JP4023609B2 - Substrate for magnetic recording medium and method for manufacturing magnetic recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium substrate and a magnetic recording medium including a recording layer.
[0002]
[Prior art]
In the field of magnetic recording, information recording by a hard disk device is essential as a primary external recording device for computers such as personal computers. As the recording density of hard disk drives increases, perpendicular magnetic recording systems capable of higher density recording are being developed instead of the conventional in-plane magnetic recording system.
[0003]
In perpendicular magnetic recording, the magnetic field from adjacent bits is the same as the magnetization direction, and a closed magnetic path is formed between adjacent bits, and self-demagnetizing field (hereinafter referred to as demagnetizing field) due to its own magnetization compared to horizontal magnetic recording. .) Is small, and the magnetization state is stable.
In terms of magnetic film thickness, it is not necessary to reduce the thickness in perpendicular magnetic recording as the recording density increases. From these points, perpendicular magnetic recording reduces demagnetization and K _u V (K _u is anisotropic energy, In particular, in the case of magnetic recording, it represents the magnetocrystalline anisotropy energy, and V represents the unit recording bit volume.), The stability against magnetization due to thermal fluctuation is large, and the recording limit is greatly expanded first. It can be said that it is a recording method that can do things. As the recording medium, the affinity with the horizontal recording medium is high, and writing and reading of magnetic recording can basically use the same techniques as those conventionally used.
[0004]
In a perpendicular magnetic recording medium, a soft magnetic backing layer (typically permalloy or the like) on a substrate, a recording film (a CoCr-based alloy, a multilayer film in which several PtCo layers and Pd and Co ultrathin films are alternately stacked, SmCo Amorphous film or the like is a candidate material), a protective film, a lubricating film, or the like. The backing layer in the perpendicular magnetic recording medium is soft magnetic and needs to have a thickness of about 100 nm to 500 nm. The soft magnetic underlayer serves as a path for magnetic flux from the upper recording film and also as a path for magnetic flux for writing from the recording head. Therefore, it plays the same role as the iron yoke in the permanent magnet magnetic circuit and needs to be thick.
[0005]
Compared to forming a nonmagnetic Cr-based underlayer on a horizontal recording medium, it is not easy to form a soft magnetic underlayer on a vertical recording medium. Normally, all the constituent films of the horizontal recording medium are formed by a dry process (mainly magnetron sputtering) (Patent Document 1). Various studies have been made on perpendicular recording media by film formation by a dry process. However, the film formation by the dry process has big problems in terms of mass productivity and productivity because of process stability, complicated setting of various parameters, and low film formation speed. In order to increase the density, it is necessary to reduce the flying height of the magnetic head that floats on the surface of the magnetic disk as much as possible. In the manufacture of perpendicular magnetic recording media, the thickness can be flattened by polishing. Although it is necessary to coat the metal film, the thick film obtained by the dry process has low adhesion, and it is very difficult to flatten by polishing. Therefore, various attempts have been made to coat a nonmagnetic substrate with a metal film by a plating method that is easy to increase in thickness compared to vacuum deposition.
[0006]
In order to perform plating with good adhesion by wet plating, it is important that a large amount of a substance that can be a catalyst for the reduction of metal ions in the plating solution exists at the base material-plating film junction. is there. Furthermore, the level of adhesion between the formed plating film and the base material to be plated depends on the mechanical anchoring effect caused by the unevenness of the surface of the object to be plated or the chemical interaction between the object to be plated and the plating film. is doing.
[0007]
For example, in order to plate the surface of a material having poor chemical reactivity, such as plastic, ceramic, and glass material, the surface of the base material is roughened by polishing and then immersed in a Pd—Sn colloid solution. A method is widely used in which the colloidal particles are fixed to the recesses of the metal, and plating is performed using the adhering colloid as a catalyst starting point to ensure adhesion due to the mechanical anchoring effect.
On the other hand, in plating on a metal such as Fe, a metal bond is formed between the plating film and the metal to be plated immediately after the start, and strong adhesion is ensured by alloying at the atomic layer level. It is said that.
[0008]
On the other hand, the surface of a silicon wafer used as a plating base material exhibits water repellency, partially becomes dry, and is inactivated by being covered with a natural oxide film of SiO _{2 having} low chemical activity on the surface. For this reason, it becomes difficult to form a chemical bond with the plating film. Further, the surface of the silicon wafer after the surface processing exhibits water repellency, partially becomes dry, and there is a problem that a non-uniform film is generated in the surface.
[0009]
[Patent Document 1]
JP-A-5-143972 [0010]
[Problems to be solved by the invention]
It is an object of the present invention to provide a magnetic recording medium including a magnetic recording medium substrate and a recording layer that have good homogeneity in film formation on a nonmagnetic substrate and can be made thick.
[0011]
[Means for Solving the Problems]
As a result of earnest research on the magnetic recording medium substrate, the soft magnetic layer, and the magnetic recording medium including the recording layer, the inventors have achieved the above object. In order to achieve this, it has been found that it is effective to provide a magnetic recording medium substrate including a nonmagnetic substrate and a base plating layer on the nonmagnetic substrate, wherein the surface of the nonmagnetic substrate is subjected to a hydrophilic treatment. It was. It has been found that this hydrophilic treatment is preferably an alcohol treatment or a hydrogen peroxide treatment. Furthermore, it has been found that a magnetic recording medium including the magnetic recording medium substrate, the soft magnetic layer, and the recording layer is suitable as a perpendicular magnetic recording medium.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Prior to film formation on a non-magnetic substrate, an underlying plating layer is formed on the non-magnetic substrate to form a highly adhesive material, thereby making the underlying plating layer on the substrate surface unnecessary roughening and various activations. It is possible to obtain a soft magnetic film having good adhesion without performing the treatment. In addition, since the present invention can be carried out by wet electroless displacement plating, the process is very simple and productivity is superior to the introduction of a base film by vapor deposition or the like. Furthermore, since the surface activity of the underlying plating film after film formation is high, it is possible to continuously form a plating film without special activation, and it has extremely excellent characteristics as an underlying film.
[0014]
The nonmagnetic substrate of the present invention is particularly preferably a Si single crystal material produced by the CZ (chocolate ski) method or the FZ (floating zone) method. Any plane orientation of the substrate may be used, including (100), (110), and (111). Further, the impurities in the substrate may contain elements such as B, P, N, As, and Sn in the total amount range of 0 to 10 ²² atoms / cm ² . However, when polycrystalline Si having different plane orientations on the same plane of the substrate and Si having extremely segregated impurities are used as the substrate, the underlying plating layer formed due to the difference in chemical reactivity is not uniform. It may become. Furthermore, when a substrate with extreme segregation is used, a local battery is formed at the segregation site on the surface of the substrate during the formation of the base plating layer, thereby achieving the base plating layer structure described in the present invention. It may be impossible.
[0015]
In the present invention, the surface oxide film of the non-magnetic substrate such as the Si substrate and the substrate surface are slightly etched so that the activation necessary for forming the base plating layer can be performed. In the present invention, it is preferable to etch in an alkaline aqueous solution such as caustic soda having a concentration of 2 to 60% by weight to remove the oxide film on the surface and to slightly corrode the substrate surface. At this time, a preferable etching rate of the base material for giving activation is 20 nm / min to 5 μm / min, and it is preferable to remove the base material Si having an etching amount of 40 nm or more. The liquid temperature during etching varies depending on the concentration and processing time, but is preferably in the range of 30 to 100 ° C. in terms of workability.
[0016]
According to the present invention, the non-magnetic substrate after etching is subjected to hydrophilic treatment. The hydrophilic treatment is preferably performed using alcohol or hydrogen peroxide solution.
As the alcohol, ethylene glycol, ethanol, isopropyl alcohol and the like are preferably used, and as the hydrogen peroxide solution, a 1 to 20% by weight aqueous solution is preferably used. A combination of hydrogen peroxide water and ammonia water having a pH range of 9-12 is also preferred.
The hydrophilic treatment can be performed by immersing the non-magnetic substrate after etching in alcohol or hydrogen peroxide solution. The preferred hydrophilic treatment time and temperature vary depending on the number of treatments, the volume of the treatment bath, etc., but are 15 to 80 ° C., more preferably 20 to 40 ° C. in 30 seconds to 10 minutes.
The non-magnetic substrate that has been subjected to hydrophilic treatment improves adhesion to the underlying plating layer formed thereon, and provides good homogeneity in film formation on the non-magnetic substrate. This is presumably because the plating bath solution spreads over the entire surface of the nonmagnetic substrate when the base plating layer is formed by the hydrophilic treatment, and the plating bath solution is circulated well.
[0017]
After performing such etching treatment and hydrophilic treatment, one or more metal ions selected from the group consisting of Ag, Co, Cu, Ni, Pd, and Pt, or 0 as an element component with these as main metal ions. A high adhesion plating material is obtained by immersing in a plating solution containing 0.01 N or more, preferably 0.05 to 0.3 N to form a surface layer. The thickness of the base plating layer is preferably 10 to 1000 nm, and more preferably 50 to 500 nm. If the thickness is smaller than 10 nm, the distribution of the individual metal polycrystal grains in a uniform layer cannot be obtained. If the thickness exceeds 1000 nm, the individual crystal grains are enlarged, which is not preferable as a base film.
[0018]
The film formation is preferably performed by a method generally known as electroless displacement plating. It is the same as conventional displacement plating that it does not contain components such as diphosphoric acid and dichloric acid that can be a reducing agent in the solution, but in the present invention, it is particularly preferably a sulfate that does not contain components such as saccharin that becomes a brightener. Melt can be used. Examples of the sulfate include nickel sulfate and copper sulfate, and a preferred concentration is 0.01 to 0.5N. In a bath containing hydrochloride or containing 0.05N or more of chlorine ions, it is not only difficult to obtain the underlying plating layer of the present invention, but it is also not preferable because plating on the Si substrate itself may be impossible. Moreover, when each element, such as K, Ca, Na, etc. exists in a liquid 0.003N or more, it is unpreferable when implementing this invention. Therefore, it is assumed that chlorine ions are contained in less than 0.05N, and K, Ca, Na, etc. are contained in the solution in less than 0.003N.
[0019]
As the plating conditions of the present invention, the bath temperature is set in the range of 7.2 to 12.8, more preferably 7.6 to 8.4 at a liquid temperature of 70 to 100 ° C. If the plating solution temperature is less than 70 ° C., plating is impossible, and if the plating solution temperature exceeds 100 ° C. or the pH at the time of plating is outside the above range, the plating itself is possible. In some cases, the base plating film described in the invention cannot be obtained. The pH adjustment is preferably performed by adding ammonia. When the pH is adjusted with a hydroxide such as caustic soda, it is difficult to implement the present invention even if the pH is in the above range. Although the reason for this is not necessarily clear, it is considered extremely important that the metal ions in the liquid are complex ionized by a complex-forming agent such as ammonia.
The amount of ammonia added may be appropriately adjusted depending on the initial pH, but is generally added in the range of 0.02 N to 0.5 N, preferably 0.05 N to 0.2 N in the plating bath.
By using the etching process and the base plating process together, the base plating layer can be formed.
[0020]
A soft magnetic layer can be formed on the underlying plating layer of the present invention. The soft magnetic layer is not particularly limited, and a known one can be used, for example, permalloy (Fe ₈₀ Ni ₂₀ ).
A method for forming the soft magnetic layer is not particularly limited, and a known method can be used. For example, a sputtering method may be used.
The thickness of the soft magnetic layer varies depending on the use and use conditions, and is, for example, 100 to 1000 nm, preferably 100 to 500 nm.
[0021]
The magnetic recording medium of the present invention is preferably a perpendicular magnetic recording medium. The magnetic recording medium of the present invention comprises a substrate, a base plating layer, and a soft magnetic layer. The soft magnetic layer may be a single layer or a multilayer body composed of a plurality of films.
An example of a perpendicular magnetic recording type hard disk medium of the present invention is shown in FIG. The magnetic recording medium substrate of the present invention including the Si substrate 1, the base plating layer 2, and the soft magnetic layer 3 can be provided with a recording layer 4 on the soft magnetic layer 2 to form a magnetic recording medium. In addition, a protective layer 5 and a lubricating layer 6 may be sequentially provided on the recording film. These layers can be formed using a known method such as sputtering.
Examples of the recording layer include a Co recording layer, examples of the protective layer include a carbon protective layer, and examples of the lubricating layer include a fluorine-based lubricating layer. That is, known recording layers, protective layers, and lubricating layers can be used. Their thickness varies depending on the application and use conditions.
According to the present invention, a soft magnetic layer and a recording layer may be provided on one side of the substrate, or a soft magnetic layer and a recording layer may be provided on both sides of the substrate.
[0022]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to this.
Example 1
Core removal, centering, and lapping were performed from a 200 mm diameter Si single crystal substrate manufactured by the CZ method to obtain a (100) Si single crystal (P-doped N-type substrate) with a diameter of 65 mm, and then an average particle size of 15 nm. Both surfaces were polished with colloidal silica to obtain a surface roughness (Rms) of 4 nm. Rms is the mean square roughness, measured using an AFM (Atomic Force Microscope). This substrate was immersed in a 10% by weight aqueous caustic soda solution at 45 ° C. for 3 minutes to remove the thin surface oxide film on the surface of the substrate and subjected to Si etching treatment on the surface, and then immersed in an ethylene glycol solution.
Next, a base plating bath was prepared by adding 0.5 N ammonium sulfate to a 0.1 N nickel sulfate aqueous solution, and the pH of the solution was raised to 9.8 by adding ammonia water. When this solution was heated to 80 ° C. and pH was measured again, the pH value was 7.6. While supplying ammonia water continuously so that the pH at 80 ° C. becomes 8.0 (ammonia was 0.1 N in total amount), the previously etched Si substrate was used as a base plating bath. A base plating layer was obtained by dipping for a minute.
When the film of this material was examined with a fluorescent X-ray analysis and a transmission electron microscope, it was confirmed that the film was a homogeneous undercoat layer at 200 nm ± 10 nm.
[0023]
Example 2
The Si substrate obtained in the same manner as in Example 1 was immersed in a 45% by weight aqueous solution of caustic soda at 50 ° C. for 2 minutes to remove the thin surface oxide film on the surface of the substrate and to etch the surface Si, followed by ammonia. It was immersed in a hydrogen peroxide solution adjusted to pH 9.5 with water. Next, a base plating solution was prepared by adding 0.2N ammonium sulfate aqueous solution to 0.2N copper sulfate aqueous solution, and the pH of the solution was raised to 8.3 by adding ammonia water. When this solution was heated to 80 ° C. and pH was measured again, the pH value was 6.9. While supplying ammonia water continuously so that the pH at 80 ° C. becomes 8.0 (ammonia was 0.2 N in total), the previously etched Si substrate was used as a base plating bath. It was immersed for 7 minutes to obtain a plating base film.
When the film of this material was examined with a fluorescent X-ray analysis and a transmission electron microscope, it was confirmed that the film was a homogeneous base plating layer at 150 nm ± 6 nm.
[0024]
【The invention's effect】
A non-magnetic substrate whose surface has been subjected to hydrophilic treatment has good homogeneity in film formation on the substrate. Therefore, it is possible to provide a magnetic recording medium substrate that can be thickened.
[Brief description of the drawings]
FIG. 1 shows an example of a magnetic recording medium of the present invention.
[Explanation of symbols]
1 Si substrate 2 Underlying plating layer 3 Soft magnetic layer 4 Recording layer 5 Protective layer 6 Lubricating layer

Claims (5)

A method for manufacturing a substrate for a magnetic recording medium comprising a Si substrate that is a nonmagnetic substrate and a base plating layer on the Si substrate, wherein the surface of the Si substrate is etched in an alkaline aqueous solution, and the etching treatment is performed. A method for manufacturing a substrate for a magnetic recording medium, wherein the surface of a subsequent Si substrate is subjected to hydrophilic treatment, and then a base plating layer is formed by electroless displacement plating . The method for producing a magnetic recording medium substrate according to claim 1, wherein the hydrophilic treatment is an alcohol treatment or a hydrogen peroxide solution treatment. The electroless substitution plating method of producing a substrate for a magnetic recording medium according to claim 1 or claim 2 ammonia was added Ru place in the range of PH7.2～12.8. The method for manufacturing a magnetic recording medium substrate according to claim 1, further comprising forming a soft magnetic layer on the base plating layer . A method for manufacturing a magnetic recording medium, wherein a recording layer is formed on a magnetic recording medium substrate obtained by using the manufacturing method according to claim 4 .

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