JP4783857B2 - Optical information recording medium and sputtering target - Google Patents

Description

  The present invention relates to an optical information recording medium such as a read-only BD (Blu-ray Disc) that performs reproduction using, for example, a blue laser, and a sputtering target for forming a reflective film of the optical information recording medium.

  Optical information recording media (optical discs) are roughly classified into three types: read-only type, write-once type, and rewritable type, based on the recording / reproducing principle.

  FIG. 1 schematically shows a typical configuration of a read-only optical information recording medium (single-layer optical disc). As shown in FIG. 1, a read-only optical information recording medium is formed by sequentially laminating a reflective film 2 mainly composed of Ag, Al, Au, etc., and a light transmission layer 3 on a substrate 1 made of transparent plastic or the like. Has a structured. Information on a combination of irregularities called land pits is recorded on the substrate 1. For example, a polycarbonate substrate having a thickness of 1.1 mm and a diameter of 12 cm is used. The light transmissive layer 3 is formed by, for example, bonding a light transmissive sheet or applying and curing a light transmissive resin. Reproduction of recorded data is performed by detecting the phase difference and reflection difference of the laser light irradiated on the optical disk.

  FIG. 1 shows a single-layer optical disc in which a reflective film 2 and a light-transmitting layer 3 are formed on a substrate 1 on which information based on a combination of lands and pits (recording data) is recorded. For example, as shown in FIG. 2, a two-layer optical disc having a first information recording surface 11 and a second information recording surface 12 is also used. Specifically, the two-layer optical disk of FIG. 2 has a first reflective film 2A, a first light transmission layer 3A, a first light transmission layer on a substrate 1 on which information by a combination of uneven land pits (recording data) is recorded. 2 reflective film 2B and second light transmission layer 3B are sequentially laminated. In the first light transmission layer 3A, information different from the substrate 1 is obtained by a combination of lands and pits. It is recorded.

  Conventionally, Au, Cu, Ag, Al, and alloys containing these as main components have been widely used as the reflective film used in optical disks. For example, Patent Document 1 is cited as a reflective film using an Al-based alloy.

  Among these, the reflective film mainly composed of Au has the advantages of excellent chemical stability and little change with time in recording characteristics, but is very expensive and is also used for recording and reproducing BD, for example. There is a problem that a sufficiently high reflectance cannot be obtained with respect to a laser (wavelength: 405 nm). In addition, although the reflective film mainly composed of Cu is inexpensive, it has the poorest chemical stability among the conventional reflective film materials and has the disadvantage of low reflectivity with respect to blue laser like Au. The use is limited. On the other hand, the reflective film mainly composed of Ag shows a sufficiently high reflectance in the practical wavelength range of 400 to 800 nm and has a high chemical stability, so a blue laser is currently used. Widely used in optical discs.

Al exhibits a sufficiently high reflectance at a wavelength of 405 nm and is cheaper than Ag and Au, but is inferior in chemical stability to Ag-based and Au-based reflective films. Therefore, in order to ensure durability, it is necessary to sufficiently increase the thickness of the reflective film. For example, in a DVD-ROM, the Al-based reflective film is sufficiently thick. However, with a BD-ROM (read-only Blu-ray Disc) that uses a blue laser, the recording signal (reproduced signal) accuracy decreases (ie, jitter value) when the Al reflective film is increased in thickness as in the past. There is a problem that stable reproduction cannot be performed. In addition, even if it has excellent characteristics (initial reflectance, initial jitter value) immediately after the formation of the reflective film, these characteristics deteriorate when stored for a long time under high temperature and high humidity. The reflective film is required to have excellent durability.

WO01 / 008145 Publication

  The present invention has been made by paying attention to the above-described circumstances, and an object of the present invention is to provide a disk reflectivity suitable for a reflective film of an optical information recording medium (for example, BD-ROM) (hereinafter simply referred to as reflectivity). In addition to the above, an optical information recording medium provided with a reflective film having excellent reproduction stability and extremely excellent durability and a sputtering target useful for forming the reflective film are provided.

  The optical information recording medium of the present invention that has solved the above problems is a read-only optical information recording medium having a reflective film, and the reflective film contains 5 to 40% of Si and / or Ge (unless otherwise specified) In the component,% means atomic%, and when Si and Ge are included, the total amount thereof is included, the same applies hereinafter), and a refractory metal element and / or rare earth element (preferably Ti, Fe) And one or more elements selected from the group consisting of Mn) in an Al-based alloy containing 0.7 to 5% (when two or more elements are included, the total amount thereof is the same). It has the characteristics.

  The optical information recording medium includes, for example, a structure in which the reflective film and the light transmission layer are laminated on a substrate, and can be suitably used as a read-only optical information recording medium that reproduces information with a blue laser. .

  The present invention relates to a sputtering target for forming a reflective film used in the optical information recording medium, and contains Si and / or Ge in an amount of 5 to 40% (when Si and Ge are included, the total amount thereof is referred to). The same applies hereinafter, and 0.7 to 5% (two or more elements) of a refractory metal element and / or a rare earth element (preferably one or more elements selected from the group consisting of Ti, Fe and Mn) In the case of inclusion, it means the total amount of these, the same applies hereinafter), and also includes a sputtering target for forming a reflective film of an optical information recording medium characterized by comprising an Al-based alloy.

  According to the present invention, it exhibits an appropriate reflectance as a reflection film of an optical information recording medium (for example, BD-ROM), has excellent reproduction stability, and maintains these characteristics even when stored for a long time under high temperature and high humidity. Therefore, it is possible to provide an optical information recording medium with a reduced manufacturing cost as compared with an optical information recording medium using a conventional Ag alloy for the reflective film.

  The optical information recording medium of the present invention is particularly suitably used for an optical information recording medium such as a BD-ROM that performs reproduction using a blue laser.

In the present invention, the above-mentioned appropriate reflectance means that the initial reflectance measured by the method shown in Examples described later is in the range of 40% to 75%. The lower limit of the initial reflectance is preferably 50%. On the other hand, the upper limit is preferably 65%, and more preferably less than 60% from the viewpoint of easily achieving the following initial jitter value.
“Excellent reproduction stability” means that the initial jitter value measured by the method shown in the examples described later is 6.5% or less. Moreover, it is excellent in durability, as shown in the examples described later, reflectivity before and after the acceleration environment test when the acceleration environment test is held for 96 hours in an environment of a temperature of 80 ° C. and a relative humidity of about 85%. Means that the jitter value before and after the acceleration environment test is 6.5% or less.

FIG. 1 is a cross-sectional view schematically showing a main part in the circumferential direction of a read-only optical information recording medium (single-layer optical disc). FIG. 2 is a cross-sectional view schematically showing a main part in the circumferential direction of another read-only optical information recording medium (double-layer optical disc).

  In order to achieve the above object, the inventors of the present invention show a reflectance that is particularly suitable as a reflective film of an optical information recording medium (for example, a BD-ROM), is excellent in reproduction stability, and exhibits excellent durability. Al-based alloys suitable for film materials were studied from various angles.

  Specifically, first, using Al-based alloys containing various alloy elements described in Patent Document 1 described above, the effects of these alloy elements on reflectivity, reproduction stability, and durability were examined in detail. . More specifically, a one-layer BD-ROM is produced in which various Al alloy films are formed by sputtering on a polycarbonate substrate on which pits and lands are formed, and then a light transmission layer of an ultraviolet curable resin is formed. The BD-ROM was evaluated for initial reflectivity, initial jitter value, and durability after an accelerated environment test by the method shown in the examples described later. As a result, in order to realize a reflective film that exhibits an appropriate reflectance as a reflective film of an optical information recording medium (for example, BD-ROM) and is excellent in reproduction stability, Si and / or Ge may be contained. In order to exhibit excellent durability that is essential and maintains these characteristics even when stored for a long time under high temperature and high humidity, it is preferable to further contain a refractory metal element and / or a rare earth element. As a result, the present invention has been reached.

  First, description will be made of adding Si and / or Ge to the reflective film according to the present invention. In order to ensure only an appropriate reflectance, several alloy elements are included in the Al alloy film. To achieve both the appropriate reflectance and excellent reproduction stability at the same time, In particular, the inventors have found that it is very effective to contain Si and / or Ge among the alloy elements, and have arrived at the present invention. Although the reason why the above elements act effectively is not clear, it can be considered as follows. In other words, in BD, reproduction is performed using reflection / interference of laser light by pits, and therefore it is considered that the reflection behavior of laser light affects reproduction characteristics. In the present invention, the reflection film that influences the reflection behavior is optimized by changing the optical constant of the reflection film by including Si and / or Ge, and as a result, suppression of an increase in initial jitter value, that is, It is considered that it effectively acts on the improvement of reproduction stability.

  In order to sufficiently exhibit the above-described effects, it is necessary to contain 5% or more of Si and / or Ge. If it is less than 5%, the effect of sufficiently reducing the jitter value will be insufficient. The Si content is preferably 10% or more, more preferably 12% or more, and the Ge content is preferably 7% or more, more preferably 12% or more. On the other hand, the upper limit of the element amount is 40%. For both Si and Ge, when the content is increased, the absorptance of the Al alloy film constituting the reflective film increases, and the reflectivity relatively decreases. From the viewpoint of the balance between the reflectance and the jitter value, the Si and / or Ge content is preferably 30% or less, more preferably 25% or less.

  Next, description will be made on the inclusion of a refractory metal element and / or a rare earth element in the reflective film according to the present invention.

  The refractory metal element is considered to contribute to the refinement of the crystal grains of the reflective film. In the initial stage of film deposition by sputtering, the refractory metal element becomes a point of nucleation and increases the nuclear density. For this reason, it is thought that the crystal grain of the deposited film becomes fine compared with the case where there is no refractory metal. Further, the rare earth element makes the structure in the reflective film amorphous. The atomic radii of rare earth elements and Al are different, and therefore, it is considered that Al in the film is difficult to assemble a crystal lattice, and therefore, surface smoothness is improved. Even after the acceleration test, it is considered that the change in the crystal structure of the reflective film (for example, coarsening of crystal grains) is suppressed, and as a result, excellent durability is exhibited.

  Examples of the refractory metal element include Ti, Fe, Mn, Ta, W, Mo, Cr, V, Zr, Nb, and Hf. Examples of the rare earth element include Nd, Y, Gd, La, and Although Dy is mentioned, Preferably it is one or more types of elements selected from the group which consists of Ti, Fe, and Mn. Ti, Fe, and Mn are preferable because they are easily available and have a melting point of about 1200 ° C. to 1700 ° C., which makes it easy to produce an Al alloy target using a melting method.

  In order to fully exhibit the above-mentioned effects, it is necessary to contain the refractory metal element and / or rare earth element in an amount of 0.7% or more. If it is less than 0.7%, the change of the structure is not sufficiently suppressed, and when an accelerated environment test is carried out, the jitter value becomes remarkably higher than the initial jitter value, resulting in poor durability. On the other hand, if the amount of the refractory metal element and / or rare earth element exceeds 5%, the optical constant of the Al alloy film changes greatly, so that the initial jitter value becomes high and the reproduction stability is poor. Therefore, in the present invention, the amount of the refractory metal element and / or rare earth element is set to 5% or less. Preferably it is 2% or less.

  The reflective film according to the present invention basically contains Si and / or Ge in the above range, and is selected from the group consisting of a refractory metal element and / or a rare earth element (preferably, Ti, Fe and Mn). Element or more) in the above range, the balance: Al and inevitable impurities.

  The reflective film according to the present invention preferably has a film thickness of 25 nm or more. Al forms a transparent oxide film (Al oxide film) in the atmosphere. This is because, with the growth of the oxide film, the substantial Al alloy portion is reduced and the reflectance is likely to be lowered. More preferably, it is 30 nm or more. On the other hand, if the thickness of the reflective film is too thick, the film formation time becomes long and the manufacturing cost increases. Therefore, from the viewpoint of productivity, the film thickness is preferably 100 nm or less.

  The optical information recording medium of the present invention is characterized in that it includes a reflective film made of an Al-based alloy that satisfies the above component composition, and the configuration of the optical disk to which the reflective film is applied is not particularly limited. The reflective film according to the present invention can be preferably used, for example, as the reflective film 2 in FIG. 1 or the first reflective film 2A in FIG. Further, the other components (types of the light transmission layer, the substrate, etc.) in the optical disc are not particularly limited, and those usually used can be adopted.

  For example, as the substrate 1 in FIGS. 1 and 2, a resin generally used for an optical disk substrate, specifically, an ultraviolet curable resin, a polycarbonate resin, an acrylic resin, or the like can be used. In view of price, mechanical properties, etc., it is preferable to use polycarbonate.

  The thickness of the substrate 1 is preferably in the range of about 0.4 to 1.2 mm. Moreover, it is preferable that the depth of the pit formed on the substrate 1 is generally in the range of 50 to 100 nm.

  The kind of the light transmission layers 3, 3A, 3B in FIGS. 1 and 2 is not limited, and for example, an ultraviolet curable resin, a polycarbonate resin, or the like can be used. The thickness of the light transmission layer is preferably about 100 μm for a single-layer optical disk, and the thickness of the first light transmission layer 3A is about 25 μm for the two-layer optical disk, and the thickness of the second light transmission layer 3B. The thickness is preferably about 75 μm.

  The reflective film according to the present invention can be formed by, for example, a sputtering method or a vapor deposition method, but the sputtering method is preferable. This is because according to the sputtering method, the above alloy elements are uniformly dispersed in the Al matrix, so that a homogeneous film can be obtained and stable optical characteristics and durability can be obtained.

The film formation conditions during sputtering are not particularly limited, but for example, the following conditions are preferably employed.
-Substrate temperature: room temperature to 50 ° C
-Ultimate vacuum: 1 x ^10-5 Torr or less (1 x ^10-3 Pa or less)
-Gas pressure during film formation: 1 to 4 mTorr
DC sputtering power density (DC sputtering power per unit area of target): 1.0 to 20 W / cm ²

  In order to form the reflective film according to the present invention by the sputtering method, the sputtering target to be used includes 5 to 40% of Si and / or Ge, and a refractory metal element (for example, Ti, Fe, Mn, Ta, One or more elements selected from the group consisting of W, Mo, Cr, V, Zr, Nb, and Hf) and / or rare earth elements (eg, Nd and / or Y), preferably Ti, Fe and Mn Sputtering of an Al-based alloy having an Al-based alloy containing 0.7 to 5% of one or more elements selected from the group consisting of substantially the same components and composition as the reflective film having a desired component and composition If a target is used, a reflective film having a desired component / composition can be formed without causing a composition shift.

  The chemical component composition of the Al-based alloy of the sputtering target of the present invention is as described above, with the balance being Al and inevitable impurities.

  The sputtering target can be produced by any method such as a melting / casting method, a powder sintering method, or a spray forming method.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  First, a substrate having a thickness of 1.1 mm was obtained by injection-molding polycarbonate using a Ni stamper having lands and pits. Then, on the obtained substrate, an Al-based alloy reflective film having each component composition having a film thickness shown in Table 1 was formed by a DC magnetron sputtering method. For the formation of the reflective film, a composite sputtering target in which pure metal chips for adding various alloys were arranged on a pure Al sputtering target or an Al-based alloy sputtering target was used.

In addition, a multi-source sputtering apparatus (CS-200 manufactured by ULVAC, Inc. or SIH-S100 manufactured by ULVAC, Inc.) capable of simultaneously discharging a plurality of targets was used as the sputtering apparatus. The sputtering conditions were Ar gas flow rate: 20 sccm, Ar gas pressure: about 0.1 Pa, DC sputtering power density: ^{2 to 5} W / cm ² , and ultimate vacuum: 2.0 × 10 ⁻⁶ Torr or less. The component composition (Table 1) of the deposited Al-based alloy reflective film was determined by ICP emission spectroscopy, ICP mass spectrometry, or fluorescent X-ray analysis.

  Next, an ultraviolet curable resin was applied on the reflective film obtained as described above by spin coating so as to have a film thickness of 100 μm, and the resin was cured by irradiating with ultraviolet rays to form a light transmission layer. . In this way, single-layer BD-ROMs having reflective films of various compositions were produced.

(Measurement of initial jitter value)
Then, using an ODU-1000 manufactured by Pulstec Corporation and TA-810 manufactured by Yokogawa Electric Corporation, the initial jitter value was measured by adjusting the tilt and focus so as to minimize the jitter value under the following conditions. A sample having an initial jitter value of 6.5% or less was accepted.
Reproduction laser power: 0.35mW
Disk rotation speed: 4.98 m / s

(Measurement of initial disk reflectivity)
In addition, the reflectivity was measured using a digital oscilloscope manufactured by Yokogawa Electric Corporation, and the reflectivity (disk reflectivity) was calculated from the maximum level of the reflected signal. And the case where this reflectance exists in the range of 40% or more and 75% or less was set as the pass (an appropriate reflecting film is shown).

(Accelerated environment test)
Using the BD-ROM on which the reflective film is formed, an accelerated environment test (constant temperature and humidity test) is performed for 96 hours in an air atmosphere at a temperature of 80 ° C. and a relative humidity of 85%. The subsequent reflectance was measured in the same manner as described above. The amount of change in reflectance before and after the acceleration environment test is within ± 5%, and the initial jitter value (jitter value before the acceleration environment test) and the jitter value after the acceleration environment test are both 6.5% or less. The case was rated as excellent in durability. These results are also shown in Table 1 and Table 2. In Table 1, No. The jitter values (96h) after the accelerated environment tests of 6 and 7 indicate that measurement could not be performed. In the table, 0h represents an initial value, and 96h represents a value after an accelerated environment test.

  From Table 1, it can be considered as follows. That is, no. In Nos. 1 to 5, since the reflective film satisfies the prescribed components and compositions, it can be seen that the reflective film exhibits an appropriate reflectance, is excellent in reproduction stability, and is excellent in durability. No. 6 to 15 are examples in which the Si amount in the Al—Si—Ti alloy reflective film was made substantially constant and the Ti amount was changed. From these, the content of Ti which is a refractory metal element is 0.7%. (Nos. 6 and 7), the durability is poor, the jitter value after the accelerated environment test cannot be measured, and the change in reflectance is large, while the Ti amount is 0.7% or more. Thus, it can be seen that excellent durability can be ensured, a low jitter value can be maintained, and the amount of change in reflectance becomes small. No. 14 and 15, it can be seen that the initial jitter value increases when the amount of Ti is excessive.

  From Table 2, the following can be considered. That is, no. Nos. 16 to 25 indicate that the reflective film satisfies the prescribed components and compositions, and thus exhibits an appropriate reflectance, is excellent in reproduction stability, and is excellent in durability.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Reflection film 3 Light transmission layer 2A First reflection film 2B Second reflection film 3A First light transmission layer 3B Second light transmission layer 11 First information recording surface 12 Second information recording surface

Claims (3)

A read-only optical information recording medium including a structure in which a reflective film and a light transmission layer are stacked on a substrate, and information is reproduced by a blue laser,
The reflective film contains 5 to 40% of Si (unless otherwise specified,% in the component means atomic%; the same applies hereinafter); Ti is 0.7 to 5%; and the balance: Al and inevitable An optical information recording medium comprising an Al-based alloy which is an impurity. When the initial jitter value was measured under the conditions of reproduction laser power: 0.35 mW and disk rotation speed: 4.98 m / s and the jitter value was minimized, the initial jitter value was 6.5% or less. The reflectance is in the range of 40% to 75%,
Furthermore, when an accelerated environment test is performed for 96 hours in an environment of a temperature of 80 ° C. and a relative humidity of about 85%, the change in reflectance before and after the accelerated environment test is within ± 5%, and before and after the accelerated environment test. The optical information recording medium according to claim 1, wherein all of the initial jitter values are 6.5% or less. A sputtering target for forming a reflective film used in the optical information recording medium according to claim 1 or 2,
Si a 5 to 40%;
A sputtering target for forming a reflective film of an optical information recording medium, comprising: Ti in an amount of 0.7 to 5%; and balance: Al and an inevitable impurity Al-based alloy.

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