JP2004146032A - Base plate for perpendicular magnetic recording hard disk medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base plate having a soft magnetic lining easy to manufacture, and to provide its manufacturing method. <P>SOLUTION: This base plate of a perpendicular magnetic recording hard disk medium has an Si single crystal base plate (1) which is 65 mm or less in diameter, 1 mm thick or less, and has an average asperity (Rms) of 1 nm or larger but 1000 nm or smaller, a base plating layer (2) which is provided on the base plate and containing at least one out of a group consisting of Ni, Cu, and Ag, and is 1 nm thick or thicker but 300 nm thick or thinner, and a plated soft magnetic layer (3) which is provided on the base plating layer, ≥50 nm and <1000 nm thick and has a coercive force of 20 Oe or less and saturation magnetization of 1T or larger with its average surface asperity (Rms) of ≥0.1 nm and ≤5 nm. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a substrate material used for a substrate hard disk for perpendicular magnetic recording and a method for manufacturing the same.
[0002]
[Prior art]
In the field of magnetic recording, information recording by a hard disk device is indispensable as a primary external recording device of a computer such as a personal computer. The improvement in magnetic recording density of hard disk drives has been remarkable in recent years, and is increasing at a rate of 100% or more per year. The recording density is close to 60 Gbit / inch2 at the research level and reaches 30 Gbit / inch2 at the product level.
[0003]
Such a high recording density is achieved by remarkable improvement in performance of each mechanical element such as an electronic component and software constituting the hard disk device. In particular, this is largely due to the progress of magnetic heads (thin-film heads, MR heads, GMR heads, etc.) for reading / writing recorded information, and correction methods (software) for improving the reliability of read signals. However, there is no particular change in the basic recording system and the device configuration, and the device configuration is based on the horizontal magnetic recording system.
[0004]
However, as the magnetic recording density is improved, the volume of the recording layer per bit for magnetic recording is rapidly reduced. To improve the recording density, it is necessary to improve both the linear recording density in the circumferential direction and the track density in the radial direction. However, in the principle of magnetic recording, there is a problem particularly in the linear recording density. This will be described in detail below.
[0005]
The magnetic recording method is roughly classified into horizontal magnetic recording and perpendicular magnetic recording as schematically shown in FIGS. 1 and 2 according to a method of arranging magnetic unit arrays (bits) for holding information on a recording medium.
Horizontal magnetic recording is a method in which recording is performed so that a magnetic information unit composed of SN magnetic poles is parallel to the plane of a recording medium, and is used for a conventional hard disk medium. On the other hand, perpendicular magnetic recording is a method of performing recording so that the magnetic information unit is perpendicular to the plane of the recording medium, and is widely used for video tapes and the like that require high-density recording.
[0006]
Now, in magnetic recording, when the recording density per unit area is increased, it is naturally necessary to reduce the volume of the magnetic recording unit (bit).
However, from the fundamental problem of magnetic theory, it is known that the ferromagnetic material responsible for recording is not kept stable as far as the volume of the magnetic material expressing it is reduced. . Thermal energy kT (k: Boltzmann constant, T: absolute temperature) at room temperature and anisotropic energy KuV (Ku: anisotropic energy, especially in the case of magnetic recording, crystal magnetic properties in magnetic recording) It is known that due to competition for anisotropic energy (V: unit recording bit volume), when the volume of a magnetic recording unit is extremely small and approaches kT to KuV, the magnetization state of the ferromagnetic material becomes unstable even at room temperature. ing. When the magnetization volume per bit is extremely small as described above, a state in which the ferromagnetic material becomes like a paramagnetic material is called superparamagnetism. It is known that there is a critical dimension (critical volume) at which the magnetic recording material becomes superparamagnetic, depending on the magnetic recording material.
[0007]
In actual magnetic recording, if the recording unit volume is reduced to a value close to the critical dimension by increasing the recording density, the problem becomes apparent before superparamagnetism is reached. The magnetization state of the ferromagnetic state subjected to the magnetic recording is attenuated with time in a relatively short time, and the magnetic azimuth is oriented in a random direction, thereby altering the magnetic recording information (the S / N ratio of the signal read from the magnetic head is reduced). Problem). When such a phenomenon occurs in magnetic recording, after a certain period of time, the recorded information written cannot be read or cannot be written. Such attenuation of recording bits due to superparamagnetism has become a very serious problem in recent years as a "thermal fluctuation" problem, which determines the magnetic recording limit.
In conventional horizontal magnetic recording, it is not clear how far the recording limit caused by thermal fluctuations is. However, in the case of a hard disk medium, it is converted to a recording density, and it may be around 100 Gbit / inch2. It is considered.
[0008]
As a method of overcoming the recording limit due to the thermal fluctuation of the conventional horizontal magnetic recording hard disk medium, various new recording methods have been proposed. Perpendicular magnetic recording is considered to be the most promising. In perpendicular magnetic recording, the magnetic field from an adjacent bit is in the same direction as the magnetization direction, and is in a direction that helps the stability of the recorded magnetization bit. In other words, a closed magnetic path is formed between adjacent bits, the self-demagnetizing field (hereinafter, referred to as demagnetizing field) due to its own magnetization is smaller than in horizontal magnetic recording, and the magnetization state is stable. . On the other hand, in horizontal magnetic recording, as the linear recording density increases, the adjacent recording bits become closer and the demagnetizing field increases. In order to further increase the linear recording density, it is necessary to make the recording layer extremely thin so that the magnetization rotation mode does not occur inside the magnetic recording layer. In horizontal magnetic recording, the recording bit volume decreases three-dimensionally as the recording density increases. With respect to the magnetic film thickness, it is not necessary to reduce the magnetic film thickness in perpendicular magnetic recording as the recording density increases. From these points, it can be said that perpendicular magnetic recording is a recording method in which the demagnetizing field can be reduced and the value of KuV can be secured, so that the stability against magnetization due to thermal fluctuation is large, and the recording limit can be greatly expanded. As a recording medium, it has a high affinity with a horizontal recording medium, and writing and reading of magnetic recording can be basically performed using the same technology as that used conventionally.
[0009]
However, in detail, there are some items that hinder the practical use of perpendicular magnetic recording. One of them is the configuration of the magnetic medium. FIG. 2 is a cross-sectional view of a schematic film configuration of a horizontal magnetic recording medium, and FIG. In the horizontal magnetic recording medium of FIG. 2, a nonmagnetic underlayer 103 having a thickness of 20 to 30 nm and a recording layer 104 having a thickness of 20 to 30 nm are formed on a substrate 101. In the perpendicular magnetic recording medium of FIG. 3, a soft magnetic layer 105 having a thickness of 100 to 500 nm and a recording layer 104 having a thickness of 20 to 30 nm are formed on a substrate 101.
As a substrate for horizontal magnetic recording, a substrate mainly made of an Al-Mg alloy substrate plated with NiP is used for 3.5 inches, and a glass substrate is mainly used for 2.5 inches. . A non-magnetic base film (mainly Cr or Cr alloy), a recording film (mainly Co-Cr alloy), a protective film (mainly DLC: diamond-like carbon), a lubricating film, etc. are formed on the substrate. .
[0010]
In practice, it is often practiced to provide one or more buffer layers between a substrate and a base film or between a base film and a recording film. As a typical film thickness configuration, the base film is about 30 nm and the recording film is about 20 nm at about 20 Gbit / inch2.
[0011]
On the other hand, in a perpendicular magnetic recording medium, a soft magnetic backing layer (typically, permalloy or the like) and a recording film (a CoCr-based alloy, a PtCo layer, and an ultra-thin film of Pd and Co are alternately laminated on the substrate in several layers) , A SmCo amorphous film or the like as a candidate material), a protective film, a lubricating film or the like. The most significant difference between the horizontal magnetic recording medium and the perpendicular magnetic recording medium is the composition of the former Cr-based nonmagnetic underlayer, the latter soft magnetic underlayer, and the recording layer. In particular, the backing layer in a perpendicular recording medium needs to be soft magnetic and have a thickness of about 100 nm to 500 nm. The soft magnetic underlayer serves as a path for the magnetic flux from the upper recording film and also for the 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 relatively thick as compared with the film on the horizontal recording medium as described above.
[0012]
Forming a soft magnetic underlayer on a perpendicular recording medium is not as easy as forming a nonmagnetic Cr-based underlayer on a horizontal recording medium.
Usually, all the constituent films of the horizontal recording medium are formed by a dry process (mainly magnetron sputtering). Even in a perpendicular recording medium, film formation by a dry process is a natural flow.
However, there is a problem in sputter deposition of a soft magnetic underlayer in a perpendicular recording medium. Magnetron sputtering is a physical vapor deposition process widely used for forming not only magnetic recording media but also metal thin films. In this method, a target is placed in a thin inert gas atmosphere, and a target atom is physically formed by applying a high frequency between the electrodes and treating the target atoms with an electrode placed in the vicinity or the target itself as one of the electrodes. It is intended to form a film by skipping. In order to increase the deposition rate, it is common practice to arrange a permanent magnet magnetic circuit on the back surface of the target material and increase the plasma density by magnetic force leaking to the front surface. However, many problems arise when an attempt is made to form a soft magnetic layer for perpendicular magnetic recording by the magnetron sputtering method. Since the target is soft magnetic, a large part of the magnetic flux generated from the magnetic circuit passes through the inside of the target and hardly leaks to the outside of the target surface. If the leakage of the magnetic flux is small, the generated plasma becomes weak and unstable, and it is not possible to sufficiently secure the film forming speed of sputtering. Also, the target is sputtered preferentially from the magnetic flux leakage portion, but the sputtered portion has a magnetic flux originally passing through the target, so the magnetic flux leakage increases from the peripheral portion, and the leaked portion is spattered more and more. Uneven wear of the digging target occurs. That is, in magnetron sputtering of a soft magnetic target, the sputtered portion is worn in a V-groove shape, and the backing plate is exposed in a relatively short time, so that the target life is shortened. On the other hand, if a thin target is used to increase magnetic flux leakage on the target, the target has a short life and needs to be replaced frequently. If the thickness of the target is increased in order to prolong the life of the target, most of the magnetic flux from the bottom magnetic circuit passes through the target and almost no external leakage of the magnetic flux occurs. Since the leakage magnetic field cannot be increased and local spatter is likely to occur, a thick film cannot be formed on the apparatus surface unless the sputtering vacuum chamber is increased. Further, uneven wear of the target also affects the uniformity of the thickness of the formed film and the uniformity of the alloy composition. On the other hand, since the recording layer formed on the soft magnetic backing film is relatively thin, it can be formed without any problem by a dry process or any process. As described above, the formation of the soft magnetic backing film on the perpendicular recording medium has a serious problem in terms of mass productivity and productivity even though it can be done in principle by a conventional sputtering method.
[0013]
[Patent Document 1]
Japanese Patent Publication No. 1-404848
[Patent Document 2]
Japanese Patent Publication No. 2-41089
[Patent Document 3]
Japanese Patent Publication No. 2-59523
[Patent Document 4]
Japanese Patent Publication No. 1-445140
[Patent Document 5]
JP-A-57-105826
[Patent Document 6]
JP-A-6-68463
[Patent Document 7]
JP-A-6-28655
[Patent Document 8]
JP-A-4-259908
[0014]
[Problems to be solved by the invention]
The present invention, in view of such a conventional film forming method and substrate configuration, proposes a substrate having a soft magnetic backing film that can be easily manufactured and a method of manufacturing the same.
[0015]
[Means for Solving the Problems]
The present invention forms a base layer and a soft magnetic metal layer having good adhesion and magnetic properties on a single crystal Si substrate, and further smoothes the substrate surface by polishing to have a good metal surface and a magnetic property. An object of the present invention is to obtain a hard disk substrate for perpendicular magnetic recording excellent in productivity. That is, a hard disk substrate is provided, in which a soft magnetic magnetic film is formed on a substrate using a Si single crystal by a wet process.
[0016]
FIG. 1 shows a cross-sectional view of a schematic film configuration of the perpendicular magnetic recording medium of the present invention.
The present invention provides a Si single crystal substrate 1 having a diameter of 65 mm or less, a thickness of 1 mm or less, and a surface average roughness (Rms) of 1 nm or more and 1000 nm or less, and Ni and / or 300 nm or less of thickness provided on the substrate. A base plating layer 2 containing Cu and / or Ag; and a plating soft magnetic layer 3 having a thickness of 50 nm or more and less than 1000 nm, a coercive force of 20 Oe (= 20 Oe) and a saturation magnetization of 1 T or more provided on the base plating layer. A medium substrate for a perpendicular magnetic recording hard disk, wherein the plated soft magnetic layer has a surface average roughness (Rms) of 0.1 nm or more and 5 nm or less. Further, the present invention provides a step of subjecting a single-crystal Si substrate having a diameter of 65 mm or less, a thickness of 1 mm or less and a surface average roughness (Rms) of 1 nm to 1000 nm to a base plating containing Ni and / or Cu and / or Ag. And a step of providing a plated soft magnetic layer having a coercive force of 20 Oe or less and a saturation magnetization of 1 T or more, and a step of polishing the plated soft magnetic layer to have a surface average roughness (Rms) of 0.1 nm or more and 5 nm or less. And a method for manufacturing a medium substrate for a perpendicular magnetic recording hard disk.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
In the present invention, a Si single crystal substrate is selected as the substrate. The Si single crystal substrate has excellent rigidity, good surface smoothness, very stable surface state, and is excellent as a magnetic recording substrate having a high recording density. The use of a Si substrate as a magnetic recording substrate is already known and various proposals have been made. For example, there are Patent Documents 1 to 8 and the like. Among these, a recording medium in which a recording layer is formed after forming an underlayer on a Si single crystal substrate is also disclosed (Patent Document 2). It is known to use a Si single crystal as a substrate for a horizontal magnetic recording medium as described above. However, as described above, the problem of thermal fluctuation cannot be solved because the substrate is a horizontal magnetic recording medium.
The present invention has been made for a substrate related to perpendicular magnetic recording, particularly for the purpose of improving thermal fluctuation.
[0018]
The Si single crystal substrate used in the present invention is intended for a substrate having a diameter of 65 mm or less and a thickness of 1 mm or less, and is intended for a small-diameter HDD. If the diameter exceeds 65 mm, the material cost ratio of the Si single crystal may be too high, which is not preferable as a recording medium substrate. When used for a substrate having a size of 65 mm or less, the Si substrate has high rigidity, so that even if it is thin, vibration is small, and it is suitable for mobile applications. On the other hand, if the thickness exceeds 1 mm, it becomes technically difficult to make the thickness variation of each part of the substrate due to polishing undesirably technical. The minimum size is desirably 15 mm or more in terms of the difficulty in manufacturing parts and the cost in relation to other parts constituting the hard disk drive. The lower limit of the thickness is preferably 0.1 mm. The thickness is more preferably 0.3 to 0.7 mm.
[0019]
The Si single crystal substrate used in the present invention preferably has a surface square average roughness (Rms) of 1 nm or more and 1000 nm or less. Here, Rms is a stage before plating. If it is less than 1 nm, the adhesion of the underlying plating layer provided on the substrate may be insufficient, and if it exceeds 1000 nm, the surface smoothness required for the hard disk may not be obtained. The surface average roughness (Rms) is a square root of a value obtained by averaging the squares of deviations from the measurement average line to the measurement line, and can be measured by AFM (atomic force microscopy: atomic force microscope).
[0020]
As described in the section of the prior art, the present inventors have considered that there is a problem in that all of the film formation for perpendicular recording is particularly performed by a dry process. Generally, molding and surface processing of a hard disk substrate material are polishing, that is, a wet process. Therefore, the process up to the soft magnetic backing layer is considered as a part of the substrate, the soft magnetic backing layer is formed by a wet process (electroplating, electroless plating, etc.), and the smoothness is ensured by mechano-chemical polishing (CMP). Were studied diligently.
When the formation of the underlayer, the wet film formation of the soft magnetic layer, and the subsequent smoothing process are regarded as a part of the substrate processing, the present invention is very compatible with the conventional substrate manufacturing process.
[0021]
Another reason for selecting a Si single crystal substrate as a substrate is that, in wet film formation (plating film formation), a film can be formed stably regardless of whether the pH value of the bath is acidic or alkaline. This is because, in the plating film formation in which the interaction with the substrate interface becomes a problem, extremely excellent uniformity of adhesion is obtained, so that a high quality soft magnetic underlayer can be formed.
[0022]
Since the surface of the hard disk medium is frequently subjected to an impact due to the striking of the head called a head slap at the time of its use, simply forming the soft magnetic backing layer by a wet method has poor adhesion and easily peels off at the time of use. Furthermore, in the present invention, it is necessary to perform CMP polishing after plating in order to ensure the smoothness of the surface, but there is a problem that the plating film is peeled off during the polishing in plating with poor adhesion.
The present inventors have studied to improve the adhesion between the Si substrate and the soft magnetic film, and a plating film having good adhesion can be formed by performing appropriate plating treatment and pre-plating treatment. It has been found that a smooth medium can be obtained by polishing this.
[0023]
The present invention is characterized in that a base plating layer is formed between the Si substrate and the soft magnetic metal layer in order to enhance the adhesion between the Si substrate and the soft magnetic metal layer and the above-described breaking strength. .
In the present invention, a layer having good adhesion can be formed between the Si substrate and the magnetic plating film by performing the pretreatment and the base plating.
[0024]
In the present invention, as long as the substrate has been subjected to a predetermined pretreatment, the subsequent plating of the underlying plating may be electrolytic plating or electroless plating. As the base plating, it is preferable to form a film with one or more metals (including alloys) selected from a group consisting of Ni, Cu and Ag, and more preferably with Ni and / or Cu. In other words, electroless plating is preferable because the plating conditions are hardly influenced by the electrical characteristics of the Si substrate.
As a method of manufacturing the base plating layer, for example, 0.02 to 1N ammonium chloride is added to 0.01 to 0.5N nickel sulfate. At this time, the pH is adjusted to 8 to 10 and plating is performed at a temperature of 75 to 90 ° C. The base plating layer may be formed by another method, and the plating layer may be formed of one or more metals (including alloys) selected from Ni, Cu, and Ag, and preferably Ni or Cu is used. .
The thickness of the base plating layer is preferably 1 nm or more and 300 nm or less. If the thickness is less than 1 nm, the substrate surface may not be uniformly coated. If the thickness exceeds 300 nm, crystals of the base film may be enlarged. It is.
[0025]
The present inventors have studied a method of removing an oxide film naturally formed on the surface of a Si single crystal wafer from the viewpoint of improving adhesion, and before applying a base plating on the surface of the Si substrate, preferably under a specific condition. In addition to the removal of the oxide film, the surface of the substrate is etched to form appropriate irregularities that improve the adhesion of the plated film to the substrate surface. In addition, a transition layer made of Si-Ni-O is formed. It has been found that the adhesiveness of the magnetic film on the Si substrate is significantly improved by being formed between the Si substrate and the underlayer.
[0026]
In the present invention, in the pre-plating process, wet etching with an acid or an alkali is used as the etching of the Si substrate surface. It is possible to use both etching of acid and alkali together, but in this case, it is desirable to carry out acid treatment after alkali treatment. By this plating pretreatment, the square average roughness (Rms) of the Si single crystal substrate is preferably set to 1 nm or more and 1000 nm or less.
[0027]
Specifically, in the etching using an acid, the substrate is immersed in an aqueous solution selected from at least one of hydrofluoric acid, hydrochloric acid, and nitric acid.
As the conditions for the etching solution, a concentration of 2 to 10% by weight for a hydrofluoric acid aqueous solution, 5 to 30% by weight for a nitric acid aqueous solution, and 2 to 15% by weight for a hydrochloric acid aqueous solution is preferable.
[0028]
In addition, as the etching with alkali, it is immersed in an aqueous solution selected from at least one of NaOH, KOH and ammonia.
In particular, as the alkali, an aqueous solution in which 0.3 to 10% by weight of ammonia and 0.5 to 25% by weight of hydrogen peroxide are mixed at a weight ratio of a pure substance of 2: 1 to 1: 2, or 2 to 50% It is preferred to treat with a weight% aqueous sodium hydroxide solution.
The treatment can be carried out by immersion at 10 ° C. to the boiling point of the solution for 30 seconds to 1 hour. In the case of acid treatment, the electrode is electrolytically etched at 1 to 20 mA / cm 2 for 1 second to 1 minute. Is also good.
[0029]
The soft magnetic backing layer formed on the Si single crystal substrate may have various alloy compositions. In order to have good soft magnetic properties (low coercive force Hc value), it is desirable to use an alloy in which the values of the magnetocrystalline anisotropy Ku and the magnetostriction λu simultaneously satisfy zero. With respect to the saturation magnetization (Bs), a material having a high magnetic permeability such as 1 T or more, particularly preferably a permalloy of 45 mol% Ni and 55 mol% Fe, having Bs of about 1.5 T is suitable. Other soft magnetic layer materials that can be used in the present invention include permalloy (NiFe-based alloys), CoNi-based alloys, CoFe-based alloys, and CoFeNi-based alloys that can be formed by a wet process and have soft magnetism. . Further, from the viewpoint of magnetic force, an alloy composition that can achieve such high saturation magnetization and low coercive force characteristics is desirable. The CoFeNi-based alloy shows a relatively high magnetization Bs, but at the same time, a low Hc can be realized if there is a condition that both Ku and λs take “0” or a value close thereto. In particular, the CoFeNi-based alloy thin film formed by electrolytic plating reported by Osaka et al. Has a fine structure and can achieve both saturation magnetization of about 2T and soft magnetic properties of Hc <20e or less. It is considered to be one of the very preferred materials. For example, T. Osaka et al., Nature 387, (1998), 796; Ohashi et al., IEEE Trans. Mag. 35, (1999), 2538; Ohashi et al., IEEE Trans. Mag. 34, (1998), 1462.
[0030]
In addition, FeTaC films and Co-based amorphous films are also candidate materials for the backing film. However, since these films are formed by a dry process such as sputtering, they may not belong to the scope of the present invention. It is desirable to use an alloy capable of forming a film by a wet process to conform to the present invention.
[0031]
The reason why the magnetic permeability of the soft magnetic layer is set to 1 T or more is to meet the limitation of the film thickness for the above-mentioned reason. When a material having Bs of less than 1T is used, it is necessary to increase the film thickness in order to obtain the required performance as the soft magnetic underlayer. In general, when forming a thick metal layer regardless of a wet type or a dry type, grains in the metal layer structure grow as the film thickness increases. In magnetic recording, in order to improve the S / N ratio, it is extremely important to suppress the enlargement of the crystal grain boundaries of the recording layer and the soft magnetic underlayer serving as a magnetic path during recording and reproduction. In the wet process of the present invention, when the thickness of the soft magnetic film exceeds 1000 nm, grain growth remarkably proceeds. Further, since the particle size distribution of the microstructure in the soft magnetic film is also widened and the non-uniformity of the particle size is increased, the film thickness is set to 50 to 1000 nm.
[0032]
As for the coercive force (Hc), if the value exceeds 20 Oe, the magnetic flux generated from the head at the time of writing becomes a great hindrance when passing through the soft magnetic layer, and as a result, the S / N ratio when the medium is used is reduced. It is known that it greatly decreases. In the present invention, based on such knowledge, the upper limit of the coercive force is specified to be 200 e or less as a requirement for defining the soft magnetic underlayer. Preferably it is 5 Oe or less.
[0033]
When forming a soft magnetic film by electroplating on a Si single crystal substrate, in order to form a strong chemical bond, the metal ions in the plating solution are formed from the surface of the single crystal Si substrate when forming the metal base film. It is necessary to send and receive electrons directly. In the case of performing electroplating film formation, it is preferable to use a material having N polarity, which is doped with impurities and contains a hyperelectron pair inside, rather than an intrinsic semiconductor Si single crystal. When a soft magnetic film is formed by electroless plating, the Si substrate may be an N-type, a P-type, or a non-doped intrinsic single crystal.
[0034]
The soft magnetic film is formed, for example, by using 0.001 to 0.1 N of DMAB (dimethylamine borane), 0.002 to 0.2 N of nickel sulfate, 0.002 to 0.2 N of iron sulfate, and 0.01 to 0.1 N of iron sulfate. Using 1N cobalt sulfate or the like, saccharin or the like as a brightener, tartaric acid, citric acid, EDTA or the like as a chelating agent, mercapol benzodiazothiazole as a stress relieving agent, etc., and appropriately adjusting the pH to 6 to 13. The film can be formed at a temperature of 55 to 75 ° C.
[0035]
The surface roughness of a soft magnetic film formed on a Si single crystal substrate by a wet process is not very good depending on the film thickness. The surface roughness on the film surface by the wet process is ensured by polishing the backing film surface by polishing. Polishing can be performed by either mechanical polishing or CMP polishing. The CMP process is different from polishing using only a normal polishing slurry while performing chemical polishing using an acidic or alkaline polishing solution. Colloidal alumina or colloidal silica is used as the polishing medium. In particular, CMP polishing using a colloidal polishing medium is suitable as a method for polishing a soft magnetic film for perpendicular magnetic recording because the polishing rate is high and the surface roughness is significantly improved. This is because the colloidal polishing medium has a very small particle size of 10 to 100 nm and can realize excellent smoothness due to its spherical shape. Furthermore, in CMP polishing, the surface is not simply mechanically scraped off, but is polished by a process that dissolves chemically. Therefore, even if a minute spherical polishing medium is used, it is industrially sufficient. Polishing speed can be secured.
[0036]
The type of polishing slurry and the pH value vary depending on the alloy composition of the material to be polished (the soft magnetic backing thin film in the present invention). For example, in the case of a CoFeNi film, the polishing slurry is desirably an alkali side having a pH of 10 or more, whereas in the case of a permalloy film, the pH value is preferably set to an acidic side from the viewpoint of a chemical etching action.
Polishing conditions are optimized so that each alloy composition film has good surface roughness. Parameters that affect polishing include the type and size of machine, polishing slurry (abrasive material, pH value, liquid temperature), buff, rotation speed, and the like, and need to be optimized in consideration of each.
[0037]
The present invention relates to a hard disk underlayer for high-density recording, and the smoothness after polishing is 0.1 to 5 nm, particularly preferably 0 to 5 nm, in terms of average surface roughness Ra or square average roughness Rms. It is desirable to polish to a thickness of 0.1 to 0.5 nm. If the thickness is set to 0.1 nm or less, the multi-stage CMP and the condition range become too severe, which is not preferable. If the thickness is 5 nm or more, the surface roughness of the recording film placed on the backing film is adversely affected. The average surface roughness (Ra) is the average of the absolute value deviation from the measurement average line to the measurement line, and the square average roughness (Rms) is the average of the square of the deviation from the measurement average line to the measurement line. Is the square root. These can be measured by AFM.
[0038]
The substrate whose smoothness has been improved by the CMP polishing is cleaned by removing particles adhering to the surface by means such as brush cleaning.
[0039]
Although it is possible to use ordinary mechanical polishing or the like using an oxide slurry used in glass polishing, the polishing rate is low as described above or multi-stage polishing is required to obtain a good polished surface. Therefore, CMP is more desirable. By using an Si single crystal substrate of the present invention that guarantees smoothness of the backing film for CMP, alloy-based recording films or multilayer films of various compositions can be formed on the substrate to provide excellent perpendicular magnetic recording. It can be used as a medium.
[0040]
【Example】
Example 1
A (100) Si single crystal (P-doped N-type substrate) having a diameter of 65 mm, which has been subjected to coring, centering and lapping, from a 200 mm Si single crystal substrate manufactured by the CZ (Chocolarski) method, is a colloid having an average particle size of 95 nm. Both surfaces were polished with silica and smoothed to a surface average roughness (Rms) of 5 nm (measured by AFM (atomic force microscope)). This substrate was immersed and etched for 15 minutes in an aqueous solution having a concentration of 5% by weight by mixing a saturated aqueous hydrogen peroxide solution with a 28% by weight aqueous ammonia solution at 60 ° C. to remove a thin surface oxide film on the substrate surface. . This substrate was subjected to electroless plating in a plating solution at 80 ° C. adjusted to pH 8 by appropriately adding ammonium chloride to a 0.1N aqueous solution of nickel sulfate and a 0.1N aqueous solution of sodium tartrate, and the surface was coated with a Ni plating film to a thickness of 100 nm. Thereafter, a CoNiFe soft magnetic film having a thickness of about 1000 nm was formed as a soft magnetic layer. The plating was performed by using an ammonium chloride bath containing mainly Co, Ni, and Fe at 80 ° C. and a pH of 9 and using diphosphoric acid as a reducing agent and adding saccharin and the like as a brightening agent and a stress relaxing agent as appropriate. .
When the constituent elements were analyzed by the EPMA wavelength dispersion method after the film formation, the composition was approximately 15 mol% Ni, 75 mol% Fe, and 10 mol% Co. When the magnetic properties were measured with a VSM (sample vibrating magnetometer: vibrating sample magnetometer), soft magnetism was exhibited with a low coercive force of Bs: 1.9 T and iHc: 150 e. The substrate with the soft magnetic film after film formation was coated with a polishing pad of 700 mm in diameter with a polishing plate of 700 mm in diameter while applying a pressure of 180 gf / cm 2 with a polishing liquid containing colloidal silica having an average particle diameter of 80 nm at a liquid temperature of 30 ° C. Then, the soft magnetic film was polished for 400 minutes to a thickness of about 400 nm. The polished surface was measured by AFM and found to have an Rms of 0.6 nm, which was almost flat over the entire surface of the substrate.
The surface of the substrate is coated with a 20 nm diamond-like carbon (DLC) protective film by magnetron sputtering in order to confirm the adhesion of the plating film, and then incorporated into a 2.5 inch hard disk unit MK-4313MAT of Toshiba Corporation. A durability test (head slap test) in which a shock of 750 G was applied by SM-105MP from AVEX in a state of being in close contact with each other was performed. After the test, the substrate surface was observed with a 30-fold optical microscope. As a result, collision traces were confirmed, but no peeling of the plated film was observed.
[0041]
Example 2
A (100) Si single crystal (P-doped N-type substrate) having a diameter of 65 mm, which has been subjected to coring, centering, and lapping from a 200 mm Si single crystal substrate manufactured by the CZ method, is made of colloidal silica (average particle diameter 95 nm) on both surfaces. It was polished and smoothed to a surface average roughness (Rms) of 0.4 nm (measured by AFM). This substrate was immersed and etched in an aqueous solution of caustic soda at 50 to 80 ° C. and 20 to 40% by weight for 5 to 15 minutes to remove a thin surface oxide film on the substrate surface and roughen the surface roughness Rms to 1 to 15 nm. . Substrates having four types of Rms values of about 1 nm, 4 nm, 10 nm, and 15 nm were manufactured. This substrate was subjected to electroless plating in a plating solution at 80 ° C. adjusted to pH 9 by appropriately adding sodium hydroxide to a 0.1N aqueous solution of nickel sulfate and a 0.1N aqueous solution of sodium tartrate, and the surface was coated with a Ni plating film to a thickness of 150 nm. . Thereafter, a CoNiFe soft magnetic film having a thickness of about 1000 nm was formed as a soft magnetic layer. The plating was carried out in an ammonium chloride bath containing mainly Co, Ni, and Fe at 80 ° C. and pH 9, using diphosphoric acid as a reducing agent, and adding a gloss material and a saccharin or the like as a stress relaxing agent as appropriate. .
The constituent elements were analyzed by a wavelength dispersion method of EPMA after film formation on each of them. As a result, the composition was approximately 60 mol% Co, 10 mol% Ni and 30 mol% Fe. When the magnetic properties were measured by VSM, it showed soft magnetism with a low coercive force of Bs: 1.9 T and iHc: 2 Oe.
A substrate with a soft magnetic film after film formation was coated with a nonwoven fabric at a pH of 11 and a polishing liquid containing colloidal silica having an average particle size of 80 nm at a liquid temperature of 30 ° C. and a pressure of 180 gf / cm 2. Polishing was performed for 6 minutes using a polishing machine to make the soft magnetic film approximately 400 nm thick. When the surface after polishing was measured by AFM, Rms was 0.6 nm, and the surface was almost flattened over the front surface of the substrate.
In order to confirm the adhesion of the plating film, each substrate surface was coated with a 20 nm diamond-like carbon (DLC) protective film by magnetron sputtering, and then incorporated into Toshiba Corporation 2.5 inch hard disk unit MK-4313MAT. A durability test (head slap test) in which a shock of 750 G was applied by SM-105MP from AVEX in a state of being in close contact with the substrate was performed. After the test, when the substrate surface was observed with a 30-fold optical microscope, collision marks were confirmed on any of the substrate surfaces, but no peeling of the plating film was observed at all.
[0042]
Example 3
A (100) Si single crystal (P-doped N-type substrate) having a diameter of 65 mm, which has been subjected to coring, centering, and lapping from a 200 mm Si single crystal substrate manufactured by the CZ method, is made of colloidal silica (average particle diameter 95 nm) on both surfaces. It was polished and smoothed to a surface roughness (Rms) of 0.4 nm (measured by AFM). This substrate is immersed in a 4% by weight HF aqueous solution at 18 ° C. for 1 minute, and energized (5 mA / cm 2) for 10 seconds to remove a thin surface oxide film on the substrate surface by anodic oxidation and to reduce the surface roughness Rms to 12 nm. Roughened. The substrate was subjected to electroless plating in a plating solution at 80 ° C. adjusted to pH 8 by appropriately adding sodium hydroxide to a 0.09 N nickel sulfate aqueous solution, a 0.01 N copper sulfate aqueous solution, and a 0.1 N sodium citrate aqueous solution. To a thickness of 180 nm. Thereafter, a CoNiFe soft magnetic film having a thickness of about 1000 nm was formed as a soft magnetic layer. Plating was performed using an ammonium chloride bath containing mainly Co, Ni, and Fe at 80 ° C. and pH 9, using dimethylamine borane as a reducing agent, and adding a gloss material and a saccharin or the like as a stress relaxing agent as appropriate. .
When the constituent elements were analyzed by the EPMA wavelength dispersion method after the film formation, the composition was approximately 60 mol% Co, 10 mol% Ni, and 30 mol% Fe. When the magnetic properties were measured by VSM, it showed soft magnetism with a low coercive force of Bs: 1.9 T and iHc: 2 Oe.
The substrate with the soft magnetic film after film formation was coated with a polishing pad of 700 mm in diameter with a polishing plate of 700 mm in diameter while applying a pressure of 180 gf / cm 2 with a polishing liquid containing colloidal silica having an average particle diameter of 80 nm at a liquid temperature of 30 ° C. Then, the soft magnetic film was polished for 400 minutes to a thickness of about 400 nm. When the surface after polishing was measured by AFM, Rms was 0.6 nm, and the surface was almost flattened over the front surface of the substrate.
The surface of the substrate is coated with a 20 nm diamond-like carbon (DLC) protective film by magnetron sputtering in order to confirm the adhesion of the plating film, and then incorporated into a 2.5 inch hard disk unit MK-4313MAT of Toshiba Corporation. A durability test (head slap test) in which a shock of 750 G was applied by SM-105MP from AVEX in a state of being in close contact with each other was performed. After the test, the substrate surface was observed with a 30-fold optical microscope. As a result, collision traces were confirmed, but no peeling of the plated film was observed.
[0043]
As a perpendicular recording medium substrate, a good soft magnetic film could be formed by a wet process, and good soft magnetic characteristics and flatness of the soft magnetic film could be realized. A substrate suitable for a perpendicular magnetic recording medium can be provided.
[0044]
【The invention's effect】
According to the present invention, it is possible to easily form a thick soft magnetic backing film on a Si single crystal substrate, and it is possible to provide a good Si single crystal substrate for perpendicular magnetic recording while ensuring surface roughness. Become.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a schematic film configuration of a perpendicular magnetic recording medium of the present invention, in which arrows indicate magnetization directions.
FIG. 2 is a cross-sectional view of a schematic film configuration of a conventional horizontal magnetic recording medium, and arrows indicate magnetization directions.
FIG. 3 is a cross-sectional view of a schematic film configuration of a conventional perpendicular magnetic recording medium, and arrows indicate magnetization directions.
[Explanation of symbols]
1 Si single crystal substrate
2 Base plating layer
3 Soft magnetic layer
101 substrate
103 Underlayer
104 recording layer
105 Soft magnetic layer

Claims (8)

A Si single crystal substrate having a diameter of 65 mm or less, a thickness of 1 mm or less, and a surface average roughness (Rms) of 1 nm or more and 1000 nm or less, and one or more selected from the group consisting of Ni, Cu, and Ag provided on the substrate. An underlying plating layer having a thickness of 1 nm or more and 300 nm or less, and a plating soft magnetic layer provided on the underlying plating layer with a thickness of 50 nm or more and less than 1000 nm and a coercive force of 20 ° Oe or less and a saturation magnetization of 1 T or more. A medium substrate for a perpendicular magnetic recording hard disk, wherein a surface average roughness (Rms) of a magnetic layer is 0.1 nm or more and 5 nm or less. Applying a base plating containing at least one selected from the group consisting of Ni, Cu and Ag on a Si single crystal substrate having a diameter of 65 mm or less, a thickness of 1 mm or less and a surface average roughness (Rms) of 1 nm or more and 1000 nm or less; Providing a plated soft magnetic layer having a coercive force of 20 ° Oe or less and a saturation magnetization of 1 T or more on the base plating layer, and polishing the plated soft magnetic layer to have a surface average roughness (Rms) of 0.1 nm or more and 5 nm or less. And a method of manufacturing a medium substrate for a perpendicular magnetic recording hard disk. 3. The method for manufacturing a medium substrate for a perpendicular magnetic recording hard disk according to claim 2, wherein the Si single crystal substrate before the underplating is obtained by a plating pretreatment step of etching the Si single crystal substrate. 4. The method for manufacturing a medium substrate for a perpendicular magnetic recording hard disk according to claim 2, wherein the step of applying the base plating is electroless plating. The method for manufacturing a medium substrate for a perpendicular magnetic recording hard disk according to any one of claims 2 to 4, wherein the plating pretreatment step is chemical etching of the Si single crystal substrate. The medium substrate for a perpendicular magnetic recording hard disk according to any one of claims 3 to 5, wherein the plating pretreatment step is an etching treatment with at least one kind of an alkaline aqueous solution selected from the group consisting of NaOH, KOH, and ammonia. Manufacturing method. The medium for a perpendicular magnetic recording hard disk according to any one of claims 3 to 5, wherein the plating pretreatment step is an etching treatment with at least one kind of an acidic aqueous solution selected from the group consisting of hydrofluoric acid, hydrochloric acid, and nitric acid. Substrate manufacturing method. The method for manufacturing a medium substrate for a perpendicular magnetic recording hard disk according to claim 2, further comprising a step of smoothing by polishing after the step of providing the plated soft magnetic layer.

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