JPH10162433A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve data preservation stability of an information recording medium and to record and erase information repeatingly many times by regulating refractive indexes of lower dielectric layers and the refractive index of a substrate within specific range. SOLUTION: When the refractive index of a lower dielectric layer 1 and the refractive index are respectively defined as n1 and nsub, this medium is made to satisfy nsub-0.3<=n1<=nsub+0.3. That is, when the refractive index n1 of the lower dielectric layer 1 is equal to the refractive index nsub of the substrate, since the lower dielectric layer 1 is optically regarded to be the same as the substrate, the layer 1 does not affect to an interference and a phase difference. As a result, it is made possible to set the film thickness of the lower dielectric layer 1 arbitrarily and it is made possible to guide the film thickness of the dielectric layer between a recording layer and the substrate to an optimum value from the point of view of durability with respect to repeated overwritings. Moreover, since lower dielectric layers are not related to an interference effect, it is preferable to allow refractive indexes of lower dielectric layers 1, 2 to have a difference of some extent and it is preferable that the refractive indexes of them are in the range of n2-n1>=0.1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium capable of recording, erasing, and reproducing information at high speed and high density by irradiation with laser light or the like.

[0002]

2. Description of the Related Art In recent years, an optical disk using a laser beam has been developed as a recording medium that meets the demand for an increase in the amount of information and a high density and high speed of recording and reproduction. Optical discs include a write-once type, which allows recording only once, and a rewritable type, which allows recording / erasing any number of times. Examples of the rewritable optical disk include a magneto-optical recording medium using a magneto-optical effect and a phase change medium using a reversible change in crystalline state.

[0003] The phase change medium does not require an external magnetic field, and can be recorded / erased only by changing the power of laser light. Furthermore, there is an advantage that one-beam overwriting in which erasing and re-recording are performed simultaneously with a single beam is possible. In a phase change recording method capable of one-beam overwriting, it is general that a recording bit is formed by amorphizing a recording film and erasing is performed by crystallization. As a recording layer material used in such a phase change recording method, a chalcogen-based alloy thin film is often used. For example, Ge-Te system, Ge-Te-Sb system,
In-Sb-Te-based and Ge-Sn-Te-based alloy thin films are exemplified.

[0004] A write-once type phase change medium can be realized by using the same material and layer structure as those of the rewritable type. In this case, information can be recorded and stored for a longer period because there is no reversibility, and almost semi-permanent storage is possible in principle. When a phase-change medium is used as a write-once type, unlike a perforated type, there is no ridge called a rim around the bit, so the signal quality is excellent, and there is no need for a gap above the recording layer, so it is necessary to use an air sandwich structure. There is no advantage.

Generally, in a rewritable phase change recording medium, two different laser beam powers are used to realize different crystal states. This method will be described by taking as an example a case where recording / erasing is performed in an erased / initial state where an amorphous bit has been crystallized. The crystallization is performed by heating the recording layer to a temperature sufficiently higher than the crystallization temperature of the recording layer and lower than the melting point. In this case, the recording layer is sandwiched between dielectric layers, or an elliptical beam long in the beam moving direction is used so that the cooling rate becomes slow enough to sufficiently crystallize.

On the other hand, the amorphization is performed by heating the recording layer to a temperature higher than the melting point and rapidly cooling the recording layer. in this case,
The dielectric layer also has a function as a heat dissipation layer for obtaining a sufficient cooling rate (supercooling rate). Furthermore, as described above, deformation and melting of the recording layer in the heating and cooling process due to the change in volume, to prevent thermal damage to the substrate, especially a plastic substrate, and also to prevent the deterioration of the recording layer due to moisture. The protective layer made of the dielectric layer is important.

The material of the protective layer is required to be optically transparent to laser light, to have a high melting point, softening point, and decomposition temperature, to be easily formed, and to have a suitable thermal conductivity. Is selected from The protective layer having sufficient heat resistance and mechanical strength includes a dielectric thin film such as a metal oxide or nitride. As the dielectric protection layer, a layer containing ZnS as a main component and mixed with SiO ₂ , Y ₂ O _3, or the like has been proposed. These composite compound protective films have better adhesion to chalcogenide-based alloy thin films such as GeTeSb and InSbTe, which are often used as recording layers, than pure oxide or nitride dielectric films.
Therefore, in addition to durability against repeated overwriting, film peeling in an accelerated test is small, and the reliability of the phase change medium is further improved.

[0008]

As described above, during recording, the dielectric layer prevents outflow and sublimation due to melting for the recording layer to become amorphous, and prevents recording (amorphization).
It has important functions such as releasing the force following the volume change accompanying erasing (crystallization) and releasing the heat accumulated in the recording layer.

Particularly, in the lower dielectric layer existing between the substrate and the recording layer, when the recording layer is made amorphous, the heat heated until the recording layer is melted is directly transmitted to the substrate, and the substrate itself is melted and deformed. It plays an important role in dissipating heat in the plane direction so that it does not occur. In order to sufficiently exhibit the effect, a certain film thickness is required. According to the results of studies performed by the present inventors using a typical (ZnS) ₈₀ (SiO ₂ ) ₂₀ composite dielectric film as a protective layer, a film thickness of about 70 nm or more was required.

If the film thickness is insufficient, when the substrate is repeatedly overwritten, the deformation of the substrate is accumulated, which leads to an increase in noise of the reproduced signal, which is not preferable. On the other hand, when the thickness is too large, there is a disadvantage that cracks are likely to occur due to thermal expansion. Further, there is a problem that a long film forming time is required in the manufacturing process.

Next, restrictions on the film thickness of the wavelength from the optical surface will be described. For example, when a four-layer optical disk having a lower dielectric layer, an AgInSbTe-based phase-change recording layer, an upper dielectric layer, and a reflective layer sequentially formed on a substrate as a medium used at a wavelength of 780 nm, a recording state and an erasing state are required. There is a restriction that the thickness of the lower dielectric layer must be 80 nm or less or 200 nm or more in order to obtain a layer configuration having a large reflectance difference and good optical characteristics.

Optically important parameters include reflectivity and the phase difference between crystalline and amorphous. Here, the phase difference δ between the crystal and the amorphous is defined by (phase of a wave passing through a crystal region) − (phase of a wave passing through an amorphous region). Specifically, as the dielectric layer of the medium, (ZnS) ₈₀ (Si
O _{2) 20} (when using a refractive index n = 2.1), the optical simulation considering optical calculations and the substrate groove shape of the multilayer film using an effective Fresnel coefficient (e.g., Nagata,
Others: Proceedings of the 4th Symposium on Phase Change Records (1992)
With p105), the relationship between the thickness of the lower dielectric layer and the reflectance, and the phase between the crystal and the amorphous phase was determined.

Here, the phase difference φ due to the depth of the groove is defined as φ = (phase in the groove) − (phase in the land). In the case of performing the groove recording, since the land portion is farther than the groove portion with respect to the light incident from the substrate surface, the reflected light at the land portion is n _sub × d (n _sub : substrate refractive index, d: groove depth) ) In phase (φ> 0). When the phase difference δ between the previous crystal and the amorphous and the phase difference φ due to the groove depth are appropriately selected and combined, apparently, the reflectance of the amorphous decreases and the signal amplitude can be increased. May be. In this case, a large contrast is desirable.

In order to satisfy this condition, the condition that the amorphous phase advances, that is, δ = (the phase of the crystalline state in the groove)
It is desirable that − (phase of the amorphous state in the groove) <0. On the other hand, in consideration of the stability at the time of manufacturing, it is desirable that the film thickness dependence of the reflectance is small. That is, the film thickness is in the vicinity where the reflectance is minimal.

When the thickness of the lower dielectric layer is selected in consideration of such conditions, the thickness of the lower dielectric layer is about 50 to 70 nm or 220 to 2 nm.
It was around 60 nm. This deviates from the range of the thickness of the lower dielectric layer, which is desirable from the viewpoint of the repetitive overwrite durability and the stability over time. The present invention has been made to solve such a problem.

[0016]

The gist of the present invention is to provide an optical information recording medium having a lower dielectric layer 1, a lower dielectric layer 2, a phase-change recording layer, an upper dielectric layer, and a reflective layer sequentially on a substrate. Where the refractive index of the lower dielectric layer 1 is n ₁ and the refractive index of the substrate is n
_Sub is the optical information recording medium characterized in that n _sub -0.3 ≦ n ₁ ≦ n _sub +0.3.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. If the refractive index n ₁ of the lower dielectric layer 1 is equal to the refractive index n _{sub of the} substrate, the lower dielectric layer 1 is optically regarded as the same as the substrate, and does not affect interference or phase difference. That is,
The thickness of the lower dielectric layer 1 can be arbitrarily set, and the thickness of the dielectric layer between the recording layer and the substrate (lower dielectric layer 1+
The lower dielectric layer 2) can be led to an optimum value from the viewpoint of durability against repeated overwriting.

However, since it is difficult to make the refractive index of the dielectric layer exactly equal to the refractive index of the substrate, n _sub -0.3
≦ n ₁ ≦ n _sub +0.3 is an allowable range. More preferably in the range of _{n s ub -0.2 ≦ n 1 ≦} n sub +0.2.

In the medium of the present invention, an appropriate interference effect and phase difference can be obtained by providing a certain difference in the refractive index n ₂ between the substrate and the lower dielectric layer 2.
Preferably, n ₂ −n _sub ≧ 0.2. More preferably, n ₂ −n _sub ≧ 0.3. On the other hand, if the thickness is too large, the fluctuation of the reflectance or the like due to the fluctuation of the film thickness becomes large. Therefore, it is preferable that n ₂ −n _sub ≦ 0.8 from the viewpoint of manufacturing stability.

Further, from the gist of the present invention that the lower dielectric layer 1 does not contribute to the interference effect and mainly causes the lower dielectric layer 2 to have the interference effect, the refractive index of the lower dielectric layers 1 and 2 is limited to some extent. It is preferable to have a difference, and it is preferable that n ₂ −n ₁ ≧ 0.1. More preferably, n ₂ −n ₁ ≧ 0.2
It is. However, as described above, if the difference is too large, the fluctuation of the reflectance and the like due to the fluctuation of the film thickness becomes large, so that n ₂ −n ₁
It is preferred that ≦ 0.7.

As the substrate of the phase change medium, generally, polycarbonate (n = 1.56), polymethyl methacrylate (n = 1.5), amorphous polyolefin (for example, Zeonex manufactured by Zeon Corporation, n = 1.53, Japan Resins and glasses (n = 1.5) such as Aaton: n = 1.51 manufactured by Synthetic Rubber Co., Ltd. and Apel: n = 1.54 manufactured by Mitsui Petrochemical Company.
In many cases, the refractive index is 1.5 to 1.6, such as 1.54 (however, the refractive index slightly varies depending on the additive). Therefore, n ₁ is 1.5 or more, which is closer to these refractive indexes. It is preferably in the range of 1.6 or less.

If the refractive index n ₂ of the lower dielectric layer 2 is too small, it is difficult to obtain an appropriate interference effect, so that it is preferably 1.7 or more. On the other hand, if the thickness is too large, the fluctuation of the reflectance or the like due to the fluctuation of the film thickness becomes large. Therefore, it is preferable that n ₂ is 2.3 or less from the viewpoint of manufacturing stability. The total thickness of the lower dielectric layer 1 and the lower dielectric layer 2 has a great influence on the repetitive recording characteristics.

The heat when the recording layer undergoes a phase change (1000
(° C. or more) escapes to the reflective layer, but heat is also transmitted to the substrate through the lower dielectric layers 1 and 2, and if the distance between the recording layer and the substrate is short, the influence of the heat on the substrate increases. That is, if the film thickness is too small, the thermal insulation effect is insufficient and the substrate surface temperature tends to increase, and the effect of suppressing thermal deformation of the substrate decreases.

Further, since the dielectric layer can receive the deformation accompanying the volume expansion of the recording layer, the combined thickness of the lower dielectric layer 1 and the lower dielectric layer 2 is preferably somewhat thicker. It is preferably at least 70 nm, more preferably at least 80 nm. However, if the thickness is too large, cracks (cracks) of the dielectric film itself are likely to occur, and problems such as strong influence of stress and peeling are likely to occur. Therefore, the film thickness is preferably 200 nm or less. More preferably, it is 160 nm or less.

The thickness of the lower dielectric layer 2 is such that the reflectance of laser light is minimal in an optical information recording medium having a lower dielectric layer 2, a phase-change recording layer, an upper dielectric layer and a reflective layer on a substrate in that order. The thickness is preferably within a range of ± 30 nm, which is the thinnest film thickness. When the thickness of the lower dielectric layer 2 changes, the reflectance changes as described above. Considering the stability at the time of manufacturing, it is desirable that the reflectance has a small dependency on the film thickness. That is,
The thickness of the lower dielectric layer 2 is preferably in the range of about ± 30 nm at which the reflectivity of the medium is minimized. It should be noted that the thickness of the lower dielectric layer 1 does not substantially affect the reflectivity and need not be considered.

According to the present invention, such an optimum film thickness as a protective film and an optimum film thickness as an interference film can be simultaneously satisfied. Next, the configuration of the optical recording medium according to the present invention will be described.

[0027] The optical recording medium of the present invention comprises:
Transparent resins such as polycarbonate, acrylic, and polyolefin, or glass can be used. Among them, a polycarbonate resin is preferably used because it has good adhesiveness to the dielectric layer and excellent optical characteristics and moldability. In addition, these substrate materials have birefringence, melting point, heat resistance,
An additive for improving fluidity, optical properties, and the like may be included. It is desirable to have a laminated structure of substrate / lower dielectric layer 1 / lower dielectric layer 2 / recording layer / upper dielectric layer / reflective layer, and to coat it with an ultraviolet or thermosetting resin.

The reflection layer is provided to increase the signal amplitude by more actively utilizing the optical interference effect, and to function as a heat dissipation layer to provide a supercooled state necessary for forming an amorphous mark. This is to make it easier to obtain For this reason, the reflective layer is desirably made of a metal having high reflectivity and high thermal conductivity, and specifically includes Au, Ag, and Al. However, semiconductors such as Si and Ge may be used to increase the degree of freedom in optical design. From the viewpoint of economy and corrosion resistance, Ta, Ti, C
r, Mo, Mg, Zr, V, Nb, etc. at 0.5 to 5 at.
% Al alloy is desirable. In particular, the addition of Ta results in a highly corrosion-resistant material (JP-A-1-169751).

According to the present invention, since the lower dielectric layer is divided into two layers, the function as an optical interference film required for the lower dielectric layer and the function as a mechanical and thermal protection film can be separated. There is an advantage that a film that satisfies both conditions can be easily manufactured. The lower dielectric layer 1 satisfying the above conditions is provided on the substrate surface. Since the dielectric layer is generally manufactured by high-frequency discharge sputtering, the deposition rate tends to be slow. From the viewpoint of productivity, it is preferable to provide a thick film in which the total of the lower dielectric layers 1 and 2 exceeds 200 nm. Absent.

When the lower dielectric layer 2 is provided on the lower dielectric layer 1, peeling is likely to occur if the adhesion between the two is not good. As a material of the lower dielectric layer 1, a material having good adhesion to a substrate and having the above-mentioned optical characteristics can be used. For example, Mg, Ca, Sr, Y, La, Ce, Pr, Nd,
Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
m, Yb, La, Ti, Zr, Hf, Y, Nb, Ta,
An oxide such as Zn, Al, Si, Ge, Sn, and Pb, a nitride, a sulfide, a fluoride such as Li, Na, Mg, and Ca, or a mixture thereof is used. More specific and suitable materials include fluorides of MgF ₂ , CaF ₂ , LiF and the like, rare earth metal fluorides and composite films containing them, SiC—S
A composite film containing SiO ₂ such as iO ₂ and SiC—SiO ₂ —Y ₂ O ₃ can be used. The composite ratio of the composite film can be set arbitrarily within the scope of the present invention.

At the interface between the recording layer and the dielectric layer, adhesion is important. For this purpose, it is desirable that the dielectric layer contains S or Se, which is a chalcogenide element. Furthermore, the dielectric layer in contact with the recording layer has high heat resistance and is soft and flexible in order to absorb heat and volume change shocks during the recording (melting, amorphization) and erasing (crystallization) processes of the recording layer. Is good. That is, the dielectric layer in contact with the recording layer preferably has a melting point of 1000 ° C. or higher and a Knoop hardness at room temperature of 500 or lower. However, it is preferable that the Knoop hardness at room temperature is 200 or more in order to prevent deformation due to excessive softness and change in optical characteristics. It is optically transparent at the wavelength used (k <0.
Those satisfying the condition 1) are preferable.

Therefore, the material of the dielectric layer in contact with the recording layer is ZnS, ZnO, ZnSe, Ce ₂ S ₃ , La ₂ S ₃
Such as lanthanoid sulfide, ZnS, Zn
O, ZnSe, Ce ₂ S ₃ , La ₂ S _{3 and} other lanthanoid sulfides include Mg, Ca, Sr, Y, Ce, Ti, Zr,
V, Nb, Tb, Cr, Mo, W, Al, In, Si,
Oxides such as Ge, Sn, Pb, Sb, nitrides, Li, N
b, Mg, Cd, and other fluorides mixed with 10 to 60 mol%, and the like. A more specific material is selected in consideration of the adhesion with the material of the lower dielectric layer,
Most preferred is _{ZnS-SiO 2, ZnS-Y} 2 O 3,
_{TaS 2 -Ta 2 O 5, Ce} 2 S 3 -ZnO, Ce 2 S 3 -S
iO _2, a composite dielectric layer consisting of either Ce ₂ S ₃ -CeO _2.

In forming these upper and lower dielectric layers, a sputtering method is widely used, but a sputtering method using a composite target is preferable. The film density of the dielectric layer is preferably 70% or more of the theoretical density. Here, the theoretical density of the film is represented by the following formula, and is an integrated value obtained by multiplying the density of each constituent compound in a bulk state by the molar content of the constituent compound.

Theoretical density = {(density in bulk state of constituent compound) × (molar content of constituent compound)} By setting the density of the dielectric layer in this way, the durability against repeated recording and aging is significantly improved. be able to. The film density can be controlled by adjusting the degree of vacuum during sputtering. In order to increase the film density, it is preferable to lower the degree of vacuum (lower the argon gas pressure). Usually, the degree of vacuum is 1 Pa or less, preferably 0.1 to 0.1 Pa.
It is good to be 8Pa.

The recording layer of the medium of the present invention is a phase change type recording layer, and its thickness is preferably in the range of 10 nm to 100 nm. If the thickness of the recording layer is thinner than 10 nm, it is difficult to obtain a sufficient contrast, and the crystallization speed tends to be slow. On the other hand, if it exceeds 100 nm, optical contrast is still difficult to obtain, and cracks tend to occur, which is not preferable.

As the recording layer, a known phase change type optical recording layer can be used. For example, GeSbTe, InSbTe, AgS
Compounds such as bTe and AgInSbTe are selected as overwritable materials. Above all, ｛(Sb _{2
Te 3) 1-x (GeTe} ) x} 1- y Sb y (0.2 <x <
0.9, 0 ≦ y <0.1) alloy or M _w (Sb _z Te)
_1-z ) _1-w (0 ≦ w <0.3, 0.5 <z <0.9, M =
In, Ga, Zn, Ge, Sn, Si, Cu, Au, A
g, at least one of Pd, Pt, Pb, Cr, Co, O, S, and Se).
Any of the amorphous states is stable, and a high-speed phase transition between the two states is possible. Further, it has the advantage that segregation hardly occurs when repeated overwriting is performed, and is the most practical material.

The above-mentioned recording layer is often obtained by sputtering an alloy target in an inert gas, particularly Ar gas. In general, Ar gas used for sputtering is taken into the film in the sputtered film, and this is repeatedly deposited during overwriting, resulting in voids (voids) on the order of 0.1 mm.
May be formed (J. Appl. Phys. 78 (1995)
pp6980-6988). To suppress this, the Ar content in the recording layer film is 1.5 at. % Is desirable.

Generally, Ar is taken into the film because
It is considered that part of Ar incident on the target at a high speed due to sputtering is bounced off the target surface and penetrates into the film. It is known that by increasing the Ar gas pressure during the sputtering of the recording layer, the amount of the recoil Ar can be reduced, and the amount of Ar in the film can be reduced. However, if the Ar gas pressure is set to be high as described above, on the contrary, the energy of Ar which is hit against the film and the energy of the flying atoms from the target are reduced, so that there is a trade-off problem that a dense film is hardly formed.

The low-density recording layer film has voids on the order of 1 mm due to repeated overwriting (the above-mentioned document). To prevent this, the recording layer density is desirably 86% or more of the theoretical density of the bulk. The bulk theoretical density can be determined from the atomic weight and atomic ratio of the constituent elements as in the case of the protective layer. As a result, the Ar content is 0.1 at% or more and 1.5
at. % Or the film density is preferably 86% or more of the theoretical density.

The general control of the amount of Ar, the effect on repeated overwriting, and the quantification of the amount of Ar in the film are disclosed in JP-A-6-262855 by the present inventors. Incidentally, the thickness of the recording layer and the protective layer, in addition to the above mechanical strength, from the viewpoint of reliability, taking into account the interference effect associated with the multilayer structure, good absorption efficiency of laser light,
The amplitude of the recording signal, that is, the contrast between the recorded state and the unrecorded state is selected so as to increase.

As described above, the recording layer, the protective layer, and the reflective layer are formed by a sputtering method or the like. It is desirable to form a film using an in-line apparatus in which a target for a recording film, a target for a protective film, and if necessary, a target for a reflective layer material are installed in the same vacuum chamber, from the viewpoint of preventing oxidation and contamination between layers. It is also excellent in productivity.

The disc may have an overcoat layer and a hard coat layer as required. The wavelength of the laser beam used for recording and reproduction on the medium of the present invention is not particularly limited, but may be, for example, 810 nm or 780 nm, or 700 nm or less for achieving high-density recording.
However, considering the ultraviolet absorption of the disk substrate, 300n
m or more is preferable.

As laser light having a wavelength of 700 nm or less,
For example, AlGaAs, AlGaAsP, AlGaIn
Output 5 of III-V semiconductor laser such as P, GaN, etc.
Laser light of 00 to 700 nm, Ar, Kr, He-C
d, 400 to 6 output by a gas laser such as He-Ne
50 nm laser light, ZnCdSe, ZnSe, ZnC
400-500 nm laser light output from II-VI group semiconductor lasers such as dS, ZnSeS, and 340-390 nm laser light obtained by outputting III-V group semiconductor laser output light through a SHG (second harmonic generation) element. A 350 nm laser beam obtained by obtaining a YAG laser output beam by a semiconductor laser excitation through a THG (third harmonic generation) element. Considering the miniaturization of the optical disk system,
Laser light of a semiconductor laser is preferred.

[0044]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. Example 1 Powder of SiC: SiO ₂ : Y ₂ O as a material for lower dielectric layer 1
₃ = 38: 57: 5 mol% was mixed and adjusted, and a composite sintered body target was obtained by a hot press method. The lower dielectric layer 2 and the upper dielectric layer are made of ZnS: S
The mixture was adjusted and mixed so that iO ₂ = 80: 20 mol%, and a composite sintered body target was obtained by a hot press method.

Polycarbonate substrate (n = 1.556)
A lower dielectric layer 1 / lower dielectric layer 2 / recording layer / upper dielectric layer / reflective layer was provided on a substrate to form a recording medium having a five-layer structure.
The thickness of each layer is 100 nm for the lower dielectric layer 1, 60 nm for the lower dielectric layer 2, 30 nm for the recording layer, and 20 n for the upper dielectric layer.
m, and the reflective layer was 100 nm. The composition of the recording layer is Ge
(22.2) Sb (22.2) Te (55.6) and the reflective layer is T
An Al alloy containing 2.5 at.% a was used.

The lower dielectric layer 1 is supplied with Ar gas and oxygen gas at 50 sccm and 1.0 sccm, respectively, at a pressure of 0.7 Pa.
The film was formed by high frequency (13.56 MHz) sputtering. The film density is 2.2 g / cm ³ and the theoretical density is 75 g / cm ^3.
%Met. The JIS Knoop hardness was 444, and the film stress was 1.1E + 9 dyn / cm ² by tensile. The refractive index n of this film was 1.57.

The lower dielectric layer 2 and the upper dielectric layer are flowed with Ar gas at 50 sccm, and under high frequency (13.
56 MHz) The film was formed by sputtering. The film density is 3.
5 g / cm ³ , 94% of the theoretical density. The JIS Knoop hardness was 360 and the Vickers hardness at 800 ° C. was 360. Film stress is 1.1E + 9dyn / c by pulling
It was m ^2. The refractive index n of this film was 2.07.

The recording layer and the reflective layer were formed under an Ar gas pressure of 0.7.
The film was formed by direct current sputtering at Pa. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided. After the disk was further initialized using an LD bulk eraser having a wavelength of 810 nm, that is, the recording layer was crystallized, dynamic characteristics of the disk were evaluated under the following conditions.

While rotating at a linear velocity of 10 m / s, using a pulse light having a wavelength of 780 nm, 4 MHz and a duty of 50%, a recording power of 11.5 mW and a base power of 7.0 m were used.
Overwriting was repeatedly performed at W and a reproduction power of 0.8 mW, and the C / N and the erasing ratio were measured each time a predetermined number of times was reached. The results are shown in FIG. Up to 20,000 repetitions, a C / N of 51 to 53 dB and an erase ratio of about 30 dB were obtained.

Comparative Example 1 The lower dielectric layer and the upper dielectric layer were made of ZnS powder:
The mixture was adjusted and mixed so that SiO ₂ = 80: 20 mol%, and a composite sintered body target was obtained by a hot press method. A lower dielectric layer / recording layer / upper dielectric layer / reflective layer was provided on a polycarbonate substrate (n = 1.556) substrate to prepare a four-layer recording medium. The thickness of each layer is 60 n for the lower dielectric layer.
m, the recording layer was 30 nm, the upper dielectric layer was 20 nm, and the reflective layer was 100 nm. The composition of the recording layer is Ge (22.2) Sb
(22.2) Te (55.6), and the reflective layer has a Ta of 2.5a.
Al alloy containing t.% was used.

The lower dielectric layer and the upper dielectric layer are made of Ar gas 5
At a pressure of 0.7 Pa and high frequency (13.5
6 MHz) The film was formed by sputtering. The film density is 3.5
g / cm ³ , 94% of the theoretical density. The JIS Knoop hardness was 360 and the Vickers hardness at 800 ° C. was 360. The film stress is 1.1E + 9dyn / cm ^{2 by} pulling.
Met. The refractive index n of this film was 2.07.

The recording layer and the reflective layer were formed under an Ar gas pressure of 0.7.
The film was formed by direct current sputtering at Pa. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided. After the disk was further initialized using an LD bulk eraser having a wavelength of 830 nm, that is, the recording layer was crystallized, the dynamic characteristics of the disk were evaluated under the following conditions.

While rotating at a linear velocity of 10 m / s, using a pulse light having a wavelength of 780 nm, 4 MHz and a duty of 50%, a recording power of 11.5 mW and a base power of 7.0 m were used.
Overwriting was repeatedly performed at W and reproduction power of 0.8 mW, and the C / N and the erasing ratio were measured each time the number of times reached a predetermined number. The results are shown in FIG. Initially C / N is 54dB
The erasing ratio was about 30 dB. However, the erase ratio sharply deteriorated after 5,000 repetitions, and became 3 dB after 20,000 repetitions. Also, the C / N is 50
dB was cut.

Example 2 Powder of SiC: SiO ₂ : Mg was used as the material of the lower dielectric layer 1
The mixture was adjusted and mixed so that F ₂ = 19: 5: 76 mol%, and a composite sintered body target was obtained by a hot press method. Also,
The lower dielectric layer 2 and the upper dielectric layer are made of powder of ZnS:
The mixture was adjusted and mixed so that SiO ₂ = 80: 20 mol%, and a composite sintered body target was obtained by a hot press method.

Polycarbonate substrate (n = 1.556)
A lower dielectric layer 1 / lower dielectric layer 2 / recording layer / upper dielectric layer / reflective layer was provided on a substrate to form a recording medium having a five-layer structure.
The thickness of each layer is as follows: the lower dielectric layer 1 has a thickness of 25 nm;
Is 75 nm, the recording layer is 20 nm, and the upper dielectric layer is 22.5
nm and the reflective layer was 200 nm. The composition of the recording layer is Ag
₅ In ₆ Sb ₅₉ Te ₃₀ and the reflective layer was made of Ta at 2.5 at.
% Al alloy was used.

The lower dielectric layer 1 was formed by high frequency (13.56 MHz) sputtering under a pressure of 0.7 Pa while flowing Ar gas at 50 sccm. The film density was 3.4 g / cm ³ , 100% of the theoretical density. The JIS Knoop hardness is 450, and the film stress is 5.03E + 9dyn / cm ^{2 by} tensile.
Met. The refractive index n of this film was 1.49. The lower dielectric layer 2 and the upper dielectric layer are flowed with Ar gas at 50 sccm,
The film was formed by high frequency (13.56 MHz) sputtering under a pressure of 0.7 Pa. The film density is 3.5 g / cm ³ ,
It was 94% of the theoretical density. JIS Knoop hardness is 360
And the Vickers hardness at 800 ° C. was 360. The film stress was 1.1E + 9 dyn / cm ² by pulling. The refractive index n of this film was 2.07.

The recording layer and the reflective layer were formed under an Ar gas pressure of 0.7.
The film was formed by direct current sputtering at Pa. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided. After the disk was further initialized using an LD bulk eraser having a wavelength of 810 nm, that is, the recording layer was crystallized, dynamic characteristics of the disk were evaluated under the following conditions.

Using a light source having a wavelength of 780 nm, 2.4 m /
While rotating at a linear speed of s, overwriting is repeatedly performed with a recording power of 14 mW, a base power of 7 mW, and a reproduction power of 0.8 mW in an EFM random pattern (using multipulses). A measurement was made. The results are shown in FIG. The initial values of the pit jitter and the land jitter (jitter between pits) are about 10.2 ns and 10.9 ns, respectively, and 12.4 ns, 15.
8 ns.

Comparative Example 2 As a material for the lower dielectric layer and the upper dielectric layer, the powder was ZnS:
The mixture was adjusted and mixed so that SiO ₂ = 80: 20 mol%, and a composite sintered body target was obtained by a hot press method. A lower dielectric layer / recording layer / upper dielectric layer / reflective layer was provided on a polycarbonate substrate (n = 1.556) substrate to prepare a four-layer recording medium. The thickness of each layer is 75 n for the lower dielectric layer.
m, the recording layer was 20 nm, the upper dielectric layer was 22.5 nm, and the reflective layer was 200 nm. The composition of the recording layer is Ag ₅ In ₆ S
b ₅₉ Te ₃₀ , and an aluminum alloy containing 2.5 at.% of Ta was used for the reflective layer.

The lower dielectric layer and the upper dielectric layer are made of Ar gas 5
At a pressure of 0.7 Pa and high frequency (13.5
6 MHz) The film was formed by sputtering. The film density is 3.5
g / cm ³ , 94% of the theoretical density. The JIS Knoop hardness was 360 and the Vickers hardness at 800 ° C. was 360. The film stress is 1.1E + 9dyn / cm ^{2 by} pulling.
Met. The refractive index n of this film was 2.07.

The recording layer and the reflective layer were formed under an Ar gas pressure of 0.7.
The film was formed by direct current sputtering at Pa. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided. After the disk was further initialized using an LD bulk eraser having a wavelength of 830 nm, that is, the recording layer was crystallized, the dynamic characteristics of the disk were evaluated under the following conditions.

Using a light source having a wavelength of 780 nm, 2.4 m /
While rotating at a linear velocity of s, overwriting was repeatedly performed with a recording power of 14 mW, a base power of 7 mW, and a reproduction power of 0.8 mW in an EFM random pattern (using multipulses), and the jitter was measured each time a predetermined number of times was reached. . The results are shown in FIG. The initial values of the pit jitter and the land jitter (jitter between pits) are each 1
The values were about 0.9 ns and 11.3 ns, which were about 0.5 times worse than those in Example 1. This is considered to be because the lower dielectric film thickness is not sufficient, so that heat during recording is transmitted to the substrate and deforms the substrate. In addition, they were 13.1 ns and 16.2 ns when the number of repetitions was 400, which was also about 0.5 times worse than that of Example 1.

[0063]

According to the present invention, it is possible to provide an optical information recording medium having a dielectric layer excellent in the interference effect and the recording layer protection effect. -It is very effective for practical use of rewritable media that can be erased.

[Brief description of the drawings]

FIG. 1 is a graph showing erasing ratios and C / N repetition characteristics of media of Example 1 and Comparative Example 1.

FIG. 2 is a graph showing repetition characteristics of pit jitter and land jitter of the media of Example 2 and Comparative Example 2.

[Explanation of symbols]

 Reference Signs List 1 C / N of medium of Example 1 2 Erase ratio of medium of Example 1 3 C / N of medium of Comparative Example 4 4 Erase ratio of medium of Comparative Example 5 Pit jitter of medium of Example 2 6 Example Land jitter of medium 2 7 Pit jitter of medium of comparative example 8 8 Land jitter of medium of comparative example 2

Claims (15)

[Claims] 1. A lower dielectric layer 1, a lower dielectric layer 2,
An optical information recording medium having a phase change recording layer, an upper dielectric layer and a reflective layer in order, wherein the refractive index of the lower dielectric layer 1 is n
₁ , when the refractive index of the substrate is n _sub , n _sub −0.3 ≦ n
An optical information recording medium, wherein ₁ ≦ n _sub +0.3. 2. The refractive index n ₁ of the lower dielectric layer ₁ is n _sub −0.2.
≤ n ₁ ≤ n _sub +0.2.
The optical information recording medium according to the above. 3. When the refractive index of the lower dielectric layer 2 is n ₂ ,
The optical information recording medium according to claim 1, wherein n ₂ −n _sub ≧ 0.2. 4. When the refractive index of the lower dielectric layer 2 is n ₂ ,
4. The optical information recording medium according to claim _{1, wherein} n ₂ −n ₁ ≧ 0.1. 5. The refractive index n ₁ of the lower dielectric layer ₁ is 1.5 ≦ n ₁ ≦
The optical information recording medium according to any one of claims 1 to 4, wherein the medium is 1.6. 6. The optical information recording medium according to claim 5, wherein the substrate is made of a polycarbonate resin. 7. When the refractive index of the lower dielectric layer 2 is n ₂ ,
7. The optical information recording medium according to claim 1, wherein 1.7 ≦ n ₂ ≦ 2.3. 8. The optical information according to claim 1, wherein the total thickness of the lower dielectric layer 1 and the lower dielectric layer 2 is 70 nm or more and 200 nm or less. Recording medium. 9. The optical information recording medium according to claim 8, wherein the total thickness of the lower dielectric layer 1 and the lower dielectric layer 2 is 80 nm or more and 160 nm or less. 10. The thickness of the lower dielectric layer 2 is determined by the reflectance of a laser beam in an optical information recording medium having a lower dielectric layer 2, a phase-change recording layer, an upper dielectric layer and a reflective layer on a substrate in that order. The optical information recording medium according to any one of claims 1 to 9, wherein? 11. The optical information recording apparatus according to claim 1, wherein the lower dielectric layer 1 contains at least SiO ₂ , or a fluoride of Mg, Ca, Li or a rare earth metal. Medium. 12. The dielectric layer in contact with the recording layer is made of S or Se.
The optical information recording medium according to any one of claims 1 to 11, comprising: 13. The method according to claim 13, wherein the dielectric layer in contact with the recording layer is ZnS-Si.
O_Two, ZnS-Y_TwoO _Three, TaS_Two-Ta_TwoO_Five, Ce_TwoS_Three−
ZnO, Ce_TwoS_Three-SiO_Two, Ce_TwoS_Three-CeO_TwoNozomi
13. The method according to claim 1, wherein the method comprises:
An optical information recording medium according to any of the preceding claims. 14. The optical information recording apparatus according to claim 1, wherein the film density of the lower dielectric layers 1, 2 and the upper dielectric layer is 70% or more of the theoretical density. Medium. 15. The lower dielectric layers 1, 2 and the upper dielectric layer,
15. The optical information recording medium according to claim 1, wherein the optical information recording medium is formed by sputtering using a composite sputtering target composed of a plurality of compounds constituting the dielectric.