JPH0765426A - Production of overwritable magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To produce an overwritable magneto-optical recording medium with a small reduction of C/N in reproducing signals. CONSTITUTION:This overwritable magneto-optical recording medium consists of at least two magnetic layers of a memory layer and a recording layer on a substrate. The magnetic layer is formed by sputtering. In this process, sputter- etching is performed before at least one of the magnetic layers is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an overwritable magneto-optical recording medium. Overwrite refers to the act of recording new information without erasing the previous information. In this case, when played back, the previous information should not be played back. The term "overwrite" as used in the present specification refers to overwrite by simply irradiating the laser beam while modulating the pulse according to the information to be recorded, without modulating the direction and intensity of the recording magnetic field Hb. Tell what to do.

[0002]

2. Description of the Related Art Recently, an optical recording / reproducing method satisfying various requirements including high density, large capacity, high access speed, and high recording / reproducing speed, and a recording apparatus, reproducing apparatus and recording medium used therefor. Efforts are being made to develop. Among a wide range of optical recording / reproducing methods, the magneto-optical recording / reproducing method has a unique advantage that information can be recorded and then erased, and new information can be recorded again and again. For being full of the greatest attraction.

A recording medium used in this magneto-optical recording / reproducing method has a perpendicular magnetic layer (perpendicular magnetic layer or layers) consisting of one layer or multiple layers as a layer for recording. This magnetic film is made of, for example, amorphous GdFe or Gd.
It is composed of Co, GdFeCo, TbFe, TbCo, TbFeCo and the like. The perpendicular magnetic film generally has concentric or spiral tracks, and information is recorded on the tracks. There are two types of tracks, explicit and implicit. [Explicit Track] The magneto-optical recording medium has a disk shape. In a disc having explicit tracks, tracks for recording information are formed in a spiral shape or a concentric circle shape when viewed in a direction perpendicular to the disk plane. There is a groove for tracking and separation between two adjacent tracks. Conversely, the space between the grooves is called a land. In reality, the land and groove are reversed on the front and back of the disc. Therefore, looking at the disk in the same way as the beam enters, the front side is called a groove and the back side is called a land. Since the perpendicularly magnetized film is formed over both the groove and the land, the groove portion may be the track or the land portion may be the track. There is no particular relationship between the width of the groove and the width of the land.

In order to form such a land and groove,
Generally, a substrate has a land formed in a spiral or concentric shape on the surface and a groove sandwiched between two adjacent lands. A thin perpendicular magnetic film is formed on such a substrate. As a result, the perpendicular magnetization film has lands and grooves. [Mark] In the present specification, “upward (upwar
d) "or" downward "
Orientation "and the other is defined as" reverse A orientation ".

The information to be recorded is binarized in advance, and this information has a mark (B ₁ ) having a magnetization in "A direction".
Then, two signals of the mark (B ₀ ) having the magnetization in the “reverse A direction” are recorded. These marks B ₁ and B ₀ correspond to either one or the other of the digital signals 1 and 0, respectively. However, generally, the magnetization of the track to be recorded is aligned in the "reverse A direction" by applying a strong external magnetic field before recording. Act to align the magnetization direction is referred to as the "initialization ^* (initialize ^*)" in the old sense. Then, the mark (B
₁ ) to form. Information is represented by the presence or absence of the mark (B ₁ ), the position, the front end position, the rear end position of the mark, the mark length, and the like. In particular, a method in which the edge position of a mark represents information is called mark length recording. A mark has been called a pit or a bit in the past, but is recently called a mark.

By the way, in order to reuse the recorded medium, (1) initialize the medium again ^* initialize it with the device ^* , or
Or (2) it is necessary to add an erasing head similar to the recording head to the recording device, or (3) it is necessary to erase the recorded information in advance by using the recording device or the erasing device as a pre-stage process. Therefore, in the magneto-optical recording system, it has hitherto been impossible to perform overwriting capable of recording new information on the spot regardless of the presence or absence of recorded information.

However, if the direction of the recording magnetic field Hb can be freely modulated between "A direction" and "reverse A direction" as required, overwriting becomes possible. However, it is impossible to modulate the direction of the recording magnetic field Hb at high speed. For example, when the recording magnetic field Hb is a permanent magnet, it is necessary to mechanically reverse the direction of the magnet. However, it is impossible to reverse the direction of the magnet at high speed. Even when the recording magnetic field Hb is an electromagnet, it is impossible to modulate the direction of a large-capacity current at such a high speed.

However, the technical progress is remarkable, and the intensity of the irradiation light beam should be recorded without modulating the intensity of the recording magnetic field Hb (including ON and OFF) or without modulating the direction of the recording magnetic field Hb. A magneto-optical recording method capable of overwriting, a magneto-optical recording medium capable of being overwritten, and an overwritable recording apparatus also employed therefor have been invented only by modulating in accordance with binary information. A patent application has been filed (JP-A-62-175948 = DE3,619,61)
8A1 = US patent pending Ser. No. 453,255). Hereinafter, this invention is referred to as a "basic invention". [Description of Basic Invention] In the basic invention, "a recording / reproducing layer basically composed of a magnetic thin film capable of perpendicular magnetization
(In this specification, this recording / reproducing layer is referred to as a memory layer Memory
layer or M layer) and a recording auxiliary layer consisting of a perpendicularly magnetizable magnetic thin film reference layer (in this specification, this recording auxiliary layer is a writing layer Writing layer or W).
Layer) and both layers are exchange-coupled (exchange-coupl
ed), and at the room temperature, the overwritable multilayer magneto-optical recording medium capable of keeping only the magnetization of the W layer in a predetermined direction without changing the magnetization direction of the M layer is used.

Information is represented and recorded by a mark having an "A direction" magnetization and a mark having an "inverse A direction" magnetization in the M layer (and also in the W layer in some cases).
In this medium, the W layer has an external means (for example, an initial auxiliary magnetic field Hin.
By i.), the direction of the magnetization can be aligned in the “A direction”. Moreover, at that time, the magnetization direction of the M layer is not reversed, and further, the magnetization direction of the W layer once aligned in the “A direction” is not reversed even when the exchange coupling force from the M layer is received. On the contrary, the magnetization direction of the M layer is not reversed even when receiving the exchange coupling force from the W layer aligned in the “A direction”.

The W layer has a lower coercive force H _C and a higher Curie point T _C than the M layer. According to the recording method of the basic invention, only the magnetization direction of the W layer of the recording medium is aligned in the “A direction” by external means before recording. This act is specifically referred to herein as "initialize". This "initialization" is unique to overwritable media.

Then, the medium is irradiated with a laser beam pulse-modulated according to the binarized information. The intensity of the laser beam has a high level P _H and a low level P _L , which correspond to the high level and low level of the pulse. This low level is higher than the reproduction level P _R that illuminates the medium during reproduction. As is already known, the laser beam may be turned on at a <very low level> even when recording is not performed, for example, to access a predetermined recording position on the medium. This <very low level> is also the same as or close to the reproduction level P _R.

For example, "initialize" for "A direction"
When the medium subjected to e) ”is irradiated with a laser beam of a low level P _L , the temperature of the medium is increased and the coercive force H _{c1 of the} M layer is increased.
Becomes very small or extremely zero. It becomes zero when the temperature of the medium is equal to or higher than the Curie point of the M layer. At this time, the coercive force H _c2 of the W layer is sufficiently large,
It is not reversed by the recording magnetic field Hb in the "reverse A direction".
Then, the force of the W layer reaches the M layer via the exchange coupling force. M
Layers and W layers are generally composed of heavy rare earth metals.
tal: hereinafter abbreviated as RE) -transition metal (transition meta
l: abbreviated as TM hereinafter). The exchange coupling force is composed of a force that aligns the RE magnetic moments of both layers and a force that aligns the TM magnetic moments of both layers. In the alloy, the sublattice magnetization of RE and the sublattice magnetization of TM have opposite directions, and the direction of the larger sublattice magnetization determines the direction of magnetization of the alloy. When both sublattice magnetizations are equal, the composition is called a compensation composition and the temperature is called a compensation temperature. Above the compensation temperature, the TM sublattice magnetization is stronger, and below the compensation temperature, the RE sublattice magnetization is stronger.

There are two types of marks before irradiation with the laser beam: a state in which an interface domain wall exists between the M layer and the W layer and a state in which no interface magnetic wall exists. The mark which does not exist corresponds to the mark to be formed.
The existing mark does not match the mark to be formed. In the latter case, as a result of the force of the W layer reaching the M layer via the exchange coupling force, the magnetization of the M layer having a very small coercive force H _c1 is determined in a predetermined direction (eg, "A direction"). As a result, a mark having no interface domain wall (target mark) is formed between the M layer and the W layer.

Even if the magnetization of the M layer is zero (T _c1 or more), the irradiation of the laser beam is stopped, and the temperature of the medium naturally lowers to slightly lower than the Curie point T _c1.
Magnetization appears in the layer. At this time, similarly, the force of the W layer reaches the M layer via the exchange coupling force. Therefore, the magnetization appearing in the M layer has a predetermined direction (for example, “A
Direction "). From this state, the temperature returns to room temperature, but the predetermined orientation is maintained. However, if there is a compensation temperature in the M layer and the W layer during returning to room temperature, the magnetization direction of the layer is reversed when the temperature exceeds the compensation temperature. This process is called a cold cycle or cold process.

On the other hand, for example, "Initialization (ini
tialize) "is media receives the irradiation of the laser beam of high level P _H, the coercive force H _c1 of the M layer is improved temperature of the medium is zero, the coercive force H _c2 of W layer is very Therefore, the magnetization of the W layer, which has a very small coercive force H _c2 , loses the recording magnetic field Hb and faces a predetermined direction (for example, the “reverse A direction”). Even if the magnetization of the W layer is zero, the irradiation of the laser beam is stopped and the temperature of the medium is naturally lowered to the Curie point T _c2.
When it goes down a little, magnetization appears in the W layer, but at this time,
Similarly, when the recording magnetic field Hb is lost, the magnetization of the W layer is oriented in a predetermined direction (for example, "reverse A direction"). Further, when the temperature of the medium cools and falls slightly below the Curie point T _c1 , magnetization appears in the M layer. At this time, the force of the W layer reaches the M layer via the exchange coupling force. Therefore, the magnetization appearing in the M layer is oriented in a predetermined direction (for example, “reverse A direction”) dominated by the W layer.
From this state, the temperature returns to room temperature, but the predetermined orientation is maintained. However, if there is a compensation temperature in the M and W layers on the way back to room temperature,
When it exceeds that, the magnetization directions of the M layer and the W layer are reversed. This process is called a high temperature cycle or high temperature process.

The above low temperature cycle and high temperature cycle are M
It occurs regardless of the direction of magnetization of the layer and the W layer. anyway,
Before the laser beam irradiation, the W layer is “initialized (initializ
e) ”, so that overwriting is possible. In the basic invention, the laser beam is pulse-modulated according to the information to be recorded. However, the means for pulse-modulating the beam intensity according to the binary information to be recorded is a known means, for example, THE BELL SYSTEM T.
It is described in detail in ECHNICAL JOURNAL, Vol.62 (1983), 1923-1936. Therefore, given the required high and low levels of beam intensity, they are readily available with some modifications to conventional modulation means. For those skilled in the art, such modification would be easy given the high and low levels of beam intensity.

One of the features of the basic invention is
There are high and low levels of beam intensity. That is, when the beam intensity is at a high level, the "A direction" magnetization of the W layer is reversed (reverse A direction) by the recording magnetic field Hb or other external means (re
verse), and the "reverse A direction" magnetization of the W layer forms a mark having "reverse A direction" magnetization (or "A direction" magnetization) in the M layer. When the beam intensity is low, the magnetization direction of the W layer is the same as in the "initialized" state, and
By the action of the layer (this action is transmitted to the M layer through the exchange coupling force), the M layer is magnetized "A direction" [or "reverse A direction"].
Magnetization] is formed.

In the present specification, ○○○ [or △△△]
With the expression, when XX outside [] is read first, XX outside [] will be read also in the following XX [or ΔΔΔ ]. On the contrary, ○○○
If you select and read the △△△ one in [] without reading, you can also read △ ○ △ in [] without reading ○○○ even in the following ○○○ [or △△△ ] Should be read.

The medium used in the basic invention is roughly classified into a first embodiment and a second embodiment. In any of the embodiments, the recording medium has a multilayer structure including an M layer and a W layer. The M layer is a magnetic layer having a high coercive force and a low magnetization reversal temperature at room temperature. The W layer is a magnetic layer having a lower coercive force and a higher magnetization reversal temperature at room temperature than the M layer. Both the M layer and the W layer may themselves be composed of a multilayer film. In some cases, an intermediate layer (for example, between the M layer and the W layer)
Exchange coupling force σ _W adjusting layer ... (Hereinafter, this layer is abbreviated as Int. Layer). For the Int. Layer, see JP-A-64-50257 and JP-A-1-273248.

Further, regarding overwritable magneto-optical recording, in addition to the above, JP-A-4-123339 and JP-A-4-13
Since many materials such as No. 4741 have been issued, here,
Omit further explanation. The disc having a four-layer structure disclosed in Japanese Patent Laid-Open No. 4-123339 has, in addition to the M layer and the W layer,
"Initializing layer" (hereinafter abbreviated as I layer), and exchange coupling between I layer and W layer is turned on.
It has a switching layer (Swithing layer: hereinafter, abbreviated as S layer) to be turned off.

In order to increase the C / N ratio, a read-out layer (Readout layer: below) having a higher Curie point and a higher Kerr effect than the M layer on the M layer (that is, on the laser beam incident side):
A laminate of R layers) is also proposed. For example, see JP-A-63-64651 and JP-A-63-48637. The proposed R layer is also composed of a RE-TM based alloy.

When forming each layer such as the recording layer of the magneto-optical recording medium, the film was formed by a thin film forming technique such as sputtering or vacuum evaporation. At this time, a dielectric protective layer was formed on the surface, and a magnetic layer was formed in layers on the dielectric protective layer to form a multilayer film.

[0023]

Each layer was formed by sputtering by a conventional method, and an overwritable magneto-optical recording medium having a multilayer film was repeatedly recorded and reproduced. As a result, the C / N of the reproduced signal may be significantly lowered.

[0024]

The inventor of the present application investigated the cause of affecting C / N. As a result of research, it was found that the recording sensitivity and the recording / reproducing power margin fluctuate because the exchange coupling force between the layers varies. Further, the present inventor has continued his research in order to investigate the cause of variations in exchange coupling force. Then, as a result of diligent research, they found that there was a problem in the method of forming each layer. It has been found that when each layer is formed by sputtering, the state of the interface changes due to the influence of the impure gas inside the apparatus before and after the film formation, the variation in the exchange coupling force between the magnetic layers increases, and as a result, the C / N decreases. It was

The present invention has been made in view of the above problems, and an object thereof is to reduce variations in exchange coupling force. Therefore, firstly, in a method of manufacturing an overwritable magneto-optical recording medium by forming at least two magnetic layers of a memory layer and a recording layer on a substrate by sputtering, forming at least one of the magnetic layers. A method (claim 1) characterized in that a sputter etching is performed before.

[0026]

In the present invention, sputter etching is performed before forming each magnetic layer. That is, the surface of the magnetic layer is subjected to so-called cleaning treatment by sputter etching. This allows
The state of the interface between the magnetic layers can be made constant between lots, and variations in exchange coupling force can be suppressed.

The sputter etching is an etching in which a reverse bias is applied to the ordinary sputtering, Ar gas is introduced into the chamber, a substrate on which a magnetic layer is formed is set, and Ar ions are made to collide with the surface. . The apparatus used for the sputter etching is the same as the conventional sputtering apparatus, but a bias converting means is required in order to reverse bias the bias voltage applied during sputtering.

The power applied during the sputter etching in the present invention is 0.1 to 1.5 [W / cm ² ],
0.2 to 0.7 [W / cm ² ] is preferable. The gas pressure introduced into the chamber is 0.15 to 0.70 [Pa], but 0.3 to
0.6 [Pa] is preferable. Further, the sputter etching time is 10 to 300 (sec), preferably 10 to 30 (se).
c].

[0029]

【Example】

(1) First, prepare a 2P substrate in which an ultraviolet curable resin (PP: Photo-polymer) having a thickness of about 50 μm is formed on a glass substrate having a diameter of 130 mm and a thickness of 1.2 mm. A large number of grooves are spirally formed on the resin layer from the inner peripheral side (radius r = 30 mm) to the outer peripheral side (radius r = 60 mm). The dimensions of the groove are 0.5 μm in width, 1.6 μm in pitch, and 600 Å in depth. (2) A magnetic layer is formed on the substrate by sputtering.
And a protective layer is formed, but reverse sputtering is performed before forming the R, M, I, and W layers. Each layer was formed under the following conditions.

Type of film Ar pressure [Pa] Input power to target [kw] Second protective layer: 0.20: 1 R layer: 0.30: 1 M layer: 0.50: 1 I layer: 0. 25: 1 W layer: 0.20: 1 1st protective layer: 0.20: 1 And a recording medium having the following constitution and film thickness is formed under such conditions.

Second protective layer: SiN: 700Å R layer: GdFeCo: 300Å M layer: TbFeCo: 200Å I layer: GdFeCo: 100Å W layer: DyFeCo: 500Å First protective layer: SiN: 700Å (3) Sputtering on substrate To form a first protective layer, before forming a W layer thereon, before forming an I layer, before forming an M layer,
Before forming the R layer, a bias voltage opposite to that used during sputtering is applied to perform sputter etching. The conditions are shown below.

Input power 0.5 W / cm ² Ar pressure 0.4 Pa Time 120 sec

[0033]

Example 2 (1) The same substrate as that of Example 1 is used. (2) The configurations of the magnetic layer and the protective layer, the manufacturing method, and the manufacturing conditions are the same as those in Example 1. (3) Sputter etching is performed before forming the W layer, before forming the I layer, before forming the M layer, and before forming the R layer, as in the first embodiment. The conditions are shown below.

Input power 1.3 W / cm ² Ar pressure 0.5 Pa Time 300 sec

[0035]

Example 3 (1) The same substrate as that of Example 1 is used. (2) The configurations and manufacturing methods of the magnetic layer and the protective layer, and the manufacturing conditions are the same as those of Example 1. (3) Sputter etching is performed before forming the W layer, before forming the I layer, before forming the M layer, and before forming the R layer, as in the first embodiment. The conditions are shown below.

Input power 0.2 W / cm ² Ar pressure 0.2 Pa Time 20 sec

[0037]

Example 4 (1) The same substrate as that of Example 1 is used. (2) The structure and manufacturing method of the magnetic layer and the protective layer, and the manufacturing conditions are the same as those of Example 1. (3) Sputter etching is performed before forming the R, I, and W layers. The conditions are shown below.

Input power 0.5 W / cm ² Ar pressure 0.4 Pa Time 120 sec

[0039]

Fifth Embodiment (1) The same substrate as that used in the first embodiment is used. (2) The configurations, manufacturing method, and manufacturing conditions of the magnetic layer and the protective layer are the same as those in the first embodiment. (3) Sputter etching is performed before forming the R and W layers.
The conditions are shown below.・ Input power 0.5 W / cm ²・ Ar pressure 0.4 Pa ・ Time 120 sec

[0040]

Comparative Example 1 (1) The same substrate as that used in Example 1 is used. (2) The structure, manufacturing method, and manufacturing conditions of the magnetic layer and the protective layer are the same as those in Example 1. (3) Sputter etching is not performed.

[0041]

Comparative Example 2 (1) The same substrate as in Example 1 is used. (2) The configurations and manufacturing methods of the magnetic layer and the protective layer, and the manufacturing conditions are the same as in Example 1. (3) Sputter etching is performed only before forming the R layer. The conditions are shown below.・ Input power 0.5 W / cm ²・ Ar pressure 0.4 Pa ・ Time 120 sec

[0042]

COMPARATIVE EXAMPLE 3 (1) The same substrate as that used in Example 1 is used. (2) The configurations, manufacturing method, and manufacturing conditions of the magnetic layer and the protective layer are the same as those in Example 1. (3) Sputter etching is performed before forming the R, M, I, and W layers. The conditions are shown below.

Input power 0.1 W / cm ² Ar pressure 0.2 Pa Time 5 sec

[0044]

Comparative Example 4 (1) The same substrate as in Example 1 is used. (2) The configurations and manufacturing methods of the magnetic layer and the protective layer, and the manufacturing conditions are the same as in Example 1. (3) Sputter etching is performed before forming the R, M, I, and W layers. The places where this sputter etching is performed are described in Examples 1 to 1.
Same as No. 3, but the sputter etching conditions were changed as follows.

Input power 2.5 W / cm ² Ar pressure 0.7 Pa Time 120 sec A for each of Examples 1 to 5 and Comparative Examples 1 to 4.
A magneto-optical recording medium was manufactured by setting two types of manufacturing conditions of type B and type B.

For the A type, the ultimate vacuum in the chamber of the sputtering apparatus was set to 3.0 × 10 ⁻⁵ [Pa] or less for each of the examples and comparative examples, and the next sputtering was performed immediately after the sputtering of a certain layer was completed. Alternatively, sputter etching was performed. For the B type, the ultimate vacuum was set to 2.0 × 10 ⁻⁴ or more and 0.5 × 10 ⁻⁴ [Pa] or less, and after the sputtering of a certain layer, an interval of 5 minutes was set and the next sputtering or sputter etching was performed. .

In this way, two samples of A type and B type were prepared. That is, the A type and the B type have the same conditions for sputtering and sputter etching, but the B type is configured by setting a certain time between sputtering and sputtering or between sputtering and sputter etching and further lowering the degree of vacuum. The magnetic layer or the sputter-etched layer surface is vulnerable to external influences, that is, the manufacturing conditions are such that the exchange coupling force is reduced. The purpose is to prove the relationship between the effect and the present invention.

For each sample, the optimum recording power was measured at a linear velocity of 11.3 m / s, a recording frequency of 4.0 MHz, a duty of 50%, and a recording magnetic field of 300 Oe, and C / after being overwritten 10 times with the recording power. N was measured. Table 1 shows the measurement results of Examples 1 to 5.

[0049]

[Table 1]

Table 2 shows the measurement results of Comparative Examples 1 to 4.

[0051]

[Table 2]

From these results, in the case where the magnetic layers were processed by the sputter etching under the conditions of the present invention (Example 1), when the sputter etching processing was not performed between the magnetic layers (conventional), the conditions other than the present invention were used. It can be seen that the decrease in C / N of the reproduction signal is smaller than that in the case where the sputter etching process is performed in (Comparative Example). Furthermore, when a magnetic layer is formed with a certain time between sputtering or between sputtering and sputter etching (B type)
Also in the above, it is understood that the C / N of the reproduction signal is small when the sputter etching is performed under the conditions of the present invention.

Therefore, even if the manufacturing method is changed to A type or B type, the magneto-optical recording medium manufactured under the conditions of the present invention can be reproduced by C / C of the reproduced signal even if the overwrite operation is repeated.
It was found that the decrease in N was small.

[0054]

As described above, according to the present invention in which the surface of the magnetic layer is sputter-etched, it is possible to minimize the change in the state of the surface of the magnetic layer due to the influence of impurities (gas, etc.) inside the sputtering apparatus. Therefore, the reproduction signal of the overwritable magneto-optical recording medium sputter-etched under the conditions of the present invention has a small decrease in C / N even when recording / reproduction is repeated, and has high durability. It is possible to manufacture a magnetic recording medium. Further, as can be seen from the examples, the signal quality is further improved depending on the sputter etching conditions.

Above

Claims (2)

[Claims] 1. A method for manufacturing an overwritable magneto-optical recording medium by forming at least two magnetic layers of a memory layer and a recording layer on a substrate by sputtering, and before forming at least one of the magnetic layers. A method comprising performing sputter etching on the substrate. 2. The overwrite according to claim 1, wherein the input power in the sputter etching, the gas pressure of the gas used in the sputtering, the sputter etching time, and the ultimate vacuum in the chamber of the sputtering apparatus are set under the following conditions. Method for manufacturing a possible magneto-optical recording medium. Input power (W / cm ² ): 0.1 or more and 1.5 or less Gas pressure (Pa): 0.15 or more and 0.70 or less Time (sec): 10 or more and 300 or less Ultimate vacuum in chamber (Pa): 1.0 x 10 ^-3 or less