JP2008115063A - High purity hafnium material and method of manufacturing the material by using solvent extraction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein a high purity hafnium material suitable for electronic materials has not been prepared so far since the separation of zirconium resembling to hafnium in chemical properties is difficult, although hafnium-based materials are expected to be used as frontier electronic materials such as insulated gate materials. <P>SOLUTION: The present invention can provide the high purity hafnium material containing 1 wt. ppm or lower of zirconium and other impurity elements by a method based on the solvent extraction method using a TBP (tributyl phosphate) solvent, and its manufacturing method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high-purity hafnium material and a method for producing the material using a solvent extraction method.

  Hafnium has been used for special purposes as a reactor control rod coating material utilizing its large thermal neutron absorption cross section or for addition to heat-resistant alloys used in gas turbines, etc. Because of its high dielectric constant, the hafnium-based oxides have attracted attention as insulating dielectric gate materials for semiconductor devices that replace current silicon oxide.

  Hafnium is originally produced by being incorporated into a zirconium mineral (zircon) and is produced as a byproduct of zirconium. Since the atomic structures and chemical properties of the two are very similar, it is difficult to separate them, and it was generally used without separation except in the nuclear field.

  However, it is desirable to reduce impurities as much as possible for advanced electronic materials that require stability in a very fine region of the order of several tens of nanometers to several nanometers, such as next-generation insulated gate materials in ULSI. As a result, research and development of high-purity hafnium for the purpose of using such electronic materials has been conducted (see Patent Documents 1 to 4 and Non-Patent Document 1).

  Hafnium separation / purification techniques include solvent extraction (Patent Document 1), strong basic anion exchange resin (Patent Document 2), flash chromatography, vacuum distillation, chelating agent adsorption and A method using a light irradiation method or the like (Patent Document 3) has been reported.

As described above, the most serious problem in achieving high purity of hafnium is the separation of zirconium having very similar chemical properties. In the patent literatures reported so far, the zirconium content is 1 The separation is limited to the order of ˜1000 ppm by weight (see Patent Document 1).
International Publication Number WO2005 / 010220 Republished Patent (A1) “High-Purity Hafnium Material, Target and Thin Film Made of the Same, and Method for Producing High-Purity Hafnium” Japanese Patent Laid-Open No. 10-204554 (A) “Purification Method of Zirconium and / or Hafnium Compound” Dowa Mining Co., Ltd. Japanese Patent Application Laid-Open No. 2005-314785 (A) “Hafnium-containing film forming material and method for producing hafnium-containing thin film made from the material” Mitsubishi Materials Corporation Patent No. 3409290 "Gate oxide film forming material" Trichemical Laboratories Co., Ltd. “Separate volume chemical industry” Vol. 26, no. 3, p. 117-124 (1982) "Separation of zirconium and hafnium" Takeo Otsuka, Hideo Miyazaki

  In order to solve the above situation, the present invention provides a high-purity hafnium material having an amount of residual zirconium of 1 ppm by weight or less corresponding to advanced electronic material applications such as next-generation insulated gate materials.

Means for Solving the Invention

  In the present invention, a solvent extraction method using a hafnium nitric acid aqueous solution dissolved in a nitric acid solution and a tributyl phosphate (TBP) solvent is adopted as a method for removing and separating zirconium, which is most important for obtaining high-purity hafnium.

  As another solvent extraction method, there is a method using methyl isobutyl ketone (MBIK) as a solvent, but since this drug is harmful and dangerous, the system using the TBP of the present invention is safer.

  In this method, it is necessary to prepare a hafnium nitric acid aqueous solution and a TBP solvent. The hafnium nitric acid aqueous solution can be prepared, for example, in the flow shown in FIG. 1 using hafnium chloride as a raw material.

  As hafnium pure metal or hafnium oxide is difficult to dissolve, it is easiest to use hafnium chloride as shown in FIG. 1, but hafnium raw material is dissolved in alkali, washed, sulfuric acid dehydrated, hydroxide precipitated and in nitric acid. A hafnium aqueous solution can also be obtained by dissolution in water, or by dissolution with buffered acid hydrofluoric acid, which is a mixed solution with hydrofluoric acid or ammonium fluoride, and a hafnium nitric acid aqueous solution can be obtained therefrom.

  After adjusting the hafnium nitric acid aqueous solution, multistage extraction is performed with an extractor using this solution and a TBP solvent (added normal dodecane as a diluent) (see FIG. 2).

  As the extractor, for example, various extractors such as a batch type extractor, a mixer-settler or a pulse column capable of multistage extraction operations can be used.

  The concentration of nitric acid in the aqueous nitric acid solution during extraction greatly affects the extraction behavior of hafnium and zirconium, but these concentrations must be optimized in consideration of the separation efficiency of hafnium and zirconium and the hafnium recovery rate. . In the present invention, based on data under various different conditions, the nitric acid concentration in the hafnium nitric acid solution supplied as a stock solution at the time of solvent extraction needs to be between 6 mol / L and 10 mol / L, and about 8 mol / L is desirable.

  The hafnium concentration in the hafnium nitric acid aqueous solution as the stock solution needs to be 10 g / L or more in consideration of the separation efficiency of hafnium and zirconium and the hafnium recovery rate, but is preferably about 100 g / L.

  In addition to zirconium, impurity elements that need to be removed include uranium, which is a radioactive element that damages semiconductor devices, and magnesium, aluminum, calcium, titanium, which may adversely affect the insulated gate junction, Examples include nickel, niobium, tantalum, and lead.

  High-purity hafnium oxide powder can be obtained by neutralizing the solution having an amount of zirconium of 1 wt ppm or less by extraction by adding an alkaline solution. After further chlorination to obtain hafnium tetrachloride, By reducing this, a high-purity hafnium pure metal material such as hafnium sponge or ingot can be obtained, and a material for forming a thin film such as a sputtering target can be provided.

  A hafnium single crystal material can also be obtained by performing single crystal growth from a high-purity hafnium pure metal material.

  In addition, examples of high-purity hafnium compounds obtained from purified hafnium materials include hafnium oxychloride, hafnium hydride, hafnium carbide, hafnium sulfide, and hafnium silicide.

  Examples of organic hafnium materials used as raw materials for synthesizing a hafnium-based oxide film from the purified hafnium material by a CVD method or the like include, for example, tetramethoxyhafnium, tetraethoxyhafnium, tetra-i-hafnium, tetra-t-butoxy. Examples thereof include hafnium, tetrakis (dibiroylmethanato) hafnium, tetrakis (dimethylami) hafnium, and organic hafnium compounds having a bond between a hafnium atom and a nitrogen atom.

The invention's effect

  According to the present invention, a high-purity hafnium material suitable as a raw material for advanced electronic materials such as next-generation insulated gate materials can be obtained, which can contribute to higher density of electronic devices.

  The present invention can provide a high-purity hafnium material in which zirconium element, which is particularly difficult to separate, is reduced to 1 ppm by weight or less by performing multistage extraction using an aqueous hafnium nitric acid solution and a TBP solvent.

  The specific methods and results are described in the following examples, which do not necessarily limit the present invention, but include other examples and derived examples within the scope of the basic idea of the present invention. It is.

  The hafnium nitric acid aqueous solution was prepared according to the flow shown in FIG. The raw material hafnium chloride used was a reagent (99.9% purity excluding Zr) manufactured by Mitsuwa Chemicals. After preparing 500 mL of an aqueous hafnium chloride solution, ammonia water was added to produce a hafnium hydroxide slurry, and the precipitate filtered by suction filtration was dissolved in nitric acid to produce a hafnium nitric acid solution as an extraction stock solution. The nitric acid concentration at this time is 8 mol / L, and the hafnium concentration is 92 g / L.

  Using this hafnium nitric acid solution and 30% TBP-normal dodecane solvent pretreated with an 8 mol / L nitric acid aqueous solution, the extraction operation was repeated up to 20 times, and zirconium, an impurity coexisting in the hafnium nitric acid solution, was added to the organic phase. To obtain a hafnium nitric acid solution having a low zirconium content. Table 1 shows changes in zirconium and hafnium concentrations every five extraction operations. It can be seen that after repeating the extraction operation 20 times, the zirconium content in the hafnium nitric acid solution has decreased to 1 ppm by weight or less. FIG. 3 is a graph showing the change in the amount of zirconium.

  The final extract solution was neutralized and then recovered as hafnium oxide. The results of the analysis of this hafnium oxide powder are summarized in Table 2. It can be seen that the analytical elements uranium, magnesium, aluminum, calcium, titanium, nickel, niobium, tantalum, and lead are all 1 ppm by weight or less.

Further, the obtained hafnium oxide was chlorinated to form hafnium tetrachloride, which was further reduced with magnesium to obtain a high-purity hafnium sponge. This hafnium sponge was melted with an electron beam to obtain a high-purity hafnium metal ingot of the order of 5N (99.999 weight percent).

Hafnium nitrate aqueous solution preparation process Hafnium extraction process using hafnium nitrate aqueous solution and TBP solvent Relationship between zirconium concentration and number of extractions

Claims (8)

  A high-purity hafnium compound material having a zirconium content of 1 ppm by weight or less.   An organic hafnium material for forming a thin film, wherein the content of zirconium is 1 ppm by weight or less.   A hafnium pure metal material having a zirconium content of 1 ppm by weight or less.   A hafnium single crystal material having a zirconium content of 1 ppm by weight or less.   The high-purity hafnium material according to any one of claims 1 to 4, wherein the contents of magnesium, aluminum, calcium, titanium, nickel, niobium, tantalum, lead, and uranium are each 1 ppm by weight or less. .   A high-purity hafnium characterized in that the hafnium material according to any one of claims 1 to 5 is obtained by removing impurities by a solvent extraction method using a hafnium nitric acid aqueous solution and a tributyl phosphate (TBP) solvent. Material manufacturing method.   The method for producing a high-purity hafnium material according to claim 6, wherein the hafnium nitric acid aqueous solution has a nitric acid concentration of 6 to 10 mol / L.   The method for producing a high purity hafnium material according to claim 6, wherein the hafnium nitric acid aqueous solution has a hafnium concentration of 10 g / L or more.

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