JP2547770B2 - Method for manufacturing information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention irradiates a light beam such as a laser beam to cause magnetization reversal in a light beam irradiation portion of a recording layer to thereby provide information. The present invention relates to a method of manufacturing an information recording medium such as a magneto-optical disk for recording and erasing.

(Prior Art) In recent years, a magneto-optical disk has attracted attention as a large-capacity information recording medium capable of erasing information. In this magneto-optical disk, a rare earth-transition metal alloy is most commonly used for the recording layer. This recording layer has an easy axis of magnetization in a direction perpendicular to the layer surface, and by irradiating the recording layer with a light beam such as a laser beam and heating the irradiated portion in the vicinity of the Curie point, The coercive force is lower than that of the external magnetic field, and that portion is magnetization-reversed by the external magnetic field to record information. The recorded information is reproduced by irradiating the recording layer in which the magnetization reversal is locally generated with a laser beam or the like and detecting the light reflected from the surface of the recording layer at that time. When erasing information, magnetization reversal is caused again in the information recording area.

In such a magneto-optical disk, the recording layer formed of a rare earth-transition metal alloy can be formed by various methods such as a sputtering method, a vapor deposition method and an ion beam method. Among them, the sputtering method, which is relatively easy to control the composition and the film forming rate, is often used. Also, as the substrate, resin materials such as polycarbonate (PC) and polymethylmethacrylate (PMMA), which are advantageous in mass production, are usually used. Since these materials are easily melted, the substrate temperature is relatively high in the sputtering method. The magnetron sputtering method, which does not increase as much, has been adopted, and the equipment for cooling the substrate has been improved.

When forming the recording layer by the sputtering method,
A plurality of substrates are set on a plate, and a target located below the plate is supplied with a predetermined amount of electric power to perform sputtering to form a recording layer having a predetermined composition on the target side surface of the substrate. In this case, it is necessary to make the composition uniform in the disks and between the disks in order to reduce variations in characteristics among the disks and to obtain disks with good characteristics.

Therefore, recently, rare earth-transition metal alloy target,
Alternatively, a composite target formed by arranging a plurality of rare earth metal chips on a transition metal disc is used, and further, a plate, substrate, or target is provided with a rotational movement mechanism to suppress composition variation in and between discs. Is being attempted. Even when a large-area magneto-optical disk having a diameter of 130 mm is manufactured by such a method, it is possible to suppress the macroscopic compositional variation of the recording layer within the disk and between the disks within 0.5 atom%.

However, when magnetron sputtering is performed using a composite target, erosion may progress unevenly due to the magnetic field distribution on the target, so in order to ensure uniformity, reproducibility and long-term stability of the film composition. The array of rare earth chips must be adjusted appropriately. Further, in the case of an alloy target, long-term stability of the composition can be secured, but impurities such as C, O, N, Al, or Ca are easily mixed in the manufacturing process, and the composition is different from the actual sputtered film. Considering the above, it is necessary to adjust the composition in advance.

For this reason, a quaternary simultaneous sputtering apparatus has been adopted in which a disk and a plate on which the disk is installed are equipped with a rotational movement mechanism to rotate and orbit the disk to perform sputtering. According to this device, each disk passes over the target uniformly, so that even if a composite target and an alloy target are not used, the macroscopic composition variation within the disk and between the disks can be reduced to 0.3 by the dual co-sputtering. It can be within atomic%.

(Problems to be Solved by the Invention) However, even if the composition variation can be suppressed to the above range by using such an apparatus,
Coercive force varies between disks. For this reason, the characteristics vary among the disks, which is a major obstacle to mass production of the disks.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing an information recording medium in which variations in coercive force due to manufacturing conditions are small.

[Structure of the Invention] (Means for Solving Problems) An information recording medium according to the present invention is a method for manufacturing an information recording medium having a recording layer formed of a rare earth-transition metal alloy, the method comprising: A step of forming an underlayer having a thickness of 2 Å or more, which is substantially made of a rare earth metal contained in a recording layer, and a plurality of substrates on which the underlayer is formed are rotatably provided on one surface of a rotating plate. Each of the plurality of holders provided, the step of arranging the rare earth metal target and the transition metal target so as to face the surface of the rotating plate on which the substrate is installed, and the substrate held in the holder is the rare earth metal Rotating the rotating plate in a predetermined direction and passing the plurality of holders in the predetermined direction so as to pass directly above the metal target and the transition metal target. A step of rotating the direction of the opposite side, by applying a predetermined electric power to said rare earth metal target and the transition metal target and sputtering,
And a step of forming a recording layer made of a rare earth-transition metal alloy having a thickness of 200 Å or more.

(Operation) The inventors of the present application have repeatedly studied the cause of the variation in coercive force. As a result, the variation in coercive force is caused by the variation in the microscopic composition of the recording layer. It was found that the content of rare earth metal atoms in a certain degree has a great influence. That is, even if the average composition of the recording layers is the same, the coercive force is remarkably different depending on the composition of a few Å parts that are initially formed, and the coercive force shows an abnormal value when the content of the rare earth element in this part is small. Such a phenomenon occurs when the layer thickness of the recording layer becomes smaller than 1000Å, and becomes more severe as the layer thickness becomes smaller. The present invention was made based on such knowledge. By providing an underlayer formed of a rare earth metal in the recording layer adjacent to the substrate side of the recording layer, this underlayer acts as the first formed portion of the recording layer, that is, the most substrate-side portion. Since the composition is substantially constant only with the rare earth element, the variation in coercive force can be reduced even when the recording layer has a small thickness.

Embodiments Embodiments of the present invention will be specifically described below with reference to the accompanying drawings.

FIG. 1 is a sectional view of an information recording medium (magneto-optical disk) according to this embodiment. The substrate 1 is made of a material that is transparent and does not easily change with time, such as glass or a resin such as polymethylmethacrylate (PMMA) or polycarbonate. A protective layer 2, a base layer 3, a recording layer 4, a protective layer 5 and a reflective layer 6 are formed in this order on the substrate 1. The protective layers 2 and 5 are made of, for example, SiN _x , and have a role of protecting the recording layer 4 from oxidation or the like.
The recording layer 4 is formed of a rare earth-transition metal alloy such as a Tb-Fe alloy or a Tb-Co alloy, and upon irradiation with a light beam such as a laser beam, magnetization reversal occurs and information is recorded and erased. . The underlayer 3 is made of a rare earth metal such as Tb contained in the recording layer, and is formed on the protective layer 2 prior to the formation of the recording layer 4. Since the underlayer 3 and the recording layer 4 need to be magnetically coupled to each other, the recording layer 4 is continuously formed after the underlayer 3 is formed. The underlayer 3 preferably has a thickness of 2 Å or more in order to obtain the effects described later, and may have an average of about 10 Å. The reflective layer 6 is made of a material having a high reflectance, such as Ti, and has a role of amplifying the irradiation light beam.

In the information recording medium having such a structure, when the recording layer 4 is irradiated with the light beam and the beam irradiation region is heated to near the Curie point, the coercive force of that portion is lower than the external magnetic field, and that portion is reduced. Information is recorded by reversing the magnetization by an external magnetic field. When erasing information, the portion on which information is recorded is irradiated with a light beam again to cause magnetization reversal. Further, information is reproduced by irradiating the recording layer with a light beam having a relatively small output and detecting the reflected light.

Next, a method of forming the recording layer 4 will be described with reference to FIGS. 2 and 3. A disk-shaped plate 21 is rotatably installed in a sputtering container (not shown) with its surface being substantially horizontal.
The individual holders 22 are rotatably installed. A rare earth metal target 23 such as Tb and a transition metal target 24 such as Co are installed below the plate 21. A disc having a protective layer 2 and a base layer 3 formed on a substrate 1 by sputtering is installed on the lower surface of each holder, and a holder 22 is rotated in a direction of an arrow 26 while a plate 21 is rotated in a direction of an arrow 25. Is passed directly above the target 23, and predetermined power is applied to the targets 23 and 24 to perform sputtering. In this case, since every position of each disk passes over each target uniformly, there is very little macroscopic compositional variation within the disk and between the disks. Also,
Since the underlayer 3 is provided, the underlayer 3 can act as the first formed portion of the recording layer 4, that is, the portion closest to the substrate, and the partial composition is substantially only the rare earth metal. Therefore, the composition is constant, and even when the recording layer has a small thickness, the variation in coercive force between the disks can be made extremely small.

Next, taking a magneto-optical disk having a Tb-Co recording layer as an example, the effect of providing the underlayer will be described more specifically. In the device shown in FIG. 2 and FIG.
When forming the recording layer by original simultaneous sputtering,
The recording layer formed on the disc installed in the holder 22 is
The compositional modulation causes microscopic compositional variations.
FIG. 5 shows Tb and Co by the apparatus of FIG. 2 and FIG.
When a 250 Å TbCo recording layer is formed without providing an underlayer by dual target sputtering, the relationship between the position at the start of film formation on each substrate and the coercive force of the formed recording layer at room temperature is shown. It is a graph figure which shows. This graph shows that the coercive force of the recording layer remarkably differs depending on the position of the substrate at the start of film formation. It should be noted that this graph shows the case where the average composition of the recording layer is Tb richer than the compensation point described later. Further, as a result of an experiment by two-way co-sputtering, the fluctuation range of the coercive force between the disks was mostly within the range of 6 to 12 kO _e .

The cause of such variations in coercive force will be described with reference to FIGS. 5 and 7. FIG. 7 is a diagram showing the relationship between the sample position and the target position at the start of film formation in FIG. In FIG. 6, T indicates a Tb target,
C indicates a Co target. Further, 11 to 16 indicate disks, and arrows 31 and 32 indicate rotation directions. As is clear from FIG. 5 and FIG.
Co, rather than disks 12 and 13 moving in the direction of the target
Disk moving from target to Tb target
Generally, 15 and 16 have higher coercive force.

By the way, there is a certain relationship between the average composition of the recording layer and the coercive force. For example, the relationship between the average composition and the coercive force when the thickness of the recording layer is 1000Å is shown by the solid line in FIG. become. Note that this graph almost agrees with the basic line obtained from the physical constants of the TbCo alloy. As shown by the solid line graph, in the Tb-Co recording layer, there is a compensation point at which the coercive force diverges to infinity when the composition of Tb is about 22 atomic%. Here, since the average composition of the recording layer is set to be Tb rich than the compensation point, the coercive force becomes higher as the average composition becomes Co rich. That is, in FIG. 4 described above, the disks 12, 13
Although the coercive force of the disks 15 and 16 is higher than that of the disk 15, the coercive force of the disks 15 and 16 relatively corresponds to the Co-rich composition by referring to the solid line graph of FIG. On the other hand, since the disks 12 and 13 are closer to the Tb target at the start of film formation, the actual composition in the initial film formation portion of the recording layer becomes relatively Tb rich, and conversely
The initial portions of the films 15 and 16 are relatively rich in Co. From these, it can be seen that when the recording layer is as thin as 250 Å as in this case, the coercive force does not depend on the average composition of the recording layer but on the composition of the portion at the initial stage of film formation. When the recording layer is thin as described above, the graph showing the relationship between the average composition of the recording layer and the coercive force shifts to the right of the solid line as indicated by the broken line in FIG. ', That is, the coercive force is different when compared with the same average composition.
Shifted to the Co rich side, and relatively in the initial part of film formation
When the content of Tb is large, the broken line is a, and when the content of Co is relatively large, the broken line is a '. In any case, when the recording layer is thin, it exhibits a coercive force shifted to the Co-rich side.

Such a phenomenon that the coercive force varies also occurs when an alloy target that does not cause compositional modulation is used. Sixth
The figure shows the positions at the start of film formation of each substrate and the film formation when the recording layer of the TbCo alloy was formed using the Tb ₃₂ Co ₆₈ alloy target by the apparatus shown in FIGS. 2 and 3. FIG. 6 is a graph showing the relationship between the recording layer and the coercive force at room temperature, which is shown when the recording layer has a layer thickness of 1000, 500, 200, 150 and 100Å. Here, the alloy target was placed immediately below the disk 15 at the start of film formation. According to this, the layer thickness is 20
In the case of 0 Å or more, there is practically no variation in coercive force, but when the layer thickness is 150 Å, only the sample 15 located directly above the target at the start of film formation shows an abnormal coercive force, It was confirmed that a coercive force corresponding to the Co-rich side near the compensation point was exhibited. Further, when the layer thickness is 100Å, the sample 15 located immediately above the target at the start of film formation has a reversed hysteresis loop compared to the other samples, and at room temperature, a composition richer in Co than the compensation point is used. It was confirmed that a coercive force corresponding to In the case of an alloy target, it has been confirmed that the transition metal element concentrates on the disk immediately above the target immediately after the start of film formation.Therefore, in this case as well, the coercive force of the recording layer depends on the composition immediately after the film formation. You can see that it changes.

As described above, the cause of the variation in coercive force is the variation in the composition of the initial number of recording layer formation Å. Therefore, if the composition in that portion can be controlled to be constant regardless of the manufacturing conditions, the variation in the coercive force will be reduced. Can be suppressed.

In order to satisfy such conditions, as described above, an underlayer made of a rare earth element contained in the recording layer, such as Tb shown in this example, is provided prior to the formation of the recording layer. By magnetically connecting this underlayer to the recording layer, this underlayer can act as a portion of the recording layer that was initially formed. Since this portion has a constant composition at all times, the storage between the discs is kept constant. The variation in magnetic force can be extremely reduced. Also, regarding the relationship between the average composition and the coercive force, as shown by the alternate long and short dash line in FIG.
It was confirmed that it was almost the same as the case of Å and was very close to the theoretically required basic line.

Next, the results of actually manufacturing and testing the magneto-optical disk according to this example will be described. The PMMA substrate was sputtered by the apparatus shown in FIGS. 2 and 3 under a reduced pressure atmosphere of argon gas, and a 1400 Å silicon nitride protective layer, a 10 Å Tb underlayer, a 250 Å TbCo recording layer, and a 1000 Å A magneto-optical disk was prepared by forming a silicon nitride protective layer and a 500Å Ti reflective layer in this order. The coercive force at room temperature of the 6 disks manufactured by this sputtering was measured. As a result of measuring this three times, as shown in FIG. 4, the coercive force is 5.1 to 5.8 kO _{e in} the graph A and 3.6 to 4.
1 KO _e, 3.05 to 3.45KO _e becomes in C, and either it has been confirmed very the variation conventionally small. The coercive force was made to correspond to the composition in FIG. 8 described above, and the variation in the coercive force was evaluated as the compositional variation. As a result, the variation range of the disk provided with the underlayer was about 0.6 atomic%. With conventional discs, the fluctuation range is 1.5 to 2.0 atomic%
It was confirmed that the underlayer was extremely effective because of its degree.

In addition, as a result of forming this underlayer to a very thin thickness of 2Å,
We were able to obtain almost the same effect as in the case of 10Å. In this case, the coercive force at room temperature was 4.8 to 5.9 kO _e , and the fluctuation range of the composition obtained from the coercive force was 0.9 atom%.

As a result of evaluating the dynamic characteristics of the disc on which the underlayer is formed, the C / N ratio (carrier / noise ratio) is similar to that of the conventional disc on which the underlayer is not formed, and the jitter amount tends to decrease. It was

In this way, it is extremely thin (average layer thickness is about 10Å)
It was possible to significantly reduce the variation in coercive force between disks at room temperature simply by providing the Tb underlayer.

Not only in the case of the TbCo recording layer but also in the case of another rare earth-transition metal alloy recording layer, the same effect can be obtained by providing the underlayer made of the rare earth metal corresponding to the recording layer. The effect of suppressing the variation of the coercive force is particularly large when the recording layer is formed of the compensation point recording material, and the underlayer is useful in such a case.

EFFECTS OF THE INVENTION According to the present invention, in the case of an information recording medium having a rare earth-transition metal alloy recording layer, an underlayer formed of the rare earth metal in this recording layer is provided, and the recording layer is continuously formed. By providing this, the underlayer can act as the portion of the recording layer closest to the substrate, and the composition of this portion is uniform, so that the variation in coercive force between products can be extremely reduced. Therefore, the yield can be improved,
Further, it can be applied to mass production and is extremely useful.

[Brief description of drawings]

FIG. 1 is a sectional view showing an information recording medium according to an embodiment of the present invention, FIG. 2 is a bottom view showing an apparatus for manufacturing this information recording medium, FIG. 3 is a side view thereof, and FIG. 5 is a graph showing the relationship between the disk position and the coercive force of the recording layer at the start of manufacturing the recording layer, and FIGS. 5 and 6 show the relationship between the disk position and the coercive force of the conventional disk at the start of manufacturing the recording layer. FIG. 7 is a graph showing the positional relationship between the disk and the target at the start of manufacturing the recording layer in the case of dual-source simultaneous sputtering, and FIG. 8 is a graph showing the relationship between the composition of the recording layer and the coercive force. Is. 1; substrate, 2, 5; protective layer, 3; base layer, 4; recording layer, 6; reflection amount.

Claims (1)

(57) [Claims] 1. A method of manufacturing an information recording medium having a recording layer formed of a rare earth-transition metal alloy, wherein an underlayer consisting essentially of the rare earth metal contained in the recording layer is provided on a substrate in an amount of 2Å. A step of forming the above-mentioned thickness, a step of respectively installing the plurality of substrates on which the base layer is formed in a plurality of holders rotatably provided on one surface of the rotating plate; Arranging the rare earth metal target and the transition metal target so as to face the installed surface, and the rotating plate so that the substrate held by the holder passes directly above the rare earth metal target and the transition metal target. Rotating in a predetermined direction and rotating the plurality of holders in a direction opposite to the predetermined direction; and the rare earth metal target. Preliminary the transition metal target by applying a predetermined power to the sputtering, 200 thickness
Å A method of manufacturing an information recording medium, comprising the step of forming a recording layer formed of the rare earth-transition metal alloy described above.