JP2007141309A - Substrate for magnetic recording medium, its manufacturing method, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate suitable for manufacturing a perpendicular magnetic recording medium having low noise and satisfactory signal reproducing characteristics, and to provide its manufacturing method. <P>SOLUTION: An under plating layer 16 of Ni or NiP is provided on an Si substrate 11 and a soft magnetic backing layer 12 is formed thereon by an electroplating method. The soft magnetic backing layer 12 has a composition containing at least two elements selected from the group consisting of Co, Ni and Fe and at least one element selected from the group consisting of B, C, P and S. Since the soft magnetic backing layer 12 is formed in such a state that an external magnetic field is applied, an in-plane diameter direction is an easily magnetized direction and the difference (δH=Hd-Hc) between the magnetization saturation magnetic field intensity (Hd) in the in-plane diameter direction and magnetization saturation magnetic field intensity (Hc) in an in-plane circumferential direction has anisotropy of 5 oersted (Oe) or more. A magnetic recording layer 13 for perpendicular magnetic recording is formed on the soft magnetic backing layer 12, and a protective layer 14 and a lubricant layer 15 are sequentially layered on the magnetic recording layer 13. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium substrate, a manufacturing method thereof, and a magnetic recording medium, and more particularly to a substrate suitable for manufacturing a perpendicular magnetic recording medium having low noise and good signal reproduction characteristics, and a manufacturing method thereof.

  In the technical field of information recording, a hard disk device, which is a means for magnetically reading and writing information such as characters, images, and music, is indispensable as a primary external recording device and built-in recording means for electronic devices such as personal computers. It has become a thing. Such a hard disk device has a built-in hard disk as a magnetic recording medium, but a conventional hard disk employs a so-called “in-plane magnetic recording system (horizontal magnetic recording system)” that writes magnetic information horizontally on the disk surface. It was.

  FIG. 1 is a schematic sectional view for explaining a general laminated structure of a horizontal magnetic recording type hard disk. A Cr-based underlayer 2 and a magnetic recording layer 3 are formed on a nonmagnetic substrate 1 by sputtering. And the carbon layer 4 as a protective film is laminated | stacked one by one, and the liquid lubricating layer 5 formed by apply | coating a liquid lubricant on the surface of this carbon layer 4 is formed (for example, refer patent document 1). The magnetic recording layer 3 is a Co alloy of uniaxial crystal magnetic anisotropy such as CoNiCr, CoCrPa, CoCrPt, etc. The crystal grains of this Co alloy are magnetized horizontally to the disk surface, and information is recorded. .

  However, in such a horizontal magnetic recording system, if the size of each crystal grain (magnetic domain) is reduced in order to increase the recording density, the N poles and S poles of adjacent magnetic domains repel each other and magnetization cancels each other. In order to increase the recording density, it is necessary to reduce the thickness of the magnetic recording layer to reduce the vertical size of the crystal grains, and as the crystal grains become finer (smaller volume) Problems such as the phenomenon of “thermal fluctuation”, in which the magnetization direction of crystal grains is disturbed by thermal energy and data is lost, are pointed out, and there is a limit to increasing the recording density. It was.

  In view of such problems, the “perpendicular magnetic recording method” has been studied. In this recording system, the magnetic recording layer is magnetized perpendicularly to the disk surface, so that N poles and S poles are alternately bundled and arranged in bits, and the N poles and S poles of the magnetic domains are adjacent to each other and are magnetized to each other. As a result, the stability of the magnetization state (magnetic recording) increases. In addition, when the magnetization direction is recorded perpendicularly, the demagnetizing fields of adjacent bits act so as to strengthen each other, so unlike the horizontal magnetic recording method, it is necessary to reduce the vertical size of the crystal grains. Absent. For this reason, even if the horizontal size of the crystal grains is reduced, if the recording layer thickness is increased and the vertical direction is increased, the volume of the crystal grains as a whole increases and the influence of “thermal fluctuation” is reduced. It is possible.

That is, the perpendicular magnetic recording method can reduce the demagnetizing field and ensure the K _u V value (K _u is the magnetocrystalline anisotropy energy of the magnetic recording layer and V is the unit recording bit volume). This is a magnetic recording system that reduces the instability of magnetization and greatly expands the limit of recording density, and is therefore expected as a system for realizing ultra-high density recording.

  FIG. 2 is a schematic cross-sectional view for explaining a basic layer structure of a hard disk as a “perpendicular two-layer magnetic recording medium” in which a recording layer for perpendicular magnetic recording is provided on a soft magnetic backing layer. On the non-magnetic substrate 11, a soft magnetic backing layer 12, a magnetic recording layer 13, a protective layer 14, and a lubricating layer 15 are sequentially laminated. Here, permalloy, CoZrTa amorphous, or the like is typically used for the soft magnetic backing layer 12. As the magnetic recording layer 13, a CoCr alloy, a multilayer film in which several PtCo layers and Pd and Co ultrathin films are alternately stacked, or an SmCo amorphous film is used.

  As shown in FIG. 2, in a perpendicular magnetic recording type hard disk, a soft magnetic backing layer 12 is provided as an underlayer of the magnetic recording layer 13, its magnetic property is “soft magnetic”, and the layer thickness is approximately 100 nm to It is about 500 nm. The soft magnetic underlayer 12 is for increasing the write magnetic field and reducing the demagnetizing field of the magnetic recording film. The soft magnetic underlayer 12 is a path for the magnetic flux from the magnetic recording layer 13 and a path for the write magnetic flux from the recording head. Function as. That is, the soft magnetic backing layer 12 plays the same role as the iron yoke in the permanent magnet magnetic circuit. For this reason, it is necessary to set the layer thickness thicker than the layer thickness of the magnetic recording layer 13 for the purpose of avoiding magnetic saturation during writing.

  From the viewpoint of the laminated structure, the soft magnetic backing layer 12 corresponds to the Cr-based underlayer 2 provided in the horizontal magnetic recording type hard disk, but the film formation is performed for the Cr-based underlayer 2 of the horizontal recording medium. It is not easy compared with film formation.

  The thickness of each layer of the hard disk in the horizontal magnetic recording system is at most about 20 nm, and all are formed by a dry process (mainly magnetron sputtering) (see Patent Document 1). Various methods for forming the magnetic recording layer 13 and the soft magnetic backing layer 12 by a dry process have been studied in the perpendicular double-layer recording medium, but when the soft magnetic backing layer 12 is formed by a dry process, sputtering is performed. The film thickness uniformity, composition uniformity, target because the target is a ferromagnetic material with a large saturation magnetization and the thickness of the soft magnetic underlayer 12 is required to be 100 nm or more. Lifetime, process stability, and above all, low film deposition speeds have major problems in terms of mass productivity and productivity.

  In order to increase the recording density, it is necessary to reduce the flying height of the magnetic head that floats on the magnetic disk surface as much as possible. The smoothness tends to deteriorate, and this may cause a head crash.

For these reasons, attempts have been made to form the soft magnetic backing layer 12 by a plating method that is easy to thicken and that can be polished (see, for example, Patent Document 2).
JP-A-5-143972 JP 2005-108407 A

  When a soft magnetic layer is formed by a plating method, a large number of magnetic domains having magnetism in a specific direction are generated over a range of several mm to several cm on the plated film surface constituting the soft magnetic layer, and at the interface between these magnetic domains. A domain wall is generated. When a soft magnetic layer having such a domain wall is used as a backing layer for a hard disk for a vertical two-layer magnetic recording medium, an isolated pulse noise called spike noise or micro spike noise is generated due to a leakage magnetic field generated from the domain wall portion, There is a possibility that the signal reproduction characteristic is greatly impaired.

  Therefore, the present inventors have earnestly studied the conditions for forming a soft magnetic film by plating and the types of applicable soft magnetic films in order to obtain a perpendicular double-layer magnetic recording medium having excellent characteristics by a simple method. Through repeated research, the substrate on which the magnetic recording medium is formed is made of an alloy composed of two or more metals selected from the group of Co, Ni, and Fe by electroless plating, and in the inner circumferential direction of the substrate. It has been found that when a soft magnetic film having anisotropy is used as a backing layer, the occurrence of a domain wall in the soft magnetic film is suppressed and effective in reducing spike noise (Patent Document 2).

  Here, “anisotropic” means the difference (δH = Hd−Hc) between the magnetization saturation magnetic field strength (Hd) in the in-plane inner diameter direction and the magnetization saturation magnetic field strength (Hc) in the in-plane circumferential direction, and δH Is positive (Hd−Hc> 0), the in-plane inner diameter direction is the easy magnetization direction, and when δH is negative (Hd−Hc <0), the in-plane peripheral direction is the easy magnetization direction. To do.

  By the way, according to the simulation result of magnetic recording, when the anisotropy of the soft magnetic backing layer is 2 kilo-Oersted (kOe) or less, the S / N of the recording medium obtained in both the circumferential direction and the radial direction can be obtained. While the ratio is hardly changed, in the case of anisotropy of 2 kilo-Oersted (kOe) or more, the easy magnetization direction is preferably the radial direction.

  However, the soft magnetic film obtained by the method described in Patent Document 2 is a soft magnetic film formed by a dry process in which the in-plane circumferential direction is the easy magnetization direction and the in-plane radial direction is the easy magnetization direction. It has a different anisotropy.

  As a result of further intensive studies, the present inventors can form a soft magnetic film having in-plane radial anisotropy even by a plating method, which is as good as a soft magnetic film having circumferential anisotropy. It has been found that a perpendicular two-layer magnetic recording medium having an S / N ratio can be obtained.

  That is, the present invention makes it possible to form a soft magnetic underlayer having in-plane radial anisotropy by a plating method, whereby a perpendicular magnetic recording medium having low noise and good signal generation characteristics can be obtained. It is an object of the present invention to provide a substrate suitable for manufacturing and a manufacturing method thereof.

  In order to solve the above problems, the present invention provides a magnetic recording medium substrate comprising: a nonmagnetic substrate having a disk shape with a diameter of 90 mm or less; and a main surface of the substrate. A soft magnetic backing layer, wherein the soft magnetic backing layer is selected from the group consisting of at least two elements selected from the group consisting of Co, Ni and Fe, and B, C, P and S A plating layer containing at least one kind of element, wherein the plating inner layer direction is the direction of easy magnetization, the magnetization saturation magnetic field strength (Hd) in the surface inner diameter direction, and the magnetization saturation in the in-plane circumferential direction. The difference (δH = Hd−Hc) from the magnetic field strength (Hc) has an anisotropy of 5 Oersted (Oe) or more.

  According to a second aspect of the present invention, in the magnetic recording medium substrate according to the first aspect, the plating layer has a thickness of 50 nm to 1000 nm.

  According to a third aspect of the present invention, in the magnetic recording medium substrate according to the first or second aspect, the nonmagnetic substrate is a silicon wafer, and Ni or NiP is interposed between the substrate main surface and the plating layer. It is characterized by comprising a base plating layer.

  According to a fourth aspect of the present invention, in the magnetic recording medium substrate according to the third aspect, the layer thickness of the base plating layer is 10 nm to 1000 nm.

  The invention according to claim 5 is a magnetic recording medium, wherein the magnetic recording layer is provided on the soft magnetic backing layer of the magnetic recording medium substrate according to any one of claims 1 to 4. It is characterized by.

  The invention according to claim 6 is a method of manufacturing a substrate for a magnetic recording medium, comprising an electroless plating step of forming a soft magnetic backing layer on a main surface of a nonmagnetic substrate having a disk shape with a diameter of 90 mm or less. The electroless plating step includes at least two metal ions selected from the group consisting of Co, Ni, and Fe and at least one element selected from the group consisting of B, C, P, and S. The substrate is immersed in a plating bath, and the plating of the soft magnetic backing layer is performed under an external magnetic field in which the substrate main surface and the magnetic field direction form an angle of 45 ° or more and 90 ° or less. To do.

  According to a seventh aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to the sixth aspect, the magnetic field strength applied to the substrate is not less than 50 Oersted (Oe) and not more than 5 kiloOersted (kOe). It is characterized by that.

  According to an eighth aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to the seventh aspect, the fluctuation range of the magnetic field strength applied to the substrate is 20% or less.

  According to a ninth aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to any one of the sixth to eighth aspects, the electroless plating step comprises rotating and revolving the substrate during the plating film formation. It is characterized by being executed.

  According to a tenth aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to the ninth aspect, the self-revolving speed of the substrate is 10 to 100 rpm.

  An eleventh aspect of the present invention is the method for manufacturing a magnetic recording medium substrate according to any one of the sixth to tenth aspects, wherein the temperature of the plating bath is set to 40 ° C. or higher and 100 ° C. or lower. It is characterized by that.

  According to a twelfth aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to any one of the sixth to eleventh aspects, a silicon wafer is selected as the substrate, and prior to the electroless plating step, Ni A step of forming a Ni or NiP undercoat layer by immersing the silicon wafer in a plating bath in which a phosphorus reducing agent is added to a plating bath containing ions or a bath containing Ni ions. Features.

  According to a thirteenth aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to the twelfth aspect of the present invention, the substrate surface treatment for removing the oxide film on the surface of the silicon wafer prior to the step of forming the base plating layer. It has the process, It is characterized by the above-mentioned.

  The invention according to claim 14 is the method for manufacturing a magnetic recording medium substrate according to any one of claims 6 to 13, wherein after the soft magnetic underlayer is plated, A polishing step for controlling surface flatness is provided.

  The soft magnetic backing layer provided on the magnetic recording medium substrate of the present invention is selected from the group consisting of at least two elements selected from the group consisting of Co, Ni and Fe, and B, C, P and S. A plating layer containing at least one element, and is formed such that the direction of easy magnetization of the plating layer is the surface inner diameter direction, and the magnetization saturation magnetic field strength (Hd) in the surface inner diameter direction and the inner surface periphery Since the difference (δH = Hd−Hc) from the magnetization saturation magnetic field strength (Hc) in the direction has an anisotropy of 5 Oersteds (Oe) or more, the occurrence of domain walls is suppressed and spike noise is reduced.

  For this reason, a hard disk having a magnetic film for perpendicular magnetic recording provided on the soft magnetic underlayer can provide a high recording density magnetic recording medium having good write characteristics by increasing the head magnetic flux.

  Further, the magnetic recording medium substrate of the present invention has a soft magnetic backing layer formed by wet electroless plating, so that the manufacturing process is significantly simpler than dry process film formation by vapor deposition or the like. And excellent productivity.

  Furthermore, since the film thickness and surface flatness can be controlled by polishing after plating the soft magnetic backing layer, it is suitable for manufacturing a magnetic recording medium having excellent head flying characteristics.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention with reference to drawings is demonstrated in detail.

  The magnetic recording medium substrate of the present invention is for perpendicular magnetic recording. By forming a magnetic recording layer on a soft magnetic underlayer, a hard disk as a perpendicular double-layer magnetic recording medium can be obtained. That is, the magnetic recording medium substrate of the present invention is provided with a soft magnetic backing layer 12 formed by electrolytic plating on a nonmagnetic substrate 11 as shown in FIG. Then, the magnetic recording layer 13 for perpendicular magnetic recording is formed on the soft magnetic underlayer 12, and the protective layer 14 and the lubricating layer 15 are sequentially laminated, whereby the magnetic recording medium of the present invention is obtained. As shown in FIG. 3, when a Si substrate is used as the nonmagnetic substrate 11, a Ni or NiP underplating layer (nucleation film) 16 is provided between the soft magnetic backing layer 12.

  Hereinafter, the configuration of each layer will be sequentially described.

  Non-magnetic substrate 11: As a non-magnetic substrate used for the magnetic recording medium substrate of the present invention, a substrate obtained by performing Ni-P electroless plating on an aluminum substrate conventionally used for manufacturing a magnetic recording medium, or a glass substrate In addition, a Si substrate can be used. Note that when a glass substrate is used, it is necessary to provide a conductive film in advance by a sputtering method or the like.

  In addition, the Si substrate is not necessarily a single crystal substrate, but when a single crystal Si substrate is used, the atomic arrangement on the surface is uniform in the plane, and the surface chemical state and surface potential state in the plating process are also in plane. There is an advantage of being homogeneous. That is, when a single crystal Si substrate is used as the nonmagnetic substrate 11, direct displacement plating on the single crystal Si substrate 11 can be performed when a Ni or NiP underplating layer (nucleation film) 16 described later is formed. In addition, there is an advantage that magnetic non-uniformity caused by non-uniform plating can be suppressed. In the following description, it is assumed that the nonmagnetic substrate 11 is a single crystal Si substrate.

The single crystal Si substrate can be easily obtained by crystal growth by the CZ (chocolate ski) method or the FZ (floating zone) method, and there is no particular limitation on the plane orientation of the substrate. (100), (110) Alternatively, any plane orientation such as (111) may be used. Further, as an impurity contained in the substrate, a donor or acceptor of about 10% (−10 ²² atoms / cm ³ ) in atomic ratio with Si or a light element such as oxygen, carbon, or nitrogen may be included.

  Regardless of whether or not the nonmagnetic substrate 11 is a single crystal Si substrate, in the present invention, the substrate diameter is 90 mm or less. This is because a uniform plating solution flow is formed on the substrate surface in an electroplating film forming step of the soft magnetic backing layer 12 described later. This point will be described later.

  Surface treatment of Si substrate: As described above, when a Si substrate is used as the nonmagnetic substrate 11 of the present invention, the base plating layer 16 is provided between the Si substrate 11 and the soft magnetic backing layer 12. For this reason, the surface activation process of the Si substrate 11 is performed prior to the formation of the base plating layer 16. This surface activation process facilitates subsequent substitution plating of the underlying plating layer and increases the adhesion of the film.

  This surface activation treatment is mainly performed by removing an oxide film naturally formed on the surface of the Si substrate 11. In the course of this treatment, Si atoms on the extreme surface of the Si substrate 11 are etched, and the substrate surface is chemically treated. Activated.

  This etching treatment can be performed by various methods such as acid treatment, alkali treatment, or electrolytic treatment. For example, when etching is performed using an alkaline aqueous solution such as caustic soda, an aqueous solution having an alkali concentration of 2 to 60% by weight is set to a liquid temperature of 30 to 100 ° C., and the surface oxide film of the Si substrate is removed and the surface of the Si substrate is removed. Slightly corrodes.

  Base plating layer 16: The base plating layer 16 is formed by substitution plating of Ni or NiP on the surface of the Si substrate subjected to the surface activation treatment. When the underlying plating layer 16 is a Ni layer, a plating solution containing Ni ions of 0.01 N or more, preferably 0.05 to 0.3 N as an element component is used, and the Si substrate 11 is immersed in this plating solution. To form a plating film. Further, when the base plating layer 16 is a NiP layer, a phosphorus (P) -based reducing agent is added to the above plating solution to perform plating film formation. Note that the surface of the Ni layer or NiP layer thus obtained may be modified with a Cu film, a Pd film, an Au film, or the like.

  The thickness of the base plating layer 16 is preferably 10 to 1000 nm, more preferably 50 to 500 nm. This is because if the underlying plating layer 16 is thinner than 10 nm, the polycrystalline grain size of the metal (alloy) tends to be non-uniform in the subsequent plating process of the soft magnetic backing layer 12, and if it is thicker than 1000 nm, the crystal grains are enlarged. It is because it ends up.

  Soft magnetic backing layer 12: The soft magnetic backing layer 12 is formed by a general method known as electroless plating so that the plating film thickness becomes 100 nm to 10 μm, and then this plating film is polished to a predetermined thickness. 50 to 1000 nm. This polishing step is performed using inorganic fine particles such as silica and ceria, and also serves to control the surface roughness simultaneously with the thickness adjustment.

  The thickness range is such that if the thickness of the soft magnetic backing layer 12 is greater than 1000 nm, magnetic noise generated from the soft magnetic backing layer 12 increases when a hard disk signal is reproduced, and the recording medium On the other hand, if the thickness is less than 50 nm, the magnetic transmission characteristics as the underlayer of the magnetic recording layer 13 are insufficient, and the overwrite characteristics as a recording medium are deteriorated. Because.

  As the electroless plating bath, either a sulfide bath or a chloride bath can be used, and various types of metal contained in the bath can be adopted. A metal salt-containing plating bath containing at least two elements selected from the group consisting of Co, Ni, and Fe is selected because the crystal structure needs to be cubic as well as the soft magnetic film. Such a metal element is selected because Co, Ni, and Fe can all be electrolessly plated, but it is difficult to obtain good soft magnetic properties from a single element plating film. Specific examples of the bath composition include a nickel sulfate and cobalt sulfate mixed bath, or a mixed bath containing iron sulfate, and the preferred concentration is 0.01 to 0.5N. In addition, it is preferable to set the temperature of a plating bath in the range of 40-100 degreeC.

In addition, such a plating bath is included in the bath as necessary so that at least one element selected from the group consisting of B, C, P, and S is significantly contained in the plating film. A reducing agent corresponding to the metal ion to be added is added. Examples of such a reducing agent include hypophosphorous acid (H ₂ PO ₂ ) and dimethylamine borane (DMAB: (CH ₃ ) ₂ HNBH ₃ ). The inclusion of at least one element of B, C, P, and S in the plated film is in consideration of the soft magnetic properties of the film, and at least one of these elements is significantly added. The point of inclusion is a significant difference from dry film forming methods such as sputtering.

  Magnetic field “anisotropy” of the soft magnetic backing layer 12: The soft magnetic backing layer 12 has a magnetization direction in the surface inner diameter direction and a magnetization saturation magnetic field strength (Hd) in the surface inner diameter direction and magnetization in the in-plane circumferential direction. Plating is performed so that the difference (δH = Hd−Hc) from the saturation magnetic field strength (Hc) has an anisotropy of 5 Oersteds (Oe) or more. As will be described later, in the present invention, since the plating of the soft magnetic film is performed with an external magnetic field applied, the film is formed so that the magnetization falls in the plane, and the surface inner diameter direction becomes the easy magnetization direction, The external magnetization intensity (magnetization saturation magnetic field intensity) at which magnetization is saturated differs between the in-plane circumferential direction and the radial direction of the plating film. When such anisotropy is imparted to the soft magnetic film, domain wall generation is remarkably suppressed and spike noise is reduced. There has been no report of a magnetic anisotropy in the radial direction in a soft magnetic film formed by plating, which has been realized for the first time by the present invention.

  FIG. 4 is a conceptual diagram of in-plane circumferential and radial magnetization curves for explaining the meaning of the above-mentioned “anisotropic”. As shown in this figure, the magnetization saturation magnetic field strength in the radial direction is higher than that in the circumferential direction, and the plating film forming conditions are selected so that this difference (δH) is 5 oersted (Oe) or more. When the magnetic anisotropy is 5 oersted (Oe) or more, for example, spike noise generated from the soft magnetic underlayer 12 can be extremely effectively suppressed. Although it is difficult in the process to make this anisotropy 2 kilo-Oersted (kOe) or more, a sufficient noise suppression effect is obtained with an anisotropy of less than 2 kilo-Oersted (kOe).

  Such a magnetization curve can be obtained by measurement using a VSM (sample vibration magnetometer) or Kerr effect. In the case of using VSM, on the contrary to the advantage that the magnetization curve including the absolute value of the magnetization is strictly determined, it is necessary to be a destructive test because it is necessary to cut out the measurement sample, and the soft magnetic film remains. There is a disadvantage that the influence on the magnetic properties due to the state of stress being different from the non-destructive state cannot be denied.

  On the other hand, when the Kerr effect is used, the magnetization curve can be measured nondestructively, and the measurement area is also a narrow range of about 2 to 3 mm, so it is easy to perform multipoint measurement to obtain an in-plane distribution. There is an advantage of being. However, since the vertical axis of the obtained magnetization curve is originally the Kerr rotation angle, the absolute value of magnetization cannot be known. In addition, since Kerr effect measurement is based on visible light reflection on the film surface, the measurement result must be based on information on the surface of the film, and may differ from the magnetization curve in the entire thickness direction of the film. There is a disadvantage that cannot be denied.

  Thus, since both measurement methods have their respective characteristics, it is important to use these methods properly when grasping magnetic anisotropy information.

  Application of magnetic field at the time of soft magnetic film plating: FIG. 5 is a conceptual diagram for explaining a state of application of an external magnetic field at the time of plating the soft magnetic film, FIG. 5 (a) is a side view, FIG. (B) is a top view. In this figure, reference numeral 10 is a substrate to be plated, 17 is a bathtub, 18 is a plating bath, 19a and 19b are magnets for applying external magnetization (N pole and S pole), and 20 is a magnet's N pole 19a to S pole. It is a magnetic force line toward 19b.

  The magnet 19 for generating an external magnetic field is not particularly limited as long as it is a means capable of generating a strong magnetic field, such as an electromagnet, a permanent magnet magnetic circuit, or a superconducting magnet. The intensity of the magnetic field applied to the substrate to be plated 10 by the magnet 19 is preferably 50 Oersted (Oe) or more and 5 kiloOersted (kOe) or less. When the magnetic field strength is less than 50 oersted (Oe), it is difficult to obtain radial anisotropy. On the other hand, if the magnetic field is stronger than 5 kilo-Oersted (kOe), the magnetic field generator becomes too large, making it difficult to incorporate the plating apparatus system including the bathtub 17, and magnetic field leakage. This is because it becomes large and adversely affects peripheral equipment and plating system.

  The generated magnetic field may be a varying magnetic field or a static magnetic field, but the fluctuation width is preferably small, and preferably the fluctuation width is 20% or less. This is because it is considered that the applied magnetic field varies slightly because the influence of the underplating layer 16 (Ni or NiP layer) is different between the initial stage and the middle stage of the plating film formation. This is because, if too much, the radial anisotropy is disturbed. Most simply, a permanent magnet magnetic circuit that can apply a constant static magnetic field and can be easily and compactly incorporated is used as the magnet 19.

  As shown in FIG. 5B, the magnetic field application direction (direction of the magnetic force lines 20) to the substrate 10 to be plated is 45 ° to 90 ° in an angle (θ) formed between the magnetic force lines 20 and the surface of the substrate 10. Selected as When this angle is less than 45 °, the magnetic field component in the vertical direction of the substrate 10 is reduced, and the magnetic field component in the horizontal direction of the substrate is increased to increase the in-plane circumferential anisotropy and radial anisotropy. This is because uniform radial anisotropy cannot be obtained due to the fact that they compete with each other. Note that the vertical component of the magnetic field with respect to the surface of the substrate 10 does not necessarily have to be uniform within the surface of the substrate 10, but 50 / √2 Oersted (Oe) or more and 5 kiloOersted (kOe) in an arbitrary region of the portion to be plated. It is preferable that it exists in the range.

  The reason why such a magnetic field application method causes radial anisotropy in the soft magnetic film is not necessarily clear, but the present inventors have determined that the flow of the plating solution in the vicinity of the substrate surface depends on the plating film formation process. It is speculated that this may be caused by making the magnetostriction of the soft magnetic plating film different in the circumferential direction and the radial direction.

  In fact, according to our experiments, the magnetic anisotropy of the soft magnetic plating film is affected by the liquid flow in the plating bath. If the diameter of the substrate to be plated exceeds 90 mm, it becomes difficult to form a uniform plating solution flow on the substrate surface. Therefore, the liquid flow in the plating bath is adjusted by adjusting the liquid circulation during plating film formation, stirring the plating liquid using a stirrer such as a paddle, or revolving the substrate to be plated. . Among these, the method of rotating and revolving the substrate to be plated in a bath is a simple and effective method for making the liquid flow rate appropriate. Therefore, the liquid flow in the plating bath is adjusted by appropriately combining the self-revolution of the substrate to be plated in the bath and the circulation and stirring of the plating solution. In addition, according to the experiment result of the present inventors, the revolution speed is preferably 10 rpm to 100 rpm, more preferably 20 rpm to 80 rpm.

  Magnetic recording layer 13: The magnetic recording layer 13 provided on the soft magnetic backing layer 12 is made of a hard magnetic material for performing perpendicular magnetization recording. The magnetic recording layer 13 may be formed directly on the soft magnetic backing layer 12, but various intermediate films may be formed as necessary for matching the crystal grain size and magnetic characteristics. It may be provided and formed on this intermediate film. As the intermediate film, for example, a Ru film is used. Further, a plurality of intermediate films may be laminated.

  The composition of the magnetic recording layer 13 is not particularly limited as long as it is a hard magnetic material capable of forming a magnetic domain easily magnetized in a direction perpendicular to the layer surface. When the sputtering method is used, for example, a Co—Cr alloy film, an Fe—Pt alloy film, a CoCr—Si granule film, a Co / Pd multilayer film, or the like can be used. Further, when the film is formed by a wet method, for example, a Co—Ni plating film or a barium / ferrite coating film made of a magnetoplumbite phase can be used.

  The thickness of the magnetic recording layer 13 is preferably about 5 to 100 nm, more preferably about 10 to 50 nm. The magnetic recording layer 13 is formed so that its coercive force is preferably 0.5 to 10 kilo-Oersted (kOe), more preferably 3 to 6 kilo-Oersted (kOe). Is done.

Protective layer 14 and lubricating layer 15: The protective layer 14 provided on the upper surface of the magnetic recording layer 13 can be formed of a material used in conventional magnetic recording media. For example, a crystalline protective film such as alumina (Al ₂ O ₃ ) as well as an amorphous carbon protective film formed by sputtering or CVD can be used. The lubricating layer 15 provided on the upper surface of the protective layer 14 can also be formed by applying a material used for a conventional magnetic recording medium, and there is no particular limitation on the type of agent and the application method. . For example, the lubricating layer 15 is formed by applying a fluorinated oil or fat to form a monomolecular film. The thicknesses of the protective layer 14 and the lubricating layer 15 are both about 2 to 20 nm, for example.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.

  Example: In this example, a single crystal Si substrate was used as the nonmagnetic substrate. From a Si single crystal having a diameter of 200 mm (8 inches) grown by the CZ method, core removal, centering, and lapping are performed to obtain a (100) Si single crystal plate (P-doped n-type) having a diameter of 65 mm. It was. This Si single crystal plate was polished on both sides using a slurry containing colloidal silica having an average particle size of 15 nm to obtain a Si substrate having a surface roughness (Rms) of 4 nm. In addition, Rms is a square average roughness, and was measured using AFM (atomic force microscope).

  This Si substrate was immersed in a 2% by weight aqueous caustic soda solution (liquid temperature: 45 ° C.) for 3 minutes to remove the thin surface oxide film on the substrate surface, and surface activation treatment was performed to etch Si on the extreme surface. A base plating bath in which 0.5N ammonium sulfate was added to a 0.1N nickel sulfate aqueous solution was prepared and immersed in a bath maintained at a liquid temperature of 80 ° C. for 5 minutes to obtain a base Ni plating layer.

  Next, a plating solution containing ammonium sulfate 0.2N, nickel sulfate 0.02N, cobalt sulfate 0.1N, iron sulfate 0.01N and dimethylamine borane 0.04N as a reducing agent is prepared, and the solution temperature becomes 65 ° C. Heated and held as such. The reason for setting the liquid temperature at 65 ° C. is that the film growth rate when the soft magnetic underlayer is electrolessly plated is 0.1 μm / min.

  The bath in which the plating bath is stored is disposed between the N pole and the S pole of the permanent magnet magnetic circuit so that the magnetic field lines generated from the magnet pass through the plating bath, and a base plating layer is formed on the plating bath. An Si substrate is immersed, electroless plating is performed for 20 minutes while the Si substrate is rotated at 60 rpm, and a Ni—Co—Fe main component containing S, C, B and having a thickness of 1200 nm is formed on the underlying plating layer. A soft magnetic film was obtained.

The substrate arrangement at the time of electroless plating is set to three so that the angle formed between the substrate surface and the lines of magnetic force is 90 °, 60 °, and 45 °, and for each of these three substrate arrangements, 500 oersted ( A soft magnetic film was obtained under a total of six conditions by applying a static magnetic field of Oe) and 2 kilo-Oersted (kOe). Table 1 summarizes the results of VSM measurement of these six types of soft magnetic films under an external magnetic field up to 100 oersted (Oe). In this table, H _ext is the external magnetic field strength, H _ext is the external magnetic field strength perpendicular to the substrate surface (effective magnetic field strength), H _c is the magnetization saturation magnetic field strength in the in-plane circumferential direction, and H _d is the surface inner diameter. The magnetization saturation magnetic field strength in the direction.

In any of the soft magnetic film, the easy magnetization direction is the surface radially inward, a difference between the magnetization saturation magnetic field strength of the surface radially inwards (H _d) in-plane circumferential direction of the magnetization saturation magnetic field strength (H _c) (δH = anisotropy of H _d -H _c) is approximately 20 Oe or more (about 20 to 30 Oe) is obtained. The coercive force exhibited good soft magnetic characteristics of about 6 oersted (Oe) or less in any soft magnetic film.

  This soft magnetic film was polished for about 600 nm with a slurry in which colloidal silica was suspended to obtain a soft magnetic backing layer having a thickness of about 600 nm. When the in-plane thickness distribution of the film after polishing was evaluated with fluorescent X-rays, both the front and back surfaces were within several percent, and the surface roughness (Rms) was 4 nm, which was the same as the Si substrate surface.

  A perpendicular magnetic recording layer was formed by sputtering on the soft magnetic backing layer. The sputtering conditions were as follows. First, a Ru film was formed to 2 nm with the substrate temperature maintained at 180 ° C., and a magnetic film having a composition of Co: Cr: Pt = 76: 19: 5 (mass%) was formed on this Ru film. A magnetic recording layer was obtained by forming a film with a thickness of 15 nm. The coercivity of this magnetic recording layer was 4.5 kilo-Oersted (kOe) in the direction perpendicular to the film surface, and 500 oersted (Oe) in the direction parallel to the film surface.

  The magnetic recording layer was coated with amorphous carbon having a thickness of 10 nm, and a fluorine lubricating film was further applied by a dipping method to obtain a perpendicular magnetic recording medium.

  After this perpendicular magnetic recording medium was placed on a spin stand and DC erase was performed, writing was performed with a nano slider head with a flying height of 10 nm and the noise level of the reproduced signal was measured. As a result, spike noise was found in the envelope pattern. I was not able to admit. The average level of the S / N ratio was as good as 21 dB.

  Comparative Example: A soft magnetic film is formed by applying an external magnetic field of 20 Oersted (Oe) so that the magnetic lines of force are at an angle of 90 ° with respect to the substrate surface, except for the application of an external magnetic field. When the film was formed, the coercive force showed a good soft magnetic characteristic of 6 Oersteds, but the magnetic anisotropy (δH) was as small as 3 Oersteds (Oe), and the film was almost isotropic.

  Further, when the characteristics of the magnetic recording layer formed on the soft magnetic underlayer under the same conditions as described above were examined, the occurrence of spike noise was recognized although the S / N ratio was as low as 15 dB.

  The present invention provides a substrate suitable for manufacturing a perpendicular magnetic recording medium having low noise and good signal reproduction characteristics, and a method for manufacturing the same.

1 is a schematic cross-sectional view for explaining a general laminated structure of a horizontal magnetic recording type hard disk. 1 is a schematic cross-sectional view for explaining the basic layer structure of a perpendicular double-layer magnetic recording medium in which a recording layer for perpendicular magnetic recording is provided on a soft magnetic underlayer. 1 is a schematic cross-sectional view for explaining a basic layer structure of a perpendicular two-layer magnetic recording medium of the present invention, in which a Si substrate is used as a nonmagnetic substrate, and a base plating layer (nucleation film) is provided. It is a conceptual diagram of the in-plane circumferential and radial magnetization curves for explaining the meaning of magnetic anisotropy of the soft magnetic underlayer provided on the magnetic recording medium substrate of the present invention. It is a conceptual diagram for demonstrating the mode of the external magnetic field application at the time of depositing a soft-magnetic film | membrane, (a) is a side view, (b) is a top view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Nonmagnetic board | substrate 2 Cr type | system | group underlayer 3,13 Magnetic recording layer 4,14 Protective layer 5,15 Lubricant layer 10 Substrate to be plated 12 Soft magnetic backing layer 16 Undercoat layer (nucleation film)
17 Bath 18 Plating bath 19a, b Magnet 20 Magnetic flux

Claims (14)

A non-magnetic substrate having a disc shape with a diameter of 90 mm or less, and a soft magnetic backing layer provided on the main surface of the substrate,
The soft magnetic underlayer includes a plating containing at least two elements selected from the group consisting of Co, Ni, and Fe and at least one element selected from the group consisting of B, C, P, and S. Layer,
The plating layer has a direction of easy magnetization in the surface inner diameter direction, and a difference (δH = Hd−Hc) between the magnetization saturation magnetic field strength (Hd) in the surface inner diameter direction and the magnetization saturation magnetic field strength (Hc) in the in-plane circumferential direction. A magnetic recording medium substrate having an anisotropy of 5 Oersted (Oe) or more. The magnetic recording medium substrate according to claim 1, wherein the plating layer has a thickness of 50 nm to 1000 nm. 3. The magnetic recording medium according to claim 1, wherein the non-magnetic substrate is a silicon wafer, and a Ni or NiP underplating layer is provided between the substrate main surface and the plating layer. Substrate. The magnetic recording medium substrate according to claim 3, wherein a thickness of the base plating layer is 10 nm to 1000 nm. 5. A magnetic recording medium, wherein a magnetic recording layer is provided on the soft magnetic backing layer of the magnetic recording medium substrate according to claim 1. Comprising an electroless plating step of forming a soft magnetic backing layer on the main surface of a nonmagnetic substrate having a disk shape with a diameter of 90 mm or less,
The electroless plating step includes a plating bath containing at least two metal ions selected from the group consisting of Co, Ni and Fe and at least one element selected from the group consisting of B, C, P and S The substrate is immersed therein, and the plating of the soft magnetic backing layer is performed under an external magnetic field in which the main surface of the substrate and the magnetic field direction form an angle of 45 ° to 90 °. A method for manufacturing a substrate for a recording medium. The method of manufacturing a magnetic recording medium substrate according to claim 6, wherein the magnetic field strength applied to the substrate is 50 oersted (Oe) or more and 5 kilooersted (kOe) or less. 8. The method of manufacturing a magnetic recording medium substrate according to claim 7, wherein the fluctuation range of the magnetic field strength applied to the substrate is 20% or less. 9. The method for manufacturing a substrate for a magnetic recording medium according to claim 6, wherein the electroless plating step is performed while the substrate being plated is rotated and revolved. The method for manufacturing a substrate for a magnetic recording medium according to claim 9, wherein a self-revolving speed of the substrate is 10 to 100 rpm. 11. The method for manufacturing a substrate for a magnetic recording medium according to claim 6, wherein the temperature of the plating bath is set to 40 ° C. or more and 100 ° C. or less. A silicon wafer is selected as the substrate, and prior to the electroless plating step,
A step of forming a Ni or NiP underplating layer by immersing the silicon wafer in a plating bath containing Ni ions or a plating bath in which a phosphorus reducing agent is added to a bath containing Ni ions; The method for manufacturing a substrate for a magnetic recording medium according to claim 6, wherein: 13. The method for manufacturing a substrate for a magnetic recording medium according to claim 12, further comprising a substrate surface treatment step of removing an oxide film on the surface of the silicon wafer prior to the film formation step of the base plating layer. 14. The method according to claim 6, further comprising a polishing step for controlling the film thickness and surface flatness of the plating film after the soft magnetic underlayer is plated. Manufacturing method of substrate for magnetic recording medium.

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