JPH05120732A - Optical recording medium and method for preventing generation of defective article - Google Patents

Abstract

PURPOSE:To prevent the generation of defective articles by balancing a contrast, sensitivity and durability at a high level and effectively executing the quality control of the optical recording medium having the excellent characteristic balance. CONSTITUTION:This optical recording medium has at least a optical recording medium layer and a reflection layer on a substrate and this reflection layer is constituted of at least aluminum and 5 to 15 atomic % oxygen. The oxygen content in the reflection layer of this optical recording medium is measured by using fluorescent X-ray spectral method and is so controlled as to attain 5 to 15 atomic %, by which the generation of the optical recording medium having the defective quality is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel optical recording medium and a defective product preventing method therefor. More specifically, the present invention has an optical recording medium which has a reflective layer composed of aluminum and oxygen which also has a function as a cooling layer, and which has excellent contrast and sensitivity, and excellent durability, The present invention relates to a method for effectively preventing the generation of defective products by controlling the oxygen content in the reflective layer of a recording medium.

[0002]

2. Description of the Related Art In recent years, in the field of information recording, the demand for image processing has been rapidly increasing, and along with this, there has been a demand for higher density and larger capacity, and research is actively conducted. Among them, the optical recording medium performs recording by using a semiconductor laser as a light source, so that it is possible to increase the recording density by about 10 to 100 times as compared with the magnetic recording medium which has conventionally been responsible for most of information recording. Further, it is definite to handle a huge amount of information in the near future, and therefore, an optical recording medium having a high density and a large capacity and a high potential is attracting attention as a promising information recording medium.

This optical recording medium is roughly classified into three types, a read-only type (ROM), a write-once type (WO), and a rewritable type, according to the purpose. Of these, the rewritable type optical recording medium is recorded and erased. There are two types: a type in which recording is performed separately and a type in which simultaneous recording can be performed while erasing (OW, overwrite). In the present day when the capacity is increasing, it is essential to increase the access speed, and the latter method is indispensable for the spread of optical discs.

As the OW system of the optical recording medium, there are known two systems, a magneto-optical system and a phase change system. The former magneto-optical method is a method in which the coercive force of the electron spin in the recording layer is lowered by the heat when irradiating the laser beam, it is reversed by an external magnetic field, and information is recorded / erased in the direction of the electron spin. is there. The recorded information is reproduced by utilizing the fact that the polarization of the reflected light of the laser light is different depending on the electron spin direction due to the Kerr effect.

Further, there are two types of methods of magnetic field modulation and optical modulation in this magneto-optical OW. In the former magnetic field modulation method, the magnetization of the recording film is erased by heating with a laser beam to modulate with a magnetic circuit.・ It is a method of recording. On the other hand, among the latter optical modulation methods, the exchange coupling multi-layer film method using a recording layer and a memory layer having different coercive force and Curie temperature characteristics is known as the one most practically used. In this principle, the recording layer is magnetized in advance only by the initialization magnet in the erasing direction, and then the bias power is applied in the recording direction (opposite to the erasing direction), and the optical power is controlled in two steps to overwrite. is there. At low power, the magnetization is erased only in the memory layer, the magnetic domains in the recording layer are transferred to erase the data, and at high power, the magnetization in the memory layer and the recording layer are simultaneously erased, and new magnetization is performed in the direction of the bias magnetic field for recording. I do.

On the other hand, the phase change method is a method in which a laser beam is focused on a recording layer and the heat of the laser beam controls the phase state of the recording layer between a crystalline state and an amorphous state to perform recording / erasing. That is, the recording is performed by heating with a strong power and then rapidly cooling to be non-crystallized, and the erasing is performed by heating at a temperature equal to or higher than the crystallization temperature and then gradually cooling to crystallize. The reproduction is performed by the difference in the reflectance of each phase state, and the recording material is usually Sb-Te-Ge system or In-S system.
A b-Te based alloy is used.

This phase change method has the highest OW potential, and the speed of data processing using this is progressing. Further, unlike the magneto-optical method, a magnet and a polarizing plate are not required, so that an optical system is required. In addition to simplifying, downsizing, thinning and cost reduction of the device can be achieved, and in order to perform reproduction by changing the reflectance, W
It has the advantage of high compatibility with O and ROM.

In any of these methods, in such an optical recording medium, in order to reduce the size of the pits and record with high density, the cooling speed of the recording medium is increased during recording so that heat is retained in the recording layer. It is desirable to prevent large diffusion. Therefore, conventionally, in the optical recording medium, a cooling layer is often provided on the recording layer via an upper protective layer. FIG. 1 is a cross-sectional view of an example of an optical recording medium having such a layer structure, in which a lower protective layer 2, a recording layer 3, an upper protective layer 4 and a reflective layer (cooling layer) 5 are sequentially arranged on a substrate 1. The stacked structure is shown.

In addition to the cooling effect, the cooling layer also plays the role of a reflection layer for enhancing the contrast of the reflectance between the portion recorded by the laser beam and the unrecorded portion and adjusting the reflectance. Aluminum is generally used as the material of such a reflective layer (cooling layer). Since this aluminum has a high thermal conductivity, it has a large cooling effect, is inexpensive, and can be formed efficiently by sputtering. Moreover, the film does not emit light of the oscillation wavelength of the semiconductor laser used for recording / erasing the medium. It has many characteristics such as reflection.

However, in the laminated structure shown in FIG. 1, the substrate 1 is a polycarbonate, the lower protective layer 2 and the upper protective layer 4 are derivatives made of ZnS and SiO ₂ , the recording layer 3 is an Sb-Te-Ge alloy, and the reflective layer is a reflective layer. When an optical recording medium in which the layer 5 was made of aluminum was treated at 90 ° C. and 80% RH for 600 hours, it was observed that many pinholes were formed in the reflective layer. It is considered that the stress was applied to the corner of the land portion 6 shown in the enlarged view of the disk and the stress migration occurred. By the way, if a pinhole is formed in the reflective layer in this way, the reflectance becomes uneven, which causes an increase in the error rate of the signal and makes recording / reproducing difficult, and finally the recording medium cannot be used. ..

The reflecting layer using aluminum has such instability, and in order to overcome this instability, a method of incorporating oxygen is usually adopted. When oxygen is mixed, aluminum oxide is formed at the crystal grain boundaries and the crystal grains are miniaturized, so that the occurrence of stress migration is suppressed.

However, as the amount of oxygen mixed increases, the content of aluminum oxide having poor thermal conductivity in the reflective layer also increases, so that the thermal conductivity of the reflective layer decreases. When the thermal conductivity of the reflective layer is lowered in this way, the cooling rate becomes slow, and the recording sensitivity of the medium is governed by the amount of oxygen mixed. Moreover, since aluminum oxide has a low reflectance,
As the amount of oxygen mixed increases, the reflectance of the reflective layer itself also decreases. Therefore, if the amount of oxygen mixed is too large, the original role of the reflective layer cannot be fulfilled.

[0013]

DISCLOSURE OF THE INVENTION The present invention provides an optical recording medium having a good balance of characteristics such as good contrast and sensitivity, and excellent durability, and at the same time, the generation of an optical recording medium of poor quality. The purpose of the invention is to provide a method for effectively preventing it.

[0014]

DISCLOSURE OF THE INVENTION As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that at least a recording layer and a reflective layer are provided on a substrate, and at least aluminum is used as the reflective layer. The optical recording medium using a specific content of oxygen is well balanced in contrast, sensitivity and durability, and the oxygen content in the reflective layer is measured by X-ray fluorescence spectroscopy. It was found that the generation of a defective optical recording medium can be effectively prevented by measuring and controlling the value to be within a specific range, and the present invention has been completed based on this finding. ..

That is, the present invention provides an optical recording medium having a structure having at least a recording layer and a reflective layer on a substrate,
An optical recording medium, characterized in that the reflective layer is composed of at least aluminum and oxygen, and the oxygen content in the reflective layer is 5 to 15% based on the atomic ratio, and the reflection of the optical recording medium. The present invention provides a method for preventing defective products by measuring the oxygen content in a layer using fluorescent X-ray spectroscopy and controlling the value to be 5 to 15% based on the atomic ratio. ..

In the optical recording medium of the present invention, a recording layer and a reflective layer are provided on the substrate as essential constituent layers,
It is necessary to use a material of at least aluminum and oxygen as the material of the reflective layer. The oxygen content in the reflective layer needs to be in the range of 5 to 15% based on the atomic ratio. If the content is less than 5%, crystal grains grow and gaps are easily formed between the grains to cause stress migration, the stabilizing effect is not sufficiently exhibited, and the recording medium has poor durability, and exceeds 15%. Since a large amount of aluminum oxide is formed, the thermal conductivity of the reflective layer decreases, the cooling rate slows down, the sensitivity of the recording medium decreases, and the reflectance of the reflective layer itself decreases and its original role. Will not be able to fulfill.

The method for forming the reflective layer is not particularly limited, and the oxide may be mixed in aluminum by a method conventionally used for forming the reflective layer, such as a co-evaporation method or a sputtering method. Oxygen may be mixed into aluminum by a reactive sputtering method.

The recording layer in the optical recording medium of the present invention is not particularly limited, and may be one conventionally used as a recording layer in an optical recording medium, such as a magneto-optical type, a phase change type or a dye type. However, a rewritable type that requires durability against repeated recording and erasing is particularly preferable. Examples of the phase change recording layer include TeOx,
Te-Ge, Sn-Te-Ge, Bi-Te-Ge, S
b-Te-Ge, Pb-Sn-Te, Tl-In-Se
Examples of the magneto-optical recording layer include Tb-Co, Tb-Fe-Co, and Gd-Tb.
-Co, Nd-Dy-Tb-Fe-Co, etc. may be mentioned.

The method for forming the recording layer is not particularly limited, and a method conventionally used for forming the recording layer, for example, a vacuum vapor deposition method or a sputtering method can be used in the alloy system.

The material of the substrate in the optical recording medium of the present invention is selected from those conventionally used as the substrate of the optical recording medium, for example, resins such as polyethylene, polypropylene, polystyrene, polycarbonate, polymethylmethacrylate, and glass. Although any one can be selected and used, among these, the optical characteristics are excellent,
Polycarbonate, polymethylmethacrylate, glass and the like, which have high mechanical strength and excellent dimensional stability, are suitable.

Further, in the optical recording medium of the present invention,
If desired, on or under the recording layer, or both, for the purpose of preventing oxidation and corrosion of the recording layer and the reflective layer,
Alternatively, a protective layer may be provided on the uppermost layer.

The present invention provides a method for preventing the production of defective products together with the above-mentioned optical recording medium. In the method for preventing the production of defective products, the oxygen content in the reflective layer of the optical recording medium is changed to fluorescence. It is measured using X-ray spectroscopy, and the value is controlled to be 5 to 15% based on the atomic ratio.

In the fluorescent X-ray spectroscopy, quantification is carried out using the fluorescent X-rays of aluminum Kα1,2 and Kα3,4. Aluminum oxide Kα1,2 wire is
Since it is derived from aluminum, it depends only on the amount of aluminum and is not affected by oxygen. However, the Kα3,4 ray depends on the band gap that increases with the bond with oxygen, and therefore increases as the bond increases. Utilizing this fact, a calibration curve for the amount of oxygen in the aluminum reflective layer is created, and the oxygen content in the reflective layer is determined using this, and the value is in the range of 5 to 15% based on the atomic ratio. By controlling in this way, generation of a defective quality optical recording medium is prevented.

[0024]

The optical recording medium of the present invention is provided with a reflective layer composed of at least aluminum and a specific amount of oxygen, and the contrast, sensitivity and durability are balanced at a high level.

Further, according to the present invention, the oxygen content in the reflective layer is measured by fluorescent X-ray spectroscopy, and the value is controlled to be within a specific range, whereby the generation of an optical recording medium of poor quality is prevented. It can be effectively prevented.

[0026]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0027] Example 1 polycarbonate substrate, lower protective layer made of a dielectric material of ZnS and SiO _2, a recording layer made of Sb-Te-Ge alloy, upper protective layer formed of a dielectric of ZnS and SiO ₂ and Each of the optical discs has a structure in which a reflective layer made of aluminum and oxygen is sequentially laminated, and the oxygen content in the reflective layer is changed at a rate of 0 to 30% based on the atomic ratio (all other conditions are the same). It was made.

Next, for each optical disk, the recording sensitivity was determined, and the signal error rate [bit error rate (BER)] when the acceleration time was 600 hours under the condition of 90 ° C. and 80% RH was measured. In addition, the reflectance was obtained for each of the samples in which only the reflective layer was separately prepared under the same conditions. The results are shown in Table 1.

[0029]

[Table 1]

It can be seen from Table 1 that the aluminum reflective layer having an oxygen content in the range of 5 to 15% has good BER, reflectance and recording sensitivity. When the oxygen content is 0%, the BER is large, and when the oxygen content is 30%, the reflectance is too low to serve as a reflective layer.

Further, since the sensitivity changes depending on the oxygen content, in order to keep the sensitivity within a certain range, the oxygen content in the reflective layer immediately after the optical disc was manufactured was measured,
It can be seen that the value may be controlled so that it falls within the desired range.

Example 2 In order to prepare a calibration curve for the relationship between oxygen content and Kα radiation, a polymethylmethacrylate substrate 1 was prepared as shown in FIG.
Aluminum was sputtered on the above under the following conditions to form a reflective layer 5.

Sputtering conditions Target: Aluminum Sputtering gas: Argon gas containing 0 to 30 atomic% oxygen Sputtering pressure: 10 mTorr Sputtering power: 0.7 kw

As the sputtering gas, a mixed gas of argon and oxygen was used, and the Kα ray of aluminum was quantitatively measured with the oxygen content in the atomic unit of oxygen being the oxygen content. Further, since the count number of fluorescent X-rays is proportional to the film thickness of the reflective layer, Kα3,4 /
The ratio of Kα1,2 was used. The result is shown in FIG. Figure 4
Is the oxygen content (atomic%) of the reflective layer on the horizontal axis and Kα on the vertical axis.
It is a calibration curve with a ratio of 3,4 / Kα1,2.

From this figure, it is found that there is a proportional relationship between Kα3,4 / Kα1,2 and the oxygen content, and this relationship is expressed by the following equation. y = 3.343 × 10 ⁻⁴ x + 0.7210 x: oxygen content (atomic%) y: Kα3,4 / Kα1,2

According to this equation, the value of y such that x becomes 5 to 15 is 0.07377 to 0.07711. Therefore, Kα3,4 / Kα1,2 is 0.07
By setting it to 377 to 0.07711, the oxygen content in the reflective layer can be controlled to 5 to 15 atom%, and the occurrence of defective products can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of an optical recording medium of the present invention.

FIG. 2 is an enlarged view of a disk.

FIG. 3 is a sectional view of a sample for preparing a calibration curve.

FIG. 4 is a calibration curve showing the relationship between the oxygen content in the reflective layer and the Kα line.

[Explanation of symbols]

 1 Substrate 2 Lower protective layer 3 Recording layer 4 Upper protective layer 5 Reflective layer 6 Land part 7 Group

Claims (2)

[Claims] 1. An optical recording medium having a structure having at least a recording layer and a reflective layer on a substrate, wherein the reflective layer is composed of at least aluminum and oxygen, and the oxygen content in the reflective layer is based on an atomic ratio. An optical recording medium characterized by being 5 to 15%. 2. The quality control of the optical recording medium according to claim 1, wherein the oxygen content in the reflective layer of the optical recording medium is measured by fluorescent X-ray spectroscopy, and the value is 5 based on the atomic ratio. A method for preventing the generation of defective products of an optical recording medium, which is characterized in that the content is controlled to be -15%.