JP4126657B2 - Polishing method of magnetic disk substrate for perpendicular recording - Google Patents

Description

  The present invention relates to a perpendicular recording magnetic disk substrate used in a magnetic disk storage device and a method of manufacturing the same.

  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 particular, a double-layer perpendicular magnetic recording medium with a soft magnetic film called a soft magnetic underlayer that is easy to pass magnetic flux generated from a magnetic head below the magnetic recording layer that plays a role in recording information is a magnetic field generated by a magnetic head. It is known that it is suitable as a perpendicular magnetic recording medium capable of high-density recording because it increases the strength and its magnetic field gradient, improves the recording resolution, and increases the magnetic flux leakage from the medium (for example, Patent Documents). 1).

  Conventionally, a NiFe alloy, an amorphous alloy mainly composed of Co, or the like is generally used as the soft magnetic backing layer. When these materials are used, a film thickness of 0.1 μm to several μm is required from the viewpoint of recording / reproducing characteristics. Such a relatively thick soft magnetic layer is very difficult to mass-produce at low cost by the sputtering method used in the manufacture of conventional magnetic recording media, and low cost by electroless plating method. Mass production is a challenge. So far, the possibility of production by electroless plating of a soft magnetic material film made of a Ni—Fe—P layer has been disclosed (for example, see Patent Document 2).

  Furthermore, although a method of performing a polishing process in a plurality of stages when manufacturing a Ni-P plated substrate has been proposed (Patent Document 3), the ratio of P is not described, and this is, for example, acidic polishing of PH4 The polishing is performed with a liquid, and as described later, the problem to be solved by the present invention is not mentioned.

Japanese Patent Publication No.58-91 JP 7-66034 A Japanese Patent Laid-Open No. 11-10492

  However, since the soft magnetic backing layer using the Ni—Fe—P layer is composed of three elements, it is very difficult to manage the composition of the plating tank in the electroless plating method, and the quality of the soft magnetic backing layer during mass production is reduced. It is difficult to maintain and control. Furthermore, since ferrous sulfate in the components of the plating solution is oxidized and gradually changes to ferric sulfate when exposed to the atmosphere, it is difficult to control the composition to a constant plating solution.

  Therefore, a plating film that can be more stably mass-produced by electroless plating was examined. As a result, it was found that a Ni—P film (hereinafter, Ni—low P film) having a P concentration of 6 wt% or less is promising. Since the Ni-low P film is composed of two elements, the plating solution is more stable, easier to manage, and more stable in quality than the plating solution consisting of three elements when made by electroless plating. It can be mass-produced stably and inexpensively. Furthermore, the film can have a soft magnetic characteristic that sufficiently functions as a soft magnetic backing layer by making the P concentration 6 wt% or less (Japanese Patent Application No. 2003-027486).

  Further, a polishing method for the Ni-low P film was examined. The polishing process is generally composed of two steps, a rough polishing step using alumina slurry and a final polishing step using colloidal silica. These polishing agents have an etching action in order to achieve both productivity and surface quality. An acidic etchant is added. A general Ni-P plating layer having a P concentration of 12% or more has high corrosion resistance in an acid solution, and this acidic polishing slurry can be used. However, a substrate subjected to Ni-low P plating with a P concentration of 6% or less has low acid resistance and the surface is eluted non-uniformly, so that mirror polishing cannot be performed. Further, when the corrosion is severe, there is a problem that Ni phosphate reprecipitates to form a black film. In contrast, the method of polishing using an alkaline abrasive having a pH of 8 or higher can satisfactorily polish the Ni-low P layer applied on the substrate. In the rough polishing step, Ni-low P It has been shown that even if the layer is polished with a conventional acidic abrasive, a surface roughness similar to that of the Ni-high P layer can be obtained, and if an alkaline abrasive is used only in the final polishing step, Ni-low P Regarding the layer, it was found that a value higher than the conventional general surface roughness can be obtained (Japanese Patent Application No. 2003-049878).

  However, since the rough polishing step using alumina slurry and the final polishing step using colloidal silica using an alkaline abrasive having a pH of 8 or more are performed using different polishing apparatuses, acidic etching is performed after the rough polishing step using alumina slurry. Corrosion progresses until the agent is removed, resulting in unevenness of the substrate surface state. Therefore, even if the desired surface roughness can be obtained by final polishing with colloidal silica using an alkaline abrasive having a pH of 8 or higher, undulation that is longer than the surface roughness occurs due to unevenness caused by corrosion after rough polishing. Resulting in. Further, in order to prevent this unevenness, when polishing with only an alkaline abrasive, the polishing rate is slow and the processing time is long.

  An object of the present invention is to propose a method of polishing a Ni-low P plating film having a low P concentration in a short time, and to polish a magnetic disk substrate for perpendicular recording well by this method, and to mass-produce it at a low cost. Another object of the present invention is to provide a magnetic disk substrate for perpendicular recording provided with a plating film.

In order to solve the above-mentioned problems, the present invention provides a perpendicular magnetic recording medium substrate in which a soft magnetic underlayer made of a Ni—P alloy containing 0.5 wt% or more and 6 wt% or less of P is formed on a nonmagnetic substrate. A slurry containing an abrasive whose pH is adjusted to 4 or lower between the substrate and the polishing member while the substrate is pressed by the polishing member while relatively moving the polishing member; Is a method for polishing a substrate for a perpendicular magnetic recording medium in which a slurry containing a polishing material adjusted to be alkaline is adjusted to 8 or more in order to polish the surface of the substrate , wherein the pH is adjusted to 8 or more The slurry containing the abrasive is characterized in that the pH is adjusted by adding a pH adjusting liquid to the slurry containing the abrasive whose pH is adjusted to 4 or less .

  Here, between the slurry containing the abrasive whose pH is adjusted to 4 or lower between the substrate and the polishing member, and the slurry containing the abrasive whose pH is adjusted to 8 or higher is switched. Pure water can be supplied.

  Moreover, the slurry containing the abrasive whose pH is adjusted to 4 or lower and the slurry containing the abrasive whose pH is adjusted to 8 or higher may be colloidal silica.

  In a preferred embodiment of the present invention, a magnetic disk substrate for perpendicular recording subjected to Ni-low P plating with a P concentration of 6 wt% or less can be polished well in a short time using the polishing method of the present invention, The ultra flat surface required for the magnetic disk substrate can be secured.

  According to the present invention, the Ni-low P layer applied to the substrate can be polished well in a short time. As a result, it is possible to form a plating film that can be mass-produced at low cost on the magnetic disk substrate for perpendicular recording, and to achieve an ultra flat surface of the plating film.

Hereinafter, preferred embodiments of the present invention will be described.
First, the perpendicular recording magnetic disk substrate of the present invention will be described. FIG. 1 and FIG. 2 show schematic cross-sectional views of a structure preferable as a magnetic disk substrate. However, these are shown as examples of the perpendicular recording magnetic disk substrate, and the perpendicular recording magnetic disk substrate of the present invention is not limited thereto.

  A disk substrate 10 shown in FIG. 1 has a structure in which a nonmagnetic substrate 1, an initial reaction layer 2, and a soft magnetic underlayer 4 are sequentially laminated.

  As the nonmagnetic substrate 1, a material used for a substrate of a general perpendicular recording magnetic disk substrate, for example, an aluminum alloy, tempered glass, crystallized glass, or the like is used. A substrate prepared by injection molding of polycarbonate, polyolefin, and other plastic resins can also be used.

Next, the initial reaction layer 2 will be described.
As an initial reaction layer on the substrate 1 using an aluminum alloy, a Zn film layer formed by immersing in a zincate solution (a solution containing zinc oxide and a sodium hydroxide aqueous solution) is generally used. The thickness of the Zn layer is desirably 0.1 to 0.8 μm, but it is also possible to have a thickness outside the range.

  The initial reaction layer on the non-conductive substrate 1 using tempered glass, crystallized glass, plastic, or the like is 20 to 40 g / l hydrochloric acid tin chloride solution and 0.1 to 0.5 g / l hydrochloric acid acidity. In general, activation treatment is performed by sequentially immersing in a palladium chloride solution to precipitate Pd nuclei on the surface. Note that Ni, Ni-P, Cu, Cr, Fe, Pd, or the like can be formed to have a thickness of 1 nm to 1000 nm using a physical vapor deposition method such as a sputtering method or an ion plating method.

  Further, a soft magnetic underlayer 4 made of a Ni-low P layer is laminated on the initial reaction layer 2 by an electroless plating method. In order to realize the soft magnetic properties of the Ni—P plating layer, the P concentration is preferably 6 wt% or less, and the Ni—low P film thickness is preferably 0.5 μm or more and 7.0 μm or less. When the saturation magnetic flux density [Bs] of the Ni-low P layer is measured by a VSM (vibrating sample magnetometer), the P concentration is 2%, the film thickness is 1 μm, 0.4 T, the P concentration is 6%, and the film thickness is 1 μm, 0.15 T. A degree of soft magnetic properties can be obtained.

  As another aspect, in the disk substrate 10 shown in FIG. 2, the nonmagnetic underlayer 3 can be provided between the initial reaction layer 2 and the soft magnetic underlayer 4. The nonmagnetic underlayer 3 can be laminated by an electroless plating method.

  As the nonmagnetic underlayer 3, a Ni-high P plating layer can be used. The plating layer can be laminated by an electroless plating method. The P concentration of the Ni-high P plating layer is desirably 10 wt% or more and 13 wt% or less. The thickness of the Ni-high P plating layer is preferably 0 μm or more and 7 μm or less.

As described above, the Ni-P plating layer can be laminated by an electroless plating method. At this time, the electroless plating solution contains Ni ions, a complexing agent, and a reducing agent. The Ni _ion, or the like can be used NiSO 4, NiCl _2. As the complexing agent, general citric acid, tartrate, and the like can be used. As a reducing agent, sodium hypophosphite is generally used, and hydrazine, formaldehyde, or sodium borohydride may be used in combination. The magnetic disk substrate is immersed in a plating tank in which a plating solution containing these is adjusted to 80 to 95 ° C., and a Ni-low P plating layer is laminated. Moreover, the Ni-high P layer that can be optionally provided can also be plated by the same method as the electroless plating method described above, except that the P concentration is changed.

The Ni-P plating layer is desirably laminated by an electroless plating method from the viewpoint of inexpensive mass production, but is not limited to this, and physical vapor deposition such as a sputtering method or an ion plating method is performed depending on required characteristics. Other general film forming methods such as a method can also be used.
Next, the surface of the magnetic disk substrate prepared as described above is polished by the polishing method of the present invention.

FIG. 4 shows a double-side polishing apparatus for polishing according to the present invention.
The double-side polishing apparatus 51 has the following configuration. Reference numeral 52 denotes a lower surface plate which is installed so as to be rotatable in the horizontal direction, and a donut-shaped polishing cloth 53 is mounted on the upper surface thereof. Reference numeral 54 denotes an upper surface plate, which is disposed on the upper surface of the lower surface plate 52 so as to be coaxial with the lower surface plate 52 and is held so as to be rotatable in the horizontal direction and movable up and down in the vertical direction. A polishing cloth 55 is attached. A sun gear 56 is disposed between the polishing cloths 53 and 55 at the axial center position of the polishing cloths 53 and 55. Reference numeral 57 denotes an internal gear, which is disposed concentrically at a radially outer position of the sun gear 56. Reference numeral 58 denotes a disk-shaped substrate holder that constitutes an external gear meshed with the internal gear 57 and the sun gear 6 and is placed on the polishing cloth 53 of the lower surface plate 52. 12 is a slurry supply means having a slurry reservoir 60 rotating together with the upper surface plate 54 and a pipe 61 for supplying the slurry from the slurry reservoir 60 to the upper surface of the substrate 59 from the upper surface plate 54. The supply and stop of the slurry 61 and 63 and the pure water 62 supplied to the slurry reservoir 60 are controlled by valves 64, 65 and 66.

  In the double-side polishing machine 51 configured as described above, the substrate 59 is placed in the substrate mounting hole of the substrate holder 58, and the upper and lower polishing cloths 53, 55 are pressed against the upper and lower surfaces of the substrate 59. Then, while supplying the slurry 61 or 63 containing the abrasive, the sun gear 56 is rotated and the upper and lower surface plates 52 and 54 are rotated in opposite directions to rotate the substrate holder 58. While revolving around the sun gear 56, both surfaces of the substrate 59 are polished.

  First, a polishing material such as silica, colloidal silk, alumina, silicon carbide, zirconia, diamond or the like is adjusted to a pH of 4 or less with an acidic etchant using a general organic acid. The particle size of these abrasives is desirably 5 nm or more and 3000 nm or less. Next, an abrasive such as silica, colloidal silk, alumina, silicon carbide, zirconia, diamond is adjusted to pH 8 or higher. The particle size of these abrasives is desirably 5 nm or more and 3000 nm or less. For adjusting the pH, a general alkaline solution such as caustic soda may be used. Then, the slurry supply valve 64 of the double-side polishing machine 51 is opened, and the Ni-low P layer on the surface of the magnetic disk substrate is polished while supplying the slurry 61 containing the polishing material adjusted to pH 4 or lower. The polishing amount in this step is preferably 100 nm or more and 1000 nm or less, and the polishing time necessary to polish the desired polishing amount is calculated according to the polishing rate with respect to the polishing conditions. Thereafter, with the double-side polishing machine 51 operating, the slurry supply valve 64 is closed, and then the slurry supply valve 66 is opened. Switch. The polishing amount in this step is preferably 50 nm or more and 200 nm or less, and the polishing time required to polish the desired polishing amount is calculated according to the polishing rate with respect to the polishing conditions. The surface roughness is desirably Ra = 0.5 nm or less.

  In the above polishing method, a step of supplying pure water by opening and closing the supply valve 65 while switching from the slurry 61 containing the abrasive adjusted to pH 4 or lower to the slurry 63 containing the abrasive adjusted to pH 8 or higher is provided. Thus, the slurry 61 containing the abrasive adjusted to pH 4 or less and the slurry 63 containing the abrasive adjusted to pH 8 or more can be prevented from intermingling, and the reaction between the abrasives can be suppressed.

  Further, in the above polishing method, both the slurry 61 containing an abrasive whose pH is adjusted to 4 or less and the slurry 63 containing an abrasive whose pH is adjusted to 8 or higher are colloidal silica. Then, other types of abrasives are not mixed, and the occurrence of scratches and the like can be suppressed.

  Further, in the above polishing method, the pH is adjusted by adding a pH adjusting solution to the slurry 61 containing an abrasive whose pH is adjusted to 4 or less, and the pH is adjusted to be alkaline by 8 or more. For the supply of the slurry 61 containing the abrasive adjusted to 4 or less acidic, it is only necessary to supply the pH adjusting liquid by opening the supply valve 66, which can be carried out very simply.

  Using the magnetic disk substrate polished by the polishing method of the present invention, a perpendicular recording magnetic disk can be produced. A schematic cross-sectional view of a preferred structure for the magnetic disk of the present invention is shown in FIG. However, the magnetic disk shown in FIG. 3 is shown as an example, and the magnetic disk of the present invention is not limited to this.

  The disk shown in FIG. 3 has a structure in which a nonmagnetic seed layer 20, a magnetic recording layer 30, and a protective layer 40 are sequentially stacked on a disk substrate 10 for perpendicular magnetic recording media.

  The disk substrate 10 for perpendicular magnetic recording media refers to any one of the disk substrates of the present invention shown in FIG. 1 or FIG. 2 and polished by the polishing method of the present invention.

Examples of the present invention will be described below.
A 3.5-inch φ Al-5Mg (at%) alloy is used as the non-magnetic substrate, a Ni-high P plating solution having a P concentration of 12.5%, and a Ni concentration of 9 μm with a P concentration of 12.5%. After forming the high P layer, a Ni-low P layer having a P concentration of 4.5% and a film thickness of 3 μm is formed using a Ni-low P plating solution having a P concentration of 3.7%. Polishing was performed using a substrate having a film thickness of 12 μm.

  As the slurry, an acidic alumina slurry obtained by mixing alumina with an abrasive grain size of 700 to 900 nm as an abrasive in a polishing liquid adjusted to pH 3.3, and an abrasive grain size of 30 to 30 as an abrasive in a polishing liquid adjusted to pH 2.8 An acidic silica slurry in which 70 nm colloidal silica was mixed, or an alkaline silica slurry in which pH was adjusted to 8 by adding a pH adjusting solution to this acidic silica slurry was used. Table 1 shows the polishing conditions and the polishing rate at that time.

  Using the slurry shown in Table 1, Examples 1-4 of the present invention and Comparative Examples 1 and 2 for comparison were carried out with the polishing time and polishing amount shown in Table 2 below.

  The number of the process of Table 2 shows the order of a process, and the comparative example 1 performs the process of the process 1 and the process of the process 2 with a separate grinding | polishing apparatus, and wash | cleans a slurry after completion | finish of the process 1. Step 2 was performed. Table 2 shows the surface roughness and waviness when the polishing in each example was performed. For the measurement of the surface roughness, the surface roughness of 10 μm × 10 μm was measured by AFM, and the waviness of 1 mm × 1 mm was measured by the optical measuring device ZYGO.

  In Examples 1 to 4 of the present invention, the processing time was the same as in Comparative Example 1, but the polished substrate had the same surface roughness, no unevenness, and a good swell. . Moreover, compared with the comparative example 2, in this invention Examples 1-4, the surface roughness and the wave | undulation were able to obtain the same value, shortening processing time from 25min to 7.5min.

FIG. 2 is a schematic cross-sectional view of a disk substrate in which an initial reaction layer and a soft magnetic underlayer are formed on a nonmagnetic substrate, among the magnetic disk substrates for perpendicular recording media of the present invention. FIG. 3 is a schematic cross-sectional view of a disk substrate in which an initial reaction layer, a nonmagnetic underlayer, and a soft magnetic underlayer are formed on a nonmagnetic substrate, among the magnetic disk substrates for perpendicular recording media of the present invention. 1 is a schematic cross-sectional view showing the configuration of a magnetic disk for perpendicular recording media according to the present invention. It is the schematic of the double-side polish machine used for implementation of grinding | polishing by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonmagnetic base | substrate 2 Initial reaction layer 3 Nonmagnetic underlayer 4 Soft magnetic underlayer 10 Magnetic disk substrate for perpendicular magnetic recording 20 Nonmagnetic seed layer 30 Magnetic recording layer 40 Protective layer 51 Double-side polisher 52 Lower surface plate 53 Polishing cloth 54 Top Surface plate 55 Abrasive cloth 56 Sun gear 57 Internal gear 58 Substrate holder 59 Substrate 60 Slurry reservoir 61 Slurry containing abrasive 62 Pure water 63 Slurry containing abrasive 64 Valve 65 Valve 66 Valve

Claims (3)

While relatively moving a substrate for perpendicular magnetic recording medium, in which a soft magnetic underlayer made of a Ni-P-based alloy containing 0.5 wt% or more and 6 wt% or less of P on a nonmagnetic substrate, and a polishing member, In a state where the substrate is pressed by the polishing member, a slurry containing an abrasive whose pH is adjusted to 4 or lower and an abrasive whose pH is adjusted to 8 or higher between the substrate and the polishing member. A slurry for containing a perpendicular magnetic recording medium by sequentially supplying the slurry and polishing the surface of the substrate,
The slurry containing the abrasive whose pH is adjusted to 8 or higher is adjusted to pH by adding a pH adjusting liquid to the slurry containing the abrasive whose pH is adjusted to 4 or lower. A method for polishing a perpendicular magnetic recording medium substrate. In claim 1,
Between the substrate and the polishing member, pure water is used while switching from the slurry containing the abrasive whose pH is adjusted to 4 or lower to the slurry containing the abrasive whose pH is adjusted to 8 or higher. A method for polishing a substrate for a perpendicular magnetic recording medium, comprising: supplying a substrate for perpendicular magnetic recording medium. In claim 1 or 2,
The slurry containing the abrasive whose pH is adjusted to 4 or lower and the abrasive of the slurry containing the abrasive whose pH is adjusted to alkaline higher than 8 are colloidal silica. A method for polishing a substrate.

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