JP2001040432A - Recovery of titanium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable technique for recovering titanium by which aluminum bonded to titanium can more easily be dissolved away with acid, the control of the reaction is easy, complicated equipment is not needed, and the surface of titanium after pickling stay neat. SOLUTION: At the time of recovering titanium from a titanium material bonded with aluminum, aluminum is preferentially dissolved away with a mixed aq.soln. of hydrofluoric acid and hydrogen peroxide or a mixed aq.soln. obtd. by adding this with inorganic acid other than hydrofluoric acid, and titanium is allowed to remain. The mixed aq.soln. contg. 0.1 to 20% hydrofluoric acid and 10 to 80% hydrogen peroxide is desirable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering titanium by removing aluminum from a titanium material to which aluminum is bonded, in particular, a titanium target for sputtering.

[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 these circumstances, electronic and device devices have been miniaturized and the degree of integration has been increasing. Many thin films are formed in many of these manufacturing processes, and titanium is also used as a titanium film and its alloy film, titanium silicide film or titanium nitride film in many electronic device thin films due to its unique metallic properties. It's being used.

In general, the above-mentioned titanium film and its alloy film, titanium silicide film, titanium nitride film and the like are often formed by a sputtering method, and a target is used for that purpose. As is well known, the sputtering method is a method in which positive ions such as Ar ions are physically collided with a target provided on a cathode to release metal atoms constituting the target with the collision energy. Since considerable heat is received at the time of sputtering, the target is cooled from the back surface of the target in order to prevent the target from being deformed due to thermal expansion or the like. In this case, in order to increase the cooling efficiency of the target, the target is generally bonded to an aluminum or copper backing plate. A combination of such a target and a backing plate is generally called a target assembly. In addition, when the sputtering is continued as described above, a specific portion of the target is worn out (erosion). Therefore, after a certain number of uses, the target is replaced with a new target assembly.

[0004] Regarding the titanium target, unlike the commonly used structural titanium material, high-purity titanium is used. Particularly in semiconductor devices, radioactive elements such as U and Th as impurities have an adverse effect on MOS due to radiation,
Alkali and alkaline earth metals such as Na and K are MOS
Since transition metals such as Fe, Ni, and Cr or refractory metals such as Fe, Ni, and Cr cause junction leakage, it is necessary to effectively suppress such contamination so as not to contaminate the semiconductor device through the titanium material. For this purpose, strict component management is performed through a plurality of manufacturing steps of the titanium material, and the titanium target material is highly purified to the order of ppm for specific impurities. For this reason, the titanium target is an expensive material, but as described above, the entire target is not subjected to erosion on average.
Many other titanium materials have been replaced. Therefore, there is a strong demand for recovering expensive titanium materials from used titanium target materials.

[0005] Generally, a titanium target is diffusion bonded to an aluminum backing plate. When recovering titanium, it is necessary to remove this aluminum. Titanium and aluminum are both very insoluble in acids, and hydrofluoric acid (H
F) about. However, concentrated hydrofluoric acid is difficult to post-process, and fluorine itself is harmful.Dense hydrofluoric acid treatment involves a rapid temperature rise, so it is difficult to control the reaction and the equipment for cooling etc. becomes complicated. There's a problem. In addition, since the surface of titanium is oxidized after pickling with hydrofluoric acid, there is a disadvantage that it is difficult to regenerate the recovered titanium. As described above, the dissolution and removal of aluminum by concentrated hydrofluoric acid, which was considered to be only possible for dissolution, was extremely difficult due to the above problem, and the titanium recovery treatment had to be abandoned until now.

[0006]

SUMMARY OF THE INVENTION
The aluminum bonded to titanium can be selectively and easily dissolved and removed with an acid, and the reaction can be easily controlled.
It is an object of the present invention to develop a stable and effective titanium recovery technology that does not require complicated equipment and can keep the surface of titanium after pickling clean.

[0007]

According to the present invention, 1) when recovering titanium from a titanium material to which aluminum is bonded, aluminum is preferentially dissolved and removed using a mixed aqueous solution containing hydrofluoric acid and hydrogen peroxide. A method for recovering titanium, characterized by allowing titanium to remain, 2) hydrofluoric acid 0.1 to
The method for recovering titanium according to the above 1), which is a mixed aqueous solution containing 20% and 10 to 80% of hydrogen peroxide.
3) The method for recovering titanium according to 1) or 2) above, wherein the titanium material contains 10% or less of an inorganic acid other than hydrofluoric acid. 4) The titanium material to which aluminum is bonded is a titanium target for sputtering. The method for recovering titanium according to any one of the above items 1) to 3), which is characterized in that:

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies to achieve the above object, the present inventors have obtained the following findings.
That is, it was found that when a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide was used instead of concentrated hydrofluoric acid, no oxide film was formed on the titanium surface after pickling, and a very clean surface could be maintained. More importantly, aluminum is preferentially dissolved and removed. And the preferential dissolution of this aluminum, while hydrogen peroxide is present,
I found it to last.

As a result, the above-mentioned problem has been eliminated, and the problem of recovering titanium has been solved at once. It has been found that the mixed aqueous solution of hydrofluoric acid and hydrogen peroxide not only selectively and preferentially dissolves and removes aluminum, but also dissolves titanium oxide and aluminum oxide. As mentioned above, when only concentrated hydrofluoric acid is used,
The post-treatment was complicated, the control of the reaction was difficult, and there were problems such as complicated equipment such as cooling.However, since it was diluted with an aqueous hydrogen peroxide solution, the total amount of hydrofluoric acid could be reduced. In addition, the reaction was easily controlled, and the recovery rate of titanium was increased, thus enabling stable production.

The mixed aqueous solution for recovering titanium of the present invention is preferably a mixed aqueous solution of 0.1 to 20% hydrofluoric acid and 10 to 80% of hydrogen peroxide. If the amount of hydrofluoric acid is less than 0.1%, it is difficult to dissolve and remove aluminum even if an appropriate amount of hydrogen peroxide is present, and if the amount of hydrofluoric acid exceeds 20%, it is harmful to the human body as in the case of using concentrated hydrofluoric acid. Problems such as the generation of fluorine and leakage occur, and the reaction is rapid and accompanied by the generation of heat, making it difficult to control the reaction. In addition, the device becomes complicated, for example, a cooling device is required. Further, there is a problem that an oxide film is formed on the titanium surface. Therefore, hydrofluoric acid needs to be in the above concentration range. On the other hand, if the hydrogen peroxide is less than 10%, it is difficult to dissolve and remove aluminum preferentially even in the presence of hydrofluoric acid. Hydrogen peroxide in the mixed aqueous solution is consumed along with the dissolution and removal of aluminum, so it is necessary to replenish each time to maintain the above concentration. Further, even if the addition exceeds 80% of hydrogen peroxide, the effect of preferential dissolution and removal of aluminum is saturated, and the efficiency does not increase. Therefore, only the consumption of hydrogen peroxide is wasted, so that the above concentration range is desirable.

Further, the mixed aqueous solution of hydrofluoric acid and hydrogen peroxide may contain 10% or less of an inorganic acid (mineral acid) other than hydrofluoric acid. Examples of the inorganic acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, borofluoric acid, oxalic acid, lactic acid,
There are perchloric acid, citric acid and the like, and these acids are used alone or in combination of one or more. These acids further promote the preferential dissolution of aluminum, and have the effect of reducing the amount of particularly harmful hydrofluoric acid by that much. Further, rapid reaction or generation of heat is suppressed, and stable recovery of titanium can be achieved. However, the above inorganic acid is 10%
When the value exceeds, the effect is saturated and is wasted. Therefore, when these acids are added, the concentration is desirably within the above range.

[0012]

Next, the present invention will be described based on embodiments.
This embodiment is merely an example, and the present invention is not limited to this example. That is, the present invention can be modified or modified in modes other than the embodiments based on the technical idea, and the present invention covers all of them. A titanium target having a diameter of 320 mm and a thickness of 10 mm was used as a titanium target to be collected. Aluminum was bonded to one side (back side) of this target by about 0.5 mm. This titanium target was immersed in a mixed aqueous solution for titanium recovery composed of a mixed aqueous solution of 3.6 vol% of hydrofluoric acid and 72.2% of hydrogen peroxide. The initial temperature of the titanium recovery mixed aqueous solution is 30 ° C. The liquid temperature from immersion to 8 hours is 30 ° C
To 47 ° C.

Every hour after immersion, the dissolved weight of titanium and aluminum was measured and the dissolution rate (mg / cm ² · Hr)
I asked. The result is shown in FIG. The dissolution rate of titanium after 1 hour is 27.82 mg / cm ² · Hr, whereas the dissolution rate of aluminum is 28.71 mg / cm 2
It was ² · Hr. At this point, it can be said that there is not much difference in the dissolution rate. However, after 2 hours, the dissolution rate of titanium is 25.20 mg / cm ² · Hr,
The dissolution rate of aluminum is 55.67 mg / cm ² · H
r, and the dissolution rate of aluminum increased rapidly.
The tendency is that hydrofluoric acid 0.1-20% and hydrogen peroxide 10-10
The same effect was obtained when an 80% mixed aqueous solution was used. Further, when the mixed aqueous solution of hydrofluoric acid and hydrogen peroxide contains 10% or less of the above inorganic acids, these acids further promote the selective dissolution of aluminum,
It was confirmed that the amount of harmful hydrofluoric acid added can be kept low by that much, and that abrupt reaction or generation of heat can be suppressed and titanium can be recovered stably. As shown in the examples, it was confirmed that the present invention can easily and preferentially remove the thinly adhered aluminum from the titanium material by utilizing the difference in the dissolution rate.

[0014]

[Comparative Example] As a titanium target to be recovered, aluminum was 0.5 mm on one side (back side) as in the example.
A titanium target having a diameter of 320 mm and a thickness of 10 mm adhered to a degree was used. Then, this titanium target was immersed in a mixed aqueous solution for titanium recovery composed of a 3.6 vol% hydrofluoric acid aqueous solution. The initial temperature of the titanium recovery mixed aqueous solution was 30 ° C., but the liquid temperature for 8 hours after immersion changed between 30 ° C. and 50 ° C.

In the same manner as in the example, the dissolved weight of titanium and aluminum was measured every hour after immersion, and the dissolution rate (mg) was determined.
/ Cm ² · Hr). The result is shown in FIG. As shown in FIG. 2, the dissolution rate of titanium after 1 hour was 40
mg / cm ² · Hr, while the dissolution rate of aluminum is 50 mg / cm ² · Hr, and although the dissolution rate of aluminum is slightly higher, the dissolution rates are almost similar, and thereafter, the dissolution rates of both are linear. Dropped. In this comparative example, preferential dissolution and removal of aluminum was difficult. After pickling, the surface of the titanium was blackened and oxidized.

[0016]

According to the present invention, when only hydrofluoric acid is used, there are problems such as complicated post-treatment, difficult control of the reaction, and complicated equipment such as cooling. Instead
By using a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide or a mixed aqueous solution to which an inorganic acid other than hydrofluoric acid is further added, aluminum can be selectively and preferentially dissolved and removed. Has the remarkable effect that the dissolution of can be sustained while hydrogen peroxide is present. The mixed aqueous solution of hydrofluoric acid and hydrogen peroxide not only dissolves and removes aluminum preferentially but also dissolves titanium oxide and aluminum oxide to form a clean titanium surface. Has excellent effects. Furthermore, since it is diluted with an aqueous solution of hydrogen peroxide, the total amount of hydrofluoric acid can be reduced, and the reaction can be easily controlled. It has a remarkable effect that enables production.

[Brief description of the drawings]

FIG. 1 is a graph showing the dissolution rate (mg / cm ² · Hr) with respect to the elapsed time of titanium and aluminum in Examples.

FIG. 2 is a graph showing the dissolution rates (mg / cm ² · Hr) of titanium and aluminum with respect to elapsed time in a comparative example.

Claims (4)

[Claims] 1. When recovering titanium from a titanium material to which aluminum is bonded, aluminum is preferentially dissolved and removed using a mixed aqueous solution containing hydrofluoric acid and hydrogen peroxide to leave titanium. How to recover titanium. 2. Hydrofluoric acid 0.1-20% and hydrogen peroxide 10
2. The method for recovering titanium according to claim 1, wherein the mixed aqueous solution contains about 80%. 3. The method for recovering titanium according to claim 1, further comprising 10% or less of an inorganic acid other than hydrofluoric acid. 4. The method for recovering titanium according to claim 1, wherein the titanium material to which aluminum is bonded is a titanium target for sputtering.