JP2001236690A - Optical information recoding medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase transition medium in which the groove signal is specified to give compatibility with the CD format although the medium has low reflectance, and which has high contrast and little deterioration in many times of data rewriting. SOLUTION: In the optical information recording medium having a lower protective layer 3, phase trasition type recording layer 4, upper protective layer 5, and reflection layer 6 formed in this order on a substrate 1 having wobbling guide grooves 2, the recording layer 4 consists of an alloy thin film having the composition of Mw(SbzTe1-z)1-w, wherein w and z satisfy 0<=w<0.3 and 0.5<z<0.9 and M is at least one kind selected from a group of In, Ga, Zn. Ge, Sn, Si, Cu, Au, Ag, Pd, Pt, Pb, Cr, Co, O, S and Se. The film thickness of the recording layer 4, the film thickness of the lower protective layer 3 and the depth and width of the guide groove 2 are specified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical disk capable of high-density recording using a rewritable phase change medium. More specifically, the present invention relates to a phase change medium in which a groove signal is limited so as to be compatible with a CD format while having a low reflectance, a high contrast is obtained, and the deterioration is small with respect to rewriting of data many times.

[0002]

2. Description of the Related Art In recent years, as the amount of information has increased, there has been a demand for a recording medium capable of recording and reproducing a large amount of data at a high density and at a high speed. . Optical discs include a write-once type, which allows recording only once, and a rewritable type, which allows recording / erasing as many times as desired.

Examples of the rewritable optical disk include a magneto-optical recording medium utilizing a magneto-optical effect and a phase change medium utilizing a change in reflectivity accompanying a reversible change in crystalline state. The phase change medium does not require an external magnetic field, and has the advantage that recording and erasing can be performed only by modulating the power of laser light, and the recording and reproducing apparatus can be downsized. Further, there is an advantage that it is possible to use a short wavelength light source to increase the recording density from a medium that can be recorded and erased at a wavelength of about 800 nm, which is currently mainstream, without changing the material of the recording layer and the like.

As such a phase change type recording layer material, a chalcogen-based alloy thin film is often used. For example, GeSbTe system, InSbTe system, GeSnTe
And AgInSbTe-based alloys. Currently, rewritable phase-change recording media that have been put into practical use
The erased state is changed to a crystalline state, and an amorphous bit is formed.

[0005] The amorphous bit is formed by heating the recording layer to a temperature higher than the melting point and rapidly cooling it. In order to prevent the recording layer from evaporating and deforming due to such a heat treatment, the recording layer is usually sandwiched above and below with a heat-resistant and chemically stable dielectric protective film. In the recording process, the protective layer promotes thermal diffusion from the recording layer, realizes a supercooled state, and contributes to the formation of amorphous bits.

[0006] Further, by adopting a four-layer structure in which a metal reflection layer is provided on the sandwich structure, heat diffusion is further promoted, and an amorphous bit is usually formed stably. 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 protective layer functions as a heat storage layer that keeps the recording layer at a high temperature sufficient for solid-phase crystallization.

In a phase change medium capable of so-called one-beam overwriting, the above-described erasing and re-recording steps can be performed only by intensity modulation of one focused light beam (Jpn. J. Appl. Phys., 26 (19
87), suppl. 26-4, p. 61-6
6).

In the phase change medium capable of one-beam overwriting, the layer structure of the recording medium and the circuit structure of the drive are simplified. For this reason, it is attracting attention as an inexpensive and high-density large-capacity recording system. In recent years, rewritable compact discs (CD-Erasable, CD-E) have been proposed ("CD-ROM professionala").
l, USA, September 1996, pp. 29-44, or Proceedings of the Phase Change Optical Recording Symposium, 19
1995, pp. 41-45).

In the CD-E, although it is difficult to be compatible with a CD including a high reflectance of 70% or more, 15-
Within the range of 25%, compatibility with CDs in terms of recording signals and groove signals can be ensured. At least, if an amplification system for covering the low reflectance is added to the reproduction system, the current C
Compatibility can be ensured in the category of D drive technology. FIG. 1 shows a schematic diagram of this. In the case of CD-E, a groove 2 is provided on a substrate 1 and recording in the groove is performed. It is considered that the groove 2 uses a meander including address information (particularly). Kaihei 5-210
No. 849).

The meander is frequency (FM) modulated at a carrier frequency of 22.05 kHz and its amplitude (Wobble)
Amplitude) is very small, about 30 nm, compared to the groove pitch of 1.6 μm. This meandering is called a wobble, and the meandering is frequency-modulated, and a signal incorporating address information of a specific position of a certain track is converted into an ATIP signal (Absolute Time In).
Pre-groove, a recordable write-once disc (CD-Recordable, CD-
R) ("CD Family", co-authored by Heitaro Nakajima, Takao Ibashi, Hiroshi Ogawa, Ohmsha (1992)
6), Chapter 4).

[0011]

In the recording process of the phase change medium, an extreme thermal cycle occurs in which the recording layer is melted and rapidly cooled to a melting point or less within several tens of nanoseconds. Even though it is covered with a dielectric protection layer, microdeformation and segregation accumulate over thousands to tens of thousands of repeated overwrites, and finally, optically recognizable noise rise, This leads to the generation of local defects on the order of microns (J. Appl. Phys., 78 (19)
95), pp 6980-6988).

Although significant improvements have been made by devising the material of the recording layer, the protective layer, and the layer configuration, there is essentially an upper limit to the number of rewritable times. One order of magnitude less than media.
In the low-reflectance CD-E medium described above, the recording condition is CD
Since the linear velocity is at most 6 times the linear velocity and the mark length modulation recording is performed, the direction is more severe from the viewpoint of repetitive overwrite durability.

In addition, according to the study of the present inventors, CDs
It has been found that the groove shape for ensuring the compatibility of the groove signal with the drive tends to reduce the repeated overwrite durability of the phase change medium. In other words, when recording is performed in a groove in a range of a groove shape (depth 20 to 100 nm, width 0.2 to 0.8 μm) that does not hinder tracking servo (push-pull and three-beam methods) with focused light having a wavelength of 780 nm. In order to make the push-pull signal after recording equal to the ROM standard (around 0.04 to 0.09) in order to obtain compatibility with the CD-ROM, the groove depth is less than 60 nm and the width is less. It is limited to the range of 0.3 to 0.6 μm (Japanese Patent Application Laid-Open No. H8-212550, but this patent does not take into account any repeated overwrite durability). This relationship is a parameter that hardly depends on the layer configuration of the phase change medium and is determined substantially only by the groove shape.

On the other hand, the narrower and deeper the groove width, the better the repetitive overwrite durability. According to the study by the present inventors, it has been found that the repetitive overwrite durability rapidly deteriorates when the groove depth becomes shallower than 50 nm. Therefore, in order to make the groove signal compatible with the conventional CD, it is necessary to sacrifice the overwrite durability to some extent, but it is desired to minimize the sacrifice.

On the other hand, along with the restrictions coming from the groove signal,
In a CD-E medium using a phase change medium, a new deterioration phenomenon that a wobble signal leaks into a recording signal due to repeated overwriting has been found. It is thought that if the groove is narrowed to eliminate the overwrite durability due to the shallow groove, the end of the recording light beam will cause thermal damage to the groove wall, and the deterioration of the signal derived from the wobble signal will be promoted. Can be

Further, the groove bottom is also deformed by the heat generated in the recording layer. The lower protective layer has a function of suppressing a temperature rise on the substrate surface by a thermal insulating effect and mechanically suppressing the deformation of the substrate.
S: An SiO ₂ mixed film or the like is widely used.

According to the studies made by the present inventors, both the overwrite durability and the productivity were both reduced due to the optical requirements for compatibility with the CD standard and the restrictions imposed on the thickness of the lower protective layer. It turned out to be extremely difficult to satisfy. Due to the additional conditions imposed for ensuring compatibility with the CD standard as described above, the number of repeatable times is further reduced by one digit or more, to about several thousand times.

The wobble is an indispensable technique for adding necessary address information for detecting an unrecorded area where information is to be recorded even in a rewritable CD. A method of using a rewritable CD medium to record and rewrite data in sector units, such as a magneto-optical disk, has not been established yet, but in that case, the number of rewrites to a specific sector must exceed 1,000. Is considered sufficiently, and the problem of deterioration due to the overwriting becomes more serious.

Improving the durability of repeated overwriting while maintaining compatibility with the current CD drive as much as possible has been an urgent issue in order to realize a highly reliable CD-E.

[0020]

That is, the gist of the present invention is that a lower protective layer, a phase-change recording layer, an upper protective layer, and a reflective layer are provided in this order on a substrate having a meandering guide groove, and the reflectivity is reduced. Is defined as an unrecorded state with a crystalline state of 15% or more and 25% or less, and a recorded state with an amorphous state having a reflectance of less than 10%.
In an optical information recording medium for recording / reproducing / erasing an amorphous mark by modulating the light intensity into two or more values using focused light from the surface of the substrate opposite to the recording layer in the guide groove,
The recording layer is M _w (Sb _z Te _1-z ) _1-w (where 0 ≦ w <
0.3, 0.5 <z <0.9, M is In, Ga, Zn,
Ge, Sn, Si, Cu, Au, Ag, Pd, Pt, P
b, Cr, Co, O, S, Se)
Wherein the film thickness of the lower protective layer is greater than 0 nm and 30 nm or less than the film thickness at which the reflectivity in the crystalline state is a minimum value. An object of the present invention is to provide an optical information recording medium.

Alternatively, a first lower protective layer, a second lower protective layer, a phase change type recording layer,
An upper protective layer and a reflective layer are provided in this order, and a crystal state having a reflectance of 15% or more and 25% or less is set as an unrecorded state and a reflectance of 10%.
The recording / reproducing / erasing of the amorphous mark is performed by using the focused light from the surface opposite to the recording layer of the substrate in the guide groove and modulating the light intensity into two or more values in the guide groove. In the optical information recording medium for performing the recording, the recording layer is formed of M _w (Sb _z
Te _1-z ) _1-w (0 ≦ w <0.3, 0.5 <z <0.9,
M is In, Ga, Zn, Ge, Sn, Si, Cu, A
u, Ag, Pd, Pt, Pb, Cr, Co, O, S, S
e), the thickness of which is at least 15 nm and at most 30 nm, the difference between the refractive index of the first lower protective layer and the refractive index of the substrate is less than 0.05, It is an object of the present invention to provide an optical information recording medium characterized in that the thickness of the lower protective layer is thinner than the minimum thickness at which the reflectance in the crystalline state becomes a minimum value by more than 0 nm and 30 nm or less.

The present invention relates to a CD-E using a phase change medium.
(Rewritable compact disc, CD-Erasabl
In the development process of e), attention was paid to the compatibility of groove signals, and A
This is because it has been found that forming a wobble for describing a TIP signal promotes deterioration during repeated overwriting. Before describing the detailed evaluation results, the structure and recording method of a phase change medium as used in the present invention will be described.

The optical recording medium of the present invention comprises a substrate
A transparent resin such as polycarbonate, acrylic, or polyolefin, or glass can be used. Among them, polycarbonate resin is the most preferable because it has the track record of being most widely used in CDs and is inexpensive.

It is desirable that the phase change type recording layer is covered with protective layers on the upper and lower sides. More preferably, as shown in FIG. 2, the substrate 1 / dielectric lower protective layer 3 / recording layer 4 /
It is desirable to have the structure of the dielectric upper protective layer 5 / reflective layer 6, and to coat the upper layer with ultraviolet or thermosetting resin (protective coat layer 7).

The recording layer 4, the protective layers 3, 5, and the reflective layer 6 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.

In order to prevent deformation due to high temperature during recording,
A lower protective layer 3 is provided on the surface of the substrate 1, and an upper protective layer 5 is provided on the recording layer 4, usually with a thickness of 10 to 500 nm. If the thickness of the protective layer made of a dielectric or the like is less than 10 nm, the effect of preventing the deformation of the substrate 1 or the recording film 4 is insufficient, and the protective layer tends not to serve as a protective layer. 5
When the thickness exceeds 00 nm, the internal stress of the dielectric itself and the difference in elastic characteristics with the substrate 1 become remarkable, and cracks are easily generated.

The material of the upper and lower protective layers is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. Generally, M which has high transparency and high melting point
g, Ca, Sr, Y, La, Ce, Ho, Er, Yb,
Ti, Zr, Hf, V, Nb, Ta, Zn, Al, S
oxides, sulfides, nitrides such as i, Ge, Pb, Ca, M
g, a fluoride such as Li can be used.

These oxides, sulfides, nitrides, and fluorides do not necessarily have 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. Considering the repetitive recording characteristics, a dielectric mixture is preferred. More specifically, a mixture of ZnS or a rare-earth sulfide and a heat-resistant compound such as an oxide, a nitride, and a carbide may be used.

The film density of these protective layers is 8 in the bulk state.
0% or more is desirable from the viewpoint of mechanical strength (T
Hin Solid Films, Vol. 278 (19
1996), pp. 74-81). When a mixture dielectric thin film is used, the theoretical density of the following equation is used as the bulk density. ρ (bulk density) = Σmi (molar concentration of each component i) ρi
(Single Bulk Density) In the present invention, particularly with respect to the lower protective layer, when the lower protective layer is formed as a single layer, its thickness is 70 nm or more and less than 150 nm, preferably 70 nm or more, and 90 n.
m or less. A preferable material is (ZnS) _1-X
(SiO ₂ ) _X (provided that 0.13 ≦ X ≦ 0.17), while a preferred embodiment of the upper protective layer has a thickness of 20
(ZnS) _1-Y (SiO ₂ ) _{Y of not} less than 30 nm and not more than 30 nm
(However, 0.18 ≦ Y ≦ 0.22).

When the lower protective layer has a two-layer structure, the difference between the refractive index of the first lower protective layer on the substrate side and the refractive index of the substrate is less than 0.05, and The thickness of the second lower protective layer is more than 0 nm and less than 30 nm thinner than the minimum thickness at which the reflectance in the crystalline state becomes a minimum, and the first lower protective layer and the second lower protective layer are combined. 70n
m or more and less than 150 nm, preferably 70 nm or more, 9
It is good to be 0 nm or less.

The recording layer of the medium of the present invention is a phase change type recording layer, and its thickness is in the range of 15 nm to 30 nm. This range is preferable in order to obtain a contrast that is compatible with a CD. If it is less than 15 nm, the reflectance is too low, and if it is more than 30 nm, the heat capacity becomes large and the recording sensitivity becomes poor.

[0032] From limit of the optical properties described later as a recording layer, composed mainly of Sb ₇₀ Te ₃₀ eutectic point near the SbTe _{alloy, M w (Sb z Te 1} -z) 1-w ( however, 0 ≦ w <0.
3, 0.5 <z <0.9, M is In, Ga, Zn, G
e, Sn, Si, Cu, Au, Ag, Pd, Pt, P
b, Cr, Co, O, S, Se)
An alloy thin film is used. This alloy thin film is stable in both crystalline and amorphous states, and is capable of high-speed phase transition between the two states. Further, it has the advantage that segregation hardly occurs when repeated overwriting is performed, and is the most practical material.

As a more specific and preferred example, AgαI
nβSbγTeη (where 3 <α <10, 3 <β <
8, 55 <γ <65, 25 <η <35, 6 <α + β <1
3, a recording layer having a composition of α + β + γ + η = 100). According to the study of the present inventors, by limiting the composition as described above, especially when overwriting the CD-E at a speed of at most about 6 times the linear velocity of the CD, repeated overwriting durability and stability over time are repeated. It was found that the composition can be selectively used as an excellent composition.

The linear velocity dependency is determined by the main components Sb and Te. % (Atomic%), it becomes difficult to form an amorphous mark at a low linear velocity.
5 at. %, The crystallization rate is too slow to be sufficiently erased. Within this range, the crystallization rate increases as the Sb / Te ratio increases, but the optimum composition is selected in consideration of the heat distribution determined by the layer configuration.

In has the effect of increasing the crystallization temperature and increasing the stability over time. In order to ensure the storage stability at room temperature, at least 3 at. % Or more is necessary. 8a
t. %, It is not preferable because phase separation is likely to occur and segregation is likely to occur due to repetitive overwriting.

Ag is used to facilitate initialization of the amorphous film immediately after film formation. 10a depending on initialization method
t. % Is sufficient, and too much is unfavorable because the stability with time is impaired. Ag and In
13 at. % Is not preferable because segregation is apt to occur during repeated overwriting.

Another example of a suitable recording layer is M _z G
e _y (Sb _x Te _1-x ) _{1 -yz} (where M is at least one of Ag and Zn, and 0.60 ≦ x ≦ 0.8
5, 0.01 ≦ y ≦ 0.20, 0.01 ≦ z ≦ 0.1
5, 0.02 ≦ y + z <0.30). This is the above AgInSbTe
It is possible to improve the ease of precipitation of the low melting point metal In and the In-containing alloy in the alloy.

The reflective layer is provided to increase the signal amplitude by more actively using 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, specifically, Au, Ag, Al, and the like. However, semiconductors such as Si and Ge may be used to increase the degree of freedom in optical design.

From the viewpoints of economy and corrosion resistance, Al is made of Ta, Ti, Cr, Mo, Mg, Zr, V, Nb, etc. at 0.5 at. % Or more and 5 at. % Or less is desirable. Particularly preferred are Ta and Ti. Generally, the thermal conductivity is controlled by utilizing the property that the thermal conductivity is reduced when the amount of impurities mixed with Al is large. In particular, the addition of Ta provides a highly corrosion-resistant material (Japanese Patent Application Laid-Open No. 1-167951). In addition, a maximum of 5 at. %, There is also an advantage that the thermal conductivity can be controlled over a wide range from 1/3 to 1/4 of pure Al.

The composition and thickness of the reflective layer are optimized from the viewpoint of controlling the cooling rate for cooling via the upper protective layer for forming an amorphous layer. If the thickness is too large, the sensitivity is lowered. If it is less than 50 nm, the cooling effect tends to be insufficient. In order to effectively utilize the cooling effect of the reflective layer, the thickness of the upper protective layer is desirably 20 nm or more and 30 nm or less.

More specifically, as a preferable example, as a layer constitution for obtaining a sufficient cooling effect without lowering the recording sensitivity, the thickness of the upper protective layer is as thick as 25 nm or more and 30 nm or less, and the heat conduction to the reflective layer is high. Al _1-V Ta _V , 0.01 ≦
V ≦ 0.02 is preferably set to 50 nm or more and 150 nm or less.

The thicknesses of the recording layer and the protective layer will be described in more detail. Considering the interference effect associated with the multilayer structure in addition to the mechanical strength and reliability limitations, the laser light absorption efficiency is good and the amplitude of the recording signal, that is, the contrast between the recorded state and the unrecorded state is large. Is chosen to be

In order to ensure compatibility as a CD-E, the degree of modulation specified by the CD standard must be set high. As shown in FIG. 3, the modulation degree is a signal strength Itop at the top of the 11T mark in a DC reproduction signal (a reproduction signal including a DC component) when an EFM signal is recorded, and
It is defined as the ratio I ₁₁ / I top to the signal amplitude I ₁₁ .
Itop actually corresponds to the reflectance in the groove of the unrecorded portion (crystal state). I ₁₁ is the intensity difference and the phase difference of the reflected light from the crystalline portion and the amorphous portion of the phase change medium is a problem.

The difference in reflected light intensity is basically determined by the difference in reflectance between the crystalline state and the amorphous state. On the other hand, when an amorphous mark recorded in a groove having a width smaller than about 1 μm is read by a focused light beam having a diameter similar to that of the amorphous mark, interference of a plane wave must be considered. That is, it is necessary to consider the phase difference between the amorphous mark and the reflected light in the crystalline state.

The phase difference δ is expressed by the following equation when reading a reflected light from a recording medium having the above-mentioned multilayer structure by inputting a reproducing light beam from the back surface of the substrate: δ = (phase of a reflected wave passing through a crystal region) − (Phase of reflected wave passing through amorphous region) (see FIG. 4). When δ is negative, the phase in the amorphous state is advanced, and when δ is positive, the phase in the crystalline state is advanced.

On the other hand, when groove recording is performed, a phase difference occurs due to the groove depth expressed by the following equation. Φ = (phase of reflected wave from groove portion) − (phase of reflected wave from land portion) When viewed from the light incident on the substrate surface, the land portion is farther and the phase advances, so that Φ <0. When Φ is added to the previous δ, local plane wave interference occurs in the focused light beam, the reflectance of the amorphous portion recorded in the groove decreases, and the reflection of a mere crystalline state and an amorphous state In some cases, the contrast may be higher than the rate difference. The condition for this is -π <δ <0. However, the phase can be irreducible with a period of 2π.

In the present invention, the lower protective layer and the recording
In a four-layer configuration provided with a layer, an upper protective layer, and a reflective layer,
The lower protective layer thickness dependency is most remarkable. Typical to FIG.
Of reflectivity and phase difference between crystal and amorphous
A calculation example is shown. FIG. 5A shows an example of the recording layer material of the present invention.
Ag_FiveIn₆Sb₆₀Te₂₉In the case of the recording layer, FIG.
Is a promising phase change media material but not suitable for the present invention.
e _{twenty two}Sb_{twenty five}Te₄₃This is the case of the recording layer. The refractive index of each layer is
Actual measured values are used. In addition, recording layer, upper protective layer, reflection
The layers are 20 nm, 22.5 nm, 200 nm, respectively.
did.

As far as the dependence on the lower protective layer is concerned, the change in amplitude is usually small and strongly depends on the denominator Itop, that is, the reflectivity of the crystalline state. Therefore, it is desirable that the crystal state reflectance be as low as possible. In the calculation example of FIG. 5, it is assumed n = 2.1 in _{(ZnS) 80 (SiO 2)} 20, the first minimum value d ₁ In 60nm or more, 80 nm or less, a second 250nm in minimum value d ₂ 270 nm
It becomes below. Thereafter, it changes periodically.

The thickness of the lower protective layer at which the reflectivity in the crystalline state is minimized is substantially determined only by the refractive index of the protective layer in a recording layer having a high reflectivity. This point can be understood from the fact that the minimum points are almost the same in both FIGS. 5 (a) and 5 (b).

If d ₁ and d ₂ are multiplied by 2.1 / n, a minimum point film thickness at almost another refractive index n can be obtained.
Since it is 1.8 to 2.3, d ₁ is at most about 85 nm. When the refractive index of the lower protective layer is smaller than 1.8, the reflectance at the minimum point increases, and the degree of modulation significantly decreases.
It is not preferable because it is less than 0.5. Conversely, if the ratio is 2.3 or more, the reflectance at the minimum point becomes too low to achieve 20%, and it becomes difficult to perform focusing and tracking servo, which is not preferable.

As described above, it is desirable for the phase difference to advance in the amorphous state as described above. However, if the influence is too large, the same effect as changing the groove shape at the same time as the recording occurs, so that the servo is not suitable. Easy to be stable. In particular, when the sum of the phase Φ due to the groove depth and the phase difference δ between the crystal and the amorphous becomes π, it is difficult to obtain a push-pull signal, which is not preferable.

The phase difference due to the groove depth is at most 0.08π in the case of the present invention. The phase difference δ is desirably less than 0.5π.

When the thickness of the recording layer is around 20 nm, FIG.
In this case, the phase difference δ is close to π near the minimum point of the crystal state reflectance, which is not preferable. Also, it is not preferable that the phase difference δ changes abruptly with a change in the thickness of the lower protective layer. It can be seen that the Ge ₂₂ Sb ₂₅ Te ₄₃ recording layer is not suitable for the recording medium of the present invention utilizing the minimum point of reflectance, although it has a composition near Ge ₂ Sb ₂ Te ₅ which is promising as a phase change medium.

In the recording layer according to the present invention in which an additive element of at most about 30 atomic% is added to the composition near the eutectic point of Sb ₇₀ Te ₃₀ ,
Optical characteristics almost similar to those in FIG. This is a major difference between Viewpoints of the conventional GeTe-Sb ₂ Te ₃ other inventions have been proposed in the pseudo binary alloy and the present invention.

Generally, the dielectric protective film is made of ZnS: SiO_Two
Even if it is a mixed film like_TwoO _FiveWith a compound like
Regardless, the deposition rate by sputtering compared to metal film
Is extremely slow, less than a fraction. For this reason, FIG.
The film thickness which becomes the second minimum value in the above is preferable because the film formation time is long.
I don't. From the viewpoint of productivity, the thickness of the lower protective layer is 150 n.
It is desirable to keep it below m. Because at present
The deposition rate of the conductor protection layer by sputtering is at most 15 nm.
/ Second, and it takes cost to take 10 seconds or more for the film formation.
Is to rise.

Further, the allowable value of the film thickness variation becomes severe, which is not preferable in production. That is, as can be seen from FIG. 5, if the reflectance deviates by Δd from the desired film thickness d ₀ , the reflectivity may be near the first minimum value d _{1 or} near the second minimum value d _2. fluctuate. Meanwhile, manufacturing the film thickness distribution is determined by some percentage relative to d _0, which is usually the limit of d ₀ ± 2 to 3% uniformity.

Therefore, as d ₀ is smaller, the variation width Δd of the film thickness is smaller.
Is small, and the reflectance variation in the disk surface or between disks can be suppressed, which is advantageous. An inexpensive stationary facing type sputtering apparatus having no substrate rotation mechanism has to adopt a film thickness near the _first minimum value d1 that can be mass-produced as a result.

On the other hand, in order to suppress the deformation of the substrate, a certain thickness of the lower protective layer is required. FIG. 6 shows the dependency of the repetitive overwrite durability on the thickness of the lower protective layer.
The groove width is almost constant at 0.55 μm. When the thickness of the lower protective layer is less than 70 nm, the durability is rapidly deteriorated. In particular, the jitter sharply increases in the early stage when the number of repetitions is less than several hundred. The deterioration of the jitter at the initial stage of repetition remarkably depends on the thickness of the lower protective layer.

According to observations made by the present inventors using an atomic force microscope (AFM), this initial deterioration is caused by the fact that the substrate surface has a thickness of 2 to 3n.
It was found that this was due to deformation by about m m. In order to suppress substrate deformation, it is necessary to have a heat insulating effect to prevent heat generation of the recording layer and to have a protective layer film thickness that mechanically suppresses deformation. In order to achieve a durability of at least 1,000 times,
It is understood that 0 nm or more, preferably 80 nm or more is required.

Accordingly, in order to realize the overwrite durability of 1,000 times, which is the minimum required for this kind of rewritable medium while maintaining a high degree of modulation, it is necessary to keep Itop close to the minimum value as much as possible. It is necessary to aim for a thick film thickness. At this time, as can be seen from FIG. 5, the phase difference δ moves in a direction in which the amplitude cannot be obtained.
> 0, there is no problem if | δ | <0.5π. When δ> 0.5π, the phase difference has an adverse effect,
The expected amplitude cannot be obtained from the reflectance difference. Requirements for this is to employ a film thickness within the first 0~30nm than minimum point d _1.

As another form of the present invention, there is a method of positively utilizing the above-mentioned phase difference. Optically, the degree of modulation is large for the same reflectance difference, which is a preferable direction.
For this reason, it is preferable to use a lower protective layer that is thinner than 0 nm and 30 nm or less from the minimum point of the reflectance.

However, FIG. 6 clearly shows that the overwrite durability is insufficient. In order to solve this, the lower protective layer 3 is preferably divided into two layers, a first lower protective layer 3 'and a second lower protective layer 3 ", as shown in FIG.

The layer structure above the second lower protective layer 3 ″ is designed with priority given to optical characteristics, and the second lower protective layer 3 ″ is designed.
Is thinner than the minimum point of the reflectance by more than 0 nm and 30 nm or less, preferably 2 to 30 nm. The lower protective layer 3 is used to increase the mechanical strength by improving the total thickness of the first lower protective layer 3 ′ and the second lower protective layer 3 ″ to 70 nm or more and to improve the overwrite durability repeatedly.

At this time, by making the refractive index n ₁ of the first lower protective layer substantially equal to the refractive index nsub of the substrate, the film thickness can be freely designed independently of the optical design. That is, the optical requirements and the durability requirements can be virtually independently optimized. Ideally, n ₁ and nsub are exactly equal, but there is no practical problem if the difference is less than 0.05.

Ns of a typical polycarbonate resin substrate
ub is 1.55, so n ₁ is 1.5 to 1.
It is preferable to use the dielectric of No. 6. As a material for that purpose, specifically, SiO ₂ or ZnS and MgF ₂ or CaF ₂
There is a mixture with. A mixture of SiO ₂ , SiC, Y ₂ O _{3 and} a mixture of ZnS, SiO ₂ , MgF ₂ or CaF ₂ are excellent in their own durability and are more preferable. In this way, by adopting a layer configuration in consideration of the balance between high modulation, productivity, and repetitive overwrite durability, it is possible to substantially maintain CD compatibility except that the recording signal quality is low in reflectance.

In the following, an experimental example shows that when the compatibility of the groove signal is taken into consideration, the deterioration phenomenon due to repeated overwriting due to the groove shape becomes a problem.

A groove pitch of 1.6 was formed on an injection-molded polycarbonate substrate having a diameter of 120 mm and a thickness of 1.2 mm.
A groove having a width of about 0.5 μm and a depth of about 40 nm was provided on the spiral. A wobble is formed in the groove with a signal of 22.05 kHz in a direction transverse to the groove. Four types of wobble amplitudes were used: 27 nm, 20 nm, 13.5 nm, and 0 nm (no wobble). The wobble amplitude is determined by a measurement method defined by the CD-R standard, but the absolute value itself is a reference value, and it suffices if the relative magnitude can be managed.

On this substrate, as a lower protective layer (Zn
S)₈₀(SiO_Two)₂₀(Mol%) is 100 nm
Ag as a recording layer on top_FiveIn₆Sb₆₁Te₂₈Is 20 nm,
(ZnS) as upper protective layer₈₀(SiO_Two)₂₀20n
m, Al as reflective layer_97.5Ta_{Two .Five}Is successively multiplied by 100 nm
Layer, and a UV curable resin (SD318, Dainippon
(Made by Niki Co., Ltd.) to prepare a phase change medium.

The recording was performed in the groove, and an amorphous mark was formed in the crystalline region. For this medium, the so-called C
Overwriting is repeatedly performed using an EFM random signal for recording a mark length of 3T to 11T with respect to the reference clock period T as shown in FIG. 8A at twice the speed of D (2.8 m / s). Was. The EFM signal is used in the CD standard.

The recording uses a method of dividing the signal of each length into pulses shown in FIG. 8B, and the recording power Pw is 1
1 mW, erase power Pe is 6 mW, bias power Pb
Is 0.8 mW. The signal quality was evaluated with the strictest 3T jitter. FIG. 9 shows the results.

It is necessary for the CD standard that the jitter be less than about 17.5 nsec at 2 × speed. As is clear from FIG. 9, in the groove having no wobble amplitude, the jitter is hardly deteriorated even after 10,000 times of overwriting.
As the wobble amplitude increases, the deterioration becomes remarkable.
It can be seen that the deterioration becomes significant at about 00 times.

Although the mechanism of the deterioration promotion due to the presence of the wobble is not always clear, it is considered that a part of the recording light beam 9 is easily irradiated to the side wall 10 of the groove as shown in FIG. Can be

That is, the focused light beam 9 to which the tracking servo is applied does not follow the wobble meandering, but proceeds straight along the groove center. If there is a meandering of the groove wall 10, the light beam 9 is easily irradiated to the groove wall 10 though slightly, as shown in FIG. 10 (FIG. 10 shows the wobble amplitude exaggerated, but this tendency is correct). it is conceivable that). Groove wall 10
Is considered to be liable to deteriorate due to thermal damage during repeated overwriting because stress concentration is likely to occur at groove walls and groove corners where the adhesion of the thin film is poor, so even a part of the light beam is irradiated here If so, the deterioration would be accelerated.

FIG. 11 shows the repetitive overwrite durability when the wobble amplitude and the groove depth were kept constant at 20 nm and 31 nm, respectively, and the groove width was changed. The measurement method and the layer configuration were the same as in FIG. The initial jitter is about 10 nsec. In groove recording of a phase change medium, there is a tendency that the deeper the groove, the thinner the groove, the better the durability.
In the case where a wobble exists, it can be understood that if the groove width is too narrow, the above-described deterioration phenomenon of the groove wall portion becomes remarkable, so that the deterioration is remarkable.

That is, the groove width is limited from the viewpoint of repeated overwrite durability, and is 0.4 μm to 0.6 μm.
It is desirable that: More preferably 0.45μ
m or more and 0.55 μm or less.

From the viewpoint of CD compatibility, it is necessary to consider a groove signal as disclosed in, for example, JP-A-8-212550. The groove shapes specifically disclosed as preferable in this patent have a groove depth of 50 to 60 nm and a groove width of 0.3 to 0.6 μm. According to the study of the present inventors, in the layer configuration in consideration of the modulation degree, productivity, and repetitive overwrite durability, unless the groove depth is less than 45 nm, the push-pull value after recording is 0.1. It has been found that the radial contrast value after recording is 0.6 or more, which tends to be excessively large, which is excessively large as compared with the value before recording of 0.1 to 0.2, which causes a problem in servo stability. .

Here, the radial contrast RC is defined as follows. _{RC = 2 (I L -I G} ) / (I L + I G) where, I _L, the I _G land portions respectively, the reflected light intensity of the groove portion. The reflected light intensity is the sum signal I ₁ + I ₂ of the photodetectors arranged on the left and right with respect to the track center. Actually, the groove and land intensity of the track crossing signal obtained by applying only the focus servo is measured. Although defined before and after the recording, the radial contrast after the recording uses an intensity obtained by averaging the signal intensity of the reflectance reduction portion due to the recording by a low-pass filter.

On the other hand, the push-pull value PPa after recording is
Again, using the average value of the difference signal, PPa = (I ₁ −I ₂ ) / I top is defined.

Each of these is a general definition ("Compact Disc Reader", written by Heitaro Nakajima and Hiroshi Ogawa, Ohmsha, 1st Edition, Chapter 6, Section 6, etc.). It is specified in the CD standard (Red Book, Orange Book). Although the rewritable medium is the same CD compatible, the above patent stipulates the groove signal and the like related to the drive design. The specific configuration of the disk for implementing the same is as follows. It is. For this reason, the recommended value of the groove depth specifically exemplified is as deep as 50 to 60 nm.

It is considered that the difference from the above-mentioned published patent arises from the fact that the thickness of the lower protective layer exceeds the scope of the present invention. In other words, it is considered that if the thickness of the lower protective layer is large, the groove is filled and the groove shape seen from the recording layer surface becomes substantially shallow, so that it is necessary to set the groove shape deeper.

The present invention is different from the above-mentioned known documents in the overall design concept in that the layer configuration and groove shape of the recording medium are designed as a set in consideration of not only the optical characteristics but also the balance between reliability and productivity. It must be said that there are significant differences, and as a result, differences have been made in the embodiments.

On the other hand, if the groove depth is too shallow, it becomes difficult to manufacture a stamper or form a substrate, or it falls below the lower limit of radial contrast or push-pull.
It cannot be shallower than nm. Considering the dependence of the repetitive overwrite durability on the groove depth shown in FIG.
m is more desirable.

The groove width is desirably 0.45 μm or more from the viewpoint of radial contrast after recording, and 0.6 μm or less from the viewpoint of overwriting durability with respect to wobble and groove shape. If it is wider than 0.6 μm, it is not preferable because it is a general phenomenon of a phase change medium, and if it is smaller than 0.4 μm, deterioration due to overwrite durability due to the presence of wobble becomes unfavorable. More preferably, it is 0.45 μm or more and 0.55 μm or less. The present invention provides a low reflectance C
It has found specific strategies for overcoming the various constraints arising from the intention of rewritable media compatible with D, and for balancing between trade-off factors beyond a mere optimization procedure. If attention is paid only to the individual elements, it does not drastically exceed the preceding phase change medium technology, but the industrial utility value of the CD compatible rewritable medium is great.

[0084]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific example of a CD-E medium which has achieved high reliability and high productivity while taking compatibility with a CD into consideration will be described with reference to an embodiment. The present invention is not limited to the following examples unless otherwise described.

Examples 1-1 and 1-2 Tables 1 and 2 show that the wobble amplitude is constant, the repetitive overwrite durability when the groove width and groove depth are changed,
Optical characteristics and groove signal characteristics are summarized. The layer configuration used in the experiment was that the lower protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ was 80 nm,
Ag ₅ In ₅ Sb ₆₀ Te ₃₀ recording layer 20 nm, upper protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ 23 nm, reflective layer Al ₉₈
Ta ₂ is 100 nm.

The film density of the (ZnS) ₈₀ (SiO ₂ ) ₂₀ protective layer was 3.5 g / cm ³ and the theoretical bulk density was 3.72 g / cm ^3.
It was 94% of cm ³ . All thin films were formed by sputtering without releasing the vacuum. The substrate was prepared by injection molding. The composition of each layer was confirmed by a combination of fluorescent X-ray analysis, atomic absorption analysis, X-ray excited photoelectron spectroscopy, and the like. The recording layer immediately after film formation is amorphous, and has a linear velocity of 3 m by a bulk eraser (Hitachi Computer Equipment, POP120, trade name).
/ S was irradiated with an initializing power of 500 mW to crystallize the entire surface to obtain an initial (unrecorded) state. With this power, it is considered that the recording layer is once melted and crystallized to be re-solidified.

The thickness of the lower protective layer is the minimum point d of the reflectance in FIG.
₁ = 5 nm thicker than 75 nm. The substrate is 1.
1. Injection molding on a 2 mm polycarbonate substrate.
A wobble conforming to the CD-R standard (Orange Book, Part 2) such as amplitude, period and modulation signal is formed at a pitch of 6 μm.

For recording, the pulse strategy shown in FIG. 8 was used. The recording power Pw, erase power Pe, and bias power Pb were 12 mW, 6 mW, and 0.8 mW, respectively.
The best jitter was obtained near this power.
The recording optical head has a wavelength of 780 nm and NA = 0.55, and the linear velocity during recording is twice as high as the so-called CD linear velocity (2.
4 m / s).

The number of times of overwrite durability is the number of times that the jitter of the 3T mark is kept at 17.5 nsc or less, which is the upper limit of the CD standard, when overwriting is repeatedly performed at 2 × speed. The table also shows the radial contrast values RCb and RCa after recording. However, if the groove depth exceeds 45 nm due to deep groove formation, RCa exceeds 0.6, which is not preferable.

If the depth is more than 50 nm, the push-pull PPa after recording will exceed 0.1, which is not preferable. Further, the reflectivity in the groove was reduced to just below or below 15%, and the tracking servo became unstable. If the groove width is not in the range of 0.4 to 0.6 μm, the number of repeated overwrites of 1,000 cannot be achieved. If the groove depth is less than 25 nm, the radial contrast ratio before and after recording is much lower than 0.3, and the number of repeated overwrites is less than 500-600, which is not preferable.

Embodiment 2-1 and Embodiment 2-2 In Embodiment 2-1 and Embodiment 2-2, the lower protective layer is formed with two film thicknesses of 80 nm (75 nm and 250 nm) near the minimum reflectance (75 nm and 250 nm). Discs were produced in Example 2-1) and 260 nm (Example 2-2). All were prepared in the same sputtering apparatus. The film density of the protective layer is about 93
%Met.

The thickness of the recording layer Ag ₅ In ₆ Sb ₅₉ Te ₃₀ is 2
0 nm, upper protective layer thickness 23 nm, reflective layer 100 n
m. Optically equivalent characteristics can be obtained. But,
As a result of measuring the reflectance distribution, as shown in FIGS. 12 and 13, it was apparent that the reflectance distribution in the disk surface was larger at 260 nm in Example 2-2.

Here, FIGS. 12 and 13 show Embodiment 2 respectively.
1 shows the radial distribution of the reflectivity of disks -1, 2-2. In the figure, the center broken line indicates the average value at each radius, and the upper and lower dotted line indicates the maximum value and the minimum value at each radius. The average value of all measurement points is set to <Rto
p> is standardized by <Rtop>.

In the embodiment 2-2, including the circumferential distribution, the average values were in the range of + 11% and -7%. On the other hand, Example 2
At -1, the average value was within ± 6%. In this experiment, since a film thickness distribution having an average value of about 3% is generated in the sputtering film forming apparatus, distributions of about 2.5 nm and 8 nm are included, respectively. This is a very good distribution in the current stationary facing type sputtering apparatus.

On the other hand, the same film thickness change Δ
Since the reflectance changes by the same amount with respect to d, about ± 8 nm
In the case of Example 2-2 in which the distribution is also large, the reflectance distribution becomes large. It is desirable for the optical disk that the reflectivity distribution is within ± 10% within the same disk surface. From this perspective,
Since the film forming time and material cost are also reduced to about 1/3, it was clearly confirmed that it is desirable to use the lower protective layer film thickness near the first minimum point from the viewpoint of productivity.

Example 3 An Ag ₅ In ₅ Sb ₅₉ Te ₃₁ recording layer having a thickness of 20 nm and a thickness of (ZnS)
₈₀ (SiO ₂ ) _{20 The} upper protective layer was 23 nm, the Al ₉₈ Ta ₂ reflective layer was 100 nm, and the composition and thickness dependency of the lower protective layer ZnS: SiO ₂ were examined. The groove depth is 35 nm and the groove width is 0.53 μm.

ZnS: SiO_TwoRefractive index n of mixed film_abIs
ZnS (refractive index n_a= 2.3), SiO_Two(Refractive index n_b=
The ratio is determined in proportion to the molar ratio of 1.45). That is, (Z
nS) _1-m(SiO_Two)_mFor a composition of n_ab= N_a(1-m) + n_bm.

FIG. 14 shows that m = 0.15, 0.20, 0.
In the case of No. 25, the dependency of the reflectance and the modulation factor near the first reflectance minimum point on the thickness of the lower protective layer was shown. The degree of modulation is indicated by a numerical value near each point in the figure.

As the molar ratio of SiO ₂ increases and the refractive index decreases, the reflectance at the minimum point increases. In this case, the range in which the film thickness can be increased without greatly lowering the modulation degree is narrowed, and is at most about 5 nm. On the other hand, when the refractive index is increased by reducing SiO ₂ to m = 0.15, the reflectivity in the groove becomes 1
In order to maintain 5%, it is necessary to remove the minimum point. There is room for increasing the film thickness by 10 to 20 nm, and the overwrite durability can be improved while maintaining the same reflectance and modulation.

As shown in FIG. 6, in this film thickness region, 5n
It is advantageous for durability to increase the film thickness even if m. In fact, FIG.
FIG. 5 shows the results of evaluating the repeated overwrite durability of the lower protective layers shown as 1, 2, and 3 in FIG. 14 in the same manner as in FIG. In particular, it can be seen that the lower protective layer indicated by 3 in the figure is a preferred example of the present invention because the optical characteristics and the repeated overwrite durability are balanced.

However, the durability of the protective layer itself is m = 0.2
0 is the best and m less than 0.1 is not preferable. On the other hand, if m is larger than 0.3, there is a problem in stability over time, which is not preferable. The same composition is used for the upper and lower protective layers, or the lower protective layer is 0.13 ≦ m ≦ 0.1
7. Whether the upper protective layer has a slight difference in composition (refractive index difference) with 0.18 ≦ m ≦ 0.22 can be appropriately selected depending on the strictness of optical requirements.

Example 4 In the substrate and the layer structure of Example 1-1 (b), the recording layer
Only Zn_ThreeGe₈Sb ₆₁Te₂₈Change to alloy layer and
After creating a disc and initializing it with a bulk eraser,
Double the speed of CD by irradiating the recording pulse strategy of FIG.
Was overwritten. Pw = 13mW, Pe =
When 6.5mW and Pb = 0.8mW, jitter is clock
Period T = less than 10% of 115 nsec, modulation degree is 0.7
0, reflectance is 18.1%, PPa = 0.076, RCb
= 0.16, RCa = 0.51 (RCb / RCa = 0.
31) was obtained. 200 overwrite durability
0 or more times.

[0103]

[Table 1]

[0104]

[Table 2]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a wobble.

FIG. 2 is an explanatory diagram showing an example of an optical recording medium according to the present invention.

FIG. 3 is a diagram for explaining a modulation factor.

FIG. 4 is an explanatory diagram of a phase difference δ.

FIG. 5 is an explanatory diagram of a reflectance in a four-layer configuration and a phase difference between a crystal and an amorphous.

FIG. 6 is a diagram illustrating the relationship between overwrite durability and the thickness of a lower protective layer.

FIG. 7 is an explanatory diagram showing an example of an optical recording medium according to the present invention.

FIG. 8 is a diagram illustrating an example of an EFM random signal.

FIG. 9 is a diagram for explaining a change in overwrite characteristics due to a wobble amplitude.

FIG. 10 is an explanatory diagram of a relationship between a wobble and a recording light beam.

FIG. 11 is a diagram for explaining a change in overwrite characteristics depending on a groove width.

FIG. 12 is an explanatory diagram of the distribution of the reflectance of the disk according to the embodiment of the present invention.

FIG. 13 is an explanatory diagram of the distribution of the reflectance of the disk according to the embodiment of the present invention.

FIG. 14 is a diagram illustrating the dependency of the reflectance and the degree of modulation on the thickness of the lower protective layer.

FIG. 15 is a diagram illustrating overwrite durability with respect to the thickness of a lower protective layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Groove 3 Lower protective layer 4 Recording layer 5 Upper protective layer 6 Reflective layer 7 Protective coat layer

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) G11B 7/24 561 G11B 7/24 561M 561Q B41M 5/26 7/006 G11B 7/006 B41M 5/26 X (72) Inventor Maeda Kubo 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory (72) Inventor Kanako Tsuboya 1000-Kamoshida-cho, Aoba-ku Yokohama City, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory (72) Inventor Towa Horie 1000, Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Inside Mitsubishi Chemical Research Institute Yokohama Research Laboratory

Claims (6)

[Claims] 1. A lower protective layer, a phase-change recording layer, an upper protective layer, and a reflective layer are provided in this order on a substrate provided with meandering guide grooves, and a crystal state having a reflectance of 15% or more and 25% or less is formed. a recording state amorphous state than the reflectance of 10% as a recorded state, focusing from the surface opposite to the recording layer of the substrate within the guide groove
In an optical information recording medium for recording, reproducing, and erasing an amorphous mark by modulating light intensity into two or more values using light, a recording layer is formed of M _w (Sb _z Te _1-z ) _1-w ( However, 0 ≦ w <
0.3, 0.5 <z <0.9, M is In, Ga, Zn,
Ge, Sn, Si, Cu, Au, Ag, Pd, Pt, P
b, Cr, Co, O, S, Se) at least one alloy thin film having a thickness of 15 nm.
Or 30nm or less, the thickness of the lower protective layer, optical recording medium in which the reflectance is equal to or greater 30nm or less beyond 0nm than thickness which is a minimum value of the crystalline state. Wherein the lower protective layer thickness 70nm or more, 150
nm or less of the _{(ZnS) 1-X (SiO} 2) X ( where 0.
13 ≦ X ≦ 0.17 ) and the upper protective layer has a thickness of 20 n.
(ZnS) _1-Y (SiO ₂ ) of not less than m and not more than 30 nm
_Y (where 0.18 ≦ Y ≦ 0.22 ).
The optical information recording medium according to the above. 3. A first lower protective layer, a second lower protective layer, a phase change recording layer, an upper protective layer, and a reflective layer are provided in this order on a substrate provided with meandering guide grooves, and the reflectance is 15%. More than 25%
The following crystalline state is an unrecorded state, an amorphous state having a reflectance of less than 10% is a recorded state, and a light intensity of two or more values is obtained by using focused light from the surface of the substrate opposite to the recording layer in the guide groove. the modulation in optical recording medium for recording, reproducing, and erasing of amorphous marks, the recording layer _{M w (Sb z Te 1-} z) 1-w ( however, 0 ≦ w <
0.3, 0.5 <z <0.9, M is In, Ga, Zn,
Ge, Sn, Si, Cu, Au, Ag, Pd, Pt, P
b, Cr, Co, O, S, Se)
An alloy thin film having a thickness of 15 nm or more and 30 nm or less, wherein the difference between the refractive index of the first lower protective layer and the refractive index of the substrate is 0.0
Less than 5, and the film thickness of the second lower protective layer is more than 0 nm and 30 nm more than the minimum film thickness at which the reflectance in the crystalline state becomes the minimum value.
An optical information recording medium characterized by being thin below. 4. The guide groove has a depth of not less than 25 nm and not more than 45 nm and a width of not more than 0.5 nm. 4 μm or more 2. The method according to claim 1, wherein the thickness is 6 μm or less.
4. The optical information recording medium according to any one of items 1 to 3. 5. The film thickness of the lower protective layer or the total film thickness of the first lower protective layer and the second lower protective layer is 70 nm or more and 90 nm or less, and the film thickness of the upper protective layer is 10 nm or more and 30 nm or less. The reflective layer has an Al of 50 nm or more and 200 nm or less.
_1-V M _V (However, 0.005 ≦ V ≦ 0.05, M is Ta
Or the optical information recording medium according to any one of claims 1 to 4, which is Ti ) . 6. The phase change type recording layer is made of AgαInβSbγ.
Teη (however, 3 <α <10 , 3 <β <8, 55 <γ
<65, 25 <η <35, 6 <α + β <13, α + β +
The optical information recording medium according to any one of claims 1 to 5, wherein γ + η = 100 ) .