JP2006260677A - Phase transition type optical recording medium and sputtering target - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase transition type optical recording medium which has high maximum recording linear velocity and fewer reproduction errors even when recording is performed in a wide range of a recording linear velocity and a reproduction error especially at an inner peripheral part is improved and to provide a sputtering target for manufacturing the same. <P>SOLUTION: (1) In the phase transition type optical recording medium having at least a phase transition recording layer consisting essentially of Sb and a protective layer coming in contact with the recording layer and consisting essentially of an germanium oxide on a substrate, germanium concentration on the inner peripheral part side of the protective layer is higher than that on the outer peripheral part side. (2) In the phase transition type optical recording medium mentioned in (1) and having at least a first protective layer, the phase transition recording layer, a second protective layer and a reflection layer on a substrate, the second protective layer consists essentially of an germanium oxide and germanium concentration on the inner peripheral part side of the second protective layer is higher than that on the outer peripheral part side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a phase change optical recording medium for high density recording having a rewritable phase change recording layer, such as a DVD-RW (Digital Versatile Disc Rewriteable), DVD + RW, DVD-RAM, and the like.

In recent years, development of optical recording media (hereinafter referred to as phase change optical disks) using a phase change material as a recording layer has been actively conducted.
In general, a phase change optical disk is formed with a specific groove on a transparent plastic substrate, and a thin film is formed thereon. The plastic material used for the substrate is mainly polycarbonate, and injection molding is often used to form the grooves. The thin film formed on the substrate is a multilayer film, and basically includes a lower protective layer, a recording layer, an upper protective layer, and a reflective layer in order from the substrate. Oxide in the lower and upper protective layer, a nitride, although such sulfides are used, often used ZnS-SiO ₂ mixed inter alia ZnS and SiO _2. A phase change material containing SbTe as a main component is often used for the recording layer. Specific examples include Ge—Sb—Te, In—Sb—Te, Ag—In—Sb—Te, Ge—In—Sb—Te, and Ge—Sn—Sb—Te. -Te, In-Sb, Ga-Sb, Ge-Sb, or the like is used. Although a metal material is used for the reflective layer, metal materials such as Al, Ag, Au, and Cu and alloy materials thereof are often used from the viewpoint of optical characteristics and thermal conductivity.
Various film formation methods such as resistance wire heating, electron beam vapor deposition, sputtering, and CVD can be used for forming these multilayer films. Of these, sputtering is preferred because of its excellent mass productivity. Is often used. After forming these multilayer films, the resin layer is coated by spin coating in order to protect the thin film.

In the phase change optical disk thus manufactured, the phase change material used for the recording layer is in an amorphous state, and it is general to perform a so-called initialization process in which the phase change material is crystallized. The phase change optical disk is initialized by irradiating a laser beam from a semiconductor laser having a width of several μm and a length of several tens to several hundreds of μm while rotating the disk, and moving the laser beam in the radial direction. In many cases, laser beam irradiation is performed more efficiently by providing a focusing function.
The produced phase change optical disk can form an arbitrary amorphous mark by irradiating an arbitrarily determined laser emission pattern (hereinafter referred to as a recording strategy). Furthermore, the phase change disk can perform so-called direct overwrite recording, in which erasing and recording are performed simultaneously. Incidentally, erasing is to crystallize an amorphous mark, and recording is to form an amorphous mark from a crystalline state.

As a frequently used recording strategy, there is ternary control (Pw>Pe> Pb) of recording power (Pw), erasing power (Pe), and bias power (Pb). A specific mark length is recorded by combining these and various pulse widths. As for the data recording / reproducing modulation system, the EFM modulation used in the CD and the EFM + modulation used in the DVD are the mark edge recording system, and therefore, the control of the mark length is very important. Jitter characteristics are generally used for evaluating the mark length control.
Such a phase change disk is applied to CD-RW, DVD + RW, DVD-RW, and the like, and is widely used for audio visual use and computer information recording use.
Recently, the recording speed onto these optical disks is expected to be improved by further increasing the digital capacity. High-speed recording on an optical disk using phase change technology requires both rewriting performance at a higher recording linear velocity and rewriting performance in a wider recording linear velocity range. The former is the maximum recording speed, and the latter corresponds to a recordable speed range. This will be described below.

When considering two types of recording methods, CAV recording in which recording is performed at a constant rotational speed (constant angular velocity) and CLV recording performed at a constant linear speed, the rotational speed varies depending on the radius value in the case of CLV recording. The higher the speed, the higher the required speed. For this reason, the maximum linear velocity is determined by the limit of the rotational capacity of the optical disk included in the optical disk recording / reproducing apparatus. When recording at a linear speed higher than that is possible, CAV recording with a constant rotational speed at the rotational capacity limit is performed. There is a need to use it.
For example, if the limit of the rotational speed of the optical disc recording / reproducing apparatus is 10,000 rpm, in the case of the limiting rotational speed, the linear velocity is about 25 m / s at a radius of 24 mm, and this is the standard linear velocity of DVD of 3.5 m / s. When standardized, the speed is about 7 times faster, and if high-speed recording is to be performed, CAV recording is performed over a specific radius range or the entire surface of the disk, or a plurality of recording linear velocities corresponding to the disk radius value are used. It is necessary to perform ZCLV recording. As described above, the improvement of the recording linear velocity requires not only the improvement of the maximum linear velocity but also the rewriting performance in a certain recording linear velocity range at the same time.

  While examining the realization of the maximum recording linear velocity and a wide recording linear velocity range required for such high-speed recording, the present inventors have found a new problem that has not been known so far. That is, the present inventors have found a phenomenon in which reproduction errors increase within a recording linear velocity range in which jitter characteristics are at a practical level as disk characteristics. Incidentally, the reproduction error referred to here represents the certainty when converting the actually recorded signal into digital data, and the lower the value, the better. Conventionally, if the jitter characteristic is good, the reproduction error is low, and the phenomenon that the two contradict each other has not been confirmed. The only contradictory case is that there are rare cases where the jitter characteristic and the reproduction error characteristic contradict each other when there are many defects on the disc, but the phenomenon found by the present inventors was in a completely different range.

  Further examination of this phenomenon revealed that many errors occurred particularly in the 3T mark. Therefore, in order to investigate the cause of the increase in reproduction error even within the recording linear velocity range where the jitter characteristic is at a practical level, a single pattern in which 3T marks and 3T spaces are alternately arranged on the disc is used using the recording strategy shown in FIG. The amorphous mark shape was recorded and observed with a transmission electron microscope. As a result, it was found that most of the amorphous mark shapes were the same, but some of the mark shapes were not normal, and there were recorded marks in which crystals were generated in the amorphous. A schematic diagram is shown in FIG. The mark A and the mark C are normal recording marks, but the crystal of the mark B is grown in an amorphous state. When such a crystal is present, the reproduction signal is distorted with respect to the normal case (dotted line) as shown in FIG. As a result, the binarized signal is as shown in FIG. 2C, and only the mark B in which the crystal is grown in the amorphous state is reproduced shorter than 3T. It has been found that the number of marks in which the crystal grows in such an amorphous exists at a ratio of about 1 to about 100 to 1000, so that the reproduction error increases even though the reproduction jitter characteristic is at a practical level. .

Next, as in CAV recording, when low-speed recording was performed on the inner circumference side and high-speed recording was performed on the outer circumference side, it was examined whether or not the reproduction error changed at the recording radius position. A single pattern in which 3T marks and 3T spaces are alternately arranged was recorded on the disc using the recording strategy shown in FIG. 1, and 3T window error (= number of short marks / number of normal marks) was measured. The recording linear velocity was 11.5 m / s at the inner circumference (radius position 23 mm), 21 m / s at the middle circumference (radius position 40 mm), and 27.9 m / s at the outer circumference (radius position 56 mm). The results are shown in FIG. It was found that the 3T window error was the smallest at the outer periphery and worsened toward the inner periphery. From this result, it has been found that an increase in reproduction error in the inner peripheral portion will become a major problem in the future in further high-speed recording.
The invention for improving the characteristics by changing the composition of the recording layer and the reflective layer at the inner and outer peripheral portions of the disc is known before this application as disclosed in Patent Documents 1 to 5, Each of the inventions is different in configuration and effect from the present invention aiming at providing a phase change type optical recording medium with few reproduction errors in high density and high speed recording on the entire surface of the medium.

JP-A-60-219645 Japanese Patent No. 674837 JP-A-8-77600 JP 11-321094 A JP 2002-31980 A

The present invention relates to a phase change type optical recording medium having a high maximum recording linear velocity and few reproduction errors even when recording in a wide recording linear velocity range, and particularly an improved reproduction error in the inner periphery, and a sputtering target for producing the same The purpose is to provide
The rewritable phase change optical discs currently on the market are an optical disc using a material system developed from a GeSbTe compound as a recording layer such as DVD-RAM, and an AgInSbTe type such as CD-RW, DVD + RW, and DVD-RW. There are mainly two types of optical discs using, as a recording layer, a material system mainly composed of Sb developed from the above.
When a crystal is precipitated from a liquid, two processes are included: crystal nucleus generation and crystal nucleus growth. The GeSbTe compound system has a high nucleation frequency, and nucleation occurs randomly at all locations in the amorphous or liquid phase, and crystal growth occurs from randomly generated nuclei. When the erase pulse is irradiated to the amorphous mark, crystal nuclei are generated at all locations in the amorphous mark, and crystal growth proceeds from each of the randomly generated crystal nuclei, so that a large number of crystals of almost the same size grow. If recording / erasing is repeated by such a mechanism, crystals larger than the average may be deposited only around the amorphous mark, and the erasure rate may deteriorate.

  Also, as disclosed in Japanese Patent Application Laid-Open No. 2003-242683, an optical disc with a high crystallization speed is necessary to realize a high transfer rate, but a wide linear velocity range is compared with an optical disc with a high crystallization speed. Problems occur when recording with. In the vicinity of the recording mark, once the temperature rises to the melting point, a recrystallization region that forms a crystal phase by crystal growth from the surrounding crystal nucleus in the cooling process is formed, but when recording on the low linear velocity side, This is a problem that the width of the recrystallized region around the recording mark becomes wide and a desired mark width cannot be obtained. This recrystallization region depends on the crystal growth rate, and the width increases as the crystal growth rate increases. When this phenomenon occurs, it occurs in all the recorded marks. Therefore, there is a problem that the signal strength of the mark decreases and the signal quality deteriorates. However, although the jitter characteristic is good, the reproduction error does not increase.

  On the other hand, a material system mainly composed of Sb, such as AgInSbTe system, has a low nucleation frequency. Therefore, an amorphous or liquid phase surface, an interface in contact with another layer, an impurity present in the amorphous or liquid phase, Crystallization proceeds from heterogeneous nucleation that occurs at the interface with different materials. When an erase pulse is irradiated to an amorphous mark, the AgInSbTe-based material has a low nucleation frequency that occurs in the amorphous mark during the recording process. Happens. Even if recording / erasing is repeated, large crystals do not precipitate around the amorphous mark unlike the GeSbTe compound-based material, and the erasing rate is good. Also, when crystal growth is due to non-uniform nucleation, the smaller the mark, the shorter the time taken to crystallize the amorphous mark, which is advantageous for high-density recording and high-speed recording over the material system based on uniform nucleation. is there.

As described above, the present inventors have found a new problem that has not been known in the past while studying to improve the maximum recording linear velocity and to realize a wide recording linear velocity range. That is, the present inventors have found a phenomenon in which reproduction errors increase within a recording linear velocity range in which jitter characteristics are at a practical level as disk characteristics. This phenomenon occurs in the case of a material system in which crystallization is caused by heterogeneous nucleation containing Sb as a main component, particularly when the crystallization speed is high. In a material system in which crystallization occurs due to uniform nucleation, nucleation occurs when the recording layer rises to the same temperature by laser irradiation and is cooled at the same speed, and many crystals grow in the same way. Even if the crystal grows large in the periphery, it cannot occur that the crystal grows only at a certain mark. Even in a material system in which crystallization occurs due to heterogeneous nucleation, crystals are not formed in the amorphous mark during the recording process if the crystallization speed is low. However, when the crystallization rate is high, the nucleation frequency in the recording process is low, but if nucleation occurs in the amorphous, the crystal growth rate is fast, so the generated nuclei grow into large crystals. Conceivable.
Further, it has been found that when the recording linear velocities are different between the inner peripheral part and the outer peripheral part as in CAV recording, the reproduction error increases particularly in the inner peripheral part where the recording linear speed is low. As described above, the maximum linear velocity is determined by the limit of the rotation capability of the optical disk included in the recording / reproducing apparatus for the optical disc, and when recording at a linear velocity higher than that is possible, the CAV recording or the radius of the rotation capability is limited. There is a need to use ZCLV recording using a plurality of recording linear velocities corresponding to values. Therefore, in the future, in order to realize further higher speed, it becomes an essential subject to reduce the reproduction error in the inner periphery.

In order to solve the above problems, the present inventors have made extensive studies focusing on the protective layer of the phase-change optical recording medium. As a result, a protective layer mainly composed of germanium oxide as a layer in contact with the recording layer has been obtained. It has been found that the above problem can be solved by providing and increasing the germanium concentration on the inner peripheral side with respect to the outer peripheral side, and the present invention has been completed based on this finding. Here, a main component means containing 60 mol% or more, Preferably it is 70 mol% or more.
That is, the said subject is solved by the following invention of 1) -3) (henceforth this invention 1-3).
1) At least a phase change recording layer containing Sb as a main component and a protective layer containing germanium oxide as a main component in contact with the recording layer on the substrate. A phase change optical recording medium characterized in that the germanium concentration is higher than that of the portion side.
2) At least a first protective layer, a phase change recording layer, a second protective layer, and a reflective layer are provided on the substrate, the second protective layer is mainly composed of germanium oxide, and is provided on the inner peripheral side of the second protective layer. The phase change optical recording medium according to 1), wherein the germanium concentration is higher than that on the outer peripheral side.
3) A sputtering target characterized in that germanium oxide is a main component, the germanium concentration has an in-plane distribution, and the germanium concentration is higher on the inner peripheral side than on the outer peripheral side.

Hereinafter, the present invention will be described in detail.
In the phase change type optical recording medium having the phase change recording layer mainly composed of Sb as in the first aspect of the invention, a protective layer mainly composed of germanium oxide is provided as a layer in contact with the recording layer, and more than the outer peripheral side. By increasing the germanium concentration on the inner peripheral side, the crystallization speed on the inner peripheral side becomes slower than on the outer peripheral side, and nucleation at the interface between the recording layer and the protective layer on the inner peripheral part is suppressed. Therefore, it is possible to reduce the reproduction error in the inner periphery. As a result, reproduction errors can be reduced over the entire recording area. The protective layer mainly composed of germanium oxide in contact with the recording layer may be provided on either the substrate side or the reflective layer side, or may be provided on both.
Here, the inner peripheral side is a side closer to the innermost peripheral part of the recording area, and the outer peripheral part side is a side closer to the innermost peripheral part of the recording area. For example, in DVD + RW, the radius position 22 mm is the innermost peripheral portion, and the germanium concentration at this radial position is maximized (in the case of film thickness, the innermost peripheral portion is also the thickest). Further, the radial position 58 mm is the outermost peripheral portion, and the germanium concentration at this radial position is made the smallest (in the case of the film thickness, the thinnest film thickness is similarly reduced at the outermost peripheral portion).

As a mode of changing the concentration, the concentration may be gradually changed from the innermost peripheral portion toward the outermost peripheral portion, or may be changed stepwise. Alternatively, the concentration may be kept constant, and the film thickness may be gradually changed from the innermost periphery to the outermost periphery.
In order to form such a protective layer, (1) a disk-shaped sputtering target whose composition is gradually changed in the radial direction is used, and (2) a disk-shaped sputtering target in which a plurality of concentric sputtering targets are combined. (3) A method of providing a plurality of cathodes having a diameter smaller than that of the substrate and having different sputtering target compositions and performing sputtering at the same time may be used.
Further, the radial position corresponding to the recording area of 22 to 58 mm may be divided into several areas, and the concentration or film thickness may be changed in 2 to 4 steps. By providing a mask, the composition or film thickness may be changed for each region.
The density difference and film thickness difference between the inner peripheral side and the outer peripheral side change depending on the recording linear velocity and cannot be uniquely specified. For example, in DVD + RW, the inner circumference (radius position 23 mm) is recorded at 21 m / s, the outer circumference ( When recording at 42 m / s at a radial position of 56 mm, the germanium concentration difference between the radial position of 23 mm and the radial position of 56 mm is preferably 5 to 10%.

Moreover, you may make germanium density | concentration of the inner peripheral part side higher than the outer peripheral part side of a 2nd protective layer like this invention 2. FIG. In this case, in addition to the effect of reducing the reproduction error, since the number of layers can be reduced as compared with the case where germanium oxide is provided as the interface layer, it can be produced at low cost, and even if Ag is used for the reflective layer, It is possible to obtain an effect that it is not necessary to provide a sulfidation prevention layer.
In order to change the germanium concentration of the layer mainly composed of germanium oxide in the in-plane direction, a sputtering target having a germanium concentration higher on the inner peripheral side than on the outer peripheral side may be used as in the third aspect of the present invention. .
When forming germanium oxide by reactive sputtering, a germanium concentration in the germanium oxide layer is reduced by introducing a large amount of oxygen outside the center of the substrate using a sputtering apparatus provided with a large number of oxygen inlets. It can be changed in the in-plane direction.

By using germanium oxide for the protective layer in contact with the recording layer, nucleation at the interface between the recording layer and the protective layer is suppressed. A protective layer mainly composed of germanium oxide may be provided as an interface layer between the first protective layer and the recording layer and / or between the second protective layer and the recording layer. Since germanium oxide has a function of suppressing nucleation at the interface, an effect is seen even in a thin layer such as an interface layer. However, if the film is too thin, the film becomes non-uniform and nucleation tends to occur. On the other hand, the thickness is preferably 1 nm or more. The second protective layer may be a protective layer mainly composed of germanium oxide.
As the germanium oxide material, it is preferable to use (GeO ₂ ) —Ge having a GeO ₂ content of 10 to 90 mol%. If GeO ₂ is less than 10 mol%, it melts during initialization and dissolves in the recording layer. On the other hand, when GeO ₂ exceeds 90 mol%, nucleation is promoted conversely, resulting in poor reproduction errors. The greater the amount of germanium in the germanium oxide material, the greater the effect of suppressing nucleation. Therefore, the amount of germanium may be controlled in consideration of the balance with the crystallization speed of the recording layer. Further, it is better to increase the amount of germanium in the outer peripheral portion as the difference in recording linear velocity between the inner peripheral portion and the outer peripheral portion is larger. Further, different oxides such as SiOx may be mixed in the germanium oxide material. In this case, in order to obtain a remarkable effect of germanium oxide, the ratio of germanium oxide is set to 60 mol% or more, preferably 70 mol% or more.

For the phase change recording layer, a phase change material containing Sb as a main component is used. Here, the main component means that Sb is contained at 55 atomic% or more, preferably 60 atomic% or more. The phase change material mainly composed of Sb has a lower nucleation frequency compared to the GeSbTe compound system, regardless of which combination of elements is added. When erasing an amorphous mark, an amorphous or liquid phase and a crystal Crystal growth occurs from the interface to the center.
When the composition of the phase change recording layer is SbXM (X is Sn and / or In, and M is an additive element), a phase change optical recording medium having a maximum recording linear velocity of 6 times or more can be obtained. By containing Sn and / or In, initial crystallization is facilitated, uniform crystals can be obtained, and the crystallization speed can be increased. In order to obtain a remarkable effect, the addition amount of Sn and / or In is preferably 5 atomic% or more.

The additive element M is selected as necessary because there is an additive effect specific to each element.
When Ge and Si are added, the storage reliability is improved. When Ga is added, the amorphous state is promoted and the amorphous mark can be recorded with good reproducibility, so that the jitter characteristic is improved. When Ga is added, the frequency of crystal generation in the mark is reduced and the reproduction error is improved. However, if it is too much, the crystallization speed is slowed down. preferable. When Bi is added, the crystallization rate can be further increased. However, since Bi promotes nucleation, if too much is added, the reproduction error becomes worse. When H, N, and O are added, the crystallization rate can be further increased. When Te, Se, or Ag is added, the amorphous generation ability is increased, so that recording can be performed even with a low recording power, and the recording sensitivity can be improved. When Au, Al, Co, Mg, and Ca are added, the recording layer becomes difficult to oxidize, and the change in crystal state after long-term storage becomes small, so that storage reliability is improved. When Ni is added, there is an effect of lowering the crystallization temperature, so that initial crystallization is facilitated.

The phenomenon related to crystallization is due to the nucleation and crystal growth rate at the recording layer and the interface, and the same effect can be obtained even if the laser wavelength is changed. In addition, when the generated crystal is small, there is no problem with a CD-RW having a long mark length, but the influence becomes larger as the mark length is shortened with DVD + RW and further with a blue-ray disc.
The film thickness of the phase change recording layer is preferably 10 to 20 nm, and if it is thinner than 10 nm, the light absorption ability is lowered and the function as the recording layer may be lost. On the other hand, if it is thicker than 20 nm, the recording sensitivity is deteriorated.
The recording layer is preferably formed by sputtering. As an example of a method for producing a sputtering target, a preparation is weighed in advance, heated and melted in a glass ampule, and then taken out and pulverized by a pulverizer, and the resulting powder is heated and sintered to obtain a disk. Can be obtained.
The initial crystallization of the recording layer is preferably carried out at a power density of 15 to 40 mW / μm ² by rotating the phase change optical recording medium at a constant linear velocity in the range of 10 to 25 m / s. The initial characteristics of repeated recording are determined by the initial crystallization conditions, but it is better to perform the initial crystallization at a higher speed as the material is faster. At a linear velocity of less than 10 m / s, large crystal grains grow, so the amorphous mark edge tends to be non-uniform, and the jitter characteristics deteriorate. Further, when the linear velocity exceeds 25 m / s, the followability of the disk is deteriorated, so that the distribution is likely to occur in the reflectance. If the power density is 15 mW / μm ² or less, a uniform crystal cannot be obtained due to insufficient power, and if it is 40 mW / μm ² or more, the power is too strong and the repeated recording characteristics deteriorate.

The transparent substrate is usually a disc-shaped substrate having a tracking guide groove on the surface and having a diameter of 12 cm and a thickness of 0.6 mm. A polycarbonate substrate is preferable in terms of low water absorption, optical characteristics, processability, cost, and the like. For example, when the present invention is applied to a DVD, the tracking guide groove may be a meandering groove having a pitch of 0.74 ± 0.03 μm, a groove depth of 22 to 40 nm, and a groove width of 0.2 to 0.4 μm. preferable. In particular, when the groove is deepened, the reflectance of the optical disk is lowered and the modulation degree can be increased.
The film thickness of the first protective layer is 50 to 250 nm, preferably 50 to 100 nm. If it is too thick, thermal damage to the substrate increases during film formation, and film peeling tends to occur. On the other hand, if it is too thin, thermal damage to the substrate at the time of recording is large, and repeated recording characteristics deteriorate. In particular, as the recording speed becomes higher, the substrate must be cooled rapidly in order to form a stable amorphous mark, so that the recording is performed with a higher power.
The film thickness of the second protective layer is 5 to 20 nm, preferably 5 to 15 nm. A thinner film thickness is preferable because it has a rapid cooling structure and a high degree of modulation even at high-speed recording. However, if it is thinner than 5 nm, the recording sensitivity is deteriorated. From the viewpoint of reducing reproduction errors, the second protective layer is preferably thin. Two or more layers of different materials may be combined.

For the reflective layer, Ag having a high thermal conductivity, or an Ag alloy such as Ag—In, Ag—Pd, Ag—Pd—Cu, or Ag—Cu is suitable. When the crystallization speed is high, recrystallization from the periphery of the amorphous mark tends to occur, the mark becomes thin, and the modulation degree tends to be small. In order to make this recrystallization region as small as possible, it is better to shorten the time for which recrystallization is held at a temperature at which recrystallization occurs. Therefore, a rapid cooling structure using Ag or an Ag alloy having high thermal conductivity for the reflective layer It is preferable to do this.
The thickness of the reflective layer is preferably 140 to 300 nm. In high-speed recording, as the film thickness increases, the degree of modulation increases, and from the viewpoint of reducing reproduction errors, it is preferable to increase the film thickness to make it easier to release heat. Therefore, although it is preferable to set it as 140 nm or more, since it will become easy to produce film | membrane peeling if it is too thick, 300 nm or less is preferable.
In the case where Ag or an Ag alloy is used for the reflective layer and a material containing S is used for the second protective layer, an antisulfurization layer may be provided between the reflective layer and the second protective layer. The sulfurization preventing layer plays a role of preventing the formation of Ag ₂ S due to the reaction between S contained in the second protective layer and Ag contained in the reflective layer.
Preferred materials include TiC, TiO, a mixture of TiC and TiO, SiC, Si, SiO ₂ , Ta ₂ O ₅ , Al ₂ O _{3 and the} like. In particular, the use of a mixture of TiC and TiO makes it possible to obtain an optical recording medium that hardly causes film floating even in a harsh environment and has good long-term storage reliability.

According to the present invention, the phase change type optical recording medium having a high maximum recording linear velocity and few reproduction errors even when recording in a wide recording linear velocity range, in particular, an improved reproduction error in the inner periphery, and its manufacture A sputtering target can be provided.
Further, according to the second aspect of the present invention, since the number of layers is small, it can be produced at low cost, and a phase change type optical recording medium can be provided that does not require the provision of an antisulfurization layer even when Ag is used for the reflective layer.

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

Example 1 and Comparative Example 1
A phase change optical recording medium (disk) was produced as follows.
A first protective layer, a germanium oxide layer, a recording layer, and a second protective layer are formed by sputtering on a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm having a guide groove with a track pitch of 0.74 μm and a groove depth of 27 nm. Then, a sulfidation prevention layer and a reflection layer were formed in this order.
For the first protective layer, (ZnS) 80 mol% (SiO ₂ ) 20 mol% was used as a target, and the film thickness was 58 nm.
The germanium oxide layer has a doughnut-shaped (GeO ₂ ) 50 mol% -Ge target having an inner diameter of 100 mm and an outer diameter of 200 mm outside the central target having a diameter of 100 mm and a composition of (GeO ₂ ) 30 mol% -Ge. The arranged concentric target was used, and the film thickness was 3 nm.
For the phase change recording layer, Sb ₇₁ Sn ₁₉ Ge ₅ Ga ₅ (atomic%) was used as a target, and the film thickness was 14 nm.
For the second protective layer, 80 mol% (ZnS) 20 mol% (SiO ₂ ) 20 mol% was used as a target, and the film thickness was 8 nm.
The anti-sulfurization layer was (TiC) 70% by weight (TiO) 30% by weight as a target, and the film thickness was 6 nm.
The reflective layer used Ag as a target and had a thickness of 200 nm.
Further, an acrylic curable resin (SD318 manufactured by Dainippon Ink Co., Ltd.) having a thickness of about 8 μm was applied on the reflective layer with a spinner, and then cured with ultraviolet rays to form an organic protective film, on which an adhesive was used. A phase change optical recording medium of Example 1 was obtained by bonding together a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm.
An initializing apparatus (POP120-7AH manufactured by Hitachi CP Co., Ltd.) having a laser head in which a focusing function is added to laser light having an output wavelength of 810 nm, a width of about 1 μm, and a length of 75 μm is initially applied to this phase change optical recording medium. Crystallization was performed. Initialization conditions were a laser output of 1800 mW, a scanning speed of 20 m / s, and a head feed of 50 μm / r.
When the RF signal after the initial crystallization was observed with an oscilloscope, the reflectance distribution in the circumference was small and the initial crystallization was uniform.

Next, recording / reproduction was performed using a DDU1000 manufactured by Pulstec Industrial Co., Ltd., which is a DVD evaluation apparatus. It is known that the crystal grows in the mark and the reproduction error becomes worse because the 3T mark, which is the shortest mark, is the most frequent. Therefore, the frequency with which the crystal grows in the mark can be easily determined. In order to investigate, the following evaluation was performed.
That is, the mark length after binarization was detected using a time interval analyzer (TIA) manufactured by Yokogawa. As shown in FIG. 4, a mark shorter than 2.5T other than the normal 3T mark distribution is a short mark in which a crystal grows in the mark.
A single pattern in which 3T marks and 3T spaces are alternately arranged is recorded by fixing the on-pulse width and changing the off-pulse width with the recording strategy shown in FIG. 1, and 3T window error (= number of short marks / normal The number of marks) was measured, and the largest value was taken as the maximum value of 3T window error. The recording linear velocity was 11.5 m / s at the inner circumference (radius position 23 mm), 21 m / s at the middle circumference (radius position 40 mm), and 27.9 m / s at the outer circumference (radius position 56 mm). The maximum 3T window error was evaluated.
On the other hand, as Comparative Example 1, a phase change optical recording medium was prepared in the same manner as in Example 1 except that a germanium oxide layer having a uniform composition (GeO ₂ ) 50 mol% -Ge target was used. Was created and initialized, and then evaluated.
The results of Example 1 and Comparative Example 1 are shown in FIG. As can be seen from the figure, in the first comparative example, the maximum 3T window error value increases toward the inner circumference, whereas in the first embodiment, the maximum 3T window error value increases between the outer circumference and the inner circumference. It was the same, and errors in the inner and middle circumferences could be suppressed.

Next, with respect to Comparative Example 1, a 3T single pattern was recorded at a recording position of 11.5 m / s at a radial position of 23 mm where the maximum 3T window error maximum value was worst, and this sample was subjected to JEOL transmission electron microscope JEM-2010. Thus, the mark was observed at a magnification of 10,000 times or 40,000 times. As a result, most of the marks had the same mark shape, but crystal grains grew at a ratio of about 1 in 100, and a small amorphous part and a shorter mark than a normal mark were observed. FIG. 6 is a schematic diagram of a normal 3T mark shape, and FIG. 7 is a schematic diagram of a 3T mark shape in which large crystal grains are grown in the mark.
Similar observations were made with respect to Example 1. As to 1500 marks, the lengths of all the marks were almost the same, and no short marks with large crystal grains growing were observed.
Next, with respect to Comparative Example 1, a random pattern was recorded, and the mark was observed in the same manner. As in the 3T single pattern, marks with crystals growing in the 3T mark were occasionally observed. In addition to the 3T mark, a mark with a crystal growing was sometimes observed in the mark. FIG. 8 shows a schematic diagram of a 4T mark shape in which large crystal grains grow in the mark.
Similar observations were made with respect to Example 1. As to 1500 marks, no marks in which large crystal grains grew were observed in the marks.

Example 2 and Comparative Example 2
A phase change optical recording medium (disk) was produced as follows.
A first protective layer, a recording layer, a germanium oxide layer, and a second protective layer are formed by sputtering on a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm having a guide groove with a track pitch of 0.74 μm and a groove depth of 27 nm. Then, a sulfidation prevention layer and a reflection layer were formed in this order.
The first protective layer, and a (ZnS) 80 mol% _(SiO 2) was used to target 20 mol%, 60 nm thickness.
The phase change recording layer was made of Sb ₈₂ In ₁₅ Ge ₃ (atomic%) as a target, and the film thickness was 14 nm.
The germanium oxide layer has a diameter of 100 mm and a composition having a composition of (GeO ₂ ) 20 mol% -Ge, and a target having an inner diameter of 100 mm and an outer diameter of 200 mm and a composition of (GeO ₂ ) 40 mol% -Ge. The arranged concentric target was used, and the film thickness was 2 nm.
For the second protective layer, 80 mol% (ZnS) (SiO ₂ ) 20 mol% was used as a target, and the film thickness was 5 nm.
The anti-sulfurization layer was (TiC) 70% by weight (TiO) 30% by weight as a target, and the film thickness was 6 nm.
The reflective layer used Ag as a target and had a thickness of 200 nm.
Subsequently, an organic protective film was formed in the same manner as in Example 1, and a polycarbonate substrate was bonded thereon to obtain the phase change type optical recording medium of Example 2, followed by initial crystallization.
When the RF signal after the initial crystallization was observed with an oscilloscope, the reflectance distribution in the circumference was small and the initial crystallization was uniform.

Next, recording and reproduction were performed in the same manner as in Example 1, and the maximum value of 3T window error after 10 repeated recordings was evaluated.
On the other hand, as Comparative Example 2, a phase change optical recording medium was formed in the same manner as in Example 2 except that a germanium oxide layer having a uniform composition (GeO ₂ ) 40 mol% -Ge target was used. Was created and initialized, and then evaluated.
The evaluation results of Example 2 and Comparative Example 2 are shown in FIG. As can be seen from the figure, in Comparative Example 2, the maximum 3T window error value increases toward the inner periphery, whereas in Example 2, the 3T window error maximum value increases between the outer periphery and the inner periphery. It was the same, and errors in the inner and middle circumferences could be suppressed.

Example 3 and Comparative Example 3
A phase change optical recording medium (disk) was produced as follows.
A first protective layer, a recording layer, a second protective layer, and a reflective layer are formed by sputtering on a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm having a guide groove with a track pitch of 0.74 μm and a groove depth of 27 nm. Films were formed in order.
The first protective layer, and a (ZnS) 80 mol% _(SiO 2) was used to target 20 mol%, 60 nm thickness.
For the phase change recording layer, Sb ₈₀ In ₁₈ Te ₂ (atomic%) was used as a target, and the film thickness was 14 nm.
The second protective layer is a target having a diameter of 100 mm and a composition of (GeO ₂ ) 30 mol% -Ge, a donut shape having an inner diameter of 100 mm and an outer diameter of 200 mm and a composition of (GeO ₂ ) 60 mol% -Ge. The film thickness was set to 9 nm.
The reflective layer used Ag as a target and had a thickness of 200 nm.
Subsequently, in the same manner as in Example 1, an organic protective film was formed, and a polycarbonate substrate was bonded thereon to obtain the phase change optical recording medium of Example 3, followed by initial crystallization.
When the RF signal after the initial crystallization was observed with an oscilloscope, the reflectance distribution in the circumference was small and the initial crystallization was uniform.

Next, the recording linear velocity was changed to 21 m / s at the inner circumference (radius position 23 mm), 32 m / s at the middle circumference (radius position 40 mm), and 42 m / s at the outer circumference (radius position 56 mm). Recording and reproduction were performed in the same manner as in 1 and the maximum value of 3T window error after 10 repeated recordings was evaluated.
On the other hand, as Comparative Example 3, the film formation of the second protective layer, the composition is uniform except using (GeO 2) ₆₀ mol% -Ge target Likewise phase-change optical recording as in Example 3 After creating and initializing the media, it was evaluated.
The evaluation results of Example 3 and Comparative Example 3 are shown in FIG. As can be seen from the figure, in the third comparative example, the maximum 3T window error value increases toward the inner periphery, whereas in the third embodiment, the maximum 3T window error value increases between the outer periphery and the inner periphery. It was the same, and errors in the inner and middle circumferences could be suppressed.

Comparative Example 4
As Comparative Example 4, a phase change optical recording medium was prepared in the same manner as in Example 3 except that a (GeO ₂ ) 30 mol% -Ge target having a uniform composition was used for forming the second protective layer. After creating and initializing, it was evaluated.
However, since the crystallization speed was slow, the amorphous mark could not be crystallized during repeated recording, and almost became amorphous after 10 repeated recordings, and the signal could not be read.

Example 4
With respect to the phase change optical recording medium of Example 3, the inner peripheral part has a recording linear velocity of 21 m / s, the outer peripheral part has a recording linear velocity of 42 m / s, a recording density of 0.267 μm / bit, and a random pattern is recorded by the EFM + modulation method Then, after storing for 300 hours in an environment of 80 ° C. and 85% RH, data to clock jitter when a recorded mark was reproduced was evaluated. The results are shown in FIG.
As can be seen from the figure, there was no change in jitter on the inner circumference recorded at a low linear velocity and the outer circumference recorded at a high linear velocity, indicating good storage characteristics.

The figure which shows a recording strategy. Explanatory drawing of the recording mark which has generate | occur | produced the crystal in an amorphous. (A) Schematic diagram of recording mark, (b) reproduction signal, (c) signal after binarization. The figure which investigated the relationship between a recording radius position and 3T window error in the case of performing low speed recording on the inner circumference side and performing high speed recording on the outer circumference side. The figure which shows distribution of the mark shorter than 2.5T other than normal 3T mark distribution. The figure which shows the evaluation result of the relationship between the recording radius position of Example 1 and the comparative example 1, and 3T window error maximum value. The schematic diagram which shows a normal 3T mark shape. The schematic diagram of 3T mark shape with which the big crystal grain has grown in the mark. The schematic diagram of 4T mark shape where the big crystal grain has grown in the mark. The figure which shows the evaluation result of the relationship between the recording radius position of Example 2 and Comparative Example 2, and 3T window error maximum value. The figure which shows the evaluation result of the relationship between the recording radius position of Example 3 and the comparative example 3, and 3T window error maximum value. FIG. 10 is a diagram illustrating an evaluation result of data-to-clock jitter according to the fourth embodiment.

Explanation of symbols

Pw Recording power Pe Erase power Pb Bias power T Basic clock period A Normal mark B Mark with crystal growing in amorphous C Normal mark

Claims (3)

  On the substrate, there is at least a phase change recording layer containing Sb as a main component and a protective layer containing germanium oxide as a main component in contact with the recording layer, and the inner peripheral side of the protective layer is the outer peripheral side. A phase change optical recording medium characterized in that the germanium concentration is higher than the above.   The substrate has at least a first protective layer, a phase change recording layer, a second protective layer, and a reflective layer, the second protective layer is mainly composed of germanium oxide, and the inner peripheral side of the second protective layer is 2. The phase change optical recording medium according to claim 1, wherein the germanium concentration is higher than that of the outer peripheral side. A sputtering target characterized in that germanium oxide is the main component, the germanium concentration has an in-plane distribution, and the germanium concentration is higher on the inner peripheral side than on the outer peripheral side.