JP2013033580A - Reflection film for optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection film for an optical information recording medium which is not only excellent in initial characteristics such as a reflection rate at the optical information recording medium or a jitter value even if film thickness of the reflection film is adjusted to thin thickness of about 25 nm or less, but also excellent in durability without degradation of these characteristics even if the reflection film for the optical information recording medium is preserved over long term under high temperature and high humidity.SOLUTION: A reflection film for an optical information recording medium consists of Al-based alloy comprising Si by 0.5 to 10% and/or Ge by 0.5 to 10% and a high melting point metal element by 0.2 to 1.0%. Film thickness of the reflection film is 25 nm or less.

Description

  The present invention relates to a reflective film used for an optical information recording medium that is reproduced or recorded by irradiating laser light such as a blue laser, a sputtering target for forming the reflective film, and an optical information recording provided with the reflective film. It relates to the medium.

  Optical information recording media (optical discs) are roughly classified into three types: read-only (reproduction) type, write-once type, and rewritable type, based on recording and reproduction principles. Of these, the write-once type and the rewritable type may be classified as a writing type.

  Among these, a read-only optical information recording medium includes a reflective film mainly composed of Ag, Al, Au, etc. on a resin substrate such as a glass substrate or polycarbonate, and a light transmission layer (cover layer) for protecting data. , Also called a transparent intermediate layer). The light transmission layer is formed by, for example, applying a light curable resin such as an ultraviolet curable resin to the surface of the reflective film, and allowing the laser light to enter from the resin side or the substrate side to cure the resin. On the other hand, write-once and rewritable optical information recording media have a structure in which one or more recording layers that change with light are provided on a substrate, and an optical adjustment layer and a reflective layer are provided above and below the recording layer. In any case, the recording signal (reproduction signal) is read by detecting the phase difference and reflection difference of the laser light irradiated on the optical information recording medium.

  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. In detail, the two-layer optical disc of FIG. 2 has a first reflective film 2A (substrate side), a first light transmission, on a substrate 1 on which information by a combination of uneven lands and pits (recording data) is recorded. The layer 3A, the second reflection film 2B (laser light pickup side), and the second light transmission layer 3B are sequentially stacked. The first light transmission layer 3A includes the substrate 1 Different information is recorded by the combination of land pits.

  In order to read signals accurately in an optical information recording medium, it is necessary that the reflective film has a high reflectance, and examples of such a reflective film material include metals such as Au, Cu, Ag, and Al. And alloys containing these metals as main components are widely used.

  Among these, the reflective film containing Au as a main component has the advantages of excellent chemical stability and little change in recording characteristics over time, but is extremely expensive. In a field called Blu-ray Disk (BD), blue laser light having a wavelength of 405 nm is used. However, since Au has absorption at 405 nm, high reflectivity cannot be obtained, and its use is limited. In addition, although the reflective film mainly composed of Cu is inexpensive, it is inferior in chemical stability among the conventional reflective film materials, and like Au, Cu also has an absorption at 405 nm, so that it is a blue laser. There is a disadvantage that the reflectance with respect to is low. 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, has a high reflectance at 405 nm, and has good chemical stability. Therefore, at present, it is widely used as a reflective film material for optical information recording media using a blue laser.

  On the other hand, Al, like Ag, has a sufficiently high reflectance at a wavelength of 405 nm, and is less expensive than Ag and Au, so that cost reduction can be expected. However, since Al forms a transparent oxide film (natural oxide film) in the atmosphere, the Al portion that contributes to the improvement in reflectivity decreases with the growth of the oxide film, depending on environmental conditions such as high temperature and high humidity. There is a risk that the reflectivity may decrease. So far, high reflectivity has been secured by controlling the thickness of the Al-based reflective film to be substantially 35 nm or more (for example, Patent Document 1) or about 1 mm (for example, Patent Document 2). Therefore, an Al-based reflective film is not used at a thin film thickness level (generally 25 nm or less) that is easily affected by the decrease in reflectance due to the formation of the Al oxide film described above.

  However, when the thickness of the reflective film is increased as in Patent Document 1 and Patent Document 2, the transmittance of the optical information recording medium is lowered, and the photo-curing resin is not sufficiently cured and the cover layer is not sufficiently cured. Occurs. That is, as described above, in the optical information recording medium, a cover layer (transparent intermediate layer) made of a photo-curing resin such as an ultraviolet-curing resin is formed on the surface of the reflective film for data protection, The resin is cured by being incident from the substrate side. When ultraviolet rays are incident from the substrate side, the ultraviolet rays pass through the reflective film formed on the substrate to cure the resin, but in reality, photocuring takes into account the amount of attenuation caused by reflection and absorption of the reflective film. It is necessary to transmit ultraviolet rays having sufficient strength for curing the resin, and the optical information recording medium is required to have a high transmittance. For this purpose, the thickness of the Al-based reflective film must be reduced, which is contrary to the guideline for increasing the thickness of the Al-based reflective film.

  Therefore, even if the film thickness of the reflective film is adjusted to be about 25 nm or less in order to ensure a sufficiently high transmittance to cure the photo-curing resin, it has the necessary reflectance for reading, and the optical disk state In addition to being excellent in initial characteristics such as reflectivity and jitter value, these characteristics are not deteriorated even when stored for a long time under high temperature and high humidity, and excellent in durability. There is an urgent need to provide a reflective film.

JP 2010-267366 A JP-A-8-241536

  The present invention has been made in view of the above circumstances, and an object of the present invention is a reflective film used in an optical information recording medium that is reproduced or recorded using a laser beam such as a blue laser. Even if the film thickness is adjusted to about 25 nm or less, the optical information recording medium has excellent initial characteristics such as transmittance, reflectance, and jitter value, as well as long periods at high temperatures and high humidity. Even when stored, these characteristics do not deteriorate, and the reflective film for optical information recording media is excellent in durability; the optical information recording medium provided with the reflective film; and used for the production of the reflective film. It is to provide a sputtering target.

  The reflective film of the present invention that has solved the above problems is a reflective film used in an optical information recording medium, and the reflective film contains 0.5 to 10% of Si (unless otherwise specified,% is an atom. And / or an Al-based alloy containing 0.5 to 10% of Ge and 0.2 to 1.0% of a refractory metal element, and the thickness of the reflective film Has a gist where it is 25 nm or less.

  In a preferred embodiment of the present invention, when the reflective film contains Si in an amount of 0.5 to 1.0%, the thickness of the reflective film is 20 nm or less, and Si is contained in excess of 1.0% and 10% or less. In some cases, the thickness of the reflective film is 25 nm or less.

  In a preferred embodiment of the present invention, Ti is contained as the refractory metal element.

  In a preferred embodiment of the present invention, the refractory metal element includes at least one selected from the group consisting of Fe, Mn, and Ta.

  In a preferred embodiment of the present invention, the reflective film is used for an optical information recording medium on which recording or reproduction is performed by irradiation with blue laser light.

  In a preferred embodiment of the present invention, the reflective film has an initial reflectance of 40% or more and a transmittance at 350 nm of 8.0% or more.

  In a preferred embodiment of the present invention, the reflective film has an initial reflectance of 10% or more and a transmittance at 350 nm of 15% or more.

  The present invention also includes an optical information recording medium comprising any one of the above-described reflective films for optical information recording media.

  In a preferred embodiment of the present invention, the optical information recording medium has an initial reflectance of 40% or more and a transmittance at 350 nm of 8.0% or more.

  Moreover, the sputtering target of the present invention that has solved the above-mentioned problems is a sputtering target for forming the reflective film for optical information recording media according to any one of the above, wherein Si is 0.5 to 10%, And / or containing 0.5 to 10% of Ge and 0.2 to 1.0% of a refractory metal element with the balance being Al and inevitable impurities.

  According to the present invention, even if the thickness of the reflective film is as thin as about 25 nm or less, it can exhibit appropriate transmittance and reflectance as a reflective film of an optical information recording medium, and can perform stable reproduction with a low jitter value. In addition, it is possible to provide an optical information recording medium that is excellent in these characteristics even when stored for a long period of time under high temperature and high humidity, and that can realize good durability.

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 give a high transmittance sufficient to cure the photo-curing resin constituting the cover layer, the present inventors have made the thickness of the reflective film approximately 25 nm or less, Appropriate transmissivity and reflectivity as a reflective film in the state of optical information recording medium, low jitter value, excellent reproduction stability, and even when stored for a long time under high temperature and high humidity In order to provide an Al-based reflective film for an optical information recording medium with little decrease in jitter value (that is, excellent durability), studies were conducted.

  Specifically, using an Al-based reflective film containing the elements (Si and / or Ge and refractory metal) described in Patent Document 1 described above, as shown in Tables 1 and 2 below, Si, Ge And how the characteristics of the Al-based reflective film of the same composition (the elements constituting the reflective film and the content thereof are the same) when the film thickness is varied are variously changed. We investigated whether it changed. As a result, the Al-based reflective film made of Al- (5-40%) Si / Ge- (0.7-5%) refractory metal described in Patent Document 1 is substantially more than about 25 nm- It is determined so that desired characteristics can be obtained when a film thickness of about 100 nm is targeted. When the film thickness of the Al-based reflective film is reduced to 25 nm or less, which is the target range of the present invention, Si It has been clarified that the desired effects may not be exhibited depending on the contents of Ge, Ge, and a refractory metal. Furthermore, the contents of Si, Ge, and refractory metal alloy that can exhibit desired characteristics vary depending on the film thickness of the reflective film, and generally vary greatly with a film thickness in the vicinity of 20 to 25 nm. It became clear for the first time by the inventors' basic experiments (details will be described later).

  Even if the thickness of the reflective film made of Al- (Si and / or Ge) -refractory metal alloy is adjusted to about 25 nm or less based on the above experimental results and many basic experiments, the above characteristics Further studies were made on the contents of Si, Ge, and refractory metal, which can provide a reflective film excellent in thickness. As a result, if a reflective film made of an Al-based alloy containing 0.5 to 10% Si and / or 0.5 to 10% Ge and 0.2 to 1.0% refractory metal element is used. The present invention was completed by finding out that the intended purpose was achieved.

  Hereinafter, differences from Patent Document 1 described above will be described. When the contents of Si, Ge, and refractory metal in the reflective film of the present invention are compared with the contents in the reflective film of Patent Document 1, the contents of Si and Ge are as follows. Similarly, in the present invention, Si is 0.5 to 10% and Ge is 0.5 to 10%, and each element has a lower content than Patent Document 1. Sliding to the side. Further, the content of the refractory metal is 0.7 to 5% in the above-mentioned Patent Document 1, whereas it is 0.2 to 1.0% in the present invention. It slides to the quantity side.

  Here, when Al- (Si and / or Ge) -refractory metal alloy is used for the reflective film, the characteristics greatly change depending on the film thickness of the reflective film. 1 to 7 (in the case of Al—Si—high melting point metal alloy), No. 1 in Table 2 described later. It is clear from the results of the experimental group of 14 to 18 (in the case of Al—Ge—refractory metal alloy).

  First, the above-mentioned No. In the experimental groups 1 to 7, the content of Ti, which is a refractory metal, is kept constant at 1.0%, and the Si amount is reduced from 0.5% (No. 1) to 15% (No. 1). 7) Various changes were made over the range of 7), and even though the Si amount was the same, only the film thickness was changed in the range of 5 to 22 nm (these were hyphen “-” after each No.). (No. 1-1 etc.). Based on the methods described in the Examples section below, each characteristic [initial characteristics (disk reflectivity, jitter value) and rate of change (jitter value and disk reflectivity) before and after the acceleration test, and further transmittance at 350 nm. Table 1 shows the measurement results.

  Similarly, the above No. In the experimental group of 14 to 18, the content of Ti, which is a refractory metal, is kept constant at 1.0%, and the Ge amount is reduced from 0.5% (No. 14) to 6% (No. 14). 18) Various changes were made over the range of 18), and even though the Ge amount was the same, only the film thickness was changed in the range of 5 to 30 nm (these were hyphen “-” after each No.). And indicated as No. 14-1). These characteristic results are shown in Table 2.

  Of these, No. 1 in Table 1. 1 to 7 (Al—Si—refractory metal alloy) will be considered in detail. No. 7-1 to No. 7-4 is an Al-based reflective film containing 15% Si and 1.0% Ti, and the contents of Si and refractory metal are within the range of the Al-based reflective film disclosed in Patent Document 1. Although included, since the Si amount exceeds the upper limit (10%) of the present invention, it corresponds to a comparative example in relation to the present invention. In the Al-based reflective film having the above composition, the film thickness ranges from 5 nm (No. 7-1) to 30 nm [exceeding the upper limit (25 nm) of the present invention and within the film thickness range defined in Patent Document 1. No. 7-4], when the film thickness was as thick as 30 nm (No. 7-4), all the characteristics except the transmittance were good, whereas the film thickness was reduced to 20 nm. When (No. 7-3), 10 nm (No. 7-2), and further 5 nm (No. 7-1), the reflectivity as an optical disk decreased rapidly. These experimental results show that the Al—Si—refractory metal reflective film described in Patent Document 1 described above has the desired characteristics even if it is applied as it is to the thin film (generally 25 nm or less) reflective film targeted by the present invention. It is very clear that it is necessary to separately set the content suitable for the reflective film for a thin film.

  On the other hand, No. in which the Si amount and the Ti amount were controlled within the range defined by the present invention. In 3-6, the favorable characteristic was able to be ensured, even if it changed the film thickness within the range of 15-22 nm. Strictly speaking, even if the Si amount is within the range defined by the present invention (0.5 to 10%), No. When the amount of Si is 1% or less as in 1-2, when the film thickness of the Al-based reflective film is 22 nm, the transmittance as an optical disk is defined by the present invention (the transmittance at 350 nm is 8.0% or more) It was also found that the desired characteristics can be obtained only when the film thickness of the Al-based reflective film is 20 nm or less. That is, the reflective film of Al-Si- refractory metal specified in the present invention has an extremely large influence on the film thickness by the content of the elements constituting the reflective film, and the characteristics can change accordingly. In producing an optical information recording medium, it is preferable to appropriately control the film thickness according to the content of each element so that desired characteristics can be obtained.

  The tendency similar to the above is shown in No. 1 using Ge instead of Si. It was also seen in the case of 14-18 Al-Ge-refractory metal alloys.

  When the reflective film of the present invention is used, it exhibits an appropriate transmittance and an appropriate reflectance, has a low jitter value, and is excellent in these characteristics even when stored for a long time under high temperature and high humidity (that is, durability) An optical information recording medium having excellent properties can be obtained. The criteria for each characteristic are as follows.

  In the optical information recording medium of the present invention, “having an appropriate transmittance” means 8.0% or more when the transmittance at 350 nm is measured by the method described in Examples described later. A preferable transmittance is 9.0% or more. As described above, the optical information recording medium of the present invention is based on the premise that the transmittance is high so that the photo-curing resin constituting the cover layer is reliably cured.

  Further, “having an appropriate reflectance” in the optical information recording medium of the present invention means that the initial reflectance of the disk itself is measured by the method shown in the examples described later and is within a range of 40% or more. means. Preferably it is 50% or more. On the other hand, the upper limit is not particularly limited from the viewpoint of securing a high reflectivity. However, since the jitter value tends to increase when the reflectivity becomes too high, it is preferably approximately 65% or less. More preferably, it is less than 60%.

  Further, “low jitter value” in the optical information recording medium of the present invention means that it is 6.50% or less when the initial jitter value is measured by the method shown in the examples described later. Preferably it is less than 6.0%.

  In the optical information recording medium of the present invention, “excellent in durability” means that an accelerated environmental test is performed for 96 hours in an environment of a temperature of 80 ° C. and a relative humidity of about 85%, as shown in the examples described later. This means that both the reflectance and the jitter value change before and after the acceleration environment test are within ± 10%.

  Furthermore, the reflective film of the present invention can be applied to various reflective films constituting an optical information recording medium. Specifically, it can be applied to the first and second reflective films described in detail below, and since the characteristics required for each reflective film are different, the preferred film thickness range of the reflective film can also be different. .

  That is, the reflective film for an optical information recording medium is mainly composed of the reflective film (2 in FIG. 1) used for the single layer (one layer) optical information recording medium in FIG. 1 and the two layers in FIG. A first reflective film (2A in FIG. 2; substrate side) and a second reflective film (2B in FIG. 2; light irradiation side) used in the optical information recording medium are roughly classified. Of these, the reflective film for a single-layer optical information recording medium and the first reflective film for a double-layer optical information recording medium both have a high reflectivity at the same level as that of the optical information recording medium and an appropriate value. Transmittance is required. In the present specification, these may be collectively referred to as a “first reflective film”.

  On the other hand, the second reflective film for the two-layer optical information recording medium has a read laser beam passing through the second information recording surface and reading information, compared with the first reflective film. High transmittance is required. For this purpose, the transmittance of the second reflective film needs to be higher than the value required for the first reflective film, while the reflectance of the second reflective film is the optical information recording. It may be lower than the level required by the medium.

  At least the characteristics required for the first and second reflective films are as follows. In the present specification, the characteristics (initial reflectance and transmittance at 350 nm) of each reflective film are evaluated by the characteristics as an optical information recording medium.

  The first reflective film is required to satisfy at least an initial reflectance as an optical information recording medium of 40% or more and a transmittance at 350 nm of 8.0% or more.

  On the other hand, the second reflective film is required to satisfy at least an initial reflectance of 10% or more as an optical information recording medium and a transmittance of 15% or more at 350 nm.

1. Regarding Reflective Film First, the reflective film of the present invention will be described in detail. The reflective film of the present invention is made of an Al-based alloy containing 0.5 to 10% of Si and / or 0.5 to 10% of Ge and 0.2 to 1.0% of a refractory metal element, The reflective film is characterized in that the film thickness is 25 nm or less.

  In this specification, “Si and / or Ge (including)” means at least one (including) Si and Ge. Specifically, as described above, there are an embodiment in which each of Si and Ge is contained alone and an embodiment in which both Si and Ge are contained.

  Hereinafter, the elements (Si, Ge, and refractory metal) constituting the Al-based alloy reflective film of the present invention will be described.

  Both Si and Ge are elements having an action of suppressing a decrease in reflectance due to the formation of a natural oxide film of Al. That is, Si and Ge are concentrated on the surface of the reflective film, and are preferentially oxidized in place of Al. As a result, it is presumed that the Si oxide film formed on the surface serves as a protective film, can suppress the formation of the Al oxide film, and can prevent a decrease in reflectance. Si and Ge may be added alone or in combination as long as the content satisfies the following requirements.

  In order to discard such an action effectively, it is necessary to add 0.5% or more of Si and 0.5% or more of Ge. A preferable Si amount is 1.0% or more, and more preferably 3.0% or more.

  On the other hand, if the Si content exceeds 10%, the absorption coefficient increases and the reflectance decreases. Therefore, in order to obtain the required reflectance, it is necessary to increase the film thickness. As the film thickness increases, the transmittance decreases, and a desired value cannot be ensured. A preferable Si amount is 7.0% or less. On the other hand, when the Ge content exceeds 10%, the reflectance tends to decrease due to an increase in the absorption coefficient, similar to Si. Further, a large amount of Ge causes an increase in cost. A preferable Ge amount is 5% or less, more preferably less than 5%, and still more preferably 3% or less.

  A refractory metal is an element having an action of suppressing a decrease in reflectance caused by surface roughness accompanying Al self-growth (Al crystal grain coarsening) by being dispersed in an Al-based alloy film. Thereby, durability comes to be improved. In order to effectively exhibit such an action, the content of the refractory metal is set to 0.2% or more. Preferably it is 0.3% or more, More preferably, it is 0.5% or more. On the other hand, if the content of the refractory metal exceeds 1.0%, the absorption coefficient increases and the desired transmittance and reflectance cannot be ensured, so the upper limit is made 1.0%. Preferably it is 0.8% or less. Here, the “content of the refractory metal” is preferably a single amount when including at least one refractory metal selected from the group consisting of the following elements, and when including two or more types It means the total amount.

  A preferable high melting point metal used in the present invention includes at least one selected from the group consisting of Ti, Fe, Mn, and Ta. These may be used alone or in combination of two or more. A more preferred refractory metal is Ti.

  The reflective film of the present invention contains at least one of the above contents of Si and Ge and a refractory metal, and the balance is Al and inevitable impurities. Examples of the inevitable impurities include elements that can be inevitably mixed in the manufacturing process of the reflective film.

  The upper limit of the thickness of the reflective film is 25 nm or less. As will be described repeatedly, in the present invention, in order to cure the photo-curing resin, the film thickness is set thinner than that of Patent Document 1 from the viewpoint of ensuring high transmittance as an optical information recording medium, and the upper limit thereof. Is assumed to be 25 nm or less.

  Strictly speaking, the upper limit of the thickness of the reflective film differs depending on the range of the amount of Si. First, the upper limit of the film thickness of the reflective film containing 0.5% or more and 1% or less of Si is 20 nm or less. As shown in the examples described later, when the film thickness of the reflective film is 22 nm, the transmittance as an optical information recording medium decreases. On the other hand, the upper limit of the thickness of the reflective film containing more than 1.0% and 10% or less of Si is 25 nm or less. As shown in the examples described later, in the case of the reflective film containing a large amount of Si, good transmittance as an optical information recording medium was obtained even when the film thickness was 22 nm. Specifically, the upper limit of the film thickness of the reflective film changes as appropriate depending on the content of Si, the refractory metal, and the like, and therefore may be appropriately controlled in consideration of these.

  On the other hand, for Ge, strictly speaking, the upper limit of the thickness of the reflective film differs depending on the amount of Ge. For example, the upper limit of the thickness of the reflective film containing about 0.5 to 5% Ge is generally 20 nm or less, and preferably 18 nm or less. However, in the case of a reflective film containing more than about 5% to 10% Ge, the upper limit of the film thickness can be allowed up to 25 nm (see Examples described later). If the film thickness becomes too thick, the transmittance as an optical information recording medium may be lowered or the jitter value may be increased depending on the composition of the Al alloy. Specifically, the upper limit of the film thickness of the reflective film changes as appropriate depending on the content of Ge, the refractory metal, and the like.

  On the other hand, if the thickness of the reflective film becomes too thin, it is impossible to ensure a high initial reflectance (40% or more) required for an optical information recording medium. From the viewpoint of satisfying the required characteristics of the optical information recording medium, a preferable lower limit of the thickness of the reflective film is generally 13 nm or more, and more preferably 15 nm or more. Specifically, the recommended lower limit of the film thickness is appropriately changed depending on the contents of Si, Ge, refractory metal, and the like, and may be appropriately controlled in consideration of these.

  The film thickness range of the reflection film described above is set from the viewpoint of satisfying the required characteristics as an optical information recording medium. However, even if the film thickness is very thin, for example, 10 nm, or even 5 nm, the reflective film of the present invention has a high transmittance (see Tables 1 and 2), so that the reflective film for optical information recording media is used. May satisfy the required characteristics. As described above, the reflection film of the present invention greatly varies in reflectance and transmittance on the optical information recording medium depending on the film thickness. It is preferable to appropriately control the lower limit and the upper limit of the thickness of the reflective film depending on the recording medium and the position of the optical information recording medium.

(When used as the first reflective film)
The reflective film 1 used for the one-layer (single-layer) optical information recording medium in FIG. 1 described above and the first reflective film such as the reflective film 2A (substrate side) in the two-layer optical information recording medium in FIG. In this case, the first reflective film has at least the initial reflectance and transmittance required for the optical information recording medium (that is, the initial reflectance at a wavelength of 405 nm is 40% or more and the transmittance at a wavelength of 350 nm is at least. 8.0% or more). The range of the film thickness of the first reflective film that can exhibit the above characteristics is as described above.

(When used as a second reflective film)
In the case of the second reflective film 2B (light irradiation side) used for the two-layer optical information recording medium of FIG. 2 described above, the second reflective film is required to have a particularly high transmittance. The initial reflectance at a wavelength of 405 nm must satisfy 10% or more, and the transmittance at a wavelength of 350 nm must satisfy 15% or more.

  Strictly speaking, the thickness of the second reflective film for satisfying the above requirements also differs depending on the content of each element constituting the reflective film. In particular, the reflectivity and transmittance as an optical information recording medium vary greatly depending on the Si and Ge contents, so that an appropriate film thickness is appropriately selected according to the composition of the reflective film so as to obtain desired characteristics. It is preferable to set. Specifically, for example, when an Al—Si—refractory metal containing Si is used as the second reflective film, it is recommended that the film thickness be about 5 nm or more and 15 nm or less. In the reflective film of Al alloy shown in Table 1 to be described later, when the film thickness was 18 nm, the transmittance was lowered regardless of the contents of Si and refractory metal.

  On the other hand, when an Al—Ge—refractory metal containing Ge is used as the second reflective film, it is recommended that the thickness of the second reflective film be approximately 5 nm or more and 19 nm or less. As shown in Table 2 to be described later, the upper limit of the film thickness that can be used as the second reflective film can be changed depending on the amount of Ge, and the transmittance mainly changes. Furthermore, in consideration of the balance with the durability required for the optical information recording medium, the more preferable film thickness of the second reflective film is generally 5 to 15 nm, more preferably 7 nm or more and 12 nm or less. It is.

  The reflection film that characterizes the present invention has been described above.

2. About the optical information recording medium The present invention also includes an optical information recording medium provided with the reflective film. Examples of the optical information recording medium include a read-only type and a write type (write-once type, rewritable type), and the reflective film of the present invention can be applied to any of these. Here, the read-only type has marks and spaces of different sizes already formed on the substrate, has a metal reflection film, is irradiated with a read laser, and information is obtained from the phase difference between the light in the mark and space portions. Is an optical information recording medium capable of reading out the data. On the other hand, in the writing type, the power of the laser beam is controlled to at least three values corresponding to the heating pulse, the cooling pulse, and the erasing pulse, and the heating pulse and the cooling pulse are alternately applied to the optical information recording medium. According to an information recording method in which predetermined information is recorded by a plurality of types of recording marks having different lengths formed by being performed and a space formed between the recording marks by irradiation of the erasing pulse. An optical information recording medium. There are two types of write type: write-once type and rewritable type.

  Examples of the optical information recording medium include CD, DVD, and BD. For example, a BD-R capable of recording and reproducing data using blue laser light having a wavelength of about 380 nm to 450 nm, preferably about 405 nm. , BD-ROM, and BD-RW are specific examples.

  The optical information recording medium of the present invention exhibits an appropriate transmittance and an appropriate reflectance, has a low jitter value, and is excellent in these characteristics even when stored for a long time under high temperature and high humidity (that is, It is excellent in durability). The details of the above characteristics are as described above.

  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 used, for example, as the reflective film 2 in FIG. 1 or the first reflective film 2A in FIG. Alternatively, for example, it can be used as the second reflective film 2B of 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 and mechanical characteristics, it is preferable to use a polycarbonate resin.

  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 types of the light transmitting layers 3, 3A, 3B in FIGS. 1 and 2 are not limited, and preferably have a high transmittance with respect to the laser and a small light absorption rate. 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 of 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 contains 0.5 to 10% of Si and is made of a refractory metal element (for example, Ti, Fe, Mn, and Ta). One or more elements selected from the group, preferably composed of an Al-based alloy containing 0.2 to 1.0% of Ti), and substantially the same component as the reflective film having a desired component and composition If an Al-based alloy sputtering target having a composition 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.

Example 1
In this embodiment, in the reflective film made of Al- (Si or Ge) -refractory metal (Ti), the content of each element of Si, Ge, and refractory metal (Ti), and the film thickness of the reflective film. When the optical disk provided with the reflection film with various changes was measured by the following method, it was examined how characteristics such as reflectance change.

(Production of optical disc)
First, a polycarbonate substrate (thickness: 1.1 mm, track pitch: 0.32 μm, groove depth: 25 nm) on which a mark / space with a diameter of 12 cm is formed is used as the substrate, and the composition and film shown in Table 1 are formed on the substrate. A thick Al-based alloy film (remainder: Al and unavoidable impurities,% means atomic%) or a pure Al film was formed by DC magnetron sputtering. 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 of the Al-based alloy reflective film thus formed was determined by ICP emission spectroscopy.

  Next, an ultraviolet curable resin (“BRD-864” manufactured by Nippon Kayaku Co., Ltd.) is applied onto the reflective film obtained as described above by a spin coat method, and cured by irradiation with ultraviolet rays. A light transmission layer (cover layer) having a thickness of 0.1 mm was formed. In this way, single-layer BD-ROMs having reflective films of various compositions were produced.

(Optical disk evaluation method)
For the evaluation of the optical disk, an optical disk evaluation apparatus (“ODU-1000” manufactured by Pulstec Industrial Co., Ltd.) was used, and a lens with a recording laser center wavelength of 405 nm and NA (numerical aperture) of 0.85 was used.

  First, the initial reflectance was calculated from the intensity of the return light of the unrecorded portion of the optical disk by irradiating the track with the laser using the above apparatus.

  The initial jitter value (signal evaluation) was measured using a multi-signal of 2T to 8T signals with a linear velocity of 4.92 m / s and a read laser power of 0.35 mW under conditions of a reference clock of 66 MHz. The standard deviation of the error value from the reference clock of 2T to 8T signals was obtained and calculated.

  As an evaluation standard for the initial characteristics, with reference to the BD-R standard value, the initial reflectance calculated as described above is 40% or more and the initial jitter value is 6.50% or less. A reflective film is shown and the reproduction stability is excellent).

(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. Then, both the reflectance and the change amount of the jitter value before and after the accelerated environment test were evaluated as passing (excellent in durability) within ± 10%.

(Measurement of transmittance)
The transmittance was determined by measuring the linear transmittance in the thickness direction with respect to light having a wavelength of 350 nm at room temperature using a spectrophotometer (UV-3150 manufactured by Shimadzu Corporation). Thus, the thing with the transmittance | permeability in 350 nm measured at 8.0% or more was set as the pass.

  These results are also shown in Tables 1 and 2. In these tables, the "disc reflectivity" and "transmittance at 350 nm" columns describe the measured value (%), respectively, and pass criteria for the first reflective film (measured by the following method). When the reflectance is 40% or more and the transmittance is 8% or more, and the acceptance criteria of the second reflective film (the reflectance when measured by the following method is 10% or more, and the transmittance is 15% or more) ) Are marked with ○, and those not filled with are marked with ×.

  Furthermore, in the rightmost column of each table, when “Evaluation” is provided and comprehensive judgment is made, the first reflective film, the second reflective film, and the optical information recording medium satisfying each acceptance standard The mark which is not satisfied with any one is marked with x. For example, No. in Table 1A. 1-4 and 1-5 satisfy the acceptance criteria of the optical information recording medium. However, since the reflectance and transmittance satisfy the acceptance criteria of the first reflection film, Means applicable. On the other hand, No. in Table 1A. 1-1 to 1-3 do not satisfy the acceptance criteria of the optical information recording medium, but the reflectance and transmittance satisfy the acceptance criteria of the second reflecting film, and therefore can be applied as the second reflecting film. Means that.

  Tables 1A and 1B show the results when using Al—Si—refractory metal (Ti). From these tables, it can be considered as follows.

  First, no. Nos. 1 to 7 make the Ti amount constant at 1.0%, change the Si amount within the range of 0.5 to 15%, and change the film thickness to 5 to 22 nm (5 to 30 nm in No. 7). The result when it is changed in is shown. Among these, the optical information recording medium provided with the reflective film of the present invention in which the Si and Ti amounts are appropriately controlled exhibits appropriate reflectivity and transmittance and is reproduced even when the film thickness is as thin as 25 nm or less. It turns out that it is excellent in stability and durability.

  Strictly speaking, the upper limit of the thickness of the reflective film that can exhibit the desired characteristics of the desired optical information recording medium can vary depending on the amount of Si. That is, when the Si amount is more than 1.0% and 10% or less, the upper limit of the thickness of the reflective film is allowable up to 25 nm, but when the Si amount is 0.5 to 1.0%, The upper limit of the thickness of the reflective film is 20 nm or less.

  It has also been found that the preferable lower limit of the thickness of the reflective film that can exhibit the required characteristics of the desired optical information recording medium is generally 13 nm or more regardless of the amount of Si.

  Further, when focusing attention on the characteristics as a reflective film, the Al-based alloy that satisfies the composition defined in the present invention has particularly different reflectance and transmittance characteristics depending on the film thickness. It was also found that even a very thin reflective film (thickness of less than 13 nm) that cannot be applied as is applicable as the second reflective film. According to the results of this example, when the Al—Si—refractory metal reflective film of the present invention containing Si is used, the range of film thickness applicable as the first reflective film is generally 13 to 25 nm. The film thickness range applicable as the second reflective film is approximately 5 to 15 nm.

  No. Nos. 8 to 13 show the results when the Si amount is kept constant at 10% and the Ti amount is changed within the range of 0.1 to 1.5% (film thickness 20 nm). No. satisfying the requirements of the present invention. Nos. 9 to 12 are excellent in all characteristics, whereas No. 9 having a small amount of Ti. No. 8 has a reduced durability (a large change in jitter value before and after the acceleration test), and No. 8 with a large Ti amount. In 13, the transmittance decreased.

  Tables 2A and 2B show the results when Al-Ge-refractory metal (Ti) is used. When Ge was used instead of Si, the same results as Si were obtained. Specifically, these tables can be considered as follows.

  First, no. Nos. 14 to 18 make the Ti amount constant at 1.0%, change the Ge amount within the range of 0.5 to 6%, and change the film thickness to 5 to 25 nm (No. The results are shown when changing within the range of 30 nm). Among these, the optical information recording medium provided with the reflective film of the present invention in which the Ge and Ti amounts are appropriately controlled exhibits an appropriate transmittance and reflectance even when the film thickness is as thin as 25 nm or less. It turns out that it is excellent in stability and durability.

  A preferable lower limit of the thickness of the reflective film that can exhibit the required characteristics of the desired optical information recording medium is generally 13 nm or more regardless of the Ge amount.

  Further, when focusing attention on the characteristics as a reflective film, the Al-based alloy that satisfies the composition defined in the present invention has particularly different reflectance and transmittance characteristics depending on the film thickness. It has also been found that even a very thin reflective film that cannot be applied as is applicable as the second reflective film. According to the result of this example, when the Al-Ge-refractory metal reflective film of the present invention containing Ge is used, the range of the film thickness applicable as the first reflective film is approximately 13 nm or more. It is 25 nm or less (depending on the amount of Ge, 20 nm or less). A more preferable range is generally 15 nm or more and 20 nm or less (18 nm or less depending on the amount of Ge). The range of film thickness applicable as the second reflective film is generally 5 nm or more and 19 nm or less (more preferably 15 nm or less).

  In the above system containing Ge, although the result when the amount of Ti is changed is not shown, it was confirmed that the same result as Si was obtained.

  In contrast, no. No. 19 is an example using pure Al, but even if the film thickness was changed in the range of 10 to 40 nm, the desired characteristics could not be ensured.

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 (10)

A reflective film used in an optical information recording medium,
The reflective film is
0.5% to 10% of Si (unless otherwise specified,% means atomic%. The same applies hereinafter), and / or 0.5% to 10% of Ge, and 0.2% to refractory metal element. Made of Al-based alloy containing 1.0%,
A reflective film for an optical information recording medium, wherein the thickness of the reflective film is 25 nm or less.   When Si is included in an amount of 0.5 to 1.0%, the thickness of the reflective film is 20 nm or less. When Si is included in an amount of more than 1.0% and 10% or less, the thickness of the reflective film is 25 nm or less. The reflective film for an optical information recording medium according to claim 1.   The reflective film for an optical information recording medium according to claim 1, wherein the refractory metal element contains Ti.   The reflective film for an optical information recording medium according to any one of claims 1 to 3, wherein the refractory metal element contains at least one selected from the group consisting of Fe, Mn, and Ta.   The reflective film for an optical information recording medium according to any one of claims 1 to 4, which is used for an optical information recording medium on which recording or reproduction is performed by irradiation with blue laser light.   6. The reflective film for an optical information recording medium according to claim 1, wherein the initial reflectance is 40% or more and the transmittance at 350 nm is 8.0% or more.   6. The reflective film for an optical information recording medium according to claim 1, wherein the initial reflectance is 10% or more and the transmittance at 350 nm is 15% or more.   An optical information recording medium comprising the reflective film for an optical information recording medium according to claim 1.   The optical information recording medium according to claim 8, wherein the initial reflectance is 40% or more and the transmittance at 350 nm is 8.0% or more. A sputtering target for forming the reflective film for an optical information recording medium according to claim 1,
It contains 0.5 to 10% of Si and / or 0.5 to 10% of Ge, 0.2 to 1.0% of a refractory metal element, and the balance: Al and inevitable impurities Sputtering target.

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