JP2004306595A - Phase-change recording material and information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase-change recording material which enables high-speed recording and erasing, and which has excellent recording characteristics, high storage stability of a recording signal and excellent repeated recording durability, and an information recording medium using the material. <P>SOLUTION: This material is mainly composed of a composition which is expressed by the formula: ä(Sb<SB>1-x</SB>Ge<SB>x</SB>)<SB>1-y</SB>In<SB>y</SB>}<SB>1-z-w</SB>M<SB>z</SB>Te<SB>w</SB>(x, y, z and w are numbers which each satisfy the expression, 0.001≤x≤0.3, 0≤y≤0.4, 0≤z≤0.2 or 0≤w≤0.1; M is at least one element selected from among lanthanoids; and both z and w are not 0.). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a phase change recording material and an information recording medium using the same.

  As a recording method using a phase change, a method of reversibly changing the crystal structure of a metal or a semiconductor by applying an energy beam or an energy flow such as light or electric current (Joule heat) is known (Non-Patent Document 1). Patent Document 1, Patent Document 1).

  Currently, a method of recording information on a recording medium using a phase-change recording material is a method that utilizes a reversible change between a crystalline phase and an amorphous phase (amorphous phase). . Specifically, this is a method in which the crystalline state is set to an unrecorded / erased state, and an amorphous mark is formed during recording. Usually, the recording layer is locally heated to a temperature higher than the melting point and rapidly cooled to form an amorphous mark. On the other hand, the recrystallization is performed by heating the recording layer to a temperature lower than the melting point and higher than the crystallization temperature and gradually cooling the recording layer to maintain the recording layer at a temperature higher than the crystallization temperature for a certain time. Thus, in general, utilizing a reversible change between a stable crystalline phase and an amorphous phase, physical parameters in a crystalline state and an amorphous state, for example, refractive index, electric resistance, volume The information is recorded / reproduced by detecting a difference such as a change in density.

  Among optical information recording media, optical information recording media use a change in reflectance accompanying a reversible change between a crystalline state and an amorphous state, which is locally generated by irradiating a focused light beam. Recording and reproduction are performed. Optical information recording media having such a phase-change recording layer have been developed and put into practical use as inexpensive large-capacity recording media having excellent portability, weather resistance, impact resistance, and the like. Rewritable phase-change optical information recording media such as RW, DVD-RW, DVD + RW, and DVD-RAM (hereinafter, a phase-change optical information recording medium is simply referred to as a “phase-change optical disc”). , "Optical disk", or "disk".). Further, developments have been made such as using a blue laser, increasing the density by increasing the NA of the objective lens, and increasing the recording speed by improving the recording pulse waveform.

  As a material for such a phase change type recording layer, a chalcogen alloy is often used. Examples of chalcogen-based alloys include Ge-Sb-Te-based, In-Sb-Te-based, Ge-Sn-Te-based, and Ag-In-Sb-Te-based alloys. These alloys are also usually overwritable materials.

  Here, overwriting is a method of overwriting without erasing before recording, that is, a method of recording while erasing, when re-recording on a medium that has already been recorded. In a phase-change type optical information recording medium, recording is usually performed by overwriting. Therefore, recording while erasing (that is, overwriting) is sometimes simply referred to as recording.

  In recent years, with the increase in the amount of information, development of an information recording medium (particularly, an optical information recording medium) capable of higher-speed recording / erasing / reproduction has been desired. As a material capable of satisfying both the excellent jitter characteristics and the storage stability of the amorphous mark even in such ultra-high speed recording, a material having a ternary composition of Sb-Ge-In as a main component is used. (Patent Documents 2 and 3). This material is promising as a material used for a phase-change type optical disk that performs high-speed recording and erasing of an information signal at a reference clock cycle of 15 ns or less.

Appl. Phys. Lett., Vol.18 (1971), pp254-257 U.S. Pat. No. 3,530,441 JP 2001-39031 A JP-A-2002-347341

  However, in a material having the above-mentioned ternary composition of Sb-Ge-In as a main component, there is a problem that it is desired to further improve the repetitive recording durability.

  For example, in many cases, the durability of repeated recording of 1000 times is guaranteed in a CD-RW (in order to guarantee the repeated recording of 1000 times, the CD-RW can be repeatedly recorded about 2000 times. There is a need.). On the other hand, the CD-RW using the ternary composition of Sb-Ge-In as a recording material has an upper limit of 1000 times of repetitive recording when evaluated from the practical viewpoint. It may be around times.

  The present invention has been made in order to solve the above problems, and its object is to enable high-speed recording and erasing, have excellent jitter characteristics, have high storage stability of a recording signal, and further repeatedly record. An object of the present invention is to provide a phase change recording material having excellent durability, and an information recording medium using the material. In particular, it is an object of the present invention to provide an optical information recording medium which is one form of application of the information recording medium.

  The present inventor has made intensive studies in view of the above-mentioned circumstances, and as a result, by adding at least one of a lanthanoid and Te to the above ternary composition, both the jitter characteristic against high-speed recording and erasing and the storage stability of a recording signal are improved. The present invention has been found to be satisfactory and to further improve repetition durability significantly.

  That is, according to the present invention, as described in claim 1, there is provided a phase-change recording material having a composition represented by the following general formula (1) as a main component.

_{{(Sb 1-x Ge x} ) 1-y In y} 1-z-w M z Te w (1)
(Where x, y, z, and w are numbers satisfying 0.001 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.2, 0 ≦ w ≦ 0.1, M is at least one element selected from lanthanoids, provided that z and w are not both 0.)

Further, according to the present invention, there is provided the phase change recording material according to claim 1, wherein 0 <z in the general formula (1).
Further, in the present invention, as described in claim 3, the phase change recording material according to claim 1 or 2, wherein z / y in the general formula (1) is 0 or more and 1 or less. .
In the present invention, as described in claim 4, the phase change recording material has a crystalline state in an unrecorded state and an amorphous state in a recorded state. A phase change recording material according to any one of the preceding claims is provided.

  Further, according to the present invention, as described in claim 5, an information recording medium having a recording layer, wherein the recording layer mainly has a composition represented by the following general formula (1). An information recording medium is provided.

_{{(Sb 1-x Ge x} ) 1-y In y} 1-z-w M z Te w (1)
(Where x, y, z, and w are numbers satisfying 0.001 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.2, 0 ≦ w ≦ 0.1, M is at least one element selected from lanthanoids, provided that both z and w do not become 0.)

According to the present invention, there is provided an information recording medium according to claim 5, wherein 0 <z in the general formula (1).
Further, according to the present invention, as described in claim 7, there is provided the information recording medium according to claim 5 or 6, wherein z / y in the general formula (1) is 0 or more and 1 or less. .
Further, in the present invention, as described in claim 8, the phase change recording medium has a crystalline state in an unrecorded state and an amorphous state in a recorded state. An information recording medium according to any one of claims is provided.

Further, in the present invention, as described in claim 9, the information recording medium is an optical information recording medium, and the information recording medium according to any one of claims 5 to 8 is described. Provide media.
Further, according to the present invention, there is provided the information recording medium according to claim 9, wherein the optical information recording medium further has a protective layer.
Furthermore, in the present invention, as described in claim 11, the optical information recording medium further has a reflective layer, and the reflective layer contains Ag as a main component. A recording medium is provided.

  According to the present invention, a phase-change recording material capable of high-speed recording and erasing, having excellent recording characteristics, high storage stability of a recording signal, and further having excellent repetitive recording durability, and the use of the material. Thus, an information recording medium can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist.

[1] Phase Change Recording Material The phase change recording material of the present invention has a composition represented by the following general formula (1) as a main component.

_{{(Sb 1-x Ge x} ) 1-y In y} 1-z-w M z Te w (1)
Here, x, y, z, and w are numbers satisfying 0.001 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.2, 0 ≦ w ≦ 0.1, and M Is at least one element selected from lanthanoids. However, both z and w do not become 0. Further, x, y, z, and w are all atomic ratios.

  The phase change recording material of the present invention is characterized in that at least one of a lanthanoid and Te is added to a specific composition of the Sb-Ge-In system at a predetermined ratio. The phase change recording material of the present invention has an effect of being excellent in repeated recording durability in addition to jitter characteristics and storage stability of a recording signal.

The point that the Sb-Ge-In based alloy is a recording material that is stable in both crystalline and amorphous states, and is capable of performing a relatively high-speed phase transition between these states. The point that the present inventors have already disclosed that the optical information recording medium having a recording layer using a system alloy with a specific composition exhibits excellent jitter characteristics and storage stability of a recording signal. (JP-A-2001-39031 and the like). With respect to these points, the present inventors have found that an Sb-Ge-In alloy is excellent as a phase change recording material as follows.
That is, since Sb has a high crystallization speed, an amorphous mark cannot be formed under the recording conditions used for a normal optical disk, but the crystallization speed decreases when Ge is mixed with Sb. Therefore, by mixing Ge with Sb, the crystallization speed can be adjusted to have a recordable crystallization speed.

  However, in an optical information recording medium having a recording layer using a composition in which Ge is mixed with Sb, jitter of a recorded signal becomes large. Therefore, the phase change recording material in which Ge is mixed with Sb has a problem in practical use. In fact, Sb-Ge based phase change recording materials are described in Appl. Phys. Lett. 60 (25), 22 June 1992, pp. As discussed in the literature such as 3123-3125, the present inventors performed recording and evaluation on an optical disk using an Sb-Ge alloy as a recording layer under general recording conditions. Although recording on this optical disk was possible, the jitter of the recording signal was increased, and it was not practically usable. Therefore, as a result of further study, the present inventors have found that the addition of an appropriate amount of In to the above Sb-Ge alloy improves the jitter characteristics of the recording signal, and that Sb-Ge is used as a phase change recording material. It has been found that the composition of the -In alloy is good.

  However, as a result of further studies by the present inventors, the phase change recording material having the composition of the Sb—Ge—In alloy tends to have a gradually lower crystallization speed as compared with the initial stage by repeatedly recording. It has been found. In other words, when the phase change recording material having the composition of the Sb—Ge—In based alloy is repeatedly recorded several thousand times, the amorphous phase previously recorded due to the decrease in the crystallization speed is reduced. The mark will not be sufficiently erased. For this reason, the jitter characteristic tends to deteriorate due to insufficient erasing of the amorphous mark. This tendency becomes remarkable when the In content is large.

  The present invention has been made in order to improve the above-mentioned tendency, in particular, by adding at least one of a lanthanoid and Te with a specific composition, to a repetitive recording durability (for example, a jitter characteristic when repetitive recording is performed). It is possible to increase. The reason why the recording durability is repeatedly improved by adding these metal elements is not clear, but is presumed as follows.

  That is, in the case of a phase change recording material having a composition of an Sb-Ge-In-based alloy, a phenomenon similar to segregation may occur when a rapid temperature change is caused by repeated recording. When segregation occurs, the crystallization speed is slowed down, so that a previously recorded amorphous mark may remain without being erased. Then, the presence of the non-erased portion of the amorphous mark causes the jitter characteristic to deteriorate. For this reason, by adding at least one of the lanthanoid and Te to the Sb-Ge-In based phase change recording material with a specific composition, segregation hardly occurs even when repeated recording is performed, and the crystallization speed accompanying the repeated recording is reduced. It is assumed that the phenomenon of slowing down is unlikely to occur. As a result, an optical information recording medium (for example, a CD-RW) using a phase change recording material in which at least one of a lanthanoid and Te is added to a Sb-Ge-In based phase change recording material with a specific composition for a recording layer. Is presumed to be able to maintain the initial crystallization rate even after about 2,000 repetitive recordings.

  In the present invention, “having a predetermined composition as a main component” means that the content of the predetermined composition is 50 atomic% or more of the entire material or the entire layer containing the predetermined composition. It is. In order to further exert the effects of the present invention, the predetermined composition is contained preferably at least 80 atomic%, more preferably at least 90 atomic%, particularly preferably at least 95 atomic%.

  Further, in the present invention, it is preferable that the phase change recording material has a crystalline state in an unrecorded state and an amorphous state in a recorded state. This is because it is presumed that there are not many crystal nuclei in the phase change recording material of the present invention. That is, in the case where a mark in a crystalline state is formed in the amorphous state with the amorphous state being unrecorded, it is preferable to use a phase change recording material having many crystal nuclei. This is because if there are many crystal nuclei in the phase change recording material, the shape of the mark in the crystalline state will not be affected by the position of the crystal nuclei. On the other hand, as described above, since a large number of crystal nuclei do not exist in the phase change recording material of the present invention, the amorphous state is set to an unrecorded state, and a recording mark of a crystalline state is formed in the amorphous state. It is easier to perform good recording by setting the crystalline state to an unrecorded state and forming an amorphous state recording mark in the crystalline state.

  As described above, in order for the phase change recording material of the present invention to realize excellent repetitive recording durability in addition to jitter characteristics and storage stability of a recording signal, each metal element as a main component thereof has a specific composition. Need to be used in This will be described in detail below.

(Sb, Ge)
The Ge amount in the total amount of Sb and Ge, that is, x in the general formula (1) is 0.001 or more and 0.3 or less. Ge has the effect of slowing down the crystallization rate, facilitating the formation of an amorphous phase, and increasing the storage stability of the amorphous phase. For this reason, when the Ge content is low, the crystallization speed may be too high to form an amorphous phase, or the storage stability of the amorphous phase may be insufficient. Therefore, since Ge must be contained in a predetermined amount or more, in the general formula (1), 0.001 ≦ x is satisfied, preferably 0.005 ≦ x, and more preferably 0.01 ≦ x. Yes, more preferably 0.02 ≦ x, particularly preferably 0.03 ≦ x.

  On the other hand, if the Ge content is too large, the crystallization speed may be too slow to erase (crystallize) the amorphous mark. Therefore, in the general formula (1), x ≦ 0.3. From the viewpoint of favorably controlling the crystallization rate, it is preferable that x ≦ 0.25, more preferably x ≦ 0.2, even more preferably x ≦ 0.15, and x ≦ 0. Particularly preferred is 1.

(In)
Incorporation of In has the effect of increasing the signal amplitude and improving jitter characteristics. If the content is too small, the improvement effect may not be obtained. Therefore, y representing the In content in the general formula (1) is set to 0 ≦ y. Preferably, 0 <y, more preferably 0.01 ≦ y, further preferably 0.05 ≦ y, particularly preferably 0.1 ≦ y, and most preferably 0.15 ≦ y. On the other hand, if the In amount is too large, a stable state of a low-reflectivity In-Sb-based stable crystal phase (low-reflectance crystal phase) may be always formed separately from the crystal phase used for recording. In this case, no phase change occurs and recording cannot be performed. Therefore, y representing the In content in the above general formula (1) is set to y ≦ 0.4, preferably y ≦ 0.35, more preferably y ≦ 0.3, and still more preferably y ≦ 0.25. And particularly preferably, y ≦ 0.2. Further, the optimum recording power tends to decrease as the In content increases, so that the above range is preferable.

(Lanthanoid)
The content of the lanthanoid is from 0 to 0.2 in the general formula (1). That is, z indicating the content of the lanthanoid in the general formula (1) is set to 0 ≦ z ≦ 0.2.
When a lanthanoid is contained, a decrease in the crystallization speed due to repeated recording is suppressed. In order to obtain this effect, when Te is not contained, 0 <z in the general formula (1). From the viewpoint of suppressing the decrease in the crystallization rate due to the repetitive recording, 0 <z is preferable, 0.005 ≦ z is more preferable, 0.01 ≦ z is more preferable, and 0.02 is more preferable. It is particularly preferable to satisfy ≦ z. It is presumed that the lanthanoid has a role of accelerating the crystallization speed of the phase change recording material when recording is repeated. For this reason, when a lanthanoid is added to the phase change recording material having the composition of the Sb—Ge—In alloy in which the crystallization speed tends to be reduced due to repeated recording, a decrease in the crystallization speed due to repeated recording is suppressed. It is supposed to be. As described above, the lanthanoid has a role of increasing the crystallization speed of the phase-change recording material at the time of repetitive recording. Therefore, when the number of lanthanoids increases, the crystallization speed may be faster than the initial one due to repetitive recording.

  On the other hand, if the content of the lanthanoid is too large, initial crystallization tends to be difficult, the initial crystallization speed becomes too slow, and the signal amplitude tends to be small. Therefore, in the above general formula (1), z ≦ 0.2, preferably z ≦ 0.15, more preferably z ≦ 0.1, and z ≦ 0.07. Is more preferred. Compared with the case of adding Te described later, the addition of the lanthanoid has a smaller decrease in the signal amplitude than that of the case where the lanthanoid is added.

  The lanthanoid refers to 15 elements of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. These lanthanoids are a series in which 4f electrons are sequentially filled in terms of electron arrangement, and are preferable because they have similar properties. Among these lanthanoids, preferred is at least one of Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and more preferred is Gd or Tb. By using the lanthanoid, a change in the crystallization speed during repeated recording can be suppressed. The lanthanoids can be used alone or in combination of two or more.

(Te)
The content of Te is set to 0 or more and 0.1 or less in the general formula (1). That is, in the general formula (1), w indicating the content of Te is set to 0 ≦ w ≦ 0.1.
Also when Te is added, a decrease in the crystallization speed due to repeated recording is suppressed. In order to obtain this effect, when no lanthanoid is contained, 0 <w in the general formula (1). From the viewpoint of suppressing the decrease in the crystallization rate due to repeated recording, 0 <w is preferable, 0.005 ≦ w is more preferable, 0.01 ≦ w is more preferable, and 0.02 is more preferable. It is particularly preferred that ≦ w.
On the other hand, the reflectance and signal amplitude of the medium tend to be reduced by the addition of Te. Therefore, in the above general formula, w ≦ 0.1, but preferably w ≦ 0.09, and preferably w ≦ 0. 08, more preferably w ≦ 0.07, and particularly preferably w ≦ 0.06.

(Relationship between In and lanthanoid)
In the phase change recording material of the present invention, as the In content in the phase change recording material increases, the crystallization rate tends to decrease more by repeated recording. On the other hand, when the content of the lanthanoid in the phase change recording material increases, the crystallization speed tends to increase by repeated recording. For this reason, in order to reduce the change in the crystallization speed due to repeated recording, it is preferable to control the relationship between the In and lanthanoid contents.

  From such a viewpoint, z / y in the general formula (1) is usually 0 or more, preferably 0.001 or more, more preferably 0.01 or more, and further more preferably 0.05 or more. It is particularly preferably at least 0.1, most preferably at least 0.15. Within this range, the change in the crystallization speed during repeated recording can be reduced.

  Further, z / y in the general formula (1) is preferably 1 or less, more preferably 0.7 or less, further preferably 0.5 or less, particularly preferably 0.3 or less, and most preferably 0 or less. .25 or less. Within this range, not only the initial crystallization (initialization performed for the first time after the production of the information recording medium) can be performed well, but also the signal amplitude can be kept large.

(Relationship between In and Te)
In the phase change recording material of the present invention, when Te is contained, the signal amplitude tends to decrease. Therefore, when Te is contained, the signal amplitude can be made favorable by containing a large amount of In. Therefore, the ratio between the In content (atomic%) and the Te content (atomic%) is preferably (In content)> (Te content), and (In content)> More preferably, 1.5 × (Te content), more preferably (In content)> 2 × (Te content), (In content)> 3 × (Te content) Is particularly preferable, and (In content)> 3.5 × (Te content) is most preferable. On the other hand, from the viewpoint of ensuring the signal amplitude, (In content) <70 × (Te content) is normally set, but (In content) <30 × (Te content) preferable.

(Relationship between lanthanoid and Te)
At least one of a lanthanoid and Te is added to the phase change recording material of the present invention. That is, either one of lanthanoid and Te may be used, or both may be used in combination. By adding these elements, the effect of suppressing a decrease in the crystallization rate due to repeated recording can be obtained. However, in order to more reliably exhibit this effect, z + w is preferably set to 0.01 or more, More preferably, it is set to 0.02 or more. On the other hand, if the lanthanoid and Te are excessively contained, the signal amplitude may be reduced or the initial crystallization may be difficult. Therefore, z + w is usually 0.3 or less, preferably 0.25 or less. It is preferably at most 0.2, more preferably at most 0.15, particularly preferably at most 0.1.
Lanthanoids have the property of increasing the crystallization speed of a phase change recording material by repeated recording. For this reason, the addition of the lanthanoid suppresses a decrease in the crystallization speed due to the repetitive recording of the composition of the Sb-Ge-In alloy. On the other hand, if too much lanthanoid is contained, initial crystallization tends to be difficult.

Te makes it possible to suppress a decrease in the crystallization speed of the phase change recording material due to repeated recording. On the other hand, if Te is excessively contained, the reflectance and the signal amplitude of the medium tend to decrease.
As described above, the lanthanoid and Te have the effect of suppressing the decrease in the crystallization speed of the phase-change recording material due to repeated recording, but make the initial crystallization difficult or reduce the reflectance and signal amplitude of the medium. Have different properties. Therefore, if the lanthanoid and Te are used in combination and their contents are controlled within the above range, the initial crystallization becomes favorable while suppressing the decrease in the crystallization speed of the phase change recording material due to repeated recording, and the medium , The reflectivity and the signal amplitude can be improved.
From the above, in the present invention, it is preferable to use a lanthanoid and Te in combination.

(Other matters)
In general, recording and erasing are performed while irradiating a recording layer with a light beam (laser beam) spot emitted from a light irradiation unit while rotating the medium at a high speed, and relatively moving the light irradiation unit and the medium at a high speed. A case where the relative moving speed is high is referred to as a high recording linear speed (recording speed), and a case where the relative moving speed is low is referred to as a low recording linear speed (recording speed).

In a state where the recording linear velocity is high, the recording layer is once heated by the light beam spot and then rapidly cooled. That is, the temperature history of the recording layer becomes quenched, and in the recording layer having the same composition, the higher the recording linear velocity, the more the amorphous phase is likely to be formed, and the more difficult it is to form the crystalline phase.
Therefore, the crystallization speed is increased in a medium having a higher target recording linear velocity, and the crystallization speed is reduced in a medium having a lower target recording linear velocity. It is desirable to adjust the amounts of Ge, In, and the lanthanoid according to the conditions.

  In order to improve various characteristics, Au, Ag, Al, Ga, Zn, Sn, Si, Cu, Mn, Pd, Pt, Rh, Pb, Cr, Co, Mo are added to the phase change recording material as required. , W, Mn, O, N, Se, V, Nb, Ta, Ti, Bi and the like may be added. In order to obtain the effect of improving the properties, the amount of addition is 0.1 at. % (Atomic%) or more is preferable. However, in order not to impair the preferable characteristics of the composition of the present invention, 10 at. % Or less is preferable.

[2] Information Recording Medium Next, the information recording medium of the present invention will be described.
An information recording medium of the present invention is an information recording medium having a recording layer, wherein the recording layer has a composition represented by the following general formula (1) as a main component.

_{{(Sb 1-x Ge x} ) 1-y In y} 1-z-w M z Te w (1)
(Where x, y, z, and w are numbers satisfying 0.001 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.2, 0 ≦ w ≦ 0.1, M is at least one element selected from lanthanoids, provided that both z and w do not become 0.)

  In the present invention, it is preferable that the information recording medium has a crystalline state in an unrecorded state and an amorphous state in a recorded state. This is because it is assumed that there are not many crystal nuclei in the recording layer composition of the present invention. That is, in the case where the amorphous state is unrecorded and a mark in a crystalline state is formed in the amorphous state, it is preferable to use a recording layer composition having many crystal nuclei. This is because, if there are many crystal nuclei in the recording layer, the shape of the mark in the crystalline state will not be affected by the position of the crystal nuclei. On the other hand, as described above, since a large number of crystal nuclei are not present in the composition of the recording layer in the present invention, the amorphous state is referred to as an unrecorded state, rather than forming a crystalline recording mark in the amorphous state. When the crystalline state is set to an unrecorded state and the recording mark in an amorphous state is formed in the crystalline state, it is easier to perform good recording.

By using the composition represented by the general formula (1) as the recording layer, excellent characteristics such as jitter characteristics, storage stability of amorphous marks, and repetitive recording durability can be obtained even in ultra-high speed recording. The information recording medium can be realized.
Such an information recording medium is not particularly limited as long as it can record and reproduce information by detecting a difference in physical parameters between a crystalline state and an amorphous state. And an information recording medium for detecting differences in electrical resistance, volume, density change and the like. Above all, an information recording medium using the phase change recording material of the present invention is an optical information recording medium utilizing a reflectance change accompanying a reversible change of a crystalline state / amorphous state caused by irradiation with a laser beam. Suitable for application to media.

Further, the information recording medium of the present invention can be applied to an information recording medium utilizing a change in electric resistivity accompanying a reversible change in a crystalline state / amorphous state utilizing Joule heat generated by passing an electric current. Can also be applied.
Hereinafter, as an example of the information recording medium of the present invention, a specific configuration of an optical information recording medium and a recording / reproducing method will be described. Further, as another example of the information recording medium of the present invention, a case where the information recording medium of the present invention is used for applications other than the optical information recording medium will be described.

[2-1] Optical information recording medium (layer structure)
As the optical information recording medium, a medium having a multilayer structure as shown in FIGS. 1A and 1B is usually used. That is, as is apparent from FIGS. 1A and 1B, a recording layer having a composition represented by the general formula (1) as a main component and a protective layer further provided on a substrate. Is preferred.

  A more preferable layer configuration of the optical information recording medium is a configuration in which a first protective layer, a recording layer, a second protective layer, and a reflective layer are provided in this order along the incident direction of the reproduction light. That is, when reproducing light is incident from the substrate side, the substrate, the first protective layer (lower protective layer), the recording layer, the second protective layer (upper protective layer), and the reflective layer have a layer configuration (FIG. 1A). In the case where the reproduction light is incident from the recording layer side, a layer structure of a substrate, a reflective layer, a second protective layer (lower protective layer), a recording layer, and a first protective layer (upper protective layer) is adopted (FIG. 1). (b)).

  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, a semi-transparent extremely thin metal, semiconductor, or dielectric having absorption is provided on the substrate / protective layer when reproducing light is incident from the substrate side or on the protective layer when reproducing light is incident from the side opposite to the substrate. It is also possible to provide a layer or the like to control the amount of light energy incident on the recording layer.

  As described above, a reflection layer is often provided on the side opposite to the recording / reproduction light beam (recording / reproduction light) incidence, but this reflection layer is not essential. Further, in a protective layer preferably provided on at least one surface of the recording layer, materials having different characteristics may be multilayered.

Hereinafter, each layer will be described in detail.
(A) Recording Layer (A-1) Materials Contained in Recording Layer and Amounts The material contained in the recording layer has a composition represented by the general formula (1) as a main component. Since the detailed description of this composition has already been made, the description here is omitted. In order to effectively exhibit the effects of the present invention, the composition represented by the above general formula (1) in the entire recording layer is usually at least 50 atomic%, preferably at least 80 atomic%, more preferably at least 90 atomic%. % Or more, particularly preferably 95 atomic% or more. The higher the content, the more remarkably the effect of the present invention is exerted. However, even if other components such as O and N are contained at the time of forming the recording layer, the content of several to 20 at. Within the range, the effects of the present invention such as high-speed recording and erasing are exhibited.

(A-2) Thickness of Recording Layer The thickness of the recording layer is usually at least 1 nm, preferably at least 3 nm, more preferably at least 5 nm, particularly preferably at least 10 nm. By doing so, the contrast of the reflectance between the crystalline state and the amorphous state is sufficient, and the crystallization speed is also sufficient, so that recording and erasing can be performed in a short time. Further, the reflectance itself has a sufficient value. On the other hand, the thickness of the recording layer is usually at most 30 nm, preferably at most 25 nm, more preferably at most 20 nm, more preferably at most 15 nm, further preferably at most 12 nm, particularly preferably at most 11 nm. In this case, sufficient optical contrast can be obtained, and cracks are less likely to occur in the recording layer. In addition, the recording sensitivity does not deteriorate due to the increase in heat capacity. Further, when the thickness is within the above range, the volume change due to the phase change can be appropriately suppressed, and the recording layer itself or a protective layer that can be provided above and below the recording layer itself, which causes noise when recording is repeated. Microscopic and irreversible deformation is hardly accumulated. Since the accumulation of such deformation tends to decrease the recording durability repeatedly, this tendency can be suppressed by setting the thickness of the recording layer within the above range.

  In the case of recording / reproducing with a focused light beam of an LD (laser diode) having a wavelength of about 650 nm and an objective lens having a numerical aperture of about 0.6 to 0.65 like a rewritable DVD, a blue LD having a wavelength of about 400 nm, and a numerical aperture In a high-density medium that performs recording and reproduction with a focused light beam of an objective lens of about 0.7 to 0.85, the requirement for noise is more severe. In such a case, the more preferable recording layer thickness is 25 nm. It is as follows.

(A-3) More Preferred Aspect of Recording Layer Thickness In the present invention, for optical information recording provided with a recording layer having a composition represented by the above general formula (1) as a main component and capable of high-speed recording and erasing. In the medium, by making the thickness of the recording layer extremely thin, it is possible to improve the second recording characteristics after long-term storage of this optical information recording medium and the decrease in reflectance after long-term storage. Conceivable. Specifically, by setting the film thickness of the recording layer to preferably 11 nm or less, the optical information recording medium using the recording layer having the composition represented by the above general formula (1) has a recording medium after long-term storage. It seems that there is a tendency that the recording characteristics at the time of the second recording are improved, and that a decrease in reflectance during long-term storage is improved.

  In an optical information recording medium using a recording layer having the composition represented by the general formula (1), the jitter in the second recording after long-term storage may be slightly inferior. Although the reason for this is not necessarily clear, it seems to be related to the fact that the signal intensity in the first recording after long-term storage tends to decrease. That is, when recording is performed after the optical information recording medium is stored for a long time, the signal amplitude in the first recording tends to decrease. Since the signal amplitude is recovered by recording a few more times, the decrease in the signal amplitude during the first recording is caused by a large recording mark when the crystal part becomes amorphous for the first time after long-term storage. This is probably due to the difficulty. The reason that the jitter is likely to be deteriorated at the time of the second recording after the long-term storage is that the portion becomes amorphous for the first time after the long-term storage (the portion where the recording beam was not irradiated in the first recording) and again (the second). It is presumed that the portion where the amorphization is performed is mixed. That is, in the second recording, it is considered that the size of the amorphous mark varies due to the above-mentioned mixture.

Although the cause of the tendency of the amorphous marks not becoming large during the first recording after the long-term storage is not clear, since the characteristics return after several times of recording, some change occurs in the crystal part of the recording layer due to the long-term storage. It is thought that it happened. By making the recording layer very thin (preferably 11 nm or less), the characteristics at the time of the second recording after long-term storage are improved. This is because the change in the crystal part of the recording layer tends to be suppressed. It is.
Further, by making the recording layer extremely thin (preferably 11 nm or less), a decrease in reflectance due to long-term storage tends to be suppressed. Although the reason for this is not clear, the change in the recording layer during long-term storage may be suppressed as in the case of improving the recording characteristics in the second recording after long-term storage.

However, if the recording layer is extremely thin, recording characteristics such as signal amplitude may be impaired. However, in this regard, by adjusting the layer configuration and the film thickness of the optical information recording medium, the recording characteristics such as the signal amplitude can be brought to a sufficiently favorable level.
That is, in the case of an optical information recording medium in which a protective layer, a recording layer having the composition represented by the general formula (1), a protective layer, and a reflective layer are provided in this order or in the reverse order, the recording layer film When the thickness is extremely thin (for example, thinner than about 12 nm), the signal intensity tends to decrease. For this reason, when the recording layer is made very thin (for example, 11 nm or less), a device is required to obtain a large signal intensity.

  For example, one method is to change the thickness of the protective layer located on the side where the laser light enters the recording layer. That is, the thickness of the protective layer is made smaller than the thickness of the protective layer at which the reflectance of the optical information recording medium has a minimum value. The film thickness at which the minimum value is obtained depends on the laser wavelength to be used. For example, a film thickness of about 650 nm for DVD is about 50 nm. This optically increases the signal intensity.

However, it is generally known that when the thickness of the light incident side protective layer is reduced, the thermal effect on the substrate and the like is increased and the repeated recording durability tends to be deteriorated. It is difficult to use the above method of reducing the thickness as described above (for example, around 50 nm). To cope with this tendency, even when the thickness of the protective layer on the side where the laser beam is incident on the recording layer is reduced (for example, 50 nm or less), the entire protective layer is formed by the protective layer A described later. (A protective layer containing a metal oxysulfide or a metal nitride), or a protective layer region in a portion of the protective layer that is in contact with the recording layer is a protective layer A described later, so that the optical information recording medium can be used. It is considered that sufficient repetitive recording durability of the medium can be obtained. The details of the protective layer A will be described later.
Based on the above, the thickness of the recording layer in this embodiment is preferably 15 nm or less, more preferably 14 nm or less, still more preferably 13 nm or less, particularly preferably 12 nm or less, and 11 nm or less. It is most preferable to set the following.

  On the other hand, as described above, even when the recording layer thickness is extremely thin in order to improve the recording characteristics after long-term storage, adjusting the layers other than the recording layer if the recording layer thickness is excessively thin. However, sufficient signal strength cannot be obtained. Although the lower limit of the signal strength depends on the performance of the reproducing apparatus, for example, in a rewritable DVD, if the recording layer thickness is less than 3 nm, the signal strength tends to be small and use tends to be difficult.

(A-4) Manufacturing Method of Recording Layer In the recording layer, a predetermined alloy target can be obtained by DC or RF sputtering in an inert gas, particularly an Ar gas.
The density of the recording layer is usually at least 80%, preferably at least 90% of the bulk density. The bulk density ρ referred to here generally uses an approximate value according to the following equation (2), but it can also be measured by preparing a mass of alloy composition constituting the recording layer.

  In the sputter film forming method, the pressure of a sputter gas (usually a rare gas such as Ar; hereinafter, the case of Ar is described as an example) at the time of film formation is reduced, or the substrate is arranged close to the front of the target. Then, 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 one in which Ar ions applied to a target for normal sputtering are partially rebounded and reach the substrate side, or Ar ions in plasma are accelerated by a sheath voltage on the entire surface of the substrate and reach the substrate. Either of

  The irradiation effect of such a high-energy rare gas is referred to as an atomic peening effect. In sputtering using a generally used Ar gas, Ar is mixed into a sputtered film by the atomic peening effect. Therefore, 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 high-energy Ar irradiation effect is small, and a film having a low density is easily formed.

On the other hand, if the amount of Ar is large, the irradiation of high-energy Ar becomes intense, and the density of the film increases, but Ar taken in the film becomes void during repeated recording and precipitates, thereby deteriorating the recording durability repeatedly. Cheap. Therefore, discharge is performed at an appropriate pressure, usually in the range of 10 ⁻² to 10 ⁻¹ Pa.

Next, other components of the structure of the optical information recording medium, which is a preferred embodiment of the present invention, will be described.
(B) Substrate As the substrate used in the present invention, a resin such as polycarbonate, acrylic resin, or polyolefin, or a metal such as glass or aluminum can be used. Usually, the substrate is provided with a guide groove having a depth of about 20 to 80 nm. Therefore, a resin substrate that can form the guide groove by molding is preferable. Further, in the case of a so-called substrate surface incidence (see FIG. 1A) where a focused light beam for recording / erasing / reproduction enters from the substrate side, the substrate is preferably transparent.

The thickness of the substrate is usually 0.05 mm or more and 1.5 mm or less, but about 1.2 mm for CD and about 0.6 mm for DVD is used.
When the optical head of the laser is set to have a high NA (about 0.7 or more) and a short wavelength for high density, a transparent resin is further provided on the upper surface of the incident light side protective layer in FIG. Is provided. The thickness is usually as thin as about 0.01 mm to about 0.1 mm.

(C) Protective Layer (C-1) General Description of Protective Layer Used in the Present Invention In order to prevent evaporation and deformation due to phase change of the recording layer and to control heat diffusion at that time, the present invention employs an optical It is preferable that the information recording medium further has a protective layer. The protective layer is usually formed on one or both sides, preferably both sides, of the recording layer. The material of the protective layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. Generally, dielectric materials such as oxides, sulfides, nitrides, and carbides of metals and semiconductors having high transparency and high melting point, and fluorides such as Ca, Mg, and Li can be used.

In this case, these oxides, sulfides, nitrides, carbides, and fluorides do not necessarily need to have a stoichiometric composition, and the compositions should be controlled or mixed for controlling the refractive index and the like. Is also effective. Considering the repetitive recording characteristics, a mixture of dielectrics is preferred. More specifically, a mixture of a chalcogen compound such as ZnS or a rare-earth sulfide and a heat-resistant compound such as an oxide, a nitride, a carbide, or a fluoride is used. For example, a mixture of a heat-resistant compound containing ZnS as a main component and a mixture of a heat-resistant compound mainly containing rare earth oxysulfide, particularly Y ₂ O ₂ S are examples of preferable protective layer compositions.

  As a material for forming the protective layer, a dielectric material can be usually mentioned. Examples of the dielectric material include oxides such as Sc, Y, Ce, La, Ti, Zr, Hf, V, Nb, Ta, Zn, Al, Cr, In, Si, and Ge; Ti, Zr, and Hf. , V, Nb, Ta, Cr, Mo, W, Zn, B, nitrides such as Al, Si, Ge, and Sn, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Si And the like, or a mixture thereof. Examples of the dielectric material include sulfides such as Zn, Y, Cd, Ga, In, Si, Ge, Sn, Pb, Sb, and Bi; selenides or tellurides; and oxysulfides such as Y and Ce. , Mg, Ca and the like, or a mixture thereof.

Further Examples of dielectric _materials include _{ZnS-SiO 2, SiN, SiO} 2, TiO 2, CrN, and TaS _2, Y _{2 O 2} S or the like. Among these materials, ZnS—SiO ₂ is widely used because of its high film formation rate, small film stress, small volume change rate due to temperature change, and excellent weather resistance. When using a ZnS-SiO _2, ZnS and the composition ratio of SiO ₂ ZnS: SiO ₂ is generally 0: 1 to 1: 0, preferably from 0.5: 0.5 to 0.95: 0.05, more Preferably, it is 0.7: 0.3 to 0.9: 0.1. Most preferably, ZnS: SiO ₂ is 0.8: 0.2.

  Considering the repetitive recording characteristics, it is desirable that the film density of the protective layer be 80% or more of the bulk state from the viewpoint of mechanical strength. When a mixture of dielectrics is used, the theoretical density of the above equation (2) is used as the bulk density.

  The thickness of the protective layer is generally generally from 1 nm to 500 nm. When the thickness is 1 nm or more, the effect of preventing deformation of the substrate and the recording layer can be ensured, and can serve as a protective layer. Further, when the thickness is 500 nm or less, it is possible to prevent the occurrence of cracks due to the remarkable difference in the internal stress of the protective layer itself and the elastic characteristic with the substrate, while acting as the protective layer. .

  In particular, when the first protective layer is provided, the thickness of the first protective layer is usually 1 nm or more, preferably 5 nm or more, particularly preferably 10 nm or more, because it is necessary to suppress deformation of the substrate due to heat. In this way, the accumulation of microscopic substrate deformation during repeated recording is suppressed, and it is possible to prevent the reproduction light from being scattered and the noise from increasing significantly.

  On the other hand, the thickness of the first protective layer is preferably 200 nm or less, more preferably 150 nm or less, and still more preferably 100 nm or less, in view of the time required for film formation. By doing so, the groove shape of the substrate viewed from the recording layer plane does not change. That is, the phenomenon that the depth and width of the groove become smaller than the intended shape on the substrate surface is less likely to occur.

  On the other hand, when the second protective layer is provided, the thickness of the second protective layer is usually at least 1 nm, preferably at least 5 nm, particularly preferably at least 10 nm, in order to suppress deformation of the recording layer. Further, in order to prevent accumulation of microscopic plastic deformation inside the second protective layer that occurs with repeated recording and to suppress noise rise due to scattering of reproduction light, preferably 200 nm or less, more preferably 150 nm or less, It is more preferably 100 nm or less, particularly preferably 50 nm or less.

The thicknesses of the recording layer and the protective layer are not limited by mechanical strength and reliability, but also take into account the interference effect associated with the multi-layer structure, so that the laser light absorption efficiency is good and the amplitude of the recording signal is small. It is selected such that the contrast between the recorded state and the unrecorded state is large.
The protective layer may be composed of a plurality of layers made of different materials as described above. In particular, it is preferable to provide an interface layer containing no sulfur or having a low sulfur content at the interface on the side in contact with the recording layer and / or the interface on the side in contact with the reflective film containing Ag as a main component.
The protective layer may be usually manufactured by a known sputtering method.

(C-2) Preferred Embodiment of Protective Layer In the information recording medium used in the present invention, the composition represented by the above-mentioned general formula (1) (hereinafter, “the composition shown by the above-mentioned general formula (1)” is changed to “the predetermined composition”) It is preferable that the protective layer A is in contact with the recording layer using the protective layer A, and the protective layer A contains a metal oxysulfide or a metal nitride.
When the information recording medium of the present invention is used as a phase-change type optical information recording medium, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is usually used as a material of the protective layer. This is because this material is excellent in transparency, adhesion to the conventional recording layer, sputtering speed, price, and the like.

However, when a protective layer of (ZnS) ₈₀ (SiO ₂ ) ₂₀ is used for a recording layer having a predetermined composition that enables high-speed recording and erasing, a problem arises in that it is desired to further improve the repetitive recording durability. There seems to be. This is considered to be one of the causes of the fact that a rapid temperature change accompanies the erasure of recording on the high-speed recording medium as compared with the case of the low-speed recording medium. For example, when the recording linear velocity is doubled, the time required for heating the recording layer by irradiating laser light is halved and the cooling rate tends to be sharp. This is because the temperature distribution in the melting region of the recording layer tends to be gentle when recording at a low linear velocity, but becomes steep when recording at a high linear velocity. Further, the positional relationship between the melted region and the laser beam tends to be relatively farther in recording at a high linear velocity than in recording at a low linear velocity. Of course, the cause of the insufficient repetitive recording durability is reported as a cause related to the recording layer material itself, such as a difference in properties related to mass transfer due to melting and solidification, and a case in which the conventional recording material is used in combination. It is also conceivable that atomic diffusion of sulfur or the like is more likely to occur.

In the present invention, a protective layer A containing, for example, GeN as a metal nitride and Y ₂ O ₂ S as a metal oxysulfide is provided in contact with a recording layer containing a recording layer material having a predetermined composition. Further, further improvement in the repetitive recording durability of the information recording medium is expected. Although the reason why the improvement of the repetitive recording durability is expected by providing the protective layer A containing a metal nitride such as GeN or a metal oxysulfide such as Y ₂ O ₂ S is not necessarily clear, It is considered that the effect of suppressing the deformation of the recording layer due to a rapid temperature change, mass transfer of the recording layer, diffusion of atoms between layers, and the like is exhibited by performing high-speed recording.

(1) Protective layer A
In the present invention, the protective layer A in contact with the recording layer preferably contains a metal oxysulfide or a metal nitride. Of course, a metal oxysulfide and a metal nitride may be used in combination. This will be described in more detail below.

(1-1) Protective layer A containing metal oxysulfide
In the present invention, it is preferable to use a protective layer A containing a metal oxysulfide. To contain a metal oxysulfide means that the constituent elements in the protective layer exist while maintaining the form of the metal oxysulfide.
In the present invention, by providing the protective layer A containing a metal oxysulfide in contact with the recording layer having a specific composition, it is expected that the durability when the information recording medium is repeatedly recorded is further improved. You. Although the reason is not clear yet, it is considered to be related to the high thermal conductivity and hardness of the protective layer A containing the metal oxysulfide, and the high uniformity of the distribution of the constituent elements. That is, the protective layer A according to the present invention has a higher thermal conductivity than a protective layer using a composite dielectric containing ZnS as a main component, as represented by a ZnS—SiO ₂ film generally used conventionally. High rate and hardness. On the other hand, although the refractive index of the protective layer A depends on the composition ratio, it is usually about 1.7 to 2.4, which is almost the same as that of a protective layer using a composite dielectric mainly composed of ZnS.

Then, since the thermal conductivity of the protective layer A containing the metal oxysulfide is high, the deformation of the recording layer due to thermal expansion is considered to be small. That is, since the thermal conductivity of the protective layer A is high, it is possible to quickly release the heated heat of the recording layer when the recording mark is formed by the laser. For this reason, the temperature difference between the interface area of the protective layer A in contact with the recording layer and the area of the protective layer A far from the recording layer, or the temperature difference between the mark forming area and the surrounding area can be eliminated quickly. As a result, the occurrence of film peeling and cracking due to a temperature difference is suppressed. In other words, it is considered that the overwrite deterioration can be delayed. The thermal conductivity can be indirectly known from the value of the laser power at the time of forming an amorphous mark in the created disk. That is, as the thermal conductivity increases, the laser power required to raise the temperature of the recording layer tends to increase. For example, when the protective layer A containing a metal oxysulfide is used, the laser power required for forming a mark is higher than when a protective layer of ZnS: SiO ₂ = 80: 20 (mol%) is used. This is because the function of the protective layer A as a heat dissipation layer is increasing due to the high thermal conductivity.

The protection layer using ZnS: SiO ₂ = 80: 20 (mol%) has a JIS Knoop hardness of about 280, whereas the protection layer A using, for example, Y ₂ O ₂ S as a metal oxysulfide. The JIS Knoop hardness is about 520. The protective layer A having a high hardness is important for preventing deformation of the recording layer. If the hardness is low, it is difficult to appropriately suppress the volume change of the recording layer due to recording / erasing, that is, the deformation caused by the volume difference between the amorphous and the crystal, and is accumulated along with the number of repeated overwrites, Eventually, the signal strength is reduced.
Further, since the protective layer A containing a metal oxysulfide metal atom is bonded with oxygen with sulfur, mixed with the sulfur and oxygen, such sulfide ZnS-SiO ₂ or ZnS-Y ₂ O ₃ And a protective layer using a mixture of oxides is incomparably high. Therefore, the protective layer A is sulfur, oxygen, and dispersibility of the metal atom such as selenium atom in higher than conventional ZnS-SiO _2, is considered to exhibit stable and high performance. For this reason, it is assumed that the phenomenon that sulfur is diffused from the protective layer to the recording layer during repeated overwriting to cause a decrease in reflectance and a change in crystallization rate is also suppressed.

When a protective layer A containing a metal oxysulfide such as Y ₂ O ₂ S is provided in contact with a recording layer having a predetermined composition used in the present invention, a metal nitride such as GeN is formed on the protective layer A. The signal amplitude of the information recording medium tends to increase as compared with the case where it is contained. Although the reason for this is not clear, it is considered that the crystal growth properties of the recording layer slightly vary depending on the protective layer A in contact with the recording layer, and the size of the formed amorphous mark is different. It is considered that such properties are determined by the combination of the material of the recording layer and the material of the protective layer A. However, in the conventional recording layer material, a change in signal intensity due to the material of the protective layer A in contact has not been noticed. .
Examples of the metal element used for the metal oxysulfide include rare earth metal elements such as Sc, yttrium, and lanthanoid elements such as La and Ce; transition metal elements such as Ti; and the like. Among them, rare earth metal elements are preferable, and yttrium and rare earth metal elements selected from the group consisting of La, Ce, Nd, Sm, Eu, Gd, Tb, and Dy are particularly preferable. Since yttrium oxysulfide (Y ₂ O ₂ S) is more thermochemically stable than Y ₂ O ₃ and Y ₂ S ₃ up to about 1000 ° C., yttrium is the most preferable element.

The content of the metal oxysulfide in the protective layer A is preferably 5 mol% or more, more preferably 10 mol% or more, and most preferably 15 mol% or more. If the content of the metal oxysulfide is too small, the overwrite characteristics may be reduced. On the other hand, from the viewpoint of the repetitive overwrite characteristics and the like, it is preferable that the content of the metal oxysulfide in the protective layer A is larger, and the content of the metal oxysulfide in the protective layer A is 100 mol% or less. Good.
Further, the content of the metal element constituting the metal oxysulfide in the protective layer A is usually at least 10 at%, preferably at least 20 at%, more preferably at least 25 at%. Since the content of the metal element constituting the metal oxysulfide is an index indicating the content of the metal oxysulfide in the protective layer A, if the content of the metal element is too small, the effect of further improving the overwrite characteristics is sufficient. Not always. On the other hand, from the viewpoint of repeated overwrite characteristics and the like, it is preferable that the content of the metal oxysulfide in the protective layer A is as large as possible. Therefore, the upper limit of the content of the metal element constituting the metal oxysulfide is limited. This is the content of the metal element when the layer A is entirely composed of metal oxysulfide.

Further, the protective layer A may be used in combination with a metal oxysulfide and another material. The other material is not particularly limited as long as it is a material generally used for the protective layer. For example, dielectric materials such as oxides, sulfides, nitrides, and carbides of metals and semiconductors, which are generally highly transparent and have a high melting point, and fluorides such as Ca, Mg, and Li can be used.
In this case, these oxides, sulfides, nitrides, carbides, and fluorides do not necessarily need to have a stoichiometric composition, and the compositions should be controlled or mixed for controlling the refractive index and the like. Is also effective. Considering the repetitive recording characteristics, a mixture of dielectrics is preferred.
Further, as a material to be contained in the protective layer A, a dielectric material can be usually mentioned. Examples of the dielectric material include oxides such as Sc, Y, Ce, La, Ti, Zr, Hf, V, Nb, Ta, Zn, Al, Cr, In, Si, and Ge; Ti, Zr, and Hf. , V, Nb, Ta, Cr, Mo, W, Zn, B, nitrides such as Al, Si, Ge, and Sn, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Si And the like, or a mixture thereof. Examples of the dielectric material include sulfides such as Zn, Y, Cd, Ga, In, Si, Ge, Sn, Pb, Sb, and Bi; selenides or tellurides; and oxysulfides such as Y and Ce. , Mg, Ca and the like, or a mixture thereof.

More specifically, oxidation of metal or semiconductor represented by zinc sulfide, zinc oxide, silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, rare earth oxide, rare earth sulfide, rare earth fluoride, magnesium fluoride, etc. , Sulfides, nitrides, carbides or fluorides. Among them, particularly preferred are zinc compounds such as zinc sulfide and zinc oxide which have excellent adhesion to the recording layer. As a result, more stable and high durability can be obtained.
When another material is contained in the protective layer A in addition to the metal oxysulfide, the content of this material is usually 99 mol% or less, preferably 90 mol% or less. On the other hand, it is usually at least 1 mol%, preferably at least 5 mol%.

However, the appropriate content varies depending on the type of the materials to be mixed. For example, when zinc sulfide is used as the above-mentioned material, there is no problem even if its content is large, and it is usually 20 mol% or more, preferably 30 mol% or more, more preferably 50 mol% or more, and most preferably 60 mol% or more.
On the other hand, when zinc oxide is used as the material, an excessively large content tends to be unfavorable, and is usually 30 mol% or less, preferably 20 mol% or less, and more preferably 10 mol% or less. Further, the molar content of zinc oxide is more preferably half or less of the molar content of metal oxysulfide.
A particularly preferred composition of the protective layer A is a mixed composition containing Y ₂ O ₂ S and ZnS. In this case, particularly excellent overwrite characteristics can be obtained. In this case, the molar ratio of ZnS to Y ₂ O ₂ S is usually 1% or more, preferably 5% or more, more preferably 10% or more, and usually 1000% or less, preferably 700% or less, and furthermore Preferably it is 500% or less.

In addition, it is also possible to make metallic zinc exist in the protective layer A. However, it is preferable to contain it in the form of a zinc compound such as zinc oxide or zinc sulfide described above.
The purity of the protective layer A in the present invention (the content of the metal oxysulfide in the protective layer A or the content of the mixture of the metal oxysulfide and another material) is preferably 90 mol% or more. The higher the purity, the better, but the effect of the amount of the impurity less than 10 mol% on the characteristics of the protective layer A is negligibly small. In particular, when the impurity is a stable compound, the adverse effect is small, but when the impurity exceeds 10 mol%, physical properties such as hardness and stress of the film are likely to change, and the characteristics of the protective layer A may be deteriorated. .

The protective layer A containing a metal oxysulfide can be formed by forming a film by a sputtering method using a target containing a metal oxysulfide. Usually, a target having a composition range substantially the same as the composition that is preferable for the protective layer A is used.
That is, it is preferable to use a target containing metal oxysulfide as a sputtering target. The type of the metal element of the metal oxysulfide used for the target is appropriately selected according to the composition of the protective layer A.
When the protective layer A contains a metal oxysulfide and another protective layer material, a target of a mixture of the metal oxysulfide and the other material is used in accordance with the composition of the other material to be used. You can do it. Alternatively, a metal oxysulfide target and a target of the other material may be separately prepared and sputtered simultaneously.

The content of the metal oxysulfide in the target is usually at least 10 mol%, preferably at least 30 mol%, more preferably at least 50 mol%. If the content of the metal oxysulfide in the target is excessively small, the metal oxysulfide may be decomposed in the target and the protective layer A may not be able to contain the metal oxysulfide. On the other hand, the content of the metal oxide in the target changes according to the content of the other protective layer material used. However, when a target composed of a metal oxysulfide alone is used, the content of the metal oxysulfide in the target is usually set to 100 mol%.
Whether or not a metal oxysulfide is contained in the target can be confirmed by measuring X-ray diffraction of the target.
In addition, a target containing a metal oxysulfide is usually manufactured using a known method such as a hot pressing method using a metal oxysulfide powder or a mixed powder of an oxide and a sulfide of the same metal. . Rare earth metal elements are preferable as the metal element used here.
Known conditions may be used for the sputtering.

In general, the composition of the protective layer A can be identified by a combination of Auger electron spectroscopy (AES), Rutherford back scattering (RBS), inductively coupled high frequency plasma spectroscopy (ICP), and the like.
(1-2) Protective layer A containing metal nitride
In the present invention, it is also preferable to use a protective layer containing a metal nitride as the protective layer A.
Since metal nitrides tend to have a high thermal conductivity like metal oxysulfides, the thermal conductivity of the protective layer A should be high, as described in the case where the metal oxysulfides are contained. It is considered that this makes it possible to suppress the occurrence of film peeling and cracks due to a temperature difference, and to delay overwrite deterioration.

Examples of the metal used for the metal nitride include at least one element selected from the group consisting of Si, Ge, Al, Ti, Ta, Cr, Mo, Nb, Zr, and Hf. Since the nitrides of these elements are stable, the storage stability of the information recording medium tends to be improved. A plurality of the above elements can be used. Preferably, the above elements are Si, Ge, Al, and Cr, which have higher transparency and better adhesion.
When one kind of the above elements is used, a nitride formed of the above element alone can be given as a material formed by the above element and nitrogen. More specifically, near-compositions such as Si-N, Ge-N, Cr-N, and Al-N can be cited. Among these, Si-N, Ge-N, Cr-N, and Si-N are preferable from the viewpoint that the effect of preventing diffusion to the recording layer is higher. It is preferable to use N (silicon nitride), Ge-N (germanium nitride), and Al-N (aluminum nitride), and it is more preferable to use Ge-N (germanium nitride).

When two or more of the above elements are used, a compound nitride of the above elements can be given as a material formed by the above elements and nitrogen. As an example using Ge-N as a typical example of such a compound, Ge-Si-N, Ge-Sb-N, Ge-Cr-N, Ge-Al-N, Ge-Mo-N, Ge -Al, B, Ba, Bi, C, Ca, Ce, Cr, Dy, Eu, Ga, In, K, La, Mo, Nb, Ni, Pb, Pd Examples include those containing Si, Sb, Sn, Ta, Te, Ti, V, W, Yb, Zn, Zr, and the like.
The content of the metal nitride in the protective layer A is preferably at least 5 mol%, more preferably at least 10 mol%, most preferably at least 15 mol%. If the content of the metal nitride is too small, the overwrite characteristics may deteriorate. On the other hand, from the viewpoint of the repetitive overwrite characteristics and the like, it is preferable that the content of the metal nitride in the protective layer A is as large as possible, and the content of the metal nitride in the protective layer A should be 100 mol% or less. .

Further, the content of the metal element constituting the metal nitride in the protective layer A is usually at least 10 at%, preferably at least 20 at%, more preferably at least 25 at%. If the content of the metal nitride is too small, the effect of further improving the overwrite characteristics may not be sufficient. On the other hand, from the viewpoint of the repetitive overwrite characteristics and the like, the higher the content of the metal nitride in the protective layer A, the more preferable. Therefore, the upper limit of the content of the metal element constituting the metal nitride is limited by the protective layer A. Is the content of the above-mentioned metal element when all are composed of metal nitride.
Further, the protective layer A may be used in combination with a metal nitride and another material. As other materials and their contents, the same materials as those described for the protective layer A containing the metal oxysulfide may be used.

In the present invention, the purity of the protective layer A (the content of the metal nitride in the protective layer A or the content of the mixture of the metal nitride and another material) is preferably 90 mol% or more. The higher the purity, the better, but the effect of the amount of the impurity less than 10 mol% on the characteristics of the protective layer A is negligibly small. In particular, when the impurity is a stable compound, the adverse effect is small, but when the impurity exceeds 10 mol%, physical properties such as hardness and stress of the film are likely to change, and the characteristics of the protective layer A may be deteriorated. .
The protective layer A containing a metal nitride can be formed by forming a film by a sputtering method using a target containing a metal nitride. Further, the protective layer A is formed by flowing a small amount of a mixed gas of Ar and N ₂ in a vacuum chamber to a predetermined vacuum pressure to form a predetermined metal (a metal element simple substance or a metal in the metal nitride contained in the protective layer A). The target may be formed by applying a voltage to a target made of a composite of elements and discharging the metal element or the composite of the metal elements, which is ejected and reacted with N ₂ to form a nitride to form a nitride film by a reactive sputtering method. Here, it should be noted that if the nitrogen content in the protective layer A is too small, it is difficult to ensure the transparency of the protective layer A, and if the nitrogen content is too large, the optical information recording medium will be difficult. Of the recording durability becomes insufficient. Therefore, when using the above reactive sputtering method, it is important to adjust the nitrogen flow rate. Further, the pressure during sputtering also affects the film quality. Normally, the protective layer A can be formed densely by lowering the pressure.

In general, the composition of the protective layer A can be identified by a combination of Auger electron spectroscopy (AES), Rutherford back scattering (RBS), inductively coupled high frequency plasma spectroscopy (ICP), and the like.
(1-3) Thickness of Protective Layer A The preferable range of the thickness of the protective layer A differs depending on the position where the protective layer A is used.
That is, when the protective layer A is provided as the first protective layer, the thickness of the first protective layer is usually 1 nm or more, preferably 5 nm or more, particularly preferably 10 nm, because it is necessary to suppress substrate deformation or the like due to heat. That is all. In this way, the accumulation of microscopic substrate deformation during repeated recording is suppressed, and it is possible to prevent the reproduction light from being scattered and the noise from increasing significantly.

On the other hand, the thickness of the first protective layer is preferably 200 nm or less, more preferably 150 nm or less, and still more preferably 100 nm or less, in view of the time required for film formation. By doing so, the groove shape of the substrate viewed from the recording layer plane does not change. That is, the phenomenon that the depth and width of the groove become smaller than the intended shape on the substrate surface is less likely to occur.
When the protective layer A is provided as a second protective layer, the thickness of the second protective layer is usually at least 1 nm, preferably at least 5 nm, particularly preferably at least 10 nm, for suppressing deformation of the recording layer. Further, in order to prevent accumulation of microscopic plastic deformation inside the second protective layer that occurs with repeated recording and to suppress noise rise due to scattering of reproduction light, preferably 200 nm or less, more preferably 150 nm or less, It is more preferably 100 nm or less, particularly preferably 50 nm or less.

However, in the present invention, the protective layer A having high thermal conductivity and high hardness is generally provided in contact with the recording layer. As described above, the recording layer can be made thin. That is, when the protective layer A is provided in contact with the recording layer surface on the side where the laser beam is incident, the thickness of the protective layer A is preferably set to 50 nm or less.
The sputtering rate of a material mainly containing a metal oxysulfide such as Y ₂ O ₂ S is compared with the sputtering rate of a conventionally used material such as (ZnS) ₈₀ (SiO ₂ ) _20. , Tends to be slow. For this reason, from the viewpoint of increasing the productivity of the information recording medium, a protective layer A containing metal oxysulfide or the like is provided relatively thin in contact with the recording layer, and a protective layer B is provided in contact with this protective layer A. Is also good. For the protective layer B, a conventionally used material (for example, (ZnS) ₈₀ (SiO ₂ ) ₂₀ ) may be used. Details of a specific mode of such an information recording medium will be described later.

  As described above, when multilayering is performed using the protective layer A and the protective layer B, the thickness of the protective layer A in the present invention is usually 0.1 nm or more, preferably 1 nm or more, more preferably 2 nm or more, and still more preferably. Is at least 3 nm, particularly preferably at least 5 nm. On the other hand, the thickness of the protective layer A is usually 100 nm or less, preferably 50 nm or less, more preferably 25 nm, and still more preferably 10 nm or less.

(1-4) Position of Protective Layer A and Recording Layer In the present invention, the protective layer A containing a metal oxysulfide or a metal nitride is preferably provided in contact with the recording layer. More preferably, the predetermined protective layer A is provided on both surfaces of the recording layer. This is because the provision of the predetermined protective layer A on both sides of the recording layer makes it possible to further improve the overwrite characteristics repeatedly. Generally, by providing the predetermined protective layer A on both sides of the recording layer, the recording layer and the protective layer A tend to peel off easily. However, in the recording layer using the predetermined composition in the present invention, It is considered that the problem of the peeling is unlikely to occur.
For example, when a protective layer A containing a metal oxysulfide such as Y ₂ O ₂ S is provided in contact with a recording layer having a conventional SbTe eutectic (Sb ₇₀ Te ₃₀ ) composition, film peeling occurs in an environmental resistance test. There is a tendency. This tendency becomes more remarkable when the protective layer A is provided on both sides of the recording layer. For example, in a conventional recording layer using a SbTe eutectic composition, when a protective layer A containing a metal oxysulfide such as Y ₂ O ₂ S is provided on both sides of the recording layer, an environmental resistance test involving high humidity is required. , Film peeling tends to occur, and the adhesion and weather resistance of the film tend not to be always sufficient.

(2) Protective layer B
Another example of a preferred layer configuration of the optical information recording medium is that one or both of the first protective layer and the second protective layer have a two-layer structure of a protective layer A and a protective layer B. From the viewpoint of repeated overwriting and the like, it is preferable that the first protective layer located on the laser light incident side has a two-layer structure (FIGS. 6A and 6B). It is more preferable that both of the protective layers have a two-layer structure of a protective layer A and a protective layer B (see FIGS. 7A and 7B).
In the preferred layer configuration, the first protective layer and the second protective layer have a two-layer structure of the protective layer A and the protective layer B. However, as long as the protective layer A is provided in contact with the recording layer, The invention is not limited to such an embodiment. For example, by providing a protective layer formed of another material in contact with the protective layer B, the number of the first protective layer and the second protective layer can be appropriately increased to three or more.

(2-1) Material of protective layer B, manufacturing method, etc. As a material of protective layer B, a material generally used for a protective layer may be appropriately used. Since such a material has already been described, a description thereof will be omitted. The protective layers A and B may be two layers made of different materials, or may have a gradient composition in which each component changes gradually.
In addition, the method of manufacturing the protective layer B may be a method generally used for the protective layer.

(2-2) Protective Layer B Thickness The protective layer B is in contact with the protective layer A, and plays a role as a protective layer in a two-layer structure of the protective layer A and the protective layer B. Therefore, the thickness of the protective layer B is a thickness obtained by subtracting the thickness of the protective layer A from the thickness generally required for the protective layer.
However, in the present invention, since the protective layer A having high thermal conductivity and high hardness is generally provided in contact with the recording layer, the thickness of the protective layer located on the side where the laser beam enters the recording layer (for example, When the protective layer is formed of only the protective layer A, the thickness of the protective layer A, and when the protective layer is formed by laminating the protective layer A and the protective layer B, the total thickness of the protective layer A and the protective layer B. The thickness can be reduced as described in the description of the recording layer.

That is, when the protective layer A is provided in contact with the recording layer surface on the side where the laser beam is incident, and the protective layer B is further provided in contact with the protective layer A, the thickness of the protective layer A is reduced. It is preferable that the total thickness of the protective layer B and the thickness of the protective layer B be 50 nm or less.
As described above, when multilayering is performed using the protective layer A and the protective layer B, the thickness of the protective layer A in the present invention is usually 0.1 nm or more, preferably 1 nm or more, more preferably 2 nm or more, and still more preferably. Is at least 3 nm, particularly preferably at least 5 nm. On the other hand, the thickness of the protective layer A is usually 100 nm or less, preferably 50 nm or less, more preferably 25 nm, and still more preferably 10 nm or less. For this reason, the thickness of the protective layer B may be the remaining portion of the total thickness of the protective layer excluding the protective layer A.
In addition, the thickness of the recording layer and the protective layer are good for the laser light absorption efficiency and the amplitude of the recording signal in consideration of the interference effect associated with the multilayer structure in addition to the limitation in terms of mechanical strength and reliability. It is selected such that the contrast between the recorded state and the unrecorded state is large.

(D) Reflective Layer In the optical information recording medium, a reflective layer can be further provided. In the present invention, from the viewpoint of enhancing the heat dissipation of the recording layer, it is preferable that the optical information recording medium further has 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 side opposite to the recording layer with respect to the incident side. That is, when reproducing light is incident from the substrate side, it is usual to provide a reflective layer on the opposite side of the recording layer with respect to the substrate. Usually, a reflective layer is provided between the reflective layers (see FIGS. 1A and 1B).

  The material used for the reflective layer is preferably a substance having a high reflectivity, particularly a metal such as Au, Ag, or Al, which can also be expected to have a heat radiation effect. Although the heat dissipation is determined by the film thickness and the thermal conductivity, the thermal conductivity is almost proportional to the volume resistivity of these metals, so that the heat dissipation performance can be represented by the sheet resistivity. The sheet resistivity is usually 0.05 Ω / □ or more, preferably 0.1 Ω / □ or more, while 0.6 Ω / □ or less, preferably 0.5 Ω / □ or less, more preferably 0.4 Ω / □ or less. And more preferably 0.2 Ω / □ or less.

This guarantees particularly high heat dissipation, and in the formation of an amorphous mark, competition between amorphization and recrystallization is remarkable, as in a recording layer used for an optical information recording medium. In some cases, it is necessary to suppress recrystallization to some extent. A small amount of Ta, Ti, Cr, Mo, Mg, V, Nb, Zr, Si or the like may be added to the above-mentioned metals for controlling the thermal conductivity of the reflection layer itself and improving the corrosion resistance. The addition amount is usually 0.01 atomic% or more and 20 atomic% or less. Aluminum alloys containing at least one of Ta and Ti in an amount of 15 atomic% or less, particularly alloys of Al _α Ta _1-α (0 ≦ α ≦ 0.15) have excellent corrosion resistance and are used for optical information recording. It is a particularly preferred reflective layer material for improving the reliability of the medium.
In particular, when the thickness of the second protective layer is set to 40 nm or more and 50 nm or less, it is preferable that the added element is set to 2 atomic% or less in order to increase the thermal conductivity of the reflective layer.

  It is particularly preferable that Ag is a main component as a material of the reflection layer. The phrase “having Ag as a main component” means that Ag is contained in an amount of 50 atomic% or more with respect to the entire reflection layer. The Ag content in the entire reflecting layer is preferably at least 70 atomic%, more preferably at least 80 atomic%, further preferably at least 90 atomic%, and more preferably at least 95 atomic%. Particularly preferred. Most preferably, the material of the reflective layer is made of pure Ag from the viewpoint of improving heat dissipation.

The reason why it is preferable to use Ag as a main component is as follows. That is, when a recording mark that has been stored for a long time is recorded again, a phenomenon that the recrystallization speed of the phase change recording layer is increased only in the first recording immediately after the storage may occur. Although the reason why such a phenomenon occurs is unknown, the size of the amorphous mark formed in the first recording immediately after the storage is desired due to an increase in the recrystallization speed of the recording layer immediately after the storage. It is presumed that it will be smaller than the size of the mark. Therefore, when such a phenomenon occurs, the cooling rate of the recording layer is increased by using Ag, which has a very high heat dissipation property, for the reflective layer, so that the recording layer can be re-used at the first recording immediately after storage. Crystallization can be suppressed and the size of the amorphous mark can be maintained at a desired size.
Ag alloys containing any one of Mg, Ti, Au, Cu, Pd, Pt, Zn, Cr, Si, Ge, Bi, and rare earth elements in an amount of 0.01 atomic% or more and 10 atomic% or less are also reflectance and thermal conductivity. It is preferable because it has a high rate and excellent heat resistance.

The thickness of the reflective layer is usually 10 nm or more in order to completely reflect incident light without transmitted light, but is preferably 20 nm or more, and more preferably 40 nm or more. Also, if the thickness is too large, the heat radiation effect is not changed and the productivity is unnecessarily deteriorated, and cracks are easily generated. Therefore, the thickness is usually set to 500 nm or less, preferably 400 nm or less, and more preferably 300 nm or less. Is more preferable.
The recording layer, the protective layer and the reflective layer are usually formed by a sputtering method or the like.

  It is desirable to form a film using an in-line apparatus in which a target for a recording layer, a target for a protective layer, and if necessary, a target for a reflective layer material are installed in the same vacuum chamber, in order to prevent oxidation and contamination between layers. It is also excellent in terms of productivity.

(E) Protective coating layer On the outermost surface side of the optical information recording medium, a protective coating made of an ultraviolet curable resin or a thermosetting resin to prevent direct contact with air and to prevent damage due to contact with foreign matter. Preferably, a layer is provided. The protective coating layer is usually 1 μm to several hundred μm thick. Further, a dielectric protection layer having high hardness may be further provided, or a resin layer may be further provided thereon.
(Initial crystallization method of optical information recording medium)
The recording layer is usually formed by a physical vapor deposition method in a vacuum such as a sputtering method. In a state immediately after the film formation (as-deposited state), the recording layer is usually amorphous. It is preferable to crystallize to make an unrecorded and erased state. This operation is called initialization (or initial crystallization). The initial crystallization operation includes, for example, oven annealing in a solid phase at a crystallization temperature (normally 150 to 300 ° C.) or higher and a melting point or lower, annealing by irradiation with light energy such as laser light or flash lamp light, and melt initialization. And the like. In the present invention, in order to use a phase change recording material with less generation of crystal nuclei, it is preferable to use melt initialization among the above initial crystallization operations.

In the melt initialization, if the recrystallization rate is too slow, there is a time margin for achieving thermal equilibrium, and other crystal phases may be formed. Therefore, it is preferable to increase the cooling rate to some extent. Further, if the recording layer is kept in the molten state for a long time, the recording layer flows, the thin film such as the protective layer is peeled off by stress, and the resin substrate or the like is deformed.
For example, the time for maintaining the temperature above the melting point is usually 10 μs or less, preferably 1 μs or less.

  Further, it is preferable to use a laser beam for the melt initialization. In particular, initial crystallization is performed using an elliptical laser beam having a short axis substantially parallel to the scanning direction (hereinafter, this initialization method is referred to as “bulk”). Erase ”). In this case, the length of the major axis is usually 10 to 1000 μm, and the length of the minor axis is usually 0.1 to 5 μm.

  Note that the lengths of the major axis and the minor axis of the beam here are defined from the half width when measuring the light energy intensity distribution in the beam. In order to easily realize local heating and rapid cooling in the minor axis direction, the beam shape is more preferably 5 μm or less, and more preferably 2 μm or less, in the minor axis direction.

  Various laser light sources such as a semiconductor laser and a gas laser can be used. The power of the laser beam is usually about 100 mW to 10 W. Other light sources may be used as long as the same power density and beam shape can be obtained. Specifically, Xe lamp light and the like can be mentioned.

  In the initialization by bulk erasing, for example, when a disc-shaped recording medium is used, the short axis direction of the elliptical beam is made substantially coincident with the circumferential direction, the disc is rotated to scan in the short axis direction, and one round (1 The entire surface can be initialized by moving in the major axis (radius) direction for each rotation. This makes it possible to realize a polycrystalline structure oriented in a specific direction with respect to the focused recording / reproducing light beam scanned along the track in the circumferential direction.

  The moving distance in the radial direction per rotation is preferably shorter than the beam major axis so as to overlap, so that the same radius is irradiated with the laser light beam a plurality of times. As a result, the initialization can be reliably performed, and the non-uniform initialization state due to the energy distribution (normally, 10 to 20%) in the beam radial direction can be avoided. On the other hand, if the amount of movement is too small, the other undesired crystal phase is likely to be formed, so that the amount of movement in the radial direction is usually set to １ ／ or more of the long axis of the beam. The scanning speed of the initialization energy beam is usually in the range of about 3 to 20 m / s.

  At least, whether or not the optical information recording medium of the present invention can be obtained by melt initialization depends on the reflectance R1 in the unrecorded state after initialization and the actual focused light beam for recording (for example, having a diameter of 1 μm It is possible to judge whether or not the reflectance R2 in an erased state by recrystallization after recording an amorphous mark with a focused light beam of a certain degree is substantially equal to each other. Here, R2 is the reflectance of the erased portion after recording 10 times.

  Therefore, the optical information recording medium of the present invention satisfies the following relational expression (3) when the reflectance R1 of the unrecorded portion after the initial crystallization is R2 and the reflectance of the erased portion after the 10th recording is R2. Is preferred.

  Here, the reason why the reflectance R2 of the erased portion after the tenth recording is used as a judgment index is that if the tenth recording is performed, the influence of the crystal state reflectance which can remain in an unrecorded state by only one recording is obtained. This is because the entire surface of the optical information recording medium can be recrystallized by recording / erasing at least once. On the other hand, if the number of recordings greatly exceeds 10, the conversely causes factors other than a change in the crystal structure of the recording layer, such as microscopic deformation of the recording layer due to repeated recording and diffusion of foreign elements from the protective layer to the recording layer. This causes a change in reflectivity, making it difficult to determine whether or not a desired crystal state has been obtained.

In the above relational expression (3), ΔR is set to 10% or less, but is preferably set to 5% or less. When the content is 5% or less, an optical information recording medium with lower signal noise can be obtained.
For example, in the case of an optical information recording medium in which R1 is about 17%, R2 should be approximately in the range of 16 to 18%.

  The erasing state can be obtained by irradiating the recording layer with DC power to melt the recording layer and re-solidifying the recording layer without necessarily modulating the recording focused laser beam according to the actual recording pulse generation method. .

In order to obtain a desired initial crystalline state for the phase-change recording material used for the recording layer in the present invention, it is particularly important to set the scanning speed of the initialization energy beam with respect to the recording layer plane. Basically, it is important that the crystal state after the initial crystallization is similar to the crystal state of the erased portion after recording, so that when the actual recording is performed using the focused light beam, the focused light beam with respect to the recording layer surface It is desirable to be close to the relative scanning line speed. More specifically, the initialization energy beam is scanned at a linear velocity of about 20 to 80% of the maximum linear velocity for recording on the optical information recording medium.
Note that the maximum recording linear velocity is, for example, a linear velocity at which the erasing ratio becomes 20 dB or more when the erasing power Pe is applied in a DC manner at that linear velocity.

  The erasing ratio is generally defined as the difference between the carrier level of the signal of the amorphous mark recorded at a single frequency and the carrier level after erasing by direct irradiation with Pe. The measurement of the erasing ratio is performed, for example, as follows. First, under a recording condition in which a sufficient signal characteristic (that is, a characteristic in which a reflectance, a signal amplitude, a jitter, or the like satisfies a specified value) is obtained, a condition having a high frequency is selected from the modulated signals to be recorded, and recording is performed 10 times as a single frequency. To form an amorphous mark, and measure the carrier level (CL during recording). Thereafter, DC irradiation was performed once on the amorphous mark while changing the erasing power Pe. At this time, the carrier level (CL after erasing) was measured, and the C.I. L. And after erasure. L. , Ie, the erase ratio is calculated. When the power Pe of the DC irradiation is changed, the erasing ratio generally increases once, decreases, and tends to increase. Here, the initial peak value of the erasing ratio observed when the power Pe is started to increase is determined by the sample. The erasure ratio is used.

  The scanning speed of the initialization energy beam is such that when the initialization energy beam is scanned at a speed lower than approximately 20% of the maximum linear velocity defined above, phase separation occurs and it is difficult to obtain a single phase. Even in the case of a phase, the crystallites may grow, particularly in the initialization beam scanning direction, or may be oriented in an undesirable direction. Preferably, the initialization energy beam may be scanned at a speed of 30% or more of the maximum recordable linear speed.

  On the other hand, when the initialization energy beam is scanned at a speed equal to the maximum recordable linear speed, that is, approximately higher than 80%, it is not preferable because a region once melted by the initialization scan becomes amorphous again. This is because if the scanning line speed is increased, the cooling rate of the melted portion is increased, and the time until re-solidification is shortened. With a focused light beam having a diameter of about 1 micron for recording, recrystallization by crystal growth from a crystal region around the melting region can be completed in a short time. However, when scanning with an initialization elliptical light beam, the area of the melting region in the major axis direction becomes large, so the scanning linear velocity is set lower than during actual recording, and recrystallization during resolidification is performed in the melting region. It needs to be spread all over. From such a viewpoint, the scanning linear velocity of the initialization energy beam is preferably 70% or less of the maximum linear velocity of recording, more preferably 60% or less, and most preferably lower than 50%. .

  The optical information recording medium of the present invention has a feature that, when initial crystallization is performed by irradiating a laser beam, the moving speed of the medium with respect to the laser beam can be increased. This is preferable in that the initial crystallization can be performed in a short period of time and productivity can be improved and cost can be reduced.

(Recording / reproducing method of optical information recording medium)
The recording / reproducing light that can be used for the optical information recording medium of the present invention is usually a laser light such as a semiconductor laser or a gas laser, and its wavelength is usually about 300 to 800 nm, preferably about 350 to 800 nm. In particular, in order to achieve a high areal recording density of 1 Gbit / inch ² or more, it is necessary to reduce the diameter of the focused light beam, and a blue to red laser beam having a wavelength of 350 to 680 nm and a numerical aperture NA of 0.5 or more. It is desirable to obtain a focused light beam using an objective lens.
In the present invention, as described above, it is usually preferable that the amorphous state be the recording mark. In the present invention, it is effective to record information by a mark length modulation method. This is particularly remarkable in a mark length recording where the shortest mark length is 4 μm or less, particularly 1 μm or less.

  When forming a recording mark, it is possible to perform recording by a conventional binary modulation method of recording light power. However, in the present invention, when forming a recording mark as described below, a multi-value of three or more values in which an off-pulse period is provided. It is particularly preferable to employ a recording method based on a value modulation method.

FIG. 2 is a schematic diagram showing a power pattern of a recording light in a method for recording an optical information recording medium. 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), m = nk ( However, k is an integer greater than or equal to 0) recording pulses, each recording pulse width is α _i T (1 ≦ i ≦ m), and each recording pulse is β _i T (1 ≦ i ≦ m). An off-pulse section of time is added. Note that, in the divided recording pulse of FIG. 2, the reference clock synchronization T is omitted from the viewpoint of the viewability of the drawing. That is, in FIG. 2, for example, what should be described as α _i T is simply described as α _i . Here, it is preferable that α _i ≦ β _i or α _i ≦ β _i−1 (2 ≦ i ≦ m or m−1). Although the Σα _i + Σβ _i usually n, accurate Shigumaarufa for obtaining nT mark _{i + Σβ i = n + j} (j is, -2 ≦ j ≦ 2 becomes constant) can be a.

At the time of recording, a recording light having an erasing power Pe capable of crystallizing an amorphous is irradiated between the marks. Further, in α _i T (i = 1 to m), the recording layer is irradiated with recording light having a recording power Pw sufficient to melt the recording layer, and in a time β _i T (1 ≦ i ≦ m−1). , Pb <Pe, and preferably recording light with a bias power Pb that satisfies Pb ≦ (１ ／) Pe.
The power Pb of the recording light irradiated during the period β _m T is usually Pb <Pe, preferably Pb ≦ １ ／ Pe, as in the period of β _i T (1 ≦ i ≦ m−1). , Pb ≦ Pe.

By employing the above recording method, the power margin and the linear velocity margin during recording can be increased. This effect is particularly remarkable when the bias power Pb is set sufficiently low so that Pb ≦ １ ／ Pe.
The above recording method is a method particularly suitable for an optical information recording medium using the phase change recording material of the present invention for a recording layer. If the Ge amount is reduced to ensure erasure (recrystallization) in a short time, the critical cooling rate required for recording an amorphous mark becomes extremely high, and conversely, a favorable amorphous This is because it becomes difficult to form a quality mark.

That is, reducing the amount of Ge promotes recrystallization from the peripheral crystal part of the amorphous mark, and also increases the crystal growth rate during melt resolidification. If the rate of recrystallization from the vicinity of the amorphous mark is increased to a certain degree or more, recrystallization from the periphery of the molten area proceeds during resolidification of the molten area formed for recording the amorphous mark. If so, the region to be made amorphous becomes more likely to recrystallize without becoming amorphous. Therefore, it is important to sufficiently lower the bias power Pb or to secure a sufficient cooling section as α _i ≦ β _i or α _i ≦ β _i−1 (2 ≦ i ≦ m to m−1).

  Furthermore, when the linear velocity at the time of recording increases, the clock cycle is shortened, so that the off-pulse section is shortened and the cooling effect tends to be impaired. In such a case, it is effective to divide the recording pulse at the time of nT mark recording and set the cooling section by the off pulse to 1 nsec or more, more preferably 5 nsec or more, in real time.

[2-2] Use of Information Recording Medium Other than Optical Information Recording Medium The information recording medium of the present invention is capable of at least reversible phase change recording by light irradiation, and is therefore an optical information recording medium. Can be used as described above. However, the rewritable information recording medium used in the present invention can also be applied to, for example, phase change recording by applying a current to a minute area. This will be described below.

FIG. 4 is a conceptual diagram of a temperature history when recording an amorphous mark (curve a) and a temperature history when erasing by recrystallization (curve b). At the time of recording, the temperature of the recording layer is raised to the melting point Tm or more in a short time by heating with a high voltage and short pulse current or a high power level light beam, and after the current pulse or light beam irradiation is stopped, It is rapidly cooled by heat radiation to the periphery and becomes amorphous. If the cooling rate of the temperature at the time τ ₀ from the melting point Tm to the crystallization temperature Tg is higher than the critical cooling rate for amorphization, the film is amorphized. On the other hand, at the time of erasing, the material is heated to a temperature higher than the crystallization temperature Tg and substantially lower than the melting point Tm by applying a relatively low voltage or irradiating light energy at a low power level, and is maintained for a certain time or longer, thereby substantially forming a solid phase , The recrystallization of the amorphous mark proceeds. That is, if the holding time τ ₁ is sufficient, the crystallization is completed.

Here, no matter what the state of the recording layer is before the recording or erasing energy is applied, if the recording layer is given a temperature history of a curve a, the recording layer becomes amorphous and the recording layer becomes amorphous. Is given the temperature history of the curve b, the recording layer is crystallized.
The reason that the rewritable information recording used in the present invention can be used not only as an optical information recording medium but also for phase change recording by applying a current to a minute area is as follows. That is, it is only the temperature history as shown in FIG. 4 that causes the reversible phase change, and the energy source that causes the temperature history is either a focused light beam or current heating (Joule heat by energization). Because it may be.

The change in resistivity due to the phase change between the crystal and the amorphous phase of the phase change recording material used in the present invention is based on the GeTe-Sb ₂ Te ₃ pseudo binary alloy, which is currently being developed as a nonvolatile memory, especially Ge. _This is sufficiently comparable to a change in resistivity of more than two orders of magnitude as shown by a ₂ Sb ₂ Te ₅ compound stoichiometric alloy (J. Appl. Phys., 87, 4130-4133, 2000 ). That is, the resistivity in the as-deposited amorphous state of the rewritable information recording medium using the phase change recording material having the composition represented by the general formula (1) as a main component, and annealing When the resistivity after crystallization was measured, a change of three digits or more was confirmed. It is considered that the amorphous state and the crystalline state obtained by amorphization and crystallization by the current pulse are slightly different from the as-deposited amorphous state and the crystalline state by the annealing, respectively. However, since the resistivity change of three digits or more is obtained, even when the phase change recording material used in the present invention is phase-changed by a current pulse, a large resistivity change of about two digits can sufficiently occur. Be expected.

FIG. 5 is a sectional view showing the structure of one cell of such a nonvolatile memory. In FIG. 5, a voltage is applied between the upper electrode 1 and the lower electrode 2, and a phase change recording layer 3 containing a phase change recording material (hereinafter, may be simply referred to as a phase change recording layer 3) and a heater unit 4. And are energized. The phase change recording layer 3 is covered with an insulator 10 such as SiO ₂ . The phase change recording layer 3 is crystallized in the initial state. The initial crystallization in this case is performed by heating the entire system of FIG. 5 to the crystallization temperature of the recording layer (usually about 100 to 300 ° C.). In the formation of integrated circuits, such a temperature rise is commonly performed.

  Particularly, in FIG. 5, the thinned portion 4 (heater portion) functions as a local heater because heat is likely to be generated by Joule heat due to energization between the upper electrode 1 and the lower electrode 2. The adjacent reversible change portion 5 is locally heated and amorphized through a temperature history as shown by a curve a in FIG. 4, and a temperature history as shown by a curve b in FIG. And recrystallized.

In the reading, a low current is applied so that the heat generated by the heater unit 4 can be ignored, and the potential difference between the upper and lower electrodes is read. Since there is a difference in electric capacity between the crystalline state and the amorphous state, the difference in electric capacity may be detected.
Actually, a memory that has been further integrated by using a semiconductor integrated circuit forming technique has been proposed (US Pat. No. 6,314,014). The basic configuration is shown in FIG. If the phase-change recording material used in the present invention is added to the composition, completely the same function can be realized.

Note that an electron beam can also be used as an energy source that causes a temperature change as shown in FIG. An example of a recording device using an electron beam is a method of locally irradiating an electron beam emitted from a field emitter to cause a phase change in a phase change recording material as disclosed in US Pat. No. 5,557,596. There is.
Note that the present invention is not limited to the above embodiment. The above embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same effect. Within the technical scope of

Hereinafter, an example in which the phase change recording material of the present invention is applied to an optical information recording medium will be described, but the present invention is applied only to an optical information recording medium unless it exceeds the scope of the gist. It is not limited.
In the following embodiments, the optical information recording medium may be simply referred to as “disk”, “optical disk”, “phase change optical disk” or the like.

(Examples 1 to 3, Comparative Examples 1 and 2)
For measuring the composition of the phase change recording material used for the recording layer of the optical information recording medium, acid-soluble ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) and X-ray fluorescence analysis Apparatus was used. With respect to acid dissolution ICP-AES, the analyzer uses a manufactured by JOBIN YVON JY 38 S, was quantified by dissolving the recording layer in dil-HNO ₃ matrix matching calibration method. As a fluorescent X-ray analyzer, RIX3001 manufactured by Rigaku Corporation was used.

[Production of phase change optical disk]
On a disc-shaped polycarbonate substrate having a groove width of 0.31 μm, a groove depth of 29 nm, and a groove pitch of 0.74 μm and having a diameter of 120 mm and a thickness of 0.6 mm, ₂₀ layers of (ZnS) ₈₀ (SiO ₂ ) (80 nm) An Sb-Ge-In-M-Te layer (13 nm), a (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer (20 nm), a Ta layer (2 nm), and an Ag layer (200 nm) are formed by a sputtering method, and further an ultraviolet curable resin. To form a phase-change optical disk.
Sb-Ge-In-M- Te composition of the recording layer _{{(Sb 1-x Ge x} ) 1-y In y} 1-z-w M z Te w in the case of representation in x, y, z, w Are shown in Table 1.

  Except for Comparative Example 2, these compositions were substantially adjusted to the crystallization speed suitable for the evaluation conditions described below. In the following initial crystallization and measurement of disk characteristics, a 0.6 mm glass substrate was superimposed on the side opposite to the light incident surface.

[Initial crystallization]
These disks were subjected to initial crystallization as follows. That is, a laser beam having a wavelength of 810 nm and a power of 800 mW having a shape of about 1 μm in width and about 75 μm in length is applied to a disk rotated at 10 m / s so that the major axis is perpendicular to the guide groove, and the laser light is irradiated. Initial crystallization was attempted by continuously moving in the radial direction at a feed rate of 50 μm per rotation. The disks of Examples 1, 2, and 3 and Comparative Example 1 could be subjected to initial crystallization without any problem. However, the disk of Comparative Example 2 did not crystallize (the reflectance did not change). Initial crystallization was similarly attempted at a linear velocity of 2 m / s and a laser power of 400 mW to 1000 mW, but no crystallization was performed. Therefore, it seems that the disk of Comparative Example 2 is practically difficult to use as a phase-change optical disk. This is probably because the recording layer of Comparative Example 2 contained too much Tb. Note that when the Ge amount is increased, the crystallization is further delayed, so that the initial crystallization becomes more difficult.

[Disk characteristics]
With respect to the discs of Examples 1, 2, 3 and Comparative Example 1, recording / erasing was performed in the guide grooves as follows using an optical disk tester DDU1000 manufactured by Pulstec having a laser wavelength of 650 nm and a NA of 0.65. The disk characteristics were evaluated.

  The EFM + modulation signal was overwritten up to 2000 times at a linear velocity of 14 m / s, and the relationship between the number of recordings and the jitter when the recorded signal was reproduced was measured. The reference clock frequency during recording was 104.9 MHz (the reference clock cycle was 9.53 ns), and the recording laser division method was as follows.

That is, when forming an amorphous mark having a length nT (T is a reference clock cycle and n is a natural number of 3 to 14), the laser irradiation time for forming a mark is divided as shown in FIG. A recording pulse having a recording power Pw and an off pulse having a bias power Pb were alternately irradiated. An erasing light having an erasing power Pe was applied during a period for forming an inter-mark portion (crystal portion). In FIG. 2B, m = n-1, α _i = 0.5 (1 ≦ i ≦ m), β _i = 0.5 (1 ≦ i ≦ m−1), β _{m for all n} = 0. Here, Pw = 16 mW, Pb = 0.8 mW, and Pe = 4.5 mW.

  At the time of reproduction, jitter measurement was performed at a linear velocity of 3.49 m / s. The jitter was standardized with a reference clock cycle of 38.2 ns at the reproduction linear velocity. Here, the jitter in the present invention refers to the jitter of the reproduced signal after passing through an equalizer and an LPF, converted into a binary signal by a slicer, and the time lag between the leading edge and the trailing edge of the binary signal with respect to the PLL clock. The standard deviation (jitter) is normalized by the reference clock cycle. The detailed measuring method is specified in the DVD-ROM standard and the DVD-RW standard.

  FIG. 3 shows the result of measuring the relationship between the number of recordings (Recording cycle) and the jitter (Jitter) when reproducing the recorded signal. The disc of Comparative Example 1 using the Sb-Ge-In based phase change recording material had a jitter value exceeding 11% due to 2,000 repetitive recordings, making it difficult to use, whereas Tb, Gd and Te were added. The discs of Examples 1, 2, and 3 had a jitter value of 10% or less even after 2,000 repetitive recordings. When erasing (crystallizing) the recording mark by irradiating the disk of Comparative Example 1 with DC light of 4.5 mW once after recording 2000 times repeatedly, a clear erasure was observed by observation with an oscilloscope. On the other hand, in the discs of Examples 1, 2, and 3, the same observation did not reveal any clear disappearance.

(Example 4)
The following experiment was conducted to show the possibility of recording by the change in electric resistance of the phase change recording material used in the present invention.
That is, a Ge—In—Sb—Tb amorphous film having the same composition as that of Example 1 and a thickness of 50 nm was formed on a polycarbonate substrate having a diameter of 120 mm by sputtering.
After measuring the resistivity of the amorphous film, the amorphous film was crystallized, and the resistivity of the crystallized film was measured.

For initial crystallization, a laser beam having a shape of about 1 μm in width / about 75 μm in length, a wavelength of 810 nm, and a power of 800 mW was used. Then, while rotating the Ge—In—Sb—Tb amorphous film formed on the substrate at a linear velocity of 12 m / s, the major axis of the laser light is perpendicular to the guide groove formed in the substrate. Thus, the laser light was applied to the amorphous film. Furthermore, initial crystallization was performed by continuously moving the laser beam in the radial direction at a feed rate of 50 μm per rotation.
For measuring the resistivity, a resistivity measuring device Loresta MP (MCP-T350) manufactured by Dia Instruments Co., Ltd. was used.

The resistivity of the amorphous film was too high to obtain an accurate value. However, in the measurement of another material of the same thickness, resistivity 1 for × 10 ^-1 [Omega] cm about values can be measured, the resistivity of the amorphous state of the composition of Example 1 1 × 10 ^{- It} can be said that it is larger than ¹ Ωcm. On the other hand, the resistivity of the Ge—In—Sb—Tb film after crystallization was 0.52 × 10 ⁻⁴ Ωcm.
From the above results, it was found that in the phase change recording material used in the present invention, a change in resistivity of three orders or more occurs between the amorphous state and the crystalline state. Therefore, the phase change recording material used in the present invention has a large difference in resistivity in the phase change between the amorphous state and the crystalline state, and is applicable to a rewritable information recording medium that performs recording by electric resistance change. It can be seen that is possible.

  According to the present invention, a phase-change recording material capable of high-speed recording and erasing, having excellent recording characteristics, high storage stability of a recording signal, and further having excellent repetitive recording durability, and the use of the material. Thus, an information recording medium can be obtained.

FIG. 2 is a schematic diagram illustrating a layer configuration of an optical information recording medium. FIG. 3 is a schematic diagram showing a power pattern of recording light in a method for recording an optical information recording medium. 6 is a graph showing the relationship between the number of recordings and the jitter when a recorded signal is reproduced in the embodiment. It is a conceptual diagram which shows the temperature history at the time of recording or erasing of rewritable information recording. It is a schematic diagram which shows the structure of one cell of a non-volatile memory. FIG. 2 is a schematic diagram illustrating a layer configuration of an optical information recording medium. FIG. 2 is a schematic diagram illustrating a layer configuration of an optical information recording medium.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Upper electrode 2 Lower electrode 3 Phase change recording layer 4 Heater part 5 Reversible change area 10 Insulating film

Claims (11)

A phase-change recording material comprising, as a main component, a composition represented by the following general formula (1).
_{{(Sb 1-x Ge x} ) 1-y In y} 1-z-w M z Te w (1)
(Where x, y, z, and w are numbers satisfying 0.001 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.2, 0 ≦ w ≦ 0.1, M is at least one element selected from lanthanoids, provided that both z and w do not become 0.) The phase change recording material according to claim 1, wherein 0 <z in the general formula (1). The phase change recording material according to claim 1, wherein in the general formula (1), z / y is 0 or more and 1 or less. 4. The phase change recording material according to claim 1, wherein the phase change recording material has a crystalline state in an unrecorded state and an amorphous state in a recorded state. An information recording medium having a recording layer, wherein the recording layer mainly has a composition represented by the following general formula (1).
_{{(Sb 1-x Ge x} ) 1-y In y} 1-z-w M z Te w (1)
(Where x, y, z, and w are numbers satisfying 0.001 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.2, 0 ≦ w ≦ 0.1, M is at least one element selected from lanthanoids, provided that both z and w do not become 0.) The information recording medium according to claim 5, wherein 0 <z in the general formula (1). 7. The information recording medium according to claim 5, wherein in the general formula (1), z / y is 0 or more and 1 or less. The information recording medium according to any one of claims 5 to 7, wherein the information recording medium has a non-recorded state in a crystalline state and a recorded state in an amorphous state. 9. The information recording medium according to claim 5, wherein the information recording medium is an optical information recording medium. 10. The information recording medium according to claim 9, wherein the optical information recording medium further has a protective layer. 11. The information recording medium according to claim 9, wherein the optical information recording medium further has a reflective layer, and the reflective layer contains Ag as a main component.

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