JP2005216465A - Disk substrate for recording medium, its polishing method, and manufacturing method of perpendicular magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for a recording medium which can be polished at low costs without corroding a Ni-low P based soft magnetic film formed on the substrate and having a low phosphorus concentration. <P>SOLUTION: A slurry for finishing polish is specified to be a slurry formed by mixing colloidal silica having 70 to 140 nm particle diameter and pure water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a recording medium disk substrate having a soft magnetic film, a polishing method thereof, and a method of manufacturing a perpendicular magnetic recording medium using the polishing method.

  As a technique for realizing a high density magnetic recording medium, a perpendicular magnetic recording system is drawing attention instead of the conventional longitudinal magnetic recording system. In the perpendicular magnetic recording system, for example, as shown in Patent Document 1, a low coercive force material layer (Mo) is formed between a magnetic recording layer made of a Co—Cr alloy film and a base surface which is a polyimide substrate. A two-layer structure in which -Fe-Ni) (hereinafter also referred to as a soft magnetic film) is formed has been proposed.

  In particular, a double-layer perpendicular magnetic recording medium with a soft magnetic film called a soft magnetic backing layer that easily passes the magnetic flux generated from the magnetic head under the magnetic recording layer that plays a role in recording information is generated in the magnetic head. It is known that it is suitable as a perpendicular magnetic recording medium capable of high-density recording because it increases the magnetic field strength and the magnetic field gradient to improve the recording resolution and increase the leakage magnetic flux from the medium.

  In a series of manufacturing steps of such a two-layer perpendicular magnetic recording medium, the surface was polished using a substrate in which a nonmagnetic NiP layer was formed on an aluminum alloy substrate by an electroless plating method or a glass substrate. A magnetic recording medium is obtained by forming a soft magnetic film later and further forming a magnetic recording layer, a protective layer, and the like on the soft magnetic film.

  As the soft magnetic underlayer, NiFe alloy or amorphous alloy mainly composed of cobalt (Co) is generally used. When these materials are used, a film thickness of 0.1 μm to several μm is required from the viewpoint of recording / reproducing characteristics. A soft magnetic layer having such a relatively thick film thickness is very difficult to mass-produce at a low cost by the sputtering method used in the production of conventional magnetic recording media. Enabling mass production at a cost is an issue.

So far, as shown in Patent Document 2, production by electroless plating on a soft magnetic material film made of a Ni—Fe—P alloy has been proposed for this problem.
However, since the soft magnetic underlayer using the Ni-Fe-P layer is composed of three elements, it is very difficult to manage the composition of the plating solution in the electroless plating method. It may be difficult to maintain and control. This is because ferrous sulfate in the components of the plating solution oxidizes and gradually changes to ferric sulfate when it comes into contact with the atmosphere, making it difficult to manage the composition of the plating solution.

On the other hand, as disclosed in Patent Document 3, it has been proposed to form a soft magnetic film of a Ni-P alloy on an aluminum substrate by electroless plating.
In addition, as shown in Patent Document 4, in a series of manufacturing steps of a magnetic recording medium, in the surface polishing step of the glass substrate for magnetic recording medium, colloidal silica having an average particle size of 0.1 μm and a pure liquid are used as a polishing liquid. It has also been proposed to use a mixture with water.

Japanese Patent Publication No.58-91 JP 7-66034 A Japanese Patent Publication No. 3-23972 JP 2003-6843 A

  As shown in the specification of Japanese Patent Application No. 2003-027486 filed earlier by the present applicant, as a result of studying a plating film (soft magnetic film) that can be more stably produced in large quantities by electroless plating, Ni Since one low-P film consists of two elements, when producing by electroless plating, the plating solution is more stable and easier to manage than the three-element plating solution, and the quality is also stable. Obtained. In particular, a Ni-P film (hereinafter also referred to as Ni-low P film) with a P concentration of 6 wt% or less is promising.

Further, as shown in the specification of Japanese Patent Application No. 2003-049878 filed earlier by the present applicant, the polishing process for such a Ni-low P film is performed by a rough polishing process using an alumina slurry and colloidal silica. It consists of two steps, the final polishing step.
A non-magnetic film of a general Ni-P alloy with a P concentration of 12% or more has high corrosion resistance in an acid solution. In the polishing process of a non-magnetic film with a P concentration of 12% or more, this acidic polishing slurry is used as a polishing liquid. Can be used.

  However, an acidic etching agent having an etching action is added to these abrasives in order to achieve both productivity and surface quality. A substrate with Ni-low P plating with a P concentration of 6% or less has low acid resistance and the surface is eluted non-uniformly, so mirror polishing is not possible. Further, when the corrosion on the surface is severe, there is a problem that nickel phosphate (Ni) is reprecipitated to form a black film.

  On the other hand, in the specification of the above-mentioned Japanese Patent Application No. 2003-049878, a method of polishing using an alkaline abrasive having a pH of 8 or more has been proposed, whereby a Ni-low P film applied on a substrate is formed. It is described that it can be polished well. At that time, the alkaline abrasive used for the final polishing is a mixture of a polishing accelerator prepared by mixing various chemicals such as organic acid, inorganic acid, pH adjusting liquid (KOH, etc.) and colloidal silica. It is said.

However, in this method, since several kinds of chemicals are mixed in order to produce a polishing accelerator, the price of the polishing agent becomes high, and the preparation amount is difficult to manage.
In view of the above problems, the present invention is a method for polishing a disk substrate for a recording medium, without corroding a low phosphorous Ni-based P soft magnetic film formed on the substrate, and An object of the present invention is to provide a disk substrate for a recording medium that can be polished inexpensively, a polishing method thereof, and a method of manufacturing a perpendicular magnetic recording medium using the polishing method.

  In order to achieve the above object, a method for polishing a disk substrate for a recording medium according to the present invention includes a soft substrate for a substrate having a soft magnetic underlayer made of a Ni-P alloy containing 1 wt% or more and 6 wt% or less of phosphorus. A first polishing step for roughly polishing the surface of the magnetic underlayer, and a surface of the soft magnetic underlayer polished by the first polishing step, comprising pure water and colloidal silica having a particle diameter of 70 nm to 140 nm. And a second polishing step for polishing with the mixed polishing liquid.

  The method for manufacturing a perpendicular magnetic recording medium according to the present invention includes a step of forming at least a magnetic recording layer on a substrate polished by the polishing method of the present invention.

  As is clear from the above description, according to the recording medium disk substrate polishing method and the perpendicular magnetic recording medium manufacturing method according to the present invention, the soft magnetic underlayer roughly polished by the first polishing step is used. Since the surface includes a second polishing step of polishing the surface with a polishing liquid in which pure water and colloidal silica having a particle diameter of 70 nm to 140 nm are mixed, Ni having a low phosphorus concentration formed on a substrate The soft magnetic film can be polished without being corroded and at a low cost.

  FIG. 2 shows a series of steps in the manufacture of a disk-shaped magnetic recording medium to which an example of a method for polishing a recording medium disk substrate according to the present invention is applied.

  The disk-shaped magnetic recording medium 10 obtained by the series of steps shown in FIG. 2 is, for example, a 3.5-inch perpendicular magnetic recording medium, and an initial reaction layer is formed on the surface of the substrate 12 as shown in FIG. 14, a nonmagnetic underlayer 24, a soft magnetic underlayer 16, a nonmagnetic seed layer 18, a magnetic recording layer 20, and a protective layer 22 are sequentially stacked. FIG. 7 schematically shows a part of a cross section in the radial direction of the disk-shaped magnetic recording medium 10.

  The base 12 is made of a nonmagnetic material, for example, an aluminum magnesium alloy (Al-5Mg (at%)). The material of the base 12 may be aluminum alloy, tempered glass, crystallized glass, or the like. Furthermore, as a material of the base body 12, for example, a substrate manufactured by injection molding of polycarbonate, polyolefin, and other plastic resins may be used.

The initial reaction layer 14 formed on the surface of the substrate 12 is, for example, a zinc (Zn) film having a predetermined film thickness (0.1 to 0.8 μm).
In addition, when an aluminum alloy is used as the material of the substrate 12, the initial reaction layer is generally a Zn film layer formed by immersing in a zincate solution (a solution containing a zinc oxide and a sodium hydroxide aqueous solution). In that case, the film thickness of the Zn layer is preferably 0.1 to 0.8 / μm, but a film thickness outside this range is also possible.

  Further, when tempered glass, crystallized glass, plastic, or the like is used as the material of the substrate 12, in forming the initial reaction layer, 20 to 40 g / 1 hydrochloric acid acidic tin chloride solution and 0.1 to 0.5 g are used. In general, activation treatment is performed by sequentially immersing in an acidic palladium chloride solution of 1/1 to precipitate Pd nuclei on the surface. It is also possible to form a thin film such as Ni, Ni-P, Cu, Cr, Fe, or Pd as an initial reaction layer by using a physical vapor deposition method such as a sputtering method or an ion plating method. is there.

  As shown in FIG. 6, the nonmagnetic underlayer 24 is, for example, a nickel-rich phosphorus-based (hereinafter also referred to as Ni-high-P) alloy plating layer having a predetermined film thickness. The plating layer is laminated by, for example, an electroless plating method. The P concentration of the plating layer of the Ni-high P alloy is desirably, for example, 10 wt% or more and 13 wt% or less, and is preferably 12.5%, for example.

The electroless plating solution for forming the nonmagnetic underlayer 24 laminated on the initial reaction layer 14 by the electroless plating method has a phosphorus concentration of 12.5%. For example, Ni ions, complexing agents, and reduction Contains agents. The Ni ion, or the like can be used NiSO _4, NiC1 _2. As the complexing agent, general citric acid, tartrate, and the like can be used. As the reducing agent, sodium hypophosphite is generally used, and hydrazine, formaldehyde, or sodium borohydride may be used in combination.

  And the nonmagnetic underlayer 24 is laminated | stacked on the initial stage reaction layer 14 by the disk board | substrate with which the initial stage reaction layer 14 was formed being immersed in the plating solution containing them adjusted to 80-95 degreeC.

  The plated layer of the Ni-P alloy is preferably laminated by an electroless plating method from the viewpoint of inexpensive mass production. However, the present invention is not limited to this, and the sputtering method or the ion plate may be used depending on the required characteristics. Other general film forming methods such as a physical vapor deposition method such as a coating method may be used.

  For example, the soft magnetic underlayer 16 formed on the nonmagnetic underlayer 24 by an electroless plating method is a nickel-low concentration phosphorus-based (hereinafter also referred to as Ni-low P-based) alloy having a predetermined film thickness. It is made of a plating layer. The plating layer has a phosphorus concentration of 4.5%, for example.

  In order to satisfactorily realize the soft magnetic properties in the plated layer of the Ni-low P alloy, the P concentration in the alloy of the plated layer is desirably 1 wt% or more and 6 wt% or less. When phosphorus (P) is less than 1 wt%, it is difficult to form a stable electroless plating film, and when phosphorus (P) exceeds 6 wt%, the saturation magnetic flux density [B s] of the plating layer This is because the thickness of the double-layered perpendicular magnetic recording medium does not function as a soft magnetic backing layer. Accordingly, the P concentration in the alloy of the plating layer is preferably 1 wt% or more and 6 wt% or less.

Further, it is desirable that the thickness of the plated layer of Ni-low P alloy is 0.5 μm or more.
The thickness of the Ni-low P alloy plating layer needs to be 0.5 μm or more in order to function as a soft magnetic backing layer on the surface of the perpendicular magnetic recording medium.

  Although the upper limit of the film thickness of the nonmagnetic underlayer 24 and the soft magnetic underlayer 16 is not particularly defined, it is preferably 9 μm or less from the viewpoint of reducing the manufacturing cost. Furthermore, the sum of the film thicknesses of the nonmagnetic underlayer 24 and the soft magnetic underlayer 16 is required to be 3 μm or more in order to ensure the hardness of the substrate surface.

  According to the verification of the inventors of the present application, when the saturation magnetic flux density [B s] of the plated layer of Ni-low P alloy is measured with a VSM (vibrating sample magnetometer), the P concentration is 2% and the film thickness is 1 μm. It has been confirmed that soft magnetic properties of about 4T can be obtained, and soft magnetic properties of about 0.15T can be obtained at a P concentration of 6% and a film thickness of 1 μm.

The electroless plating solution for forming the soft magnetic underlayer 16 laminated on the nonmagnetic underlayer 24 by the electroless plating method has a phosphorus concentration of 3.7%. For example, Ni ions, complexing agents, and Contains a reducing agent. The Ni ion, or the like can be used NiSO _4, NiC1 _2. As the complexing agent, general citric acid, tartrate, and the like can be used. As the reducing agent, sodium hypophosphite is generally used, and hydrazine, formaldehyde, or sodium borohydride may be used in combination.

And the soft magnetic underlayer 16 is laminated | stacked on the nonmagnetic underlayer 24 by immersing the disk substrate in which the nonmagnetic underlayer 24 was formed in the plating solution containing them adjusted to 80-95 degreeC. The Note that when the soft magnetic underlayer 16 is formed, only the film thickness and the phosphorous concentration of the plating bath are different from the above-described case of forming the nonmagnetic underlayer 24.
The nonmagnetic seed layer 18 is a material for preferably controlling the crystal orientation and crystal grain size of the magnetic recording layer 20 described later, for example, a magnetic recording layer 20 in which a Co-based alloy or the like and Pt or Pd or the like are laminated. In the case of a magnetic film, it is made of Pt, Pd, or the like. As a material for forming the nonmagnetic seed layer 18, a CoCr alloy, Ti, Ti alloy, Ru, or the like may be used. The film thickness of the nonmagnetic seed layer 18 is preferably 1 to 500 nm, for example.

  As a material of the magnetic recording layer 20 formed on the nonmagnetic seed layer 18, any material capable of performing recording / reproduction as a perpendicular magnetic recording medium, for example, a Co-based alloy, Pt or Pd as described above is used. Can also be used.

The protective layer 22 formed on the magnetic recording layer 20 is, for example, a thin film mainly composed of carbon. The film thickness of the protective layer 22 is preferably 1 to 10 nm, for example.
The nonmagnetic seed layer 18, the magnetic recording layer 20, and the protective layer 22 can be formed by any thin film forming method such as sputtering, CVD, vacuum evaporation, or plating.

  In the above example, the nonmagnetic underlayer 24 is formed on the initial reaction layer 14. However, the present invention is not limited to such an example. For example, as shown in FIG. Alternatively, the soft magnetic underlayer 16 may be directly formed. Further, although not shown, the above-described layers may be laminated on both surfaces of the base body 12, respectively.

  In manufacturing the disk-shaped magnetic recording medium 10 described above, first, as shown in FIG. 2, the surface of the disk-shaped substrate 12 is cleaned by alkali cleaning and acid etching in the pretreatment step S1. Next, the cleaned substrate 12 is immersed in the zincate solution in the initial reaction layer forming step S2. As a result, a predetermined zinc (Zn) film having a predetermined film thickness is formed as the initial reaction layer 14.

  Subsequently, in the underlayer forming step S3, the nonmagnetic underlayer 24 and the soft magnetic underlayer 16 are formed on the substrate 12 on which the initial reaction layer 14 is formed by electroless plating. That is, by using a plating solution of Ni—high P alloy having a P concentration of 12.5%, the nonmagnetic underlayer 24 (Ni one high P alloy layer) having a P concentration of 12.5% and a film thickness of 9 μm is formed. It is formed on the initial reaction layer 14 of the substrate 12. After that, by using a plating solution of Ni-low P alloy with a P concentration of 3.7%, a soft magnetic underlayer 16 (Ni low-P alloy layer) with a P concentration of 4.5% and a film thickness of 3 μm is formed. It is formed on the nonmagnetic underlayer 24. Therefore, the total film thickness in the nonmagnetic underlayer 24 and the soft magnetic underlayer 16 (Ni—P alloy layer) is 12 μm.

  Subsequently, in the heat treatment step S4, the base 12 on which the nonmagnetic underlayer 24 and the soft magnetic underlayer 16 are formed is heated in a predetermined temperature range for a predetermined period in order to improve the saturation magnetic flux density [B s]. Is given. Note that the heat treatment step S4 may be omitted.

  Subsequently, in the rough polishing step S5 shown in FIG. 2, the surface of the soft magnetic underlayer 16 is polished. For the polishing, for example, a double-side polishing apparatus as shown in FIG. 3 is used.

  In FIG. 3, the double-side polishing apparatus has an annular polishing cloth 42 on one surface, a lower surface plate portion 40 that is rotatably supported, and a lower surface plate portion that can rotate and face the lower surface plate portion 40. The driving force is controlled through a planetary gear train (not shown) that is arranged in an opening at the center of the lower platen 40 and supported by the carrier 50. A drive shaft 54 having a sun gear 54 that transmits to the tooth gear 48 and the lower surface plate portion 40 are connected so as to surround the outer periphery of the lower surface plate portion 40, and the driving force from the planetary gear train described above is applied to the lower surface plate portion 40. Although not shown, the internal gear 48 that transmits the upper surface plate 44 is moved closer to or away from the lower surface plate 40, for example, an elevating drive mechanism that moves up and down, and the lower surface plate portion 40 and the upper surface plate portion 44. Consists of main components including a drive motor that rotates each It has been.

  The upper surface plate portion 44 having an annular polishing cloth 46 on the surface facing the polishing cloth 42 has one end of the drive shaft 56 connected to the center of the upper surface plate portion 44 on the same axis as the central axis of the drive shaft 54. The other end of the drive shaft 56 is connected to the output portion of the drive motor and the lifting drive mechanism. As a result, when the drive motor is activated, the drive shaft 56 with the upper surface plate 44 is rotated in the direction indicated by the arrow shown in FIG. Thus, it is pressed toward the lower surface plate part 40.

  The rotational speed Rv of the drive shaft 56 with the upper surface plate 44 is controlled, for example, according to the characteristic line La shown in FIG.

  FIG. 4 shows a characteristic line La in which the vertical axis represents the rotation speed Rv of the drive shaft 56, the horizontal axis represents the polishing time t, and the change in the rotation speed Rv according to the polishing time. The rotation speed Rv accelerates from the start of polishing to a predetermined time point to and reaches a predetermined speed Rm. The rotation speed Rv is maintained at a predetermined speed Rm from the time point to to a time point tr after a predetermined period, and then starts decelerating from the time point tr and becomes zero at the time point tf. Therefore, the period from the start of rotation to the time point tf is the polishing time.

  Around the drive shaft 56 is disposed a polishing liquid storage member 58 that supplies pure water, slurry, and the like, which will be described later, between the polishing cloth 42 and the polishing cloth 46 via the supply path 60. The annular polishing liquid storage member 58 is connected to the upper surface plate portion 44 by a support member (not shown). The polishing liquid storage member 58 has an annular groove 58G that stores the supplied pure water, slurry, and the like. One end of each of the plurality of supply paths 60 is connected to the inside of the groove 58G. The supply paths 60 are arranged at predetermined angular intervals along the circumferential direction of the polishing liquid storage member 58. The other end of each supply path 60 opens between the upper surface plate portion 44 and the lower surface plate portion 40 through the upper surface plate portion 44 and the polishing pad 46.

  One end of a supply path 62 for supplying pure water is disposed at a predetermined distance directly above the groove 58G of the polishing liquid storage member 58. The other end of the supply path 62 is connected to a pure water tank that stores pure water. The supply path 62 is provided with a control valve 62V for controlling the supply amount of pure water.

  Further, one end of a supply path 64 that supplies the slurry to the supply path 62 is connected to one end side of the supply path 62. A slurry tank for storing slurry is connected to the other end of the supply path 64. The supply path 64 is provided with a control valve 64V that controls the amount of slurry supplied.

Accordingly, when slurry or pure water is supplied through the supply path 62 and the drive shaft 56 is rotated, the polishing cloth is passed through the groove 58G of the polishing liquid storage member 58 and the supply paths 60 to which the slurry or pure water is rotated. 42 and the polishing pad 46 are supplied.
The carrier 50 also functions as a substrate holding member and has a plurality of holes for holding the substrate 28 (see FIG. 6) to be polished. Each board | substrate 28 distribute | arranged with the predetermined clearance gap in the hole is distribute | arranged so that rotation is possible.

  When the driving motor connected to the drive shaft 54 is activated, the lower surface plate portion 40 is in the direction indicated by the arrow in FIG. 3, that is, in the direction opposite to the rotation direction of the upper surface plate portion 44 described above. It can be rotated. The rotational speed Rv of the lower surface plate unit 40 is similarly controlled according to the characteristic line La shown in FIG. 4 described above.

  Accordingly, when the drive shafts 54 and 56 are rotated, the sliding contact surface of the substrate 28 held by the carrier 50 is relative to the polishing cloth 42, the lower surface plate 40, and the polishing cloth 46 that are rotated together with the internal gear 48. As a result of the relative movement, the slurry is polished while being supplied. Further, since the polishing amount per unit time is proportional to the predetermined pressing force between the upper surface plate 44 and the lower surface plate 40 and the rotational speed thereof, the required polishing time is controlled to a predetermined value. It will be controlled by this.

  Under such a double-side polishing apparatus, in the rough polishing step S5, the slurry is an acid etching using a general organic acid with an abrasive such as silica, colloidal silk, alumina, silicon carbide, zirconia, and diamond. A slurry for rough polishing is prepared by mixing with an agent.

  Preferably, the slurry is an acidic alumina slurry in which alumina is mixed with a polishing liquid having a pH of 3.3. The particle size of these abrasives is desirably 5 nm or more and 3000 nm or less, and preferably 700 to 900 nm. The polishing amount is preferably 100 nm or more and 1000 nm or less.

  In polishing, the control valve 64V is opened and the control valve 62V is closed, so that the surface of the soft magnetic underlayer 16 is polished while the acidic alumina slurry is supplied. After the polishing time elapses from the time point tr after the start of polishing, the control valve 64V is closed and the control valve 62V is opened. As a result, the slurry on the substrate 28 is easily removed by pure water.

  Subsequently, in the final polishing step S6 in FIG. 2, the final polishing is performed on the soft magnetic underlayer 16 of the roughly polished substrate 28. The slurry for finish polishing is a slurry in which colloidal silker and pure water are mixed. Thereby, an inexpensive polishing liquid that does not require chemical preparation without corroding the soft magnetic film can be obtained for polishing the soft magnetic underlayer 16 of the Ni-low P alloy.

The particle size of the colloidal silica is desirably 70 nm or more and 140 nm or less. This is because, as will be described later, when the colloidal silica particle size is less than 70 nm, it has been confirmed by verification by the inventors that the surface roughness is deteriorated. Moreover, it is because it was verified and confirmed that surface roughness deteriorates when the particle size of colloidal silica is larger than 140 nm.
The polishing amount of the soft magnetic underlayer 16 is preferably 50 nm or more and 200 nm or less. The surface roughness is desirably Ra = less than 0.5 nm. The reason why Ra is less than 0.5 nm is to further improve the storage capacity.

  In polishing, the control valve 64V is opened and the control valve 62V is closed, so that a slurry in which the colloidal silker and pure water are mixed is supplied. 16 surfaces are polished. After the polishing time elapses from the time point tr after the start of polishing, the control valve 64V is closed and the control valve 62V is opened. As a result, the slurry on the substrate 28 is easily removed by pure water.

Subsequently, after washing and drying steps (not shown), in the magnetic recording layer forming step S7 in FIG. 2, as shown in FIG. 7, the nonmagnetic seed layer 18, the magnetic recording layer 20, and the protective layer 22 are performed. Are sequentially laminated and formed on the soft magnetic underlayer 16 by sputtering or the like, for example. Thereby, the disk-shaped magnetic recording medium 10 is obtained.
1 and 5 show experimental results of a comparative example verified by the inventors of the present application.

  In the experiment of the comparative example, the double-side polishing apparatus shown in FIG. 3 was used and the Ni-low P alloy soft magnetic film (film thickness: 3 μm) formed on the 3.5-inch substrate was as described above. The rough polishing step S5 and the finish polishing step S6 are performed.

FIG. 5 shows the polishing conditions in the above-described rough polishing step S5 in the experiment of the comparative example. The main processing pressure (g / cm ² ), the rotational speeds (rpm) of the upper surface plate portion 44 and the lower surface plate portion 40 are shown. ), The particle size range (nm) of the used abrasive, the slurry (polishing liquid) flow rate (ml / min), and the polishing rate (nm / min), respectively.

  The slurry is an acidic alumina slurry in which an abrasive having an abrasive particle size of 700 to 900 nm is mixed as an abrasive with a polishing liquid adjusted to pH 3.3.

  FIG. 1 shows the particle diameter of the colloidal silica used in the above-described finish polishing step S6 in the experiment of the comparative example, the polishing time (min), the total polishing amount (μm) of steps 1 and 2 described later, and finish polishing. The subsequent surface roughness (Ra) values are shown respectively.

In FIG. 1, step 1 and step 2 represent a rough polishing step S5 and a finish polishing step S6, respectively. The finishing slurries were colloidal silica (condition 1) with an abrasive grain diameter of 20 nm, colloidal silica with an abrasive grain diameter of 40 nm (condition 2), colloidal silica with an abrasive grain diameter of 70 nm (condition 3), and colloidal silica with an abrasive grain diameter of 140 nm. (Condition 4) and colloidal silica (Condition 5) having an abrasive particle size of 240 nm are mixed with pure water (H ₂ 0) so as to have a concentration of 3 wt%. Colloidal silica is selected from the ST series of Nissan Chemical Industry Co., Ltd., having the above particle size and used for polishing.
The surface roughness Ra is measured by measuring the surface roughness in the range of 10 μm × 10 μm by AFM.

  As is clear from FIG. 1, in the polishing using the slurry having a colloidal silica particle size of 70 nm or 140 nm, the surface roughness of the substrate after polishing is Ra = 0.3 nm, respectively (Condition 3, Condition Four).

  On the other hand, in polishing using a slurry having a colloidal silica particle size of 20 nm or 40 nm, Ra = 0.7 nm (condition 1) and Ra = 0.6 nm (condition 2). In polishing using a slurry having a particle size of 240 nm, Ra = 0.5 nm (condition 5).

Therefore, when using a colloidal silica having a relatively small particle diameter of 40 nm or less, and using a colloidal silica having a large particle diameter of 240 nm or more, the surface roughness after polishing is as follows: It will be getting worse.
That is, a favorable result can be obtained in surface roughness by setting the particle size of colloidal silica to 70 nm to 140 nm.

  By setting the particle size of the colloidal silica used in the slurry to 70 nm to 140 nm, the surface roughness Ra of the final finished surface can be lowered, and an ultra flat surface required for the magnetic disk substrate can be secured.

It is a table | surface which shows the experimental result of the Example and comparative example to which an example of the grinding | polishing method of the disc substrate for recording media which concerns on this invention was applied. It is process drawing which shows the manufacturing process of the recording medium to which an example of the grinding | polishing method of the disc substrate for recording media which concerns on this invention is applied. It is a block diagram which shows roughly the principal part of the grinding | polishing apparatus with which an example of the grinding | polishing method of the disc substrate for recording media which concerns on this invention is applied. It is a characteristic view which shows the change of the rotational speed according to the grinding | polishing time in the upper surface plate part and lower surface plate part of the grinding | polishing apparatus shown by FIG. It is a table which shows the value of various conditions of the rough finishing process in the experiment of the Example and comparative example which are shown by FIG. It is a fragmentary sectional view of the board | substrate to which an example of the grinding | polishing method of the disc substrate for recording media which concerns on this invention was applied. It is a fragmentary sectional view of the magnetic recording medium to which an example of the grinding | polishing method of the disk substrate for recording media which concerns on this invention was applied. It is a fragmentary sectional view of the disk substrate for recording media to which an example of the grinding method of the disk substrate for recording media concerning the present invention was applied.

Explanation of symbols

12 Substrate 16 Soft magnetic layer 10 Disk-shaped magnetic recording medium

Claims (3)

A first polishing step of roughly polishing a surface of the soft magnetic underlayer of a substrate having a soft magnetic underlayer made of a Ni-P-based alloy containing 1 wt% or more and 6 wt% or less of phosphorus;
A second polishing step of polishing the surface of the soft magnetic underlayer polished by the first polishing step with a polishing liquid in which pure water and colloidal silica having a particle diameter of 70 nm to 140 nm are mixed;
A method for polishing a disk substrate for a recording medium comprising:   2. The disk substrate for a recording medium polished by the polishing method according to claim 1, wherein the surface roughness Ra of the soft magnetic underlayer polished by the second polishing step is less than 0.5 nm. A method for producing a perpendicular magnetic recording medium, comprising the step of forming at least a magnetic recording layer on a disk substrate for a recording medium polished by the polishing method according to claim 1.

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