JP4126607B2 - Method for producing and using sputtering target - Google Patents

Description

    The present invention relates to a sputtering target used for manufacturing a medium such as a hard disk medium, a magneto-optical disk, a magnetic head such as a spin valve head, and in particular, a target capable of forming a thin film compatible with ultrahigh density magnetic recording. It relates to the manufacturing method.

  In magnetic recording media, a thin film material with a high holding force is required to achieve ultra-high density recording, but the conventional thin film material itself has a high holding force, but the target is not highly pure, so a thin film material is required. The holding power of the material itself is not fully exerted. As a countermeasure, the current situation is dealt with by increasing the potential field of the material by adding an additive element such as Pt. However, it is considered that this method cannot be applied to an ultra-high density magnetic medium in which the fine structure control of the ultrathin film is indispensable because the impurity amount of the material itself is greatly affected.

  Furthermore, in an ultra-high density spin valve head, it is necessary to make the film thickness of the spin valve thin film less than 20 nm in order to cope with a reproduction gap in a narrow region. In some cases, diamagnetic materials based on active metals such as Mn and Cr are included, and in this case, impurities dissolved in the thin film prevent formation of a desired thin film structure. Therefore, in order to obtain a good thin film structure, an ultra-high-purity sputtering target in which the amount of released gas during sputtering in an ultra-high vacuum atmosphere is extremely small and the amount of impurities including gas impurities is suppressed to several ppm or less is used. It is necessary to manufacture.

  For example, in the case of a disk shape, a conventional target has a diameter of 100 to 200 mm and a thickness of 2.5 to 7.0 mm, and in the case of a square plate shape, a 100 to 200 square and a thickness of 2.5 to 7.0 mm. Is used. The manufacturing method of these targets is divided into a melt casting method and a powder sintering method. In the case of the melting casting method, a refractory crucible such as magnesia is used, and a vacuum melting furnace having a melting casting atmosphere with a vacuum degree of 10 to 0.1 Pa is mainly used, and after melting, it is cast into a refractory mold with tilted hot water, An ingot having a length of about 200 to 300 mm is manufactured. The target is obtained by cutting a cylindrical or prismatic ingot into a slice shape and polishing and polishing both sides and side surfaces thereof. However, the target obtained by this method contains impurities of about 50 ppm in general and about 30 ppm even in high purity products due to the inclusion of refractories during melt casting.

  On the other hand, in the powder sintering method, since it can be manufactured in units of one target disk material, the processing required for manufacturing the target can be largely omitted as compared with the melt casting method. Further, it is often used when the melting casting method cannot be employed, for example, when the material composition contains a refractory metal exceeding the heat resistance temperature of the refractory material, or when it is desired to make the target material composition uniform. However, in the powder sintering method, since an oxide film or the like adheres to the surface of the powder as a raw material, the purity of the target material to be manufactured is generally worse than that of the melt casting method, and the amount of impurities is about 50 to several hundred ppm. In particular, when the powder particle size to be used is small, the ratio of the material surface area to the material capacity tends to increase and the amount of impurities tends to increase.

For this reason, if these targets are used to form a film in an ultrahigh vacuum atmosphere of the order of 10 ⁻⁶ to 10 ⁻⁸ Pa, impurity gas is released from the target during sputtering, so that the film forming conditions deteriorate, and the desired film formation is achieved. The problem that cannot be done arises. In order to reduce gas emission, it is necessary to set the target so that the amount of impurities including the amount of gas is several Wt.ppm (for example, 3 Wt.ppm) or less.

  Therefore, it is conceivable to use a water-cooled crucible high-frequency induction melting method as a melting method without mixing impurities from the crucible. Are listed. In the high-frequency induction melting method using a water-cooled crucible, the material is melted with an apparatus in which a high-frequency induction coil is wound around a metal crucible such as water-cooled copper. This device has a floating melting device and a skull melting device due to the difference in the melting state in the crucible, but both are common in that impurities from the crucible are not mixed. A floating dissolution apparatus is described in, for example, Patent Document 2, and a skull dissolution apparatus is described in, for example, Patent Document 3.

  In the water-cooled crucible induction melting method, a metal is placed inside a crucible containing a slit and a high-frequency current is passed through the outer coil of the crucible. A magnetic field that has entered through the slit of the crucible induces an eddy current in the metal. Dissolves when heated. The metal is not only a non-magnetic material, but also the magnetic material is heated to the Curie point and becomes a non-magnetic material, and the eddy current induced in the crucible and the eddy current induced in the metal are opposite in the opposite surface part, A repulsive force acts on the metal from the crucible.

  In skull melting, the top of the metal melts away from the crucible side, and the bottom side and bottom are in contact with the crucible, but the crucible is water-cooled, so there is a solidified layer of the same composition as the molten metal called skull on the crucible contact surface. It is formed and the metal is in the melted state, and no impurities are mixed from the crucible material. In levitation melting, there are cases where the metal is in contact with a part of the lower part of the crucible and when the whole is non-contact, but because the amount of skull formation is small compared to skull melting, the inclusion of impurities from the crucible material In addition to being less, the alloy is more excellent in terms of uniform composition of an alloy containing a refractory metal.

JP 11-293453 A JP 2000-88467 A JP 10-246578 A

  An object of the present invention is to obtain an ultra-high purity target by performing a subsequent process more appropriately while dissolving a metal by using a water-cooled crucible high-frequency induction melting method with little contamination of impurities.

  In order to solve the above-described problems, the present invention is a method for melting a target material in a vacuum using a high-frequency induction melting apparatus using a water-cooled crucible, casting the column material in a mold in a vacuum, One end surface of the substrate is polished, and a target having the polished end surface as a mounting surface for a sputtering apparatus and the opposite non-polished end surface as a sputtering surface is formed. Since the mounting surface of the target that is in close contact with the sputtering apparatus is required to be flat, polishing is performed. However, if the sputtering surface is processed, impurities may enter from the atmosphere during processing, leading to a decrease in purity. Therefore, in the first aspect of the invention, the sputtering surface is not processed, and the cast surface during casting is left as it is.

  In the invention of claim 1, the target material can be dissolved by a flotation dissolution method or a skull dissolution method (invention 2).

  In the invention of claim 1, if the cylindrical member is cut into two in the axial direction and the cut surface is polished to produce two targets, two targets are taken from the cast material. And it is efficient (Claim 3). In order to avoid a reaction from the atmosphere during processing, the cylindrical material is preferably cut in an inert atmosphere.

In the invention of claim 1, the melting degree of the target material and the degree of vacuum of the casting atmosphere are preferably 10 ⁻⁶ Pa or less (invention 4).

  In the invention of claim 1, the columnar material is preferably cast by a centrifugal casting method (invention 5).

  When using the target manufactured by the method according to claim 1, it is preferable to start film formation after removing the surface layer of the non-polished end surface by an initial baking operation after attaching the target to a sputtering apparatus. (Claim 6). By cleaning the surface layer of the non-polished end surface (cast surface) of the target with an empty baking operation, that is, sputtering blanking, even in sputtering in an ultra-high vacuum atmosphere, the emitted gas is extremely reduced and the amount of impurities is a gas impurity. It is possible to form an ultrahigh purity material of several Wt.ppm or less including

According to the present invention, the target material is melted in a vacuum by a high-frequency induction melting device using a water-cooled crucible, and then cast into a mold in a vacuum to cast a cylindrical material, and the polished end surface of this cylindrical material is transferred to a sputtering device. On the other hand, by forming a target having a non-polished end surface (cast surface) of a cylindrical material as a sputtering surface, an extremely high purity target can be obtained by minimizing the chance of mixing impurities. . As a result, even in sputtering in an ultrahigh vacuum atmosphere on the order of 10 ⁻⁶ to 10 ⁻⁸ Pa, a thin film having an impurity amount of several ppm or less including gas impurities is not hindered by film formation conditions due to impurity gas emission from the target. Can be formed.

Embodiments of the present invention will be described below with reference to FIGS. First, FIG. 11 is a principle diagram of a target material melting / casting apparatus used in the practice of the present invention. This apparatus combines skull melting and centrifugal casting. In FIG. 11, a centrifugal casting mold 2 and a skull melting furnace 3 are installed in a vacuum vessel 1, and the vacuum vessel 1 is kept in a high vacuum atmosphere smaller than 10 ⁻⁶ Pa. The centrifugal casting mold 2 is rotationally driven as indicated by an arrow by a drive mechanism 5 sealed with a container 4, and the drive mechanism 5 has a drive shaft 9 driven by a motor 7 on a lifter lifter 6 via a belt 8. ing. The drive shaft 9 rotatably supported by the bearing 10 protrudes out of the hermetic container through the seal device 11, and the centrifugal casting mold 2 is attached to a turntable 12 directly connected to the drive shaft 9.

  On the other hand, in FIG. 11, the water-cooled crucible 13 of the skull melting furnace 3 is supported to be tiltable as shown, and the molten metal 14 is cast into the centrifugal casting mold 2 by the tilt of the water-cooled crucible 13. FIG. 12 is a principle diagram of a target material melting / casting apparatus combining flotation melting and centrifugal casting, and is the same as the apparatus of FIG. 11 except that a flotation melting furnace 15 is used as a water-cooled crucible high frequency induction melting apparatus. It is. The molten metal 14 in the water-cooled crucible 16 is cast into the centrifugal casting mold 2 from the tapping height 8 at the bottom of the crucible by opening the water-cooled crucible 16 by the tapping drive mechanism 17.

  4 and 5 show an example of a centrifugal casting mold 2 for casting a columnar material as a target material. FIG. 4 is a perspective view and FIG. 5 is a longitudinal sectional view thereof. 4 and 5, the mold 2 is made of a material having low reactivity with the cast metal in order to prevent impurities from being mixed, and has a cylindrical outer die 19 with a bottom and a cylindrical inner portion arranged on the inside thereof. It consists of a child 20. The lower part of the inner cavity of the outer mold 19 has a larger diameter than the upper part, and the target material is cast at the larger diameter part by the molten metal injected from the annular gate 21 formed by the core 20 in the smaller diameter part. The In this case, 0 <a <b is set, where the mold center axis is the rotation center axis, where a is the distance from the rotation center axis to the tapping center axis, and b is the radius of the cast cylindrical material 22.

  FIG. 1 shows a process of forming a desired target from a target material (cylindrical material) cast with the molds of FIGS. In FIG. 1, an annular gate 22 a on one end surface of a cylindrical member 22 is first cut along a plane 23, and then the cut surface 22 b and the side surface 22 c are polished to form a target 24. This target 24 uses the polishing end surface 24a as a mounting surface for a sputtering apparatus, and uses the opposite non-polishing end surface (cast surface) 24b as a sputtering surface.

  FIG. 6 is a perspective view showing another example of the centrifugal casting mold 2, and FIG. 7 is a longitudinal sectional view thereof. In this example, the mold 2 is a shell-like hollow body, and a tubular gate 21 is provided at a position eccentric from the center axis of the mold, and the center axis of the gate is a rotation center axis. The distance from the rotation center axis to the mold center axis is a, the maximum distance from the rotation center axis to the outer peripheral surface of the cylindrical member 22 is b, and the diameter of the cylindrical member 22 is c, and b> c / 2> a> 0 is set. Has been. FIG. 2 shows a target material (cylindrical material) 22 cast with the mold of FIGS. After the columnar gate portion 22a on one end surface of the cylindrical member 22 is cut along the plane 23, the cut surface 22b and the side surface 22c are polished to form the target 24.

  FIG. 8 is a perspective view showing still another example of the centrifugal casting mold 2, and FIG. 9 is a longitudinal sectional view thereof. In this example, an L-shaped tubular gate 21 is provided on the side surface of the shell-shaped hollow body mold 2, and the central axis of the gate is the rotation center axis. The distance from the rotation center axis to the mold center axis is a, the maximum distance from the rotation center axis to the outer peripheral surface of the cylindrical member 22 is b, the diameter of the cylindrical member 22 is c, and the distance from the rotation central axis to the outer peripheral surface of the cylindrical member 22 is Assuming that the minimum distance is d, b> c> a> 0 and d ≧ 0 are set.

  FIG. 3 shows a target material (cylindrical material) 22 cast with the molds of FIGS. In this case, since the gate part 22a is on the side surface of the columnar member 22, the columnar member 22 can be divided in half so that two targets 24 can be taken. That is, in FIG. 3, the columnar gate 22a on the side surface of the cylindrical member 22 is cut along the curved surface 25, and then the cylindrical member 22 is cut in two along the plane 26 in the axial direction. And the two targets 24 are formed by polishing each of the side surfaces 22c.

  FIG. 10 is a longitudinal sectional view showing a mold 2 in which a large number of the molds of FIGS. 8 and 9 are integrally formed in a tree shape. In this case, the rotation center axis coincides with the gate center axis and the tapping center axis. In any of the molds 2 of FIGS. 4 to 10, a water cooling structure or a heat retaining structure can be used to maintain an appropriate mold temperature according to the solidification rate of the molten metal material and the temperature of the molten metal.

It is a processing process figure of the target material which shows an embodiment of this invention. It is a processing process figure of the target material which shows different embodiment of this invention. It is a processing process figure of the target material which shows further another embodiment of this invention. It is a perspective view of the centrifugal casting mold used for casting of the target material of FIG. It is a longitudinal cross-sectional view of the centrifugal casting mold of FIG. It is a perspective view of the centrifugal casting mold used for casting of the target material of FIG. It is a longitudinal cross-sectional view of the centrifugal casting mold of FIG. It is a perspective view of the centrifugal casting mold used for casting of the target material of FIG. It is a longitudinal cross-sectional view of the centrifugal casting mold of FIG. It is a longitudinal cross-sectional view which shows different embodiment of the centrifugal casting mold used for casting of the target material of FIG. It is a principle diagram of a target material melting / casting apparatus used for carrying out the present invention. It is a principle figure which shows different embodiment of the target material melting | dissolving / casting apparatus used for implementation of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Centrifugal casting mold 3 Skull melting furnace 15 Levitation melting furnace 22 Cylindrical material 24 Target

Claims (6)

  The target material is melted in a vacuum with a high-frequency induction melting apparatus using a water-cooled crucible, cast into a mold in a vacuum to cast a cylindrical material, and one end surface of the cylindrical material is polished, and the polished end surface is A method for producing a sputtering target, comprising forming a target as a surface to be attached to a sputtering apparatus and having a non-polished end surface on the opposite side as a sputtering surface.   The method of manufacturing a sputtering target according to claim 1, wherein the target material is dissolved by a levitation dissolution method or a skull dissolution method.   2. The method of manufacturing a sputtering target according to claim 1, wherein the cylindrical member is cut into two in the axial direction, and the cut surface is polished to manufacture two targets. The method for producing a sputtering target according to claim 1, wherein the melting of the target material and the degree of vacuum in the casting atmosphere are set to 10 ^-6 Pa or less.   The method of manufacturing a sputtering target according to claim 1, wherein the cylindrical member is cast by a centrifugal casting method. The method of using a target manufactured by the method according to claim 1, wherein after the target is attached to a sputtering apparatus, the surface layer of the non-polished end surface is removed by an initial empty baking operation, and then film formation is started.

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