JPH0778364A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To inhibit the occurrence of uneveness in quality between the layers of a laminated film, to suppress a variation in reflectance and to prevent the deterioration of C/N value in reproduction in a magneto-optical recording medium using a protective film as a film having a laminated structure so as to allow the time required to form the protective film disposed in contact with the substrate and requiring a relatively long film formation time as compared with other constituent layers of the medium to accord with processing cycle time on and after the ensuing stage. CONSTITUTION:A protective film interposed between a substrate and a magnetic recording film has a laminated structure consisting of plural layers of the same material and the difference in refractive index between the constituent layers of the protective film is <=+ or -3.0% or the difference in compositional ratio between the layers is <=+ or -3.0%. The protective film preferably has an interfacial oxidized film having <=10Angstrom thickness between the layers. The surface roughness Rmax of each of the layers is preferably <=20Angstrom .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording such as a magneto-optical disk for recording / reproducing and erasing information by using a laser beam, which is used for still image files, medical files and other personal information management files. The present invention relates to a medium, and more particularly, to a layer structure of a protective film provided in contact with a substrate for improving its productivity.

[0002]

2. Description of the Related Art With the recent increase in the recording capacity of application software and files for personal computers and workstations, the conventional floppy disk (FD) has been replaced by about 10
Although a magneto-optical disk (MO) having a recording capacity of 0 times has been widely used and used, the price is still high and the cost reduction in the future is desired.

Here, the general structure and manufacturing process of a magneto-optical disk will be described first, and problems of the prior art will be clarified.

A magneto-optical disk uses a disk-shaped plastic substrate having a groove called an uneven guide track on which a four-layer film is usually laminated. In this case, from the substrate side, the first layer protective film, the second layer magnetic recording film, the third layer
It is generally composed of a layer protective film and finally a fourth layer reflective film, but there is also a configuration without the fourth layer reflective film. Each of the four-layer films is usually produced by a sputtering method.

In the sputtering method, the vacuum container is depressurized to a predetermined pressure, a rare gas such as argon is introduced into the container, and at the same time, a voltage is applied to the target so that the rare gas is ionized and induced by an electric field to collide with the target. At this time, atoms are ejected from the target material and adhere to the substrate to form a thin film.

That is, actually, the plastic substrate is put into the first vacuum chamber, and first the first-layer protective film is formed. A raw material target such as Si is preliminarily provided in the first vacuum chamber, and argon gas and nitrogen gas are flown to apply a voltage to form a film. The film thickness is 100
About 0Å is required, and the time required for this is about 6 minutes. When this step is completed, the second-layer magnetic recording film is formed in the second chamber to a thickness of about 200Å. in this way,
The substrate processed in the previous step is sent to the next step, and the fourth layer is sequentially and repeatedly manufactured continuously.

Here, the process that requires time for manufacturing is film formation of the first-layer protective film provided in contact with the substrate, and generally, the time required for each film-forming process for the second and subsequent layers is several times as long. In short, in the sputtering devices arranged in series, the process of forming the first-layer protective film is rate-determining, and the production cycle cannot be shortened. Therefore, recently, two or more vacuum chambers are serially added between the first protective film chamber and the second magnetic recording film chamber to increase the total takt time to 2.
It is being considered to increase productivity several times depending on the minutes.

For example, the first film having a total film thickness of 1000Å
In order to form the layer protective film, two or more vacuum chambers are provided in series with respect to the process of forming the first layer protective film and the second layer magnetic recording film subsequent to the first layer protective film. The film thickness in the chamber is 333Å and 1/3 of 1000Å divided by time, and the film formation time of the first layer protective film is matched with the tact of the process after the second layer magnetic recording film to improve efficiency. It is a thing. A problem at this time is that when the first-layer protective film is formed in a laminated structure, variations in the quality of each laminated film affect the signal characteristics of the disc, causing a significant quality problem.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the film formation time of a protective film provided in contact with a substrate, which requires a relatively long film formation time as compared with the other layers of the medium structure, in the subsequent steps. In a magneto-optical recording medium having a laminated structure of a protective film in order to match the production tact, it is to suppress the variation in the quality of each layer of the laminated film to reduce the reflectance fluctuation and prevent the reproduction C / N value from deteriorating. .

[0010]

In order to achieve the above object, according to the present invention, a protective film provided between a substrate and a magnetic recording film has a structure in which a plurality of layers made of the same material are laminated. And the difference in the refractive index of the laminated films constituting the protective film is within ± 3.0%, or the difference in the composition ratio of the laminated films is ±.
There is provided a magneto-optical recording medium characterized by being within 3.0%. Further, according to the present invention, there is provided a magneto-optical recording medium having the above-mentioned structure, which has an interfacial oxide film having a film thickness of 10 Å or less between each laminated film. Further, according to the present invention, there is provided a magneto-optical recording medium having the above-mentioned structure, wherein the surface roughness Rmax of each laminated film is 20 Å or less.

The present invention is a conventional type magneto-optical disk produced by sputtering a first layer protective film in contact with a substrate to form a single layer by changing the time, and sputtering the second layer magnetic recording film and the subsequent layers in series. (Hereinafter referred to as a single layer type protective film disk), the first layer protective film is divided into a plurality of layers,
The magneto-optical disk having the same performance as that of the conventional single-layer type protective film disk (hereinafter referred to as a laminated layer), in which the operating rate of the sputtering apparatus is increased by adjusting to the takt time of the process after the second layer magnetic recording film following the layer protective film. Type protective film disk)
Is provided. That is, by defining the characteristics of each laminated film of the first layer protective film as described above, it is possible to suppress the characteristic deterioration as a magneto-optical disk due to the laminated structure of the first layer protective film, and to significantly reduce the manufacturing cost. Can be reduced to.

In the present invention, the difference in the refractive index between the layers formed by stacking the protective film made of the same material in a plurality of times is ± 3.0% or less. A laminated protective film having a composition ratio difference of ± 3.0% or less is provided. In comparison with the conventional first layer protective film of the single-layer type protective film disc having a uniform refractive index, in the laminated type protective film disc, a difference easily occurs in the refractive index between the respective laminated protective films. The reflectance and C / N as a magnetic disk fluctuates. In order to set the allowable range of the reflectance of the laminated protective film disc to ± 1% with respect to the conventional single-layer protective film disc, the refractive index difference of the laminated protective film must be suppressed within ± 3%. In the present invention, the refractive index of each layer of the first layer laminated protective film is changed by changing the flow rate of the reaction gas to be introduced together with the rare gas at the time of sputtering. Therefore, the refractive index difference of each layer is ± 3%.
In order to suppress the change within the range, the change in the flow rate of the reaction gas during sputtering may be appropriately controlled.

In the present invention, a protective film composed of at least two kinds of elements is used. Specific examples thereof include SiN, TaO, SiAIN, SiON, SiAIN, etc., and nitrogen gas can be used in forming these films. , Oxygen gas corresponds to the reaction gas.

Here, by appropriately controlling the change of the reaction gas inflow at the time of sputtering, the composition ratio difference of each layer of the laminated protective film is ±.
Since the difference in the refractive index of each layer of the laminated protective film can be kept within ± 3.0% by suppressing it within 3%, the allowable range of the reflectance of the laminated protective film disc with respect to the conventional single-layer protective film disc. Can be maintained at ± 1%. The composition ratio mentioned here is applied to all the constituents of the protective film, and is the ratio of one of the constituents of each layer of the laminated protective film to the other composition, and the ratio of the target components in the binary system. Is one set, but three sets in the ternary system are six sets in the quaternary system.

In the present invention, it is necessary that the film thickness of the interfacial oxide film layer existing between the laminated films of the laminated protective film is 10 Å or less. As the thickness of the interfacial oxide film layer increases, both reflectance and C / N decrease, and the oxide layer thickness is limited to about 10Å.

Further, in the present invention, it is desirable that the surface roughness Rmax of the interfacial oxide film layer existing between the respective laminated films of the laminated protective film is 20 Å or less. The surface roughness of the interfacial oxide film layer is Rmax
When exceeds 20Å, the noise level rises and C / N decreases.

[0017]

EXAMPLES Examples of the present invention will be specifically described below in comparison with conventional single-layer type protective film disks and comparative examples, but the present invention is not limited to these.

FIG. 1 shows a first conventional single layer type protective film disk.
The chamber structure of the sputtering process which produces from a layer protective film to a 4th layer reflective film is shown. In FIG. 1, the first layer protective film, the second layer magnetic recording film, the third layer protective film and finally the fourth layer
The chambers of the layer reflective film are in series.

FIG. 2 shows a chamber structure for manufacturing the disk of the present invention. In the conventional type, the chambers of the first layer protective film to the fourth layer reflective film are in series, whereas in the vacuum chamber of the first layer protective film. Is arranged in series with respect to the next step (a laminated 1st film chamber, a laminated 2nd film chamber and a laminated 3rd film chamber).

Conventional Example In order to compare with the magneto-optical disk of the example, a conventional single layer type protective film disk was manufactured as follows. First, a diameter of 8 cm was used as a target in the apparatus having the chamber configuration in FIG.
Using a Si target of No. 1 and flowing argon gas and nitrogen gas on a polycarbonate substrate having a guide track under a gas pressure of 2 mtorr (the flow rates of argon and nitrogen gas at this time are standard gas flow rates), a total thickness of about 1000
The laminated protective film of Å was formed in 6 minutes. Next, TbDyFeCo is 500 Å as the second magnetic recording film, SiN is 300 Å as the third protective film, and AlTi is the fourth reflective film.
500 Å was sputtered for about 2 minutes to produce a magneto-optical disk.

Example 1 After setting a Si target having a diameter of 8 cm as a target in each laminated film chamber of the apparatus having the chamber structure shown in FIG. 2, argon gas and nitrogen gas were placed on a polycarbonate substrate having a guide track in the laminated 1st film chamber. 340 Å laminated 1st film is provided in about 2 minutes while flowing, and is transferred to the laminated 2nd film chamber, and 330 Å laminated 2nd film is provided in the same manner as the laminated 1st film in about 2 minutes, and further transferred to the laminated 3rd film chamber. A 330 Å laminated 3rd film was provided in about 2 minutes, and a laminated protective film with a total pressure of about 1000 Å was provided. At this time, the vacuum degree during movement of each laminated film chamber was kept constant at a vacuum degree during movement of 0.5 × 10 ⁻⁵ torr, and the refractive index of the laminated 1st protective film was 2 mtor for the gas thickness in the chamber.
The laminated protective film of Examples 1-1 to 1-7 shown in Table 1 was prepared by increasing and decreasing the nitrogen gas flow rate centering on the standard gas flow rate state (Example 1-4 corresponds to this) while keeping r constant. . In addition,
The gas flow rate standard state refers to the flow rates of argon and nitrogen gas when the first-layer protective film of the conventional example is formed. Next, as in the conventional disk, TbD was used as the second layer magnetic recording film.
yFeCo is 200Å and SiN is 3 as a third layer protective film.
00 Å, AlTi was sputtered at 500 Å as the fourth layer reflective film to fabricate the magneto-optical disks of Examples 1-1 to 1-7.

Comparative Example 1 Magneto-optical disks of Comparative Examples 1-1 to 1-4 were manufactured in the same manner as in Example 1 except that the laminated 1st film was provided at a nitrogen gas flow rate outside the range adopted in Example 1. did.

Table 1 shows the characteristics of each laminated film of the first layer protective film of the conventional example, Examples 1-1 to 1-7, and Comparative examples 1-1 to 1-4.
And the characteristics of the magneto-optical disk are shown. The conventional example is displayed as a reference for the example and the comparative example. The refractive index and the film thickness are measured by an ellipsometer after being formed on a monitor glass set at the same time as the plastic substrate. Moreover, Examples 1-1 to 1-7 and Comparative Example 1
The composition ratio of each laminated film of the first-layer protective film of -1 to 1-4 was obtained by measuring the profile in the depth direction by Auger electron spectroscopy. The difference in refractive index is {(refractive index of laminated 1st film−refractive index of laminated 2nd film) / refractive index of laminated 2nd film} × 10
0, the composition ratio difference is {(composition ratio of laminated 1st film−laminated 2sn
The composition ratio of the d film) / the composition ratio of the laminated 2nd film} × 100. Furthermore, the signal characteristics are Nakamichi OMS2000.
It was measured at.

[0023]

[Table 1]

From the results shown in Table 1, nitrogen gas can be used in order to set the allowable range of the reflectance of the laminated protective film disc to ± 1% with respect to the conventional single-layer protective film disc so that C / N ≧ 52 (dB). Adjust the flow rate to make the refractive index difference of the laminated protective film ± 3 (%)
You can see that Further, it is also understood that in order to keep the refractive index difference of each layer within ± 3 (%), the element ratio difference of each layer should be within ± 3%.

Example 2 In Example 1, the nitrogen gas flow rate during the production of the laminated 1st film and the laminated 2nd film was set to a standard gas flow rate state to keep the refractive index constant, and the laminated 3rd film was changed to a standard gas flow rate of the standard gas flow rate. Examples 2-1 and 2-2 are performed in the same manner as in Example 1 except that the flow rate state is changed to the center (Example 2-4 corresponds to this).
A -7 magneto-optical disk was produced.

Comparative Example 2 Magneto-optical disks of Comparative Examples 2-1 to 2-4 were produced in the same manner as in Example 1 except that the laminated 3rd film was provided at a nitrogen gas flow rate outside the range adopted in Example 2. did.

Table 2 shows the characteristics of the first layer protective film of the conventional example, Examples 2-1 to 2-7 and Comparative examples 2-1 to 2-4, and the characteristics of the magneto-optical disk. The refractive index and the film thickness are measured by an ellipsometer after being formed on a monitor glass set at the same time as the plastic substrate. Further, the difference in refractive index is {(refractive index of laminated 1st film−laminated 2nd
The refractive index of the film) / the refractive index of the laminated 2nd film} × 100. The film thickness of the prepared sample was obtained by measuring the profile in the depth direction by Auger electron spectroscopy. further,
The signal characteristics were measured by Nakamichi OMS2000.

[0028]

[Table 2]

From the results shown in Table 2, the allowable range of reflectance of the laminated protective film disk is ±± compared with the conventional single layer protective film disk.
It can be seen that in order to set C / N ≧ 52 (dB) to 1%, the nitrogen gas flow rate should be adjusted so that the difference in refractive index between the laminated films becomes ± 3 (%).

Example 3 Examples 3-1, 3 and 3 were carried out in the same manner as in Example 1 except that the standard gas flow rate was used and the vacuum degree during movement was set to 10 ⁻⁵ torr and 10 ⁻⁶ torr. A magneto-optical disk No. 2 was produced.

Comparative Example 3 In Example 3, the degree of vacuum during movement was set to 10 ⁻⁴ torr and 10
Comparative Example 3-1 in the same manner as in Example 3 except that ^-3 torr was used.
And 3-2 magneto-optical disks were produced. Table 3 shows the characteristics of the laminated films of the conventional example, Example 3-1, and Comparative examples 3-1, 3-2, and the characteristics of the magneto-optical disk. The refractive index and the film thickness are measured by an ellipsometer formed on a monitor glass set in the same manner as the plastic substrate. The thickness of the oxide film of the formed protective film was obtained by measuring the profile in the depth direction by Auger electron spectroscopy. Furthermore, the signal characteristics were measured by Nakamichi OMS2000.

[0033]

[Table 3]

In Table 3, in the conventional example, the protective film was manufactured by a single process, and the interface oxide film was not formed. In the embodiment, an interfacial oxide film of 10 Å or less is formed,
The performance is comparable to the conventional example. However, as in the comparative example, both the reflectance and the C / N decrease as the thickness of the interfacial oxide film increases, so it can be seen that the thickness of the interfacial oxide film is preferably 10 Å or less.

Example 4 In Example 1, the gas pressure of the laminated 1st film was changed from 1 to 4 mtorr around the reference gas pressure of 2 mtorr of the conventional example as shown in Table 4 (corresponding to Example 4-2). Magneto-optical disks of Examples 4-1 to 4-4 were prepared in the same manner as in Example 1 except that the film was prepared.

Comparative Example 4 A magneto-optical disk of Comparative Example 4-1 was prepared in the same manner as in Example 4 except that the gas pressure was changed to 5 mtorr as shown in Table 4.

Separately from the magneto-optical discs of Example 4 and Comparative Example 4, each layer of the first layer laminated protective film was prepared under the same conditions as a sample for measuring surface roughness, and the surface roughness was measured by a film thickness difference meter. Was measured. Table 4 shows the surface roughness of each layer of the first layer laminated protective film of Conventional Example, Examples 4-1 to 4-4 and Comparative Example 4-1, and the characteristics (noise level) of the magneto-optical disk. The noise level of the signal characteristics was measured with Nakamichi OMS2000.

[0038]

[Table 4]

When the roughness of the laminated film is increased, the noise level is increased and the C / N is decreased. In Example 4-4, the surface roughness is 18 Å and the deterioration is 1 dB, and the surface roughness is 20.
It can be seen that Å or less is preferable. Comparative Example 4-1
The surface roughness is 25Å, and deterioration of 4 dB is recognized.

[0040]

According to the present invention, in order to speed up the production tact, in a magneto-optical recording medium in which a protective film provided on a substrate and a magnetic recording layer film has a multi-layered structure, each layer of laminated films constituting the protective film is It is possible to suppress variation in quality, reduce reflectance fluctuation, and prevent reproduction C / N value from deteriorating.

[Brief description of drawings]

FIG. 1 is a diagram showing a chamber configuration for producing a conventional single-layer type protective film disk.

FIG. 2 is a diagram showing a chamber configuration for producing a laminated protective film disk according to the present invention.

Claims (3)

[Claims] 1. A protective film provided between a substrate and a magnetic recording film has a structure in which a plurality of layers made of the same material are laminated, and a difference in refractive index between laminated films forming the protective film is ±. 3.
Within 0%, or the composition ratio difference of each laminated film is ± 3.0
%, A magneto-optical recording medium. 2. The magneto-optical recording medium according to claim 1, wherein an interfacial oxide film having a film thickness of 10 Å or less is provided between each laminated film. 3. The magneto-optical recording medium according to claim 1, wherein the surface roughness Rmax of each laminated film is 20 Å or less.