JPH11154352A - Information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information recording medium reproducing multilayer information recording surfaces without changing medium constitution for plural reproducing laser wavelengths and securing reproduction compatibility for future short wavelength formation of a drive. SOLUTION: This information recording medium 10 is an optical information recording medium provided with a transparent substrate 101 having an information recording surface 111, transparent space layers 131 having a translucent film 121 and the information recording surface 112 alternately overlapped and laminated on the information recording surface 111 of the transparent film 101 and a reflection film 102 provided on the final information recording surface. The translucent film 121 is a multilayer film constituted of alternately laminating a low refractive index layer 141 and a high refractive index layer 142.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium having a plurality of layers of information recording surfaces and recording and reproducing information by using a laser beam. It is about.

[0002]

2. Description of the Related Art With the development of information communication systems, information recording media have been increasing in capacity, and as one of them, a plurality of information recording surfaces are provided, and information is recorded using laser light. Information recording medium to be reproduced, for example, DVD-ROM
Recently, a two-layer optical disk, commonly referred to as, has been offered to the market. Here, with reference to FIG. 9, a configuration of a conventionally developed two-layer optical disk (DVD-ROM) will be described. FIG. 9 is a schematic sectional view showing the configuration of a conventional two-layer optical disc. Conventional two-layer optical disk (DVD-ROM)
As shown in FIG. 9, 1 has a structure in which a reflection layer is formed on the signal surface side of two resin base materials on which signal pits are formed, and the signal surfaces are bonded to face each other. Uses a translucent film. The two-layer optical disc 1 has a two-layer information recording surface structure including a translucent film having a first information recording surface 2 and a reflective layer having a second information recording surface 3. . As the translucent film, a metal thin film such as Au (gold) or Al (aluminum), or silicon carbide or a silicon-based oxide disclosed in International Patent WO96 / 04650 is used.

[0003]

However, in a conventional information recording medium such as a two-layer optical disc, Au or A
Since a metal thin film such as 1 or a silicon-based oxide is used, information recorded on the first information recording surface and the second information recording surface can be reproduced by red laser light having a wavelength of 635 nm. Reproduction with a blue laser beam having a wavelength of 400 nm in a short wavelength region has a disadvantage that the light absorption and reflectance of the translucent film increase, and the information recorded on the second information surface cannot be reproduced. . When a metal thin film such as Au or Al is used for the translucent film,
Since the translucency of the translucent film is high even for red laser light having a wavelength of 35 nm, it is necessary to make the translucent film a thin film having a thickness of 15 nm or less. For this reason, there has been an inconvenience that the margin in the step of forming the translucent film becomes very narrow.

Here, referring to FIGS. 7 and 8, a problem in the case where an Au or silicon oxide film is used as a translucent film of a two-layer optical disc (DVD-ROM) will be described. FIG.
Means that the wavelength of the laser light is 650 nm, 635 nm and 60 nm.
"0" layer (semi-transparent film, Au thin film) and "0 nm"
It shows the dependency of the reflectivity of the 1 "layer (high reflectivity film, Al thin film) on the thickness of Au. The thickness of the Al thin film of the" 1 "layer (high reflectivity film) is fixed to 80 nm. In the figure, a white square, a white circle, and a white triangle indicate the “0” layer,
A black square, a black circle, and a black triangle indicate the “1” layer. The white and black squares indicate the laser wavelength of 6
The optical calculation value of 50 nm, the white and black circles are the optical calculation values of the laser wavelength of 635 nm, the white and black triangles are the
The optical calculation value at a laser wavelength of 600 nm is shown. From the optical calculation results, the range of the Au film thickness satisfying the DVD-ROM reflectance standard (25% to 40%) for each laser wavelength is 13.2 nm to 14.8 n for the wavelength of 650 nm.
m, 13.6 nm to 15.0 n for a wavelength of 635 nm
m is a pinpoint of 16.1 nm for a wavelength of 600 nm. Therefore, when an Au thin film is used for the “0” layer,
It can be seen that the reproduction wavelength limit is about 600 nm, and a short wavelength blue laser of 600 nm or less cannot be used.

FIG. 8 shows the short wavelength limit of the reproduction wavelength when a silicon oxide film is used for the “0” layer (semi-transparent film). A reproduction wavelength of 460 nm is used. In the figure, the solid line is ″
The layer 0 (semi-transparent film) and the broken line indicate the layer 1 (Al reflective film) As shown in Fig. 8, the oxygen concentration in the SiOx film is 0.56 for the reproduction laser light of 460 nm. ≤X ≤
In the range of 0.60, the standard value of the reflectance of DVD-9 is satisfied at a pinpoint. In other words, when the SiOx film is used as a "0" layer (translucent film), the reproduction wavelength limit is about 460 nm even if the thickness of the SiOx film and the oxygen concentration are adjusted.

[0006] Even when a two-layer disk is used in which the thickness of the translucent film is adjusted to be compatible with a 635 nm laser wavelength, the short wavelength limit at which reproduction is possible is 600 nm when Au is used for the translucent film. When a silicon carbide oxide film is used as the translucent film, the thickness is about 550 nm.
Therefore, if the future reproduction wavelength becomes a short wavelength in the 400 nm range, reproduction cannot be performed with the conventional two-layer optical disc. Conversely, in order to enable reproduction, there is an inconvenience that a laser device for a reproduction drive must be prepared so as to emit a plurality of laser beams having different wavelengths.

[0007] The problem of the limit of the reproduction wavelength of the conventional optical information recording medium has been described by taking a two-layer optical disc as an example. However, the same problem exists with an information recording medium having three or more layers of information recording surface. In an information recording medium having a multilayer information recording surface of three or more layers, the reflectance of the semi-transparent film increases from the semi-transparent film on the near side to the translucent film on the back side in the laser incident direction, and the laser incident direction A high-reflection film having a high reflectance is provided on the innermost information recording surface.

For the above reasons, an object of the present invention is to improve the disadvantages of the conventional information recording medium and to enable the information recorded on the multilayer information recording surface to be reproduced in a wide reproduction wavelength range. And for multiple reproduction laser wavelengths corresponding to the future short wavelength of the drive,
An object of the present invention is to provide an information recording medium capable of ensuring reproduction compatibility without changing the medium configuration.

[0009]

Means for Solving the Problems To achieve the above object, an information recording medium according to the present invention comprises a transparent substrate having an information recording surface and an information recording surface of the transparent substrate which is alternately stacked on the information recording surface. A transparent space layer having a translucent film and an information recording surface, and an optical information recording medium having a reflective film provided on the information recording surface of the uppermost transparent space layer, the translucent film has a low refractive index layer and It is characterized in that it is a multilayer film in which high refractive index layers are alternately laminated.

The translucent film is a multilayer film in which a high-refractive-index layer and a low-refractive-index layer are laminated, and the thickness and the refractive index of the high-refractive-index layer and the low-refractive-index layer are adjusted to be 400 nm to 650 n.
m, and for reproduction laser wavelengths up to 800 nm,
Since the amount of reflected light returning from each information recording surface provided in the transparent space layer to the reproduction optical system can be equalized, the load on the reproduction optical system is reduced, and reproduction can be performed with laser light in a wide wavelength band.

Preferably, the optical constants n and k (n: refractive index, k: extinction coefficient) of the high refractive index layer and the low refractive index layer constituting the semi-transparent film correspond to laser light having a wavelength of 400 nm to 800 nm. On the other hand, the refractive index n and the extinction coefficient k of the high refractive index layer are in the range of 2.0 <n <2.6 and k <0.4, respectively.
The refractive index n and the extinction coefficient k of the low refractive index layer are each 1.3.
<N <1.46 and k <0.01. The refractive index n and the extinction coefficient k of the high refractive index layer and the low refractive index layer can be controlled by a film forming material and film forming conditions. For example, when the high refractive index layer is formed of nitrogen deficient aluminum, the refractive index and extinction coefficient of the high refractive index layer, when sputtering aluminum to form nitrogen deficient aluminum,
It can be controlled by adjusting the ratio of the N ₂ gas in the mixed gas introduced into the sputtering chamber.

In another embodiment of the present invention, the multilayer film constituting the translucent film is formed of a high refractive index layer and a high refractive index layer sandwiching the high refractive index layer from both sides of the high refractive index layer. It has a three-layer structure of low refractive index layers laminated on both sides, respectively, and the wavelength λ of the laser beam used for reproducing the information recorded on the information recording surface of the information recording medium is in the range of λ ₁ ≦ λ ≦ λ ₂ . When the refractive indices of the low refractive index layer with respect to the wavelengths λ ₁ and λ ₂ of the laser beam are n ₁ and n ₂ , respectively, the thickness of the low refractive index layer is λ ₁ / (4n ₁ ) to λ ₂ / (4n ₂ ).

With the above arrangement, the difference in the wavelength dependence of the reflectance, absorptance and transmittance of the translucent film is reduced,
It is possible to perform stable reproduction with respect to a laser wavelength of from nm to 650 nm, and further, 800 nm.

The material of the high refractive index layer has the effect of the present invention.
There are no restrictions as far as possible, for example, nitrogen-deficient aluminum,
Oxygen deficient aluminum, oxygen deficient titanium, nitrogen deficient titanium
Metal or metal compound of titanium, titanium nitride, and titanium oxide
And silicon nitride, silicon oxide, and oxide it
At least one selected from the group consisting of lithium and zinc sulfide.
At least one of Fe, Co and Ni for the bright dielectric
Selected from the group consisting of mixtures of
Form a translucent high refractive index layer with at least one type of material
I do. Further, the material of the low refractive index layer also exhibits the effects of the present invention.
There are no restrictions as far as possible._Two, NaF and M
gF_TwoOr CaF_Two, NaF and MgF _Two
Forming a low refractive index layer with a mixture of at least two of the above
I do.

By setting the thickness of the transparent space layer to 40 μm or more, interference from upper and lower information recording surfaces can be separated, and a high quality reproduced signal can be obtained.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Embodiment 1 This embodiment is an example of an embodiment of an information recording medium according to the present invention. FIG. 1A is a cross-sectional view of a substrate showing a configuration of an embodiment of this embodiment. (B) is a detailed view showing the configuration of the translucent film. Information recording medium 1 of the present embodiment
0 is an information recording surface 11 on the upper surface as shown in FIG.
1 and a semi-transparent film 121 and an information recording surface 1 which are alternately stacked on the transparent substrate 101 in multiple stages.
It has a laminated structure composed of a transparent space layer 131 having an upper surface 12, a reflective layer 102, and a protective film 103. The information recording surface 111 is formed by, for example, irregularities corresponding to (0) and (1). Transparent substrate 101
Is, for example, a translucent disk made of polycarbonate.
The semi-transparent film 121 deposited on the information recording surface 111 has the structure shown in FIG.
As shown in (b), the multilayer film has a high refractive index layer 142 and low refractive index layers 141 and 143 laminated on both surfaces of the high refractive index layer 142 with the high refractive index layer 142 interposed therebetween.

The optical constants n, k (n;
Refractive index, k; extinction coefficient) is from 400 nm to 800 nm
The refractive index n is 2.0 <n <2.6 for the laser wavelength of
And the extinction coefficient k is k <0.4. On the other hand, the optical constants n and k of the low refractive index layers 141 and 143 (n: refractive index,
k: extinction coefficient), for a laser wavelength of 400 nm to 800 nm, the refractive index n is in the range of 1.3 <n <1.46, and the extinction coefficient k is k <0.01. High refractive index layer 14
2 is formed of, for example, nitrogen-deficient aluminum, and the low refractive index layers 141 and 143 are formed of NaF. The transparent spacer layer 131 is formed of, for example, an ultraviolet curable resin. Information recording medium 10 of this embodiment
Here, the optical constants n and k of the translucent films 121 of each layer are all equal.

The high-refractive-index layer 142 and the low-refractive-index layers 141 and 143 of the translucent film 121 may be formed of other materials as long as they function similarly to the above-mentioned materials. For example, instead of nitrogen-deficient aluminum, the high-refractive-index layer 142 includes, for example, oxygen-deficient aluminum, oxygen-deficient titanium, nitrogen-deficient titanium, titanium nitride, titanium oxide, or silicon nitride.
A material obtained by mixing a metal element such as Fe, Co, or Ni with a transparent dielectric such as silicon oxide, yttrium oxide, or zinc sulfide, or a combination thereof may be used.

In the present embodiment, the high refractive index layer 142 of the translucent film 121 is formed of nitrogen-deficient aluminum, and the low refractive index layers 141 and 143 are formed of NaF. FIG. 2 shows a semi-transparent film for a laser wavelength of 400 nm for the information recording medium 10 of the present embodiment using nitrogen deficient aluminum for the high refractive index layer 142 of the translucent film 121 and NaF for the low refractive index layers 141 and 143. 12 shows the result of optical calculation of the relationship between the reflectance (R) of 121 and the refractive index of the high refractive index layer, and shows the dependency of the refractive index of the translucent film on the refractive index change with respect to the refractive index of the high refractive index layer. . As is clear from FIG. 2, the reflectance R of the high refractive index layer 142 of the translucent film 121 increases as the refractive index of the high refractive index layer increases. Therefore, the reflectance can be controlled by adjusting the refractive index of the high refractive index layer, so that nitrogen-deficient aluminum is suitable as a translucent reflective film for a multilayer information recording medium. As described below, the refractive index and the extinction coefficient of nitrogen-deficient aluminum are adjusted by adjusting the ratio of N ₂ gas in the mixed gas introduced into the sputtering chamber when sputtering aluminum to form nitrogen-deficient aluminum. Thus, control can be performed.

Further, referring to FIG. 3 and FIG.
As a high refractive index layer of the translucent reflective film of the recording medium,
Supplementary explanation that luminium is effective. FIG.
Aluminum and Ar and N_TwoSputter in a mixed gas of
Dependence of refractive index of nitrogen-deficient aluminum film on wavelength
Show. FIG. 4 shows that aluminum is converted to Ar and N _TwoIn the gas mixture
Extinction coefficient of nitrogen-deficient aluminum formed by sputtering
Shows the wavelength dependence of. In the figure, 10%, 12% and 14%
Are respectively Ar and N_TwoN in mixed gas of_TwoGas volume
Indicates the amount%. As shown in FIGS. 3 and 4, N_TwoGas capacity
% Increase in refractive index of nitrogen-deficient aluminum film
Rate and extinction coefficient decrease, and N_TwoGas volume% is 12% or more
In, the wavelength dependence of the refractive index and the extinction coefficient is extremely small,
Since the extinction coefficient is almost 0 (zero), the nitrogen deficiency
Minium is effective as a high refractive index layer in multilayer media
Became clear.

Embodiment 2 This embodiment is another example of the embodiment of the information recording medium according to the present invention, and FIG. 5A shows a substrate showing the configuration of the information recording medium of this embodiment. FIG. 5B is a cross-sectional view showing a detailed configuration of the translucent film. Embodiment 20 of the present embodiment
Are the information recording surfaces 2 as shown in FIG.
Two transparent substrates 201 and 20 having 11 and 212
2, a translucent film 221 formed on the information recording surface 211 of one transparent substrate 201, and a high reflectivity film 222 formed below the information recording surface of the other transparent substrate 202. The transparent substrates 201 and 202 have their respective information recording surfaces 2
11 and 212 are opposed to each other, a transparent space layer 231 is interposed between the two, and the two are bonded to each other, thereby forming an information recording medium 20 having two information recording surfaces 211 and 212. Is done. Information recording surface 21
Like the information recording surface 111 of the information recording medium 10 according to the first embodiment, the reference numerals 1 and 212 are formed by unevenness corresponding to (0) and (1).

Translucent film 2 deposited on information recording surface 211
Reference numeral 21 denotes a multilayer film in which low refractive index layers 241 and 243 are laminated on both surfaces of the high refractive index layer 242 with the high refractive index layer 242 interposed therebetween, as shown in FIG. The optical constants n and k (n: refractive index, k: extinction coefficient) of the high refractive index layer 242 are such that the refractive index n is 2.0 <n <2.6 with respect to a laser wavelength of 400 nm to 800 nm. , The extinction coefficient k is k <0.4, and the optical constants n and k (n; refractive index, k; extinction coefficient) of the low refractive index layers 241 and 243 are 400.
For a laser wavelength from nm to 800 nm, the refractive index n is in the range of 1.3 <n <1.46, and the extinction coefficient k is k <0.0.
It is one. In this embodiment, the high refractive index layer 242 has nitrogen deficient aluminum, and the low refractive index layers 241 and 243 have NaF.
You are using For example, Al
(Aluminum). Further, in the present information recording medium, the reflectance increases from the translucent film on the near side to the translucent film on the back side when viewed in the direction of incidence of the laser beam, and a high reflectance is provided on the innermost information recording surface. 1 is an example of an information recording medium having a highly reflective film. The other configuration of the information recording medium 20 of the present embodiment is the same as that of the above-described embodiment of FIG.

FIG. 6 shows a laser wavelength of 400 nm and 450 nm.
Dependence of the reflectance (R) of the high refractive index layer on the film thickness for m, 500 nm and 635 nm, that is, the reflectance of the translucent film and the high reflectance film (the reflectance measured at the reflected light detecting end of the information recording medium) The relationship between the thickness and the thickness of the high refractive index layer is shown. In the figure, the broken line indicates the reflectance of the translucent film, and the solid line indicates the reflectance of the high reflectance film. In FIG. 6, A is applied to the high refractive index layer 242 of the translucent film 221.
A nitrogen-deficient aluminum film formed with an N ₂ content of r and N ₂ gas of 11% is used, and NaF is used for the low refractive index layer 241. The low-refractive index layer 241 is made of Na having a thickness of 75 nm.
F film (λ ₁ / 4n ₁ ; λ ₁ = 400 nm, n ₁ = 2.6
3) NaF having a thickness of 120 nm is applied to the low refractive index layer 243 (λ ₂ / 4n ₂ ; λ ₂ = 635 nm, n ₂ = 2.32).
The high reflectance film is fixed to an 80 nm-thick Al film.

As shown in FIG. 6, the reflectance range for the reproduction optical system to obtain a stable signal, that is, the thickness range of the nitrogen-deficient aluminum film satisfying 25% to 40% is 40 nm.
24 nm to 52 nm at 0 nm, 26 n at 450 nm
m to 63 nm, 30 nm to 73 nm at a wavelength of 500 nm,
A wavelength of 635 nm is in the range of 46 nm to 98 nm. In particular, in the range of 46 nm to 52 nm, a stable reflected light amount can be obtained even if any wavelength of 400 nm to 635 nm is used for the reproduction laser, and the reproduction wavelength dependency is extremely small. Is shown. From the above optical calculations, 400 nm to 8
The optical constants (refractive index n and extinction coefficient k) of a material that can be used as a semi-transparent film for a laser wavelength of 00 nm are obtained as follows. High refractive index layer; n is in the range of 2.0 <n <2.6, k is k <
0.4 low refractive index layer; n is in the range of 1.3 <n <1.46, k is k
<0.01

[0025]

According to the present invention, a translucent film of an optical information recording medium having a translucent film alternately laminated on an information recording surface of an information transparent substrate and a transparent space layer having an information recording surface. Is formed by a multilayer film in which high refractive index layers and low refractive index layers are alternately laminated, so that the application wavelength range of the reproduction laser light is expanded to a range of 400 nm to 800 nm, and the reproduction wavelength dependence is small. Therefore, an information recording medium capable of obtaining a good reproduction signal even with a plurality of laser beams having different wavelengths is realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a laminated structure of an information recording medium according to a first embodiment.

FIG. 2 is a diagram illustrating a calculation result of a relationship between a change in refractive index and a reflectance R with respect to a laser wavelength of 400 nm in a high refractive index layer of a semitransparent film of the information recording medium of Embodiment 1.

FIG. 3 shows the wavelength dependence of the refractive index of nitrogen-deficient aluminum formed by sputtering aluminum in a mixed gas of Ar and N ₂ .

FIG. 4 shows the wavelength dependence of the extinction coefficient of nitrogen-deficient aluminum formed by sputtering aluminum in a mixed gas of Ar and N ₂ .

FIG. 5 is a cross-sectional view illustrating a laminated structure of an information recording medium according to a second embodiment.

FIG. 6 shows a high refractive index layer of a semi-transparent film according to an embodiment of Embodiment 2, which is 400 nm, 450 nm, 500 nm, and 6 nm.
FIG. 14 is a diagram showing a calculation result of a relationship between a reflectance R and a thickness of a translucent film with respect to a reproduction laser wavelength of 35 nm.

FIG. 7 is a diagram showing a calculation result of obtaining a reproduction wavelength limit when an Au thin film is used as a translucent film.

FIG. 8 is a diagram showing a calculation result of obtaining a reproduction wavelength limit when a silicon oxide thin film is used as a translucent film.

FIG. 9 is a schematic diagram showing a configuration of a conventional two-layer optical disc.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conventional two-layer optical disk 2 First information recording surface having a translucent film 3 Second information recording surface having a reflective layer 10 Information recording medium of Embodiment 1 20 Information recording medium of Embodiment 2 101 Transparent substrate 102 Reflective layer 103 Protective film 111, 112 Information recording surface 121 Translucent film 131 Transparent space layer 141, 143 Low refractive index layer 142 High refractive index layer 201, 202 Transparent substrate 211, 212 Information recording surface 221 Semi-transparent film 222 High reflectivity Film 231 transparent space layer

Claims (7)

[Claims] 1. A transparent substrate having an information recording surface, a transparent space layer having a translucent film and an information recording surface alternately stacked on the information recording surface of the transparent substrate, and information on an uppermost transparent space layer. An optical information recording medium having a reflective film provided on a recording surface, wherein the translucent film is a multilayer film in which a low refractive index layer and a high refractive index layer are alternately laminated. Information recording medium. 2. The optical constants n and k (n: refractive index, k: extinction coefficient) of a high refractive index layer and a low refractive index layer constituting a semi-transparent film with respect to a laser beam having a wavelength of 400 nm to 800 nm. The refractive index n and the extinction coefficient k of the high refractive index layer are in the range of 2.0 <n <2.6 and k <0.4, respectively, and the refractive index n and the extinction coefficient k of the low refractive index layer are 1.3 <n
2. The information recording medium according to claim 1, wherein a range of <1.46 and k <0.01 are satisfied. 3. A high refractive index layer, and a low refractive index laminated on both sides of the high refractive index layer such that the high refractive index layer is sandwiched between both surfaces of the high refractive index layer. The wavelength λ of the laser beam used for reproducing the information recorded on the information recording surface of the information recording medium is in the range of λ ₁ ≦ λ ≦ λ ₂ , and the wavelength λ _{1 of the} laser beam is And when the refractive index of the low refractive index layer with respect to λ ₂ is n ₁ and n ₂ , respectively, the thickness of the low refractive index layer is in the range of λ ₁ / (4n ₁ ) to λ ₂ / (4n ₂ ). The information recording medium according to claim 1, wherein: 4. The high refractive index layer of the translucent film is made of a metal or a metal compound of nitrogen-deficient aluminum, oxygen-deficient aluminum, oxygen-deficient titanium, nitrogen-deficient titanium, titanium nitride, and titanium oxide; silicon,
Formed of at least one material selected from the group consisting of a mixture of at least one transparent element selected from yttrium oxide and zinc sulfide and at least one metal element of Fe, Co and Ni The information recording medium according to any one of claims 1 to 3, wherein: 5. The low refractive index layer is made of CaF ₂ , NaF and M
gF ₂ , or CaF ₂ , NaF and MgF ₂
The information recording medium according to any one of claims 1 to 5, wherein the information recording medium is formed of a mixture of at least two of the following. 6. The information recording medium according to claim 4, wherein the high refractive index layer of the translucent film is a nitrogen-deficient aluminum film having a thickness in a range from 24 nm to 98 nm. 7. The information recording medium according to claim 1, wherein the thickness of the transparent space layer is 40 μm or more.