JP2003166052A - Sputtering target - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sputtering target used for forming a dielectric layer which is required for realizing a phase-change type optical recording medium with high storing reliability and adequate recording/playback characteristics. <P>SOLUTION: The sputtering target includes CeO<SB>2</SB>and an additive compound, wherein the additive compound is at least one of Cr<SB>2</SB>O<SB>3</SB>, Fe<SB>3</SB>O<SB>4</SB>, Mn<SB>3</SB>O<SB>4</SB>, Nb<SB>2</SB>O<SB>5</SB>, MgO, and ZnO. The sputtering target includes CeO<SB>2</SB>, and the additive compound which is at least one of Al<SB>2</SB>O<SB>3</SB>, TiO<SB>2</SB>, Y<SB>2</SB>O<SB>3</SB>, Ta<SB>2</SB>O<SB>5</SB>, Sb<SB>2</SB>O<SB>3</SB>, ZrO<SB>2</SB>, and Bi<SB>2</SB>O<SB>3</SB>, wherein an area of a high concentration region of the additive compound is 0.5 A% or more with respect to the total area in a composition image by a scanning electron microscope, when the image shows a high concentration region of the additive compound, in which the concentration of a metal included in the additive compound is higher than in the surrounding area, and a volume percentage of the additive compound to a total of CeO<SB>2</SB>and the additive compound is defined as A%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputter target used for forming a dielectric layer of an optical recording medium.

[0002]

2. Description of the Related Art In recent years, an optical recording medium capable of high-density recording and capable of erasing and rewriting recorded information has attracted attention. Among rewritable optical recording media, the phase-change optical recording media record by changing the crystalline state of the recording layer by irradiating with a laser beam, and reflectivity of the recording layer accompanying such state change. The reproduction is performed by detecting the change. The phase-change type optical recording medium is drawing attention because the optical system of the driving device is simpler than that of the magneto-optical recording medium.

The phase-change type recording layer has a large difference in reflectance between the crystalline state and the amorphous state, and has a relatively high stability in the amorphous state. Therefore, Ge-Sb-Te is used. In many cases, chalcogenide-based materials such as a system are used.

When recording information on a phase-change optical recording medium, a laser beam of high power (recording power) is applied so that the temperature of the recording layer rises above the melting point. In the portion to which the recording power is applied, the recording layer is melted and then rapidly cooled to form an amorphous recording mark. On the other hand, when the recording mark is erased, a laser beam having a relatively low power (erasing power) is applied so that the recording layer is heated to a temperature higher than its crystallization temperature and lower than its melting point.
The recording mark to which the erasing power is applied is heated to a temperature higher than the crystallization temperature and then gradually cooled, so that the recording mark returns to a crystalline state. Therefore, the phase-change optical recording medium can be overwritten by modulating the intensity of a single laser beam.

In order to realize higher recording density and higher transfer rate, the recording / reproducing wavelength has been shortened, the numerical aperture of the objective lens of the recording / reproducing optical system has been increased, and the linear velocity of the medium has been increased. The spot diameter of the recording laser beam on the surface of the recording layer is λ /, where λ is the laser wavelength and NA is the numerical aperture.
It is expressed by NA and is divided by the linear velocity V of the medium (λ /
NA) / V is the laser irradiation time (time required for passing the beam spot) to the recording layer. The laser irradiation time to the recording layer becomes shorter and shorter as the recording density and transfer rate increase. Therefore, it is becoming difficult to optimize the overwrite condition.

Here, a problem when overwriting is performed by increasing the linear velocity will be described.

When the linear velocity is increased, the irradiation time of recording light is shortened. For this reason, it is common to prevent the lowering of the reached temperature of the recording layer by increasing the recording power as the linear velocity increases. However, as the linear velocity becomes faster, the cooling rate after the recording light irradiation becomes faster. In order to form the amorphous recording marks, it is necessary to cool the recording layer melted by the irradiation of the recording light at a speed equal to or higher than a certain rate depending on the crystallization speed. When the structure of the recording layer and the thermal design of the medium are the same, the cooling rate of the recording layer depends on the linear velocity, and the cooling rate increases at high linear velocity and decreases at low linear velocity.

On the other hand, in order to erase (recrystallize) the amorphous recording marks, it is necessary to irradiate the recording layer with erasing light so that the recording layer can be kept at a temperature not lower than the crystallization temperature and not higher than the melting point for a certain time or longer. is there. Even if the erasing power is increased as the linear velocity increases to prevent the temperature reaching the recording layer from lowering, the irradiation time becomes shorter as the linear velocity increases, so that the recording marks are less likely to be erased.

Therefore, in order to increase the linear velocity and improve the data transfer rate, the composition of the recording layer should be relatively fast so that the recrystallization can be performed in a relatively short time. Kaihei 1-78444, the same 10-3
No. 26436), it is necessary to have a medium structure (slow cooling structure) in which heat does not easily escape from the recording layer. Further, as described in JP-A-7-262613 and JP-A-8-63784, it is preferable that the medium has a slow cooling structure in order to prevent a decrease in recording sensitivity due to a higher linear velocity. Is believed.

[0010]

On the other hand, the inventors of the present invention, when overwriting at a high transfer rate,
It has been found that it is preferable to have a quenching structure in which heat easily escapes from the recording layer (Japanese Patent Application No. 2001-109137).
issue).

FIG. 3 shows an example of the structure of a phase change type optical recording medium. In the medium shown in FIG. 3, a reflective layer 5, a second dielectric layer 32, a phase-change recording layer 4, a first dielectric layer 31, and a translucent substrate 2 are laminated in this order on a support substrate 20. It was formed by. The recording light and the reproducing light are transmitted through the transparent substrate 2
Incident on the recording layer 4. Conventionally, the reflective layer 5 is made of Al
Alternatively, the second dielectric layer 32 is generally made of an alloy containing this as a main component, and the second dielectric layer 32 is made of ZnS-SiO.
It is generally composed of _two .

The inventors of the present invention preferably form the reflective layer 5 and / or the second dielectric layer 32 in FIG. 3 from a material having a high thermal conductivity in order to make the medium have a rapidly cooled structure. The second dielectric layer 32 is Al ₂ O ₃ or S
It has been found that it is preferable that the reflective layer 5 is composed of iO ₂ and the reflective layer 5 is composed of Ag or an alloy containing this as a main component.

However, when the second dielectric layer 32 is made of Al ₂ O ₃ or SiO ₂ , the second dielectric layer 32 and the recording layer 4 are separated between the second dielectric layer 32 and the recording layer 4 when the medium is stored under high temperature and high humidity conditions. It was found that peeling is likely to occur and storage reliability is low. On the other hand, in order to prevent this peeling, the second dielectric layer 32 is Z
If the reflective layer 5 is composed of nS-SiO ₂ and the reflective layer 5 is composed of Ag or an alloy containing this as a main component, Ag in the reflective layer 5 reacts with sulfur S contained in the second dielectric layer 32. It was found that the reflective layer 5 was corroded, which adversely affected the recording / reproducing characteristics.

The present invention provides a sputter target which can be used for forming a dielectric layer required for realizing a phase change type optical recording medium having high storage reliability and good recording / reproducing characteristics. The purpose is to provide.

[0015]

The above objects are achieved by the present invention described in (1) to (6) below. (1) A sputter target containing cerium oxide and an additive compound, wherein the additive compound is at least one selected from chromium oxide, iron oxide, manganese oxide, niobium oxide, magnesium oxide and zinc oxide. (2) In the composition image of the scanning electron microscope, there is a high concentration range of the added compound in which the concentration of the metal contained in the added compound is higher than the surroundings, and the volume percentage of the added compound with respect to the total of cerium oxide and the added compound is A%. And the area of the high concentration region of the added compound is 0.5 A% or more of the whole, the sputtering target according to (1) above. (3) Containing cerium oxide and an additive compound, the additive compound being at least one selected from aluminum oxide, titanium oxide, yttrium oxide, tantalum oxide, antimony oxide, zirconium oxide and bismuth oxide.
In the composition image of the scanning electron microscope, there is a high concentration region of the added compound in which the concentration of the metal contained in the added compound is higher than the surroundings, and the volume percentage of the added compound with respect to the total of cerium oxide and the added compound is A %, The sputter target has an area of the high concentration region of the added compound of 0.5 A% or more of the whole. (4) The above (1), wherein the mole percentage of the added compound is 10 to 80% with respect to the total of the cerium oxide and the added compound.
~ A sputter target according to any one of (3). (5) The above (1), in which the content of chlorine is 10 ppm or less
~ A sputter target according to any one of (4). (6) The sputter target according to any one of (1) to (5), which is used for forming a dielectric layer included in an optical recording medium.

[0016]

In the medium structure shown in FIG. 3, the inventors of the present invention have a higher thermal conductivity than ZnS-SiO ₂ and, moreover, separate the second dielectric layer 32 and the recording layer 4 from each other. As a result of searching for a constituent material of the second dielectric layer 32 capable of preventing corrosion of Ag in the reflective layer 5 when the reflective layer 5 is composed of Ag or an alloy containing this as a main component, We have found that cerium oxide is preferred.
Even when at least the region of the first dielectric layer 31 in contact with the recording layer 4 is made of cerium oxide, the heat radiation from the recording layer 4 is good, and the space between the first dielectric layer 31 and the recording layer 4 is good. It was found that peeling was less likely to occur.

However, it has been found that when the dielectric layer is formed by the sputtering method using the target made of cerium oxide, the dielectric layer is likely to be cracked. If cracks exist in the dielectric layer, recording / reproducing errors will occur there.

As a result of further researches conducted by the present inventors, it was found that when a dielectric target was formed by using a sintered target composed of a mixture of cerium oxide and other predetermined compound (additive compound in the present invention). It turned out that it can prevent the cracks.

If a dielectric layer containing cerium oxide and the above-mentioned additive compound (referred to as a mixed dielectric layer in the present specification) is provided in contact with the recording layer 4, the above-mentioned mixture will be obtained even when stored under high temperature and high humidity conditions. Peeling does not easily occur between the dielectric layer and the recording layer 4. If the mixed dielectric layer is provided in contact with the reflective layer 5 made of Ag or an alloy containing Ag as a main component, the reflective layer 5 is not corroded. Further, the mixed dielectric layer is less likely to have cracks when formed by the sputtering method. Further, in the above mixed dielectric layer, the refractive index can be widely controlled by changing the mixing ratio of cerium oxide and the above-mentioned additive mixture, which facilitates the optical design of the medium.

The difficulty of peeling the mixed dielectric layer from the recording layer is realized when the recording layer is made of a metal or an alloy. As the recording layer made of metal or alloy,
For example, a phase-change recording layer containing Sb and Te as main components, a phase-change recording layer having a composition near Ge ₂ Sb ₂ Te ₅ (atomic ratio), and a magneto-optical recording layer made of a rare earth element-transition element alloy are available. Can be mentioned. However, since the separation between the recording layer and the dielectric layer is likely to occur even when a thermal shock is applied, a phase change medium in which the recording layer is heated to 200 to 600 ° C. during initialization (crystallization) or recording. On the other hand, the present invention is particularly effective.

When a thin film containing a plurality of kinds of oxides is formed by a sputtering method, a multi-source sputtering method using a plurality of targets made of respective oxides or a single target containing a plurality of kinds of oxides (sintering) is used. Target) method. However, in the multi-source sputtering method, since it is necessary to supply high-frequency power to each target independently, the sputtering apparatus becomes large and
Further, compositional deviation is likely to occur in the formed dielectric layer. Therefore, it is preferable to use a sintering target for forming the dielectric layer containing plural kinds of oxides. The present invention provides a sintering target that can be used to form the mixed dielectric layer.

However, when a target containing cerium oxide and the above-mentioned additive compound is manufactured by a sintering method, cracks may occur in the target. In particular, when using aluminum oxide, titanium oxide, yttrium oxide, tantalum oxide, antimony oxide, zirconium oxide or bismuth oxide among the above-mentioned additive compounds, and when the target diameter or major axis is 150 mm or more, a practical yield is obtained. I couldn't get it.

As a result of repeated research for preventing cracking of the sintered target, the inventors have found that cracking can be prevented by controlling element diffusion during sintering of the target.

The sintering target is manufactured by mixing the cerium oxide powder and the additive compound powder and sintering the molded body of the obtained mixture. When the sintered target is observed by a scanning electron microscope (SEM) composition image (backscattered electron image), light and shade depending on the element distribution is recognized. The smaller the atomic number, the weaker the reflection intensity of the backscattered electrons, and therefore the smaller the atomic number, the lower the brightness in the composition image. Metal element in the above additive compound (hereinafter referred to as additive metal)
Has a smaller atomic number than Ce except for Ta, and therefore, when an additive metal other than Ta is used, the lightness becomes relatively high in a region where the Ce concentration is relatively high (hereinafter referred to as cerium oxide high concentration region). In the region where the concentration of the added metal is relatively high (hereinafter referred to as the high concentration region of the added compound), the brightness is relatively low. On the other hand, when Ta is used as the additive metal, the brightness in the high concentration region of cerium oxide is relatively low,
The brightness of the high concentration range of the added compound becomes relatively high. Therefore, the state of element diffusion in the sintering target can be known by analyzing the composition image of the SEM. Specifically, as the diffusion of Ce and the added metal in the sintering target progresses, the areas of the cerium oxide high-concentration region and the additive compound high-concentration region both become smaller, while the cerium oxide high-concentration region has a smaller area. The ratio of the middle lightness region showing the lightness between the lightness and the lightness of the high concentration region of the added compound increases.
The medium lightness region is formed by element diffusion, and has a Ce concentration lower than that of the cerium oxide high concentration region and a concentration of a metal contained in the additive compound lower than that of the additive compound high concentration region (in the present specification, diffusion). Area).

The inventors of the present invention sinter under the condition that element diffusion is suppressed, that is, in the composition image of SEM, the area of the above-mentioned added compound high concentration region where the concentration of the added metal is higher than the surroundings becomes relatively large. It was found that such sintering can suppress cracking of the target when producing a large-diameter sintered target containing cerium oxide and the above-mentioned additive compound.

By the way, in Japanese Patent Laid-Open No. 1-92365, cerium oxide is mixed with titanium oxide, yttrium oxide,
One or more of aluminum oxide, tantalum oxide, antimony oxide, magnesium fluoride, zirconium oxide and bismuth oxide, the content of which is 0.5 to 50.
A cerium oxide composition for vacuum vapor deposition or sputtering, which is mixed in a weight percentage, is described. This composition
It is similar to the sputtering target used in the present invention in that it includes a sputtering composition in which cerium oxide is mixed with aluminum oxide, titanium oxide, yttrium oxide, tantalum oxide, antimony oxide, zirconium oxide or bismuth oxide.

In Example 1 of the same publication, 25% by weight of titanium oxide was added to cerium oxide, and after press molding, about 1
Sintering is performed at 300 ° C. for 2 hours to produce vapor deposition pellets. Further, in Example 2 of the same publication, 40% by weight of tantalum oxide was added to cerium oxide, and a sputter target having a diameter of 100 mm and a thickness of 6 mm was prepared in the same manner as in Example 1. Further, in Example 3 of the same publication, 25 wt% of aluminum oxide was added to cerium oxide, and a vapor deposition pellet was produced in the same manner as in Example 1. In these examples, only the second example produced the sputter target.

The publication describes that when cerium oxide is used for the sputtering target, the cerium oxide is vulnerable to thermal shock and may be cracked or cracked. The purpose is to remedy the drawbacks. However, the publication does not describe that the target is cracked when the target is manufactured by the sintering method. Further, the publication does not describe the texture structure (element distribution) of a sintering target containing two kinds of oxides.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The sputter target of the present invention is
Although it can be used for forming various dielectric thin films, it is particularly effective when used for forming a dielectric layer of an optical recording medium as described above.

The sputter target of the present invention is a sintered target containing cerium oxide and an additive compound. The additive compound is at least one compound selected from chromium oxide, iron oxide, manganese oxide, niobium oxide, magnesium oxide and zinc oxide, or aluminum oxide, titanium oxide, yttrium oxide, tantalum oxide, antimony oxide, It is at least one compound selected from zirconium oxide and bismuth oxide.
Among these, the use of aluminum oxide or magnesium oxide makes the effect of the present invention particularly excellent.

The composition of the sputter target may be appropriately determined according to the purpose. For example, when used for forming a mixed dielectric layer of an optical recording medium, the composition of the sputter target may be determined according to the composition required for the mixed dielectric layer. In the mixed dielectric layer formed using the sputter target of the present invention, the molar ratio of the additive compound to the total amount of cerium oxide and the additive compound is preferably 1
It is 0 to 80%, more preferably 20 to 60%. If this molar ratio is too small, the effect of containing the additive compound becomes insufficient. On the other hand, if this molar ratio is too large, peeling easily occurs between the mixed dielectric layer and the recording layer.

Since there is no significant difference between the composition of the target and the composition of the mixed dielectric layer formed by sputtering using the target, the composition usually depends on the composition required for the mixed dielectric layer. The target composition may be determined by However, when strict control of the composition of the mixed dielectric layer is required, the correspondence relationship between the composition of the target and the composition of the mixed dielectric layer formed by the target is experimentally understood, and this correspondence relationship is obtained. The target composition may be determined based on

In the production of the target, the mixing ratio of each compound is often expressed as a mass percentage, and the mol percentage and the mass percentage can be easily converted using the atomic weight.

The molar ratio of the added compound in the mixed dielectric layer can be directly measured by the following procedure.
First, the content of each metal element contained in the mixed dielectric layer is obtained. The amount of metallic elements was determined by X-ray fluorescence analysis, E
It can be determined by PMA (electron probe X-ray microanalysis), Auger electron spectroscopy, or the like. Next, assuming that the metal element contained in the mixed dielectric layer exists as a compound having a stoichiometric composition, the molar ratio of the added compound is calculated. That is, chromium oxide, iron oxide, manganese oxide, niobium oxide, magnesium oxide, zinc oxide, aluminum oxide, titanium oxide, yttrium oxide, tantalum oxide, antimony oxide, zirconium oxide, bismuth oxide and cerium oxide are each added to Cr ₂
O ₃ , Fe ₃ O ₄ , Mn ₃ O ₄ , Nb ₂ O ₅ , MgO, Zn
O, Al ₂ O ₃ , TiO ₂ , Y ₂ O ₃ , Ta ₂ O ₅ , Sb
The molar ratio in the mixed dielectric layer is calculated in terms of ₂ O ₃ , ZrO ₂ , Bi ₂ O ₃ and CeO ₂ .

The mixed dielectric layer is preferably composed only of cerium oxide and the above-mentioned added compound, but may contain other compounds such as silicon oxide and at least one kind of rare earth element oxide other than cerium oxide. Good. However, if the content of the other compound is large, the effect of the present invention may be impaired. Therefore, the total content of the other compound is preferably 30 mol% or less of the entire mixed dielectric layer. Since sulfides such as ZnS impair the effects of the present invention, it is preferable not to contain sulfides. In addition,
This mole percentage is calculated assuming that the other compound is present as a compound having a stoichiometric composition.

As described above, when the dielectric layer containing the mixture of cerium oxide and the additive compound is formed, in order to prevent the composition deviation of the dielectric layer, the sintering target containing the cerium oxide and the additive compound is formed. To use. However, this sintering target is liable to cause cracks when manufactured by a sintering method, and when aluminum oxide, titanium oxide, yttrium oxide, tantalum oxide, antimony oxide, zirconium oxide or bismuth oxide is used as an addition compound, When the diameter or major axis of the sintered target is 150 mm or more, particularly 200 mm or more, cracking is particularly likely to occur.

In order to prevent cracks during the production of the sintered target, it is preferable that the sintered target has a texture structure described below in the SEM composition image. In the following description, the case where aluminum oxide is used as the additive compound is given as an example, but the same applies to other additive compounds.

As described above, when the additive compound is other than tantalum oxide, in the composition image, the cerium oxide high-concentration region has high lightness, the additive compound high-concentration region has low lightness, and the diffusion region has an intermediate value. It becomes brightness. 1 and 2 are composition images of a sintered target, FIG. 1 is a target without cracks, and FIG. 2 is a target with cracks.

In FIG. 2, there are a cerium oxide high-concentration region close to white, an additive compound high-concentration region close to black, and a gray diffusion region. The cerium oxide high-concentration region in FIG. 2 has a composition substantially close to cerium oxide, the additive compound high-concentration region in FIG. 2 has a composition substantially close to aluminum oxide, and the diffusion region diffuses Ce and Al. Is an area where

On the other hand, almost no gray diffusion region is recognized in FIG. 1, and the area of the high concentration region of the added compound, which is close to black, is larger than that in FIG. In FIG. 1, the high concentration region of the added compound having a diameter of 5 to 10 μm is uniformly dispersed. That is, in FIG. 1, diffusion of Ce and Al does not proceed as compared with FIG.

The sintered targets shown in FIGS. 1 and 2 are
The composition is 70% by volume of cerium oxide and 30% by volume of aluminum oxide. On the other hand, the area ratio of the high concentration region of the added compound in the visual field is 28% in FIG. 1 and 5% in FIG.
Is. The inventors conducted an experiment in which the target was produced by changing the aluminum oxide content and the sintering conditions variously, and when the volume percentage of aluminum oxide with respect to the total of cerium oxide and aluminum oxide was A%, It has been found that when the area of the high concentration region of the added compound in which Al is present at a high concentration is 0.5 A% or more, preferably 0.8 A% or more of the entire visual field, cracking of the target can be significantly suppressed. However, if the area of the high concentration region of the added compound is too large, that is, if the sintering is performed under the condition that the diffusion of Ce and Al hardly progresses, the sintering of the target becomes insufficient. As a result, the target becomes more hygroscopic,
It becomes fragile due to moisture absorption. Therefore, the area of the high concentration region of the added compound is less than A% of the entire visual field, especially 0.99A%.
The following is preferable.

Whether the content of the added compound is smaller or larger than the target shown in FIGS. 1 and 2,
The cerium oxide high-concentration region, the added compound high-concentration region, and the diffusion region can be clearly distinguished in the SEM composition image as in FIGS. 1 and 2. Further, almost no diffusion region is observed in the target of the present invention shown in FIG. 1, but even the target of the present invention may have a larger area of the diffusion region depending on the area ratio of the high concentration region of the additive compound. .

When obtaining the area ratio in the high concentration region of the added compound, it is not necessary to perform the measurement on the entire surface of the target, but it is sufficient to perform the measurement on the area of at least 8000 μm ² of the target surface.

In the present invention, the volume percentage of each compound in the target is calculated from the mass percentage of each compound in the target by the following procedure. M _C : mass percentage of CeO ₂ , M _A : mass percentage of added compound, ρ _C : density of CeO ₂ , ρ _A : density of added compound, V _C : volume percentage of CeO ₂ , _VA : volume of added compound When expressed as a percentage, V _C = (100 * M _C / ρ _C ) / (M _C / ρ _C + M _A /
[rho _A), a _{V A = (100 * M A} / ρ A) / (M C / ρ C + M A / ρ A).

The effect of preventing cracking of the target by controlling the structure of the structure is particularly effective when the major axis or diameter of the target is 150 mm or more, particularly 200 mm or more. However, if the target diameter is extremely large, cracks are likely to occur, so the major axis or diameter of the target is preferably 330 mm or less.

In order to set the area ratio of the high concentration region of the additive compound within the above-mentioned limited range, it is necessary to control the sintering conditions according to various conditions such as the particle size of the raw material powder of the sintering target and the particle size distribution and composition. Good. Specific sintering conditions may be experimentally determined so that the area ratio of the high concentration region of the added compound becomes a desired value, but the sintering temperature is within a range of 1000 to 1400 ° C, particularly 1200 to 1250 ° C. The sintering time (stable temperature or the time for passing within the above preferable temperature range) is preferably 0.5 to 2 hours. Note that hot pressing (hot pressure firing) may be used for sintering. The pressure applied during hot pressing is preferably about 5 to 30 MPa.

The sintering target is manufactured by mixing the cerium oxide powder and the additive compound powder, molding the mixture, and then sintering the mixture. The average particle size of the cerium oxide powder and the additive compound powder is not particularly limited, but is usually 0.01 to 3
It may be in the range of μm.

The cerium oxide powder can be produced by a coprecipitation method.
Chlorine of about 0 ppm tends to remain. This chlorine is also contained in the mixed dielectric layer, and as a result, black spots occur in the recording layer in contact with the mixed dielectric layer, which may affect the recording / reproducing characteristics. In order to prevent such problems from occurring, the chlorine content in the target should be 10 ppm by mass.
It is preferable to suppress it to the following.

Next, a structural example of an optical recording medium having a composite dielectric layer formed by using the sputter target of the present invention will be described.

FIG . 3 shows an example of the structure of the structure optical recording medium shown in FIG. This optical recording medium comprises a supporting substrate 20, a reflecting layer 5, a second dielectric layer 32,
The phase-change recording layer 4, the first dielectric layer 31, and the translucent substrate 2 are laminated in this order. The laser beam for recording or reproduction enters the recording layer 4 through the transparent substrate 2. An intermediate layer made of a dielectric material may be provided between the support base 20 and the reflective layer 5. The configuration of each part of this medium will be described below.

First Dielectric Layer 31 and Second Dielectric Layer 32 These dielectric layers prevent the recording layer 4 from being oxidized and altered. Moreover, the modulation degree can be improved by providing these dielectric layers. The first dielectric layer 31 protects the translucent substrate 2 by blocking or releasing heat transferred from the recording layer 4 in the in-plane direction during recording. Further, the second dielectric layer 32 has a function of radiating the heat transmitted from the recording layer 4 to the reflective layer 5 at the time of recording to cool the recording layer 4.

First dielectric layer 31 and second dielectric layer 32
The thickness of the first dielectric layer 31 may be appropriately determined so that the cooling effect, the protective effect, and the modulation degree improving effect are sufficiently obtained, but normally, the thickness of the first dielectric layer 31 is preferably 30 to 300 nm, and more preferably 50 to 250 nm, and the thickness of the second dielectric layer 32 is preferably 2 to 50 nm. However, the thickness of the second dielectric layer 32 is preferably 3 in order to obtain a quenching structure.
The thickness is 0 nm or less, more preferably 25 nm or less.

First dielectric layer 31 and second dielectric layer 32
Examples of the dielectric used for Si include Ge, Ge, Zn,
Various compounds containing at least one metal component selected from Al, rare earth elements and the like are preferable. As a compound,
Oxides, nitrides or sulfides are preferable, and a mixture containing two or more of these compounds can also be used.

However, in the present invention, at least a part of the first dielectric layer 31 and / or at least a part of the second dielectric layer 32 are formed of a mixed dielectric layer containing cerium oxide and an additive compound.

In the present invention, the entire first dielectric layer 31 and / or the entire second dielectric layer 32 may be the mixed dielectric layer, and the first dielectric layer 31 and / or the second dielectric layer 32 may be used. Alternatively, at least two sub-dielectric layers may be laminated, and at least one sub-dielectric layer may be the mixed dielectric layer. In any case, if the mixed dielectric layer exists in contact with the recording layer 4, peeling between the recording layer 4 and the mixed dielectric layer does not easily occur even when stored under high temperature and high humidity conditions. If the mixed dielectric layer is present in contact with the reflective layer 5 containing Ag, the reflective layer 5 is less likely to corrode.

Support Base 20 The support base 20 is provided to maintain the rigidity of the medium. The thickness of the supporting substrate 20 is usually 0.2 to 1.2 mm,
The thickness is preferably 0.4 to 1.2 mm and may be transparent or opaque. The support base 20 may be made of resin as in the case of an ordinary optical recording medium.
It may be made of metal or ceramic. The groove (guide groove) 21 usually provided in the optical recording medium can be formed by transferring the groove provided in the supporting substrate 20 to each layer formed thereon, as shown in the figure. The groove 21 is a region existing relatively on the front side when viewed from the recording / reproducing light incident side, and a region existing between adjacent grooves is a land 22.

Reflective Layer 5 The material constituting the reflective layer is not particularly limited, and usually Al, Au,
It may be made of a metal or semimetal such as Ag, Pt, Cu, Ni, Cr, Ti, or Si, or an alloy containing one or more of these. However, since the dielectric layer constituent material in the present invention is selected in order to make the medium a quenching structure, the reflecting layer is also preferably made of a material having a high thermal conductivity suitable for the quenching structure. As a material having high thermal conductivity, Ag or an alloy containing this as a main component is preferable. However, since Ag alone does not provide sufficient corrosion resistance, it is preferable to add an element for improving the corrosion resistance. Further, in the medium having the structure shown in FIG. 3, the surface roughness of the reflective layer on the laser beam incident side tends to increase due to crystal growth during the formation of the reflective layer. When the surface roughness increases, the reproduction noise increases. Therefore, it is preferable to reduce the crystal grain size of the reflection layer, but also for that purpose, in order to reduce the crystal grain size of the reflection layer or to form the reflection layer as an amorphous layer, not Ag alone. In addition, it is preferable to add an additional element.

Examples of sub-component elements that are preferably added to Ag include Mg, Pd, Ce, Cu, Ge and L.
At least one selected from a, Sb, Si, Te and Zr can be mentioned. It is preferable to use at least one, and preferably two or more of these sub-component elements. The content of the sub-component element in the reflective layer is preferably 0.05 to 2.0 atom%, more preferably 0.2 to 1.0 atom% with respect to each metal, and the total content of the sub-components is preferably 0. It is 2 to 5 atom%, more preferably 0.5 to 3 atom%. If the content of the subordinate element is too small, the effect due to the inclusion of these becomes insufficient. On the other hand, if the content of the sub-component element is too large, the thermal conductivity will decrease.

The smaller the crystal grain size, the lower the thermal conductivity of the reflective layer. Therefore, if the reflective layer is amorphous, it is difficult to obtain a sufficient cooling rate during recording. Therefore, it is preferable that the reflective layer is first formed as an amorphous layer and then heat-treated to be crystallized. When the amorphous layer is once formed and then crystallized, the surface roughness in the amorphous state can be almost maintained, and the thermal conductivity can be improved by the crystallization.

The thickness of the reflective layer is usually preferably 10 to 300 nm. If the thickness is less than the above range, it becomes difficult to obtain sufficient reflectance. Further, even if it exceeds the above range, the improvement in reflectance is small, which is disadvantageous in terms of cost. The reflective layer is preferably formed by a vapor phase growth method such as a sputtering method or a vapor deposition method.

Recording Layer 4 The composition of the recording layer is not particularly limited. However, in order to increase the data transfer rate, it is necessary to perform overwriting at a high linear velocity, and for that purpose, the amorphous recording marks are crystallized so that they can be erased (crystallized) in a short time. A recording layer having a high quality transition rate (crystallization rate) is preferred. For that purpose, Sb and Te are the main components, and Sb
It is preferable that the composition has a relatively large content.

Since the crystallization temperature of the recording layer made of only Sb and Te is as low as about 130 ° C. and the storage reliability is insufficient, it is preferable to add another element to improve the crystallization temperature. In this case, the additional element is I
n, Ag, Au, Bi, Se, Al, P, Ge, H, S
i, C, V, W, Ta, Zn, Ti, Sn, Pb, Pd
And at least one selected from rare earth elements (Sc, Y and lanthanoids) is preferable. Of these, at least one selected from rare earth elements, Ag, In, and Ge has a particularly high effect of improving storage reliability.
Seeds are preferred.

The composition of the recording layer is preferably represented by the formula I (Sb _x Te _1-x ) _1-y M _y . In the above formula I, the element M
Represents an element excluding Sb and Te, and x and y represent atomic ratios, preferably 0.2 ≦ x ≦ 0.90, 0 ≦ y ≦ 0.25, and more preferably 0.55 ≦ x. ≦ 0.85 and 0.01 ≦ y ≦ 0.20. By making the recording layer have such a composition, it becomes easy to increase the data transfer rate.

Translucent Substrate 2 The translucent substrate 2 has a translucent property for transmitting recording / reproducing light. A resin plate or a glass plate having the same thickness as that of the supporting substrate 20 may be used for the translucent substrate 2. However, the present invention is particularly effective when high density recording is performed. Therefore, in order to achieve a high recording density by increasing the NA of the recording / reproducing optical system, it is preferable to make the translucent substrate 2 thin. In this case, the thickness of the translucent substrate is preferably selected from the range of 30 to 300 μm. If the light-transmitting substrate is too thin, the dust on the surface of the light-transmitting substrate has a large optical effect. On the other hand, if the translucent substrate is too thick, it will have a high NA.
It is difficult to achieve high recording density due to the trend toward higher recording density.

When thinning the light-transmitting substrate 2, for example, a light-transmitting sheet made of a light-transmitting resin is attached to the first dielectric layer 31 with various adhesives or pressure-sensitive adhesives to form a light-transmitting substrate. Alternatively, a translucent resin layer may be directly formed on the first dielectric layer 31 using a coating method to form a translucent substrate.

Structure shown in FIG. 4 In the optical recording medium shown in FIG. 4, a first dielectric layer 31, a recording layer 4, a second dielectric layer 32, a reflective layer 5 and a protective layer 6 are formed on a transparent substrate 2. In this order, the recording light and the reproducing light are incident through the transparent base 2.

Even with the structure shown in FIG. 4, the effect of the present invention can be realized by controlling the composition of the second dielectric layer 32 according to the present invention.

The light-transmitting substrate 2 shown in FIG. 4 may be the same as the support substrate 20 shown in FIG. 3, but needs to have light-transmitting properties.

The protective layer 6 is provided for improving scratch resistance and corrosion resistance. This protective layer is preferably composed of various organic substances, but particularly preferably composed of a substance obtained by curing a radiation-curable compound or its composition with radiation such as electron beam or ultraviolet ray. . The thickness of the protective layer is usually about 0.1 to 100 μm, and may be formed by a usual method such as spin coating, gravure coating, spray coating, dipping or the like.

The other layers are the same as in the configuration example shown in FIG.

[0071]

Example 1 FIG. 1 shows an SEM photograph (composition image) of a sintered target containing CeO ₂ and Al ₂ O ₃ . This target is a disc-shaped having a diameter of 200 mm and a thickness of 6 mm, and is made by a coprecipitation method and has an average particle diameter of 0.5 μm CeO ₂ powder (chlorine content 3 ppm) and an average particle diameter of 0.5 μm Al ₂ O. _Three powders were mixed and molded, and then sintered in an Ar atmosphere at 1200 ° C. for 1 hour to manufacture. The mixing ratio of CeO ₂ and Al ₂ O ₃ in the target is such that the volume ratio obtained by the above procedure is CeO ₂ : Al ₂ O ₃ = 70: 3.
It was decided to be 0.

A target was prepared in the same manner as the target shown in FIG. 1 except that the sintering temperature was 1300 ° C.
FIG. 2 shows an SEM photograph (composition image) of this sintered target.

In FIG. 1, the area of the high concentration region of the additive compound in which Al is present at a high concentration is the area of the entire visual field (about 9100 μm).
28% of m ² ). In this target, Al ₂ O ₃ /
(CeO ₂ + Al ₂ O ₃ ) = 30%, that is, volume ratio A%
Is 30%, this target satisfies the limitation in the present invention. On the other hand, in FIG. 2, the area of the high concentration region of the additive compound in which Al is present at a high concentration is 5 of the total area of the visual field.
%, That is, less than 0.5 A%, does not satisfy the limitation in the present invention.

Thirty targets were produced under the same conditions as those of the target shown in FIG. 1, and thirty targets were produced under the same conditions as those of FIG. As a result, the target produced under the same conditions as the target shown in FIG. 1 has a crack occurrence rate of 3.3%.
Further, when left in the air for 3 days after the production, no new cracks were found, and no target surface was powdered in the bonding step. On the other hand, in the target manufactured under the same conditions as the target shown in FIG. 2, the crack occurrence rate was 66.7%, and when left in the air for 3 days, the crack occurrence rate was 83.3%.
Increased.

From these results, the effect of limiting the area ratio of the high concentration region of the added compound in the SEM composition image is clear.

When 30 targets were produced in the same manner as above using chromium oxide, iron oxide, manganese oxide, niobium oxide, magnesium oxide or zinc oxide instead of aluminum oxide, the high concentration range of the added compound was obtained. Even if the area ratio was less than 0.5 A%, the number of cracks was relatively small, and when the sintering was performed under the condition that the area ratio in the high concentration region of the added compound was 0.5 A% or more, the number of cracks was further reduced. The effect was particularly high when magnesium oxide was 30 mol% (15% by volume).
It was when added. In the target to which magnesium oxide was added, the area ratio in the high concentration region of the added compound was 0.28.
Even with A%, the crack occurrence rate was as low as 13.3%.
When the area ratio of the additive compound high concentration region is 0.66A% in the target of magnesium oxide addition, the crack occurrence rate is 3.3%, and when the area ratio of the additive compound high concentration region is 0.87A%. The crack occurrence rate is 0%, and
In any of these cases, no cracks were formed by standing in the air for 3 days, and none of the surfaces were powdered in the bonding step.

When titanium oxide, yttrium oxide, tantalum oxide, antimony oxide, zirconium oxide or bismuth oxide is used instead of aluminum oxide, the area ratio of the high concentration region of the added compound should be 0.5 A% or more. This significantly reduced the cracking of the target during sintering and the cracking of the target after standing in the air. Example 2 Sample No. 1 An optical recording disk sample having the structure shown in FIG. 3 was produced by the following procedure.

For the supporting substrate 20, a disc-shaped polycarbonate having a diameter of 120 mm and a thickness of 1.1 mm, which was simultaneously formed with a groove by injection molding, was used.

The reflective layer 5 was formed by sputtering in an Ar atmosphere. Ag ₉₈ Pd ₁ Cu _{1 for the} target
Was used. The thickness of the reflective layer 5 was 100 nm.

The second dielectric layer 32 was formed by a sputtering method in an Ar atmosphere using a CeO ₂ --Al ₂ O ₃ sintered target produced under the same conditions as the target shown in FIG.
The composition of this sintering target was determined so that the molar ratio CeO ₂ : Al ₂ O ₃ of the formed dielectric layer was 80:20. The thickness of the second dielectric layer 32 was 12.5 nm.

For the recording layer 4, an alloy target is used and Ar is used.
It was formed by sputtering in an atmosphere. The composition of the recording layer 4 (atomic ratio), the formula _{I (Sb x Te 1-x} ) 1-y M y in M = In, Ge, In: Ge = 1: 5, x = 0.78, y = 0 It was set to 0.06. The thickness of the recording layer was 12 nm.

The first dielectric layer 31 was formed by using a ZnS (80 mol%)-SiO ₂ (20 mol%) target and Ar.
It was formed by sputtering in an atmosphere. First dielectric layer 3
The thickness of 1 was 130 nm.

The transparent substrate 2 was formed by adhering a 100 μm thick polycarbonate sheet to the surface of the first dielectric layer 31.

Sample No. 2 (comparative) The second dielectric layer 32 was composed only of CeO ₂ and the second
Sample No. except that the thickness of the dielectric layer 32 was set to 12 nm.
It was produced in the same manner as 1.

Sample No. 3 (comparative) The second dielectric layer 32 was composed of Al ₂ O ₃ only, and
Sample No. except that the thickness of the dielectric layer 32 was set to 20 nm.
It was produced in the same manner as 1.

Evaluation After the recording layer of each sample was initialized (crystallized) by a bulk eraser, it was placed on an optical recording medium evaluation device, laser wavelength λ: 405 nm, numerical aperture NA: 0.85, linear velocity: 5. Recording was performed under the conditions of 3 m / s and bit length: 0.12 μm.

Next, the recorded signal was reproduced and the jitter was measured. This jitter is clock jitter, and is a value calculated by calculating σ / Tw (%) using the detection window width Tw by measuring the reproduced signal with a time interval analyzer to obtain “signal fluctuation (σ)”. The optimum recording power / optimum erasing power that minimizes the jitter was determined to be 5.4 mW / 2.8 mW in all samples, and the jitter at that time was 7.4%. From these results, it was confirmed that there was no problem in recording / reproducing characteristics in any of the samples.

Next, these samples were heated at 80 ° C. and 85%.
When stored in a high temperature and high humidity environment of RH for 50 hours, sample No. 1 and No. 2 did not change, but the sample
In No. 3, peeling occurred between the recording layer 4 and the second dielectric layer 32.

Further, with respect to Sample No. 1 and No. 2, 1000 sheets were continuously produced, and the second dielectric layer 3
The quality of 2 was checked. As a result, in sample No. 2 having the second dielectric layer 32 made of CeO ₂ , as many as 50% had cracks in the second dielectric layer 32. On the other hand, in sample No. 1 having the second dielectric layer 32 made of a mixture of CeO ₂ and Al ₂ O ₃ , there was no crack in the second dielectric layer 32.

Example 3 The second dielectric layer 32 was composed of CeO ₂ --Al ₂ O ₃ or CeO ₂ , and the content of Al ₂ O ₃ in the second dielectric layer 32 is shown in Table 1.
An optical recording disk sample was prepared in the same manner as in Sample No. 1 except that the values shown in Table 1 and the thickness of the second dielectric layer 32 were shown in Table 1. The thickness of the second dielectric layer 32 of each sample was set so that all samples had the same reflectance.

For these samples, the optimum recording power Pw that minimizes the jitter was determined under the same conditions as in Example 1. In addition, these samples were stored under the conditions of high temperature and high humidity in the same manner as in Example 1, and after the storage, the presence or absence of peeling between the recording layer 4 and the second dielectric layer 32 was examined. The results are shown in Table 1.

[0092]

[Table 1]

From Table 1, it can be seen that when the Al ₂ O ₃ content exceeds 60 mol%, peeling easily occurs between the recording layer 4 and the second dielectric layer 32. The peeling was measured for each of 10 samples. Al ₂ O ₃ content is 80
The peeling frequency in sample No. 9 which is mol% is
It was 4/10. On the other hand, the peeling occurrence frequency in the sample No. ₃ having an Al ₂ O ₃ content of 100 mol% is
It was 10/10. From these results, the preferable range of the Al ₂ O ₃ content is 10 to 80 mol%, particularly 20 to 60 mol%.
It can be seen that it is mol%.

From the results shown in Table 1, Al ₂ O ₃
Since increasing the content lowers the refractive index,
It can be seen that the dielectric layer 32 can be made thicker, and as a result, the recording sensitivity is improved (the optimum recording power is lowered). In each of the samples shown in Table 1, the minimum value of jitter was 8% or less.

In place of Al ₂ O ₃ , Cr ₂ O ₃ and Fe
₃ O ₄ , Mn ₃ O ₄ , Nb ₂ O ₅ , MgO, ZnO, Ti
O ₂ , Y ₂ O ₃ , Ta ₂ O ₅ , Sb ₂ O ₃ , ZrO ₂ or Bi
The second dielectric layer 3 by using a sintered target containing ₂ O ₃
Even when No. 2 was formed, cracking of the second dielectric layer 32 was suppressed, and peeling of the second dielectric layer was not observed. In particular, when MgO was used, the same crack suppressing effect as when Al ₂ O ₃ was used was recognized.

[Brief description of drawings]

FIG. 1 is a drawing-substituting photograph showing the structure of a ceramic material, which is a scanning electron microscope photograph (composition image) of a sputter target in which element diffusion has not progressed.

FIG. 2 is a drawing-substituting photograph showing the structure of a ceramic material, which is a scanning electron microscope photograph (composition image) of a sputter target in which element diffusion is progressing.

FIG. 3 is a partial cross-sectional view showing a configuration example of an optical recording medium.

FIG. 4 is a partial cross-sectional view showing another configuration example of the optical recording medium.

[Explanation of symbols]

2 Translucent substrate 20 Support substrate 31 First Dielectric Layer 32 second dielectric layer 4 recording layers 5 Reflective layer 6 protective layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroyasu Inoue             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. F-term (reference) 4K029 BA43 BC00 BD12 CA05 DC05                       DC09                 5D029 LA14                 5D121 AA04 EE09 EE14

Claims (6)

[Claims] 1. A sputter target containing cerium oxide and an additive compound, wherein the additive compound is at least one selected from chromium oxide, iron oxide, manganese oxide, niobium oxide, magnesium oxide and zinc oxide. 2. In the composition image of the scanning electron microscope, there is a high concentration range of the added compound in which the concentration of the metal contained in the added compound is higher than the surroundings, and the volume percentage of the added compound with respect to the total of cerium oxide and the added compound is The sputter target according to claim 1, wherein the area of the high concentration region of the added compound is 0.5 A% or more of the whole when A%. 3. Cerium oxide and an additive compound, wherein the additive compound is aluminum oxide, titanium oxide,
It is at least one selected from yttrium oxide, tantalum oxide, antimony oxide, zirconium oxide, and bismuth oxide. In the composition image of the scanning electron microscope, the concentration of the metal contained in the additive compound is higher than that of the surroundings. Exists, and when the volume percentage of the additive compound with respect to the total of cerium oxide and the additive compound is A%, the area of the high concentration region of the additive compound is 0.5 A% or more of the whole sputtering target. 4. The sputter target according to claim 1, wherein the mole percentage of the additive compound with respect to the total of cerium oxide and the additive compound is 10 to 80%. 5. The sputtering target according to claim 1, wherein the chlorine content is 10 ppm or less. 6. The sputter target according to claim 1, which is used for forming a dielectric layer of an optical recording medium.