization of the catalysts several methods have been applied, like X-ray fluorescence, CO-chemisorption, and N 2 -adsorption. The prepared catalyst shows a selectivity of 65–85 mol% for the desired product Ch 2 F 2 at all conversion levels of CCl 2 F 2 . It is observed that when too many impurities are removed, the performance of the catalyst is not as good. Therefore, it is concluded that the impurities play an important role in its performance. This is in harmony with the performance of the catalysts prepared from very pure, synthetic carbons which also do not show a good performance. It is postulated that the impurities play a role as either a promoter or anchoring site, which influences the Pd-dispersion.

A Comparative Electrochemical Study of Copper Deposition onto Silicon from Dilute and Buffered Hydrofluoric Acids

Abstract: An electrochemical direct current polarization method was used to investigate characteristics of copper deposition onto silicon from dilute and buffered hydrofluoric acid solutions. The corrosion current density and corrosion potential of silicon were not very sensitive to the Cu 2+ concentration, up to 1000 parts per billion, in buffered hydrofluoric acid. However, the extent of copper deposition, as measured by total reflection X-ray fluorescence, increased as the Cu 2+ concentration in solution increased. In dilute hydrofluoric acid, Cu 3+ addition had a significant and systematic effect on the corrosion potential and corrosion current density of silicon. However, in both types of solution, the cathodic current calculated from the measured copper deposition was found to be only a small fraction of the corrosion current (less than 1%). This indicates that the primary cathodic reaction is not copper ion reduction but hydrogen ion reduction. Illumination affected the electrochemical behavior of both p- and n-type silicon in Cu 2+ spiked dilute hydrofluoric acid, but only that of p-type silicon in buffered hydrofluoric acid.

Improved formation of silicon dioxide films in liquid phase deposition

Abstract: This work is to reveal the novel technique of liquid phase deposition silicon dioxide (SiO2) films which will increase the deposition rate and also improve the film quality. It is well known that deposition at a lower temperature without residual OH− on the substrate is difficult to achieve. Therefore, it is important to treat the substrate wafer before deposition. The substrate surface dipped into hydrofluoric acid (HF) is usually terminated with hydrogen (H) and has hydrides (Si–H) which react with water so that hydroxyls (Si–OH) can be obtained. No silicon dioxide can be grown on a clean Si substrate without native oxide. Therefore, a model is proposed to show that native oxide growth with chemical pretreatment of HF and ultrapure deionized water has rich hydroxyl (OH) molecules on surface in order to grow silicon dioxide. Another constant parameter, the growth rate of SiO2 is found to increase linearly with the time of reaction with ultrapure deionized water. At the same concentration of boric acid an...

Electrochemical Impedance Spectroscopy of Copper Deposition on Silicon from Dilute Hydrofluoric Acid Solutions

Abstract: Electrochemical impedance spectroscopy was used to probe the mechanism of copper deposition on silicon from dilute hydrofluoric acid solutions. Reaction parameters such as polarization resistance and space-charge capacitance were evaluated using an equivalent circuit model. The electrochemical impedance technique was found to be sensitive to parts per billion levels of Cu 2+ ion in dilute hydrofluoric acid solutions. An inductive loop appeared in Nyquist plots only when Cu 2+ ions were present in hydrofluoric acid solutions. Both the polarization resistance and inductance decreased significantly as the solution Cu 2+ concentration increased. Addition of a nonionic surfactant to hydrofluoric acid solutions significantly altered impedance characteristics of the silicon/solution interface. Total reflection X-ray fluorescence results showed that illumination enhanced deposition of copper on silicon nearly an order of magnitude.

Washing solution of semiconductor substrate and washing method using the same

Abstract: Disclosed is a washing solution of a semiconductor substrate which comprises 0.0001 to 0.1 % by weight of an organic acid and 0.005 to 0.25 % by weight of hydrofluoric acid and has pH of 2 to 4. When a contaminated substrate is immersed in a washing solution, a naturally oxidized film on the surface of the substrate is removed by hydrofluoric acid, and fine particles on the film, metal impurities and metal impurities in the film transfer to the liquid. Since the washing solution is an acidic solution containing an organic acid and having pH of 2 to 4, fine particles are charged to minus as those of the fine particles, and the metal impurities ions in the liquid becomes minus complex ions due to complexing effect of the organic acid. As the results, surface potentials of the respective fine particles and metal impurities are each minus which is the same as that of surface potential of the substrate so that adhesion or re-adhesion to the substrate can be prevented.

Ion exchange equilibria and stoichiometry of complexes of element 104 and hafnium in hydrofluoric acid solutions

Abstract: In bombardments of a \"\"\"Cm + <=2 t^rget with \"O ions, atoms of 78-s \"< '̂104 and \">=-'®Hf (half-lives of a few minutes) wäre simultaneously produced. They were continuously on-line processed in a Wofatit HS 36 anion exchanger column with 0.27 M HF 0.2 or 0.1 M HNO, as the eluent. The elution time and then the distribution coefficients, K^, of fluoride complexes of the elements were evaluated from the numbers of the shortlived nuclei that decayed in the column as well as those which survived. Actually, long-lived descendants rather than the mother activities were detected, which is a distinctive feature of the employed technique. In particular, a total of more than 120 decays of ^^'Es descending from ^^'104 were registered in the three experiments performed. The obtained K^ values for element 104 and Hf are nearly equal. From measurements of K^ versus the concentration of HNO,, the ionic Charge of the element 104 complex is -1 .9±0 .2 , thus pointing to [104]F;\" as the chemical State of the element.

Use of boric acid to improve the microwave-assisted dissolution process to determine fluoride forming elements in steels by flow injection inductively coupled plasma mass spectrometry

Abstract: The applicability of FI-ICP-MS combined with microwave sample digestion for the simultaneous determination of trace amounts of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu in iron and steel samples was investigated. The use of hydrofluoric acid in the sample dissolution process produced nearly invisible insoluble particles with the REEs, leading to erroneous quantification of these elements. The addition of boric acid, complexing HF, solved this problem. By monitoring the transient signals produced by the FI microsampling system, it was possible to evaluate the effectiveness of the sample dissolution procedure. Severe depressive matrix effects caused by the sample matrix were encountered when the signals were compared with those from HNO3 solutions; in contrast, no effects were observed with the addition of boric acid. A highly alloyed steel, stainless steel certified reference material JK 37 (Sandvik Steel), was used to evaluate the effectiveness of the dissolution procedure and to develop the method. The limits of quantification (LOQ) calculated on the basis of 10√s ranged between 0.008 µg g–1 for Lu and 0.040 µg g–1 for Nd. The relative standard deviation for all the analytes was better than 3% (n=4) for concentrations above 10 times the LOQ.

Process for manufacture of lithium hexafluorophosphate

Abstract: The process of the present invention consists in bringing into contact, on the one hand, (A) gaseous phosphorus pentafluoride or a gaseous mixture comprising phosphorus pentafluoride and hydrochloric acid, and, on the other hand, (B) a solution of lithium fluoride in hydrofluoric acid, in a column (10) having a sufficient number of transfer units to carry out the reaction of PF5 with LiF under the chosen conditions of temperature, of pressure and of molar ratio of the two contrasting reactants and with complete or substantially complete absorption of the PF5 in the column This process makes it possible to solve the problems of blockage by preventing recrystallizations of salts; to discharge the heat given off by the reaction by the evaporation of a portion of the HF; and to separate the HCl which may be contained in the starting PF5, without loss of PF5, thus allowing subsequent recovery/value enhancement of this HCl Moreover, this process is very simple, with a very small number of stages, which makes it possible to avoid any entry of air or moisture capable of contaminating the final LiPF6

Studies on SiO/sub 2/-SiO/sub 2/ bonding with hydrofluoric acid-room temperature and low stress bonding technique for MEMS

Abstract: Studies on SiO/sub 2/-SiO/sub 2/ bonding with hydrofluoric acid (HF) are described. This method has a remarkable feature that bonding can be obtained at room temperature. Advantages of this method are low thermal damage, low residual stress and simplicity of the bonding process, which are expected for the packaging and assembly of MEMS. The bond characteristics were measured under different bonding conditions of HF concentration, pressure, chemicals and so on. The bond strength depends on the applied pressure during bonding. HF concentration can be reduced to 0.1%. The bonding is also observed using KOH solution instead of HF. TEM, SIMS, RI and EPMA were applied to evaluate the bonded interface. From the TEM results, an interlayer is formed between SiO/sub 2/-SiO/sub 2/. The thickness of the interlayer depends strongly on the applied pressure during bonding. The SIMS results showed that hydrogen and fluorine partially exist in the interlayer. Considering the result of the RI analysis, surplus HF solution is squeezed out from the interface as the bonding progress. From these results, both surfaces of the SiO/sub 2/ are solved by HF and an interlayer, which is a binding layer, is formed. Formation of the interlayer plays a very important role for the characteristics of HF-bonding.

Method of forming a fluorine-added insulating film

Abstract: There is provided a method of forming an insulating film containing fluorine therein, including the steps of dissociating a process gas containing no hydrogen molecules and atoms with plasma in a reduced pressure, and varying said pressure while said insulating film is being formed, for controlling a content of fluorine in said insulating film. For instance, the pressure is first set low, then raised, and then lowered in the second step. The insulating film containing fluorine therein may be an amorphous carbon fluoride film or a silicon dioxide film containing fluorine therein. In accordance with the above-mentioned method, it is possible to form a fluorine-added insulating film in which hydrofluoric acid, a product causing many problems, is not generated, by using material containing no hydride. In addition, a control for a content of fluorine in an insulating film, which was difficult because the insulating film contains no hydride, can be carried out by varying a pressure while the insulating film is being formed.

Manufacture of high purity tin

Abstract: PROBLEM TO BE SOLVED: To provide a manufacturing method for high purity tin for semiconductor, for example, high purity tin to be used for solder, BAG(ball grid array), etc. SOLUTION: Nitric acid is added to a heated aqueous soln., to which crude metallic tin is added, whereby metastannic acid is settled and is filtrated off. The obtd. metastannic acid is washed, the washed metastannic acid is dissolved by hydrochloric acid or hydrofluoric acid and the metallic tin of ≥5N is obtd. by electrolysis with this dissolved liq. as an electrolytic soln. Otherwise, the metastannic acid is settled and is filtrated off by electrolytic oxidation using an anode consisting of crude metallic tin with a nitric acid liq. as an electrolytic soln. The obtd. metastannic acid is washed, the washed metastannic acid is dissolved by hydrochloric acid or hydrofluoric acid and the metallic tin of ≥5N is obtd. by electrolysis with this dissolved liq. as an electrolytic soln. again. COPYRIGHT: (C)1999,JPO

Synthesis of functional ceramic materials from aqueous solutions

Abstract: Methods for synthesizing ceramic materials from aqueous solutions at ordinary temperature and pressure are advantageous because of the applicability to making films with wide areas and/or complicated shapes with no requirement of vacuum or high temperature, and because of lower cost. Powder of ZrO2 or LnMeO3 (Ln = La, Nd; Me = Cr, Mn, Fe, Co) perovskite was dissolved in hydrofluoric acid and a solution of fluoro-complex ions was obtained. Boric acid was added to the solution, the fluoride ions were consumed by the formation of BF4 -, and then the fluoro-complex ions were hydrolyzed to ZrO2 or LnMeO3 in order to increase the amount of fluoride ions. A number of synthesized particles of ZrO2 or LnMeO3 were observed on the substrates in scanning electron microscope images.

Long range ordered semiconductor interface phase and oxides

Abstract: A semiconductor processing method capable of producing highly ordered, ultra thin dielectrics, including gate oxide and other semiconductor dielectrics, and interphase phases with low defect density. The process includes a degrease step, an etch, primary oxidation and then a passivation step which utilizes hydrofluoric acid to passivate the cleaned silicon surface with hydrogen. Dielectric layers may then be formed with low interface defect density, low flat band voltages and low fixed charge on semiconductor substrates.

Method for processing semiconductor substrate

Abstract: An object is to provide a method for processing a semiconductor substrate that can form an oxide film less prone to take in impurities affecting semiconductor characteristics on the surface. An RCA-cleaned semiconductor substrate is treated with diluted hydrofluoric acid (HF) to remove a native oxide film formed on the semiconductor substrate during the RCA cleaning process (step S 8 ). For conditions of the treatment with diluted hydrofluoric acid, the concentration of hydrofluoric acid is about 50%, the ratio of hydrofluoric acid to pure water is 1:100, and the processing time is about one minute. Finally, the semiconductor substrate from which the native oxide film has been removed is stored in a clean atmosphere of oxygen for a predetermined time period to form an oxide film on the semiconductor substrate surface (step S 9 ). The percentage of oxygen in the atmosphere of oxygen in the place for storage is about 20 to 100%.

Method for in situ removal of particulate residues resulting from cleaning treatments

Abstract: Disclosed is a process for cleaning silicon surfaces of native oxide films. The process utilizes fluorine containing cleaning materials such as anhydrous hydrofluoric acid to clean the oxide from the surface. A fluorine containing particulate matter which forms on the surface as a result of the fluorine containing cleaning materials is then removed by heating the surface to a high temperature. The process is conducted in a non-oxidizing ambient and is preferably conducted in a cluster tool so that the heating step can take place in the same chamber of the cluster tool as later metal deposition step.

Manufacture of semiconductor device

Abstract: PROBLEM TO BE SOLVED: To obtain excellent contact characteristics between silicon and a metal and between high-melting metal silicide and the metal, in a silicon semiconductor layer in a part of which a silicide layer is formed SOLUTION: After a layer insulating film 13 is formed, a contact hole 15 is opened and a contact plug 17 is formed by burying a conductor in this hole In order to ensure excellent electric connection between a diffusion layer 5 and metal 17 and between a silicide layer 11 and the metal 17 at this time, a natural oxide film formed in the contact hole 15 is removed For this purpose, a substrate is wet-etched by using a solution which contains a hydrofluoric acid, ammonium fluoride, water and ethylene glycol at least and of which the total content of the hydrofluoric acid and the ammonium fluoride is 5wt% or below

Benign method for etching silicon dioxide

Abstract: Traditionally, hydrofluoric acid (HF) or buffered bydrofluoric acid (NH 4 F) is mixed with water to form a etching solution for cleaning silicon dioxide from semiconductor wafer surfaces. An etching solution formed by mixing ammonium hydrogen bifluoride ((NH 4 )HF 2 ) with water provides a benign alternative for cleaning silicon dioxide.

Process for etching semiconductor wafers

Abstract: A process is taught for etching semiconductor wafers with an etching mixture comprising nitric and hydrofluoric acids and optionally a surfactant. To this mixture are added either more hydrofluoric acid, or more hydrofluoric and nitric acids, with the added acids having concentrations of at least 70% by weight. The use of concentrated acids reduces the loss of substrate material and extends etching bath life.

Washing solution and washing of glass substrate

Abstract: PROBLEM TO BE SOLVED: To effectively wash off polishing particles bonded to the surface of glass remaining thereon and to prevent the generation of etching irregularity. SOLUTION: Polishing particles bonded to the surface of glass remaining thereon after a glass substrate 12 is subjected to polishing treatment are washed with a washing soln. being a mixed acid soln. consisting of 0.05-0.15 wt.% of hydrofluoric acid and 1-20 wt.% of sulfuric acid, nitric acid or phosphoric acid. By this method, the polishing particles bonded to the surface of the glass substrate 12 remaining remain thereon can be effectively washed off and etching irregularity is also not generated.

Refininig of silicon powder

Abstract: PROBLEM TO BE SOLVED: To reduce impurities in silicon powder to a level fit for a material for a high efficiency silicon solar cell by bringing the silicon powder into contact with a solution consisting of a mineral acid and a hydrogen peroxide aq.solution and then bringing the powder into contact with hydrofluoric acid or an ammonium fluoride solution. SOLUTION: In a 1st step, silicon powder is brought into contact with a mixed solution containing hydrochloric acid or sulfuric acid and a hydrogen peroxide aq.solution to dissolve metallic impurities sticking to the surface of the powder in the solution and to form a silicon oxide film on the surface of the powder. In a 2nd step, the silicon powder is brought into contact with hydrofluoric acid or an ammonium fluoride solution to remove the oxide film on the surface. The silicon powder is preferably silicon cutting scrap or grinding scrap discharged in a step for producing a silicon wafer or a silicon semiconductor device. The average particle diameter of the silicon powder is about 1-50 μm. The contents of Fe, Al, Ti, Ni, Cr and Cu as impurities after refining are each ≤1 ppm 4 and the content of carbon is ≤100 ppm. COPYRIGHT: (C)2000,JPO

Method and apparatus for quantitative analysis of mixed acid solution in etching process as well as etching control method and preparation of the mixed acid solution

Abstract: PROBLEM TO BE SOLVED: To provide a method and an apparatus, for the quantitative analysis of a mixed acid solution in an etching process, in which the concentration of every acid component can be found simply and in a short time, to provide an etching control method which can use the method and the apparatus and to provide a preparation method for the mixed acid solution. SOLUTION: In an analytical method for a mixed acid solution in an etching process, nitric acid is contained as a strong acid component, and, in addition, one kind out of hydrofluoric acid and/or other strong acids (excluding the nitric acid and the hydrofluoric acid) and hexafluorosilicic acid are contained. By a nonacqueous neutralization titration method, concentrations of components of the hydrofluoric acid and/or the other acids are quantitatively analyzed. Separately, only the concentration of the nitric acid is quantitatively analyzed by an ultraviolet-part absorption spectrophotometric method. The respective concentrations of the components of the nitric acid, the hydrofluoric acid and/or the other strong acids are classified and found.

Formation of porous silicon using an ammonium fluoride based electrolyte for application as a sacrificial layer

Abstract: A new electrolyte is presented for the electrochemical formation of porous silicon. The electrolyte, an ammonium fluoride etch mixture (AFEM), is used instead of hydrofluoric acid (HF) which is normally used for porous silicon (PS) formation. The main advantage of AFEM is that it attacks aluminium at a significantly lower rate than HF thus allowing porous formation to be performed as a post-processing step, without the need to protect aluminium. This method has been applied to an epi-micromachining process where the epitaxial layer is used as the structural layer and a buried region of the p-type substrate is made porous (the sacrificial layer). Initial results are presented, with comparisons made to HF-formed porous layers, illustrated by SEM images of epi-micromachined structures.

Characteristics and Production Mechanism of Sulfuric Acid and Nitric-Hydrofluoric Acid Pickling Sludge Produced in Manufacture of Stainless Steel

Abstract: Stainless steel pickling sludge consists largely of surface scale from stainless steel strips, being composed mainly of Cr oxides. Moreover, the present work shows that the Cr concentration of the sludge is approximately twice that of ordinary stainless steels. The particle size of sulfuric acid sludge is 0.325 μm, while that of nitric-hydrofluoric acid sludge is 9.2 μm. Nitric-hydrofluoric acid sludge tends to coagulate in a relatively short time, while sulfuric acid sludge essentially does not tend to coagulate. The main components of sulfuric acid sludge and nitric-hydrofluoric acid sludge are FeCr2O4 and Cr2O3. In the mechanism of sludge precipitation in the pickling process, acid penetrates cracks in the scale and dissolves part of the scale and the substrate. The undissolved scale then loses the ability to bond with other scale and the substrate and settles out in the pickling tanks.