JP4411134B2 - Perpendicular magnetic recording medium - Google Patents

Description

  The present invention relates to a perpendicular magnetic recording medium, and more particularly to a high recording density perpendicular magnetic recording medium excellent in magnetic characteristics.

  In order to achieve higher recording density of magnetic recording media, perpendicular magnetic recording has attracted attention in place of in-plane magnetic recording. In the perpendicular magnetic recording system, for example, a Co-based thin film having a hexagonal close-packed (hcp) structure or a multilayer film such as Co / Pd having a face-centered cubic (f c c) structure is mainly used as a recording layer.

  In the case of a Co-based thin film having a hexagonal close-packed (hcp) structure, in order to achieve further higher recording density and improved magnetic properties, for example, nonmagnetic oxidation at the grain boundaries of ferromagnetic crystal grains in the magnetic recording layer It is indispensable to segregate materials and the like, to reduce the crystal grain size and to reduce the magnetic interaction between the crystal grains, and to improve the vertical orientation of the crystal grains. As a measure for that, a medium configuration in which a Ru or Ti film of about 40 nm, for example, is provided as an underlayer of the magnetic layer is disclosed.

On the other hand, a perpendicular magnetic recording medium generally has a structure in which a soft magnetic backing layer is provided below the magnetic recording layer (that is, a two-layer perpendicular medium structure). In order to further increase (corresponding to the writing ability), the distance between the magnetic recording layer and the soft magnetic backing layer is preferably set to 20 nm or less, for example.
Therefore, in order to realize both the improvement of the orientation of the ferromagnetic crystal grains and the improvement of the writing ability, a configuration in which a seed layer such as NiFe, Cr, Ti or the like is provided under the underlayer has been proposed. .

In the case of a perpendicular recording medium using a Co / Pd-based multilayer film having a face-centered cubic (f c c) structure, as a measure for improving the crystal orientation of the ferromagnetic crystal grains, about 30 nm is also used. A base layer of Pd or the like having a thickness of 5 mm is provided.
JP 2003-77122 A JP2001-6158 Appl. Phys. Lett. 59, 2898 (1991).

As described above, the orientation of the ferromagnetic crystal grains has been improved by providing a seed layer under the underlayer. However, for higher-density and high-performance next-generation magnetic media, further grain orientation is required. Along with improvement in properties, it is required to make the underlayer and seed layer thinner.
Under such circumstances, the present inventor has made various studies on the combination of the magnetic layer, the underlayer, and the seed layer, and investigated the relationship between the medium configuration and formation method, crystal orientation, and magnetic properties. By using an alloy and further using an underlayer having the same crystal structure as that of the magnetic layer, the orientation and magnetic properties of the ferromagnetic crystal grains are improved regardless of whether the magnetic layer has the hcp crystal structure or the fcc crystal structure. It was found that the underlayer and the seed layer can be thinned.

  The present invention has been completed by further investigation based on such knowledge, and provides a perpendicular magnetic recording medium that is low in cost, excellent in magnetic characteristics and recording / reproducing characteristics, and capable of further increasing recording density. With the goal.

The perpendicular magnetic recording medium of the present invention comprises, on a substrate, at least a nonmagnetic underlayer made of Ru having a hexagonal close-packed crystal structure, a magnetic crystal grain having a hexagonal close-packed crystal structure, and a nonmagnetic grain boundary. and a magnetic layer of CoCrPt Ri Tona, and a protective layer is a perpendicular magnetic recording medium formed by sequentially stacking, binary alloys Tona Ri thickness of the nonmagnetic underlayer Ni and Cr are at 1~5nm Formed on a seed layer, and the Cr atom content of the seed layer is 30 to 42 at. %.

  In the present invention, the Cr atom content of the seed layer is 30 to 42 at. % Is preferable.

The present invention, i.e., using a NiCr alloy seed layer, with the configuration of laminating an underlayer and the magnetic layer of the hexagonal close-packed structure on the seed layer, to improve the crystal orientation of the underlayer crystal grain As a result, the crystal grain orientation of the magnetic layer is improved, and the magnetic properties of the medium are greatly improved.
Further, the seed layer and the underlayer can be thinned, and the recording density can be increased, and the perpendicular magnetic medium having improved recording ability and excellent recording / reproducing characteristics can be realized.

  Hereinafter, the present invention will be described in more detail with reference to examples.

FIG. 1A shows a configuration example of the perpendicular magnetic recording medium of the present invention. As shown in FIG. 1A, the perpendicular magnetic recording medium of the present embodiment has a soft magnetic backing layer 6, a NiCr seed layer 2, a non-magnetic layer on a substrate 1. The underlayer 3, the magnetic layer 4, and the protective film 5 are sequentially stacked. In this embodiment, the soft magnetic backing layer is provided, but it goes without saying that it may be omitted.

Here, a NiCr alloy is used for the NiCr seed layer 2, and the thickness is preferably 1 to 10 nm. In order to form such a thin layer by sputtering with good film thickness uniformity, the pressure in the vicinity of the substrate is preferably as low as possible. For example, a low-pressure sputtering apparatus shown in FIG. 6 is used.
In this sputtering apparatus 10, as shown in the figure, a magnetron cathode 12 including a target 13, a backing plate 14 and a magnet unit 15 and a substrate holder 18 that holds a substrate 17 are opposed to each other inside a vacuum chamber 11. Be placed. On the target side of the vacuum chamber 11, a gas introduction pipe 19 that blows out sputtering gas in the vicinity of the surface of the target 13 is attached. On the other hand, an exhaust port 27 is provided on the substrate holder side, and a first exhaust device ( For example, a turbo molecular pump 21 is attached. The magnetron cathode 12 is fixed to the vacuum chamber 11 via an insulating member 16 and connected to a direct current or a high frequency power source (not shown). The gas introduction pipe 19 is connected to a gas supply system (not shown).

Furthermore, first and second pressure adjusting means are arranged to form a pressure difference in the vacuum chamber. In the case of the figure, a tapered nozzle-shaped member is used as the first pressure adjusting means 23 and is disposed so as to surround the target 13. As the second pressure adjusting means 24 arranged on the outside, a member having a shape in which a cylinder having the same diameter is attached to the tip in addition to the tapered nozzle shape is used.
Further, an exhaust port 27 ′ communicating with a space (intermediate space) between the first and second pressure adjusting means is provided behind the magnetron cathode 12, and a second exhaust device (for example, , Turbo molecular pump) 22 is attached via a valve 20 '.

  Sputtering gas is discharged from the gas supply system to the target surface through the gas introduction pipe 19, passes through the inside of the first pressure adjusting means 23 and the second pressure adjusting means 24, and is exhausted to the outside from the exhaust device 21. At the same time, it passes between the first adjusting means 23 and the second adjusting means 24 and is discharged from the second exhaust device 22 to the outside.

As described above, the first and second pressure adjusting means are provided to generate a pressure difference between the target vicinity space, the substrate vicinity space, and the intermediate space therebetween, and further, the second exhaust for exhausting the intermediate space. By providing the apparatus, the sputter gas directed toward the substrate is reduced, and as a result, the pressure difference between the space near the target and the space near the substrate can be further increased, while maintaining a stable sputter discharge, The pressure can be further reduced. Thus, for example, when the pressure near the target is 1.0 × 10 ⁻² Pa, it becomes possible to achieve 1.0 × 10 ⁻⁴ Pa around the substrate.

The NiCr seed layer uses a NiCr alloy target of a desired composition or a binary target of a Cr target and a Ni target, and forms a desired film thickness by setting the pressure in the vicinity of the substrate to 3.0 × 10 ⁻² Pa or less. By setting the pressure to 3.0 × 10 ⁻² Pa or less, the flatness of the NiCr seed layer is further improved, and the crystal growth of the nonmagnetic underlayer formed on the NiCr seed layer is promoted, so that the c-axis orientation is obtained over the entire surface. Can be formed. The pressure is preferably low, but is determined by the configuration of the sputtering apparatus.

  The nonmagnetic underlayer 3 is made of a nonmagnetic metal or alloy having a hexagonal close-packed structure, and is formed so that the c-axis is perpendicular to the substrate surface. As such a metal / alloy, Ru, Ti, Rh, Zr, or an alloy containing any of these is preferably used, and the layer thickness is preferably 3 to 15 nm, and the seed layer and the nonmagnetic underlayer are formed. The combined thickness is preferably 5 to 20 nm.

The magnetic layer is composed of ferromagnetic crystal grains having a hexagonal close-packed crystal structure and nonmagnetic crystal grain boundaries. Specifically, for example, CoCrPt, CoCrPtB, CoCrPtTa, CoCrPt—SiO ₂ , CoCrPt—Nb ₂ O ₅ and CoCrPtO are exemplified. The thickness of this magnetic layer is usually 5 to 25 nm.

As described above, by using a NiCr alloy for the seed layer, even if it is very thin, for example, 1 nm, an underlayer made of crystal grains with the c-axis aligned in the direction perpendicular to the substrate is formed thereon. be able to. Furthermore, it becomes possible to make the underlayer as extremely thin as 3 to 15 nm, and even in such a thin case, the crystal grains of the magnetic layer formed thereon have a uniform c-axis orientation. A high coercive force can be obtained, and a magnetic recording medium with high density and high reliability can be obtained. In addition, Cr content is 30-42 at. % NiCr alloy can be used to further improve the above effects.
Further, the distance between the magnetic layer 4 and the soft magnetic backing layer 6 can be made extremely small as 5 to 20 nm, and a perpendicular magnetic medium having excellent write characteristics and higher recording density is possible.

  As the soft magnetic backing layer of this example, CoTaZr, CoNbZr, FeTaN, FeSiAlN, NiFe and the like are used, but CoTaZr, CoNbZr, FeTaN and FeSiAlN are particularly preferable, and it is preferable to form a backing layer having excellent surface flatness. it can. The thickness of the soft magnetic backing layer is usually about 100 to 500 nm. The substrate is, for example, a glass substrate, an aluminum substrate, or a plastic substrate, and the protective layer is, for example, C, SiN, BC, or the like, and is usually formed with a thickness of about 2 to 10 nm.

(Experimental example 1)
Next, an experiment comparing the case of using a NiCr alloy as a seed layer with the case of using another metal or alloy will be described below.
A glass substrate (2.5 inch disk) 17 was mounted in a vacuum chamber 11 equipped with a NiCr target (Cr content; 40 at.%) 13. Ar gas was introduced through the gas introduction pipe 19 to cause discharge, and the main valves 20 and 20 ′ of the exhaust devices 21 and 22 were adjusted so that the pressure in the vicinity of the substrate was 3.0 × 10 ⁻² Pa. In this way, a NiCr seed layer having a thickness of 1 to 5 nm was formed on the substrate.
Subsequently, a 20 nm Ru nonmagnetic underlayer was formed on the NiCr seed layer at an Ar gas pressure of 6.7 × 10 ⁻¹ Pa. Further, a 5 nm C protective layer was formed. On the other hand, for comparison, NiFeCr, NiFeCu, NiFe, Ti, Au, and Cu were similarly formed with seed layers having various film thicknesses, and subsequently formed a Ru underlayer and a C protective film.

These samples were evaluated by X-ray diffraction, and the relationship between the diffraction intensity of the hcp (002) plane of the Ru underlayer and the seed layer thickness is summarized in FIG. As apparent from FIG. 2, the diffraction intensity of Ru-hcp (002) is the highest in the sample using the NiCr seed layer, and even when the NiCr seed layer is as thin as 1 nm, It was found that a sufficiently large diffraction intensity was obtained even when compared. In addition, as shown in FIG. 2, NiFeCr also has a sufficient diffraction strength. On the other hand, sufficient diffraction strength was not obtained for NiFeCu, NiFe, Ti, Au and Cu.
Further, the rocking curve of the sample was evaluated by an X-ray diffraction method, and the half width Δθ ₅₀ of the Ru-hcp (002) peak was plotted in FIG. 3 with respect to the layer thickness of the seed layer. It can be seen that the half-value width Δθ ₅₀ of the sample using the NiCr seed layer and the NiFeCr seed layer is extremely small compared to the other seed layers, and the c-axis orientation of the crystal grains is high. That is, it was found that the vertical orientation of the crystal grain c-axis was high and the variation between the crystal grains was small.

(Experimental example 2)
Next, experimental results of examining the relationship between the Cr content of the NiCr seed layer, the crystal orientation of the Ru underlayer, and the coercive force of the perpendicular magnetic medium will be described with reference to FIGS.
First, a NiCr seed layer having a thickness of 4 nm was formed using CrNi targets having various compositions. Subsequently, a Ru underlayer was formed to have a thickness of 5 nm and a C protective film was formed to have a thickness of 5 nm in the same manner as in the above experiment, thereby preparing a sample for X-ray diffraction measurement. . Similarly, a seed layer 4 nm, a Ru underlayer 5 nm, a CoCrPt magnetic layer 10 nm, and a C protective film 5 nm were formed to prepare a coercive force measurement sample. The measurement results for these samples are shown in FIGS.

FIG. 4 is a graph plotting the relationship between Ru-hcp (002) diffraction intensity and NiCr composition. FIG. 5 is a graph plotting the relationship between the coercive force and the NiCr composition.
As is clear from these figures, the content of Cr atoms in the NiCr seed layer is 30 to 42 at. By setting the ratio to%, the c-axis orientation of the Ru underlayer crystal grains increased rapidly. It can also be seen that the coercive force of the recording medium changes corresponding to the c-axis orientation of the Ru underlayer. Note that the coercive force of the medium without the NiCr seed layer was 2.0 KOe.

As described above, NiCr alloy is used as a seed layer, and by forming this by low-pressure sputtering, a seed layer having excellent film thickness uniformity and flatness can be formed, and hexagonal close-packed packing is possible. It is possible to increase the crystal grains of the underlying layer of the structure and improve the c-axis orientation, and to reduce the size of the hexagonal close-packed ferromagnetic crystal grains formed thereon and to improve the c-axis orientation. Improvements can be achieved at the same time. As a result, a perpendicular recording medium capable of higher recording density and excellent magnetic characteristics can be realized .

It is a schematic diagram which shows the structural example of the perpendicular magnetic medium of this invention. It is a graph which shows the relationship between the (002) diffraction intensity of Ru base layer, and the film thickness of a seed layer. It is a graph which shows the relationship between the half value width of the (002) diffraction peak of Ru base layer, and the film thickness of a seed layer. It is a graph which shows the relationship between Ru (002) diffraction intensity and the NiCr composition of a seed layer. It is a graph which shows the relationship between the coercive force of a medium, and the NiCr composition of a seed layer. It is a typical sectional view showing an example of a low-pressure sputtering device.

Explanation of symbols

1 substrate,
2 NiCr seed layer,
3 Underlayer,
4 Magnetic layer,
5 Protective film,
6 Soft magnetic backing layer.
10 Sputtering device,
11 Vacuum chamber,
12 magnetron cathode,
13 targets,
14 backing plate,
15 magnet unit,
16 Insulating member,
17 substrate,
18 substrate holder,
19 Gas introduction piping,
20, 20 'valve,
21 a first exhaust device (eg a turbomolecular pump),
22 second exhaust device,
23 first pressure adjusting means 23,
24 second pressure adjusting means 24,
27, 27 'exhaust port.

Claims (2)

On a substrate, at least a nonmagnetic underlayer made of Ru hexagonal close-packed crystal structure and a hexagonal close-packed magnetic crystal grains and the non-magnetic grain boundary from Do Ri CoCrPt Tona Ru magnetic layer of the crystal structure And a perpendicular magnetic recording medium in which a protective layer is sequentially laminated,
The binary alloy Tona Ri thickness of the nonmagnetic underlayer Ni and Cr is formed on the seed layer is 1 to 5 nm,
The seed layer has a Cr atom content of 30 to 42 at. %, A perpendicular magnetic recording medium. The perpendicular magnetic recording medium according to claim 1, wherein the NiCr alloy seed layer is formed on a soft magnetic underlayer.

Images