JP2002367222A - Multilayered information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayered information recording medium which has good recording and reproducing characteristics when the recording and reproducing are performed by a blue laser. SOLUTION: This multilayered information recording medium has, successively from a light incident side, a substrate 1, first recording film 3, first reflecting layer 5, spacer layer 7, second recording film 9 and second reflecting layer 11. The first recording film 3 and the second recording film 9 contain Sb and the difference in the Sb contents is regulated to >=30 atm.%.

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 used for an optical disk, and more particularly, to a multilayer information recording medium having a plurality of recording films.

[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. Among them, a laser, such as a phase change (also called phase transition) of a film material and a photodarkening, is used. Since the method using the atomic arrangement change by light irradiation hardly involves deformation of a thin film, two disk members are directly bonded to each other to record information on a double-sided disk structure information recording medium or a multilayer structure information recording having a plurality of information surfaces. It has the advantage of being able to obtain media.

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 include a lower protective layer, GeS on a substrate.
bTe recording film, ZnS-SiO ₂ based upper protective layer, such as a system,
It has a structure in which reflective layers of high reflectivity such as Al are sequentially laminated. There are several ways to increase the recording capacity.
A method using a light source having a shorter wavelength than the wavelength around 60 nm and a method of forming a multilayer structure have been proposed. ODS / I
Wavelength 400 in SOM'99 Proceedings, p. 110 (Reference 1)
A two-layer information recording medium for the vicinity of nm is shown. This medium has a first information surface having no reflective layer on the light incident side and a second information surface having an Al alloy reflective layer on the side far from the light. However, this data is only a calculation result and does not indicate a problem at the time of recording / reproduction. In addition, a similar wavelength 4
A two-layer information recording medium for the vicinity of 00 nm is disclosed in PCOS '99 Lecture Proceedings, p. 22 (Reference 2), but this medium also does not show any problem in recording / reproducing each layer. Note that a short-wavelength laser having a wavelength of about 400 nm is generally called a blue laser, a blue-green laser, a blue-violet laser, a green laser, or the like in comparison with a long-wavelength red laser. Call.

[0004] In this specification, the term "phase change" includes not only a phase change between a crystal and an amorphous phase, but also melting (change to a liquid phase) and recrystallization, and a phase change between a crystalline state and a crystalline state. And "atomic arrangement changes." 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 a mark are made to correspond to a signal "0". In this specification, an optical disk refers to a disk (disk) on which information that can be reproduced by light irradiation is written, and / or an apparatus that reproduces information by light irradiation.

[0005]

When any of the conventional multilayer information recording media is used as a high-density rewritable phase-change multilayer information recording medium using a blue laser, the characteristic difference in each layer during recording / reproducing. And control during recording is difficult.

Accordingly, an object of the present invention is to provide a multi-layer information recording medium having improved reproduction characteristics when recording / reproducing with a blue laser so as to match the characteristic difference between the respective layers, and having good reproduction characteristics. It is in.

[0007]

The above object can be attained by making the recording films of the multilayer recording layers contain Sb and varying the Sb content of each recording film by 30 atomic% or more. . In particular, it is preferable to reduce the Sb content of the recording film on the light incident side and increase the Sb content of the recording film on the opposite side.

Another object of the present invention is to provide the recording film on the substrate side with Sb.
Is achieved by setting the content of Sb to 15 at% or more and 35 at% or less, and setting the Sb content of the recording film opposite to the substrate across the space layer to 60 at% or more and 80 at% or less. . The Sb content of the recording film on the substrate side was
Preferably, the content is 20 atom% or more and 30% or less. Further, Sb of the recording film on the opposite side of the substrate with respect to the space layer
Is preferably set to 65 atomic% or more and 75 atomic% or less.

If a multi-layer recording film is used to increase the recording density, the thermal characteristics of each film will differ. That is, on the recording film side on the light incident side, light must be transmitted to some extent by the reflective layer, and the properties of the reflective layer are limited. This reflection layer has a small cooling effect and is gradually cooled. on the other hand,
On the recording film side opposite to the substrate with the spacer layer interposed therebetween, the reflection layer (cooling layer) does not need to transmit light, unlike the reflection layer on the recording film side on the light incident side. Therefore, in the reflective layer on the recording film side opposite to the substrate with the spacer layer interposed,
Excellent cooling effect, rapid cooling. Therefore, if an attempt is made to fill a region of these recording films having good overwrite characteristics with one type of recording film, the margin becomes extremely narrow.
However, by making the Sb content of the recording films different as in the present invention, regions with good overwrite characteristics of each recording film can be used, and as a result, the overwrite characteristics are improved.

A recording film having a low Sb content is generally of a compound type and has a somewhat high transmittance. This recording film has a relatively small recrystallization and a relatively small contrast. Therefore, it is optimal for the recording film on the light incident side. on the other hand,
Recording films having a high Sb content are generally eutectic,
High recrystallization and high contrast. Therefore, it is optimal for a recording film provided on the side opposite to the substrate with respect to the space layer.

[0011]

[Example 1]

(Configuration and Manufacturing Method of Information Recording Medium of the Present Invention) FIG. 1 is a schematic view showing a cross-sectional structure of a disc-shaped information recording medium according to a first embodiment of the present invention. This medium was manufactured as follows.
First, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 30 nm and Al ₄₀ O ₅ having a thickness of about 4 nm are formed on a polycarbonate substrate 1 having a diameter of 12 cm, a thickness of 0.6 mm and a groove for tracking on the surface. ₇ N ₃ film and the film thickness of about 1nm of Cr
L0 lower protective layer 2 formed by laminating ₄₀ O ₅₇ N ₃ films, Ge ₅ Sb ₂ Te ₈ L0 recording film 3 having a thickness of about 6 nm, and film thickness of about 1 n
The L0 upper protective layer 4 is formed by laminating a Cr ₂ O ₃ film having a thickness of about m, an Al ₂ O ₃ film having a thickness of about 4 nm, and a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 125 nm. (Al ₂
An L0 transparent reflection layer 5 made of an O ₃ ) film and an L0 uppermost protection layer 6 made of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 50 nm were sequentially formed. The lamination film is formed by magnetron
This was performed by a sputtering device. Thus, a first disk member was obtained.

On the other hand, by the same sputtering method,
A second disk member having a configuration different from that of the first disk member was obtained. The second disk member is made of Ag ₉₈ Pd ₁ C having a thickness of about 80 nm on the polycarbonate protective substrate 12.
A (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about ₈₀ nm and a C film having a thickness of about 5 nm are formed on the L1 reflection layer 11 made of a u ₁ film.
L1 upper protective layer 10 formed by laminating r ₂ O ₃ , thickness about 1
8 nm Ge ₁ Sb ₇ Te ₂ L1 recording film 9, thickness about 5 n
m Cr ₄₀ O ₅₇ N ₃ film and about 80 nm thick (Zn
S) An L1 lower protective layer 8 formed by laminating ₈₀ (SiO ₂ ) ₂₀ films in order.

Then, the first disk member and the second disk member
Place the disk members under their respective L0 top protective layers 6 and L1
The protective layer 8 is bonded through the spacer layer 7 and is shown in FIG.
The indicated two-layer information recording medium (disc A) was obtained. Each information side
Are the constituent films on the light incident side (from the L0 lower protective layer 2 to the L0 top
L0 for the protective layer 6 and the constituent film farther from the light (below L1).
The portion from the protective layer 8 to the L1 reflection layer 11) was designated as L1. (Configuration and manufacturing method of conventional information recording medium) Conventional information recording
The recording medium has the same basic configuration as shown in FIG.
However, the recording film composition is different. This medium is manufactured as follows.
Made. First, on the surface with a diameter of 12 cm and a thickness of 0.6 mm
On a polycarbonate substrate 1 having a groove for tracking
About 30 nm thick (ZnS)₈₀(SiO₂)₂₀
Al with a thickness of about 4 nm ₄₀O₅₇N₃Film and film thickness about 1n
m Cr₄₀O₅₇N₃L0 lower protective layer made by laminating films
2. Ge with a thickness of about 6 nm₅Sb₂Te₈L0 recording film 3, film
Cr about 1 nm thick ₂O₃Al with a thickness of about 4 nm₂O₃
Film and thickness of about 125 nm (ZnS)₈₀(SiO₂)
₂₀L0 upper protective layer 4 having a thickness of about 35 nm
(Al₂O ₃) L0 transparent reflection layer 5 made of film, film thickness about 5
0 nm (ZnS)₈₀(SiO₂) ₂₀L0 consisting of membrane
An uppermost protective layer 6 was sequentially formed. The formation of the laminated film is magnetic
This was performed using a tron sputtering apparatus. Thus the
Thus, one disk member was obtained.

On the other hand, by the same sputtering method,
A second disk member having a configuration different from that of the first disk member was obtained. The second disk member is made of Ag ₉₈ Pd ₁ C having a thickness of about 80 nm on the polycarbonate protective substrate 12.
A (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about ₈₀ nm and a C film having a thickness of about 5 nm are formed on the L1 reflection layer 11 made of a u ₁ film.
L1 upper protective layer 10 formed by laminating r ₂ O ₃ , thickness about 1
8 nm Ge ₅ Sb ₂ Te ₈ L1 recording film 9, thickness about 5 n
m Cr ₄₀ O ₅₇ N ₃ film and about 80 nm thick (Zn
S) An L1 lower protective layer 8 formed by laminating ₈₀ (SiO ₂ ) ₂₀ films in order.

Thereafter, the first disk member and the second disk member are bonded to each other via the L0 uppermost protective layer 6 and the L1 lower protective layer 8 via the spacer layer 7, and the two-layer information recording shown in FIG. A medium (disk A) was obtained. In each information surface, the component film on the light incident side (from the L0 lower protective layer 2 to the L0 uppermost protective layer 6) is L0, and the component film farther from the light (from the L1 lower protective layer 8 to the L1 reflective layer 11) is L1. And An information recording medium (disk B) was obtained. (Initial crystallization) Initial crystallization was performed on the L0 recording film 3 of the disks A and B manufactured as described above as follows. Although only the L0 recording film 3 and the L1 recording film 9 will be described below, the same applies to the recording films of other multilayer media.

The medium (disk A, disk B) is rotated such that the linear velocity at a point on the recording track is 5 m / s, and the laser power of a semiconductor laser having a wavelength of about 810 nm is set to 300 mW to focus on the L1 recording film. After that, the laser power was set to 700 mW, and the substrate 1 and the L0 film were
The recording film 9 was irradiated to the recording film 9 through the spacer layer in the form of an elliptical spot long in the radial direction of the medium. The movement of the spot
1 / one of the radial spot length of the medium per rotation of the medium
It shifted by 24. 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. Next, the laser power of the semiconductor laser having a wavelength of about 810 nm is set to 300 mW, the focus position of the laser is changed to focus on the L0 recording film, and then the laser power is set to 700 mW. Irradiation was performed in the form of a long oblong spot. The movement of the spot was shifted by 1/24 of the spot length in the radial direction of the medium per rotation 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. The initialization may be performed from the L1 recording film, from the L0 recording film, or randomly in a multilayer information recording medium having three or more layers. (Recording / Erasing / Reproducing) With respect to the medium manufactured as described above and subjected to the initial crystallization, recording / erasing / reproduction is performed as follows.
Playback specific evaluation was performed. In the following, only the recording film 9 of L1 will be described, but the same applies to the recording film 3 of L0, and the same applies to the recording film of each information surface in a multilayer information recording medium having three or more layers. .

The power of the recording laser beam is changed between the intermediate power level Pe (3 mW) and the high power level Ph (7 mW) while performing tracking and automatic focusing on the recording area of the recording film 9 on which the initial crystallization is completed. The information was recorded by changing the above. The linear velocity of the recording track is 9 m / s, the wavelength of the semiconductor laser is 405 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 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 formation of one recording mark, the power is repeatedly reduced by half (Tw / 2) of the window width to a bottom power level Pb lower than the intermediate power level Pe, and the cooling power level Pc is changed to a recording pulse. When recording / reproducing was performed by an apparatus having a means for generating a last waveform, the jitter value and error rate of the reproduced signal waveform were reduced. The cooling power level Pc is lower than the intermediate power level Pe, and the bottom power level Pb
Higher or the same level. This waveform has a characteristic that 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). 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 shorter the Tp, the longer the space immediately before the mark, and the shorter the mark, the longer the Tp. However, depending on the structure of the medium, 6 Tw
When the recording waveform for mark recording had a particularly long Tp, the effect of reducing jitter was large. 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.

FIG. 3 shows 3Tw, 4Tw, 6Tw, and 11T.
Although only the recording waveform of w is shown, 5Tw is TW out of a series of high power level pulse trains of 6Tw recording waveform.
In this example, the w / 2 high power level Ph and the immediately subsequent Tw / 2 bottom power level Pb are respectively reduced 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.

Here, the shortest recording mark length corresponding to 3 Tw was set to 0.26 μm. After passing through the portion to be recorded, the laser light power is reduced to the low power level Pr (1 mW) of the reproducing (reading) laser light.

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 first disc at the time of rewriting
The above-mentioned power-modulated recording
The intermediate power level of the light (3 mW) or near
Irradiate the continuous light of the
Erase, then bottom power level in next one revolution
(0.5 mW) and high power level (7 mW)
Or medium power level (3 mW) and high power level (7
mW), a power modulated according to the information signal.
The recording may be performed by irradiating the light. like this
If you try to erase information before recording it,
There is little leftover information that has been lost. Therefore, the linear velocity
Rewriting when the value is doubled becomes easy. (Effect of the present invention) The shortest recording mark of both information recording media
C when recording a repetition signal of 3Tw and 3T space
/ N was measured, the L0 was 50 dB in the conventional medium,
L1 remains at 45 dB, but in the information recording medium of the present invention,
L0 is 50dB and L1 is 50dB, practical level for both layers
C / N was secured. (Lower Protective Layer) In this embodiment, the L1 lower protective layer 8 is
nS)₈₀(SiO₂)₂₀And Cr_{4 0}O₅₇N₃Layer of
It has a two-layer structure. Further, the L0 lower protective layer 2 is made of (Zn
S)_{8 0}(SiO₂)₂₀Al with a thickness of about 4 nm₄₀
O₅₇N₃Film and Cr about 1 nm thick₄₀O₅₇N₃Membrane
It has a laminated three-layer structure. Lower protection with a two-layer structure
Layers 2 and 8 (ZnS)₈₀(SiO₂)₂₀Alternative to wood
As materials, ZnS and SiO₂With different mixing ratio of
preferable. Also, ZnS, Si-N-based materials, Si-O-
N-based material, SiO₂, SiO, TiO₂, Al₂O₃,
Y₂O₃, CeO ₂, La₂O₃, In₂O₃, Ge
O, GeO₂, PbO, SnO, SnO₂, BeO, B
i₂O₃, TeO₂, WO₂, WO₃, Sc₂O₃, T
a₂O₅, ZrO₂, Cu₂Oxides such as O and MgO,
TaN, AlN, BN, Si₃N₄, GeN, Al-S
i-N-based material (for example, AlSiN₂), Etc., Z
nS, Sb₂S₃, CdS, In₂S₃, Ga₂S₃,
GeS, SnS₂, PbS, Bi₂S₃Sulfides, such as
SnSe₂, Sb₂Se₃, CdSe, ZnSe, In
₂Se₃, Ga₂Se₃, GeSe, GeSe₂, Sn
Se, PbSe, Bi₂Se₃Such as selenide, Ce
F₃, MgF₂, CaF₂Such as fluoride, or S
i, Ge, TiB₂, B₄C, B, C, or above
A material having a composition close to the material may be used. Also, ZnS-
SiO₂, ZnS-Al₂O₃Such as these mixed materials
Or multiple layers thereof. Among them, ZnS is
Large putter rate, ZnS occupies 60 mol% or more
In this case, the film formation time can be shortened.
In the case of a mixture containing the above, the sputtering rate of ZnS is large.
Combined with good chemical stability of oxides and nitrides
Be forgotten. Other sulfides and selenides are similar to ZnS.
Characteristic was obtained.

The element ratio in these compounds is, for example, the ratio of the metal element to the oxygen element or the sulfur element in oxides and sulfides is as follows: Al ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ is 2:
_{3, SiO 2, ZrO 2,} GeO 2 is 1: 2, _Ta 2 O
₅ is preferably 2: 5 and ZnS is preferably 1: 1 or close to that ratio, but the same effect can be obtained even if the ratio is out of the ratio. However, when the ratio is out of the above integer ratio, for example, Al—O has a ratio of Al and O of ± 10 atomic% or less from Al ₂ O ₃ to Al, and Si—O has a ratio of Si and O of SiO ₂ to Si. 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.

The above material is 90% of the total number of atoms of the lower protective layer.
It is preferable that it is above. 1 impurities other than the above materials
At 0 atomic% or more, the number of rewritable times becomes 以下 or less, and the rewriting characteristics deteriorated.

The extinction coefficient k of the lower protective layer used in this embodiment
Is preferably 0 or close to 0. further,
Extinction coefficient k at a film thickness of 80% or more of lower protective layer material
Is preferably k ≦ 0.01, since the decrease in contrast can be suppressed to 2% or less.

The lower protective layer is composed of two or more layers,
Cr for the protective layer material₂O₃Or Cr₄₀O₅₇N₃You
This suppresses the diffusion of Zn and S into the recording film during rewriting many times.
And the rewriting characteristics were good. Record
Cr of lower protective layer material on the recording film side₂O₃As an alternative material
The Cr₂O₃SiO₂, Ta₂O₅, Al
₂O ₃, ZrO₂-Y₂O₃A mixed mixture is preferred
No. Then, CoO or GeO₂, NiO, and these
Cr₂O₃Are preferred. These oxides are decay agents
Small number k, very low absorption in lower interface layer
No. This has the advantage that the modulation depth can be kept large.
You. In addition, Cr₂O₃Or Cr₄₀O₅₇N₃Part of
To Al₂O₃Or Al₄₀O₅₇N₃Is changed to
Since absorption outside the recording film is reduced and transmittance can be increased, L
C / N can be increased in the 0th layer, which is preferable. Al₂O₃Ma
Or Al₄₀O₅₇N ₃Instead of SiO_TwoOr Si₃₃
O₆₃N_FourEtc. and the ratio of these nitrogen and oxygen amount is different
Similar characteristics were obtained by using the same.

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 materials, nitrides such as TaN, TiN, ZrN, and the like have a longer storage life and are more resistant to changes in external temperature, and are more preferable. 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 ,
Cu ₂ O, CuO, CdO, Dy ₂ O ₃ , FeO, Fe
₂ O ₃ , Fe ₃ O ₄ , GeO, GeO ₂ , HfO ₂ , I
n ₂ O ₃ , La ₂ O ₃ , MgO, MnO, MoO ₂ , M
oO ₃ , NbO, NbO ₂ , PbO, PdO, SnO,
SnO ₂ , Sc ₂ O ₃ , SrO, ThO ₂ , TiO ₂ ,
Ti ₂ O ₃ , TiO, TeO ₂ , VO, V ₂ O ₃ , VO
₂ , WO ₂ , WO ₃ and other oxides, C, Cr ₃ C ₂ , C
r ₂₃ C ₆ , Cr ₇ C ₃ , Fe ₃ C, Mo ₂ C, WC,
A carbide such as W ₂ C, HfC, TaC, CaC ₂ , or a material having a composition close to the above materials, or a mixed material thereof may be used.

When an oxide or nitride layer is provided on the recording film side of the lower protective layer, diffusion of Zn, S, etc. into the recording film can be prevented, and an increase in unerased residue can be suppressed. Further, in order not to lower the recording sensitivity, the thickness is preferably 25 nm or less, and more preferably 10 nm or less. A uniform film can be formed at about 2 nm or more.
nm or more was even better. Accordingly, it is preferable that the thickness of the lower protective layer on the recording film side be 2 to 25 nm because the recording / reproducing characteristics are further improved. If less, the C / N was reduced due to recrystallization. The lower protective layer has a thickness of 10 n.
When it is less than m, the protection effect of the recording film is lost, and the number of rewritable times is reduced by one digit or more. What is described as the lower protective layer means the L0 lower protective layer, the L1 lower protective layer, and the lower protective layer of the multilayer information recording medium. (Recording Film) In this embodiment, the recording film 3 and the recording film 9 are made of Ge _5.
It is formed of Sb ₂ Te ₈ . The refractive index at the reproduction wavelength of the present recording film is 2.0 in the crystalline state and 2.6 in the amorphous state, which is smaller in the crystalline state.

Recording films 3, 9 instead of Ge ₅ Sb ₂ Te ₈
Ag ₃ Ge ₃₀ Sb ₁₄ Te ₅₃ , C
Ag-Ge-Sb-, such as r ₃ Ge ₃₂ Sb ₁₃ Te ₅₂
Te-based and Cr-Ge-Sb-Te-based materials having different composition ratios are preferable because the degree of modulation is increased. If the amount of Ag or Cr in the recording film 3 and / or the recording film 9 is large, the change in reflectance at short wavelengths increases, but the crystallization speed decreases.
Therefore, it is preferable that the amount of Ag or Cr added is 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. Elements to be added to the recording films 3 and 9 instead of Ag 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 all of these recording films 3 and 9, the refractive index at the reproduction wavelength is lower in the crystalline state than in the amorphous state.

In this embodiment, the thickness of the recording film 9 is changed to
The jitter (σ / Tw) after 0 rewriting and 100,000 rewriting was measured, and the results are as shown in Table 1.
With respect to the thickness (nm) of the recording film 9, the value (%) of the lower jitter of the leading edge or the trailing edge after rewriting 10 times is the jitter value (%) of the leading edge after rewriting 10,000 times. showed that.

[0032]

[Table 1]Thus, when the thickness of the recording film 9 is reduced, the flow of the recording film and the unevenness
Analysis, the jitter after 10 rewrites increased,
When the thickness is increased, the jitter after rewriting 10,000 times increases.
I understood. Thus, the thickness of the recording film 9 is 4 nm or less.
Above, 25nm or less is preferable because jitter can be reduced to 20% or less.
If it is 5 nm or more and 20 nm or less, the jitter is 15
% Or less. The thickness of the recording film 3 and 1
To the N-1 information layer (layer)
If the thickness of the recording film on the information surface satisfies the relationship of information surface 1 ≦ information surface 2 ≦.
Therefore, it is preferable. In addition, 1-N-
The total thickness of the first information surface recording film is 10 nm or less.
Then, the C / N of the Nth information surface is as large as 48 dB or more.
It is preferable. When the total film thickness becomes 8 nm or less,
The C / N of the information surface can be as large as 49 dB or more
Good. (Upper Protective Layer) In this embodiment, the upper protective layer 10 is made of ZnS
-SiO₂And Cr₄₀O₆₀Formed. Also, L0
The upper protective layer 4 is made of (ZnS)₈₀(SiO₂)₂₀Membrane and membrane
Al about 4nm thick₄₀O₆₀Film and Cr about 1 nm thick₄₀
O₆₀It has a three-layer structure in which films are stacked. ZnS-SiO
₂As the material of the upper protective layer in place of
Material, Si-ON-based material, ZnS, SiO₂, SiO,
TiO₂, Al₂O₃, Y₂O₃, CeO₂, La₂O
₃, In₂O₃, GeO, GeO₂, PbO, SnO,
SnO₂, BeO, Bi₂O₃, TeO₂, WO₂, W
O₃, Sc₂O₃, Ta₂O ₅, ZrO₂, Cu₂O,
Oxides such as MgO, TaN, AlN, BN, Si₃N
₄, GeN, Al-Si-N-based materials (eg, AlSiN
₂), Etc., ZnS, Sb₂S₃, CdS, In
₂S₃, Ga₂S₃, GeS, SnS₂, PbS, Bi
₂S₃Such as sulfide, SnSe₂, Sb₂Se₃, Cd
Se, ZnSe, In₂Se₃, Ga₂Se₃, GeS
e, GeSe₂, SnSe, PbSe, Bi₂Se₃What
Which selenide, CeF₃, MgF₂, CaF₂Such as
Fluoride or Si, Ge, TiB₂, B₄C, B,
C or a composition close to the above materials may be used.
No. Also, ZnS-SiO₂, ZnS-Al₂O₃Such
It may be a layer of these mixed materials or a multi-layer thereof. Extinction
Preferably, the coefficient is zero or close to zero.

The element ratio in these compounds is, for example, the ratio of the metal element to the oxygen element or the sulfur element in the oxide or sulfide is Al ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃
The _{2: 3, SiO 2, ZrO} 2, GeO 2 is 1: 2, T
It is preferable that a ₂ O ₅ has a ratio of 2: 5 and ZnS has a ratio of 1: 1 or close to the 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 of ± 10 atomic% or less in Al amount from Al ₂ O ₃ , 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.

The above material is 90% of the total number of atoms of the upper protective layer.
It is preferable that it is above. 1 impurities other than the above materials
At 0 atomic% or more, the number of rewritable times becomes 以下 or less, and the rewriting characteristics deteriorated.

When the upper protective layer is composed of two or more layers and the material of the upper 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 improved. I understand. Further, part of the Al ₂ O
_3, or when changing the SiO ₂ proved preferable contrast can be increased. What is described as the upper protective layer means the L0 upper protective layer, the L1 upper protective layer, and the upper protective layer of the multilayer information recording medium. (Reflective Layer) In this embodiment, the reflective layer 11 is made of Ag ₉₈ Pd ₁ C.
using u ₁ film. Other reflective layer materials include Ag-P
Those having an Ag alloy as a main component, such as t and Ag-Au, are preferable. Ag can also be used. When the content of elements other than Ag in the Ag alloy is in the range of 0.5 atomic% or more and 4 atomic% or less, the characteristics and the bit error rate after many rewrites are improved, and 1 atomic% or more and 2 atomic% or less. It was found that the range was better.

Also, a Zn ₉₈ Pd ₂ film, a Zn ₉₈ Pt ₂
Film, Zn ₉₈ Cu ₂ film, Zn ₉₈ Ni ₂ film, Zn-Pd
The film, the Zn—Pt film, the Zn—Cu film, and the Zn—Ni film
There is an advantage that the cost is lower than that of the g-based material. Zn can also be used. When the content of elements other than Zn in the Zn alloy is in the range of 0.5 atomic% or more and 4 atomic% or less, the characteristics and bit error rate at the time of rewriting many times are improved, and 1 atomic% or more and 2 atomic% or less It was found that the range was better.

Next, Au, Al, Cu, Ni, Fe,
Co, Cr, Ti, Pd, Pt, W, Ta, Mo, S
b, Bi, Dy, Cd, Mn, Mg, V, a single element, or an alloy containing these as a main component such as an Au alloy, an Ag alloy, a Cu alloy, a Pd alloy, a Pt alloy, or an alloy thereof May be used. Thus, the reflective layer is composed of metal elements, metalloid elements, their alloys,
Consists of a mixture.

Among them, those having a large reflectance, such as Ag, Al, Al alloy, Ag alloy, etc., have a large contrast ratio and good rewriting characteristics. An alloy has a higher adhesive strength than a simple substance. In this case, the content of elements other than Al and Ag, which are the main components, is the same as that of the Ag alloy.
When the content is in the range of 0.5 atomic% or more and 5 atomic% or less, the contrast ratio is large and the adhesive strength is large, which is good. In the range of 1 atomic% or more and 2 atomic% or less, the result is further improved. Comparing the reflectance around the wavelength of 400 nm,
g or Ag alloy is about 95%, Al, Al alloy is about 92%
%, And the Ag type is larger, but the material cost is higher. Next to these materials, Zn and Zn alloy are about 89%,
The reflectivity of Pt and Pt alloy at a short wavelength of about 65% was large, and the contrast was increased.

The material is preferably 95% or more of the total number of atoms in the reflective layer. When the amount of impurities other than the above-mentioned materials becomes 5 atomic% or more, the number of rewritable times becomes 以下 or less, and the rewriting characteristics are deteriorated.

When the thickness of the reflective layer is less than 20 nm, the strength is low, the heat diffusion is small, and the recording film is likely to flow.
Jitter after rewriting 10,000 times becomes larger than 15%.
At 30 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, such as by dividing the process into two or more steps or providing two or more vacuum chambers for sputtering. When the thickness of the reflection layer was 5 nm or less, the film was formed in an island shape, and noise increased. From this, the thickness of the reflective layer is 5 nm or more from the noise and jitter and the formation time.
200 nm or less is preferable. (Substrate) In the present embodiment, the polycarbonate substrate 1 having a tracking groove directly on the surface is used, but instead, a polyolefin, epoxy, acrylic resin,
Chemically strengthened glass having an ultraviolet curable resin layer formed on the surface may be used. Quartz or CaF may be used instead of tempered glass.

Further, a substrate having a groove for tracking is defined as having a depth of λ / 12n ′ (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 was found that when the groove depth was about λ / 6n ′, the crosstalk was small, which was preferable. Further, when the groove depth is deeper than about λ / 3n ', the yield during the formation of the substrate is deteriorated, but the cross erase is reduced, which is preferable.

The groove width may vary 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 may be equal to or more than の of the spot diameter (the area where the light intensity is 1 / e ² ). preferable.

The disk size is not limited to 12 cm in diameter,
Other sizes such as 13 cm, 8 cm, 3.5 inches, 2.5 inches, etc. may be used. The disc thickness is not limited to 0.6 mm, but 1.2 mm, 0.8 mm, 0.4 mm, 0.1 mm
Other thicknesses may be used.

In this embodiment, the bonding is performed with the spacer layer interposed therebetween. However, a disk member having another configuration or a protection substrate may be used instead of the second disk member. As shown in FIG. 5, a disk member or a protective substrate used for bonding may be formed from the protective substrate side, and finally the substrate 1 on the light incident side may be formed or bonded. Alternatively, the two discs thus produced may be bonded together to form a double-sided disc. When the transmittance in the ultraviolet wavelength region is large, bonding can be performed using an ultraviolet curable resin. The bonding may be performed by another method. Further, if an ultraviolet curable resin is applied to a thickness of about 10 μm on the uppermost layers of the first and second disk members before the first and second disk members are bonded, and bonding is performed after curing, an error may occur. The rate can be further reduced. (Thickness and material of each layer) The recording / reproducing characteristics and the like can be improved by simply setting each of the preferred thicknesses and materials for each layer. However, the effect is further enhanced by combining the respective preferred ranges.

Items not described in this embodiment are the same as those in Embodiments 1 to 3 and 6 to 7.

[0046]

As described above, according to the present invention, an information recording medium having good recording / reproducing characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of an information recording medium according to the present invention.

[Explanation of symbols]

1, 1 ': substrate, 2, 2': lower protective layer, 3, 3 ': recording film, 4, 4': upper protective layer, 5, 5 ': cooling control layer,
6, 6 ': reflection layer, 7: bonding resin, 8, 8': contrast enhancement layer, 14: substrate.

Continued on the front page (72) Inventor Keikichi Ando 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. In-house (72) Inventor Toshimichi Shintani 1-280 Higashi-Koigabo, Kokubunji-shi, Tokyo F-term (reference) 2H111 EA04 EA12 EA23 EA32 FA02 FA11 FA12 FB09 FB30 5D029 JA01 JB13 JC20

Claims (6)

[Claims] 1. A light-incident side, comprising: a substrate; a first recording film on which information is recorded by an atomic arrangement change caused by light irradiation; a first reflective layer; a spacer layer; A second recording film on which information is recorded by an atomic arrangement change, and a second reflective layer, wherein the first recording film and the second recording film have Sb,
The Sb content of the first recording film and the second recording film is:
A multilayer recording medium which differs by 30 atomic% or more. 2. The multi-layer information recording medium according to claim 1, wherein the Sb content of said first recording film is smaller than the Sb content of said second recording film. 3. The method according to claim 1, wherein the first recording film is a compound type, and the second recording film is a eutectic type.
Or the multilayer information recording medium according to 2. 4. A substrate, N recording films (N is an integer of 2 or more) on which information is recorded by an atomic arrangement change caused by light irradiation, and N recording films formed between the N recording films. It has N-1 spacer layers, and N reflective layers formed on the opposite side of the N recording films from the substrate, and each of the N recording films contains Sb. Wherein the Sb content differs by 30 atomic% or more. 5. A light-incident side, a substrate, a first recording film on which information is recorded by an atomic arrangement change caused by light irradiation, a first reflective layer, a spacer layer, and light-irradiated light. A second recording film on which information is recorded by an atomic arrangement change, and a second reflective layer, wherein the first recording film contains Sb, and the content of Sb is 15 atomic% or more and 35 atomic% or more. The second recording film contains Sb, and the content of Sb is 60 atomic% or more and 80 atomic% or less. 6. The S of the first recording film and the second recording film.
6. The multilayer recording medium according to claim 5, wherein the difference in the b content is 30 atomic% or more.