JPH01242733A - Manufacture of alloy powder for rare earth metal-transition metal target and manufacture of rare earth metal-transition metal target - Google Patents

Abstract

PURPOSE:To reduce the oxygen content in a target or the like in the manufacture of subjecting the mixture of rapidly solidified alloy powder and rare earth metal to pressure sintering under a nonoxidizing atmosphere in the specific temp. by specifying the oxygen content in the above alloy material. CONSTITUTION:The mixture of each alloy powder constituted of rare earth metal and transition metal in the compositional range where eutectic structure is revealed and subjected to rapid solidifying treatment and transition metal powder less than the objective compsn. of the target is prepd. The mixture is subjected to pressure sintering in a vacuum or under the atmosphere of an inert gas in the temp. range less than the liquid-phase revealing temp. of the mixture. In the manufacture of the rare earth metal-transition metal target, the oxygen content of the molten material in the alloy to be subjected to rapid solidifying treatment is regulated to <=500ppm. By this method, the oxygen content in the target can regulatively be reduced, and, as the result, the magnetic anisotropy of a sputter film can be relieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an alloy powder for a rare earth metal-transition metal target used as a magneto-optical recording medium, and a method for producing a rare earth metal-transition metal target.

[Conventional technology]

Recently, magneto-optical disks have been developed that are replaceable and capable of high-density recording by forming a rare earth metal-transition metal thin film of a desired composition on a glass or resin substrate using a sputtering method and using this as a recording medium. It is being done.

Conventionally, the following methods have been proposed as methods for manufacturing targets used in this sputtering.

(1) A method of manufacturing a target by melting a rare earth metal-transition metal alloy with a desired composition in a vacuum or an inert gas atmosphere, and then casting it into a predetermined shape in a vacuum or an inert gas atmosphere (Nikkei News). Material 1986 11
Month 24th - Issue P61).

(2) A method in which an ingot is created by melting and casting an alloy with a desired composition in a vacuum or an inert gas atmosphere, and the ingot is crushed and the resulting powder is pressure sintered (Japanese Patent Application Laid-open No. No. 61-91336).

(3) A method in which rare earth metal powder and transition metal powder are mixed to a desired composition, and the mixed powder is sintered under pressure in a temperature range below the liquid phase development temperature (Japanese Patent Laid-Open No. 61-99640).

(4) A method of producing transition metal-rare earth metal powder with a smaller amount of transition metal than the target component by a melting and pulverizing method, mixing the alloy powder and transition metal powder to a desired composition, then molding and sintering. (Unexamined Japanese Patent Publication No. 60-230903).

However, when the target is created using the manufacturing method described in (1) above.

(a) Segregation of added elements tends to occur during U manufacturing, making it difficult to obtain a homogeneous target.

(b) Rare earth metal-transition metal alloys form extremely brittle intermetallic compounds, making it difficult to undergo structural homogenization processes such as forging. Therefore, defects such as cavities that occur during casting are removed. It is impossible.

(c) Since the material is brittle, chipping and cracking easily occur when processing into a target shape, making machining very difficult. Furthermore, the target may crack due to thermal stress during bonding and sputtering.

(d) The composition of the thin film created by sputtering the target according to this manufacturing method is 7 to 10% from the target composition.
A shift of nearly t% occurs in the transition metal alloy, making it difficult to control the thin film composition.

There are other problems.

When a target is manufactured using the manufacturing method described in (2) above, it is possible to manufacture a homogeneous target, but since the constituent particles of the powder themselves are made of a brittle intermetallic compound, the same problem as that of the target manufactured using the process described in (1) above occurs. There is a point.

When produced using the manufacturing method described in (3) above, (a) Rare earth metals have a strong affinity for oxygen, so the rare earth metals are oxidized during powder production, powder handling, and pressure sintering, resulting in low oxygen It may not be possible to obtain a molded body. When such a molded body is used as a sputtering target,
The oxygen contained in the target is taken into the thin film,
Since the rare earth metal is selectively oxidized, the magnetic properties of the thin film, especially the coercive force Hc, vary greatly.

(b) At the initial stage of sputtering, the rare earth metal phase is sputtered preferentially than the transition metal phase, and thereafter the sputtering rates of the transition metal phase and the rare earth metal phase reach equilibrium. For this reason, it is necessary to perform pre-sputtering for a long time until the composition of the thin film becomes stable, resulting in poor target usage efficiency.

There is a problem.

The manufacturing method of (4) above, specifically, as disclosed as an example in the published patent publication of (4), a transition metal-rare earth metal alloy powder is mixed with a transition metal of about 1 to 2 IO weight in a desired composition. When the mixed powder is mixed so that Although it takes a short time, the difference between the target composition and the thin film composition is large, and the amount of composition change within the thin film plane is also large.

(b) After compacting the mixed powder, in an inert gas or
Simply sintering in a vacuum does not increase the density of the compact, and pores remain in the target, which can cause abnormal discharge during sputtering.

(c) From the viewpoint of machining, the above (1) and (2)
), but since all the rare earth metals contained in the material exist as intermetallic compounds with transition metals, cracks and cracks may occur when machining with a lathe etc. Easy to cause chipping.

There are other problems.

JP-A No. 62-70550 discloses an intermetallic compound of a rare earth metal and one or more of Fe, Co, and Ni (referred to as iron group metals) as Targera 1-, which attempts to solve the problems of the prior art described above. , a target having a fine mixed structure in which an elemental iron group metal is bonded by sintering is disclosed.

That is, rare earth metal powder and iron group metal J1M powder are mixed to a desired composition, and then pressure sintered at a temperature below the liquid phase development temperature to form a compact made of rare earth metal and iron group metal. The rare earth metal in the compact is converted into an intermetallic compound by heating the compact for a short time at a temperature equal to or higher than the onset temperature, thereby obtaining a target with the above-mentioned structure.

According to this target, the rare earth metal converted into an intermetallic compound has a sputtering rate that is lower than that of a single element and approaches the sputtering rate of a single iron group metal, resulting in unstable thin film composition, which has been proposed in the past. This problem is solved by the iron group metals present in the target.

It is also possible to have strength that sufficiently guarantees workability.

However, according to the inventor's study, Japanese Patent Application Laid-Open No. 62-705
The technique disclosed in No. 50 also has the following problems, and further improvements are desired.

That is, (a) According to the 10th Academic Conference Abstracts of the Journal of Applied Magnetics (1,986, I) 128-129), the compositional deviation between the target and the thin film is due to rare earth metals, transition metals,
It has been reported that improvements can be made by appropriately controlling the ratio of rare earth metal-transition metal intermetallic compounds.

However, in the method of controlling the structure by heat treatment as in JP-A No. 62-70550, l) the intermetallic compound layer around the single iron group metal grows abnormally; 1i) Fig. 6 of JP-A No. 62-70550. According to C, in addition to the iron group metal elemental phase and the intermetallic compound phase, there is a eutectic alloy phase consisting of the alpha phase of the rare earth metal and the rare earth metal-iron group metal intermetallic compound phase. It is very difficult to control the crystallization site and shape of the α phase of the rare earth metal in the crystal alloy phase and the rare earth metal-iron group metal interlayer compound, iii) It is easy to cause unevenness in the structure, etc. There are drawbacks. Therefore, when sputtering is performed using the above target, i) the film composition and characteristics will change as the sputtering time becomes longer; Different characteristics. There is a problem that so-called lot-to-lot variation is large.

(b) From the viewpoint of mechanical strength, it is necessary to thin the fragile rare earth metal-iron group metal intermetallic compound that exists around the iron group metal, but as mentioned above, it is preferable because the layer thickness becomes thick due to abnormal growth. do not have.

(c) A target made by sintering a mixture of rare earth metal powder and iron group metal powder tends to have a high oxygen content, and since it undergoes heat treatment, the final product tends to have a high oxygen content, which has a negative effect on thin film properties. .

(d) When cooling from the heat treatment temperature to room temperature, the molded product is likely to warp or bend.

[Problem to be solved by the invention]

As a means to solve the above problems, the present inventors have developed a rare earth metal-transition system in which the alpha phase and intermetallic compound phase of a rare earth metal obtained by a rapid solidification process such as a gas atomization method are uniformly and finely crystallized. We have previously proposed a method in which a mixture of metal alloy powder and transition metal powder is sintered under pressure at a temperature below the liquid phase onset temperature.

The target obtained by this method has a eutectic alloy layer in which the α phase of the rare earth metal and an intermetallic compound of the rare earth metal and a transition metal are uniformly and finely dispersed, and a transition metal elemental phase mainly composed of the intermetallic compound. The structure is bonded by a solid-phase bonding layer, which reduces the compositional deviation between the target and the thin film and stabilizes the thin film composition during long-term sputtering.

By the way, when considering a thin film obtained by sputtering using a rare earth metal-transition metal target, it is necessary to suppress the amount of oxygen contained in the target.

In other words, a perpendicularly magnetized film is a necessary condition for magneto-optical recording media, but if the target contains a large amount of oxygen, a stable perpendicularly magnetized film cannot be obtained, and a so-called in-plane magnetized film cannot be obtained. It may show similar behavior.

In view of the above facts, the present invention aims to provide a method for producing a rare earth metal-transition metal target with a low oxygen content.

[Means to solve the problem]

As a result of various studies, the present inventors found that rare earth metal α obtained by using a rare earth metal-transition metal eutectic alloy as the main melting raw material and then performing a rapid solidification process such as gas atomization.
A mixture of a rare earth metal-transition metal alloy powder and a transition metal in which a phase and an intermetallic compound phase are uniformly and finely crystallized is sintered under pressure at a temperature below the liquid phase manifestation temperature of the mixture in a vacuum or an inert gas atmosphere. By doing so, we were able to solve the above problem.

The present invention will be explained in detail below.

A feature of the present invention is that a rare earth metal-transition metal eutectic alloy is mainly used as a raw material for melting prior to rapid solidification treatment.

That is, it is possible to weigh and use a predetermined amount of pure rare earth metals or pure transition metals as the raw material for melting.1 For example, if the amount of oxygen contained in commercially available high-purity Tb is 900 to 1200 ppm.
Since the temperature at which the raw materials are completely dissolved is high and the dissolution time is long, it is difficult to limit the oxygen content of the powder obtained by rapid solidification treatment to a low level.

On the other hand, if a rare earth metal-transition metal eutectic alloy is used as the main melting raw material as in the present invention.

■ For example, according to the molten salt electrolysis method, the oxygen content is 100
It is possible to produce rare earth metal-transition metal eutectic alloys with low oxygen levels of ~500 ppm.

■ The temperature at which the raw materials completely melt is lower than when pure rare earth metals and pure transition metals are mixed, making it possible to shorten the melting time and contributing to suppressing the oxygen content.

Therefore, even when it is finally used as a target, it is possible to achieve low oxygen levels.

Note that in the present invention, in addition to the case where the melting raw material is only the rare earth metal-transition metal eutectic alloy, a small amount of pure rare earth metal or transition metal may be added as long as it does not contradict the above spirit. Additions may be necessary to match the composition of the rare earth metal-transition metal eutectic alloy to the desired target composition.

After melting the above raw materials, a rapid solidification process is performed. Through this rapid solidification process, α of rare earth metals can be obtained at the powder level.
Achieve uniformity and refinement of phases and intermetallic compounds. Therefore, from a compositional standpoint, the composition of the rare earth metal and transition metal needs to be within a composition range that produces a eutectic structure.

As a method for the rapid solidification treatment, an inert gas atomization method, a vacuum atomization method, a rotating roll method, etc., which are produced from a molten alloy, and a rotating electrode method, which uses an electrode that is once produced from the molten alloy, can be applied. Even in the water-cooled roll method, rotating electrode method, etc., the atmosphere must be a vacuum or an inert gas atmosphere to prevent oxidation of the alloy.

In addition, rare earth metal-transition metal alloy powder has much better oxidation resistance than pure rare earth metal powder, so the oxygen content in the target can be reduced by sintering a mixture of rare earth metal powder and transition metal powder. 500-11000pp compared to
It is possible to reduce even more than that.

It is desirable that the average particle size of the raw material powder is 1 mm or less. This is because if the average particle size exceeds 1 rrn, non-uniformity will occur in the compact, and if this is used as a target, the composition of the obtained thin film will be This is because it becomes partially non-uniform.

After mixing the above raw material powders, pressure sintering is performed at a temperature below the liquid phase development temperature in a vacuum or an inert gas atmosphere.

The reason why the pressure sintering temperature is lower than the liquid phase temperature is because if the temperature is higher than the liquid phase temperature, the transition metal phase and the rare earth metal -
The bonding layer between the transition metal eutectic alloy phase grows abnormally and the mechanical strength of the compact decreases, and the rare earth metal
This is because the alpha phase of the rare earth metal contained in the eutectic alloy phase consisting of the transition metal reacts with the transition metal and crystallizes.

Preferably within the range from a temperature below the liquid phase onset temperature (below the liquid phase onset temperature -100°C), more preferably within the range from a temperature below the liquid phase onset temperature (below the liquid phase onset temperature -30°C). be. In addition, to give an example of the liquid phase development temperature, Tb
-840℃ for Fe, 69℃ for Tb-Fe-Co
5°C, and 630°C for Tb-Gd-Fe.

Hot isostatic pressing (HIP) is a method of pressure sintering.
, hot pressing, hot pack rolling, hot pack forging, etc. can be applied. In the case of hot isostatic pressing, the specific conditions are from below the liquid phase development temperature (below the liquid phase development temperature -30
℃) and an inert gas pressure of 1000 to 1500 atm for 2 to 3 hours, the J risa of the diffusion bonding layer between the transition metal simple phase and the rare earth metal-transition metal eutectic alloy phase increases to 10 It is possible to suppress the thickness to within 30 μm, and the density of the molded product reaches 97% or more.

In the case of hot pressing, when trying to obtain a molded product with a density of 95% or more, the heating temperature must be kept within a range of less than the liquid phase onset temperature (-30°C below the liquid phase onset temperature) and a molding pressure of 150 kg/- or more for 2 hours. It is desirable to maintain the temperature.

In the case of hot pack rolling and hot pack forging, the heating temperature may be the same as HIP, but the reduction rate for each pass should be 1-0%.
It is necessary to process it within the following range.

The above manufacturing method makes it possible to control the oxygen content in the target to a low level.

Note that the structure of the target obtained by the present invention will be explained below using a Tb-Fe system as an example.

The first characteristic of the target tissue according to the present invention is Tb-
The Fe eutectic alloy phase is extremely uniform and finely dispersed Fe.
, is composed of a Tb crystallized phase and an α-Tb crystallized phase. This method uses as a raw material a powder with a structure in which α-Tb crystallization phase and Fe2Tb crystallization phase are uniformly and finely crystallized obtained by a rapid solidification process such as the atomization method, and in order to maintain this structure, a liquid phase is developed. This is due to pressure sintering being performed at a temperature lower than that.

Since the target of the present invention has one or more uniform fine structures, the compositional deviation between the target and the thin film sputtered from it can be extremely small, and the time for pre-sputtering performed prior to sputtering can be shortened. be able to.

10th Japanese Society of Applied Magnetics Academic Lecture Abstracts (1986
, P12g), when sputtering a composite targeter 1-1, that is, a target composed of an elemental rare earth metal and an elemental transition metal, the transition metal is more likely to be sputtered laterally than the rare earth metal, and as a result, the thin film composition is transitional. become metal poor. On the other hand, in the case of a target composed of an intermetallic compound, rare earth metals are more easily sputtered laterally than transition metals, so it has been reported that the thin film composition becomes rich in transition metals. In contrast, according to the present invention, as described above, the α phase of the rare earth metal and the eutectic alloy phase consisting of the rare earth metal-transition metal intermetallic compound, as well as the solid phase bonding and transition metal elemental phases are uniform and fine. Because of the dispersion, the anisotropy in the emission direction of the rare earth metal sputtered particles and the transition metal sputtered particles is relaxed, and as a result, it is thought that the composition deviation becomes smaller.

The reasons why the bliss sputtering time is shortened are (1)
The sputtering rate difference between transition metals and rare earth metal-transition metal intermetallic compounds compared to the sputtering rate difference between transition metals and rare earth metals as described in JP-A-62-70550. (2) Because the rare earth metal-transition metal alloy powder is created by rapid cooling, the alpha phase of the rare earth metal and the intermetallic compound phase are uniformly and finely dispersed. In other words, the rare earth metal phase is finely divided. Although the sputtering speed of rare earth metals does not change microscopically,
This is thought to be due to the fact that the sputtering rate of the α phase of the rare earth metal becomes equal to the sputtering rate of the intermetallic compound phase.

A second feature of the structure of the target of the present invention is that the diffusion bonding layer mainly composed of an intermetallic compound of a rare earth metal and a transition metal is extremely thin.

This is because the bonding layer is an in-phase diffusion bonding layer formed by pressure sintering at a temperature below the liquid phase development temperature.

Since the diffusion bonding layer is thin and does not cause unevenness in the structure, stable thin IE3 characteristics can be obtained even if the sputtering time is long, and the mechanical strength does not deteriorate. It is.

By having such a structure and reducing the oxygen content, it is possible to reduce the compositional deviation between the target and the thin film, stabilize the thin film composition during long-time sputtering, and achieve even better perpendicular magnetic anisotropy. A large amount of spatter can now be obtained.

In the present invention, the rare earth metal has a conventionally known T'b
, Gd, DY, Nd, Sm, Ha, Tm, etc., or two or more thereof can be used. Its content is 15at
If it is less than 45at% or more than 45at%, it will be difficult to obtain a thin film that functions as a magneto-optical recording medium.
It is necessary to set it to 15-45 at%.

On the other hand, regarding transition metals, Fe
, Go, and Ni or two or more thereof can be applied.

From the above, the intermetallic compound in the present invention is, for example, F
It goes without saying that the concept includes not only compounds of e and Tb, but also compounds of different types of transition metals and rare earth metals, such as FeCoTb and the like.

〔Example〕

Table 1 shows the composition and oxygen content of the rare earth metal-transition metal alloy raw materials and transition metals used in the examples, and the composition and oxygen content of the gas atomized powder prepared using the raw materials. Next, the method for producing the powder of the present invention will be described.1 In the present invention, a low-oxygen rare earth metal-transition metal alloy (oxygen content 100 to 300 ppm) produced by molten salt electrolysis is mixed with rare earth metal or transition metal to achieve the target composition. Metal alloy,
It was placed in a crucible with a nozzle for spraying molten metal at the bottom. After the crucible was placed in a gas atomization device, the inside of the device was evacuated to a level of 10-2 to 10-' torr and heated by high-frequency induction to melt the atomized raw material in the crucible. When the raw materials were completely dissolved, pressure was applied to the molten metal using gas A and at the same time the valve of the injection nozzle was opened to perform gas atomization.

It has been found that the average oxygen content of the rare earth metal-transition metal alloy powder prepared by the above method can be reduced by more than 11,000 pp compared to the case where a rare earth metal or transition metal alone is used as a raw material. Table 2 shows the acid content of target materials produced using the rare earth metal-transition metal alloy powders shown in Table 1.

Table 1 Table 2 A hot isostatic press (I-IIP) was used to sinter the powder. The sintering temperature is set 20℃ lower than the liquid phase appearance temperature.
Pressure sintering was performed at a pressure of 1200 atm.

From Table 2, the amount of oxygen contained in the target material manufactured using the rare earth metal-transition total bending alloy powder of the present invention is 1500p.
pm or less, which is low oxygen, whereas in the comparative example it is 2000 pm or less.
It can be seen that when the concentration exceeds ppm, the oxygen level becomes high.

Next, sputtering was performed using the sintered bodies manufactured using the powders of the present invention and the comparative example as targets, and thin film evaluation was performed.

In the evaluation, all targets were used with a magnetron type sputtering device equipped with a high frequency power source.
The film was formed on Corning 7059 glass having a thickness of +nm. The film forming conditions are high frequency power 2.54
W/a&Ar gas pressure was 5 x 1O-3 torr, the distance between the target and the glass substrate was 70 ffn, and the glass substrate was not rotated during film formation, but the target and the glass substrate were opposed to each other. After measuring the magnetic anisotropy constant Ku (J/rn') of the prepared film with a torque meter, it was subjected to EPM.
The composition was analyzed in A. Figure 1 shows sample 4 shown in Table 2 (
Figure 2 shows the relationship between the amount of Tb, the magnetic anisotropy constant Ku, and the sputtering time of the thin film formed using the sample 11 (of the present invention).
The relationship between Tbi and Ku in the thin film and sputtering time when using Comparative Example) is shown.

The amount of Tb in the thin film for both samples of the present invention and comparative example is approximately 26a.
t%, and it can be seen that the sputtering time is stable even when the sputtering time becomes long. However, the behavior of the magnetic anisotropy constant Ku is stable after the cumulative sputtering time of 411r in the present invention and shows good perpendicular magnetic anisotropy of Ku = 1.25 J/rn', whereas in the comparative example it is completely unstable. It is stable;
It was found that Ku was significantly reduced and the film exhibited behavior similar to that of an in-plane magnetized film.

〔Effect of the invention〕

As explained above, according to the present invention, the oxygen content of Targera 1- can be regulated low, and as a result, the span,
The resulting film has good magnetic anisotropy, which is very useful industrially.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the cumulative sputtering time, the amount of Tb in the thin film, and the magnetic anisotropy constant when sputtering the target obtained according to the present invention, and Figure 2 is a graph showing the relationship between the cumulative sputtering time and the amount of Tb in the thin film and the magnetic anisotropy constant when sputtering the target obtained according to the present invention. 2 is a graph showing the relationship between the cumulative sputtering time, the amount of Tb in the thin film, and the magnetic anisotropy constant when sputtering.

Claims (1)

[Claims] 1. A mixture of a rapidly solidified alloy powder consisting of a rare earth metal and a transition metal within a composition range that exhibits a eutectic structure, and a transition metal powder that is insufficient to the target composition. , in a method for producing a rare earth metal-transition metal target in which pressure sintering is performed in a temperature range below the liquid phase development temperature of the mixture in a vacuum or an inert gas atmosphere, the melted raw material of the alloy to be subjected to the rapid solidification treatment is oxygenated. A method for producing a rare earth metal-transition metal target, characterized in that the target is mainly a rare earth metal-transition metal eutectic alloy having a content of 500 ppm or less. 2. A mixture of a rapidly solidified alloy powder consisting of a rare earth metal and a transition metal within the composition range that produces a eutectic structure, and a transition metal powder that is insufficient to the target composition, is heated in a vacuum or inert gas. In a method for producing a rare earth metal-transition metal target in which pressure sintering is performed in an atmosphere in a temperature range below the liquid phase development temperature of the mixture, the melted raw material of the alloy to be subjected to the rapid solidification treatment is obtained by a molten salt electrolysis method. A method for producing a rare earth metal-transition metal target, characterized in that the target is mainly a rare earth metal-transition metal eutectic alloy. 3. In a method for producing an alloy powder for a rare earth metal-transition metal target, in which a molten alloy consisting of a rare earth metal and a transition metal within a composition range that exhibits a eutectic structure is rapidly solidified, the alloy to be subjected to the rapid solidification treatment is melted. A method for producing an alloy powder for a rare earth metal-transition metal target, characterized in that the raw material is a rare earth metal-transition metal eutectic alloy having an oxygen content of 500 ppm or less. 4. In a method for producing an alloy powder for a rare earth metal-transition metal target in which a molten alloy consisting of a rare earth metal and a transition metal within a composition range that exhibits a eutectic structure is rapidly solidified, melting of the alloy to be subjected to the rapid solidification treatment is performed. A method for producing an alloy powder for a rare earth metal-transition metal target, characterized in that the raw material is mainly a rare earth metal-transition metal eutectic alloy obtained by a molten salt electrolysis method.