JP2008023545A - Method for manufacturing hardly workable alloy sputtering target material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for effectively manufacturing a hardly workable alloy sputtering target material with which, concretely, a casting process is contrived, and the unevenness of structure on the inner part and the surface part of a cast block is reduced and the cast block having fine and uniformed cast structure is obtained and thus, plastic working process thereafter, e.g. the number of times of rolling in the rolling process can be reduced and the yield in the rolling can be improved. <P>SOLUTION: The method for manufacturing the alloy sputtering target material having the fine and uniformed structure, the method having the casting process of the alloy, is performed as the followings, that is, in the casting process, when the cast block is obtained by pouring molten alloy into a mold and solidifying the alloy, the solidification speed of the poured molten metal is adjusted into the range of 1-10 mm/sec. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing an alloy sputtering target material. More specifically, the present invention relates to a method for manufacturing an alloy sputtering target material that has a small plastic deformability and is difficult to perform plastic working.

  With the recent enhancement of functions of thin film devices, the elements constituting the thin film have been varied. For example, taking a magnetic film for a magnetic disk as an example, the material is from a Co—Cr alloy to a Co—Cr—Ta alloy, and further from a Co—Cr—Pt—Ta alloy and a Co—Cr—Pt—B alloy. The number of constituent element species in the thin film is steadily increasing. At present, a Co—Cr—Pt—B alloy having a B concentration of less than 7 at% is mainly used as the material of the magnetic film.

  Such a magnetic film can be produced by sputtering a sputtering target material having the same composition (hereinafter also simply referred to as a target material). From the viewpoint of preventing the generation of nodules during sputtering and improving the properties of thin films such as magnetic films obtained by sputtering, the target material is required to have a finer and more uniform structure.

  When the target material is an alloy target material, generally, the alloy target material is prepared by weighing each metal component so as to have a desired alloy composition, melting them, and casting to obtain an ingot, and then The lump is manufactured by subjecting it to plastic working such as rolling, forging, and upsetting, and then cutting it into the required shape. In this case, as the number of constituent element species of the alloy increases, basically casting and plastic working (rolling, forging, upsetting, etc.) become difficult. -Cr-Pt-B alloy target materials, for example, Co-Cr-Pt-B alloy target materials having a B concentration of 5 to 6 at% could be manufactured (see Patent Documents 1 and 2).

  This is because the Co-Cr-Pt-B alloy target material having a B concentration of less than 7 at% has a large plastic deformability (the range in which plastic deformation is possible) and is explained by taking rolling as an example. This is because even if the structure (cast structure) varies, the structure can be made finer and uniform in the ingot after rolling by increasing the rolling rate and rolling. In other words, when there is variation in the cast structure, the ingot may be rolled to a certain rolling rate.

  However, the high B content alloy target material, which is currently being developed, that is, the Co—Cr—Pt—B alloy target material having a B concentration of 7 at% or more has a high content of Cr—B compound in the alloy. Since it is an extremely hard and brittle material and its plastic deformability is small, it is necessary to reduce the rolling reduction of one pass (per rolling) in order to prevent cracking during rolling. Therefore, in order to roll the obtained ingot to a rolling rate of a certain level or more, it has to be rolled many times, and there has been a problem that work time and cost are increased. Moreover, even if the rolling reduction of one pass is reduced, there are problems that cracks are easily generated and the rolling yield is extremely low.

  On the other hand, as a method for reducing the target rolling rate itself in the ingot rolling, there is known a method for rapidly solidifying an alloy melt to obtain an ingot during casting, but the B concentration is 7 at%. When the above-mentioned Co—Cr—Pt—B alloy is rapidly solidified, there is a problem that nests (such as bubble nests and sinkholes) and cracks are generated in the ingot and the casting yield is lowered.

  In addition, in the alloy casting process, a method has been proposed in which the cast ingot thickness is set to 15 mm or less so as to make the cast structure fine and uniform, and a Co—Cr—Pt—B alloy having a B concentration of 14 at%. It is applied to the production of a target material (see Patent Document 3). However, in this case, there is a problem that a nest is formed at the upper part of the ingot and the casting yield is poor, although the thickness of the resulting ingot ingot is thin. Further, although the position of the bubble nest has been studied, it is not described whether both the inside of the ingot and the cast structure of the surface portion are made fine and uniform, and it depends on the site of the ingot. There is concern about the variation of the tissue (the presence of coarse grains, etc.). Furthermore, only about 10% or less of rolling is described as being possible for rolling, and no specific study has been made.

A method of annealing the ingot has also been proposed (see Patent Document 4). However, the work time and cost required for the annealing treatment are increased, and the ingot is oxidized by the annealing treatment, so that the yield of the target material is increased. There is a problem that decreases.
JP 2001-262327 A JP 2002-066963 A JP 2005-146290 A US Pat. No. 6,521,062

  This invention makes it a subject to solve the said problem and to provide the method of manufacturing a difficult workability alloy sputtering target material efficiently. Specifically, by devising the casting process, reducing the variation in the structure of the inside and the surface of the ingot, obtaining an ingot having a finely uniform cast structure, a subsequent plastic working process, for example, It is an object of the present invention to provide a method for producing a difficult-to-work alloy sputtering target material that can reduce the rolling rate, reduce the number of rolling operations, and improve the rolling yield in the rolling process.

  As a result of intensive studies, the inventor has adjusted the solidification rate when the molten metal cast into the mold is solidified within a specific range in the casting process of the alloy, so that there is no cracking or nest formation. Can be obtained in an ingot with reduced internal and surface structure variations, and by using the ingot, a rolling rate in a subsequent plastic working process, for example, a rolling process, can be obtained. The present inventors have found that the number of rolling operations can be reduced, and the rolling yield can be improved.

That is, the present invention relates to the following matters.
The manufacturing method of an alloy sputtering target material having a fine and uniform structure according to the present invention includes an alloy casting step, in which a molten alloy is poured into a mold and solidified to be an ingot. Is obtained, the solidification rate of the poured molten metal is adjusted to a range of 1 to 10 mm / sec.

In the present invention, the alloy preferably has a Vickers hardness of greater than 450.
Moreover, as said alloy, a Co-Cr-Pt-B type | system | group alloy is mentioned preferably, Furthermore, it is desirable that the B content is 7 at% or more.

  In the present invention, the mold is a carbon mold having a rectangular cross section with a rectangular hollow portion (cavity) when cut perpendicularly to the height direction at a substantially half position, The ratio of the half length of the cavity short side to the mold wall thickness is preferably 1: 2 to 10.

Furthermore, in the present invention, the ingot obtained in the casting step has a center part of the ingot and the same height position as the center part of the ingot in the mold, and the contact surface with the mold has a thickness of 0.5 mm. Of Vickers hardness [Vickers hardness variation (%) = 100 × (Vickers hardness of the ingot surface portion−Vickers hardness of the ingot center portion) / Vickers hardness of the ingot surface portion] ] Is preferably 10% or less.

  Moreover, this invention may further have the plastic working process performed after the said casting process, and a rolling process is mentioned as said plastic working process.

  According to the present invention, a difficult-to-work alloy sputtering target material having a fine and uniform structure can be efficiently produced. That is, in the present invention, in the casting process, an ingot having a finely uniform cast structure can be obtained, and variation in plastic deformability at each part of the ingot is reduced. Thus, when rolling is performed, the number of rolling operations can be reduced, the rolling yield can be improved, and a target material having a desired fine and uniform structure can be produced with high production efficiency.

Hereinafter, the present invention will be specifically described.
As described above, in general, an alloy target material is obtained by weighing a predetermined amount of each metal component as a constituent element of the alloy so as to have a desired alloy composition, melting them, and casting to obtain an ingot. The ingot is manufactured by plastic working and cutting.

Therefore, generally the manufacturing method of an alloy target material has a casting process, a plastic working process, and a cutting process.
The manufacturing method of the alloy target material of this invention has a casting process at least, and may further have a plastic working process and a cutting process as needed.

  Among them, in the casting process, in the casting process, when a molten alloy is poured into a mold and solidified to obtain an ingot, the solidification rate of the poured molten metal is usually 1 to 10 mm / sec, preferably It is characterized by adjusting to a range of 3 to 7 mm / sec, more preferably 4 to 6 mm / sec.

  Thus, by adjusting the solidification rate of the molten metal (hereinafter also referred to as a casting) to the above specific range, the cast structure (cast crystal grains) can be made fine and uniform without causing casting cracks, and the inside of the ingot and The distribution of crystal grain size on the surface is reduced. Therefore, in the subsequent plastic working step, the rolling rate to be achieved when rolling the ingot is reduced, and the number of rolling operations can be reduced even if the rolling reduction rate for one pass is lowered. Furthermore, in such an ingot, since the variation in plastic deformability at each part of the ingot is also reduced, as a result, the plastic deformability of the entire ingot is improved, which contributes to the improvement of the yield of plastic working. It is thought to do.

In the present specification, the solidification rate of the molten metal means the moving speed of the solidification interface of the molten metal calculated by a two-dimensional explicit difference method (the latent heat of fusion uses the enthalpy method) (Eisuke Niiyama, (See “Cast Heat Transfer Engineering-Fundamentals of Casting Design”, Agne Technology Center, 2001, p.75-94)
.

In addition, each condition used for this calculation is as follows (1)-(4).
(1) Calculation method In the two-dimensional explicit difference method, the latent heat of fusion uses the enthalpy method to calculate the moving speed of the solidification interface of the casting (molten metal). The movement of the solidification interface is assumed to be from the surface of the casting to the center line when the mold is line-symmetrical with the vertical center line in the cross section when the mold is cut in parallel to the height direction (see FIG. 1).

(2) Boundary conditions Casting / mold interface: The heat transfer coefficient shown in Table 1 below is assumed.
Mold / Outside air: Heat insulation for vacuum casting.

(3) Initial conditions Casting temperature: casting temperature is fixed at 1580 ° C. (calculated by replacing the casting with Fe).
Mold temperature: 20 ° C constant.

(4) Other physical property values As shown in Table 1.

  The present invention can be applied to the production of all alloy target materials including Co-Cr-Pt-B alloy target materials, Co-Zr-Ta alloy target materials, and Co-Zr-Nb alloy target materials. However, the effects of the present invention are more clearly exhibited when applied to the production of an alloy target material that is a brittle material. This is because if the alloy target material to be manufactured is a brittle material, it is difficult to plastically process the ingot. For example, when the ingot obtained in the casting process is rolled in the plastic working process, if the rolling reduction of one pass is increased, the number of rolling operations can be reduced, but if the ingot to be rolled is a brittle material, the rolling is performed. Since there is a high risk of cracking, the rolling reduction of one pass cannot be increased. Therefore, in order to achieve a desired rolling rate, a great number of rolling operations are required.

Furthermore, among brittle materials, alloys having a Vickers hardness of over 450 are brittle and extremely hard, and therefore are more difficult to plastically process.
Examples of the brittle material (alloy) having a Vickers hardness exceeding 450 include, for example, B: 7 to 20 at%, Cr: 10 to 30 at%, Pt: 5 to 30 at%, and Co—Cr—Pt—B made of Co balance. B: 7-20 at%, Cr: 10-30 at%, Pt: 5-30 at%, Ta, Cu, Nb, Nd, Ti, Zr, Hf, W, V, Mo, Ag, Au Or 2 or more types: Co—Cr—Pt—B alloy composed of more than 0 and 5 at% or less and Co balance; (hereinafter, these are combined to form a Co—Cr—Pt—B system having a B content of 7 at% or more) Also referred to as an alloy).

  The present invention may be applied to the manufacture of such a Co—Cr—Pt—B alloy target material having a B content of 7 at% or more. This is because the demand for the target material has increased in recent years as a target material for magnetic films, and the development of an efficient manufacturing method is desired.

  In the present invention, as an example of means for adjusting the solidification rate of the molten metal in the casting process of the alloy to the above specific range, the material and shape of the mold used in the casting process are selected in consideration of the composition of the casting. And mold design.

As a result of the mold design, the embodied mold is, for example, made of carbon having a rectangular cross section with a rectangular hollow portion (cavity) when cut perpendicularly in the height direction at a substantially half position. In the mold, the ratio of the half length of the cavity short side and the mold thickness in the cross section is:
Usually, a mold in the range of 1: 2 to 10, preferably 1: 4 to 6, more preferably 1: 4.5 to 5.5 can be used. This ratio is calculated by aligning a unit system (for example, mm, cm, m, etc.) of the half length of the cavity short side and the mold thickness.

An example of the mold is shown in FIG. In FIG. 2, the mold 1 is made of carbon, and has a rectangular cross section with a rectangular cavity 3 when cut perpendicularly to the height direction at a substantially half position. The ratio of the half length a of the cavity short side in the cross section to the mold wall thickness b is within the specific range.

By using such a mold in the casting process, the above-described solidification rate can be adjusted.
Moreover, as a means for adjusting the solidification rate of the molten metal in the casting process to the above specific range, in addition to the mold design, a cooling metal is installed around the mold, or the mold is surrounded by sand. And temperature adjustment from the outside of the mold.

The ingot obtained in the casting process has reduced variations in the structure of the inside and the surface portion. More specifically, the ingot surface of the ingot has the same height position as the ingot center portion in the mold and the contact surface with the mold is cut to a thickness of 0.5 mm. The Vickers hardness variation [Vickers hardness variation (%) = 100 × (Vickers hardness at the ingot surface portion−Vickers hardness at the center portion of the ingot) / Vickers hardness at the ingot surface portion] is usually 10
% Or less, preferably 8% or less, more preferably 4% or less. The smaller the variation in the Vickers hardness, the better. Thus, when there is little variation in the Vickers hardness between the ingot center portion and the ingot surface portion, it can be said that the cast structure is uniform. Therefore, the lower limit value of the variation in the Vickers hardness is not particularly limited, but there is no practical problem even if it is 2% or more.

  As described above, it is speculated that the cast structure with little variation in Vickers hardness is assumed to be not only uniform but also refined. However, as to whether the cast structure is actually miniaturized, various optical instruments are considered. For example, it can be confirmed by observing with a scanning electron microscope (SEM).

  In addition, the present invention may further include a plastic working process performed after the casting process. When the plastic working step is included, it is possible to obtain a target material having a finer and more uniform structure than the cast structure.

  Examples of the plastic working include rolling, forging, upsetting, etc. Among these, rolling is preferable from the viewpoint of productivity. Rolling can be performed according to known methods and conditions such as hot rolling.

  When rolling the ingot obtained in the above casting process, since the cast structure is originally fine and uniform, compared with the ingot obtained by the conventional method, the desired fine and uniform structure is obtained. The rolling rate required to process the target material is low. Therefore, when rolling, even if the rolling reduction of one pass is lowered, the number of rolling can be reduced, and the target material can be obtained under sufficiently efficient operating conditions.

Further, in the ingot obtained in the casting process, since the variation in plastic deformability at each part of the ingot is reduced, as a result, the plastic deformability of the entire ingot is improved, and the rolling yield is increased. improves. For example, even when the rolling rate required for the ingot is about 45% to 65%, rolling can be performed with a success rate of 90% or more.

Furthermore, the present invention may further include a cutting process as necessary. The cutting process is performed to obtain a target material having a desired shape, and a known technique such as cutting and surface grinding can be employed.Hereinafter, the present invention will be described more specifically based on examples. The present invention is not limited to these examples.

[Example 1]
Co, Cr, Pt, and B raw materials were prepared by weighing so that B: 11 at%, Cr: 13 at%, Pt: 14 at%, Co balance, and then the raw materials were melted at high frequency in a vacuum atmosphere to obtain a molten metal .

The obtained molten metal was cast into a mold designed by calculation using a two-dimensional explicit differential method (latent heat of fusion uses the enthalpy method) so that the solidification rate becomes 3 mm / sec, and allowed to cool. And cast. As shown in FIG. 2, the mold used has a shape having a rectangular cross section with a rectangular hollow portion (cavity) when cut perpendicularly in the height direction at a substantially half position. Table 2 shows the ratio of the half length of the cavity short side to the mold wall thickness and the mold material.
It is as shown in.

Table 2 also shows the parameters used for calculating the solidification rate at this time.
The center part of the ingot thus obtained (ingot center part) and the same height position as the ingot center part in the mold and the contact surface with the mold were shaved with a thickness of 0.5 mm. When the structure of the ingot surface portion was observed with SEM (JSM-6380A; manufactured by JEOL), it was found that all of them were the same refined cast structure. FIG. 3 shows the respective structure photographs at this time.

Moreover, as a result of measuring the Vickers hardness of the ingot center portion and the ingot surface portion, they were 513 and 547, respectively, and the Vickers hardness variation was 6% (= 100 × (547-513) / 547) The tissue was made uniform.

Subsequently, the ingot was hot-rolled at a reduction rate of 1.33% in one pass and a temperature of 1100 ° C., and 48 rolling operations were required to reduce the crystal grain size of the alloy to 100 μm or less. The rolling rate at this time was 55%. When the target material was cut out from the obtained rolled material and the structure of the target material central part and the surface part was observed by SEM, it was found that both had a similar structure that was made more uniform than the cast structure. all right. Each organization photograph at this time is shown in FIG.

In addition, when 49 target materials were continuously manufactured, the target was able to be manufactured without any problems except that the two were cracked and could not be manufactured, and the success rate was 96%.

These results are summarized in Table 2.
[Example 2] to [Example 4]
The cast was cast into the designed mold so that the calculated solidification rates were 1, 7, and 10 mm / sec, respectively, and allowed to cool to cast. The used mold was the same as in Example 1 except that the ratio of the half length of the cavity short side to the mold wall thickness was changed as shown in Table 2.

Next, as in Example 1, after observing the cast structure at the center of the ingot and the surface of the ingot by SEM and hot rolling under the conditions shown in Table 2, the crystal grain size of the alloy is reduced to 100 μm or less. Therefore, 55 times, 43 times, and 33 times of rolling were required (rolling ratios were 64%, 50%, and 47%, respectively).

  The obtained rolled material was cut out to obtain a target material, and the structure of the central portion and the surface portion of the target material was observed in the same manner as in Example 1. The results of these structural observations were almost the same as in Example 1.

Furthermore, when 49 target materials were manufactured in succession, the success rates were 94%, 96% and 94%, respectively.
These results are summarized in Table 2.

[Comparative Example 1]
Co, Cr, Pt, and B raw materials were prepared by weighing so that B: 11 at%, Cr: 13 at%, Pt: 14 at%, Co balance, and then the raw materials were melted at high frequency in a vacuum atmosphere to obtain a molten metal . The obtained molten metal was cast into a mold designed so that the calculated solidification rate was 0.5 mm / sec, and allowed to cool and cast. The used mold was the same as in Example 1 except that the ratio of the half length of the cavity short side to the mold wall thickness was changed as shown in Table 2.

  When the structure of the obtained ingot was observed in the same manner as in Example 1, it was also found that the cast structure at the center of the ingot and the surface of the ingot was completely different and not sufficiently refined. Coarse particles were also observed at the center of the ingot. Each organization photograph at this time is shown in FIG.

  In addition, as in Example 1, the Vickers hardness of the ingot center portion and the ingot surface portion was measured. As a result, 529 and 690 were obtained, the Vickers hardness variation was 24%, and the cast structure was made uniform. I found out.

  The ingot was then hot rolled at a 1-pass reduction of 1.33% and a temperature of 1100 ° C., and 155 rollings were required to reduce the crystal grain size of the alloy to 100 μm or less. The rolling rate at this time was 85%. When the target material was cut out from the obtained rolled material and the structure of the central portion and the surface portion of the target material was observed in the same manner as in Example 1, all were finer and uniform than the cast structure. It can be seen that the number of rolling operations required for this is much larger than in Examples 1 to 4, and the production efficiency is remarkably poor. Each organization photograph at this time is shown in FIG.

In addition, when 49 target materials were produced in succession, rolling cracks occurred and the success rate was 32%.
These results are summarized in Table 2.

[Comparative Example 2]
Casting was performed in the designed mold so that the calculated solidification rates were 0.8 mm / sec, and the mold was allowed to cool and cast. The used mold was the same as in Example 1 except that the ratio of the half length of the cavity short side to the mold wall thickness was changed as shown in Table 2.

  Next, as in Example 1, when the cast structure was observed by SEM at the ingot center part and the ingot surface part, it was found that these structures were different from each other and not sufficiently refined.

  In addition, as in Example 1, the Vickers hardness of the ingot central part and the ingot surface part was measured. As a result, 527 and 596 were obtained, the Vickers hardness variation was 12%, and the cast structure was made uniform. I found out.

The ingot was then hot rolled at a 1-pass reduction of 1.00% and a temperature of 1100 ° C., and 74 rolling operations were required to reduce the crystal grain size of the alloy to 100 μm or less. The rolling rate at this time was 80%. The target material was cut out from the obtained rolled material, and when the structure of the central portion and the surface portion of the target material was observed in the same manner as in Example 1, both were finely homogenized to some extent as compared with the cast structure. However, it was found that the central part and the surface part still have different structures. Each organization photograph at this time is shown in FIG.

In addition, when 49 target materials were produced in succession, rolling cracks occurred and the success rate was 42%.
These results are summarized in Table 2.

[Comparative Example 3]
Casting was performed in the same manner as in Example 1 except that the water-cooled copper mold used in the rapid solidification method was used. The solidification rate at this time was calculated to be 30 mm / sec.

  However, the ingot was cracked in the casting process, and subsequent evaluation could not be performed.

FIG. 1 is an image diagram of solidification interface movement of a casting. FIG. 2 is a schematic view of a mold that can be used in the present invention. FIG. 3 shows a structure photograph of the ingot of Example 1. 4 shows a structure photograph of the target material of Example 1. FIG. FIG. 5 shows a structure photograph of the ingot of Comparative Example 1. FIG. 6 shows a structure photograph of the target material of Comparative Example 1. FIG. 7 shows a structure photograph of the target material of Comparative Example 2.

Explanation of symbols

1: Mold 3: Cavity a: Half length of cavity short side b: Mold thickness

Claims (8)

An alloy casting process, in the casting process,
When a molten alloy is poured into a mold and solidified to obtain an ingot, the solidification rate of the poured molten metal is adjusted to a range of 1 to 10 mm / sec. A method for producing an alloy sputtering target material having a structure.   The method for producing an alloy sputtering target material according to claim 1, wherein the alloy has a Vickers hardness of more than 450.   The said alloy is a Co-Cr-Pt-B type alloy, The manufacturing method of the alloy sputtering target material of Claim 1 or 2 characterized by the above-mentioned.   The method for producing an alloy sputtering target material according to claim 3, wherein a B content of the Co—Cr—Pt—B alloy is 7 at% or more. The mold is a carbon mold having a rectangular cross section with a rectangular hollow portion (cavity) when cut perpendicularly to the height direction at a substantially half position, and the short side of the cavity in the cross section The ratio of 1/2 length to mold wall thickness is 1: 2 to 10, characterized in that
5. A method for producing an alloy sputtering target material according to any one of 4 above. About the ingot obtained in the casting process, the ingot center portion and the ingot surface having the same height position as the ingot center portion in the mold and the contact surface with the mold being cut to a thickness of 0.5 mm Variation in Vickers hardness [Vickers hardness variation (%) = 100 × (Vickers hardness of the ingot surface portion−Vickers hardness of the ingot center portion) / Vickers hardness of the ingot surface portion] of 10% or less It exists, The manufacturing method of the alloy sputtering target material in any one of Claims 1-5 characterized by the above-mentioned.   The method of manufacturing an alloy sputtering target material according to any one of claims 1 to 6, further comprising a plastic working step performed after the casting step.   The method for producing an alloy sputtering target material according to claim 7, wherein the plastic working step is a rolling step.