JPH06336675A - Sputtering target for magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To produce a target made of a Co alloy contg. group Va elements and having a uniform structure. CONSTITUTION:This target consists essentially of Co, contains one or more kinds of group Va elements and has a structure in which a compd. contg. the group Va elements has been dispersed in the rolling direction in a striped or netted state. This target preferably has <=50X average grain diameter and is obtd. by covering the periphery of a cast ingot having the above-mentioned compsn. with a metal and carrying out hot rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering target used for forming a Co alloy type magnetic layer to be a magnetic recording medium by sputtering and a method for producing the same.

[0002]

2. Description of the Related Art In a magnetic disk device, a magnetic head is opposed to a magnetic recording medium at minute intervals to magnetically record on the magnetic recording medium, and the recorded magnetic information is read by the magnetic head to perform recording / reproduction. It has become. This magnetic recording medium has a C
o-Ni-Cr, Co-Cr-Ta, Co-Cr-Pt
The alloy magnetic film having Co as a main component is used.

Recently, as one of the methods for increasing the recording density of a magnetic film, there is a method of adopting a perpendicular magnetic recording system. The perpendicular magnetic recording method is a method of magnetizing the magnetic film in the perpendicular direction as described in, for example, JP-A-61-204804. This perpendicular magnetic recording system has attracted attention as a solution to the conventional horizontal magnetic recording (also called in-plane magnetic recording) system, in which the demagnetizing field becomes large when the recording density is increased and the predetermined recording cannot be performed. Has been converted. A magnetic film suitable for this perpendicular magnetic recording system needs to have perpendicular magnetic anisotropy. For this reason, V, Nb, and Ta, which are 5A group elements, are added to the Co-based magnetic film to make the structure of the magnetic film. The method of miniaturization is taken.

[0004]

When the above-mentioned magnetic film containing a Group 5A element is to be obtained by sputtering, a sputtering target having a composition substantially equal to that of the magnetic film is required. Such an alloy target has been manufactured as an as-cast target or a sintered target by a hot isostatic press, as described in, for example, Japanese Patent Application Laid-Open No. 4-276070. Of these, the as-cast target has the advantage that it can be manufactured at a lower cost than a sintered target that requires powder manufacturing, sintering, and forging.

Recently, along with the demand for higher efficiency in the production of magnetic recording media, it has become necessary to make the above-mentioned alloy target used for the production of magnetic films into a large flat plate. Further, since the concentration of the 5A group element has a great influence on the coercive force and the saturation magnetic flux density of the magnetic film, it needs to be uniformly distributed in the magnetic film.
For that purpose, it is necessary that the alloy target used for producing the magnetic film has a uniform composition even if it is made into a large flat plate. However, in the case of a target that has just been cast, especially when the target becomes large, as shown in FIG.
As shown in FIG. 4, the target just wrought has a dendritic structure (dendrite structure) and a compound containing a group 5A element is aggregated in the crystal grain boundaries, which causes a problem of nonuniformity of the target structure. .

If the target structure is not uniform, the uniform leakage magnetic flux required for magnetron sputtering cannot be obtained, and the erosion progresses unevenly during the sputtering period, resulting in a short target life. The present inventor tried hot rolling to eliminate the uneven distribution of the group 5A element on the aforementioned alloy target mainly composed of Co, but the group 5A element mainly segregated as a compound with Co in the cast ingot. The cast ingot was brittle and could not be hot rolled after casting. An object of the present invention is to provide a target mainly composed of Co in which a compound containing a group 5A element, which is a segregation element, is dispersed, and which has a uniform structure and a long target life. It is to provide a manufacturing method suitable for obtaining a target.

[0007]

Means for Solving the Problems The present inventor has investigated a method of applying hot rolling to the production of a target having a uniform composition, and by covering the outer periphery of a cast ingot with a metal and performing hot rolling, It was found that cracks do not occur during hot rolling and a new target having a uniform structure suitable for magnetic recording media can be obtained. That is, the production method of the present invention is
o as a main component, 5A group element (specifically, V, Nb, T
(meaning a), and a hot-rolling method is carried out by covering the outer circumference of a cast ingot containing one or more of them with a metal and performing hot rolling. The present invention is particularly suitable for obtaining a target having a composition containing a large amount of a compound containing a Group 5A element in an amount of 4 atom% or more.

Co is a main component by the above-mentioned manufacturing method,
A target containing one or more 5A group elements, wherein the compound containing a 5A group element is dispersed in a striped or net form in the rolling direction, and preferably has an average particle size of 50μ.
A sputtering target for a magnetic recording medium of the present invention, which has a structure of m or less, can be obtained.

[0009]

One of the greatest features of the manufacturing method of the present invention is that the outer circumference of the cast ingot is covered with metal and hot rolling is performed. The Group 5A element makes the ingot itself brittle by precipitating as a compound, and is an element that is very easily oxidized. Therefore, if it is directly exposed to an oxidizing atmosphere during hot rolling, an oxide is formed on the surface. It becomes the starting point of cracking. In the present invention, by covering the cast ingot with a metal, it is possible to prevent the oxidation of the surface of the ingot and prevent the occurrence of cracks during hot rolling. By this method, it is possible to obtain a large flat plate target by hot rolling which could not be manufactured conventionally. Mild steel, stainless steel, or the like can be used as the metal for covering the cast ingot.

Further, one of the greatest features of the target of the present invention obtained by the above-described method of the present invention is that the target is 5 in the rolling direction.
It means that the compound containing the group A element is dispersed in a stripe shape or a net shape to make the structure uniform. Since the target of the present invention has a uniform fine structure, it can improve the life of the target, which was a problem of the as-cast alloy target. It is considered that this is because the target of the present invention was able to reduce variations in the leakage magnetic flux as compared with the as-cast target. Further, in the target of the present invention, by dispersing a compound containing a Group 5A element in the rolling direction, the crystal grains become finer, the maximum magnetic permeability of the target can be lowered, and it is convenient to obtain a leakage magnetic flux in magnetron sputtering. Be a target. It is considered that the crystal grains become fine because the compound containing a Group 5A element suppresses crystal growth. The preferable average crystal grain size due to the refinement of the structure is 50 μm or less.

In the present invention, the structure in which the compound containing the 5A group element is dispersed in the rolling direction is defined as a structure in which the content of the 5A group element is so small that the compound containing the 5A group element is not dispersed. This is because the nonuniformity of the target structure due to segregation does not pose a problem. Also, 5
This is because embrittlement of the cast ingot does not pose a problem if the compound containing the group A element does not exist, and hot rolling can be performed without covering the cast ingot with metal as in the present invention. In particular, in the target containing 4 atomic% or more of the 5A group element, the life of the target can be remarkably improved by dispersing the compound containing the 5A group element in the rolling direction in a stripe shape or a net shape. The present invention is a target used for forming a magnetic film, and the upper limit of the content of the 5A group element is limited by the required magnetic characteristics. The Group 5A element is an element effective for refining the crystal grains of the Co-based magnetic film and imparting perpendicular magnetic anisotropy, but when the content in the magnetic film increases, the coercive force and saturation required for the magnetic film are increased. In order to reduce the magnetic flux density, the desirable range is usually limited to 10 atomic% or less.

In a magnetic film containing Co as a main component and containing a 5A group element, Cr is often added in an amount of 25 atomic% or less for the purpose of improving corrosion resistance and magnetic properties. Further, in order to improve the magnetic properties, a part of Co may be replaced with Ni by 40 atomic% or less. Also as a sputtering target for producing these magnetic films, the target and the producing method of the present invention are effective for the purpose of eliminating uneven distribution of the group 5A element. That is, in the present invention, the meaning of “having Co as a main component” means that the main component is not only Co but also contains Cr at 25 atomic% or less or a part of Co is 40 by Ni.
%, And alloys that are replaced by less than 100% are also included.

[0013]

EXAMPLE A cast ingot having the composition shown in Table 1 was obtained by vacuum melting and vacuum casting. Mild steel (JIS S15C) was deposited as metal on the outer periphery of this alloy by TIG welding. After that, the cast ingot was heated to 1150 ° C.
7 × 200 × 1000 (mm)
Finished into a plate material. At this time, the temperature of hot working is 900 ° C.
It was managed so that it would not be less than. The obtained plate material was machined to obtain a target of 6 × 127 × 381 (mm). Also, as a comparative example, a cast ingot having a composition other than sample No. 9 shown in Table 1 was directly machined to obtain a target of the same shape. I got the material. The cast ingot having the composition of Sample No. 9 contained 5% of Group 5A as small as 4%, and thus was used as a target material after hot forging. Table 1 shows the maximum magnetic permeability and the average crystal grain size of the texture of these targets.

[0014]

[Table 1]

Using these target materials, the argon gas pressure is 10 minus the square of Torr, and the input power is 720 W.
By using a magnetron sputtering apparatus under the conditions described above, sputtering was performed to determine the efficiency of use of the target when erosion progressed to a thickness of 1 mm. The usage efficiency of the target is a reduction in the weight of the target, and a larger value indicates a longer target life.
The results are shown in Table 1. As shown in Table 1, it can be seen that the target of the present invention has a smaller crystal grain size, lower maximum magnetic permeability, and higher target usage efficiency than the target of the as-cast comparative example. .

FIG. 1 is a microstructure photograph of the hot-rolled target of Sample No. 1 of the present invention, and FIG. 2 is a microstructure photograph of the as-cast target of Sample No. 8 of the comparative example having the same composition as Sample No. 1. Is. The net-like precipitates in the target structure of the present invention shown in FIG. 1 were mainly compounds of tantalum and Co. As shown in FIG. 1, in the target of the present invention, it is confirmed that the compound of tantalum and Co forms a net and is distributed in the rolling direction (horizontal direction in FIG. 1). On the other hand, the target structure of the comparative example shown in FIG. 2 has a dendritic structure in which the tantalum compound is aggregated in the final solidified portion. As is clear from comparison between FIG. 1 and FIG. 2, the structure of the target of the present invention and the structure of the target of the comparative example are greatly different from each other, and the structure of the target of the present invention in which Group 5A is dispersed in a net shape in the rolling direction. It can be seen that this has led to an improvement in the target usage efficiency.

FIG. 3 is a microstructure photograph of the hot rolling target of sample No. 2 of the present invention, and FIG. 4 is sample No. 2
9 is a microstructure photograph of a target obtained by forging Sample No. 9 having the same composition as that of FIG. The striped precipitates in the structure of the target of the present invention shown in FIG. 3 were mainly compounds of tantalum and Co. As shown in FIG. 3, in the target of the present invention, it was confirmed that the compound of tantalum and Co was distributed in stripes along the rolling direction (the horizontal direction in FIG. 3). It can be seen that the structure of the target shown in FIG. 3 has a small tantalum content, and therefore the tantalum compound is dispersed in a striped pattern instead of the net-like pattern shown in FIG. On the other hand, the target structure of the comparative example shown in FIG. 4 was a structure in which the tantalum compound was aggregated at the crystal grain boundaries. As is clear from comparison between FIG. 3 and FIG. 4, even in a target having a composition with a small amount of tantalum,
It can be seen that the use efficiency of the target can be improved by using the structure of the target of the present invention in which the tantalum compound is dispersed in the stripe shape shown in FIG.

[0018]

According to the present invention, since the target is used more efficiently than the as-cast target, an expensive target containing Co as a main component can be effectively used, and the cost of manufacturing the magnetic recording medium can be improved. Can be lowered.
Further, the target of the present invention has a uniform and fine structure as compared with the as-cast target, and it is possible to suppress the variation in the composition of the thin film due to the variation in the composition of the target. Furthermore, the target of the present invention has a smaller maximum magnetic permeability than that of the as-cast target, and is therefore suitable as a target for a magnetron sputtering apparatus. Further, in the manufacturing method of the present invention, since it is possible to prevent surface oxidation that causes cracking of the cast ingot in hot rolling,
It is especially effective when a large flat plate target is required.

[Brief description of drawings]

FIG. 1 is a metal microstructure photograph showing an example of a target of the present invention.

FIG. 2 is a metal microstructure photograph showing an example of a target of a comparative example.

FIG. 3 is a metal microstructure photograph showing another example of the target of the present invention.

FIG. 4 is a photograph of a metal microstructure showing an example of a target of a comparative example.

Claims (4)

[Claims] 1. A target containing Co as a main component and containing one or more members of a 5A group element, said 5A
A target for a magnetic recording medium, which has a structure in which a compound containing a group element is dispersed in a striped or net shape in the rolling direction. 2. A target containing Co as a main component and containing at least 4 atomic% of one or more 5A group elements, wherein the compound containing the 5A group element is striped or net-like in the rolling direction. A target for a magnetic recording medium, characterized in that it has a structure dispersed in the. 3. The sputtering target for a magnetic recording medium according to claim 1, which has an average particle size of 50 μm or less. 4. A method for manufacturing a sputtering target for a magnetic recording medium, which comprises hot-rolling a cast ingot containing Co as a main component and containing one or more of Group 5A elements with a metal and performing hot rolling. .