JP4333563B2 - Magnetic recording medium and manufacturing method thereof - Google Patents

Description

  The present invention relates to a magnetic recording medium mounted on a fixed magnetic recording device (HDD) and a manufacturing method thereof. More specifically, the present invention relates to an anisotropic magnetic recording medium using a glass-based material substrate.

In so-called longitudinal magnetic recording media in which magnetization is recorded in parallel in the substrate surface, it is common to use the easy magnetization axis of the magnetic layer oriented in the circumferential direction for recording. A magnetic recording medium in which the residual magnetization (Mrc) in the circumferential direction and the residual magnetization (Mrr) in the radial direction are different is called an anisotropic magnetic recording medium. Generally, the larger the ratio Mrc / Mrr is, the more magnetic the medium becomes. The performance of the recording medium is improved. Hereinafter, Mrc / Mrr is expressed as OR-Mrt.
In a magnetic recording medium using an aluminum-based material as a substrate, anisotropy is obtained by forming circumferential grooves called textures on the substrate surface. In general, NiP plating is performed on an aluminum substrate, and texture processing is performed on the surface thereof to form a circumferential groove, and the difference between the residual magnetization in the circumferential direction and the radial direction of the magnetic layer by the groove. Is generated. Texture processing also has a role of preventing the magnetic recording medium and the magnetic head from coming into contact with each other and wearing when the magnetic head floats and seeks on the magnetic recording medium.

On the other hand, a magnetic recording medium using a substrate made of a conventional glass material has a high hardness of the substrate material itself, a small thermal expansion, and can obtain a difference in residual magnetization between the circumferential direction and the radial direction even after texturing. Therefore, so-called isotropic magnetic recording media are common.
In recent years, the density of magnetic recording media has increased, and the bit size, which is the minimum unit of data written to the magnetic recording media, has become smaller. In an isotropic medium using a glass-based substrate, as the bit size decreases, the resolution is lower than that of an anisotropic magnetic recording medium such as an aluminum-based substrate, and the signal-to-noise ratio (SNR) deteriorates. Has become prominent. In order to obtain characteristics equivalent to those of an anisotropic magnetic recording medium with an isotropic magnetic recording medium, it is necessary to increase the product (Mr · t) of the residual magnetization in the circumferential direction and the film thickness. This is because as a result of increasing the thickness, noise due to the magnetic layer increases. For this reason, in the magnetic recording medium using a glass substrate, various ideas for improving the orientation of the magnetic layer have been proposed. For example, it has been proposed to improve the in-plane orientation of the easy axis of the magnetic layer by oxidizing the surface of the underlayer formed on the substrate (see, for example, Patent Document 1). Although this method is effective for a specific underlayer material, it results in deterioration of properties in other materials. In addition, there has been proposed a method of increasing the coercive force in the circumferential direction by inclining crystal grains constituting the magnetic layer with respect to the substrate surface and directing them in the circumferential direction (see, for example, Patent Document 2). . In this method, a special film forming apparatus is required, and the use efficiency of raw materials at the time of sputtering film formation is reduced. In any of the methods proposed so far, the present situation is that sufficient performance is not obtained.
Japanese Patent Laid-Open No. 10-143865 JP 2002-260208 A

  The present invention has been made in view of the above problems, and provides a magnetic recording medium having a high anisotropy and excellent electromagnetic characteristics in a magnetic recording medium using a glass substrate. With the goal.

The present invention provides a magnetic recording medium comprising a glass substrate, a seed layer, and a magnetic layer, wherein the glass substrate is textured, and the seed layer is a first seed layer made of Cr and a second one made of NiNb alloy. A seed layer, a third seed layer made of Cr, and a fourth seed layer made of a NiNb alloy are sequentially stacked.
The texture processing is preferably 25 or more and 60 or less substantially concentric grooves per 1 μm square, and the depth of the substantially concentric grooves is preferably 3 nm or more and 5 nm or less.
Moreover, it is preferable that the NiNb alloy of the second seed layer and the fourth seed layer contains Nb of 30 atomic% or more and 50 atomic% or less.
The first seed layer to the fourth seed layer are preferably amorphous, and are preferably formed by sputtering using a gas obtained by mixing approximately 20% by weight of N ₂ gas with Ar gas.

  By configuring the magnetic recording medium as described above, even in a magnetic recording medium using a glass substrate, it can be an anisotropic magnetic recording medium having high anisotropy, and has excellent magnetic characteristics and electromagnetic conversion characteristics. Can be realized. Furthermore, even in a glass substrate having an insulating property, it is possible to use a film forming method in which a bias is applied in the film forming process of each layer.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a configuration example of a magnetic recording medium of the present invention. In the magnetic recording medium, a seed layer 2, an underlayer 3, a magnetic layer 4 and a protective layer 5 are sequentially laminated on a glass substrate 1. In addition, a lubricating layer 6 is formed on the protective layer 5. The seed layer 2 is configured by laminating a first seed layer 21, a second seed layer 22, a third seed layer 23, and a fourth seed layer 24 in this order.
The material used for the glass substrate 1 can be a normal glass-based material used for magnetic recording media, such as chemically strengthened glass and crystallized glass. A disk shape having a circular hole in the center is preferable, and the diameter of the circular hole in the center, the outer diameter of the substrate, the thickness of the substrate, and the like are appropriately set according to the desired application.

  The glass substrate 1 is textured. Prior to texture processing, it is preferable to polish the glass substrate by polishing it by a conventional method. Ra (center line average roughness) after polishing is preferably 0.2 to 0.5 nm. Texture processing is applied to the substrate whose surface is smoothed to form substantially concentric grooves in the circumferential direction. As the texture processing method, the free abrasive grain method is preferable. Specifically, a work cloth (urethane, polyester, nylon, etc.) that does not contain abrasive grains is pressed against the substrate surface, and polishing slurry (diamond, aluminum oxide, cerium oxide, colloidal silica, silicon carbide, etc.) is applied to the work cloth. ) Is included while rotating the substrate. It is preferable that 25 to 60 concentric grooves in the circumferential direction are formed per 1 μm square on the textured substrate. If the number is less than 25, desired residual magnetization anisotropy cannot be obtained. It is preferable that the number of grooves is large, but if it exceeds 60, it becomes difficult to obtain a desired groove depth.

The depth of the groove formed in the substrate is preferably 3 to 5 nm. If the thickness is less than 3 nm, the desired remanent magnetization anisotropy cannot be obtained, and if the depth of the groove is deeper than 5 nm, the error of the magnetic recording medium increases to deteriorate the signal quality and become unusable.
The glass substrate textured in this way is thoroughly washed, and after removing foreign substances on the surface, film formation is performed.
The seed layer 2 is formed by laminating a first seed layer 21, a second seed layer 22, a third seed layer 23, and a fourth seed layer 24. The crystal orientation and crystal grain size of a layer formed on the seed layer These layers are provided for controlling the characteristics and the like to obtain desired characteristics of the magnetic recording medium. By using Cr as the first seed layer 21, using a NiNb alloy made of Ni and Nb as the second seed layer 22, using Cr again for the third seed layer 23, and using a NiNb alloy for the fourth seed layer 24, The circumferential residual magnetization can be remarkably increased with respect to the radial residual magnetization, and OR-Mrt can be 1.5 or more. Each layer constituting the seed layer 2 is preferably formed by sputtering. The first seed layer has a thickness of 2 to 4 nm, the second seed layer has a thickness of 8 to 15 nm, the third seed layer has a thickness of 1 to 3 nm, and the fourth seed layer has a thickness of 5 to 10 nm. preferable.

  The magnetic layer and the protective layer are preferably formed by applying a bias. In the course of forming the seed layer 2, the substrate is taken out into the atmosphere and a process for applying the bias is performed. A method of providing a step of taking out the air between the second seed layer and the third seed layer has the least influence on the deterioration of the magnetic characteristics and the recording / reproducing characteristics. Since the glass substrate is insulative, in order to apply a bias, an electrode (bias electrode) that applies a bias is brought into contact with the second seed layer, but the substrate holder that holds the substrate also serves as the bias electrode. Then, the bias can be applied by changing the holding position of the substrate after the second seed layer is formed. The holding position may be changed by a method of adding a position changing function to the substrate holder. Alternatively, after the second seed layer is formed, the substrate is taken out into the atmosphere and the position where the substrate is supported is changed. It is also possible to use a method of ensuring conductivity between the substrate holder and the substrate holder. By doing so, it is possible to apply a bias even in the subsequent deposition of each layer. When the magnetic recording medium in the process of film formation is taken out into the atmosphere, the characteristics of the magnetic recording medium are usually deteriorated. However, Cr is used as the first seed layer, NiNb alloy is used as the second seed layer, and the third By using Cr as the seed layer and NiNb as the fourth seed layer, the third seed layer and the fourth seed layer can be formed again even if a step for taking out into the atmosphere after the second seed layer is formed is provided. Thus, it is possible to eliminate the influence of exposing the second seed layer to the atmosphere and to produce a magnetic recording medium without causing deterioration of characteristics.

The NiNb alloy preferably contains 30 atomic% or more and 50 atomic% or less of Nb. When Nb is less than 30 atomic% and Nb exceeds 50 atomic%, OR-Mrt tends to decrease.
By making the compositions of the second seed layer and the fourth seed layer the same, it becomes possible to use one sputter chamber in common.
Layers constituting the seed layer 2 is preferably deposited by a sputtering method using 20 wt% of the N ₂ gas mixture was Ar gas (hereinafter referred to as Ar + 20% N ₂ gas.), The The crystalline state is preferably amorphous.
The underlayer 3 is used to obtain a magnetic recording medium having desired characteristics by controlling the crystal orientation and crystal grain size of the magnetic layer formed thereon. As a material for the underlayer, Cr or CrMo-based alloy can be used. The underlayer is also preferably formed by sputtering, and the thickness is preferably 10 nm or less.

The underlayer 3 can have a multilayer structure of two or more layers. In this case, for example, if the first underlayer is Cr and the second underlayer is CrMo or the like, there is an effect of increasing OR-Mrt and further facilitating the epitaxial growth of the magnetic layer formed on the underlayer. When the underlayer is a multilayer, the thickness of the entire underlayer is preferably 10 nm or less.
The magnetic layer 4 is formed of a magnetic material mainly containing Co. For example, a CoCr alloy, a CoCrTa alloy, a CoCrPt alloy, a CoCrPtB alloy, a CoCrPtBCu alloy, or the like can be used. The film formation method of the magnetic layer is preferably a sputtering method, and the film thickness is preferably 5 to 20 nm.
Further, the magnetic layer 4 can be composed of two or more layers. For example, if the first magnetic layer is made of a CoCrTa alloy, the second magnetic layer is made of a CoCrPtB alloy, and the third magnetic layer is made of a CoCrPtBCu alloy, the recording density can be improved. When the magnetic layer is a multilayer, the film thickness of the entire magnetic layer is preferably 25 nm or less.

The protective layer 5 is formed to prevent layers below the magnetic layer from being destroyed by contact with the magnetic head. Therefore, it is preferable to use a material having high hardness, and C, CN (carbon nitride), DLC (diamond-like carbon), or the like can be used. The protective layer is formed by sputtering or CVD. The protective layer is preferably thinner in order to improve the characteristics of the magnetic recording medium, and preferably has a thickness of 2 to 5 nm.
In forming the underlayer 3, the magnetic layer 4, and the protective layer 5 described above, it is preferable to apply a DC or RF bias to the substrate.
The lubricating layer 6 is formed for the purpose of reducing friction when the magnetic recording medium and the magnetic head come into contact with each other, and a liquid lubricant such as perfluoropolyether used in a normal magnetic recording medium is used. Can do. The lubricating layer can be formed by a method such as spin coating or dip coating with a liquid lubricant, and the thickness is preferably 1 to 2 nm.

As the glass substrate 1, a chemically strengthened glass substrate (glass substrate manufactured by Asahi Glass Co., Ltd.) having a diameter of 21.6 mm and a plate thickness of 0.381 mm was used, and this was polished to a surface roughness Ra of 0.3 nm. Subsequently, using a non-woven fabric and diamond slurry, texture processing was performed by a floating abrasive grain method, and an average of 60 circumferentially substantially concentric grooves per 1 μm square was formed. The average depth of the grooves was 3 nm.
Subsequently, the glass substrate was thoroughly cleaned and then introduced into a film forming apparatus. First, a Cr film as the first seed layer 21 was formed on a glass substrate by a DC magnetron sputtering method. Using a Cr sputtering target, Ar + 20 wt% N ₂ gas as sputtering gas, gas pressure was 1 Pa, and a first seed layer having a thickness of 2.5 nm was formed. Subsequently, a NiNb film as the second seed layer 22 was formed by a DC magnetron sputtering method. A sputtering target of Ni 50 Nb (where the number represents atomic%, Nb represents 50 atomic%, and the remainder represents Ni. The same applies hereinafter), and Ar + 20 wt% N ₂ gas is used as the sputtering gas. Thus, a second seed layer having a film thickness of 12 nm was formed at a gas pressure of 1 Pa. Take out the second seed layer to the atmosphere, remove the substrate from the substrate holder, change the position where the substrate is held, attach it to the substrate holder again, and secure conductivity between the substrate and the substrate holder. Thus, it was possible to apply a bias to the subsequent film formation. By making it possible to apply a bias, the CVD method can be used to significantly improve the characteristics of the magnetic recording medium and to form a protective film. The substrate was again put into the sputtering apparatus, and a Cr film as the third seed layer 23 was formed on the second seed layer by DC magnetron sputtering. A third seed layer having a thickness of 2 nm was formed using a Cr sputtering target, Ar + 20 wt% N ₂ gas as the sputtering gas, and a gas pressure of 1 Pa. Subsequently, a NiNb film as the fourth seed layer 24 was formed by a DC magnetron sputtering method. A fourth seed layer having a thickness of 8 nm was formed using a sputtering target of Ni 50 Nb, Ar + 20 wt% N ₂ gas as the sputtering gas, and a gas pressure of 1 Pa.

The substrate on which the seed layer 2 having four layers is formed is exposed to Ar + 30 wt% O ₂ gas under a gas pressure of 1 Pa to perform a process of adsorbing oxygen on the surface of NiNb as the fourth seed layer. It was. Next, the substrate was heated to about 270 ° C. with a heater to form the underlayer 3. The underlayer 3 has a three-layer structure, and was formed in the order of a Cr film, a CrMoB film, and a CrMo film. Each film was formed by using a DC magnetron sputtering method using Ar gas as a sputtering gas and a gas pressure of 1 Pa. The Cr film was formed with a film thickness of 3 nm using a sputtering target made of Cr. The CrMoB film was formed with a film thickness of 1 nm using a Cr15Mo7B target. The CrMo film was formed with a film thickness of 2 nm using a Cr30Mo target.
Subsequently, the magnetic layer 4 was formed. The magnetic layer 4 has a four-layer structure, and is formed in the order of a CoCrTa film, a Ru film, a CoCrPtBCu film, and a CoCrPtBCu film having different compositions. Each film was formed by using a DC magnetron sputtering method using Ar gas as a sputtering gas and a gas pressure of 1 Pa. The CoCrTa film was formed to a thickness of 3 nm using a Co17Cr5Ta sputter target. The Ru film was formed with a film thickness of 0.8 nm using a Ru sputtering target. Next, the substrate was heated again to 270 ° C. with a heater, and then a CoCrPtBCu film was formed. Using a Co24Cr14Pt8B4Cu film target, the substrate was formed with a film thickness of 11 nm while applying a DC bias of −300 V to the substrate. Subsequently, a CoCrPtBCu film was formed. Using a target of a Co13Cr11Pt10B4Cu film, the substrate was formed with a film thickness of 8 nm while applying a DC bias of −300 V to the substrate.

Subsequently, a protective layer 5 made of carbon was formed by an RF-CVD method. C ₂ H ₄ gas was introduced and an RF bias of −200 V was applied to the substrate to form a film with a thickness of 3 nm.
Subsequently, a magnetic recording medium was obtained by applying 1.6 nm of a lubricant made of perfluoropolyether to obtain Example 1.

A magnetic recording medium was manufactured in the same manner as in Example 1 except that the sputtering gas used when forming the first seed layer to the fourth seed layer was Ar + 10 wt% N ₂ gas.

  A magnetic recording medium was manufactured in the same manner as in Example 1 except that the thickness of the second seed layer was 10 nm, and Example 3 was obtained.

A magnetic recording medium was manufactured in the same manner as in Example 1 except that the sputtering gas for forming the first seed layer to the fourth seed layer was Ar + 30 wt% N ₂ gas.

A magnetic recording medium was manufactured in the same manner as in Example 1 except that the sputtering gas used when forming the first seed layer to the fourth seed layer was pure Ar (Ar 100%) gas, and Example 5 was obtained.
(Comparative Example 1)
Example 1 except that after the second seed layer is formed, the substrate is taken out, the substrate is changed, and then the third seed layer and the fourth seed layer are not formed, and the base layer 3 and subsequent layers are directly formed. A magnetic recording medium was produced in the same manner as in Comparative Example 1.
(Comparative Example 2)
Ni37Ta sputter targets during the second seed layer deposition, the sputtering gas is Ar + 20 wt% N _2, after the second seed layer deposition, the substrate is taken out, after dimensional worlds the substrate, the third seed layer and the fourth seed layer A comparative example 2 was prepared by preparing a magnetic recording medium in the same manner as in Example 1 except that the underlying layer 3 and subsequent layers were directly formed without forming a film.

  Table 1 shows OR-Mrt of Examples 1 to 3 and Comparative Examples 1 and 2.

第１シード層としてＣｒを用い、第２シード層としてＮｉＮｂを用い、第３シード層としてＣｒを用い、第４シード層としてＮｉＮｂを用いた場合にスパッタガスをＡｒ＋２０重量％Ｎ_２ガスとすると、ガラス基板を用いてもＯＲ−Ｍｒｔが１．５以上と高い値が得られている。第２シード層成膜後に大気中に出したとき表面に酸素や炭素などの吸着ガスがつくと考えられるが、第３シード層と第４シード層を成膜することで吸着ガスの影響をなくすことができる。
表２に第１シード層ないし第４シード層を成膜するときのスパッタガス中のＮ_２濃度と電磁変換特性の一つである信号対雑音比（ＳＮＲ）の関係を示す。ＳＮＲはスピンスタンドを用いて３５０ｋＦＣＩ（ｋｉｌｏ ｆｌｕｘ ｃｈａｎｇｅ ｐｅｒ ｉｎｃｈ）にて測定を行った。

When Cr is used as the first seed layer, NiNb is used as the second seed layer, Cr is used as the third seed layer, and NiNb is used as the fourth seed layer, the sputtering gas is Ar + 20 wt% N ₂ gas. Even when a glass substrate is used, a high value of OR-Mrt of 1.5 or more is obtained. When exposed to the atmosphere after film formation of the second seed layer, it is considered that adsorbed gas such as oxygen and carbon is attached to the surface. However, the influence of the adsorbed gas is eliminated by forming the third seed layer and the fourth seed layer. be able to.
Table 2 shows the relationship between the N ₂ concentration in the sputtering gas and the signal-to-noise ratio (SNR), which is one of the electromagnetic conversion characteristics, when forming the first seed layer to the fourth seed layer. SNR was measured at 350 kFCI (kilo flux change per inch) using a spin stand.

Ａｒ１００％でのＳＮＲに比較して、Ａｒ＋２０重量％Ｎ_２のＳＮＲは＋１．３２ｄＢの向上が見られた。Ｎ_２ガス混合比が略２０重量％でＳＮＲは最大に達し、略２０重量％から外れるに従ってＳＮＲは低下する。Ｎ_２ガスを略２０重量％混合することでＣｒおよびＮｉＮｂのシード層は非晶質状態になっていることをＸ線回折法で確認している。
表３に実施例１および２と比較例１の磁気記録媒体の保磁力（Ｈｃｒ）、ＳＮＲを示す
第１シード層としてＣｒを用い、第２シード層としてＮｉＮｂを用い、第３シード層としてＣｒを用い、第４シード層としてＮｉＮｂを用いることで、ＯＲ−Ｍｒｔを１．５以上とすることにより、保磁力、ＳＮＲが大きく向上することが分かる。

Compared to the SNR at 100% Ar, the SNR of Ar + 20 wt% N ₂ was improved by +1.32 dB. The SNR reaches the maximum when the N ₂ gas mixture ratio is approximately 20% by weight, and the SNR decreases as it deviates from approximately 20% by weight. It has been confirmed by X-ray diffraction that the seed layer of Cr and NiNb is in an amorphous state by mixing approximately 20% by weight of N ₂ gas.
Table 3 shows coercivity (Hcr) and SNR of the magnetic recording media of Examples 1 and 2 and Comparative Example 1. Cr is used as the first seed layer, NiNb is used as the second seed layer, and Cr is used as the third seed layer. By using NiNb as the fourth seed layer, the coercive force and SNR are greatly improved by setting OR-Mrt to 1.5 or more.

FIG. 3 is a schematic cross-sectional view for explaining a configuration example of the magnetic recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Seed layer 21 1st seed layer 22 2nd seed layer 23 3rd seed layer 24 4th seed layer 3 Underlayer 4 Magnetic layer 5 Protective layer 6 Lubrication layer

Claims (7)

In a magnetic recording medium comprising a glass substrate, a seed layer and a magnetic layer,
The glass substrate is textured,
The seed layer is formed by sequentially laminating a first seed layer made of Cr, a second seed layer made of NiNb alloy, a third seed layer made of Cr, and a fourth seed layer made of NiNb alloy. .   2. The magnetic recording medium according to claim 1, wherein the texturing is a substantially concentric groove of 25 to 60 per 1 μm square.   The magnetic recording medium according to claim 2, wherein a depth of the substantially concentric groove is 3 nm or more and 5 nm or less.   4. The magnetic recording medium according to claim 1, wherein the second seed layer is made of a NiNb alloy containing 30 atomic% or more and 50 atomic% or less of Nb.   5. The magnetic recording medium according to claim 1, wherein the fourth seed layer is made of a NiNb alloy containing Nb of 30 atomic% to 50 atomic%.   6. The magnetic recording medium according to claim 1, wherein the first seed layer to the fourth seed layer are amorphous. The first seed layer through fourth seed layer, a magnetic recording medium according to claim 6, characterized in that formed by sputtering using a substantially 20 wt% mixed gas of N ₂ gas to the Ar gas.

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