JP3031135B2 - Optical information recording medium - Google Patents

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 by irradiating a laser beam or the like. In particular, it relates to an optical information recording medium that can be directly reproduced by a conventional CD-only drive.

[0002]

2. Description of the Related Art Optical discs include a read-only type, an optical recordable type, and a rewritable type.
It has already been put to practical use as an audio disk, and even as a large-capacity computer disk memory. Among these, compact discs (CDs) are widely used for audio reproduction of music and the like. A compact disc (CD) is a CD-formatted EFM (Ei
ght to Fourteen Modulatio
n) Signal holes (pits) are transferred to a substrate made of plastic, and a reflective film and a protective layer made of a metal such as aluminum are provided thereon.

The reading of information from a CD is performed by irradiating an optical disk with a semiconductor laser beam incident from the substrate side, and a CD format signal or the like is read by a change in reflectance depending on the presence or absence of pits. In this case, the conventional CD is characterized by having a high reflectance of 70% or more and a modulation degree of 60% or more. However, this read-only CD cannot record, edit, or rewrite information.

Also, files such as software, data files, still images, etc., are stored on CD-ROMs (Read
only memory) or CD-I (inte
There is a demand for an optical recording / erasable optical disk for operative. On the other hand, typical optical recordable types include a perforated / deformed type, a magneto-optical type and a phase change type. Drilling
As the deformation type, a recording layer made of a low melting point metal such as Te or a dye is used, and is locally heated by laser beam irradiation to form holes or concave portions.

[0005] In practice, such perforated molds must have voids on the recording layer. For this purpose, two disks are attached to each other using a spacer so as to face each other, so that a gap is provided between the recording layers. As a matter of course, a disc having such a bonded structure cannot be mounted on a CD drive which is currently widely used.

[0006] The magneto-optical type performs recording and erasing according to the direction of magnetization of the recording layer, and performs reproduction by the magneto-optical effect, so that it cannot be reproduced by a conventional CD drive utilizing a difference in reflectance. As a disk for recording a CD format signal, an optical disk having a recording layer made of a dye or a polymer containing a dye on a substrate, and an optical information recording method using the optical disk have been proposed (JP-A-61-237239). No. 61-233943), these optical disks cannot be made rewritable.

On the other hand, the phase change type utilizes the fact that the reflectance changes before and after the phase change, and is common to the CD in that the reproduction is performed with the difference in the reflectance without the need for an external magnetic field. I have. Further, there is an advantage that recording / erasing can be performed only by modulating the power of the laser beam, and one-beam overwriting, in which erasing and re-recording are performed simultaneously with a single beam, is also possible.

In the phase change recording system 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-based, In-Sb-Te-based, Ge-Sn-Te-based alloy thin films and the like can be mentioned.

Usually, a dielectric protection layer is provided above and below the recording layer for protection against deformation of the recording layer and the like, protection from deterioration such as oxidation, and furthermore, utilization of the interference effect. Further, a layer structure in which a reflective layer is provided on a dielectric layer above a recording layer for adjusting a cooling rate and utilizing an interference effect is often used. That is, a layer configuration in which a dielectric protective layer, a phase change recording layer, a dielectric protective layer, and a reflective layer are sequentially provided on a substrate is generally used.

[0010] A write-once phase change medium can be realized with almost the same material and layer structure as 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.

[0011]

However, the phase change optical disk having the above-mentioned general layer structure has a low reflectance and cannot be reproduced by a CD drive. Although it is possible to increase the reflectivity by changing the thickness of the dielectric layer above and below the recording layer, a sufficient degree of modulation cannot be obtained at that time.

Further, in order to reproduce data with a CD drive, it is necessary to have a high reflectance in an unrecorded portion. Therefore, in the case of a Ge-Te or Ge-Sb-Te type phase change medium requiring initialization, Although it is necessary to increase the reflectance in the crystalline state, the reflectance in the amorphous state having a small absorption coefficient (imaginary part of the complex refractive index) tends to increase at a high reflectance. Attempts have been made to increase the reflectance by using two dielectric layers below the recording layer (Japanese Patent Laid-Open No. 1-27324), but it cannot be said that the reflectance and contrast are sufficient.

When the reflectance is further increased, the thermal energy absorbed by the recording layer is reduced, so that the sensitivity is deteriorated and a large laser power is required.

[0014]

According to the present invention, there is provided an optical device comprising at least two dielectric intermediate layers having different refractive indices, a phase change optical recording layer, a dielectric layer, and a reflective layer sequentially laminated on a substrate. Phase-change optical recording layer has a thickness of 1
(GeTe) _1-X α _X (x is 0 to 30 nm)
Represents a number from 0.1 to 0.1, and α is Sb, Se, Bi, In , S
n, Pb, As, Si, Au, Ti, Cu, Ag, P
t, Pd, Co, and Ni ), and the reflectance (calculated value) of the dielectric intermediate layer at the used laser wavelength is 30% or more and 60% or less, and the recording layer in the disk mirror portion is The optical information recording medium is characterized in that the medium has a reflectance of at least 65% in a crystalline state and a reflectance difference of 35% or more between a crystalline state and an amorphous state.

When a composition near GeTe is used for the recording layer, it is necessary to provide an intermediate layer having a certain degree of reflectance between the substrate and the recording layer in order to achieve high reflectance and high contrast. When the reflectivity of the intermediate layer is less than 30%, the thickness of the recording layer needs to be thicker than 30 nm. When the reflectivity of the intermediate layer increases, high reflectivity and high contrast are achieved even if the thickness of the recording layer is smaller. You.

From the viewpoint of recording sensitivity, it is preferable that the thickness of the recording layer is small, and therefore it is preferable that the reflectivity of the intermediate layer is large to some extent. As the intermediate layer, it is preferable to stack two or more types of dielectrics having different refractive indexes. In this case, if the number of dielectric layers is increased, the intermediate layer reflectance can be increased.
If the reflectivity of the intermediate layer is too large, high contrast cannot be obtained, and the number of dielectric intermediate layers should be small in order to simplify the manufacturing process and reduce peeling at the interface. preferable.

For this reason, the reflectance of the intermediate layer is from 30% to 60%.
% Is preferred. When a thin metal or the like is used as the intermediate layer, the reflectance of the intermediate layer can be increased with a small number of layers, but the thermal conductivity of the metal is generally large,
Since the metal intermediate layer absorbs incident energy, it is not optically and sensitively appropriate.

The dielectric used for the intermediate layer in the present invention includes:
Various combinations are possible, and are determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. Generally, Mg, Ca, which have high transparency and high melting point
Sr, Y, La, Ce, Ho, Er, Yb, Ti, Z
r, Hf, V, Nb, Ta, Zn, Al, Si, Ge,
Oxides such as Pb, sulfides, nitrides, and fluorides such as Ca, Mg, and Li can be used.

These oxides, sulfides, nitrides and fluorides do not always need to have a stoichiometric composition, and it is effective to control the composition for controlling the refractive index and the like, or to use a mixture thereof. It is. It is preferable that the number of dielectric intermediate layers be small in order to simplify the manufacturing process and to reduce peeling at the interface, and to achieve high reflectance and high contrast with a small number of dielectric intermediate layers. It is preferable to use two or more types of dielectrics having a large difference in the rates.

As those having a relatively small refractive index, Ca
There are F ₂ , MgF ₂ , Na ₃ AlF ₆ , SiO _{2 and the} like, and TiO ₂ , ZnS, T
There are a ₂ O _5, a mixture of ZnS and SiO _2. In order to increase the reflectance of the dielectric intermediate layer, it is preferable to stack the dielectric layers with an optical film thickness of λ / 4 (λ is a laser wavelength), but it is not always necessary to have an optical film thickness of λ / 4. By deviating from this film thickness, it is possible to adjust the reflectance of the intermediate layer and the wavelength dependence of the reflectance.

Here, the reflectance of the dielectric intermediate layer can be defined as the reflectance assuming that the thickness of the dielectric layer immediately below the recording layer is infinitely thick. That is, it can be obtained by calculation from the refractive index and the film thickness of the dielectric. The method of calculating the reflectance when 1 to N intermediate layers are stacked on a substrate will be described below. In the formula, the substrate complex refractive index is n ₀ -ik ₀ , the r-th layer complex refractive index is n _r -ik _r , and the r-th layer thickness is dr. B,
When C is expressed by Expression 1, the intermediate layer reflectance is obtained as in Expression 2.

[0022]

(Equation 1)

[0023]

(Equation 2)

From the viewpoint of recording sensitivity, it is considered that the dielectric layer in contact with the recording layer should be made of a material having a small thermal conductivity and a small specific heat. A mixture of ZnS and SiO ₂ is preferable as a dielectric having an excellent protection effect against rewrite characteristics and a low thermal conductivity, and (ZnS) ₈₀ (SiO ₂ ) ₂₀ is particularly preferable. Usually, the phase change optical recording layer is GeSbTe-based, InSbT
An e-system or the like is used, but a material having a large change in the refractive index is preferable for increasing the contrast.

As for the GeSbTe system, Sb ₂ Te ₃ −
A composition on a GeTe line or a composition obtained by adding a small amount of Sb or the like to this composition is suitable for phase change recording, but a refractive index change is preferably closer to GeTe. Therefore, a material based on GeTe is preferable, and the bit shape, the crystal grain shape, the stability over time, the recording sensitivity, the optical properties, and the like can be improved by adding a third element.

As the third element, Sb, Sn, In, Te,
Ge, Pb, As, Se, Si, Bi, Au, Ti, C
u, Ag, Pt, Pd, Co, Ni, etc., may be added. In the present invention, at least one of Sb, Se, Bi, and In may be added at 10 at. % Or less. This gives G
The ability to form an amorphous bit can be controlled without impairing the intrinsic optical properties and high crystallization rate of eTe.

The composition ratio of GeTe does not necessarily have to be an atomic ratio of 1: 1. % (Atomic%) to ±
5 at. A deviation of about% is not a problem. A thin recording layer is preferable in terms of recording sensitivity, but if the thickness is less than 10 nm, a sufficient contrast cannot be obtained.
It needs to be 0 nm or less.

The reflective layer is preferably made of a material having a high reflectivity.
Au, Ag, Cu, Al, etc. are used, and Ta, Ti, Cr, Mo, Mg, V, Nb, Zr are used for controlling the thermal conductivity.
May be added in small amounts. The recording medium of the present invention has a mirror surface portion of a disk (a smooth portion such as a mirror surface having no unevenness such as a tracking groove) for one purpose of being capable of being played back by a CD playback device. The reflectance of the medium when the recording layer is in the crystalline state is 65% or more, and the reflectance of the medium when the recording layer is in the crystalline state and the reflectance when the recording layer is in the amorphous state in the same portion. The difference needs to be 35% or more.

As the substrate of the recording medium in the present invention,
The material may be any of glass, plastic, and a material in which a photocurable resin is provided on glass, but a polycarbonate resin is preferable in terms of CD compatibility. The recording layer, the dielectric layer, and the reflection 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.

[0030]

The present invention will be described in detail with reference to the following examples. Example 1 (ZnS) ₈₀ (Si
O ₂ ) ₂₀ (mol%) layer 90 nm, SiO 2 layer 12
0 nm, the layer of (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 90 nm,
The layer of SiO ₂ is made 120 nm, and (ZnS) ₈₀ (SiO ₂ ) ₂₀
Layer of 220 nm, a layer of Ge ₄₆ Sb ₈ Te ₄₆ (at.%) Of 20 nm, and a layer of (ZnS) ₈₀ (SiO ₂ ) ₂₀ of 20
Discs were prepared by sequentially forming layers of 0 nm and Au by 100 nm by a magnetron sputtering method.

The reflectance in a non-crystalline state at a wavelength of 780 nm and the reflectance in a crystalline state after initialization by an Ar laser were measured at a mirror portion (a smooth portion without grooves or irregularities), and were 16% and 67%, respectively. Was. The reflectance (calculated value) of the dielectric intermediate layer portion is 46%. This disc contains 1.
196 kHz at 4 m / sec, duty 50%, 19 m
When a W signal was recorded, C / N 53 dB was obtained.
When a 0 mW DC laser was applied, an erasing rate of 25 dB or more was obtained. The laser wavelength is 780 nm and the NA is 0.55. The thickness of the dielectric layer above and below the recording layer is ±
There is no problem even if the displacement is about 10 nm.

Example 2 (ZnS) ₈₀ (Si) was placed on a polycarbonate resin substrate.
O ₂ ) ₂₀ layer 90 nm, SiO ₂ layer 120 nm, (Z
nS) ₈₀ (SiO ₂ ) ₂₀ layer 90 nm, SiO ₂ layer 120 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer 130
nm, a layer of Ge ₄₆ Sb ₈ Te ₄₆ of 30 nm, (ZnS)
₈₀ (SiO ₂ ) ₂₀ layer of 220 nm, Au layer of 100
Disks were formed by forming the layers sequentially by magnetron sputtering. When the reflectance in a non-crystalline state at a wavelength of 780 nm and the reflectance in a crystalline state after initialization by an Ar laser were measured at mirror surfaces, they were 16% and 6%, respectively.
6%. The reflectance (calculated value) of the dielectric intermediate layer is 46
%. When the same recording as in Example 1 was performed on this disk, C / N of 52 dB was obtained.

Example 3 A layer of Ta ₂ O ₅ was formed on a polycarbonate resin substrate by 90 n.
m, SiO ₂ layer is 120 nm, (ZnS) ₈₀ (Si
O ₂ ) ₂₀ layer 90 nm, SiO ₂ layer 120 nm,
(ZnS) ₈₀ (SiO ₂ ) ₂₀ layer of 220 nm, Ge ₄₆
20 nm of Sb ₈ Te ₄₆ layer, (ZnS) ₈₀ (SiO ₂ ) ₂₀
The disc was manufactured by sequentially laminating the layers with a thickness of 200 nm and the Au layers with a thickness of 100 nm by a magnetron sputtering method. The reflectance in a non-crystalline state at a wavelength of 780 nm and the reflectance in a crystalline state after initialization with an Ar laser were measured at a mirror surface portion, and were 17% and 68%, respectively. The reflectance (calculated value) of the dielectric intermediate layer portion is 46%. When the same recording as in Example 1 was performed on this disc, C / N5
2 dB was obtained.

Example 4 A layer of TiO ₂ was formed on a polycarbonate resin substrate by 70 n.
m, the layer of CaF ₂ is 190 nm, (ZnS) ₈₀ (Si
O ₂ ) ₂₀ layer is 200 nm, Ge ₄₆ Sb ₈ Te ₄₆ layer is 20 nm.
nm, a layer of (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 180 nm,
Au layers were sequentially laminated by magnetron sputtering to a thickness of 100 nm to produce a disk. The reflectance in a non-crystalline state at a wavelength of 780 nm and the reflectance in a crystalline state after initialization with an Ar laser were measured at a mirror surface portion, and were 16% and 67%, respectively. The reflectance (calculated value) of the dielectric intermediate layer is 50%. When the same recording as in Example 1 was performed on this disk, a C / N of 50 dB was obtained.

Example 5 (ZnS) on a polycarbonate resin substrate₈₀(Si
O_Two)₂₀Layer of 90 nm, SiO_TwoLayer of 120 nm,
(ZnS)₈₀(SiO_Two)₂₀Layer of 90 nm, SiO _Twoof
120 nm layer, (ZnS)₈₀(SiO_Two)₂₀Layer 2
20 nm, Ge₄₇Se ₆Te₄₇Layer of 20 nm, (Zn
S)₈₀(SiO_Two)₂₀200 nm, Au layer 1
00nm sequentially laminated by magnetron sputtering method
A disc was prepared. Amorphous at 780 nm wavelength
State reflectivity and crystal state after initialization by Ar laser
When the reflectance at the mirror was measured on the mirror surface,
%, 66%. Reflectance of dielectric intermediate layer (calculated value)
Is 46%. The same recording as in the first embodiment
And C / N 52 dB was obtained.

Example 6 (ZnS) ₈₀ (Si) was coated on a polycarbonate resin substrate.
O ₂ ) ₂₀ layer 90 nm, SiO ₂ layer 120 nm, (Z
nS) ₈₀ (SiO ₂ ) ₂₀ layer 90 nm, SiO ₂ layer 1
20 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer of 220 n
m, a layer of Ge ₄₇ Bi ₆ Te ₄₇ of 20 nm, (ZnS) ₈₀
A disk was prepared by sequentially laminating ₂₀ layers of (SiO ₂ ) by 200 nm and an Au layer by 100 nm by a magnetron sputtering method. The reflectance in a non-crystalline state at a wavelength of 780 nm and the reflectance in a crystalline state after initialization by an Ar laser were measured at a mirror surface portion, and were 17% and 66%, respectively. The reflectance (calculated value) of the dielectric intermediate layer portion is 46%. When the same recording as in Example 1 was performed on this disk, C / N of 51 dB was obtained.

Example 7 (ZnS) on a polycarbonate resin substrate₈₀(Si
O_Two)₂₀Layer of 90 nm, SiO_TwoLayer of 120 nm,
(ZnS)₈₀(SiO_Two)₂₀Layer of 90 nm, SiO _Twoof
120 nm layer, (ZnS)₈₀(SiO_Two)₂₀Layer 2
20 nm, Ge₄₇In ₆Te₄₇Layer of 20 nm, (Zn
S)₈₀(SiO_Two)₂₀200 nm, Au layer 1
00nm sequentially laminated by magnetron sputtering method
A disc was prepared. Amorphous at 780 nm wavelength
State reflectivity and crystal state after initialization by Ar laser
When the reflectance at the mirror was measured on the mirror surface, it was 18
%, 66%. Reflectance of dielectric intermediate layer (calculated value)
Is 46%. The same recording as in the first embodiment
And C / N 51 dB was obtained.

Example 8 (ZnS) on a polycarbonate resin substrate₈₀(Si
O_Two)₂₀Layer of 90 nm, SiO_TwoLayer of 120 nm,
(ZnS)₈₀(SiO_Two)₂₀Layer of 90 nm, SiO _Twolayer
120 nm, (ZnS)₈₀(SiO_Two)₂₀Layer 22
0 nm, Ge₄₆Sb₈Te₄₆Layer of 20 nm, (Zn
S)₈₀(SiO_Two)₂₀Layer 200 nm, Al layer 1
00nm sequentially laminated by magnetron sputtering method
A disc was prepared.

The reflectance in a non-crystalline state at a wavelength of 780 nm and the reflectance in a crystalline state after initialization with an Ar laser were measured at a mirror surface, and were 22% and 66%, respectively.
Met. The reflectance (calculated value) of the dielectric intermediate layer portion is 46%. When the same recording as in Example 1 was performed on this disk, C / N of 51 dB was obtained.

Comparative Example 1 (ZnS) on a polycarbonate resin substrate₈₀(Si
O_Two)₂₀Layer of 90 nm, SiO_TwoLayer of 120 nm,
(ZnS)₈₀(SiO_Two)₂₀Layer of 90 nm, SiO _Twolayer
120 nm, (ZnS)₈₀(SiO_Two)₂₀130 layers
nm, Ge₄₆Sb₈Te₄₆Layer of 40 nm, (ZnS)
₈₀(SiO_Two)₂₀Layer 200 nm, Au layer 100 nm
layer by magnetron sputtering method.
A mask was prepared.

The reflectance in a non-crystalline state at a wavelength of 780 nm and the reflectance in a crystalline state after initialization by an Ar laser were measured at a mirror surface portion, and were 24% and 67%, respectively.
Met. The reflectance (calculated value) of the dielectric intermediate layer portion is 46%. When the same recording as in Example 1 was performed on this disk, the C / N was 44 dB. This is probably because the laser power was insufficient and the thickness of the recording layer was increased.

Comparative Example 2 (ZnS) on a polycarbonate resin substrate₈₀(Si
O_Two)₂₀Layer of 90 nm, SiO_TwoLayer of 120 nm,
(ZnS)₈₀(SiO_Two)₂₀Layer of 180 nm, Ge ₄₆
Sb₈Te₄₆Layer of 20 nm, (ZnS)₈₀(SiO_Two)
₂₀185 nm layer and 100 nm Au layer
The disks were laminated by the Ron sputtering method.

The reflectance in a non-crystalline state at a wavelength of 780 nm and the reflectance in a crystalline state after initialization with an Ar laser were measured at a mirror surface, and were 35% and 65%, respectively.
And the reflectance difference is not sufficient. The reflectance (calculated value) of the dielectric intermediate layer portion is 22%. Reflectance of dielectric intermediate layer 22
%, A disk having a recording layer thickness of 20 nm cannot provide a disk with high reflectivity and high contrast even if the film thickness of other layers is changed.

From the above results, when the recording layer thickness is 40 nm or more, the recording sensitivity is insufficient, and the dielectric intermediate layer reflectivity is 22%.
In the following, it became clear that sufficient contrast could not be obtained when the thickness of the recording layer was small. Therefore, in order to obtain a medium with high reflectivity, high contrast and high sensitivity, the dielectric intermediate layer reflectivity is 30% or more and the recording layer thickness is 1
It can be determined that it is necessary to set the thickness to 0 to 30 nm.

[0045]

The optical recording medium of the present invention has a high reflectance,
Since the recording layer thickness can be reduced with high contrast, it can be reproduced by a CD player and can be recorded with a relatively small laser power.

Claims (4)

(57) [Claims] 1. An optical information recording medium comprising a substrate, on which at least two or more dielectric intermediate layers having different refractive indexes, a phase-change optical recording layer, a dielectric layer, and a reflective layer are sequentially laminated. The transition type optical recording layer has a film thickness of 10 nm or more and 30 nm or less (GeTe) _1-x α _x (x represents a number of 0 to 0.1;
Are Sb, Se, Bi, In , Sn, Pb, As, Si,
Au, Ti, Cu, Ag, Pt, Pd, Co, or Ni ), and the reflectance (calculated value) of the dielectric intermediate layer at the used laser wavelength is 30.
% To 60%, the reflectance of the medium when the recording layer in the mirror portion of the disk is in the crystalline state is 65% or more, and the difference in reflectance between the crystalline state and the amorphous state is 35% or more. Information recording medium. 2. α is at least Sb, Se, Bi, In.
2. The optical information recording medium according to claim 1, wherein the optical information recording medium is also one kind. 3. The method of claim 1, wherein the dielectric of the dielectric intermediate layer is M
g, Ca, Sr, Y, La, Ce, Ho, Er, Yb,
Ti, Zr, Hf, V, Nb, Ta, Zn, Al, S
oxide, sulfide or nitride of i, Ge or Pb
Or fluoride of Ca, Mg or Li
The optical information recording medium according to claim 1. 4. The dielectric layer in contact with the recording layer is made of Zn.
_2. A mixture of S and SiO2.
4. The optical information recording medium according to any one of items 1 to 3 .