JP2003147454A - Method for manufacturing low-oxygen titanium material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a low-oxygen titanium material used for a target for semiconductor use by a Kroll method. SOLUTION: In the method for manufacturing the low-oxygen titanium material, sponge titanium after vacuum separation is cooled in a reactor vessel and a nitride film is formed on the surface of the sponge titanium in the reactor vessel and then the sponge titanium is taken out of the reactor vessel and cut or crushed. The nitride film forms desirably by changing low-oxygen nitrogen gas having a ratio of the partial pressure of nitrogen to the partial pressure of oxygen of >=20 into the reactor vessel and to change the nitrogen gas after the temperature in the central part of the sponge titanium reaches <=200 deg.C in the reactor vessel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing low oxygen titanium, and more particularly to a method for producing a high-purity titanium material for forming a thin film, which is useful as a material used when forming a wiring network on the surface of a semiconductor element. With respect to, more specifically, suitable as a material for a sputtering target prepared from the high-purity titanium material for thin film formation, the oxygen concentration is 200ppm
The following relates to a method for producing a titanium material having low oxygen content.

[0002]

2. Description of the Related Art Conventionally, high-purity refractory metal materials have been used as wiring materials for semiconductors. Specific examples of the metal material used as the wiring material include molybdenum, tungsten, niobium, titanium, and their silicides. Among them, titanium is widely used because it has excellent specific strength, workability, and corrosion resistance. There is.

At present, as a method for producing a titanium material which has been industrially adopted, there is a method for producing a pure titanium metal by producing a titanium chlorine compound by chlorinating titanium oxide and reducing it as an intermediate raw material. is there. Specifically, Kroll that uses titanium tetrachloride (TiCl ₄ ) as an intermediate material and uses magnesium (Mg) as a reducing agent.
Method and a Hunter method using sodium (Na) as a reducing agent. Comparing the production methods of these titanium materials, the Kroll method is considered to be an excellent production method from the viewpoint of productivity and energy saving.

FIG. 1 is a diagram for explaining the manufacturing process of titanium sponge obtained as a titanium material by the Kroll method, along with reduction, vacuum separation and crushing.

In the reduction step (), TiCl ₄ is sprayed from the nozzle 2 in the reduction furnace 1 to react with molten Mg. At this time, if oxygen or the like is mixed in the reaction atmosphere in the reduction furnace 1, titanium sponge will be contaminated, so the reaction is carried out in the closed steel reaction container 3.

The Mg required for the reaction is charged in the reaction vessel 3 and
After substituting the interior of the container with an inert gas, the temperature is raised by heating to melt the Mg. Nozzle 2 in reaction vessel 3 containing molten Mg
Is supplied with TiCl ₄ , and Ti and a by-product MgCl ₂ are produced. The by-product MgCl ₂ is appropriately extracted to the outside of the reaction container 3, and finally spongy titanium containing unreacted Mg and residual MgCl ₂ is obtained in the reaction container 3.

In the vacuum separation step (), the reaction container 3 is housed in a vacuum separation furnace 4 to bring the inside of the reaction container 3 into a vacuum state, and the inside of the reaction container 3 is further heated from the outside, Unreacted Mg and residual MgCl ₂ contained in titanium sponge in the reaction container 3 are evaporated. The evaporated unreacted Mg and residual MgCl ₂ are recovered by the condenser 5 outside the vacuum separation furnace 4. The titanium sponge that has been vacuum-separated is extruded from the reaction vessel 3 as a cylindrical mass. In the crushing process (), the extruded titanium sponge has its bottom,
After the top portion and the circumferential portion are removed, cutting is performed by the cutting press 6. Then, it is crushed into fine particles (less than 1/2 inch) with a jaw crusher. The titanium sponge thus crushed to a predetermined particle size is further mixed to maintain uniform quality, and then stored in a closed drum can filled with argon gas. After that, it is used as a raw material for melting the titanium material for semiconductors and the titanium material for wrought.

On the other hand, with the recent increase in the density of LSI devices, titanium used for semiconductors is required to have high purity, and further, the oxygen concentration contained in the titanium is required to be further reduced. For example, a titanium material used as a 64 Mbit wiring material, which is the mainstream of DRAM, is required to have an oxygen concentration of 250 ppm or less. Furthermore, in recent years, full-scale production has begun to be considered, and when it comes to titanium materials used for highly integrated wiring materials of 128 Mbits or 256 Mbits, the oxygen concentration contained will be further reduced, and 200 ppm or less is required. Has been done.

In response to such demands, various methods for producing low oxygen titanium materials have been proposed. For example,
In the 10-259432 publication, the oxygen content is set to 25 by specifying the humidity condition or the temperature condition in the crushing process.
A method for producing a low-oxygen titanium material having a high quality of 0 ppm or less, further 200 ppm or less and applicable to a sputtering target has been proposed. In the method proposed here, MgCl ₂ remaining in the sponge cake by absorbing moisture in the atmosphere, attention is paid to the amount of oxygen contained in the sponge cake increases.

Specifically, the step of cutting titanium sponge,
In particular, when the humidity in the atmosphere in the crushing step is high, the oxygen content in titanium sponge increases, and conversely, when the humidity in the atmosphere in the crushing step is low, the oxygen contained in titanium sponge is suppressed. I am trying. Therefore, when the sponge titanium cake produced by the Kroll method is cut and the selected titanium sponge is crushed, the absolute humidity is “10 g-H ₂ O / m ³ or less”, and more preferably the ambient temperature is 25 ℃
I will keep it below.

However, if the method proposed in the above-mentioned Japanese Patent Laid-Open No. 10-259432 is to be carried out, an apparatus for adjusting the atmospheric humidity and the atmospheric temperature in the crushing step is required, and the cost associated with it is high. This will increase the manufacturing cost. Also, oxygen contained in the sponge titanium taken out of the reaction vessel due to moisture absorption can be suppressed, but since sponge titanium is active against oxygen in the air atmosphere, it is not possible to increase the oxygen concentration due to oxidation. It is not an effective means.

Further, in Japanese Patent Laid-Open No. 2000-309833, sponge titanium produced by the Kroll method is cooled until the temperature of the central portion after vacuum separation is substantially 100 ° C. or lower, and then the central portion of titanium sponge is cooled. A method for producing a low-oxygen high-purity titanium material having an oxygen content of 200 ppm or less is disclosed. In this method, since the surface of titanium sponge after vacuum separation is active, an oxide film is formed on the surface when exposed to the atmosphere, and the thickness of the oxide film depends on the temperature of titanium sponge. It was noted that the higher the thickness, the thicker the oxide film and the higher the oxygen concentration contained in titanium sponge.

However, in the above method of defining the central temperature, it is necessary to cool the reaction vessel for a relatively long time after vacuum separation. Therefore, from the viewpoint of efficient production of low oxygen titanium materials, there is room for improvement in shortening the cooling time.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the problem in producing a low oxygen titanium material, for example, titanium having an oxygen concentration of 200 ppm or less, and is a reaction for cooling titanium sponge. An object of the present invention is to provide a method for producing a low-oxygen titanium material suitable for producing a sputtering target by forming a nitride film on the titanium sponge surface in a container and then taking out the titanium sponge.

[0015]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present inventor has conducted various studies using the method disclosed in Japanese Patent Laid-Open No. 2000-309833. When the titanium sponge is cooled to below 100 ° C in the reaction vessel, a thin oxide film is formed on the surface of the titanium sponge taken out from the reaction vessel at the time of cutting and sampling. Like Then, when an oxide film is formed on the surface of the collected titanium sponge, it becomes difficult to supply oxygen to the inside, so that it is possible to suppress the subsequent increase in oxygen content.

Next, the cooling time in the reaction vessel is shortened,
When the sponge titanium is taken out at the center temperature of about 150 ° C,
By reacting with oxygen in the atmosphere, an oxide film is formed on the surface. Due to the influence of reaction heat associated with the formation of the oxide film, the surface temperature locally rises and the oxidation further proceeds, so that a relatively thick film is formed on the surface of titanium sponge. Furthermore, when cutting or crushing, a new cutting surface or crushing surface appears with processing, so the processing heat associated with processing and the reaction heat of the cutting surface or crushing surface combine, and the sponge titanium surface The film formation is promoted and the oxygen content is increased.

In order to suppress the oxide film formed on the titanium sponge surface even if the cooling time in the reaction container is shortened, after introducing nitrogen gas into the reaction container to form a nitride film on the titanium sponge surface. , Decided to take out the titanium sponge into the atmosphere. Since the bulk property of titanium sponge is porous, nitrogen gas permeates to the central portion of titanium sponge in the reaction vessel, so that the nitride film is formed almost entirely.

Even when the titanium sponge having the nitride film formed thereon is exposed to the atmosphere, the formation of an oxide film due to the subsequent oxidation reaction is significantly suppressed. For example, according to a study by the present inventor, the thickness of the oxide film on the titanium sponge surface by the method disclosed in JP 2000-309833 A is 100 to 150 Å, whereas a nitride film is formed. The thickness of the oxide film on the titanium sponge surface remains below 100Å.

Further, when cutting and crushing, a new cutting surface and a crushing surface appear due to processing, and even if the temperature rises, an oxide film is formed on the titanium sponge surface on which the nitride film is formed. Will be suppressed.

The present invention has been completed based on the above findings, and has as its gist the following methods (1) and (2) for producing a low oxygen titanium material. (1) A method for producing a low-oxygen titanium material from titanium sponge obtained by the Kroll method, in which titanium sponge after vacuum separation is cooled in a reaction vessel, and then a nitride film is formed on the titanium sponge surface in the reaction vessel. After the formation, titanium sponge is taken out from the reaction vessel and cut and / or crushed, which is a method for producing a low oxygen titanium material. (2) In the manufacturing method of (1) above, the formation of the nitride film is performed at a nitrogen partial pressure / oxygen partial pressure ratio of 20.
It is desirable to introduce the low oxygen-containing nitrogen gas as described above into the reaction vessel, and then introduce the nitrogen gas after the temperature of the titanium sponge central portion becomes 200 ° C. or lower in the reaction vessel.

By adopting the production methods (1) and (2), it is possible to produce a titanium material having a low oxygen concentration of 200 ppm or less and high purity. In the present invention, the high-purity titanium material means that the content of Fe, Ni, Cr, Al and Si as impurities is 10 ppm or less and the content of Na and K is 0.1 pp.
intended to be less than or equal to m.

In the current production method of the Kroll method,
The lump weight of titanium sponge is often 6 to 10 tons depending on the capacity of the reaction vessel used. According to the study by the present inventor, the production method of the present invention is not limited to 6 to 10 ton weight sponge titanium, and other than that, for example, 1 ton to 5 ton sponge titanium lumps should be applied. You can

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION In the production method of the present invention, titanium sponge after vacuum separation is cooled in a reaction vessel, and then a nitride film is formed on the titanium sponge surface in the reaction vessel.
The feature is that the sponge titanium is taken out from the reaction vessel and cut or crushed. Hereinafter, the conditions for forming a nitride film, the cooling time, and the contents of cutting and crushing in the production of low oxygen titanium according to the present invention will be described.

Usually, when the titanium sponge is cooled to substantially 100 ° C. or lower in the reaction vessel by using the method disclosed in the above-mentioned JP-A-2000-309833, the cooling time is 70-80. It's time. On the other hand, the cooling time of the present invention may be 50 to 70 hours (see Examples described later), and therefore the cooling time can be significantly reduced.

The formation of the nitride film is carried out by introducing nitrogen gas into the reaction vessel, but the introduction timing may be any timing immediately before taking out the sponge titanium from the reaction vessel. For example, the time to complete cooling, that is, to open the lid of the reaction vessel
15 to 20 minutes before, the inside of the reaction vessel is evacuated and then filled with nitrogen gas. At this time, argon gas in the container is discharged by evacuation, but this is injected from the start of cooling in order to speed up the cooling rate of titanium sponge and to prevent leakage of air into the reaction container. It is a thing.

Even if the argon gas remains in the reaction vessel when the nitrogen gas is introduced, the nitrogen in the reaction vessel has a mass ratio (ma
If the ss%) is 10% or more, the nitride film is properly formed by the nitrogen gas.

The nitrogen gas used for forming the nitride layer in the present invention is preferably a low oxygen-containing nitrogen gas having a nitrogen partial pressure / oxygen partial pressure ratio of 20 or more. This is because even if nitrogen gas contains oxygen gas, the formation of the nitride film has priority over the formation of the oxide film by controlling the oxygen partial pressure, that is, the low concentration.

Therefore, the ratio of nitrogen partial pressure / oxygen partial pressure is 20.
When the nitrogen gas is used in an amount less than the above, the oxide film is mainly formed, and the originally necessary nitrogen film may not be sufficiently formed. On the other hand, since the nitriding gas to be used may be pure nitrogen gas, the upper limit of the ratio of nitrogen partial pressure / oxygen partial pressure does not need to be specified.

In the present invention, it is desirable to introduce the low oxygen-containing nitrogen gas after the temperature of the titanium sponge center portion cooled in the reaction vessel reaches 200 ° C. or lower. More preferably, it is introduced after the temperature of the central portion has reached 150 ° C. or lower. If nitrogen gas is introduced when the temperature of the central part is 200 ° C or higher, the thickness of the nitride film that is formed will increase rapidly, and the concentration of nitrogen contained will increase, affecting high-purity titanium. To be done.

Usually, the temperature control of the central portion is controlled by the cooling time after the completion of vacuum separation. For this reason, the titanium sponge that has undergone the reaction is cooled, drilled from the top and a thermocouple is inserted into the central portion, and then the temperature is raised to the temperature at which vacuum separation is performed. Then, after performing vacuum separation, cooling is performed, and the relationship between the time from the start of cooling and the temperature of the central portion is measured. Based on this measurement result, the cooling time after vacuum separation is managed.

Furthermore, in the production method of the present invention, it is desirable that after the titanium sponge is taken out from the reaction vessel, the cut sponge having the measured oxygen concentration satisfying the required concentration is selected and cut and crushed. This is to strictly control the concentration and quality of manufactured titanium.

At present, the content of impurities required for a sputtering target which is an application of a high-purity titanium material is 30 ppm or less for nitrogen concentration and 250 ppm or less for oxygen concentration. Recently, the required nitrogen concentration is not a problem, but the oxygen concentration is shifting to severe conditions, and the oxygen concentration affects the yield of high-purity titanium materials. Therefore, the standard oxygen concentration here is 180 ppm.

In an actual operation, not all cut lumps of titanium sponge are measured, but the cut lumps in the central portion excluding the peripheral portion are measured. For example, as a central portion, a portion having a thickness of 15% or more of the lump height from the bottom of the titanium sponge lump and a portion having a thickness of 5% or more of the lump height from the top are cut and removed, and The portion corresponding to the peripheral portion of which the thickness is 10% or more of the lump diameter is cut and removed.

According to the method of the present invention, in the production of a low oxygen titanium material, a thin nitride film is formed on the surface of titanium sponge after vacuum separation, and thereafter, when the film is exposed to the atmosphere, the formation of an oxide film is suppressed. This is an effective manufacturing method without requiring any new equipment or device. Further, this method is not only effective for high-purity titanium materials, but also applicable for wrought materials, powder production, and precision casting titanium material production.

[0035]

EXAMPLES The effects of the manufacturing method of the present invention will be described in detail based on specific examples. A cylindrical sponge titanium having a weight of about 6T after vacuum separation was manufactured by the Kroll method.

In the invention examples, the cooling time after the completion of the vacuum separation was controlled to 50 to 76 hours, and the inside of the reaction vessel was generally evacuated for 10 minutes from 15 minutes before the reaction vessel was opened to 5 minutes before. Then, within 5 minutes from 5 minutes before opening the reaction vessel to 5 minutes before opening, the ratio of the nitrogen partial pressure / oxygen partial pressure from the vessel lid is
100 or more nitrogen gas was introduced, the lid was opened, and the titanium sponge mass in the reaction vessel was taken out into the atmosphere. The titanium sponge taken out has a particle size of 10 ~
After the particles were sized to 30 mm and uniformly mixed, the oxygen concentration and nitrogen concentration in the center of the lump were measured.

In the comparative example, the cooling time after completion of vacuum separation was set to 50 to 76 hours, without introducing nitrogen gas,
The titanium sponge taken out from the reaction vessel was sized by cutting and crushing to a particle size of 10 to 30 mm and uniformly mixed,
The oxygen concentration and nitrogen concentration in the center of the lump were measured.

[0038]

[Table 1]

As is clear from the results shown in Table 1, Invention Example 1
Although the cooling time was significantly shortened, the result was that the oxygen concentration was less than 200 ppm, and low-oxygen titanium that could be used for high-purity titanium was obtained. On the other hand, in Invention Example 3, if the same cooling time as the conventional one is secured, it becomes possible to manufacture a low oxygen titanium material which has not been obtained conventionally.

[0040]

According to the method for producing a low oxygen titanium material of the present invention, nitrogen gas is introduced into the reaction vessel to form a nitride film up to the central portion of the cylindrical titanium sponge, thereby producing a sputtering target. It is possible to produce a low oxygen titanium material having an oxygen concentration of 200 ppm or less, which is suitable for the production of.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a production process of titanium sponge by the Kroll method along with reduction, vacuum separation, and crushing.

[Explanation of symbols]

1 ... Reduction furnace, 2 ... Nozzle, 3 ... Reaction vessel 4 ... Vacuum separation furnace, 5 ... condenser 6 ... Cutting press

Claims (3)

[Claims] 1. A method for producing a low-oxygen titanium material from titanium sponge obtained by the Kroll method, wherein titanium sponge after vacuum separation is cooled in a reaction vessel, and then titanium sponge surface in the reaction vessel is nitrided. After forming the film, the sponge titanium is taken out from the reaction vessel and cut and / or crushed, which is a method for producing a low oxygen titanium material. 2. The method according to claim 1, wherein the formation of the nitride film is performed by introducing a low oxygen-containing nitrogen gas having a nitrogen partial pressure / oxygen partial pressure ratio of 20 or more into a reaction vessel. Manufacturing method of low oxygen titanium material. 3. The low oxygen titanium material according to claim 1, wherein the low oxygen content nitrogen gas is introduced after the temperature of the titanium sponge central portion becomes 200 ° C. or lower in the reaction vessel. Manufacturing method.