JP2001039031A - Optical information recording medium and optical recording method - Google Patents

Abstract

[PROBLEMS] To provide a phase change type optical information recording medium excellent in recording signal characteristics and an optical recording method thereof. SOLUTION: This is a rewritable optical information recording medium having a phase change type recording layer, wherein the recording layer is composed of (Sb _x G).
e _1-x ) _1-y In _y (where 0.65 ≦ x ≦ 0.95,
An optical information recording medium mainly containing an alloy satisfying 0 <y ≦ 0.2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical information recording medium having a phase-change recording layer, such as a rewritable compact disk (CD) or DVD, and an optical recording method thereof.

[0002]

2. Description of the Related Art In general, a compact disk (CD) or D
In the VD, recording of a binary signal and detection of a tracking signal are performed by utilizing a change in reflectance caused by interference of reflected light from the bottom and the mirror surface of the concave pit. In recent years, as a medium compatible with a CD, a phase-change rewritable compact disc (CD-RW, CD-Rewritab)
le) is becoming widely used. As for DVDs, various phase-change rewritable DVDs have been proposed.

These phase-change type rewritable CDs and Ds
The VD detects a recorded information signal by utilizing a change in a reflectance and a change in a phase difference caused by a difference in a refractive index between an amorphous state and a crystalline state. An ordinary phase change medium has a structure in which a lower protective layer, a phase change recording layer, an upper protective layer, and a reflective layer are provided on a substrate, and a reflectance difference and a phase difference are obtained by using multiple interference of these layers. It can be controlled to make it compatible with CDs and DVDs. In the CD-RW, it is difficult to achieve compatibility including a high reflectance of 70% or more, but within the range where the reflectance is reduced to 15 to 25%, compatibility of the recording signal and the groove signal can be secured. A CD drive in which an amplification system for covering a low reflectivity is added to a reproduction system can perform reproduction.

Further, in order to increase the amount of information, shorten the recording time, and speed up the information transfer, recently, a medium capable of recording and reproducing at a higher speed has been demanded. For example, the standard speed of a CD is 1.2 to 1.4 m / s.
A CD-RW capable of recording at double speed has been commercialized, and a CD-RW capable of recording at 8 × speed and 10 × speed has been demanded. On the other hand, rewritable DVDs include DVD
Various types such as -RAM, DVD + RW, DVD-R / W have been proposed or commercialized. In the case of a phase-change type recording medium, the erasing and re-recording processes can be performed only by intensity modulation of one focused light beam. Therefore, in CD-RW or rewritable DVD, recording means overwriting recording in which recording and erasing are performed simultaneously. Say

[0005]

For recording information utilizing a phase change, a crystal, an amorphous state, or a mixed state thereof can be used, and a plurality of crystal phases can be used. Generally, a rewritable phase-change type recording medium is converted into an unrecorded / erased state in a crystalline state, and is recorded by forming an amorphous mark. As a material of the rewritable phase-change recording layer, a chalcogen element, that is, a chalcogenide alloy containing S, Se, and Te has been used. For example, GeTe-Sb ₂ Te
₃ GeSbTe system a pseudo-binary alloy as a main component, InT
InSb containing e-Sb ₂ Te ₃ pseudo binary alloy as a main component
Ag-based eutectic based Te, Sb ₇₀ Te ₃₀
SbTe-based alloys, GeSnTe-based alloys, and the like. That is, conventionally, the chalcogen element has been considered as an essential component for performing phase change recording.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found a new phase-change type recording layer material which does not require a chalcogen component, and have reached the present invention. That is, the gist of the present invention is a rewritable optical information recording medium having a phase change type recording layer, wherein the recording layer is (Sb _x Ge)
_1-x ) _1-y In _y (0.65 ≦ x ≦ 0.95,0
<Y ≦ 0.2) An optical information recording medium characterized by comprising an alloy as a main component. In order to use the above alloy as a main component, Sb, Ge, and In are combined at 80 at% in total.
As described above, preferably, the content is 90 at% or more, and the ratio of each metal element is within the above range. Another aspect of the present invention is a recording method of the optical information recording medium,
When recording mark length modulated information on a recording medium having a phase change type recording layer with a plurality of recording mark lengths, an erasing power Pe capable of crystallizing an amorphous is provided between the recording marks.
, And the time length of one recording mark is defined as nT (T is a reference clock cycle, n is an integer of 2 or more).

[0007]

Η ₁ T, α ₁ T, β ₁ T, α ₂ T, β ₂ T,.
.., α _i T, β _i T,..., Α _m T, β _m T, η ₂
T

(Where m is the number of pulse divisions and m = n−
k and k are integers satisfying 0 ≦ k ≦ 2. Also, Σ _i (α _i
+ Β _i ) + η ₁ + η ₂ = n, η ₁ is a real number satisfying η ₁ ≧ 0, η ₂ is a real number satisfying η ₂ ≧ 0, and 0 ≦ η ₁ + η ₂ ≦ 2.0
And α _i (1 ≦ i ≦ m) is a real number satisfying α _i > 0,
β _i (1 ≦ i ≦ m) is a real number satisfying β _i > 0, and α _i ≦ β
_i (2 ≦ i ≦ m−1). ) And α _i T
During the time of (1 ≦ i ≦ m), a recording light having a recording power Pw of Pw> Pe is applied to melt the recording layer, and within the time of β _i T (1 ≦ i ≦ m), 0 is emitted. <P
b ≦ 0.5 Pe (However, in β _m T, 0 <Pb
≦ Pe) is applied to the recording light having a bias power Pb.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Since Sb has a high crystallization speed, an amorphous mark cannot be formed under the recording conditions used for a normal optical disk. As Ge is mixed with Sb, the crystallization speed becomes slower and can be adjusted to have a recordable crystallization speed. However, the jitter of the recorded signal is large and there is a problem in practical use. In fact, Sb
The possibility of a Ge-based alloy as a phase-change recording material has been described in Appl. Phys. Lett. 60, 3123, etc., the present inventor has performed recording and evaluation under general recording conditions of an optical disc. As a result, although the SbGe alloy can record, the recording signal has a jitter (fluctuation). ) Was large and not practical.

As a result of further study, the present inventors have found that GeSb
It has been found that by adding an appropriate amount of In to the system, the jitter of the recording signal is remarkably improved, and the present invention has been achieved.
That is, the recording layer is made mainly of an alloy of (Sb _x Ge _1-x ) _1-y In _y (where 0.65 ≦ x ≦ 0.95, 0 <y ≦ 0.2). By having this composition, it has a crystallization rate that can be used as a recording layer of an optical recording medium,
An excellent recording layer with low jitter of the recording signal is obtained. Addition of Ge and In to Sb can also be expected to improve the stability over time of the formed amorphous mark. More preferably, 0.
7 ≦ x ≦ 0.85 and 0.05 ≦ y ≦ 0.2.

If x exceeds 0.95 and Sb is too large, the crystallization speed is too high, and an amorphous mark cannot be formed under the recording conditions used for an ordinary optical disk. On the other hand, if x is less than 0.65 and Sb is too small, the crystallization speed becomes too slow, and crystallization erasure becomes difficult or takes much time. In general, a medium having a high crystallization speed is suitable for a medium for a high linear velocity, and a medium having a low crystallization speed is suitable for a medium for a low linear velocity.
0.65 ≦ x ≦ 0.85 at relatively low linear velocity below s
Is preferable, and at a high linear velocity of 9 m / s or more, usually 0.8 ≦ x
≦ 0.95 is preferred. In order to obtain good recording characteristics over a wide linear velocity range, 0.8 ≦ x ≦ 0.85 is particularly preferable. Even when using at the same linear velocity, the preferable value of x changes to some extent depending on the pulse strategy and the layer configuration.

In is 30 at. %, An effect of improving jitter can be seen. %, The influence of the low-reflectance crystal phase observed in the InSb-based material becomes large, and the characteristics may be deteriorated. Therefore, 0 <y ≦ 0.2. In order to further ensure the effect of the addition of In, preferably, 0.05 ≦ y ≦ 0.2. G
Although the reason why the recording signal jitter of the eSb system is large is not always clear, the present inventors presume that it may be related to the generation of crystal nuclei in the recording film. In a phase-change optical disk, not all the portions where the recording film is melted during recording become amorphous marks, and there are portions around the marks that recrystallize after melting. If the crystal nuclei are sparse when the crystal in the recrystallized portion grows, it is considered that the formed amorphous marks vary in shape depending on the presence or absence of the crystal nuclei. If there is no crystal nucleus at all, crystal growth will occur only from the portion in contact with the crystal around the melted portion. In this case, the mark shape is completely controlled by the heat distribution, and the shape variation will be small.

The present inventors conducted the following experiments on optical recording media having recording layers of various compositions. First, after recording a long amorphous mark, when a weak power DC laser beam is irradiated several times to crystallize only the central portion in the mark width direction, whether crystallization occurs only from before or after the mark, or It was determined by observing the reproduced waveform with an oscilloscope. As a result, crystal nuclei existed in the GeSb system, but no crystal nuclei existed in the system to which In was added, and it was speculated that the recording signal jitter would be superior in the system to which In was added.

The recording layer of the present invention may contain additional elements to such an extent that the recording characteristics are not impaired. The additional element is Ag,
Au, Cu, Pd, Pt, Al, Bi, Sn, Zn, N
i, Zr, Ti, Si, Ga, O, N, etc .; % Or less is preferable. Of these, the addition of O and N increases the crystallization rate, and these are also effective in controlling the crystallization rate. If necessary, a chalcogen element such as Te, Se, or S may be added.
t. % Or less. Next, a preferred embodiment of the optical information recording medium of the present invention will be described. The amorphous mark is formed by heating the recording layer to a temperature higher than the melting point and rapidly cooling the recording layer. In order to prevent evaporation and deformation of the recording layer due to such heat treatment, it is preferable to sandwich the upper and lower portions of the recording layer with a heat-resistant and chemically stable dielectric protective film.

In the recording process, the protective layer promotes heat diffusion from the recording layer, realizes a supercooled state, and contributes to the formation of an amorphous mark. Further, by adopting a four-layer structure in which a metal reflective layer is provided on top of the sandwich structure,
It is preferable to further promote thermal diffusion to stably form an amorphous mark. Erasing (crystallization) is performed by heating the recording layer to a temperature higher than the crystallization temperature of the recording layer and lower than the melting point. In this case, the dielectric protection layer functions as a heat storage layer for keeping the recording layer at a high temperature sufficient for solid-phase crystallization. Incidentally, the optical information recording medium of the present invention, a substrate, a protective layer, a recording layer, a protective layer, a reflective layer may be stacked in this order and irradiated with recording and reproducing light through the substrate, or a substrate, a reflective layer, The protective layer, the recording layer, and the protective layer may be laminated in this order, and the recording / reproducing light may be irradiated from the side opposite to the substrate. In each case, the top layer
In order to prevent direct contact with air and to prevent damage due to contact with foreign matter or a recording / reproducing head, an ultraviolet or thermosetting resin layer having a thickness of 1 μm to several hundred μm is provided. Alternatively, a dielectric protection layer having high hardness may be provided, or a resin layer may be further provided thereon.

It is preferable that the protective layer in contact with the recording layer is on both sides of the recording layer, but it is possible to omit one of the protective layers in some cases. Further, each of the reflection layer and the protective layer may be composed of a plurality of metal layers or dielectric layers. Furthermore, a very thin metal, semiconductor, or dielectric layer having absorption, which is a semi-transparent film, is provided on the substrate / protective layer in the case of substrate side incidence or on the protective layer in the case of incidence opposite to the substrate, It is also possible to control the amount of light energy incident on the recording layer. In any case, laser light such as a semiconductor laser or a gas laser is usually used as the recording / reproducing light, and the wavelength is 40
0-800 nm is often used. Especially 1Gbi
In order to achieve a high areal recording density of t / inch ² or more, it is necessary to reduce the diameter of the focused light beam.
0 to 680 nm blue to red laser light with numerical aperture N
It is desirable that the focused light beam passes through an objective lens having A of 0.5 or more.

As the substrate, a resin such as polycarbonate, acrylic, or polyolefin, or a metal such as glass or aluminum can be used. When irradiating recording / reproducing light through the substrate, the substrate needs to be transparent to the irradiating light. When a protective layer is provided above and below the recording layer, the thickness of the protective layer is preferably about 10 nm to 500 nm. The material of the protective layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, etc., but is highly transparent and has a high melting point, such as a metal or semiconductor oxide,
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 also effective to control the composition for controlling the refractive index and the like, or to use a mixture. Considering the repetitive recording characteristics, a mixture of dielectrics is preferred.

More specifically, a mixture of ZnS, TaS ₂ , a rare earth sulfide, and a heat-resistant compound such as an oxide, a nitride, a carbide, and a fluoride can be given. For example, ZnS and SiO
₂ , ZnS and rare earth oxide, ZnS and ZnO, ZnS-
Mixtures such as SiO ₂ —TaO _x and ZnS—ZnO—SiO ₂ are preferred. Considering the repetitive recording characteristics, it is desirable that the film density of these protective layers be 80% or more of the bulk state from the viewpoint of mechanical strength. When a mixture dielectric thin film is used, the theoretical density of the following equation is used as the bulk density. ρ = Σm _i ρ _i (1) m _i : molar concentration of each component i ρ _i : single bulk density When the thickness of the dielectric layer is less than 10 nm, the effect of preventing deformation of the substrate and the recording film is insufficient. Tend not to serve as a protective layer. If the thickness exceeds 500 nm, the internal stress of the dielectric itself and the difference in elastic characteristics with the substrate become remarkable, and cracks are easily generated.

In particular, the protective layer (lower protective layer) inserted between the substrate and the recording layer needs to suppress substrate deformation due to heat, and is preferably 50 nm or more. Below 50 nm,
During the repeated overwriting, microscopic substrate deformation is accumulated, and the reproduction light is scattered, so that the noise rises remarkably. The lower protective layer has a practical upper limit of about 200 nm in view of the film formation time. However, if the thickness is larger than 200 nm, the groove shape on the recording layer is not preferable because it greatly changes from the groove shape on the substrate. That is, the groove depth becomes shallower than the intended shape on the substrate surface, and the groove width becomes smaller than the intended shape on the substrate surface, which is not preferable. More preferably, it is 150 nm or less.

On the other hand, the protective layer (upper protective layer) inserted between the recording layer and the reflective layer needs to be at least 10 nm in order to suppress deformation of the recording layer. On the other hand, if the thickness is more than 50 nm, microscopic plastic deformation is liable to accumulate in the upper protective layer repeatedly during overwriting, which undesirably scatters reproduction light and increases noise.
According to the experiment, the thinner the upper protective layer thickness is in the range of 10 to 50 nm, the smaller the deterioration during repeated overwriting becomes. At the time of recording at a relatively low linear velocity, the thickness of the upper protective layer is desirably less than 30 nm if importance is placed on repeated overwrite durability.

When recording at a high linear velocity, a high laser power is required if the recording sensitivity is the same. Therefore, it is preferable to increase the recording sensitivity, and it is therefore preferable to make the protective layer relatively thick. It is valid. For example, when recording at a linear velocity of 9 m / s or more, the thickness of the upper protective layer is preferably about 25 to 50 nm. In order to widen the usable linear velocity range even when the recording linear velocity is low, it is effective to increase the thickness of the reflective layer. In some cases, it may be effective to increase the thickness of the protective layer. At this time, the thickness of the upper protective layer is 25 to 5
About 0 nm is preferable. The thickness of the recording layer is from 10 nm to 3
A range of 0 nm is preferred. If the thickness of the recording layer is less than 10 nm, it is difficult to obtain a sufficient contrast between the reflectance of the crystal and the amorphous state, and the crystallization speed tends to be slow, so that it is difficult to perform recording and erasing in a short time. . 30
If it exceeds nm, optical contrast is still difficult to obtain, and cracks tend to occur, which is not preferable.

When the thickness is less than 10 nm, the reflectance is too low, and when the thickness is more than 30 nm, the heat capacity is increased and the recording sensitivity is apt to deteriorate. Furthermore, the recording layer thickness is 30 nm.
If it is thicker, the volume change accompanying the phase change will be remarkable, and the recording layer itself and the upper and lower protective layers will have a remarkable effect on the repetitive volume change due to repetitive overwriting, and microscopic and irreversible deformation will accumulate, causing noise. It is easy to be. result,
Overwrite durability decreases repeatedly. In a high-density recording medium such as a rewritable DVD, the demand for noise is more severe.
It is preferred that: The recording layer is formed by directing the alloy target to DC (direct current) or RF in an inert gas, particularly Ar gas.
It is generally obtained by (high frequency) sputtering. Further, the density of the recording layer is desirably 80% or more, more preferably 90% or more of the bulk density. Here, the bulk density can be measured by, of course, preparing an alloy ingot. In the above equation (1), the molar concentration of each component is set to the atomic% of each element, and the bulk density is set to each element. May be used instead of the approximate molecular weight.

In the sputtering method, the density of the recording layer is reduced by lowering the pressure of a sputter gas (a rare gas such as Ar) at the time of film formation or by disposing a substrate close to the front of the target. It is necessary to increase the amount of high-energy Ar irradiated to the substrate. High-energy Ar means that Ar ions irradiated to the target for sputtering are partially rebounded and reach the substrate side, or Ar ions in the plasma are accelerated by the sheath voltage on the entire surface of the substrate and reach the substrate. Is one of Such an irradiation effect of a high-energy rare gas is called an atomic peening effect.

In sputtering using Ar gas, which is generally used, Ar is mixed into a sputtered film by an atomic peening effect. Depending on the amount of Ar in the film, ato
The mic peening effect can be estimated.
That is, if the amount of Ar is small, it means that the high-energy Ar irradiation effect is small, and a film having a low density is easily formed. On the other hand, when the amount of Ar is large, irradiation with high-energy Ar is intense and the density becomes high, but Ar taken in the film precipitates as voids during repeated overwriting, thereby deteriorating the durability of repetition. An appropriate amount of Ar in the recording layer film is 0.1 atomic% or more and less than 1.5 atomic%. Further, it is preferable to use high-frequency sputtering rather than DC sputtering because the amount of Ar in the film is reduced and a high-density film can be obtained.

The reflective layer is preferably made of a material having a high reflectivity.
In the present invention, a metal having high reflectivity, such as Au, Ag, or Al, which has a high thermal conductivity and can be expected to have a heat radiation effect even through the upper dielectric layer, or an alloy containing this as a main component is used. In order to control the thermal conductivity of the reflective layer itself and improve corrosion resistance,
Ta, Ti, Cr, Mo, Mg, V, Nb, Zr, M
An alloy in which n, Si, or the like is added in a small amount, for example, 15 at% or less is preferable. In particular, Al ₁ -z _Taz (0 <z ≦ 0.15)
The alloy is excellent in corrosion resistance and is effective in improving the reliability of the present optical information recording medium. The thickness of the reflective layer is preferably 50 nm or more in order to completely reflect incident light without transmitted light. When the film thickness is larger than 500 nm, the heat radiation effect is not changed and the productivity is unnecessarily deteriorated.
Further, it is preferable to set the thickness to 500 nm or less because cracks are easily generated. The thickness of the upper protective layer is 40 to 50.
In particular, in the case of nm or less, the amount of impurities contained is set to less than 2 atomic% in order to increase the thermal conductivity of the reflective layer.

The recording layer, the protective layer, and the reflective layer described above 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 layer, a target for a protective layer, and if necessary, a target for a reflective layer material are installed in the same vacuum chamber, in order to prevent oxidation and contamination between layers. It is also excellent in productivity. Next, a method for initializing the optical information recording medium of the present invention will be described. Since the recording layer of the optical information recording medium of the present invention is amorphous in the as-depo state (the state immediately after film formation), the entire surface of the disk is crystallized in a short time in order to make the initial state a crystalline state. There is a need to. This step is called initial crystallization. Usually, this initial crystallization is performed by irradiating a rotating disk with a laser beam focused to several tens to hundreds of microns.

In particular, melting initialization is effective for shortening the time required for initialization and for surely performing initialization with one light beam irradiation. In addition, as long as the recording medium has a sandwich structure in the protective layer, the recording medium is not immediately destroyed just because it is melted. For example, a light beam (gas or semiconductor laser light) focused to a diameter of about 10 to several hundred μm or a major axis of 50 to several hundred μm and a minor axis of 1 to 10 μm
By locally heating using a light beam converged in an elliptical shape of about m and melting only at the center of the beam, the recording medium will not be destroyed. In addition, the cooling rate is slowed down due to the preheating of the molten part due to the heating around the beam,
Good recrystallization is performed. By using this method, for example, the initialization time can be reduced to one tenth of that of the conventional solid-phase crystallization, the productivity can be significantly reduced, and the change in crystallinity at the time of erasing after overwriting can be reduced. Can be prevented.

Next, a preferred optical recording method for the optical information recording medium of the present invention will be described. By using the following recording method in combination with the medium of the present invention, the cooling rate at the time of re-solidification of the recording layer can be accurately controlled, and the characteristics of the recording layer material of the present invention suitable for mark length recording become clearer. FIG. 1 is a diagram showing an example of the recording method of the present invention. Assuming that a mark length that can be taken in mark length modulation recording is nT (T is a reference clock cycle and n is an integer of 2 or more), a record mark modulated to a mark length of nT is formed. Between the recording marks, a recording light having an erasing power Pe that can crystallize the amorphous is irradiated. When recording a mark having a length of nT, the recording light is divided according to the following equation.

[0029]

Η ₁ T, α ₁ T, β ₁ T, α ₂ T, β ₂ T,.
.., α _i T, β _i T,..., Α _m T, β _m T, η ₂
T

(Where m is the number of pulse divisions and m = n−
k and k are integers satisfying 0 ≦ k ≦ 2. Also, Σ _i (α _i
+ Β _i ) + η ₁ + η ₂ = n, η ₁ is a real number satisfying η ₁ ≧ 0, η ₂ is a real number satisfying η ₂ ≧ 0, and 0 ≦ η ₁ + η ₂ ≦ 2.0
And α _i (1 ≦ i ≦ m) is a real number satisfying α _i > 0,
β _i (1 ≦ i ≦ m) is a real number satisfying β _i > 0, and α _i ≦ β
_i (2 ≦ i ≦ m−1). That is, the recording light is m = nk (an integer satisfying 0 ≦ k ≦ 2).
And dividing the recording pulse width into α _i T
And β _i T (where 2 ≦ i ≦ m
Α _i ≦ β _i for _i = 1. ) Is accompanied by an off-pulse period of time.

In the recording pulse section α ₁ T to α _m T, Pw is sufficient to melt the recording layer and form an amorphous mark.
The recording light having a recording power Pw of Pe is applied. In the off-pulse section β ₁ T to β _m T, the recording light of the bias power Pb is irradiated, and Pb is 0 <in the range of 1 ≦ i ≦ m−1.
Pb ≦ １ ／ Pe, and when i = m, 0 <Pb ≦ Pe. However, in order to obtain an accurate nT mark when the mark length is detected, sections η ₁ T and η ₂ T are provided before and after the recording pulse section and the off pulse section, respectively.
_It can be adjusted so that _i (α _i + β _i ) + η ₁ + η ₂ = n. Note that η ₁ is a real number satisfying η ₁ ≧ 0, η ₂ is a real number satisfying η ₂ ≧ 0, and 0 ≦ η ₁ + η ₂ ≦ 2.0. η
₁ T, the eta ₂ T become section irradiates the recording light of erasure power Pe.

The optical information recording medium of the present invention provides the above-mentioned off-pulse section and provides three values including the bias power Pb, rather than recording with the recording light modulated only by the two values of the recording power Pw and the erasing power Pe. It is desirable to perform recording with the recording light modulated in step (1). Although overwrite recording by binary modulation is possible, the power margin and the linear velocity margin during recording can be expanded by using the ternary modulation method.
In particular, in the recording layer of the present invention, it is preferable that the bias power Pb at the time of off-pulse is sufficiently low, and 0 <Pb ≦ 1 / 2P
e. The effect of the magnitude of the bias power Pb on the recording layer temperature will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating the time change of the recording layer temperature. α _i = β _i = 0.
5, the temperature change of the recording layer is schematically shown when Pb is increased and Pb = Pe (a), and when Pb is reduced and Pb ≒ 0 (extreme case) (b). .

The position where the first pulse of the three divided pulses is irradiated is assumed. In (a), since the influence of heating by the subsequent recording pulse extends forward,
Since the cooling rate after the first recording pulse irradiation is low and Pe is irradiated even in the off-pulse section, the minimum temperature TL reached by the temperature drop in the off-pulse section stays near the melting point. On the other hand, in (b), since Pb in the off-pulse section is almost 0, the TL drops to a point sufficiently lower than the melting point, and the cooling rate in the middle is high. The amorphous mark is melted during the first pulse irradiation, and is formed by rapid cooling during the subsequent off-pulse. As described above, it is considered that the recording layer in the phase change medium of the present invention shows a large crystallization rate only near the melting point. Therefore, taking the temperature profile shown in FIG. 2A is important for suppressing recrystallization and obtaining a good amorphous mark. Conversely, by controlling the cooling rate and the TL, recrystallization is almost completely suppressed, and an amorphous mark having a clear contour substantially matching the molten region is obtained, so that low jitter is obtained at the mark edge.

On the other hand, in the case of the GeTe-Sb ₂ Te ₃ pseudo binary alloy, there is no significant difference in the process of forming an amorphous mark in any of the temperature profiles of FIGS. 2 (a) and 2 (b). The reason for this is that although the rate is slightly slower over a wide temperature range, recrystallization occurs. In this case, a certain degree of recrystallization occurs regardless of the pulse division method, which tends to result in coarse grains around the amorphous mark and deteriorate the jitter at the mark end. In this recording layer composition, an off-pulse is not essential, but rather, overwriting by conventional binary modulation is desirable.

[0035]

(Example 1) (ZnS) ₈₀ on a 1.2 mm thick polycarbonate substrate
(SiO ₂ ) ₂₀ Lower protective layer (95 nm), SbGeIn
Recording layer (17 nm), (ZnS) ₈₀ (SiO ₂ ) ₂₀ Upper protective layer (40 nm), Al _95.5 Ta _0.5 reflective layer (200
nm) were sequentially formed by a sputtering method, and a protective coat made of an ultraviolet curable resin was further applied thereon. The recording layer was obtained by simultaneously sputtering an Sb ₇₀ Ge ₃₀ target and an Sb ₅₀ In ₅₀ target. At the time of sputtering, the Ar gas pressure was set to 0.4 Pa, and Sb ₇₀ Ge
RF (high frequency) power of 200 W was applied to ₃₀ targets. Sb ₅₀ an In ₅₀ to about 20W at the target in the current control
Of DC (direct current) power was applied.

The composition of the obtained film was Sb ₆₉ Ge ₂₁ In ₁₀ (x = 0.767). The protective layer is (ZnS) ₈₀ (S
iO ₂ ) ₂₀ target was obtained by RF sputtering. The reflective layer is made of Al _95.5 Ta _0.5 target
C was obtained by sputtering. The disc is rotated, and a 520 mW laser beam narrowed to an elliptical shape having a major axis of about 100 μm and a minor axis of about 2 μm is irradiated so that the major axis direction forms an angle of about 40 degrees with the radial direction of the disc, and the laser beam is emitted.
Initial crystallization was performed while moving the laser beam in the radial direction at a feed rate of μm / rotation. Next, at a wavelength of 780 nm,
The following recording and measurement were performed using an optical system of NA 0.55.

[0037] The display is adjusted so that the linear velocity becomes 2.4 m / s.
The EFM random signal (3T ~ 11T) to 1
Overwrite recording was performed 00 times. The recording pulse is shown in FIG.
Pw = 11 mW, Pe = 5.5 mW, P
b = 0.8 mW, k = 1, η ₁= 0.5, η_Two= 0, α
₁= 1, α_Two~ Α_Ten= 0.5, β₁~ Β_Ten= 0.5, T
= 115.7 ns. Jitter between 3T marks of recording signal
The measured value was 16.1 ns. In addition,
If the linear velocity is 2.4 m / s, the speed should be 17.5 ns or less.
Signal can be read without any inconvenience. Now, as described above, I
The nSb-based low-reflectance crystal phase is the same as the high-reflection crystal phase used in this example.
Adversely affects the phase change recording between the crystalline and amorphous phases
It is thought that. The easiness of the phase change to the low reflectance phase is D
Due to the change in reflectivity when the C laser beam is irradiated several times
Since it can be estimated, the following experiment was performed. Line on this disc
Irradiating 6 mW DC light 10 times at a speed of 2.4 m / s
At this time, the reflectance changed from 16.0% to 15.9%.
The rate of change is very small, and it is difficult to change phase to a low reflectance phase
Can be estimated.

Example 2 A disc was produced in the same manner as in Example 1 except for the conditions for producing the recording layer. The recording layer is Sb ₆₈ Ge ₁₇
It was obtained by simultaneously sputtering an In ₁₅ target and a Ge target. At the time of sputtering, the Ar gas pressure was set to 0.4 Pa, and RF power of 200 W was applied to the Sb ₆₈ Ge _{17 In 15} target. About 10 W of DC power was applied to the Ge target by current control. The composition of the obtained film was Sb ₆₆ Ge ₁₉ In ₁₅ (x = 0.77).
6). As a result of performing the same recording and measurement as in Example 1,
The jitter between 3T marks is 14.3 ns at a linear velocity of 2.4 m / s.
Met. The jitter is 1 at a linear velocity of 2.4 m / s.
If it is less than 7.5 ns, the signal can be read without any inconvenience.
When this disk was irradiated 10 times with 6 mW DC light at a linear velocity of 2.4 m / s, the reflectance was 22.1% to 21.3.
%, But the rate of change is small, and it can be estimated that the phase does not easily change to the low reflectance phase.

Example 3 A disk was manufactured in the same manner as in Example 1 except for the conditions for manufacturing the recording layer. The recording layer is Sb ₆₈ Ge ₁₇
Obtained by sputtering an In ₁₅ target. At the time of sputtering, the Ar gas pressure was 0.4 Pa,
RF power of 200 W was applied to the Sb ₆₈ Ge ₁₇ In ₁₅ target. The composition of the obtained film was Sb ₇₀ Ge ₁₄ In ₁₆ (x = 0.833). Recording and measurement were performed in the same manner as in Example 1 except for the recording pulse strategy. However, since the disc has a large amount of Sb in the recording layer and a high crystallization speed,
The recording pulse was Pw = 11 mW and Pe = 5.5 m in FIG.
W, Pb = 0.8 mW, k = 1, η ₁ = 0.5, η ₂ =
0, α ₁ = 0.65, α _{2 to} α ₁₀ = 0.15, β _{1 to} β
₁₀ was changed to 0.85, and T was changed to 115.7 ns. The jitter between 3T marks was 12.5 ns at a linear velocity of 2.4 m / s. The jitter was 17.5 at a linear velocity of 2.4 m / s.
If it is less than ns, the signal can be read without inconvenience.

Next, the linear velocity was set to 9.6 m / s, and the recording pulse was Pw = 13 mW, Pe = 6.5 mW, and Pb =
0.8 mW, k = 1, η ₁ = 0.5, η ₂ = 0, α ₁ =
1, α _{2 to} α ₁₀ = 0.5, β _{1 to} β ₁₀ = 0.5, T = 2
The EFM random signal was overwritten 100 times at 8.9 ns. The jitter between 3T marks was measured at a linear velocity of 2.4 m / s and found to be 14.3 ns.
Thus, this disk has a linear velocity of 2.4 m / s to 9.6 m.
Good recording characteristics were obtained in a wide linear velocity range of / s. DC light of 6 mW at a linear velocity of 2.4 m / s was applied to this disk for 1 minute.
When irradiated 0 times, the reflectance is 23.1% to 22.5%
However, the rate of change is small, and it can be estimated that the phase does not easily change to the low reflectance phase.

Comparative Example 1 A disc was produced in the same manner as in Example 1 except for the conditions for producing the recording layer. The recording layer was obtained by simultaneously sputtering an Sb target and a Ge target. At the time of sputtering, Ar gas pressure 0.4 Pa
The RF power of 200 W was applied to the Sb target. About 20-90 W of D is controlled by current control for Ge target.
C power was applied. The obtained films were of 5 types and the composition was S
b ₉₃ Ge ₇ , Sb ₈₈ Ge ₁₂ , Sb ₈₄ Ge ₁₆ , Sb ₇₅ Ge
₂₅ and Sb ₆₆ Ge ₃₄ . Recording and measurement were performed in the same manner as in Examples 1 to 3, but the jitter between 3T marks was 29 ns or more at a linear velocity of 2.4 m / s, regardless of the combination of any disk, pulse strategy, and linear velocity. Had a problem.

Comparative Example 2 A disc was produced in the same manner as in Example 1 except for the conditions for producing the recording layer. The recording layer is Sb ₇₀ Ge ₃₀
It was obtained by simultaneously sputtering a target and an Sb ₅₀ In ₅₀ target. At the time of sputtering, Ar
The gas pressure was 0.4 Pa, and 2 for the Sb ₇₀ Ge ₃₀ target.
00W RF power was applied. DC power of about 60 W was applied to the Sb ₅₀ In ₅₀ target by current control. The composition of the obtained film was Sb ₆₁ Ge ₁₇ In ₂₂ (x = 0.7
92). When this disk was irradiated 10 times with 6 mW DC light at a linear velocity of 2.4 m / s, the reflectance changed from 17.9% to 16.4%. It was presumed that the rate of change was large and the phase was easily changed to a low reflectance phase.

[0043]

As described above, the optical information recording medium of the present invention has a crystallization speed in an appropriate range, has low recording signal jitter, and has excellent recording signal characteristics. Further, when the recording method of the present invention is used together, mark length modulation recording with low jitter and excellent recording signal characteristics can be performed.

[Brief description of the drawings]

FIG. 1 shows an example of a recording method according to the present invention.

FIG. 2 is a schematic diagram illustrating a time change of a recording layer temperature.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/24 538 G11B 7/24 538F

Claims (4)

[Claims] 1. A rewritable optical information recording medium having a phase change type recording layer, wherein the recording layer is composed of (Sb _x G
e _1-x ) _1-y In _y (where 0.65 ≦ x ≦ 0.95,
An optical information recording medium comprising an alloy of 0 <y ≦ 0.2) as a main component. 2. The condition of 0.7 ≦ x ≦ 0.85, 0.05 ≦ y ≦
2. The optical information recording medium according to claim 1, which is 0.2. 3. The optical information recording medium according to claim 1, wherein the medium has at least a dielectric protective layer, a phase-change recording layer, a dielectric protective layer, and a reflective layer provided on a substrate. Medium. 4. When erasing mark-length modulated information on a recording medium according to claim 1 with a plurality of recording mark lengths, an erasure that can crystallize an amorphous phase between the recording marks. When the recording light of power Pe is irradiated and the time length of one recording mark is set to nT (T is a reference clock cycle, n is an integer of 2 or more), the time length nT of the recording mark is expressed as follows. 1] η ₁ T, α ₁ T, β ₁ T, α ₂ T, β ₂ T,.
.., α _i T, β _i T,..., Α _m T, β _m T, η ₂
T (where m is the number of pulse divisions, m = nk, k is 0 ≦ k
≤2. Also, Σ _i (α _i + β _i ) + η ₁
+ Η ₂ = n, η ₁ is a real number satisfying η ₁ ≧ 0, η ₂ is η ₂
A real number satisfying ≧ 0, and 0 ≦ η ₁ + η ₂ ≦ 2.0. α
_i (1 ≦ i ≦ m) is a real number satisfying α _i > 0, and β _i (1 ≦ m)
i ≦ m) is a real number satisfying β _i > 0, and α _i ≦ β _i (2 ≦ i)
≤ m-1). ) And α _i T (1 ≦ i ≦
In the time of m), Pw required to melt the recording layer
> Pe is applied to the recording light having a recording power Pw, and β _i T
Within the time of (1 ≦ i ≦ m), 0 <Pb ≦ 0.5
An optical recording method for an optical information recording medium, characterized by irradiating recording light having a bias power Pb of Pe (however, in β _m T, 0 <Pb ≦ Pe).