JPH0119448B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a target used in the production of thin films made of rare earth metals and iron group metals, which have recently attracted attention as magneto-optical recording materials, by sputtering. The invention relates to a method for manufacturing materials.

[Conventional technology]

Conventionally, target materials used when manufacturing magneto-optical recording media made of rare earth metals and iron group metals by sputtering are: A method of finishing an alloy ingot material manufactured by arc melting into a target of a predetermined size by cutting, grinding, etc.; (2) placing a rare earth metal chip on an iron group metal plate;
or vice versa, a method of making a composite target material by combining two types of target materials by placing an iron group metal chip on a rare earth metal plate; (3) an alloy produced by the method of (1) above; (4) A method in which alloy powder obtained by crushing an ingot is molded by hot pressing (Japanese Patent Application No. 1982-211967); Hot forming is performed in an active gas atmosphere at a temperature below the eutectic point of the metal components present in this mixture to form an intermetallic compound at the interface between the rare earth metal and the iron group metal, and to form an intermetallic compound at the interface between the rare earth metal and iron. It has been obtained by a method of joining metals of the group (Japanese Patent Application No. 59-219227).

[Problem that the invention seeks to solve]

However, the alloy target material manufactured by the method (1) above has the following problems: (i) a target with a large diameter cannot be obtained because the dimensions of the target depend on the size and shape of the melting furnace, and (ii) ) Furthermore, since it is not possible to obtain target materials with the desired dimensions and shape, especially thin-walled targets, by arc melting alone, post-processing such as cutting and grinding is required, which reduces productivity. Since the target material is brittle, it is difficult to perform post-processing and the yield is low.Next, the composite target material constructed by the method (2) above has the following problems: (i) abnormal electrical discharge between the plate and the chip; (ii) rare earth metals and iron group metals are distributed in large clumps, and the sputtering speed of single rare earth metals and iron group metals is different; The composition of the resulting film is not uniform over the entire film, and in the method (3) above in which alloy powder is formed by hot pressing, (i) impurities may be mixed in due to the crushing of the alloy ingot. (ii) Since the alloy powder was simply hot-pressed, the resulting target was mechanically brittle; (iii) The rare earth metal itself was extremely susceptible to oxidation, so it was difficult to avoid the above grinding process. As a result, the amount of rare earth metal oxide in the target material increases, and the proportion of elemental rare earth metal decreases accordingly, which not only makes it impossible to obtain a film with desired magnetic properties by sputtering. In severe cases, the film produced by sputtering often fails to become a perpendicularly magnetized film required for magneto-optical recording due to the influence of the oxides. Step (4) above of subjecting the combined mixture to hot forming.
In the target material manufactured by the method of The composition of the film being formed during sputtering changes over time, and the composition of the film becomes stable. The problem was that it didn't.

[Findings based on research]

Therefore, the inventors of the present invention have conducted various studies to solve such problems, and as a result, (1) finely divided Gd, Tb, Dy, Ho,
The rare earth metal formed by mixing a rare earth metal consisting of any one or more of Tm, Er, and alloys thereof, and an iron group metal consisting of Fe, Co, Ni, and alloys thereof in a similar state. : 30 to 50% by weight, and the remainder: The iron group metal is obtained by hot forming the mixture at a temperature below the liquid phase temperature of the metal component system present in the mixture. When the compact molded body is subjected to an appropriate heat treatment, that is, the molded body is heated for a short time to a temperature higher than the liquid phase onset temperature of the metal component system present in the molded body, the shape of the molded body changes. (2) In this way, the intermetallic compound forming reaction between the rare earth metal and the iron group metal is significantly promoted, and all the rare earth metals present in the compact are transformed into intermetallic compounds without collapsing; In a target material that no longer contains an elemental rare earth metal because all the rare earth metals have changed into intermetallic compounds, the difference in sputtering speed between rare earth metals and iron group metals will almost disappear, resulting in a film formation during sputtering. (3) Although the content of intermetallic compounds in such target materials increases significantly, it is expected that their strength will decrease. Due to the single iron group metal mixed in the structure of the target material, the strength of the target material does not decrease unexpectedly, ensuring sufficient workability, and also avoiding the occurrence of cracks due to heat shrinkage. I discovered what I could do.

[Means for solving problems]

This invention was invented based on the above knowledge, and when a film made of a rare earth metal and an iron group metal used as a magneto-optical recording medium is manufactured by sputtering, the composition of the film changes during the sputtering. (a) Finely divided Gd, Tb, Dy, Ho, Tm
and one or more rare earth metals selected from the group consisting of Er and alloys thereof, and one or more iron group metals selected from the group consisting of finely divided Fe, Co, and Ni, and alloys thereof. The above rare earth metal by mixing two or more kinds:
(b) forming a mixture having a composition of 30 to 50% by weight of the iron group metal, and the remainder: (b) adding the metal present in the mixture to the mixture in vacuum or in an inert gas atmosphere; Hot forming is performed at a temperature below the liquid phase development temperature of the component system to form a dense compact consisting of the rare earth metal and the iron group metal; (c) then, in a vacuum or in an inert gas atmosphere; , by subjecting the molded body to a heat treatment in which the molded body is heated for a short time to a temperature higher than the liquid phase onset temperature of the metal component system present in the molded body, the rare earth metal and the iron group metal are combined. The present invention relates to a method for producing a target material having a mixed structure of an intermetallic compound and an elemental iron group metal.

[Specific description of the invention]

Hereinafter, the configuration of the present invention will be specifically explained.

1 Raw materials Gd, Tb, Dy, which are the raw materials for the target material.
Rare earth metals selected from Ho, Tm, Er, and their alloys are generally not limited in their shape as long as they are finely divided. Desirably, when the average particle size is less than 10 μm, the oxygen concentration of the obtained target material increases to 0.5% or more, and the film produced by sputtering this material has the magnetic properties necessary for magneto-optical recording. On the other hand, if it exceeds 300 μm, the rare earth metal will not completely react with the iron group metal, and the rare earth metal will remain in the structure of the target material, so the average particle size is generally 10 to 300 μm. and preferably 10 to 100 μm.

The purity of rare earth metals is high purity (purity: 99% by weight)
above), and particularly preferably a low oxygen concentration (oxygen concentration: 0.4% by weight or less).

These alloys include Gd, Tb, Dy, Ho,
It means an alloy consisting of two or more of Tm and Er, such as Tb ₅₀ Gd ₅₀ , Tb ₇₅ Dy ₂₅ ,
Means alloys like Gd ₉₀ Ho ₁₀ .

Fe, which is another raw material for the target material,
Iron group metals selected from Co, Ni, and their alloys can generally have any shape as long as they are finely divided; however, these iron group metals are usually powders or small particles. If the average particle size is less than 1μ, the particles are too fine and the size of the iron group metal single particles remaining after heat treatment becomes too small, resulting in a significant decrease in the strength of the target material. On the other hand, if it exceeds 300 μm, the particle size of each individual iron group metal in the manufactured target material becomes too large, making it impossible to perform sputtering with a stable film composition. should generally be between 1 and 300 μm, preferably between 50 and 300 μm.

It is desirable that the purity of the iron group metal is high (purity: 99.99% by weight or more), and in particular, it has a low oxygen concentration (oxygen concentration: 0.01% by weight or less).

These alloys refer to alloys consisting of two or more of Fe, Co, and Ni, such as
Fe ₇₅ Co ₂₅ , Fe ₅₀ Co ₅₀ , Fe ₇₅ CO ₂₀ Ni ₅ , Co ₉₀ Ni ₁₀
means an alloy such as

In addition, in this invention, even if the proportion of rare earth metal blended in the mixture of rare earth metal and iron group metal is less than 30% by weight,
Even if the ratio of rare earth metals in the mixture exceeds 30 to 30, the resulting target material will not form a film with magnetic properties suitable for use as a magneto-optical recording medium. It was set at 50% by weight.

2 Hot Forming In this invention, in order to make the mixture into a dense compact, the mixture is subjected to hot forming by hot pressing, hot pack rolling, hot isostatic pressing (HIP), hot forging, etc. However, hot pressing and hot rolling are particularly suitable for producing thin plate-shaped target materials, and in order to prevent oxygen from entering the compact during hot forming, hot forming is carried out in a vacuum or in a vacuum. Must be carried out under an inert gas atmosphere, generally under pressure: 0.01
~10 ^-6 Torr vacuum or e.g. dew point −60
Argon gas at temperatures below °C is used.

The temperature applied to the mixture during hot forming must be below the liquid phase onset temperature of the metal component system present in the mixture, which would otherwise This is based on the fact that as a result of the metal being easily oxidized by the liquid phase that is generated, the oxygen concentration in the target material increases to more than 0.5% by weight, and this causes problems such as only the liquid phase flowing. The temperature applied in this hot forming differs depending on the forming method, but for example, in hot rolling, it is generally maintained 20 to 350°C lower than the liquid phase onset temperature.
The liquid phase development temperature of the metal component system is, for example, 840°C if the system is Fe-Tb, 695°C if it is Fe-Co-Tb, 830°C if it is Fe-Tb-Gd, and Co- In the case of Gd, it is 630℃.

Because hot forming results in plastic deformation of each metal particle in the mixture, partial solid phase diffusion between rare earth metals and iron group metals, and consequent formation and bonding of intermetallic compounds at the interface. , densification of the molded body and bonding between each particle therein are achieved, resulting in a dense, high-strength molded body with a relative density of generally 95-100%.

Usually 100-200Kg/cm ² in hot press
The pressure is applied, and the hot pressing time is sufficient as long as it is sufficient to cause the above-mentioned effect, and it varies depending on the temperature and pressure, but
Generally it is 1 hour or more.

In hot pack rolling, a mixed powder of rare earth metals and iron group metals is placed in a container made of iron alloy, and then the mixture is rolled until the pressure inside the container drops to 10 ^-5 Torr or less.
After the mixture is vacuum-packed in an iron alloy container by evacuating the gas in the container, it is heated at a temperature below the liquid phase of the metal component system present in the mixture. Roll.

The molded product formed by rolling is removed from the can by removing the surrounding can with a lathe or shaper.

3 Heat treatment Since the rare earth metal still remains in the form of an element in the molded body produced by the hot forming, all of this is converted into an intermetallic compound, and at the same time, the intermetallic compound and the elemental iron group metal are Heat treatment is performed to form a uniform mixed structure, but in order to do so, it is necessary to heat the molded body to a temperature higher than the liquid phase temperature of the metal component system present in the heat treatment. Generally, this temperature is suitable to be at the liquid phase onset temperature or 100 to 300 degrees Celsius higher than this temperature, and if the heating is continued for too long, the shape of the molded product may be distorted or the amount of oxygen in the target material may increase. Therefore, the heating time must be short, and although it varies depending on the composition, size, heat treatment temperature, etc. of the target material, it is usually about 10 to 900 seconds.

A heat treatment that satisfies these conditions is particularly advantageously achieved by high-frequency heating and electron beam irradiation heating, and even in this heat treatment, in order to prevent an increase in the oxygen content of the target material, the atmosphere used in the hot forming is A similar vacuum or inert gas atmosphere is applied.

High-frequency heating can ^be carried out, for example, by the following method: placing the molded body on a graphite or alumina jig in a high-frequency heating furnace,
10 ^-6 Torr vacuum or pressure: 0.1 to 10 ^-3 Torr
The molded body was heated to 900 to 1200°C in argon gas at a heating rate of 10 to 40°C/sec by high frequency heating.
Heat treatment by electron beam irradiation is carried out by, for example, the following method:
In an electron beam melting furnace maintained at a vacuum level of 1×10 ^-5 Torr or higher, a molded body placed on a water-cooled Cu hearth was heated with an output of 6.0×10 ^-2 to 3.0×10 ^-1 KW.
This is accomplished by rapid cooling after irradiation with an electron beam.

4. Composition and structure of the target material The target material manufactured through the above process is free from impurities that are unavoidably contained in the rare earth metals and iron group metals that are the raw materials, such as elements from Group A of the periodic table. , Si, Ca, Al, C, P, S,
Although it is unavoidable to contain small amounts of Ta, Mn, O, etc., it essentially consists of a uniform mixed structure of intermetallic compounds of rare earth metals and iron group metals, and single iron group metals, and in that structure, The sputtering rate of rare earth metals transformed into intermetallic compounds is adjusted to the same level as that of iron group metals, and the sputtering rate of iron group metals is generally adjusted to the same level as that of iron group metals. ~300μm
spherical or flake-like particles with dimensions of , giving the target material the necessary strength.

[Examples and effects based on the examples]

Next, the present invention will be explained by examples and in comparison with comparative examples.

Example 1 (a) Purity with average particle size: 100 μm:
99.9wt% Tb powder and purity: 99.99wt% Fe
The blending ratio of Tb:Fe is 44.52:55.48.
(% by weight) was mixed in toluene for 30 minutes using a ball mill and dried to prepare a mixed powder with a total weight of 250 g.

(b) Next, a stainless steel can with a wall thickness of 1.2 mm and a disc-shaped space of 120 mm in diameter x 4.0 mm in thickness (height) inside is placed in a stainless steel can with an inner diameter of 12.7 mm and a length of 500 mm. × Thickness: A stainless steel tube of 2.0 mm is installed vertically and the mixed powder is filled into the disc-shaped space, and the inside of the stainless steel can is evacuated to obtain a vacuum level of 1×10 ^-5 Torr. After evacuating to a maximum temperature, the base of the stainless steel tube was heated and pressed with a gas burner to seal the mixed powder inside the stainless steel can. The mixed powder thus vacuum-packed into a stainless steel can was hot rolled at a temperature of 550°C until the total thickness of the can was 4 mm, and the rolled stainless steel can was removed with a lathe to reveal its interior. The disk-shaped Tb-Fe molded body formed in the was taken out.

(c) After that, this molded body was set on a graphite jig in a high-frequency heating furnace, and the pressure: 1×
Under an argon gas atmosphere of 10 ^-3 Torr, 20
The temperature was raised to 1100°C at a heating rate of °C/sec, held at this temperature for 60 seconds, and then cooled to room temperature by blowing room temperature argon gas.

When the structure of the thus obtained target material having the composition of Tb ₂₂ Fe ₇₈ was observed using a microscope, it was found that all of the Tb forms intermetallic compounds with Fe, and some of the Tb undergoes a eutectic reaction. This causes a melt to precipitate, and in this target material, a mixed structure in which elemental Fe is uniformly distributed between the intermetallic compound and its eutectic, as shown in Figure 5 a and b, is formed. The size of this single Fe particle is 20 to 70μ.
m, and the relative density of this target material is
At 100%, the resistance force was 10.8 Kg/mm ² .

Next, in order to evaluate the performance of this target material, based on a target processed into a disk with a diameter of 127 mm and a thickness of 2 mm, the argon partial pressure was determined as follows:
After pre-sputtering at 5×10 ^-2 Torr for 30 to 60 seconds, bias voltage: 0V, sputtering power: 75W
While rotating the target material at a constant speed of 2 to 5 rpm, the slide glass was separated from the target by 70 mm, and magnetron sputtering was performed by changing the position from the center directly above the target, 3 cm from the center, and 6 cm from the center. A film for magneto-optical recording was manufactured using this method.

The oxygen content of the film obtained at this time was 1.5~
Figure 1 shows the change in the amount of Tb in the film with the elapse of sputtering time at 2.1 at.%.

From FIG. 1, it can be seen that even if the sputtering time is extended for a long time, the change in the film composition is extremely small at ±0.2 at.%.

Example 2 (a) Purity 99.9 with average particle size: 100 μm
% Tb powder, 99.99% purity Fe powder and 99.99% purity Fe-Co alloy (Fe:Co=75:25at.
%) powder, the blending ratio of Tb:Fe:Co is 45.4:
A predetermined amount was weighed so that the ratio was 47.9:6.73 (wt%), mixed in toluene for 30 minutes using a ball mill, and dried to produce a mixed powder.

(b) Next, 200 g of the mixed powder was filled into a hot press mold with an inner diameter of 127 mm, and the temperature was raised at a rate of 800°C/hr. When the temperature reached 660°C, the mixed powder was heated to a vacuum degree of: 1×10 ^-5 Torr or more,
Hot pressing was performed under the conditions of pressure: 200 Kg/cm ² and holding time: 1 hour, and after heating, the product was cooled in a furnace and a dense disc-shaped compact was taken out.

(c) This compact is then water-cooled in an electron beam furnace.
Placed on a Cu hearth, the molded body was irradiated with an electron beam of 1.3×10 ^-1 KW at a vacuum level of 1×10 ^-5 Torr or higher to form a target material with a composition of Tb _22.7 Fe _68.2 Co _9.1 . Manufactured.

When the structure of this target material was observed in the same manner as in Example 1, all of the Tb formed intermetallic compounds with Fe and Fe-Co, and some of them formed eutectics.
Between these intermetallic compounds and their eutectic
A mixed structure in which single crystal Fe particles of 60 μm in size were uniformly distributed was formed, and the relative density of this target material was 98% and the anti-deposition strength was 9.1 Kg/mm ² .

Next, in order to evaluate the performance of the target material, sputtering was performed under exactly the same conditions as in Example 1, except that the position was not changed using the target obtained from this target material, and a sputtering material for magneto-optical recording was prepared. A membrane was produced.

The oxygen content of the film obtained at this time was 1.5~
Figure 2 shows the changes in the Tb and Co contents of the film with the sputtering time at 1.9 at.%.

From FIG. 2, it can be seen that the change in composition of the film is extremely small at ±0.2 at.% over a long sputtering time.

Comparative Example 1 Purity with dimensions of diameter: 127 mm x thickness: 2.0 mm
Fe and Tb were formed by arranging 102 Tb chips with a purity of 99.9% having dimensions of diameter: 8 mm x thickness: 2.0 mm in concentric circles on a 99.99% Fe plate.
Sputtering was carried out under exactly the same conditions as in Example 1 using a composite target with Viewed from above, this composite target corresponded to a Tb ₂₀ Fe ₈₀ target expressed in % atomic weight.

The oxygen content of the film obtained at this time was 1.8~
Figure 3 shows the change in the amount of Tb in the film with the elapse of sputtering time at 2.5 at.%.

From FIG. 3, it can be seen that the composition of the film changes significantly over time.

Comparative Example 2 Sputtering was carried out under exactly the same conditions as in Example 1 using a target manufactured by finishing the Tb-Fe molded body obtained in Example 1 (b).

The oxygen content of the film obtained at this time was 1.3~
Figure 4 shows the change in the amount of Tb in the film with the elapse of sputtering time at 1.7 at.%.

It can be seen from FIG. 4 that the composition of the film obtained using this target also changes significantly over time.

[Overall effect of the invention]

As is clear from the above description, according to the present invention, it is possible to provide a high-strength sputtering target material that produces a magneto-optical recording medium with a stable composition and a low oxygen concentration.

[Brief explanation of drawings]

1 and 2 are graphs showing compositional changes that occur in a thin film during sputtering when a thin film is produced using a target material produced according to the present invention, and FIGS. The figure is a graph showing the compositional change of a similar thin film when a target material manufactured by the comparative method is used. Figure 5a is a micrograph showing the metal structure of the target material manufactured by the present invention. , and FIG. 5b is a schematic explanatory diagram for making the metal structure shown by the micrograph easier to understand.

Claims (1)

[Claims] 1 (a) Finely divided Gd, Tb, Dy, Ho,
one or more rare earth metals selected from the group consisting of Tm, Er, and alloys thereof;
One or more iron group metals selected from the group consisting of finely divided Fe, Co, and Ni, and alloys thereof are mixed to form a mixture of 30 to 50% by weight of the rare earth metal and the iron group metal. (b) the mixture is then heated in vacuum or in an inert gas atmosphere to a temperature below the liquid phase onset temperature of the metal component system present in said mixture; (c) Then, in a vacuum or in an inert gas atmosphere, the metal components present in the compact are heated to form a dense compact made of the rare earth metal and the iron group metal; By subjecting the compact to a heat treatment in which the compact is heated for a short time to a temperature above the liquid phase onset temperature of the system, the intermetallic compound of the rare earth metal and the iron group metal and the simple iron group metal are separated. A method for producing a target material having a mixed structure of 2 Claims characterized in that the hot forming is performed by vacuum packing the mixture of the rare earth metal and iron group metal in a metal container and then subjecting the mixture to hot pack rolling. The manufacturing method according to item 1. 3. The manufacturing method according to claim 1, wherein the hot forming is performed by hot pressing the mixture of the rare earth metal and the iron group metal. 4. Rapidly heat the molded body made of the rare earth metal and iron group metal by high-frequency heating to a temperature equal to or higher than the liquid phase onset temperature of the metal component system, and keep the shape of the molded body intact for a period of time. 4. The manufacturing method according to claim 1, wherein the heat treatment is carried out by maintaining the molded body at the temperature. 5 The process of irradiating the molded body made of the rare earth metal and the iron group metal with an electron beam and heating the molded body to a temperature equal to or higher than the liquid phase manifestation temperature of the metal component system is performed by scanning the electron beam. The manufacturing method according to any one of claims 1 to 3, characterized in that the heat treatment is performed by applying the heat treatment to the entire molded body.