JP2007118463A - Recording layer and spattering 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 superior in initial reflectance and recording characteristics such as formability of a recording mark, which has a high C/N ratio (more specifically, a low noise), and which can be sufficiently applied to a next-generation optical disk employing a blue-violet laser. <P>SOLUTION: In the recording layer, the recording mark is formed by laser light irradiation. The recording layer consists of an Sn based alloy containing 1-30 atom% B. <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. Although the recording characteristics (low thermal conductivity, high initial reflectivity, formability of recording marks, etc.) have been improved by the information recording technology using the above-described hole recording method, there is a problem that the C / N ratio is low. . Furthermore, the durability under a high temperature and high humidity environment is also poor.

  The present invention has been made in view of the above circumstances, and its object is not only excellent in recording characteristics such as initial reflectivity and recording mark formability but also a high C / N ratio (in detail). Is low noise), and preferably has good durability under high-temperature and high-humidity environments. Therefore, the optical information recording medium can be sufficiently applied to a next-generation optical disk using a blue-violet laser. Another object of the present invention is to provide a sputtering target made of a material for forming a recording layer, a material for forming the recording layer, and an optical information recording medium including the recording layer.

  The recording layer for an optical information recording medium of the present invention that has solved the above problems is a recording layer in which a recording mark is formed by irradiation with a laser beam, and the recording layer contains B in an amount of 1% to 30% ( The gist lies in the fact that it is made of an Sn-based alloy contained in the range of the meaning of atomic% (hereinafter the same).

  In a preferred embodiment, the recording layer further contains In in a range of 50% or less (not including 0%). In order to improve durability under high temperature and high humidity, it is preferable to contain In within a range of 5% to 50%.

  In a preferred embodiment, the recording layer further contains at least one selected from the group consisting of Y, La, Nd, and Gd in a total range of 15% or less (excluding 0%). In order to improve the durability under high temperature and high humidity, it is preferable to contain at least one of these elements in the range of 1.0% to 15% in total.

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

  The gist of the sputtering target for an optical information recording medium of the present invention is that it is made of an Sn-based alloy containing B in a range of 1% to 30%.

  In a preferred embodiment, In is further contained in a range of 50% or less (excluding 0%).

  In a preferred embodiment, at least one selected from the group consisting of Y, La, Nd, and Gd is further contained in a total range of 15% or less (excluding 0%).

  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 excellent in recording characteristics such as initial reflectivity and formability of recording marks, and high. It has a C / N ratio. Furthermore, durability under a high temperature and high humidity environment can be improved. 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 drilling recording method, and in particular, to provide a recording layer having a high C / N ratio (specifically, having low noise), paying attention to an Sn-based alloy. Study was carried out. As a result, the inventors have found that the intended purpose can be achieved by using an Sn-based alloy containing a predetermined amount of B (hereinafter sometimes referred to as “Sn—B alloy”), and the present invention has been completed. Further, the Sn-B alloy contains a predetermined amount of at least one element selected from the group consisting of Y, La, Nd, and Gd (hereinafter sometimes referred to as an element belonging to group Z) ( In the following, it has also been found that the use of “Sn—B—Z alloy” may improve the durability under a high temperature and high humidity environment (the amount of decrease in reflectance is small).

  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.

  However, the hole recording method has a problem that the C / N ratio becomes low as described above. The C / N ratio is the ratio of the signal (carrier, C) in the recorded mark portion to the noise (noise, N) in the unrecorded portion. The recording film is irradiated with light and the change in reflectance is measured. Is calculated. The higher the C / N ratio, the smaller the apparent noise level and the better the response speed. For example, in an optical disk, a C / N ratio of 40 dB or more is generally required. Sn used in the present invention has a low melting point and a relatively high reflectivity, but still could not achieve a sufficiently high C / N ratio.

  In order to increase the C / N ratio of the Sn-based alloy, for example, in Patent Document 5 described above, an element (Zn, Ga, Ge) having a predetermined surface tension is added to an Sn-based alloy containing elements such as Bi, Sb, and Pb. , Y, Sm, Eu, Tb, Dy) have been proposed. This focuses on the fact that there is a predetermined relationship between surface tension and recording characteristics (signal characteristics). That is, in the hole recording method, when a hole is formed in a part of the portion irradiated with the laser beam, the hole tends to spread rapidly due to surface tension. If the surface tension of the recording member is too strong, the recording member becomes a small ball-like lump and remains inside or around the hole. On the other hand, if the surface tension of the recording member is too weak, an irregularly shaped residue remains inside the hole. As a result, in any case, the C / N ratio decreases. According to Patent Document 5, since the surface tension of the recording film can be controlled within an appropriate range by adding the above element, the C / N ratio is improved.

  On the other hand, in the present invention, in order to increase the C / N ratio, the surface roughness (Ra) of the recording film should be made as small as possible and the noise (N) of the unrecorded portion should be reduced. The element which can be added to Sn was studied earnestly. In general, it is known that the reflectance is caused by the shape of the recording film. If the surface of the recording film is rough, light scattering is likely to occur. Therefore, the reflectance is low, and noise in an unrecorded portion increases. On the other hand, when the surface of the recording film is smooth and the average particle diameter of the film is reduced, the reflectance is increased, the C / N ratio is increased, and the response speed is improved.

  Here, in order to reduce the surface roughness of the recording film, it is effective to add an element having an atomic radius extremely different from that of Sn to Sn. Thereby, in order to relieve the strain, the particle size becomes small, and the unevenness of the surface can be suppressed. The present inventor conducted an investigation in order to search for an element that satisfies the above requirements and that does not impair the excellent recording characteristics (initial reflectivity, formability of recording marks) due to Sn. As a result, it was found that when a predetermined amount of B was added to Sn, the intended purpose was achieved.

  The atomic radius of B is generally 1 Å or less, which is very small compared to the atomic radius of Sn (1.6 Å). When Sn and B having completely different atomic radii are mixed in this way, strain heat is generated as described above, the particle size is reduced to reduce the strain, and the surface roughness is also reduced.

  FIG. 1 shows the surface shape of a Sn—B alloy thin film produced by changing the amount of B added in Sn in the examples described later. Fig.1 (a) is a SEM image of a Sn-B alloy thin film, and the measurement result of an average particle diameter is written together. FIG. 1B is an AFM image of the Sn—B alloy thin film, and also shows the measurement result of the surface roughness (Ra). In FIG. 1A and FIG. 1B, in order from the left, B = 0% (Sample 1 in Table 1 described later), B = 10% (Sample 5 in Table 1), and B = 20% (Table 1). An example of the sample 6) is shown.

  From FIG. 1, when 10% to 20% of B is added to Sn (average particle size 150.1 nm, surface roughness Ra 5.4 nm), the average particle size is reduced to about 36 nm to 44 nm, and the surface roughness Ra As can be seen from FIG. The noise of these samples was small as shown in Table 1 to be described later, and a high C / N ratio was obtained. The average particle size is on the line obtained by taking a SEM image using a scanning electron microscope S-4000 (SEM) manufactured by Hitachi, Ltd., and writing a line of 1 μm length calculated from the scale on this SEM image. The number of crystal grains was counted and the line length was divided by the number of grains. The surface roughness Ra was measured in the AFM mode of an SPI4000 probe station manufactured by Seiko Instruments Inc.

  Furthermore, in the present invention, in addition to the improvement of the C / N ratio, an element for improving the durability under a high temperature and high humidity environment (an element capable of improving the durability of the Sn-B alloy) was repeatedly studied. . Specifically, an Sn-B based alloy recording layer in which various alloy components are added to Sn-B was made as a prototype, and the formation of recording marks when irradiated with blue laser light having a wavelength of 405 nm was investigated. Changes in reflectivity (durability) when exposed to high temperature and high humidity were investigated.

  As a result, as will be described in detail in the column of Examples described later, a predetermined amount of Sn-B alloy to which a predetermined amount of In was added and at least one element belonging to the group Z of Y, La, Nd, and Gd was added. It has been found that the use of the Sn-BZ alloy can satisfy the durability index defined in the present invention while maintaining excellent recording characteristics and a high C / N ratio.

  In the present invention, the durability index is as follows: “A recording layer on which a recording mark is formed by irradiating a blue-violet laser beam having a wavelength of 405 nm is maintained for 96 hours in an environment of a temperature of 80 ° C. and a relative humidity of 85% RH. The change in reflectivity is less than 15%, preferably less than 10% ”. Since the wavelength of the blue-violet 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 or reproduced using a blue-violet laser will be lower than when a red laser is used. That is, in order to apply to a blue-violet laser optical disc, higher durability is required than before. Therefore, in the present invention, the protective film was not provided, and the film was exposed to extremely severe conditions such as being maintained for a long time of 96 hours in a high temperature and high humidity environment where the temperature was 80 ° C. and the relative humidity was 85% RH as described above. However, the fact that the reflectance hardly decreases was listed as an index 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. The test is carried out (the temperature is kept at 80 ° C. and the relative humidity is 85% for 50 hours), and none of them is a long-term durability test in a high temperature and high humidity environment as in the present invention.

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

  The recording layer of the present invention contains B in the range of 1% to 30%. As shown in the experimental examples to be described later, Sn is excellent in recording characteristics such as initial reflectivity and recording mark formation, but has a low C / N ratio and inferior durability in a high-temperature and high-humidity environment. . On the other hand, when a predetermined amount of B is added, the surface roughness Ra is reduced, and noise is reduced. As a result, the C / N ratio is also increased.

  The addition amount of B is 1% or more and 30% or less. If the total amount of addition is less than 1%, a desired noise reduction effect cannot be obtained. However, when the element is added excessively, as shown in the examples described later, the initial reflectivity is lowered, so the upper limit of the total amount of the element added is set to 30%. The addition amount of B is preferably 5% or more and 25% or less, and more preferably 10% or more and 20% or less.

  Thus, the Sn-B alloy of the present invention has excellent recording characteristics and a high C / N ratio. However, it is slightly inferior in durability under high temperature and high humidity (see Examples described later).

  In order to improve the durability in the above Sn-B alloy, as shown below, (a) In is added in a range of 50% or less, and / or (b) Y, La, Nd, and It is preferable to add at least one element belonging to the group Z of Gd within a range of 15% or less in total. Thereby, durability is remarkably enhanced while maintaining excellent recording characteristics and a high C / N ratio in the Sn-B alloy.

  The addition amount of In is preferably set to 50% or less based on data of examples described later. When excessively adding In, the initial reflectance decreases, so the upper limit of the amount of In added is set to 50%. In order to effectively exhibit the durability improving effect, it is recommended to add 5% or more of In. The addition amount of In is preferably 10% or more and 40% or less, and more preferably 20% or more and 30% or less.

  The addition amount of elements belonging to the group Z of Y, La, Nd, and Gd is preferably 15% or less in total based on data of examples described later. When the element is added excessively, the initial reflectance is lowered, so the upper limit of the total amount of the element added is set to 15%. In order to effectively exhibit the effect of improving durability, it is recommended to add 1.0% or more in total of the elements belonging to the above group Z. The total amount of the elements added is preferably 2% or more and 13% or less, and more preferably 5% or more and 10% or less.

  Each element belonging to group Z may be added alone or in combination.

  For the purpose of further improving durability, In and at least one element belonging to group Z may be added to the Sn—B alloy.

  The reason why the durability is enhanced by adding the above-described In and / or an element belonging to group Z is not clear in detail, but these elements are more easily oxidized than Sn. Addition suppresses the oxidation of Sn, so that the durability can be improved.

  From the standpoint of “achieving excellent recording characteristics and C / N ratio”, which is the original object of the present invention, the lower limit of these elements is not particularly limited. As shown in the examples described later, Sn—B—Y (Y is an element belonging to group Z) alloy (sample 9 in Table 1) or Sn—B—In alloy (sample 18 in Table 1) below the lower limit described above. Even so, excellent recording characteristics and a high C / N ratio comparable to those of the Sn-B alloys of the inventive examples (Samples 2 to 7 in Table 1) have been achieved.

The recording layer of the present invention is composed of an Sn-based alloy containing the above components and the remaining Sn. Sn is preferably contained at 40%, more preferably 50% or more, and more preferably 60% or more. The Sn-based alloy of the present invention may contain other components 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. 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. 2 schematically shows a configuration of a preferred embodiment of an optical information recording medium (optical disk) according to the present invention. FIG. 2 shows a write-once optical disc 10 that can record and reproduce data by irradiating a recording layer with blue-violet 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 can be produced by a method usually used for forming a thin film, but is particularly preferably produced by a sputtering method. For example, a composite sputtering target can be manufactured based on the method of the Example mentioned later.

  In sputtering, it is preferable to use a Sn-based alloy sputtering target containing the above elements as a sputtering target material.

  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—B alloy thin film, Sn—B—Y alloy thin film, and Sn—B—In alloy thin film) shown in Table 1 were made as prototypes, and their initial reflectance and recording were made as follows. The mark formability, durability, surface roughness Ra, and media noise were 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 thickness of all thin films is 25 nm. 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, an ultimate vacuum of 10 ⁻⁵ Torr or less, and a sputtering time of 6 to 30 seconds. The composition of the Sn-based alloy thin film thus obtained was determined by ICP mass spectrometry and ICP emission analysis.

(Record mark formation)
A recording mark was formed by irradiating the sample with blue-violet laser light as follows while changing the magnitude of the laser power. 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, a sample with an area ratio of 85% or more was regarded as acceptable, and the formability of the recording mark 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 reflectance 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% RH for 96 hours, and then the spectral absolute reflectance was measured in the same manner as described above. 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 this invention, the result of the high-temperature and high-humidity test when it was kept for 96 hours was evaluated as being acceptable.
●: 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

(Measurement of surface roughness Ra)
For the sample on which the recording film was formed, Ra was measured based on the method described above and evaluated according to the following criteria. In the present invention, a Ra evaluation result of ◯ or ◎ is regarded as acceptable. As shown in Table 1, when Ra is ◯ or メ デ ィ ア, the media noise evaluation (described later) is also ◯ or ◎, which is a pass level.
A: Less than 2.0 nm B: 2.0 nm or more and 4.0 nm or less X: More than 4.0 nm

(Measurement of noise)
With respect to the sample on which the recording film was formed, the media noise at a frequency of 16.5 MHz was measured at a linear velocity of 5.2 m / s using a disk evaluation device ODV-1000 manufactured by Pulstec and a spectrum analyzer R3131A manufactured by Advantest. It was evaluated with. In the present invention, those having a noise evaluation result of ◯ or ◎ are regarded as acceptable. When the noise evaluation result is ◯ or ◎, the C / N ratio is in the range of 40 dB or more, which sufficiently satisfies the level required for the optical disc.
A: Less than -75 dB B: -75 dB or more and -65 dB or less X: More than -65 dB

Table 1 shows these results together.
In Table 1, Sample 1 is a pure Sn thin film, Samples 2 to 8 are Sn-B thin films, Samples 9 to 17 are Sn-B-Y thin films, and Samples 18 to 24 are Sn-B-In thin film results. .

  From Table 1, it can be considered as follows.

  Sn-B thin films (samples 2 to 7) satisfying the requirements of the present invention are excellent in initial reflectivity and recording mark formation, and have low noise. Therefore, the C / N ratio becomes high.

  Furthermore, Sn—B—Y thin films (samples 10 to 12, 14 to 17) to which a predetermined amount of Y is added as an element belonging to group Z and a predetermined amount of In are added to the Sn—B alloy that satisfies the requirements of the present invention. The added Sn—B—In thin films (Samples 19 to 23) all have higher durability while maintaining good recording characteristics and low noise in the Sn—B alloy.

  On the other hand, the sample 1 of a pure Sn thin film has a large surface roughness Ra and a reduced noise. Moreover, it is inferior to durability.

  Further, Sample 8 (Sn—B alloy) with a large amount of B added had a low initial reflectance.

  On the other hand, Sample 9 (Sn—B—Y alloy) with a small amount of Y and Sample 18 (Sn—B—In alloy) with a small amount of In cannot obtain a desired durability improving effect, and Sn It was the same level as -B alloy. Therefore, in order to achieve the effect of improving corrosion resistance, it is preferable to set the lower limit of In to 5% and the lower limit of Y (element belonging to group Z) to 1.0%.

  In addition, the sample 13 (Sn—B—Y alloy) with a large amount of Y added and the sample 24 (Sn—B—In alloy) with a large amount of In added have durability compared to the Sn—B alloy. Although an improving effect was observed, the initial reflectivity decreased.

  Table 1 shows the result of the Sn—B—Y thin film to which Y is added as an element belonging to the group Z. However, the present invention is not limited to this, and other elements belonging to the group Z (La, Nd, It has been confirmed that the same experimental results can be obtained using Gd) (not shown in the table).

  Table 1 does not show the average particle size of each thin film, but it was confirmed that the average particle size of the thin film having a noise evaluation result of “○” or “◎” was as small as 60 nm or less. (Not shown in Table 1).

FIG. 1 is a photograph showing the surface properties (average particle diameter and surface roughness Ra) of the Sn—B alloy thin film for Samples 1, 5, and 6 of the Example, and FIG. 1 (a) is a Sn—B alloy. An SEM image of the thin film, FIG. 1B is an AFM image of the Sn—B alloy thin film. FIG. 2 is a cross-sectional view schematically illustrating the configuration of the embodiment of the 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 (8)

A recording layer in which a recording mark is formed by laser light irradiation,
The recording layer is made of an Sn-based alloy containing B in a range of 1% to 30% (meaning atomic%, hereinafter the same), and 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 further contains In in a range of 50% or less (not including 0%).   3. The recording layer according to claim 1, wherein the recording layer further contains at least one selected from the group consisting of Y, La, Nd, and Gd in a total range of 15% or less (not including 0%). Recording layer for optical information recording media.   The recording layer for an optical information recording medium according to any one of claims 1 to 3, wherein a wavelength of the laser beam is in a range of 380 nm to 450 nm.   A sputtering target for optical information recording media, comprising an Sn-based alloy containing B in a range of 1% to 30%.   Furthermore, the sputtering target for optical information recording media of Claim 5 which contains In in 50% or less (0% is not included).   The optical information recording medium according to claim 5 or 6, further comprising at least one selected from the group consisting of Y, La, Nd, and Gd in a total range of 15% or less (excluding 0%). Sputtering target.   An optical information recording medium comprising the recording layer for an optical information recording medium according to claim 1.