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This application is a divisional of U. Patent Application Ser. This invention relates to a method and apparatus for producing high purity tantalum and the high purity tantalum so produced. In particular, the invention relates to production of high purity tantalum. Tantalum is currently used extensively in the electronics industry which employs tantalum in the manufacture of highly effective electronic capacitors.
This is mainly attributed to the strong and stable dielectric properties of the oxide film on the anodized metal. Both wrought thin foils and powders are used to manufacture bulk capacitors. In addition, thin film capacitors for microcircuit applications are formed by anodization of tantalum films, which are normally produced by sputtering. Tantalum is also sputtered in an Ar—N 2 ambient to form an ultra thin TaN layer which is used as a diffusion barrier between a Cu layer and a silicon substrate in new generation chips to ensure that the cross section of the interconnects can make use of the high conductivity properties of Cu.
It is reported that the microstructure and stoichiometry of the TaN film are, unlike TiN, relatively insensitive to the deposition conditions. Therefore, TaN is considered a much better diffusion barrier than TiN for chip manufacture using copper as metallization material.
For these thin film applications in the microelectronics industry, high purity tantalum sputtering targets are needed. Most of the tantalum metal produced in the world today is derived from sodium reduction of potassium heptafluotantalate K 2 TaF 7. Processes which are not adapted commercially to any significant extent include the reduction of tantalum oxide Ta 2 O 5 with metallic reductants such as calcium and aluminum, and non metallic reductants carbon and carbon nitrogen; the reduction of the tantalum pentachloride TaCl 5 with magnesium, sodium or hydrogen; and the thermal dissociation of TaCl 5.
Reduced tantalum is obtained either as powder, sponge or massive metal. It invariably contains significant amounts of oxygen, as well as other impurities such as reductants and impurities that may be present in the starting tantalum compounds. For removal of impurities in tantalum, electron beam melting is often conducted. Essentially all elements, except niobium, tungsten, molybdenum, uranium and thorium can be eliminated this way.
While the metallic impurities and nitrogen are removed by direct volatilization, the removal of oxygen takes place via mechanisms involving formation and evaporation of carbon oxides, aluminum oxides, water, as well as suboxides of tantalum. The purity can be further improved by repeated electron beam melting. Other refining processes include vacuum arc melting, vacuum sintering, molten salt electrorefining and tantalum iodide refining, with the iodide process being the most promising technique for removing tungsten and molybdenum.
The above mentioned refining methods are not effective for removal of niobium from tantalum. Since tantalum and niobium are closely associated with each other in nature, the removal of niobium is critical to prepare very high pure tantalum.
In practice, their separation is conducted before reduction via methods such as solvent extraction, chlorination and fractional crystallization.
The tantalum target manufacturing process includes forging ingot into billet, surface machining billet, cutting billet into pieces, cold rolling the pieces into blanks, annealing blanks, final finishing and bonding to backing plates. In accordance with the present invention there is provided a method and apparatus for producing high purity tantalum sputtering targets and the high purity tantalum so produced.
The method comprises purifying potassium heptafloutantalate, K 2 TaF 7 , reducing the purified K 2 TaF 7 to produce tantalum powder, refining the tantalum by reacting with iodine and finally electron beam melting the tantalum to form a high purity tantalum ingot. The starting material is commercial K 2 TaF 7 salt, made by dissolving tantalum ores in hydrofluoric and sulfuric acid mixture, followed by filtration, solvent extraction using methkylisobutylketone MIBK and crystallization of K 2 TaF 7.
This can be repeated several times to lower the impurity levels, in particular the level of Nb. Molten sodium is then injected into the retort for reacting with K 2 TaF 7.
Agitation of the reactants is provided to accelerate the reduction reaction. After cooling, the mass is taken out of the retort, crushed, leached and washed to separate tantalum powder from the salt mixture. Tantalum refining is done by the iodide process or electron beam melting. These methods can be used in parallel or in series. Electron beam melting is preferred as the last step because it results in an ingot which is suitable for further physical metallurgical steps toward the goal of target manufacture.
Electron beam melted ingot is forged into billets and surface machined. After surface machining, the forged billet is cut into pieces, which are further cold rolled into blanks. Blank annealing is carried out in an inert atmosphere to obtain a recrystallized microstructure.
The blanks are then machined to obtain a final finish and bonded to copper or aluminum backing plates. For characterization of targets produced by the invented process, chemical analyses are conducted. The methods of chemical analysis used to derive the chemical descriptions set forth herein are the methods known as glow discharge mass spectroscopy GDMS for metallic elements and LECO gas analyzer for non metallic elements.
The highly purified tantalum material of the present invention has less than ppm by weight, total metallic impurities, an oxygen content of less than about ppm, by weight, a molybdenum or tungsten content of not more than 50 ppm, by weight, and a uranium and thorium content of not more than 10 ppb, by weight. It is also possible to produce tantalum having less than 5 ppm, by weight, total of molybdenum and tungsten. In nature, tantalum generally occurs in close association with niobium, tin and other elements.
The minerals most commonly used as raw materials in tantalum production are Tantalite, Wodginite, Micolite and Samarskite. These minerals are enriched by wet gravity, magnetic or electrostatic methods. The concentrates are dissolved in a mixture of hydrofluoric and sulfuric acid. The resulting solution is filtered, then separated from niobium and other impurities in a solvent extraction plant. The tantalum concentrate is transferred into an aqueous solution and precipitated with ammonia to yield tantalum acid Ta 2 O 5 xH 2 O , calcined at an elevated temperature to yield tantalum oxide.
Alternatively, the tantalum is crystallized to potassium heptafloutantalate, by addition of KF and KCl to the hot aqueous solution obtained from solvent extraction. Impure potassium heptafloutantalate obtained by these methods must be further purified for use as a source of tantalum for the electronics industry.
In general, potassium heptafloutantalate may be purified by a procedure such as follows:. Since the dissolution rate is very slow at room temperature, the mixture is heated e. The solution containing K 2 TaF 7 is covered, to prevent losses due to evaporation, and stirred continuously. Time to dissolution is approximately one hour.
KCl solution is added to the K 2 TaF 7 solution and the resulting solution is stirred while cooling to room temperature. The precipitate is filtered, washed and dried. Niobium, tungsten, molybdenum, zirconium, uranium and thorium remain in solution. Repeated dissolution and precipitation may be useful in order to obtain extremely high purity tantalum.
Elements such as niobium, tungsten, molybdenum, uranium and thorium, which are difficult to remove by electron beam melting, are easily removed by this process. Potassium heptafloutantalate can be reduced to tantalum metal by fused salt electrolysis or reduction by sodium. The rate of reduction by electrolysis is very slow, therefore sodium reduction is used for processing large quantities of K 2 TaF 7 into tantalum metal.
The overall reduction reaction can be written as. Referring to the drawings, FIG. Molten sodium is injected into the reactor and stirred while controlling the temperature.
After cooling, the mass is removed from the reactor, crushed and leached with a dilute acid to recover tantalum metal powder. The powder is compacted and melted in an electron beam furnace. Tantalum metal is produced from the reduction of commercially available K 2 TaF 7 by sodium, which is a process similar to the Hunter process used for the production of sponge titanium.
The metal is in the form of powder and has a very high oxygen content. The method described herein is capable of producing high purity tantalum from scrap or impure tantalum metal. The process is based on chemical transport reactions, in which tantalum iodides are formed by the reaction of impure tantalum metal with iodine gas synthesis zone , at lower temperatures, then the tantalum iodides are decomposed on a hot wire filament, at higher temperatures, to produce a very pure metal deposition or thermal decomposition zone.
Similar reactions can be written for the other tantalum iodide species, such as TaI 3 and TaI 2. The thermodynamic factors are important to understanding and controlling the process. Thermodynamic calculations have been carried out to determine advantageous operating conditions, such as temperature and pressure, in the synthesis and decomposition zones. A schematic diagram of the apparatus is shown in FIG.
The process apparatus contains a cell, filament and feed material and is designed to run batch operations. After each run the apparatus is cooled to room temperature and disassembled.
The preferred iodide cell, for the refining of tantalum, is an alloy Inconel container clad with a metal more electrochemically noble than tantalum according to the chloride electromotive series, such as molybdenum or tungsten or an alloy thereof.
The cladding prevents contamination of the refined tantalum by cell components since molybdenum and tungsten do not react with iodine at cell operating temperatures. Alloy Inconel containers are also used for the refining of metals such as Ti and Zr, without cladding, since these metals are refined under different operating conditions.
A filament made of pure tantalum rod is used for the decomposition surface. The filament can be in the shape of a U or can be a different shape to increase its surface area. It is also possible to use multiple filaments to increase the surface area and cell productivity.
The filament is heated resistively by an external power supply. Tantalum crystals then grow on the filament. A cylindrical molybdenum screen is placed in the cell to provide an annular space 1 to 3 inches wide. The annular space if filled with tantalum feed material in the form of chips, chunks or small pellets. This type of arrangement gives a high surface area for the reaction between feed material and iodine gas in the cell. The crude tantalum can also be compacted to a donut shape and placed in the reactor.
The feed materials are cleaned with cleaning agents before they are charged into the cell. A good vacuum system is advantageous to producing tantalum with low impurities.
Therefore, the cell is connected to a vacuum system producing 1 micron or less of pressure. The temperature in the synthesis zone effects the rate of reaction. The temperature in the synthesis zone should be uniform and kept much higher than boiling point of TaI 5.
Without this heater, iodine must be continuously added to the system. Oxygen in tantalum originates from numerous sources, starting with the precursor and on through electron beam melting.
Oxygen is undesirable at high concentrations due to its effect on the resistivity of deposited tantalum thin films. Currently available methods cannot easily decrease the oxygen levels to less than 30 ppm.
Thermodynamic calculations, as well as the experimental results, indicate that the metal oxides formed or present in the feed material do not react with iodine and are not transported to the decomposition zone.
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Emerging nanotechnologies for manufacturing
Electrolytic manganese dioxide EMD is the critical component of the cathode material in modern alkaline, lithium, and sodium batteries including electrochemical capacitors and hydrogen production. In terms of environmental and cost considerations, EMD is likely to remain the preferred energy material for the future generation, as it has been in recent decades. Diminishing fossil fuels and increasing oil prices have created the need to derive energy from sustainable sources. The energy storage device from alternative and inexpensive sources, such as low grade manganese ores, has a niche in the renewable energy and portable electronics market. Despite vast manganese sources along with the current activity in producing modified EMD materials from secondary sources, to a surprise, India mostly imports EMD to meet its demand. Keeping this in view, a comprehensive review has been prepared on the synthesis, physical and electrochemical characterization of EMD produced from synthetic solutions and secondary sources. This review summarizes the available EMD sources in the world including Indian deposits and the recent investigations of fundamental advances in understanding the electrochemical mechanism involved in aqueous rechargeable batteries and electrochemical capacitors, thus leading to an improved energy storage performance, which is essential for their long term use in storing renewable energy supply.
Polypropylene is the material of choice in the field of film capacitors because it does not have any type of polar group whose chains are oriented under electrical field stress. As a result, polypropylene has inherently low loss rates and high volume resistivity. These properties, combined with relatively high dielectric constant and self-recovery properties in the capacitor and good mechanical properties such as high melting temperature and high stiffness make polypropylene very valuable in this technical field. The dielectric breakdown voltage or breakdown voltage of polypropylene can be increased in the biaxially oriented case where polypropylene is obtained by stretching the heated film sheet in two opposite directions, longitudinal and transverse machine directions to induce more perfect crystalline formation and orientation. However, when a Ziegler-Natta catalyst is used during the production of polypropylene, typically a dielectric film made of the polypropylene will contain a polar residue originating from the Ziegler-Natta catalyst used, such as chlorine, aluminum, titanium, magnesium,. These residues reduce the resistivity, i. Increase the conductivity of the polymer, rendering the polymer unsuitable for use in applications requiring very low conductivity, such as films for capacitors. Thus, in order to make the polypropylene commercially attractive in this technical field, it has to be cleaned, typically cleaned, in order to remove unwanted residues from the polymer material, which is time consuming and cost-intensive. Typically, the purification of the polymer is carried out at an additional step after the remaining polymerization step.
US6955938B2 - Tantalum sputtering target and method of manufacture - Google Patents
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Environmental Protection Agency, -and approved for publication. JMention of trade names or, commer- cial products does not constitute endorsement or recommendation use. The Industrial Environmental Research Laboratory - Cincinnati lERL-Ci assists in developing and demonstrating new and im- proved methodologies that will meet these needs both efficiently and economically. This report presents a multimedia air, liquid, and solid wastes environmental assessment of the domestic mineral mining industry. The primary objective of the study is to identify the major pollution problems associated with the industry. A secondary objective is to define research and development needs for adequate control of air pollutants and liquid and solid wastes connected with mineral mining. This study provides lERL-Ci with 1 an initial data base on the type and quantity of wastes generated and the treatment and disposal techniques now applied for their control; 2 a data base for technical assis- tance activities; and 3 the necessary background information to implement research and development programs, to document effec- tive pollution control techniques, and to fill gaps in the data base. For further information the Resource Extraction and Handling Division can be contacted. A secondary objective is to -define '1 research and development needs for adequate control of air pollu- Dimension stone " Crushed stone Construction sand and gravel Industrial sand -. Zirconium Nonferrous Metals Imports ; These nonferrous metals are hot recovered from domestic ores; they are either imported in a finished or semifinished form or are produced from imported raw ores.
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This application claims benefit pursua U. Espe invention relates to an activated carbon havi stocking property, and high adsorption quant such as hydrocarbon gas having low molecular if BET specific surface area is low. Also th relates to an activated carbon useful as m Background Art. Natural gas mainly contains methane Generally speaking, an activated carbon bein BET specific surface area and being larger i micro pore having pore diameter of lnm or le more adsorption of gas having small molecula as methane, ethane, or other hydrocarbon gas molecular weight, or hydrogen. In JP-A is described an acti obtained by activating with alkali metallic co activated carbon has volume of micro pore, wh diameter of approximately 0.
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