JP4023610B2 - Substrate for perpendicular magnetic recording medium and method for producing perpendicular 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 plating on the silicon wafers used as a base material, reactivity with oxygen is very high, is covered already in the natural oxide film of a low SiO ₂ in chemical activity on the surface in a few hours after manufacture thus inactivated. For this reason, it is difficult to form a chemical bond with the plating film.
Although it is well known that such a natural oxide film on the Si surface can be dissolved and removed by immersion such as HF, the Si surface from which the natural oxide film has been removed is very easily oxidized, and when immersed in a plating solution, By reacting with the OH groups in the liquid, the oxide film is re-formed before the plating film is formed, and a good plating film cannot be obtained.
For this reason, when plating on the Si substrate, the surface of the substrate is roughened in the same manner as the plating on the plastic or the like described above, and then immersed in Pd—Sn colloid for plating. Or after introducing a metal layer by vapor phase vapor deposition such as sputtering, plating is performed on the metal layer.
[0009]
However, in the method of plating by roughening the substrate, it is necessary to increase the roughness of the surface of the substrate as the adhesion of the plating film is improved, and to the semiconductor wafer used for electronic materials, etc. It cannot be said that it is suitable as plating. Further, when the substrate surface is roughened by machining, a processing mark is generated by the processing, and the strength of the substrate is greatly impaired depending on the size and shape of the processing mark.
[0010]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-143972
[Problems to be solved by the invention]
The present invention provides a magnetic recording medium including a magnetic recording medium substrate and a recording layer that have good adhesion that can withstand planarization such as polishing in film formation on a nonmagnetic substrate and can be made thicker. The purpose is to do.
[0012]
[Means for Solving the Problems]
The inventors of the present invention have achieved the above object as a result of intensive research on a magnetic recording medium substrate having a close adhesion to a nonmagnetic substrate, a soft magnetic layer, and a magnetic recording medium including a recording layer. A magnetic recording medium substrate comprising a nonmagnetic substrate, a base plating layer on the nonmagnetic substrate, and a soft magnetic layer on the base plating layer, the base plating layer and the soft magnetic layer It has been found that it is effective to include a non-magnetic intermediate layer. Further, it has been found that it is effective that the nonmagnetic intermediate layer is a Ni-P layer. Furthermore, it has been found that the nonmagnetic intermediate layer is preferably a Cu layer or a Pd layer. Further, the surface of the nonmagnetic intermediate layer has a mean square roughness (Rms) of 0.1 nm to 1 nm and a thickness of 10 nm to 500 nm, and further, the underplating layer, the nonmagnetic intermediate layer, and the soft layer. It is preferable that the magnetic layer is formed by wet plating, and the 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. It was.
[0013]
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.
[0015]
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 may be formed at the segregation site on the substrate surface during the formation of the base plating layer, making it impossible to achieve the base plating layer structure. is there.
[0016]
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.
[0017]
After performing such an etching treatment, one or more metal ions selected from the group consisting of Ag, Co, Cu, Ni, Pd, and Pt, or 0.01N or more as an element component using these as main metal ions, Preferably, a highly adhesive plating material is obtained by immersing in a plating solution containing 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 diachloric 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]
The present invention is characterized in that a nonmagnetic intermediate layer is included between the base plating layer and the soft magnetic layer. The thickness of the magnetic intermediate layer is preferably 10 nm or more and 500 nm or less from the viewpoint of magnetic shielding (in the case of a magnetic material) between the base plating layer and the soft magnetic layer, uniform film formation of the soft magnetic layer, and improved adhesion. If it is less than 10 nm, there may be no effect, and if it is more than 500 nm, the medium becomes thick.
The nonmagnetic intermediate layer is not particularly limited as long as it is a nonmagnetic layer, but is preferably selected from the group consisting of a Ni—P layer, a Cu layer, and a Pd layer in terms of adhesion and ease of film formation.
The Ni-P layer is formed, for example, by immersion in a nickel sulfate aqueous solution containing hypophosphorous acid, and the Cu layer is formed, for example, by immersion in a copper sulfate aqueous solution. Further, the Pd layer is formed, for example, by immersion in an aqueous palladium sulfate solution.
[0021]
After forming the nonmagnetic intermediate layer, it is preferable to adjust the surface roughness by polishing.
The square average roughness (Rms) of the surface of the nonmagnetic intermediate layer is preferably 0.1 nm or more and 1 nm or less. It is preferable to set the square average roughness within this range for uniform film formation and adhesion improvement of the soft magnetic film, and if it is smaller than this range, it is not only technically difficult but also the adhesion deteriorates and is large. In particular, the adhesion of the underlying plating layer is deteriorated. The surface mean square roughness (Rms) is the square root of the average of the squares of the deviations from the measurement mean line to the measurement line, and measured with an AFM (Atomic Force Microscope: Atomic Force Microscope). it can.
The polishing is not particularly limited, and may be mechanical polishing or mechanochemical polishing (CMP). CMP is processed while coexisting with chemical polishing with an acidic or alkaline polishing solution, unlike polishing with only a normal polishing slurry. Colloidal alumina or colloidal silica is used as the polishing medium. In particular, CMP using a colloidal polishing medium is suitable as a method for polishing a perpendicular magnetic recording medium because the polishing rate is high and the surface roughness is remarkably improved. This is because the colloidal polishing medium has a very small particle size of 10 to 100 nm, and its shape is almost spherical and can exhibit excellent smoothness. Furthermore, in CMP, the surface is not simply mechanically scraped off, but is polished by a process that dissolves chemically, so even if a fine spherical polishing medium is used, industrially sufficient polishing is possible. Speed can be secured.
[0022]
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.
[0023]
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 nonmagnetic substrate, a base plating layer, a nonmagnetic intermediate 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. According to the present invention, the base plating layer, the nonmagnetic intermediate layer, and the soft magnetic layer are preferably formed by wet plating. By forming these layers using wet plating, the process is easy, the productivity is excellent, the film can be continuously formed while maintaining the activity, and extremely excellent characteristics can be obtained.
[0024]
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 nonmagnetic substrate 1, the base plating layer 2, the intermediate nonmagnetic layer 3 and the soft magnetic layer 4 is provided with a recording layer 5 on the soft magnetic layer 4 to form a magnetic recording medium. be able to. Further, a protective layer 6 and a lubricating layer 7 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.
[0025]
【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 65 mm diameter (100) Si single crystal (P-doped N-type substrate), 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. Subsequently, it was immersed in a 0.1N nickel sulfate aqueous solution containing hypophosphorous acid for 5 minutes to obtain an intermediate layer.
When the surface portion of this material was observed with a transmission electron microscope and AMF, the thickness was 250 nm and Rms was 0.8 nm.
Although a grid-like cut was made at intervals of 5 mm in this base plating film and a peeling test was performed using cello tape (registered trademark), no peeling of the plating film was observed.
[0026]
Example 2
The Si substrate obtained in the same manner as in Example 1 was immersed in a 45% by weight aqueous caustic soda solution at 50 ° C. for 2 minutes to remove the thin surface oxide film on the substrate surface and to etch the surface Si.
Next, a base plating solution was prepared by adding 0.2N ammonium sulfate aqueous solution to 0.2N nickel sulfate aqueous solution, and ammonia water was added to raise the pH of the solution to 8.3. 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 0.2N in total amount), the previously etched Si substrate was used as a base plating bath. It was immersed for 7 minutes to obtain a plating base film. Then, it was immersed in 0.1N copper sulfate aqueous solution for 5 minutes, and the intermediate | middle layer was obtained.
When the surface portion of this material was observed with a transmission electron microscope and AMF, the thickness was 15 nm and Rms was 0.2 nm.
Although a grid-like cut was made at intervals of 5 mm in this base plating film and a peeling test was performed using cello tape (registered trademark), no peeling of the plating film was observed.
[0027]
【The invention's effect】
Providing a substrate for a magnetic recording medium that has a good adhesiveness that can withstand flattening processing such as polishing and can be thickened by including a nonmagnetic intermediate layer between the base plating layer and the soft magnetic layer it can.
[Brief description of the drawings]
FIG. 1 shows an example of a perpendicular magnetic recording type hard disk medium of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Nonmagnetic substrate 2 Base plating layer 3 Intermediate nonmagnetic layer 4 Soft magnetic layer 5 Recording layer 6 Protective layer 7 Lubrication layer

Claims (6)

A method of manufacturing a substrate for a perpendicular magnetic recording medium, comprising: a Si substrate that is a nonmagnetic substrate; a base plating layer on the Si substrate; and a nonmagnetic intermediate layer on the base plating layer, wherein the surface of the Si substrate is After etching in an alkaline aqueous solution, electroless displacement plating is performed, and one or more metal ions selected from the group consisting of Ag, Co, Cu, Ni, Pd and Pt, or the metal ions as main metal ions. And forming a non-magnetic intermediate layer selected from the group consisting of a Ni—P layer, a Cu layer, and a Pd layer on the under plating layer. Manufacturing method . The method for manufacturing a substrate for a perpendicular magnetic recording medium according to claim 1, wherein the electroless displacement plating is performed in a pH range of 7.2 to 12.8 by adding ammonia . 3. The perpendicular magnetic recording medium substrate according to claim 1, wherein the surface of the nonmagnetic intermediate layer has a square average roughness (Rms) of 0.1 nm to 1 nm and a thickness of 10 nm to 500 nm . Manufacturing method . The formation of the primary plating layer, and the formation of the non-magnetic intermediate layer, The method of manufacturing a substrate for a perpendicular magnetic recording medium according to any one of claims 1 to 3 Ru deposition der that by the wet plating. The nonmagnetic intermediate layer, The method of manufacturing a substrate for a perpendicular magnetic recording medium according to any one of claims 1 to 4 forming the soft magnetic layer by wet plating. A method for manufacturing a perpendicular magnetic recording medium, wherein a recording layer is formed on a substrate for a perpendicular magnetic recording medium obtained by using the manufacturing method according to claim 5 .

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