JP2005149616A - Phase change optical information recording medium and manufacturing method therefor, and recording method for multi-valued mark - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a phase change optical information recording medium free from fluctuation in reflection of an Rf signal before recording, capable of maintaining a practically permissible error rate as an optical recording system, in an initial period, after repetitive recording and after preservation, and having high reliability, to provide the phase change optical information recording medium obtained by the manufacturing method, to provide its intermediate, and to provide a recording method for a multi-valued mark to the recording medium. <P>SOLUTION: The manufacturing method for the phase change optical information recording medium is disclosed which utilizes a phase change phenomenon between crystal and amorphous phases by optical irradiation, the recording medium in which a recording mark forming region is divided into areas equal to each other (the divided virtual region is called a cell), one recording mark is formed in one cell, and information to be recorded is modulated into a multi-valued information and recorded as information of the occupation ratio of the recording mark to the cell. The manufacturing method comprises at least a step of film-depositing a crystallization promoting layer, successively a recording layer containing Sb and Te as main component, a step of film-depositing an impurity layer in contact with the crystallization promoting layer and/or the recording layer and a step of mixing the crystallization promoting layer, the recording layer and the impurity layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a phase change type multilevel optical information recording medium having a recording / reproducing signal level of a recording pit higher than binary, an intermediate thereof, a manufacturing method thereof, and a multilevel mark recording method.

A so-called phase change type optical information recording medium using a reversible phase change between a crystalline state and an amorphous state is known as an optical information recording medium currently in practical use. As the recording material, have a _GeTe-Sb 2 Te ₃ pseudo binary _{composition, Ge 2 Sb 2 Te 5 Ge} -Sb-Te 3 binary alloy material represented by compounds compositions such as, and _Sb 70 Te There are AgInSbTe-based materials typified by Ag-In-Sb-Te, mainly composed of ₃₀ eutectic compositions. The former GeSbTe-based material is widely used as DVD-RAM, and the latter AgInSbTe-based material is widely used as CD-RW, DVD-RW, and DVD + RW. Each of these phase change optical recording media has a structure in which a lower protective layer, a recording layer, an upper protective layer, a reflective layer, and the like are laminated on a plastic substrate having spiral or concentric grooves. In this case, the reflectance is controlled by using the optical constant change in the crystal and amorphous and the multiple interference of the laminated structure, and binary information is recorded and reproduced.

  On the other hand, in recent years, with the progress of digitalization and the spread of broadband, the amount of information handled has increased, and a new recording medium capable of recording and reproducing data at high density and high speed has been demanded. From such a background, in the phase change type optical recording medium, the size of the mark to be recorded is reduced by reducing the condensed beam diameter by shortening the recording / reproducing wavelength or increasing the numerical aperture NA (Numerical Aperture). Technology development aiming at high density and high speed has been actively conducted. For example, the current recordable DVD has a recording / reproducing wavelength λ = 650 nm, a numerical aperture NA = 0.65, and a recording capacity 4.7 GB, but the recording / reproducing wavelength is shortened to λ = 400 to 420 nm, and the numerical aperture NA An optical recording system having a recording capacity of 20 GB or more with 0.85 is proposed (Japanese Patent Laid-Open No. 10-326435 ... Patent Document 1). However, this system has a fatal problem that compatibility with DVD becomes difficult due to high NA, and in addition, it is vulnerable to dirt on the surface of the recording medium such as fingerprints.

  On the other hand, a multi-value recording method has attracted attention as a technique for realizing higher density and higher speed while keeping the numerical aperture NA at about 0.65 of the conventional recordable DVD system. The present applicants have already proposed a method for recording multi-value information with a difference in the occupation ratio of the amorphous recording mark with respect to the peripheral crystal part and achieving a recording capacity of 20 GB or more (Data Detection using Pattern Recognition, International Symposium on). Optical Memory 2001, Technical Digest 2001, Pd-27). Hereinafter, this prior art will be described.

  FIG. 1 is a conceptual diagram of mark occupancy and Rf signal. The recording mark is located at the approximate center of each cell. The same relationship applies to phase pits in which the recording marks are recorded as rewritable phase change materials or asperities on the substrate. When the recording mark is a phase pit recorded as an uneven shape on the substrate, the optical groove depth of the phase pit is λ / 4 (λ is the wavelength of the recording / reproducing laser) so that the signal gain of the Rf signal is maximized. ). The Rf signal value is given as a value when the recording / reproducing focused beam is located at the center of the cell, and changes depending on the occupation ratio of the recording mark in one cell. In general, the Rf signal value is maximum when no recording mark exists, and is minimum when the occupation ratio of the recording mark is the highest.

  For example, when multi-value recording is performed with the number of recording mark patterns (number of multi-value levels) = 6 by such an area modulation method, Rf signal values from the respective recording mark patterns show a distribution as shown in FIG. The Rf signal value is represented by a numerical value normalized with the width (dynamic range DR) of the maximum value and the minimum value being 1. Recording / reproduction is performed using an optical system with λ = 650 nm and NA = 0.65 (condensed beam diameter = about 0.8 μm), and the circumferential length of the cell (hereinafter referred to as cell length) is about 0. .6 μm. Such a multi-valued recording mark can be formed by laser modulation using the recording strategy as shown in FIG. 3 with the Pw, Pe, and Pb powers and their start times as parameters.

  In the multi-value recording method as described above, when the recording linear density is increased (= the cell length is shortened), the cell length gradually becomes shorter with respect to the focused beam diameter, and is a target. When the cell is reproduced, the focused beam protrudes from the front and rear cells of interest. For this reason, even if the mark occupancy of the target cell is the same, the Rf signal value reproduced from the target cell is affected by the combination of the mark occupancy of the preceding and subsequent cells. That is, intersymbol interference occurs with the front and rear marks. Due to this influence, as shown in FIG. 2, the Rf signal value in each pattern has a distribution with a deviation. That is, in order to determine which recording mark pattern the target cell has, the interval between the Rf signal values reproduced from each recording mark needs to be larger than the deviation. In the case of FIG. 2, the intervals and deviations of the Rf signal values of the recording marks are almost equal, which is a limit for determining the recording mark pattern.

As a technology to overcome this limitation, a multi-value determination technology DDPR (Data Detection using Pattern Recognition, International Symposium on Optical Memory 2001, Technical Digest 2001, Pd-27) using three consecutive data cells has been proposed. In this technique, a step of learning a multi-value signal distribution composed of a combination pattern of three consecutive data cells (8 ³ = 512 patterns at the time of 8-level recording) and creating a pattern table thereof, and a reproduction signal result of unknown data After the three consecutive mark patterns are predicted, the unknown signal to be reproduced is multi-valued with reference to the pattern table. This makes it possible to reduce the error rate of multilevel signal determination even in the conventional cell density or SDR value that causes intersymbol interference during reproduction. Here, the SDR value is the ratio of the average value of the standard deviation σi of each multilevel signal when the number of multilevel gradations is n to the dynamic range DR of the multilevel Rf signal = Σσi / (n × DR The signal quality is equivalent to jitter in binary recording. In general, if the number n of multi-value gradations is constant, the SDR value becomes smaller as the standard deviation σi of the multi-value signal is smaller and the dynamic range DR is larger, and the separability of the multi-value signal is improved. Becomes lower. On the contrary, when the multi-value gradation number n is increased, the SDR value is increased and the error rate is increased.
When such a multi-value determination technique is used, for example, even when the number of multi-value gradations is increased to 8 and the distributions of the Rf signal values overlap each other, an 8-value multi-value determination is possible. It becomes.

  However, even with the above technique, it has been difficult to reduce the error rate to a practical value for an optical recording system. As a result of an extensive analysis by the present inventors on this cause, it was found that the main cause was a minute reflectance fluctuation existing in the Rf signal before recording.

  FIG. 5 shows a step-like multilevel recording signal and an analog signal waveform obtained by repeatedly recording the stepped multi-level recording signal within one circumference of the disk. The staircase waveform is obtained by sequentially recording ten multi-level levels from 0 to 7 with a 00700 signal interposed therebetween. The Rf signal waveform before recording includes a portion where the reflectance varies discontinuously, but the staircase waveform also includes a discontinuous variation at substantially the same position. Since each cell length is 0.25 μm, the size of the discontinuous portion is at least 8 × 15 × 0.25 = 30 μm or more. In addition, since the reflectance variation is observed at the same position in the adjacent tracks, the discontinuous portion is clearly a defect having a size extending over a plurality of tracks.

  These discontinuous portions are considered to be caused by thermal damage in the initialization process using a large-diameter laser beam. For initialization, a laser beam having a width of 100 μm and an output of about 1 W is used in consideration of production tact. However, the optical recording medium is irreversible due to differences in in-plane intensity distribution and focus offset amount. May cause serious heat damage. In particular, recently, a recording material having a high crystallization speed is used to increase the transfer speed. Therefore, initialization is performed with a high power and a high linear speed, that is, crystallization is performed at a high cooling speed, thereby preventing coarsening of crystal grains. Because it is necessary, such thermal damage is likely to occur.

In order to avoid this, if initialization is performed with a low power, the crystallinity is insufficient, and therefore, the reflectance fluctuates easily at the beginning of repeated recording. In addition, the amorphous part remains spot-like, which sometimes becomes a burst-like defect source.
Such a change in reflectance is not a problem in the conventional binary recording in which the mark length is determined from the mark edge, but an error that cannot be corrected is caused in the multi-value recording method by the area modulation of the mark. In particular, when the recording / reproducing wavelength is shortened as the recording density is increased, the beam spot diameter and the recording mark size are reduced. For example, multi-level recording using an LD with a wavelength of 650 nm, which is employed in a recording DVD. The multilevel recording system using an LD having a wavelength of around 400 nm, which is currently under development, becomes a more serious problem than the system.

Therefore, the present applicant has proposed a so-called initialization-free optical recording medium as a technique for solving the problems associated with such initialization. For example, it is a technique that does not require initialization, which includes a crystallization promoting layer, a recording layer, and an impurity layer (Japanese Patent Laid-Open No. 2002-304746). In this technique, the three layers are mixed by recording to achieve both crystallization immediately after film formation and stability of the recording mark, but the mixing of the three layers is insufficient in a region where the number of repeated recordings is small. In such a case, satisfactory storage characteristics may not be obtained, and further improvement is necessary for practical use.
Japanese Patent Application Laid-Open No. 9-161316 discloses a method in which a crystallization promoting layer and a conventional initialization method are used in combination. Japanese Patent Application Laid-Open No. 9-161316 discloses a technique in which Sb _z Te _1-z (0.3 ≦ z ≦ 0.5) or Sb ₂ Te ₃ is used for the crystallization promoting layer. Although it has been shown that binary recording at a wavelength of 780 nm is possible, there has been no recognition of the above-described problem with respect to reflectance fluctuation that is problematic only in the multi-value recording method. There is no specific description or suggestion regarding the media structure or manufacturing method. In the present invention, as described later, the impurity layer is an essential constituent element, and the impurity layer is provided in contact with the crystallization promoting layer and / or the recording layer, but the crystallization promoting layer and the recording layer are in contact with each other. The structure is different from that of Japanese Patent Laid-Open No. 9-161316 having a composition auxiliary layer in that the impurity layer cannot substantially take a structure sandwiched between the crystallization promoting layer and the recording layer. That is, it is impossible to recall the present invention from Japanese Patent Application Laid-Open No. 9-161316.

  Japanese Patent Laid-Open No. 2001-84591 is known as a conventional multi-level recording method. However, there is no description about the above problem, and there is a suggestion about a specific medium structure and manufacturing method for solving this problem. Nothing at all.

JP-A-10-326435 JP 2002-304767 A

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to eliminate reflectance fluctuation of an Rf signal before recording in a phase change type multi-value recording medium using a multi-value determination technique DDPR, and A method of manufacturing a phase change optical information recording medium capable of obtaining a practically acceptable error rate BER (Bit Error Rate) as a recording system, a phase change optical information recording medium obtained by the manufacturing method, and an intermediate thereof, Another object of the present invention is to provide a method for recording a multilevel mark on the recording medium.

According to the present invention, the following (1) to (9) are provided.
(1) Of an optical recording medium that utilizes a phase transition phenomenon between crystal and amorphous due to light irradiation, a region for forming a recording mark (hereinafter, this divided virtual region is called a cell) is divided into equal areas, An optical information recording medium in which one recording mark is formed for the cell and information to be recorded is modulated and recorded as multi-value information as information of a ratio occupied by the recording mark with respect to the cell. And a step of forming a recording layer mainly comprising Sb and Te following the crystallization promoting layer, and an impurity layer being formed in contact with the crystallization promoting layer and / or the recording layer. And a step of mixing the crystallization promoting layer, the recording layer, and the impurity layer. A method of manufacturing a phase change optical information recording medium, comprising:
(2) At least a reflective layer and a first dielectric layer are formed in this order on a first substrate having a concentric or spiral groove on the film formation surface, and then in contact with the crystallization promoting layer, the recording layer, An impurity layer is formed in contact with the recording layer and / or the crystallization promoting layer, then a second dielectric layer is formed, and then a second substrate having no groove is disposed through the resin layer. The method for producing a phase-change optical information recording medium as described in (1) above.
(3) A phase change optical information recording medium manufactured by the manufacturing method according to (1) or (2).
(4) The phase change optical information recording medium according to (3), wherein the crystallization promoting layer contains Bi as a main component and the impurity layer contains Ge.
(5) The phase change optical information recording medium as described in (3) or (4) above, wherein the impurity layer contains Ge and Sn, In and / or Te.
(6) The phase change optical information recording medium as described in any one of (3) to (5) above, wherein the Bi concentration in the recording layer after the mixing treatment is 1.5 atomic% or less.
(7) The phase change optical information recording medium according to any one of (3) to (6), wherein the thickness of the substrate is 0.6 mm.
(8) The intermediate of the phase change optical information recording medium according to any one of (3) to (7), before mixing the crystallization promoting layer, the recording layer, and the impurity layer.
(9) To the phase change optical information recording medium according to any one of (3) to (7), wherein a multi-value recording mark is formed by modulating the recording power Pw and the cooling pulse Pb with the erase pulse Pe being constant. In this recording method, a laser with a wavelength of 400 nm and an optical system with a numerical aperture of 0.65 are used to irradiate each cell with one pulse of recording power Pw, and the irradiation power and irradiation time of the recording power Pw. A multi-value mark recording method characterized by being constant.

According to the present invention, phase change type light having an error rate BER of less than IE-4, which is practically acceptable as an optical recording system, can eliminate the reflectance fluctuation of the Rf signal before recording, and the error rate BER using the multi-value determination technique DDPR is practically acceptable as an optical recording system. A method for manufacturing an information recording medium can be provided.
Further, according to the present invention, it is possible to provide a phase change optical information recording medium manufactured by the above manufacturing method, an intermediate thereof, and a method for recording a multi-value mark on the recording medium.

As described above, the discontinuous reflectance fluctuation on the Rf signal due to thermal damage due to the initialization process is the cause of the error. This thermal damage is considered to include a change in the layer quality of the upper and lower dielectric layers and a thermal damage of the recording layer, but the details are unknown.
As a result of intensive studies, the inventors have formed a step of forming at least a recording layer mainly composed of Sb and Te following the crystallization promoting layer, as in the first aspect of the present invention according to claim 1, According to the manufacturing method comprising the step of forming an impurity layer in contact with the crystallization promoting layer and / or the recording layer, and the step of mixing the crystallization promoting layer, the recording layer and the impurity layer, I found that the damage was resolved.

Here, the recording layer is mainly composed of Sb and Te. The total amount of Sb and Te occupying the recording layer is 95 atomic% or more, preferably 98 atomic% or more, and most preferably composed of only Sb and Te. Indicates that The composition of the recording layer is preferably such that the Sb atomic ratio = Sb / (Sb + Te) in the vicinity of the Sb ₇₀ Te ₃₀ eutectic composition is 0.65 or more and 0.85 or less. In addition, the recording layer has a purpose of adjusting crystallization speed, sensitivity, storage stability, etc., Ag, Au, Cu, Ca, Cr, Zn, B, Al, Ga, In, Si, Sn, Pb, Mg. , Mn, N, P, Bi, La, Ce, Cd, Tb, Dy, and the like.

According to the present invention, the crystallization transition temperature of the recording layer is lowered to around 120 ° C., so that the recording layer is sufficient even immediately after completion of the film formation due to the natural heating of the substrate during film formation and the action of the crystallization promoting layer. Crystallization is progressing. Therefore, by mixing and recrystallizing the crystallization promoting layer, the recording layer, and the impurity layer at a lower energy density than when crystallizing a very stable amorphous material immediately after film formation as in the past by crystallization at a stretch, a new It can be set as a simple recording layer. For this reason, the thermal damage as described above does not occur in the optical information recording medium. Also during the mixing process, the crystallization promoting layer promotes the formation of crystal nuclei, so that the crystal grains are not coarsened.
Here, the impurity layer refers to Ag, Au, Cu, Ca, Cr, Zn, B, Al, Ga, which can be originally included in the recording layer for the purpose of adjusting the crystallization speed, sensitivity, storage stability, and the like. It is composed of a layer containing at least one element selected from In, Si, Sn, Pb, Mg, Mn, N, P, Bi, La, Ce, Cd, Tb, Dy and the like. These elements are mixed as impurities in the binary recording layer made of Sb and Te, and exhibit the above-described effect on the Sb—Te recording layer. However, when these impurity elements are contained in the recording layer, the crystallization transition temperature of the recording layer generally increases, so that crystallization immediately after the film formation is insufficient. Therefore, in the present invention, the total amount of Sb and Te occupying the recording layer is 95 atomic% or more of the whole, preferably 98 atomic% or more, and most preferably, the recording layer is composed of only Sb and Te. Is supplied as an impurity layer.

In the present invention, the step of mixing the crystallization promoting layer, the recording layer and the impurity layer is to remelt these three layers, uniformly mix the constituent elements of these layers, and recrystallize as one recording layer. It refers to the process of making it.
The mixing step can be performed using a large-diameter laser beam as in the conventional initialization step, but the energy density used may be 60 to 70% or less of the initialization step.
Here, the crystallization transition temperature refers to a temperature at which solid-phase crystallization occurs when an amorphous recording material formed by sputtering is heated at a rate of temperature increase of 10 ° C./min. It is a measure of ease. Specifically, a recording material thin film having a film thickness of about 200 nm is formed on a glass substrate and mechanically scraped off into a powder form and measured by differential scanning calorimetry (DSC).

  Further, as in the second aspect of the present invention according to the second aspect, in the method for manufacturing an optical information recording medium according to the present invention, at least a reflective layer is formed on the first substrate having a concentric or spiral groove on the film formation surface. The first dielectric layer is formed in this order, and further, the recording layer and the impurity layer are formed in contact with the recording layer and / or the crystallization promoting layer in contact with the crystallization promoting layer, and then the second dielectric It is preferable to form a layer and then dispose a second substrate having no groove through the resin layer.

  According to this preferred example, since the reflective film having a heat dissipation function is provided on the substrate having the groove, and the second substrate without the groove, that is, an optical recording medium for recording and reproducing from the so-called cover substrate side, Thus, the thermal damage to the grooves can be reduced, and an optical recording medium having good repeated recording characteristics can be provided. Further, the first substrate material does not need to be translucent, and the degree of freedom of selection is widened from the viewpoint of heat resistance and groove transferability.

Further, in the phase change type optical information recording medium of the third aspect of the present invention according to the third aspect of the present invention as in the fourth aspect of the present invention according to the fourth aspect, the crystallization promoting layer is mainly composed of Bi. And the impurity layer preferably contains Ge.
Here, the crystallization promoting layer is mainly composed of Bi. The total amount of Bi in the crystallization promoting layer is 70 atomic% or more, preferably 90 atomic% or more, most preferably 95 atomic% or more of the whole. Indicates that The crystallization promoting layer and the impurity layer include Ag, Au, Cu, Ca, Cr, Zn, B, Al, Ga, In, Si, Sn, and the like for the purpose of adjusting the crystallization speed, sensitivity, storage stability, and the like. It can contain at least one element selected from Pb, Mg, Mn, N, P, La, Ce, Cd, Tb, Dy and the like.

  The impurity layer preferably contains Ge for improving the storage stability of the recording layer after mixing. The Ge content suitable for ensuring the storage stability of the recording mark is preferably 10 atomic% or less, more preferably 3 to 8 atomic%, and further preferably 4 to 8 atomic%. When the Ge amount exceeds 10 atomic%, phase separation is likely to occur in repeated recording. As described above, the optimum amount of Ge is 4 to 8 atomic%. In the recording layer after mixing, it is desirable to select the composition and film thickness of the impurity layer so that the Ge concentration becomes the above-mentioned preferable concentration.

  According to this preferred example, a recording layer having high crystallinity can be obtained immediately after film formation by Bi having a high crystallization promoting effect. For this reason, a crystallized recording layer is obtained by mixing the crystallization promoting layer, the recording layer, and the impurity layer at a lower energy density than when crystallizing an extremely stable amorphous material as in the prior art at a stretch. Can do. For this reason, the above-described thermal damage does not occur in the phase change optical information recording medium. In addition, Ge, which improves amorphous stability, is introduced into the mixed recording layer by the mixing operation, so that the storage stability of the recording mark is improved.

In the phase change type optical information recording medium according to the fifth aspect of the present invention, it is preferable that the impurity layer contains Ge and Sn, In, and / or Te.
According to this preferable example, since the high melting point Ge is supplied in the form of a low melting point compound, it is possible to mix uniformly. In addition, Sn, In and / or Te can be replaced with Sb to adjust the crystallization speed and the crystallization transition temperature. In addition, the impurity layer includes Ag, Au, Cu, Ca, Cr, Zn, B, Al, Ga, Si, Pb, Mg, Mn, N, P, Bi, La, Ce, Cd, Tb, Dy, etc. It can contain at least one element selected from

Further, as in the sixth aspect of the present invention according to the sixth aspect, in the phase change optical information recording medium according to the manufacturing method of the present invention, the Bi concentration in the recording layer after the mixing process is 1.5 atomic% or less. Is desirable.
According to this preferred example, since the Bi concentration in the recording layer after the mixing process is sufficiently low, a highly reliable phase change optical information recording medium having good storage stability of the amorphous mark and good reproduction light deterioration can be obtained. . If the Bi concentration exceeds 1.5 atomic%, particularly 3 atomic%, the error increase after the storage test is increased, and reproduction light deterioration is likely to occur.

In the phase change type optical information recording medium according to the seventh aspect of the present invention, it is desirable that the thickness of the substrate is 0.6 mm. 0.6 mm is preferably 0.6 ± 0.1 mm, more preferably 0.6 ± 0.05 mm.
According to this preferred example, when recording / reproduction is performed using a general optical system having a numerical aperture of 0.60 to 0.70, the beam spot diameter at the substrate incident surface is about φ0.5 mm. A highly reliable recording medium with few recording / reproducing errors against scratches and dirt can be obtained. In addition, since it is substantially the same as the thickness of the substrate used in many recordable DVDs, it is a drive device having an optical system having a numerical aperture of 0.65, and is a medium that is easily backward compatible with recordable DVDs. It is.

Further, as in the ninth aspect of the present invention according to the ninth aspect, with respect to the optical information recording medium according to the manufacturing method of the present invention, the erase pulse Pe is constant, and the modulation is performed on the recording power Pw and the cooling pulse Pb to the cell. When forming a multi-value recording mark, each cell is irradiated with one pulse of recording power Pw using a laser with a wavelength of 400 nm and an optical system with a numerical aperture of 0.65, and the irradiation power of the recording power Pw and It is preferable to make the irradiation time constant.
Here, the wavelength of 400 nm refers to the wavelength of a blue laser diode in the vicinity of a wavelength of 390 to 410 nm that is currently in practical use. The numerical aperture 0.65 is preferably a numerical aperture of 0.60 to 0.68, and is substantially the same as the numerical aperture of 0.65 used in many recordable DVDs. Means.

  According to this preferred recording method, each cell is irradiated with one pulse of recording power Pw, and the irradiation power and irradiation time of the recording pulse Pw are made constant, so that it is used for recording in all mark formation. Energy is constant. For this reason, if an appropriate groove shape, track pitch, and layer configuration capable of substantially allowing thermal interference and thermal diffusion to adjacent tracks are set, a phase-change optical information recording medium having no cross erase in any mark modulation method The design becomes easier.

Next, in the manufacturing method of the present invention, an example of the phase change optical information recording medium intermediate before the mixing treatment is shown in FIGS.
In the example of FIG. 6, a lower dielectric layer made of a mixture of ZnS and SiO ₂ , a GeInTe impurity layer, a Bi crystallization promoting layer, a recording layer made of Sb and Te, and a ZnS and SiO ₂ layer on a substrate having guide grooves. An upper dielectric layer made of a mixture and a reflective layer made of an Ag alloy were sequentially formed, and a cover substrate was bonded through a resin adhesive layer. In this configuration, the recording / reproducing laser is incident from the substrate side having the guide groove after the mixing process.

In the example of FIG. 7, on a first substrate having guide grooves, a reflective layer made of an Ag alloy, a first dielectric layer made of a mixture of ZnS and SiO ₂ , a Bi crystallization promoting layer, a recording made of Sb and Te. A layer, a GeInTe impurity layer, and a second dielectric layer made of a mixture of ZnS and SiO ₂ were sequentially formed, and the second substrate was bonded via a resin adhesive layer. In this configuration, the recording / reproducing laser is incident from the second substrate side after the mixing process.

In the example of FIGS. 6 and 7, an ultraviolet curing protective layer may be separately provided below the resin adhesive layer as necessary. In the above configuration example, the resin adhesive layer also functions as the protective layer. As for the thickness of a board | substrate, it is desirable that all are 0.6 mm.
If the recording layer, the crystallization promoting layer, and the impurity layer are in contact with the crystallization promoting layer and the impurity layer is formed in contact with the recording layer, the recording layer, and / or the crystallization promoting layer, the film formation order of the above configuration example It is not limited to. That is, in FIG. 7, the three layers may be formed in the order of an impurity layer, a crystallization promoting layer, and a recording layer, and further, impurities such as an impurity layer, a crystallization promoting layer, a recording layer, and an impurity layer may be formed. The layers may be separated into multiple layers. However, in order to improve the crystallinity of the recording layer, it is necessary to form the recording layer immediately after the formation of the crystallization promoting layer.

  The mixing step can be performed using a large-diameter laser beam as in the conventional initialization step, but the energy density used may be 60 to 70% or less of the initialization step. The laser beam for mixing processing is incident from the same substrate surface as the recording / reproducing laser. By the mixing process, the impurity layer, the crystallization promoting layer, and the recording layer are remelted and recrystallized as a single recording layer in which these constituent elements are uniformly mixed.

  6 and 7, the recording layer is sufficiently crystallized even immediately after the film formation, due to the natural heating of the substrate during film formation and the action of the crystallization promoting layer. Therefore, the recrystallized recording is performed by mixing the crystallization promoting layer, the recording layer, and the impurity layer at a lower energy density than when crystallizing an extremely stable amorphous material immediately after film formation as in the past by crystallization at once. It can be a layer. For this reason, the phase change type optical information recording medium is not thermally damaged as shown in FIG. Also during the mixing process, the crystallization promoting layer promotes the formation of crystal nuclei, so that the crystal grains are not coarsened.

  In the configuration example of FIG. 7, since the Ag alloy reflective layer with high heat dissipation is formed on the first substrate having the guide groove, the guide groove is not easily damaged by repeated recording, and the reliability of repeated recording is increased. This is a preferable configuration for increasing the height.

  As the substrate material, a transparent resin such as a polycarbonate resin, an acrylic resin, or a polyolefin resin can be used. Of these, polycarbonate resins are most preferred because they have a track record in CDs and DVDs and are inexpensive. However, in the configuration example of FIG. 7, the first substrate does not need to be a transparent resin, and can be freely selected according to heat resistance and groove transferability. The depth of the guide groove is usually 20 to 45 nm, and the groove pitch is usually 0.40 to 0.60 μm.

  A desirable film thickness including the crystallization promoting layer, the recording layer, and the impurity layer is 5 to 25 nm. If the thickness is less than 5 nm, the reflectivity of the recording layer becomes too low after mixing, and sufficient contrast cannot be obtained. On the other hand, if it is thicker than 25 nm, the heat capacity is increased and the recording sensitivity is deteriorated. In addition, since the crystal growth becomes three-dimensional, the edge of the amorphous mark is disturbed and the SDR tends to increase.

As the dielectric material, a high-melting-point material having high transparency such as an oxide, sulfide, nitride, or carbide of metal or semiconductor can be used. _{Specifically, SiOx, ZnO, SnO 2,} Al 2 O 3, TiO 2, In 2 O 3, MgO, ZrO 2, Ta 2 O metal oxide such as _{5, Si 3 N 4, AlN} , TiN, BN And nitrides such as ZrN, sulfides such as ZnS and TaS ₄ , and carbides such as SiC, TaC, B ₄ C, WC, TiC, and ZrC, and can be used alone or as a mixture.

  The optimum material for the dielectric layer is determined in consideration of refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like.

As a result of studying various materials by the present inventors, the dielectric material is most preferably a mixture of ZnS and SiO ₂ . A suitable mixing amount of SiO ₂ is 10 to 40 mol%.
The film thicknesses of the upper dielectric layer and the first dielectric layer are desirably 5 to 20 nm. If the film thickness is less than 5 nm, most of the laser energy is transferred to the reflective layer, and the mark width becomes smaller as the melting region becomes smaller, so that the dynamic range of the signal cannot be obtained. In addition, the sensitivity is low and the medium becomes impractical without a power margin. On the other hand, if the film thickness is greater than 20 nm, the heat dissipation effect is reduced, a quenching structure cannot be obtained, and mark formation becomes difficult.

  The film thickness of the lower dielectric layer and the second dielectric layer is preferably in the range of 30 to 200 nm. If the thickness is less than 30 nm, the environmental resistance protection function is lowered, the heat resistance is lowered, and the livestock heat effect is lowered. On the other hand, if it is thicker than 200 nm, it is not preferable because film peeling or cracking occurs due to an increase in film temperature or a decrease in recording sensitivity of media in a film forming process such as sputtering.

  As the reflective layer, Au, Ag, Cu, and Al are preferable, and among them, Ag having a high thermal conductivity is most preferable. Ag is preferably an alloy of Pd, Nd, Cu, Zn, etc., in order to make the crystal grains of the reflective layer finer, suppress migration, and improve corrosion resistance. The thickness of the reflective film is preferably 80 to 150 nm. If the film thickness is 80 nm or more, the transmitted light is almost eliminated, so that the light can be used efficiently. The thicker the reflective film, the faster the cooling rate and the faster the crystallization speed can be used. However, even if it is thicker than 150 nm, the recording characteristics do not change and only the film formation takes time. The following is preferable.

  Next, examples and comparative examples of the phase change optical information recording medium according to the present invention will be shown. The embodiments described below are preferred embodiments of the present invention, and various technically preferable limitations are given. However, in the following description, a description that the present invention is particularly limited is provided. As long as there is no, it is not limited to these embodiments.

(Examples 1-5, Comparative Examples 1-5)
A polycarbonate substrate having a thickness of 0.6 mm and a diameter of 120 mm was prepared by an injection molding method, and an intermediate having the structure shown in FIG. 6 was produced using the impurity layer, crystallization promoting layer, and recording layer shown in Table 1. In either case, the dielectric layer was a ZnS-20 mol% SiO ₂ film, and the reflective film was Ag-1 wt% Pd-1 wt% Cu. On the information substrate, a groove having a track pitch = 0.45 μm, a groove depth = 20 nm, and a groove width = 0.25 μm is formed. Next, using a large-diameter laser beam having a width of 100 μm and an output of 1 W, a mixing process was performed at an output of 350 mW and a linear velocity of 6 m / s to produce phase change optical information recording media of Examples 1 to 5.
Next, using the recording layer corresponding to the recording layer composition after the mixing treatment of Examples 1 to 5, a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective layer are formed on the same information substrate, The same laminated structure as in the example was initialized using a large-diameter laser beam having a width of 100 μm and an output of 1 W at an output of 650 mW and a linear velocity of 3 m / s. An information recording medium was produced.

  For these media, a 405 nm blue laser and an NA = 0.65 optical system (converging diameter = φ0.51 μm) were used, and multi-value recording was performed at a recording linear velocity = 6.0 m / s. The cell length was 0.25 μm (= cell cycle 42 ns). In the schematic diagram of FIG. 3, the recording strategy is Pw = 8.5 mW, Pe = 5 mW, Pb = 0.4 mW, each pulse is irradiated with a recording power Pw of 1 pulse for 4.5 ns, and Pw and Pe The start time was optimized.

(Evaluation)
(1) Reproduction evaluation of recording characteristics was performed by obtaining an error rate BER using a multi-value determination technique DDPR and determining whether BER <1E-4 which is acceptable as a practical system. The evaluation is (1) error rate at the time of initial recording, (2) maximum value of error rate at 10 times, 100 times, and 1000 times of DOW (direct over write), and (3) 80 ° C. of the first recorded medium. , 85% RH, with an error rate after 100 hours storage test.
(2) Comprehensive evaluation indicates that the error rate of the initial recording was good and the error rate was not significantly increased in the repeated recording and storage tests (good), less than 1E-4 acceptable as a system A rise was evaluated as Δ (possible), and an error rate of initial recording exceeding 1E-4 was judged as × (impractical).
The evaluation results are shown in Table 2.

From the results in Table 2, the following is clear.
In Examples 1 to 5, in the recording medium intermediate shown in FIG. 6, the crystallization transition temperature of the recording layer is lowered to about 120 ° C., so that the substrate is naturally heated during film formation and the action of the crystallization promoting layer. The crystallization is sufficiently advanced even immediately after the recording layer is formed. Therefore, the crystallization promoting layer, the recording layer, and the impurity layer are mixed and recrystallized at a lower energy density than the case where the extremely stable amorphous immediately after film formation as in Comparative Examples 1 to 5 is crystallized all at once by the initialization process. Thus, a new recording layer can be obtained. As a result, the above-described thermal damage is not generated in the phase-change optical information recording medium, and the error rate at the first recording is smaller than 8E-5 and both are good.
Furthermore, in Examples 1, 2, and 4, since the Bi concentration in the recording layer after mixing is 1.5 atomic% or less, there is no significant increase in error even after storage. In Examples 3 and 5, the Bi concentration was slightly high and the error rate slightly increased after storage, but it was less than 1E-4 acceptable for the system. In repeated recording (DOW), the error rate slightly increased, but it was less than 1E-4 acceptable for the system.
On the other hand, in all of Comparative Examples 1 to 5, the error rate of the initial recording exceeded 1E-4, which was not practical (x). For this reason, repeated recording and storage tests were not carried out (-mark in the table).

(Examples 6 to 8)
Using the impurity layer, the crystallization promoting layer, and the recording layer of Examples 1, 2, and 4, an intermediate having the structure shown in FIG. 7 was produced. The same material was used for the dielectric layer and the reflective film. Similarly, using a large-diameter laser beam having a width of 100 μm and an output of 1 W, a mixing process was performed at an output of 350 mW and a linear velocity of 6 m / s to produce phase change optical information recording media of Examples 6, 7 and 8, respectively.

  Recording was performed on these media in the same manner as in Examples 1 to 5, and reproduction evaluation and overall evaluation of the same recording characteristics were performed. The results are shown in Table 3. In Examples 6, 7 and 8, the error rate of the initial recording was good, and the error rate was not significantly increased even in the repeated recording and storage test, so that they were extremely good and reliable media. The overall evaluation is ◎. In Examples 6, 7 and 8, a reflective film having a heat dissipation function is provided on a substrate having a groove, and recording and reproduction are performed from the second substrate having no groove, that is, a so-called cover substrate side. It is considered that the heat damage is reduced and the error rise during repeated recording can be prevented.

It is the schematic of the mark occupation rate and Rf signal of the conventional phase change type optical information recording medium. It is a figure which shows Rf signal value distribution from a multi-recording mark pattern at the time of performing multi-value recording with the recording mark pattern number of 6 with the area modulation system with respect to the conventional phase change type optical information recording medium. It is a figure which shows the example of the recording strategy of the conventional multi-value recording mark. It is a figure which shows Rf signal value distribution at the time of setting the multi-value gradation number to 8 in the conventional multi-value recording in FIG. It is the figure which showed the Rf signal waveform before the conventional recording, and the staircase waveform when this was continuously recorded in the circumference of 15 8-valued marks each. It is a figure which shows the example of a layer structure of the phase change type optical information recording medium intermediate body before the mixing process of this invention. It is a figure which shows another example of the layer structure of the phase change type | mold optical information recording medium intermediate body before the mixing process of this invention.

Claims (9)

  Of the optical recording medium using the phase transition phenomenon between crystal and amorphous due to light irradiation, a region for forming a recording mark (hereinafter, this divided virtual region is referred to as a cell) is divided into equal areas, and the cell Manufacturing method of an optical information recording medium in which information to be recorded is modulated into multi-value information and recorded as information on the ratio of the recording mark to the cell. And at least a step of forming a recording layer mainly composed of Sb and Te after the crystallization promoting layer, and a step of forming an impurity layer in contact with the crystallization promoting layer and / or the recording layer. And a step of mixing the crystallization promoting layer, the recording layer, and the impurity layer. A method for producing a phase change optical information recording medium, comprising:   At least a reflective layer and a first dielectric layer are formed in this order on a first substrate having a concentric or spiral groove on the film formation surface, and then in contact with the crystallization promoting layer, the recording layer, the recording layer, and / Or forming an impurity layer in contact with the crystallization promoting layer, then forming a second dielectric layer, and then disposing a second substrate having no groove through the resin layer A method of manufacturing a phase change optical information recording medium according to claim 1.   A phase change optical information recording medium manufactured by the manufacturing method according to claim 1.   4. The phase change optical information recording medium according to claim 3, wherein the crystallization promoting layer contains Bi as a main component and the impurity layer contains Ge.   5. The phase change optical information recording medium according to claim 3, wherein the impurity layer contains Ge and Sn, In and / or Te.   6. The phase change optical information recording medium according to claim 3, wherein the Bi concentration in the recording layer after the mixing treatment is 1.5 atomic% or less.   7. The phase change optical information recording medium according to claim 3, wherein the thickness of the substrate is 0.6 mm.   The intermediate of the phase change optical information recording medium according to any one of claims 3 to 7, wherein the crystallization promoting layer, the recording layer, and the impurity layer are mixed. 8. The method for recording on a phase change optical information recording medium according to claim 3, wherein the multi-value recording mark is formed by modulating the recording power Pw and the cooling pulse Pb with the erasing pulse Pe being constant. Using a laser with a wavelength of 400 nm and an optical system with a numerical aperture of 0.65, each cell is irradiated with one pulse of recording power Pw, and the irradiation power and irradiation time of the recording power Pw are constant. Multi-value mark recording method.