JP5787274B2 - Method for producing Fe-Co-Ta-based sputtering target material and Fe-Co-Ta-based sputtering target material - Google Patents

Description

  The present invention relates to a method for producing an Fe—Co—Ta based sputtering target material for forming a soft magnetic film in a magnetic recording medium, and an Fe—Co—Ta based sputtering target material.

In recent years, the progress of magnetic recording technology has been remarkable, and the recording density of magnetic recording media has been increased to increase the capacity of drives. However, in the longitudinal magnetic recording type magnetic recording medium that has been widely used in the past, when trying to achieve a high recording density, the recording bit becomes finer and a high coercive force that cannot be recorded by the recording head is required. The Therefore, a perpendicular magnetic recording system has been put into practical use as a means for solving these problems and improving the recording density.
Perpendicular magnetic recording is a method in which the magnetic film of a perpendicular magnetic recording medium is formed so that the axis of easy magnetization is oriented perpendicular to the medium surface. Even if the recording density is increased, the demagnetizing field in the bit is used. This is a method suitable for high recording density with a small decrease in recording and reproduction characteristics. In the perpendicular magnetic recording system, a recording medium having a magnetic recording film layer and a soft magnetic film layer with improved recording sensitivity has been developed.

  As a soft magnetic film of such a magnetic recording medium, in addition to having a high saturation magnetic flux density, an amorphous film is required, and an amorphous Fe-Co alloy mainly composed of Fe having a high saturation magnetic flux density is required. An alloy film to which an element for promoting crystallization is added is used. On the other hand, these alloy films are also required to have corrosion resistance. For the formation of an alloy film, for example, a soft magnetic material containing 10 to 20 atomic% of one or two elements selected from Nb or Ta in an Fe—Co alloy. Fe-Co alloy sputtering target materials for films have been proposed. (See Patent Document 1) In Patent Document 1, a Fe-Co-based target material is mixed with pure metal powder raw materials each having a purity of 99.9% or more so as to have the composition of the target material, and the obtained mixed powder is sintered. It is manufactured by tying.

WO2009 / 104509

The Fe-Co alloy sputtering target material disclosed in Patent Document 1 described above is a soft magnetic film having high corrosion resistance in addition to high saturation magnetic flux density and amorphousness by adding a single element of Ta or Nb. This is advantageous in that it can be formed and component control is facilitated.
However, when the Fe—Co—Ta alloy target material produced by the manufacturing method disclosed in Patent Document 1 was sputtered, it was confirmed that a large amount of foreign matter called particles may be generated from the target material. One of the causes of the particles generated during sputtering is that a protrusion called a nodule is formed on the surface of the target material due to a difference in sputtering rate, and abnormal discharge occurs from the nodule as a base point. In addition, even when there are foreign substances such as vacancies and oxides in the structure of the target material, abnormal discharge occurs from them as a base point, which can cause generation of particles as in the case of nodules.
According to the study of the present inventors, it was confirmed that nodules were formed on the surface of the sputtering target material produced by the production method disclosed in Patent Document 1, and the main cause was the presence of pure Ta phase in the target structure. It was confirmed that It was also confirmed that there was a hole in the target structure that was one of the causes of particles.
An object of the present invention is to provide an Fe—Co—Ta based sputtering target material that solves the above-described problems and can suppress the generation of particles during sputtering.

As a result of examining the composition of the powder raw material and the sintering conditions of the mixed powder, the present inventor is able to reduce the pure Ta phase and vacancies, which are the main causes of nodule generation, to the limit in the structure of the target material And reached the present invention.
That is, the present invention includes a step of mixing a Fe—Ta powder, a Co—Ta powder, and a pure Ta powder to obtain a mixed powder, and the mixed powder is sintered at 1100 to 1400 ° C. at a pressure of 125 to 200 MPa and 1 to 10 It is a manufacturing method of the Fe-Co-Ta type | system | group sputtering target material which has the process of carrying out pressure sintering of time.
In the Fe—Co—Ta based sputtering target material of the present invention, the pure Ta phase in a 6 mm ² field of view is 1.5 area% or less, and the sum of the major diameters of vacancies existing in the same field of view is 15 μm or less. It is.

  According to the present invention, an Fe—Co—Ta based target material that suppresses the generation of particles during sputtering can be realized, and a soft magnetic film of an Fe—Co—Ta based alloy of a magnetic recording medium can be stably formed. .

Sample No. of the present invention example. 5 is a microstructural photograph taken by a scanning electron microscope in FIG. Sample No. of the conventional example. 1 is a microstructural photograph of 1 of a scanning electron microscope. Sample No. of Comparative Example 2 is a microstructural photograph taken by a scanning electron microscope in FIG.

  As described above, an important feature of the present invention is that Fe-Ta powder and Co-Ta are used as raw powders in order to suppress the pure Ta phase in the target material, which is the main cause of particle generation during sputtering. It is the point which discovered the suitable powder sintering conditions for using a powder and pure Ta powder, and also suppressing a pure Ta phase and a void | hole.

The method for producing the Fe—Co—Ta based sputtering target material of the present invention comprises mixing Fe—Ta powder, Co—Ta powder, and pure Ta powder, followed by, for example, press firing by hot isostatic pressing or hot pressing. Do the tie. For example, when the above mixed powder is subjected to pressure sintering by hot isostatic pressing, the powder is filled in a pressure vessel made of mild steel, the inside of the pressure vessel is evacuated and sealed, and then pressure sintering is performed. . The pressure sintering is performed at a sintering temperature of 1100 to 1400 ° C. and a pressure of 125 to 200 MPa within a sintering time of 1 to 10 hours.
When the sintering temperature is lower than 1100 ° C., the pure Ta powder, which is a high melting point metal, does not sufficiently sinter and pores are formed. On the other hand, if the sintering temperature exceeds 1400 ° C., there is a problem that the devices that can withstand are limited. For this reason, in this invention, sintering temperature was 1100-1400 degreeC. When the sintering temperature exceeds 1270 ° C., the liquid phase of the Co—Ta alloy powder appears, so that sintering is preferably performed at 1270 ° C. or less.
On the other hand, if the pressurizing pressure is less than 125 MPa, sufficient sintering cannot be performed, and voids are easily formed in the target structure. On the other hand, when the pressurization pressure exceeds 200 MPa, there is a problem that an apparatus that can withstand is limited. For this reason, in this invention, the pressurization pressure was 125-200 MPa.
Further, when the sintering time is less than 1 hour, the sintering cannot proceed sufficiently, and it is difficult to suppress the formation of pure Ta phase and pores. On the other hand, if the sintering time exceeds 10 hours, the production efficiency is remarkably deteriorated. Therefore, in the present invention, the sintering time is set to 1 to 10 hours.

The raw material powder used in the present invention is Fe-Ta alloy powder, Co-Ta alloy powder, and pure Ta powder. It is possible to use one or two types of Fe—Co—Ta alloy powders and pure Ta powders having different composition ratios as raw material powders, but mutual diffusion between the Fe—Co—Ta alloy powders and the pure Ta powders has progressed. It becomes difficult to form a pure Ta phase in the target material structure after sintering. For this reason, in this invention, Fe-Ta alloy powder, Co-Ta alloy powder, and pure Ta powder are used.
It is desirable that the Fe—Ta alloy powder and the Co—Ta alloy powder have a composition near the eutectic. When each alloy powder deviates significantly from the eutectic composition, the liquidus temperature rises significantly, making it easy to damage surrounding refractories during alloying, and fine refractories are mixed in the alloy powder. There is a possibility. When refractories are mixed in the sputtering target material, these refractories are insulators, and thus easily become a base point of abnormal discharge that generates particles during sputtering. For this reason, in the Fe-Ta alloy powder, the Ta atomic ratio is desirably 12% or less, and in the Co-Ta alloy powder, the Ta atomic ratio is desirably 18% or less. In the Fe-Ta alloy powder, the Ta atomic ratio is more preferably 4 to 10%. In the Co—Ta alloy powder, the Ta atomic ratio is more preferably 5 to 13%.
In addition, when the particle diameter is coarse in each alloy powder, the bulk density when filling a pressure vessel made of mild steel with a mixed powder of Fe-Ta alloy powder, Co-Ta alloy powder and pure Ta powder is remarkable. Therefore, the particle size of the alloy powder is preferably 250 μm or less.

The Fe—Co alloy serving as the base of the sputtering target material of the present invention preferably has a component region in which the composition formula in atomic ratio is (Fe _X —Co _100-X ) and 30 ≦ X ≦ 80. This is because the Fe—Co binary alloy, which is known to have the highest saturation magnetic moment among transition metal alloys, has the highest saturation magnetic moment near the composition ratio of Fe: Co = 65: 35 in atomic ratio. This is because a high saturation magnetic moment can be obtained in an Fe—Co alloy in which the atomic ratio of Fe is in the range of 30 to 80%.
When the saturation magnetic moment needs to be maximized, the atomic ratio X of Fe is preferably 50 to 80%. When the magnetostriction as a thin film is to be reduced, the Fe atom ratio X The ratio X is preferably 30 to 50%.

  The Fe—Co—Ta based sputtering target material of the present invention preferably contains 14 to 30 atomic% of Ta. This is because the addition of Ta has the effect of improving the corrosion resistance at the same time as the Fe—Co alloy becomes amorphous during sputtering. In addition, said effect does not become amorphous when the addition amount of Ta is less than 14 atomic%, and when it exceeds 30 atomic%, the magnetization decreases, so it is made 14 to 30 atomic%. Is preferred.

For the above reasons, it is necessary to use pure Ta powder in order to produce an Fe—Co—Ta-based sputtering target material containing Ta at least 14 atomic%, but the use amount of pure Ta powder is minimized. It is desirable to do. This is because when a large amount of pure Ta powder is used, a pure Ta phase is easily formed in the microstructure after sintering of the mixed powder, and nodules are easily formed during sputtering.
The pure Ta powder preferably has a fine particle size. This is because when the particle size of the pure Ta powder is coarse, a pure Ta phase is easily formed in the microstructure after sintering of the mixed powder, and nodules are easily formed during sputtering. In consideration of easy handling, the average particle diameter of the pure Ta powder is preferably 45 μm or less.
The pure Ta powder can be a pure Ta powder produced by a chemical extraction method or a mechanical pulverization method, and among them, a powder produced by a mechanical pulverization method is preferably used. By using powder produced by mechanical grinding, the fluidity of the powder is improved, the bulk density when filled into a pressurized container is increased, and voids are formed in the microstructure after pressure sintering Can be further suppressed.

In addition to containing Ta in the above range, the Fe—Co—Ta based sputtering target material of the present invention may contain 5 atomic% or less of Zr to replace a part of Ta. By adding Zr to the Fe—Co—Ta alloy, it becomes possible to promote the amorphization of the thin film during the sputtering film formation and to suppress the amount of Ta added.
When adding 5 atomic% or less of Zr to the Fe—Co—Ta based sputtering target material produced according to the present invention, in addition to the above-described Fe—Ta alloy powder, Co—Ta alloy powder, and pure Ta powder, Fe— It can be produced by adding Zr, Co-Zr, Fe-Ta-Zr, Co-Ta-Zr.
This is because, in addition to the above-mentioned reasons, Zr as a pure metal has a very high reactivity with oxygen, and it is desirable to use it by alloying for safety of work.

  In the Fe—Co—Ta based sputtering target material of the present invention, the balance other than containing Ta and Zr in the above range is Fe and Co and inevitable impurities. It is desirable that the impurity content is as low as possible, oxygen and nitrogen as gas components are 1000 ppm or less, and inevitably contained impurity elements other than gas components such as Ni, Si, Al are preferably 1000 ppm or less in total. .

In the Fe—Co—Ta-based sputtering target material obtained by the present invention, the pure Ta phase in a 6 mm ² field of view is 1.5 area% or less, and the sum of the major diameters of the existing holes is 15 μm or less. This is because the abundance ratio of pure Ta phase and vacancies, which are likely to be nodulated, is reduced to a range that does not cause a problem during sputtering. The presence ratio of pure Ta phase and vacancies is preferably as low as possible. In order to suppress the generation of particles during sputtering, the pure Ta phase should be 1.5 area% or less and the major axis of the vacancies present Needs to be 15 μm or less.

The following examples further illustrate the present invention.
First, powders of each combination shown in Table 1 were prepared so that the atomic ratio was (Fe ₆₅ —Co ₃₅ ) ₈₂ —Ta _18, and weighed and mixed to prepare a mixed powder. Here, the Fe—Ta alloy powder and the Co—Ta alloy powder were produced by a gas atomizing method, and each particle diameter was 250 μm or less, and each of eutectic compositions Fe-8Ta (atomic%) and Co-8Ta (atomic%). Was used. For pure Ta powder, sample no. Nos. 1 to 5 use a pure Ta powder having a particle size of 45 μm or less produced by a commercially available chemical extraction method. 6-10 used the pure Ta powder with a particle size of 45 micrometers or less manufactured by the commercially available mechanical grinding method.
Each mixed powder obtained above was filled in a pressure vessel made of mild steel and degassed and sealed, and then subjected to the conditions of sintering temperature, pressure and sintering time shown in Table 1 by hot isostatic pressing. Sintering was performed to obtain a sintered body having a diameter of 194 mm and a thickness of 14 mm.
The sintered body obtained above was processed into a size of 180 mm diameter × 7 mm thickness by machining to obtain an Fe—Co—Ta based sputtering target material.

The sintered body produced above was observed with a scanning electron microscope (JSM-6610LA, manufactured by JEOL Ltd.), and the area% of pure Ta phase in a 6 mm ² field of view was measured. Further, the major axis of each hole existing in the observed 6 mm ² field of view was measured, and the sum total was calculated. Observed Sample No. 1 to 3 show the microstructures of the sintered bodies 1, 2 and 5, and Table 1 shows the results of measuring the total area percentage of pure Ta phase and the major axis of the pores.
1 to 3, the white portion is a pure Ta phase, the light gray portion around it is an alloy phase containing a large amount of Ta, and the remainder is an alloy phase having a low Ta content. From FIG. 1 to FIG. 3 and Table 1, it was confirmed that the formation of pure Ta phase and pores could be suppressed by increasing the pressing pressure and extending the sintering time. In addition, the formation of pores in the microstructure can be further suppressed by using pure Ta powder produced by a mechanical pulverization method compared to pure Ta powder produced by a chemical extraction method. It could be confirmed.

Moreover, after arrange | positioning the sputtering target material produced above in the chamber of DC magnetron sputtering apparatus (C3010 by Canon Anelva Co., Ltd.), and reducing the pressure in the chamber to 1 × 10 ⁻⁶ Pa or less, the Ar gas pressure is 0. The discharge test was conducted 120 seconds at a time of .6 Pa and an input power of 1500 W. At this time, changes in applied voltage every 0.1 seconds are recorded, and the absolute value of the applied voltage difference is used as a statistical management standard for monitoring abnormal values. The median (average value) is three times the standard deviation. The number of times that became equal to or greater than the value obtained by adding was measured as the number of times abnormal discharge occurred.
Since there is a strong positive correlation between the amount of particles generated from the target material and the number of abnormal discharges, it is possible to evaluate the number of particles generated during sputtering by measuring the number of abnormal discharges. is there. The number of abnormal discharges was measured by the above method. Table 1 shows the results of the abnormal discharge occurrence ratio obtained with reference to 1 conventional material (100%).
From Table 1, it was confirmed that the abnormal discharge occurrence ratio also decreased as the area percentage of the pure Ta phase in the Fe-Co-Ta-based target material decreased and the total of the major diameters of the holes decreased. By producing within the range of the pressure sintering conditions of the present invention, pure Ta phase and vacancies can be suppressed. As a result, the generation of particles during sputtering can be reduced, and the effectiveness of the present invention has been confirmed. .

Claims (2)

It means a particle diameter of 250 [mu] m or less of Fe- 4 to 10 atomic% Ta powder with an average particle size of less 250 [mu] m Co- 5 to 13 atomic% Ta powder with an average particle diameter of 45μm or less pure Ta powder, a Ta 18 30 contains atomic%, a step of the balance to obtain a mixed powder mixture serves as _{(Fe X -Co 100-X)} , 30 ≦ X ≦ 80 and unavoidable impurities, a composition formula in atomic ratio,
The mixed powder sintering temperature 1100 to 1400 ° C., possess a step of pressure sintering 1 to 10 hours at a pressure 125～200MPa,
A Fe—Co—Ta-based sputtering target material in which the pure Ta phase in a 6 mm ² field of view is 0.12 to 1.5 area% and the total length of vacancies existing in the same field of view is 15 μm or less is obtained. The manufacturing method of the Fe-Co-Ta type sputtering target material characterized by the above-mentioned. It contains 18 to 30 atomic% of Ta, the balance is composed of the composition formula in terms of atomic ratio (Fe _X -Co _100-X ), 30 ≦ X ≦ 80, and inevitable impurities, and a pure Ta phase in a 6 mm ² field of view A Fe—Co—Ta-based sputtering target material, which is 0.12 to 1.5 area % and has a total length of vacancies in the same field of view of 15 μm or less.