JP2000204494A - High-purity titanium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively produce high-purity titanium to be used in a sputtering target suppressing the contamination due to the mutual diffusion between the substances constituting a laminated thin film and not causing the generation of particles or an abnormal discharge. SOLUTION: High-purity titanium tetrachloride is used to conduct fused-salt electrolysis, and further the volatile component is removed by an electron-beam melting method, or the like, to obtain a high-purity titanium material. The total content of the heavy metals such as Fe, Cr, Ni and Cu, light metals such as Al, alkali metals such as Na and K and the radioactive elements such as Th is controlled to <=50 ppm, preferably to <=10 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-purity titanium obtained by subjecting TiCl ₄ to molten salt electrolysis and further melting by electron beam or the like, and a method for producing the same. It relates to high-purity titanium that can be used.

[0002]

2. Description of the Related Art In recent years, a variety of electronic devices have been born starting from the dramatic progress of semiconductors, and their performance has been improved and new devices have been developed every day. Under such circumstances, there is a tendency that the size of electronic devices and device devices is further reduced and the degree of integration is increased. Numerous thin films are formed in many of these manufacturing processes, and titanium has many unique thin film properties due to its unique metallic properties, such as titanium and its alloy films, titanium silicide films, or titanium nitride films. It is used for When forming such a thin film of titanium (including alloys and compounds), care must be taken that
As such, it requires extremely high purity.

[0003] Thin films used in semiconductor devices and the like tend to be thinner and shorter, and the distance between them is extremely small and the integration density is improved. The problem arises that impurities to be diffused into the adjacent thin film. As a result, the balance between the constituent materials of the self-film and the adjacent film is lost, and a major problem occurs in that the function of the film that must be originally possessed is reduced. In the process of manufacturing such a thin film, the thin film may be heated to several hundred degrees, and the temperature may increase during use of an electronic device incorporating the semiconductor device. Such a rise in temperature further increases the diffusion coefficient of the substance, and causes a serious problem in that the function of electronic devices is reduced due to diffusion.

In general, the above-mentioned titanium and its alloy film, titanium silicide film, titanium nitride film and the like can be formed by physical vapor deposition such as sputtering and vacuum vapor deposition. The most widely used sputtering method among them will be described. This sputtering method is a method in which positive ions such as Ar + physically collide with a target provided on a cathode, and metal atoms constituting the target are emitted with the collision energy. The nitride can be formed by using titanium or an alloy thereof (such as a TiAl alloy) as a target and performing sputtering in a mixed gas atmosphere of argon gas and nitrogen.

In the formation of this sputtering film, if impurities are present in the titanium (alloy / compound) target, coarse particles floating in the sputtering chamber adhere to the substrate and short-circuit the thin-film circuit, When the amount of generated particles that cause substances increases, and when gas components such as oxygen, carbon, hydrogen, and nitrogen are present, an abnormal discharge that is considered to be caused by the sudden occurrence of the gas occurs during sputtering, and a uniform film is formed. The problem of not being formed occurs.

For these reasons, it has been desired to produce high-purity titanium in which gas components such as transition metals, refractory metals, alkali metals, alkaline earth metals or other metals, which are impurities, and oxygen are reduced. Was rare. Conventionally, as a method for producing this high-purity titanium, titanium tetrachloride (Ti
Cl ₄ ) is reduced by magnesium (Mg), and a method of refining crude titanium by molten salt electrolysis is used. However, it was not satisfactory from both viewpoints of cost reduction and high purification. For example, when high-purity titanium is obtained by the above-mentioned Kroll method, the cost is significantly increased, for example, by cutting and using only a high-purity portion of the obtained titanium material. Moreover, according to these ordinary methods, alkali metals, transition metals, radioactive elements, and other metals are contained in large amounts, and the content of oxygen is high. High purification of titanium has not been realized.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and in particular, suppresses contaminants caused by mutual diffusion of materials constituting a laminated thin film, and produces a sputtering target free from particles and abnormal discharge. It is an object of the present invention to provide a high-purity titanium that can be used at low cost.

[0008]

The technical means for solving the above problems is to control high-purity titanium which can be used for a sputtering target or the like by controlling impurities by strictly controlled molten salt electrolysis. The knowledge that it can be obtained was obtained. Based on this finding, the present invention relates to a high-purity titanium material obtained by subjecting titanium tetrachloride to molten salt electrolysis and further removing volatile components by electron beam melting or the like, such as heavy metals such as Fe, Cr, Ni, and Cu; High purity titanium 2 Fe, heavy metals such as Cr, Ni, Cu, etc., characterized in that the total content of light metals, alkali metals such as Na and K and radioactive elements such as U and Th is 50 ppm or less. The total content of light metals, alkali metals such as Na and K, and radioactive elements such as U and Th is 10 ppm or less. The high-purity titanium 3 according to 1 above, wherein oxygen is 200 ppm or less and carbon is 50 ppm or less.
high purity titanium 4 Fe, Cr, Ni, Cu, etc., heavy metals such as Al, light metals such as Al, alkali metals such as Na and K, and radioactivity such as U, Th, etc. A method for producing high-purity titanium, comprising subjecting molten salt electrolysis to titanium tetrachloride having a total content of elements of 10 ppm or less and further performing electron beam melting. 5 Molten salt electrolysis using titanium tetrachloride having a total content of heavy metals such as Fe, Cr, Ni, and Cu, light metals such as Al, alkali metals such as Na and K, and radioactive elements such as U and Th that are 5 ppm or less. 5. The method for producing high-purity titanium according to the above item 4, wherein the method comprises:

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, molten salt electrolysis is performed using high-purity titanium tetrachloride (TiCl ₄ ), and volatile components are removed by electron beam melting or the like.
The total content of heavy metals such as Cu, light metals such as Al, alkali metals such as Na and K, and radioactive elements such as U and Th is 50 p.
pm or less, preferably 10 ppm or less. The purpose of dissolving an electron beam or the like is to remove volatile components. Therefore, as an alternative to the electron beam, a plasma melting method, a vacuum arc melting method, an induction melting method, or the like can be used, but from the viewpoint of stable manufacturing conditions, the electron beam melting method is particularly preferable. The titanium material has a strong bond with oxygen and necessarily has a high content.
ppm or less, preferably 50 ppm or less. Carbon as other gas components is 50 ppm, and nitrogen and oxygen are each 10 ppm or less. Other elements such as sulfur, phosphorus, and chlorine are each 10 ppm or less.

Conventionally, the purity of titanium tetrachloride was low, and it was not considered that high purity titanium could be obtained by molten salt electrolysis. However, the purity of titanium tetrachloride was increased by distillation.
This was achieved by using high corrosion resistant nickel, tantalum and graphite as the material of the apparatus used in the molten salt electrolysis apparatus and preventing contamination caused by the material of the apparatus. As the distillation method, multistage distillation under a weak reduced pressure or under an inert atmosphere is preferable. At the time of molten salt electrolysis, Fe obtained by such a distillation method,
Heavy metals such as Cr, Ni and Cu, light metals such as Al, Na,
Titanium tetrachloride having a total content of alkali metals such as K and radioactive elements such as U and Th of 10 ppm or less is used.

In the stage of molten salt electrolysis of titanium tetrachloride (TiCl ₄ ), alkali metals such as sodium and potassium usually increase to 200 ppm. Since these alkali metal elements move in the gate insulating film and deteriorate the MOS interface characteristics, they are impurities particularly disliked in semiconductor devices. These alkali metal elements can be easily removed by electron beam melting or the like.
It can be reduced to: Similarly, transition metals, heavy metals, and light metals that generate interface states and cause junction leakage can be reduced to 5 ppm or less, and radioactive elements that adversely affect MOS devices can be reduced to 1 ppb or less.

[0012]

Embodiment 1 Next, an embodiment of the present invention will be described.
This embodiment is merely an example, and the present invention is not limited to this example. That is, the present invention is limited only by the scope of the claims, and covers all aspects or modifications other than the examples included in the present invention. In the embodiment of the present invention, a chloride bath of a sodium chloride (NaCl) -potassium chloride (KCl) bath was used as the electrolytic bath. As the electrolytic bath, a chloride-fluoride bath or a fluoride bath can be used. Prior to use, this electrolytic bath was subjected to preliminary electrolysis at 30 A for 20 hours to remove impurities and moisture. Nickel, which has high corrosion resistance, was used for the electrolytic cell and its peripheral devices to prevent contamination of impurities and contamination. In addition, high-purity graphite was used for the anode from which chlorine gas was generated, and porous graphite was used for the diaphragm.

FIG. 1 is a schematic explanatory view of an electrolysis apparatus used for carrying out the present invention. Reference numeral 1 denotes an introduction pipe for introducing titanium tetrachloride into the electrolytic bath 5. Since chlorine gas is generated on the anode 3 side as described above, it is necessary to prevent the chlorine gas from going to the cathode 2 side by the anode diaphragm 4. The generated chlorine gas can be used as a source for converting titanium as a raw material into titanium tetrachloride. This may be subjected to waste liquid treatment with sodium hydroxide or the like. Reference numeral 6 denotes a gate valve, and reference numeral 7 denotes a neutralization tank for generating the chlorine gas or a pipe for discharging the chlorine gas.

The titanium tetrachloride introduced on the cathode side is 9
9% pure titanium tetrachloride is distilled in advance to give 99.99% pure titanium tetrachloride. Specifically put titanium tetrachloride in a glass container, a weak reduced pressure or an inert atmosphere (Ar, N ₂
Etc.), multistage distillation was performed at a temperature of 120 ° C. This is important in obtaining the high-purity titanium material of the present invention, and by using titanium tetrachloride having such high purity, high-purity titanium can be obtained by direct molten salt electrolysis. The titanium tetrachloride (TiCl ₄ ) is TiCl ₂
It is more preferable to convert to and introduce. Electrolysis temperature is 68
0 ° to 850 ° C, cathode initial current density 0.25A /
Electrolyzed at cm ² .

Table 1 shows the impurity analysis values of titanium tetrachloride, electrolytically deposited titanium, and ingot after electron beam melting. Alkali metal elements are greatly increased by molten salt electrolysis,
Since it can be greatly reduced by electron beam melting, there is no particular problem. U, Th of radioactive element
Is concentrated in the bath at the time of electrolysis, so that it is further reduced as an impurity of electrolytically deposited titanium. In addition, it increases during molten salt electrolysis and electron beam melting, but such an increase does not pose a problem. In any case, high-purity titanium can be obtained at lower cost than in the conventional method.

[0016]

[Table 1]

[0017]

Example 2 Electrolysis was performed under the same conditions as in Example 1 except that electrolysis was performed at a cathode initial current density of 0.8 A / cm ² . Table 2 shows the results. Fe and Cr tend to slightly increase, but all other impurities are further reduced as compared with Example 1. In particular, the reduction of gas components such as oxygen and carbon is remarkable. In addition, it can be seen that the purity is significantly improved in each case as compared with the comparative examples described below.

[0018]

[Table 2]

[0019]

[Comparative Example] Next, an example in which molten salt electrolysis and electron beam melting are performed using a conventionally used material having a low purity of titanium tetrachloride will be described. The conditions of the molten salt electrolysis and the electron beam melting are the same as in the first embodiment. Table 3 shows the impurity analysis values of the titanium tetrachloride used in this case, the electrolytically deposited titanium after the electrolysis of the molten salt, and the ingot after the electron beam melting. As is clear from the comparison between the above example and this comparative example, the electrolytically deposited titanium obtained by the comparative example shows a slight decrease in radioactive elements, but heavy metals, light metals, and any gas components such as oxygen. Has also increased significantly. Further, in the ingot after the electron beam melting, a decrease in the alkali metal element is observed, but other impurities continue to be large, and it can be seen that both are much inferior to Examples 1 and 2.

[0020]

[Table 3]

Next, the titanium materials of the example and the comparative example thus obtained were processed into a target shape, and the electrical resistance of the film formed by sputtering and the number of generated particles were compared. Table 4 shows the results. As is clear from Table 4, the electric resistance of each of Examples 1 and 2 of the present invention was 7.4 μΩ · cm in the comparative example, whereas
It is 6.9 μΩ · cm and 6.5 μΩ · cm. In addition, the number of generated particles is 50 / wafer in the comparative example, but 25 / wafer and 10 / wafer in Examples 1 and 2, respectively, and the present invention is superior in both cases. As described above, since the purity of the present invention is improved, the electric resistance is reduced, and the number of particles generated during sputtering is significantly reduced.

[0022]

[Table 4]

[0023]

According to the present invention, molten salt electrolysis is performed using high-purity TiCl ₄ to obtain high-purity electrodeposited (deposited) titanium, which is further dissolved by an electron beam or the like to remove volatile components. Can be obtained at low cost and under stable production conditions. In addition, by sputtering using a target manufactured from the melted titanium ingot, a high-purity titanium (alloy or compound) thin film having few impurities and particularly suitable for a semiconductor device can be formed. And the electrical resistance is small.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a titanium tetrachloride electrolytic device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Introduction pipe of titanium tetrachloride 2 Cathode 3 Anode 4 Anode diaphragm 5 Electrolysis bath 6 Gate valve 7 Discharge pipe toward neutralization tank or titanium reaction tank

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K001 AA27 BA08 DB21 EA01 FA13 GA13 4K058 AA11 BA10 BB06 CB03 CB04 CB17 CB23 DD02 ED03

Claims (5)

[Claims] 1. A high-purity titanium material obtained by subjecting titanium tetrachloride to molten salt electrolysis and further removing volatile components by electron beam melting or the like, comprising heavy metals such as Fe, Cr, Ni, and Cu;
High-purity titanium characterized in that the total content of light metals such as Na and K, alkali metals such as Na and K and radioactive elements such as U and Th is 50 ppm or less. 2. A heavy metal such as Fe, Cr, Ni, or Cu;
l, alkali metals such as Na and K, and U, Th
2. The high-purity titanium according to claim 1, wherein the total content of radioactive elements such as is 10 ppm or less. 3. The method according to claim 1, wherein oxygen as an impurity is 200 ppm or less.
The carbon content is 50 ppm or less.
Or the high-purity titanium according to 2. 4. A heavy metal such as Fe, Cr, Ni, or Cu;
l, alkali metals such as Na and K, and U, Th
A molten salt electrolysis using titanium tetrachloride having a total content of radioactive elements such as 10 ppm or less, followed by electron beam melting, and a method for producing high-purity titanium. 5. A heavy metal such as Fe, Cr, Ni, Cu, etc., A
l, alkali metals such as Na and K, and U, Th
The method for producing high-purity titanium according to claim 4, wherein molten salt electrolysis is performed using titanium tetrachloride having a total content of radioactive elements such as 5 ppm or less.