JP4023432B2 - Phase change optical recording medium, method for producing the same, and sputtering target for forming a protective layer used therefor - Google Patents

Description

  The present invention relates to a phase change optical recording medium, a method for producing the same, and a sputtering target for forming a protective layer used therefor, and more particularly, high-speed recording formed by forming a protective layer having good optical characteristics and weather resistance film characteristics. In particular, the present invention relates to a phase change optical recording medium having good weather resistance, a production method for forming the protective layer at an industrially sufficient film formation rate, and a sputtering target for forming the protective layer used therefor.

  In recent years, phase-change optical recording media have been actively researched and developed as rewritable optical recording disks. It is applied to rewritable DVDs. The phase change type optical recording medium is capable of optical modulation overwriting with a single recording layer and reads a signal due to a change in reflectivity due to a phase change, so that it is highly compatible with an existing optical disc such as a CD-ROM. It has the characteristics.

  The phase change optical recording medium is configured by sequentially stacking a protective layer, a recording layer, a protective layer, and a reflective layer on a transparent substrate. Here, recording and erasing of information are performed by a reversible phase change of the recording layer, for example, a phase change between crystal and amorphous (amorphous). That is, irradiation with a laser beam or the like causes a phase change between a crystalline phase and an amorphous phase in the recording layer. In general, the phase change is performed by utilizing the temperature change of the recording layer accompanying the intensity of the laser beam. Recording is performed by forming an amorphous phase recording mark when the laser is strong, and forming a crystalline phase when the laser is weak, and a reproduction signal is obtained by detecting a difference in reflectance between the crystalline phase and the amorphous phase. Here, the formation of the amorphous phase requires that the recording layer dissolved by laser light irradiation be cooled faster than the critical crystallization rate. In addition, the formation of the crystal phase requires the amorphous phase to be crystallized at a temperature below the melting point.

  As described above, in the phase change type optical recording medium, it is important to control the maximum temperature and the rate of temperature change of the recording layer during amorphization and crystallization. Therefore, it is essential to optimize the thermal conductivity and heat capacity of each layer constituting the phase change optical recording medium. In order to perform high-speed recording using the optical recording medium, it is important that the recording layer has a rapid thermal quenching structure. For this purpose, it is desired to increase the thermal conductivity of the reflective layer. .

Conventionally, Ag is used as a reflective layer material having high thermal conductivity, and a protective layer for a phase change optical recording medium is required to have a transparent film characteristic with a high refractive index and low absorption in the visible light region. Usually, a layer containing a ZnS-based sulfide such as a [ZnS + SiO ₂ ] (ZnS and SiO ₂ mixture) layer is used (see, for example, Patent Document 1). Therefore, there is a problem that Ag in the reflective layer is sulfided and the reflectance is lowered. As a solution, there is a method of adding a rare earth element to Ag in order to improve the sulfidation resistance of Ag (see, for example, Patent Document 2). However, when rare earth is added to such an extent that sulfidation resistance is improved, problems such as a decrease in thermal conductivity and reflectivity occur, and the performance as a reflective layer of Ag having high thermal conductivity and high reflectivity is lost. .

Further, as a protective layer other than the ZnS-based layer, nitrides or oxides such as SiN _x and Ta ₂ O ₅ have been studied for magneto-optical disks that have been put into practical use before the phase change optical recording disk. For example, Ta ₂ O ₅ —Nb ₂ O ₅ -based oxides (see, for example, Patent Document 3) have been proposed for magneto-optical disks. However, when an oxide is formed by a sputtering method that is generally used as a method for forming a protective layer, there is a problem that the film formation rate is slower than that of a ZnS system, and the production efficiency is deteriorated. In addition, when a conventional oxide film is used as the protective layer, optical absorption in the visible light region is large unless oxygen is added in an appropriate amount during sputtering, and adhesion to the recording layer is reduced during recording erasure. There was a problem of doing.

On the other hand, as a high refractive index transparent film used for light, at least one oxide selected from the group consisting of Ta, Nb, Mo, W, Zr and Hf, or Nb ₂ O ₅ —SiO ₂ is reduced. Then, a method of forming a film by DC (direct current) sputtering, which has a film formation rate higher than that of RF (high frequency) sputtering, using a conductive target is proposed (for example, see Patent Document 4 or 5). Yes. However, when a transparent oxide layer is formed using a sputtering target in which oxygen is less than the stoichiometric composition, oxygen is added to the sputtering gas and reactive sputtering is performed. As the addition amount is increased, the film formation rate is lowered, and the effect of improving the film formation rate by DC sputtering is reduced, so that the film formation rate is low and productivity is poor. SiNx cannot be used as a protective layer of a phase change optical recording medium because it is not stable at a temperature of 500 ° C. to 600 ° C. at which the recording layer changes phase.

  From the above situation, the optical characteristics are good, that is, the refractive index is high, the absorption in the visible light region is small and transparent, and the weather resistance of the reflective layer due to the sulfide is not deteriorated and the adhesion to the recording layer does not occur. There has been a demand for a phase change optical recording medium having a protective layer that has good film characteristics and can be formed at a higher film formation rate.

JP-A-63-103453 (first page, second page, FIG. 3) JP 2002-323611 A (first page, second page) JP 62-281139 A (first page) JP-A-8-283935 (first page, second page) Japanese Unexamined Patent Publication No. 2000-160331 (first page, second page)

  In view of the above-mentioned problems of the prior art, an object of the present invention is a phase change type light suitable for high-speed recording and having good weather resistance formed by forming a protective layer having film characteristics with good optical characteristics and weather resistance. It is an object of the present invention to provide a recording medium, a production method for forming the protective layer at an industrially sufficient film formation rate, and a sputtering target for forming a protective layer used therefor.

  In order to achieve the above object, the present inventors have conducted extensive studies on a protective layer formed between a recording layer and a reflective layer in a phase change optical recording medium. When an oxide protective layer with a composition is formed, it has film characteristics with good optical characteristics and weather resistance, and when film formation is performed under specific conditions, an industrially sufficient film formation speed can be obtained. The present inventors have found that a phase change optical recording medium using the same is suitable for high-speed recording and has good weather resistance, and the present invention has been completed.

That is, according to the first aspect of the present invention, there is provided a phase change optical recording medium in which a protective layer, a recording layer, a protective layer, and a reflective layer are sequentially laminated on a transparent substrate,
The protective layer formed between the recording layer and the reflective layer is a mixture of amorphous niobium oxide and / or amorphous tantalum oxide, amorphous cerium oxide, and glass, Phase change characterized by having a glassy concentration in the mixture of 10 to 35 mol%, an amorphous cerium oxide concentration of 1 to 30 mol%, and transparency in the visible light region A type optical recording medium is provided.

  According to a second aspect of the present invention, there is provided the phase change type optical recording medium according to the first aspect, wherein the concentration of the amorphous cerium oxide is 5 to 30 mol%. The

  According to a third aspect of the present invention, in the first aspect, the protective layer formed between the recording layer and the reflective layer has a refractive index of 2.1 to 2.3. A phase change optical recording medium is provided.

  According to a fourth aspect of the present invention, there is provided the phase change optical recording medium according to the first aspect, wherein the vitreous material is silicon dioxide and / or silicon monoxide.

  According to a fifth invention of the present invention, in any one of the first to fourth inventions, the reflective layer is at least one selected from the group consisting of Ag alone or Pd, Cu, Au, Nd and Bi. There is provided a phase change optical recording medium formed from an Ag alloy to which a seed metal element is added at a concentration of 0.5 mol% or less.

According to a sixth aspect of the present invention, there is provided a method for producing a phase change optical recording medium by sequentially laminating a protective layer, a recording layer, a protective layer and a reflective layer on a transparent substrate,
In forming a protective layer between the recording layer and the reflective layer, a target containing niobium oxide and / or tantalum oxide, cerium oxide, and glass is used, and under an oxygen partial pressure of 0.003 to 0.010 Pa. A method for producing a phase change optical recording medium characterized by sputtering is provided.

  According to a seventh aspect of the present invention, in the manufacturing method of the sixth aspect of the present invention, the method comprises a mixed sintered body containing niobium oxide and / or tantalum oxide, cerium oxide and vitreous. A sputtering target for forming a protective layer to be used is provided.

  The phase change type optical recording medium of the present invention is an optical recording medium suitable for high-speed recording and having good weather resistance formed by forming an oxide protective layer having film characteristics with good optical characteristics and weather resistance. In the production method, the oxide protective layer can be formed at an industrially sufficient film formation rate, and the sputtering target for forming the protective layer is a target that can be suitably used for it, and its industrial value is extremely large. .

Hereinafter, the phase change optical recording medium of the present invention, the production method thereof and the sputtering target for forming a protective layer used therein will be described in detail.
The phase change optical recording medium of the present invention is a phase change optical recording medium in which a protective layer, a recording layer, a protective layer, and a reflective layer are sequentially laminated on a transparent substrate, and the recording layer, the reflective layer, The protective layer formed between the layers is a mixture of amorphous niobium oxide and / or amorphous tantalum oxide, amorphous cerium oxide, and vitreous, and the vitreous in the mixture The concentration is 10 to 35 mol%, the concentration of amorphous cerium oxide is 1 to 30 mol%, and it has transparency in the visible light region.

  In the phase change optical recording medium of the present invention, the protective layer formed between the recording layer and the reflective layer is amorphous niobium oxide and / or amorphous tantalum oxide, amorphous cerium oxide, and glass. It is important to be a mixture of 3 to 4 types of oxides. As a result, the optical characteristics are good, that is, the refractive index is high, the absorption is small and transparent in the visible light region (wavelength 350 nm to 800 nm), and the film characteristics are excellent in weather resistance with no characteristic deterioration due to sulfide. An oxide protective layer formed at an industrially sufficient film formation rate is obtained.

  In general, the protective layer formed between the recording layer and the reflective layer preferably has a refractive index of 2.0 or more, more preferably 2.2 or more for interference characteristics and thinning. A desired refractive index can be achieved with a mixture of amorphous tantalum oxide, amorphous cerium oxide, and glass.

On the other hand, the conventional oxide protective layer has a problem in any one of refractive index, transparency, and film formation speed. For example, when amorphous niobium oxide is formed by sputtering, the refractive index of the obtained film is 2.3 or more when the oxygen partial pressure during sputtering is 0.003 to 0.010 Pa. This is probably because a mixture of Nb ₂ O ₅ and NbO was formed as a film composition. However, if the oxygen partial pressure is less than 0.003 Pa, light absorption increases in the visible light region, which is not preferable. If the oxygen partial pressure exceeds 0.010 Pa, the refractive index is 2.1 to 2.2, but this is not preferable because the film formation rate is reduced.

For example, when an amorphous tantalum oxide layer is formed by sputtering, the refractive index of the amorphous tantalum oxide layer is 2.1 to 2.2, and its oxygen partial pressure dependency is small. However, this is not preferable because the heat capacity is high and the laser power required for recording / erasing increases.
When niobium oxide and tantalum oxide are simultaneously formed by sputtering, the resulting oxide protective layer made of amorphous niobium oxide and amorphous tantalum oxide has improved weather resistance, and the concentration of tantalum oxide. If it is 30 mol% or less, an increase in heat capacity can be suppressed.

However, if the power is increased by RF sputtering to increase the deposition rate and the input power is increased to 3 W / cm ² or more, there arises a problem that the transmittance of the obtained film is lowered. That is, since amorphous niobium oxide and amorphous tantalum oxide are easily reduced by plasma during sputtering, the resulting film composition has less oxygen than the stoichiometric composition, and transparency is lowered.

  The glassy concentration of the protective layer formed between the recording layer and the reflective layer in the phase change type optical recording medium of the present invention includes amorphous niobium oxide and / or amorphous tantalum oxide, and amorphous cerium oxide. And 10 to 35 mol% of the mixture composed of glassy material, and preferably 15 to 30 mol%. That is, when the concentration is less than 10 mol%, the effect of improving the transmittance of the film is small. On the other hand, when the concentration exceeds 35 mol%, the refractive index of the film decreases to less than 2.1. In the protective layer, the vitreous acts to improve the transmittance of the film by suppressing light absorption in the visible light region.

The glassy material is not particularly limited, and a glassy material that can enhance the permeability of the film is used, and among these, silicon dioxide (SiO ₂ ) and / or silicon monoxide (SiO ) Is preferred.

The density | concentration of the amorphous cerium oxide of the said protective layer is 1-30 mol% of the said mixture, 5-30 mol% is preferable and 15-30 mol% is more preferable. That is, when the concentration is less than 1 mol%, the effect of improving the adhesion with the recording layer is small. On the other hand, if the concentration exceeds 30 mol%, absorption near a wavelength of 400 nm increases, which is not preferable. In the protective layer, amorphous cerium oxide acts as a high refractive index material together with amorphous niobium oxide and tantalum oxide, but in addition to improving the thermal expansion coefficient of the mixture, the phase change type This has the effect of preventing the adhesiveness with the recording layer from being lowered when recording and erasing the optical recording medium.

That is, since a laser is used for recording, erasing and reading information on an optical disk using a phase change optical recording medium, the temperature of the recording layer is about 600 ° C. during recording, 400 to 500 ° C. during erasing, and 100 to 100 at reading. It rises to 250 ° C. Therefore, when the thermal expansion coefficients of the recording layer and the protective layer are greatly different, stress is applied between the layers, and peeling occurs due to repeated recording erasure.
For example, the thermal expansion coefficient of the AgInSbTe-based recording layer is 8 to 12 × 10 ⁻⁶ / ° C. (room temperature to 400 ° C.), whereas the thermal expansion coefficient of the 30 mol% CeO ₂ —Nb ₂ O ₅ system is It is 1.8 to 3.4 × 10 ⁻⁶ / ° C. (room temperature to 500 ° C.). This is larger than the thermal expansion coefficient of the Nb ₂ O ₅ system of 0.8 to 1 × 10 ⁻⁶ / ° C. (room temperature to 500 ° C.), approaches the thermal expansion coefficient of the recording layer, and increases the adhesion.

  The film thickness of the protective layer is not particularly limited, and is preferably 10 to 100 nm, more preferably 20 to 50 nm, from the optical design of the multilayer film.

  As is clear from the above, the protective layer formed between the recording layer and the reflective layer provided in the phase change optical recording medium of the present invention is composed of amorphous niobium oxide and / or amorphous tantalum oxide, It consists of a mixture of crystalline cerium oxide and glass, has a refractive index of 2.1 to 2.3, is transparent with little absorption in the visible light region, and has good adhesion to the recording layer, and It is a protective layer with good weather resistance without deterioration of the properties of the reflective layer due to sulfide.

  The transparent substrate used for the phase change optical recording medium is not particularly limited, and a substrate such as a glass plate or a plastic film is used, but a grooved polycarbonate substrate is particularly preferable from the viewpoint of processability and optical characteristics.

The protective layer on the transparent substrate used in the phase change optical recording medium is not particularly limited, and a commonly used [ZnS + SiO ₂ ] film is formed. The film thickness is not particularly limited, and is selected so that, for example, the optical interference of the phase change optical recording medium is optimized between 50 and 150 nm. That is, when the film thickness is less than 50 nm, when a polycarbonate substrate is used, thermal deterioration and recording layer deterioration during long-term storage are likely to occur. On the other hand, when the film thickness exceeds 150 nm, the film formation time becomes longer and the productivity is lowered.

  The recording layer used in the phase change optical recording medium is not particularly limited, and phase change materials are used. Among them, AgInSbTe system, GeSbTe system, GaSb system, etc. are used depending on the application. It is done. The film thickness is not particularly limited and is preferably 100 to 500 nm. That is, when the film thickness is less than 100 nm, the reflectance is too low and the signal intensity tends to be insufficient. On the other hand, if the film thickness exceeds 500 nm, the laser output required for recording / erasing becomes too large, resulting in an increase in cost.

  The reflective layer used in the phase change optical recording medium is not particularly limited, and is at least one metal element selected from Al, Al alloy, Au, Ag, or Pd, Cu, Au, Nd and Bi. In particular, Ag, which is a material having high thermal conductivity, and Pd, Cu, Au, Nd, and Bi are used to make the phase change optical recording medium have a rapid thermal quenching structure. An Ag alloy to which at least one metal element selected from 1 is added at a concentration of 0.5 mol% or less is selected. As a result, a phase change optical recording medium suitable for high-speed recording can be obtained. The film thickness is not particularly limited and is preferably 50 to 150 nm. That is, when the film thickness is less than 50 nm, since the thickness is small, the heat conduction in the planar direction is insufficient, the quenching effect after laser irradiation is small, and the formation of the signal mark (amorphous phase) becomes difficult. On the other hand, when the film thickness exceeds 150 nm, the heat conduction becomes too large and the recording sensitivity is lowered.

  As is clear from the above, the weather resistance of the phase change recording medium is greatly increased by using the oxide protective layer, so that the change in reflectance with time is reduced. Further, the use of a reflective layer having the above composition is suitable for high-speed recording.

  The method for producing a phase change optical recording medium of the present invention is a method for forming a phase change optical recording medium by sequentially laminating a protective layer, a recording layer, a protective layer and a reflective layer on a transparent substrate. In forming the protective layer between the reflective layers, sputtering is performed using a target containing niobium oxide and / or tantalum oxide, cerium oxide, and glass, and under an oxygen partial pressure of 0.003 to 0.010 Pa. Is the method. Thereby, an oxide protective layer in which the reflective layer is not deteriorated by sulfide can be formed at an industrially sufficient film formation rate.

  That is, by sputtering at an oxygen partial pressure of 0.003 to 0.010 Pa, an industrially sufficient film formation rate of about 30% when forming a conventional [ZnS + SiO 2] layer can be secured. When the oxygen partial pressure is less than 0.003 Pa, the light absorption rate in the visible light region of the obtained oxide protective layer is increased and the transparency is lowered. On the other hand, when the oxygen partial pressure exceeds 0.010 Pa, the film formation rate decreases and productivity decreases.

  A sputtering apparatus used for forming the oxide protective layer by the above manufacturing method is not particularly limited, but an RF sputtering apparatus is preferable. The sputtering method is not particularly limited. For example, after a target containing niobium oxide and / or tantalum oxide, cerium oxide, and glass is attached to the sputtering apparatus, the inside of the apparatus is vacuum-treated. Sputtering is performed in a vacuum with a predetermined oxygen partial pressure and an argon partial pressure to form a protective layer with a predetermined film thickness on the surface of the recording layer already laminated on the substrate.

  The target containing niobium oxide and / or tantalum oxide, cerium oxide, and vitreous used in the above production method is not particularly limited, and an oxide that can form an oxide protective layer having a predetermined composition. Among them, in particular, tantalum oxide, niobium oxide, cerium oxide and vitreous are used, and the composition of the oxide protective layer, that is, niobium oxide and / or tantalum oxide, cerium oxide, and vitreous A mixed sintered body obtained by adjusting the composition so that the glassy concentration is 10 to 35 mol% and the cerium oxide concentration is 1 to 30 mol% is preferable.

  The method for producing the mixed sintered body is not particularly limited, and various methods for producing a sintered body using an oxide powder as a raw material are used. Among these, cerium oxide and niobium oxide are particularly preferable. In order to obtain a sintered body having a desired density and strength without causing reaction, a hot press (high temperature high pressure press) method capable of sintering at a low temperature is preferable. As a hot press method, for example, a raw material in which commercially available tantalum oxide powder, niobium oxide powder, cerium oxide powder and glassy powder are blended in a predetermined composition ratio is mixed with a pulverizer using distilled water as a dispersant and dried. After crushing, it is filled into a hot press mold and sintered at a predetermined temperature and a predetermined pressure under a vacuum using a hot press apparatus.

  The particle size of the raw material powder used in the hot pressing method is not particularly limited, and an average particle size of 0.5 to 30 μm by a laser scattering method (Microtrac X100) is preferable. The conditions are not particularly limited, and the temperature is preferably 800 to 1200 ° C. in which the raw material powder does not form a compound, and the pressure is preferably 15 to 50 MPa. The obtained sintered body is machined to a predetermined size to obtain a target. Further, the target is used by being metal bonded to a copper backing plate in order to prevent cracking.

  As is clear from the above, by forming the oxide protective layer by the method for producing the phase change recording medium, a protective layer having a high refractive index of 2.1 to 2.3 and transparent in the visible light region can be produced. Therefore, the film can be formed at a sufficient film formation rate.

  Moreover, in the said manufacturing method, it does not specifically limit as a method of laminating | stacking a protective layer, a recording layer, a protective layer, and a reflection layer in order on a transparent substrate, The method of performing each layer sequentially by sputtering method is preferable. The sputtering apparatus used for forming the protective layer, the recording layer, and the reflective layer on the transparent substrate is not particularly limited, and an RF sputtering apparatus, a DC sputtering apparatus, or the like is used.

The sputtering method of each layer is not particularly limited. For example, after attaching a target capable of forming a predetermined film composition to the sputtering apparatus, the inside of the apparatus is vacuum-processed and sputtered in a predetermined atmosphere. This can be done by forming a film with a predetermined thickness.
The phase change type recording medium obtained by the above production method is a recording medium suitable for high-speed recording, in particular, without causing deterioration of characteristics of the reflective layer and poor adhesion with the recording layer.

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, the analysis method of the metal used in the Example and the Comparative Example and the evaluation method of the refractive index, the optical absorption rate, and the film formation rate of the oxide protective layer are as follows.
(1) Metal analysis: ICP emission analysis was performed.
(2) Measurement of refractive index of oxide protective layer: Using an ellipsometer (manufactured by Mizojiri Optics), the measurement was performed with light having a wavelength of 633 nm.
(3) Measurement of optical absorptance of oxide protective layer: The transmittance and reflectance of the film were measured between 250 and 1000 nm using a spectrophotometer (UV-4000 manufactured by Shimadzu Corporation).
(4) Evaluation of film formation rate: The film thickness at a predetermined film formation time is measured using a stylus type surface roughness meter (S
Measured and calculated using URFCOM).

Further, in Examples and Comparative Examples were used and the target created by the raw material-blended A~I oxides shown in Table 1, a target obtained by blending SiO ₂ powder 30 mol% ZnS powder. Nb ₂ O ₅ powder is manufactured by Taki Chemical (average particle size 3 μm), Ta ₂ O ₅ powder is manufactured by Taki Chemical (average particle size 0.8 μm), and CeO ₂ powder is manufactured by Anan Chemical (average particle size 0). 0.8 μm), SiO ₂ powder manufactured by Asahi Glass (trade name SILDEX-H121, average particle size 12 μm), and ZnS powder manufactured by Sakai Chemical (average particle size 0.75 μm) were used.

Example 1
A target having a predetermined composition was prepared, a film was formed using the target, and then the film characteristics of the obtained oxide were evaluated.
(1) Preparation of target The raw material was mix | blended in the ratio of the raw material mixing | blending A of Table 1, and it dried after mixing with a ball mill by using distilled water as a dispersing agent. Next, the dried product was filled in a graphite hot press mold and sintered in a hot press apparatus at 1000 ° C. for 1 hour under vacuum. The hot press pressure at this time was 19.6 MPa. The density of the sintered body obtained at this time was 3.55 g / cm ³ .
The obtained sintered body was machined to dimensions of 102 mm in diameter and 5 mm in thickness to produce a target. The target was bonded to a copper backing plate.

(2) Film formation Next, the target was attached to a magnetron RF sputtering apparatus (SPF210H manufactured by Anelva) to form a film. As sputtering conditions, the input power is DC 250 W (3.3 W / cm ² ), the ultimate vacuum is 8 × 10 ⁻⁴ Pa, the oxygen partial pressure is 0.005 Pa, the remainder is Ar, and the total sputtering pressure is 0.12 Pa. Met.
A slide glass (S-1111 made by MATUNAMI) was used for the substrate. In addition, the substrate was not intentionally heated. The film formation was performed until the thickness of the obtained oxide film was about 100 nm.

(3) Evaluation of oxide film Thereafter, the refractive index, the optical absorption rate, and the deposition rate of the obtained oxide film were determined. The results are shown in Table 2. The film formation rate was the same as that described above except that sputtering was performed without adding oxygen using a target obtained by mixing 30 mol% of SiO ₂ with ZnS. 1 is expressed as a relative value.

(Example 2)
The preparation of the target was carried out in the same manner as in Example 1 except that the raw material composition was changed to the ratio B in Table 1, and the refractive index, optical absorption rate, and film formation rate of the obtained oxide film were determined. The results are shown in Table 2.

(Example 3)
The preparation of the target was carried out in the same manner as in Example 1 except that the raw material composition was changed to the ratio of C in Table 1, and the refractive index, optical absorption rate, and film formation rate of the obtained oxide film were determined. The results are shown in Table 2.

(Example 4)
The preparation of the target was carried out in the same manner as in Example 1 except that the raw material composition was changed to the ratio of D in Table 1, and the refractive index, optical absorption rate, and film formation rate of the obtained oxide film were determined. The results are shown in Table 2.

(Example 5)
The preparation of the target was carried out in the same manner as in Example 1 except that the raw material composition was changed to the ratio E in Table 1, and the refractive index, optical absorption rate, and film formation rate of the obtained oxide film were determined. The results are shown in Table 2.

(Comparative Example 1)
The preparation of the target was carried out in the same manner as in Example 1 except that the raw material composition was changed to the ratio of F in Table 1, and the refractive index, optical absorption rate, and deposition rate of the obtained oxide film were determined. The results are shown in Table 2.

(Comparative Example 2)
The preparation of the target was carried out in the same manner as in Example 1 except that the raw material composition was changed to the ratio of G in Table 1, and the refractive index, optical absorption rate, and film formation rate of the obtained oxide film were determined. The results are shown in Table 2.

(Comparative Example 3)
The preparation of the target was carried out in the same manner as in Example 1 except that the raw material composition was changed to the ratio of H in Table 1, and the refractive index, optical absorption rate, and deposition rate of the obtained oxide film were determined. The results are shown in Table 2.

(Comparative Example 4)
The preparation of the target was carried out in the same manner as in Example 1 except that the raw material composition was changed to the ratio I in Table 1, and the refractive index, optical absorption rate, and deposition rate of the obtained oxide film were determined. The results are shown in Table 2.

  As is clear from Table 2, in Examples 1 to 5, the protective layer and the method for forming the protective layer are in accordance with the present invention, so that the film has good optical characteristics and is protected at an industrially sufficient film forming speed. It can be seen that a layer can be formed. In other words, it can be seen that it is suitable as a protective layer formed between the recording layer and the reflective layer of the phase change optical recording medium. On the other hand, in Comparative Examples 1-4, since the composition of the protective layer does not meet these conditions, a satisfactory result cannot be obtained in either the refractive index or the optical absorptance of the protective layer. I understand.

(Comparative Examples 5-9)
The film was formed in the same manner as in Examples 1 to 5 except that the oxygen partial pressure during sputtering was less than 0.001 Pa, and the optical absorptance of the obtained oxide film was determined. The results are shown in Table 3.

  As is apparent from Table 3, in Comparative Examples 5 to 9, since the oxygen partial pressure of sputtering is low in the film formation, it is understood that the absorption of the protective layer is increased to 600 to 800 nm.

(Examples 6 to 10)
In order to evaluate performance deterioration due to the reaction between the reflective layer and the protective layer, particularly as a weather resistance evaluation, a glass having a predetermined composition is formed thereon using a glass as a complete barrier layer, and a protective layer having a predetermined composition is further formed. A weather resistance test was performed using a sample obtained by forming a film.
First, an Ag target having a diameter of 102 mm was attached to an RF magnetron sputtering apparatus (SPF210H manufactured by Anelva), and a reflective layer was formed on a slide glass (S-1111 manufactured by MATUNAMI) so as to have a film thickness of 100 nm. Next, a sputtering target for an oxide protective layer of the above raw material blends A, B, C, D, and E was attached, and a protective layer was formed on the surface to a film thickness of 100 nm. After that, the obtained sample is put in a constant temperature and humidity chamber, held at a temperature of 80 ° C. and a humidity of 80% for 500 hours, the reflectance before and after holding is measured, and the reflectance before holding is reflected from the reflectance after holding. The difference minus the rate was determined. The results are shown in Table 4.

(Examples 11 to 15)
Except that an Ag alloy target having a concentration of 0.1 mol% Au was used in the formation of the reflective layer, it was performed in the same manner as in Examples 6 to 10, respectively. Thereafter, the reflectance before and after holding the constant temperature and humidity chamber was measured to obtain the difference. The results are shown in Table 4.

(Examples 16 to 20)
Except for using a Pd alloy target having a concentration of 0.1 mol% Au in the formation of the reflective layer, the same procedure as in Examples 6 to 10 was performed. Thereafter, the reflectance before and after holding the constant temperature and humidity chamber was measured to obtain the difference. The results are shown in Table 4.

(Comparative Example 10)
The protective layer was formed in the same manner as in Example 6 except that a target containing 30 mol% of SiO ₂ powder in ZnS powder was used. Thereafter, the reflectance before and after holding the constant temperature and humidity chamber was measured. The difference was determined. The results are shown in Table 4.

(Comparative Example 11)
In forming the protective layer, except for using a target containing a combination of 30 mol% of SiO ₂ powder ZnS powder were performed in the same manner as in Example 11, then measuring the reflectance before and after the constant temperature and humidity chamber maintained its The difference was determined. The results are shown in Table 4.

(Comparative Example 12)
The protective layer was formed in the same manner as in Example 16 except that a target in which 30 mol% of SiO ₂ powder was blended with ZnS powder was used, and then the reflectance before and after holding the constant temperature and humidity chamber was measured. The difference was determined. The results are shown in Table 4.

  As is clear from Table 4, in Examples 6 to 20, when a reflective layer of Ag or an Ag alloy having a predetermined composition is formed and the protective layer is in accordance with the present invention, the change in reflectance is 0.5% or less. I understand that it is small. That is, it can be seen that it is suitable as a protective layer formed between the recording layer and the reflective layer of the phase change optical recording medium and as a reflective layer. On the other hand, in Comparative Examples 10-12, since a protective layer does not match these conditions, it turns out that the fall of a reflectance is large and is inferior to a weather resistance, and a satisfactory result is not obtained.

Claims (7)

A phase change optical recording medium in which a protective layer, a recording layer, a protective layer and a reflective layer are sequentially laminated on a transparent substrate,
The protective layer formed between the recording layer and the reflective layer is a mixture of amorphous niobium oxide and / or amorphous tantalum oxide, amorphous cerium oxide, and glass, Phase change characterized by having a glassy concentration in the mixture of 10 to 35 mol%, an amorphous cerium oxide concentration of 1 to 30 mol%, and transparency in the visible light region Type optical recording medium.   The phase change optical recording medium according to claim 1, wherein the concentration of the amorphous cerium oxide is 5 to 30 mol%.   The phase change optical recording medium according to claim 1, wherein the protective layer formed between the recording layer and the reflective layer has a refractive index of 2.1 to 2.3.   2. The phase change optical recording medium according to claim 1, wherein the vitreous material is silicon dioxide and / or silicon monoxide.   The reflective layer is formed of Ag alone or an Ag alloy to which at least one metal element selected from the group consisting of Pd, Cu, Au, Nd and Bi is added at a concentration of 0.5 mol% or less. The phase change optical recording medium according to claim 1, wherein: A method for producing a phase change optical recording medium by sequentially laminating a protective layer, a recording layer, a protective layer and a reflective layer on a transparent substrate,
In forming a protective layer between the recording layer and the reflective layer, a target containing niobium oxide and / or tantalum oxide, cerium oxide, and glass is used, and the oxygen partial pressure is 0.003 to 0.010 Pa. A method of manufacturing a phase change optical recording medium, characterized by sputtering at   The sputtering target for protective layer formation used for the manufacturing method of Claim 6 which consists of a mixed sintered compact containing niobium oxide and / or a tantalum oxide, a cerium oxide, and a glassy material.