JPS62137753A - Laminar photomagnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To provide excellent durability and uniform magnetic characteristics to a titled medium by constituting a thin film layer of >=2 layers of laminar films consisting of rare earth-transition metals and forming said layer in such a manner that the compsn. ratio in number of atom % of the rare earth metal and transition metal in one of the adjacent two layers of such laminar film is different from the compsn. ratio in number of atom % of the other layer. CONSTITUTION:The thin film layer is constituted of >=2 layers of the laminar films consisting of the rare earth-transition metals. The adjacent two layers of such laminar film are constituted of the layer rich with the rare earth element and the layer rich with the transition element and/or the compsn. ratio in number of atom % of the rare earth element and transition element in the adjacent two layers are deviated from each other and/or either or RM and TM is rich at the boundary faces of the two adjacent layer. The film having the approximately specified recording characteristic over a large area is thus produced. The film structure is produced from the backscattering intensity spectra by He<+> using a Rutherford backscattering method.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a magneto-optical recording medium and a method for manufacturing the same, and particularly relates to a rare earth-transition metal recording medium for recording on the submicron order using laser light. This article concerns magneto-optical recording media such as magneto-optical disks, tapes, and cards that use amorphous thin films of alloys, and their manufacturing methods.

(Prior art) Various materials have already been proposed as recording materials for high-density information recording media such as E-DRAW discs, but among them, rare earth metals (RM) and transition metals (TM) have been physically The amorphous RM-TM alloy film, which is formed in the form of a thin film on a substrate made of glass, plastic, etc. using the vapor deposition method, is a perpendicularly magnetized film that can be relatively easily formed over a large area, so it is being developed for practical use. It is progressing.

This RM-TM amorphous film meets the conditions required as a magneto-optical recording medium, namely (1) ability to form homogeneous perpendicular magnetization over a large area (Ku > 2πMs), and (2) stable minimum magnetic domain diameter (δW / M s T (c) is sufficiently small (He is large) (3) Write power (difference between Tc or T comp and holding temperature TO) is 100 to 200°
(4) The light absorption coefficient (α) is sufficient (αt > 2: t is the film thickness') (5) The S/N ratio is large. Although,
It has not yet been manufactured in Komanjarges. The biggest reason for this is that they lack durability, that is, long-term storage stability. This is thought to be because the amorphous film undergoes chemical changes such as oxidation, resulting in alteration of the film composition. There are two ways to prevent this deterioration: use a protective film, or create a film composition that is less susceptible to deterioration such as oxidation.
There are two possible countermeasures. Various proposals have been made for the former, but the method proposed for the latter is the third method.
The main methods are to prevent oxidation by adding components or to use CO-based transition metals. The method of adding a third component to prevent oxidation tends to have a negative effect on other requirements for magneto-optical properties, and in the case of Go-based films, the film-forming conditions to achieve perpendicular magnetization are strict, making it difficult for industrial production. is difficult.

The present inventors investigated the fine structure of the RM-TM amorphous film using X-ray diffraction, replica electron microscopy, '1'' EM method, Auger analysis, magnetic hysteresis measurement, and Rutherford backscattering method, and found that In the process of conducting basic research to elucidate the magnetic microstructure, we discovered an extremely interesting phenomenon, and discovered that this could be a key to solving the problems in the practical application of magneto-optical recording media. , completed the invention.

(Object of the Invention) Therefore, an object of the present invention is to provide an RM-TM amorphous magneto-optical recording medium that is highly durable and has uniform magnetic properties, and a method for manufacturing the same.

Another object of the present invention is to provide a superlattice layered structure or a novel film similar thereto, and a method for manufacturing the same. The method of manufacturing this novel layered structure according to the present invention is not limited to the industrial manufacturing method of magneto-optical recording media;
In general, it is an extremely important method for elucidating the relationship between the fine structure of a material and its physical properties, and for applying it to other industrial applications. In other words, whereas conventional superlattices could only be created in small areas using extremely expensive equipment such as molecular beam epitaxial techniques, this method has great significance in that superlattice layered bodies can be created industrially over large areas. have.

Still another object of the present invention is to use Co-based R with excellent oxidation resistance.
The object of the present invention is to provide a new method for uniformly producing an M-TM amorphous film over a large area.

(Structure of the Invention) The magneto-optical recording medium provided by the first aspect of the present invention is composed of a substrate and a rare earth-transition metal alloy thin film layer formed on the substrate, and the rare earth metal and transition metal In the magneto-optical recording medium, the thin film layer is composed of a layered film of two or more layers of rare earth-transition metal, and two adjacent layers of the layered film are The atomic percentage composition ratio of rare earth elements and transition metals in one layer is different from the atomic percentage composition ratio in the other layer.

The thickness of each layer of the above layered film is preferably 600 Å or less, more preferably 100 Å or less.

The rare earth metals (RM) include Tb, Gd, Dy
.

Ho, Er, etc., and G as a transition metal ('rM).
For example, carbon dioxide, Fe, Ni, etc. can be mentioned, but in order to improve the oxidation resistance, it is preferable to use CO as a base, and TbCo and TbCoPe are particularly preferable in view of the characteristics of the pond. .

The composition range in which a perpendicularly magnetized film can be obtained from the above RM-TM alloy thin film is known, and when the film is made by sputtering, for example, Tbx Go +oo-x (13<X<32),
Gdx Co 100-X (13<x<
35), DYXCo +00 X (15<
X<25), f(OX Co Ion X(
18<x<35), Tbx (Coy F e +
oo-Y)+oo X(15<X<25.5<Y<3
0) etc.

Any material such as glass, plastic, or metal can be used as the substrate.

The feature of the present invention is that at least two or more layers of the RM TM alloy 7 Rulfurous thin film are laminated, and in two adjacent layers, the atomic % composition ratio of RM and TM in one layer is the same as the atomic % composition ratio of the other layer. This is different from the ratio. That is, the perpendicular magnetization film is composed of a layered stacked structure film, and (1) two adjacent layers are composed of a combination of a layer rich in rare earth elements and a layer rich in transition elements, and/ or (2) the atomic percentage composition ratios of rare earth elements and transition elements in two adjacent layers are shifted from each other, and/or (3) one of RM and TM is rich at the interface between two adjacent layers. ing.

- As an example, a multilayer film made using the following method of the present invention using a Tb Fe or Tb Co target has a first layer made of pure iron or pure cobalt, and a second layer made of perpendicular magnetization. TbFe that becomes the film.

It is possible to form multiple layers of pure iron or pure cobalt in the Tb Co layer and the third layer, and the second layer can be further formed into multiple layers with different composition ratios. in general,
When sputtering is used, an inert gas such as argon is contained between particles of metal elements (or clusters thereof). On the other hand, in the vapor deposition method, oxygen tends to enter between the particles, resulting in oxidative deterioration. In particular, when bias sputtering is used, the intrusion of oxygen can be reduced to a large degree. Argon 1-) +@Fjf m rh +-NoヱConcave A, 1
``-tf I+ Medium 'I (,f-s, ÷11.7g) Replaces atmospheric oxygen and promotes RMTM rearrangement.

In order to practically control such a phenomenon, it is necessary to control the composition ratio, particle distribution, arrangement, etc. of RMTM, but this can be easily achieved in the method of the present invention by forming a layered structure.

Note that the layered magneto-optical recording layer of the present invention may be combined with any other known protective film, such as SiOx, ArN, etc.

The overall thickness of the above layered film can be appropriately selected depending on the application.
In the case of an optical disc, a maximum performance of about 1000 is selected.

The thickness of each layer of this layered film is determined by considering the composition of the desired film, and varies depending on the combination of RM-TMs used and film formation conditions (e.g. bias value of bias sputtering), but is generally The thickness is preferably 600 Å or less, preferably 100 Å or less.

FIG. 1 is a diagram showing the concept of the layered film of the present invention. In the figure, ○ indicates one metal (for example, RM), and 0 indicates the other metal (for example, TM), and each of them is a single prefecture. It is a child or an aggregate of the same or different elements (for example, a cluster or a microcrystal). Figure 1 (a) shows a case in which each of the two adjacent layers is rich in a single element;
When the atomic percentage composition ratio of each layer is different, (c
) are conceptual diagrams showing cases where the atomic percentage of one element is large at the interface between two adjacent layers.

This FIG. 1 is merely a conceptual diagram, and each layer or boundary layer may have a note-like structure or may have a local ordering.

Additionally, an inert gas such as argon is present between each particle.

In short, it is sufficient that the composition ratio of RM-TM in atomic percentages differs in the direction perpendicular to the film surface. Further, the thickness of each layer does not need to be constant, and the combination of three or more layers may not be a repetition of the same combination, but may be a completely different combination.

In a particular embodiment of the invention, Tb is used as RM and Tb is
Co is used as MA and has excellent oxidation resistance. This T
IIX CQ +oo-X system has X of about 13<X and about 3
2, it becomes a compensation composition and is used for compensation point recording, but there are two problems in practical use because the recording operation temperature changes rapidly due to composition changes. That is, a film with a composition ratio in an extremely narrow range must be produced over a large area, but it is actually impossible to produce a film with a composition ratio in such a narrow range over a large area using conventional sputtering.

By using the novel method of the present invention described below, it is possible to create a film that has almost constant recording characteristics over a large area, and furthermore, it can be considered that the film structure has a novel structure as defined above. can be obtained from the backscattered intensity spectrum of He+ using the Raddaford backscattering method. The causal relationship between this membrane structure and the above advantages cannot be explained theoretically at present.

A method for producing a layered laminated film provided by the second aspect of the present invention is a thin film forming method in which two or more metals are deposited in a thin film form on a substrate using sputtering, and the sputtering operation conditions are changed over time. By doing so, the atomic percentage composition ratios of the two types of metals are different in two adjacent layers, thereby forming a multilayer film including at least two or more layers having mutually different composition ratios.

The specific method of temporally changing the sputtering operation described above is to apply a negative bias to the substrate during the sputtering operation and change this bias value over time, and/or to change the partial pressure of an inert gas during the sputtering operation. All you have to do is change the value over time.

In a preferred embodiment of the present invention, the two or more metals are rare earths and transition metals. This alloy of rare earth metal (RM) and transition metal (TM) is important as a recording material for magneto-optical recording media.

Therefore, a preferred embodiment provided by the second aspect of the present invention is to form a perpendicularly magnetized film on a substrate by atomic percent
In a method for manufacturing a magneto-optical recording medium by forming an amorphous thin film of a rare earth-transition metal at a composition ratio by sputtering, the above-mentioned atomic percentage composition k is obtained in two adjacent layers by temporally changing the sputtering operation conditions. 912 (Kori Bift, 'JE No. 1; Il
-/7'1EifIka 1-TohefuμThe feature is that a perpendicular magnetization film is formed.

In order to temporally change the above sputtering operating conditions, the time to apply a negative bias to the substrate is changed, but the bias value can be changed over time and/or the amount of inert gas such as Ar in the sputtering equipment can be changed. What is necessary is to change the pressure over time. This temporal variation of the sputtering conditions causes one of the two metals, for example a rare earth, to be knocked out by a selective resputtering effect, resulting in a thin film rich in metal.

Magneto-optical recording films with a multilayer structure like this are not only important for theoretically explaining the relationship between the physical and magnetic microstructures of perpendicularly magnetized films, but also superlattice-like films are being used industrially. This is important in that it can be obtained from

One particular embodiment of the invention uses terbium as the rare earth metal and cobalt as the transition metal.

This Tb Co-based magneto-optical recording film is being developed because it has the fl1 advantage of being able to obtain a perpendicularly magnetized film with excellent oxidation resistance. Submitted "Method for manufacturing magneto-optical recording media"
It is described in Japanese Patent Application No. 1984-45553 and Japanese Journal of Applied Magnetics 8(2) 149-152 (1984).

However, the practical drawbacks of this Tb Co-based film are (1)
(2) It is difficult to form a uniform recording film over a large area due to the high compositional dependence of Hc, Ms, Ku, etc.;
Generally, when bias sputtering is used to form a perpendicularly magnetized TbCo film, the magnetic properties change significantly over time. (3) When a high bias is applied, the substrate temperature rises, making it impossible to use a plastic substrate. Since the above (1) and (3) are well known, please refer to other documents. Regarding (2) above, please refer to FIGS. 2 and 3. This figure 2 shows T b.

Bias value (VB) of C073 is 0V and -50V, respectively.

-100V, -+50V, -200V (: Film created by bias sputtering by varying argon partial pressure = 10mT
orr, film thickness = 1000 people) Ms time left in the atmosphere (h
r) indicates a change. (In addition, Ms is V.

As is clear from the figure (measured at S and M), Ms changes greatly over time when VB is 1100 V or more. Figure 3 also shows the holding force (I-1) of the Faraday loop.
c) It shows the change in air exposure time (hr), which also shows a large change.

By using the method of the present invention, the above-mentioned drawbacks can be greatly improved. The present invention will be explained below using Examples.

(Example 1) A composite target with a Tb chip placed on a Go disk (
A Tb Co amorphous film was formed on a glass substrate by RF sputtering using Tbz, C073). The input power was 100 W, and the Ar pressure was 3 to 60 mTorr.

According to the features of the present invention, a bias voltage was applied to the substrate in a time-varying manner. That is, the substrate bias voltage (VB)
+, :VB=0V and VB=-toov were alternately changed every minute to form a film having a film thickness of 1.5μ.

Figure 4 shows the backscattered intensity spectrum of the film prepared as described above due to 2.5 MeV He+ using the Loveford backscattering method. and 3
The rise near channel 50 is due to scattering by Co atoms. FIG. 4 shows that the atomic density of Tb is modulated.

This film was a perpendicularly magnetized film.

(Example 2)・ Bias sputtering similar to Example 1 was performed.

However, in Example 2, VB=0V and VB=-1o.

The alternating time with V was varied. In other words, the number of layers of the layered film is increased to 5th so that the total film thickness is approximately 3000.
Changed to the horizontal axis of the figure.

This operation changes the bias value in the bias circuit at a variable time.
A circuit that changes between v and -toov was built-in.

Therefore, for example, in the case of two layers, the thickness of each layer is 3000/2
= 1500 people, and in the case of 72 layers, the thickness of each layer is 30
It can be roughly estimated that there were 42 people in 00/72. However, based on a simple calculation, the effects of sputtering rate and re-sputtering are actually different between 0V and -100V, and each layer does not necessarily have the same thickness.

In the film thus created, the composition ratio of Tb-Co in each layer is naturally limited.

In FIG. 5, on I-1c corresponding to the above number of layers, M s,
The change in K u is an indication. As can be seen from FIG. 5, in the case of a single layer, each magnetic property changes greatly between 0V and -toov, but by using the multilayer film of the present invention, it is possible to control it to the desired value. . In other words, it becomes possible to control the holding force.

Furthermore, it becomes easy to balance stability over time and magnetic properties. That is, as for the stability over time, as shown in FIG. 1, VB=0V is more stable than 110V. on the other hand,
The perpendicular magnetic anisotropy energy Ku is 0V for -toov.
Other experimental data (not shown) suggest that it is much more stable. The layered membrane according to the invention can stabilize Ku.

Furthermore, in the bias sputtering method, when the bias value is increased, the substrate temperature increases;
By repeating 00V, it is possible to prevent the substrate temperature from increasing and it is possible to use a plastic substrate.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing an example of the distribution of different elements (two types in the figure) in a part of the layered film of the present invention (in the figure, only two adjacent layers). Figures 2 and 3 show the M s (emu/cm3) and r-1c (K) of the recording film when the substrate bias value (VB) is changed.
FIG. 3 is a diagram showing changes in Oe) with respect to air exposure time (hr). FIG. 4 shows a 2.5 MeV He+ layered film according to the present invention.
backscattered intensity spectrum. FIG. 5 shows a layered film Hc” according to a special embodiment of the present invention;
Ku(xi Oo-5er/cc), Ms(em
FIG. 2 is a diagram showing the number of layers (u/cc) on the film axis.

Claims (1)

[Scope of Claims] 1) A composition comprising a substrate and a rare earth-transition metal alloy thin film layer formed on the substrate, the rare earth metal and the transition metal having a composition ratio of atomic % to form a perpendicularly magnetized film. In the magneto-optical recording medium, the thin film layer is composed of a layered film of two or more rare earth metal-transition metal layers, and in two adjacent layers of the layered film, atoms of the rare earth metal and the transition metal in one layer are 1. A magneto-optical recording medium characterized in that a composition ratio of several % is different from a composition ratio of several atomic % of the other layer. 2) The magneto-optical recording medium according to claim 1, wherein each layer of the layered film has a thickness of 600 Å or less. 3) The magneto-optical recording medium according to claim 1, wherein the transition metal is cobalt. 4) The magneto-optical recording medium according to claim 1, wherein the rare earth metal is terbium and the transition metal is cobalt. 5) In a method of manufacturing a magneto-optical recording medium by forming by sputtering a thin alloy film of a rare earth metal and a transition metal at a ratio of several atomic percentages to form a perpendicularly magnetized film on a substrate, the sputtering operating conditions are temporally varied. A method characterized in that the perpendicularly magnetized film is constituted by a layered film of at least two or more layers having different composition ratios, such that the atomic percentage composition ratios are different between two adjacent layers. 6) Temporally changing the sputtering operating conditions described above may include temporally changing the time and bias value for applying a negative bias to the substrate, and/or temporally changing the partial pressure of the inert gas in the sputtering apparatus. 6. The method according to claim 5, characterized in that the method is achieved by changing. 7) The method according to claim 5, wherein each layer of the layered film has a thickness of 600 Å or less. 8) The method according to claim 5, wherein the transition metal is cobalt. 9) Claim 5, wherein the transition metal is cobalt, the rare earth metal is terbium, and the temporal change in the sputtering operating conditions is a temporal change in the negative bias value applied to the substrate. The method described in section. 10) The time change of the above bias value is 0V and -100
10. A method according to claim 9, characterized in that the method is achieved by repeating alternately between V and V every minute. 11) The method according to claim 10, characterized in that the above repetitive operation is performed at least twice.