JP2002123977A - Write once read many optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a write once read many optical recording medium capable of controlling recording sensitivity as well as of improving corrosion resistance. SOLUTION: In the write once read many optical recording medium obtained by stacking a first protective layer 3, a phase change recording layer 4 of 10-40 nm thickness so formed that it can record an information signal by a phase change, a crystallization promoting layer 5 and a reflecting layer 7 on a disk substrate 2, a second protective layer 6 of 1-100 nm thickness comprising SiN or ZnS-SiO2 is disposed between the crystallization promoting layer 5 and the reflecting layer 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a write-once optical recording medium, and more particularly, to a write-once optical recording medium which is adapted to record information additionally by phase change recording.

[0002]

2. Description of the Related Art As an optical information recording medium for recording and reproducing data by irradiating an optical recording layer with a laser beam, a write-once optical disc which can be recorded only once, and erasing and re-recording of a recorded information signal. 2. Description of the Related Art A rewritable optical disk capable of performing the following is known.

The recording principle of a write-once optical disc includes, for example, a method of making a hole in the recording layer, a method of thermally deforming the recording layer, a method of alloying or aggregating a metal, a method of changing the phase of the recording layer, and a method of using an organic dye. Conventionally, a method of causing heat has been proposed.

[0004] Among these methods, CD-R (Compact Disc R), which is often used recently as a write-once optical disc, is used.
ecordable: write-once CD) has a disc reflectivity of 65
%, The recording principle is mainly based on a method of heat-sensing an organic dye. The reason is,
This is because the recording principle other than the method of heat-sensing the organic dye cannot simultaneously satisfy the two points that the optical constant of the recording layer is an appropriate value and that recording is possible while having a high reflectance. .

A DVD having a higher recording density than a CD-R
-R (Digital Versatile Disc Recordable: write-once D
VD) has also been commercialized. In this DVD-R, the reflectance of the disk does not need to be as high as that of a CD-R. However, the method of making organic dyes heat-sensitive is still the main recording principle. The reason is as follows. In DVD-R, the recording method is mark edge recording (pit edge recording) and recording is performed at high density.
Therefore, the recording marks (recording pits) need to be sharply formed with the correct shape at the set position. It has been difficult to control such mark edges by a recording principle other than the method of heating an organic dye.

However, the recording principle based on the method of causing an organic dye to heat-sensitive has a problem that the wavelength of a laser beam to be recorded has a high wavelength, and recording and reproduction cannot be performed even if the wavelength fluctuates by several tens of nm. In addition, the wavelength of laser light capable of high-density recording on a write-once optical disk employing an organic dye is different from the wavelength for recording on a conventional optical disk. Therefore, there is also a problem that the disk drive cannot be shared with the conventional product, and the compatibility is low.

On the other hand, many write-once optical disks using the recording principle of changing the recording layer in phase have been commercialized.
In this case, a material that undergoes a phase change between crystalline and amorphous due to the difference in the intensity of the laser light to be irradiated is used as the recording layer material. This recording principle has an advantage that the wavelength dependence of laser light to be recorded is lower than that of a recording principle in which an organic dye is heat-sensitive.

The structure of this type of optical disk is as follows.
A structure in which a metal reflective layer is provided on a recording layer has been proposed (JP-A-62-154341, JP-A-63-1).
No. 76185). According to these documents, by providing a reflective layer containing antimony (Sb), tellurium (Te) or bismuth (Bi) as a main component on a recording layer, sensitivity is increased and optical contrast is increased. Like that.

However, the reflective layer materials mentioned in these proposals are suitable when the recording method is mark position recording (pit position recording). Unlike mark edge recording, mark position recording does not require precise control of edges of recording marks. Even if a reflective layer containing Sb, Te or Bi as a main component is provided on the recording layer, the edge controllability of the recording mark is not improved. Therefore, these proposals are made when the recording method is mark edge recording. Is not suitable.

Japanese Patent Application Laid-Open No. Sho 60-164937 discloses a method in which a recording layer of an optical disc has a three-layer structure having a light absorbing layer between two phase change layers in order to improve recording sensitivity. Is described. The phase change layer is made of selenium (S
e) It is composed of a simple substance, a Se compound, or a Se alloy.
Further, the absorption layer is made of Bi alone, Te alone, or an alloy thereof. However, even this method is not suitable for the case where the recording method is mark edge recording.

Japanese Patent Application Laid-Open No. Sho 60-28045 discloses an information recording medium having a recording layer having a two-layer structure. The first layer constituting the recording layer is made of a chalcogenide glass (for example, Te, Bi, Sb, indium (In)) or a compound thereof (for example, Bi-Te).
Consists of The recording principle of this medium is a method of alloying or aggregating the above-mentioned metals.

Japanese Patent Application Laid-Open No. 9-66668 discloses that
An optical disc having a recording layer having a three-layer structure is disclosed. The recording layer is composed of a Sb-Se based thin film, Bi-
It is composed of a Te-based thin film and an Sb-Se-based thin film. The recording principle of this medium is a method of alloying or aggregating the above-mentioned metals.

Japanese Patent Application Laid-Open No. 5-342629 discloses that a recording layer made of a Te—Ge—Sb alloy is
An information recording medium having an auxiliary layer composed of Te alone, a Se alloy, or Te—Ge—Sb having a higher Te content than the recording layer is described. In this medium, recording is performed by changing the phase of the recording layer from crystalline to amorphous. Therefore, on this medium, an initialization step of setting the recording layer to a uniform crystalline state is performed before shipment so that stable recording is performed from the first time. The auxiliary layer is provided to simplify this initialization step. This medium is of a rewritable type.

In addition, recently published WO 99/3090
No. 8 discloses a write-once optical information recording medium having a phase change recording layer and an interface layer (crystallization assisting layer). In this write-once optical information recording medium, a recording mark is formed by crystallization of the phase change recording layer reflecting the unit cell of the interface layer. For this reason, it is possible to form marks suitable for the mark edge recording method with high edge controllability.

At this time, as a material of the phase change recording layer,
To improve the recording signal, a material having a high crystallization speed and a high optical contrast before and after crystallization is selected. Also,
As a material for the interface layer, a material having a lattice constant close to that of the phase-change recording layer after crystallization is selected to assist crystallization of the phase-change recording layer.

[0016]

As a write-once optical recording medium using a material satisfying such conditions, the above-mentioned W
In O99 / 30908, a GdSbTe alloy is used as a material for a phase change recording layer, and SnT is used as a material for an interface layer.
A medium using an e-based alloy is illustrated. However, according to the knowledge obtained by the inventor's earnest studies, in such an optical recording medium, the intensity of light required at the time of recording is high, and the sensitivity is deteriorated.

Further, according to the knowledge obtained by the inventor's earnest study, the above-mentioned optical recording medium is susceptible to corrosion, and it has been difficult to sufficiently secure the reliability of the optical recording medium. .

Accordingly, an object of the present invention is to provide a write-once optical recording medium capable of improving the corrosion resistance and controlling the recording sensitivity.

[0019]

Means for Solving the Problems The present inventor has made intensive studies in order to solve the above-mentioned problems of the prior art. The outline is described below.

That is, as described above, the conventional write-once optical recording medium has a structure in which the crystallization auxiliary layer and the reflection layer are in contact with each other, and a structure in which the phase change recording layer and the reflection layer are in contact with each other. . The present inventor pays attention to this point, and the reason that corrosion is likely to occur in the write-once optical recording medium is that the crystallization assisting layer and the reflective layer have different ionization tendencies, and two metals having different ionization tendencies are brought into contact with each other. Thus, it has been recalled that even when a very small amount of water exists on the substrate of the recording medium, corrosion occurs due to the difference in the ionization tendency.

As described above, the material for the phase change recording layer and the material for the crystallization auxiliary layer are selected so that the lattice constants of these layers are close to each other. As a material of the phase change recording layer, a material having a high crystallization rate, for example, GeTe is selected in order to improve recording signal characteristics. As the material of the crystallization assist layer, for example, SnTe is selected as described above. However, in such an optical recording medium,
The intensity of the laser beam required for recording is high, and the sensitivity is deteriorated.

According to the knowledge of the present inventor, in order to improve the recording sensitivity of the optical disk, a method of changing the composition of the phase change recording layer and the crystallization assisting layer can be considered. However,
In such a method, there is a problem that the lattice constant of the phase change recording layer and the crystallization auxiliary layer are shifted or the crystallization speed is reduced. Then, in order to avoid this adverse effect, it is desirable to improve the recording sensitivity by another method.

Therefore, as a result of further experiments and intensive studies conducted by the present inventor, as a method for preventing corrosion in an optical recording medium, a method of providing a protective layer at least between a crystallization assisting layer and a reflective layer is proposed. I came to remember. Further, they have found that the recording sensitivity can be corrected without changing the compositions of the phase change recording layer and the crystallization auxiliary layer.

That is, in order to achieve the above object, according to the present invention, a first protective layer is provided on a disk substrate,
On the first protective layer, there is provided a laminated film in which at least a phase change recording layer configured to record an information signal by a phase change and a crystallization auxiliary layer are laminated, and on the laminated film, a reflective layer is provided. In a write-once optical recording medium on which information signals are recorded in a write-once manner, a second protective layer is provided at least between the laminated film and the reflective layer.

In the present invention, typically, a phase change recording layer and a crystallization auxiliary layer are sequentially laminated on the first protective layer, and a reflection layer is provided in contact with the crystallization auxiliary layer.

In the present invention, typically, a crystallization auxiliary layer and a phase change recording layer are sequentially laminated on the first protective layer, and a reflection layer is provided in contact with the phase change recording layer.

In the present invention, the thickness of the phase-change recording layer is typically 10 nm in order to obtain good signals, maintain good optical contrast, and suppress thermal diffusion. It is selected to be not less than 40 nm or less.

In the present invention, the first protective layer is typically made of a zinc sulfide / silicon oxide mixture (ZnS-SiO ₂ ) having a refractive index of about 2.1 or a refractive index of about 2.0. It is made of silicon nitride (SiN, Si ₃ N ₄ ), but other materials can be used. In the present invention, typically, the thickness of the first protective layer is 200
nm or less.

In the present invention, typically, the second protective layer is made of a dielectric material, preferably ZnS-SiO ₂ having a refractive index of about 2.1, or a refractive index of about 2.0. It is made of silicon nitride (SiN, Si ₃ N ₄ ). In the present invention, typically, the thickness of the second protective layer is 1
nm or more and 100 nm or less.

In the present invention, typically, the thickness of the reflection layer is from 20 nm to 100 nm.

In the present invention, a phase change recording layer is typically used to improve the stability of a recording mark against reproduction light and to secure good jitter characteristics when performing high-density recording by mark edge recording. Is Te-Ge-
An Sb-based alloy (Te, Ge, and Sb may contain elements other than these elements), and the composition thereof is represented by the coordinates of the three components of Te, Ge, and Sb shown in FIG.
In the triangular graph shown by Ge, Sb), A (0.475,
0.05, 0.475), B (0.665, 0.05,
0.285), C (0.60, 0.40, 0), D
A range surrounded by four points (0.40, 0.60, 0) (point A has a composition of Te _47.5 Ge ₅ Sb _47.5 , and point B has a composition of Te _47.5
66.5 Ge ₅ Sb _28.5 , composition of point C is Te ₆₀ Ge ₄₀ , point D
Has a composition of Te ₄₀ Ge ₆₀ ). Preferably, PbSe, PbTe, SnS is provided directly above or directly below the phase change recording layer.
A crystallization assist layer is provided, which contains at least one compound selected from the group consisting of e, SnTe, Bi ₂ Te ₃ and Sb ₂ Te ₃ as a main component. Further, the composition of the phase change recording layer is outside the straight line connecting points A and B in the triangular graph of FIG. 5 (that is, the Ge content is 5 atomic%).
), The crystallization temperature is lowered, and the portion where the recording mark is not formed (unrecorded portion) is easily crystallized by the reproduction light. As a result, the boundary between the recording mark and the unrecorded portion may not be clear, and the recording mark may be deteriorated. Further, if the composition of the phase change recording layer is outside the straight line connecting point B and point C and outside the straight line connecting point D and point A in the triangular graph of FIG. 5, the jitter characteristics deteriorate. . Although the composition of the phase change recording layer is within the range surrounded by the points ABCD in the triangular graph of FIG. 5, the composition is close to a straight line connecting the points A and B (that is, the content of Ge is 5 atom). % Or more, but a relatively small composition), the difference in optical constant between the amorphous state and the crystalline state becomes small. As a result, the amplitude of the reproduced signal decreases, which is not preferable in terms of signal quality.

In the present invention, a more preferable range of the composition of the phase change recording layer is a triangular graph similar to FIG. 5, in which the coordinates (Te, Ge, Sb) are E (0.
47, 0.30, 0.23), F (0.58, 0.3
0, 0.12), G (0.56, 0.44, 0), H
(0.44, 0.56, 0). The composition at point E is Te ₄₇ Ge ₃₀ Sb ₂₃ and the composition at point F is Te ₅₈ G
e ₃₀ Sb ₁₂ , the composition of point G is Te ₅₆ Ge ₄₄ ,
The composition of the point H is Te ₄₄ Ge _56.

In the present invention, a more preferable range of the composition of the phase change recording layer is a triangular graph similar to FIG. 5, in which the coordinates (Te, Ge, Sb) are J (0.
47, 0.40, 0.13), K (0.55, 0.4
0, 0.05), L (0.52, 0.48, 0), M
This is a range surrounded by four points (0.44, 0.56, 0). The composition at point J is Te ₄₇ Ge ₄₀ Sb ₁₃ , the composition at point K is Te ₅₅ Ge ₄₀ Sb ₅ , and the composition at point L is Te ₅₂ G
e ₄₈ and the composition of the point M is Te ₄₄ Ge ₅₆ .

In the present invention, specifically, as a material of the phase change recording layer, Ge-Te, Te-Sb, Te-
Ge-Sb, Te-Ge-Sb-Pd, Te-Ge-S
b-Cr, Te-Ge-Sb-Bi, Te-Ge-Sn
-O, Te-Ge-Sb-Se, Te-Ge-Sn-A
u, In-Sb-Te, In-Sb-Se, Te-Ge
-Se-Sn, In-Sb-Te-Ag, In-Se,
Te-Bi or the like can be used.

In the present invention, specifically, as a material of the crystallization assisting layer, thorium phosphide (ThP), lanthanum sulfide (LaS), scandium / antimony (Sc)
Sb), thorium selenium (ThSe), calcium
Selenium (CaSe), lead sulfide (PbS), scandium bismuth (ScBi), thorium arsenide (ThAs),
BiSe, indium arsenide (InAs), yttrium tellurium (YTe), gallium antimony (GaS
b), PbSe, tin-antimony (SnSb), aluminum-antimony (AlSb), copper iodide (Cu)
I), strontium selenium (SrSe), SnT
e, thorium antimony (ThSb), CaTe, barium sulfide (BaS), LaTe, PbTe, BiT
e, SrTe, silver iodide (AgI), Sb ₂ Te ₃ , Bi
₂ Se ₃ , Bi ₂ Te _3, etc. can be used, but other materials can be used if necessary.

In the present invention, more preferably, the crystallization assisting layer is made of PbSe, PbTe, SnSe, SnTe,
The main component is at least one compound selected from the group consisting of Bi ₂ Te ₃ and Sb ₂ Te ₃ .
The crystallization assisting layer may be in a mixed crystal state by mixing any one or more of these compounds.
From the viewpoint of the storage life of the write-once optical recording medium, it is preferable to use SnTe among these compounds as a main component of the crystallization auxiliary layer. Further, in the present invention, the crystallization assisting layer has the above-mentioned specific compound as a main component, and may contain substances other than these. In this case, the content of the above-described specific compound in the entire material constituting the crystallization assisting layer is set to 50% by volume or more. If the content of the specific compound described above is less than 50% by volume, the crystallization of the phase-change recording layer may not be satisfactorily performed, and the jitter characteristic of the reproduction light may be deteriorated. The content of the above-mentioned specific compound in the crystallization assisting layer is preferably 70% by volume or more. Further, in the present invention, typically, the thickness of the crystallization assisting layer is 2 nm or more and 50 nm or less.

In the present invention, in order to precisely control the length of a recording mark by mark edge recording, a reflection layer for reflecting light transmitted through the phase change recording layer is typically provided with a heat conductive layer. It is preferable to use a material having a ratio of 50 W / m · K or more. And the thermal conductivity is 50W
/ M · K or more include Al, Cr, Ni,
Metals selected from the group consisting of Au, Hf, Pd, Ta, Co, Mo, W, Cu, and Ti, or alloys of these metals. Among these materials, a material preferable as a reflective layer material from various viewpoints is Al-Ti.
Alloy, Al-Cr alloy, Al-Ta alloy, Al-Pd alloy, Al-Cu alloy, Ti-Al alloy, Ti-V alloy,
Ti-Pd-Cu alloy, Ag alloy and the like. The composition ratio of these alloys is set according to the required characteristics.

In the present invention, typically, the upper surface of the reflection layer on the disk substrate (the surface opposite to the disk substrate)
In order to protect and strengthen the reflective layer, it is preferable to provide a synthetic resin layer made of a UV-curable resin (urethane-based, acrylic-based, silicone-based, polyester-based, etc.) or a hot-melt-based adhesive. .

In the present invention, typically, Al, Cr, Ni, Au, hafnium (H
f), metals such as palladium (Pd), tantalum (Ta), cobalt (Co), Mo, W, Ti, or alloys of these metals can be used, but other materials may be used if necessary. Can also be used.

In the present invention, the first protective layer, the phase change recording layer, the crystallization auxiliary layer, the second protective layer and the reflection layer
Typically, a film is formed by a sputtering method, but other film forming methods can also be used. Specifically, an electron beam evaporation method, a vacuum evaporation method, an epitaxial growth method, a chemical vapor deposition (CVD) ) Method, physical vapor deposition (PV)
Any method such as the method D) can be used.

According to the write-once optical recording medium according to the present invention having the above-described structure, the second protective layer is provided at least between the crystallization assist layer and the reflective layer. It is possible to reduce the occurrence of a reaction that causes corrosion between the chemical conversion assisting layer and the reflection layer.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a write-once optical disc according to this embodiment.

As shown in FIG. 1, a write-once optical disc 1 according to this embodiment has a first protective layer 3, a phase change recording layer 4, and a crystallization assist layer 5 on one main surface 2a of a disc substrate 2. , A second protective layer 6, a reflective layer 7, and an ultraviolet curable resin layer 8 are sequentially laminated.

The disk substrate 2 is made of a plastic material such as a polycarbonate resin, a polyolefin resin or an acrylic resin, or glass. As a material of the disk substrate 2, at least information signal recording /
A material that can transmit laser light used for reproduction is selected. Further, it is desirable to use a plastic material from the viewpoint of cost and the like, and in this embodiment, it is made of, for example, polycarbonate. The thickness of the disk substrate 2 is, for example, about 1.2 mm. Further, on one main surface 2a of the disk substrate 2, a convex portion (land) and a concave portion (groove) are formed in a track shape. Here, the track pitch (Tp) in the groove track having the unevenness is, for example, 0.77 μm. In this embodiment, the groove depth is, for example, 70 nm,
The groove width is, for example, 0.77 μm.

The material of the first protective layer 3 is a material having a low absorption capacity (absorption rate) with respect to a recording / reproducing laser beam.
Specifically, it is preferable to use a material having an extinction coefficient k of 0.3 or less. In consideration of heat resistance, for example, ZnS—SiO ₂ (particularly, the one having a molar ratio of about 4: 1) ). Further, the thickness of the first protective layer 3 is selected to be 200 nm or less, and in this embodiment, it is selected to be, for example, 10 nm.

The phase change recording layer 4 is made of, for example, GeTe
Made of alloy. Here, the film thickness of the phase change recording layer 4 is specifically selected from 10 to 40 nm, and in this embodiment, is selected to be, for example, 20 nm. The details of the thickness of the phase change recording layer 4 will be described later.

The material of the crystallization assisting layer 5 is SnTe.
Alloy, SnSe alloy, PbSe alloy, Bi ₂ Te _3, and a material containing, as a main component, at least one compound selected from the group consisting of Sb ₂ Te ₃ , and specifically, containing the specific compound described above. The ratio is set to 50% by volume or more, more preferably 70% by volume or more. In this embodiment, the crystallization assisting layer 5 is made of, for example, SnT.
e. The thickness of the crystallization assisting layer 5 is desirably in uniform contact with the recording layer 4, and may be a very small film. A material having a high optical absorption capacity, a material having a small thermal conductivity, or a material having a small heat capacity causes heat to be stored in the recording layer 4, thereby causing deterioration due to reproduction light,
Typically, 2 to 50 n
m, preferably selected from the range of 2 to 10 nm,
In this embodiment, for example, 10 nm is selected.

The material of the second protective layer 6 is made of a material having a low absorption capability for recording / reproducing laser light, specifically, a material having an extinction coefficient k of 0.3 or less. It is preferable that considering the viewpoint of heat resistance, for example, ZnS
—SiO ₂ (especially those having a molar ratio of about 4: 1). Note that in this embodiment, the first protective layer 3 and is constituted from a second allogeneic to each other a protective layer 6 of the material (ZnS-SiO _2), respectively can also be used different materials Needless to say, The thickness of the second protective layer 6 will be described later.

The reflection layer 7 is made of, for example, an Al alloy, and in this embodiment, is made of, for example, an AlTi alloy. The thickness of the reflective layer 7 is set to 20 nm.
If it is less than 3, the diffusion of the heat generated in the phase change recording layer 4 cannot be sufficiently performed, and the thermal cooling becomes insufficient. On the other hand, if the thickness of the reflective layer 7 is larger than 100 nm, thermal characteristics and optical characteristics are affected, and
The resulting stress affects mechanical properties such as skew, making it impossible to obtain desired properties. Therefore, the film thickness of the reflection layer 7 is specifically selected from 20 to 100 nm, and in this embodiment, is selected to be, for example, 60 nm.

The ultraviolet-curable resin layer 8 is made of an ultraviolet-curable resin cured by irradiation with ultraviolet light.

Next, a method of manufacturing the write-once optical disc 1 according to the embodiment having the above-described configuration will be described.

That is, first, a clean disk substrate 2 (1.2 mm thick, track pitch 0.77 μm) provided with guide grooves (irregular groove tracks) by, for example, injection molding.
m, groove width 0.77 μm, groove depth 70 nm), for example, by a sputtering method, a first protective layer 3 made of ZnS—SiO ₂ , for example, a phase change recording layer 4 made of a GeTe alloy, for example, made of SnTe Crystallization assist layer 5,
For example, the second protective layer 6 made of ZnS—SiO ₂ , Al
A reflective layer 7 made of a Ti alloy is sequentially formed. Thereafter, an ultraviolet curable resin layer 8 is formed on the surface of the reflective layer 7 by, for example, a spin coating method or a roll coating method. As described above, the write-once optical disc 1 is manufactured. Phase change recording layer 4
Is formed using a GeTe alloy target whose composition is adjusted so that the composition after film formation is, for example, Ge ₅₀ Te ₅₀ .

The present inventor has determined that the write-once optical disc 1 according to this embodiment, constructed and manufactured as described above,
A plurality of write-once optical disks 1 each having a thickness of the second protective layer 6 of 0 nm (when the second protective layer 6 is not provided), 5 nm, 10 nm, and 20 nm are manufactured. Experiments were conducted on the corrosion resistance and the optimum recording power of the write-once optical disc 1.

First, in an experiment on corrosion resistance, a first optical disk in which the thickness of the second protective layer 6 was 0 nm and a second optical disk in which the thickness of the second protective layer 6 was 10 nm were used. Was left in a thermostat at a temperature of 80 ° C. and a humidity of 85%, and the number of occurrences of corrosion per write-once optical disc and the maximum value of the corrosion were measured. The results are shown in Table 1 below. In Table 1, the number per write-once optical disk is the average value of the number of corrosions, and the numerical value below the number indicates the maximum value of corrosion.

[0055]

[Table 1]

From Table 1, it can be seen that the second optical disk having the thickness of 10 nm is smaller than the first optical disk on which the second protective layer 6 is not provided.
In the second optical disk provided with the protective layer 6 of the above, the occurrence of corrosion after leaving in a thermostat for 130 hours is 1/10
It can be seen that it has been reduced to a degree. Further, after leaving the write-once optical disc 1 for 4 times and leaving it in the constant temperature bath for 520 hours, the first optical disc is corroded by several tens per one write-once optical disc. While the value is 1 mm or more, the second optical disc has a corrosion occurrence number of 0.1 mm per write-once optical disc.
The maximum value of the corrosion was 150 μm or less, indicating that the corrosion was significantly reduced. That is, it can be seen that almost no corrosion occurs in the write-once optical disc according to this embodiment.

Next, in the write-once optical disc 1 according to this embodiment, the thickness of the second protective layer 6 is set to 0 nm, 5 n
m, 10 nm, and 20 nm, each of which was rotated at a linear velocity of 9.5 m / s, and the optical disk 1 having a wavelength of 660 nm and NA = 0.575 was used. Mark length is 0.42μm
A single mark was recorded. Then, the dependence of the film thickness of the second protective layer 6 on the optimum recording power at this time was measured. Table 2 shows the results.

[0058]

[Table 2]

From Table 2, it can be seen that by increasing the thickness of the second protective layer 6, the optimum recording power is reduced, and that the recording sensitivity can be improved.

Next, the thickness of the first protective layer 3 made of ZnS-SiO ₂ is 10 nm, the thickness of the auxiliary crystallization layer 5 made of SnTe is 10 nm, and the thickness of the _second protective layer 3 made of ZnS-SiO ₂ is 10 nm.
The write-once type in which the thickness of the protective layer 6 is 10 nm, the thickness of the reflective layer 7 made of AlTi is 60 nm, and the thickness of the phase change recording layer 4 made of GeTe is variously changed within a range of 10 to 40 nm. The optical disc 1 was manufactured. Then, each write-once optical disc 1 is rotated at a linear velocity of 9.5 m / s, and a mark length of 0.42 μm is applied to these write-once optical discs 1 using an optical system having a wavelength of 660 nm and NA = 0.575. Was recorded, and the carrier at that time was measured. The result is shown in FIG. In FIG. 2, lands are indicated by “▲”, and grooves are indicated by “●”.

FIG. 2 shows that although the optimum values of the land and the groove are slightly different, the thickness of the phase change recording layer 4 made of a GeTe alloy is preferably in the range of 10 nm to 40 nm. That is, the range of 10 to 40 nm in the film thickness of the phase change recording layer 4 is considered to be a range in which a good signal can be obtained. A film thickness outside this range is considered to be unfavorable because optical contrast decreases and thermal diffusion increases.

Further, the present inventor, in order to examine a change in optical contrast, similarly to the above,
The reflectance when the film thickness of the phase change recording layer 4 was variously changed was calculated using the effective Fresnel coefficient method. The result is shown in FIG. In FIG. 3, the vertical axis represents relative decibels (d) in order to enable comparison with carrier values.
B) Displayed.

FIG. 3 shows that the phase change recording layer 4 has a thickness of 20 n.
It can be seen that the amplitude is maximized at about m, and FIG.
It can be seen that they are similar to the experimental measurement values shown in FIG.

Further, the present inventor investigated the first change of ZnS-SiO _{2 in} order to examine the change in optical contrast.
The thickness of the protective layer 3 is 10 nm, the thickness of the phase change recording layer 4 made of GeTe is 20 nm, which is the optimum value, the thickness of the crystallization assisting layer 5 made of SnTe is 10 nm, and the thickness of the reflective layer 7 made of AlTi. In the write-once optical disc having a thickness of 60 nm, the reflectance when the thickness of the second protective layer 6 made of ZnS—SiO ₂ is variously changed within the range of 0 to 200 nm is determined by using the effective Fresnel coefficient method. Calculated. The result is shown in FIG.

FIG. 4 shows that the second protective layer 6 has a thickness of 120
It can be seen that the amplitude becomes a minimum value when it is set to about nm, and that when it is larger than 100 nm, the recording sensitivity becomes too high and the signal characteristics are significantly deteriorated.
If the thickness of the second protective layer 6 is smaller than 1 nm, the film itself has an island-like structure, making it difficult to form a uniform film. Therefore, it is understood that the thickness of the second protective layer 6 is preferably 1 to 100 nm in consideration of the optical contrast.

As described above, according to this embodiment, the first protective layer 3, the phase change recording layer 4, the crystallization auxiliary layer 5, and the reflective layer 7 are laminated on the disk substrate 2. In a write-once optical disc, a crystallization assist layer 5 and a reflection layer 7
By providing the second protective layer 6 between the second protective layer 6 and the write-once optical disc using the phase change recording method, the corrosion resistance can be improved and the second protective layer 6 By changing the film thickness, it becomes possible to control the recording sensitivity. Therefore, a write-once optical disc having high reliability can be obtained.

As another example of the write-once optical disc 1 according to this embodiment, as shown in FIG. 8, a first protective layer 3 and a crystallization assist layer are formed on one main surface 2a of a disc substrate 2. 5, the phase change recording layer 4, the second protective layer 6, the reflective layer 7, and the ultraviolet curable resin layer 8 may be sequentially laminated. Then, it was confirmed that the same effect as in the above-described embodiment can be obtained also in the write-once optical disc 1 configured as described above.

As described above, one embodiment of the present invention has been specifically described. However, the present invention is not limited to the above embodiment, and various modifications based on the technical idea of the present invention are possible. .

For example, the numerical values and materials given in the above embodiments are merely examples, and different numerical values and materials may be used as needed.

[0070]

As described above, according to the present invention, the first protective layer is provided on the disk substrate, and the first protective layer is provided.
In a write-once optical recording medium in which a laminated film in which at least a phase change recording layer and a crystallization assisting layer are laminated on a protective layer is provided, and a reflective layer is provided on the laminated film, between the laminated film and the reflective layer By providing the second protective layer, the corrosion resistance can be improved, the recording sensitivity can be controlled, and a write-once optical recording medium having high reliability can be obtained. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing a write-once optical disc according to an embodiment of the present invention.

FIG. 2 is a graph showing the dependence of recording characteristics of a write-once optical disc according to an embodiment of the present invention on the thickness of a phase-change recording layer.

FIG. 3 is a graph showing the dependency of the reflectance of the write-once optical disc according to one embodiment of the present invention on the thickness of the phase-change recording layer.

FIG. 4 is a graph showing the dependency of the reflectance of the write-once optical disc according to one embodiment of the present invention on the thickness of a second protective layer.

FIG. 5 is a triangular graph showing a preferred composition of a phase change recording layer in a write-once optical recording medium according to the present invention.

FIG. 6 is a triangular graph showing a preferred composition of a phase change recording layer in a write-once optical recording medium according to the present invention.

FIG. 7 is a triangular graph showing a preferred composition of a phase change recording layer in a write-once optical recording medium according to the present invention.

FIG. 8 is a sectional view showing another example of the write-once optical recording medium according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Write-once optical disk, 2 ... Disk substrate, 2
a: one main surface, 3: first protective layer, 4: phase change recording layer, 5: crystallization assist layer, 6: second protective layer, 7 ... Reflective layer, 8 ... UV curable resin layer

[Procedure amendment]

[Submission date] November 10, 2000 (200.11.
10)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0025

[Correction method] Change

[Correction contents]

In the present invention, typically, a phase change recording layer and a crystallization auxiliary layer are sequentially laminated on the first protection layer, and a second protection layer is provided in contact with the crystallization auxiliary layer. ing.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

In the present invention, typically, a crystallization auxiliary layer and a phase change recording layer are sequentially laminated on the first protection layer, and a second protection layer is provided in contact with the phase change recording layer. ing.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction contents]

In the present invention, specifically, as a material of the phase change recording layer, Ge-Te, Te-Sb, Te-
Ge-Sb, Te-Ge-Sb-Pd, Te-Ge-S
b-Cr, Te-Ge-Sb-Bi, Te-Ge-Sn
-O, Te-Ge-Sb-Se, Te-Ge-Sn-A
u, In-Sb-Te, In-Sb-Se, Te-Ge
- Sb -Sn, In-Sb- Te-Ag, In-Se,
Te-Bi or the like can be used.

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) G11B 7/24 535 G11B 7/24 535G B41M 5/26 B41M 5/26 X (72) Inventor Katsuya Owada Shinagawa-ku, Tokyo 6-7-35 Kitashinagawa Sony Corporation (72) Inventor Kazuyuki Furuya 2-1, Samejima, Fuji-shi, Shizuoka Prefecture FB05 FB09 FB12 5D029 HA04 JA01 JB03 JB05 JB17 JB35 LA13 LB01 LB02 LB07

Claims (12)

[Claims] A first protection layer is provided on a disk substrate, and a phase change recording layer configured to record an information signal by a phase change and a crystallization auxiliary layer are provided on the first protection layer. At least a laminated film is provided, a reflective layer is provided on the laminated film, and in the write-once optical recording medium in which the recording of the information signal is performed additionally, at least the laminated film and the reflective layer A write-once optical recording medium, wherein a second protective layer is provided therebetween. 2. The method according to claim 1, wherein the phase change recording layer and the crystallization auxiliary layer are sequentially laminated on the first protective layer, and the reflection layer is provided in contact with the crystallization auxiliary layer. The write-once optical recording medium according to claim 1, wherein 3. The method according to claim 1, wherein the crystallization assisting layer and the phase change recording layer are sequentially laminated on the first protective layer, and the reflection layer is provided in contact with the phase change recording layer. The write-once optical recording medium according to claim 1, wherein 4. The write-once optical recording medium according to claim 1, wherein the second protective layer is made of a dielectric. 5. The film thickness of the second protective layer is 1 nm or more and 1
2. The write-once optical recording medium according to claim 1, wherein the thickness is not more than 00 nm. 6. The write-once optical recording medium according to claim 1, wherein the phase change recording layer is made of a GeTe alloy or a GeSbTe alloy. 7. The write-once optical recording medium according to claim 1, wherein the thickness of the phase change recording layer is 10 nm or more and 40 nm or less. 8. The write-once optical recording medium according to claim 1, wherein the thickness of the first protective layer is 200 nm or less. 9. The method according to claim 1, wherein the crystallization assisting layer is made of an SnTe alloy, S
nSe alloy, PbSe alloy, PbTe alloy, Bi ₂ Te ₃
And at least one selected from the group consisting of Sb ₂ Te ₃
2. The write-once optical recording medium according to claim 1, comprising a material containing various kinds of compounds as main components. 10. The write-once optical recording medium according to claim 1, wherein the thickness of the crystallization assisting layer is 2 nm or more and 50 nm or less. 11. The reflective layer has a thickness of 20 nm to 10 nm.
2. The write-once optical recording medium according to claim 1, wherein the thickness is 0 nm or less. 12. The write-once optical recording medium according to claim 1, wherein a layer made of a synthetic resin is provided on the surface of the reflection layer on the disk substrate.