JP2009070497A - Master disk for optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a maser disk for optical disk which is hardly broken, is easily handled and has a high definition pattern. <P>SOLUTION: The master disk for optical disk has a substrate 10 having a polished surface, a first underlayer 11 formed on the polished surface of the substrate 10, a second underlayer 12 formed on the substrate 10 so as to cover the first underlayer 11 and an inorganic resist layer 13 formed on the second underlayer 12. The first underlayer 11 has thermal conductivity higher than that of the substrate 10 and the second underlayer 12 is hardly dissolved in an alkali solution more than the first underlayer 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a master disk for disks having an inorganic resist layer on a substrate, and particularly to provide a master disk for optical disks that is easy to handle and that can form a high-precision concavo-convex pattern by exposing the inorganic resist layer. is there.

  As recording media for recording acoustic data, image data, and other various digital data, recording and reproducing information signals by irradiating laser light from the outside in terms of recording capacity, random accessibility, portability, price, etc. Etc. are widely used from industrial use to consumer use.

  As these optical disks, CD (Compact Disc), DVD-VIDEO (Digital Versatile Disc-Video) and other reproduction-only types, CD-R (CD-Recordable), DVD-R (DVD-Recordable) and the like only once. Recordable write-once type, CD-RW (CD-Rewritable), DVD-RW (DVD-Rewritable), DVD-RAM (DVD-Random Access Memory) and other rewritable types that can be recorded multiple times, and even higher capacity Various optical discs such as BD (Blu-ray Disc) have been developed.

  An optical disc such as a CD is formed by forming a concave / convex pattern called a pit in a spiral on a light-transmitting optical disc substrate, and forming a reflective film or a protective film on the concave / convex pattern. In general, the optical disc generally includes a predetermined groove mainly composed of grooves and lands formed alternately on the surface in a spiral or concentric manner, and pits formed as information signals in at least one of the grooves and lands. For example, it is composed of a light-transmitting disk substrate having a concavo-convex pattern and various functional films such as a reflective film and a recording film formed on the concavo-convex pattern according to the type of the optical disk.

  A high-capacity optical disk can be created by forming a concave-convex pattern at a high density, and by providing high dimensional accuracy, a good eye pattern of a signal can be obtained during disk reproduction, and an optical disk with few reproduction errors can be obtained. Can do.

  Therefore, in producing a good optical disk, it is particularly important to form a concavo-convex pattern with a high dimensional accuracy of 1/1000 μm unit on the surface of the disk substrate.

  In recent years, thermoplastic and light-transmitting synthetic resins such as polycarbonate resins are generally used as disk substrate materials in terms of formability and cost. As a method for forming a concavo-convex pattern on these synthetic resin disk substrates, a synthetic resin softened by heating is press-fitted into a mold including an optical disk stamper board having a concavo-convex pattern matrix formed on the disk substrate on one side. In general, it is performed by a so-called injection molding method in which the disk substrate is molded while transferring the uneven pattern on the stamper board. Here, the disk disk used for molding the optical disk substrate is referred to as a stamper disk, and the disk disk on which irregularities corresponding to the digital signals to be formed on the optical disk substrate for producing the stamper disk are referred to as an optical disk master. In order to form a concavo-convex pattern with high dimensional accuracy on the surface of a disk substrate, it is necessary to form the concavo-convex pattern of the original master for optical disc with high dimensional accuracy.

  Here, a configuration diagram of a conventional method for manufacturing an optical disc master and a stamper disc will be described with reference to FIG.

  First, as shown in FIG. 8A, after optical polishing is performed on the surface, a photoresist (organic) as a photosensitive resin as shown in FIG. 8B is formed on a glass substrate 20 that has been cleaned and dried. A photoresist layer 21 is formed by applying and drying a resist) to a predetermined thickness by spin coating or the like. This is a master for an optical disc before a concave / convex corresponding to a digital signal to be formed on the optical disc substrate (in a state where no digital signal is recorded).

  Next, as shown in FIG. 8C, for example, laser light 22 emitted intermittently according to a predetermined information signal is condensed by the objective lens 23 and irradiated to the photoresist layer 21. The portion of the photoresist layer 21 irradiated with the laser beam 22 is exposed to light and becomes a latent image 24 having the same shape as a pit or guide groove having a predetermined shape. This operation is generally called cutting.

  Next, the photoresist layer 21 on which the latent image 24 is formed is developed with an alkaline developer. As a result, the latent image 24 portion is removed, and as shown in FIG. 8D, a concavo-convex pattern having a predetermined shape is formed on the photoresist layer 21 to form an optical disc master in which signals are recorded.

  Next, as shown in FIG. 8E, a first metal layer (conductive layer) 25 made of a conductive metal such as nickel is not provided so as to follow the uneven pattern formed on the photoresist layer 21. The film is formed by electrolytic plating, vapor deposition, sputtering, or the like.

  Next, as shown in FIG. 8F, the first metal layer 25 is used as a conductive layer for electroforming, and the second metal layer 26 made of a metal such as nickel is electroformed on the first metal layer 25. To form. Thereby, the metal layer 27 composed of the first metal layer 25 and the second metal layer 26 to which the uneven pattern on the photoresist layer 21 is transferred is formed.

  Finally, as shown in FIG. 8G, the metal layer 27 is peeled from the substrate 20 and the photoresist layer 21. The peeled metal layer 27 is subjected to post-processing such as inner / outer diameter processing and back surface polishing to form an optical disc stamper board.

  This optical disk stamper board is incorporated in a mold of an injection molding machine and used for manufacturing a disk substrate onto which the concave / convex pattern is transferred.

  Although the method for producing an optical disc master and a stamper disc by the above procedure is a commonly used method, it responds to the increase in capacity of optical discs due to the rapid development of information communication and image processing technology in recent years. May be difficult. In other words, one of the main methods for increasing the capacity of optical disks, the track pitches and pits of concavo-convex patterns formed on the optical disk surface are made finer, and the recording density on the surface (also referred to as recording surface density) is increased. In contrast to the technique of increasing the capacity by increasing the photon mode optical disk stamper disk using the organic resist, the micronized concave / convex pattern is applied to the optical disk due to restrictions of laser light and organic resist. This is because it becomes difficult to form the master disk with high accuracy.

  For example, in the case of a high-density optical disc having a recording capacity of 25 GB (gigabytes) in one layer, it is necessary to miniaturize the shortest pit length to about 0.14 μm and the track pitch to about 0.32 μm. The organic resist used is generally made of an organic polymer material such as a novolak resist or a chemically amplified resist. Chemically amplified resist is based on the photoreaction by the irradiation of light or electron beam, while the conventional resist generates acid in the resist film by photoreaction, and by heating after exposure using acid as catalyst, The basic resin of the resist reacts to obtain a pattern. Such an organic resist has a large molecular weight, and it is difficult to form such a fine uneven pattern with high dimensional accuracy.

  For this reason, when producing a high-density optical disc master, it is possible to replace a conventional novolac resist or an organic resist made of an organic polymer material such as a chemically amplified resist with a molecular weight capable of forming a fine uneven pattern. A small inorganic resist is used.

  In an optical disc master manufactured using an inorganic material as a resist material, when the inorganic resist layer is exposed with laser light, the inorganic resist absorbs the laser light, and the temperature of the exposed portion rises. Descend. The state of the inorganic resist layer changes due to this temperature change, and the exposed portion becomes selectively soluble in the developer. However, it has been confirmed that the following problems arise due to the selection of the substrate material. .

  For example, when a glass substrate is used, it is hard to break and easy to handle, but its thermal conductivity is low at about 1 W / (m · K) at room temperature, high exposure sensitivity, but slow cooling after heating. is there. If the cooling is slow, the inorganic resist material in the periphery of the exposed portion becomes an undesired crystal state, and the shape of the guide groove, pit, etc. is lost and the signal eye pattern at the time of disk reproduction deteriorates. Therefore, it is not suitable for producing a high-definition pattern.

  Further, when using a silicon substrate, it is easy to break and difficult to handle. Furthermore, since the thermal conductivity is as high as about 168 W / (m · K) at room temperature, it is difficult to give a sufficient amount of heat to change the state of the inorganic resist layer, resulting in low exposure sensitivity and difficult processing. .

  Conventionally, proposals have been made to solve the problem that the exposure sensitivity decreases when a silicon substrate is used. For example, the following [Patent Document 1] discloses an invention for improving exposure sensitivity with respect to a method of manufacturing an optical disc master using an inorganic resist containing an incomplete oxide of a transition metal.

JP, 2003-315988, A In the resist material and fine processing method indicated by above-mentioned patent documents 1, as a method of reducing the thermal conductivity of a silicon substrate and raising exposure sensitivity, it is between a silicon substrate and an inorganic resist layer. The problem of decreased exposure sensitivity when a silicon substrate is used by forming a base layer of a-Si (amorphous silicon), SiO2 (silicon dioxide) SiN (silicon nitride), Al2O3 (alumina) or the like having low thermal conductivity. A method for solving the problem has been proposed.

  According to Patent Document 1, by forming a base layer having low thermal conductivity on a silicon substrate, heat accumulation in a resist material during exposure is improved, so that exposure sensitivity can be improved appropriately.

  However, when silicon is used as a substrate, it is not easy to handle because it is easily broken. Therefore, an optical disc master that is difficult to break and easy to handle and capable of forming a high-definition pattern is desired.

The present invention has been made in view of the above problems,
A substrate whose surface is polished;
A first underlayer formed on the polished surface of the substrate;
A second underlayer formed on the substrate so as to cover the first underlayer;
An inorganic resist layer formed on the second underlayer;
An optical disc master having
The first underlayer is an underlayer having a higher thermal conductivity than the substrate;
The second base layer is a base layer that is less soluble in an alkaline solution than the first base layer, thereby providing an optical disc master, which solves the above problems.

  Moreover, the said subject is solved by providing the original disc for optical discs, wherein the said board | substrate is a board | substrate made from glass or a synthetic resin.

  ADVANTAGE OF THE INVENTION According to this invention, the master for optical disks which can be formed easily and can form a highly detailed uneven | corrugated pattern by exposing an inorganic resist layer can be provided.

  Embodiments of an optical disc master according to the present invention will be described below with reference to the drawings.

  The optical disk master of the present invention includes a substrate whose surface is polished (for example, a glass substrate or a synthetic resin substrate), and a first underlayer having a higher thermal conductivity than the substrate formed on the polished surface on the substrate. An optical disc master having a second underlayer that is less soluble in an alkaline solution than the first underlayer formed so as to cover the first underlayer, and an inorganic resist layer formed on the second underlayer It is.

  FIG. 1 is a block diagram showing the configuration of an embodiment of an optical disc master according to the present invention.

  First, as shown in FIG. 1A, for example, the surface of a disk-shaped glass substrate 10 having a diameter of about 200 mm and a thickness of about 0.7 mm is precisely polished, and then washed and dried. In the embodiment, glass is used for the substrate. However, in addition to glass, a well-known substrate material that is difficult to break and easy to handle, such as synthetic resin such as polycarbonate, can be used.

  Sputtering is performed, for example, in an Ar atmosphere on the precision-polished surface of the glass substrate 10 to form a first underlayer 11 of Ag (silver) as shown in FIG. In the embodiment, Ag is used as the first underlayer 11, but depending on the required thermal conductivity, Au (gold), Cu (copper), Al (aluminum), or an alloy thereof can be used. The first underlayer 11 is formed of a material having a higher thermal conductivity than that of the substrate 10. The thickness of the first base layer 11 is preferably in the range of 50 nm to 100 nm in consideration of thermal conductivity. In the example, first, the thickness of the first underlayer 11 (Ag layer) was set to 100 nm.

Then, as shown in FIG. 1C, a second underlayer 12 is formed so as to cover the first underlayer 11. The second underlayer 12 is formed as a ZnS—SiO ₂ layer having an atomic weight ratio of ZnS (zinc sulfide): SiO ₂ (silicon oxide) = 80: 20 by sputtering in an Ar atmosphere, for example. In the embodiment, ZnS—SiO ₂ is used as the second underlayer 12, but SiN (silicon nitride) or Si (silicon) may be used as long as the material can cover the first underlayer 11. However, the second underlayer 12 is made of a material that is less soluble in an alkaline solution than the first underlayer 11. The purpose of this is to protect the first underlayer 11 against the alkaline solution because an alkaline solution is used as a developing solution in the later-described developing process of the optical disc master. Since the first underlayer 11 is made of a material having a higher thermal conductivity than the substrate 10, it is considered that a metal material is often used. When this metal material is exposed, it is easily dissolved in an alkaline solution. Therefore, it is important to provide the second underlayer 12 as a protective layer so as to cover the first underlayer 11.

  The thickness of the second underlayer 12 is preferably 25 nm to 100 nm in consideration of the development process, and is preferably in the range of 50 nm to 100 nm in order to obtain better data.

  Next, as shown in FIG. 1D, an inorganic resist layer 13 made of an oxide of W (tungsten) and Mo (molybdenum) is formed on the second underlayer 12 by sputtering, for example. In the examples, an inorganic resist made of an oxide of W and Mo was used. In addition, an oxide such as W, Mo, Cr (chromium), Nb (niobium), or an alloy containing two or more of these elements. Well-known inorganic resists such as oxides of these alloys, oxides of alloys obtained by adding transition metals to these elements, and chalcogenide-based inorganic resists can be used.

  By cutting the optical disc master manufactured as described above, an optical disc master having irregularities corresponding to information signals (digital signals) to be recorded on the replica optical disc is produced.

  FIG. 2 is a diagram showing a configuration of an optical disc master having irregularities formed in one embodiment of the present invention.

  That is, while rotating the optical disc master at a predetermined speed, as shown in FIG. 2A, laser light 14 emitted intermittently based on a light emission pattern corresponding to a predetermined information signal is applied to the inorganic resist layer 13. Focusing and irradiating a predetermined position through the objective lens 15. By irradiating the laser beam 14, a latent image 16 having a predetermined shape is formed on the inorganic resist layer. In the embodiment, for example, a laser beam having a laser wavelength of 405 nm and an objective lens numerical aperture NA of 0.95 output from a modulation signal generator is irradiated, and the inorganic resist layer 13 is defined by the shortest length at a density equivalent to BD. A pit latent image corresponding to 2T (1T = 15.15 ns) was formed. FIG. 5 shows the cutting data used in the example.

  In FIG. 5, the horizontal axis represents time, and the vertical axis represents laser intensity. Pw (mW) indicates the highest laser intensity, and Pcl (mW) indicates the lowest laser intensity. Tt corresponds to the time for maintaining the intensity of Pw (mW), and for unit time T (1T = 15.15 ns), Tt = 1.3T, 1.4T, 1.5T, 1.6T, An optical disc master of the example was manufactured using data changed between 1.7T, 1.8T, 1.9T, and 2.0T. In the example, the substrate rotation linear velocity during cutting was 4.92 m / s at a constant linear velocity, the light source feed pitch was 0.32 μm, and the laser power was 11 mW at the maximum.

  Next, returning to FIG. 2A, a developing solution is dropped onto the inorganic resist layer 13 while rotating the optical disc master on which the latent image 16 is formed, and the inorganic resist layer 13 is developed. As a result, as shown in FIG. 2 (b), an optical disc master A in which irregularities corresponding to digital signals to be formed on the optical disc substrate are formed.

  For example, when the inorganic resist layer is formed of a positive resist, the exposed portion exposed with the laser beam has a higher dissolution rate with respect to the developer than the unexposed portion. An inorganic resist layer is formed. As the developer, an alkali developer such as a tetramethylammonium hydroxide solution can be used. In Examples, after the latent image was formed, development was performed using a wet process with an organic alkali developer under the condition of a development time of 10 minutes, and the latent image portion of the pit was removed. Next, the optical disc master after development was sufficiently washed with pure water and dried by air blow or the like to produce an optical disc master A having predetermined pits.

  An optical disc stamper disc used for molding an optical disc substrate is produced using the optical disc master A produced as described above.

  FIG. 3 is a diagram showing the structure of an optical disc stamper disk. As shown in FIG. 3 (a), a nickel film or the like is formed on the concave / convex pattern of the optical disk master A manufactured as described above. A conductive film 17 is formed. Thereafter, the optical disc master on which the conductive film 17 is formed is attached to an electroforming apparatus, and the conductive film is plated to a thickness of, for example, about 300 ± 5 μm by an electroplating method. As shown in b), 18 layers of plating having a concavo-convex pattern are formed. As a material constituting the plating layer 18, for example, a metal such as nickel can be used. Thereby, a metal layer 19 composed of the conductive film 17 and the plating layer 18 is formed.

  Next, as shown in FIG. 3C, the metal layer 19 is peeled from the optical disk master. Thereafter, the metal layer 19 is trimmed to a predetermined size, and then the inorganic resist adhering to the signal forming surface of the metal layer 19 is washed using, for example, acetone. Thus, the optical disk stamper board B can be obtained.

  The concavo-convex pattern of the optical disc stamper board B produced as described above is transferred to a resin material such as polycarbonate by an injection molding method to produce an optical disc substrate.

  Optical disk substrate materials include polycarbonate, polymethyl methacrylate, polystyrene, polycarbonate / polystyrene copolymers, polyvinyl chloride, alicyclic polyolefin, polymethylpentene, and other thermoplastic resins, thermosetting resins, ultraviolet curable resins, and visible materials. Examples thereof include synthetic resins such as photo-curing resins, ceramics such as soda lime glass, aluminosilicate glass, borosilicate glass, and quartz glass. Of these, polycarbonates excellent in moldability and productivity are often used.

  Here, an optical disk substrate made of polycarbonate having a diameter of 12 cm and a thickness of 1.1 mm having pits on one side was manufactured by an injection molding method using the optical disk stamper disk B manufactured as described above.

  After the optical disk substrate is peeled from the optical disk stamper board B, a functional layer such as a reflective layer is formed on the disk substrate by a known method such as sputtering or vapor deposition. As the material of the reflective layer, Al (aluminum), Au (gold), Ag (silver), Cu (copper), Ti (titanium), Cr (chromium), Ni (nickel), Ta (tantalum), Mo (molybdenum) ), Fe (iron), Zn (zinc), Ga (gallium), As (arsenic), Pd (palladium), etc., alloys of these metals, alloys of these metals with these metals, metal oxides, metals Examples thereof include a mixture of metal compounds such as nitride, metal carbide, metal sulfide, and metal fluoride. Among these, metals or alloys such as Al, Au, and Ag have both high reflectance and thermal conductivity, and are particularly suitable as a material for the reflective layer. In addition to the reflective layer, the functional layer includes an optical adjustment layer that adjusts the irradiated laser light, a radiation layer that improves the heat cooling capability of the laser light, a diffusion prevention layer that prevents diffusion of constituent elements between the layers, etc. May be appropriately formed as necessary to form a multilayer.

  Here, a reflective layer made of an Ag alloy having a thickness of 30 nm was formed on the surface of the disk substrate having pits by a sputtering method.

  An optical disk is produced by forming a protective layer on the functional layer. As a method for forming the protective layer, it is preferable to apply a photo-curing resin such as an ultraviolet-curing resin to a predetermined thickness and then cure, but a substrate or film of the same material as the disk substrate is bonded. May be formed.

  Here, after the ultraviolet curable resin was applied with a predetermined thickness, it was cured by irradiating with ultraviolet rays to form a protective layer having a thickness of 0.1 mm. As a result, an optical disk having a thickness of 1.2 mm and a diameter of 12 cm was obtained.

  Each optical disk obtained as described above from the optical disk master of the example with Tt = 1.3T to 2.0T was obtained by using ODU1000 (reproduction light wavelength 405 nm, objective lens numerical aperture NA 0.85) manufactured by Pulstic Industries, Ltd. The reproduction characteristics of the information signal formed on each optical disk was evaluated under a reproduction light power of 0.5 mW, and the C / N (Carrier to Noise ratio) was measured using a spectrum analyzer manufactured by Advantest. Shown in a). As is clear from FIG. 6A, Tt = 1.7T was the most stable and high C / N.

  Here, in order to evaluate the reproduction characteristics of the information signal formed on the optical disk obtained as described above, an optical disk using silicon as a substrate was manufactured as a comparative example.

  FIG. 4 is a diagram for explaining an optical disc master of a comparative example.

  First, as shown in FIG. 4A, for example, a disk-shaped silicon substrate 30 having a diameter of about 200 mm and a thickness of about 0.7 mm was precisely polished, and then washed and dried.

Next, as shown in FIG. 4B, the atomic weight ratio of ZnS (zinc sulfide): SiO ₂ (silicon oxide) = 80: 20 is 100 nm in thickness on the silicon substrate 30 by sputtering in an Ar atmosphere. A base layer 31 of ZnS—SiO ₂ was formed.

Next, sputtering is performed in a mixed atmosphere of Ar and O ₂ using an alloy target of W and Mo, and as shown in FIG. 4C, an inorganic resist layer having a thickness of 60 nm made of an oxide of W and Mo. 32 was uniformly formed.

  Next, as shown in FIG. 4D, a laser beam 33 having a laser wavelength of 405 nm and an objective lens numerical aperture NA of 0.95 is output from the modulation signal generator using a general cutting machine for this optical disc master. Is condensed and irradiated through the objective lens 34, and a latent image 35 of pits corresponding to 2T (1T = 15.15 ns) defined by the shortest length is formed on the inorganic resist layer 32 at a density equivalent to BD. . As the cutting data, the same data as shown in FIG. 5 is used. Tt = 1.3T to 2.0T.

  In addition, the rotating linear velocity of the substrate during cutting was a constant linear velocity of 4.92 m / s, the light source feed rate was 0.32 μm, and the laser power was 11 mW at the maximum.

  Next, a developer was dropped on the inorganic resist layer 32 while rotating the optical disk master, and the inorganic resist layer 32 was developed as shown in FIG. As a result, an optical disc master A1 in which irregularities corresponding to digital signals to be formed on the optical disc substrate were formed.

  Next, as shown in FIG. 4F, a conductive film 36 such as a nickel film was formed on the concavo-convex pattern of the developed optical disk master A1 by, for example, electroless plating.

  Thereafter, the master for optical disk on which the conductive film 36 is formed is attached to an electroforming apparatus, and the conductive film is plated to have a thickness of, for example, about 300 ± 5 μm by an electroplating method. As shown in g), a plating layer 37 having an uneven pattern was formed. Thereby, a metal layer 38 composed of the conductive film 36 and the plating layer 37 is formed.

  Next, as shown in FIG. 4 (h), the metal layer 38 was peeled from the optical disc master. Thereafter, the metal layer 38 was trimmed to a predetermined size, and the inorganic resist adhering to the signal forming surface of the metal layer 38 was washed using, for example, acetone. Thus, the optical disk stamper board B1 was obtained.

  Next, a polycarbonate disk substrate having a diameter of 12 cm and a thickness of 1.1 mm having pits on one side was manufactured by an injection molding method using the optical disk stamper board B1 manufactured as described above.

  After the disk substrate was peeled from the optical disk stamper board B1, a reflective layer made of an Ag alloy having a thickness of 30 nm was formed on the disk substrate by a sputtering method.

  Next, after an ultraviolet curable resin was applied at a predetermined thickness, it was cured by irradiating with ultraviolet rays to form a protective layer having a thickness of 0.1 mm. As a result, an optical disk having a thickness of 1.2 mm and a diameter of 12 cm was obtained.

  Using the ODU1000 (reproduction light wavelength 405 nm, objective lens NA 0.85) manufactured by Pulstic Industrial Co., Ltd. for the optical disk obtained in the comparative example, evaluation of reproduction characteristics of information signals formed on each optical disk under the condition of reproduction light power 0.5 mW FIG. 6 (b) shows the result of the C / N (Carrier to Noise ratio) measurement performed using a spectrum analyzer manufactured by Advantest Corporation. As is clear from FIG. 6B, the comparative disk obtained the most stable high C / N at Tt = 1.8T.

  Further, as shown in FIG. 6A, the highest C / N of the optical disk obtained in the example is 48.9 dB (Carrier: −34.1 dB, Noise: −83.0 dB), and FIG. As shown, the optical disk obtained in the comparative example had the highest C / N of 47.9 dB (Carrier: -34.1 dB, Noise: -82.0 dB).

  When the result of said C / N measurement is seen, compared with the master disk obtained using the silicon substrate of the comparative example, the master disk using the glass substrate of the example has the same or better result. That is, in the example, C / N = 48.9 dB is obtained with a value of Tt = 1.6T, whereas the comparative example side finds the optimum value of Tt even if Tt = 1.7T, 1.8T. In this case, C / N is 47.9 dB, and the value of C / N is lower than that of the example. From this, it can be said that the optical disk obtained in the example can obtain a high C / N when the Tt is optimized.

  Regarding the carrier level, since the same inorganic resist was used, it is considered that there is no difference, and it can be said that the shape of the pits was the same. Conventionally, a silicon substrate has been used because it has a higher cooling effect than a glass and can form a steep temperature distribution, so that the shape of the pit is improved. The present invention provides a high thermal conductivity not possessed by glass in the first underlayer, a cooling effect equivalent to that of a silicon substrate is obtained, a pit shape is good, and an equivalent carrier level is obtained.

  Looking at Noise in the breakdown of C / N, it is -83.0 dB in the present example while it is -82.0 dB in the comparative example, and 1 dB noise is reduced in this example. Reasons for obtaining good characteristics include that the Ag used for the underlayer has high thermal conductivity, and that the surface has good smoothness when made into a thin film, and the smoothness of the master disk It is thought that the Noise level decreased due to the increase. That is, since Carrier is dominated by the pits in the inorganic resist layer, there is no difference. However, since the noise level is reduced, it is considered that a higher C / N can be obtained than before.

  Also, in the manufacturing process, the plating layer was peeled off from the optical disc master, and in the examples the glass was used for the substrate, so the master was never broken. At that time, there were many cases where silicon could not withstand the stress applied to the master and cracked.

  Next, in the optical disk master using the glass substrate, the thickness of the Ag layer as the first underlayer was changed to 0 nm, 25 nm, 50 nm, and 75 nm, and an optical disk was manufactured in the same process as above. Similarly to the case of the Ag layer having a thickness of 100 nm in the above example, Tt = 1.3T to 2.0T.

  Each of the obtained optical disks was evaluated using the ODU1000 (reproduction light wavelength 405 nm, objective lens NA 0.85) manufactured by Pulstic Industrial Co., Ltd., to evaluate the reproduction characteristics of information signals formed on each optical disk under the condition of a reproduction light power of 0.5 mW. The C / N (Carrier to Noise ratio) was measured using a spectrum analyzer manufactured by Advantest Corporation. The measurement results are shown in FIG.

  FIG. 7B shows the measurement result of the optical disk obtained with the Ag layer (first underlayer) = 0 nm of the optical disk master. According to FIG. 7B, the highest C / N is obtained at Tt = 1.3T and 1.4Tsdq.

  FIG. 7C shows the measurement results of the optical disk obtained when the Ag layer of the optical disk master is 25 nm. According to FIG.7 (c), the highest C / N is obtained in Tt = 1.6T-1.7T.

  FIG. 7 (d) shows the measurement results of the optical disk obtained when the Ag layer of the optical disk master is 50 nm. According to FIG.7 (d), the highest C / N is obtained in Tt = 1.7T-1.8T.

  FIG. 7 (e) shows the measurement results of the optical disk obtained when the Ag layer of the optical disk master is 75 nm. According to FIG.7 (e), the highest C / N is obtained in Tt = 1.7T-1.8T.

  FIG. 7A is a plot of the best C / N obtained from the disk measurement result of the thickness of each Ag layer.

According to FIG. 7A, the C / N obtained when the thickness of the Ag layer is 25 nm is 48.7 dB, which is 0.8 dB better than 47.9 dB which is the C / N of the comparative example. Have been gained.
The C / N obtained when the thickness of the Ag layer is 50 nm, 75 nm, and 100 nm is 48.9 dB, which is 1.0 dB better than the 47.9 dB C / N of the comparative example. Yes.
That is, the C / N obtained when the thickness of the Ag layer is 25 nm, 50 nm, 75 nm, and 100 nm is higher than the C / N obtained in the comparative example. On the other hand, it is desirable that the C / N value be as high as possible in order to improve data errors during recording and reproduction.
As is clear from this, the thickness of the Ag layer is preferably 25 nm to 100 nm in order to obtain high C / N, and 50 nm to 100 nm in order to obtain better data.

  By setting the film thickness to produce a steep temperature gradient, a high C / N value can be obtained, leading to improvement in recording density (high density recording). Further, as shown in FIGS. 7C, 7D, and 7E, the value of N (noise) when the Ag film is formed in the embodiment is stably low regardless of the value of Tt. It has a value and a small Tt value can be set, and a high-definition pattern can be formed.

  From the above, according to the present invention, it is possible to provide an optical disc master that is easy to handle and can form a high-definition uneven pattern by exposing an inorganic resist layer.

It is a figure which shows the structure of one Example of the optical disk original disc based on this invention. It is a figure which shows the structure of the optical disk original disk in which the unevenness | corrugation formed by cutting one Example of the optical disk original disk which concerns on this invention was formed. It is a figure which shows the structure of the optical disk stamper board used for shaping | molding of the optical disk board | substrate produced using the optical disk original disk of an Example. It is a figure for demonstrating the optical disk original disc of the comparative example produced using the substrate for silicon | silicone. It is a figure which shows the cutting data of an Example. It is a figure which shows the measurement result of C / N (Carrier to Noise ratio) with the optical disk obtained from the Example and the comparative example. It is a figure which shows the result of having measured C / N of the optical disk obtained from each Example which changed the thickness of the 1st base layer. It is a figure for demonstrating the conventional optical disk master.

Explanation of symbols

A Master disc for optical discs with concavo-convex pattern
B Stamper board for optical disc
10 Substrate
11 First underlayer
12 Second underlayer
13 Inorganic resist layer
14 Laser light
15 Objective lens
16 Latent image
17 Conductive film
18 plating layer
19 Metal layer
20 substrates
21 Photoresist layer
22 Laser light
23 Objective lens
24 latent image
25 First metal layer
26 Second metal layer
27 Metal layer
30 substrates
31 Underlayer
32 Inorganic resist layer
33 Laser light
34 Objective lens
35 latent image
36 Conductive film
37 plating layer
38 metal layers

Claims (2)

A substrate whose surface is polished;
A first underlayer formed on the polished surface of the substrate;
A second underlayer formed on the substrate so as to cover the first underlayer;
An inorganic resist layer formed on the second underlayer;
An optical disc master having
The first underlayer is an underlayer having a higher thermal conductivity than the substrate;
The optical disc master, wherein the second underlayer is an underlayer that is less soluble in an alkaline solution than the first underlayer.   2. The optical disc master according to claim 1, wherein the substrate is a substrate made of glass or synthetic resin.

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