JP3328921B2 - Target for magneto-optical recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sputtering target used for manufacturing a magneto-optical recording medium and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a sputtering method for forming a thin film by sputtering a target has been applied to the production of an alloy thin film of a rare earth metal and a transition metal as a magneto-optical recording medium. In the production of this sputtering target,
For example, as described in JP-A-63-45366, a melting casting method using an induction heating furnace under an argon atmosphere can be used. The advantage of the melt casting method is that the oxygen content is low and the used target can be easily recycled. On the other hand, the target obtained by the melt casting method has a problem that the crystal grain size is large due to the dissolved structure, and the structure tends to be uneven because the segregation is likely to occur. Further, the composition for obtaining magneto-optical recording properties is as follows:
Since the composition is substantially an intermetallic compound, there is a problem that the target obtained by the melt casting method is brittle and easily cracked.

[0003] In recent years, a manufacturing method using powder sintering has been proposed in order to reduce the unevenness of the structure due to the segregation described above. For example, Japanese Patent Application Laid-Open No. 61-91336 describes a production method in which an arc-melted alloy ingot is pulverized and sintered by hot pressing to eliminate segregation and obtain a uniform structure. Also, JP-A-61-13963
No. 7 discloses a manufacturing method in which a quenched alloy powder is sintered in a vacuum or an inert gas atmosphere, and the crystal grain size of a target structure is specified to be 20 μm or less. According to this method, the amount of oxygen in the sintered body can be reduced and brittleness can be reduced as compared with the case where an alloy powder is produced by performing ingot grinding. Also, Japanese Patent Application Laid-Open No. 61-139637 proposes that the crystal grain size of the target structure is specified to be 20 μm or less so as to eliminate unevenness in composition. These targets are called pre-alloy targets because they use raw material powders that have been alloyed in advance.

[0004]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-open No.
The method of using quenched alloy powder as a raw material and reducing the oxygen amount of a target described in 139637 is an effective method for improving the brittleness of the target. However, at present, further improvement in mechanical strength is required. In such a situation, as a method for increasing the mechanical strength, a target in which a rare earth metal element and a transition metal are combined in a diffusion phase has been proposed in JP-A-61-119648. Further, a target having a structure in which a rapidly solidified powder of a rare earth metal and an iron group metal is joined to an iron group metal powder is disclosed in JP-A-1-2597.
No. 7 is proposed. Such a target is called a composite target and can achieve an improvement in mechanical strength.

[0005] In recent sputtering, a magnetron sputtering apparatus capable of increasing a sputtering rate by generating a magnetic field on a target surface and confining plasma during sputtering has been used. In this magnetron sputtering apparatus, it is required to provide a sufficient leakage magnetic flux to the target surface. However, in the above-described composite target, an iron group metal exhibiting ferromagnetism basically remains in the structure, and there is a problem that it is difficult to obtain a leakage magnetic flux. On the other hand, the pre-alloy target disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-139637 has a smaller magnetic permeability due to alloying, and is more advantageous than the above-mentioned composite target in applying magnetron sputtering.

Particularly, in a target using an expensive rare earth metal, it is necessary to use one target as efficiently as possible, and it is a serious problem that it is difficult to obtain a leakage magnetic flux. Therefore, pre-alloy targets are being reviewed in place of the above-described composite targets. Further, there has been a strong demand for further improvement of mechanical strength, which is a problem of pre-alloy targets. The present invention has been made in view of the above-described problems, and has as its object to provide a target capable of obtaining a sufficient leakage magnetic flux and having high mechanical strength, and a method of manufacturing the same.

[0007]

Means for Solving the Problems The present inventor has studied in detail the method for further increasing the mechanical strength of the pre-alloy target in relation to the structure of the target. Then, instead of making the target structure a uniform structure, powder metallurgy is adopted, and sintering is performed in a state where the form of the prealloyed raw material powder substantially composed of an intermetallic compound is obtained. The inventors have found that the mechanical strength can be increased as compared with the above, and have reached the present invention.

[0008] That is, the present invention relates to the method of
An alloy powder comprising 0% of a rare earth metal and the balance transition metal is
This is a target for a magneto-optical recording medium having a target structure sintered substantially while leaving the form of an alloy powder. Specifically, the target is a target having a trace of the particle surface of the alloy raw material powder having the above composition left in the structure. More specifically, the present invention relates to a method in which a particulate structure having a form of an alloy powder having a composition of 15 to 30% by atom% of a rare earth metal and a balance of a transition metal is connected via a grain boundary phase. This is a target for a magneto-optical recording medium having a tissue and a bending strength of the target of 50 MPa or more. Preferably, in the microstructure of the target, the particulate structure connected via the intergranular phase between the alloy powders has a particle diameter d of substantially d ≦ 3.
50 μm, more preferably d ≦ 250 μm, and the volume average diameter dav is set to 50 ≦ dav ≦ 120 μm.

It is desirable that the target has a relative density of 99% or more and an oxygen content of 1000 ppm or less in terms of relative density.
It is desirable to set it to a or more.

For the above-mentioned target, for example, a pre-alloyed alloy powder having a target composition of 15 to 30% by atom% of a rare earth metal and a balance transition metal is manufactured in advance, and then the alloy powder is mixed with a liquid having the target composition. It can be manufactured under the condition that pressure sintering is performed at a temperature 30 ° C. or more lower than the phase onset temperature and a high pressure of 90 MPa or more.
Required.

[0011]

As described above, the greatest feature of the microstructure of the present invention is that the grain structure whose size is the alloy powder to be used is connected via the grain boundary phase to form the target structure. That is what we did. In a conventional method for manufacturing a target from a pre-alloy, as the sintering of alloy powders having an intermetallic compound composition proceeds, the structure becomes uniform through diffusion at the interface of the alloy powder. That is, finally, the shape of the original raw material powder is not retained, and the boundaries of the particles are eliminated. A typical microstructure of a conventional target of this type is as shown in FIG. In this state, the entire target is composed of one intermetallic compound, that is, it approaches the structure of the melt casting method,
It will have the brittleness peculiar to the intermetallic compound.

Therefore, in the present invention, sintering is not advanced until a uniform structure is obtained, and the sintering is performed in a state where raw material powders having a granular structure are connected via a grain boundary phase generated between alloy powders. The sintering was stopped and the progress of diffusion by sintering was stopped to some extent. The microstructure of the target of the present invention is such that the surface morphology of the raw material powder is almost left, that is, a trace of the raw material powder is left, as typically shown in FIG. In addition, FIG. 1 shows what was etched with a nital solution and magnified 50 times and 100 times. When pressure sintering is used as in the production method of the present invention, the outermost portion of each powder is slightly deformed due to pressure, and some diffused portions are recognized, but the original shape and size of the particles are recognized. Is clearly recognized even from a microstructure of about 50 times that of the target of the present invention which is a sintered body. Sintering "substantially" in the form of an alloy powder indicates such a state. The existence of this particulate structure is confirmed by the above-described etching, and a grain boundary phase formed from the raw material powder, in which the etching easily proceeds, is formed between the particulate structures that are substantially intermetallic compounds. Have been. Due to the presence of the grain boundary phase, a region for buffering thermal stress and the like during the sputtering period is formed, and the generation of cracks, chips, and the like during the sputtering period of the target can be prevented. In addition, since the formation of the grain boundary phase increases the mechanical strength of the target itself as compared with a target having a uniform structure, processing into a target shape is easy and handling is also easy.

In the present invention, the grain structure constituting the target of the present invention, that is, the composition of the alloy powder is defined as atomic%.
Thus, the composition was made up of 15 to 30% of the rare earth metal and the balance transition metal. This composition range corresponds to a composition range in which practical characteristics (coercive force, Kerr rotation angle, Curie temperature) as a magneto-optical recording medium can be obtained. This composition range forms an intermetallic compound having a low magnetic permeability between the rare earth metal and the transition metal. According to the present invention, the target itself can have a low magnetic permeability because the particulate structure of such an intermetallic compound having a low magnetic permeability is formed by bonding through a bonding interface.

In the target of the present invention, the particle size of the particulate structure observed microscopically is preferably d ≦ 35.
0 μm, more preferably d ≦ 250 μm, and the average volume diameter is 50 ≦ dav ≦ 120 μm. The reason why the upper limit of the particulate structure is set to 350 μm, preferably 250 μm is that when the particle structure is large, the amount of the bonding interface is reduced, the transverse rupture strength is reduced, and cracks are easily generated. When only alloy powders having the same particle size are used, the filling property between the particles is deteriorated. Therefore, it is preferable that the particle size has a distribution. The average volume diameter dav is set to 50 ≦ dav.
≦ 120 μm means that it is necessary to prepare a raw material powder in order to make the granular structure fine, but if the raw material is too fine, it is likely to contain oxygen, and there is a risk of becoming brittle due to the inclusion of oxygen. That's why. On the other hand, if the particle size is too small, diffusion tends to proceed excessively when trying to increase the density, making it difficult to maintain a particulate structure and reducing the strength in some cases. The volume average diameter is an average diameter of particles based on the following equation. dav = ((Σndp∧3) / Σn) ∧1 / 3, n: number of particles, dp: particle size of each particle, ＾: power number

The raw material powder prepared for producing the target of the present invention has substantially the same shape as the raw material powder and becomes a particulate structure, and the particle size of the granular structure of the target structure of the present invention. In order to make the above range, it is necessary to similarly limit the particle size of the raw material powder. According to such a rule, the relative density is 99% or more and the oxygen content is 1000 pp.
m or less, and a target having a transverse rupture strength of 70 MPa or more can be obtained.

In the production method of the present invention, in order to obtain a particulate structure as described above, 15%
A raw material powder having a target composition consisting of up to 30% of a rare earth metal and a balance transition metal is produced as a prealloy. Then, the raw material powder is pressure-sintered at a temperature of 30 ° C. or more lower than the liquid phase onset temperature of the target composition under a high pressure of 90 MPa or more, and when the target is viewed microscopically, the particulate structure becomes an alloy. A target structure connected via a grain boundary phase between particles is obtained. What is important here is the relationship between pressure, temperature, and composition. The liquid phase onset temperature varies greatly depending on the composition. Near the liquid phase onset temperature, solid phase diffusion occurs rapidly,
The structure becomes invisible at the bonding interface, and reduces the mechanical strength of the target. On the other hand, if the pressure is too low, sintering will not proceed, and pores will be present, which also causes insufficient density and mechanical strength as a target. In the present invention, it is necessary to perform sintering under the conditions satisfying the above-described temperature and pressure, and to stop sintering in a state where the bonding interface exists.

The sintering temperature is preferably 30 to 100.degree. C. lower than the liquid phase onset temperature because too low a temperature causes insufficient consolidation. In the production of the raw material powder of the present invention, a rapid solidification method such as gas atomization or centrifugal quenching is preferable to pulverization for reducing oxygen. Since sintering of raw material powder requires low temperature and high pressure,
It is preferable to perform pressure sintering using (hot isostatic pressing). By the HIP method, it is possible to easily obtain a high-density sintered body having a relative density of 99% or more when the density of the cast ingot is 100%. In a normal hot press, the load is limited to about 10 to 20 MPa, and it is difficult to perform sufficient consolidation to a high density close to the true density. The hot pressing is uniaxial compression, but the HIP method is isotropic compression, so that the sintered body has no anisotropy and is advantageous in improving mechanical strength.

The HIP method capable of performing isotropic compression is effective for maintaining the shape of the raw material powder and securing the bonding interface. In uniaxial compression such as hot pressing, sintering of raw material powders proceeds in the compression direction,
If you try to increase the density, the diffusion in the compression direction will progress too much,
The grain boundary phase effective for securing mechanical strength partially disappears, which may lead to insufficient strength, which is not preferable.

In the target of the present invention, a single or composite iron group element of Fe, Co, and Ni is preferably selected as a transition metal for obtaining magneto-optical characteristics. Rare earth metals for obtaining magneto-optical characteristics include Nd, Gd, and Td.
b, Dx, Ho, Ev, and Tm can be used alone or in combination. In addition, as a thin film for a magneto-optical recording medium,
In addition to the basic characteristics of magneto-optical characteristics, as elements for improving corrosion resistance, Ti, Al, V, Nb, Ta, Cr, Mo,
One, two or more of W, Pd, and Pt can be added in an amount of 15 atomic% or less. Specifically, Tb 20 to 30
%, Fe 60 to 80%, and Co 10% or less, for example, Cr 1 to 4% or Nb 0.5 to 3% may be added alone or in combination. These elements for improving the corrosion resistance are not preferable for the magneto-optical properties, and the smallest possible amount is added according to the required corrosion resistance. Regarding the form of addition, it may be added as a simple substance or may be added after being alloyed.

[0020]

【Example】

(Example 1) Atomic%, Tb 26%, Fe 68%, Co6
% Of rare earth-transition metal alloy ingots were produced in a vacuum induction melting furnace. The charge weight was 12 kg, the degree of vacuum was 6 × 10−3 Pa, and the casting was performed in a vacuum after the melting was completed. Using this ingot, it was put into an atomizing device having a molten metal dropping nozzle at the bottom of the crucible, and powdered by argon gas atomizing. The particle size of the raw material powder was adjusted by sieving. In addition, the minimum particle size dmin and the maximum particle size dmax of the raw material powder were measured by a sedimentation type particle size analyzer.
The volume average diameter dav was determined. Although the obtained powder is a ternary alloy, the exact liquid phase onset temperature is unknown, but in the phase diagram, the liquid phase onset temperature is determined by the binary phase diagram of Fe and Tb, which are the main constituent elements of the iron group. 1187 ° C.

Next, this powder was sealed in a mild steel capsule and subjected to hot isostatic pressing (HIP) sintering to obtain a target material. HIP conditions: temperature 1140 ° C, pressure 100MP
a, Hold for 2 hours. The obtained target material is
Etching the surface using a 5% nitric acid ethyl alcohol solution (a nital solution), then 50 times or 100 times
The microstructure was observed at × 2, the volume average diameter of the particles was determined from the extracted particles by the intercept method, and the volume average diameter of the particulate structure was determined. In addition to the measurement of the bending strength as the mechanical strength, the measurement of the oxygen amount, the measurement of the density, and the measurement of the relative magnetic permeability were performed. As a comparative example,
Sample No. 2 was manufactured as an example in which the HIP temperature was increased, and sample No. 3 was manufactured using a target of the same composition manufactured by melting. Similar measurements were performed for these targets. These results are summarized in Tables 1 and 2. Note that the density is 10% of the density of the cast ingot manufactured before gas atomization.
This is the relative density when 0% is set.

[0022]

[Table 1]

[0023]

[Table 2]

FIGS. 1, 2 and 3 show photographs of the metal microstructures when the structures of the samples 1 to 3 were etched and observed. 1 to 3, which show sample No. 1 of the present invention, the shape of the sintering raw material powder is substantially maintained to form a granular structure, and this granular structure is It can be seen that the target tissue is constituted by being connected via the boundary phase. On the other hand, the target having a high HIP temperature shown in FIG. 2 showing the sample No. 2 cannot specify the boundary of the particulate structure even by etching. It can be seen that the target of this structure has a lower bending strength than the target of sample No. 1 of the present invention.

On the other hand, the casting target sample No. 3, which is one of the prior arts, has a low oxygen content, but has a segregated casting structure as shown in FIG.
Further, it can be seen that the transverse rupture strength is significantly reduced as compared with the target of sample No. 1 of the present invention. Further, from the measurement results of the relative magnetic permeability, it can be seen that Sample No. 1 of the present invention has both low relative magnetic permeability and high bending strength, and is suitable for magnetron sputtering.

Example 2 Raw material powders having compositions and particle diameters shown in Table 3 were produced in the same manner as in Example 1. The liquid phase onset temperatures shown in Table 3 are based on the assumption that the element with the highest content among the rare earth metals of Gd, Tb and Dy contains the total amount of the rare earth metals,
This is determined from the binary phase diagram assuming that the remainder is Fe. This powder was sealed in a mild steel capsule and subjected to hot isostatic pressing (HIP) sintering to obtain a target material. HIP
The conditions are 100 MPa, 2 hours, and the temperatures are as shown in Table 3.

After the surface of the obtained target material is etched using a 5% nitric acid ethyl alcohol solution, the volume average diameter of the particles is determined from the extracted particles by an intercept method, and the volume of the particulate structure is determined. The average diameter was determined. In addition to the measurement of the bending strength as the mechanical strength, the measurement of the oxygen amount, the measurement of the density, and the measurement of the relative magnetic permeability were performed. Sample No. 9 using fine granules as the raw material was HIP
The temperature is slightly lowered (1100 ° C). These results are summarized in Table 4. The density is a relative density when the density of the casting target is 100%.

[0028]

[Table 3]

[0029]

[Table 4]

The structure obtained by etching the obtained target of the present invention is such that the grain structure as observed in Example 1 and the grain boundary phase between the alloy particles as shown in FIG. As shown in Tables 2 and 3, the volume average diameter of the raw material is smaller than the other samples, and the volume average diameter of the particulate structure in the target structure is smaller.
There is a tendency for the bending strength to decrease slightly. Sample No. 7, which has a larger average particle size of the raw material than the other samples and a large particulate structure in the target structure, has a low oxygen content, but has a tendency for the transverse rupture strength to decrease slightly, and Also tended to be slightly lower. On the other hand, d ≦ 2
Within the range of 50 μm and the volume average diameter dav of the particulate structure
Sample Nos. 4, 5, 6, and 8 in which approximately 50 ≦ dav ≦ 120 μm
Indicates that a target with high bending strength and high mechanical strength was obtained. The relative permeability of each sample was 5
It was as low as below, and was suitable for magnetron sputtering.

Example 3 Atomic%, Tb 25%, Fe7
A rare earth-transition metal alloy ingot having a composition of 0% and 5% Co was manufactured in a vacuum high-frequency melting furnace. Charge weight is 12
kg, the degree of vacuum was 6 × 10−3 Pa, and after melting was completed, casting was performed in a vacuum. In this composition, the liquid phase onset temperature was determined to be 1187 ° C. in the same manner as in Example 1. In order to see the influence of the raw material powder, the ingot was first used to put it into an atomizing device having a molten metal dropping nozzle at the bottom of a crucible, and a raw material powder (hereinafter, atomized powder) was obtained by argon gas atomization. Further, the same raw material melt was applied to a rotating disk and centrifugally quenched to obtain a raw material powder (centrifugally quenched powder). The ingot was pulverized with a ball mill to obtain a raw material powder (pulverized powder). For these raw material powders, the particle size of the raw material powder is adjusted by sieving classification, and the maximum particle size is 250 μm,
The particles were adjusted to have a minimum particle size of 15 μm and an average particle size of 90 μm.

As a sintering method, HI at 1120 ° C.
P was applied in the same manner as in Example 1, and was sintered and consolidated.
20 MPa, 112 under a vacuum of 0-3 or less Pa
Hot press (HP) at 0 ° C for 2 hours, and 300M by CIP (cold isostatic press) method
Pre-forming was performed at Pa, and a normal pressure sintering method was used in which the mixture was heated at 1120 ° C. for 2 hours in a vacuum furnace having a pressure of 10 −3 Pa or less. The characteristics of the target obtained when the production method of the raw material powder and the sintering method were changed were evaluated in the same manner as in Example 1.
Table 5 shows the results. Under these conditions, a particulate structure was confirmed by etching.

[0033]

[Table 5]

As shown in Samples Nos. 11 and 15 shown in Table 5, in a hot press (HP) having a low pressure during sintering, the density could not be increased under these conditions. Also, sample
In the normal pressure sintering method applied to No. 13, only a target having a lower density than that of the hot press method was obtained, and the transverse rupture strength was extremely small, indicating that this is not a preferable method. In addition, when the atomizing method or the centrifugal quenching method, which is a rapid solidification method, is applied as a method for producing the powder, the amount of oxygen in the target can be suppressed to a low level.

Example 4 As shown in Table 6, an alloy powder and Cr and Nb powders were prepared. The alloy powder was produced by the same gas atomization method as in Example 3. The particle diameter of the alloy powder was adjusted by sieving to adjust the particle diameter of the raw material powder. The maximum particle diameter was 250 μm, the minimum particle diameter was 15 μm, and the average particle diameter was 90 μm. Was prepared. Cr and Nb are commercially available powders having a particle size of under 44 μm. These powders were prepared to have the compositions shown in Table 6 as simple powders or mixed powders.
These powders are encapsulated in mild steel capsules and hot isostatic pressing
(HIP) sintering was performed to obtain a target material. The HIP conditions are 100 MPa, 2 hours, and 1120 ° C. The obtained target was evaluated in the same manner as in Example 1. Table 7 shows the results
Shown in In addition, in the microstructure of the obtained target obtained by sintering, it was confirmed that a particulate structure was present, and the particle size of the particulate structure was evaluated.

[0036]

[Table 6]

[0037]

[Table 7]

As shown in Tables 6 and 7, Cr and Nb
It can be seen that a target having both high bending strength and low relative magnetic permeability, that is, a bending strength of 70 MPa or more and a relative magnetic permeability of 5 or less was obtained even in the case where was added. When Cr and Nb were mixed and obtained as a powder, it was confirmed that a single phase of Cr and Nb remained in the structure. Since the presence of a different phase in the target may hinder uniform erosion progress during the sputtering period, it is desirable to introduce Cr and Nb in advance not as a simple substance but as an alloy powder.

[0039]

According to the present invention, a pre-alloy target having a low magnetic permeability is made to have a particularly high transverse rupture strength by forming a structure in which the form of the raw material powder is left, instead of a uniform structure. be able to. Therefore, the target of the present invention has high strength, and it is possible to sufficiently secure the leakage magnetic flux on the target surface required for magnetron sputtering by reducing the magnetic permeability. Therefore, the use efficiency of the target is increased, and abnormal discharge or the like during sputtering can be prevented. In addition, according to the method of the present invention, since high densification can be achieved in addition to high bending strength, prevention of processing cracks, prevention of contaminant contamination, further improvement of use efficiency (extension of life), and occurrence of abnormal discharge Prevention can be expected.

[Brief description of the drawings]

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

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

FIG. 3 is a photograph showing a metal microstructure of a target manufactured by a melting method of a comparative example.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification code FI G11B 11/105 546 G11B 11/105 546K (58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 14/00-14 / 58 B22F 1/00-8/00 C22C 1/04-1/05 C22C 33/02

Claims (8)

(57) [Claims] 1. A magneto-optical device characterized in that an alloy powder comprising 15 to 30% of a rare earth metal and a balance transition metal in atomic% has a sintered target structure substantially in the form of an alloy powder. Target for recording media. 2. A sintered body composed of 15 to 30% of a rare earth metal and a balance transition metal in atomic%, wherein when the sintered body is observed microscopically, an alloy material having the above composition is contained in the structure. A target for a magneto-optical recording medium, characterized by leaving a trace on the surface of a powder particle. 3. A target structure in which a particle structure in the form of an alloy powder having a composition of 15 to 30% of a rare earth metal and a balance of transition metal in atomic% is connected via a grain boundary phase. And the bending strength of the target is 50MP
a. The target for a magneto-optical recording medium, which is not less than a. 4. The target microstructure according to claim 3, wherein the grain structure connected via the grain boundary phase between the alloy powders has a particle diameter d substantially d ≦ 350 μm. Target for magneto-optical recording media. 5. The particle size d of the particulate structure is d ≦ 250 μm.
And the volume average diameter dav of the particulate structure is 50 ≦
5. The target for a magneto-optical recording medium according to claim 1, wherein dav ≦ 120 μm. 6. A target having a relative density of 9
6. The target for a magneto-optical recording medium according to claim 1, wherein the target is 9% or more. 7. The oxygen content of the target is 1000 pp.
and m or less.
5. The target for a magneto-optical recording medium according to any one of the above. 8. The target for a magneto-optical recording medium according to claim 1, wherein the transverse rupture strength of the target is 70 MPa or more .