JP2009137205A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium which has an excellent recording characteristic while assuring process stability even in Blu-ray (R) Disc high speed recording. <P>SOLUTION: (1) The optical recording medium is characterized by containing Ge, Sb, Sn and S as principal components of a phase change recording layer. (2) The optical recording medium described in (1) is characterized by containing S in the recording layer in a range of 2 to 9 atom%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical recording medium for high density recording such as a Blu-ray disc having a rewritable phase change recording layer.

A recording layer of a high-density recording optical recording medium using Ge—Sb—Sn is known. However, since it is difficult to obtain desired characteristics only with GeSbSn, recording characteristics and storage stability are obtained. Therefore, various additive elements have been studied, and there are examples such as Patent Documents 1 and 2.
In Patent Document 1, SbSnGeTeM1 having a predetermined composition (M1 is In, Ga, Pt, Pd, Ag, rare earth element, Se, N, O, C, Zn, Si, Al, Bi, Ta, W, Nb, and V). A recording material comprising as a main component at least one element selected from the group consisting of: By using a SbSnGe phase change recording material in which Ge, which has a function of controlling the crystallization speed, is added to the Sb—Sn alloy, noise increases due to crystal non-uniformity in the case of high-speed erasure, and recording signal storage stability It is possible to form an information recording medium excellent in high-speed recording characteristics and storage stability, and to improve recording characteristics after long-term storage by adding Te. Yes. Although the effect of the additive element M1 is also described, there is no description about S, and no description relating to the problem of the present invention described later is found.

Patent Document 2 discloses a recording layer using a material to which GeSbSnMnX (X is at least one element selected from In, Bi, Te, Ag, Al, Zn, Co, Ni, and Cu) and Ga is added. Are listed. Mn is used to improve storage reliability in a high temperature environment, X is used to improve reliability and DOW, and Ga is used to facilitate initialization. However, there is no description about S, and there is no description related to the problem of the present invention described later.
An example in which S (sulfur) is used for the recording layer is disclosed in Patent Document 3.
This document describes that, in addition to S, a material containing Sb, Sn, In, Ge, O or the like is used as a recording layer of a write-once recording medium, and formally used in the present invention. The case where the combination of the recording layer material and the element type is the same is also included.
However, since the recording layer described in the document is composed of an inorganic material mainly composed of a metal or metalloid sulfide, the recording layer of the present application based on the Ge—Sb—Sn ternary system is used. Is fundamentally different. In addition, the document does not show an example including all four elements of GeSbSnS, and does not describe or suggest a combination of materials suitable for the phase change recording layer as in the present invention. Is not helpful.

JP 2004-203011 A JP 2006-192876 A JP-A-4-193586

  The inventors have studied adding various elements to Ge—Sb—Sn for the purpose of obtaining a phase change material suitable for a Blu-ray disc. When Mn, Ga, or Zn is added, jitter and recording sensitivity are improved. I found out. For example, in the case of the same transition linear velocity (described later), jitter tends to be improved by about 0.5% to 1% when Mn is added or not. However, when these elements are added, there is a problem in that variations in recording characteristics occur unless management during the manufacturing process of the substrate is performed more strictly than in the past (when Mn or the like is not added). I understood.

Hereinafter, this problem will be specifically described.
The present inventors have noticed that the recording characteristics of the media prepared under the same sputtering conditions may be significantly different, and investigated the cause of the failure, because the dummy substrate used before this substrate was not baked. It turns out that.
At the time of mass production, the line is put into the sputtering equipment after the substrate is molded, but at the time of development to examine various recording layer compositions, the already molded substrate stored at room temperature is taken out and used. . The material of the substrate is usually polycarbonate and absorbs moisture when stored at room temperature. Therefore, if it is used as it is, the storage reliability is adversely affected by the moisture of the substrate. Therefore, normally, after sufficiently baking in a constant temperature bath of about 60 ° C., it is put into a sputtering apparatus and used. In addition, before forming a film using the substrate thus baked, the film is usually formed using several substrates called dummy substrates first. This is performed in order to stabilize the discharge of sputtering. Since a medium created with a dummy substrate does not evaluate recording characteristics, storage characteristics, etc., a substrate that is not normally baked is used as the dummy substrate. Conventionally, there has been no particular problem even in such a process, but it becomes a problem when recording at a high speed on a high-density recording medium such as a Blu-ray disc.

1 and 2, Ge (19.5) Sb (59.0) Sn (15.0) Mn (6.5) (atomic%) is used as a phase change material, and a dummy substrate is used to form a film. Then, the transition linear velocity of the two media sequentially formed using the two main substrates is shown.
The transition linear velocity is one of the indices used by the present inventors as a substitute characteristic of the crystallization speed, and an evaluation machine used for normal recording / reproduction is used for the measurement. The medium is rotated at a constant linear velocity, and a laser beam with sufficient power that can melt the recording layer is irradiated over one round, and the reflectance is measured. When the same measurement is performed while changing the linear velocity with the power of the continuous light to be irradiated constant, the reflectance is high when the linear velocity is low, but the reflectance starts to decrease when the linear velocity is exceeded. The linear velocity when the reflectance starts to decrease is called the transition linear velocity. At a linear velocity slower than the transition linear velocity, the recording layer is once melted and then recrystallized.However, once the linear velocity is faster than the transition linear velocity, once it has melted, all cannot be recrystallized. It shows that a part remains as amorphous. In addition to the composition of the recording layer, the transition linear velocity is determined by the power of continuous light to be irradiated and the type and thickness of each layer forming the medium, that is, optical conditions and thermal conditions.

Evaluation of FIG. 1, FIG. 2 was implemented using the continuous light of 6.0 mW by the evaluation apparatus ODU-1000 (wavelength 405nm, NA0.85) for BD-R / RE made from a pulse tech industry company.
FIG. 1 shows the results of two media B1 (first sheet) and B2 (second sheet), which were formed using a dummy substrate that was baked and then successively formed using two substrates. However, the way of changing the reflectance with respect to the linear velocities of B1 and B2 is the same, and the two transition linear velocities coincide with 8 m / s. FIG. 2 shows two media X1 (first sheet) and X2 (second sheet) sequentially formed using two non-baked dummy substrates and subsequently using two main substrates. As a result, the method of changing the reflectance with respect to the linear velocities of X1 and X2 is different, and the two transition linear velocities are also different from X1 of 10 m / s and X2 of 9 m / s.
In X1 and X2, since X1 is formed first, it is considered that X1 is more influenced by the gas etc. adsorbed on the dummy substrate. Although the influence is reduced in X2 formed after X1, the influence is not completely eliminated. Therefore, it is considered that the transition linear velocity is faster than B1 and B2.

FIG. 3 and FIG. 4 show jitters when these media are repeatedly recorded 10 times at the Blu-ray disc 1 × speed and 2 × speed.
B1 and B2 have the same recording characteristics for both the 1 × speed and the 2 × speed. On the other hand, when X1 and X2 are viewed, in the case of 1 × speed, X2 matches B1 and B2, but X1 has different recording characteristics on the low power side. Furthermore, at double speed, X2 is also different in recording characteristics from B1 and B2, and the difference in recording characteristics between X1 and X2 is large. As described above, the transition linear velocity varies depending on whether or not the dummy substrate used before film formation using the present substrate is baked, and as a result, the recording characteristics also vary. In particular, there is a large variation in characteristics when recording at higher speed.
Even with CD-RW and DVD + RW, the transition linear velocity sometimes varied, but the recording characteristics were hardly affected. However, in the case of a high-density recording medium such as a Blu-ray disc, it has been found that the variation becomes particularly large at a high speed.

If the dummy substrate is not baked, after the film is formed using the dummy substrate, the characteristics of the medium that is subsequently formed using this substrate are affected and the characteristics change. It is easy to be affected, and it can be said that it is susceptible to some change in production conditions even during mass production. For example, in mass production, it is thrown into the sputtering equipment under certain conditions from substrate molding, but if it is temporarily stopped due to trouble, the retained substrate can be used because it is thought that the adsorption conditions of gas and moisture are different, Waste occurs. In addition, it is considered that it is easily affected when the back pressure of the sputtering apparatus becomes higher than usual for some reason. Basically, it is expected that variations will be avoided by measures such as discarding the substrate that has accumulated, or strictly controlling the process, but this is not preferable from the viewpoint of yield. In addition, although an example of double speed is shown here, the problem is expected to become even greater if a medium that supports higher speed recording is required in the future.
On the other hand, when Te was added, the transition linear velocity did not fluctuate depending on whether or not the dummy substrate was baked, but the bottom jitter was high and the recording characteristics had to be improved (Comparative Example 1 described later). reference).
Accordingly, an object of the present invention is to provide an optical recording medium having excellent recording characteristics even in high-speed Blu-ray disc recording while ensuring process stability.

The above problems are solved by the following inventions 1) to 2).
1) An optical recording medium comprising Ge, Sb, Sn and S as main components of a phase change recording layer.
2) The optical recording medium according to 1), wherein S is contained in the recording layer in a range of 2 atomic% to 9 atomic%.

Hereinafter, the present invention will be described in detail.
In the present invention, a material containing Ge, Sb, Sn and S as main components is used as a material for the phase change recording layer. Here, the main component means that it accounts for 90 atomic% or more of the entire material.
First, the Ge—Sb—Sn ternary system will be described. Sb is used as a base material for phase change type optical recording media because the optical constants of crystal and amorphous are greatly different. However, since Sb is not easily amorphized by itself, it is an element that promotes amorphization. Is added. Ge is one of the elements that promotes amorphization, and has an excellent effect on the stability of the amorphous phase and the increase in signal amplitude. However, since the crystal state is not uniform only with the Ge—Sb binary system, the noise is large and the jitter during recording is also large. Therefore, if Sn is further added, the non-uniformity of the Ge—Sb crystal is improved and both noise and jitter are reduced. In order to obtain the effect of improving the non-uniformity of the crystal, it is desirable to add 10 atomic% or more of Sn with respect to Sb. Further, if the amount of Sn is too large, characteristic deterioration may occur when recording is performed after storage. Therefore, it is desirable that the amount be at most 25 atomic% with respect to Sb. If Ge is 5 atomic% or more, it is effective in increasing the stability of the amorphous material and the signal amplitude. However, if too much is added, even if Sn is added, the crystal non-uniformity will not be improved, and noise and jitter will increase, and further the sensitivity will decrease, so the upper limit is set to 30 atomic%.
However, the above composition ratio of GeSbSn is suitable for Blu-ray double speed (9.84 m / s) recording, and is not limited to this. That is, the composition ratio of GeSbSn can be adjusted as appropriate together with the material and film thickness of each layer (especially the protective layer) according to the desired recording linear velocity. For example, in the case of low linear velocity recording, the transition linear velocity In the case of high linear velocity recording, it is conceivable to decrease the Ge proportion so as to increase the transition linear velocity.

Even with the Ge—Sb—Sn ternary system having the above composition range, a certain degree of recording characteristics can be realized. However, when applied to a high-density recording medium such as a Blu-ray disc, it is good if it is about 1 × speed. However, when high-speed recording of 2 × speed or more is achieved, bottom jitter does not decrease so much, and recording sensitivity also increases. Because it is bad, the margin becomes narrow. Such a tendency is seen from about double speed, and further improvement is required at high speed of 3 times speed or higher. Therefore, it is necessary to improve by adding other elements. However, as described above, depending on the type of element to be added, even if the recording characteristics are improved, a problem occurs in process stability.
In order to cope with this problem, the present inventors have found that S is appropriate as a result of searching for an additive element that can improve recording characteristics and does not impair process stability.
As will be described in detail in the examples, when S is added, even if a non-baked dummy substrate is used, it is not affected, and therefore it can be determined that there is no problem in process stability. Although the cause of the influence when using a non-baked dummy substrate has not been elucidated, it is presumed that the cause is that the additive element is easily oxidized. In the case of S, it is considered that it is difficult to oxidize because the bonding strength with Ge, Sb, Sn, etc. in the recording layer is strong.

Although the addition of S has improved bottom jitter, repeated recording durability, and recording sensitivity, it is not clear why this effect is obtained. When S is added, the transition linear velocity tends to be slow. Therefore, adjustment is usually made so as to obtain an appropriate transition linear velocity by reducing Ge. As described above, Ge is an excellent element that promotes amorphization and is effective in increasing amorphous stability and signal amplitude. However, if it is too much, it increases noise, jitter, and sensitivity. Invite. If it is 30 atomic% or less, it is generally good, but as much as possible, jitter and sensitivity tend to be good. However, it is preferable to add S because the effect of Ge can be compensated and Ge can be reduced. For example, when S is increased by 2 atomic%, Ge may be adjusted to be decreased by 1 atomic%.
If the addition amount of S is too small, the effect of improving the jitter is not seen, so it is preferable to set it to 2 atomic% or more. Moreover, since an adverse effect of increasing the jitter is observed when the amount is too large, it is desirable that the amount be at most 9 atomic%.
Therefore, in combination with the above description, the preferred composition ratio of GeSbSnS at the double speed of Blu-ray is Ge _α (Sb _100-β Sn _β ) _100-α-γ S _γ (α, β, γ are atomic%) 5 ≦ α + (γ / 2) ≦ 30, 10 ≦ β ≦ 25, and 2 ≦ γ ≦ 9.

Next, a specific example of the physical structure of a BD-RE that is a rewritable optical recording medium for a Blu-ray disc (BD) will be described. Although the present invention has been confirmed to be effective with an optical recording medium compliant with the Blu-ray Disc standard, it may be used with an optical recording medium compliant with CD, DVD, or HD DVD in addition to the Blu-ray Disc.
FIG. 10 shows a cross-sectional structure of a BD-RE that is a rewritable optical recording medium using a phase change material as a recording layer. On the substrate having the guide groove, at least a cover layer, a first protective layer, a recording layer, a second protective layer, and a reflective layer are laminated in this order as viewed from the light incident side. In the case of DVD and HD DVD, an organic protective film is formed on the reflective layer by spin coating. In the case of Blu-ray Disc, a transparent cover layer is formed on the first protective layer.
In addition, although the example shown here is of a type having one recording layer, there is also a two-layer type having two recording layers via a transparent intermediate layer. In the case of this two-layer type, the layer on the near side as viewed from the light incident side needs to be translucent in order to perform recording / reproduction of the inner layer.

[Transparent substrate]
The material of the substrate is usually glass, ceramics, or resin, and the resin substrate is preferable in terms of moldability and cost. Examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, etc. Polycarbonate resins and acrylic resins that are excellent in terms of moldability, optical characteristics, and cost are preferred.
The size, thickness, and groove shape of the substrate are formed so as to conform to the standards that comply.
A BD has a diameter of 12 cm, a thickness of 1.1 mm, and a track pitch of 0.32 μm. Usually, a guide groove having a width of 0.14 to 0.18 μm and a depth of 20 to 35 nm is provided, and is projected from the light incident side. So-called on-groove recording, which is recorded in the groove of the part, is employed.
This guide groove is usually a meandering groove (wobble) in order for the recording device to sample the frequency during recording, and the phase of the wobble is reversed or the frequency is changed in a predetermined area. The address and information necessary for recording can be input.
In particular, in the recording method of the optical recording medium of the present invention, the recording apparatus reads the information necessary for recording such as strategy information and recording power into the innermost peripheral part (lead-in area) of the disc, By performing recording under the recording strategy and power conditions, recording suitable for the recording speed is performed.

[First protective layer]
Materials for the first protective layer include Si, Zn, Sn, In, Mg, Al, Ti, Zr, Nb, Ta and other oxides; Si, Ge, Al, Ti, B, Zr and other nitrides Each sulfide such as Zn and Ta; each carbide such as Si, Ta, B, W, Ti and Zr; diamond-like carbon; or a mixture thereof. Among these, a mixture of ZnS and SiO ₂ having a molar ratio of from 7: 3 to 8: 2 is preferable, and the first protective layer is located between the recording layer and the substrate that are particularly susceptible to thermal expansion change and thermal damage due to high temperature / room temperature change. (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) in which the optical constant, the thermal expansion coefficient, and the elastic modulus are optimized. In addition, different materials may be stacked and used.
The film thickness of the first protective layer greatly affects the reflectance, the degree of modulation, and the recording sensitivity. Therefore, it is desirable to use a film thickness at which the disk reflectivity becomes a minimum value, since the recording sensitivity increases. In BD-RE, the range of 20-50 nm is suitable. When the thickness is less than 20 nm, thermal damage to the substrate increases and the groove shape changes. On the other hand, if it is thicker than 50 nm, the disk reflectivity increases and the recording sensitivity decreases.

[Phase change recording layer]
As described above, the composition ratio of GeSbSn is the composition formula Geα (Sb _100-β Sn _β ) _100-α-γ S _γ (α, β, in the case of Blu-ray double speed (9.84 m / s) recording. It is preferable that 5 ≦ α + (γ / 2) ≦ 30, 10 ≦ β ≦ 25, 2 ≦ γ ≦ 9.
The film thickness of the recording layer is 6 nm or more. If it is thinner than this range, the crystallization speed and the degree of modulation will be extremely reduced, and good recording will be difficult. The upper limit is 30 nm for the back layer of the single layer type or the double layer type, more preferably 22 nm or less, and 10 nm or less, more preferably 8 nm or less for the near layer of the two layer type. If it is thicker than this, the recording sensitivity will decrease and the repeated recording durability will deteriorate, and in the case of a two-layer type front layer, it will be difficult to secure transmitted light, and it will be difficult to record / reproduce the back layer. End up.

[Second protective layer]
As the material of the second protective layer, similarly to the first protective layer, each oxide such as Si, Zn, Sn, In, Mg, Al, Ti, Zr, Nb, Ta, and Sb; Si, Ge, Al, Examples thereof include nitrides such as Ti, B, and Zr; sulfides such as Zn and Ta; carbides such as Si, Ta, B, W, Ti, and Zr; diamond-like carbon; or a mixture thereof.
Although the second protective layer also affects the reflectance and the degree of modulation, it is important to use a layer that has the greatest influence on the recording sensitivity and has an appropriate thermal conductivity. A mixture of ZnS and SiO ₂ having a molar ratio in the vicinity of 7: 3 to 8: 2 has a low thermal conductivity and a low heat dissipation rate to the reflective layer, so that the recording sensitivity is good. However, when the NA is high and the energy density of the beam is high as in the case of a Blu-ray disc, the reproduction light is liable to deteriorate, so it is preferable that the thermal conductivity is large. Also, since the recording density is high, it is preferable that the thermal conductivity be large in order to prevent an increase in jitter due to thermal interference.
As a material having a high thermal conductivity, a material mainly containing In ₂ O ₃ , ZnO, SnO ₂ or a mixture thereof known as a transparent conductive film, or a mixture thereof, or TiO ₂ , Nb ₂ O ₅ , ZrO ₂ are the main components. Or a mixture thereof can be used. Furthermore, different materials may be used in a stacked manner.
The thickness of the second protective layer is preferably 4 to 50 nm. If it is thinner than 4 nm, the light absorptance of the recording layer is lowered, and further, heat generated in the recording layer is easily diffused to the reflective layer, so that the recording sensitivity is greatly lowered, which is not preferable. If it is thicker than 50 nm, cracks tend to occur, which is not preferable.

[Reflective layer]
The reflective layer is preferably made of a metal such as Al, Au, Ag, or Cu and an alloy containing them as a main component. Bi, In, Cr, Ti, Si, Cu, Ag, Pd, Ta, Nd, etc. can be used as additive elements when alloying.
The reflective layer reflects the light at the time of recording / reproducing to increase the light use efficiency and also serves as a heat radiating layer for releasing the heat generated at the time of recording. In the case of a single-layer type optical recording medium, or in the case of recording on a recording layer on the back side when viewed from the light incident side in a two-layer type optical recording medium, the reflective layer has a viewpoint of ensuring the light use efficiency and the cooling rate. Therefore, the thickness is desirably 70 nm or more. However, the light utilization efficiency and the cooling rate are saturated at a certain film thickness or more, and if it is too thick, the substrate may be warped or the film may be peeled off due to film stress. It is desirable.
In the two-layer type optical recording medium, the reflection layer on the near side as viewed from the light incident side needs to transmit light, so it cannot be made too thick and is preferably in the range of 5 to 15 nm. . However, since heat dissipation characteristics are poor in this case, good recording may not be possible. Therefore, a heat dissipation layer described below is used.

[Heat dissipation layer]
The heat-dissipating layer is provided between the reflective layer and the intermediate layer in order to ensure heat dissipation and adjust the reflectivity when recording on the front layer as viewed from the light incident side in the two-layer type optical recording medium. . It is desirable that the transmittance is high and the thermal conductivity is high, and those containing In ₂ O ₃ , ZnO, SnO, which are known as transparent conductive films, and mixtures thereof, or TiO ₂ , Al ₂ O ₃ , ZrO _{2 are used.} , Nb ₂ O ₅ as a main component, or a mixture thereof can be used. Depending on the composition of the recording layer, heat dissipation may not be required. In that case, a mixture of ZnS and SiO ₂ often used as a protective film may be used.
The thickness of the heat dissipation layer is preferably about 10 to 150 nm. When the thickness is less than 10 nm, the function as a heat dissipation layer or an optical adjustment layer is insufficient. When the thickness is more than 150 nm, the substrate may be warped or peeled off due to film stress.

[Sulfurization prevention layer]
When using Ag or an Ag alloy as the reflective layer and using a film containing S as the mixture of ZnS and SiO ₂ as the second protective layer, in order to prevent the occurrence of defects due to sulfurization of the reflective layer during storage, An antisulfurization layer is provided between the second protective layer and the reflective layer. Suitable materials for the sulfidation prevention layer include Si, SiC, TiC, TiO ₂ , a mixture of TiC and TiO ₂ , and the like.
Since the uniform film cannot be formed unless the film thickness of the sulfidation prevention layer is 1 nm or more, the sulfidation prevention function is impaired. Preferably it is 2 nm or more. The upper limit of the film thickness is determined while considering the balance of the optical characteristics and thermal characteristics of the medium. Usually, the balance is better when the thickness is 10 nm or less, and good repeated recording characteristics are often obtained.
[Middle layer]
It is a layer for separating two recording layers in a two-layer type optical recording medium, and is usually formed of a transparent resin having a thickness of about 50 μm for a DVD or HD DVD and a thickness of about 25 μm for a Blu-ray disc.
[Cover layer]
In the case of a Blu-ray disc, it is a layer through which light is incident and transmitted, and is usually formed of a transparent resin having a thickness of about 100 μm for a one-layer type medium and a thickness of about 75 μm for a two-layer type medium. .

A film as described above is sequentially formed on a substrate by sputtering, and after forming a cover layer, the film is used as an optical recording medium after an initialization process.
In the initializing step, laser light of about 1 to 2 W shaped to be about 1 × (several 10 to several 100) μm is irradiated while scanning, and the amorphous recording layer is crystallized immediately after film formation. .

  By including S in addition to Ge, Sb, and Sn as the main component of the phase change recording layer, the recording characteristics and the recording characteristics can be improved as compared with the phase change recording layer made only of Ge, Sb, and Sn without deteriorating process stability An optical recording medium with improved recording sensitivity can be provided.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples.

Example 1 and Comparative Example 1
A polycarbonate substrate for BD-RE to which a spiral continuous groove is transferred, a reflective layer, a second protective layer, a phase change recording layer, a first protective layer, and a cover layer are sequentially laminated, and the recording layer is initially crystallized. Used as a sample.
Using a sputtering apparatus DVD Sprinter manufactured by Oerlikon (formerly Unaxis), a reflective layer with a thickness of 140 nm made of an Ag-0.5 wt% Bi alloy, a 12 nm thick film made of ZnO-2 wt% Al ₂ O ₃ Two protective layers, a 11 nm-thick phase change recording layer comprising Ge (20.0) Sb (60.0) Sn (15.0) S (5.0) (atomic%), ZnS-20 mol% SiO ₂ A first protective layer having a thickness of 39 nm was sequentially formed.
Next, an ultraviolet curable resin (manufactured by Nippon Kayaku Co., Ltd.) was applied on the first protective layer by a spin coating method to form a cover layer having a thickness of 100 μm, whereby an optical recording medium of Example 1 was obtained.
Moreover, it is the same as that of Example 1 except the point which changed the material of the phase change recording layer into Ge (20.0) Sb (60.0) Sn (15.0) Te (5.0) (atomic%). Thus, an optical recording medium of Comparative Example 1 was obtained.
Next, the recording layers of these optical recording media were initially crystallized by an optical disc initialization apparatus manufactured by Hitachi CP having a head having a wavelength of 830 nm and a beam diameter of 1 × 96 μm.

Using the BD-R / RE recording / reproduction signal evaluation apparatus ODU-1000 manufactured by Pulstec Industrial Co., Ltd., the transition linear velocity was measured and information was recorded on the sample obtained as described above. The specifications of the optical pickup used are a wavelength of 405 nm and NA of 0.85. The information to be recorded was a random pattern based on 1-7PP, which is a BD modulation method, and the recording density was such that the shortest mark length 2T corresponds to 0.149 μm. The recording speed was 1 × (4.92 m / s) and 2 × (9.84 m / s), and the recording strategy was based on the (n-1) strategy used in BD-RE.
The recording power dependency of jitter after the limit eco-evaluation was evaluated. At this time, the erasing power is Pwo, the erasing power is Peo, and ε = Peo / Pwo, when the jitter of 10 repeated recordings is the smallest. Ε was set to be constant.
FIG. 5 shows two media S1 (first sheet) and S2 (2) of Example 1 that were formed using a dummy substrate that was not baked, and then sequentially formed using two main substrates. The transition linear velocity of the first sheet) is shown. FIG. 6 shows two media T1 (first sheet) and T2 of Comparative Example 1 in which a film was formed using a non-baked dummy substrate and subsequently formed using two main substrates. The transition linear velocity of (second sheet) is shown. Referring to FIG. 5, the transition linear velocity is 11 m / s for both S1 and S2, and the transition linear velocity is 8 m / s for both T1 and T2 in FIG. It can be seen that the transition linear velocities of the sheets of media coincide and are not affected by the unbaked dummy substrate.
However, even though the layers are the same, the reflectance in the case of all crystals is higher in the first embodiment, and the degree of design freedom is higher in the first embodiment.
FIGS. 7 and 8 show the jitters of the media of Example 1 and Comparative Example 1 when repeated recording was performed 10 times at 1 × speed and 2 × speed, respectively. In the standard up to double speed of BD-RE, the jitter needs to be 7% or less. Since comparatively good recording is possible when the relationship of “transition linear velocity> recording linear velocity” is satisfied, in the case of Comparative Example 1 where the transition linear velocity is slow, there is a disadvantage in the double-speed recording. Is bad. However, even in Comparative Example 1, it can be regarded that the transition linear velocity is sufficient for 1 × speed recording, but the jitter of 1 × speed recording is not so good. Therefore, although there is room for optimization, it can be said that it is more advantageous to add S than Te.
Note that there was no problem with respect to the stability of reproduction light.

Examples 2-6, Comparative Example 2
Except for changing the composition of the recording layer as shown in Table 1, optical recording media of Examples 2 to 6 and Comparative Example 2 were prepared and initialized in the same manner as in Example 1. These are obtained by changing the amount of S from 0 to 11 atomic%. However, since S also has an action of promoting amorphization, the transition linear velocity, that is, the crystallization speed increases as the amount of S increases. It becomes slow and it becomes difficult to repeatedly record at double speed. Therefore, every time S was increased by 2 atomic%, the transition linear velocity was adjusted by decreasing Ge by 1 atomic%. Sb and Sn were determined so that Sb: Sn was constant. As a result, the transition linear velocity was almost the same value. In addition, for the process stability check, after forming a film using a non-baked dummy substrate, the transition linear velocity of the medium formed using two main substrates was examined. Comparative Example 2 In both cases including the above, the transition linear velocities of the two sheets were almost the same, and it was confirmed that there was no problem in process stability.
Table 1 shows evaluation results of double-speed repeated recording characteristics, recording sensitivity, and transition linear velocity difference when the amount of S in the recording layer composition is changed together with Example 1 and Comparative Example 1.
The recording characteristics are evaluated at the double speed (9.84 m / s) of BD, using the (n-1) strategy, and first, the recording power Pwo and the erasing power Peo that minimize the jitter when repeated recording is performed 10 times. Decided. When the jitter of 10 repeated recordings at this time is 7% or less, the 10 times of repeated recording is “◯”, and when it exceeds 7%, it is “X”. In addition, when the repeat recording is 1000 times with Pwo and Peo, the jitter is 8.5% or less, the repeat recording 1000 times is “◯”, and when it exceeds 8.5%, it is “X”. did.
The recording sensitivity was “◯” when Pwo was 7 mW or less, and “X” when it exceeded 7 mW. The upper limit of jitter and power was set with reference to the BD-RE standard. According to the standard, the jitter is evaluated individually for the front and rear ends of the mark, but here, the jitter is determined by an average value.
The transition linear velocity difference was defined as “◯” when the transition linear velocity difference of the sample with different substrate loading time was less than 1 m / s, and “x” when the sample was 1 m / s or more.
From the results of Table 1, it can be seen that the addition of S to Ge—Sb—Sn reduces the jitter of 10 repeated recordings, and improves the deterioration and recording sensitivity of 1000 repeated recordings. Further, as can be seen from comparison with Comparative Example 2, even when S is added at about 1% of Example 2, the effect of improving the repeated recording and the recording sensitivity can be obtained, but the jitter reduction of 10 times of repeated recording is not sufficient. However, there is no problem if 3% is added as in Example 3. In addition, even if the amount of addition is too large as in Example 6 (11%), the jitter of repeated recording 10 times deteriorates, so the upper limit is desirably 9% or less.
In addition, there was no problem in any case regarding the stability of the reproduction light.
Incidentally, the jitter of 1000 times repeated recording at double speed of the medium of Comparative Example 1 was greater than 8.5% and was “x”.

Examples 7-12
Except that the composition of the recording layer was changed as shown in Table 1, optical recording media of Examples 7 to 12 were prepared and initialized in the same manner as in Example 1. The transition linear velocity was adjusted by changing the amount of S and decreasing Ge by 1 atomic% each time S was increased by 2 atomic%. Sb and Sn were determined so that Sb: Sn was almost constant. As a result, the transition linear velocity was almost the same value. In addition, for the process stability check, after forming a film using a non-baked dummy substrate, the transition linear velocity of the medium formed using two main substrates was investigated. The two transition linear velocities were almost the same, and it was confirmed that there was no problem in process stability.
Table 1 shows the evaluation results of the double-speed repetition recording characteristics, recording sensitivity, and transition linear velocity difference. Evaluation means and evaluation criteria are the same as those in Examples 2-6.
From the results of Table 1, as in Examples 2 to 6, the addition of S to Ge—Sb—Sn reduces the jitter of 10 repeated recordings, and improves the deterioration and recording sensitivity of 1000 repeated recordings. You can see that Further, S can be added repeatedly in about 7% as in Example 7, but the effect of improving the repeated recording and the recording sensitivity can be obtained. Further, even if the addition amount is too large, such as 11% in Example 12, the jitter of 10 repeated recordings deteriorates, so the upper limit is desirably 9% or less.
In addition, there was no problem in any case regarding the stability of the reproduction light.

Example 13
An optical recording medium was prepared, initialized and evaluated in the same manner as in Example 1 except that SnO ₂ -5 mol% Sb ₂ O ₃ was used as the second protective layer. The process stability and recording characteristics were evaluated, and the contents of the evaluation are the same as in Example 1.
After the film was formed using the dummy substrate that was not baked, the transition linear velocities of the two media that were subsequently formed using this substrate were the same, and it was confirmed that there was no problem in process stability. FIG. 9 shows the jitter when repeated recording is performed 10 times at 1 × speed and 2 × speed.
From the figure, it can be seen that both the recording sensitivity and the bottom jitter are good. Further, repeated recording was performed up to 1000 times with Pwo, but the jitter was 8.5% or less at double speed, the repeated recording durability was good, and the reproduction light stability was satisfactory.

The figure which shows the transfer linear velocity of two sheets of media (B1, B2) which formed into a film using the baked dummy board | substrate and then formed into a film sequentially using two main board | substrates. The figure which shows the transition linear velocity of two media (X1, X2) formed into a film using two dummy substrates after forming into a film using the dummy substrate which is not baked. The figure which shows the jitter when repeated recording is performed 10 times at Blu-ray Disc 1 time speed about medium B1, B2, X1, and X2. The figure which shows the jitter when repeated recording is performed 10 times by Blu-ray Disc 2 times speed about medium B1, B2, X1, X2. The figure which shows the transition linear velocity (S1, S2) of two media produced sequentially using two main board | substrates after producing the medium of Example 1 using the unbaked dummy board | substrate. The figure which shows the transition linear velocity (T1, T2) of two media produced sequentially using two main board | substrates after producing the medium of the comparative example 1 using the dummy substrate which is not baked. The figure which shows the jitter when the recording of 1 time is repeated 10 times about the medium of Example 1 and Comparative Example 1. FIG. The figure which shows the jitter when the recording of 2 times is repeated about the medium of Example 1 and Comparative Example 1 ten times. The figure which shows the jitter when the medium of Example 13 is repeatedly recorded 10 times at 1 time and 2 times speed. The figure which shows the cross-section of BD-RE which is a rewritable optical recording medium using a phase change material as a recording layer.

Explanation of symbols

As a B1 phase change material, Ge (19.5) Sb (59.0) Sn (15.0) Mn (6.5) (atomic%) was used, and after the film was formed using a baked dummy substrate, As a phase change material, the first medium B2 B1 following the first medium B2 B1 is formed by using Ge substrate (19.5) Sb (59.0) Sn (15 0.0) Mn (6.5) (atomic%), after forming a film using a non-baked dummy substrate, and subsequently forming the film sequentially using two main substrates Medium X2 X1 Second medium following S1 S1 Film formed using a non-baked dummy substrate, and then sequentially formed using two main substrates S1 First medium S2 S1 After the second medium T1 is formed using a non-baked dummy substrate, two books are subsequently First medium of Comparative Example 1 sequentially formed using a substrate T2 Second medium following T2 T1

Claims (2)

  An optical recording medium comprising Ge, Sb, Sn and S as a main component of a phase change recording layer.   2. The optical recording medium according to claim 1, wherein S is contained in the recording layer in a range of 2 atomic% to 9 atomic%.

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