JP2006073086A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium of a single-side two-layered recording and reproduction type having satisfactory in-plane uniformity of reflectivity of an optical information recording medium. <P>SOLUTION: The optical recording medium is constituted by bonding together a first substrate 1 having a first information layer laminated with a first recording layer 2 composed of at least an organic dye and a light translucent first reflection layer 3 and a second substrate 8 having a second information layer laminated with at least a second reflection layer 7 and a second recording layer 6 composed of an organic dye in such a manner that the laminated films face each other via a transparent intermediate layer 4 and optically records and reproduces information, wherein the film thickness on the inner peripheral side of the first reflection layer is made thicker in the film thickness on the inner peripheral side than the film thickness on the middle and outer peripheral sides of the first reflection layer 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical recording medium that records and reproduces information by irradiating a light beam, and particularly to a dual-layer DVD (Digital Video Disc or Digital Versatile Disc) having two write-once information recording layers. It is.

  In addition to optical recording media such as read-only DVD-ROMs, recordable DVDs (DVD + RW, DVD + R, DVD-R, DVD-RW, DVD-RAM, etc.) have been put into practical use. These DVD + R, DVD + RW, etc. are positioned on the extension of conventional recordable CD-R, CD-RW (recordable compact disc) technology, and are recorded to ensure playback compatibility with playback-only DVDs. The density (track pitch, signal mark length) and substrate thickness are designed to meet the DVD conditions from the CD conditions.

  For example, in DVD + R, an information recording substrate in which an optical recording layer is provided by spin-coating a dye on a substrate and a metal reflective layer is provided behind the substrate is formed in the same shape as a CD-R through a bonding material. The structure of pasting together is adopted. In this case, a dye material is used for the optical recording layer. One feature of CD-R is that it has a high reflectivity (65%) that satisfies the CD standard. In order to obtain a high reflectivity in the above configuration, an optical recording layer that is also a light absorption layer is used. It is necessary to satisfy a specific complex refractive index at the recording / reproducing light wavelength. Since the light absorption characteristics of the dye are suitable for the above requirements, a dye-based material is used for the optical recording layer. The same applies to DVDs.

  By the way, a read-only DVD has been proposed which has two information recording layers in order to increase the recording capacity. FIG. 1 is a sectional view showing the structure of a DVD having such two information recording layers. The board | substrate 11 and the board | substrate 12 are bonded together on both sides of the transparent intermediate | middle layer 15 formed with the ultraviolet curing resin. A transflective layer 13 as a first information recording layer is formed on the inner surface of the substrate 11 where the concave and convex pits are formed, and a reflective layer 14 is formed on the inner surface of the substrate 12. The semi-transmissive layer 13 is made of a dielectric film or a thin metal film. The reflective layer 14 also serves as the second information recording layer and is made of a metal film or the like.

  In the read-only DVD, the recording signal recorded on each information recording layer is read by the effect of reflecting / interfering the reproduction laser beam. Since signals are read from the two information recording layers, a maximum storage capacity of about 8.5 GB can be obtained. Moreover, the thickness of the board | substrate 11 and the board | substrate 12 is 0.6 mm, respectively, and the thickness of the transparent intermediate | middle layer 15 is about 50 micrometers. The semi-transmissive layer 13 that is the first information recording layer is formed so that the reflectance thereof is about 30%, and the laser irradiated to reproduce the reflective layer 14 that is the second information recording layer. About 30% of the total amount of light is reflected and attenuated by the semi-transmissive layer 13, then reflected by the reflective layer 14, which is the second information recording layer, further attenuated by the semi-transmissive layer 13, and then from the disc. to go out. The signal of each information recording layer can be reproduced by squeezing the laser beam, which is the reproduction light, so that the focal point is positioned on the first or second information recording layer and detecting the reflected light. In the case of DVD, the laser beam wavelength used for recording and reproduction is about 650 nm.

  However, in the recordable DVD, that is, DVD + R, DVD-R, DVD-RW, DVD + RW, etc., there is only one information recording layer that can be read from one side, and in order to obtain a larger storage capacity with these optical information media. It was necessary to reproduce from both sides. The reason for this is that, since a single-sided dual-layer recording / reproducing type optical information medium has two information recording layers, when a signal is recorded by irradiating a writing laser beam with focus on the information recording layer at the back from the optical pickup Since the first information recording layer attenuates the laser beam, there is a problem that light absorption and light reflection necessary for recording of the second information recording layer cannot be achieved at the same time.

As a technique for addressing the above problem, Patent Document 1 discloses a single-sided dual-layer recording / reproducing type optical recording medium having an information layer having a translucent reflective film and an information layer having a reflective film, the translucent reflective film A material using an alloy containing Ag as a main component and adding Au or the like is disclosed. However, there is no specific explanation about the medium using the dye recording layer, and of course, the problem of the present invention relating to the nonuniform reflectance from the first information recording layer and the solution thereof are of course the subject of the present invention. There is no description.
Japanese Patent Application Laid-Open No. 2004-228688 also discloses a light having a configuration in which two information recording layers made of an organic dye can be written from one side of an optical recording medium during recording and the two information recording layers are read from one side of the optical recording medium during reproduction. Although a recording medium is disclosed, as a specific example, only a conventional substrate surface incident recording configuration and a recording film surface incident configuration are bonded to each other, and there is no description of the problem of the present invention.
In Patent Document 3, when forming a dye recording layer by a spin coating method, it is difficult to make the dye film thickness and the degree of embedding in the groove strictly uniform. Therefore, the groove depth and groove width are changed from the inner periphery to the outer periphery. Although an optical recording medium is disclosed, the reflective layer is sufficiently thick and the reflectance of the reflective layer is uniform, which is different from the present invention.

JP 2002-140838 A JP 11-66622 A Japanese Patent Laid-Open No. 05-198012

An object of the present invention is to provide a single-sided dual-layer recording / reproducing type optical recording medium that solves the above-mentioned problems and that can obtain good recording signal characteristics from two information recording layers.

  In order to achieve the above object, the present invention has been accomplished as a result of intensive studies to provide a single-sided dual-layer recording / reproducing type optical recording medium in which good recording signal characteristics can be obtained from two information recording layers. Hereinafter, the present invention will be specifically described.

The present invention provides a first substrate having a first information layer in which a first recording layer made of at least an organic dye and a semi-transmissive first reflecting layer are laminated, and a second recording made of at least a second reflecting layer and an organic dye. An optical recording medium on which information is optically recorded / reproduced by being bonded to a second substrate having a second information layer on which layers are laminated so that the laminated films face each other via a transparent intermediate layer ,
The optical recording medium is characterized in that the film thickness on the inner circumference side of the first reflective layer is thicker than the film thickness on the middle / outer circumference side.
In the present invention, it is preferable that the film thickness on the middle circumference side of the first reflective layer is thicker than the film thickness on the outer circumference side.

As described above, in the prior art, since the first information recording layer attenuates the laser light, it is difficult to achieve both light absorption and light reflection necessary for recording on the second information recording layer. As a means for solving this problem, it is necessary to make the semi-transmissive first reflective layer thin. In that case, in order to make the reflectance uniform over the entire surface, the thickness of the semi-transmissive reflective layer is made uniform. However, the reflectance does not become uniform due to the difference in groove shape between the inner and outer peripheral sides of the substrate, the dye film thickness, and the degree of filling of the dye into the groove. In the present invention, this problem is solved by providing a film thickness distribution of the semi-transmissive reflective layer corresponding to the difference in the groove shape of the substrate. That is, in the present invention, the film thickness distribution shape of the semi-transmissive reflective layer that cancels the difference in reflectance due to the difference between the groove width and groove depth on the inner and outer peripheral sides, that is, the inner periphery of the first reflective layer. By making the film thickness on the side thicker than the film thickness on the middle and outer peripheral sides, the uniformity of the unrecorded signal characteristics and the post-recording signal characteristics of the optical recording medium can be improved.
Further, by making the film thickness on the middle circumference side of the first reflective layer larger than the film thickness on the outer circumference side, it is possible to further improve the uniformity of the unrecorded signal characteristics and the post-recording signal characteristics of the optical recording medium.

  According to the present invention, it is possible to provide a single-sided dual-layer recording / reproducing type optical recording medium in which the in-plane uniformity of reflectance of the optical information recording medium is good.

Embodiments of the present invention will be described below with reference to the drawings.
An example of the layer structure of the optical recording medium of the present invention is shown in FIG.
A first substrate 1 having a first information layer in which a first recording layer 2 made of an organic dye and a semi-transmissive first reflective layer 3 are sequentially laminated on a surface having a light guide groove, and a surface having a light guide groove A second reflective layer 7, a second recording layer 6 made of an organic dye, and a second substrate 8 having a second information layer in which a barrier layer (light-transmissive protective layer) 5 is sequentially laminated, with a transparent intermediate layer 4 interposed therebetween. Optical recording that records and reproduces signal information on the first and second recording layers by laminating the recording layers so that the laminated films face each other and irradiating laser light from the first substrate side It is a medium.
The first reflective layer 3 is formed of an alloy, formed of a mixture of an alloy and a metal or metalloid oxide and / or nitride, or at least selected from a metal or metalloid simple substance, oxide, or nitride. By forming with two types of mixture, an optical recording medium with few defects and high reliability can be obtained.

The semi-transmissive first reflective layer 3 needs to have a light transmittance of 30 to 60% and a light reflectance of 15 to 35% with respect to the recording / reproducing laser beam. Outside this numerical range, the light transmittance is too low to make recording / reproduction of the second recording layer 6 difficult, or the light reflectance is too low to make recording / reproduction of the first recording layer 2 difficult. Layer recording / playback becomes difficult.
In order to make the above numerical range, the film thickness may be selected in accordance with a material appropriately selected from the materials described later. The film thickness is usually 5 to 30 nm. If the thickness is less than 5 nm, it is difficult to prevent the characteristics of the first recording layer 2 from being deteriorated, and if it exceeds 30 nm, it is difficult to satisfy the light transmittance.

  For the first information layer, a conventional single recording layer medium (DVD + R, DVD-R, etc.) in which the first recording layer 2 and the first reflective layer 3 formed on the first substrate 1 are bonded to the second substrate; By adopting the same configuration, the reflectance and the recording signal modulation degree (contrast) are obtained by the multiple interference effect at both the upper and lower interfaces of the first recording layer 2 and the substrate deformation at the time of mark formation.

  Further, for the second information layer having a configuration different from that of the first information layer, the reflectance and the recording signal modulation degree (contrast) are obtained by the substrate groove shape and the light absorption characteristics of the second recording layer 6 made of organic dye. It is preferable to arrange the recording mark shape by disposing the second recording layer between the hardly deformable inorganic layers (the second reflective layer 7 and the barrier layer 5).

  In order to obtain the above effect, the thickness of the second recording layer is preferably 1.5 to 2.5 times the thickness of the first recording layer. When the film thickness ratio of the recording layer is out of this range, the ease of spreading of the recording mark differs, making it difficult to record the two recording layers with the same recording strategy (light emission pulse pattern of the recording laser). The recording layer made of an organic dye is generally formed by spin coating a dye dissolved in a coating solvent. When a film is formed on a substrate having guide grooves, the gap between the groove portion and the groove is determined. The difference in the pigment film thickness occurs at the part.

  As shown in FIG. 2, the groove shapes formed on the first substrate 1 and the second substrate 8 are not the same. In the case of 4.7 GB, 0.74 μm pitch DVD + R, DVD-R, the groove shape of the first substrate 1 is preferably groove depth: 1000 to 2000 mm and groove width (bottom width): 0.2 to 0.3 μm. . In the case of spin coating, the groove tends to be filled with a dye, and therefore the interface shape between the first recording layer 2 and the first reflective layer 3 is determined by this filling amount and the substrate groove shape. The above range is suitable for utilizing reflection.

  On the other hand, the groove shape of the second substrate 8 is preferably groove depth: 200 to 600 mm and groove width: 0.2 to 0.4 μm. As shown in FIG. 2, since the interface shape between the second recording layer 6 and the second reflective layer 7 is determined by the substrate groove shape, the above range is suitable for utilizing the interface reflection.

  If both the first substrate 1 and the second substrate 8 have a groove depth deeper than the groove shape range, the reflectance is likely to decrease. Further, when the groove depth is shallower than the groove shape range or the groove width is shifted, the shape of the formed recording mark is difficult to be obtained, and jitter is likely to increase.

In DVD + R, in order to achieve reproduction compatibility with DVD-ROM, a tracking guide groove called groove forms a meander called wobble, and the wobble cycle is 32 times the data clock, that is, about It is 818 kHz. The relationship between this wobble and data sector is that 93 out of 26 EFM Sync Frames (8-14 modulation / sync frame) in one data sector correspond to 2 EFM Sync Frames. . Of the 93 wobbles, 8 are composed of a phase modulation part called ADIP Unit (address in pregroove unit) and 85 monotone wobbles, and the sync part of the data sector is the 16th. The relationship is located in the wobble. Further, four ECC addresses (words) are stored in one ECC block (error correction code block), which is an error correction block of data, in a basic unit. That is, one address is included in four data sectors. The ADIP Word is composed of one ADIP Sync Unit (sink unit) and 51 ADIP Data Units (data units). Each Unit corresponds to the 93 wobbles. Of the 51 ADIP Data Units, 1 bit (bit) is reserved, 2 bits to 23 bits are address information ADIP Data Bit, 24 bits to 31 bits are 8 bits auxiliary data for storing various information about the disk, 32 bits to 51 bits The remaining 20 bits up to are configured as parity bits (parity bits) for error correction.
In DVD-R, the pre-format is a continuous groove and CLV shape by wobbled grooves as in DVD + R, but the wobble signal is a single frequency (186 T period) signal without modulation, and the address signal is a land between grooves. A pre-pit system is used.

  In the recording layers 2 and 6, a preferable film thickness is 40 to 1000 mm in the first recording layer 2 (groove portion) and 600 to 3000 mm in the second recording layer 6 (inter-groove portion). This is because if the dye film thickness is thinner than this range, it is difficult to obtain the degree of signal modulation (contrast). On the contrary, if the dye film thickness is thick, the mark shapes are difficult to align and jitter is likely to increase.

Hereinafter, materials used for the optical recording medium of the present invention will be specifically described.
The optical recording medium of the present invention is configured to obtain high reflectivity by the multiple interference effect on both the upper and lower interfaces of a recording layer made of an organic dye, like DVD + R and CD-R, and as a recording layer made of an organic dye. Requires optical characteristics having a large refractive index n and a relatively small absorption k at the recording / reproducing wavelength. Preferred ranges are n> 2, 0.03 <k <0.2. Such optical characteristics can be obtained by utilizing the characteristics of the long wavelength end of the light absorption band of the dye film.

Examples of organic dye materials that can be used for the first and second recording layers 2 and 6 include cyanine dyes, phthalocyanine dyes, pyrylium / thiopyrylium dyes, azurenium dyes, squarylium dyes, azo dyes, Formazan chelate dyes, metal complex dyes such as Ni and Cr, naphthoquinone dyes / anthraquinone dyes, indophenol dyes, indoaniline dyes, triphenylmethane dyes, triallylmethane dyes, aminium dyes / diimonium dyes And nitroso compounds.
Furthermore, other 3rd components, for example, a binder, a stabilizer, etc. can be contained as needed. Among them, as a dye compound in which the maximum absorption wavelength of the light absorption spectrum of the film is 580 to 620 nm and desired optical characteristics can be easily obtained at the laser beam wavelength for DVD (about 650 nm), the film forming property and optical characteristics by solvent coating can be obtained. In view of ease of adjustment, at least one dye selected from a phthalocyanine dye, a cyanine dye, an azo dye, and a squarylium dye is preferable.

  The materials for the substrates 1 and 8 used in the present invention can be arbitrarily selected from various materials used in conventional information recording media. Examples include acrylic resins such as polymethyl methacrylate, vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers, epoxy resins, polycarbonate resins, amorphous polyolefins, polyesters, glass and ceramics such as soda lime glass. Can be mentioned. In particular, polymethyl methacrylate, polycarbonate resin, epoxy resin, amorphous polyolefin, polyester and glass are preferable from the viewpoint of dimensional stability, transparency, flatness, etc., but polycarbonate resin is most preferable from the viewpoint of ease of molding.

  As the material of the semi-transmissive first reflective layer 3, a substance having a high reflectance with respect to the wavelength of the laser beam is preferable, and examples thereof include Au, Ag, Cu, Al, Ti, V, Cr, Ni, Nd, and Mg. , Pd, Zr, Pt, Ta, W, Si, Zn, and at least one kind of metal and metalloid selected from In, among them, one of Au, Ag, and Cu as a main component, 0.1 to 10% by weight of at least one selected from Au, Ag, Cu, Al, Ti, V, Cr, Ni, Nd, Mg, Pd, Zr, Pt, Ta, W, Si, Zn, and In An added alloy is preferable (because it is an alloy, naturally a combination of Au and Au, Ag and Ag, and Cu and Cu is excluded). By adding the additive metal in an amount of 0.1% by weight or more, the crystal grains are refined and a thin film having excellent corrosion resistance is obtained. However, adding more than 10% by weight is not preferable because the reflectance decreases. As the base material, Ag having a low raw material price and a high sputtering rate is most preferable, and as the additive, Au, Cu, Mg, and In are particularly preferable because they have a small refractive index and a large absorption coefficient. Ag has the smallest n among all elements and has the highest light utilization efficiency. Therefore, the total amount of additives is particularly preferably 5 wt% or less so as not to impair the characteristics.

  In order to protect the first reflective layer 3 chemically and physically, a first overcoat layer may be provided on the first reflective layer. As these materials, ultraviolet curable resin (eg, acrylic resin) or the like can be used.

  In the present invention, since the first recording layer 2 made of organic dye and the transparent intermediate layer 4 made of resin or the first overcoat layer are in contact with each other through the very thin first reflective layer 3, the component of the resin layer is the first reflective layer. It is necessary that the organic dye of the first recording layer 2 does not dissolve or react via the layer 3. When the crystal grains of the first reflective layer 3 are large as in the case of a pure metal thin film, the thin film tends to be island-like and resin or the like easily penetrates from the grain boundary, so that the characteristics of the first recording layer 2 deteriorate. End up.

A barrier layer (light-transmitting protective layer) 5 may be provided between the second recording layer 6 and the transparent intermediate layer 4 for the purpose of chemically and physically protecting the second recording layer 6 made of a dye. Examples of materials used for the barrier layer 5 include inorganic substances having high light transmissivity such as SiO, SiO ₂ , MgF ₂ , SnO ₂ , ZnS, ZnS—SiO _{2 and the} like. The film thickness of the barrier layer needs to be in the range of 100 to 2000 mm.

  The transparent intermediate layer 4 is preferably used as an adhesive layer, and an existing acrylate-based, epoxy-based, urethane-based ultraviolet curable or thermosetting adhesive can be used as the material. Furthermore, the method of bonding with a transparent sheet may be used.

  Further, a second overcoat layer may be provided between the barrier layer 5 and the transparent intermediate layer 4 with an acrylic, epoxy-based ultraviolet curable resin or the like for chemical and physical protection.

  The plastic substrate of the optical recording medium is generally manufactured by injection molding or injection compression molding. This is done by using an injection molding machine, placing a stamper with a pattern shape such as pits or grooves in the cavity between the fixed mold body and the movable mold body, and entering the cavity from the center of the cavity. It is manufactured by an injection molding method in which a molten resin is injected and cooled to mold a substrate for an optical recording medium in which pits and grooves of the stamper are transferred to one surface. Therefore, the temperature of the resin at the time when the resin has spread into the cavity tends to be higher as the inner circumference is lower. Therefore, the substrate formed by cooling transfers the groove shape of the stamper completely toward the inner periphery, and the transfer becomes incomplete at the outer periphery. In other words, the groove shape of the substrate tends to have a deep groove on the inner periphery, a narrow opening width, and a sharp cross-sectional angle. Therefore, the signal characteristics of the completed optical recording medium are characterized in that the inner unrecorded reflectance and the post-recording R14H (14T space reflectance) are small, the PPA (push-pull amplitude) is large, and the wobble C / N is large. . Therefore, for example, push-pull uniformity as in the DVD + R DL standard: (PPmax−PPmin) / (PPmax + PPmin) <0.15 or reflectance after recording: (I14Hmax−I14Hmin) /I14Hmax≦0.25 The problem of not being in the standard arises.

  In the present invention, in order to solve the above-described problems, the film thickness on the inner peripheral side of the first reflective layer 3 is made thicker than the film thickness on the middle and outer peripheral side. The film thickness distribution may be continuous or discontinuous. In addition, the film thickness distribution is not limited to specifying the positional relationship as a result of the film thickness on the inner peripheral side being thicker than the film thickness of the peripheral surface on the outer side.

As a method for forming the first reflective layer 3, when an alloy mainly containing any one of Au, Ag, and Cu is used as the material of the semi-transmissive first reflective layer, a high reflectivity serving as a base material is used. 1 to 10 weights of at least one selected from Au, Ag, Cu, Al, Ti, V, Cr, Ni, Nd, Mg, Pd, Zr, Pt, Ta, W, Si, Zn, and In An alloy reflective layer can be formed by sputtering at a power of 1 to ²⁰ W / cm ^{2 in} an Ar atmosphere with a pressure of 0.01 Pa to several Pa using a target with a% added.

Here, for example, the following method can be used to increase the inner / outer difference, particularly the inner peripheral film thickness, in the thickness of the semi-transmissive reflective layer (first reflective layer).
(1) As shown in FIG. 3, the target surface shape is stepped to reduce the distance between the substrate and the target on the inner periphery. 3A is a plan view of the target, and FIG. 3B is a cross-sectional view of the target. In the case of DVD, the substrate has a diameter of 120 mm, the outer diameter B of the target 31 on the backing plate 32 is about 180 to 200 mm, A is preferably about 30 to 100 mm, and the step C is preferably about 2 to 5 mm. Can be made 2-10% thicker than the middle and outer circumferences.
(2) As shown in FIG. 4, the inner circumference can be made thicker by dividing the target 41 on the inner circumference side and the target 43 on the outer circumference side and supplying different powers to the respective targets with different sputtering power sources. 4A is a plan view of the target, and FIG. 4B is a cross-sectional view of the target. The outer diameter D of the inner target 41 is preferably about 40 to 110 mm, and (power density of the inner target 41) / (power density of the outer target 43) is preferably 1.05 to 1.4.
(3) In the case of DC magnetron sputtering, the inner peripheral film thickness can be made thicker than the middle circumference and the outer circumference by increasing the magnetic flux density on the inner circumference as compared with the outer circumference.
(4) A film thickness correcting plate 51 as shown in FIG. 5 is inserted outside the outer periphery of the substrate 52 so that the sputtered particles from the outer periphery of the target 53 do not reach the substrate. It can be thicker than the outer periphery. In the figure, reference numeral 54 denotes a backing plate, and reference numerals 55 and 56 denote an inner mask and an outer mask for masking a non-formed portion of the reflective layer.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples.

Example 1
A first substrate having a guide groove uneven pattern having a depth of about 150 nm, a groove width of about 0.25 μm, and a track pitch of 0.74 μm is prepared on the surface of a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.57 mm. The compound and the formazan chelate dye were mixed at a ratio of 7: 3, dissolved in 2,2,3,3-tetrafluoropropanol, and spin coated as a coating solution to provide the first recording layer. This recording layer had a maximum absorption wavelength of 609 nm and an absorbance (Abs) at the maximum absorption wavelength of 0.65. At this time, the thickness of the recording layer in the groove portion was 60 nm.
Further, a semi-transmissive reflective layer (first reflective layer) was formed on the first recording layer by the method (1) using Ar as a sputtering gas. That is, in FIG. 3, using a target having a shape of A = 80 mm, B = 200 mm, and C = 3 mm, sputtering was performed with a sputtering target having a composition of Ag0.995In0.005 wt% to form a semi-transmissive reflective layer. Sputtering was performed using a sputtering apparatus Big Sprinter manufactured by Unaxis, with an Ar flow rate of 20 sccm and a sputtering power of 0.5 kW, and the sputtering rate was approximately 5.5 nm / s.
When the film thickness distribution was measured using an ETA-RT manufactured by Steag for an AgIn alloy thin film sputtered onto a 0.6 mm thick polycarbonate substrate under the same conditions as the above sputtering conditions, the film thickness (with a radius of 23 mm) FIG. 6 shows the radial distribution when the average film thickness is 12 nm.

On the other hand, a second substrate having a guide groove uneven pattern having a depth of about 20 nm, a groove width of about 0.25 μm, and a track pitch of 0.74 μm is prepared on the surface of a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.60 mm. As a sputtering gas, Ag was formed to a thickness of about 140 nm by sputtering to form a second reflective layer. Sputtering was performed using the same apparatus as the first reflective layer at an Ar flow rate of 20 sccm and a sputtering power of 3.5 kW, and the sputtering rate was 30 nm / s.
Further, a second recording layer is formed on the second reflective layer by spin coating the squarylium dye compound so that the absorbance is 1.1, and a sputtering method using Ar as a sputtering gas thereon. Thus, ZnS—SiO ₂ was provided to a thickness of about 150 nm to form a barrier layer.
Next, the film-formed first substrate and second substrate were bonded with an ultraviolet curable adhesive (KARAYAD DVD003 manufactured by Nippon Kayaku Co., Ltd.) to obtain an optical recording medium having a layer structure shown in FIG.

For this optical recording medium, a DVD (8-16) was used while changing the recording power under the condition of a linear velocity of 9.2 m / s using a DVD evaluation apparatus (Pulstec DDU1000, wavelength: 657 nm, NA: 0.65). ) When the signal was recorded and reproduced and evaluated at a linear velocity of 3.8 m / s, a reflectance distribution as shown in FIG. 7 was obtained. The recording strategy was (n-2) T multi-pulse system, and the multi-pulse width was 10/16.
Thus, the standard of DVD + R DL (I14Hmax−I14Hmin) / I14Hmax was 0.12, which was well within the standard.

Example 2
In the same manner as in Example 1, on the first recording layer, a coaxial cathode divided into an inner periphery and an outer periphery as described in (2) above was used, and a semi-transmissive reflective layer was formed using Ar as a sputtering gas. Formed. More specifically, in the above (2), using a target having a shape of D = 100 mm, E = 104 mm, and F = 200 mm, sputtering was performed with a sputtering target having a composition of Ag0.995In0.005 wt% to form a semi-transmissive reflective layer. . At this time, Ar flow rate was 20 sccm, inner sputtering power was 0.18 kW, outer sputtering power was 0.4 kW, and the sputtering rate was about 6.0 nm / s.
When the film thickness distribution of the AgIn alloy thin film sputtered on a polycarbonate substrate having a thickness of 0.6 mm without grooves under the same conditions as the above sputtering conditions was measured in the same manner as in Example 1 using an ETA-RT manufactured by Steag, the average was obtained. A film having a film thickness of 12 nm and a radial distribution as shown in FIG. 6 was obtained.
When this recording medium was evaluated in the same manner as in Example 1, a reflectance distribution as shown in FIG. 7 was obtained, and (I14Hmax-I14Hmin) / I14Hmax was 0.07, which was sufficiently within the specifications.

Comparative Example When a semi-transparent reflective layer was sputtered with a Big Sprinter target having a diameter of 200 mm and a thickness of 6 mm and an AgIn target was sputtered with an Ar flow rate of 40 sccm and a power of 0.4 kW, the film thickness uniformity was very good as shown in FIG. The post-recording reflectance distribution was 28%, which was out of specification.

It is sectional drawing which shows the structure of DVD which has a two-layer information recording layer. It is sectional drawing which shows the layer structural example of the optical recording medium of this invention. It is the top view (a) and sectional drawing (b) which show the example of the target shape used for formation of the 1st reflective layer in the optical recording medium of this invention. It is the top view (a) and sectional drawing (b) which show the example of the division | segmentation target shape used for formation of the 1st reflection layer in the optical recording medium of this invention. It is explanatory drawing which shows an example of the film thickness correction board shape used for formation of the 1st reflection layer in the optical recording medium of this invention. It is a figure which shows radial direction distribution of the film thickness normalized by the film thickness of radius 23mm. It is a figure which shows radial distribution of the after-recording reflectance I14H normalized by the after-recording reflectance I14H with a radius of 23 mm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st board | substrate 2 1st recording layer 3 1st reflection layer 4 Transparent intermediate | middle layer 5 Light-transmissive protective layer 6 2nd recording layer 7 2nd reflection layer 8 2nd board | substrate 11 board | substrate 12 board | substrate 13 semi-transmission layer 14 reflection layer 15 Transparent intermediate layer 31 Target 32 Backing plate 41 Target 42 Backing plate 43 Target 44 Backing plate 51 Correction plate 52 Substrate 53 Target 54 Backing plate 55 Inner mask 56 Outer mask

Claims (2)

A first substrate having a first information layer in which at least a first recording layer made of an organic dye and a semi-transmissive first reflective layer are laminated, and a second recording layer made of at least a second reflective layer and an organic dye are laminated. And an optical recording medium for optically recording / reproducing information, wherein the second substrate having the second information layer is bonded so that the laminated films face each other via a transparent intermediate layer,
An optical recording medium characterized in that the film thickness on the inner circumference side of the first reflective layer is thicker than the film thickness on the middle and outer circumference side. 2. The optical recording medium according to claim 1, wherein the film thickness on the inner peripheral side of the first reflective layer is thicker than the film thickness on the outer peripheral side.

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