JPH06136526A - Sputtering target for forming ground surface of magnetic thin film and its production - Google Patents

Abstract

PURPOSE:To produce the sputtering target for forming the ground surface of a magnetic thin film by compounding a low phosphorus-side raw material and a high phosphorus side raw material in such a manner that nickel and phosphorus attain desired compounding ratios, then sintering these materials. CONSTITUTION:The low phosphorus-side raw material is obtd. by heating the powder of the nickel alone or >=1 kinds of the powders selected from the powders of compds. or alloys of <=25atm.% content of phosphorus in a reducing atmosphere. The high phosphorus-side raw material is obtd. by subjecting the >=1 kinds of powders selected from the compds. or alloys of >=33.3atm.% content of phosphorus to a heat treatment in the reducing atmosphere. Both raw materials are then so compounded that the nickel and the phosphorus attain the desired compsn. ratios. The raw material mixture is then sintered, by which the sputtering target for forming the ground surface of the magnetic thin film substantially consisting of the nickel and the phosphorus and having <=200ppm content of oxygen which is the impurity and >=97% density ratio is produced. The magnetic thin film having a high coercive force is stably formed by using the target.

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 an underlying film of a magnetic thin film used in a magnetic recording medium such as a hard disk and a method for manufacturing the same.

[0002]

2. Description of the Related Art A magnetic recording medium such as a hard disk used as an external recording medium of a computer has a magnetic thin film formed on a substrate such as a substrate provided with a hard layer made of nickel and phosphorus on aluminum or a substrate such as ceramics. A base film of chromium or the like, which can align the axes of easy magnetization, C
It has a structure in which a magnetic thin film such as o-Ni-Cr or Co-Ni-Pt and a carbon film to be a lubricating layer are laminated in this order. Recently, JP-A-63-217525, or IEEE TRANSACTION ON MAGNETICS, VOL.27, No.6 NOVE
As described in MBER 1991, P4729-4742, as a base film formed on the substrate, a film made of nickel and phosphorus (hereinafter referred to as a nickel-phosphorus base film) is formed by sputtering, and chromium is used as the base film. With higher quality magnetic properties, smaller bit shift, higher resolution,
It has been found that a magnetic thin film having low noise and high uniformity over the entire surface of the disk can be obtained.

When the nickel-phosphorus base film is formed by sputtering, it becomes an amorphous or almost amorphous film. This nickel-phosphorus base film serves as a layer that prevents the non-uniformity of the substrate surface from being transmitted to the magnetic thin film,
And since it is amorphous or almost amorphous, there are innumerable nuclei where the crystals of the magnetic thin film grow, and the magnetic thin film grows uniformly and finely, so it is considered that the above-mentioned effects can be obtained. There is. Also,
As a method of manufacturing a target for a nickel-phosphorus base film, it is difficult to control the composition of phosphorus, which is one of the main components in the melting-casting method, because the vapor pressure of phosphorus is large. Being manufactured.

[0004]

As described above, the nickel-phosphorus base film has very promising properties as a base film of a magnetic thin film when forming a magnetic recording medium such as a hard disk. However, phosphorus is a substance that is easily oxidized, and the oxygen concentration of the target used for sputtering was 3000 ppm or more. When a nickel-phosphorus underlayer film is formed using such a target having a high oxygen concentration, a large amount of oxygen exists on the surface of the underlayer film, and the magnetic film cannot grow epitaxially on the nickel-phosphorus underlayer film. . In a magnetic film that cannot be grown epitaxially, the axes of easy magnetization are not aligned in the in-plane direction, and as a result, the coercive force, which is a basic characteristic required for a magnetic thin film, is reduced.

In order to solve such a problem, the present inventors have found a target made of nickel-phosphorus having a low oxygen concentration by subjecting a raw material powder to a reduction treatment and then sintering the powder. Filed as No. 4-178752. When the present inventors examined this target in more detail,
In particular, in the region where the phosphorus composition exceeds 25 at% and is less than 33.3 at% in the equilibrium theory, the Ni ₅ P ₂ or Ni ₁₂ P ₅ phase is the main phase of the sintered body, the problem is that the consolidation tends to be insufficient. It was When a low-density target with insufficient consolidation is subjected to sputtering, the sputtering rate fluctuates momentarily due to the presence of pores, and foreign matter frequently occurs in the film due to abnormal discharge, making it difficult to achieve a uniform film composition and bit errors. And the uniformity of the magnetic thin film is impaired due to noise and noise. The purpose of the present invention is to
Nickel that enables stable formation of magnetic thin films with high coercive force
It is an object of the present invention to provide a sputtering target for forming a phosphorus base film and a manufacturing method thereof.

[0006]

Means for Solving the Problems The present inventor has proposed a low oxygen nickel-phosphorus underlayer film consisting of nickel and phosphorus, having a low oxygen content of 2000 ppm or less, and having a high density of 97% or more. We have found a sputtering target that has not been available in the past and that can be stably obtained. At the same time, as a specific means for obtaining the sputtering target, in the powder reduction treatment performed as a pre-stage of sintering, Ni ₅ P having poor sinterability is used.
_In order to prevent the formation of ₂ to Ni ₁₂ P ₅ phases, the low phosphorus side raw material with a phosphorus content of 25 at% or less and the phosphorus content of 33.3a
It has been found that the reduction treatment may be performed by dividing the raw material on the high phosphorus side of t% or more, and then mixing and sintering them.

That is, the method for producing a target of the present invention was obtained by heat-treating, in a reducing atmosphere, one or more powders selected from a powder of nickel alone or a powder of a compound or alloy having a phosphorus content of 25 at% or less. Low phosphorus-side raw material, high phosphorus-side raw material obtained by heat-treating one or more powders selected from compounds or alloys having a phosphorus content of 33.3 at% or more in a reducing atmosphere, of desired nickel and phosphorus A method for producing a sputtering target for forming an underlayer of a magnetic thin film, which is compounded in a composition ratio and sintered, preferably the low phosphorus-side raw material and the high phosphorus-side raw material are mixed and pulverized or individually pulverized. A method of manufacturing a sputtering target for forming an underlayer of a magnetic thin film, the method comprising the steps of: Further, it is more preferable that the sintering is performed below the liquidus temperature.

[0008]

Function: The target of the present invention has an oxygen content of 2000 ppm.
Below is a sputtering target consisting of a combination of a low density of 97% or more, which is unprecedented, and a high density, and according to the production method of the present invention, the oxygen content is 20% or less.
It is possible to stably obtain a low-oxygen base film of 00 ppm or less. Therefore, the magnetic thin film can be epitaxially grown without being obstructed by oxygen, and the coercive force of the formed magnetic thin film is at least 1200 Oe or more, which is sound and has few bit errors and noise. One of the most important features of the production method of the present invention is a heat treatment in a reducing atmosphere for reducing oxygen, which is Ni ₅ P ₂ or Ni.
_Since the content of phosphorus such as ₁₂ P ₅ is 25 at% to 33.3 at% and the compound forming the main phase is not formed, the content of phosphorus is
That is, the heat treatment was performed in a reducing atmosphere separately for the low phosphorus side raw material of 25 at% or less and the high phosphorus side raw material of 33.3 at% or more.

In the reduction treatment, Ni ₅ P ₂ to Ni ₁₂ P
By suppressing the formation of _5, the sintered density can be remarkably increased and the oxygen content becomes low. The heat treatment described above may be performed for each type of powder, or the powders that are low phosphorus side raw materials or the powders that are high phosphorus side raw materials may be mixed and heat treated. The temperature of the heat treatment in the reducing atmosphere carried out in the present invention is preferably 600 ° C.
To 1000 ° C. Reduction is more effective at higher temperatures, but above 1000 ° C, phosphorus evaporates and the composition of the target fluctuates, and the sintering of the powder progresses and powder agglomeration becomes severe, making it difficult to pulverize after heat treatment. This is because the powder filling becomes insufficient. Further, at 600 ° C or lower, the reducing effect is small.

In the present invention, the powder is preferably crushed after being heat-treated in a reducing atmosphere or after being mixed in a desired composition ratio of nickel and phosphorus and mixed. It prevents powder particles from partially sintering and agglomerating during heat treatment in an atmosphere containing hydrogen, resulting in insufficient powder filling and pressure sintering, and eliminating composition segregation by eliminating component segregation. This is to make it uniform. The main purpose of the pulverization carried out in the present invention is to release the agglomeration of the powder and restore the particle size before the agglomeration. For the operation, a ball mill, an attritor, a planetary ball mill, a vibrating ball mill or the like can be used. In order to prevent the oxygen content from increasing due to the adsorption of oxygen during the pulverization, it is preferable to carry out in a vacuum or in an atmosphere of an inert gas such as argon gas.

After the reduction by the above heat treatment, the individual powder is blended in a desired composition ratio of nickel and phosphorus and mixed, or pulverized, or the individual powder is pulverized and then mixed in a desired composition ratio. Both are possible, but if the degree of aggregation of the powder due to heat treatment differs depending on the individual powder,
The latter is preferable, and the former is more efficient when there is no difference. In the nickel-phosphorus system, since the raw material itself containing phosphorus has a relatively high oxygen content and the phosphorus is easily oxidized, the oxide film on the powder surface may hinder sintering due to the inhibition of sintering. is there. Therefore, it is preferable to sinter under pressure by hot isostatic pressing (hereinafter referred to as HIP), hot pressing, or the like.

The sintering temperature is preferably a temperature at which the mixed powder does not develop a liquid phase during sintering. That is, with the phosphorus content of 33.3 at% as the boundary composition, the eutectic temperature of Ni and Ni ₃ P is 880 ° C. or less at the phosphorus content below this, and the Ni ₂ P and Ni ₅ P at the phosphorus content above this. Eutectic temperature of ₄
It is below 830 ℃. Preferably, the temperature is lower than the eutectic temperature by 30 ° C. or lower (eutectic temperature −30 ° C.). This is because hot press dies and HIPs are used when the liquidus temperature is locally exceeded.
This is because the iron can and the nickel and phosphorus react with each other and the target may be contaminated. Solid phase sintering is also preferable from the viewpoint of ensuring the uniformity of the composition distribution and preventing the occurrence of uneven density and local embrittlement due to the non-uniformity of the composition distribution.

[0013]

【Example】

Example 1 Pure Ni raw material powder having an average particle diameter of 12 μm and an oxygen content of 5600 ppm was heated in a pure hydrogen atmosphere at 600 ° C. for 2 hours to obtain a low phosphorus-side raw material. The powder after heating was partially agglomerated, but the oxygen content was 1150 ppm. On the other hand, a Ni ₂ P raw material powder (Ni having an average particle size of 30 μm and an oxygen content of 3700 ppm (Ni
−33.4 at% P powder) was heated in a pure hydrogen atmosphere at 800 ° C. for 2 hours to obtain a high phosphorus-side raw material. The powder after heating was partially agglomerated, but the oxygen content was 1250 ppm. The above-mentioned two kinds of powders in the calcined state were individually coarsely crushed, transferred to a ball mill, replaced with argon gas in the ball mill, and then pulverized for 2 hours. Next, these two kinds of powders are mixed with Ni-30.
Ni powder 15.0%, Ni ₂ so that at% P (18.44 wt% P)
P powder was mixed with 85.0% and mixed with a V-type blender. The obtained mixed powder is filled in a can for HIP made of soft iron, and 1200
HIP was carried out at kgf / cm ² and 840 ° C., and the obtained sintered body was machined into a target of φ200 mm × 4 mmt (Sample N
o.1).

As a comparative example, the above-mentioned two kinds of raw material powders were blended in the above proportion as they were without heat treatment in a hydrogen atmosphere and mixed in a V-type blender. The oxygen content of this mixed powder was 4080 ppm. When this powder was subjected to X-ray diffraction, only the presence of the raw materials Ni and Ni ₂ P was confirmed.
This powder was subjected to HIP in the same manner as above, and was machined into a target of the same size (Sample No. 2). As a comparative example, the above-mentioned two kinds of raw material powders of pure Ni and Ni ₂ P were blended in the above proportions and mixed by a V-type blender. This mixed powder
It was heated in a pure hydrogen atmosphere at 800 ° C. for 2 hours. The powder after heating was partly aggregated, but the oxygen content was 1180 ppm. When this powder was subjected to X-ray diffraction, a slight amount of Ni ₂
Although the presence of P was confirmed, the diffraction pattern confirmed that the presence of Ni ₁₂ P ₅ was predominant, and that the phase composition corresponded to the blended composition Ni-30 at% P. This powder was also subjected to HIP as described above. However, the sintered compact after removing the HIP can had a dull metallic luster and was insufficiently compacted (Sample No. 3).

As a result of X-ray diffraction of the fragments of the three types of targets obtained as described above, almost all of them were Ni ₁₂ P.
₅ , Ni ₂ P was present in a very small amount, and the composition was N
The phase composition corresponded to i-30 at% P. Table 1 shows the density ratio of the target (relative density to the true density) and the oxygen content contained in the target. As shown, the target (sample No. 1) of the present invention in which the raw material powders were individually heated in hydrogen so as not to contain Ni ₁₂ P ₅ as a raw material immediately before sintering, and reduced and then mixed, It can be seen that the density ratio is higher and the oxygen content is lower than the target of the comparative example.

[0016]

[Table 1]

(Example 2) Average particle size 10 μm, oxygen content
1550ppm pure Ni raw material powder in pure hydrogen atmosphere at 600 ℃
After heating for 2 hours, a low phosphorus-side raw material was obtained. The powder after heating was partly aggregated, but the oxygen content was 540 ppm. on the other hand,
A Ni ₂ P raw material powder (Ni-33.4 at% P powder) having an average particle diameter of 8 μm and an oxygen content of 2850 ppm was heated in a pure hydrogen atmosphere at 800 ° C. for 2 hours to obtain a high phosphorus-side raw material. The powder after heating was partially agglomerated, but the oxygen content was 820 ppm. In addition, a raw material powder (Ni-40.5at% P powder) of a Ni ₂ P-Ni ₅ P ₄ eutectic alloy having an average particle size of 8 μm and an oxygen content of 3600 ppm was heated for 2 hours in a pure hydrogen atmosphere at 800 ° C. A high phosphorus side raw material was obtained.
The powder after heating was partially agglomerated, but the oxygen content was 1280.
It was ppm.

The three kinds of powders in the calcined state were individually crushed, transferred to a ball mill, replaced with argon gas in the ball mill, and crushed for 2 hours. Then, these 3 kinds of powders were combined in the combination shown in Table 2 to obtain Ni-20at% P (1
1.65 wt% P), and mixed with a V-type blender. The obtained mixed powder was filled in a can for HIP made of soft iron, HIP was performed at 1200 kgf / cm ² and 840 ° C., and the obtained sintered body was machined to be a target of φ200 mm × 4 mmt of the present invention ( Sample No.4,5,6). As a comparative example, powders similar to the above three types of raw materials were blended in the V type blender in the proportions of the three types shown in Table 2 as they were without performing heat treatment in a hydrogen atmosphere. The oxygen content was as shown in Table 2. HIP was applied to these powders in the same manner as described above, and targets having the same dimensions were machined (Samples No. 7, 8, 9).
From the above, the obtained target fragments after sintering are X-rayed.
As a result of line diffraction, both were hypereutectic Ni-Ni ₃ P,
The phase composition corresponded to the compounding composition Ni-20 at% P.

[0019]

[Table 2]

Table 3 shows the density ratio (relative density to the true density) of the target obtained by HIPing the mixed powder of Table 2 and the oxygen content contained in the target. As shown in the table, it is understood that the target of the present invention, which is a mixture of powders heated and reduced in hydrogen, has a higher density ratio and a lower oxygen content than the target of the comparative example.

[0021]

[Table 3]

(Example 3) The target of the present invention produced in Examples 1 and 2 was placed on an aluminum substrate having a nickel-phosphorous electroless plating layer having a thickness of 15 µm and having a textured surface. A nickel-phosphorus base film was formed by sputtering to have a film thickness of 300 Å.
A magnetic film of 80Co-10Cr-10Pt at at% was formed on the base film by sputtering to have a film thickness of 500Å. The target of the sample No. 3 of Example 1 had a low density ratio, and thus was excluded from the target of sputtering. Further, a 200 Å carbon film was formed on the magnetic film by sputtering to form a hard disk.

The oxygen content of the nickel-phosphorus underlayer of this hard disk, the coercive force of the magnetic layer, the average crystal grain size of the magnetic layer, the track width of 13 μm, and the MI of the gap length of 0.46 μm.
Table 4 shows the S / N ratio when measured with a G head at a peripheral speed of 7 m / s, a flying height of 0.1 μm, a recording frequency of 5 MHz, and a recording density of 36 kfci. The sample numbers in Table 4 correspond to the sample numbers of Examples 1 and 2. From Table 4, by using the target of the present invention, a low-oxygen underlayer film is obtained as compared with the case of using a conventional target with a high oxygen content, and it is possible to form the low-oxygen underlayer film. It can be seen that, as the coercive force of the magnetic thin film increased, the average crystal grain size decreased, and an excellent hard disk with less noise was obtained.

[0024]

[Table 4]

[0025]

According to the present invention, a target composed of low oxygen and high density nickel and phosphorus can be manufactured.
By using this target, the crystal in-plane orientation of the magnetic thin film can be improved, and as a result, the coercive force, which is a basic characteristic required for the magnetic thin film for the magnetic recording medium, can be improved. Further, forming a thin film with a target having a high density ratio and reducing the oxygen content of the base film are also effective in improving the S / N ratio.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G11B 5/84 Z 7303-5D H01F 10/26 41/18

Claims (4)

[Claims] 1. A sputtering target for forming an underlayer of a magnetic thin film, which is essentially composed of nickel and phosphorus, has an oxygen content of 2000 ppm or less, and has a density ratio of 97% or more. 2. The content of nickel simple substance powder or phosphorus
Low phosphorus side raw material obtained by heat-treating one or more powders selected from compound or alloy powders of 25 at% or less in a reducing atmosphere, and one selected from compounds or alloys having a phosphorus content of 33.3 at% or more A high-phosphorus-side raw material obtained by heating the above powders in a reducing atmosphere, is mixed in a desired composition ratio of nickel and phosphorus, and sintered to form a sputtering target for forming an underlayer of a magnetic thin film. Production method. 3. The sputtering target for forming an underlayer of a magnetic thin film according to claim 2, wherein the low phosphorus-side raw material and the high phosphorus-side raw material are mixed and pulverized, or pulverized individually and then sintered. Manufacturing method. 4. The method for producing a sputtering target for forming an underlayer of a magnetic thin film according to claim 2, wherein the sintering is performed at a temperature lower than a liquidus temperature.