JPH05205319A - Manufacture of optical recording medium - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of an optical recording medium capable of reducing occurrence of data error by carrying out an initialization process for a recording surface of the optical recording medium in a state that foreign matters such as dusts are not present on the substrate surface CONSTITUTION:In the initialization process for a recording layer which is carried out for a phase transition type optical recording disk 1, after each layer is formed by sputtering, while gaseous nitrogen 13a in an electrically charged state is blown to the substrate surface of the phase transition type optical disk 1, it is irradiated with Ar-laser beam 11a and then the recording layer is made to a crystal state (initialization state).

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 optical recording medium, and more particularly to an initialization technique for its recording layer.

[0002]

2. Description of the Related Art With the increasing demand for higher density and larger capacity of information recording, an optical recording medium has a higher recording density than a magnetic recording medium, and a reproducing head and a recording medium Since it is possible to record and reproduce information in a non-contact state, it is regarded as a promising recording method capable of reliably recording an enormous amount of information. Such optical recording media can be roughly classified into three types, a read-only type, a write-once type, and a rewritable type, depending on the application.
Of these, rewritable optical recording media are the most promising because they can erase and rewrite recorded information. Among such rewritable optical recording media, a typical one is a phase-change optical recording disc 1 (phase-change optical recording medium) shown in FIG. Includes a lower protective layer 3 made of ceramic or the like, a recording layer 4 made of Ge ₂ Sb ₂ Te ₅ or the like on the surface, an upper protective layer 5 made of ceramic or the like on the surface, and an aluminum alloy on the surface. And a surface protective layer 7 made of an ultraviolet curable resin or the like on the surface thereof. In the phase-change optical recording disc 1 having such a configuration, the phase state of the irradiation portion is changed, for example, in accordance with the pulse output and pulse width of the laser light with which the recording layer 4 is irradiated from the polycarbonate substrate 2 side. Information is recorded or erased by reversibly transitioning or transitioning between a crystalline state and an amorphous state. That is, the output of the laser light is modulated into a high output level (writing level) and a low output level (erasing level), as shown by the solid line 31 in FIG. 3, and the recording layer 4 is irradiated from the polycarbonate substrate 2 side. To do. Here, when laser light of a high output level is irradiated at the time of information recording, regardless of whether the state before irradiation is a crystalline state or an amorphous state, the laser beam is melted and then rapidly cooled, as shown in FIG. Thus, the non-crystalline recording spot 22 (recording bit) is formed. On the other hand, when laser light of a low output level is irradiated at the time of erasing, even if the state before irradiation is an amorphous state, it is annealed, and as shown in FIG.
Return to (Erase Bit). Therefore, overwriting is possible. During reproduction, the reflectance of the laser beam differs between the crystalline state and the amorphous state, that is, the reflectance of the erase spot 23 in the crystalline state is higher than the reflectance of the recording spot 22 in the amorphous state. Then, the information is reproduced by utilizing the high price. In addition, in FIG. 4, 21 is
This is an area in which the initialized state (crystal state) in the recording area is maintained as it is.

In the phase change type optical recording disk 1 having such a structure, the recording layer 4 is entirely crystallized (erased state) after the respective layers constituting the same are sputtered in the manufacturing process. The initialization process is performed. this is,
The recording layer 4 after each layer of the phase-change optical recording disk 1 is formed by sputtering is in an amorphous state, and even if an erasing level of laser light is irradiated in this state, the transition to the crystalline state is sufficient. This is because a large difference does not occur between the reflectance of the recording spot 22 and the reflectance of the erasing spot 23. Therefore, conventionally, as shown in FIG. 6, while the phase-change optical recording disk 1 is rotated, the laser beam 40a of low energy density emitted from the laser 40 is reflected by the mirror 42.
The phase-change optical recording disk 1 is irradiated with a spot diameter larger than the spot diameter of the laser light irradiated during recording or reproduction, for example, 50 μm through an optical system such as the above. The entire surface of the recording layer 4 is crystallized (initial state).

[0004]

However, in the conventional initialization method, the phase change type optical recording disk 1 after each layer is formed by sputtering is directly irradiated with the laser beam 40a. Variable optical recording disk 1
If a foreign substance such as dust or dust is present on the substrate surface, the laser beam 40a is blocked and does not reach the recording layer 4, and unevenness in the crystal state is likely to occur. Also, A
When the initialization process is performed using the r laser, the power level is relatively large, and the energy received by foreign matter is also large. Therefore, it burns and burns on the substrate surface of the phase change optical recording disk 1. There is also a problem that the substrate surface of the phase change optical recording disk 1 is damaged and a defective portion is generated there. Here, when the initialization process is performed by using a laser beam having a small spot diameter like a semiconductor laser, the laser beam 40a is easily blocked by a foreign substance, and a non-irradiated portion is generated in the recording layer 4 to cause a crystal. The state (initialized state) is likely to be uneven and defective portions are likely to occur. Such a defective portion is a phase change type optical recording disk 1
If it exists on the surface of the substrate, the signal is not normally recorded in the defective portion, which hinders the recording and reproduction of information. Therefore, the defective portion generated in the phase-change optical recording disk 1 in the initialization step causes an increase in data errors (fixed bit errors) that occur in a fixed manner, resulting in a bit error rate of the phase-change optical recording disk 1. Will be high. For example, for a phase change type optical recording disc 1 rotating at a rotation speed of 1800 r / min, the output level is about 2.5 w,
The feed rate of Ar laser light having a spot light flux diameter of 50 μm in the radial direction of the phase-change optical recording disk 1 is 20 μm /
In the phase-change optical recording disk 1 that has been subjected to the initialization process while being moved under the condition of r, the foreign matter existing on the substrate surface causes crystals to form on the substrate surface of the phase-change optical recording disk 1. It has been confirmed by observing the phase-change optical recording disk 1 with an optical microscope that defects such as unevenness and image sticking of foreign matter occur in the state. When information is reproduced from the phase-change optical recording disk 1 in the state where such a defective portion exists, disturbance (noise) 32a may occur in the reproduced signal as shown by the solid line 32 in FIG. It has been confirmed. Particularly, since the recording density of the phase change type optical recording disk 1 is about 1 bit / μm ^{2 which} is higher than that of the magnetic disk or the magnetic tape by one digit or more, even if a minute defect exists, many Since a fixed bit error occurs, the feature of the recording system with high reliability and high density is lost.

In view of the above problems, the object of the present invention is to
An object of the present invention is to realize an optical recording medium manufacturing method capable of preventing the occurrence of a data error by performing an initialization process for a recording layer of an optical recording medium in a state where foreign matter such as dust is not present on the substrate surface. ..

[0006]

In order to solve the above problems, according to the present invention, a recording layer whose optical characteristics are changed by irradiation of laser light, for example, a phase change which reversibly changes its phase by irradiation of laser light. In the method of manufacturing an optical recording medium having a recording layer made of a type recording material, the means taken for the initializing step is an Ar laser while blowing an inert gas onto the substrate surface side of the optical recording medium. That is, the recording layer is initialized by irradiating laser light such as light.

Here, it is preferable to spray the inert gas in a charged state onto the substrate surface side of the optical recording medium.

[0008]

In the method of manufacturing an optical recording medium according to the present invention, when the laser beam is applied to the optical recording medium to initialize the state of the recording layer, the laser beam is applied from the substrate surface side of the optical recording medium. Is performed while the substrate surface side of the optical recording medium is irradiated with an inert gas, even if foreign matter such as dust or dust is present on the substrate surface of the optical recording medium, Foreign matter is removed. Therefore, since the laser beam applied to the optical recording medium is applied to the recording layer without being blocked by the foreign matter, the entire surface of the recording layer is uniformly initialized, and the foreign matter is removed from the substrate surface of the optical recording medium. It is not burnt into the substrate and the substrate surface of the optical recording medium is not damaged. Therefore, the optical recording medium has no defective portion. In particular, when an inert gas is blown in a charged state by passing it through an electrostatic field, the substrate surface of the optical recording medium side or the foreign matter side is charged even if it is charged. Since foreign matter can be easily removed from the recording medium, the entire surface of the recording layer can be initialized more uniformly, and the occurrence of fixed bit errors can be prevented more reliably.

[0009]

EXAMPLES Next, the initialization step of the method of manufacturing a phase change optical recording disk (optical recording medium) according to the examples of the present invention will be described.

Here, the structure of the phase-change optical recording disk of this example is expressed in the same manner as the structure of the conventional phase-change optical recording disk, and will be described with reference to FIG.

In the figure, a phase change type optical recording disk 1 is shown.
Is a lower protective layer 3 made of a mixture (ceramic) of ZnS and SiO ₂ and having a thickness of about 10 nm on the surface side of a polycarbonate substrate 2 having a diameter of 90 mm.
And the thickness of Ge ₂ Sb ₂ Te ₅ etc. on the surface is about 2
The recording layer 4 having a thickness of 0 nm, the upper protective layer 5 having a thickness of about 120 nm made of ceramic or the like on the surface thereof, the reflective cooling layer 6 made of an aluminum alloy or the like on the surface, and the surface thereof are formed by spin coating. It is laminated with the adhered surface protective layer 7 made of an ultraviolet curable resin or the like. Here, in the phase-change optical recording disc 1 after forming each layer, since the recording layer 4 is in an amorphous state, the light reflectance thereof is low, about 5%. The reflective cooling layer 6
Has a function of efficiently absorbing the irradiated laser light into the recording layer 4 to enhance its utilization efficiency and a function of increasing the cooling rate when the recording layer 4 is transitioned from a crystalline state to an amorphous state.

In the phase-change type optical recording disk 1 having such a structure, as described in detail with reference to FIGS. 3 and 4, the pulse of the laser beam applied to the recording layer 4 from the polycarbonate substrate 2 side. Corresponding to output and pulse width,
Information is recorded or erased by reversibly shifting or phase-shifting the phase state of the irradiated portion between the crystalline state and the amorphous state. Here, the recording layer 4 is formed in an amorphous state after each layer is formed by sputtering on the surface side of the polycarbonate substrate 2, and even if the laser beam of the erasing level is irradiated in this state, the recording layer 4 shifts to the crystalline state. Is not sufficient, and a large difference does not occur between the reflectance of the recording spot and the reflectance of the erasing spot. Therefore, an initialization step is performed in which the entire surface of the recording layer 4 formed in the amorphous state is preliminarily brought into the crystalline state.

As an initialization step therefor, in this example, as shown in FIG. 1 which is a sectional view of the step, the phase change type optical recording disk 1 is rotated at a rotation speed of about 1800 r / min while By irradiating the substrate surface 1a side with the Ar laser light 11a having a laser spot light flux output from the large-diameter Ar laser 11 having an output power of about 2.5 w and having an output power of about 50 μm, the entire circumference of the substrate 1a is irradiated. Irradiate with Ar laser light 11a. At the same time, by adjusting the conditions of the optical system such as the arrangement angle of the mirror 12,
The Ar laser light 11a is irradiated in the radial direction of the substrate surface 1a of the phase change optical recording disk 1 under the condition that the feed rate is about 20 μm / r. As a result, the Ar laser light 11a is applied to both the circumferential and radial areas of the phase-change optical recording disk 1. Here, the Ar laser light 11a
The phase change optical recording disk 1 is irradiated with Ar laser light 1
It is performed on the laser waist of 1a (on the focal plane) or, if necessary, in a state of being shifted from the laser waist toward the laser light source side.

Further, in the initialization process of this example, A
The nitrogen gas gun 13 blows the nitrogen gas 13a as an inert gas toward the substrate surface 1a of the phase-change optical recording disk 1 irradiated with the r laser light 11a. An electrode for forming an electrostatic field is arranged inside the nitrogen gas gun 13 with respect to the gas flow path, and the nitrogen gas 13a is sprayed in a charged state by passing through the electrostatic field. .. Therefore, even if foreign matter such as dust or dust is present on the substrate surface 1a side of the phase change type optical recording disk 1, these foreign matter are blown off by the nitrogen gas 13a and the phase change occurs. The substrate surface 1a of the optical recording disk 1 is always in a clean state. Moreover, since the nitrogen gas 13a is ionized and charged, even if the side of the phase change type optical recording disk 1 or the side of the foreign matter is charged, these foreign matters are removed from the phase change type optical recording disk. It can be easily removed from the first substrate surface 1a.

As described above, in the initialization process of this example, even if the phase-change optical recording disk 1 is conveyed to the initialization process with foreign matter on the substrate surface 1a side, When the substrate surface 1a is irradiated with the Ar laser light 11a, the foreign matter is completely blown off by the charged inert gas, so that the recording layer 4 is uniformly initialized. Therefore, even when the substrate surface 1a of the phase-change optical recording disk 1 is observed with an optical microscope, it is confirmed that there is no defect portion due to unevenness of the crystalline state or burning of foreign matter. ing. Further, the reproduction signal obtained by irradiating the phase-change optical recording disk 1 which has been subjected to the initialization process of the present example with the reproduction-level laser light is flat as shown by the solid line 33 in FIG. A reproduced signal is obtained, and unlike the reproduced signal (shown in FIG. 7) obtained from a phase change type optical recording disk employing a conventional initialization process, no signal disturbance (noise) is observed. That is, on the substrate surface 1a of the phase-change optical recording disk 1, there is no portion where the Ar laser light 11a is not irradiated due to the presence of foreign matter, that is, there is no region where defect temperature is generated due to insufficient temperature rise, Even uneven initialization is unlikely to occur. Therefore, the bit error rate (error occurrence frequency after repeating recording and erasing) measured by repeatedly performing recording and erasing on the phase-change optical recording disk 1 is 10 ⁻⁶ , which is the same as the conventional bit error rate. Rate 10
^-It has been confirmed that it has been greatly improved compared to ⁴ units.

The conditions such as the rotation speed of the phase change type optical recording disk in the initialization step and the laser output for the initialization are not limited to the conditions used in the above embodiment, but the phase change is performed. The optical recording disc has a property that it should be set to optimum conditions according to the structure of each layer of the optical recording disk, for example, the thickness and material of the recording layer.

Also, the gas to be blown is not limited to nitrogen gas, and a rare gas such as Ar may be used alone or as a mixed gas. Furthermore, the method of charging the gas is not limited.

[0018]

As described above, in the method of manufacturing an optical recording medium according to the present invention, the initialization step of irradiating the optical recording medium with laser light in a state of being blown with an inert gas is performed. Since it is characterized, it has the following effects.

Even if foreign substances such as dust and dust are present on the substrate surface side of the optical recording medium, the initialization process is performed by irradiating the laser beam while removing them with an inert gas. It is unlikely that a non-irradiated part of the laser beam or seizure of foreign matter will occur on the side. Therefore, it is possible to prevent the generation of the defective portion due to the unevenness of the initialization state and the burning, so that the recording layer can be uniformly initialized and the occurrence rate of the data error can be reduced.

Since the burn-in does not occur on the substrate surface of the optical recording medium, the yield does not decrease even if the initialization process is performed with a laser beam of higher power. Therefore, the initialization step can be performed in a short time, and the laser power margin in the initialization step is large, so that the production efficiency and the yield of the optical recording medium are improved.

When the inert gas is blown in a charged state, the foreign matter can be easily removed even if the optical recording medium or the foreign matter is charged, so that the reliability and the production of the optical recording medium are improved. The effect of improving the property is remarkable.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an initialization process performed in a method for manufacturing a phase change optical recording disk according to an example of the present invention.

FIG. 2 is a sectional view showing a general structure of a phase change optical recording medium.

FIG. 3 is a graph showing a laser output level modulation state used for writing and erasing on the phase-change optical recording medium shown in FIG.

4 is a schematic diagram showing recording spots and erasing spots formed on the phase-change optical recording medium shown in FIG.

FIG. 5 is a waveform diagram of a reproduction signal obtained from the phase change type optical recording disk according to the example of the present invention.

FIG. 6 is a conceptual diagram of an initialization process performed in a conventional method for manufacturing a phase change optical recording disk.

FIG. 7 is a waveform diagram of a reproduction signal obtained from a conventional phase change type optical recording disk.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Phase change type optical recording disk (optical recording medium) 1a ... Substrate surface 2 ... Polycarbonate substrate 4 ... Recording layer 11, 40 ... Ar laser 11a, 40a ... Ar laser light 12, 42 ... Mirror 13 ... Nitrogen gas gun 13a ... Nitrogen gas 22 ... Recording spot 23 ... Erase spot

Front page continued (72) Inventor Kaichi Sato 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Fuji Electric Co., Ltd. (72) Inventor Haruo Kawakami 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Within Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. A method of manufacturing an optical recording medium having a recording layer, the optical characteristics of which change when irradiated with laser light.
A method for manufacturing an optical recording medium, which comprises an initialization step of irradiating a laser beam onto the substrate surface side of the optical recording medium while irradiating the same with a laser beam to initialize the recording layer. .. 2. The method for manufacturing an optical recording medium according to claim 1, wherein the inert gas is blown onto the substrate surface side of the optical recording medium in a charged state. 3. The method for manufacturing an optical recording medium according to claim 1, wherein the recording layer is made of a phase-change recording material that reversibly changes its phase when irradiated with a laser beam.