JP2007287216A - 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 forming characteristics. <P>SOLUTION: An under plating layer 16 is formed by subjecting an Si substrate 11 to surface treatment to chemically activate the surface thereof and form an adequate ruggedness (R<SB>a</SB>:1 nm to 1 μm). The under plating layer 16 is made of metal or an alloy comprising one or more metal elements selected from the group consisting of Ni, Cu and Ag and has 1 to 500 nm thickness. A soft magnetic backing layer 12 is formed on the under plating layer 16 by an electroplating or electroless plating method. The soft magnetic backing layer 12 is a film having a composition containing 40 to 60 at% Co, 20 to 40 at% Ni and 10 to 40 at% Fe as a main component and 50 to 1,000 nm film thickness. By such film constitution, the soft magnetic backing film capable of suppressing spike noise without using steps for film-depositing an anti-ferromagnetic film and performing thermal treatment in a magnetic field can be formed by the plating method. <P>COPYRIGHT: (C)2008,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 with reduced spike noise caused by a soft magnetic film and a manufacturing method thereof.

In the technical field of information recording, hard disk devices, which are means for magnetically reading and writing information such as characters, images, and music, are electronic devices such as personal computers, portable music players, car navigation systems, and DVD video recorders. The primary external recording device and built-in recording means are essential. In recent years, there has been a remarkable improvement in the magnetic recording density of a hard disk built in a hard disk device as a magnetic recording medium, which has been improved at an annual rate of 100% or more, and the recording density is about 200 Gbit / inch ² at the research level. The level has reached about 100 Gbit / inch ² .

  Such a high recording density is achieved by improving the performance of individual technical elements such as electronic components and software constituting the hard disk device. In particular, a magnetic head (for reading / writing recorded information) ( Thin film heads, MR heads, GMR heads, and the like) and software for improving the reliability of read signals are largely due to significant progress. However, the basic recording method has not changed greatly, and a so-called “in-plane magnetic recording method (horizontal magnetic recording method)” in which magnetic information is horizontally written in the disk surface has been adopted.

  FIG. 1A is a schematic cross-sectional view for explaining a general laminated structure of a horizontal magnetic recording type hard disk, and a nonmagnetic Cr-based film formed on a nonmagnetic substrate 1 by sputtering. A base layer 2, a magnetic recording layer 3, and a carbon layer 4 as a protective film are sequentially laminated, and a liquid lubricant layer 5 formed by applying a liquid lubricant to the surface of the carbon layer 4 is formed. The thickness of each of these layers is at most about 20 nm, and all film formation is generally performed by a dry process such as a magnetron sputtering method (see, for example, Patent Document 1). The magnetic recording layer 3 is a uniaxial magnetic anisotropy Co alloy such as CoNiCr or CoCrPt. As shown in FIG. 1B, the crystal grains (3a to 3e) of the Co alloy are parallel to the disk surface. The information is recorded by being magnetized.

  In order to increase the density of magnetic recording, it is necessary to reduce the volume of magnetic grains per unit bit (1 bit) responsible for magnetic recording and increase the number of bits that can be recorded in the magnetic recording layer. On the other hand, according to the theoretical analysis on the magnetic material, it is known that when the volume of the magnetic grains that carry the magnetic recording is reduced, instabilities appear in the developed ferromagnetism for the following reasons. .

An index for determining the magnetization state of a ferromagnetic material while maintaining the magnetic moment of the magnetic material in a specific direction is anisotropy energy K _u V (K _u is an anisotropy constant. V is a magnetic recording unit (bit) volume), but this anisotropic energy K _u V competes with thermal energy kT (k is a Boltzmann constant and T is an absolute temperature). Yes. Therefore, when the volume V of the magnetic recording unit is reduced and the anisotropic energy K _u V and the thermal energy kT are approximately equal, the magnetization state of the ferromagnetic material becomes unstable even at room temperature. obtain. When the bit volume V falls below the critical dimension (critical volume) V _c determined by the material, the ferromagnetic material becomes a superparamagnetic state that behaves like a paramagnetic material and loses its function as a ferromagnetic material. .

Further, in an actual magnetic recording medium, when the bit volume V approaches the critical dimension V _c , the magnetic recording state (magnetization direction) is disturbed by heat energy in a relatively short time, and the magnetic recording information is lost or altered. The problem of “thermal fluctuation” is also caused. Although it is not clear how much the recording limit due to “thermal fluctuation” in conventional horizontal magnetic recording media in general is, it is estimated that the recording density of a hard disk is approximately 100 Gbit / inch ^2. ing.

  As described above, in the horizontal magnetic recording method, when the size of each magnetic crystal grain is reduced in order to increase the recording density, the N poles and S poles of adjacent crystal grains repel each other and magnetization cancels each other. Therefore, 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 energy and data is lost have been pointed out, and the limit to higher recording density has been recognized.

  In view of such problems, the “perpendicular magnetic recording method” has been studied. In this recording method, since the magnetic recording layer is magnetized perpendicularly to the disk surface, the N poles and the S poles are alternately bundled and arranged in bits, and the N and S poles of the magnetic domains are adjacent to each other. As a result of strengthening the magnetization, the self-demagnetizing field (demagnetizing field) in the bit is small, so that the stability of the magnetized state (magnetic recording) is increased. 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. Therefore, there is no need to reduce the thickness of the magnetic recording layer. 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.

In other words, since the perpendicular magnetic recording method can reduce the demagnetizing field and secure the K _u V value, the magnetic instability due to “thermal fluctuation” is reduced, and the limit of the recording density can be greatly increased. Because of this method, it is expected as a method for realizing ultra-high density recording.

  FIG. 2A shows a basic layer structure of a hard disk as a “perpendicular dual-layer magnetic recording medium” in which a recording layer for perpendicular magnetic recording is provided on a soft magnetic underlayer (SUL). In the schematic sectional view for explanation, a soft magnetic backing layer (SUL) 12, a magnetic recording layer 13, a protective layer 14, and a lubricating layer 15 are sequentially laminated on a nonmagnetic substrate 11. Here, the soft magnetic underlayer 12 is a layer that effectively acts to increase the write magnetic field and reduce the demagnetizing field of the magnetic recording layer 13, and typically uses permalloy or CoZrTa amorphous. As the magnetic recording layer 13, a CoCr alloy, a CoCrTaPt alloy, a multilayer film in which several PtCo layers and Pd and Co ultrathin films are alternately stacked, an SmCo amorphous film, or the like is used. As shown in B), the magnetic crystal grains (13a to 13f) are magnetized perpendicularly to the disk surface to record information.

  As shown in FIG. 2 (A), in a perpendicular magnetic recording type hard disk, a soft magnetic backing layer 12 is provided as a base of a magnetic recording layer 13, its magnetic property is “soft magnetic”, and the layer thickness is It is about 100 nm to 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 nonmagnetic Cr-based underlayer 2 provided in the horizontal magnetic recording type hard disk shown in FIG. Compared to the formation of the underlayer 2, it is not easy.

  As already described, 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.
JP-A-5-143972 JP 2005-108407 A JP-A-2005-240162 Japanese Patent Publication No. 1-42048 Japanese Examined Patent Publication No. 2-41089 Japanese Examined Patent Publication No. 2-59523 Japanese Patent Publication No. 1-445140 JP-A-57-105826 JP-A-6-68463 JP-A-6-28655 JP-A-4-259908 Japanese Examined Patent Publication No. 2-41089

  For these reasons, attempts are being made to form the soft magnetic backing layer 12 by a plating method that is easy to thicken and that can be polished.

  However, when the soft magnetic layer is formed by plating, a large number of magnetic domains having magnetism in a specific direction are generated over a range of several mm to several cm in the surface of the plating film constituting the soft magnetic layer. A domain wall is generated at the interface. When such a soft magnetic layer having a domain wall is used as a soft magnetic backing layer for a perpendicular double-layer magnetic recording medium, an isolated pulse noise called spike noise or micro spike noise is caused by a leakage magnetic field generated from the domain wall portion. May occur and signal reproduction characteristics may be greatly impaired.

  Among the noises generated from such a soft magnetic underlayer, the occurrence of spike noise, which is steep noise, is a serious problem. Since the soft magnetic backing film is required to have a soft magnetic property of high “magnetization” and low “coercive force”, in general, in the soft magnetic film, a plurality of magnetic domains are formed so as to reduce the magnetostatic energy in the in-plane direction. The phenomenon of being divided into occurs. At this time, although the magnetic moment falls in the plane within each magnetic domain, the magnetic moment gradually rotates from the in-plane to the direction perpendicular to the plane at the boundary between the magnetic domains and the reverse direction in the plane again. There is a region (Bloch domain wall) that can fall. The magnetic flux leaking from the Bloch domain wall portion in the direction perpendicular to the plane is detected by the read head and becomes spike noise.

  Therefore, in order to obtain a perpendicular double-layer type magnetic recording medium having excellent characteristics by a simple method, film formation conditions for forming a soft magnetic backing layer by a plating method, and soft magnetism suitable as a soft magnetic backing layer Research has been conducted on the types of films, which are made of an alloy composed of two or more metals selected from the group of Co, Ni, and Fe by an electroless plating method on a substrate on which a magnetic recording medium is formed, and are parallel to the layers. When a soft magnetic film having a magnetic anisotropy with a coercive force on the surface of less than 20 Oersted (Oe) and a ratio of saturation magnetization to residual magnetization in the range of 4: 1 to 4: 3 is used as the backing layer, It has been found that generation of a domain wall in the magnetic film is suppressed and effective in reducing noise (Patent Document 2).

  The plating film forming method disclosed in Patent Document 2 controls the plating film forming speed of the soft magnetic film, the ratio of the plating film forming speed of the soft magnetic film and the plating liquid speed on the surface of the plating substrate, and the plating liquid. Among them, the structure of the soft magnetic film is controlled by forming the film while revolving the substrate.

  However, the mechanism of why the soft magnetic film having the above magnetic anisotropy can be obtained by the condition setting described in Patent Document 2 is not necessarily clear. For this reason, it is not easy to control the degree of magnetic anisotropy of the soft magnetic film or obtain a predetermined magnetic anisotropy with high reproducibility by this film forming method.

  By the way, it has been conventionally known that when a soft magnetic film is formed and then heat-treated in a magnetic field, the magnetic anisotropy can be imparted to the soft magnetic film. Is in the direction of application of the magnetic field, so controllability is also high. For this reason, one method for imparting magnetic anisotropy to a GMR head or TMR head having a spin valve structure is to heat-treat a soft magnetic film in an environment where a magnetic field is generated in a certain direction. (See, for example, paragraph [0030] of Patent Document 3).

  The magnetic anisotropy of the soft magnetic film obtained by such a heat treatment in a magnetic field is limited to the direction in which the magnetic field is applied, but in order to obtain a film as a soft magnetic backing layer of a perpendicular two-layer magnetic recording medium, It is required to have magnetic anisotropy in the inner radial direction or circumferential direction, and that the magnetic anisotropy has symmetry with respect to the central axis of the substrate. For these reasons, there has been no report that a magnetically anisotropic soft magnetic film suitable for a soft magnetic underlayer of a perpendicular two-layer magnetic recording medium has been obtained by a conventional heat treatment in a magnetic field.

There is also known a method in which an antiferromagnetic film is provided in advance under a soft magnetic film and the medium is subjected to heat treatment in a magnetic field to suppress spike noise. In this method, the soft magnetic film is once heated above a temperature called a blocking temperature (T _B ) of the antiferromagnetic film, and then the medium is cooled to the blocking temperature or lower while applying a magnetic field in the radial direction of the medium. By this heat treatment in the magnetic field, the magnetic moment in the antiferromagnetic film is oriented and fixed in the magnetic field application direction, and the magnetic moment of the soft magnetic film is fixed in the magnetic field application direction by exchange coupling with the magnetic moment of the antiferromagnetic film surface. Is done. Then, by fixing this magnetic moment in the magnetic field application direction, the entire soft magnetic film becomes a single magnetic domain, and as a result, the domain wall disappears and spike noise is suppressed.

  Such a heat treatment in a magnetic field is effective in suppressing spike noise from the soft magnetic film, but requires a process of forming an antiferromagnetic film in advance. In view of manufacturing convenience, it is preferable not to require a special process of heat treatment in a magnetic field.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a soft magnetic backing film that can suppress spike noise without using an antiferromagnetic film formation process or a heat treatment in a magnetic field. An object of the present invention is to provide a substrate suitable for the manufacture of a perpendicular magnetic recording medium which is formed by a plating method and thereby has low noise and good signal generation characteristics.

  In order to solve such a problem, the present invention provides a magnetic recording medium substrate according to claim 1, which is a silicon (Si) substrate having a diameter of 90 mm or less and a main surface of the Si substrate. A base plating layer and a soft magnetic backing layer that are sequentially stacked on each other, and the base plating layer contains, as a main component, one or more metal elements selected from the group consisting of Ni, Cu, and Ag. The soft magnetic backing layer has a thickness of 1 nm to 500 nm, and the soft magnetic underlayer contains 40 to 60 atomic% Co, 20 to 40 atomic% Ni, and 10 to 40 atomic% Fe. It is an alloy formed by 1000 nm plating.

According to a second aspect of the present invention, in the magnetic recording medium substrate according to the first aspect, the soft magnetic underlayer has an absolute value of saturation magnetization (M _s ) of 1 T (Tesla) or more and a coercive force (H _c). the absolute value of) is equal to or less than 1.6 kA / m, the absolute value H _s of the magnetic field corresponding to the M _s, the absolute value M ₉₀ 90% of the magnetization of the M _s, the absolute magnetic field corresponding to the M ₉₀ The following formulas (1) and (2) hold between the value H ₉₀ and the absolute value M _r of magnetization when the magnetic field is 0 (zero) corresponding to H _c . Here, Formula (1) is M _r <M ₉₀ <M _s and H _c <H ₉₀ <H _s , and Formula (2) is M _r / M _s <0.75.

  According to a third aspect of the present invention, in the magnetic recording medium substrate according to the first or second aspect, the Si substrate has a diameter of 25 mm to 65 mm and a thickness of 0.1 mm to 1 mm. .

  The invention according to claim 4 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 3. It is characterized by.

  The invention according to claim 5 is a method for manufacturing a substrate for a magnetic recording medium, wherein a first plating step of forming a base plating layer on a main surface of a Si substrate having a diameter of 90 mm or less, and the base plating layer And a second plating step for forming a soft magnetic film, wherein the first plating step includes one or more metal ions selected from the group consisting of Ni, Cu, and Ag as a main component. The Si substrate is immersed in a bath, and the second plating step is performed by immersing the Si substrate in a pH 7-13 plating bath containing Co, Ni, and Fe metal ions as main components. It is characterized by being executed.

  According to a sixth aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to the fifth aspect, in the first plating step, the Si substrate is immersed in a plating bath containing nickel sulfate and ammonium sulfate. It is characterized by being executed.

  According to a seventh aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to the fifth or sixth aspect, the second plating step is at least selected from the group consisting of nickel sulfate, iron sulfate, and cobalt sulfate. The present invention is characterized by being performed by immersing the Si substrate in a plating bath containing one kind.

  According to an eighth aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to any one of the fifth to seventh aspects, an oxide film on the surface of the Si substrate is formed prior to the first plating step. It is characterized by having a surface treatment process to be removed.

  According to a ninth aspect of the present invention, in the method for manufacturing a magnetic recording medium substrate according to the eighth aspect, the surface treatment step is selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia. Etching treatment using an alkaline aqueous solution containing at least one kind of alkali or an acid aqueous solution containing at least one kind of acid selected from the group of hydrofluoric acid, hydrochloric acid, and nitric acid.

According to a tenth aspect of the present invention, in the method for manufacturing a substrate for a magnetic recording medium according to the eighth or ninth aspect, the surface treatment step is carried out on the surface of the Si substrate by a square average roughness (R _{a of} 1 nm to 1 μm). ) Is performed so as to form the unevenness.

  The invention according to claim 11 is the method for manufacturing a magnetic recording medium substrate according to any one of claims 5 to 10, wherein after the soft magnetic film is plated, the thickness of the soft magnetic film and A polishing step for controlling surface flatness is provided.

  According to the present invention, the composition and film thickness of the soft magnetic film formed by plating and the composition and film thickness of the underlying plating layer provided between the soft magnetic film and the Si substrate can be appropriately selected. Therefore, spike noise caused by the soft magnetic underlayer can be suppressed without using special processes such as antiferromagnetic film formation for noise suppression and heat treatment in a magnetic field. Thus, a substrate suitable for manufacturing a perpendicular magnetic recording medium having low noise and good signal generation characteristics is provided.

  Further, in the present invention, since the surface treatment conditions of the Si substrate applied prior to the formation of the base plating layer are optimized, the adhesion between the Si substrate and the base plating layer is improved, and as a result, the soft magnetic film The substrate adhesion is improved.

  Furthermore, the magnetic recording medium substrate of the present invention has a soft magnetic backing layer formed by a wet plating method, which greatly simplifies the manufacturing process compared to dry process film formation by vapor deposition or the like. It is also excellent in productivity.

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

  FIG. 3 is a schematic cross-sectional view for explaining the film configuration of the magnetic recording medium substrate of the present invention. The soft magnetic backing layer is formed by plating on a silicon (Si) substrate 11 which is a nonmagnetic substrate. 12, a magnetic recording layer 13 for perpendicular magnetic recording, a protective layer 14, and a lubricating layer 15 are sequentially stacked, and the Si substrate 11 and the soft magnetic backing layer are interposed between the Si substrate 11 and the soft magnetic backing layer 12. A base plating layer 16 is provided for improving the adhesion of the layer 12. This magnetic recording medium substrate is a perpendicular magnetic recording medium substrate. As shown in FIG. 2B, magnetic crystal grains are magnetized perpendicularly to the disk surface and information is recorded on the magnetic recording layer 13. The A substrate in which the base plating layer 16 and the soft magnetic backing layer 12 are sequentially laminated on the Si substrate 11, that is, a substrate in which the magnetic recording layer 13 is not yet formed is also treated as a “magnetic recording medium substrate”. obtain.

  The recording surface of a magnetic recording medium is required to have high adhesion because the impact of a magnetic head called “head slap” is frequently applied, but the soft magnetic backing layer formed by direct plating on the Si substrate is in close contact with the substrate. The film is easily peeled off during use as a magnetic recording medium, but the adhesion between the Si substrate 11 and the soft magnetic backing layer 12 depends on the combination of the underlying plating layer 16 and the soft magnetic backing layer 12 described later. Is increased to eliminate the problem of film peeling. Hereinafter, the configuration of each layer will be sequentially described.

  Silicon substrate 11: The non-magnetic substrate used for the magnetic recording medium substrate of the present invention is a Si substrate. The first reason for selecting Si as the substrate is that it has excellent rigidity, good surface smoothness, and extremely stable chemical state of the surface. The second reason is that the Si substrate can form a stable plating film regardless of whether the plating bath is acidic or alkaline, and the film formation uniformity when the base plating layer 16 is formed by plating. This is to ensure. In plating film formation, the interaction between the substrate interface and the plating ions is important in the film formation process. However, since the Si substrate is a material composed of a single element called Si, the adhesion of the plating ions to the substrate is improved. Are better.

  Examples of using a Si substrate as a substrate for a magnetic recording medium have already been reported in Patent Documents 4 to 11 and the like. In Patent Document 12, a base layer is previously formed on a single crystal Si substrate, and then the base layer is formed on the base layer. A magnetic recording medium produced by forming a magnetic recording layer has also been reported. However, these are all related to the horizontal magnetic recording technology, and by these technologies, it is not possible to obtain the effect of suppressing spike noise caused by the above-mentioned “thermal fluctuation” which is one of the objects of the present invention.

  The Si substrate does not necessarily need to be a single crystal substrate, but if a single crystal Si substrate is used, the atomic arrangement of the surface is uniform in the plane, and the surface chemical state and surface potential state in the plating process are also uniform in the plane. There is an advantage of becoming. In other words, when a single crystal Si substrate is used as the nonmagnetic substrate, direct displacement plating on the single crystal Si substrate can be performed when forming a base plating layer 16 described later, and the single crystal Si is extremely homogeneous. Due to the high quality crystallinity, there is an advantage that magnetic non-uniformity due to non-uniform plating can be suppressed.

  In the following description, the Si substrate 11 will be described as a single crystal Si substrate.

As the single crystal Si substrate, a crystal grown by the CZ (Czochralski) method or the FZ (floating zone) method can be easily obtained. The surface orientation of the Si substrate is not particularly limited, and may be any surface orientation such as (100), (110), or (111). Further, the impurity level contained in the Si substrate is not severely limited as it is used as a substrate for manufacturing a semiconductor element, and is about 10% (−10 ²² atoms / cm ³ ) of impurities (donor or It may contain an acceptor or light elements such as oxygen, carbon, and nitrogen).

  When forming a film on the Si substrate by the electrolytic plating method, in order to form a strong chemical bond between the plating film and the substrate, metal ions in the plating bath directly transfer and receive electrons from the surface of the Si substrate. There is a need. For this reason, when performing electrolytic plating film formation, it is preferable to use an n-type Si crystal that contains excess electrons inside the crystal rather than an Si substrate that is an intrinsic semiconductor. In the case of forming a film by electroless plating, there is no difference whether the conductivity type of the Si substrate is n-type, p-type, or intrinsic (i-type).

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

  Preferably, the Si substrate has a diameter of 65 mm or less and a substrate thickness of 1 mm or less. The reason why the substrate diameter is preferably 65 mm or less is that the amount of vibration during disk rotation can be suppressed even when the substrate thickness is reduced. That is, if the substrate diameter is large, the amount of vibration in the state of rotating as a hard disk tends to increase. However, if the diameter is set to 65 mm or less, this amount of vibration can be suppressed to a range that does not hinder practical use, and mobile Particularly advantageous effects can be obtained for the magnetic recording medium of the application. In general, the substrate diameter is generally 25 mm (1 inch) or more in practice.

  The reason why the thickness of the substrate is preferably 1 mm or less is that if the thickness exceeds this, the variation in the substrate thickness within the Si substrate surface tends to increase. In order to sufficiently secure the rigidity of the substrate, the substrate thickness is preferably 0.1 mm or more, and is generally selected in the range of 0.3 to 0.7 mm.

The surface of the Si substrate 11 preferably has a flatness with a square average roughness (R _a ) of 1 nm or more and 1 μm or less. When R _a is less than 1 nm, the adhesion of the underlying plating layer provided on the Si substrate may be insufficient. When R _a exceeds 1 μm, the surface smoothness required for the magnetic recording medium is obtained. It is because it cannot be done. Here, the square average roughness (R _a ) is a value obtained by averaging the absolute values of deviations from the measurement average line to the measurement line, and is a value measured by an AFM (atomic force microscope).

  Surface treatment of Si substrate: As described above, in 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 plating 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. In addition, the surface activation treatment causes moderate irregularities on the surface of the Si substrate, and the adhesion with the underlying plating layer 16 can be improved. The improvement in the adhesion strength of the base plating layer 16 means that the adhesion of the magnetic recording layer 12 formed on the base plating layer 16 is increased.

This surface activation treatment is performed by wet etching with acid or alkali. It is possible to use both acid and alkali wet etching. In this case, it is desirable to perform acid treatment after alkali treatment. By such surface activation treatment, Si atoms on the extreme surface of the Si substrate 11 are etched to chemically activate the substrate surface, and moderate irregularities are formed. As described above, the degree of the unevenness is preferably flatness with _a square average roughness (R _a ) of 1 nm or more and 1 μm or less.

  When this etching treatment is performed by acid treatment, at least one acid selected from hydrofluoric acid, hydrochloric acid, and nitric acid is selected and immersed in an aqueous solution prepared. In this case, the etching solution conditions are 2 to 10% by mass for hydrofluoric acid aqueous solution, 2 to 15% by mass for hydrochloric acid aqueous solution, and 5 to 30% by mass for nitric acid aqueous solution. Is preferred.

  Moreover, when performing an etching process by an alkali treatment, it immerses in the aqueous solution which selected and prepared at least 1 or more types of alkali from NaOH, KOH, and ammonia. Preferable etching solution conditions include an aqueous solution in which 0.3 to 10% by mass of ammonia and 0.5 to 25% by mass of hydrogen peroxide are mixed in a mass ratio of 2: 1 to 1: 2, or 2 to 50%. % Aqueous sodium hydroxide solution is exemplified.

The etching solution temperature and the etching time are, for example, 10 ° C. to a boiling point temperature of the solution of 30 seconds to 1 hour. In the case of acid treatment, electroetching may be performed by applying current for 1 second to 1 minute at a current density of 1 to ²⁰ mA / cm ² .

  Underlying plating layer 16: The underlying plating layer 16 is for improving the adhesion between the Si substrate and the soft magnetic backing layer, and the surface of the Si substrate 11 subjected to the surface activation treatment is plated. It is formed as a film. The underlying plating layer can be formed by either electrolytic plating or electroless plating. However, in the electroless plating, the interaction between the plating ions and the Si substrate 11 is caused by the electrical surface on the Si substrate 11. There is an advantage that it is not easily influenced by characteristics (state).

  The composition of the preferred undercoat layer is Ni, Cu, or an alloy thereof (Ni-Cu), for example, 0.02 to 1 mol / L in 0.005 to 0.25 mol / L (liter) of nickel sulfate. Ammonium sulfate is added to adjust the pH of the plating bath to 7 to 10, and the base plating layer 16 is formed by immersing in a plating bath having a bath temperature of 60 to 90 ° C. A metal or alloy composed of one or more metal elements selected from the group of Ni, Cu, and Ag is also suitable for the base plating layer.

  The thickness of these base plating layers is preferably 1 nm or more and 500 nm or less. This may occur when the Si substrate surface cannot be uniformly coated with a layer thickness of less than 1 nm, and when it is thicker than 500 nm, the individual crystal grains of the plating film of the underlying plating layer are enlarged during the plating process. This is because it may be too much.

Soft magnetic backing layer 12: The soft magnetic backing layer 12 is formed by electrolytic plating or electroless plating, and as its soft magnetic properties, it has a high saturation magnetization (M _s ) of 1T (Tesla) or higher and 1.6 kA. It is a film having a low coercive force (H _c ) with an absolute value of / m or less. The absolute value of the saturation magnetization (M _s ) is set to 1 T or more because the saturation magnetization ( _Ms ) required for the soft magnetic underlayer is not required to be a thick film that causes enlargement of the magnetic crystal grains of the soft magnetic underlayer. _s ) to ensure. Also, the absolute value of the coercive force (H _c ) is set to 1.6 kA / m or less. When the film has a coercive force exceeding this value, the magnetic flux generated from the magnetic head during writing to the magnetic recording medium is soft magnetic. This is because the S / N ratio as a recording medium is greatly reduced due to an impediment when passing through the backing layer. The absolute value of the coercive force (H _c ) is preferably 0.4 kA / m (400 A / m) or less.

  Further, the soft magnetic backing layer 12 has a fine stripe magnetic domain (FIG. 4 (A)) having a width of 2 μm or less in the in-plane direction as schematically shown in FIGS. 4 (A) and 4 (B). It is preferable to have at least one magnetic domain of a stray magnetic domain (FIG. 4B). As a result of the absence of a macroscopic magnetic domain structure in the film having such a magnetic domain structure, an antiferromagnetic film is formed in advance, or without performing a special process such as performing a heat treatment in a magnetic field after film formation. Spike noise is suppressed.

Further, a film showing an isotropic magnetization-magnetic field loop as described below is preferable. That is, the absolute value of the saturation magnetization of the soft magnetic underlayer is M _s , the absolute value of the magnetic field at that time is H _s , the absolute value of the magnetization of 90% of the absolute value of the saturation magnetization M _s is M ₉₀ , when H ₉₀ the absolute value of the magnetic field, the absolute value M _r of the magnetization when the magnetic field is 0 (zero), the absolute value of the magnetic field at that time (which corresponds to the coercive force) was H _c, A film exhibiting an isotropic magnetization-magnetic field loop satisfying the following expressions (1) and (2) is preferable.

Equation _{(1) M r <M 90} <M s and H _c <H ₉₀ <H _s

Formula (2) _Mr / _Ms <0.75

Since the plated film must have the above-mentioned soft magnetic characteristics and its crystal structure needs to be cubic, Co is 40 to 60 atomic%, Ni is 20 to 40 atomic%, and Fe is 10 to 40 atoms as main components. % Containing composition. When a soft magnetic film having such a composition is formed by plating, which will be described later, a film having a high saturation magnetization (M _s ) of 1 T (tesla) or more and a low coercive force (H _c ) of 1.6 kA / m or less. A soft magnetic underlayer showing a magnetization-magnetic field loop satisfying the above formulas (1) and (2) and having fine stripe-like magnetic domains and / or stray-like magnetic domains with a width of 2 μm or less in the in-plane direction Can be obtained.

The plating film forming conditions for obtaining such a soft magnetic film are, for example, as follows. That is, 0.001 to 0.1 mol / L (liter) dimethylamine borane (DMAB: (CH ₃ ) ₂ HNBH ₃ ) aqueous solution, 0.001 to 0.1 mol / L nickel sulfate aqueous solution, 0.001 to 0 A 1 mol / L iron sulfate aqueous solution, 0.01 to 0.5 mol / L cobalt sulfate aqueous solution, etc. are mixed, and a brightener such as saccharin and tartaric acid, citric acid, or EDTA (Ethylene Diamine) A chelating agent such as Tetraacetic Acid) is appropriately added to form a plating bath. Then, while adjusting the bath temperature to 55 to 90 ° C. and adjusting the pH to 7 to 13 with alkali, the substrate is immersed in this plating bath to form a soft magnetic film on the underlying plating layer. Examples of the alkali in this case include sodium hydroxide and potassium hydroxide.

  In this plating film forming step, 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, in the present invention, the diameter of the Si substrate 11 is set to 90 mm or less so as to form a uniform plating solution flow on the substrate surface. Also, in order to form a uniform plating solution flow, the solution circulation during plating film formation is adjusted, the plating solution is stirred using a stirrer such as a paddle, or the substrate to be plated is rotated and revolved. It is also effective to adjust the liquid flow in the plating bath. Such liquid circulation and stirring are also effective during the formation of the above-described base plating layer.

  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, it is preferable to adjust the liquid flow in the plating bath by appropriately combining the 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, a suitable rotation speed is 10 rpm to 100 rpm, and more preferably 20 rpm to 80 rpm.

  The thickness of the film formed by plating is 50 nm to 1000 nm. The upper limit of the thickness is set to 1000 nm because when the thickness of the soft magnetic film to be plated exceeds 1000 nm (1 μm), the individual magnetic crystal grains grow too much and the size of the magnetic crystal grains is not large. When the thickness of the soft magnetic backing layer is larger than 1 μm in addition to the uniformity, the magnetic noise generated from the soft magnetic backing layer increases when the hard disk signal is reproduced, resulting in a recording medium. This is because the S / N characteristic is likely to be deteriorated. The lower limit of the thickness is 50 nm because, if the thickness is less than 50 nm, the magnetic transmission characteristics as the underlayer of the magnetic recording layer are insufficient and the overwrite characteristics as the recording medium are deteriorated.

  The surface of the soft magnetic film formed on the Si substrate by a wet process (plating method) is generally not excellent in flatness although it depends on the thickness of the soft magnetic film. For this reason, the surface flatness (unevenness level) of the soft magnetic film after plating film formation is adjusted by performing a polishing process. This polishing can be performed by mechanical polishing or CMP, but CMP using a colloidal slurry is suitable as a method for polishing a magnetic recording medium. In CMP, polishing proceeds by mechanical polishing using a polishing slurry and chemical polishing using an acidic or alkaline polishing solution, and CMP is performed using a colloidal abrasive such as colloidal alumina or colloidal silica as the polishing slurry. This is because a high polishing rate and high surface flatness can be obtained.

  As the polishing slurry type and pH value, an appropriate one is selected according to the metal / alloy composition of the soft magnetic underlayer. For example, when the soft magnetic underlayer is a CoNiFe film, an alkaline polishing slurry having a pH of 10 or more is desirable. When the soft magnetic backing layer is a permalloy film, a polishing slurry having an acidic pH value is desirable from the viewpoint of chemical etching action.

  As polishing conditions (parameters) affecting the surface flatness of the soft magnetic backing layer, there are polishing apparatus characteristics, buffing, self-rotational speed during polishing, etc. in addition to the polishing slurry used. It is optimized so that the surface flatness of the soft magnetic backing layer can be sufficiently secured.

Here, the surface flatness after polishing of the soft magnetic underlayer is preferably 5 nm or less in terms of _Ra value, and particularly preferably the _Ra value is 0.5 nm or less. This is because surface irregularities exceeding 5 nm in _Ra value result in deterioration of the surface flatness of the magnetic recording layer formed on the soft magnetic underlayer. On the other hand, when it is attempted to make the _Ra value smaller than 0.1 nm, it is necessary to perform the CMP process in multiple stages, and the polishing conditions become extremely severe. Therefore, the _Ra value is preferably 0.1 to 5 nm, more preferably _Ra value is set to 0.1 to 0.5 nm.

  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 such a 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 1: In this example, a (100) Si single crystal plate having a diameter of 65 mm is obtained by performing core removal, centering, and lapping from a 200 mm (8 inch) diameter Si single crystal grown by the CZ method. (P-doped n-type) was obtained. This Si single crystal plate was polished on both sides using a slurry containing colloidal silica having an average particle diameter of 50 nm to obtain a Si substrate having _a surface roughness (R _a ) of 0.8 nm. The surface roughness (R _a ) was measured using an AFM (atomic force microscope).

  This Si substrate was etched by immersion for 5 minutes in an aqueous solution in which a saturated hydrogen peroxide solution was mixed with an aqueous ammonia solution at 80 ° C. and 30% by mass and each concentration was 2% by mass, and a thin surface oxide film on the substrate surface Was removed.

  The substrate after this surface activation treatment was electrolessly electrolyzed in a plating bath at a pH of 8 and a liquid temperature of 80 ° C. by appropriately adding ammonium sulfate to a 0.05 mol / L nickel sulfate aqueous solution and a 0.05 mol / L sodium tartrate aqueous solution. Plating was performed to form a Ni underplating layer of 300 nm on the surface of the Si substrate. Then, a CoNiFe soft magnetic film having a thickness of about 0.9 to 1 μm was formed as a soft magnetic backing layer on the underlying plating layer. The plating bath at this time was an ammonium sulfate bath containing Co, Ni, and Fe as main ions, DMAB (dimethylamine borane) was used as the reducing agent, and the bath temperature was adjusted to 80 ° C. Further, while adjusting with sodium hydroxide, the pH of the plating bath was adjusted to 9 during film formation.

The substrate after plating the soft magnetic film is polished with a polishing liquid containing colloidal silica having an average particle diameter of 50 nm (pH value 11, liquid temperature 30 ° C.) to adjust the thickness of the soft magnetic film and flatten the surface. Turned into. For this polishing, a double-side polishing machine having a surface plate (diameter: 700 mm) with a nonwoven fabric was used, and polishing was performed at a polishing pressure of 17.6 kPa for 6 minutes to make the thickness of the soft magnetic film approximately 400 nm. When the surface of the soft magnetic film after polishing was measured by AFM, the surface roughness (R _a ) was 0.6 nm, and the front surface was uniformly flattened.

  As a result of elemental element analysis of the soft magnetic film using a fluorescent X-ray apparatus, the composition ratio was approximately 50 atomic% Co, 28 atomic% Ni, and 22 atomic% Fe. Further, when the magnetic properties were measured with a VSM (sample vibration type magnetometer), the magnetization-magnetic field loop shown in FIG.

When the saturation magnetization M _s and the coercive force H _c were determined from the magnetization-magnetic loop of FIG. 5, the saturation magnetization M _s was 1.48 T, and the coercive force H _c was 970 A / m. Further, when M ₉₀ and M _r and H ₉₀ and H _s are obtained, M ₉₀ is 1.33 T, M _r is 0.77 T, H ₉₀ is 2.9 kA / m, and H _s is 9.7 kA / m. And it was confirmed that the relationship of the above-mentioned formulas (1) and (2) was satisfied. Furthermore, when the magnetic domain structure on the surface was observed by a bitter method using magnetic fluid, a magnetic domain structure with a stray pattern with a width of about 1 μm was observed as shown in FIG. 6, and the magnetic image was observed on the surface using the Kerr effect. When observed with the apparatus, an image in which a clear domain wall could not be confirmed as shown in FIG. 7 was obtained.

  In order to confirm the presence or absence of spike noise caused by the soft magnetic underlayer, the surface of the soft magnetic underlayer is coated with a 20 nm carbon protective film by magnetron sputtering, and then a lubricant is applied to the electromagnetic conversion characteristics using a spin stand. As a result of measurement, no spike noise was observed.

  Example 2 In this example, the composition ratio of the soft magnetic film is substantially the same as in Example 1 except that the plating film is formed so that Co is 53 atomic%, Ni is 36 atomic%, and Fe is 11 atomic%. A sample was prepared in the same manner as above.

When the magnetic characteristics were evaluated by VSM, it was confirmed that the magnetic characteristics were in-plane isotropic. From the magnetization-magnetic field loop, the saturation magnetization M _s was 1.35 T, and the coercive force H _c was 2.2 kA. A value of / m was obtained. Further, when M ₉₀ and M _r and H ₉₀ and H _s are obtained, M ₉₀ is 1.22 T, M _r is 0.65 T, H ₉₀ is 9.9 kA / m, and H _s is 16.6 kA / m. And it was confirmed that the relationship of the above-mentioned formulas (1) and (2) was satisfied. Furthermore, when the magnetic domain structure on the surface was observed by the bitter method using magnetic fluid, a magnetic domain structure with a stray pattern with a width of about 1 μm was observed, and the surface was observed with a magnetic image observation apparatus using the Kerr effect. As a result, an image in which a clear domain wall could not be confirmed was obtained.

  In order to confirm the presence or absence of spike noise caused by the soft magnetic underlayer, the surface of the soft magnetic underlayer is coated with a 20 nm carbon protective film by magnetron sputtering, and then a lubricant is applied to the electromagnetic conversion characteristics using a spin stand. As a result of measurement, no spike noise was observed.

  Comparative Example: In this comparative example, a sample was prepared in the same manner as in Examples 1 and 2, except that a CoZrNb soft magnetic film was formed by magnetron sputtering.

  When the surface of this sample was observed with a magnetic image observation apparatus using the Kerr effect, a large number of domain walls were observed. In addition, in order to confirm the presence or absence of spike noise caused by the soft magnetic underlayer, the surface of the soft magnetic underlayer is coated with a 20 nm carbon protective film by magnetron sputtering, and then a lubricant is applied and electromagnetic conversion is performed by a spin stand. When the characteristics were measured, the occurrence of spike noise was observed.

  In the present invention, a soft magnetic backing film capable of suppressing spike noise is formed by a plating method without using an antiferromagnetic film formation process or a heat treatment in a magnetic field, thereby achieving good signal generation characteristics with low noise. A substrate suitable for manufacturing a perpendicular magnetic recording medium is provided.

1 is a schematic cross-sectional view for explaining a general laminated structure of a horizontal magnetic recording type hard disk. FIG. 3 is a schematic cross-sectional view for explaining the layer structure of a perpendicular magnetic recording medium in which a recording layer for perpendicular magnetic recording is provided on a soft magnetic underlayer. FIG. 3 is a schematic cross-sectional view for explaining the layer structure of the perpendicular two-layer magnetic recording medium of the present invention using a Si substrate as a nonmagnetic substrate and provided with a base plating layer. It is a figure which illustrates typically the mode of a fine striped magnetic domain (A) and a stray magnetic domain (B) formed in a preferable soft magnetic backing layer. It is a figure which shows the magnetization-magnetic field loop obtained by the sample vibration type magnetometer. It is an image which shows the magnetic domain structure of a stray pattern pattern obtained by observing the surface by the bitter method using a magnetic fluid. It is an image obtained by observing the surface with a magnetic image observation apparatus using the Kerr effect.

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 Lubricating layer 10 The board | substrate with which the soft-magnetic backing layer was formed 12 Soft-magnetic backing layer 16 Undercoat layer

Claims (11)

A silicon (Si) substrate having a diameter of 90 mm or less, and a base plating layer and a soft magnetic backing layer that are sequentially laminated on the main surface of the Si substrate;
The base plating layer is a metal or an alloy having a film thickness of 1 nm or more and 500 nm or less that contains one or more metal elements selected from the group of Ni, Cu, and Ag as a main component,
The soft magnetic underlayer is a plated alloy having a thickness of 50 nm to 1000 nm containing Co of 40 to 60 atomic%, Ni of 20 to 40 atomic%, and Fe of 10 to 40 atomic%. A magnetic recording medium substrate. The soft magnetic underlayer has an absolute value of saturation magnetization (M _s ) of 1 T (tesla) or more and an absolute value of coercive force (H _c ) of 1.6 kA / m or less,
Absolute value H _s of the magnetic field corresponding to the M _s, the M absolute values M ₉₀ of 90% of the magnetization _s, an absolute value H ₉₀ of the magnetic field corresponding to the M _90, the magnetic field corresponding to the H _c 0 (zero 2. The magnetic recording medium substrate according to claim 1, wherein the following expressions (1) and (2) hold between the absolute value of magnetization M _r at the time of
Equation _{(1) M r <M 90} <M s and H _c <H ₉₀ <H _s
Formula (2) _Mr / _Ms <0.75 The magnetic recording medium substrate according to claim 1, wherein the Si substrate has a diameter of 25 mm to 65 mm and a thickness of 0.1 mm to 1 mm. 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 any one of claims 1 to 3. A first plating step of forming a base plating layer on a main surface of a Si substrate having a diameter of 90 mm or less, and a second plating step of forming a soft magnetic film on the base plating layer,
The first plating step is performed by immersing the Si substrate in a plating bath containing as a main component one or more metal ions selected from the group of Ni, Cu, and Ag.
The second plating step is performed by immersing the Si substrate in a plating bath having a pH of 7 to 13 containing metal ions of Co, Ni, and Fe as main components. A method for manufacturing a substrate. 6. The method for manufacturing a magnetic recording medium substrate according to claim 5, wherein the first plating step is performed by immersing the Si substrate in a plating bath containing nickel sulfate and ammonium sulfate. 6. The second plating step is performed by immersing the Si substrate in a plating bath containing at least one selected from the group consisting of nickel sulfate, iron sulfate, and cobalt sulfate. Or a method for producing a magnetic recording medium substrate according to 6. 8. The magnetic recording medium substrate according to claim 5, further comprising a surface treatment step of removing an oxide film on the surface of the Si substrate prior to the first plating step. Manufacturing method. The surface treatment step is selected from an aqueous alkali solution containing at least one alkali selected from the group of sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia, or a group of hydrofluoric acid, hydrochloric acid, and nitric acid. The method for producing a substrate for a magnetic recording medium according to claim 8, wherein the etching process is performed using an acid aqueous solution containing at least one kind of acid. 10. The magnetic recording medium according to claim 8, wherein the surface treatment step is performed so as to form irregularities having _a square average roughness (R _a ) of 1 nm or more and 1 μm or less on the surface of the Si substrate. Manufacturing method for industrial use. 11. The method according to claim 5, further comprising a polishing step for controlling the film thickness and surface flatness of the soft magnetic film after plating the soft magnetic film. A method for manufacturing a substrate for a magnetic recording medium.