JP3731372B2 - Optical information recording medium, reproducing method and recording method thereof - Google Patents

Description

【００３６】
【表２】

【００３７】
【表３】

【００３８】
【発明の効果】
本発明によれば、信号強度が大きく、記録マークが安定に存在し、総合的にみて優れた相変化記録媒体が得られる。また、これに適した再生方法及び記録方法が提供できる。
【図面の簡単な説明】
【図１】本発明の記録方法における記録光のパワーパターンを示す模式図。
【図２】本発明の記録方法の効果を示す、記録層の温度変化を示す模式図。
【図３】実施例１、２及び比較例１における結果を示すプロット図（７８０ｎｍ）。
【図４】実施例１、２及び比較例１における結果を示すプロット図（６３５ｎｍ）。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-density optical disk using a rewritable phase change medium. Specifically, the present invention relates to a phase change medium having a large reproduction signal intensity in a wide wavelength range.
[0002]
[Prior art]
As a rewritable optical disc, a phase change medium using a change in reflectance accompanying a reversible change between a crystalline state and an amorphous state is known. The phase change medium does not require an external magnetic field and can be recorded / erased only by modulating the power of the laser beam, and has the advantage that the recording / reproducing apparatus can be downsized.
A general phase change medium is provided with a phase change recording layer on a substrate, and has protective layers made of a dielectric on both sides thereof. Further, it is usual that a reflective layer is further provided. In addition, the phase change type recording layer is usually formed with the unrecorded / erased state in the crystalline state and amorphous bits as the recording marks.
Conventionally, as such a phase change recording layer, an SbTe eutectic point composition (Sb₇₀Te₃₀A composition having an excess of Sb than that of (A) is known. For example, Japanese Patent Laid-Open No. 1-303643 discloses (Sb_1-xTe_x)_1-yM_y(M is at least one element selected from the group consisting of Ag, Al, As, Au, Bi, Cu, Ga, Ge, In, Pb, Pd, Pt, Se, Si, Sn, and Zn) Is used as a recording layer.
[0003]
[Problems to be solved by the invention]
Conventionally, although an alloy material in the vicinity of the eutectic point has a high amorphous forming ability, it is accompanied by phase separation during crystallization, so that it cannot be crystallized by heating in a short time of less than 100 nsec and can be overwritten. It has been considered that the recording layer is inappropriate.
On the other hand, the present inventor paid attention to such a binary alloy made of SbTe, and examined the crystallization / amorphization characteristics in the vicinity of the eutectic composition using an optical disk evaluation machine suitable for higher density recording. Went. As a result, Sb₇₀Te₃₀Although it is difficult to initially crystallize a recording layer mainly composed of an SbTe alloy in the vicinity of the eutectic composition, once the initial crystallization is performed, recording erasure by the amorphous-crystalline phase change can be performed at a very high speed. I found out that I can do it. Another advantage of using a composition near the eutectic point is that coarse grains having different reflectivities from the initialized state are less likely to occur in the periphery of the amorphous mark or in the erased mark. This is a phenomenon peculiar to an alloy near the eutectic point where crystal growth is rate-determined by phase separation. Furthermore, the above composition has the conventional Ge, especially when recording between marks.₂Sb₂Te_FiveSince a clear reproduction signal can be obtained from a recording layer having a composition in the vicinity, it is suitable for high density.
[0004]
However, according to the study of the present inventor, such Sb₇₀Te₃₀It has been found that an SbTe alloy containing excess Sb in the composition near the eutectic point does not function as a recording layer as it is. The reason is that the recorded amorphous mark crystallizes with time, and the mark tends to disappear. Since any phase change recording film is more stable in a crystalline state than an amorphous mark at room temperature, it is expected that it will crystallize after a sufficiently long time. However, as a recording medium, it is necessary that recording marks exist stably for at least 10 years. The Sbx Te1-x (0.6 <x <0.9) phase change film has a low crystallization temperature in the amorphous state of around 100 ° C., and the time for which a stable amorphous mark exists is too short. This is not suitable for a typical phase change recording film.
[0005]
In general, the phase change medium has a problem that the signal strength is not sufficient. The signal intensity can be increased by adjusting the film thickness of each layer such as a recording layer, a protective layer, and a reflective layer. However, in many cases, other characteristics deteriorate at the same time. The deteriorated characteristics are, for example, repetitive recording characteristics, reflectance, optimum recording power, recording linear velocity dependency, and the like. Therefore, in the current situation, the signal strength is not sufficient particularly when manufacturing with a certain margin in all the disk characteristics during mass production. In addition, the laser wavelength used to increase the recording density in recent years tends to be shortened, but the signal intensity tends to decrease as the phase change medium becomes shorter, so in the short wavelength region. The lack of signal strength becomes even more serious.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor has found that the stability of the amorphous mark can be improved by allowing a specific amount of a specific element to be present in a composition that is Sb-excess than the vicinity of the SbTe eutectic point. In addition, the present inventors have found that a phase change type recording medium utilizing the characteristics of the SbTe alloy can be obtained.
That is, the gist of the present invention is an optical information recording medium having at least a phase change recording layer on a substrate, wherein the phase change recording layer has a composition represented by the following general formula (I). It is a characteristic optical information recording medium.
[0007]
[Chemical Formula 3]
      ((Sb_x  Te_1-x)_y  Ge_1-y)_z  Al_1-z (I)
(Where x is a number in the range of 0.6 ≦ x ≦ 0.9, and y is0.9≦ y <1 is the number in the range, and z is the number in the range of 0.95 ≦ z <1. )
[0008]
[Action]
Although details are not clear, it is presumed that the amorphous mark can be stabilized by adding Ge to a composition richer in Sb than in the vicinity of the SbTe eutectic point. Further, it is presumed that the presence of Al increases the signal intensity and further increases the crystallization speed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
One of the features of the present invention is that as the composition of the recording layer,
[0010]
[Formula 4]
((Sb_xTe_1-x)_yGe_1-y)_zAl_1-z
[0011]
It is to use what becomes.
Here, although x is 0.6-0.9, a preferable lower limit is 0.7 and a preferable upper limit is 0.8. If x is too large, the crystallization rate becomes too high and amorphous tends to be difficult to form. On the other hand, if it is too small, the crystallization rate tends to be too slow to make it difficult to crystallize.
As can be seen from the above description, in the present invention, the crystallization rate can be controlled by the Sb / Te ratio. That is, the amount of excess Sb relative to the base SbTe eutectic point composition is one factor that determines the crystallization rate. If Sb increases, it is considered that Sb cluster sites that precipitate in a rapidly cooled state increase and crystal nucleation is promoted. This means that even if the same crystal growth rate is assumed from each crystal nucleus, the time required for filling with the grown crystal grains is reduced, and as a result, the time required for crystallizing the amorphous mark is reduced. Means. Therefore, it is advantageous when erasing is performed by laser beam irradiation for a short time at a high linear velocity. On the other hand, the cooling rate of the recording layer also depends on the linear velocity during recording. That is, even with the same layer configuration, the cooling rate decreases as the linear velocity decreases. Therefore, the lower the linear velocity, the smaller the critical cooling rate for amorphous formation, that is, the smaller the amount of excess Sb. In summary, based on the SbTe eutectic point composition, it can be said that a composition having a larger amount of excess Sb is suitable for a higher linear velocity.
[0012]
  Also,y is 0.9 or more and less than 1,The upper limit is preferably 0.97 or less. If y is too large, it is difficult to maintain low jitter characteristics at a high density for a long period of time, and the effect of the present invention tends to be insufficient. On the other hand, if y is too small, noise during recording increases, and it tends to be difficult to reduce jitter particularly when mark length recording is performed at a high density. Furthermore, although z is 0.95 or more and less than 1, a preferable upper limit is 0.999. If z is too small, the noise of the recording signal increases and the effect of the present invention tends to be insufficient. On the other hand, if z is too large, the signal intensity tends to decrease.
[0013]
The recording layer used in the present invention may further contain other elements as long as the effects of the present invention are not impaired, but usually has the quaternary composition described above.
The thickness of the recording layer is preferably in the range of 10 nm to 30 nm. In particular, 15 nm or more is preferable, and 25 nm or less is preferable. If it is too thin, 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 recording erasure in a short time tends to be difficult. Also, the reflectance tends to be too low. On the other hand, if it is too thick, it is difficult to obtain optical contrast, and cracks are likely to occur. Also, the heat capacity tends to increase and the recording sensitivity tends to deteriorate. Furthermore, since the volume change accompanying the phase change becomes remarkable, when overwriting is repeated, microscopic and irreversible deformations are accumulated in the recording layer itself and the protective layer that can be provided above and below the recording layer. As a result, the repeated overwrite durability tends to decrease. In a high-density medium such as a rewritable DVD, the requirement for noise is more severe, and therefore a more preferable recording layer thickness is 25 nm or less.
[0014]
The recording layer can be obtained by DC or RF sputtering of a predetermined alloy target in an inert gas, particularly Ar gas.
The density of the recording layer is usually 80% or more, preferably 90% or more of the bulk density. As the bulk density here, an approximate value according to the following formula (II) is usually used, but an alloy lump can be prepared and actually measured.
[0015]
[Chemical formula 5]
ρ = Σm_iρ_i    (II)
[0016]
(Where m_iIs the molar concentration of each element i and ρ_iIs the atomic weight of element i. ) In the sputter film formation method, the pressure of the sputtering gas (usually a rare gas such as Ar, which will be described below using Ar as an example) during the film formation is reduced, or the substrate is disposed close to the front of the target. Thus, the density of the recording layer can be increased by increasing the amount of high energy Ar irradiated to the recording layer. The high energy Ar is usually one in which 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 across the substrate and reach the substrate. Either. The irradiation effect of such a high energy rare gas is referred to as an atomic peening effect. In sputtering with Ar gas that is generally used, Ar is mixed into the sputtered film due to the atomic peening effect. The atomic peening effect can be estimated from the amount of Ar in the film. That is, if the amount of Ar is small, it means that the effect of high energy Ar irradiation is small, and a film with a low density is likely to be formed. On the other hand, if the amount of Ar is large, the irradiation with high energy Ar is intense and the density becomes high, but Ar taken in the film precipitates as void during repeated overwriting and tends to deteriorate repeated durability (J Appl. Phys., Vol. 78 (1995), pp 6980-6988). Therefore, an appropriate amount of Ar in the recording layer is 0.1 atomic% or more and less than 1.5 atomic%. Furthermore, it is preferable to use high frequency sputtering rather than direct current sputtering because the amount of Ar in the film is reduced and a high density film can be obtained.
Another component of the structure of the optical information recording medium of the present invention will be described.
[0017]
As a substrate used in the present invention, a transparent resin such as polycarbonate, acrylic or polyolefin, or a metal such as glass or aluminum can be used. Since a guide groove of about 20-80 nm is usually provided on the substrate, a resin substrate that can form the guide groove by molding is preferable.
In order to prevent evaporation / deformation accompanying the phase change of the recording layer and to control thermal diffusion at that time, a protective layer is usually formed on one or both of the recording layer, preferably both. The material for the protective layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. In general, a dielectric having a high transparency and a high melting point such as a metal, a semiconductor oxide, a sulfide, a nitride, or a fluoride such as Ca, Mg, or Li can be used. In this case, these oxides, sulfides, nitrides, and fluorides do not necessarily have a stoichiometric composition, and it is also effective to control the composition for controlling the refractive index, or to mix them. It is. In consideration of repetitive recording characteristics, a mixture of dielectrics is preferable. More specifically, a mixture of a chalcogen compound such as ZnS or rare earth sulfide and a heat-resistant compound such as oxide, nitride, carbide, or fluoride can be used. For example, ZnS and SiO₂This mixture is an example of a preferred protective layer composition.
In consideration of repeated recording characteristics, the film density of the protective layer is preferably 80% or more of the bulk state from the viewpoint of mechanical strength (Thin Solid Films, Vol. 278 (1996), pages 74 to 81). When using a mixture of dielectrics, the theoretical density of the following formula (III) is used as the bulk density.
[0018]
[Chemical 6]
ρ = Σmiρi (III)
[0019]
(Where mi is the molar concentration of each component i, and ρi is the single bulk density of component i.)
The thickness of the protective layer is generally 10 nm to 500 nm. If it is too thin, the effect of preventing deformation of the substrate and the recording film is insufficient, and it may not serve as a protective layer. On the other hand, if it is too thick, the internal stress of the protective layer itself, the difference in elastic characteristics with the substrate, etc. become prominent, and cracks are likely to occur.
In particular, when a protective layer (sometimes referred to as a lower protective layer) is provided between the substrate and the recording layer, the lower protective layer needs to suppress substrate deformation due to heat, and thus the thickness is preferably 50 nm or more. . If it is too thin, microscopic substrate deformation is accumulated during repeated overwriting, and the reproduction light is scattered and the noise rises significantly. On the other hand, the thickness of the lower protective layer is usually about 200 nm or less, preferably about 150 nm or less, because of the time required for film formation. If it is too thick, the groove shape of the substrate viewed from the recording layer surface may change. That is, a phenomenon that the depth and width of the groove become smaller than the intended shape on the substrate surface is likely to occur.
[0020]
On the other hand, when a protective layer (sometimes referred to as an upper protective layer) is provided on the opposite side of the recording layer from the substrate, the upper protective layer usually has a thickness of 10 nm or more for suppressing deformation of the recording layer. . On the other hand, if it is too thick, microscopic plastic deformation accumulates inside the upper protective layer with repeated overwriting, and there is a tendency for noise to increase due to scattering of reproduction light. Is 30 nm or less.
The thickness of the recording layer and the protective layer is not limited from the viewpoint of mechanical strength and reliability, but also takes into account the interference effect associated with the multi-layer structure. It is selected so that the contrast between the recorded state and the unrecorded state is increased.
[0021]
The phase change information recording medium of the present invention can further be provided with a reflective layer. The position where the reflective layer is provided usually depends on the incident direction of the reproduction light, and is provided on the opposite side of the recording layer with respect to the incident side. That is, when reproducing light is incident from the substrate side, it is normal to provide a reflective layer on the opposite side of the recording layer with respect to the substrate. When reproducing light is incident from the recording layer side, the recording layer and the substrate It is usual to provide a reflective layer between them.
The material used for the reflective layer is preferably a substance having a high reflectivity, and is particularly preferably a metal such as Au, Ag, or Al that can be expected to have a heat dissipation effect. A small amount of Ta, Ti, Cr, Mo, Mg, V, Nb, Zr, or the like may be added to the above metal for controlling the thermal conductivity of the reflective layer itself or improving the corrosion resistance. The amount added is usually about 0.01-20 atomic%. Aluminum alloy containing 15 atomic% or less of Ta and / or Ti, especially Al_xTa_1-xAn alloy of (0 <x <0.15) is excellent in corrosion resistance and is a particularly preferable reflective layer material for improving the reliability of the optical information recording medium. The thickness of the reflective layer is preferably 50 nm or more so that there is no transmitted light and the incident light is completely reflected. On the other hand, if it is too thick, there is no change in the heat dissipation effect, and the productivity is worsened and cracks are likely to occur. In particular, when the thickness of the upper protective layer is 40 nm or more and 50 nm or less, the amount of impurities contained is preferably less than 2 atomic% in order to make the reflective layer have high thermal conductivity.
[0022]
A preferred layer structure of the information recording medium of the present invention is a structure in which a first protective layer, a recording layer, a second protective layer, and a reflective layer are provided in order along the incident direction of the reproduction light. That is, when reproducing light is incident from the substrate side, the layer structure is a substrate, a lower protective layer, a recording layer, an upper protective layer, and a reflective layer in order. When reproducing light is incident from the recording film side, the substrate, It is preferable that the reflective layer, the lower protective layer, the recording layer, and the upper protective layer have a layer structure. Of course, each of these layers may be formed of two or more layers, and an intermediate layer may be provided between them. For example, on the substrate / protection layer in the case of incidence on the substrate side, or on the protection layer in the case of incidence from the side opposite to the substrate, a semi-transparent extremely thin metal, semiconductor, dielectric layer having absorption, etc. are provided, It is also possible to control the amount of light energy incident on the recording layer.
[0023]
The recording layer, protective layer, and reflective layer are usually formed by sputtering or the like.
In order to prevent oxidation and contamination between layers, it is desirable to form a film with 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. It is also excellent in terms of productivity. The uppermost layer of the recording medium of the present invention is preferably provided with a protective coat made of an ultraviolet curable resin or a thermosetting resin in order to prevent direct contact with air or damage due to contact with foreign matter. The protective coat is usually 1 μm to several hundred μm thick. Alternatively, a dielectric protective layer having a high hardness can be further provided, and a resin layer can be further provided thereon.
[0024]
In the phase change recording method capable of one-beam overwriting, a recording bit is generally formed by making the recording film amorphous and erasing is performed by crystallization, which is a preferable method. In this case, since the as-depo state is generally amorphous, it is usually necessary to perform initial crystallization for crystallization of the entire disk surface in a short time in order to change the initial state to the crystalline state. Initial crystallization is usually performed by irradiating a rotating disk with a laser beam focused to about several tens to one hundred microns.
[0025]
In the present invention, the initial crystallization by melting is effective in the above case because the time required for the initialization is shortened and the initialization is ensured by one light beam irradiation. At this time, if protective layers are provided above and below the recording layer, destruction of the recording medium due to melting can be more reliably prevented. For example, a medium using a light beam focused on a diameter of about 10 to several hundred μm (for example, gas or semiconductor laser light) or a light beam condensed into an ellipse having a major axis of 50 to several hundred μm and a minor axis of about 1 to 10 μm. If the recording medium is locally heated and melted only at the center of the beam, the recording medium will not be destroyed. In addition, since the melted portion is preheated by heating the beam peripheral portion, the cooling rate is slowed down and good recrystallization is performed. In the present invention, if this method is used, for example, the initialization time can be shortened to about one-tenth of the conventional solid-phase crystallization, the productivity can be greatly reduced, and at the time of erasing after overwriting. It is possible to prevent the crystallinity from changing.
[0026]
The recording / reproducing light that can be used in the recording medium of the present invention is usually a laser beam such as a semiconductor laser or a gas laser, and its wavelength is usually about 400 to 800 nm. Especially 1Gbit / inch²In order to achieve the above-mentioned high surface recording density, it is necessary to reduce the diameter of the focused light beam, using blue to red laser light having a wavelength of 400 to 680 nm and an objective lens having a numerical aperture NA of 0.5 or more. It is desirable to obtain a focused light beam.
[0027]
In the present invention, the amorphous state is usually used as the recording mark as described above. In the present invention, it is effective to record information by the mark length modulation method. In this case, recording by the conventional binary modulation method can be performed. However, in the present invention, a recording method by a multi-value modulation method having three or more values that provides an off-pulse period when forming the following recording mark is adopted. It is particularly preferable to do this.
FIG. 1 is a schematic diagram showing a power pattern of recording light in the recording method of the present invention. When forming an amorphous mark having a mark length modulated to a length nT (T is a reference clock period, n is a mark length that can be taken in mark length modulation recording and is an integer value), nT is set to m = n −k (k is an integer satisfying 0 ≦ k ≦ 2) number of recording pulses, and each recording pulse width is expressed as α._iT (1 ≦ i ≦ m) and β for each recording pulse_iAn off-pulse interval of time T (1 ≦ i ≦ m) is accompanied. Where α_i≦ β_iIs preferable. During recording, recording light having an erasing power Pe that can crystallize amorphous is irradiated between the marks. Α_iAt T, recording light having a recording power Pw sufficient to melt the recording layer is irradiated, and β_iIn the time T (1 ≦ i ≦ m), the recording light with the bias power Pb satisfying Pb <Pe, preferably Pb ≦ 1 / 2Pe is irradiated. At this time, in order to obtain an accurate nT mark when the mark length is detected, Σα_i+ Σβ_i= N−j (j is a real number satisfying 0.0 ≦ j ≦ 2.0).
[0028]
By adopting the above recording method, the power margin and the recording linear velocity margin can be expanded. This effect is particularly remarkable when the bias power Pb is sufficiently low so that Pb ≦ 1 / 2Pe.
Figure 2 shows α_i= Β_iThe temperature change of the recording layer is schematically shown when Pb = Pe (a) and Pb≈0 (extreme case) (b) when P = 0.5. Here, the position where the first pulse of the divided pulses divided into three is irradiated is assumed. In (a), since the influence of the heating by the subsequent recording pulse extends forward, the cooling rate after the first recording pulse irradiation is slow, and Pe is irradiated even in the off-pulse section, so the temperature drop in the off-pulse section Minimum temperature T to reach_LRemains near the melting point. On the other hand, in (b), since Pb in the off-pulse interval is almost 0, T_LDecreases to a point sufficiently lower than the melting point, and the cooling rate on the way is also large. The amorphous mark dissolves at the time of the first pulse irradiation, and is formed by rapid cooling at the subsequent off pulse. Since the recording layer of the present invention is considered to exhibit a large crystallization rate only near the melting point, taking the temperature profile shown in (b) suppresses recrystallization and obtains a good amorphous mark. It is important. Conversely, the cooling rate and T_LBy controlling the above, recrystallization is almost completely suppressed, and an amorphous mark having a clear outline almost coinciding with the molten region is obtained, so that low jitter is obtained at the mark end. Conventionally used GeTe-Sb₂Te_ThreeIn the case of a pseudo binary alloy, there is no great difference in the amorphous mark formation process regardless of the temperature profile of FIGS. This is because recrystallization occurs in a wide temperature range although the speed is slightly low. In this case, a certain degree of recrystallization occurs regardless of the pulse division method, and this tends to become coarse grains around the amorphous mark and deteriorate the jitter at the mark end. In such a recording layer composition, the off-pulse is not essential, but rather the overwrite by the conventional binary modulation is simple and desirable. That is, although the above recording method is extremely effective for the recording layer of the present invention, the conventional GeTe-Sb₂Te_ThreeThere is no necessity of adopting such a recording method when the system recording layer is used or when it is applied to pit position recording.
The recording mark can be provided in either the groove portion or the inter-groove portion, and can be provided in both, but is preferably provided in the groove portion.
[0029]
【Example】
Comparative Example 1
By sputtering a GeSbTe alloy target, a Ge film having a thickness of about 400 nm is formed on the slide glass._FourSb₇₁Te_{twenty five}A recording layer comprising a film was formed. At the time of sputtering, Ar gas pressure was 0.4 Pa, and 300 W of RF power was applied to the GeSbTe alloy target. This film was an amorphous film. The results of measuring the complex refractive index of 635 nm and 780 nm using an ellipsometer (JASCO, MEL-30S type) are shown in Table 1. Next, while monitoring the reflectance of the film, the temperature was increased at about 30 ° C./min to crystallize the film. The complex refractive indexes of 635 nm and 780 nm in the crystalline state are as shown in Table-1. The density of the recording layer film obtained directly from the film thickness and weight change of the recording layer formed on the glass substrate as thick as about 500 nm was approximately 90%.
[0030]
Next, assuming the layer structure of substrate / lower protective layer / recording layer / upper protective layer / reflective layer, the complex refractive index measured above is used, and the thickness of each layer, reflectivity, reflected light from the amorphous state, and A combination of film thicknesses that satisfies the conditions by adding restrictions as shown in Table 3 to the phase difference of the reflected light from the crystalline state was determined by calculation. The materials and dielectric constants of the lower protective layer, the upper protective layer, and the substrate were as shown in Table-2.
The plots of the obtained solutions are shown in FIG. 3 (a) (780 nm) and FIG. 4 (a) (635 nm).
The reason for the conditions described in Table 3 is as follows.
That is, the lower limit of the reflectance in the crystalline state of 13% or 15% is because focusing and tracking servo are difficult to be applied if the reflectance in the unrecorded crystalline state is lower than this. The range of the thickness of the lower protective layer is a film thickness that minimizes the reflectance when the other layers are fixed and the dependency of the crystalline or amorphous reflectance on the lower protective layer thickness is measured or calculated. This is because a range from 50-60 nm to 150 nm, which is the film thickness at which the reflectance is maximized, is taken into consideration. Regarding the film thickness beyond this, since the lower protective layer is transparent, the optical film thickness nd (n protective layer refractive index, d film thickness) only changes periodically every time one wavelength is reached. The film thickness of the recording layer and the film thickness of the upper protective layer were limited to the preferred ranges for the reasons described above. The reflection layer may be any thickness as long as the transmitted light is negligible in the optical calculation, but it is 200 nm which is the film thickness used in the actually produced disk. The phase difference between the amorphous reflected light and the crystal reflected light is preferably π ± 0 since the vicinity of π is desirable as the condition that the reflectance of the amorphous mark is the lowest when the reflected light of the both interferes in the focused light beam. A range of 1π was selected. In this case, it is preferable that the difference in reflectance between the two can be ensured more than the difference in reflectance between crystal and amorphous, the maximum contrast can be obtained, and the signal amplitude can be increased.
[0031]
Examples 1 and 2
A GeSbTe alloy target and an Al target were simultaneously sputtered to obtain an AlGeSbTe film having a thickness of about 400 nm on a slide glass. At the time of sputtering, Ar gas pressure was 0.4 Pa, and 300 W of RF power was applied to the GeSbTe alloy target. DC power was applied to the Al target by current control, and the current values were set to 0.1 A (Example 1) and 0.14 A (Example 2). The composition of the obtained film is Al₁Ge_FourSb₆₉Te₂₆(((Sb_0.73Te_0.27)_0.96Ge_0.04)_0.99Al_0.01Example 1), Al₂Ge_FourSb₆₈Te₂₆(((Sb_0.72Te_0.28)_0.96Ge_0.04)_0.98Al_0.02Example 2).
Hereinafter, in the same manner as in Comparative Example 1, the complex refractive index of the amorphous state and the crystalline state was measured, and a plot of the solution based on the complex refractive index was obtained. The results are shown in Table-1, Table-2, Table-3, FIGS. 3B and 3C, and FIGS. 4B and 4C.
The results of FIGS. 3 and 4 are compared. First, it can be seen from FIGS. 3 and 4 that there is a solution up to the point where the reflectance is higher under the condition where Al is present. For example, at 780 nm, the GeSbTe system has no solution where the reflectance is greater than 0.17, but the system in which Al is present has a solution. This means that the presence of Al increases the signal intensity with high reflectivity.
[0032]
Furthermore, if the lower protective layer is too thin, the substrate protective effect is reduced. However, as shown in FIGS. 3 and 4, it can be seen that the AlGeSbTe system has a solution up to the thicker lower protective layer than the GeSbTe system. . It can also be seen that the thinner the upper protective layer, the smaller the deterioration during overwriting, but the Al-added system has a solution up to the thin upper protective layer. This means that it is suitable for a layer structure capable of reducing deterioration due to repeated overwriting as described above. From these results, it can be seen that when disk characteristics such as signal intensity, reflectance, and repetitive recording characteristics are taken into account, an excellent phase change optical disk can be obtained by adding Al. This tendency is the same at 780 nm and 635 nm.
[0033]
Examples 3 and 4
A phase change optical disk was produced using the same recording layer composition as used in Examples 1 and 2.
ZnS-SiO2 on a 1.2mm thick polycarbonate substrate₂Lower protective layer (90 nm), AlGeSbTe recording layer (15 nm), ZnS-SiO₂The upper protective layer (40 nm) and the Al alloy reflective layer (200 nm) were formed by sputtering, and a protective coat made of an ultraviolet curable resin was further formed thereon. The sputtering conditions for the recording layer are the same as in Example 1. After melting and crystallizing these discs, a linear velocity of 2.4 m / s was obtained using an optical system of 780 nm, NA of 0.55, and a recording method in accordance with the standards of the Orange Book Part 3 standard (rewritable CD, CD-RW). At a recording power of 12 mW and an erasing power of 6 mW, an amorphous mark was formed in the groove, and overwriting was performed 5 times. As a result, the reflectance modulation factor and 3T space jitter were 21.4%, 77%, and 9.7 ns in Example 1, and 19.3%, 76%, and 9.4 ns in Example 2. These values fully satisfy the Orange Book Part 3 standard.
[0034]
Comparative Example 2
A GeSbTe target and an Al target were simultaneously sputtered to obtain an AlGeSbTe film having a thickness of about 400 nm on a slide glass. At the time of sputtering, Ar gas pressure was 0.4 Pa, and 300 W RF power was applied to the GeSbTe target. DC power was applied to the Al target by current control, and the current value was set to 0.3A. The composition of the obtained film is Al₆Ge_FourSb₆₆Te_{twenty four}(((Sb_0.73Te_0.27)_0.96Ge_0.04)_0.94Al_0.06)Met. Next, a phase change optical disk was produced using this recording layer. ZnS-SiO on polycarbonate substrate₂Lower protective layer (90 nm), AlGeSbTe recording layer (15 nm) having the same composition as described above, ZnS-SiO₂The upper protective layer (40 nm) and the Al alloy reflective layer (200 nm) were formed by sputtering, and a protective coat made of an ultraviolet curable resin was further formed thereon. The sputtering conditions for the recording layer are the same as described above. After melting and crystallizing this disc, the optical system at 780 nm, NA 0.55 and the recording method according to the standard of the Orange Book Part 3 standard (rewritable CD, CD-RW) at a linear velocity of 2.4 m / s. Recording was performed with an amorphous mark formed in the groove, but the recording waveform was dirty and the 3T jitter was higher than 17.5 ns, which did not satisfy the Orange Book Part 3 standard.
[0035]
[Table 1]

[0036]
[Table 2]

[0037]
[Table 3]

[0038]
【The invention's effect】
According to the present invention, it is possible to obtain a phase change recording medium having high signal intensity, stable recording marks, and excellent overall performance. In addition, a reproducing method and a recording method suitable for this can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a power pattern of recording light in a recording method of the present invention.
FIG. 2 is a schematic diagram showing a temperature change of a recording layer, showing the effect of the recording method of the present invention.
FIG. 3 is a plot (780 nm) showing the results in Examples 1 and 2 and Comparative Example 1.
4 is a plot diagram (635 nm) showing the results in Examples 1 and 2 and Comparative Example 1. FIG.

Claims (10)

An optical information recording medium having at least a phase change recording layer on a substrate, wherein the phase change recording layer has a composition represented by the following general formula (I): Medium.
[Chemical 1]
((Sb _x T _e1-x ) _y G _e1-y ) _z Al _1-z (I)
(Where x is a number in the range 0.6 ≦ x ≦ 0.9, y is a number in the range 0.9 ≦ y <1, and z is a number in the range 0.95 ≦ z <1. .)   The optical information recording medium according to claim 1, wherein 0.7 ≦ x ≦ 0.9.   The optical information recording medium according to claim 1, wherein 0.7 ≦ x ≦ 0.8. Phase-change recording layer optical information recording medium according to any one of claims 1 to 3 on one side or the protective layer on either side are provided in. The optical information recording medium according to any one of claims 1 to 4 further reflecting layer is provided. On a substrate, in order from the incident direction of the recording and reproducing light beam, at least a first protective layer, a phase change type recording layer, a second protective layer and a reflective layer in any one of claims 1 to 5 provided in this order The optical information recording medium described. Phase-change optical information recording medium according to any one of recording the thickness of the layer is 10-30nm claims 1 to 6. The optical information recording medium according to any one of claims 1 to 7 information by the mark length modulation scheme is recorded. Focusing the optical information recording medium according to any one of claims 1 to 8, the following laser light wavelength 400nm or 800 nm, the numerical aperture NA is condensed by 0.5 or more objective lens A reproducing method of an optical information recording medium, wherein the reproducing is performed by irradiating light. In recording the mark length modulated information on the optical information recording medium according to any one of claims 1 to 8 ,
The crystalline portion is in an unrecorded state / erased state, and the amorphous portion is in a recorded state,
Between the recording marks, irradiating recording light with an erasing power Pe that can crystallize amorphous,
For a recording mark, when the time length of the recording mark is nT (T is a reference clock period, n is a natural number of 2 or more), the time nT is expressed as follows.
α ₁ T, β ₁ T, α ₂ T, β ₂ T,..., α _m T, β _m T,
(Where Σα _i + Σβ _i = n−j, j is an arbitrary number from 0-2, m is a number satisfying m = n−k, k is an integer from 0-2), and In the time of α _i T (1 ≦ i ≦ m), the recording light having a recording power Pw sufficient to melt the recording layer is irradiated, and in the time of β _i T (1 ≦ i ≦ m), Pb <A recording method of an optical information recording medium which irradiates recording light having a bias power Pb of Pe.

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