JP2007111898A - Recording layer and sputtering target for optical information recording medium, and optical information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording layer for an optical information recording medium which is excellent in initial reflectance, the formability of a recording mark, etc., as a matter of course, and also extremely excellent in the durability in an environment of high temperature and high humidity and can be sufficiently applied to a next-generation optical disk for a bluish-purple laser. <P>SOLUTION: On the recording layer for the optical information recording medium, the recording mark is formed by irradiation with laser light. The recording layer contains at least one kind selected from the group consisting of Nd, Gd and La, in the range of 1.0-15 atom% in total. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a recording layer and a sputtering target for an optical information recording medium, and an optical information recording medium. The recording layer for an optical information recording medium of the present invention is used not only for the current CD (Compact Disc) and DVD (Digital Versatile Disc), but also for the next generation optical information recording medium (HD DVD and Blu-ray Disc), It is suitably used for a write once optical information recording medium, particularly an optical information recording medium using a blue-violet laser.

  Optical information recording media (optical discs) are roughly classified into three types according to recording / reproducing systems: a reproduction-only type, a rewritable type, and a write-once type.

  Among these, in the write once type optical disc, data is recorded mainly by utilizing the change in physical properties of the recording layer material irradiated with the laser beam. A write-once optical disc is called write-once (which can be written once) because it can be recorded but cannot be erased or rewritten. Using such characteristics, write-once optical disks are widely used for applications that require prevention of data tampering, such as document files and image files, and examples include CD-R, DVD-R, and DVD + R. .

  Examples of the recording layer material used for the write-once optical disc include organic dye materials such as cyanine dyes, phthalocyanine dyes, and azo dyes. When the organic dye material is irradiated with a laser beam, the dye and the substrate are decomposed, melted and evaporated by heat absorption of the dye to form a recording mark. However, when an organic dye material is used, the dye must be dissolved in an organic solvent and then applied onto the substrate, which reduces productivity. There is also a problem in terms of storage stability of the recording signal.

  Therefore, a method of recording by using a thin film of an inorganic material as a recording layer instead of an organic dye material and irradiating the thin film with a laser beam to form holes (record marks) or deformations (pits) (hereinafter referred to as “recording layer”). (Sometimes called “drilling recording method”) has been proposed (Non-patent Document 1, Patent Document 1 to Patent Document 8).

  Non-Patent Document 1 discloses a technique of making a hole with low power using a Te thin film having a low melting point and low thermal conductivity.

  Patent Documents 1 and 2 disclose a recording layer in which a reaction layer made of a Cu-based alloy containing Al and a reaction layer containing Si or the like are laminated. By irradiation with laser light, a region where elements contained in each reaction layer are mixed is partially formed on the substrate, and the reflectance changes greatly. Therefore, even if a short wavelength laser such as a blue laser is used, Information can be recorded with high sensitivity.

  Patent Documents 3 to 5 prevent the reduction of C / N (carrier to noise ratio, carrier to noise output level) due to the hole recording method, and the optical recording medium having high C / N and reflectivity. Regarding technology. Here, a Cu-based alloy containing In (Patent Document 3), an Ag-based alloy containing Bi or the like (Patent Document 4), or an Sn-based alloy containing Bi or the like (Patent Document 5) is used as the recording layer.

Patent Documents 6 to 8 and Patent Document 5 described above relate to an Sn-based alloy. Patent Document 6 relates to an optical recording medium in which a metal alloy layer contains two or more elements that can at least partially aggregate during heat treatment. Specifically, for example, a Sn—Cu base alloy layer (thickness of 1 to 8 nm) containing Bi or In is disclosed, whereby a recording medium having a high melting point and high thermal conductivity is obtained. Patent Document 7 discloses a recording layer in which an oxidizable substance that is more easily oxidized than Sn and Bi is added to an Sn—Bi alloy having excellent recording characteristics. According to Patent Document 7, in particular, an optical recording medium having improved durability under a high-temperature and high-humidity environment (for example, holding for 120 hours in an environment of a temperature of 60 ° C. and a relative humidity of 90%) can be obtained. In Patent Document 8, the composition of the compound constituting the optical recording layer is Sn _x N _y O _z , 30 <x <70 (atomic%), 1 <y <20 (atomic%), 20 <z <. An optical recording medium controlled to 60 (atomic%) is disclosed. According to Patent Document 8, there is a problem in recording information by using Sn as a recording material and irradiating a short wavelength laser beam having a wavelength of about 380 nm to 420 nm using an objective lens having a numerical aperture of about 0.8. The point (a good recording mark is not formed and jitter increases) can be solved.
JP 2004-5922 A JP 2004-234717 A JP 2002-172861 A JP 2002-144730 A JP 2002-225433 A Japanese Patent Laid-Open No. 2-117878 JP 2001-180114 A Japanese Patent Laid-Open No. 2004-90610 Appl. Phys. Lett. , 34 (1979), 835 pages.

  As the demand for higher density recording information increases, it is particularly desirable to record and reproduce information using a short wavelength laser such as a blue-violet laser. Recording characteristics (low thermal conductivity, high initial reflectivity, record mark formation, etc.) have been improved by the information recording technology using the above-described hole recording method, but it is inferior in durability in a high-temperature and high-humidity environment. .

  The present invention has been made in view of the above circumstances, and its purpose is not only excellent in initial reflectivity and formability of recording marks, but also in durability in a high temperature and high humidity environment. A recording layer for an optical information recording medium that is extremely excellent and can be sufficiently applied to a next-generation optical disk using a blue-violet laser, a sputtering target made of a material forming the recording layer, and light provided with the recording layer It is to provide an information recording medium.

  The recording layer for an optical information recording medium of the present invention that has solved the above problems is a recording layer on which a recording mark is formed by irradiation with laser light, and the recording layer is made of Nd, Gd, and La. The gist lies in that it is made of an Sn-based alloy containing at least one selected from the group in a total range of 1.0% to 15%.

  In a preferred embodiment, the recording layer has a thickness in the range of 10 nm to 50 nm.

  In a preferred embodiment, the wavelength of the laser beam is in the range of 380 nm to 450 nm.

  The sputtering target for optical information recording media of the present invention is composed of an Sn-based alloy containing at least one selected from the group consisting of Nd, Gd, and La in a total range of 1.0% to 15%. Exists.

  The optical information recording medium of the present invention includes any one of the recording layers for optical information recording media described above.

  Since the recording layer of the present invention is configured as described above, the optical information recording medium provided with the recording layer is not only excellent in recording characteristics such as initial reflectivity and recording mark formability. In addition, it is extremely excellent in durability under a high temperature and high humidity environment. Therefore, the recording layer of the present invention is suitably used for a write-once optical disc capable of recording and reproducing information at a high density and at a high speed, and particularly suitably for a next generation optical disc using a blue-violet laser.

  The present inventor can record information by a punching recording method, and in particular, provides a recording layer that is extremely excellent in durability under a high-temperature and high-humidity environment (the amount of decrease in reflectance is small). A study was conducted focusing on the base alloy. As a result, the inventors have found that the intended purpose can be achieved by using a Sn-based alloy containing a predetermined amount of at least one selected from the group consisting of Nd, Gd, and La, and the present invention has been completed.

  First, how the present invention is reached will be described.

  In the present invention, the reason for focusing on the Sn-based alloy is as follows. In terms of reflectivity, Al, Ag, and Cu are superior to Sn, but Sn is superior in the formation of recording marks by laser light irradiation. Sn has a melting point of about 232 ° C., which is very low compared to Al (melting point of about 660 ° C.), Ag (melting point of about 962 ° C.), and Cu (melting point of about 1085 ° C.). It is considered that the thin film of the base alloy is easily melted by laser light irradiation and the recording characteristics are improved. When the main purpose is to apply to a next generation optical disk using a blue-violet laser as in the present invention, it is difficult to form a recording mark when Al or the like is used. I decided to adopt it.

  On the other hand, in the present invention, the durability index is “when a recording layer on which a recording mark is formed by irradiating a blue laser beam having a wavelength of 405 nm is held for 96 hours in an environment of a temperature of 80 ° C. and a relative humidity of 85% The change in the reflectance of the light source is less than 15%, preferably less than 10% ”. Since the wavelength of the blue laser is shorter than that of the red laser, the change in reflectance with respect to film deterioration is more remarkable. For this reason, it is expected that the durability of an optical disk recorded and reproduced using a blue laser will be lower than that when a red laser is used. That is, in order to apply to a blue laser optical disk, higher durability is required than before. Therefore, in the present invention, even if it is exposed to extremely severe conditions such as holding a long time of 96 hours in a high temperature and high humidity environment with a temperature of 80 ° C. and a relative humidity of 85% as described above without providing a protective film. In addition, the fact that the reflection hardly decreases was listed as an indicator of durability. In Patent Document 1 and Patent Document 7 described above, the durability of the optical disk is examined, but only the durability under a milder environment than the conditions defined in the present invention is examined. In Patent Document 7, a durability test at a lower temperature than that of the present invention is performed (temperature maintained at 60 ° C. and relative humidity of 90% for 120 hours). In Patent Document 1, durability is shorter than that of the present invention. Tests are carried out (temperature is kept at 80 ° C. and relative humidity is 85% for 50 hours), and none of them is a durability test under a high temperature and long time environment as in the present invention.

  Next, an Sn-based alloy recording layer in which various alloy components are added to Sn is made as a prototype, and the formation of recording marks when irradiated with blue laser light having a wavelength of 405 nm is examined, and in a high temperature and high humidity environment. The change in reflectance (durability) upon exposure was examined.

  As a result, as will be described in detail in the Examples section that will be described later, when an Sn-based alloy to which at least one of Nd, Gd, and La is added in a predetermined amount is used, excellent recording characteristics such as recording mark forming property and reflectance. It was found that the durability index defined in the present invention can be satisfied while maintaining the above.

  Hereinafter, the recording layer of the present invention will be described in detail.

  The recording layer of the present invention is made of a Sn-based alloy containing at least one selected from the group consisting of Nd, Gd, and La in a total range of 1.0% to 15%. As shown in the experimental examples to be described later, Sn is excellent in recording characteristics such as the formability of recording marks, but is inferior in durability under a high temperature environment. By adding a predetermined amount of at least one element selected from the group consisting of Nd, Gd, and La, durability is remarkably enhanced while maintaining excellent recording characteristics. The reason why such an action can be obtained is unknown in detail, but the addition of the above-mentioned element that is easier to oxidize than Sn suppresses the oxidation of Sn, which may improve durability. .

  Nd, Gd, and La may be added alone or in combination.

  Based on the data of the Example mentioned later, the addition amount of the said element shall be 1.0% or more and 15% or less in total. If the total amount added is less than 1.0%, the desired durability cannot be obtained. However, since the initial reflectance is reduced when the element is added excessively, the upper limit of the total amount of the element added is set to 15%. The total amount of the elements added is preferably 3% or more and 12% or less, and more preferably 5% or more and 10% or less.

The recording layer of the present invention contains the above components and the remaining Sn, but other components may be added as long as the effects of the present invention are not impaired. For example, gas components (O ₂ , N _2, etc.) that are inevitably introduced when the recording layer is produced using a sputtering method, and impurities that are previously contained in an Sn-based alloy used as a melting raw material are included. It may be included.

  The thickness of the recording layer is preferably in the range of 10 nm to 50 nm. As shown in an experimental example to be described later, when the thickness of the recording layer is 10 nm or more, the initial reflectance is increased. On the other hand, the thickness of the recording layer is not limited from the viewpoint of the initial reflectivity, but is preferably 50 nm or less in consideration of the formation of recording marks. The thickness of the recording layer is more preferably 15 nm or more and 40 nm or less, and more preferably 20 nm or more and 35 nm or less.

  The optical information recording medium of the present invention includes the above Sn-based alloy recording layer. The configuration other than the recording layer is not particularly limited, and a configuration known in the field of optical information recording media can be employed.

  FIG. 1 schematically shows a configuration of a preferred embodiment of an optical information recording medium (optical disc) according to the present invention. FIG. 1 shows a write-once optical disc 10 that can record and reproduce data by irradiating a recording layer with blue laser light having a wavelength of about 380 nm to 450 nm, preferably about 405 nm. The optical disk 10 includes a support substrate 1, an optical adjustment layer 2, dielectric layers 3 and 5, a recording layer 4 sandwiched between the dielectric layers 3 and 5, and a light transmission layer 6. The dielectric layers 3 and 5 are provided in order to protect the recording layer 4, whereby recording information can be stored for a long time.

  The optical disk of the present embodiment is characterized in that an Sn-based alloy that satisfies the above-described requirements is used as the material of the recording layer 4, and the support substrate 1 other than the recording layer 4 and the layers (the optical adjustment layer 2, the dielectric) The materials for the layers 3 and 5) are not particularly limited, and those commonly used can be appropriately selected. As a material for the optical adjustment layer 2, for example, an Ag alloy or the like can be used to increase the reflectance. If the recording layer of the present invention is used, the dielectric layers 3 and 5 can be omitted.

  The Sn-based alloy thin film is preferably produced by a sputtering method. The alloy elements (Nd, Gd, La) used in the present invention have a solid solubility limit with respect to Sn of 10 atomic% or less in an equilibrium state, but a thin film formed by sputtering is vapor-phase quenching peculiar to sputtering. Makes it possible to forcibly dissolve. Therefore, as compared with the case where the Sn-based alloy thin film is formed by a thin film forming method other than the sputtering method, the alloy elements are uniformly present in the Sn matrix, so that the durability and the like are remarkably improved.

  In sputtering, it is preferable to use an Sn-based alloy (hereinafter referred to as “melted Sn-based alloy target material”) produced by a melting / casting method or the like as a sputtering target material. Since the structure of the melted Sn-based alloy target material is uniform and the sputtering rate and the emission angle are uniform, the recording layer of the Sn-based alloy thin film having a uniform composition and film thickness can be stably obtained, resulting in higher performance. An optical disc is manufactured. If the oxygen content of the molten Sn-based alloy target material is controlled to 100 ppm or less, the film formation rate can be easily maintained, and the oxygen content of the Sn-based alloy thin film is also reduced. Reflectivity and durability are further enhanced.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention, and modifications within the technical scope of the present invention are made as appropriate without departing from the spirit of the preceding and following descriptions.

(Prototype example)
Various Sn-based alloy thin films (Sn—Nd alloy thin film, Sn—Gd alloy thin film, and Sn—La alloy thin film) shown in Table 1 were made as trial samples, and their initial reflectivity, recording mark forming property, And the durability was examined. For comparison, the above properties of pure Sn thin films were also examined.

(Formation of Sn-based alloy thin film and pure Sn thin film)
Using a pure Sn sputtering target, a pure Sn thin film or Sn-based alloy thin film was formed on a transparent polycarbonate resin substrate (thickness 0.6 mm, diameter 120 mm). The Sn-based alloy thin film was formed using a composite sputtering target in which a chip of an alloy element to be added was placed on a pure Sn sputtering target. The sputtering conditions were an Ar flow rate of 30 sccm, an Ar gas partial pressure of 2 mTorr, a film formation power of DC 50 W, and an ultimate vacuum of 10 ⁻⁵ Torr or less. Note that the thickness of the Sn-based alloy thin film was changed within the range shown in Table 1 by changing the sputtering time from 5 seconds to 45 seconds. The composition of the Sn-based alloy thin film thus obtained was determined by ICP mass spectrometry.

(Record mark formation)
The sample was irradiated with blue laser light as follows while changing the laser power, thereby forming a recording mark. Laser light was irradiated from the Sn-based alloy thin film side.
Light source: Semiconductor laser with a wavelength of 405 nm Laser spot size: Diameter 0.8 μm
Linear velocity: 10 m / s

The shape of the recording mark thus formed was observed with an optical microscope (magnification: 1000 times), and the ratio (area ratio) of the recording mark formation area to the laser light irradiation area was calculated. In the present invention, samples with an area ratio of 85% or more (◎ and ○) were accepted and the formation of recording marks was evaluated based on the following criteria.
A: An area ratio of 85% or more can be obtained even when laser light is irradiated at a low laser power of 10 mW to 15 mW. ○: When laser light is irradiated at a laser power of more than 15 mW and 25 mW or less.
An area ratio of 85% or more is obtained. X: An area ratio of 85% or more cannot be obtained even when laser light is irradiated with a laser power exceeding 25 mW.

(Measurement of initial reflectance)
For a thin film immediately after film formation by sputtering (before recording marks are formed), using a visible / ultraviolet spectrophotometer “V-570” manufactured by JASCO Corporation, a spectral wavelength in the range of 1000 to 250 nm is measured. The reflectance was measured. In the present invention, a sample having an initial reflectance of more than 30% at a wavelength of 405 nm is regarded as acceptable.

(Durability measurement)
The sample whose initial reflectivity was measured as described above was subjected to a high-temperature and high-humidity test that was held in an air atmosphere at a temperature of 80 ° C. and a relative humidity of 85% for 48 hours or 96 hours. Absolute reflectance was measured. A difference in reflectance at a wavelength of 405 nm before and after the high-temperature and high-humidity test (reduction amount of reflectance after completion of the test) was calculated, and durability was evaluated based on the following criteria. In the present invention, the results of the high-temperature and high-humidity test when held for 96 hours are evaluated as “good”, “good”, and “good”.
●: Less than 10% decrease in reflectance
◎: Reflection decrease 10% or more and less than 15% ○: Reflection decrease 15% or more and less than 20% ×: Reflection decrease 20% or more

  Table 1 shows these results together.

  In Table 1, Sample 1 is a pure Sn thin film, Samples 2 to 12 are Sn-Nd thin films, Samples 13 to 20 are Sn-Gd thin films, and Samples 21 to 27 are Sn-La thin films. It is.

  From Table 1, it can be considered as follows.

  Sn-Nd thin films (samples 3 to 5, samples 8 to 11), Sn-Gd thin films (samples 14 to 19), and Sn-La thin films (samples 22 to 26) satisfying the requirements of the present invention are all It has excellent initial reflectivity and formability of recording marks, and not only has good recording characteristics, but also has excellent durability.

  In contrast, the pure Sn thin film sample 1 is inferior in durability.

  Moreover, the sample 2 with a small amount of Nd added, the sample 13 with a small amount of Gd added, and the sample 21 with a small amount of La added are inferior in durability.

  On the other hand, the sample 12 with a large amount of Nd added, the sample 20 with a large amount of Gd added, and the sample 27 with a large amount of La added had a low initial reflectance.

  Further, with respect to the Sn—Nd thin film, the sample 6 having a thick thin film has a low recording mark formability, and the sample 7 having a thin thin film has a low initial reflectance. Table 1 shows only the experimental results obtained by changing the thickness of the Sn—Nd thin film. It was confirmed that similar experimental results were also observed for the Sn—Gd thin film and the Sn—La thin film. (Not shown in the table).

FIG. 1 is a cross-sectional view schematically illustrating the configuration of an embodiment of an optical information recording medium according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support substrate 2 Optical adjustment layer 3, 5 Dielectric layer 4 Recording layer 6 Light transmission layer 10 Optical disk

Claims (5)

A recording layer in which a recording mark is formed by laser light irradiation,
The recording layer is made of a Sn-based alloy containing at least one selected from the group consisting of Nd, Gd, and La in a total range of 1.0% to 15% (meaning atomic%, hereinafter the same). A recording layer for an optical information recording medium.   The recording layer for an optical information recording medium according to claim 1, wherein the recording layer has a thickness in a range of 10 nm to 50 nm.   The recording layer for an optical information recording medium according to claim 1 or 2, wherein the wavelength of the laser beam is in a range of 380 nm to 450 nm.   A sputtering target for optical information recording media, comprising a Sn-based alloy containing at least one selected from the group consisting of Nd, Gd, and La in a total range of 1.0% to 15%.   An optical information recording medium comprising the recording layer for an optical information recording medium according to claim 1.

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