JP2005174402A - Protecting layer for phase change optical recording medium, and method of manufacturing protecting layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protecting layer of a phase change optical recording medium which is a stable film not to react with a recording layer or a reflecting layer and has a high refractive index (≥1.9) and transparent optical characteristics. <P>SOLUTION: The protecting layer which is mainly composed of a zinc oxide, a niobium oxide and a tantalum oxide but not of a zinc-sulfide system and has a zinc-oxide content of 50 to 90 mol% is formed by sputtering without gaseous oxygen addition. The thus obtained protecting layer has a high refractive index, is transparent and stable with low reactivity with the recording layer or the reflecting layer and has film characteristics of excellent weather resistance in long-term storage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a protective layer for a phase change optical recording medium comprising zinc oxide, niobium oxide and tantalum oxide, and a method for producing the same.

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

In general, a phase change type optical recording medium has a Ge-Sb-Te-based recording layer sandwiched on both sides by a zinc sulfide-silica oxide (ZnS-SiO ₂ ) -based protective layer, and an alloy-based reflective layer is further laminated. A four-layer structure is formed.

  Here, the principle of recording / reproducing information will be briefly described. In a phase change optical recording medium, a recording layer is heated and heated by laser light irradiation to cause a reversible phase change (phase change between crystal and amorphous) in the crystallographic structure of the recording layer. Record and play back. The phase change is performed by utilizing the temperature change of the recording layer according to the intensity of the laser beam. Recording is performed by forming an amorphous phase recording mark when the laser beam is strong, and forming a crystalline phase when the laser beam is weak, and a reproduction signal is obtained by detecting a difference in reflectance between the crystalline phase and the amorphous phase. At that time, the amorphous phase is formed by cooling the recording layer melted by laser beam irradiation faster than the critical crystallization rate, or the crystalline phase is formed by the temperature of the amorphous phase below the melting point. It is necessary to crystallize. Therefore, in order to perform high-speed recording using an 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.

Ag or the like is used as the reflective layer material having high thermal conductivity. As the protective layer, a transparent film characteristic having a high refractive index and low absorption in the visible light region is required. Therefore, zinc sulfide-silicate (ZnS · SiO ₂ ), which is one of ZnS, is used as a high melting point dielectric. (See Patent Document 1). However, when a ZnS-based protective layer is used for a phase-change optical recording medium, S diffuses into the Ge-Sb-Te-based recording layer and the overwriting can be performed only about several hundred times. There was a problem that Ag of the layer was sulfided and the reflectance was lowered.

  Therefore, as the protective layer other than the ZnS-based layer, nitride (SiNx), oxide, and the like have been studied for magneto-optical disks put to practical use before the phase change optical recording medium.

  Since SiNx is unstable at a temperature of 500 ° C. to 600 ° C. at which the recording layer changes phase, it cannot be used for the protective layer of the phase change optical recording medium.

  In the example of the oxide film studied for light, the film is formed more than RF (high frequency) using at least one oxide target selected from the group consisting of Ta, Nb, Mo, W, Zr, and Hf. A method of forming a film by DC (direct current) sputtering having a high speed has been proposed (see Patent Document 2). However, when forming a transparent oxide layer, reactive sputtering is performed by adding oxygen to the sputtering gas using a sputtering target in which oxygen is insufficient compared to the stoichiometric composition. As the amount is increased, the film formation rate is lowered, the effect of improving the film formation rate by DC sputtering is reduced, the film formation rate is low, and industrial mass productivity is poor.

As another example, an Nb oxide-Si oxide-based DC sputtering film forming method (see Patent Document 3) has been proposed. However, this system has a problem that a high refractive index (1.9 or more) required for a phase change optical recording medium cannot be obtained.
JP 63-103453 A JP-A-8-283935 JP 2000-160331 A

  The object of the present invention is 1) a stable film that does not react with the Ge—Sb—Te-based recording layer and Ag-based reflective layer, 2) high refractive index (1.9 or more), and 3) transparent optical characteristics. It is to provide a protective layer. It is also important that the production method allows film formation with industrial mass productivity.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have developed an oxide protective layer mainly composed of zinc oxide, niobium oxide, and tantalum oxide that does not cause the problem of sulfurization of Ag by S. When deposited by sputtering without gas addition, it has a high refractive index and transparent optical properties, does not cause a reaction with the recording layer and the reflective layer, and has excellent weather characteristics during long-term storage. The inventors found that an industrially sufficient film formation rate can be obtained and completed the present invention.

  That is, according to the first aspect of the present invention, the protective layer formed on both sides of the recording layer is composed of a mixture containing zinc oxide and niobium oxide and / or tantalum oxide, and the zinc oxide content in the mixture is Provided is a protective layer characterized by having a high refractive index and being transparent in the visible light region.

  According to the second aspect of the present invention, in the phase change optical recording medium obtained by sequentially laminating a protective layer, a recording layer, a protective layer and a reflective layer on a transparent substrate, the first layer is used as the protective layer. There is provided a phase change recording medium using the protective layer of the invention.

  Further, according to the third invention of the present invention, it is possible to form a film with industrial mass productivity by sputtering without adding oxygen gas using a sputtering target containing zinc oxide and niobium oxide and / or tantalum oxide. A method for producing a protective layer for a phase change optical recording medium is provided.

  The protective layer of the phase change type optical recording medium of the present invention has a high refractive index and a transparency with low absorption in the visible high region, which are required characteristics of the protective layer necessary for high-speed recording. In addition, there is a remarkable effect that a protective layer having high thermal stability with little deterioration in characteristics due to reaction with the recording layer / reflection layer and high weather resistance during long-term storage can be obtained. Furthermore, in the manufacturing method of the protective layer, it is possible to form a film at a sufficient film forming speed with sufficient industrial mass productivity, and its industrial value is extremely large.

  The protective layer of the phase change optical recording medium of the present invention, the method for obtaining the protective layer, and the phase change optical recording medium having this protective layer will be described in detail below.

  The protective layer is made of a mixture containing zinc oxide and niobium oxide or tantalum oxide, the zinc oxide content in the mixture is 50 to 90 mol%, and the balance is niobium oxide or tantalum oxide.

  The film characteristics of the protective layer of the phase change optical recording medium are required to have a high refractive index and be transparent with little absorption in the visible light region. A high refractive index is desirable for the optical interference properties and thinning of the protective layer, and 1.9 or more is required. The mixture having the above composition of the present invention provides a high refractive index of 1.9 or more and sufficient transparency in the visible light region (wavelength 350 nm to 800 nm).

  The zinc oxide content of the protective layer of the phase change optical recording medium according to the present invention is 50 to 90 mol%, and more preferably 60 to 85 mol%. Since the protective layer is mainly composed of stable zinc oxide, it is difficult to be reduced and becomes a transparent and stable film.

  When X-ray diffraction measurement of the protective layer formed by such a sputtering method is performed, new diffraction lines other than ZnO appear at around 14 to 15 ° (X-ray source Cu) at 2θ. It was found that the light absorption edge of the protective layer where the diffraction line appeared shifted to a shorter wavelength than the ZnO absorption edge.

  On the other hand, if the content of zinc oxide is less than 50 mol%, the thermal stability of the film is low and the reduction resistance is insufficient, and oxygen addition is required for the sputtering gas, which is not preferable because the film formation rate becomes slow. On the other hand, if the zinc oxide content exceeds 90 mol%, the above diffraction lines do not appear, and the light absorption edge of the protective layer approaches the absorption edge of ZnO, and the light absorption around the wavelength of 400 nm increases.

  The recording layer used in the phase change optical recording medium of the present invention is not particularly limited, and phase change materials are used. Among them, AgInSbTe system, GeSbTe system, GaSb system, and the like are used. Is used.

  The reflective layer is not particularly limited, and an Al alloy, an Al alloy, Au, Ag, or an Ag alloy to which at least one metal element selected from Pd, Cu, Au, Nd, and Bi is added is used. . Among them, in particular, at least one metal element selected from Ag, which is a material having high thermal conductivity, and Pd, Cu, Au, Nd, and Bi, in order to make the phase change optical recording medium have a rapid thermal quenching structure. An Ag alloy to which is added at a concentration of 0.5 mol% or less is more preferable.

  Next, a method for manufacturing the phase change optical recording medium protective layer according to the present invention will be described. As described in the structure of the phase change optical recording medium of the present invention, a protective layer, a recording layer, a protective layer, and a reflective layer are sequentially laminated on a transparent substrate.

  First, a sputtering target used for forming a protective layer will be described. A sintered body is produced using zinc oxide powder, niobium oxide powder, and tantalum oxide powder, which are components of the protective layer according to the present invention, as raw materials. In general, various methods are used for producing a sintered body, and in order to obtain a sintered body having a desired density and strength, a hot press (high temperature and high pressure press) method capable of sintering at a low temperature is preferable. . Commercially available zinc oxide powder, niobium oxide powder, and tantalum oxide powder are blended in the prescribed composition ratio, mixed with a pulverizer using distilled water as a dispersant, dried and pulverized, then filled into a graphite mold for hot press, Sintering is performed at a predetermined temperature and a predetermined pressure in a vacuum using a pressing device.

  Although the particle size of the raw material powder used for the said hot press method is not specifically limited, The average particle diameter of 0.5-30 micrometers by a laser scattering method (Microtrac X100) is preferable. The conditions are not particularly limited, but the temperature is preferably a temperature region where the raw material powder does not form a compound, 800 to 1200 ° C., and the pressure is preferably 15 to 50 MPa. The target thus obtained is not in an oxygen-deficient state.

  Next, a method for forming a protective layer by sputtering using the protective layer-forming sputtering target thus obtained will be described. In general, when forming a transparent oxide layer, reactive sputtering is performed by adding oxygen to the sputtering gas using a sputtering target that is oxygen-deficient than the stoichiometric composition. descend. In the present invention, sputtering is performed using a target that is not in an oxygen-deficient state without adding oxygen gas to the sputtering gas, so that a film formation rate with industrial mass productivity can be obtained.

  A sputtering apparatus that can be used for the film formation is not particularly limited, and an RF sputtering apparatus, a DC sputtering apparatus, or the like is used.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, the analysis method of the metal used by the Example and the comparative example, and the evaluation method of the refractive index and optical absorptance of an oxide are as follows.
(1) Metal analysis: ICP emission analysis was performed.
(2) Refractive index measurement of oxide protective layer: Using an ellipsometer (manufactured by Mizojiri Optical Co., Ltd.), 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 was measured and calculated using a stylus type surface roughness meter (SURFCOM manufactured by Tokyo Seimitsu).
(5) Evaluation of thermal stability: 2,000 oxide protective layers were laminated on a Si substrate, and AgInSbTe formed into a 5 mm square was placed thereon, using an RTA treatment furnace (manufactured by Vacuum Riko, mila-3000). Ag4In6Sb60Te30 was melted by heating at 720 ° C. for 10 minutes in a nitrogen atmosphere. Thermal stability is judged by visually observing the interface after annealing with almost no reaction mark ◎, reaction mark 30% or less of contact area ○, reaction mark exceeding 30% of contact area × did.

In the examples and comparative examples, the targets prepared by the raw material blends A to L described in Table 1 were used. Nb ₂ O ₅ powder is manufactured by Taki Chemical (average particle size is 3 μm), Ta ₂ O ₅ powder is manufactured by Taki Chemical (average particle size is 0.8 μm), ZnO powder is manufactured by Hakusui Chemical (JIS Class 1, specific area) 5m2 / g) and ZnS powders were commercially available from Sakai Chemical (average particle size of 0.75 μm).

（実施例１）
表1に従い、所定の組成のターゲットを作製し、これを用いて成膜を行い、その後得られた酸化物保護層の膜特性を評価した。
（１）ターゲットの作製
表1に示したとおり原料配合Ａの割合で酸化亜鉛粉末、酸化タンタル粉末、酸化ニオブ粉末を配合し、蒸留水を分散剤としてボールミルで混合後、混合物を乾燥した。次に、この乾燥物を黒鉛製のホットプレス型に充填し、ホットプレス装置中で真空下１０００℃にて1時間保持して焼結した。このときのホットプレス圧力は１９．６ＭＰａであった。このときに得られた焼結体密度は５．４５ｇ/ｃｍ3であった。得られた焼結体を直径１０２ｍｍ、厚さ５ｍｍの寸法に機械加工し、ターゲットを作製した。ターゲットは銅製のバッキングプレートにボンディングした。

(Example 1)
According to Table 1, a target having a predetermined composition was prepared, and a film was formed using the target, and then the film properties of the obtained oxide protective layer were evaluated.
(1) Preparation of target As shown in Table 1, zinc oxide powder, tantalum oxide powder, and niobium oxide powder were blended in the proportion of raw material blend A, mixed with distilled water using a ball mill as a dispersant, and then the mixture was dried. Next, the dried product was filled in a graphite hot press mold and sintered by holding it at 1000 ° C. for 1 hour in a hot press apparatus. The hot press pressure at this time was 19.6 MPa. The density of the sintered body obtained at this time was 5.45 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) Formation of oxide protective layer Next, the target was attached to a magnetron RF sputtering apparatus (SPF210H manufactured by Anelva) to form a film. The conditions at this time were DC250 W (3.3 W / cm 2) input power, the ultimate vacuum was 2 × 10 ⁻⁴ Pa, Ar was added without adding oxygen gas, and the total sputtering pressure was 0.71 Pa. Note that a slide glass (S-1111 manufactured by MATUNAMI) and a Si (100) substrate were used as the substrate. In addition, the substrate was not intentionally heated. The thickness of the obtained oxide protective layer was set to about 100 nm.

(3) Evaluation of oxide protective layer The refractive index of the obtained oxide protective layer, the optical absorption factor, and the film-forming speed | rate were calculated | required. The results are shown in Table 2. The film formation rate is expressed as a relative value with the film formation rate obtained in the same manner as described above using a target obtained by blending 30 mol% of SiO2 with ZnS.

(Examples 2-6, Comparative Examples 1-5)
The target powder was prepared in the same manner as in Example 1 except that the raw material powder was blended in the proportions B to L in Table 1 above, and the refractive index, optical absorption rate, and film formation rate of the obtained protective layer were determined. It was. The results are shown in Table 2.

表2の実施例1〜６において、酸化亜鉛含有量が５０モル％〜９０モル％で残りが酸化ニオブ、酸化タンタルである本発明の保護層は、高屈折率で可視光領域の吸収が少なく透明性の高いの良好な膜特性を有し、また十分な工業的量産性で保護層を成膜することができることがわかる。

In Examples 1 to 6 in Table 2, the protective layer of the present invention having a zinc oxide content of 50 mol% to 90 mol% and the remainder being niobium oxide and tantalum oxide has a high refractive index and little absorption in the visible light region. It can be seen that the protective layer can be formed with high transparency and good film characteristics and sufficient industrial mass productivity.

On the other hand, the protective layer having a zinc oxide content of less than 50 mol% or more than 90 mol% as in Comparative Examples 1 to 5 has an optical absorptance of 5% or more at a wavelength of 400 nm in the visible light region and is transparent. It turns out that falls. It can also be seen that when the ZnO content is less than 50% as in Comparative Examples 3 to 5, a reaction with the recording layer occurs and the stability of the film becomes insufficient.
(Examples 7 to 9)
A weather resistance evaluation was performed to evaluate the deterioration of the protective layer performance due to long-term storage. Using a glass as a complete barrier layer, a reflective layer and a protective layer were formed thereon to prepare a sample.

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, the oxide sintered compact target of the said raw material mixing | blending A, B, and C was attached, and the protective layer of 100 nm was formed on the reflective layer. 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 3.
(Examples 10 to 12)
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 7 to 9, 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 3.
(Examples 13 to 15)
The reflective layer was formed in the same manner as in Examples 7 to 9 except that an Ag alloy target having a concentration of 0.1 mol% Pd was used. 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 3.
(Comparative Examples 6-8)
Samples were prepared by forming a reflective layer under the same conditions as in Examples 7, 10, and 13. The protective layer was formed with a target of raw material blend L in which 30 mol% of SiO 2 powder was added to ZnS powder. 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 3.

表３の実施例７〜１５において、本発明の保護層では、反射率の変化は０．５％以下と小さく、長期保管時の耐候性が優れていることがわかる。一方、従来から一般的に使用されているＺｎＳ系の保護層では反射率の低下が大きく膜の安定性が不十分であることがわかる。

In Examples 7-15 of Table 3, in the protective layer of this invention, the change of a reflectance is as small as 0.5% or less, and it turns out that the weather resistance at the time of long-term storage is excellent. On the other hand, it can be seen that ZnS-based protective layers generally used in the past have a large decrease in reflectivity and insufficient film stability.

Claims (3)

  In a phase change optical recording medium having a structure in which a protective layer, a recording layer, a protective layer and a reflective layer are laminated on a transparent substrate, the protective layer comprises a mixture of zinc oxide and niobium oxide and / or tantalum oxide, and the mixture of zinc oxide A protective layer for a phase change optical recording medium having a content of 50 mol% to 90 mol% and having a high refractive index and transparency in the visible light region.   In a phase change optical recording medium obtained by sequentially laminating a protective layer, a recording layer, a protective layer and a reflective layer on a transparent substrate, the phase change characterized by using the protective layer according to claim 1 as the protective layer Type recording medium. In the phase change optical recording medium, the phase change optical recording medium protective layer is formed by sputtering without adding oxygen using a sputtering target containing zinc oxide and niobium oxide and / or tantalum oxide. Manufacturing method.