Patent Publication Number: US-2004051052-A1

Title: Method for manufacturing original disk for recording medium, and stamper manufacturing method

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to a method of manufacturing original plate used for manufacturing a recording medium, e.g., an optical recording medium, and a method of manufacturing stamper.  
       BACKGROUND ART  
       [0002] Optical discs as optical recording medium adapted so that at least either one of audio data, video data and computer data, etc. is to be recorded, or has been recorded are widely used. As the optical disc, when roughly classified, there are optical disc of the reproduction (playback) only type and recordable disc. As the recordable type optical disc, there are write-once type optical disc which can record either one of the above-described data, but cannot carry out erasing (rewrite) operation, and erasable (rewrite) type optical disc which once records either one of the above-described data thereafter to have ability to carry out erasing (rewrite) operation.  
       [0003] These optical discs include a disc base (substrate)  201  having light transmission property such as polycarbonate, etc. as shown in FIG. 1, even if they are optical discs of either types of reproduction (playback) only type and recordable type. One surface of the disc base (substrate)  201  is caused to be a so called signal recording surface  201   a , and the other surface is caused to be an incident surface  201   b  on which laser beams as light beams for recording or reproduction are incident.  
       [0004] In the case where the optical disc is recordable type optical disc, concentrical or spiral grooves  211  are formed from the inner circumferential side toward the outer circumferential side as shown in FIG. 2A at the signal recording surface  201   a  of the disc base (substrate)  201 . In the case where the optical disc is the write-once type optical disc, recording layer consisting of organic pigmental material, reflection layer and protective layer are laminated in order so as to cover the grooves  211 . In the case where the optical disc is erasable (rewrite) type optical disc, recording layer consisting of phase change optical recording material or magneto-optical recording material, reflection layer and protective layer are laminated in order so as to cover the grooves  211 .  
       [0005] It is to be noted that track pitch P of the optical disc shown in FIG. 2A is distance from the falling wall portion of a certain groove  211  to the falling wall portion of the next groove  211 .  
       [0006] In the case where the optical disc is optical disc of the reproduction only type, recording track consisting of plural pits  212  is formed as shown in FIG. 2B at the signal recording surface  201   a  of the disc base (substrate)  201  constituting this optical disc. This recording track is spirally formed from the inner circumferential side toward the outer circumferential side of the disc base (substrate)  201 . Reflection layer and protective layer consisting of metallic material such as aluminum or gold, etc. are laminated so as to cover the pits  212  on the signal recording surface  201   a  of this disc base (substrate)  201  so that the optical disc of the reproduction only type is formed.  
       [0007] Read-out of data recorded in advance at the optical disc constituted as described above is carried out by irradiating laser beams for reproduction from the incident surface  201   b  side of the disc base  201  onto the signal recording surface  201   a  so that such laser beams are caused to be in focus state by object lens (objective) to detect laser beams reflected by the recording layer or the reflection layer. In order to record data onto the optical disc, laser beams for recording are irradiated from the incident surface  201   b  side of the disc base  201  onto at least the recording layer so that such laser beams are caused to be in focus state by object lens to record data with respect to at least either one of grooves  211  or so called land portions between grooves  211  along the grooves  211 .  
       [0008] Meanwhile, with a view to realizing high recording density of data to be recorded onto optical disc, a method of shortening wavelength of laser beams emitted from semiconductor laser, which are used for recording data onto the optical disc or reproducing data recorded on the optical disc is being advanced. For example, when laser beams of short wavelength such as 410 nm or 405 nm, etc. like violet semiconductor laser are used, spot on the optical disc which has been converged by the object lens can be further reduced as compared to conventionally used laser beams of red or infrared semiconductor where wavelength is 780 nm or 650 nm, etc. Thus, spatial frequency characteristic is improved. Of course, in order to realize high recording density of optical disc, as shown in FIGS. 2A and 2B, this can be attained by shortening track pitch P, i.e., reducing track pitch P. However, reduction of track pitch P leads to physical limitation such as problem when disc base  201  is molded or formed, etc. Accordingly, attention is greatly drawn to realization of short wavelength of laser beams.  
       [0009] On the other hand, in the case where laser beams of short wavelength emitted from violet semiconductor laser are used to carry out recording of data onto the optical disc or to carry out reproduction of data recorded on the optical disc, it becomes apt to cope with also more fine structure of the disc surface. For example, by fine surface roughness of the signal recording surface  201   a  of the disc base  201  and/or molding (forming) distortion of the recording layer or the reflection layer at sharp twilled line portion constituted by uneven structure such as grooves  211  or pits  212  of the signal recording surface  201   a , scattering, etc. takes place in reflected light of irradiated laser beams. For this reason, following realization of short wavelength of laser beams emitted from semiconductor laser, laser beams are scattered by fine surface roughness, etc. of the signal recording surface  201   a  at the time of recording data onto the optical disc, failing to sufficiently heat the recording layer. As a result, there is the possibility that correct data recording cannot be carried out.  
       [0010] In the case of carrying out reproduction of data recorded on the optical disc, noise component resulting from film formation distortion, etc. is increased in laser beams as reflected light reflected by the optical disc.  
       [0011] In order to reduce such noise component, it is sufficient to reduce fine surface roughness of the signal recording surface  201   a  of the disc base  201  to carry out chamfering of twilled line portion constituted by uneven structure such as groove  211 , etc. For example, there is conceivable a method of irradiating ultraviolet rays onto the signal recording surface  201   a  of the disc base  201  consisting of synthetic resin to simultaneously realize smoothing of the surface of the signal recording surface  201   a  and curved surface of twilled line portion constituted by uneven structure such as groove  211 , etc.  
       [0012] Since the time required for irradiating ultraviolet rays onto respective disc bases  201  one by one becomes order of “minute” in order to obtain valid effect by this method, productivity is very poor. The method of individually irradiating ultraviolet rays onto all disc bases  201  in the mass-production process of optical discs is not preferable in view of cost and time.  
       DISCLOSURE OF THE INVENTION  
       [0013] An object of the present invention is to provide a method of manufacturing original plate used for manufacturing optical recording medium and a method of manufacturing stamper which can solve problems as described above that the optical disc has.  
       [0014] Another object of the present invention is to provide a method of manufacturing stamper and a method of manufacturing original plate used for manufacturing this stamper which can efficiently manufacture optical recording media adapted for carrying out recording of data and for carrying out reproduction of recorded data in the state where reduction of S/N (signal-to-noise ratio) is realized so that satisfactory recording/reproducing characteristic is obtained.  
       [0015] The present invention proposed in order to attain objects as described above is directed to a method of manufacturing original plate used for manufacturing optical recording medium, and this method comprises: exposing and developing a photoresist layer provided on a base; forming uneven pattern at the photoresist layer; irradiating ultraviolet rays onto the photoresist layer where the uneven pattern is formed; and thereafter irradiating infrared rays onto the photoresist layer.  
       [0016] In this method, plating processing is further implemented to the photoresist layer onto which infrared rays have been irradiated, whereby original plate is manufactured.  
       [0017] The present invention is directed to a method of manufacturing stamper for manufacturing an optical recording medium, which comprises: irradiating ultraviolet rays onto a ultraviolet hardening resin layer provide on a base and adapted so that uneven pattern is formed; and manufacturing a stamper by using the base including the ultraviolet hardening resin layer to which the ultraviolet rays have been irradiated.  
       [0018] The method of manufacturing stamper according to the present invention comprises: allowing a further base where a further ultraviolet rays hardening layer is provided to be in closely contact with the ultraviolet hardening resin layer to which the ultraviolet rays have been irradiated; irradiating ultraviolet rays to harden the further ultraviolet hardening resin layer to transfer the uneven pattern formed at the ultraviolet hardening resin layer to the further ultraviolet hardening resin layer; and implementing plating processing to the further ultraviolet hardening resin layer to which the uneven pattern has been transferred to form a stamper.  
       [0019] The present invention is directed to a further method of manufacturing stamper for manufacturing an optical recording medium, and this method comprises: exposing and developing a photoresist layer provided on an original plate to form uneven pattern at the photoresist layer; implementing plating processing to the photoresist layer where the uneven pattern has been formed to form master stamper; irradiating ultraviolet rays to a base where a ultraviolet hardening resin layer is provided and the master stamper in the state they are caused to be closely in contact with each other to transfer the uneven pattern of the master stamper to the ultraviolet hardening resin layer; thereafter further irradiating ultraviolet rays to the ultraviolet hardening resin layer; and manufacturing a stamper by using the base including the ultraviolet hardening resin layer to which the ultraviolet rays have been irradiated.  
       [0020] A further method of manufacturing stamper according to the present invention comprises: allowing a further base where a further ultraviolet hardening resin layer is provided to be in closely contact with ultraviolet hardening resin layer to which ultraviolet rays have been irradiated; irradiating ultraviolet rays to harden the further ultraviolet hardening resin layer to transfer the uneven pattern formed at the ultraviolet hardening resin layer to the further ultraviolet hardening resin layer; and implementing plating processing to the further ultraviolet hardening resin layer to which the uneven pattern has been transferred to form a stamper.  
       [0021] Still other objects of the present invention and practical merits obtained by the present invention will become more apparent from the description of the embodiments which will be given below with reference to the attached drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022]FIG. 1 is a perspective view showing an example of an optical disc.  
     [0023]FIG. 2A is an essential part perspective view showing grooves provided at optical disc of the recordable type, and FIG. 2B is an essential part perspective view showing pits constituting recording track provided at an optical disc of the reproduction only type.  
     [0024]FIGS. 3A to  3 D are cross sectional views showing, in step order, main steps of a method of manufacturing original plate of stamper for manufacturing optical recording medium and optical recording medium of a first embodiment according to the present invention.  
     [0025]FIGS. 4A to  4 D are cross sectional views showing, in step order, further steps of the method of manufacturing original plate of stamper for manufacturing optical recording medium and optical recording medium of the first embodiment according to the present invention.  
     [0026]FIG. 5 is a view showing irradiating intensity at ultraviolet rays irradiation used in the method of manufacturing original plate of stamper for manufacturing optical recording medium according to the present invention.  
     [0027]FIGS. 6A to  6 E are cross sectional views showing, in step order, main steps of a method of manufacturing original plate of stamper for manufacturing optical recording medium and optical recording medium of a second embodiment according to the present invention.  
     [0028]FIGS. 7A to  7 C are cross sectional views showing, in step order, further steps of the method of manufacturing original plate of stamper for manufacturing optical recording medium and optical recording medium of a second embodiment according to the present invention.  
     [0029]FIGS. 8A to  8 D are cross sectional views showing, in step order, main steps of a method of manufacturing original plate of stamper for manufacturing optical recording medium and optical recording medium of a third embodiment according to the present invention.  
     [0030]FIGS. 9A to  9 C are cross sectional views showing, in step order, further steps of the method of manufacturing original plate of stamper for manufacturing optical recording medium and optical recording medium of the third embodiment according to the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
     [0031] Embodiments of the present invention will now be described in detail with reference to the attached drawings.  
     [0032] First Embodiment  
     [0033]FIGS. 3A to  3 D are cross sectional views showing steps of manufacturing an original plate of a stamper for manufacturing optical recording medium by the first embodiment of the present invention, and FIGS. 4A to  4 D are cross sectional views showing steps of manufacturing optical disc which is optical recording medium.  
     [0034] In order to manufacture an original plate used for manufacturing a stamper by the method of the present invention, as shown in FIG. 3A, e.g., a glass original plate  10  polished and rinsed so that the surface thereof is flat is mounted on rotational stage (not shown) to rotate this glass original plate  10  under the condition where, e.g., linear velocity is constant. On this rotating glass original plate  10 , e.g., photoresist  11  of the so-called positive type which is photosensitive material layer which becomes alkali soluble, e.g., by carrying out sensitizing is coated so that it has uniform thickness of, e.g., about 100 nm. In this case, this photoresist  11  may be of negative type. For example, there may be employed resist of any kind such as novolak system resist or chemical amplification type resist, etc. It is sufficient that film thickness of this photoresist  11  is about 30˜150 nm.  
     [0035] Then, the glass original plate  10  on which the photoresist  11  is coated is rotated to converge laser beams which has been caused to undergo intensity modulation in correspondence with recording signal onto the photoresist  11  by an object lens (objective)  12  to expose the photoresist  11 . At this time, positions of the glass original plate  10  and the object lens  12  are caused to relatively undergo parallel displacement at a predetermined velocity in a radial direction of the glass original plate  10  to thereby form latent image of an uneven pattern  14  in a spiral form which will be described later. For example, at least the object lens  12  is caused to undergo parallel displacement at a predetermined velocity in a radial direction of the glass original plate  10  while rotating the glass original plate  10  to irradiate intensity-modulated laser beams onto the photoresist  11  to thereby form latent image. Without limiting to this, there may be also employed an approach to move the glass original plate  10  at a predetermined velocity also in the radial direction while rotating it at a predetermined number of revolutions in the state where the object lens  12  is not moved to thereby form latent image at the photoresist  11 .  
     [0036] When the region sensitized by laser beams is dissolved by developing photoresist  11  exposed in a manner as described above by, e.g., alkali developer, uneven pattern  14  corresponding to at least either one of grooves and pits recorded onto the optical disc is formed as shown in FIG. 3B. For example, laser beams irradiated onto the photoresist  11  are intermittently turned ON and OFF on the basis of data to be recorded, whereby uneven pattern  14  corresponding to pits shown in FIG. 2B is formed. Laser beams are continuously irradiated onto the photoresist  11 , whereby uneven pattern  14  corresponding to grooves shown in FIG. 2A is formed. This uneven pattern  14  consists of a glass flat surface portion  141  which is the surface exposed as the result of the fact that the photoresist  11  on the original plate  10  is dissolved, and a photoresist flat surface portion  142  which is the remaining surface which is not dissolved by development processing because it is not sensitized on the photoresist  11 . The remaining portion which is not dissolved on the photoresist  11  forms an inclined surface portion  143  as shown in FIG. 3B. Twilled line portions  144  are formed at the boundary between the photoresist flat surface portion  142  and the inclined surface portion  143  and the boundary between the glass flat surface portion  141  and the inclined surface portion  143 .  
     [0037] Ultraviolet ray irradiation and infrared ray irradiation are implemented onto the surface of the photoresist  11  where the uneven pattern is formed on the glass original plate  10  in this way in a manner as described below. Thus, an original plate  30  for duplication of stamper which is an original plate of stamper for manufacturing optical recording medium is made or produced.  
     [0038] Namely, as shown in FIG. 3C, the surface opposite to the surface where the uneven pattern  14  is formed of the glass original plate  10  is attached to a rotary stage  15  to rotate the glass original plate  10  at a constant velocity, e.g., about 60 rpm. Onto the surface of the photoresist  11  where the uneven pattern  14  is formed on the rotated glass original plate  10 , ultraviolet rays are irradiated, e.g., for about four minutes and at the intensity of about 10 mW/cm 2  by plural ultraviolet lamps  20  arranged in parallel to each other under existence of oxygen or air. These ultraviolet lamps  20  are disposed in the state where they are in parallel to the surface of the photoresist  11  where the uneven pattern  14  is formed on the glass original plate  10 , and height from the surface of the photoresist  11  is caused to be constant, e.g., about 100 mm. The glass original plate  10  is rotated at a fixed velocity by the rotary stage  15  and height from the glass original plate  10  of the ultraviolet lamp  20  is caused to be constant, whereby irradiation intensity of ultraviolet rays substantially becomes constant and irradiation intensity surface density of ultraviolet rays also substantially becomes constant within the effective size R 1  of the surface where the uneven pattern  14  is formed of the glass original plate  10 . In this example, as the ultraviolet lamp  20 , e.g., excimer lamp having wavelength of 174 nm or low pressure mercury lamp, etc. may be used. In place of rotating the glass original plate  10  by using the rotary stage  15 , ultraviolet lamp  20  may be rotated at a constant velocity.  
     [0039] The above-described respective conditions are values determined by the result of the experiment. For example, when product of intensity of ultraviolet rays and irradiation time thereof becomes great, roughness of the surface of the photoresist  11  becomes great and thickness of the photoresist  11  becomes thin. Conversely, when that product becomes small, there takes place the problem that realization of curved surface of the twilled line portion which will be described later of the photoresist  11  is not sufficiently carried out, etc. The intensity and the irradiation time of ultraviolet rays are not limited to those of the above-described example, but may be suitably selected in accordance with material of the photoresist  11 .  
     [0040] When ultraviolet rays are irradiated from the ultraviolet lamps  20  under existence of oxygen or air onto the surface of the photoresist  11  where the uneven pattern  14  is formed on the glass original plate  10 , ultraviolet rays are first irradiated to oxygen (O 2 ) so that ozone (O 3 ) is produced. Since this ozone (O 3 ) is unstable, it is decomposed into oxygen (O 2 ) and excited oxygen (O*) having very strong oxidation power. This excited oxygen (O*) oxidizes the surface of the photoresist  11  which is organic matter to reform it. Thus, as shown in FIG. 3D, the twilled line portion  144  of the uneven pattern  14  is chamfered and is curved.  
     [0041] On the other hand, at the same time when the twilled line portion  144  of the uneven pattern  14  is rounded, roughness of the surface of the photoresist  11  including the photoresist flat surface portion  142  and the inclined surface portion  143  constituting the uneven pattern  14  is slightly increased. In view of this, the ultraviolet lamps  20  are replaced by plural infrared lamps  21  arranged in parallel to each other. By these infrared lamps  21 , infrared rays are irradiated, e.g., for about three minutes and at the intensity of about 20 W/cm 2  onto the surface where the uneven pattern  14  is formed of the glass original plate  10  rotated at a constant velocity by the rotary stage  15  subsequently to irradiation of ultraviolet rays. As this infrared lamp  21 , e.g. halogen lamp is used. It is preferable that surface arrival temperature with respect to the glass original plate  10  by the infrared lamp  21  is more than about 200° C. although it is varied in dependency upon wavelength of infrared rays. In the case where, e.g., near infrared rays (visible light˜wavelength about 5 μm) is used, it is preferable that the surface arrival temperature is about 250° C. In the case where far infrared rays (wavelength about 1˜8 μm) is used, it is preferable that the surface arrival temperature is about 400° C. The reason why it is preferable that the surface arrival temperature is more than about 200° C. is that it is necessary to heat the photoresist  11  so that temperature reaches more than softening point in order to carry out smoothing of the surface of the photoresist  11  by irradiation of infrared rays as described later. It is to be noted that the reason why arrival temperatures by near infrared rays and far infrared rays are different is that absorption factor with respect to photoresist is varied by wavelength of infrared rays.  
     [0042] The above-described irradiation time and irradiation intensity of infrared rays are based on the result of the experiment. When product of the irradiation time and the irradiation intensity becomes great, the uneven pattern  14  itself of the photoresist  11  is deformed and/or the photoresist  11  is carbonized in a manner exceeding smoothing of the photoresist  11 . Conversely, when product of the irradiation time and the irradiation intensity becomes small, smoothing of the surface of the photoresist  11  cannot be sufficiently carried out.  
     [0043] It is to be noted that the fact that the glass original plate  10  is rotated at a constant velocity on the rotary stage  15  and the infrared lamp  21  is disposed at a predetermined height from the glass original plate  10  so that irradiation intensity surface density within the effective size of the surface where the uneven pattern  14  is formed of the glass original plate  10  substantially becomes constant is similar to the case of the above-described ultraviolet irradiation. By irradiation of infrared rays onto the surface where the uneven patten  14  is formed of this glass original plate  10 , as shown in FIG. 4A, the surface of the photoresist  11  including the photoresist flat surface portion  142  and the inclined surface portion  143  constituting the uneven pattern  14  is softened as the result of the fact that temperature rises, and becomes smooth by surface tension. As a result, there can be obtained the original plate  30  for duplication of stamper in which the surfaces of the photoresist flat surface portion  142  and the photoresist inclined surface portion  143  constituting the uneven pattern  14  are smoothed, and the twilled line portion  144  of the uneven pattern  14  is curved.  
     [0044] In the above-described example, in order to carry out ultraviolet irradiation and infrared irradiation with respect to the glass original plate  10 , ultraviolet lamps  20  and infrared lamps  21  were used. In place of these lamps, ultraviolet irradiation unit and infrared irradiation unit may be respectively used.  
     [0045] As shown in FIG. 4B, electrically conductive film (not shown) is formed by, e.g., electroless plating method on the surface where the uneven pattern  14  is formed of the original plate  30  for duplication of stamper obtained in this way thereafter to implement, e.g., Ni (nickel) plating by electroplating method to form a Ni plating layer  40 . This Ni plating layer  40  is peeled off from the original plate  30  for duplication of stamper. As a result, the uneven pattern  14  of the original plate  30  for duplication of stamper is transferred to the Ni plating layer  40  which has been peeled off. Thus, there results stamper  40  in which the uneven pattern  41  has been formed. It is to be noted that organic matter such as photoresist  11 , etc. reformed by the above-described irradiation of ultraviolet rays, etc. is attached on the surface where the uneven pattern  41  is formed of the Ni plating layer  40 , i.e., the stamper  40 . For this reason, e.g., it is necessary to rinse, by organic solvent, the surface where the uneven pattern  41  has been formed of the stamper  40  thereafter to irradiate deep ultraviolet rays to dissolve and rinse organic matter such as photoresist  11 , etc.  
     [0046] Then, as shown in FIG. 4C, this stamper  40  is used to press, by a predetermined pressure, the stamper  40  to ultraviolet hardening resin coated on a disc base  51  consisting of flat transparent resin, e.g., glass, polymethyl methacrylate (PMMA) or polycarbonate (PC), etc. by, e.g., Photo Polymerization method (2P method) to irradiate ultraviolet rays from the other surface of the disc base in that state to harden it, whereby a transfer layer  53  where uneven pattern  41  has been transferred of the stamper  40  is formed. Thus, an uneven pattern  52  comprised of train of grooves and/or pits is formed at the disc base  51  which is a base for optical recording medium. It is to be noted that, in addition to the 2P method, stamper  40  may be attached to metal mold to form uneven pattern  52  at one surface of the disc base  51  by injection molding or compression molding by using polymethyl methacrylate (PMMA) or polycarbonate (PC).  
     [0047] As shown in FIG. 4D, on the transfer layer  53  of the disc base  51  where the uneven pattern  52  has been formed, a recording layer  54  including phase change film or magnetic film, etc. consisting of, e.g., recordable optical recording material of the phase change type or magneto-optical recording material and a protective layer  55  are formed in order. In practical sense, e.g., dielectric film consisting of SiN, etc., perpendicular magnetic recording film consisting of TeFeCo alloy, etc., dielectric film consisting of SiN, etc. and reflection film consisting of Al, etc. are laminated in order by the sputtering method on the surface where the uneven pattern  52  is formed to thereby form the recording layer  54 . Thereafter, ultraviolet hardening resin is coated on this recording layer  54  by the spin-coat method to irradiate ultraviolet rays onto the coated ultraviolet hardening resin to harden it so that the protective layer  55  is formed. Thus, optical disc  50  which is optical recording medium can be obtained. This optical disc  50  is not limited to magneto-optical disc or phase change type optical disc, but may be, e.g., reproduction only optical disc or optical card, etc. In the case of the reproduction only optical disc, it is sufficient to form light reflection layer consisting of, e.g., Al, etc. and protective layer consisting of, e.g., ultraviolet hardening resin, etc. on this light reflection layer.  
     [0048] While recording layer  54  and protective layer  55  are formed on transfer layer  53  in the above-described example, when uneven pattern  52  is formed on one surface of disc base  51 , recording layer  54  and protective layer  55  may be formed in order on one surface of base  51 .  
     [0049] As stated above, in this embodiment, ultraviolet rays and infrared rays are irradiated at a uniform intensity onto the surface of the photoresist  11  where the uneven pattern  14  has been formed on the glass original plate  10 , thereby making it possible to manufacture original plate  30  for duplication of stamper in which twilled line portion  144  of uneven pattern  14  has been curved and the surfaces of the photoresist flat surface portion  142  and the inclined surface portion  143  have been smoothed. This original plate  30  for duplication of stamper is used to transfer uneven pattern  14  onto stamper  40 , thus making it possible to form, at the disc base  51  manufactured by using this stamper  40 , uneven pattern  52  including a flat portion  522  and an inclined surface portion  523  of which surfaces have been smoothed, and a twilled line portion  524  which has been curved. In the optical disc  50  including this optical disc base  51 , it can be prevented that surface roughness takes place at the surface where the uneven pattern  52  is formed of the disc base  51 , and/or distortion in film formation takes place in recording layer  54 , etc. at the twilled line portion  524  of the uneven pattern  52 .  
     [0050] As described above, even in the case where laser beams of short wavelength like, e.g., violet semiconductor laser are irradiated onto this optical disc  50  to carry out recording or reproduction of information, noise can be reduced so that sufficient S/N can be ensured. It becomes unnecessary to irradiate ultraviolet rays onto respective disc bases one by one as previously described above to manufacture such optical discs. In the above-described embodiment, stamper  40  in which uneven pattern  14  has been transferred from original plate  30  for duplication of stamper to which ultraviolet rays and infrared rays have been irradiated is used, thereby making it possible to efficiently mass-produce disc bases and optical discs at low cost and in a short time.  
     [0051] Second Embodiment  
     [0052] Then, a method of manufacturing original plate of a stamper for manufacturing optical recording medium and a method of manufacturing stamper which are a second embodiment according to the present invention will be explained with reference to FIGS. 6A to  6 E and FIGS. 7A to  7 C. In the second embodiment, steps up to ones for manufacturing optical recording medium from stamper are similar to those of the first embodiment. Accordingly, explanation will be given below only in connection with points different from the first embodiment, and the explanation of the first embodiment is invoked (applied) in connection with other points.  
     [0053] First, as shown in FIG. 6A, photoresist  11  coated on glass original plate  10  so as to have uniform thickness of about 200˜300 nm is exposed and developed similarly to the first embodiment to thereby form uneven pattern  16 .  
     [0054] Anisotropic etching is implemented to the glass original plate  10  where the uneven pattern  16  has been formed by, e.g., Reactive Ion Etching (RIE). As shown in FIG. 6B, a portion of the photoresist  11  which has been left by development is removed by this Reactive Ion Etching, and the glass original plate  10  of the portion exposed as the result of the fact that the photoresist  11  is removed by development is dug down. The quantity in which the glass original plate  10  is dug down is caused to be, e.g., about 100 nm. As described above, by thickening coating film of the photoresist  11  so that its thickness becomes equal to about 200˜300 nm, or setting kind of etching gas or chamber internal pressure, etc. so that etching rate, i.e., ratio between height in which the glass original plate  10  is dug down and height in which the photoresist  11  is dug down becomes great, it can be prevented that even the glass original plate  10  under the photoresist  11  left by development is also dug down.  
     [0055] Then, as shown in FIG. 6C, the photresist  11  left on the surface of the glass original plate  10  after Reactive Ion Etching is removed by rinsing it with organic solvent, or by irradiating deep ultraviolet light thereto, etc. Thus, on the glass original plate  10  from which the photoresist  11  has been removed, an uneven pattern  17  corresponding to grooves and/or pits is formed. It is to be noted that there can be also obtained the effect or advantage that the surface of the uneven pattern  17  on the glass original plate  10  is smoothed by this Reactive Ion Etching.  
     [0056] Then, as shown in FIG. 6D, the surface of the glass original plate  10  is sufficiently rinsed by ultrasonic pure water cleaning thereafter to transfer the uneven pattern  17  of the glass original plate  10  to, e.g., an acrylic original plate  60  by the 2P method with this glass original plate  10  being as matrix. Namely, ultraviolet hardening resin is first coated onto the glass original plate  10  where the uneven pattern  17  has been formed to allow the acrylic original plate  60  to be closely stuck onto this ultraviolet hardening resin layer  61 . After ultraviolet rays are irradiated from either the glass original plate  60  or the acrylic original plate  60  to harden ultraviolet hardening resin layer  61 , the glass original plate  10  is peeled off from the ultraviolet hardening resin layer  61 . Thus, the uneven pattern  17  of the glass original plate  10  is transferred to the ultraviolet hardening resin layer  61 . Thus, the acrylic original plate  60  including the ultraviolet hardening resin layer  61  where the uneven pattern  62  has been formed is produced. This uneven pattern  62  is composed of a flat surface portion  622 , an inclined surface portion  623 , and a twilled line portion  624 . It is to be noted that glass original plate  10  which has been caused to undergo anisotropic etching can be used many times for manufacturing of the acrylic original plate  60  by the 2P method as matrix.  
     [0057] Then, as shown in FIG. 6E, the surface opposite to the surface where the uneven pattern  62  has been formed of the acrylic original plate  60  is supported by the rotary stage  15  to rotate this rotary stage  15  at a constant velocity, e.g., about 60 rpm. Onto the surface of the hardened ultraviolet hardening resin layer  61  where the uneven pattern  62  has been formed on the rotated acrylic original plate  60 , ultraviolet rays are irradiated, e.g., for about four minutes and at an intensity of about 10 mW/cm 2  by plural ultraviolet lamps  20  arranged in parallel to each other under the existence of oxygen or air. The irradiation time and the irradiation intensity of ultraviolet rays are based on result of the experiment, and time and intensity are suitably selected in accordance with composition of material of ultraviolet hardening resin and to what degree the uneven pattern  62  is curved. These ultraviolet lamps  20  are adapted so that height from the surface of the ultraviolet hardening resin layer  61  where the uneven pattern  62  has been formed of the acrylic original plate  60  on the rotary stage  15  is caused to be constant, whereby irradiation intensity surface density within the effective size of the surface where the uneven pattern  62  has been formed of the acrylic original plate  60  substantially becomes constant similarly to the previously described first embodiment. As the ultraviolet lamp  20 , e.g., excimer lamp having wavelength of 174 nm or low pressure mercury lamp, etc. may be used. In place of rotating the acrylic original plate  60  by using the rotary stage  15 , ultraviolet lamp  20  may be rotated at a constant velocity similarly to the first embodiment.  
     [0058] Ultraviolet rays are irradiated from the ultraviolet lamps  20  onto the surface of the ultraviolet hardening resin layer  61  where the uneven pattern  62  has been formed on this acrylic original plate  60  under existence of oxygen or air, and ultraviolet rays are first irradiated to oxygen (O 2 ) so that ozone (O 3 ) is produced. Since this ozone (O 3 ) is unstable, it is decomposed into oxygen (O 2 ) and excited oxygen (O*) having very strong oxidation power. This excited oxygen (O*) oxidizes the surface of the ultraviolet hardening layer  61  which is organic matter to reform it. Thus, as shown in FIG. 7A, the twilled line portion  624  of the uneven pattern  62  is chamfered and is curved, and the surface of the ultraviolet hardening resin layer  61  including the flat surface portion  622  and the inclined surface portion  623  constituting the uneven pattern  62  is smoothed at the same time.  
     [0059] It is to be noted that while there were cases in the first embodiment such that ultraviolet rays are irradiated onto the photoresist  11 , whereby roughness of the surface thereof is slightly increased, there is no possibility in the second embodiment that even if ultraviolet rays are irradiated onto the hardened ultraviolet hardening resin layer  61 , roughness of the surface is increased, but the surface becomes more smooth. Accordingly, in the second embodiment, there is no necessity of irradiating infrared rays as in the case of the first embodiment. It should be noted that while plural ultraviolet lamps arranged in parallel to each other were used for the purpose of carrying out ultraviolet rays irradiation with respect to the acrylic original plate  60  in the above-described second embodiment, an ultraviolet irradiation unit may be used in place of these ultraviolet lamps.  
     [0060] Then, as shown in FIG. 7B, with this acrylic original plate  60  to which ultraviolet rays have been irradiated being as matrix, the uneven pattern  62  of the acrylic original plate  60  is transferred to a polished glass original plate  70  by the 2P method. Namely, first, ultraviolet hardening resin is further coated onto the ultraviolet hardening resin layer  61  where the uneven pattern  62  has been formed on the acrylic original plate  60  to closely stick the glass original plate  70  onto this coated ultraviolet hardening resin layer  71 . Of course, ultraviolet hardening resin may be coated onto glass original plate  70  to closely stick acrylic original plate  60  thereto. Ultraviolet rays are irradiated from either the acrylic original plate  60  or the glass original plate  70  to harden ultraviolet hardening resin layer  71  thereafter to peel off the acrylic original plate  60  from the ultraviolet hardening resin layer  71 . Thus, there is produced or manufactured an original plate  73  for duplication of stamper including the ultraviolet hardening resin layer  71  in which there has been formed an even pattern  72  to which the uneven pattern  62  of the acrylic original plate  60  has been transferred. The step of transferring uneven pattern  62  to the glass original plate  70  by the 2P method with this acrylic original plate  60  being as matrix is a step provided for the reason why it is difficult to implement Ni plating to the surface where the uneven pattern  62  has been formed at the ultraviolet hardening resin layer  61  on the acrylic original plate  60  because the surface of the ultraviolet hardening resin layer  61  to which ultraviolet rays have been irradiated is reformed. It is to be noted that acrylic original plate  60  to which ultraviolet rays have been irradiated can be used many times for manufacturing of glass original plate  70  by the 2P method as matrix.  
     [0061] Then, as shown in FIG. 7C, electrically conductive film (not shown) is formed by, e.g., electroless plating method on the surface where the uneven pattern  72  has been formed at the ultraviolet hardening resin layer  71  on the original plate  73  for duplication of stamper thereafter to implement, e.g., Ni plating by the elctroplating method to form Ni plating layer  40 . By peeling off this Ni plating layer  40  from the original plate  73  for duplication of stamper, the Ni plating layer  40  which has been peeled off results in the stamper  40  in which the uneven pattern where there has been formed the uneven pattern  72  of the original plate  73  for duplication of stamper has been transferred. It is to be noted that the original plate  73  for duplication of a stamper can be used many times for manufacturing of the stamper  40  as matrix. Steps subsequent to the step of transferring uneven pattern  41  from this stamper  40  onto disc base  51  are carried out similarly to the first embodiment.  
     [0062] As stated above, in the second embodiment, by irradiating ultraviolet rays at a uniform intensity onto the ultraviolet hardening resin layer  61  where uneven pattern  62  has been formed, it is possible to manufacture acrylic original plate  60  in which the surfaces of the flat surface portion  622  and the inclined surface portion  623  constituting the uneven pattern  62  have been smoothed, and the twilled line portion  624  of the uneven pattern  62  has been curved. By using this acrylic original plate  60 , it is possible to manufacture an original plate  73  for duplication of stamper in which the surfaces of a flat surface portion  722  and an inclined surface portion  723  of the uneven pattern  72  have been smoothed, and a twilled line portion  724  of the uneven pattern  72  has been curved. As disc base  51  manufactured by using the stamper  40  manufactured on the basis of this original plate for duplication of stamper, it is possible to form uneven pattern  52  including flat surface portion  522  and inclined surface portion  523  of which surfaces have been smoothed and twilled line portion  524  which has been curved. Thus, in the optical disc  50  including this disc base  51 , it can be prevented that surface roughness takes place at the surface where uneven pattern  52  is formed of the disc base  51 , and/or distortion in film formation takes place in the recording layer  54 , etc. at the twilled line portion  524  of the uneven pattern  52 .  
     [0063] As described above, even in the case where laser beams of short wavelength like, e.g., violet semiconductor laser are irradiated onto this optical disc  50  to carry out recording of information or to carry out reproduction of recorded information, noise can be reduced, and sufficient S/N can be ensured. In addition, it is possible to efficiently mass-produce such optical discs  50  at low cost and in a short time by using stamper  40  including uneven pattern  41  based on uneven pattern  62  of acrylic original plate  60 .  
     [0064] Since this glass original plate  10  which has been caused to undergo anisotropic etching can be used many times for manufacturing of acrylic original plate  60  by the 2P method as matrix, it is possible to produce, at low cost and in a short time, acrylic original plate  60  including ultraviolet hardening resin layer  61  where uneven pattern  62  has been formed.  
     [0065] Further, since the acrylic original plate  60  can be used many times for manufacturing of glass original plate  70  by the 2P method as matrix, it is possible to produce original plate  73  for duplication of stamper including ultraviolet hardening resin layer  71  where uneven pattern  72  has been formed.  
     [0066] Since the original plate  73  for duplication of stamper can be used many times for manufacturing of the stamper  40  as matrix, it is possible to produce, at a low cost and in a short time, stamper  40  in which uneven pattern  41  has been formed.  
     [0067] Third Embodiment  
     [0068] Then, a method of manufacturing original plate of stamper for manufacturing optical recording medium and a method of manufacturing stamper which are the third embodiment according to the present invention will be explained with reference to FIGS. 8A to  8 D and FIGS. 9A to  9 C. In the third embodiment, steps up to ones of forming uneven pattern at photoresist on glass original plate, and steps up to ones of manufacturing optical disc from stamper are similar to those of the first embodiment. Accordingly, explanation will be given below only in connection with the points different from the first embodiment, and explanation of the first embodiment is invoked or applied in connection with other points.  
     [0069] First, as shown in FIG. 8A, photoresist  11  coated on glass original plate  10  is exposed and developed so that electrically conductive film (not shown) is formed by, e.g., electroless plating method on the surface where uneven pattern  14  comprised of train of grooves and/or pits thereafter to implement, e.g., Ni plating by electric plating method to form Ni plating layer  80 . By peeling off this Ni plating layer  80  from glass original plate  10 , the Ni plating layer  80  results in master stamper  80  including uneven pattern  81  in which uneven pattern  14  of the glass original plate  10  has been transferred.  
     [0070] Then, as shown in FIG. 8B, electrically conductive film (not shown) is formed by, e.g., electroless plating method is formed on the surface where uneven pattern  81  of the Ni plating layer  80 , i.e., the master stamper  80  has been formed thereafter to implement, e.g., Ni plating by electroplating method to form a Ni plating layer  90 . By peeling off this Ni plating layer  90  from the master stamper  80 , the Ni plating layer  90  results in mother stamper  90  including uneven pattern  91  in which uneven pattern  81  of master stamper  80  has been transferred. The step of producing Ni plating layer  90 , i.e., mother stamper  90  from this master stamper  80  is a step for preventing that uneven pattern  52  of disc base  51  finally produced is inverted.  
     [0071] Then, as shown in FIG. 8C, the uneven pattern  91  of the mother stamper  90  is transferred to, e.g., a polished acrylic original plate  100  by the 2P method with this mother stamper  90  being as matrix. Namely, first, ultraviolet hardening resin is coated onto the mother stamper  90  where the uneven pattern  91  has been formed to closely stick the acrylic original plate  100  onto this formed ultraviolet hardening resin layer  101 . It is a matter of course that ultraviolet hardening resin may be coated on the acrylic original plate  100  to closely stick mother stamper  90  thereto. For example, ultraviolet rays are irradiated through the acrylic original plate  100  to harden ultraviolet hardening resin layer  101  thereafter to peel off the mother stamper  90  from the acrylic original plate  100 . Thus, the uneven pattern  91  is transferred onto the ultraviolet hardening resin layer  101  so that uneven pattern  102  is formed. As a result, acrylic original plate  100  provided with ultraviolet hardening resin layer  101  including uneven pattern  102  based on the uneven pattern  91  is produced. This uneven pattern  102  consists of a flat surface portion  105 , an inclined surface portion  103  and a twilled line portion  104 .  
     [0072] Then, as shown in FIG. 8D, the surface opposite to the surface where the uneven pattern  102  has been formed of the acrylic original plate  100  is supported at the rotary stage  15  to rotate this rotary stage  15  at a constant velocity, e.g., about 60 rpm. Onto the surface of the ultraviolet hardening resin layer  101  where the uneven pattern  102  has been formed on the rotated acrylic original plate  100 , ultraviolet rays are irradiated, e.g., for about four minutes and at intensity of about 10 mw/cm 2  by ultraviolet lamps  20  arranged under existence of oxygen or air. These ultraviolet lamps  20  are adapted so that height from the surface of the ultraviolet hardening resin layer  101  where the uneven pattern  102  has been formed on the acrylic original plate  100  on the rotary stage  15  is caused to be constant so that irradiation intensity surface density within the effective size of the surface where the uneven pattern  102  has been formed of the acrylic original plate  100  substantially becomes constant similarly to the first embodiment. In this example, as the ultraviolet lamp  20 , e.g., excimer lamp having wavelength of 174 nm or low pressure mercury lamp, etc. may be used. In place of rotating acrylic original plate  60  by using rotary stage  15 , ultraviolet lamp  20  may be rotated at a fixed velocity similarly to the first embodiment. The irradiation time and the irradiation intensity of ultraviolet rays are suitably selected by difference of composition of material of ultraviolet hardening resin and/or to what degree uneven pattern  102  is curved by irradiation of ultraviolet rays as described later similarly to the previously described respective embodiments.  
     [0073] Ultraviolet rays are irradiated from the ultraviolet lamps  20  onto the surface of the ultraviolet hardening resin layer  101  where the uneven pattern  102  has been formed on this acrylic original plate  100  under existence of oxygen or air, and ultraviolet rays are irradiated to oxygen (O 2 ) SO that ozone (O 3 ) is produced. Since this ozone (O 3 ) is unstable, it is decomposed into oxygen (O 2 ) and excited oxygen (O*) having very strong oxidation power. This excited oxygen (O*) oxidizes the surface of the ultraviolet hardening resin layer  101  which is organic matter to reform it. Thus, as shown in FIG. 9A, twilled line portion  104  of the uneven pattern  102  is chamfered and is curved, and the surface of the ultraviolet hardening resin layer  101  including flat surface portion  105  and inclined surface portion  103  constituting the uneven pattern  102  is smoothed at the same time. It is to be noted that there were cases in the first embodiment that roughness of the surface of photoresist  11  is slightly increased by irradiating ultraviolet rays onto the photoresist  11 , but there is no possibility similarly to the second embodiment in the third embodiment that even if ultraviolet rays are irradiated onto the hardened ultraviolet hardening resin layer  101 , roughness of the surface is increased, but the surface becomes more smooth. Accordingly, in the third embodiment, there is no necessity of irradiating infrared rays as in the case of the first embodiment. It is to be noted that, for the purpose of carrying out violet irradiation with respect to the acrylic original plate  100 , violet irradiation unit may be used similarly to the first embodiment.  
     [0074] Then, as shown in FIG. 9B, the uneven pattern  102  of the acrylic original plate  100  is transferred onto a polished glass original plate  110  by the 2P method with this acrylic original plate  100  to which ultraviolet rays have been irradiated being as matrix. Namely, first, ultraviolet hardening resin is coated onto the acrylic original plate  100  where the uneven pattern  102  has been formed to closely stick the glass original plate  110  onto the ultraviolet hardening resin layer  111  formed by this coating. Of course, ultraviolet hardening resin may be coated onto the glass original plate  110  to closely stick the acrylic original plate  100 . Ultraviolet rays are irradiated through the glass original plate  110  or the acrylic original plate  100  to harden the ultraviolet hardening resin layer  111  thereafter to peel off the acrylic original plate  100  from the ultraviolet hardening resin layer  111 . Thus, the uneven pattern  102  is transferred to the ultraviolet hardening resin  111 , and an original plate  120  for duplication of stamper including the ultraviolet hardening resin layer  111  where the uneven pattern  112  has been formed is produced or made. The step of transferring the uneven pattern  102  onto the glass original plate  110  by the 2P method with this acrylic original plate  100  being as matrix is a step provided for the reason why it is difficult to implement Ni plating to the surface where the uneven pattern  102  has been formed of the ultraviolet hardening resin layer  101  on the acrylic original plate  100  to produce or make stamper  40  because the surface of the ultraviolet hardening layer  101  is reformed as the result of the fact that ultraviolet rays have been irradiated. It is to be noted that acrylic original plate  100  to which ultraviolet rays have been irradiated can be used many times for the purpose of manufacturing of glass original plate  110  by the 2P method as matrix.  
     [0075] Then, as shown in FIG. 9C, electrically conductive film (not shown) is formed on the surface where the uneven pattern  112  has been formed on the original plate  120  for duplication of stamper by, e.g., electroless plating method thereafter to implement, e.g., Ni plating by electroplating method to form Ni plating layer  40 . By peeling off this Ni plating layer  40  from the original plate  120  for duplication of stamper, the Ni plating layer  40  results in stamper  40  including uneven pattern  41  in which the uneven pattern  112  of the original plate  120  for duplication of stamper has been transferred. It is to be noted that the original plate  120  for duplication of stamper can be used many times for the purpose of manufacturing stamper  40  as matrix. Steps subsequent to ones of transferring uneven pattern  41  from this Ni plating layer  40 , i.e., the stamper  40  to the disc base  51  are carried out similarly to the first embodiment.  
     [0076] As stated above, in the third embodiment, ultraviolet rays are irradiated onto the ultraviolet hardening resin layer  101  at a uniform intensity, whereby the surfaces of the flat surface portion  105  and the inclined surface portion  103  constituting the uneven pattern  102  are smoothed, and the twilled line portion  104  of the uneven pattern  102  can be curved. By transferring the uneven pattern  102  to the ultraviolet hardening resin layer  111  of the glass original plate  110  by using this acrylic original plate  100 , it is possible to manufacture original plate  120  for duplication of stamper in which the surfaces of a flat surface portion  115  and an inclined surface portion  113  of the uneven pattern  112  have been smoothed, and a twilled line portion  114  of the uneven pattern  112  has been curved. By using this original plate  120  for duplication of stamper, the uneven pattern  112  is transferred to one surface of the disc base  51  through the stamper  40 . At the optical disc base  51 , it is possible to form uneven structure  52  including a flat portion  522  and an inclined surface portion  523  of which surfaces have been smoothed, and a twilled line portion  524  which has been curved. Thus, in the optical disc  50  using this disc base  51 , it can be prevented that surface roughness takes place at the surface where the uneven structure  52  is formed of the disc base  51 , and/or distortion in film formation takes place in recording layer  54 , etc. at the twilled line portion  524  of the uneven structure  52 .  
     [0077] As described above, even in the case where laser beams of short wavelength like, e.g., violet semiconductor laser are irradiated onto this optical disc  50  to carry out recording of information or to carry out reproduction of recorded information, noise can be reduced, and sufficient S/N can be ensured. In addition, it is possible to efficiently mass-produce, at low cost and in a short time, optical discs  50  capable of ensuring sufficient S/N in this way by the stamper  40  in which the uneven pattern  102  has been transferred through the original plate  120  for duplication of stamper from the acrylic original plate  100  to which ultraviolet rays have been irradiated.  
     [0078] While the present invention has been explained as above by taking several embodiments, the present invention is not limited to the above-described embodiments, but may be modified or changed in various manners. For example, while explanation has been given in the third embodiment in connection with the example where mother stamper  90  is produced from master stamper  80 , plastic base may be produced from master stamper  80  by injection molding, compression molding or 2P method. It is sufficient to transfer uneven pattern to acrylic original plate  100  by the 2P method with this plastic base being as matrix. It is to be noted that in the case where uneven pattern is transferred to acrylic original plate  100  by the 2P method with molded disc which is plastic base produced by injection molding from master stamper  80  being as matrix, it is necessary to embed center hole of the molded disc.  
     [0079] While explanation has been given in the third embodiment in connection with the example where uneven pattern  91  is transferred to acrylic original plate  100  by the 2P method with mother stamper  90  being as matrix, plastic base in which uneven pattern  91  has been transferred by injection molding, compression molding or 2P method may be produced from mother stamper  90 . It is sufficient to carry out ultraviolet irradiation with respect to this plastic base to produce stamper  40  with this plastic base to which ultraviolet irradiation has been carried out being as matrix. It is to be noted that in the case of plastic base produced from mother stamper  90  by the 2P method, it cannot be directly used as mold (matrix) for production of stamper  40  after ultraviolet rays have been irradiated, and it is therefore necessary to once transfer uneven pattern to glass original plate  110  by the 2P method. In the case where stamper  40  is produced with molded disc which is plastic base produced from mother stamper  90  by injection molding being as matrix, it is necessary to embed center hole of the molded disc. As material of this plastic base, e.g., polymethyl methacrylate and polycarbonate, etc. are preferable.  
     [0080] The irradiation conditions such as irradiation times and irradiation intensities, etc. of ultraviolet rays and infrared rays irradiated onto photoresist  11  in the first embodiment, ultraviolet rays irradiated onto the ultraviolet hardening resin layer  61  in the second embodiment, and ultraviolet rays irradiated onto the ultraviolet hardening resin layer  101  in the third embodiment are suitably changed by film thickness and/or material, etc. of the photoresist  11 , the ultraviolet hardening resin layer  61  and the ultraviolet hardening resin layer  101 .  
     INDUSTRIAL APPLICABILITY  
     [0081] As explained above, in accordance with the present invention, it is possible to manufacture original plate of stamper for manufacturing optical recording medium in which the surface of uneven pattern corresponding to grooves, etc. recorded with respect to optical recording medium is smoothed, and twilled line portion of the uneven pattern is curved. Accordingly, uneven pattern is transferred from original plate of this stamper for manufacturing optical recording medium, thereby making it possible to obtain optical recording media which can efficiently ensure sufficient S/N ratio at the time of recording and/or reproduction of information.