JP2001014723A - Information recording medium - Google Patents

Abstract

(57) [Summary] [Objective] An information recording medium having good recording / reproducing characteristics when recording / reproducing with a blue laser. In an information recording medium, an information recording thin film on which information is recorded by a change in atomic arrangement caused by light irradiation is provided as a recording layer on a substrate, and the recording film has an amorphous n at a reproduction wavelength. (Refractive index) n in the crystalline state
By having larger features, it has good recording / reproducing characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an information recording medium used for an optical disk.

[0002]

2. Description of the Related Art There are various known principles for recording information on a thin film (recording film) by irradiating a laser beam, and among them, a laser such as a phase transition (also called phase change) of a film material or photodarkening is used. The method utilizing the atomic arrangement change due to light irradiation hardly involves deformation of a thin film, and thus has an advantage that an information recording medium having a double-sided disk structure can be obtained by directly bonding two disk members.

In a normal optical disk, the wavelength is 660 nm.
A light source generally called a red laser in the vicinity is used. These information recording media are provided on a substrate with a protective layer, GeSb.
The recording film is made of a Te-based recording film, a ZnS-SiO2 based protective layer, and a reflective layer. At a wavelength near 660 nm, n (refractive index) of the recording film is larger in a crystalline state than in an amorphous state.

The reflectivity of the crystalline state is higher than that of the amorphous state. Thereby, the absorptance in the recording film is higher in the amorphous state. If you perform overwriting in this state,
Since the temperature of the recording mark portion in the amorphous state is more likely to rise than the temperature in the crystalline state portion, the newly recorded mark becomes larger and the reproduced signal is distorted.

[0005] To prevent this, attempts have been made to make the recording film have a higher absorptance in the crystalline state than in the amorphous state. For example, Reference 1 (Yamada et al., IEICE Technical Report)
For MR92-71, CPM92-148 (1992-12) P.37), a very thin Au reflection layer of 10 nm is provided for a type of medium whose reflectivity in the crystalline state is higher than that in the amorphous state at the wavelength of the red laser. This reverses the absorption.

On the other hand, at a wavelength near 410 nm, the n (refractive index) of the recording film is higher in the crystalline state than in the amorphous state because the crystalline state is smaller than the amorphous state.
Moreover, it is difficult to increase the absorptance ratio. Short-wavelength lasers in the vicinity are generally called blue, blue-green, blue-violet, and green lasers as compared with long-wavelength red lasers, but are collectively referred to herein as blue lasers.

In this specification, not only the phase change between the crystal and the amorphous phase, but also the melting (change to the liquid phase) and the recrystallization,
The term "phase change" is used to include the phase change between crystalline states. Mark edge recording refers to a recording method in which an edge portion of a recording mark is made to correspond to a signal “1”, and between and within marks are made to correspond to a signal “0”.

[0008]

Any conventional information recording medium has a problem that the recording characteristics are poor when used as a high-density rewritable phase transition type information recording medium using a blue laser. are doing.

It is an object of the present invention to provide an information recording medium having good recording / reproducing characteristics when recording / reproducing with a blue laser.

[0010]

(1) In an information recording medium, an information recording thin film on which information is recorded by a change in an atomic arrangement caused by irradiation of light is provided as a recording layer on a substrate, and the information recording medium has a recording wavelength. The recording film is characterized in that n in the amorphous state (refractive index) is larger than n in the crystalline state.

(2) In the information recording medium described in (1),
When recording is performed on the recording film, the reflectance in the amorphous state is lower than the reflectance in the crystalline state, and the recording start power when the shortest mark is recorded on the amorphous state is the same as that on the crystalline state. The recording start power when the shortest mark is recorded under the condition is the same or smaller.

(3) In the information recording medium described in (2),
It has a structure in which an absorptance control layer is laminated between substrates of the recording film.

(4) In the information recording medium described in (3),
The film thickness of the absorptance control layer is in the range of 5 nm to 40 nm.

(5) The information recording medium according to any one of (3) to (4), wherein the absorptance control layer is made of a non-stoichiometric compound.

(6) In the information recording medium according to the item (1), when recording is performed on the recording film, the reflectivity in the amorphous state is higher than the reflectivity in the crystalline state, and the shortest mark is formed on the amorphous state. Is characterized in that the recording start power is the same or smaller when the shortest mark is recorded on the crystalline state under the same conditions.

(7) The information recording medium according to (6), further comprising the recording film and at least one protective layer, wherein the protective layer and the recording layer are laminated in this order from the light incident side, and then the intermediate of at least one layer Having a structure in which at least one reflective layer is laminated via a layer, and having a thickness d (nm) of the intermediate layer
, A is an integer of 0 or more, b is the refractive index of the intermediate layer, and λ (n
When m) is the wavelength of the reproduction light, 0.5 × a × λ {b + 0.16 ≦ d ≦ 0.5 × a × λ}
b + 0.39.

(8) The information recording medium according to any one of (6) to (7), wherein the information recording medium has a structure in which an absorptance control layer is laminated between the intermediate layer and the reflective layer.

(9) The information recording medium according to any one of (6) to (8), wherein the absorptivity control layer is made of a non-stoichiometric compound.

(10) It has been found that when the thickness of the absorptance control layer is reduced, the jitter after overwriting increases, and when the thickness is increased, the modulation degree increases. The thickness of the absorptance control layer is preferably 3 nm or more and 40 nm or less, and more preferably 5 nm or more and 20 nm or less.

The n of the absorptance control layer is preferably 1.5 or more and 5 or less, more preferably 2 or more and 4 or less. The k of the absorptance control layer is preferably 0.4 or more and 4 or less, more preferably 1 or more and 3 or less.

The amount of Cr in the absorption control layer is 22 mol.
% Or more and 43 mol% or less.

Materials that can replace the Cr—O film used for the absorption control layer include VO, Co—O, Cu—O, and Mo.
-O, WO, Fe-O, Sb-O, Mn-O, Ti-
O, Ge-O, Pt-O, Ni-O, Nb-O, Pd-
Similar results were obtained when O, Be-O, and Ta-O were used. In addition, Ta-N, Al-N, BN, Cr-N,
Ge-N, Hf-N, Si-N, Al-Si-N-based materials, Si-ON-based materials, Ti-N, Zr-N, and the like can also be used. In addition, Si-O, Al-O, B
e-O, Bi-O, Ni-O, Pb-O, Pd-O, S
n-O, Sc-O, Sr-O, Th-O, Te-O, Y
-O, Zr-O, oxides such _{as, ZnS, Sb 2 S 3,} C
dS, In ₂ S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , Pb
S, Bi ₂ S ₃ , SrS, MgS, CrS, CeS, Ta
Sulfides such as S ₄ , SnSe ₂ , Sb ₂ Se ₃ , CdS
e, ZnSe, In ₂ Se ₃ , Ga ₂ Se ₃ , GeSe, G
selenides such as eSe ₂ , SnSe, PbSe, Bi ₂ Se ₃ , CeF ₃ , MgF ₂ , CaF ₂ , TiF ₃ , NiF
_3, fluorides such as FeF _2, FeF _3, or Si, G,
e, TiB ₂ , B ₄ C, B, CrB, HfB ₂ , TiB
₂ , borides such as WB, C, Cr ₃ C ₂ , Cr ₂₃ C
₆ , Cr ₇ C ₃ , Fe ₃ C, Mo ₂ C, WC, W ₂ C, H
A carbide such as fC, TaC, CaC ₂ , or a composition close to the above-mentioned materials may be used, but k of each absorptivity control layer is preferably 0.4 or more and 4 or less. Further, a mixed material thereof may be used. These absorptivity control layers are preferably nonstoichiometric compounds deviating from the stoichiometric composition, since the extinction coefficient k is larger than 0.4.

Of these, Cr-O was preferred because of its high adhesive strength and high thermal stability. If the melting point of the compound and / or the metal alone in the material of the absorptance control layer is higher than the melting point of the recording film (about 600 ° C.), the rise in jitter after 10,000 rewrites can be reduced. The melting point of both is 600
When the temperature is not less than ℃, it can be suppressed to 3% or less, and more preferable.

For the absorptance control layer, it is necessary to select a material whose optical characteristics do not change abruptly with respect to wavelength as shown in FIG. The use of a material that undergoes a rapid change when the wavelength changes causes the disadvantage that the productivity is reduced and the optical characteristics are changed when the wavelength of the light source shifts due to the environmental temperature, resulting in poor reproduction characteristics.

Further, it was found that when the impurity element in the absorptance control layer exceeded 2 atomic% of the component of the absorptivity control layer, the jitter of the leading edge or the trailing edge after rewriting 10 times exceeded 15%. Further, it was found that when the impurity element exceeded 5 atomic%, the jitter became 18% or more. Therefore, it is preferable that the impurity element in the absorptance control layer be 5 atomic% or less of the components of the absorptivity control layer because the deterioration of the rewriting characteristics can be reduced. More preferably, it is 2 atomic% or less.

Since it is difficult to produce a high-power laser with a blue laser as compared with a red laser, recording sensitivity of a medium is required more. Therefore, it is not preferable to use a material having a high thermal conductivity, such as Au, Al, or Cu, for the absorption control layer, because the recording film is rapidly cooled and easily disappears. However, if the thickness of the intermediate layer is extremely large, such as 100 nm or more, heat can be prevented from escaping in the direction of the reflective layer, and the structure becomes slightly cooled, so that a material having high thermal conductivity can be used. .

(11) The protective layer is made of (ZnS) ₈₀ (Si
O ₂ ) ₂₀ .

As a material replacing the (ZnS) ₈₀ (SiO ₂ ) ₂₀ of the protective layer, a material in which the mixing ratio of ZnS and SiO ₂ is changed is preferable. Further, ZnS, Si—N-based material, Si
-O-N-based _{material, SiO 2, SiO, TiO 2} , Al
₂ O ₃ , Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , In ₂ O ₃ , Ge
O, GeO ₂ , PbO, SnO, SnO ₂ , BeO, Bi
₂ O ₃ , TeO ₂ , WO ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ ,
Oxides such as ZrO ₂ , Cu ₂ O and MgO, TaN, A
nitrides such as 1N, BN, Si ₃ N ₄ , GeN, Al—Si—N-based materials (eg, AlSiN ₂ ), ZnS, Sb ₂ S
₃ , CdS, In ₂ S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , P
sulfides such as bS, Bi ₂ S ₃ , SnSe ₂ , Sb ₂ S
e ₃ , CdSe, ZnSe, In ₂ Se ₃ , Ga ₂ Se ₃ ,
GeSe, GeSe ₂ , SnSe, PbSe, Bi ₂ Se
₃ , a fluoride such as CeF ₃ , MgF ₂ , CaF ₂ , or Si, Ge, TiB ₂ , B ₄ C, B,
C or a material having a composition close to the above materials may be used. Further, a layer of a mixed material of ZnS—SiO ₂ , ZnS—Al ₂ O ₃ , or the like, or a multi-layer thereof may be used. Among them, ZnS has a large n and can maintain a large modulation degree. Therefore, in the case of a mixture containing 60 mol% or more of ZnS,
The combination of the large n of ZnS and the good chemical stability of the oxide is combined. ZnS has a higher sputter rate. If ZnS accounts for 80 mol% or more, the film formation time can be shortened. Other sulfides and selenides also provided similar properties.

The element ratio in these compounds is, for example, the ratio of the metal element to the oxygen element in oxides and sulfides, or Al ₂ O ₃ , Y ₂ O ₃ ,
La ₂ O ₃ is 2: 3, SiO ₂ , ZrO ₂ , GeO ₂ is 1:
It is preferable that 2, Ta ₂ O ₅ has a ratio of 2: 5 and ZnS has a ratio of 1: 1 or close to that ratio, but the same effect can be obtained even if the ratio is out of the ratio. In the case where the ratio is out of the above integer ratio, for example, Al—O has a ratio of Al and O from Al ₂ O ₃ to ± 10 atom% or less in Al amount, and Si—O has a ratio of Si and O in SiO ₂ to Si amount. It is preferable that the deviation of the amount of the metal element be 10 atomic% or less, such as ± 10 atomic% or less. When the amount is shifted by 10 atomic% or more, the optical characteristics are changed, so that the degree of modulation is reduced by 10% or more.

It is preferable that the protective layer 2 and the material used for the protective layer 2 be 90% or more of the total number of atoms in each protective layer. When impurities other than the above materials become 10 atomic% or more,
Degradation of the rewriting characteristics was observed, for example, the number of rewriting times became 以下 or less.

When the protective layer n used in this embodiment is 2.4 or more, the degree of modulation can be made 47%, which is more preferable. The extinction coefficient is preferably 0 or close to 0.

When two or more protective layers are used and the material of the protective layer on the recording film side is Cr ₂ O ₃ , diffusion of Zn and S into the recording film at the time of rewriting many times can be suppressed, and the rewriting characteristics are good. I understand.

As a material in place of Cr ₂ O ₃ as a protective layer material on the recording film side, CoO or GeO ₂ , NiO, or a mixture of these with Cr ₂ O ₃ is preferable. Next, S is added to Cr ₂ O ₃ .
A mixture of iO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ , and ZrO ₂ —Y ₂ O ₃ is good. These oxides have a small extinction coefficient k and very low absorption in the lower interface layer. Therefore, there is an advantage that the modulation degree can be kept large.

Further, AlN, BN, CrN, Cr ₂ N,
_{GeN, HfN, Si 3 N 4} , Al-Si-N material (e.g., AlSiN _2), Si-N-based material, Si-O-N-based material, TaN, TiN, ZrN, nitrides, such as adhesion This is more preferable because deterioration of the information recording medium due to external impact is small. Even with a recording film composition containing nitrogen or a material having a composition close thereto, the adhesive strength is improved.

In addition, BeO, Bi ₂ O ₃ , CeO ₂ , C
u ₂ O, CuO, CdO, Dy ₂ O ₃ , FeO, Fe
₂ O ₃ , Fe ₃ O ₄ , GeO, GeO ₂ , HfO ₂ , In
₂ O ₃ , La ₂ O ₃ , MgO, MnO, MoO ₂ , MoO ₃ ,
NbO, NbO ₂ , PbO, PdO, SnO, Sn
O ₂ , Sc ₂ O ₃ , SrO, ThO ₂ , TiO ₂ , Ti
₂ O ₃ , TiO, TeO ₂ , VO, V ₂ O ₃ , VO ₂ , W
Oxides such as O ₂ and WO ₃ , C, Cr ₃ C ₂ , Cr ₂₃ C
₆ , Cr ₇ C ₃ , Fe ₃ C, Mo ₂ C, WC, W ₂ C, H
A carbide such as fC, TaC, CaC ₂ , or a material having a composition close to the above materials may be used. Further, a mixed material thereof may be used.

When a protective layer on the recording film side is provided, Zn,
It is possible to prevent S and the like from diffusing into the recording film, and suppress an increase in unerased parts. Furthermore, in order not to lower the recording sensitivity, the thickness is preferably set to 25 nm or less, and the following is more preferable. Approximately 2 nm can form a uniform film
And 5 nm or more was even better. Accordingly, it is preferable that the thickness of the protective layer on the recording film side be 2 to 25 nm because the recording / reproducing characteristics are further improved.

(12) The recording film is made of Ag ₈ Ge ₁₉ Sb ₂₆
And forming a Te _47.

As a material replacing the Ag ₈ Ge ₁₉ Sb ₂₆ Te ₄₇ of the recording film, an Ag—Ge—Sb—Te-based material having a different composition ratio is preferable because the degree of modulation is increased. When the amount of Ag in the recording film is large, the change in reflectance at a short wavelength is large, but the crystallization speed is low. Therefore, it is preferable that the amount of Ag added is 2 atomic% or more and 10 atomic% or less. But,
Overwriting is possible even with a Ge-Sb-Te-based material to which Ag is not added. And instead of Ag, Ge-
Elements to be added to the recording film instead of Ag to Sb-Te include Cr, W, Mo, Pt, Co, Ni, Pd, S
It was found that the overwrite characteristics were good even when replaced with at least one of i, Au, Cu, V, Mn, Fe, Ti, and Bi.

The thickness of the recording film is preferably from 6 nm to 25 nm, more preferably from 7 nm to 20 nm.

(13) The intermediate layer is formed of ZnS-SiO ₂ .

Materials that can be used in place of ZnS—SiO ₂ for the intermediate layer include Si—N-based materials, Si—ON-based materials, and Zn—
S, SiO ₂ , SiO, TiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , C
eO ₂ , La ₂ O ₃ , In ₂ O ₃ , GeO, GeO ₂ , Pb
O, SnO, SnO ₂ , BeO, Bi ₂ O ₃ , TeO ₂ , W
O ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Cu ₂ O,
Oxides such as MgO, TaN, AlN, BN, Si ₃ N
₄ , GeN, Al-Si-N-based materials (for example, AlSi
Nitrides such as N ₂ ), ZnS, Sb ₂ S ₃ , CdS, In ₂
Sulfides such as S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , PbS, Bi ₂ S ₃ , SnSe ₂ , Sb ₂ Se ₃ , CdSe, Zn
Se, In ₂ Se ₃ , Ga ₂ Se ₃ , GeSe, GeS
e _2, SnSe, PbSe, selenides, such as _{Bi 2 Se 3, CeF 3,} MgF 2, fluorides such as CaF _2, or _{Si, Ge, TiB 2, B} 4 C,, B, C , or above materials A composition close to the above may be used. Also, ZnS
A layer of a mixed material of these, such as —SiO ₂ , ZnS—Al ₂ O ₃ , or a multi-layer thereof may be used. Among them, the modulation degree can be increased by using a material having a small refractive index. The refractive index is 2.
When the value is 1 or less, the modulation degree can be made 47% or more, and it is found that the modulation is more excellent. The extinction coefficient is preferably 0 or close to 0.

The element ratio of these compounds is, for example, the ratio of metal element to oxygen element in oxides and sulfides, or Al ₂ O ₃ , Y ₂ O ₃ ,
La ₂ O ₃ is 2: 3, SiO ₂ , ZrO ₂ , GeO ₂ is 1:
It is preferable that 2, Ta ₂ O ₅ has a ratio of 2: 5 and ZnS has a ratio of 1: 1 or close to that ratio, but the same effect can be obtained even if the ratio is out of the ratio. In the case where the ratio is out of the above integer ratio, for example, Al—O has a ratio of Al and O from Al ₂ O ₃ to ± 10 atom% or less in Al amount, and Si—O has a ratio of Si and O in SiO ₂ to Si amount. It is preferable that the deviation of the amount of the metal element be 10 atomic% or less, such as ± 10 atomic% or less. When the amount is shifted by 10 atomic% or more, the optical characteristics are changed, so that the degree of modulation is reduced by 10% or more.

It is preferable that the intermediate layer 5 and the material used for the intermediate layer 5 be 90% or more of the total number of atoms in each protective layer. When impurities other than the above materials become 10 atomic% or more,
Degradation of the rewriting characteristics was observed, for example, the number of rewriting times became 以下 or less.

When two or more intermediate layers are provided on the recording film side, and the material of the intermediate layer is made of Cr ₂ O ₃ , the diffusion of Zn and S into the recording film at the time of rewriting many times can be suppressed, and the rewriting characteristics can be improved. Was found to be good.

(14) The reflection layer is made of Al-Cr.

As a material for the reflective layer instead of Al-Cr, a material mainly composed of an Al alloy such as Al-Ag, Al-Cu, or Al-Ti is preferable. Al can also be used.

Thus, when the content of elements other than Al in the Al alloy is in the range of 0.5 atomic% to 4 atomic%, the characteristics and bit error rate after many rewrites are improved, and It has been found that the content becomes better in the range of not less than 2 atomic% and not more than 2 atomic%. Similar characteristics were obtained with other Al alloys.

Next, Au, Ag, Cu, Ni, F
e, Co, Cr, Ti, Pd, Pt, W, Ta, Mo,
Elemental elements of Sb, Bi, Dy, Cd, Mn, Mg, V,
Or Au alloy, Ag alloy, Cu alloy, Pd alloy, Pt
An alloy containing these as a main component, such as an alloy, or a layer made of these alloys may be used. As described above, the reflection layer is made of a metal element, a metalloid element, an alloy thereof, or a mixture thereof.

Among them, Al, Au, Ag, Al alloy,
Those having a high reflectance, such as an Au alloy and an Ag alloy, have a high contrast ratio and good rewriting characteristics. An alloy has a higher adhesive strength than a simple substance. In this case, when the content of elements other than Al, Au, Ag, etc., which are the main components, is in the range of 0.5 atomic% to 5 atomic% as in the case of the Al alloy, the contrast ratio can be increased and the adhesive strength can be increased. It was good. In the range of 1 atomic% or more and 2 atomic% or less, the result is further improved.

The material of the reflective layer is 95% of the total number of atoms in the reflective layer.
It is preferable that it is above. 5 impurities other than the above materials
At an atomic percentage or more, the rewriting characteristics were deteriorated, such as the number of rewrites being reduced to half or less.

When the thickness of the reflective layer is less than 30 nm, the strength is weak, the heat diffusion is small, and the recording film is likely to flow.
Jitter after rewriting 10,000 times becomes larger than 15%.
At 40 nm, it can be reduced to 15%. When the thickness of the reflective layer was greater than 200 nm, the time required to form each reflective layer was increased, and the formation time was doubled by dividing the process into two or more steps or providing two or more vacuum chambers for sputtering. If the thickness of the reflective layer is 5 nm or less, it is difficult to form a uniform film.

Thus, the thickness of the reflective layer is 5 nm or more,
00 nm or less is preferable.

(15) The substrate is characterized by comprising a polycarbonate substrate 1 having a groove for tracking directly on the surface. Instead, a polyolefin, epoxy, acrylic resin, chemically strengthened glass having an ultraviolet curable resin layer formed on the surface, or the like may be used. Quartz or CaF may be used instead of tempered glass.

A substrate having a tracking groove is defined as having a depth of not less than λ / 8n ′ (n ′ is the refractive index of the substrate material) when the recording / reproducing wavelength is λ on all or a part of the substrate surface. This is a substrate having a groove. The groove may be formed continuously in one round, or may be divided in the middle. It has been found that when the groove depth is about λ / 6n ′, the crosstalk is small, which is preferable. Further, it was found that when the groove depth was deeper than about λ / 3n ′, the yield at the time of forming the substrate was poor, but the cross erase was small, which was preferable.

The groove width may be different depending on the location. A substrate having no groove, a substrate of a sample servo format, a substrate of another tracking method, a substrate of another format, or the like may be used. A substrate having a format in which recording and reproduction can be performed on both the groove portion and the land portion, or a substrate having a format in which recording is performed on either one may be used. If the track pitch is small, signal leakage from an adjacent track is detected and becomes noise, so that the track pitch is at least 以上 of the spot diameter (the area where the light intensity is 1 / e ² ). preferable.

The disk size is not limited to 12 cm.
Other sizes such as cm, 8 cm, 3.5 inches, and 2.5 inches may be used. The disk thickness is not limited to 0.6 mm,
1.2mm, 0.8mm, 0.4mm, 0.1mm etc.
Other thicknesses may be used.

Instead of the second disk member, a disk member of another configuration or a protective substrate may be used. When the transmittance in the ultraviolet wavelength region of a disk member or a protective substrate used for bonding is large, the bonding can be performed using an ultraviolet curable resin. The bonding may be performed by another method. Further, in the case of a single-sided disk as shown in FIG. 7, the substrate 1 may be formed or bonded at the end by laminating the reflective layer 6 on the bonded substrate 14 in reverse. When performing recording / reproduction, it is sufficient that the respective layers are formed in the above order from the light incident side, and the manufacturing procedure does not have to be laminated in order from the light incident side.

The error rate can be further reduced by applying an ultraviolet curable resin to the reflective layers 6 and 6 'of the first and second disk members before the lamination to a thickness of about 10 μm and performing lamination after curing. .

Without bonding, an ultraviolet curable resin having a thickness of about 10 μm was formed on the reflective layer 6 of the first disk member.
The above may be applied.

In the case of a disk member having no reflective layer 6, an ultraviolet curable resin may be applied on the uppermost layer.

(16) Although it is possible to improve the recording / reproducing characteristics, etc., by setting the thickness and material of each layer to a single preferable range, the effect is further improved by combining the respective preferable ranges.

[0062]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments.

(1) Embodiment 1 (Structure and Manufacturing Method of Information Recording Medium of the Present Invention) FIG. 1 is a sectional structural view of a disc-shaped information recording medium of a first embodiment of the present invention. This medium was manufactured as follows.

First, on a polycarbonate substrate 1 having a diameter of 12 cm, a thickness of 0.6 mm and a tracking groove on the surface, an absorptance control layer 2 made of a Cr ₅₆ O ₄₄ film is formed to a thickness of about 10 nm and a thickness of about 135 nm. (ZnS) ₈₀ (SiO
₂ ) After laminating the protective layer 3 composed of ₂₀ films, Ag ₈ Ge ₁₉ Sb ₂₆
The Te ₄₇ recording film 4 is formed to have a thickness of about 14 nm and a thickness of (ZnS) ₈₀ (S
iO ₂ ) An intermediate layer 5 consisting of ₂₀ films is
A reflective layer 6 made of l ₉₈ Cr ₂ film was sequentially formed to a thickness of about 80 nm. The formation of the laminated film was performed by a magnetron sputtering apparatus. Thus, a first disk member was obtained.

On the other hand, a second disk member having the same configuration as the first disk member was obtained in exactly the same manner.
The second disk member, on a polycarbonate substrate 1 ', about the thickness of the absorptance control layer 2 made of Cr ₅₆ O ₄₄ film 10
After the lamination, a (ZnS) ₈₀ (SiO
_{2) 20} protective layer 3 made of _{films, Ag 8 Ge 19 Sb 26 Te} 47 recording layer 4 a thickness of about _{14nm, (ZnS) 80 (SiO} 2) 20
The intermediate layer 5 made of a film is formed to have a thickness of about 135 nm and Al ₉₈ Cr ₂
A reflective layer 6 made of a film was sequentially formed to a thickness of about 80 nm.

Thereafter, the first disk member and the second disk member are adhered to each other with the reflection layers 6 and 6 'interposed therebetween via an adhesive layer 7, and the disk-shaped information recording medium (disk A) shown in FIG. ) Got.

(Configuration and Manufacturing Method of Conventional Information Recording Medium) In order to clarify the effect of the absorption control layer, a disk-shaped information recording medium having no absorption control layer was manufactured. FIG. 2 shows a sectional structural view of this medium. This medium was manufactured as follows.

First, on a polycarbonate substrate 1 having a diameter of 12 cm, a thickness of 0.6 mm and a tracking groove on the surface, a (ZnS) ₈₀ (Si
After laminating the protective layer 3 made of O ₂ ) ₂₀ film, Ag ₈ Ge ₁₉ Sb
₂₆ Te ₄₇ recording film 4 is about 14 nm thick (ZnS)
_The intermediate layer 5 composed of ₈₀ (SiO ₂ ) ₂₀ films is formed to a thickness of about 135 n.
m, a reflective layer 6 of Al ₉₈ Cr ₂ film having a thickness of about 80 n
m. The formation of the laminated film was performed by a magnetron sputtering apparatus. Thus, a first disk member was obtained.

On the other hand, a second disk member having the same configuration as the first disk member was obtained in exactly the same manner.
The second disk member has a protection layer 3 made of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 135 nm and an Ag ₈ Ge ₁₉ Sb ₂₆ Te ₄₇ recording film 4 having a thickness of about 135 nm on a polycarbonate substrate 1 ′. An intermediate layer 5 of 14 nm, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film was formed to a thickness of about 135 nm, and a reflective layer 6 of an Al ₉₈ Cr ₂ film was formed to a thickness of about 80 nm.

Thereafter, the first disk member and the second disk member are adhered to each other with the reflection layers 6 and 6 'interposed therebetween via an adhesive layer 7, and the disk-shaped information recording medium (disk B) shown in FIG. ) Got.

(Initial Crystallization) The recording films 4, 4 'of the medium manufactured as described above were subjected to initial crystallization as follows. It is to be noted that the recording film 4 'is completely the same, so that only the recording film 4 will be described below.

When the linear velocity at a point on the recording track is 4 m /
The recording film 4 was irradiated through the substrate 1 with the laser light power of an oblong semiconductor laser (wavelength: about 810 nm) having a spot shape long in the radial direction of the medium set to 700 mW. The movement of the spot was shifted by 4 of the spot length in the radial direction of the medium. Thus, initial crystallization was performed. This initial crystallization may be performed once, but when it is repeated three times, a rise in noise due to the initial crystallization can be slightly reduced.
This initial crystallization has the advantage that it can be performed at high speed.

(Recording / Erasing / Reproducing) Next, while performing tracking and automatic focusing on the recording area of the recording film 4 on which the initial crystallization is completed as described above, the power of the recording laser beam is changed to the intermediate power level. Information was recorded by changing between Pe (5 mW) and high power level Ph (10 mW). The linear velocity of the recording track is 4 m / s, the wavelength of the semiconductor laser (λ) is 410 nm, and the numerical aperture (NA) of the lens is 0.65. An amorphous portion or a portion close to the amorphous portion formed in the recording area by the recording laser beam is a recording point. The reflectivity of this medium is higher in the crystalline state, and the reflectivity of the recorded and amorphous region is lower.

The power ratio between the high level and the intermediate level of the recording laser beam is particularly preferably in the range of 1: 0.3 to 1: 0.7. In addition, other power levels may be set for each short time. As shown in FIG. 3, during the formation of one recording mark, the power is repeatedly reduced to a bottom power level Pb lower than the intermediate power level by half the window width (Tw / 2), and the cooling power level Pc is changed to the recording pulse level. When recording / reproducing was performed by an apparatus having a means for generating the last waveform, a particularly low jitter value and error rate of the reproduced signal waveform were obtained. The cooling power level is lower than the intermediate power level and higher than or equal to the bottom power level. In this waveform, the characteristic in which the first pulse width Tp changes according to the combination of the recording mark and the length of the space provided immediately before the mark and the cooling pulse width Tc (the time width at which the recording pulse is lowered to the Pc level at the end of the recording pulse) are obtained. It has a feature that is determined by a combination of a recording mark and a subsequent space length of the mark. The space length immediately before the mark is short, and the longer the mark, the longer the Tp, the longer the space length immediately before the mark, and the shorter the mark, the longer the Tp. However, depending on the structure of the medium, 6T
When Tp of the recording waveform for recording the w mark is particularly long,
The effect of reducing jitter was great. Also, the longer the subsequent space length and the longer the mark, the shorter the Tc, and the shorter the subsequent space length and the shorter the mark, the longer the Tc.

In FIG. 3, 3Tw, 4Tw, 6Tw, 11T
Although only the recording waveform of w is shown, 5Tw is a pulse train of a series of high power levels of the recording waveform of 6Tw.
The high power level Ph of w / 2 and the bottom power level Pb of Tw / 2 immediately after are reduced one by one. Also, the recording waveform for 7Tw to 10Tw is obtained immediately before the high power level pulse at the end of the recording waveform for 6Tw.
This is obtained by adding a pair of a high power level Ph of Tw / 2 and a bottom power level Pb of Tw / 2. Therefore, 11 Tw is obtained by adding five sets. The shortest recording mark length corresponding to 3 Tw is 0.24 μm
And After passing through the portion to be recorded, the laser light power is reduced to a low power level Pr of the reproducing (reading) laser light.
(1.0 mW). The recording signal includes, for example, a 4 Tw mark and 4 at the beginning and end of the information signal.
Dummy data such as repetition of Tw space is included. The starting end also includes VFO.

In such a recording method, if new information is recorded by overwriting without erasing a portion in which information has already been recorded, the information is rewritten with new information. That is, overwriting with a single substantially circular light spot is possible.

However, the recording is performed by irradiating the medium with the intermediate power level (5 mW) of the power-modulated recording laser light or a power close thereto at the first rotation or plural rotations of the disk at the time of rewriting. The information is erased once, and then the bottom power level (1
mW) and a high power level (10 mW) or an intermediate power level (5 mW) and a high power level (10 mW).
The recording may be performed by irradiating a laser beam whose power has been modulated in accordance with the information signal with W). in this way,
If the information is erased before recording, the previously written information is less likely to remain unerased. Therefore, rewriting when the linear velocity is doubled becomes easy.

These methods are effective not only for the recording film used for the medium of the present invention but also for the recording film of another medium.

(Effect of Absorption Control Layer) The information recording medium (disk A) shown in FIG. 1 having the absorption control layer described in this embodiment and the conventional information shown in FIG. 2 having no absorption control layer are shown. When the effective erasing ratio of the recording medium (disk B) was compared, the erasing ratio of the disk A was 15 dB, but the erasing residual of the disk B was as large as 7 dB. The effective erase ratio was obtained by recording the longest recording signal (11 Tw) and measuring the change of the 11 Tw signal recorded at the beginning of recording the shortest recording signal (3 Tw). If the effective erasing ratio is small, the unerased portion at the time of overwriting increases, so that it is preferable that the effective erasing ratio is large. The reason why the effective erasing ratio can be increased is that the absorption ratio (Ac / Aa) can be made larger than 1 by providing the absorption control layer.

The recording mark is observed with a transmission electron microscope, and the mark size (mark size) when rewriting is performed on a long mark (amorphous state) and when rewriting is performed on a long space (crystalline state). Area) were compared.
In the case of the information recording medium (disk A) of this example, it was found that the former was almost the same as the latter. When the absorption rate control was strong, the former was slightly smaller than the latter. On the other hand, a conventional information recording medium (disk B)
So the former was bigger than the latter.

Although the effect of the absorptance control layer is effective in other recording systems, it is particularly effective in mark edge recording to accurately record an edge portion and reduce jitter.
Mark edge recording refers to a recording method in which an edge portion of a recording mark is made to correspond to a signal “1”, and between and within marks are made to correspond to a signal “0”.

(Thickness of Absorbance Control Layer) In this example, the thickness of the film used for the absorptance control layers 2 and 2 ′ was changed, and the jitter (σ / Tw) after overwriting was measured. It became so.

The jitter is an index indicating how much the reproduced signal fluctuates with respect to the window width (Tw) when the position of the edge of the recording mark is reproduced. When the jitter value becomes large, the detection position of the edge part occupies almost the window width, so that the recorded signal cannot be reproduced accurately.
Therefore, it is preferable that the jitter is small. The window width (Tw) in jitter measurement is 20 ns, the shortest recording signal is 3 Tw, and the longest recording signal is 11 Tw, and these are recorded at random. A reproduction equalization circuit was used for these measurements.

The jitter value of the leading edge and the trailing edge after overwriting is 2 with respect to the thickness (nm) of the absorption control layer.
The values of the root mean square (%) and the degree of modulation (%) are shown. Unless otherwise specified, the jitter means the mean square value of the jitter values of the leading edge and the trailing edge.

The modulation (Mod) was calculated according to the following equation.

MOD (%) = 100 × (Ic−Ia) / Ic where Ic is the highest level of the reflectivity in the crystal (erasing) state during EFM signal recording, and Ia is the amorphous level during EFM signal recording. This is the lowest level of reflectance in the quality (recording) state.

Mod (%) = 100 × (Ic−Ia) / Ic Absorbance control layer thickness (nm) Jitter after rewriting 10 times (%) Modulation degree (%) 0 25 −315 −5 13 10 13 48 20 13 47  40-43 50-38 From this, it can be seen that when the thickness of the absorption control layer is reduced,
And the thicker the jitter, the higher the modulation depth.
It turned out to be added. Increased jitter when thinning
The causes are Ac absorption rate in the recording film in the crystalline state, A
a is defined as the absorptivity in the recording film in the amorphous state
Time, the absorption ratio (Ac / Aa) becomes smaller,
It is thought that the rate control is not enough and it disappears.
It is. Since the absorption ratio (Ac / Aa) cannot be measured,
It was determined by scientific calculation. Thus, the thickness of the absorptance control layer is 3
nm or more and 40 nm or less, preferably 5 nm or more and 20 nm or less.
nm or less is more preferable.

In the present embodiment, when the material of the film used for the absorptance control layers 2 and 2 ′ is changed and the optical constant is changed,
Optical calculations were performed by changing the input values of the refractive index n and the extinction coefficient k. These are values at the wavelength of the reproduction light. First, k
Was kept at 2 and n was changed, and the degree of modulation when the absorptance ratio (Ac / Aa) was set to 1.05 was obtained as follows.

N contrast ratio 0.5 35 1 40 1.5 43 43 47 47 75 4 47 5 43 6 40 From this, it was found that changing n of the absorptance control layer changed the degree of modulation. Accordingly, n of the absorptance control layer is preferably 1.5 or more and 5 or less, more preferably 2 or more and 4 or less.

Next, n was kept at 2, k was changed, and the degree of modulation when the absorptance ratio (Ac / Aa) was 1.05 or more was obtained. The result was as follows.

K Modulation Degree 0 20 0.2 30 0.4 43 0.8 45 147 248 347 434 43 540 The modulation degree changes when k of the absorptance control layer is changed. Was. Accordingly, k of the absorptance control layer is preferably 0.4 or more and 4 or less, more preferably 1 or more and 3 or less.

In this example, the composition ratio of Cr—O used for the absorptivity control layers 2 and 2 ′ was changed, and the jitter (σ / Tw) after overwriting and the recording sensitivity were measured. Was. The recording sensitivity was based on the case of Cr ₇₆ O ₂₄ , and was evaluated as + when it was better, − when it was worse, and 0 when it was not changed.

Absorbance control layer composition Jitter (%) Recording sensitivity (%) Cr ₄₀ O ₆₀ 21 Not measured Cr ₄₆ O ₅₄ 18 Not measured Cr ₄₉ O ₅₁ 15 Not measured Cr ₅₃ O ₄₇ 13 +10 Cr ₅₆ O ₄₄ 13 +5 _{Cr 58 O 42 13 +5 Cr 64} O 36 13 0 Cr 66 O 34 - 0 Cr 80 O 20 - than -5 this, jitter after overwriting was able to be reduced when increasing the amount of Cr for absorptance control layer component . The cause of the decrease in jitter is the absorption ratio (Ac / A
This is considered to be because a) is large and it is difficult for unremoved portions to occur. From this, the amount of Cr with respect to all components of the absorptance control layer was 1
5 mol% or more is preferable. In the case of only Cr,
The thermal conductivity is larger than Cr ₇₆ O _{24 and the} recording sensitivity is lowered. Therefore, it is more preferable that the content be 22 mol% or more and 43 mol% or less. About the composition ratio of the absorption control layer,
The ratio of Cr to O was measured by Rutherford backscattering analysis.

In the present embodiment, as a material replacing the Cr—O film used for the absorptivity control layers 2 and 2 ′, VO, Co—O,
Cu-O, Mo-O, WO, Fe-O, Sb-O, M
n-O, Ti-O, Ge-O, Pt-O, Ni-O, N
Similar results were obtained using b-O, Pd-O, Be-O, and Ta-O. In addition, Ta-N, Al-N, B-
N, Cr-N, Ge-N, Hf-N, Si-N, Al-
Si-N based material, Si-ON based material, Ti-N, Zr
-N, etc. can also be used.

In addition, Si-O, Al-O, Be-O,
Bi-O, Ni-O, Pb-O, Pd-O, Sn-O,
Sc-O, Sr-O, Th-O, Te-O, YO, Z
oxides of r-O, _{etc., ZnS, Sb 2 S 3,} CdS, I
n ₂ S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , PbS, Bi ₂ S
Sulfide such as ₃ , SrS, MgS, CrS, CeS, TaS ₄ , SnSe ₂ , Sb ₂ Se ₃ , CdSe, ZnS
e, In ₂ Se ₃ , Ga ₂ Se ₃ , GeSe, GeSe ₂ ,
Selenides such as SnSe, PbSe, Bi ₂ Se ₃ , C
eF ₃ , MgF ₂ , CaF ₂ , TiF ₃ , NiF ₃ , Fe
Fluoride such as F ₂ , FeF ₃ or Si, Ge, Ti
B ₂ , B ₄ C, B, CrB, HfB ₂ , TiB ₂ , WB,
Borides such as C, Cr ₃ C ₂ , Cr ₂₃ C ₆ , Cr ₇
C ₃ , Fe ₃ C, Mo ₂ C, WC, W ₂ C, HfC, T
A carbide such as aC, CaC ₂ , or a material having a composition close to the above materials may be used, but k of each absorptance control layer is preferably 0.4 or more and 4 or less. Further, a mixed material thereof may be used. These absorptivity control layers are preferably nonstoichiometric compounds deviating from the stoichiometric composition, since the extinction coefficient k is larger than 0.4.

Of these, Cr-O was preferred because of its high adhesive strength and high thermal stability. When the melting point of the compound and / or the metal alone in the material of the absorptance control layer is higher than the melting point of the recording film (about 600 ° C.), the increase in jitter at 10,000 rewriting can be reduced. The melting point of both is 600
When the temperature is not less than ℃, it can be suppressed to 3% or less, and more preferable.

For the absorptance control layer, it is necessary to select a material whose optical characteristics do not change abruptly with wavelength as shown in FIG. The use of a material that undergoes a rapid change when the wavelength changes causes the disadvantage that the productivity is reduced and the optical characteristics are changed when the wavelength of the light source shifts due to the environmental temperature, resulting in poor reproduction characteristics.

Further, it was found that when the impurity element in the absorption control layer exceeded 2 atomic% of the component of the absorption control layer, the jitter of the front edge or the rear edge after rewriting 10 times exceeded 15%. Further, it was found that when the impurity element exceeded 5 atomic%, the jitter became 18% or more. Therefore, it is preferable that the impurity element in the absorptance control layer be 5 atomic% or less of the components of the absorptivity control layer because the deterioration of the rewriting characteristics can be reduced. More preferably, it is 2 atomic% or less.

It is more difficult to produce a high-output laser with a blue laser than with a red laser, so that the recording sensitivity of the medium is more required. Therefore, it is not preferable to use a material having a high thermal conductivity, such as Au, Al, or Cu, for the absorption control layer, because the recording film is rapidly cooled and easily disappears. However, if the thickness of the intermediate layer is extremely large, such as 100 nm or more, heat can be prevented from escaping in the direction of the reflective layer, and the structure becomes slightly cooled, so that a material having high thermal conductivity can be used. .

(Protective Layer) In this embodiment, the protective layer 2 is formed of (Z
nS) ₈₀ (SiO ₂ ) ₂₀ .

As a material replacing the (ZnS) ₈₀ (SiO ₂ ) ₂₀ of the protective layer 2, a material in which the mixing ratio between ZnS and SiO ₂ is changed is preferable. Further, ZnS, Si-N based material, S
i-O-N-based _{material, SiO 2, SiO, TiO 2} , Al 2
O ₃ , Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , In ₂ O ₃ , GeO,
GeO ₂ , PbO, SnO, SnO ₂ , BeO, Bi
₂ O ₃ , TeO ₂ , WO ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ ,
Oxides such as ZrO ₂ , Cu ₂ O, MgO, TaN, Al
N, BN, Si ₃ N ₄ , GeN, nitrides such as Al—Si—N-based materials (eg, AlSiN ₂ ), ZnS, Sb ₂ S
₃ , CdS, In ₂ S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , P
sulfides such as bS, Bi ₂ S ₃ , SnSe ₂ , Sb ₂ S
e ₃ , CdSe, ZnSe, In ₂ Se ₃ , Ga ₂ Se ₃ ,
GeSe, GeSe ₂ , SnSe, PbSe, Bi ₂ Se
₃ , a fluoride such as CeF ₃ , MgF ₂ , CaF ₂ , or Si, Ge, TiB ₂ , B ₄ C, B,
C or a material having a composition close to the above materials may be used. Further, a layer of a mixed material of ZnS—SiO ₂ , ZnS—Al ₂ O ₃ , or the like, or a multi-layer thereof may be used. Among them, ZnS has a large n and can maintain a large modulation degree. Therefore, in the case of a mixture containing 60 mol% or more of ZnS,
The combination of the large n of ZnS and the good chemical stability of the oxide is combined. ZnS has a higher sputter rate. If ZnS accounts for 80 mol% or more, the film formation time can be shortened. Other sulfides and selenides also provided similar properties.

The element ratio of these compounds is, for example, the ratio of the metal element to the oxygen element in oxides and sulfides, or Al ₂ O ₃ , Y ₂ O ₃ ,
La ₂ O ₃ is 2: 3, SiO ₂ , ZrO ₂ , GeO ₂ is 1:
It is preferable that 2, Ta ₂ O ₅ has a ratio of 2: 5 and ZnS has a ratio of 1: 1 or close to that ratio, but the same effect can be obtained even if the ratio is out of the ratio. In the case where the ratio is out of the above integer ratio, for example, Al—O has a ratio of Al and O from Al ₂ O ₃ to ± 10 atom% or less in Al amount, and Si—O has a ratio of Si and O in SiO ₂ to Si amount. It is preferable that the deviation of the amount of the metal element be 10 atomic% or less, such as ± 10 atomic% or less. When the amount is shifted by 10 atomic% or more, the optical characteristics are changed, so that the degree of modulation is reduced by 10% or more.

It is preferable that the material of the protective layer 2 and the material used for the protective layer 2 be 90% or more of the total number of atoms of each protective layer. When impurities other than the above materials become 10 atomic% or more,
Degradation of the rewriting characteristics was observed, for example, the number of rewriting times became 以下 or less.

It is more preferable that the protective layer n used in this embodiment has a thickness of 2.4 or more, since the degree of modulation can be 47%. The extinction coefficient is preferably 0 or close to 0.

When the protective layer has two or more layers and the material of the protective layer on the recording film side is Cr ₂ O ₃ , the diffusion of Zn and S into the recording film at the time of rewriting many times can be suppressed, and the rewriting characteristics are good. I understand.

As a material replacing Cr ₂ O ₃ as a protective layer material on the recording film side, CoO or GeO ₂ , NiO, or a mixture of these with Cr ₂ O ₃ is preferable. Next, S is added to Cr ₂ O ₃ .
A mixture of iO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ , and ZrO ₂ —Y ₂ O ₃ is good. These oxides have a small extinction coefficient k and very low absorption in the lower interface layer. Therefore, there is an advantage that the modulation degree can be kept large.

Also, AlN, BN, CrN, Cr ₂ N,
_{GeN, HfN, Si 3 N 4} , Al-Si-N material (e.g., AlSiN _2), Si-N-based material, Si-O-N-based material, TaN, TiN, ZrN, nitrides, such as adhesion This is more preferable because deterioration of the information recording medium due to external impact is small. Even with a recording film composition containing nitrogen or a material having a composition close thereto, the adhesive strength is improved.

In addition, BeO, Bi ₂ O ₃ , CeO ₂ , C
u ₂ O, CuO, CdO, Dy ₂ O ₃ , FeO, Fe
₂ O ₃ , Fe ₃ O ₄ , GeO, GeO ₂ , HfO ₂ , In
₂ O ₃ , La ₂ O ₃ , MgO, MnO, MoO ₂ , MoO ₃ ,
NbO, NbO ₂ , PbO, PdO, SnO, Sn
O ₂ , Sc ₂ O ₃ , SrO, ThO ₂ , TiO ₂ , Ti
₂ O ₃ , TiO, TeO ₂ , VO, V ₂ O ₃ , VO ₂ , W
Oxides such as O ₂ and WO ₃ , C, Cr ₃ C ₂ , Cr ₂₃ C
₆ , Cr ₇ C ₃ , Fe ₃ C, Mo ₂ C, WC, W ₂ C, H
A carbide such as fC, TaC, CaC ₂ , or a material having a composition close to the above materials may be used. Further, a mixed material thereof may be used.

When a protective layer on the recording film side is provided, Zn,
It is possible to prevent S and the like from diffusing into the recording film, and suppress an increase in unerased parts. Furthermore, in order not to lower the recording sensitivity, the thickness is preferably set to 25 nm or less, and the following is more preferable. Approximately 2 nm can form a uniform film
And 5 nm or more was even better. Accordingly, it is preferable that the thickness of the protective layer on the recording film side be 2 to 25 nm because the recording / reproducing characteristics are further improved.

(Recording Film) In this embodiment, the recording film 4 is made of Ag.
It is formed by ₈ Ge ₁₉ Sb ₂₆ Te _47.

As a material replacing the Ag ₈ Ge ₁₉ Sb ₂₆ Te ₄₇ of the recording film 4, an Ag—Ge—Sb—Te-based material having a different composition ratio is preferable because of its high degree of modulation. When the amount of Ag in the recording film is large, the change in reflectance at a short wavelength is large, but the crystallization speed is low. Therefore, the added Ag
The amount is preferably 2 atomic% or more and 10 atomic% or less. However, overwriting is possible even with a Ge-Sb-Te-based material to which Ag is not added. And G instead of Ag
Elements to be added to the recording film instead of Ag to e-Sb-Te include Cr, W, Mo, Pt, Co, Ni, P
It was found that the overwrite characteristics were good even when replaced with at least one of d, Si, Au, Cu, V, Mn, Fe, Ti, and Bi.

In the present embodiment, the film thickness of the recording films used as the recording films 4 and 4 'was changed, and the jitter (σ / Tw) after rewriting 10 times and after rewriting 100,000 times was measured. became. With respect to the thickness of the recording film (nm), the jitter (%) of the leading edge or the trailing edge after 10 times rewriting shows the jitter value (%) of the leading edge after rewriting 10,000 times. Was.

Recording Film Thickness Jitter after Rewriting 10 Times Jitter after 10,000 Rewritings 423-618-715 15 10 14 14 20 15 15 25-25-2035-25 The recording film thickness is made thinner. Then, it was found that the jitter after 10 rewrites due to recording film flow and segregation increased, and that when the thickness was increased, the jitter after 10,000 rewrites increased. Thus, the recording film thickness is 6 nm or more and 25 n
m or less, more preferably 7 nm or more and 20 nm or less.

(Intermediate Layer) In this embodiment, the intermediate layer 5 is made of Zn.
It is formed by S-SiO _2.

Examples of materials that can be used in place of ZnS—SiO ₂ for the intermediate layer 5 include Si—N-based materials, Si—ON-based materials, and Zn
S, SiO ₂ , SiO, TiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , C
eO ₂ , La ₂ O ₃ , In ₂ O ₃ , GeO, GeO ₂ , Pb
O, SnO, SnO ₂ , BeO, Bi ₂ O ₃ , TeO ₂ , W
O ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Cu ₂ O,
Oxides such as MgO, TaN, AlN, BN, Si ₃ N
₄ , GeN, Al-Si-N-based materials (for example, AlSi
Nitrides such as N ₂ ), ZnS, Sb ₂ S ₃ , CdS, In ₂
Sulfides such as S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , PbS, Bi ₂ S ₃ , SnSe ₂ , Sb ₂ Se ₃ , CdSe, Zn
Se, In ₂ Se ₃ , Ga ₂ Se ₃ , GeSe, GeS
e _2, SnSe, PbSe, selenides, such as _{Bi 2 Se 3, CeF 3,} MgF 2, fluorides such as CaF _2, or _{Si, Ge, TiB 2, B} 4 C,, B, C , or above materials A composition close to the above may be used. Also, ZnS
A layer of a mixed material of these, such as —SiO ₂ , ZnS—Al ₂ O ₃ , or a multi-layer thereof may be used. Among them, the modulation degree can be increased by using a material having a small refractive index. The refractive index is 2.
When the value is 1 or less, the modulation degree can be made 47% or more, and it is found that the modulation is more excellent. The extinction coefficient is preferably 0 or close to 0.

The element ratio of these compounds is, for example, the ratio of the metal element to the oxygen element in oxides and sulfides, or Al ₂ O ₃ , Y ₂ O ₃ ,
La ₂ O ₃ is 2: 3, SiO ₂ , ZrO ₂ , GeO ₂ is 1:
It is preferable that 2, Ta ₂ O ₅ has a ratio of 2: 5 and ZnS has a ratio of 1: 1 or close to that ratio, but the same effect can be obtained even if the ratio is out of the ratio. In the case where the ratio is out of the above integer ratio, for example, Al—O has a ratio of Al and O from Al ₂ O ₃ to ± 10 atom% or less in Al amount, and Si—O has a ratio of Si and O in SiO ₂ to Si amount. It is preferable that the deviation of the amount of the metal element be 10 atomic% or less, such as ± 10 atomic% or less. When the amount is shifted by 10 atomic% or more, the optical characteristics are changed, so that the degree of modulation is reduced by 10% or more.

It is preferable that the intermediate layer 5 and the material used for the intermediate layer 5 be 90% or more of the total number of atoms in each protective layer. When impurities other than the above materials become 10 atomic% or more,
Degradation of the rewriting characteristics was observed, for example, the number of rewriting times became 以下 or less.

When the intermediate layer is formed of two or more layers on the recording film side and the material of the intermediate layer is Cr ₂ O ₃ , the diffusion of Zn and S into the recording film at the time of rewriting many times can be suppressed, and the rewriting characteristics can be improved. Was found to be good.

(Reflection Layer) A used in the reflection layer 6 in this embodiment
As a material for the reflective layer instead of l-Cr, Al-A
g, Al-Cu, Al-Ti, etc. which are mainly composed of Al alloys are preferable. Al can also be used.

Thus, when the content of elements other than Al in the Al alloy is in the range of 0.5 atomic% or more and 4 atomic% or less, the characteristics and bit error rate after many rewrites are improved, and It has been found that the content becomes better in the range of not less than 2 atomic% and not more than 2 atomic%. Similar characteristics were obtained with other Al alloys.

Next, Au, Ag, Cu, Ni, F
e, Co, Cr, Ti, Pd, Pt, W, Ta, Mo,
Elemental elements of Sb, Bi, Dy, Cd, Mn, Mg, V,
Or Au alloy, Ag alloy, Cu alloy, Pd alloy, Pt
An alloy containing these as a main component, such as an alloy, or a layer made of these alloys may be used. As described above, the reflection layer is made of a metal element, a metalloid element, an alloy thereof, or a mixture thereof.

Among these, Al, Au, Ag, Al alloy,
Those having a high reflectance, such as an Au alloy and an Ag alloy, have a high contrast ratio and good rewriting characteristics. An alloy has a higher adhesive strength than a simple substance. In this case, when the content of elements other than Al, Au, Ag, etc., which are the main components, is in the range of 0.5 atomic% to 5 atomic% as in the case of the Al alloy, the contrast ratio can be increased and the adhesive strength can be increased. It was good. In the range of 1 atomic% or more and 2 atomic% or less, the result is further improved.

The material of the reflective layer is 95% of the total number of atoms in the reflective layer.
It is preferable that it is above. 5 impurities other than the above materials
At an atomic percentage or more, the rewriting characteristics were deteriorated, such as the number of rewrites being reduced to half or less.

When the thickness of the reflective layer is less than 30 nm, the strength is weak, the heat diffusion is small, and the recording film is likely to flow.
Jitter after rewriting 10,000 times becomes larger than 15%.
At 40 nm, it can be reduced to 15%. When the thickness of the reflective layer was greater than 200 nm, the time required to form each reflective layer was increased, and the formation time was doubled by dividing the process into two or more steps or providing two or more vacuum chambers for sputtering. If the thickness of the reflective layer is 5 nm or less, it is difficult to form a uniform film.

Thus, the thickness of the reflection layer is 5 nm or more,
00 nm or less is preferable.

(Substrate) In this embodiment, the polycarbonate substrate 1 having a groove for tracking directly on the surface is used. Instead, a polyolefin, epoxy,
Acrylic resin, chemically strengthened glass having an ultraviolet curable resin layer formed on the surface, or the like may be used. Quartz or CaF may be used instead of tempered glass.

A substrate having a tracking groove is defined as having a depth of λ / 8n ′ (n ′ is the refractive index of the substrate material) or more when the recording / reproducing wavelength is λ on all or a part of the substrate surface. This is a substrate having a groove. The groove may be formed continuously in one round, or may be divided in the middle. It has been found that when the groove depth is about λ / 6n ′, the crosstalk is small, which is preferable. Further, it was found that when the groove depth was deeper than about λ / 3n ′, the yield at the time of forming the substrate was poor, but the cross erase was small, which was preferable.

Further, the groove width may be different depending on the location. A substrate having no groove, a substrate of a sample servo format, a substrate of another tracking method, a substrate of another format, or the like may be used. A substrate having a format in which recording and reproduction can be performed on both the groove portion and the land portion, or a substrate having a format in which recording is performed on either one may be used. If the track pitch is small, signal leakage from an adjacent track is detected and becomes noise, so that the track pitch is at least 以上 of the spot diameter (the area where the light intensity is 1 / e ² ). preferable.

The disc size is not limited to 12 cm.
Other sizes such as cm, 8 cm, 3.5 inches, and 2.5 inches may be used. The disk thickness is not limited to 0.6 mm,
1.2mm, 0.8mm, 0.4mm, 0.1mm etc.
Other thicknesses may be used.

In this embodiment, two disk members are produced in exactly the same manner, and the two
Although the reflection layers 6, 6 'of the first and second disk members are attached to each other, a disk member of another configuration, a protection substrate, or the like may be used instead of the second disk member. . When the transmittance in the ultraviolet wavelength region of a disk member or a protective substrate used for bonding is large, the bonding can be performed using an ultraviolet curable resin. The bonding may be performed by another method. As shown in FIG. 7, in the case of a single-sided disk, the reflective layer 6 is stacked on the bonded substrate 14 in a reverse direction.
May be formed or bonded. When performing recording / reproduction, it is sufficient that the respective layers are formed in the above order from the light incident side, and the manufacturing procedure does not have to be laminated in order from the light incident side.

In this embodiment, two disk members are manufactured, and the reflection layers 6 and 6 'of the first and second disk members are bonded to each other via the adhesive layer 7. The error rate can be further reduced by applying an ultraviolet curable resin to the reflective layers 6 and 6 'of the first and second disk members before applying the resin to a thickness of about 10 [mu] m and bonding the resin after curing.

In this embodiment, two disk members are manufactured, and the reflection layers 6 of the first and second disk members are bonded to each other via the adhesive layer 7, but the bonding is not performed. Then, an ultraviolet curable resin having a thickness of about 10 μm or more may be applied on the reflective layer 6 of the first disk member.

In the case of a disk member having no reflective layer 6, an ultraviolet curable resin may be applied on the uppermost layer.

(Thickness and Material of Each Layer) The recording and reproducing characteristics can be improved by simply setting the thickness and material of each layer independently. However, the effect can be further improved by combining the respective preferable ranges. Go up.

(2) Embodiment 2 (Structure and Manufacturing Method) (Structure and Manufacturing Method of Information Recording Medium of the Present Invention) FIG. 5 is a sectional structural view of a disk-shaped information recording medium according to a second embodiment of the present invention. This medium was manufactured as follows.

First, on a polycarbonate substrate 8 having a diameter of 12 cm, a thickness of 0.6 mm and a tracking groove on the surface, a (ZnS) ₈₀ (Si
After laminating the protective layer 9 made of O ₂ ) ₂₀ film, Ag ₈ Ge ₁₉ Sb
₂₆ Te _{47 The} recording film 10 is about 10 nm thick, (ZnS) ₈₀
(SiO ₂ ) The intermediate layer 11 composed of ₂₀ films is formed to a thickness of about 50 n.
m, a reflective layer 12 of Al ₉₈ Cr ₂ film having a thickness of about 80 n
m. The formation of the laminated film was performed by a magnetron sputtering apparatus. Thus, a first disk member was obtained.

On the other hand, a second disk member having the same configuration as the first disk member was obtained in exactly the same manner.
The second disk member is composed of a protective layer 9 made of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 100 nm and an Ag ₈ Ge ₁₉ Sb ₂₆ Te ₄₇ recording film 10 on a polycarbonate substrate 8 ′.
Was formed to a thickness of about 10 nm, an intermediate layer 11 of (ZnS) ₈₀ (SiO ₂ ) ₂₀ film of about 50 nm, and a reflective layer 12 of Al ₉₈ Cr ₂ film of about 80 nm.

Thereafter, the first disk member and the second disk member are bonded together with the respective reflective layers 12 and 12 ′ interposed therebetween via an adhesive layer 13 to obtain a disk-shaped information recording medium C shown in FIG. Was.

(Configuration and Manufacturing Method of Conventional Information Recording Medium) In order to clarify the effects of the information recording medium described in Example 2, disk-shaped information recording media having different intermediate layer thicknesses were manufactured. This medium was manufactured as follows.

First, on a polycarbonate substrate 8 having a diameter of 12 cm, a thickness of 0.6 mm and a tracking groove on the surface, a (ZnS) ₈₀ (Si
After the protective layer 9 made of O ₂ ) ₂₀ film is laminated, Ag ₈ Ge ₁₉
The Sb ₂₆ Te ₄₇ recording film 10 is formed to a thickness of about 10 nm (Zn
S) ₈₀ (SiO ₂₎ film thickness of the intermediate layer 11 made of ₂₀ film about 2
0 nm, the reflective layer 12 made of an Al ₉₈ Cr ₂ film
It was sequentially formed at 0 nm. The formation of the laminated film was performed by a magnetron sputtering apparatus. Thus, a first disk member was obtained.

On the other hand, a second disk member having the same configuration as that of the first disk member was obtained in exactly the same manner.
The second disk member is composed of a protective layer 9 made of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 100 nm and an Ag ₈ Ge ₁₉ Sb ₂₆ Te ₄₇ recording film 10 on a polycarbonate substrate 8 ′.
Was formed to a thickness of about 10 nm, an intermediate layer 11 composed of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film to a thickness of about 20 nm, and a reflective layer 12 composed of an Al ₉₈ Cr ₂ film to a thickness of about 80 nm.

Thereafter, the first disk member and the second disk member were bonded together with the respective reflective layers 12 and 12 ′ interposed therebetween via an adhesive layer 13 to obtain a disk-shaped information recording medium D.

(Effect of Increasing Interlayer Thickness) A comparison was made between the effective erasing ratio of the disk C (FIG. 5) in which the thickness of the intermediate layer described in this example was large and that of the conventional disk D in which the thickness of the intermediate layer was small. The disk C had an erasing ratio of 15 dB, but the disk D had a large erasure ratio of 7 dB. The effective erase ratio was obtained by recording the longest recording signal (11 Tw) and measuring the change of the 11 Tw signal recorded at the beginning of recording the shortest recording signal (3 Tw). If the effective erasing ratio is small, the unerased portion at the time of overwriting increases, so that it is preferable that the effective erasing ratio is large. The reason why the effective erasing ratio can be increased is that the absorption ratio (Ac / Aa) can be made larger than 1 by increasing the thickness of the intermediate layer.

When the film thickness d (nm) at which the effective erasing ratio is large and the degree of modulation is large was examined by changing the thickness of the intermediate layer, a was an integer of 0 or more, b was the refractive index of the intermediate layer, and λ ( n
When m) was the reproduction wavelength, the following relationship was obtained.

0.5 × a × λ ÷ b + 0.16 ≦ d ≦ 0.
5 × a × λ ÷ b + 0.39 The recording marks were observed with a transmission electron microscope, and rewriting was performed on a long mark (amorphous state) and on a long space (crystalline state). The mark size (mark area) in each case was compared. In the case of the information recording medium (disk C) of this embodiment, it was found that the former was almost the same as the latter. When the absorption rate control was strong, the former was slightly smaller than the latter.
On the other hand, in the case of the information recording medium (disk D), the former was larger than the latter.

(Structure and manufacturing method of medium having absorption rate control layer)
FIG. 6 shows that the addition of the absorptance control layer to the disc-shaped information recording medium (disc C) of the second embodiment of the present invention increased the absorptivity ratio. FIG. 2 shows a sectional structural view of this disc-shaped information recording medium (disc E). This medium was manufactured as follows.

First, on a polycarbonate substrate 8 having a diameter of 12 cm, a thickness of 0.6 mm and a tracking groove on the surface, a (ZnS) ₈₀ (Si
After laminating the protective layer 9 made of O ₂ ) ₂₀ film, Ag ₈ Ge ₁₉ Sb
₂₆ Te _{47 The} recording film 10 is about 10 nm thick, (ZnS) ₈₀
(SiO ₂ ) The intermediate layer 11 composed of ₂₀ films is formed to a thickness of about 50 n.
m, the absorptance control layer 14 composed of a Cr ₅₆ O ₄₄ film having a thickness of about 1
0 nm, the reflective layer 12 made of an Al ₉₈ Cr ₂ film
It was sequentially formed at 0 nm. The formation of the laminated film was performed by a magnetron sputtering apparatus. Thus, a first disk member was obtained.

On the other hand, a second disk member having the same configuration as the first disk member was obtained in exactly the same manner.
The second disk member is composed of a protective layer 9 made of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 100 nm and an Ag ₈ Ge ₁₉ Sb ₂₆ Te ₄₇ recording film 10 on a polycarbonate substrate 8 ′.
Is about 10 nm, the intermediate layer 11 made of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film is about 50 nm, the absorptivity control layer 14 ′ made of a Cr ₅₆ O ₄₄ film is about 10 nm, and Al ₉₈ Cr
_The reflective layer 12 composed of _two films was formed sequentially to a thickness of about 80 nm.

Thereafter, the first disk member and the second disk member are bonded together with the respective reflective layers 12 and 12 'interposed therebetween via an adhesive layer 13, and the disk-shaped information recording medium (disk E) shown in FIG. ) Got.

When the effective erasing ratio of the disk E was measured in the same manner as the disks C to D, it was as good as 18 dB.

The thickness of the absorptivity control layer is 3 nm or more and 40 nm or more.
The following is preferable, and it is more preferable that it is 5 nm or more and 20 nm or less.

Items not described in the present embodiment are described in the first embodiment.
Is the same as

[0153]

As described above, the information recording medium of the present invention, that is, an information recording thin film on which information is recorded by a change in the atomic arrangement caused by irradiation of light, is provided as a recording layer, According to the information recording medium, the n (refractive index) in the amorphous state of the recording film is larger than the n in the crystalline state of the recording film. When used as a medium, the recording characteristics are good.

In a medium in which the reflectivity in the amorphous state is lower than the reflectivity in the crystalline state, the presence of the absorptance control layer allows the recording film to have an absorptance of Ac> Aa, and the unerased portion can be reduced.

The protective layer is provided between the recording film and the substrate, and has an effect of protecting the recording film and an effect of increasing C / N.
The reflective layer has the effect of increasing the number of rewritable times. The intermediate layer has the effect of further improving C / N. In a medium in which the reflectance in the amorphous state is higher than the reflectance in the crystalline state, the absorption rate can be controlled by optimizing the thickness of the intermediate layer.

[Brief description of the drawings]

FIG. 1 is a structural sectional view of an information recording medium according to a first embodiment of the present invention.

FIG. 2 is a structural sectional view of an information recording medium having a conventional structure.

FIG. 3 shows a recording waveform used for evaluating the recording / reproducing characteristics of the information recording medium of the present invention.

FIG. 4 shows the optical characteristics of the absorption control layer of the present invention.

FIG. 5 is a structural sectional view of an information recording medium according to a second embodiment of the present invention.

FIG. 6 is a structural sectional view of an information recording medium according to a second embodiment of the present invention.

FIG. 7 is a structural sectional view of a single-sided information recording medium according to the first embodiment of the present invention.

[Explanation of symbols]

T: Window width (Tw), Pc: Cooling pulse power level, Pe: Intermediate power level, Ph: High power level, Pp: Preheat power level, P1: Power level of 0, Tc: Cooling pulse width, Tp: No. One pulse width.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Motoyasu Terao, Inventor, Central Research Laboratory, Hitachi, Ltd. 1-280, Higashi-Koigakubo, Kokubunji-shi, Tokyo (72) Inventor Keikichi Ando 1-280, Higashi-Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. In Central Research Laboratory (72) Inventor Yumiko Anzai 1-280 Higashi-Koigakubo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 5D029 JC02 JC06 JC06 JC20 LA14 LB01 LB07 LB11 LC05 LC06

Claims (9)

[Claims] An information recording thin film on which information is recorded by a change in atomic arrangement caused by light irradiation is provided as a recording layer on a substrate, and n (refractive index) of the amorphous state of the recording film at a reproduction wavelength is provided. ) Is larger than n in a crystalline state. 2. When recording is performed on the recording film, the reflectivity in the amorphous state is lower than the reflectivity in the crystalline state, and the recording start power when the shortest mark is recorded on the amorphous state is reduced. 2. The information recording medium according to claim 1, wherein the recording start power when recording the shortest mark on the crystal state under the same conditions is the same or smaller. 3. The information recording medium according to claim 1, wherein the information recording medium has a structure in which an absorptance control layer is laminated between substrates of the recording film. 4. The method according to claim 1, wherein the thickness of the absorptance control layer is 5 nm or more and 40% or more.
4. The information recording medium according to claim 3, wherein the distance is in the range of nm or less. 5. The information recording medium according to claim 3, wherein said absorption control layer is made of a non-stoichiometric compound. 6. When recording is performed on the recording film, the reflectivity in the amorphous state is higher than the reflectivity in the crystalline state, and the recording start power when the shortest mark is recorded on the amorphous state is reduced. 2. The information recording medium according to claim 1, wherein the recording start power when the shortest mark is recorded on the crystal state under the same conditions is the same or smaller. 7. A recording medium comprising: the recording film and at least one protective layer; and a protective layer and a recording layer are laminated in this order from the light incident side;
Then at least one intermediate layer
And the intermediate layer has a thickness d (nm) where a is an integer of 0 or more, b is the refractive index of the intermediate layer, and λ (nm) is the wavelength of the reproduction light. 0.5 × a × λ ÷ b + 0.16 ≦ d ≦ 0.5 × a × λ ÷
7. The information recording medium according to claim 6, wherein the value is in the range of b + 0.39. 8. The information recording medium according to claim 6, wherein the information recording medium has a structure in which an absorptance control layer is laminated between the intermediate layer and the reflective layer. 9. The information recording medium according to claim 6, wherein said absorption control layer is made of a non-stoichiometric compound.