JPH11350051A - Manufacture of titanium ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solidified titanium of high purity with high yield by giving the ultrasonic wave oscillation to a hearth in which a raw titanium is melted with the electronic beam, oscillating the molten metal in the hearth, and pouring it into a mold to promote the emission of impurities from the molten metal and to suppress the evaporation of titanium. SOLUTION: A melting material 5 of a raw titanium is melted by an electron beam 1 to generate a molten metal 6 in a hearth 3 at a lower part, and made to flow into a bottomless mold 4. The molten metal 6 is rapidly cooled in the mold 4 while keeping the molten condition with the electron beam 2, the generated solidified titanium 7 is lowered through a starting block 8 to obtain a titanium ingot. An ultrasonic wave oscillation device 9 is mounted on a bottom part of the hearth 3, and the ultrasonic wave oscillation of >=20 kHz in frequency is given to the hearth 3. The oscillation gives the oscillation mainly consisting of the perpendicular component to the molten metal 6 in the hearth to run its surface high. Impurities high in vapor pressure are evaporated from titanium in the molten metal and reduced in quantity to obtain the titanium ingot of high purity.

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 a titanium ingot suitable for producing high-purity titanium used as a wiring material for a semiconductor device.

[0002]

2. Description of the Related Art In recent years, high-purity titanium has been used as a wiring material for semiconductor devices. When titanium is used as a wiring material for a semiconductor element, it is necessary that the titanium be a high-purity titanium with a small amount of impurities, because impurities in the titanium cause deterioration of the performance of the semiconductor element.

[0003] For example, alkali metals such as Na and K easily move in silicon and cause deterioration of device characteristics. Radioactive elements such as U cause soft errors in the device due to α rays. Heavy metals such as Fe also cause troubles at the interface joint. Oxygen causes an increase in the electrical resistance of the thin film. For this reason, high-purity titanium with few impurities is required for the wiring material of the semiconductor element.

At present, the purity of high-purity titanium generally used as a wiring material for semiconductor elements is 4N5 (9
9.995%), alkali metals such as Na and K are 0.1 ppm or less, radioactive elements such as U are 1 ppb or less, heavy metals such as Fe are 10 ppm or less, and oxygen is 300 ppm or less.
pm or less.

However, as the degree of integration of semiconductor elements has increased, there has been an increasing demand for high-purity titanium used in wiring materials. As a method for producing high-purity titanium, an electron beam melting method is disclosed in JP-A-4-358030 and JP-A-3-130339.
And Japanese Patent Application Laid-Open No. Sho 62-280335. When a high melting point metal such as titanium is melted by an electron beam, a method using a hearth is generally used as disclosed in JP-A-6-287661.

In this electron beam melting method, the molten metal generated in the hearth by the irradiation of the electron beam is continuously injected into a bottomless mold, which solidifies in the mold and is continuously drawn downward. , To produce titanium ingots. According to the electron beam melting method, highly volatile elements such as Na and K are 0.1 ppm in a molten state.
It is easily reduced to: Further, elements such as Fe, Cr, and Al which have a higher vapor pressure than Ti and are easily evaporated can be reduced.

[0007]

In order to accelerate the release of impurities from the molten metal in the electron beam melting method, a method of increasing the temperature of the molten metal is considered. Further, it is considered that a method of extending the evaporation time of the molten metal or increasing the evaporation area of the molten metal is also effective. However, when the melting output of the electron beam is increased to increase the temperature of the molten metal, or when the melting speed is reduced to increase the evaporation time of the molten metal, the melting mold is enlarged to increase the evaporation area of the molten metal. In each case, the evaporation amount of titanium as a base material increases, and problems such as an increase in melting cost occur.

It is an object of the present invention to suppress the evaporation of titanium, which is a problem when promoting the release of impurities from a molten metal in an electron beam melting method, thereby enabling the production of titanium with a low impurity content and high purity. An ingot manufacturing method is provided.

[0009]

According to the investigations of the present inventors, the method of imparting vibration to the molten metal and making the surface of the molten metal ruffled to increase the surface area is very effective in promoting the release of impurities in the molten metal. It was confirmed that it was possible to effectively suppress the amount of titanium evaporated. However, the method of imparting vibration to the molten metal in the mold, as described in JP-A-6-287661, aims at reducing the crystal grain size. It turned out to be almost ineffective.

[0010] That is, JP-A-6-287661 discloses a method of applying vibration to a molten metal in a mold, a method of vibrating a mold and a method of vibrating a solidified metal continuously drawn downward from a mold. Although two are specifically described, since the solidified metal in the mold hardly contacts the inner surface of the mold, even if the mold is vibrated, the vibration is hardly transmitted to the solidified metal in the mold, Therefore, the molten metal held on the solidified metal hardly vibrates.

In addition, according to the investigation by the present inventors, it is effective to apply vibration in a direction perpendicular to the surface of the molten metal, particularly ultrasonic vibration, in order to effectively undulate the surface of the molten metal. It was confirmed that
Since the mold described in the above publication has no bottom and a structure in which a solidified metal penetrates the inside, when the mold is vibrated in the vertical direction, the vibration is hardly transmitted to the solidified metal. In any case, in the method of vibrating the mold, it is impossible to effectively vibrate the molten metal held on the solidified metal in the mold.

On the other hand, in the case of the method of vibrating the solidified metal continuously drawn downward from the mold, a vibration in the drawing direction is applied to a starting block or the like that supports the solidified metal from below, so that the solidified metal is temporarily set. Vibration can be imparted to the metal and solidification nuclei. However, in order to effectively release impurities in the molten metal, it is necessary to apply ultrasonic vibration in a direction perpendicular to the molten metal. Ultrasonic vibration is remarkably attenuated in titanium, so when applying vibration in the direction perpendicular to the molten metal to a starting block or the like, the amount of solidified metal pulled out is small in the early stage of casting and the direction perpendicular to the molten metal surface Vibration is applied, but during the casting in which the amount of solidified metal drawn out increases, vibration in the direction perpendicular to the molten metal is not effectively applied due to attenuation. Therefore, in the case of this method, there is a problem that ultrasonic vibration cannot be effectively applied.

Therefore, the present inventors have studied a method capable of effectively applying ultrasonic vibration in a direction perpendicular to the molten metal in the electron beam melting method. As a result, it was found that it is better to apply vibration to the hearth before the mold. That is, the hearth is a shallow dish, and the molten metal is housed in the shallow dish.If an ultrasonic vibrator is attached to the bottom of the hearth, ultrasonic vibration is applied to the hearth,
Ultrasonic vibration in the direction perpendicular to the molten metal in the hearth is effectively applied.

[0014] The method for producing a titanium ingot of the present invention comprises:
It has been developed based on the above-mentioned knowledge, and in a method of manufacturing a titanium ingot by melting a raw material titanium in a hearth by an electron beam melting method and then pouring a molten metal in the hearth into a mold, a vibration is applied to the hearth. It is characterized by giving.

The vibration applied to the hearth is preferably a vibration mainly composed of a component in a direction perpendicular to the molten metal in the hearth. This vibration is also preferably an ultrasonic vibration having a frequency of 20 kHz or more.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an electron beam melting furnace used for performing a method for manufacturing a titanium ingot according to an embodiment of the present invention.

The electron beam melting furnace includes electron guns 1 and 2 for irradiating an electron beam downward into the furnace, a hearth 3 and a mold 4 disposed below each of the electron guns 1 and 2, and a hearth 3.
And a vibrating device 9 attached to the bottom surface. The hearth 3, which is a shallow dish, and the mold 4 having a bottomless structure,
Both are made of water-cooled copper.

One of the electron guns 1 irradiates an electron beam to a molten material 5 supplied thereunder to generate a molten titanium 6 in a lower hearth 3. The molten metal 6 generated in the hearth 3 flows into the mold 4 and is quenched into solidified titanium 7. The other electron gun 2 irradiates the molten metal 6 flowing into the mold 4 with an electron beam in order to form a predetermined amount of molten metal 6 on the solidified titanium 7.

The solidified titanium 7 is a starting block 8
When the starting block 8 is lowered in accordance with the amount of the molten metal 6 flowing into the mold 4, the solidified titanium 7 is gradually pulled downward in accordance with the growth thereof, and the solidified titanium 7 is pulled out by a predetermined length. It becomes a titanium ingot.

The vibration device 9 attached to the bottom of the hearth 3 generates ultrasonic waves mainly in the vertical direction, and applies the ultrasonic waves to the hearth 3. As a result, the molten metal 6 in the hearth 3 is subjected to ultrasonic vibration in a direction perpendicular to the molten metal.

As the melting material 5, for example, a rod-shaped titanium compact manufactured and compacted by the Kroll method is used.

In the method for manufacturing a titanium ingot according to the embodiment of the present invention, the titanium inside the hearth 3 is irradiated with the electron beam from the electron gun 1 while the inside of the electron beam melting furnace is sucked and evacuated to a predetermined degree of vacuum. Is produced, and the molten metal 6 is injected into the mold 4 from within the hearth 3 to produce a titanium ingot.

At this time, the impurities in the molten metal 6 are released to the outside in the hearth 3, but the ultrasonic vibration in a direction perpendicular to the molten metal 6 is applied to the hearth 3 by the operation of the vibration device 9 attached to the bottom surface. Since the ultrasonic vibration is applied to the molten metal 6 in a direction perpendicular to the molten metal, the surface of the molten metal 6 is wavy. Thereby, emission of impurities is promoted while evaporation of titanium from the molten metal 6 is suppressed. The reason is considered as follows.

The amount of impurities released from the surface of the titanium melt in the electron beam melting method is constant for each element under the same melting conditions. This is because when the molten metal is retained as it is, impurities on the surface of the molten metal are first released, and then impurities transferred to the surface of the molten metal by diffusion are released. However, when vibration is applied to the molten metal in a direction perpendicular to the molten metal, it is considered that the release of impurities is promoted by two synergistic effects of an increase in surface area due to the undulation of the molten metal and promotion of diffusion of impurities in the molten metal.

In the electron beam melting, the vibration device 9 can be attached to the bottom surface of the hearth 3, whereby
It is also important that the hearth 3 efficiently oscillates ultrasonically in a direction perpendicular to the surface of the molten metal 6 and that the vibration is efficiently transmitted to the molten metal 6 in the hearth 3.

As described above, in the method for manufacturing a titanium ingot according to the embodiment of the present invention, impurities are efficiently reduced in the electron beam melting process. The produced titanium ingot can be further purified to a higher purity by an iodide pyrolysis method or the like. Also, high-purity titanium purified by an iodide pyrolysis method or the like can be purified by the method for producing a titanium ingot.

In the above-described embodiment, the ultrasonic vibration is applied to the hearth 3, but it is also possible to apply vibration having a lower frequency than the ultrasonic wave by changing the vibration device 9. When a low-frequency vibration such as 20 Hz or less is applied, the hearth 3 can be tiltably supported in a cantilever manner, and the non-supporting side can be vertically reciprocated by a vibration device.

[0028]

EXAMPLES Next, examples of the present invention will be shown, and the effects of the present invention will be clarified by comparing with the conventional example.

Using the electron beam melting furnace shown in FIG.
High-purity titanium with an outer diameter of 50 mm manufactured by the roll method
Electron beam melting was performed using the rod as a melting material. Haas
Has an effective volume of 300,000 mm made of water-cooled copper^Three, Dissolved
Hot water surface area is 10,000mm ^TwoIt is a dish. Mold
It is a cylindrical body made of water-cooled copper and having an inner diameter of 100 mm.

The frequency of the vibration applied to the hearth is 20 kHz.
z, 100 Hz, and 5 Hz. The vibration of 20 kHz was applied by an ultrasonic vibration device attached to the bottom surface of the hearth. Vibrations of 100 Hz and 5 Hz were applied by an electric vibrating device that supported the hearth in a cantilever manner and was attached to the opposite side. Both vibration directions are vertical directions, that is, directions perpendicular to the molten metal.

The vibration of 20 kHz is applied to the horizontal direction by an ultrasonic vibrator attached to the side of the hearth.
That is, vibration in a direction parallel to the molten metal was also applied.

The irradiation output of the electron beam to the molten metal in the hearth and the mold was set to 20 kW and 25 kW, respectively. This output is a condition under which the amount of titanium evaporated from the molten metal is 5% or less. The degree of vacuum in the furnace is 1.0 × 10 ^-2 P
a, The dissolution rate was 10 kg / hour.

For comparison, the hearth was melted without applying vibration. Instead of applying vibration to the hearth, the starting block was ultrasonically vibrated in the vertical direction. The degree of vacuum and the dissolution rate were the same.

Table 1 shows the results of impurity analysis of the manufactured titanium ingot and the dissolved material.

[0035]

[Table 1]

By applying vibration to the hearth, impurities in the molten metal are removed. Also, no oxygen pickup occurs. This effect increases as the frequency increases, and a particularly remarkable effect is obtained with ultrasonic vibration. The direction of vibration is effective in a direction perpendicular to the molten metal.

The vibration of the solidified titanium caused by the vibration of the starting block may be effective for the bottom part of the ingot cast in the early stage of melting, but is effective for the other parts by damping the vibration. Absent.

[0038]

As described above, the method for manufacturing a titanium ingot of the present invention can effectively reduce impurities in titanium by applying vibration to the hearth in the electron beam melting method. In addition, high-purity titanium used as a wiring material for a semiconductor element can be manufactured with high productivity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an electron beam melting furnace used in a method for manufacturing a titanium ingot according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 2 electron beam 3 hearth 4 mold 5 molten material 6 molten metal 7 solidified titanium 8 starting block 9 vibrating device

Claims (3)

[Claims] 1. A method for manufacturing a titanium ingot by melting raw titanium in a hearth by an electron beam melting method and then pouring a molten metal in the hearth into a mold, wherein vibration is applied to the hearth. Manufacturing method of titanium ingot. 2. The method for producing a titanium ingot according to claim 1, wherein the vibration applied to the hearth is a vibration mainly composed of a component perpendicular to the molten metal in the hearth. 3. The method according to claim 1, wherein the vibration applied to the hearth is an ultrasonic vibration having a frequency of 20 kHz or more.