JP6279326B2 - Manufacturing method of sputtering target - Google Patents

Description

  The present invention relates to a magnetic material sputtering target manufactured by a melt casting method, and particularly to a magnetic material sputtering target having a high leakage magnetic flux density and a manufacturing method thereof.

  Research and development of a magnetic recording element (MRAM) is underway as a next-generation high-speed recording element, and a magnetic material containing boron (B) is used as a material used for a layer constituting the MRAM. For example, a composition composed of Co, Fe, Ni or the like and B, that is, Co-B, Co-Fe-B, or a composition obtained by adding Ni, Al, Cu, Mn or the like to these is known.

  Generally, the magnetic material layer constituting these MRAMs is produced using a sputtering target having a composition composed of Co, Fe, Ni, etc. and B. However, since the sputtering target having such a composition contains B, it is very fragile, and cracks and cracks may occur when casting or processing an ingot as a target base material.

  For this reason, the present applicant has previously provided a technique for reducing the occurrence of cracks in the target by rapidly cooling the molten casting at 30 to 60 ° C./min (Patent Document 1). However, even if such a method is used, the brittleness cannot be sufficiently improved, cold working is difficult, and it is difficult to improve the leakage magnetic flux density (PTF) by cold working. It was.

Japanese Patent No. 4837805

  The present invention provides a target having an improved leakage magnetic flux density without causing cracks or cracks by controlling the casting conditions in the melt casting process in a magnetic material sputtering target containing B. Let it be an issue. Accordingly, an object is to enable good film formation by magnetron sputtering.

In order to solve the above problems, the present inventor has conducted intensive research, and as a result, the structure of the alloy ingot can be modified by slowing down the cooling rate of the molten casting, thereby reducing the leakage magnetic flux density. The knowledge that it can improve was obtained.

Based on this finding, the present invention provides the following inventions.
1) A sputtering target containing B at 10 at% or more and 30 at% or less, Co at 30 at% or more and 50 at% or less, and Fe at 30 at% or more and 50 at% or less, and a visual field in the eutectic structure of the target 25 μm × A sputtering target characterized in that the average number of B poor particles having a major axis of 2 μm or less within 25 μm is 20 or less.
2) An ingot is produced by melting and casting a raw material containing B at 10 at% to 30 at%, Co at 30 at% to 50 at%, and Fe at 30 at% to 50 at%, and machining it. A sputtering target manufacturing method for manufacturing a sputtering target, wherein the raw material is melted and cast and then cooled at 5 to 30 ° C./min to prepare an ingot.

The magnetic material sputtering target containing B has high brittleness, so it is difficult to cold work, and it is difficult to improve the leakage magnetic flux density by cold working. According to the present invention, the cooling rate decreases. As a result, the structure of the target is changed and the leakage magnetic flux density is improved.

The structure photograph (low magnification) of the sputtering target of Example 1 of this invention is shown. The structure photograph (high magnification) of the sputtering target of Example 1 of this invention is shown. The structure photograph (high magnification) of the sputtering target of Example 4 of this invention is shown. The structure photograph (high magnification) of the sputtering target of the comparative example 1 of this invention is shown.

  The sputtering target of the present invention is composed of a B content of 10 at% to 30 at%, a Co content of 30 at% to 50 at%, and an Fe content of 30 at% to 50 at%. The target of the present invention is used for forming a magnetic material layer in MRAM or the like, and the component composition of the target is appropriately selected within the above numerical range according to the desired magnetic properties.

After preparing these raw materials, melt casting is performed to produce an ingot. The ingot is subjected to mechanical processing such as adjustment of the target shape and polishing of the target surface so that the function as a target can be exhibited in the sputtering apparatus, thereby producing a sputtering target. The melting conditions such as the melting temperature naturally vary depending on the alloy type and the blending ratio, but dissolve in the range of approximately 1100 ° C to 1500 ° C.

  What is particularly important in the manufacturing process described above is that after the melting, the molten metal is poured out from the crucible into the mold and the ingot is cooled at 5 to 30 ° C./min. Methods for controlling the cooling rate of the ingot include changing the thickness and material of the mold, keeping the mold warm and insulating, and cooling the molten metal while vibrating it as will be described later. This makes it possible to obtain a target having an average of 20 or less B poor particles having a major axis of 2 μm or less within a visual field of 25 μm × 25 μm in the eutectic structure. And the target which has such a structure | tissue has the outstanding effect that a leakage magnetic flux density improves.

  FIG. 1 shows a structure photograph (magnification: 10 times) of the sputtering target of Example 1 described later. Normally, when the molten alloy is cooled, the primary crystal is first crystallized, and when the cooling proceeds further, the remaining molten alloy is solidified at a certain temperature. The structure that solidifies at this time is called a eutectic structure. As shown in FIG. 1, the target of the present invention is composed of a primary crystal and a eutectic structure, and the eutectic structure is composed of a B rich phase and a B poor phase. Here, the B-rich phase means a phase having a B content of 15 at% or more, and the B poor phase means a phase having a B content of less than 15 at%.

The mold can be made of a metal such as Cu, Fe, Co, or carbon. Carbon molds are more preferred because they have lower thermal conductivity than metal molds. Further, although the mechanism is unknown at present, it is presumed that there is an effect that the cooling rate can be slowed by applying vibration during cooling, and the structure is changed. As the vibration method, known means such as a vibrator or an ultrasonic vibrator can be used, and the frequency is not particularly limited.

  Hereinafter, description will be made based on Examples and Comparative Examples. In addition, a present Example is an example to the last, and is not restrict | limited at all by this example. In other words, the present invention is limited only by the scope of the claims, and includes various modifications other than the examples included in the present invention.

Example 1
Co, Fe, and B were used as raw materials, and these were prepared at Co: 40 at%, Fe: 40 at%, and B: 20 at%. Next, this is put in a ceramic crucible, heated and melted at about 1200 ° C., the vibrator directly under the metal mold is operated at 30 Hz, and then the molten metal is transferred to the metal mold and cooled at 5 to 30 ° C./min. And removed from the furnace. Next, this was cut into a shape having a diameter of 164 mm and a thickness of 4 mm to obtain a sputtering target. A structure photograph of the target (magnification: 300 times) is shown in FIG. As a result of observing four spots in the visual field of 25 μm × 25 μm in the eutectic structure of this target at random, the average number of B poor particles having a major axis of 2 μm or less (size that fits in a circle of 2 μm in diameter) was small. Moreover, as a result of measuring the leakage magnetic flux density of this target, it improved 30.4% compared with the comparative example 1 mentioned later. The results are shown in Table 1.
Note that no matter what part of the target is observed, the eutectic structure has no significant change in particle diameter and the variation is small, but for the primary crystal, the end of the target is smaller and the center is larger. It tends to be.

The leakage magnetic flux density conformed to ASTM F2086-01 (Standard Test Method for Pass Through Flux of Circular Magnetic Sputtering Targets, Method 2). Specifically, the center of the target is fixed, and the leakage magnetic flux density is measured by rotating at 0 degree, 30 degrees, 60 degrees, 90 degrees, and 120 degrees, and each measured value is a reference filed defined by ASTM. The average leakage magnetic flux density (%) was obtained from the average value of these five points. The same applies to the following examples and comparative examples.

(Example 2)
Co, Fe, and B were used as raw materials, and these were prepared at Co: 40 at%, Fe: 40 at%, and B: 20 at%. Next, this is put in a ceramic crucible, heated and melted at about 1200 ° C., the vibrator directly under the metal mold is operated at 150 Hz, and then the molten metal is transferred to the metal mold and cooled at 5 to 30 ° C./min. And removed from the furnace. Next, this was cut into a shape having a diameter of 164 mm and a thickness of 4 mm to obtain a sputtering target. As a result of observing four spots in the visual field 25 μm × 25 μm in the eutectic structure of this target at random, the average number of B poor particles having a major axis of 2 μm or less was small. Moreover, as a result of measuring the leakage magnetic flux density of this target, it improved 32.4% compared with the comparative example 1 mentioned later.

(Example 3)
Co, Fe, and B were used as raw materials, and these were prepared at Co: 40 at%, Fe: 40 at%, and B: 20 at%. Next, this was put into a ceramic crucible, heated and melted at about 1200 ° C., the molten metal was transferred to a metal mold preheated to 800 ° C., cooled at 5 to 20 ° C./min, and taken out from the furnace. Next, this was cut into a shape having a diameter of 164 mm and a thickness of 4 mm to obtain a sputtering target. As a result of observing four random locations within a visual field of 25 μm × 25 μm in the eutectic structure of this target, the average number of B poor particles having a major axis of 2 μm or less was small. Moreover, as a result of measuring the leakage magnetic flux density of this target, it was 31.0%, which is an improvement over Comparative Example 1 described later.

Example 4
Co, Fe, and B were used as raw materials, and these were prepared at Co: 40 at%, Fe: 40 at%, and B: 20 at%. Next, this was put in a ceramic crucible and heated and melted at about 1200 ° C., and then the molten metal was transferred to a carbon mold, cooled at 5 to 30 ° C./min, and taken out from the furnace. Next, this was cut into a shape having a diameter of 164 mm and a thickness of 4 mm to obtain a sputtering target. A structure photograph of the target (magnification: 300 times) is shown in FIG. As a result of observing four spots in the visual field 25 μm × 25 μm in the eutectic structure of this target at random, the average number of B poor particles having a major axis of 2 μm or less was few. Moreover, as a result of measuring the leakage magnetic flux density of this target, it was 31.7%, which was improved compared to Comparative Example 1 described later.

(Comparative Example 1)
Co, Fe, and B were used as raw materials, and these were prepared at Co: 40 at%, Fe: 40 at%, and B: 20 at%. Next, this was put in a ceramic crucible and heated and melted at about 1200 ° C., then transferred to a metal mold, cooled at 30 to 50 ° C./min without vibration, and taken out from the furnace. Next, this was cut into a shape having a diameter of 164 mm and a thickness of 4 mm to obtain a sputtering target. A structural photograph of the target (magnification: 300 times) is shown in FIG. As a result of observing randomly within the visual field 25 μm × 25 μm in the eutectic structure of this target at four locations, the average number of B poor particles having a major axis of 2 μm or less was 56. Moreover, as a result of measuring the leakage magnetic flux density of this target, it was 15.7%.

Sputtering of the present invention is manufactured from a melt-cast ingot, and since it is highly brittle, it is difficult to cold work and it is difficult to improve the leakage magnetic flux density by cold working. According to the above, there is an excellent effect that the structure of the target is changed due to a decrease in the cooling rate, and the leakage magnetic flux density is improved. The present invention is useful as a magnetic material sputtering target for forming a magnetic material layer for MRAM.

Claims (1)

A method for producing a sputtering target containing B at 10 at% to 30 at%, Co at 30 at% to 50 at%, and Fe at 30 at% to 50 at% , after dissolving Co, Fe and B raw materials, An ingot is produced by cooling at 5-30 ° C./min while vibrating the molten metal, and this is machined. B pore particles having a major axis of 2 μm or less in the visual field 25 μm × 25 μm in the target eutectic structure are averaged. A method for producing a sputtering target, comprising producing 20 or less targets.