JP3151848B2 - Optical information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium used for an information recording / reproducing apparatus using a laser beam, and more particularly to a rewritable optical information recording medium.

[0002]

2. Description of the Related Art As an example of an optical recording medium capable of recording, reproducing and erasing signals, a phase-change optical disk using a chalcogenide as a recording thin film material is known. Generally, a signal is recorded by setting the recording thin film material in a crystalline state to an unrecorded state and rapidly heating and quenching by laser irradiation to make the recording thin film amorphous. In addition, the crystal becomes a crystalline state again by rapid heating and slow cooling, and the recorded signal is erased.

As recording thin film materials, for example, Te, In,
It is common to use a material which is mainly composed of Sb, Se and the like and which changes phase between an amorphous and a crystal, or a substance which reversibly changes phase between two different types of crystal structures.

As a material for the protective layer, for example, Al ₂ O ₃ ,
SiO ₂ , SiO, Ta ₂ O ₅ , MoO ₃ , WO ₃ , ZnS, Zr
O ₂ , AlN, BN, SiNx, TiN, ZrN, PbF ₂ , M
dielectric or of suitable combinations of such gF ₂ are known.

[0005]

The number of repetitions of recording / erasing of the phase change type optical disk can be improved by optimizing the material of the recording thin film and the protective layer, the disk configuration, the recording / erasing beam power, and the like. However, considering the case where an optical disk is used for personal use, the optical disk is not always used under a favorable environment. For example, it is desirable that the optical disc has good repetition characteristics even when the power deviates from the optimum power due to a change in laser power.

[0006] Regarding the recording thin film mainly composed of Te, In, etc., regardless of the material of the recording thin film and the protective layer, when the recording power is higher than the optimum value, the recording thin film is easily deformed, and the number of repetitions is limited. I will.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical information recording medium having improved recording / erasing repetition characteristics, in particular, having an increased laser power allowance for recording / erasing.

[0008]

According to the present invention, a standard free energy of formation at 1000 ° C. is -900 kJ / mol O _{2 in} a recording thin film material component of a phase change type optical information recording medium. A smaller oxide is added.

[0009]

By adding an oxide having a standard free energy of formation of less than -900 kJ / mol O ₂ at 1000 ° C. to the material component of the recording thin film, the recording thin film can be repeatedly destroyed even when recording at a power higher than the optimum power. Less likely to occur. That is, the allowable range of the recording power at which good repetition characteristics can be obtained is expanded.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 shows a typical structure example of the recording medium of the present invention.
Shown in The laser beam for recording, reproducing and erasing is applied to the substrate 1
From the side.

As the substrate 1, a resin having a smooth surface such as a resin such as PMMA or polycarbonate or glass is used. In the case of an optical disc, the substrate plane 8 is usually covered with spiral or concentric tracks for guiding laser light.

It is desirable that the material of the protective layers 2 and 4 is physically and chemically stable, that is, has a higher melting point and softening temperature than the melting point of the recording material, and does not form a solid solution with the recording material. For example, Al ₂ O ₃ , SiO x, Ta ₂ O ₅ , MoO ₃ , WO
_{3, ZnS, ZrO 2, AlNx} , BN, SiNx, TiN, Zr
It is made of a dielectric material such as N, PbF ₂ , MgF ₂ or an appropriate combination of these. The protective layer need not be dielectric or transparent. For example, it may be formed of ZnTe having a light absorbing property for visible light and infrared light. Further, when the protective layers 2 and 4 are formed of different materials, there is an advantage that the degree of freedom of thermal and optical disc design is increased. Of course, they may be formed of the same material.

The recording thin film 3 is made of a material that reversibly changes its structure between a crystalline state and an amorphous state, for example, Te or I.
It is made of a phase change material containing n, Se and the like as main components. The main components of well-known phase change materials are Te-Sb-Ge, Te-
Ge, Te-Ge-Sn, Te-Ge-Sn-Au, Sb-Te, Sb-S
e-Te, In-Te, In-Se, In-Se-Tl, In-Sb, In-
Sb-Se, In-Se-Te, and the like.

The reflection layer 5 is made of a metal element such as Au, Al, Ni, Fe, or Cr, or an alloy thereof, and functions to increase the light absorption efficiency of the recording thin film. However, it is also possible to adopt a configuration in which the reflective layer 5 is not provided, for example, by increasing the thickness of the recording thin film 3 to improve the light absorption efficiency. Alternatively, by adopting a configuration in which the recording thin film and the protective layer are alternately stacked a plurality of times, the light absorption efficiency can be increased as a whole even if the film thickness per recording thin film is small.

The protective substrate 7 is formed by spin-coating a resin or bonding a resin plate, a glass plate, a metal plate, or the like similar to the substrate using an adhesive 6. Furthermore, a structure in which recording, reproduction, and erasing can be performed from both surfaces may be performed by bonding two sets of recording media using an adhesive with the intermediate substrate or the reflective layer inside.

The recording thin film and the protective layer are usually formed by electron beam evaporation, sputtering, ion plating, CV
It is formed by a D method, a laser sputtering method, or the like.

In various rewritable phase-change optical disks mainly composed of Te or In, when the same signal pattern is repeatedly recorded in a specific area, the end of the area (the part where a series of signals has been written) , A phenomenon in which the recording thin film is broken is observed. Hereinafter, this phenomenon is referred to as repeated deterioration at the end of the recording area. The phenomenon of repetitive degradation at the end of the recording area is that during laser irradiation, the constituent elements of the recording thin film slightly diffuse and move in the radial direction of the disk or in the circumferential direction of the disk, and the amount of diffusion and movement of the constituent elements of the recording thin film by repeated laser irradiation. It is thought to be due to the addition. Repeated deterioration at the end of the recording area
This is particularly noticeable when the recording power is high. As a means for solving this phenomenon, an attempt was made to add an oxide to the recording thin film material component. As a result, when an oxide having a standard free energy of formation at 1000 ° C. smaller than −900 kJ / mol O ₂ was added, repetitive deterioration at the end of the recording area was reduced. In particular, when the recording power was slightly higher than the optimum value, the repetitive deterioration was remarkably reduced. As a method of introducing an oxide into a recording thin film, 1) a mixed target of a main component of the recording thin film and an oxide to be added to the recording thin film is prepared, and the recording thin film is formed by a sputtering method or the like. 2) A method of forming a main component of the recording thin film, an oxide to be added, and an independent target and forming the recording thin film by a sputtering method, a vacuum evaporation method, or the like can be considered.

There are an infinite number of combinations of phase change type recording thin film compositions containing Te or In as a main component and capable of repeating recording and erasing, and it is impossible to experimentally confirm the effect of adding an oxide to all of them. Impossible. However, the main components of a typical phase-change type recording thin film which has been publicly known and which can be repeatedly recorded and erased with Te or In as a main component are Te-Sb, Te.
-Ge, Te-Se, In-Te, In-Sb, and In-Se. The effect of adding various oxides on the representative recording thin film composition in the above classification was examined.
Standard free energy of formation at 00 ゜ C is -900kJ / m
Only when an appropriate amount of oxide smaller than ol O ₂ was added as a recording thin material component, the effect of suppressing repeated deterioration of recording / erasing was remarkable. From the experimental results, it was found that the addition of the oxide having the above-mentioned physical properties was mainly based on Te or In.
It can be determined that it is effective in suppressing the repeated deterioration of the recording / erasing of the phase change type recording thin film in which the erasing can be repeated, more specifically, the repeated deterioration of the end portion of the recording area.

As described above, in the case of an erasable phase-change optical disk device, the amorphous phase of the recording thin film generally corresponds to the recording signal, and the crystalline phase corresponds to the erased state.
In some cases, two different optically identifiable crystal states are associated with recording and erasing, respectively. In any case, of the two optically distinguishable recording thin film states,
In order to obtain at least one of the states, it is necessary to melt the recording thin film by laser beam irradiation or to raise the temperature of the recording thin film to a transition temperature or higher. Molten state,
Alternatively, in a recording thin film in a high temperature state, the constituent elements of the recording thin film easily diffuse and move. In other words, it can be said that a phase change type optical disk capable of repeating recording / erasing inherently has a possibility that the recording thin film is repeatedly deteriorated due to its recording / erasing mechanism. The mechanism by which repetitive deterioration is suppressed when a thermally stable oxide is added as a recording thin film material with a high melting point is not well understood, but the additive does not form a solid solution with other constituent elements of the recording thin film, and the laser irradiation is not performed. It is considered that the crystallization phenomenon of the main component of the recording thin film is affected in some way.

As a result of further study, it has been found that in a structure in which an inactive layer is provided in contact with the recording thin film, the main component of the inactive layer has a standard free energy of formation at −1000 ° C. of −9.
When the oxide was smaller than 00 kJ / mol O _2, it was confirmed that the repetitive deterioration was suppressed as in the case where the oxide was added as a recording thin film material component. This indicates that some change has occurred in the crystallization phenomenon of the recording thin film due to the presence of the inactive layer in the laser irradiated portion.

Hereinafter, the present invention will be described in detail with specific examples. Example 1 Ge ₂ Sb ₂ Te ₅ was selected as a representative recording thin film composition, and the repetition characteristics of recording / erasing when various oxides were added, particularly the allowable range of recording power for repetition, were compared. Ge ₂ Sb ₂ Te ₅ is known as a material capable of obtaining good recording / erasing characteristics and repetition characteristics (Japanese Unexamined Patent Publication No.
62-209742 No.).

FIG. 1 shows a disk structure. The material of the substrate is
The glass was 5.25 inches in diameter. The thickness of the recording thin film is 60 nm
The protective layer made of silicon nitride (Si ₃ N ₄ ) is sandwiched on both sides. The thickness of the protective layer was determined so as to obtain optically optimal characteristics. Specifically, the film thickness on the substrate side was 150 nm, and 200 nm on the recording thin film.
Gold (Au) was used for the reflective layer material, and the film thickness was 20 nm. Each layer was formed by a sputtering method. For the formation of the recording thin film, a main component Ge ₂ Sb ₂ Te ₅ target and an oxide target as an additive material are prepared, and the ratio of the oxide to the recording thin film constituting material is 5 wt% by a co-sputtering method.
It was made to become.

Using the disk having the above configuration, a recording / erasing repeated test was performed. Here, the laser beam (wavelength:
830 nm) and the relative speed of the disk is 10 m / sec.
The signal was overwritten 10,000 times (overwrite recording) at an erasing frequency of 5 MHz. (The recording conditions for examining the recording / erasing characteristics in the following examples follow this condition.) At this time, the C / N is 50 dB or more, the erasing rate is 25 dB or more, and the deterioration at the end of the recording area. The length (length of the area where the amplitude of the reproduction signal of the recording mark is small) is 0.
The recording / erasing power range of less than 01 mm was examined. C / N
Are 50 dB or more and the erasure rate is 25 dB or more, which is a sufficiently practical value for digital recording. Hereinafter, a power range satisfying such recording / erasing conditions will be referred to as an optimum power range. The optimum power range of the recording power is shown in (Table 1). Table 1 also shows the melting point of the added oxide and the standard free energy of formation at 1000 ° C. Each physical property value was quoted from Chemical Handbook, 3rd Edition, Basic Edition, and Iron and Steel Handbook, 3rd Edition (edited by the Iron and Steel Institute of Japan).

[0025]

[Table 1]

From Table 1, it can be seen that when an oxide having a standard free energy of formation at 1000 ° C. of less than -900 kJ / mol O ₂ is added, the recording power range in which good repetitive recording / erasing can be performed is expanded. Understand. It was confirmed by optical microscope observation that such an improvement in the repetition characteristics was caused by the suppression of the repetitive deterioration at the end portion of the recording area by adding the oxide. Meanwhile, CoO the standard free energy of 1000 ° C was taken as an example of a large oxide than _{-900kJ / mol O 2, GeO 2} , SnO 2, Ta 2 O 5, TiO,
It can be seen that none of the disks having the recording thin film to which V ₂ O ₃ , WO ₂ , and ZnO were added had good repetition characteristics. From these results, a preferable material to be added to the recording thin film for the purpose of improving the repetition characteristics is
Thermally stable, i.e. as a guide, when the standard free energy of 1000 ° C is less oxide than -900kJ / mol O _2, can be concluded.

Further, an appropriate amount of the oxide to be added to the recording thin film was determined by an experiment. FIG. 2 shows an example of Ge ₂ Sb ₂ T
The relationship between the weight ratio of Gd ₂ O ₃ occupying the recording thin film and the erasing rate of the disk having the e ₅ -Gd ₂ O ₃ recording thin film is shown. Beforehand, a signal was recorded with a recording power of 18 mW, and thereafter, erasing (crystallization) was performed by irradiating a laser beam DC. G
When the amount of d ₂ O ₃ is small, crystallization (erasing) can be performed using the same laser spot as that for signal recording. That is,
So-called single beam overwriting is possible. Gd ₂
In the erasing characteristics when the added amount of O ₃ was changed, the amount of Gd ₂ O ₃ was 8
In the case of wt% or less, an erasing rate of 25 dB or more is obtained,
It can be seen from FIG. 2 that the addition of more than this lowers the erasing rate. This is because when the amount of Gd ₂ O ₃ increases, the crystallization speed or crystallization sensitivity of the recording thin film decreases. Ho ₂
O ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Sc ₂ O ₃ , Sm ₂ O ₃ , SrO, T
The same experiment was performed on b ₂ O ₃ , ThO ₂ , and Y ₂ O ₃ as in the case of adding Gd ₂ O _3. As a result, when the weight ratio of the recording thin film to all of the oxides was 10 wt% or more, the erasing ratio was 10%. Was remarkably reduced, and it was found that it was not preferable as a recording thin film of a recordable / erasable optical disk.

In addition, when a plurality of oxides having the above characteristics were combined and added in an appropriate amount to the recording thin film, a remarkable improvement in the repetition characteristics was observed. As an example in (Table 1),
Gd ₂ O ₃ and Ho ₂ O ₃ are each 2.5 wt% of the recording thin film material.
The improvement of the repetition characteristics when a considerable amount was added was shown. Various experiments have indirectly confirmed that, even when a plurality of types of oxides are added, the total amount of the added oxides must not exceed 10 wt% with respect to the recording thin film.

Example 2 The composition of the main component is (Ge) _x (Sb) _y (Te) _z , x + y + z = 1
In addition, oxides having a standard free energy of formation at 1000 ° C. smaller than -900 kJ / mol O ₂ (specifically, Gd ₂ O ₃ , Ho ₂ O ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Sc ₂₎ O ₃ , Sm
Various types of disks having a recording thin film to which 10 types of oxides of ₂ O ₃ , SrO, Tb ₂ O ₃ , ThO ₂ , and Y ₂ O ₃ were added) were prepared by sputtering and various crystallization characteristics were obtained. ,
Amorphization characteristics and repetition characteristics of recording / erasing 10,000 times were examined. FIG. 1 shows the disk structure. The thickness of the recording thin film is 60 nm, and a protective layer made of silicon nitride is sandwiched on both sides. The thickness of the protective layer is 150 on the substrate side.
nm and the reflective layer side were 200 nm. The reflective layer was formed of a 20 nm-thick Au thin film.

As a result of the experiment, both the crystallization and the amorphization sensitivity were good (the heating time required for crystallization was 100 nsec or less in consideration of overwriting with a single beam), and the recording and erasing were repeated. Ge-S hardly causes deterioration of recording area end
The composition range of the b-Te main component is (Ge) _x (Sb) _y (Te) _z 0.10 ≦ x ≦ 0.35 0.10 ≦ y 0.45 ≦ z ≦ 0.65 x + y + z = 1, and the appropriate amount of oxide to be added is at most It was 10 wt%. As shown in Example 1, it was confirmed that the addition of these oxides widened the power range in which good recording / erasing can be performed repeatedly. As an additive, 100
Standard free energy of formation at 0 ゜ C is -900 kJ / mol
A plurality of oxides smaller than O ₂ may be combined.

The Ge—Sb—Te composition range of the main component of the recording thin film is a range surrounded by A, B, C, D, and E in FIG.

For comparison, a disk having a recording thin film doped with an oxide having a standard free energy of formation at 1000 ° C. greater than -900 kJ / mol O ₂ was prepared.
The repetition characteristics were examined. CoO, GeO used in Examples
Experiments were conducted on eight kinds of oxides, ₂ , SnO ₂ , Ta ₂ O ₅ , TiO, V ₂ O ₃ , WO ₂ , and ZnO. Not seen or very small.

As a result of further detailed study of the Ge—Sb—Te composition range of the main component of the recording thin film, it was found that (Ge) _x (Sb) _y (Te) _z 0.10 ≦ x ≦ 0.35 0.10 ≦ y 0.45 ≦ z ≦ 0.65 x + y + z = 1 among the composition range _{also, (Ge 2 Sb 2 Te 5} ) x (GeSb 2 Te 4) 1-x 0 ≦ x ≦ range of the recording thin film set represented by 1, inter alia faster crystallization rate (JP 62 At the same time, remarkable deterioration of the end portion of the recording area due to repeated recording / erasing was remarkable. A high crystallization rate is very preferable for a rewritable phase-change optical disk. Therefore,
Inhibitory effect of repeated deterioration due to the recording thin film is added a thermally stable _{oxides, (Ge 2 Sb 2 Te 5} ) x (GeSb 2 Te 4) 1-x 0 ≦ x ≦ 1 significantly in composition, and is important.

Embodiment 3 In Embodiments 1 and 2, the recording thin film has a composition in which a thermally stable oxide is added to Ge—Sb—Te, thereby deteriorating the end portion of the recording area when recording / erasing is repeated. Are less likely to occur. In addition, a recording thin film mainly containing Te or In, for example, Te-Ge, Te-Ge-Sn, Te-Ge-Sn-Au,
Sb-Te, Sb-Se-Te, In-Te, In-Se, In-Se-T
l, In-Sb, In- Sb-Se, thermally stable oxides In-Se-Te (specifically, the standard free energy of formation less oxidation than -900kJ / mol O ₂ at 1000 ° C object)
In any case, the deterioration of the end portion of the recording area at the time of repetition of recording / erasing hardly occurs. As an example,
Table 2 shows the repetition characteristics of an optical disc having a recording thin film whose main component is (InSb) ₂ Te and to which various oxides are added. The disc has a glass substrate, a recording thin film having a thickness of 40 nm, and a protective layer made of silicon nitride sandwiched on both sides. The thickness of the protective layer is 150 n on the substrate side.
m, and 200 nm on the reflective layer side. Table 2 shows a power region (optimal recording power range) where deterioration of a recording region end portion becomes 0.03 mm or less when a signal is recorded 1000 times by overwriting under the recording conditions shown in the first embodiment. is there.

[0035]

[Table 2]

From Table 2, it can be seen that when an oxide whose standard free energy of formation at 1000 ° C. is smaller than -900 kJ / mO ₂ is added, the recording power range in which good repetitive recording / erasing can be performed is expanded. Understand. On the other hand, 10
Standard free energy of formation at 00 ゜ C is -900kJ / m
ol Co ₂ as an example of an oxide larger than O ₂
O, GeO ₂ , SnO ₂ , Ta ₂ O ₅ , TiO, V ₂ O ₃ , W
It can be seen that none of the disks having the recording thin film to which O ₂ and ZnO were added had good repetition characteristics. From these results, a material that is preferable to be added to the recording thin film for the purpose of improving the repetition characteristics is thermally stable, that is, the standard free energy of formation at 1000 ° C. is smaller than −900 kJ / mol O ₂ as a guide. It can be concluded that it is an oxide.

Also, the effect of adding a thermally stable oxide to a recording thin film can be obtained even for a recording thin film made of a material whose crystallization speed is relatively slow and cannot be overwritten by one beam or is difficult. Admitted. For example, an optical disk having a Te-Ge-Sn-Au recording thin film has a relatively low crystallization speed of the recording thin film and it is difficult to overwrite with one beam, but two lasers for recording / reproducing and erasing are used. By using light and making the laser spot for erasing relatively longer than the laser spot for recording, recording and erasing can be repeated (Japanese Patent Application No. 60-112420). Even in the case of a Te-Ge-Sn-Au recording thin film, by adding one or more kinds of oxides having a standard free energy of formation at 1000 ° C smaller than -900 kJ / mol O ₂ to the recording thin film,
It was confirmed that the repetitive deterioration of the end portion of the recording area was suppressed.

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

By adding an oxide having a standard free energy of formation of less than -900 kJ / mol O _{2 at} 1000 ° C. to a recording thin film, the allowable range of recording power for obtaining good repetition characteristics is expanded.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a recording medium according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the weight ratio of Gd ₂ O ₃ occupying the recording thin film and the erasing rate of a disk having a Ge ₂ Sb ₂ Te ₅ -Gd ₂ O ₃ recording thin film.

[3] Ru FIG der showing a main component composition range of a recording thin film whose main component is Ge-Sb-Te.

[Explanation of symbols]

1 substrate 2 protective layer 3 recording thin film 4 protective layer 5 reflecting layer 6 adhesive layer 7 protective substrate 8 substrate Rights surface

Continuation of the front page (56) References JP-A-63-29332 (JP, A) JP-A-62-152786 (JP, A) JP-A-61-258787 (JP, A) JP-A 1-211250 (JP) JP-A-2-48988 (JP, A) JP-A-3-258590 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/26

Claims (5)

(57) [Claims] 1. A substrate, formed on the substrate, and reversibly changed between a crystalline phase and an amorphous phase by irradiation with a laser beam.
An optical information recording medium comprising at least a recordable thin film, wherein the record thin film contains an oxide, and the standard free energy of formation at 1000 ° C. of the oxide is smaller than −900 kJ / mol O _2. Optical information recording medium. 2. The method according to claim 2, wherein the oxide contained in the recording thin film is Gd ₂
O ₃ , Ho ₂ O ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Sc ₂ O ₃ , Sm _{2
O 3, SrO, Tb 2 O} 3, ThO 2, Y 2 or one type of O 10 kinds of oxides of ₃ or optical according to claim 1, wherein said to be a combination of these oxides Information recording medium. 3. The optical information recording medium according to claim 1, wherein a main component of the recording thin film is Te or In. 4. The main component of the recording thin film is Ge, Sb, Te, and the composition ratio of the main component is (Ge) _x (Sb) _y (Te) _z 0.10 ≦ x ≦ 0.35 0.10 ≦ y 0.45 ≦ z 2. The optical information recording medium according to claim 1, wherein the ratio is within a range represented by ≦ 0.65 x + y + z = 1, and a ratio of the main component to the recording thin film is 90 wt% or more. 5. The composition ratio of Ge, Sb, and Te of the main component is within a range represented by (Ge ₂ Sb ₂ Te ₅ ) _x (GeSb ₂ Te ₄ ) _1-x 0 ≦ x ≦ 1. The optical information recording medium according to claim 4, wherein: