JP5019285B2 - Method for producing high purity zirconium powder - Google Patents

Description

The present invention is low in impurities, particularly alkali metal elements such as Na and K, radioactive elements such as U and Th, transition metals or heavy metals such as Fe, Ni, Co, Cr, Cu, Mo, Ta, and V, or a high melting point. The present invention relates to a method for producing a high-purity zirconium powder , which can obtain a high-purity zirconium powder in which the content of gas components such as metal elements and gas components such as C and O is extremely reduced at a low cost.

Conventionally, a silicon (SiO ₂ ) film has been used as a gate oxide film in a semiconductor device. However, as a recent trend of semiconductor devices, a tendency toward thinning and downsizing is remarkable, and particularly when such a gate oxide film is thinned, Problems such as insulation resistance, boron penetration, gate leakage, and gate depletion occur.
Therefore, useless in conventional silicon, must be using a high dielectric constant material than silicon, it has a high dielectric constant of around 20 Such materials, contemplated for use mix hard ZrO ₂ and Si .
However, ZrO ₂ be easily passed through the oxidizing agent, and because there is a disadvantage that by forming a small interfacial layer dielectric constant in the film forming time and a subsequent annealing is believed the use of ZrSi ₂ instead of ZrO ₂ .
When used as such a gate oxide film or silicide film, it is considered that the Zr target or these silicide targets are formed by sputtering in an inert gas atmosphere such as argon or in a reactive gas atmosphere. In either case, Zr is the central raw material.

On the other hand, as a material used for a semiconductor device, in order to guarantee the operation performance as a reliable semiconductor, impurities that are harmful to the semiconductor device are included in the above-mentioned material formed after sputtering as much as possible. It is important to reduce it.
That is,
(1) Alkali metal elements such as Na and K (2) Radioactive elements such as U and Th (3) Transition metals or heavy metals such as Fe, Ni, Co, Cr and Cu, or refractory metal elements (4) C and O It is necessary to reduce the gas component elements such as N, H, and the like as much as possible and to have a purity of 4N, that is, 99.99% (weight) or more. In addition,%, ppm, and ppb used in this specification all indicate% by weight, ppm by weight, and ppb by weight.
Alkaline metals such as Na and K, which are impurities present in the semiconductor device, easily move through the gate insulating film and cause deterioration of MOS-LSI interface characteristics. Radioactive elements such as U and Th are more The emitted alpha rays cause a soft error of the device, and transition metals such as Fe, Ni, Co, Cr, and Cu, or heavy metals or refractory metal elements contained as impurities may cause trouble at the interface junction. I know.

As shown in Table 1, the raw material zirconium sponge having a purity of 3N level, which is generally obtained, is Co: 10 ppm, Cr: 50 ppm, Cu: 10 ppm, Fe: 50 ppm, Mn: 25 ppm, Nb: 50 ppm, Ni: 35 ppm, Ta: A large amount of impurities such as 50 ppm, C: 2000 ppm, O: 5000 ppm, N: 200 ppm are contained.
All of these impurities impede the operation function as a semiconductor, and it is necessary to efficiently remove impurities that are harmful to such semiconductor devices.
However, in the past, zirconium has been rarely used as a gate oxide film in semiconductor devices, and the purification technology for removing these impurities is special and expensive, so it is equivalent to being left unconsidered. It was in a state.

Generally, zirconium is highly purified by an electron beam melting method. However, when manufacturing a sputtering target using the highly purified zirconium as a raw material as described above, it is necessary to manufacture highly purified zirconium powder. .
Therefore, after the high purity zirconium obtained by the above electron beam melting method is cast into an ingot, it is necessary to further form a powder. Powdering from an ingot is usually performed by crushing, but high-purity zirconium powder has a risk of ignition and explosion, and powdering from an ingot is dangerous. For this reason, there is a problem that the process of pulverizing from the ingot needs to be adequately controlled and the cost is increased.

The present invention reduces impurities that hinder the operation performance of the semiconductor as described above, that is, alkali metal elements such as Na and K, radioactive elements such as U and Th, Fe, Ni, Co, Method for producing high-purity zirconium powder capable of safely and inexpensively obtaining high-purity zirconium powder in which the content of transition metals such as Cr, Cu, Mo, Ta, V, or heavy metals or refractory metal elements is extremely reduced And a method for producing high-purity zirconium powder that is useful for a zirconium sputtering target with a small amount of gas components that can effectively reduce the generation of particles during sputtering by suppressing the generation of gas components such as oxygen and carbon. It is a problem to obtain.

From the above, the present invention
1. Zirconium raw material is melted by electron beam and purified to ingot, and the resulting high purity zirconium ingot is acid washed and then heated to 500 ° C or more in a hydrogen atmosphere to hydrogenate the zirconium hydride powder. A step of obtaining hydrogenated high-purity zirconium powder by peeling off from the substrate, or acid-washing the chips obtained by cutting the high-purity zirconium ingot, and then heating to 500 ° C or higher in a hydrogen atmosphere to hydrogenate hydrogenated hydrogen A method for producing high-purity zirconium powder, comprising a step of obtaining zirconium fluoride powder , and a step of removing hydrogen from the hydrogenated high-purity zirconium powder, wherein an impurity content excluding gas components is less than 100 ppm. provide.
In addition, the present invention
2. Zirconium raw material is melted by electron beam and purified to ingot, and the resulting high purity zirconium ingot is acid washed and then heated to 500 ° C or more in a hydrogen atmosphere to hydrogenate the zirconium hydride powder. A step of obtaining hydrogenated high-purity zirconium powder by peeling off from the substrate, or acid-washing the chips obtained by cutting the high-purity zirconium ingot, and then heating to 500 ° C or higher in a hydrogen atmosphere to hydrogenate hydrogenated hydrogen Comprising a step of obtaining zirconium oxide powder and a step of removing hydrogen from the hydrogenated high-purity zirconium powder. The total content of alkali metal elements such as Na and K is 1 ppm or less, and the content of radioactive elements such as U and Th The total amount is 5 ppb or less, and transition metals such as Fe, Ni, Co, Cr and Cu excluding Hf or heavy metals or refractory metal elements There is provided a method for producing high-purity zirconium powder, characterized in that the total is 50 ppm or less and the balance is zirconium and other inevitable impurities .

Furthermore, the present invention
3. The total content of alkali metal elements such as Na and K is 1 ppm or less, the total content of radioactive elements such as U and Th is 5 ppb or less, transition metals such as Fe, Ni, Co, Cr and Cu excluding Hf, or 2. The method for producing high-purity zirconium powder according to 1 above, wherein the total amount of heavy metals or refractory metal elements is 50 ppm or less, and the balance is zirconium and other inevitable impurities .
4). 4. The method for producing high-purity zirconium powder according to any one of 1 to 3, wherein the hydrogenation is performed by heating to 700 ° C. or higher in a hydrogen atmosphere.
5. The method for producing high-purity zirconium powder according to any one of the above 1 to 4, wherein an inert gas such as argon is introduced during cooling.
6). 6. The method for producing a high purity zirconium powder according to any one of the above 1 to 5, wherein an ingot or cutting powder is cooled to 500 ° C. or less to obtain a hydrogenated high purity zirconium powder .
7). The high-purity zirconium powder spalled from the ingot further process for producing a high-purity zirconium powder according to any one of the above 1 to 6, characterized in that grinding.
8). The method for producing high-purity zirconium powder according to any one of 1 to 7 above, wherein hydrogen is removed by heating in a vacuum or in an inert atmosphere.

By the electron beam melting method, impurities that hinder the operation function of the semiconductor, that is, alkali metal elements such as Na and K, radioactive elements such as U and Th, Fe, Ni, Co, Cr, Cu, Mo, A high-purity zirconium powder in which transition metals such as Ta and V or heavy metals or refractory metal elements are extremely reduced has an excellent effect of preventing dangers such as ignition and explosion and can be produced at low cost.
Moreover, it is possible to obtain a zirconium sputtering target with a small amount of gas components that can effectively reduce the generation of particles during sputtering by suppressing the generation of gas components such as oxygen and carbon, and the like such as a gate oxide film in a semiconductor device. It has the remarkable feature that high purity zirconium powder useful for production can be obtained.

In the present invention, a zirconium sponge raw material of 2N to 3N level which is generally commercially available is used as a raw material for electron beam melting. A large amount of contaminants such as organic substances (impurities C increase) and inorganic substances adhere to these surfaces, which are removed by hydrofluoric acid having a strong cleaning effect.
Usually, the sponge raw material is compressed by a press to make it compact so that the electron beam can be melted after cleaning the surface of the sponge, but in this case, the problem is that the zirconium sponge raw material is very brittle and collapses. is there.
For this reason, a compact material is formed by wrapping with a foil of a volatile element such as Al, Zn, Cu, and Mg. It is desirable to melt the electron beam while putting this compact material into the electron beam melting furnace.
In the compact material, since the electron beam melting is performed in a vacuum, the volatile metal element is volatilized and removed together with the gas component, the molten metal, or other impurities floating on the molten metal element immediately after melting. Must not.

By this purification by electron beam melting, high-purity zirconium having an impurity content excluding gas components such as oxygen and carbon of less than 100 ppm can be obtained. That is, 4N (99.99%) high-purity zirconium can be produced.
Zirconium contains a considerable amount of hafnium, and it may be difficult to separate and purify between them, but it is not harmful for the intended use of each material and can be ignored.

As described above, in high purity zirconium , the content of impurities that lower the function of the semiconductor material, that is, the content of alkali metal elements such as Na and K is 1 ppm or less in total, and the content of radioactive elements such as U and Th is 5 ppb in total. Hereinafter, transition metals or heavy metals such as Fe, Ni, Co, Cr, and Cu other than Hf, or refractory metal elements are 50 ppm or less in total, and can be reduced to a problem level or less.

Zirconium melted and purified to high purity is cast into an ingot. Next, this high-purity zirconium ingot or chips that have been subjected to acid cleaning with a large surface area are heated to 500 ° C. or higher in a hydrogen atmosphere to be hydrogenated. This step is an important step in obtaining fine zirconium powder.
At the time of hydrogenation, the ingot or chips are put into a furnace in a hydrogen atmosphere or air stream as described above, and heated to 500 ° C. or higher. The zirconium ingot starts to be hydrogenated at about 500 ° C., and the hydrogenation progresses rapidly at 700 ° C. If kept in this furnace temperature for 10 minutes or more, a considerable amount is hydrogenated.

When this is cooled to a temperature of 500 ° C. or less, the hydrogenated zirconium peels off (peels) from the surface of the ingot. The atmosphere in the cooling furnace is preferably an inert gas atmosphere such as argon. When hydrogenation is not sufficient, hydrogenation can be easily performed by repeating the above operation.
Some of the peeled material is powdered even in this state, but the flaky material can be pulverized as necessary to obtain fine zirconium hydride powder .
The fine zirconium hydride powder thus obtained has a remarkable effect that it can be stably and easily produced, unlike the case of a single zirconium powder , without the risk of ignition and explosion. Furthermore, since it is a powdering step in a reducing (hydrogen) atmosphere, there is an advantage that oxidation of the ingot and oxidation of the powder can be prevented.
The zirconium hydride powder can be used as it is depending on the application. However, when dehydrogenation is required, the hydrogen can be easily removed by heating in a vacuum or in an inert atmosphere. be able to. As a result, external contamination and oxidation can be prevented, and high-purity zirconium powder can be easily obtained.

Next, the present invention will be described based on examples. The examples are for easy understanding of the present invention, and the present invention is not limited thereby. That is, the present invention includes other embodiments and modifications based on the technical idea of the present invention.
Example 1
The raw material zirconium sponge of purity (3N level) shown in Table 1 was washed with hydrofluoric acid to remove impurities adhering to the surface, and then wrapped with Zn foil to make it compact. The raw material zirconium sponge shown in Table 1 shows only main impurities.
Next, this compact was introduced into an electron beam melting furnace to perform electron beam melting. The conditions for electron beam melting are as follows.
Degree of vacuum: 2 × 10 ⁻⁴ Torr
Current: 1.25A
Casting speed: 20kg / hr
Power source unit: 4kwh / kg

After melting the electron beam, it was cast into a high purity zirconium ingot. At the time of electron beam melting, the Zn foil was volatilized at the time of electron beam melting, and the amount contained in zirconium was less than 0.1 ppm.
Although it was attempted to make it compact by compacting only with a zirconium sponge by pressing without being wrapped with such a foil of Zn or the like, it collapsed in the middle of the pressing operation and could not be made compact. Therefore, wrapping with a foil of a volatile element such as Al, Zn, Cu, and Mg is a desirable condition for producing the high-purity zirconium.

Next, 1 kg was taken from the high-purity zirconium ingot, put into a hydrogen atmosphere furnace, kept in a hydrogen stream at 800 ° C. for 30 minutes, and then cooled. When the temperature reached 400 ° C. by cooling, hydrogen was replaced with argon, and after cooling to room temperature, the ingot was taken out.
As a result, zirconium powder in which 30% of the ingot, that is, 300 g was hydrogenated was obtained. Thereafter, the same operation was performed again on the non-hydrogenated zirconium, and as a result, all the remaining hydrogenated zirconium powder was obtained. Those not in powder form could be easily made into powder by pulverization.
Moreover, there was no risk of ignition or explosion during the production process of the hydrogenated zirconium powder, and it was possible to operate safely. Furthermore, the zirconium powder was easily obtained by heating the hydrogenated zirconium powder in a vacuum or in an inert atmosphere such as argon gas.
Table 2 shows the analysis results of the high-purity zirconium powder thus obtained.

As a result, the impurity content excluding gas components such as oxygen and carbon became less than 100 ppm, and a 4N (99.99%) level high-purity zirconium powder was obtained.
In particular, the content of alkali metal elements such as Na and K is 1 ppm or less in total, the content of radioactive elements such as U and Th is 5 ppb or less in total, transition metals such as Fe, Ni, Cr and Zr excluding Hf or A high-purity zirconium powder in which heavy metals or refractory metal elements were 50 ppm or less in total and the balance being zirconium and other inevitable impurities was obtained.
As shown in Table 2, most of the impurities other than the above were less than 0.1 ppm.

(Example 2)
A zirconium ingot produced in the same manner as in Example 1 was cut into chips with a lathe, washed with hydrofluoric acid, and then hydrogenated under the same conditions. As a result, the powder could be easily made into powder. The analysis results were almost the same as in Table 2.

By the electron beam melting method, impurities that hinder the operation function of the semiconductor, that is, alkali metal elements such as Na and K, radioactive elements such as U and Th, Fe, Ni, Co, Cr, Cu, Mo, A high-purity zirconium powder in which transition metals such as Ta and V or heavy metals or refractory metal elements are extremely reduced has an excellent effect of preventing dangers such as ignition and explosion and can be produced at low cost. Moreover, it is possible to obtain a zirconium sputtering target with a small amount of gas components that can effectively reduce the generation of particles during sputtering by suppressing the generation of gas components such as oxygen and carbon, and the like such as a gate oxide film in a semiconductor device. It has the remarkable feature that high purity zirconium powder useful for production can be obtained.
Therefore, it is useful for the production of a zirconium sputtering target with a small amount of gas components, which can suppress the generation of gas components such as oxygen and carbon and effectively reduce the generation of particles during sputtering.

Claims (6)

After the surface of the zirconium raw material is cleaned with hydrofluoric acid, the raw material is wrapped in a volatile element foil to form a compact material, and the compact material is melted with an electron beam to be purified to an ingot. Heating the hydrogenated zirconium ingot to 500 ° C. or higher in a hydrogen atmosphere and then cooling the hydrogenated zirconium ingot to remove hydrogenated zirconium powder from the ingot to obtain a hydrogenated high purity zirconium powder, or After the chips obtained by cutting the high-purity zirconium ingot are acid washed, they are heated to 500 ° C or higher in a hydrogen atmosphere to be hydrogenated, and cooled to obtain zirconium hydride powder, and consists removing hydrogen hydrogenated high-purity zirconium powder, Ri 100ppm less der impurity content excluding gas components, Na, an alkali metal source, such as K Elemental content is 1ppm or less in total, content of radioactive elements such as U and Th is 5ppb or less in total, transition metals or heavy metals such as Fe, Ni, Co, Cr and Cu excluding Hf, or refractory metal elements in total 50ppm or less, the method of producing a high-purity zirconium powder and the balance zirconium and other unavoidable impurities der Rukoto. The method for producing high-purity zirconium powder according to claim 1 , wherein the hydrogenation is performed by heating to 700 ° C or higher in a hydrogen atmosphere. Process for producing a high-purity zirconium powder according to any one of claims 1-2, characterized in that introducing an inert gas such as argon during cooling. The method for producing high-purity zirconium powder according to any one of claims 1 to 3 , wherein the ingot or the cutting powder is cooled to 500 ° C or lower to obtain hydrogenated high-purity zirconium powder. The method for producing high-purity zirconium powder according to any one of claims 1 to 4 , wherein the high-purity zirconium powder peeled off from the ingot is further pulverized. The method for producing high-purity zirconium powder according to any one of claims 1 to 5 , wherein hydrogen is removed by heating in a vacuum or in an inert atmosphere.