JPH11126370A - Optical record medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize accurate reproducing without depending on wavelengths of reproducing laser light by constituting a first reflecting layer of two layers of a metal layer and a dielectric layer. SOLUTION: The first reflecting layer 3 has a two-layer structure comprising a metal layer 4a formed on a first information recording surface 2 of a first substrate 1 and a dielectric layer 3b on the metal layer 3a. The metal layer 3a consists of, for example, Al, Au, Cu, Ni, Pt, Zn and Ag. As for the material of the dielectric layer 3b, a material having high refractive index than that of polycarbonate used for the first substrate 1 is preferably used, and for example, nitrides such as SiNx and AlNx and metal sulfides such as ZnS and CeS are used. Further, a protective film comprising SiO2 or the like as a protective film for the metal layer 3a is formed between the first substrate 1 and the metal layer 3a to prevent corrosion due to water permeating through the first substrate 1 or due to the reaction with residual monomers in the first substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium having a plurality of information recording surfaces for reproducing information by laser light.

[0002]

2. Description of the Related Art Optical recording media having a plurality of information recording surfaces are being put to practical use. An optical disc is mainly used as such a recording medium. For example, a DVD (digital versatile disc) has not one but two or four information recording surfaces.

FIG. 8 is a diagram showing an example of a disc having two information recording surfaces in a DVD (hereinafter, referred to as a double-layer disc). The first substrate 1 is formed of a light-transmitting material and has a first information recording surface 2. On the first information recording surface 2, a first reflection layer 3, which is an intermediate reflection layer made of a metal such as gold (Au), is formed. A second information recording surface 6 is provided on the second substrate 7, and a second reflective layer 5 made of a metal such as aluminum (Al) is formed on the second information recording surface 6. Also, the first substrate 1
The second substrate 7 is bonded with a photocurable resin such as an acrylic ultraviolet curable resin in a state where the respective information recording surfaces face each other. The spacer layer 4 is formed from the photocurable resin. Each information recording surface is a substrate surface on which pits having a size corresponding to a wavelength of 650 nm carrying information are formed.

In reproducing such a dual-layer disc, first, an information recording surface to be reproduced is selected. In the case of the first information recording surface 2, red laser light having a wavelength of 650 nm is focused on the first information recording surface 2, and a change in the intensity of light reflected from the first reflection layer 3 is detected. To reproduce the recorded information. In the case of the second information recording surface 6, the laser light is transmitted through the first substrate 1, the first reflection layer 3, and the spacer layer 4, and is focused on the second information recording surface 6, The recorded information is reproduced by detecting a change in the intensity of light reflected from the spacer layer 4, the first reflective layer 3, and the second reflective layer 5 transmitted through the first substrate.

Thus, the two-layer disc shown in FIG.
The recorded information on the first and second information recording surfaces can be selectively and continuously reproduced by the laser light incident from the first substrate 1 side. In the case of this two-layer disc, there is no need to make laser light incident from the second substrate 7 side, and it is not necessary to form the second substrate 7 with a light-transmitting material. In order to read recorded information on the second information recording surface 6,
The first reflective layer 3 must be capable of transmitting laser light to some extent. Therefore, the first reflection layer 3 is made of a material having a certain degree of reflectance and transmittance, and generally uses a gold (Au) thin film of about 15 nm.

[0006]

In recent years, next-generation DVDs in which the pit size and track pitch are reduced by using a blue laser beam near 440 nm to perform higher-density recording have been studied. In this next-generation DVD, a two-layer disc is naturally considered. By the way, the gold (Au) thin film has a small reflectance for blue laser light,
In addition, it has an optical characteristic that transmittance is small. The first reflective layer of the two-layer disc corresponding to the blue laser light is formed of gold (A
u) If the film is formed as a thin film, the reflected light from the first reflective layer cannot be sufficiently obtained, and the information recorded on the first information recording surface cannot be reproduced. Further, since the amount of transmitted light passing through the first reflective layer is also small, the reflected light from the second information recording surface cannot be sufficiently obtained, and the recorded information on the second information recording surface cannot be reproduced. Therefore, in order to obtain the amount of reflected light required for reproduction, it is desired that the first reflective layer of the two-layer disc has a certain degree of reflectance and transmittance for blue laser light.

[0007] Further, reproduction of a two-layer disc (hereinafter, an existing two-layer disc) corresponding to a red laser beam having a wavelength of 650 nm using a blue laser beam is being studied. This is to make the existing two-layer disc compatible with the next-generation two-layer disc. For this purpose, it is necessary that the first reflective layer of the existing two-layer disc has a certain degree of reflectance and transmittance for both red laser light and blue laser light.

[0008] The present invention has been made in view of the above points, and by using a reflection layer having no wavelength dependence,
An object of the present invention is to provide an optical recording medium capable of reliably reproducing recorded information on each information recording surface regardless of the wavelength of a laser beam used for reproduction.

[0009]

According to the first aspect of the present invention,
At least a first information recording surface, a first reflective layer formed on the first information recording surface, a second information recording surface, and a second information recording surface.
An optical recording medium comprising: a second reflective layer formed on the information recording surface of (1), wherein the first reflective layer comprises a metal layer and a dielectric layer. According to the operation of the first aspect of the present invention, since the first reflective layer has a two-layer structure of the metal layer and the dielectric layer, it can be a wavelength-independent reflective layer.

[0010] The second aspect of the present invention provides at least the first aspect.
, An information recording surface, a first reflective layer formed on the first information recording surface, a second information recording surface, and a second reflective layer formed on the second information recording surface. An optical recording medium according to claim 1, wherein the first reflection layer comprises three layers in which a metal layer is sandwiched between dielectric layers. According to the operation of the second aspect of the invention, the first reflective layer has a three-layer structure in which the metal layer is sandwiched between the dielectric layers, so that the reflective layer has no wavelength dependency.

According to a third aspect of the present invention, in the optical recording medium according to the first or second aspect, the first information recording surface is formed on a first substrate having a light-transmitting property. The refractive index of the dielectric used for the first substrate is larger than the refractive index of the first substrate. According to the operation of the third aspect of the present invention, the dielectric layer is made of a material having a higher refractive index than the first substrate, so that the dielectric layer can be made thin.

According to a fourth aspect of the present invention, in the optical recording medium according to the first, second or third aspect, the metal layer is formed of silver alone or a metal containing silver as a main component.
According to the operation of the invention described in claim 4, the first layer is formed by using silver alone or a metal containing silver as a main component for the metal layer.
And the reflectance of the second reflective layer can be between 25% and 45%.

[0013] The invention according to claim 5 is the invention according to claims 1 to 4.
3. The optical recording medium according to claim 1, wherein the dielectric layer is formed of silicon nitride. According to the operation of the fifth aspect, when forming the dielectric layer, it is possible to use a nitrogen gas with less side reaction.

The invention according to claim 6 is the first to fifth aspects.
The optical recording medium according to any one of the above, wherein the second reflective layer is formed of a metal containing aluminum as a main component. According to the function described in claim 6, since aluminum is used for the second reflection layer, the reflection efficiency can be increased.

The invention according to claim 7 is the first to sixth aspects of the present invention.
In the optical recording medium according to any one of the above, the second information recording surface is formed on the second substrate, and the first and second information recording surfaces are formed on the second substrate.
Is characterized in that the substrate is bonded by a photocurable resin provided between the first reflection layer and the second reflection layer. According to the operation described in claim 7, the laser light is irradiated from the first substrate side, and the recorded information on the first and second information recording surfaces can be selectively and continuously reproduced.

[0016] The invention according to claim 8 is the invention according to claims 1 to 7.
In the optical recording medium according to any one of the above, the reflectance of the first and second reflective layers is between 25% and 45% regardless of the wavelength of the laser beam used for reproducing the optical recording medium. It is characterized by the following. According to the operation described in claim 8, it is possible to obtain the amount of reflected light necessary for reproducing the recorded information regardless of the wavelength of the laser light used for reproduction. The recorded information on the recording surface can be reliably reproduced.

[0017]

Embodiments of the present invention will be described below. (First Embodiment) A first embodiment of an optical recording medium according to the present invention will be described with reference to FIG. FIG. 1 shows the first
It is a figure showing the composition of the double-layer disc of an embodiment. FIG.
, A first substrate 1 having a first information recording surface 2
And a first reflective layer 3 formed on the first information recording surface 2
A second substrate 7 having a second information recording surface 6;
The second reflection layer 5 formed on the information recording surface 6 of the first embodiment. Further, the first substrate 1 and the second substrate 7 are bonded by a photocurable resin provided between the first reflection layer 3 and the second reflection layer 5. The spacer layer 4 is formed from the photocurable resin.

The first and second information recording surfaces are the surfaces of the substrates 1 and 7 on which a plurality of pits carrying information of a size corresponding to the wavelength of the laser beam for reproduction are formed. Substrates 1 and 7
Are disc-shaped, pits are arranged concentrically or spirally to form a track. In the case of a DVD, the thickness of the first substrate 1 and the second substrate 7 is about 0.6 mm, and is made of a transparent resin such as polycarbonate (refractive index: about 1.6). The spacer layer 4 is a photocurable resin such as an acrylic ultraviolet curable resin (refractive index: about 1.5) and has a thickness of about 40 μm. The second reflection layer 5 is formed of a metal containing aluminum as a main component, and has a thickness of about 50 nm.

Next, the structure of the first reflection layer 3 will be described. The first reflective layer 3 has a two-layer structure of a metal layer 3a formed on the first information recording surface 2 of the first substrate 1 and a dielectric layer 3b formed on the metal layer 3a. ing. The material of the metal layer 3a is, for example, aluminum (Al), gold (Au),
Examples thereof include copper (Cu), nickel (Ni), platinum (Pt), zinc (Zn), and silver (Ag). Particularly, when the lower limit of the reflectance in each reflective layer is set to 25% or more, Silver (A
It is desirable to use g). Further, an alloy or a metal mixture in which other elements for preventing oxidation or corrosion are added as a main component of each of the above metals to such an extent that the optical characteristics are not significantly changed may be used.

The dielectric material of the dielectric layer 3b is SiNx
(Silicon nitride: general formula Si ₃ N ₄ ), nitride such as AlNx (aluminum nitride), metal sulfide such as ZnS, CeS, or TiO ₂ , In ₂ O ₃ , Zr
O ₂ , ZnO, Bi ₂ O ₃ , CeO ₂ , Eu ₂ O ₃ , H
fO ₂ , La ₂ O ₃ , Nd ₂ O ₅ , MoO ₃ , Mg
_{O, Pr 6 O 11, Sm} 2 O 3, Sb 2 O 3, Sc
₂ O ₃ , SnO ₃ , SrTiO ₃ , Ta ₂ O ₅ , Y ₂ O
₃ or a metal fluoride such as PbF ₂ , or ITO (In ₂ O ₃ + SnO ₂ (5
%)). Further, a mixture of a plurality of the above-described dielectric materials may be used.

The dielectric material used for the dielectric layer 3b is
A material having a higher refractive index than the polycarbonate (refractive index 1.6) used for the first substrate 1 is desirable. Since the thickness of the dielectric layer can be reduced as the refractive index of the material used for the dielectric layer 3b is increased, advantages such as a reduction in production time and a reduction in the amount of the dielectric material used are brought about. Particularly, ZnS (refractive index: 2.2), SiNx (refractive index: 2.0), and the like are inexpensive materials, and thus are suitable as the dielectric material used in the present invention.

It should be noted that the larger the refractive index of the dielectric used for the dielectric layer forming the first reflection layer, the better.
The same applies to not only the first embodiment but also the second and third embodiments described below.

Further, a protective film (thickness: 50 nm) made of SiO ₂ or the like may be formed as a protective film for the metal layer 3a between the first substrate 1 and the metal layer 3a. This protective film is for preventing the metal of the metal layer 3a from being oxidized or corroded by the reaction with the moisture permeating the first substrate 1 and the residual monomer contained in the first substrate 1. It is. If the protective film is formed by SiO _2, SiO ₂
Has a refractive index of about 1.5, which is almost the same as that of the polycarbonate of the first substrate 1 (refractive index: 1.6). Therefore S
The protective film made of iO _{2 can} be regarded as integral with the first substrate 1. Therefore, the protective film made of SiO ₂ has no effect on the reflectance and transmittance of the first reflective layer 3 made of the metal layer 3a and the dielectric layer 3b. The material of the protective film is SiO ₂
Not only that, other dielectrics having the same refractive index as the first substrate 1 may be used.

Next, the optical characteristics (reflectance and transmittance) of the first reflection layer 3 will be described. FIG. 2 shows the optical characteristics of the first reflective layer 3 when the metal layer 3a and the dielectric layer 3b are made of Au and ZnS, respectively. FIG. 3 shows the optical characteristics of the first reflective layer 3 when the metal layer 3a and the dielectric layer 3b are made of Ag and ZnS, respectively. FIG.

In the case of Au / ZnS FIG. 2A shows that the thickness of ZnS used for the dielectric layer 3b is 45
FIG. 6 is a diagram showing a relationship between the Au layer thickness of the metal layer 3a and the reflectance and transmittance of the first reflective layer 3 when the thickness is set to nm. In the figure, reference numerals 18 and 19 indicate that the wavelength of the laser beam used for reproduction is 650.
The reflectance R and the transmittance T in the case of nm are shown. Reference numerals 20 and 21 denote 43 wavelengths of the laser beam used for reproduction.
It is a curve which shows the reflectance R and the transmittance | permeability T at 0 nm.

FIG. 2B shows the relationship between the ZnS layer thickness of the dielectric layer 3b and the reflectance and transmittance of the first reflective layer 3 when the thickness of Au used for the metal layer 3a is 10 nm. FIG. In the drawing, reference numerals 22 and 23 indicate the reflectance R and the transmittance T, respectively, when the wavelength of the laser beam used for reproduction is 650 nm. 24 and 25 are curves showing the reflectance R and the transmittance T when the wavelength of the laser beam used for reproduction is 430 nm.

From FIG. 2A, the range of the Au layer thickness is from 8 to
At 10 nm, the reflectance R of the first reflective layer 3 exceeds 20% and the transmittance T is 5 regardless of the wavelength of the laser beam.
It turns out that it becomes 0% or more. Therefore, the optimal range of the thickness of the metal layer 3a made of Au in which the reflectance R and the transmittance T of the first reflective layer 3 are optimal is 8 to 10 nm.

FIG. 2B shows that the ZnS layer has a thickness of 5 mm.
When the wavelength is from 0 to 70 nm, the first
The reflectance R of the reflective layer 3 exceeds 20% and the transmittance T
Is more than 50%. Therefore, the optimum range of the thickness of the dielectric layer 3b made of ZnS in which the reflectance R and the transmittance T of the first reflection layer 3 are optimum is 50 to 70 nm.

Therefore, the thickness of the metal layer 3a made of Au is 8 to 10 nm, and the thickness of the dielectric layer 3b made of ZnS is 5 nm.
The second reflective layer 5 has a high reflectivity such as aluminum (the second reflective layer 5 made of aluminum).
Has a reflectance of about 70%. ), The first material
Of the reflective layer 3 and the second reflective layer 5 (the ratio of the amount of reflected light that can be used for reproducing information reflected by each reflective layer, where the amount of light incident on the recording medium is 100. The same) between 20 and 45%.

In the case of Ag / ZnS FIG. 3A shows that the thickness of ZnS used for the dielectric layer 3b is 45
FIG. 5 is a diagram showing a relationship between the Ag layer thickness of the metal layer 3a and the reflectance and transmittance of the first reflective layer 3 when the thickness is set to nm. In the figure, reference numerals 10 and 11 indicate that the wavelength of the laser beam used for reproduction is 650.
The reflectance R and the transmittance T in the case of nm are shown. Reference numerals 12 and 13 indicate that the wavelength of the laser beam used for reproduction is 45.
It is a curve which shows the reflectance R and the transmittance | permeability T at 0 nm.

FIG. 3B shows the relationship between the ZnS layer thickness of the dielectric layer 3b and the reflectivity and transmittance of the first reflective layer 3 when the Ag layer thickness used for the metal layer 3a is 12 nm. FIG. 14 and 15 show the reflectance R and the transmittance T, respectively, when the wavelength of the laser beam used for reproduction is 650 nm. Reference numerals 16 and 17 are curves showing the reflectance R and the transmittance T when the wavelength of the laser beam used for reproduction is 450 nm.

FIG. 3A shows that the range of the Ag layer thickness is 12
It can be seen that the reflectivity R of the first reflective layer 3 exceeds 25% and the transmittance T exceeds 60%, irrespective of the wavelength of the laser light, when the wavelength is up to 14 nm. Therefore, the optimal range of the thickness of the metal layer 3a made of Ag, at which the reflectance R and the transmittance T of the first reflective layer 3 are optimal, is 12 to 14 nm.

FIG. 3B shows that the ZnS layer thickness is 4 mm.
When the wavelength is 5 to 60 nm, regardless of the wavelength of the laser beam, the first
The reflectance R of the reflective layer 3 exceeds 25% and the transmittance T
Is more than 60%. Therefore, the optimal range of the thickness of the dielectric layer 3b made of ZnS in which the reflectance R and the transmittance T of the first reflective layer 3 are optimal is 45 to 60 nm.

Therefore, the thickness of the dielectric layer 3b made of ZnS is set to 45 to 60 nm, the thickness of the metal layer 3a made of Ag is set to 12 to 14 nm, and the second reflective layer 5 is made of a material having high reflectivity such as aluminum. Is used, the reflectance of each of the first reflective layer 3 and the second reflective layer 5 can be 25 to 45%.

(Second Embodiment) Next, an optical recording medium according to a second embodiment of the present invention will be described with reference to FIG. Except for the configuration of the first reflection layer 3, the configuration is the same as that of the first embodiment. FIG. 4 is a diagram showing the configuration of the dual-layer disc of the second embodiment in detail. In FIG. 4, the first reflective layer 3 includes a dielectric layer 3c formed on the information recording surface of the first substrate 1 (that is, the first information recording surface 2) and a dielectric layer 3c formed on the dielectric layer 3c. It is composed of two layers of the formed metal layer 3d. The materials listed in the first embodiment can be used as the material of the dielectric layer 3c. The material of the metal layer 3d may be the material listed in the first embodiment, but in the second embodiment, the reflectance of the first reflective layer 3 and the second reflective layer 5 can be set to 25 to 45%. The material of the metal layer 3d is only silver (Ag). This was confirmed by the experiment of the present inventor.

A thin film (thickness: 50 nm) made of SiO ₂ or the like may be formed between the metal layer 3d and the spacer layer 3 as a protective film for the metal layer 3d. This protective film is for preventing the metal layer 3d from oxidizing or corroding. When the protective film is formed of SiO ₂ ,
The refractive index of ₂ is 1.5, which is almost the same as that of the acrylic ultraviolet curing resin (refractive index: 1.5) constituting the spacer layer. Therefore, the protective film made of SiO _{2 can} be regarded as integral with the spacer layer 3. Therefore, the protective film made of SiO ₂ is the first reflective layer 3 made of the metal layer 3d and the dielectric layer 3c.
Has no effect on the reflectance or transmittance of the light. Further, as the material of the protective film, not only SiO ₂ but also a dielectric having a refractive index similar to that of the spacer layer 4 may be used.

Next, the optical characteristics (reflectance and transmittance) of the first reflection layer 3 will be described. FIG. 5 shows the dielectric layer 3c,
FIG. 4 is a diagram illustrating optical characteristics of a first reflective layer 3 when a metal layer 3d is made of SiNx and Ag, respectively.

In the case of SiNx / Ag FIG. 5A shows that the thickness of the SiNx used for the dielectric layer 3c is 6
FIG. 9 is a diagram illustrating a relationship between the Ag layer thickness of the metal layer 3d and the reflectance and transmittance of the first reflective layer 3 when the thickness is 0 nm.
In the figure, reference numerals 39 and 40 denote wavelengths of laser light used for reproduction of 65.
The reflectance R and the transmittance T in the case of 0 nm are shown. Reference numerals 41 and 42 denote the wavelength of the laser beam used for reproduction as 4
It is a curve which shows the reflectance R and the transmittance | permeability T at 30 nm.

FIG. 5B shows the SiNx of the dielectric layer 3c when the thickness of Ag used for the metal layer 3d is 11.5 nm.
FIG. 3 is a diagram showing a relationship between the layer thickness of the first reflective layer 3 and the reflectance and transmittance of the first reflective layer 3. In the drawing, 43 and 44 indicate the reflectance R and the transmittance T, respectively, when the wavelength of the laser beam used for reproduction is 650 nm. 45 and 46 are curves showing the reflectance R and the transmittance T when the wavelength of the laser beam used for reproduction is 430 nm.

FIG. 5A shows that the range of the Ag layer thickness is 10
It can be seen that the reflectivity R at the first reflective layer 3 exceeds 25% and the transmittance T exceeds 60%, irrespective of the wavelength of the laser light, when the wavelength is 12 nm. Therefore, the optimal range of the thickness of the metal layer 3d made of Ag, in which the reflectance R and the transmittance T of the first reflective layer 3 are optimal, is 10 to 12 nm.

FIG. 5B shows that when the layer thickness of SiNx is 53 to 64 nm, the reflectance R of the first reflective layer 3 exceeds 25% regardless of the wavelength of the laser beam, and It can be seen that the transmittance T is 60% or more. Therefore, the optimum range of the thickness of the dielectric layer 3c made of SiNx at which the reflectance R and the transmittance T of the first reflection layer 3 are optimal is 53 to 64 n.
m.

Accordingly, the thickness of the metal layer 3d made of Ag is set to 10 to 12 nm, the thickness of the dielectric layer 3c made of SiNx is set to 53 to 64 nm, and the second reflection layer 5 is made of a material having high reflectivity such as aluminum. Is used, the reflectance of the first reflective layer 3 and the second reflective layer 5 can be set to be between 25% and 45%.

(Third Embodiment) Next, a third embodiment of the optical recording medium according to the present invention will be described with reference to FIG. Except for the structure of the first reflection layer 3, the configuration is the same as that of the first embodiment. FIG. 6 is a diagram showing a configuration of a double-layer disc according to the third embodiment. In FIG. 6, a first reflective layer 3 includes a dielectric layer 3e formed on an information recording surface of the first substrate 1 (that is, the first information recording surface 2), and a dielectric layer 3e.
e, and a metal layer 3f formed on the metal layer 3f and a dielectric layer 3g formed on the metal layer 3f.

As the material of the dielectric layers 3e and 3g,
The materials listed in the embodiment can be used. Although the material of the metal layer 3f may be the material listed in the first embodiment, the second embodiment can set the reflectance of the first reflective layer 3 and the second reflective layer 5 to 25 to 45%. Metal layer 3
The material of f is only silver (Ag). This was confirmed by the experiment of the present inventor.

Next, the optical characteristics (reflectance and transmittance) of the first reflection layer 3 will be described. FIG. 7 shows the first reflection layer 3
SiNx as the dielectric layer 3e and A as the metal layer 3f
g, the case where SiNx is used as the dielectric layer 3g.

FIG. 7 (a) shows the Si used for the dielectric layer 3e.
The thickness of Nx (the dielectric layer on the first substrate 1 side) is 60 nm,
When the thickness of the SiNx (dielectric layer on the side of the spacer layer 4) used for the dielectric layer 3g is 45 nm, the Ag thickness used for the metal layer 3f and the optical characteristics (reflectance and FIG. 27, 28 in the figure
Indicates the reflectance R and the transmittance T when the wavelength of the laser beam used for reproduction is 650 nm. 29,
Reference numeral 30 denotes a curve showing the reflectance R and the transmittance T when the wavelength of the laser beam used for reproduction is 442 nm.

FIG. 7B shows that the thickness of Ag used for the metal layer 3f is 11.5 nm and the thickness of SiNx used for the dielectric layer 3g is
When the layer thickness of the (dielectric layer on the spacer layer 4 side) is 45 nm, SiNx (the first substrate 1) used for the dielectric layer 3e is used.
FIG. 4 is a diagram showing a relationship between a layer thickness of a first dielectric layer and optical characteristics (reflectance and transmittance) of a first reflection layer 3. 3 in the figure
Reference numerals 1 and 32 indicate that the wavelength of the laser beam used for reproduction is 650 nm.
Respectively, the reflectance R and the transmittance T are shown. Reference numerals 33 and 34 denote 442 wavelengths of laser light used for reproduction.
It is a curve which shows the reflectance R and the transmittance | permeability T when it is set to nm.

FIG. 7C shows that the thickness of Ag used for the metal layer 3f is 11.5 nm and the thickness of SiNx used for the dielectric layer 3e is
When the thickness of the (dielectric layer on the first substrate 1 side) is 60 nm, SiNx (spacer layer 4) used for the dielectric layer 3g is used.
FIG. 4 is a diagram showing a relationship between a layer thickness of a first dielectric layer and optical characteristics (reflectance and transmittance) of a first reflection layer 3. 3 in the figure
Reference numerals 5 and 36 indicate that the wavelength of the laser beam used for reproduction is 650 nm.
Respectively, the reflectance R and the transmittance T are shown. Reference numerals 37 and 38 denote 442 wavelengths of laser light used for reproduction.
It is a curve which shows the reflectance R and the transmittance | permeability T when it is set to nm.

As shown in FIG. 7A, the range of the Ag layer thickness is 14
It can be seen that the reflectivity R of the first reflective layer 3 exceeds 25% and the transmittance T exceeds 60%, regardless of the wavelength of the laser light, when the wavelength is 16 nm. Therefore, the optimal range of the layer thickness of the metal layer 3f made of Ag at which the reflectance R and the transmittance T of the first reflective layer 3 are optimal is 14 to 16 nm.

As shown in FIG. 7B, the SiN on the first substrate 1 side
When the range of the layer thickness of x is 59 to 78 nm, the reflectance R of the first reflective layer 3 exceeds 25% and the transmittance T exceeds 60% regardless of the wavelength of the laser light. You can see that. Therefore, the dielectric layer 3e on the first substrate 1 side made of SiNx, in which the reflectance R and the transmittance T of the first reflection layer 3 are optimized.
The optimum range of the layer thickness is 59 to 78 nm.

FIG. 7C shows that the SiN on the spacer layer 4 side
When the range of the layer thickness of x is 44 to 64 nm, the reflectance R of the first reflective layer 3 exceeds 25% and the transmittance T exceeds 60% regardless of the wavelength of the laser beam. You can see that. Therefore, the dielectric layer 3e on the side of the spacer layer 4 made of SiNx in which the reflectance R and the transmittance T of the first reflection layer 3 are optimized.
The optimum range of the layer thickness is 44 to 64 nm.

Therefore, the dielectric layer 3e made of SiNx on the first substrate 1 side has a thickness of 59 to 78 nm, the metal layer 3f made of Ag has a layer thickness of 14 to 16 nm, and the dielectric layer 3 made of SiNx has a dielectric layer thickness of 14 to 16 nm. The layer thickness of the body layer 3g is 44 to 64
nm, and if a material having a high reflectivity such as aluminum is used for the second reflective layer 5, the reflectivities of the first reflective layer 3 and the second reflective layer 5 can be between 25% and 45%. .

In each of the above embodiments, the material of the dielectric layer constituting the first reflection layer 3 is SiNx
There is also an advantage in the process of manufacturing a two-layer disc by using. Generally, SiNx is formed by a reactive sputtering method in which Si is sputtered in a nitrogen gas atmosphere. The reactive sputtering method using nitrogen gas has a high deposition rate. In addition, since the nitrogen gas has poor reactivity, there is no side reaction other than the desired reaction and the sputtering apparatus is not contaminated. Therefore, the performance of the sputtering apparatus can be easily maintained, and the number of maintenance operations can be reduced, which is suitable for mass production of a two-layer disc.

Further, in each of the above-described embodiments, the use of silver (Ag) as the metal layer constituting the first reflective layer 3 makes it possible to use the first and second metal layers in comparison with the case where other metals are used. 2 can improve the reflectance of the reflective layer.

Further, the reflectance of the first and second reflective layers is 25 to 45% with the laser light having a wavelength of 350 to 850 nm as well as the laser light having a wavelength of 650 nm.
It has been confirmed by the present inventor that what can be done between them.

If the first reflective layer of each of the above-described embodiments is used for an existing two-layer disc corresponding to red laser light, it is possible to reproduce recorded information on each information recording surface even with blue laser light. Therefore, compatibility between the red laser light and the blue laser light can be achieved. Needless to say, the first reflective layer of each embodiment may be used for a two-layer disc corresponding to a blue laser.

By the way, a reflective layer having no wavelength dependency can be formed by using only the dielectric layer. However, since a dielectric multilayer film is required for each wavelength, the total thickness of the reflective layer is 1000 nm or more. And the manufacturing process becomes complicated. However, by using the reflective layer composed of the metal layer and the dielectric layer of the present invention, it is possible to obtain a reflective layer having no wavelength dependence in a small number of steps as compared with a reflective layer composed of a dielectric multilayer film. .

The first reflective layer in each of the above-described embodiments is not limited to the reflective layer of a two-layer disk, but may be applied to a four-layer disk having a structure in which two-layer disks are laminated. Each of the above-described embodiments is applied to a two-layer disc in which the first information recording surface is a so-called ROM type in which pits are formed and the second information recording surface is a recording layer using a phase change. May be applied.

[0059]

According to the first aspect of the present invention, since the first reflective layer has a two-layer structure of a metal layer and a dielectric layer, a reflective layer having no wavelength dependency can be obtained. According to the second aspect of the invention, the first reflective layer has a three-layer structure in which the metal layer is sandwiched between the dielectric layers, so that a reflective layer having no wavelength dependency can be obtained. According to the third aspect of the present invention, since the dielectric layer is made of a dielectric material having a refractive index higher than that of the first substrate, the thickness of the dielectric layer can be reduced. According to the fourth aspect of the present invention, the reflectance of the first and second reflective layers can be set to 25 to 45% by using silver alone or a metal containing silver as a main component for the metal layer. it can. According to the fifth aspect of the present invention, it is possible to use a nitrogen gas with less side reaction when forming the dielectric layer at the time of manufacturing the reflective layer, and it is possible to increase the manufacturing efficiency. According to the sixth aspect of the present invention, since aluminum is used for the second reflective layer, the reflection efficiency can be improved. According to the seventh aspect of the present invention, by irradiating the laser light from the first substrate side, the recorded information on the first and second information recording surfaces can be selectively reproduced. According to the invention described in claim 8,
It is possible to obtain the amount of reflected light necessary for reproducing recorded information regardless of the wavelength of the laser light used for reproduction, and to reproduce the recorded information on each information recording surface even when using laser light having a wavelength different from the specification. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing optical characteristics when a first reflective layer is made of Au / ZnS.

FIG. 3 is a diagram showing optical characteristics when a first reflective layer is made of SiNx / Ag.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing optical characteristics when the first reflection layer is made of SiNx / Ag.

FIG. 6 is a diagram showing a third embodiment of the present invention.

FIG. 7 is a diagram showing optical characteristics when the first reflection layer is made of SiNx / Ag / SiNx.

FIG. 8 is a diagram showing a state of reproduction of a two-layer disc.

[Explanation of symbols]

 1 First substrate 2 First information recording surface 3 First reflective layer 3a Metal layer 3b Dielectric layer 3c ... dielectric layer 3d ... metal layer 3e ... dielectric layer 3f ... metal layer 3g ... dielectric layer 4 ... spacer layer 5 ... Second reflective layer 6 Second information recording surface 7 Second substrate

Claims (8)

[Claims] At least a first information recording surface, a first reflective layer formed on the first information recording surface, a second information recording surface, and a second information recording surface. An optical recording medium comprising: a second reflective layer formed; wherein the first reflective layer comprises two layers, a metal layer and a dielectric layer. 2. At least a first information recording surface, a first reflective layer formed on the first information recording surface, a second information recording surface, and a second information recording surface. An optical recording medium comprising: a second reflective layer formed thereon, wherein the first reflective layer comprises three layers in which a metal layer is sandwiched between dielectric layers. 3. The optical recording medium according to claim 1, wherein the first information recording surface is formed on a first substrate having a light-transmitting property, and a dielectric used for the dielectric layer. The refractive index of the body is the first
An optical recording medium having a refractive index higher than that of the substrate. 4. The optical recording medium according to claim 1, wherein the metal layer is formed of silver alone or a metal containing silver as a main component. 5. The optical recording medium according to claim 1, wherein said dielectric layer is formed of silicon nitride. 6. The optical recording medium according to claim 1, wherein the second reflection layer is formed of a metal containing aluminum as a main component. 7. The optical recording medium according to claim 1, wherein the second information recording surface is formed on the second substrate, and wherein the first and second substrates are provided. An optical recording medium characterized in that the optical recording medium is bonded with a photo-curing resin provided between the first reflection layer and the second reflection layer. 8. The optical recording medium according to claim 1, wherein the reflection of the first and second reflection layers is independent of the wavelength of a laser beam used for reproducing the optical recording medium. 25-45%
An optical recording medium characterized by being between.