MXPA01000014A - Optical disk and method of manufacture thereof - Google Patents

Abstract

A high-capacity optical disk, such as of 15 GB or greater, is provided. The optical disk comprises an optical disk substrate (3) on which lines of pits (2) corresponding to the record signals are formed;a reflective coating (4) covering the surface of the optical disk substrate (3) where lines of pits (2) are formed;and a transparent layer (5) formed on the reflective coating (4). For reading or reproduction, a laser beam of 350- to 420-nm wavelength is emitted through the transparent layer (5) on the surface to read the signals recorded as lines of pits. The pits are of 80 nm to 250 nm in length and width as viewed from the transparent layer side where the laser beam for reproduction is incident. The thickness of the reflective coating is less than 20 nm, for example, 8 nm or more.

Description

OPTICAL DISC AND MANUFACTURING METHOD OF THE SAME TECHNICAL FIELD The present invention relates to an optical disc which can increase its recording density and a manufacturing method thereof. BACKGROUND OF THE ART A conventional optical disk, eg, DVD (Digital Versatile Disk) is formed so that, as shown in its cross section of FIGURE 6, a reflection film 102 having a thickness of several tens of nanometers, for example, a thickness of 50 nm, is formed on a light transmitting substrate 101 having a recording portion of signal 100 in which successive pits are formed and a protective layer 103 made of an organic material having a thickness, for example, of about 10 μm, and covers the surface of the reflective film. To read a signal from this DVI, a reproducing laser light 105 is irradiated on the signal recording portion through an objective lens 104 from the side of the light transmitting substrate 101, and impinges on the signal recording portion 100, and it is detected, that is, the recorded data is read by the reflected light of the reproducing laser light. In the case of an ordinary DVD, since the disc substrate has a thickness of 0.6 mm and a signal is reproduced through this substrate of the disc 101, the numerical aperture NA of a target lens that includes a reproduction detector is restricted to about 0.6. By the way, the size of the point of the reproductive light is in proportion to a ratio? / N. A. between a wavelength (of the reproducing laser light 105 and an N.A. of the objective lens 104). In the conventional ordinary DVD, the wavelength of the reproductive light is 650 nm; N.A. is 0.6; and one side of the disk has a recording capacity of 4.7 GB. For example, consider an optical disk which is reproduced by a reproductive laser light that has a wavelength? 400 nm through an objective lens having a numerical aperture N. A. of 0.85. Then, the recording capacity of one side of this optical disk can be calculated simply as 25 GB based on the ratio of this disk to the 17D mentioned above. However, the recording capacity thus calculated is obtained in consideration only of the characteristics of the reproduction detector. In practice, the size of the hole in the optical disc must also be made miniscule and with great precision. A method of manufacturing an ordinary optical disk is as follows. As shown in FIGURE 7, on a glass disk having a diameter of about 200 mm and a thickness of several millimeters and whose surface was precisely polished, a photoresistant layer 107 having a film thickness of about 0.1 μm, in which a photoresist sufficiently sensitive to a wavelength of the source of recording laser light 107 of a laser cutting apparatus is deposited by rotation. This photoresistant layer 107 is subjected to an exposure. When this exposure is carried out, a pattern exposure is employed in which the laser light 109 having a wavelength of 413 nm from a recording laser light source 108 is e.g. Kr, is modulated by on / off by means of an optical acoustic modulator, this being, AOM 110 in response to a recording signal and focused to irradiate the photoresistant layer 107 through an expander 111 and an objective lens 112, causing this point of laser light to move on the photoresist layer 107 spirally to form latent images of pits and grooves. Hereinafter, while this photoresistant layer 107 is revealed by means of an alkaline developer, the exposed portion dissolves, and a master disk 121 is formed, as shown in FIGURE 8, in which an uneven pattern 120 comprising holes and grooves is formed on the photo-resistant layer 107 that covers the disc 106. Then, on this uneven pattern 120 of this master disc 121, as shown in FIGURE 8, a metallic layer 122 having a thickness of about 300 nm is deposited by non-electrical sequential process of nickel plating and electrolytic coating (Ni) so that this uneven pattern is filled. Then, this metallic layer 122 is detached from the optical disk 121, and a die 123 is obtained having an inverted version of the unequal pattern 120 of the master disk 121 of the metal layer 122. This die 123 is disposed within, for example, a die of injection molding to produce the substrate of the optical disk 101 made of polycarbonate (PC) or the like. As shown in FIGURE 9. On this substrate of the optical disc 101, the uneven patterns of the die 123 are transferred, this being, the holes and grooves corresponding to the uneven pattern of the master disc are formed, thereby causing the recording section signal 100 shown in FIGURE 6. On this substrate of optical disk 101 on its surface in which the signal recording portion 100 is formed, the reflection film 102 shown in FIG. 9 is deposited as shown in FIG. FIGURE 6 by splashing using aluminum (Al) 124 as an objective for example. In addition, the protective film 103 is formed on this reflection film. This protective film 103 is generally made of ultraviolet light curable resin cured by ultraviolet irradiation after curing the resin with ultraviolet is applied to the reflection film 102 by rotating coating in order to have a uniform thickness. Since the limit of the numerical aperture of the objective lens 112 is generally 0.9, the optical disk thus obtained after producing the master disk by the pattern exposure effect by laser light having a wavelength of 413 nm will have successive pits formed on it, which have a shorter hole length of 0. 4 μm and the track inclination of 0.74 μm. In addition, the width of the hole, being this, the length along the radial direction of the disk is about 0.35 μm which is half of 'the inclination of the track. Due to such restrictions imposed on the size of the hole when it is made small and with high precision, the size of the hole can not be as small and with high precision dicrià ³ that an optical disc that has a recording capacity of, for example, 15 GB or more, in particular 25 GB can be obtained by conventional pattern exposure using laser light having a wavelength of 413 nm. PRESENTATION OF THE INVENTION The present invention provides an optical disk and a manufacturing method which can provide high density recording, this being, which can provide the aforementioned recording capacity of, for example, 15 GB or recording capacity greater than, say, 25 GB. An optical disk according to the present invention may comprise an optical disc substrate in which successive pits corresponding to a recording signal are formed, a reflection film on this substrate of the optical disk on its surface that the successive pits are formed and a light transmitting layer formed on this reflection film. When a recording signal is read, this being reproduced from this optical disc, a signal recorded in the successive pits is read from the optical disc by irradiating short wavelength laser light having a wavelength of 350 nm to 420 nm on the side of the light transmitting layer formed on the surface of the optical disk. Additionally, when the optical disk is viewed from the transmitting side of light irradiated by reproducible laser light, the successive pits contain holes having a width and a length ranging between 80 and 250 nm, and the thickness of the reflecting film is selected to be of 20 nm or less, for example, 8 nm greater. The method of manufacturing the optical disk according to the present invention is the manufacturing method for producing the optical disk described above according to the present invention, comprising the steps of producing a master disk of the optical disk forming successive pits using laser light that has a wavelength between 200 nm and 370 nm for exposure in response to a recording signal, producing an optical disc substrate in which successive pits contain pits having a width and a length between 80 nm and 250 nm are formed by transfer of the successive pits of this master disk by forming a reflective film having a film thickness of 20 nm or less on the substrate of the optical disc and its surface on which the successive pits are formed. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic cross-sectional view of an example of an optical disc according to the present invention. FIGURE 2 is an enlarged cross-sectional view of pits of an optical disc according to the present invention. FIGURE 3 is a diagram showing results of background vibration values of a reproducing signal obtained when a film thickness of a reflective film Al is varied as a parameter. FIGURE 4 is a diagram of an arrangement of an example of a laser cutting apparatus. FIGURE 5 is a diagram of optical tracks showing an optical auto-focusing system of an example of laser cutting apparatus. FIGURE 6 is a cross-sectional view of an optical disc according to the prior art. FIGURE 7 is a diagram of an array of a laser cutting apparatus for producing a master disk for manufacturing an optical disk according to the prior art. FIGURE 8 is a diagram to explain the manner in which a die is produced from the manufacturing master disk for an optical disk. FIGURE 9 is a diagram for explaining a method of manufacturing an optical disc. PREFERRED MODE OF THE INVENTION An optical disk 1 according to the present invention comprises, as shown in a schematic cross-sectional view of this example in FIGURE 1, an optical disc substrate 3 having a thickness of 1.1 mm for example, in which successive pits are formed containing holes 2 corresponding to a recording signal, a reflective film 4 formed in this optical disc substrate 3 on its surface in which the holes 2 are formed and a light transmitting layer 5 formed on this reflective film 4. When a recorded signal is read, this being , reproduced from this optical disc 1, a recorded signal as the successive pits is read from the optical disc by irradiating it with a laser light of short wavelength having a wavelength between 350 and 420 nm from the side of the light transmitting layer 5 formed on the surface of the optical disc. Additionally, when this optical disk is viewed from the side of the light transmitting layer 5 irradiated by laser reproductive light, the successive pits contain the holes 2 having a length and a width between 80 nm and 250 nm. The reflective film 4 is made of one or more materials of aluminum (Al), silver (Ag) and gold (Au) or of two or more types of alloys of these materials. The thickness of the reflective film is selected to be 20 nm or less, and with a reflectivity of the reflective film is selected to be 15% or greater. If the thickness t of the light transmitting layer 5 is selected between 10 μm and 177 μm, for example 100 μm (0.1 mm), then a detector uses a laser light of short wavelength as a laser light, for example, violet laser light of a GAN-based laser having a short wavelength, for example, a wavelength between 350 nm and 420 nm and which also uses a target lens having a numerical aperture, for example, of 0.85 which will be able to ensure a disk deviation, this being the so-called deviation margin. In other words, according to the optical disc of the present invention, because the optical disk is arranged so that a signal is not read by irradiating laser light from the thick substrate side of the optical disk having a thickness of 0.6 mm for example, as in the past, but a signal is read by irradiating reproducing laser light from the side of the light transmitting layer 5 which has a considerably thin thickness of 0.1 mm for example, it is possible to use a target lens having a numerical aperture of 0.85 for example, and a laser point can be reduced in size, which in turn increases the recording density of an optical disc. Unfortunately, if the holes are made small as described above, then when the same reflective film is formed in the conventional manner, a good quality signal can not be reproduced from the optical disc. The reason for this is as follows. If an EFM signal (Modulation between Eight and Fourteen) is recorded as successive holes that have a length of short flush pit of 220 mm and a track inclination of 410 mm and having about 15 GB, as a recording capacity on one face of the optical disk, then when a conventional AL reflective layer having a thickness of about 30 nm is formed, the interior of the holes are filled with this reflective film by an amount corresponding to the thickness of this reflective film so that the size of the hole when the holes are viewed from the side of the light transmitting layer 5 can not be adjusted to the aforementioned target size. As shown in FIGURE 2, for example, if the reflective film 4 has a cross section with an angle of inclination? relative to the major surface 3a of the substrate of the optical disk 3 in which the hole 2 is formed and this reflective film 4 having a thickness T is formed on the surface of the wall, the bottom surface and the larger surface of the hole 2 By splash, for example, then the effective length B of the hole when the holes are observed from the side of the light transmitting layer 5 irradiated by the reproducing laser light after forming the reflective film can be calculated based on the thickness of the film T of the reflecting film 4 and the length A of the bottom surface of the hole as: B = A - 2 • T • tan (? / 2) The angle of inclination? falls generally within the range of approximately 40 ° to 80 °. Additionally, the length A of the bottom surface of the hole is considerably small in the shortest hole due to the angle of inclination?. Therefore, if the depth of the hole, for example, is assumed to be 90 nm and the angle of inclination is assumed to be 60 °, then the above-mentioned length will be about 120 nm in the direction of the track and close 100 nm in the radial direction of the disk.

Accordingly, if the reflective film has a thickness of 30 nm and above, then the value of the effective hole size B will be 85 nm in the direction of the track and 65 nm in the radial direction of the optical disk. Therefore, the value of the effective size of the hole will inevitably decrease to approximately 1/3 of the appropriate hole size mentioned above. However, the longest hole that has a length of about 3.7 times the length of the shortest hole can also cause a similar hole reduction effect. In this case, the reason for reducing the hole length in the direction of the track will be about 75% relative to the appropriate hole length. If the length of the hole deviates from the appropriate size and the imbalance of the longest and shortest length occurs, then a reproduced signal is affected by that deviation and becomes unbalanced so that the vibrations are greatly increased. In contrast, according to the optical disk of the present invention mentioned above, the vibrations can be prevented from increasing by making the thickness of the reflective film 4 equal to or less than 20 nm. Therefore, in the optical disc according to the present invention the disadvantages can be avoided that the successive holes in which each hole of very small size equal to or less than 250 nm is filled with the reflective film 4 so that the reproduced signal remains deteriorated, when the recorded data is reproduced from the optical disc by irradiating it with laser light from the side of the reflective film 4 formed in the signal pits. FIGURE 3 shows measured results of background vibration values of a reproduced signal obtained when the thickness of the AL film as a parameter is varied to 15 nm, 20 nm and 30 nm respectively, using the optical disc in which successive pits they are formed by the signal EFM equivalent to the current recording density of 15 GB. In this case, the optical disk has said structure that a signal is read from the optical disk by irradiation with laser light from the side of the light transmitting layer., and the thickness of the film of the light transmitting layer 5 was selected as 100 nm. In this case, although the optical reproductive system used the wavelength of 352 nm, the N.A. was selected as 0.94. Typically, the horizontal axis in FIGURE 3 represents the asymmetry of the reproduced signal, and the vertical axis of it represents the value of vibration. As is evident in FIGURE 3, when the thickness of the film of the Al reflective film is 30 nm as in the prior art optical disc, the value of the background vibration is increased approximately up to 10%, which makes the signal quality unsatisfactory. However, when the thickness of the film is 20 nm or less, the value of the vibration becomes approximately 8%. When the thickness of the film is decreased to 15 nm, a vibration level of 6% satisfactory can be obtained. However, if the thickness of the film is progressively decreased in order to prevent the shortest hole from being filled with the reflective film, then the reflectance of the substrate of the optical disc 3 is decreased with the result that the S / N of the reproduced signal will deteriorate. From this point of view, the thickness of the film should preferably be selected as 8 nm or greater. Table 1 shows the dependence of the reflectance of the reading laser light (wavelength of 407 nm) on the surface of the reflective film of Al in the film thickness of the reflective film of Al. TABLE; 1 Film thickness (nm) 40 30 20 15 8 5 From the film Reflecting AL Reflectance (%) 88 82 67 43 15 8 From the description above, it can be seen that the optical disk having high recording capacity of 15 GB or greater in which the film thickness is within the range between 8 nm and 20 nm and the reflectance is 15% or greater is able to provide a reproduced signal of good quality. Additionally, as described above, the reflective film 4 of the optical disk according to the present invention can be manufactured from, in addition to Al which is widely used, metallic materials which have high reflectance to a thin film thickness, such as Au (gold) and Ag (silver), or alloys of materials of two or more types of these metals, or alloys of metallic materials in which Ti (titanium) or the like is added to these respective materials. Additionally, the optical disc according to the present invention can be formed as so-called optical disc types for various recordings by arranging a signal recording film such as a phase change film hec. of, for example, GeSb, Te or similar, between the reflective film 4 and the light transmitting layer 5. Furthermore, the optical disk according to the present invention can be modified to an optical disk having the so-called muLti-layer structure. forming two or more layers of the reflective film 4 and the signal recording film, or two or more layers of only the signal recording film of the present invention. For example, by laminating the signal recording films each having the successive pits through reflecting films having a required reflectance, an optical disc can be formed, in which the recorded signals are reproduced from respective signal recording films by means of a suitable method such as focusing a reproducing laser light on the respective signal recording films during playback. A method for manufacturing an optical disk according to the present invention will be described below. This manufacturing method is to obtain the optical disc according to the present invention described above, including successive pits which contain pits having length and width between 80 nm and 250 nm. In the method of manufacturing the optical disk according to the present invention, the optical disk is manufactured by the process of producing a master disk for manufacturing an optical isolate in which successive holes are formed per exposure corresponding to a recording signal using light laser having a wavelength between 200 nm and 370 nm, producing an optical disc substrate having successive pits containing pits with a length and a width between 80 nm and 250 nm by transferring successive pits of this master disc and forming a reflecting film having a film thickness of 20 nm or less on this optical disc substrate on its surface in which the successive pits are formed. The exposure process for producing the master disc in the manufacturing method according to the present invention takes place using the laser cutter apparatus. An example of this laser cutter apparatus will be described below with reference to a schematic diagram of FIGURE 4. Although this laser cutter apparatus uses short wave recording laser light, its fundamental arrangement may be based on a conventional laser cutting apparatus. This apparatus is provided with a laser light source recorder 20 which can generate laser light with a wavelength of 266 nm for example. This laser light source recorder 20 comprises a solid state laser 21, a phase modulator 22, an external resonator 23 and an anamorphic optical system 24. The solid state laser 21 comprises a YAG laser (yttrium aluminum garnet) (length g 1064 nm wave), for example, and a SHG (secondary harmonic generator) to generate laser light having a wavelength of 532 nm by converting the laser light of the laser mentioned above to the double wave laser light of this laser solid state 21 is introduced through the phase modulator 22 to the external resonator 23. This external resonator 23 includes a wavelength conversion optical crystal 25 made of, for example, a BBO crystal (β-BaB; 04) having sufficient light transmissivity to the high ultraviolet region to convert the overhead laser light into dual wave laser light having a wavelength of 266 nm as well as an optical resonator forming a predetermined resonator length by means of mirrors Ml and M4, for example. As illustrated, the mirrors Ml and M4 are formed of mirrors having the necessary reflectance and necessary transmissivity. The mirrors Ml and M4 are formed of mirrors having a reflectance of, for example, close to 100%. In addition, a mirror, for example, mirror M3 can be moved and adjusted by an electromagnetic device 26 having the structure of the so-called VCM (voice coil motor) for example, thereby allowing the length of the resonator to be controlled. Then, the light passing through the mirror Ml, for example, is detected in this resonator by means of a photo-detector 27 such as a photo-diode PD, and the actuator 26 is controlled by the output of this photo-diode . Therefore, the servo-control is performed to provide an optimum resonator length, this being the resonance wavelength, and a laser light with a wavelength of 266 nm can be obtained based on wavelength with oscillation of stable continuous wave of high production. Then, the laser light derived from the external resonator 26 is reformed in its beam shape by means of the amorphous optical system 24. In this way, a laser light 50 can be derived from stable continuous oscillation of several tenths of milliwatts having a wavelength 266 nm from a recording laser light source 20. Then, the laser light 50 obtained from this recording laser light source 20 is separated by the beam splitter 28, for example, a part of the laser light is supplied to a photo-detector 29 such as a photo-diode, in which power or similar of the laser light 50 is viewed. The other part of the laser light, which is separated by the separator 28, is focused by a lens capacitor 30 and then introduced into a modulator 31 such as the AOM where it is modulated in response to the recording signal. The laser light thus modulated is introduced through a collimator lens 34 and 35, and expanded by this beam expander 36 and introduced into an objective lens 37 as a beam point of a diameter several times the size as the diameter of the entrance pupil . The reference numeral 40 indicates a mirror for directing laser light from the beam expander 36 to an objective lens 37. The laser light thus focused by the objective lens 37 is irradiated on a resistor disk 39, the which is installed a rotary table 38 by a high precision rotating air spindle, to obtain a master disk for optical disk manufactara. The resistor disk 39 rotates about a central axis when rotating the turntable 38. This resistor disk 39 has such a structure that a photosensitive photoresist layer at the wavelength of the laser light 50 is precoated on a substrate. which forms the master disk, for example, a glass disk. Then, the laser light 50 which is turned on or off in response to the recording signal by means of the aforementioned modulator, being this, exposure light is irradiated on the photo resistant layer of this resistance disc 39 with a point of 0.3 μm or less. On the other hand, the laser light cutting apparatus is provided with a moving optical table 41 which moves in the direction along a radial direction of the rotating table 38. On this moving optical table, it is mounted, for example, the beam expander 36 and the auto focus optical system to be described below although not shown. In this way, as this moving optical table 41 moves and the rotary table 38 is rotated, the exposure laser light moves on the photoresist layer of the resistive disc 39 spirally or annularly for example. On the other hand, a part of the laser light which passes through the collimator lens 32 mentioned above, and is separated by the beam splitter 33 is detected by a photo-detector 42 such as a photo-diode and thereby the modulated laser light is monitored. Light returned from the exposure laser light from the disk 39 passes through the beam splitter 33 and the track optics extended by the mirrors 43, 44, 45 or the like for example and is converged by a condenser lens 46, thereby causes the exposure laser light to be monitored, for example, by a CCD (charge coupled device) or surveillance camera 47 to monitor the exposure laser light. Then, the objective lens 37 is arranged to be constantly focused on the resistive photo layer of the resistive disk 39 under the control of the focusing server. An optical system of a self-focusing server means for executing this approach is located on the mobile optical table 41 mentioned above. FIGURE 5 shows a schematic arrangement of an example of the optical system of this self-focusing server means. The objective lens 37 is supported in such a way that it can be moved slightly in the direction of the optical axis by an actuator having for example VCM structures. In this case, the optical system comprises a self-focusing laser light source 61, optical lenses 62, 63, mirrors 64, 65 and a position detection device (PSD) 66. The laser light source 61 can be comprised of a semiconductor laser having a wavelength of 680 nm, to which a high-frequency over-position with a frequency of 400 MHz and a pulse rate of 50% is applied. The laser light 67 of this laser light source 61 is deviated relative to the optical axes of the optical systems of the lenses 62, 63 and irradiated on the resistance disk 39 through the objective lens 37. The light returned from said laser light it is detected by a position detection device (PSD) 66 through the mirror 65, and the actuator 60 is controlled by the detected output in order to move the objective lens 37 on its optical axis for focus control. Since the optical system of the focusing servo means thus adjusted does not use a polarized PBS beam splitter and a polarized optical system such as a QWP quarter-wave plate or the like as in the conventional conventional focusing server, the optical system of above is not limited by the numerical apertures of these optical elements and therefore the angle of deviation of the incident laser light on the objective lens 37 can be sufficiently increased. Specifically, a large aperture angle can be formed between the incident laser light 67a incident on the objective lens 37 of the laser light source 61 and the light returned from the focusing surface of the resistive disc 39 after passing through the lens objective 37, this being, incoming laser light 67b, whereby the output laser light 67a and the incoming laser light 67b can be completely separated from each other and the focusing state can be detected by the position detection device 66, thereby allowing a focus server signal to be obtained without failure. By making the optical system, as it were, a non-polarized auto-focus optical system, the angle of deviation of the incident laser light 67a in the objective lens 37 can be increased as much as possible, and the value of the incident height of the laser light in The objective lens can also be increased sufficiently. Accordingly, an optical gain expressed by an equation proportional to the above-described height of incidence of laser light with objective lenses can also be markedly increased compared to the conventional auto-focus optical system, which can greatly contribute to improvements in the characteristics of the auto focus system server. Specifically, in the position of the detector device in the auto focus system, there is, in addition to the original exposure laser light to be detected, which has returned through the objective lens after being reflected on the surface of the photographic layer. resistant of exposure, slightly expanded laser light (hereinafter referred to as laser light noise) which has not reached the surface of the photoresistant layer, but is reflected on the back surface of the objective lens, being this on the surface of the opposite side of the lens. Objective lens surface facing the photo-resistant layer. This laser light noise exerts a bad influence on the operation of the auto focus server as a component of the background noise of the detected output of the position detection device. Then, when this laser light noise interferes with the originally returned light, which must be originally detected, from the photoresistive cap to cause interference limits, the server characteristics are greatly deteriorated so that the occurrence of said limits of interference has a serious effect. In general, since the laser light on which the high frequency is not superimposed has a coherence length of several tenths of centimeters, an optical track difference between the returned light, which must originally be detected, of the photographic layer. Resistant and laser light noise caused by light reflected from the back surface of the objective lens falls near this range. Therefore, it is inevitable that the interference limits occur in the position of the detection device. These interference limits move the frequency at the position of the position detection device as the objective lens moves slightly on the optical axis of the objective lens, thereby causing the position sensing position of the originally returned laser light to be inaccurate. . In actual practice, if the auto-focus server is operated under the condition where the limit interference occurs, then the server will oscillate frequently. As a result, it is difficult to maintain a normal auto-focus operation. In contrast, when the above-mentioned laser light source 61 on which the high frequency of 400 MHz is superimposed, because the coherence of the length is sufficiently diminished, it is possible to avoid the originally returned (input) laser light 76b and the Noise of laser light caused by light reflected from the back surface of the objective lens that interfere with each other, thus allowing the occurrence of interference limits to be avoided. In other words, because only the laser light 76b that must originally be detected is projected onto the position of the detection device 66, the position of the cut-off point relative to the photoresistant layer can be detected accurately. Actually, in the case of the aforementioned fix, it was confirmed that the auto focus server barely oscillates so that the normal operation of the auto focus server can be maintained. The light cutting apparatus using the auto focus optical system described with reference to FIGURE 5 can perform the highly accurate stable auto-focus server operation. Therefore, this light cutting apparatus can constantly and stably perform cutting of a high density recording optical disk with high productivity.

Therefore, it is possible to produce a master disc for manufacturing an optical disc to obtain an optical disc substrate having successive pits with a recording density of 15 GB by means of this laser cutting apparatus. An example of the method of producing this master disk using the aforementioned laser cutter apparatus will be described in detail below. Initially, a glass disc is prepared which serves as a substrate to produce a master disc, having a diameter of about 200 nm and a thickness of several millimeters and whose surface is polished with high precision. A resistive disk 39 is then prepared in which the photo-resistant layer is made by uniform rotating coating in a thickness of about 0.1 μm sensitive to laser light with a wavelength of ultraviolet rays (wavelength: 266 nm) of the lu? above mentioned laser engraver 50 formed on the polished surface with high precision. Next, by means of the laser cutter apparatus described with reference to FIGURES 4 and 5, the laser light recorder 50 is focused on the resistance disk 39 by means of the objective lens 37 having a height NA of about 0.9 as a point of 0.3 μm or less in size. In this case, the laser light 50 travels the resistance disk 50 spirally or annularly as mentioned above while turning on and off the laser light flow in response to the recording signal of the AOM modulator 31 for example, with which form the latent images of uneven pattern of successive marOacs containing holes in which their length in the direction of the track and their width in the radial direction of the disc are within the range of 80 nm to 250 nm (exposure process) . The inclination of the track of the successive pits is selected between 150 nm and 450 nm. In the resistor disk 39 on which the latent images of the holes or slot pattern are formed as described above it is immersed in an alkaline developer and the exposed portion of the photoresist is dissolved, then the uneven patterns of the successive pits containing holes in which their length in the direction of the track and their width in the radial direction are within the range of 80 nm and 250 nm can be obtained on the resistance disk 39 (development process). In this way, a master insulation is produced for the manufacture of an optical disk on which the uneven pattern is formed according to the pattern of the photoresist layer. Then, a thin film of Ni (nickel) with a thickness of several hundred angstroms is deposited on this master disk by splash or non-electrolytic coating. The metal layer is then formed on this thin film which serves as a conductive film in the electrolytic coating, this metal layer is peeled off in the same manner described with reference to FIGURE 8, thereby making it into a Ni die having a thickness about 300 μm to be produced. The back surface of this Ni die is polished and the end face is machined (die manufacturing process). Next, this Ni die is disposed within a mold die and the injection molding, for example, of polycarbonate or the like is carried out. Therefore, the substrate of the optical disc 3 having a diameter of 120 mm for example, made of plastic material shown in FIGURE 1 is produced as a replica of the Ni die. On the signal recording portion on the substrate of the optical disc 3 thus produced, the uneven pattern is transferred based on the successive pits and grooves recorded by means of the aforementioned cut and containing the pits in which their length in the direction of The track and its width in the radial direction of the disc are within the range of 80 nm and 250 nm (transfer process). Subsequently, by means of the spraying apparatus, a reflective film 4 of AL is formed with a film thickness of 20 nm or less, for example, 15 nm, on the surface of the side of the signal recording portion where the holes or the groove pattern of the optical disc substrate 3 are formed (reflective film forming process). Furthermore, on this reflecting film 4, the light transmitting layer 5 having a thickness of about 0.1 mm is cured and formed by a rotating coating of ultraviolet light curable resin and ultraviolet ray irradiation (forming process of the transmitting layer). of light) . In this manner, the optical cisco 1 according to the present invention shown in FIGURE 1 is terminated. It is desirable that the diameter of the reproducing laser light spot 6 of the recording high density optical disc 3 according to the present invention manufactured by means of the aforementioned manufacturing method according to the present invention is selected within the range of 200 nm and 5C0 nm. Incidentally, concrete shapes and structures of the respective portions shown in the above-mentioned embodiment only illustrate an example of the modes for carrying out the present invention. It will be appreciated that the technical scope of the present invention should not be interpreted to a limited extent in these particular forms and structures. As described above, the optical disk according to the present invention comprises the substrate of the optical disk on which the successive pits corresponding to the recording signal are formed, the reflection film formed on the substrate of the optical disk on its surface which the successive pits are formed in the light transmitting layer in the reflection film, wherein the signal recorded as successive pits is read from the optical disc by irradiation of laser light from the side of the light transmitting layer. When the successive pits are observed from the side of the transmitter layer, the successive pits contain pits having a length and a width both having a range between 80 nm and 250 nm and the thickness of the film is selected as 20 nm or less. Therefore, even when successive holes of very small size of 250 nm or less are cut, it is possible to avoid filling the holes with the reflection film so that the reproduced signal will not deteriorate. Therefore, it is possible to obtain an optical disk with high recording density of excellent quality. Additionally, since the film is made of one or more types of aluminum, silver, gold or alloy materials containing these materials, using an optimum material as a reflective film material to reflect the laser light, it is possible to obtain reflective characteristics satisfactory as the reflecting film of the high density recording optical disc. Additionally, since the reflectance of the reflective film is selected to be 15% or greater, it is possible to reliably read the recorded information from the successive holes.

However, in the manufacturing method of the optical disc for manufacturing the optical disc by transferring the successive pits formed in the master disk by exposure in response to the recording signal on the optical disc substrate, because the disc manufacturing method Optical according to the present invention comprises the steps of exposing by laser light having the wavelength of 20 nm or more, to form the successive pits containing the pits with a length and a width within the range of 80 tm and 250 nm transferring the successive pits forming the reflective film having a film thickness of 20 nm or less on the substrate of the optical disk on its surface so that the successive pits are transferred, even when the successive pits are cut they are very small of less than 250 nm or less, the hoyes can be prevented from being filled with the reflective film so that the reproduced signal is not damaged. By el -.c, it is possible to manufacture high-density recording optical disc of good quality. Additionally, since the reflective film is made of one or more types of aluminum, silver, gold or alloy materials of materials containing these materials and the optimum material can be used as reflective film material to reflect the laser light, it is possible manufacturing the high density recording optical disc in which the reflective film has satisfactory reflection characteristics. Additionally, since the reflectance of the reflective film is selected to be 15% or greater, it is possible to manufacture the high density recording optical disc in which the recorded information can be read from the successive pits.

Claims (15)

1. CLAIMS An optical disc comprising an optical disc substrate in which successive pits corresponding to a recording signal are formed, a reflective film formed on said optical disc substrate on its surface so that successive pits are formed and a transmitting layer is formed. light formed on said reflective film, wherein a signal recorded as said successive pits is read by irradiating with laser light having a wavelength between 350 nm and 420 nm, characterized in that when the successive pits are observed from the side of said transmitter layer of light, said successive pits contain pits having a length and a width between 80 n and 250 nm and said reflective film has a thickness selected to be 2C nm or less. An optical disk according to Claim 1, which comprises a signal recording film such as a phase change film between the reflective film and the light transmitting layer. An optical disk according to Claim 2, wherein the reflective film and / or the recording film is formed as two or more layers. An optical disk according to Claim 1, wherein said reflective film is made of two or more types of aluminum, silver and gold materials or two or more types of alloys of materials thereof. An optical disk according to Claim 2, wherein said reflective film is made of one or more types of aluminum, silver and gold materials or two or more types of alloys of materials thereof. 6. An optical disk according to Claim 3, wherein said reflective film is made of one or more types of aluminum, silver and gold materials or two or more types of alloys of materials thereof. 7. An optical disk according to Claim 1, wherein said reflective film has a reflectance selected to be 15% or greater. 8. An optical disk according to Claim 2, wherein said reflective film has a reflectance selected to be 15% or greater. 9. An optical disk in accordance with Claim 3, wherein said reflective film has a reflectance selected to be 15% or greater. 10. An optical disk according to Claim 4, wherein said reflective film has a reflectance selected to be 15% or greater. 11. An optical disk according to Claim 5, wherein said reflective film has a reflectance selected to be 15% or greater. 12. An optical disk according to Claim 6, wherein said reflective film has a reflectance selected to be 15% or greater. 13. A method of manufacturing an optical disk comprising the steps of: producing a master disk for manufacturing an optical disk to form successive holes by exposure corresponding to a recording signal using laser light having a wavelength between 200 nm and 370 nm; producing an optical disc substrate in which successive pits are formed containing pits having a length and a width between 80 nm and 250 nm by transfer of said successive pits of said master disk; and forming a reflective film having a thickness of 20 nm or less er. said optical disc substrate on said surface in which the successive pits are formed. 14. An optical disc manufacturing method according to claim 13, wherein said reflective film is made of one or more types of aluminum, silver and gold materials or alloys of materials containing these materials. 15. An optical disc manufacturing method according to claim 13, wherein said reflective film has a reflectance selected to be 15% or greater.