JPS6275953A - Photomagnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve characteristics as a vertically magnetized film and to improve corrosion resistance by setting the atomic concn. of Tb and Co in a TbCo film which is a recording layer to a prescribed value or above so that the atoms are thoroughly magnetically bound with each other. CONSTITUTION:The inside of a sputtering chamber 11 is evacuated by a discharge system 24 and gaseous Ar in a cylinder 20 is admitted into the chamber while the flow rate thereof is monitored by a flow meter 23 to maintain the gaseous pressure at a prescribed value. Electric power is supplied from DC power sources 18, 19 to a TB target and Co target in sputtering guns 12, 13 to excite magnetron discharge and to clean up the surfaces of the targets by presputtering while shutters 14, 15 are held closed; thereafter the shutters 14, 15 are opened and the TbCo film is formed on a substrate 16 which is kept rotated. The concn. of the Tb atoms in the TbCo film is thereby made >=1.2X10<22>pieces/cm<3> and the concn. of the Co atoms to >=3.0X10<22>pieces/cm<3>, by which the Tb atoms and Co atoms are magnetically thoroughly bound with each other.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a magneto-optical recording medium, particularly an amorphous ferrimagnetic TbC
The present invention relates to a magneto-optical recording medium having an o-alloy thin film as a recording layer and a method for manufacturing the same.

[Technical background of the invention and its problems]

Heavy rare earth elements (RE) such as Gd, Tb, and DV, and Fe,
Amorphous ferrimagnetic alloy thin II whose main component is a transition metal element (TM) such as Co! (RE-TM film) is expected to be put to practical use as a recording layer material in rewritable magneto-optical recording media. The features of this RE-TM film are listed below.

(1) A perpendicularly magnetized film having relatively large perpendicular magnetic anisotropy can be formed by a simple method such as sputtering or vapor deposition.

(Since it is 21 ferrimagnetic, magnetization, that is, self-demagnetizing field, can be reduced by carefully considering the compositional component ratio, and extremely good square characteristics can be obtained.

(3) Since the coercive force is relatively large, the stability of minute inversion magnetic domains is good (particularly good when Tb or Dy is used as the heavy rare earth element).

(4) Coercive force decreases quickly as temperature rises, so
Magnetization reversal bits can be formed by irradiation with a low-power laser beam and application of a small external magnetic field.

(5) A rotation angle as large as possible for practical use can be obtained.

Reference 1; Journal of the Japanese Society of Applied Magnetics, vol. 9. N(12
, 1985, the TbCo film has the best corrosion resistance among the RE-7M films. That is, T
Since the bCo film can be expected to have a practical lifespan with simple protection measures such as overcoating the dielectric formed by sputtering, it can be used as a substrate material because it has high gas permeability but is difficult to form guide grooves compared to glass. Organic resin materials (polymethyl methacrylate, polycarbonate, epoxy, etc.) that have the advantage of ease of use can be used and are preferred in practice.

Reference 2: A1) pl, phys, Lett, 45
(8), 15°1984, +1872, Reference 3
; Proc, 8th 5VIII1. OnIS
I AT' 84. p298, document 4: J a
paneseJournal of Applied
Physics vol, 23°Nα, 2, 1984
．． p188, References 5-7: Proceedings of the 32nd Applied Physics Association Conference 29a-G-1, 29a-G-2゜29
As disclosed in a-Q-3 (D353) etc.
The magnetic properties of a TbCo film largely depend on the composition of the film and the conditions for its formation. However, the composition of a TbCo film to become a perpendicular magnetization film necessary as a recording layer in a magneto-optical recording medium, especially the atomic concentration ratio, the relationship between the atomic concentration ratio and corrosion resistance, and the formation of a TbCo film with an optimal atomic concentration The reality is that there is a lack of careful examination of methods.

For example, References 6 and 7 give contradictory results.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned conventional problems, and is a magneto-optical film comprising an amorphous ferrimagnetic TbCo alloy thin film as a recording magnetic layer, which has good properties as a perpendicular magnetization film and has excellent corrosion resistance. The purpose is to provide a recording medium and its manufacturing method.

[Summary of the invention]

As a recording layer according to the present invention, an amorphous ferrimagnetic TbCo alloy thin film (hereinafter referred to as
A magneto-optical recording medium formed with a TbCo film (simply referred to as a TbCo film) is
Amorphous ferrimagnetic TbC.

The Tb atomic concentration in the alloy thin film is 1.2X1022 [pieces/c
m"3 or more, and the co atom concentration is 3.0x1022 [pieces/cm3] or more.

Further, in the method for manufacturing a magneto-optical recording medium according to the present invention, a TbCo film serving as a recording layer is prepared such that the Tb atomic concentration in the thin film is 1.2.
X1022 [pieces/cm3] or more.

The recording layer is formed by a sputtering method under the condition that Ve with respect to the ground potential of the substrate on which the recording layer is formed is VB≧-150 [V] so that the CO atomic concentration is 3.0×1022 [pieces/cm3] or more. shall be.

〔Effect of the invention〕

The magneto-optical recording medium according to the present invention has TbC as a recording layer.
Since the o film is dense enough to achieve magnetic coupling between Tb atoms and co atoms (spins of adjacent atoms are aligned antiparallel), the squareness ratio of Kerr hysteresis loops and VSM loops is extremely high. This results in a very good perpendicularly magnetized film with a large perpendicular magnetic anisotropy constant in which magnetization reversal occurs very sharply, and also has sufficient corrosion resistance and a very long life.

Further, according to the method for manufacturing a magneto-optical recording medium according to the present invention, TbC having the above-mentioned good properties.

The film can be formed by a sputtering method with excellent mass productivity and reproducibility.

[Embodiments of the invention]

The present invention will be explained in detail below. FIG. 1 is a cross-sectional view of a magneto-optical recording medium according to an embodiment of the present invention, in which a TbCo film 2 as a recording layer is formed on a substrate 1. TbC
o film 2 has a Tb concentration of 1.2×1022 [pieces/c
m3] or more, Co atomic depth is 3.0XIO22 [pieces/c
m3] or more, and its thickness is 1000. The film thickness was measured by etching off a part of the film and measuring the difference in level using a stylus-type film thickness meter. Further, the composition of the TbCo film 2 was quantitatively analyzed by inductively coupled argon plasma optical emission spectroscopy (ICP method). From the film thickness and ICP method results, Tb in the film
and the atomic concentration of Co were derived.

FIG. 2 shows the results of actual measurements of the relationship between the atomic concentrations of Tb and Go in TbCoI12 and the perpendicular magnetic anisotropy constant KU. When using a TbCo film as a recording layer in a magneto-optical recording medium, it is essential that the KLI be positive, that is, that the film be perpendicularly magnetized.

From Figure 2, the Tb atomic concentration is 1.2X1022 [pieces/
α3] and Co atom concentration is 3.0x1022 [
/Cm3] In the non-vortex region, KIJ<0, and it can be seen that a perpendicularly magnetized film is not formed.

As a specific example, the atomic concentration of Tb is 1.3X10"! [pieces/cIl!3], the atomic concentration of co is 3.6X1022 [pieces/cm3], and Tb
The following Table 1 shows the results of magneto-optical evaluation of the TbCo film when the composition ratio of TbCo was set to 26.5 [at, %].

Table 1 From these results, it is clear that the TbCo film in which the atomic concentrations of Tb and Co are within the range based on the present invention has very good characteristics as a perpendicularly magnetized film.

FIG. 3 is a diagram showing an example of the configuration of an apparatus for forming a TbCo film based on the present invention. In the sputtering chamber 11, a magnetron sputtering gun 12 containing a Tb target and a Co
Magnetron sputter gun 13 with target stored,
Shutters 14 and 15 are arranged in front of these, and a substrate 16 is arranged thereon. An RF power source 17 is connected to the substrate 16 by capacitive coupling, and DC power sources 18 and 19 are connected to the magnetron sputter guns 12 and 13, respectively. Gas cylinder 20 has a purity of 99.995%
The above-mentioned Ar gas is stored and connected to the sputtering chamber 11 via a pressure regulator 21 and a mass flow meter 22. The sputtering chamber 11 is further connected to an exhaust system 24 equipped with a cryopump.

To explain the procedure for forming a TbCo film using this sputtering apparatus, first, the inside of the sputtering chamber 11 is
4, the Ar gas in the cylinder 20 is evacuated to 10-6 [Torr] by the pressure regulator 22 while being monitored by the mass flowmeter 23, and then flows into the sputtering chamber 11 at a flow rate of 70 [5ccII], and is exhausted. The gas pressure was maintained at 5 mTorr by adjusting the valve in system 24. Next, with the shutters 14 and 15 closed, power was supplied to the Tb target and Co target in the magnetron sputtering gun 12.13 from the DC power supply 118.19 to excite magnetron discharge on the target surface. The input current was set to 0.4 [A] for the Tb target and 1.4 [A] for the Go target, and bliss sputtering was performed for 5 minutes to clean the target surface, and then the shutter 14.
15 at the same time, and rotate the substrate 16.
The film was formed for 3 minutes. The rotation speed of the substrate 16 is 60
As [rom], Tb sputtered particles and Co sputtered particles were sufficiently mixed on the substrate 16. Also,
The RF power supply 17 was turned off, and the substrate 16 was set at ground potential, that is, VB=O. TbCo1 obtained in this way
The film quality and characteristics of IIl are as already explained.

Using the sputtering apparatus shown in FIG. 3, TbC
The results of a concrete study of the conditions for forming the o-film will be described in the following examples.

<Example 1> Power is supplied to the board 16 from the RF power supply 17, and the board 16
The potential (substrate bias potential) relative to the ground potential on the surface is VB.
The film quality was investigated when a TbCo film was formed by generating a self-bias voltage and varying VB variously. Figures 4 to 6 show the results. Figure 4 shows the relationship between substrate bias potential VB and Kerr rotation angle θ, and Figure 5 shows the relationship between VB and Kerr rotation angle θ.
FIG. 6 shows the relationship between B and the coercive force HC, FIG. 6 shows the relationship between VB and the Tb atomic concentration and CO atomic concentration in the film, and FIG. 7 shows the relationship between Ve and the perpendicular magnetic anisotropy constant KU. In FIG. 4, FIG. 5, and FIG. 7, the values of films formed by the non-bias sputtering method (VB=0) with the same composition ratio are also shown by broken lines.

As is clear from Figures 4, 5 and 7, -2
It can be seen that the TbCo film formed by the bias sputtering method where 00v≧VB≧−350V is an in-plane magnetized film, and only TbCo films formed within other Ve ranges can be used as the recording layer. Ve≦-35
Tb formed by 0V bias sputtering method
Although the Co film is a perpendicularly magnetized film, it is insufficient in both θ and 1-1c when compared with a film of the same composition produced by non-bias sputtering as shown in FIGS. 4 and 5.

Furthermore, a film formed by a bias sputtering method with Ve≦-350v can be a perpendicularly magnetized film with Kl >O, but as shown in FIG.
The film quality is porous, with a CO atom concentration of less than 1022 [pieces/Cm3] and a CO atom concentration of less than 3.0×1022 [pieces/C#+3]. Therefore, when subjected to an accelerated deterioration test, oxidation easily occurs, resulting in an in-plane magnetized film. FIG. 8 is a diagram showing this state, and shows the state in which the film is formed (
as, depo, ) and Kerr hysteresis loop at
70°C-85% R,H.

A comparison is shown below with that after being left for 24 hours. V
The TbCo film formed at s≧-175V showed no change before and after the accelerated aging test, whereas when Ve≦-35
The TbCo film formed at 0V changes its Kerr loop shape due to accelerated deterioration, and the degree of this change increases as VB decreases (as it increases toward the negative side), and VB≦
In the −540V region, after accelerated deterioration, the film has changed into an in-plane magnetized film. Therefore, in order to form a TbCo film as a good perpendicular magnetization film, it is necessary to form it by a bias sputtering method in which the substrate bias potential Ve is set to Va≧-150V as in the present invention.

The reason why the TbCo film becomes porous as the substrate bias potential VB increases is that the impact of sputtering gas ions on the film surface during film formation increases as VB increases, and Tb atoms and CO
This is because atoms are scattered outside the film by the re-sputtering effect and vacancies are generated in the film, and as a result, Tb and C
It is thought that this reduces the magnetic coupling and interaction with O, thereby significantly impairing the magneto-optical properties.

<Example 2> The substrate bias potential during the formation of the Tt) Go film was set to Ov (ground potential), and the gas pressure PA of the Ar gas used as the sputtering gas during film formation was varied. Figure 9 ~ 1st
Figure 1 shows the results, Figure 9 shows the relationship between PA and 1-1c, Figure 10 shows the relationship between PA and the Tb atomic concentration and CO atomic concentration in the film, and Figure 11 shows the relationship between PA and perpendicular magnetic anisotropy. sexual constant K
The relationship with IJ is shown respectively. Figure 9 and 1
In Figure 1, a broken line further indicates that PA with the same composition = 5 [mT
The values for each of the TbCo films formed using [Orr ] are also shown.

As is clear from FIG. 11, the TbCo film has a
In a region where the r gas pressure is 15 [mTOrr] or more, the film becomes an in-plane magnetized film and cannot be used as a recording layer of a magneto-optical recording medium. Also, from FIG. 10 and FIG. 11, it can be seen that the perpendicular magnetic anisotropy constant) (U) is porous and deviates from the range of Tb and CO atomic concentrations in <TbCo11 based on the present invention. Therefore, in the present invention, the sputtering gas pressure when forming the TbCo film is desirably 10 [mTorr] or less.

<Example 3> TbCo1! Substrate bias potential VB at the time of formation is Ve=O
V, the sputtering gas pressure was 5 [mTorr], and the span gas was Ar-N2°Ar-N2, Ar
-02 mixed gas was used, and each additive gas (N2, N2.
Films were formed by changing the partial pressure ratio of 02), and each case was evaluated.

Figures 12 and 13 show the results. Figure 12 shows the relationship between the partial pressure ratio of each additive gas and the perpendicular magnetic anisotropy constant Ku, and Figure 13 shows the relationship between the partial pressure ratio of each additive gas and Tb.

The relationship with the atomic concentration of CO is shown.

For Ar=H2 type sputtering gas, H2 partial pressure ratio is 4% or more, and for Ar-N2 type sputtering gas, N2 partial pressure ratio is 2.
．． 5% or more, 02 for H-R-02 type sputtering gas
It can be seen that a partial pressure ratio of 1% or more results in an in-plane magnetized film. On the other hand, looking at the Tb and CO atomic concentration ratios, for Ar-82 sputtering gas, the N2 partial pressure ratio is 7% or more, and the Ar-N
For 2-system sputtering gas, N2 partial pressure ratio is 4% or less, Ar
-02 series sputter gas has an 02 partial pressure ratio of 4% or less, and <Tb, C, respectively, according to the present invention.

Although the atomic concentration is obtained, since reactive gases are used in both cases, the reaction products of Tb and the additive gas are incorporated into the film, so even if the atomic concentration ratio is sufficient, the in-plane magnetization film is It is thought that it will become.

Based on these results, when using gases other than rare gases (reactive gases) as sputtering gases, the reactive gas partial pressure ratio should be 4% or less (depending on the type of reactive gas).
rare gas partial pressure ratio of 96% or more), more preferably 1% or less (
It is desirable that the rare gas partial pressure ratio be 99% or more. Furthermore, from an industrial standpoint, Ar gas is most suitable as the rare gas.

<Example 4> Ar gas with a purity of 99.995% was used as the sputtering gas, the gas pressure was set to 5 [mTorr], and TbCo
A TbCo film was formed by a magnetron sputtering method and a TbCo film was formed by a conventional sputtering method (not a magnetron sputtering method) with the substrate bias potential at the time of film formation set to Ov, and each case was evaluated. The results are shown in FIGS. 14 and 15. Figure 14 shows the film composition of the TbCo film formed by the magnetron sputtering method (the film composition is
In the device shown in the figure, the input power to the Tb target and the CO
The solid line shows the relationship between the coercive force (the vertical coercive force measured from the hysteresis loop) and the coercive force (changed by changing the ratio of the input power to the sitat),
Also, Tb in the film.

The relationship with the atomic concentration of Co is shown by a broken line. As shown in the figure, dense TbCo11 based on the present invention was obtained in a wide range, and the squareness ratio of the Kerr hysteresis loop was also good, and the coercive force was large enough to be used practically. Figure 15 shows the composition of one TbCo film formed by the functioner's same sputtering method (a composite target with Tb chips arranged on a Co disk was used as a target, and the area ratio of the Tb chips was changed to The relationship between the perpendicular coercive force and the atomic concentration of TbCo is shown. As is clear from FIG. 15, the TbCo film formed by the conventional sputtering method has a very narrow composition range in which a perpendicularly magnetized film can be obtained, and the film is entirely formed by the magnetron sputtering method. It is porous. The reason for this is that in the magnetron sputtering method, the plasma is focused near the target, which suppresses the impact of Ar ions on the substrate surface, whereas in the conventional spankling method, the plasma is focused near the target and the substrate. This is thought to be due to Ar ions colliding with the substrate surface and damaging the density of the film.The conventional sputtering method is equivalently considered to be a magnetron sputtering type sputtering method with a substrate bias of -150V or less. It will be done.

Further, in the above embodiment, an example was shown in which the recording layer was formed directly on the substrate, but the present invention is not limited to this, and the present invention is not limited to this. For example, 5iiN+Il* may be formed on this recording layer.
It may also be formed by laminating a second interference layer consisting of a light reflecting layer and a light reflecting layer.

In the above-mentioned four-layered medium that utilizes light transmitted through a recording layer made of a TbCo film, S constituting the second interference layer is
The film thickness of i3N+ was evaluated at 3 points between 0 and 1100 people (0 people,
250 people, 500 people, 800 people, 100 people) were formed to form samples, and the reflectance from the back side of the substrate and Kerr rotation angle were measured using a He-Ne laser.
The thickness of the second interference layer is 500 Å or less, especially 250 Å or less.
For humans, the reflectance x Kerr rotation angle was extremely large. Therefore, it is appropriate that the thickness of the second interference layer be 500 Å or less.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing the structure of a magneto-optical recording medium according to an embodiment of the present invention, and FIG. 2 shows the relationship between the Tb and co atomic concentrations in the TbCo film and the perpendicular magnetic anisotropy constant. Figures 3 and 3 are diagrams showing the configuration of the sputtering apparatus used to form the TbCo film in the present invention, and Figures 4 to 15.
The figures are diagrams for explaining the effects of the method for manufacturing a magneto-optical recording medium according to the present invention.
The figure also shows the relationship between substrate bias potential and coercive force, Figure 6 also shows the relationship between substrate bias potential and Tb and CO atomic concentrations, and Figure 7 also shows the relationship between substrate bias potential and perpendicular magnetic difference. Figure 8 shows a comparison of the Kerr hysteresis loop of a TbCo film during film formation and after an accelerated test with respect to changes in substrate bias potential. Figure 9 shows the relationship between Ar in sputtering gas and Figure 10 shows the relationship between the gas pressure and coercive force, Figure 10 shows the relationship between the same <Ar gas pressure and the atomic concentrations of Tb and Co, and Figure 11 shows the relationship between the same <Ar gas pressure and perpendicular magnetic anisotropy. Figure 12 is a diagram showing the relationship between the partial pressure ratio of the additive gas in the sputtering gas and the perpendicular magnetic anisotropy constant, and Figure 13 is a diagram showing the relationship between the partial pressure ratio of the additive gas in the sputtering gas and the atoms of Tb and CO. Figure 14 is a diagram showing the relationship between the Tb composition ratio and coercive force and the atomic concentration of Tb and GO in a TbCo film formed by magnetron sputtering, and Figure 15 is a diagram showing the relationship between Tb and GO atomic concentrations in a TbCo film formed by magnetron sputtering. FIG. 3 is a diagram showing the relationship between the Tb composition ratio, the coercive force, and the atomic concentrations of Tb and CO in the formed TbCo film. 1... Substrate, 2... TbCo film (recording layer). Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 3 Figure 2 Figure 4 LJ -7tJIJ -1dJU
-600- [, 田]/times] Marf failure [:aO') 4]) H... going [εyama 15''a''In)4''f; !
■?・F --

Claims (6)

[Claims] (1) In a magneto-optical recording medium in which an amorphous ferrimagnetic TbCo alloy thin film having an easy axis of magnetization in a direction perpendicular to the film surface is formed as a recording layer on a substrate, the amorphous ferrimagnetic
The Tb atomic concentration in the bCo alloy thin film is 1.2×10^2^
2 [pieces/cm^3] or more, Co atom concentration is 3.0×10
A magneto-optical recording medium characterized in that the magnetic flux density is ^2^2 [pieces/cm^3] or more. (2) In a method for manufacturing a magneto-optical recording medium in which an amorphous ferrimagnetic TbCo alloy thin film having an axis of easy magnetization in a direction perpendicular to the film surface is formed as a recording layer on a substrate, the amorphous ferrimagnetic TbCo alloy thin film The Tb atom concentration in the thin film is 1.2×10^2^2 [pieces/cm^3] or more, and the Co atom concentration is 3.0×10^2^2 [pieces/cm^3] or more. , the potential V_B of the substrate with respect to the ground potential is V
A method for manufacturing a magneto-optical recording medium, characterized in that it is formed by a sputtering method under the condition of _B≧-150 [V]. (3) The magneto-optical recording medium according to claim 2, wherein the sputtering gas used to form the amorphous ferrimagnetic TbCo alloy thin film contains a rare gas with a partial pressure ratio of 96% or more. Production method. (4) The method for manufacturing a magneto-optical recording medium according to claim 3, wherein the rare gas is Ar gas. (5) The method for manufacturing a magneto-optical recording medium according to claim 3 or 4, wherein the gas pressure of the sputtering gas is 10 mTorr or less. (6) The method for manufacturing a magneto-optical recording medium according to claim 2, characterized in that a magnetron sputtering method is used as the sputtering method for forming the amorphous ferrimagnetic TbCo alloy thin film.