JP3756047B2 - High purity titanium sponge material and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-purity sponge titanium material suitable for a sputtering target material and a method for producing the same.
[0002]
[Prior art]
As an industrial manufacturing method of titanium metal, a method of cutting and crushing a sponge titanium material manufactured by a crawl method, then hardening it to a briquette, and melting and casting it is frequently used. The crawl method is a reduction step in which molten Mg and titanium tetrachloride are reacted in a reaction vessel, and after the reduction, the reaction vessel is heated in a vacuum state, thereby allowing unreacted Mg and residual secondary substances contained in the material in the vessel. A vacuum separation step of evaporating and removing organisms.
[0003]
On the other hand, as a new application of titanium metal, there is a wiring material in a semiconductor element such as LSI. This wiring is formed by performing sputtering using high-purity metallic titanium as a target material. This sputtering target material is required to be low in impurities, and the sponge titanium material, which is the material, has an oxygen content of 200 ppm or less and the content of each metal element of Fe, Ni, Cr, Al, and Si. About 10 ppm or less is required.
[0004]
However, since the crawl method is a method that prioritizes productivity, it is not easy to ensure an impurity level that is required for a sputtering target material. Therefore, the following method has been proposed. One is a centering method in which a portion near the center excluding the upper, lower and outer peripheral portions of the titanium sponge material obtained in the reaction vessel after vacuum separation is commercialized (Japanese Patent No. 2863469). One is a low-humidity crushing method of cutting and crushing a sponge titanium material taken out from the reaction vessel in a low-humidity atmosphere (Japanese Patent No. 2921790).
[0005]
[Problems to be solved by the invention]
However, in the former centering method, the level required for the sputtering target material can be secured for each metal element of Fe, Ni, Cr, Al and Si, but the level of oxygen is secured. Difficult to do. On the other hand, in the latter method of low-humidity crushing, it is possible to ensure the level required for the sputtering target material for oxygen, but for each metal element of Fe, Ni, Cr, Al and Si, the level is required. It is difficult to ensure.
[0006]
Therefore, in order to ensure the level required for the sputtering target material for each of the metallic elements of Fe, Ni, Cr, Al and Si, and oxygen, the former centering method and the latter low-humidity crushing It is necessary to combine methods. However, as a practical problem, the former centering method is easy to implement, but in the latter case of the low-humidity crushing method, the oxygen level actually required for the sputtering target material should be stably secured. Then, a very large isolated work space in which the inside is kept at a low humidity is required, and a large amount of expenses are required for the construction of the space and the atmosphere maintenance, which is not a realistic method.
[0007]
An object of the present invention is to provide a high-purity sponge titanium material that is low in both oxygen content and metal element content and excellent in economic efficiency, and a method for producing the same.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors paid attention to the relationship between the sample collection position of the sponge titanium material manufactured by the crawl method and the amount of oxygen.
[0009]
FIG. 1 is a longitudinal sectional view of a sponge titanium material in a reaction vessel in a vacuum separation process. The reaction vessel 20 is accommodated in the heating furnace 30. The sponge titanium material 10 in the reaction vessel 20 has a shape in which the middle stage portion is constricted because titanium is deposited on the rooster 21 in the reaction vessel 20 and the inner surface of the side wall of the reaction vessel 20 in the previous reduction step. Yes.
[0010]
In the sponge titanium material 10 after the vacuum separation process, the content of each metal element of Fe, Ni, Cr, Al, and Si decreases as the distance from the upper surface, the lower surface, and the outer peripheral surface increases. This is because the content of each metal element is mainly due to contamination from the reaction vessel 20. For this reason, by removing the upper, lower and outer peripheral portions of the titanium sponge material 10 and collecting the remaining portion 11 near the center, the level required for the sputtering target material can be relatively easily secured for the metal element. it can.
[0011]
However, the amount of oxygen, particularly the amount of oxygen after cutting and crushing, is unexpectedly reduced at the surface layer portion of the sponge titanium material 10. For example, the portion from Oite top A to the center position of the titanium sponge material 10 to 1/2 parts of C, when investigating the amount of oxygen distribution after cutting and crushing, the amount of oxygen is increased closer to 1/2 parts C . For example, when the amount of oxygen in the titanium grains obtained from the uppermost part A is 250 ppm, it becomes about 300 ppm at ¼ part B and about 350 ppm at ½ part C. Due to this tendency, even if the portion 11 near the center of the sponge titanium material 10 is collected, it becomes difficult to ensure the level of oxygen required for the sputtering target material after cutting and crushing.
[0012]
The present inventors investigated the cause of the decrease in the amount of oxygen in the surface layer portion of the sponge titanium material 10 from both the physical properties and the manufacturing method. As a result, the following facts were found.
[0013]
FIG. 2 shows the temperature change of the titanium sponge material in the vacuum separation process for the uppermost part A, 1/4 part B, 1/2 part C at the center position. The temperature of any portion tends to temporarily decrease from the start of the vacuum separation, then increases, and reaches a stable temperature close to the furnace temperature. This is because the evaporation of residual Mg begins with the start of vacuum separation, and the temperature temporarily decreases due to the heat of vaporization, but the temperature starts to increase due to the decrease in residual Mg, and close to the furnace temperature when the evaporation is completed. By the temperature stabilizes to the level.
[0014]
This tendency is common to all of the uppermost part A, 1/4 part B, and 1/2 part C, but the lowest temperature is lower in the order of the uppermost part A, 1/4 part B, and 1/2 part C. The time from the start to the start of rising and the time to reach the stable temperature increase in the order of the uppermost part A, 1/4 part B, 1/2 part C. This is because the portion closer to the center of the titanium sponge material is more difficult to remove residual Mg. The central portion where the residual Mg is most difficult to escape, that is, the residual Mg of 1/2 part C is removed, and the temperature Tc of this part is stable. The time when the temperature To is reached is the end of the vacuum separation. The reason why the stable temperature is lower in the order of the uppermost part A, ¼ part B, and ½ part C is that heat radiation to the opening side (upward) of the reaction vessel is remarkable.
[0015]
As a result of performing the vacuum separation in such a process, the surface layer portion far from the center of the sponge titanium material is heated for a long time after the Mg evaporation is finished, and is in a so-called empty state. The present inventor considered that the heating time after the evaporation of Mg was related to the amount of oxygen after cutting and crushing, and conducted various investigations. The farthest part from the center of the sponge titanium material, Sintering progresses during heating and the specific surface area decreases, and the smaller the specific surface area, the more the increase in the amount of oxygen due to oxidation in the cutting and crushing process is suppressed. As a result, 1/2 part C, 1/4 If the amount of oxygen after cutting and crushing decreases in the order of part B and top part A, and heating is continued after the evaporation of 1/2 part C Mg is completed, the sintering of this part proceeds and the specific surface area It has been found that the reduction of oxygen concentration and the reduction of oxygen are realized.
[0016]
The present invention has been completed on the basis of such knowledge, and the high-purity sponge titanium material is a sponge titanium material manufactured by the crawl method, and the specific surface area measured by the BET method is determined at the time of vacuum separation. It is 0.03 m ² / g or less due to the progress of sintering , and each metal element content of Fe, Ni, Cr, Al, and Si is 10 ppm or less.
[0017]
By limiting the specific surface area by the BET method to 0.03 m ² / g or less, the oxygen content of the titanium particles in the sponge titanium for a sputtering target for a semiconductor device can be reduced even when cutting and crushing in a normal air atmosphere. The required 200 ppm or less is suppressed. A more preferable oxygen content after cutting and crushing is 100 ppm or less. The lower limit of the specific surface area is preferably as low as possible from the viewpoint of reducing the amount of oxygen. However, if the specific surface area is too small, cutting and crushing becomes difficult, so 0.01 m ² / g or more is preferable.
[0018]
The reason why the metal element contents of Fe, Ni, Cr, Al, and Si are limited to 10 ppm or less is to exclude the upper part, the lower part, and the outer peripheral part of the sponge titanium material. These surface layer portions, for example, the uppermost portion A shown in FIG. 1, have been subjected to heating in the air in the past, and have a small specific surface area by the BET method. However, in this part, each metal element content exceeds 10 ppm. The particularly preferable content of each metal element is 7 ppm or less.
[0019]
Further, in the method for producing a high purity titanium sponge material of the present invention, when the sponge titanium material is produced by the crawl method, the vacuum separation time t in the vacuum separation step is set to the center temperature of the material in the reaction vessel from the start of the vacuum separation. Tc is the time until reaching a stable temperature to near furnace temperature as to the time, t = to + (20 ~35 ) was set to a time after the end vacuum separation, the mass height of the material in the reaction vessel H, Katamari径, D is an upper part with a thickness h1 from the upper surface of 0.1H or more, a lower part with a thickness h2 from the lower surface of 0.25H or more, and an outer peripheral part with a thickness d of 0.18D or more from the outer peripheral surface. The remaining portion and the portion near the center of less than 30% of the mass of the material are produced.
[0020]
With the vacuum separation time t (to + 20) hours or more, the top of the material in the reaction vessel, the specific surface area near the center portion excluding the lower and outer peripheral portion is reduced, a low-oxygen after cutting crushing, semiconductor It is realized at a level required for a sponge titanium for a sputtering target for an element . And by commercializing the parts in the vicinity of the center excluding the upper part, the lower part and the outer peripheral part of the material in the reaction vessel, the content of each metal element of Fe, Ni, Cr, Al and Si is suppressed to a low level. .
[0021]
When the vacuum separation time t exceeds (to + 35) time, the specific surface area becomes too small and cutting and crushing becomes difficult. In addition, the thermal economy is worse than necessary. A particularly preferable vacuum separation time t is (to + 30) hours or less for the upper limit .
[0022]
In the actual operation, the center temperature of the sponge titanium material is not actually measured. The time until the center temperature reaches a stable temperature is obtained from the temperature change data obtained by test operation and temperature analysis for each operation equipment, and the heating time in the vacuum separation process is set based on this time.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0024]
A sponge titanium material is produced by melting Mg in a reaction vessel and dropping a titanium tetrachloride solution. When this reduction process is completed, the process proceeds to a vacuum separation process. In the vacuum separation step, the reaction vessel is evacuated and heated to a predetermined temperature by a heating furnace to remove unreacted Mg and by-products.
[0025]
This vacuum separation step will be described in detail for the operation example of FIG. The temperature Ta of the uppermost part A of the sponge titanium material in the reaction vessel is slightly lowered at the beginning of the vacuum separation, but immediately starts to rise and reaches a stable temperature in about 20 to 30 hours from the start of the vacuum separation. On the other hand, the temperature Tc at the center (1/2 part C) continues to decrease for about 30 hours from the start of the vacuum separation, and then starts to rise and reaches the stable temperature To 70 hours after the start of the vacuum separation.
[0026]
Conventionally, the vacuum separation is completed in about 70 hours when the center temperature Tc reaches the stable temperature To, and there has been an attempt to shorten this time, but no attempt has been made to bother this. . As a result, in the portion near the center where the amount of the metal element is small, heating in an empty state after evaporation of Mg is not performed and sintering does not proceed, so that the specific surface area is not sufficiently reduced. For this reason, even if a portion near the center is collected after vacuum separation, an increase in the amount of oxygen due to oxidation becomes significant in cutting and crushing in the air atmosphere, and a low oxygen level required for the sputtering target material is realized. It was difficult.
[0027]
Therefore, in this embodiment, after the center temperature Tc reaches the stable temperature To, the heating is continued for another 20 to 35 hours, preferably 20 to 30 hours. As a result, the specific surface area according to the BET method is reduced to 0.03 m ² / g or less by the progress of sintering even in the vicinity of the center where the amount of metal element is small. As a result, by collecting the portion near the center after vacuum separation, an increase in the amount of oxygen due to oxidation in the cutting and crushing process is suppressed, and both the oxygen amount and the metal element amount are required for sputtering target materials for semiconductor elements. Impurity levels can be realized.
[0028]
In the collection of the vicinity of the center after the vacuum separation, as shown in FIG. 1, the lump height of the sponge titanium material 10 is H, the lump diameter is D, and the thickness h1 from the upper surface is 0.1 H or more from the upper and lower surfaces. The thickness h2 is lower than 0.25H and the outer peripheral portion having a thickness d of 0.18D or more from the outer peripheral surface is cut and removed, and the remainder is less than 30% of the lump weight of the sponge titanium material 10. The center vicinity portion 11 is collected.
[0029]
The collected portion 11 near the center is usually cut and crushed in an air atmosphere to obtain sponge titanium particles having a predetermined particle size. In spite of normal cutting and crushing in an air atmosphere, the amount of oxygen is suppressed to 200 ppm or less, and the amount of each metal element of Fe, Ni, Cr, Al, and Si is also suppressed to 10 ppm or less. The average particle size after crushing is preferably 10 to 300 mm.
[0030]
The result of investigating the preferable vacuum separation time in the vacuum separation step is shown in FIG. A preferable vacuum separation time is a region indicated by hatching in FIG.
[0031]
The vacuum separation time is affected by the diameter (retort diameter) of the reaction vessel, and the longer this diameter is, the longer the time is. +20 hours to +35 hours relative to conventional vacuum separation time indicated by a solid line Ru vacuum separation time der the definitive present invention. The specific surface area by the BET method in the vicinity of the center becomes 0.03 m ² / g or less after +20 hours or more, and the oxygen amount after cutting and crushing satisfies 200 ppm or less required for sponge titanium for sputtering targets for semiconductor elements. become. When the specific surface area by the BET method is less than 0.01 m ² / g, cutting and crushing become difficult.
[0032]
About the diameter (retort diameter) of a reaction container, 1350-2000 mm is preferable. If it is less than 1350 mm, metal impurities tend to increase even if centering is performed. If it exceeds 2000 mm, there may be a problem in equipment such as thermal deformation of the reaction vessel.
[0033]
Incidentally, the temperature change shown in FIG. 2 is when the diameter (retort diameter) of the reaction vessel is 1700 mm, the conventional vacuum separation time is 70 hours, and the vacuum separation time in the present invention in this case is 90 to 105 hours. 90-100 hours are particularly preferred.
[0034]
When the diameter of the reaction vessel (retort diameter) is 1700 mm, micrographs of samples taken from the center part of the sponge titanium material are shown in FIGS. 4 (a) and 4 (b) for the cases where the vacuum separation time is 70 hours and 95 hours. ) At the same magnification.
[0035]
The specific surface area according to the BET method is 0.1 m ² / g when the vacuum separation time is 70 hours, whereas it is 0.03 m ² / g when the vacuum separation time is 95 hours. This difference is also apparent from FIGS. 4 (a) and 4 (b). As a result of the difference in specific surface area, the amount of oxygen at the stage of cutting and crushing to an average particle size of 65 mm in the air atmosphere was 280 ppm when the vacuum separation time was 70 hours, and 190 ppm when the vacuum separation time was 95 hours. . As for the amount of metal element, the content of each metal element of Fe, Ni, Cr, Al, and Si was 10 ppm or less in any case.
[0036]
In addition, the area | region shown with the oblique line in FIG. 3 is expressed with a numerical formula as follows.
Vacuum separation time = (0.0698 × [retort diameter] −24) −5− (0.0698 × [retort diameter] −24) +10
[0037]
The BET method is a method for calculating the specific surface area from the amount of liquid nitrogen absorbed, and is widely used in adsorbents and the like.
[0038]
【The invention's effect】
As described above, the high-purity titanium sponge material of the present invention limits the specific surface area by the BET method to 0.03 m ² / g or less, so that the amount of oxygen can be lowered even when cutting and crushing in the air atmosphere. In combination with reduction of metal impurities by centering, the impurity level required for the sputtering target material for semiconductor elements can be economically secured.
[0039]
Moreover, the manufacturing method of the high purity sponge titanium material of this invention is the vacuum separation time t in a vacuum separation process until the center temperature Tc of the material in reaction container reaches the stable temperature To near furnace temperature from the start of vacuum separation. by setting the time t = to + (20 ~35) time as to the time, the BET specific surface area can easily be limited to less than 0.03 m ² / g, and the reduction of this by the oxygen amount, the center picking By reducing the metal impurities due to the above, the impurity level required for the sputtering target material for semiconductor elements can be economically ensured.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a sponge titanium material in a reaction vessel in a vacuum separation step.
FIG. 2 is a graph showing temperature changes of the titanium sponge material over time in the vacuum separation process for the uppermost part A, 1/4 part B, 1/2 part C at the center position.
FIG. 3 is a graph showing a preferable vacuum separation time in a vacuum separation step with a diameter (retort diameter) of a reaction vessel as a parameter.
FIG. 4 is a photomicrograph of samples taken from the center of two types of sponge titanium materials with different vacuum separation times.
[Explanation of symbols]
10 Sponge titanium material 11 Center vicinity portion 20 Reaction vessel 30 Heating furnace

Claims (2)

A sponge titanium material manufactured by the crawl method, the specific surface area measured by the BET method is 0.03 m ² / g or less due to the progress of sintering during vacuum separation , and Fe, Ni, Cr , Al and Si metal element content of high purity sponge titanium material of 10 ppm or less When producing a sponge titanium material by the crawl method, the vacuum separation time t in the vacuum separation step is the time from the start of the vacuum separation until the center temperature Tc of the material in the reaction vessel reaches the stable temperature To near the furnace temperature. set t = to + (20 ~35) time as to time, after the end of vacuum separation, the mass height of the material in the reaction vessel H, the Katamari径as D, from the top surface thickness h1 is not less than 0.1H The upper part, the lower part with a thickness h2 from the lower surface of 0.25H or more, and the outer peripheral part with a thickness d from the outer peripheral surface of 0.18D or more are cut and removed, and the remainder is less than 30% of the mass of the material. A method for producing a high-purity sponge titanium material, characterized in that a portion near the center of the product is commercialized.

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