Patent Publication Number: US-2009226766-A1

Title: Stamper for transferring pattern, method for manufacturing magnetic recording medium by using the stamper,  and the magnetic recording medium

Description:
This application is a U.S. Continuation of International Application Serial No. PCT/JP2006/320936, filed Oct. 20, 2006. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a pattern transfer stamper for transferring a fine uneven pattern onto a magnetic disc in manufacturing a magnetic recording medium (e.g. magnetic disc). The invention also relates to a method for manufacturing a magnetic recording medium using a pattern transfer stamper, and a magnetic recording medium. 
     BACKGROUND ART 
     For instance, as depicted in  FIG. 15 , the surface of a magnetic disc has a data region  81  and a servo region  82 . The data region  81  is provided with a plurality of concentric tracks (not illustrated). The data region  81  is further provided with a plurality of guard bands (not illustrated) extending in the circumferential direction of the magnetic disc D. The guard bands serve to separate the tracks from each other. The servo region  82  is provided adjacent to the data region  81  in the circumferential direction. The servo region  82  is utilized for detecting each track. The servo region  82  is provided with a servo pattern which represents servo information such as positional information of each track. 
     As a method for manufacturing a magnetic disc D of a high density, a transferring method called nanoimprinting has been proposed as disclosed in e.g. Patent Document 1. The nanoimprinting is a technique to transfer an uneven pattern to the surface of a resin layer formed on a substrate which is a base. The uneven pattern is formed by pressing a pattern transfer stamper (hereinafter simply referred to as “stamper”) against the resin layer. The surface of the stamper is formed with fine projections or recesses in units of nanometers. The uneven pattern represents e.g. tracks or servo patterns. 
     Patent Document 1: Japanese Lain-open Patent Publication No. 2005-286222 
       FIG. 16  is a perspective view depicting a principal portion of a conventional stamper. The stamper  86  has an uneven surface  87  including a guard band pattern portion  88  and a servo pattern portion  89 . The guard band pattern portion  88  corresponds to the data region  81  of the magnetic disc D. The servo pattern portion  89  corresponds to the servo region  82  of the magnetic disc D. 
     The guard band pattern portion  88 A includes a plurality of linear projections  90  extending in the circumferential direction. The linear projections  90  serve to form guard bands on the surface of the magnetic disc D. The servo pattern portion  89  includes square projections  91  projecting to be substantially rectangular. The square projections  91  form a servo burst portion representing e.g. positional information. In the stamper  86  depicted in  FIG. 16 , the linear projections  90  and the square projections  91  are spaced from each other by a predetermined distance. 
     To manufacture the magnetic disc D by nanoimprinting, the stamper  86  depicted in  FIG. 16  is pressed against a resin layer of the magnetic disc D. Since the linear projections  90  and the square projections  91  are spaced from each other, the pressure in the pressing concentrates on the ends  90   a  and the nearby portion of the linear projections  90 . Thus, when the stamper  86  is repetitively used for manufacturing magnetic discs D, the ends  90   a  of the linear projections  90  may be deformed to be bent in the radial direction, as depicted in  FIG. 17 . Depending on the use conditions, the ends  90   a  of the linear projections  90  may be damaged or broken. 
     When the stamper  86  having the shape depicted in  FIG. 17  is pressed against the resin layer of the magnetic disc D, offset occurs at the guard bands corresponding to the linear projections  90  and the adjacent tracks. Thus, it is difficult to accurately transfer a proper uneven pattern. As a result, the data magnetized in the tracks cannot be read properly, and the quality of data signals is deteriorated. Moreover, when the stamper  86  depicted in  FIG. 17  is used repetitively, the margin for the offset of tracks is reduced. As a result, the read/write margin of the entire magnetic disc D is reduced, which has a bad influence on the use of the magnetic disc D. 
     DISCLOSURE OF THE INVENTION 
     The present invention has been proposed under the circumstances described above. Therefore, an object of the present invention is to provide a pattern transfer stamper capable of transferring an uneven pattern properly and precisely. Another object of the present invention is to provide a method for manufacturing a magnetic recording medium using the pattern transfer stamper. Still another object of the present invention is to provide a magnetic recording medium manufactured by the manufacturing method. 
     According to a first aspect of the present invention, there is provided a pattern transfer stamper for transferring an uneven pattern to a deformable surface of a member which is a base for manufacturing a disc-shaped magnetic recording medium. The magnetic recording medium includes a data region and a servo region positioned adjacent to the data region in a circumferential direction. The pattern transfer stamper includes at least a data-region-corresponding uneven pattern portion corresponding to the data region of the disc-shaped magnetic recording medium. The data-region-corresponding uneven pattern portion includes linear projections extending in the circumferential direction and spaced from each other in a radial direction. A support projection for supporting an end of at least one of the linear projections is provided to be integrally connected to the end. 
     Preferably, the support projection extends in the radial direction and is connected to the ends of the plurality of linear projections. 
     Preferably, the support projection has a width which is larger than the width of the linear projections. 
     Preferably, the pattern transfer stamper further includes a servo-region-corresponding uneven pattern portion corresponding to the servo region of the disc-shaped magnetic recording medium. The servo-region-corresponding uneven pattern portion includes a plurality of servo-region-corresponding linear projections extending in the radial direction and spaced from each other in the circumferential direction. Of the plurality of servo-region-corresponding linear projections, the servo-region-corresponding linear projection positioned adjacent to the data-region-corresponding uneven pattern portion serves as the support projection. 
     Preferably, the support projection has a substantially square shape and is connected to the ends of at least two of the linear projections. 
     Preferably, the support projection has a substantially square shape and is connected to the end of every other linear projection. 
     Preferably, the pattern transfer stamper further includes a servo-region-corresponding uneven pattern portion corresponding to the servo region of the disc-shaped magnetic recording medium. The servo-region-corresponding uneven pattern portion includes a plurality of rectangular projections having a substantially rectangular shape. Of the plurality of rectangular projections, the rectangular projection positioned adjacent to the data-region-corresponding uneven pattern portion serves as the support projection. 
     Preferably, the support projection extends obliquely with respect to the radial direction and is connected to the ends of at least two of the linear projections. 
     Preferably, the pattern transfer stamper further includes a servo-region-corresponding uneven pattern portion corresponding to the servo region of the disc-shaped magnetic recording medium. The servo-region-corresponding uneven pattern portion includes a plurality of servo-region-corresponding linear projections extending obliquely with respect to the radial direction. Of the plurality of servo-region-corresponding linear projections, the servo-region-corresponding linear projection positioned adjacent to the data-region-corresponding uneven pattern portion serves as the support projection. 
     According to a second aspect of the present invention, there is provided a method for manufacturing a magnetic recording medium. The manufacturing method includes the steps of forming a magnetic layer on a substrate which is a base of the disc-shaped magnetic recording medium, forming a resin layer on the magnetic layer, and forming an uneven pattern by transferring an uneven pattern of the pattern transfer stamper provided according to the first aspect of the present invention onto the resin layer by pressing the uneven surface of the pattern transfer stamper against the resin layer and etching the exposed magnetic layer using the resin layer on the magnetic layer as a mask. 
     According to a third aspect of the present invention, there is provided a method for manufacturing a magnetic recording medium. The method includes the steps of transferring an uneven pattern of the pattern transfer stamper provided according to the first aspect of the present invention onto a deformable substrate which is a base of the disc-shaped magnetic recording medium by pressing the uneven surface of the pattern transfer stamper against the substrate, and forming a pattern of presence/absence of a magnetic member by forming a magnetic layer in recesses of the uneven pattern. 
     According to a fourth aspect of the present invention, there is provided a magnetic recording medium manufactured by the method provided according to the second or the third aspect of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view depicting a principal portion of a pattern transfer stamper according to a first embodiment of the present invention. 
         FIG. 2  depicts the surface of a magnetic disc. 
         FIG. 3  depicts the surface configuration of a magnetic disc after being pressed by a pattern transfer stamper. 
         FIG. 4  depicts the structure of a pattern transfer apparatus. 
         FIG. 5  depicts steps of a method for manufacturing a magnetic disc. 
         FIG. 6  depicts steps of the method for manufacturing a magnetic disc. 
         FIG. 7  depicts steps of another method for manufacturing a magnetic disc. 
         FIG. 8  depicts steps of the method for manufacturing a magnetic disc. 
         FIG. 9  is a perspective view depicting a principal portion of a pattern transfer stamper according to a second embodiment of the present invention. 
         FIG. 10  is a perspective view depicting a principal portion of a pattern transfer stamper according to a third embodiment of the present invention. 
         FIG. 11  is a perspective view depicting a principal portion of a pattern transfer stamper according to a fourth embodiment of the present invention. 
         FIG. 12  is a perspective view depicting a principal portion of a pattern transfer stamper according to a fifth embodiment of the present invention. 
         FIG. 13  is a perspective view depicting a principal portion of a pattern transfer stamper according to a sixth embodiment of the present invention. 
         FIG. 14  is a perspective view depicting a principal portion of a pattern transfer stamper according to a seventh embodiment of the present invention. 
         FIG. 15  depicts the appearance of a magnetic disc. 
         FIG. 16  is a perspective view depicting a principal portion of a conventional pattern transfer stamper. 
         FIG. 17  is a perspective view depicting a principal portion of a conventional pattern transfer stamper. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 
       FIG. 1  is a perspective view depicting a principal portion of a stamper for transferring a pattern according to a first embodiment of the present invention. The pattern transfer stamper  1  (hereinafter simply referred to as “stamper  1 ”) is used in manufacturing a magnetic disc D as a magnetic recording medium. For instance, the magnetic disc D is called a discrete track media. The stamper  1  is used for transferring a fine uneven pattern onto a magnetic disc D by nanoimprinting. 
     As depicted in  FIG. 15 , which has been referred to for describing the background art, the magnetic disc D has a rounded shape. At least one surface of the magnetic disc D includes a data region  81  and a servo region  82 . 
       FIG. 2  is a perspective view depicting the data region  81  and the servo region  82  of the magnetic disc D. The data region  81  is formed with a plurality of concentric tracks  2 . The data region  81  is further formed with a plurality of guard bands  3  (see circumferential, hatched portions) extending in the circumferential direction of the magnetic disc D. The guard bands  3  serve to separate the tracks  2  from each other. As will be described later, the tracks  2  may be made of e.g. a magnetic material, whereas the guard bands  3  may be made of e.g. a nonmagnetic material. 
     The servo region  82  is provided adjacent to the data region  81  in the circumferential direction. The servo region  82  is utilized for detecting tracks  2 . The servo region  82  is formed with a servo pattern  4 . The servo pattern  4  represents servo information such as positional information of the tracks  2 .  FIG. 2  depicts a servo burst portion  5  which constitutes part of the servo pattern  4 . The servo burst portion  5  is used for the tracking of a non-illustrated magnetic head. 
     The tacks  3  and the servo pattern  4  are formed by transferring an uneven pattern by the stamper  1 . Specifically, to manufacture the magnetic disc D, the stamper  1  is pressed against the base member (e.g. a resin layer) of the magnetic disc D. By this operation, a fine uneven pattern corresponding to the tracks  3  and the servo pattern  4  is transferred onto the resin layer. For this purpose, the stamper  1  has an uneven surface  10  (see  FIG. 1 ) corresponding to the uneven pattern for the tracks  3  and the servo pattern  4 . 
     The tracks  3  and the servo pattern  4  can be formed individually. Thus, the stamper  1  may have only the projection or recesses corresponding to the uneven pattern of the track  3  and may not have the projections or recesses corresponding to the uneven pattern of the servo pattern  4 . That is, a stamper having only the projections or recesses corresponding to the uneven pattern of the tracks  3  is used to transfer the uneven pattern of the tracks  3 . Then, another stamper having only the projections or recesses corresponding to the uneven pattern of the servo pattern  4  is used to transfer the uneven pattern of the servo pattern  4 . In this case, the servo pattern  4  may be later formed on the magnetic disc D by a technique other than nanoimprinting. For instance, the servo pattern may be magnetically formed using a servo track writer. 
     The stamper  1  may include e.g. an Ni substrate or an SiO 2  substrate. The uneven surface  10  of the stamper  1  has substantially the same size as that of the disc surface of the magnetic disc D. The stamper  1  is formed by performing application of a resist, light exposure by electronic beams, development and plating or etching with respect to a surface of a material substrate. 
     Preferably, as depicted in  FIG. 1 , the uneven surface  10  of the stamper  1  is provided with a guard band pattern portion  11  and a servo pattern portion  12 . The guard band pattern portion  11  corresponds to the data region  81  of the magnetic disc D and is formed with an uneven pattern in the radial direction. Specifically, a plurality of linear projections  11   a  extending in the circumferential direction are formed in the guard band pattern portion  11 . The linear projections  11   a  are arranged at predetermined intervals in the radial direction. 
     The servo pattern portion  12  is provided with an uneven pattern corresponding to the servo region  82  of the magnetic recording medium. As depicted in  FIG. 1 , the servo pattern portion  12  includes a servo burst pattern portion  13  and a non-patterned portion  14 . The servo burst pattern portion  13  is provided with a plurality of square projections  13   a  projecting to have a substantially rectangular shape. The square projections  13   a  are arranged in rows and columns. The servo burst pattern portion  13  corresponds to the servo burst portion  5  (see  FIG. 2 ) provided in the servo region  82  of the magnetic recording medium D. The non-patterned portion  14  is not provided with an uneven pattern and is flat. 
     A support projection  15  for supporting the ends  11   b  of the linear support projections  11   a  of the guard band pattern portion  11  is provided to be integrally connected to the ends. The support projection  15  extends in the radial direction. The support projection  15  is connected to an end  11   b  of each of the linear projections  11   a . The width W 1  of the support projection  15  is substantially equal to the width A of the linear projections  11   a.    
     Though not illustrated in  FIG. 1 , in addition to the servo burst pattern portion  13 , a preamble pattern portion (which will be described later) or the like is formed in the servo pattern portion  12 . The preamble pattern portion is provided with a plurality of linear projections extending in the radial direction. A phase difference signal pattern portion (which will be described later) may be provided instead of the servo burst pattern portion  13 . The phase difference signal pattern portion is provided with a plurality of linear projections extending obliquely with respect to the circumferential direction. 
       FIG. 3  is a perspective view depicting a principal portion of the surface of a base member of a magnetic recording medium D after being pressed by the stamper  1 . As depicted in  FIG. 3 , the base member of the magnetic recording medium D includes a glass substrate  31 , a magnetic film  32  and a resin layer  33 . The magnetic film  32  is formed on the glass substrate  31 . The resin layer  33  is formed on the magnetic film  32 . 
     By the pressing with the stamper  1 , the resin layer  33  is formed with a fine uneven pattern corresponding to the uneven surface  10  of the stamper. For instance, by the linear projections  11   a  of the stamper  1 , a plurality of recesses  16  extending in the circumferential direction are formed at the surface of the resin layer  33 . By the support projection  15  of the stamper  1 , a recess  17  extending in the radial direction is formed at the surface of the resin layer  33 . The recesses  16  communicate with each other via the recess  17 . Further, by the square projections  13   a  of the stamper  1 , a plurality of square recesses  18  formed on the surface of the resin layer  33 . 
     As described above, according to the first embodiment, the support projection  15  is provided to be integrally connected to the ends  11   b  of the linear projections  11   a , so that the linear projections  11   a  are connected to each other via the support projection  15 . Thus, the ends  11   b  of the linear projections  11   a  are supported by the support projection  15 , so that the ends  11   b  and the nearby portion are rigid. Thus, even when the stamper  1  is repetitively used in nanoimprinting, the ends  11   b  of the linear projections  11   a  are prevented from being deformed to be bent in the radial direction, damaged or broken. 
     Therefore, according to the first embodiment, the provision of the support projection  15  in the stamper  1  ensures that recesses  16  having a proper shape are formed in the resin layer  33 . Thus, the uneven pattern is transferred properly and precisely. As will be described later, the resin layer  33  is used as a mask for etching. Owing to the provision of the recesses  16 , the etching is performed precisely, so that tracks  2  are formed properly. 
     It is to be noted that the width W 1  of the support projection  15  may be larger than the width A of the linear projections  11   a . With this arrangement, the support projection  15  supports the ends  11   b  of the linear projections  11   a  more firmly. Alternatively, the width W 1  of the support projection  15  may be smaller than the width A of the linear projections  11   a  if the support projection  15  can support the linear projections  11   a.    
     To manufacture the magnetic disc D, the stamper  1  is pressed against the base member of the magnetic disc D, so that the pressure concentrates in the radial direction of the stamper  1 . The support projection  15  and the linear projections  11   a  support each other. When the width W 1  of the support projection  15  is small, the area occupied by the support projection  15  on the magnetic disc D is small, so that the density of the magnetic disc D can be increased. For these reasons, when the support projection  15  is provided individually on the stamper  1 , it is preferable that the width W 1  of the support projection  15  is smaller than the width A of the linear projections  11   a.    
     A method for manufacturing a magnetic disc D using the stamper  1  will be described below. In manufacturing a magnetic disc D, e.g. a pattern transfer apparatus  20  as depicted in  FIG. 4  is used for transferring an uneven pattern by nanoimprinting using the stamper  1 . 
     For instance, the pattern transfer apparatus  20  is set in a working chamber  21 . The pattern transfer apparatus  20  includes the stamper  1 , an upper holder  24 , a lower panel  25 , a lower elevating member  26  and a drive motor  27 . The upper holder  24  holds the stamper  1  and the upper panel  22  horizontally. The upper holder further holds an upper unit  23 . The lower panel  25  holds the upper holder  24  and the magnetic disc D horizontally. The lower elevating member  26  moves vertically while holding the lower panel  25 . The drive motor  27  causes the vertical movement of the lower elevating member  26 . In the working chamber  21 , a vacuum pump for reducing the pressure in the working chamber  21  is provided. For instance, the vacuum pump  28  has the ability to reduce the pressure in the working chamber  21  to about 1 Torr. 
     The upper panel  22  is made of e.g. quartz glass and transmits the light for positioning. The upper unit  23  incorporates a mechanism (e.g. an illuminator or a photodetector) (not illustrated) for properly positioning the stamper  1  relative to the magnetic disc D within a horizontal plane. Thus, it is preferable that the stamper  1  is made of an SiO 2  substrate which transmits light. 
     The lower panel  25  incorporates a heater  29  for heating the stamper  1  and the magnetic disc D in contact with these. A heater for heating the stamper  1  and the magnetic disc D may be provided in the upper panel  25 . When the lower elevating member  26  is moved vertically by the drive motor  27 , the lower panel  25  moves vertically along with the elevating member. As a result, the magnetic disc D held horizontally by the lower panel  25  moves toward or away from the stamper  1  held at a predetermined height from the floor. In the state in which the magnetic disc is held in close contact with the uneven surface  10  of the stamper  1 , the stamper  1  and the magnetic disc D are pressed against each other. 
       FIGS. 5 and 6  depict a manufacturing process of the magnetic disc D. In  FIGS. 5 and 6 , the uneven patterns of the stamper  1  and the magnetic disc D are enlarged to be clearer. Actually, however, the magnetic disc D of the size depicted in  FIG. 9  is mounted. 
     First, in the manufacturing process, a base member of the magnetic disc D as depicted in  FIG. 5A  is prepared. For instance, the base member includes a glass substrate  31 , a magnetic film  32  formed on a surface of the glass substrate  31 , and a resin layer  33  formed on the magnetic film  32 . In the manufacturing process, the resin layer  33  is to be used as a mask (which will be described later). The resin layer  33  is formed by e.g. spin coating. The resin layer  33  is made of e.g. a thermoplastic resin such as polymethyl methacrylate resin (PMMA). The glass transition point of the resin layer  33  is about 100° C. 
     As depicted in  FIG. 5A , the uneven surface  10  of the stamper  1  is brought into close contact with the surface of the resin layer  33 . In bringing the uneven surface  10  of the stamper  1  into close contact with the resin layer  33 , the vacuum pump  28  (not illustrated in the figure) is actuated. As a result, the working chamber  21  is held in vacuum of about 1 Torr. 
     Then, under the vacuum condition, pressure application and heating are performed with respect to the uneven surface  10  of the stamper  1  and the resin layer  33 . Specifically, as depicted in  FIG. 5B , with the press surface  10  and the resin layer  33  held in contact with each other, the stamper  1  and the magnetic disc D are sandwiched between the upper panel  22  and the lower panel  25 . The stamper  1  and the magnetic disc D are pressed by the upper panel  22  and the lower panel  25  with a pressing force F of e.g. about 2500 kgf. The stamper  1  and the magnetic disc D are heated by the heater  29  to about 135° C., which is higher than the glass transition point of the resin layer  33 . 
     Then, after the lapse of a predetermined cooling period, the vacuum of the working chamber  21  is eliminated. Then, as depicted in  FIG. 5C , the uneven surface  10  of the stamper  1  is separated from the resin layer  33 . Thus, the resin layer  33 , on which the uneven pattern corresponding to the uneven surface  10  is transferred and which is hardened, is obtained. The uneven pattern of the resin layer  3  is used as a mask for etching, which will be described later. 
     In this way, the uneven pattern corresponding to the uneven surface  10  of the stamper  1  is transferred onto the resin layer  33 . As noted before, the stamper is formed with the support projection  15  connected to the ends  11   b  of the linear projections  11   a . Thus, even when the stamper  1  is repetitively used, the ends  11   b  of the linear projections  11   a  are prevented to be bent. Thus, the uneven pattern corresponding to the uneven surface  10  is formed on the resin layer  33  without a transfer defect. Thus, the fine uneven pattern is properly transferred onto the resin layer  33 . 
     After the uneven pattern is transferred, portions of the resin layer  33  which are not necessary as a mask remain. As depicted in  FIG. 5D , such residual portions of the resin layer  33  are removed. As a result, the magnetic film  32  is exposed at the bottom of the recesses of the resin layer  33 . 
     Then, etching is performed with respect to the magnetic film  32  using the resin layer  33  as a mask. As depicted in  FIG. 6A , by subsequently removing the resin layer  33 , recesses  34  are formed in the magnetic film  32 . 
     Thereafter, as depicted in  FIG. 6B , a non-magnetic material  35  is fixed to the magnetic film  32  to fill the recesses  34 . Then, as depicted in  FIG. 6C , the surfaces of the magnetic film  32  and the non-magnetic material  35  are ground. Thus, the magnetic film  32  is divided into portions separated by the non-magnetic film  35  filling the recesses  34 . Further, on these surfaces, a protective film or a lubricating film (both not illustrated) may be formed. In this way, the magnetic disc D as a discrete track media is completed. 
       FIGS. 7 and 8  depict another method for manufacturing the magnetic disc D. In  FIGS. 7 and 8 , the uneven patterns of the stamper  1  and the magnetic disc D are enlarged to be clearer. Actually, however, the magnetic disc D of the size depicted in  FIG. 9  is mounted. This manufacturing method differs from the above-described manufacturing method in that a resin substrate  36  is used instead of the glass substrate  31 . Further, unlike the above-described manufacturing method in which the magnetic film  32  is formed on the glass substrate  31  in advance, the magnetic film  32  is formed after the pressing with the resin stamper  1  is performed in this method. 
     First, in this manufacturing process, a deformable resin substrate  36  is prepared as the base member of the magnetic disc D. As depicted in  FIG. 7A , after a vacuum is produced in the vacuum chamber  21 , the uneven surface  10  of the stamper  1  is directly brought into close contact with the surface of the resin substrate  36 . 
     Then, under the vacuum condition, pressure application and heating are performed with respect to the uneven surface  10  and the resin layer  36 . Specifically, as depicted in  FIG. 7B , with the uneven surface  10  and the resin substrate  36  held in contact with each other, the stamper  1  and the resin substrate  36  are sandwiched between the upper panel  22  and the lower panel  25 . The stamper  1  and the resin substrate  36  are pressed with a pressing force F. Then, the stamper  1  and the resin substrate  36  are heated by the heater  29 . 
     Then, after the lapse of a predetermined cooling period, the vacuum of the working chamber  21  is eliminated. Then, as depicted in  FIG. 7C , the uneven surface  10  of the stamper  1  is separated from the resin substrate  36 . Thus, as depicted in  FIG. 7D , the resin substrate  36 , on which the uneven pattern corresponding to the uneven surface  10  is transferred and which is hardened, is obtained. 
     Thereafter, as depicted in  FIG. 8A , a magnetic film  37  is fixed to entirely cover the resin substrate  36 . Then, as depicted in  FIG. 8B , the surface of the magnetic film  37  is ground, so that the magnetic film  37  is separated from the resin substrate  36  on the surface of the base member. In this way, the magnetic disc D as a discrete track media is completed. 
       FIGS. 9-14  depicts a second through a seventh embodiments of the present invention. These embodiments are variations of the support projection  15  of the first embodiment. That is, these embodiments teach other structures for supporting the ends  11   b  of the linear projections  11   a  of the guard band pattern portion  11 . 
       FIG. 9  is a perspective view depicting a principal portion of a stamper according to the second embodiment of the present invention. In this stamper  1 A, the square projections  13   a  of the servo burst pattern portion  13  are utilized instead of the support projection  15  of the first embodiment. 
     Each of the square projections  13   a  is integrally connected to the ends  11   b  of two adjacent linear projections  11   a  of the guard band pattern portion  11 . Of the square projections  13   a  of the servo burst pattern portion  13 , those formed adjacent to the guard band pattern  11  are connected to the linear projections  11   a.    
     The length D of each side of the square projection  13   a  is larger than the distance L between two adjacent linear projections  11   a  so that the square projection  13   a  is connected to the ends  11   b  of the two adjacent linear projections  11   a . In this way, in the second embodiment, the non-patterned portion  14  of the first embodiment (see  FIG. 1 ) is eliminated so that the guard band pattern portion  11  and the servo burst pattern portion  13  are arranged adjacent to each other. 
     In the second embodiment, the square projection  13   a  serving as a support member connects the ends  11   b  of two adjacent linear projections  11   a  to each other. Thus, the ends  11   b  of the two adjacent linear projections  11   a  are supported to be rigid. Alternatively, the square projection  13   a  may be arranged to connect the ends  11   b  of three or more linear projections  11   a  to each other. 
       FIG. 10  is a perspective view depicting a principal portion of a stamper according to the third embodiment of the present invention. The stamper  1 B of this embodiment differs from that of the second embodiment in that a square projection  13   a  illustrated in the second embodiment (see  FIG. 9 ) is integrally connected to the end  11   b  of every other linear projection  11   a.    
     Although the ends  11   b  of two linear projections  11   a  are not connected to each other in the arrangement of the third embodiment, the end  11   b  of every other linear projection  11   a  and the nearby portion can be made rigid. 
       FIG. 11  is a perspective view depicting a principal portion of a stamper according to the fourth embodiment of the present invention. In this stamper  1 C, linear projections  16   a  of the preamble pattern portion  16  are utilized instead of the support projection  15  of the first embodiment. 
     The preamble pattern portion  16  is formed in the servo pattern portion  12  and corresponds to a preamble portion (not illustrated) in the servo region  82  of the magnetic disc D. The preamble portion represents clock information for reading the data of the tracks  2 . The preamble pattern portion  16  is formed with a plurality of linear projections  16   a  extending in the radial direction. 
     In the fourth embodiment, of the linear projections  16   a  of the preamble pattern  16 , the one arranged adjacent to the guard band pattern portion  11  is connected to the ends  11   b  of the linear projections  11   a  of the guard band pattern portion  11 . Thus, the ends  11   b  of the linear projections  11   a  are supported to be rigid. 
       FIG. 12  is a perspective view depicting a principal portion of a stamper according to the fifth embodiment of the present invention. In this stamper  1 D, linear projections  17   a  of a phase difference signal pattern portion  17  are utilized instead of the support projection  15  of the first embodiment. 
     The phase difference signal pattern portion  17  is formed in the servo pattern portion  12  and corresponds to a phase difference signal portion (not illustrated) in the servo region  82  of the magnetic disc D. The phase difference signal portion represents positional information or sector information. The phase difference signal pattern portion  17  is provided with a plurality of linear projections  17   a  extending obliquely with respect to the circumferential direction. 
     In the fifth embodiment, the linear projections  17   a  are so formed that an end of each linear projection  17   a  connects the ends  11   b  of two adjacent linear projections  11   a  of the guard band pattern portion  11  to each other. That is, of the linear projections  17   a  of the phase difference signal pattern portion  17 , the ends of the linear projections  17   a  which are adjacent to the guard band pattern portion  11  are connected to the linear projections  11   a . With this arrangement, the ends  11   b  of adjacent two linear projections  11   a  are supported to be rigid by the linear projection  17   a . Alternatively, the linear projection  17   a  may be arranged to connect the ends  11   b  of three or more linear projections  11   a  to each other. 
       FIG. 13  is a perspective view depicting a principal portion of a stamper according to the sixth embodiment of the present invention. In this stamper  1 E, a linear projection  16   b  of the preamble pattern portion  16  is utilized instead of the support projection  15  of the first embodiment. The linear projection  16   b  extends in the radial direction. The width W 2  of the linear projection  16   b  is relatively small. Specifically, the width W 2  of the linear projection  16   b  is smaller than the width W 3  of linear projections  16   a  of the preamble pattern portion  16 . 
     For instance, in the fourth embodiment (see  FIG. 11 ) the linear projection  16   a  is integrally connected to the linear projections  11   a  of the guard pattern portion  11 , so that the recess formed between the linear projections  11   a  are enclosed by the linear projection  16   a . With this arrangement, when the stamper  1 C (see  FIG. 11 ) is pressed against the resin layer of the magnetic disc D, resin or air pushed out by the linear projection  16   a  integrally connected to the linear projections  11   a  cannot flow smoothly between the guard band pattern portion  11  and the servo pattern portion  12 . As a result, excessive supply of resin due to the accumulation of resin or insufficient loading of resin due to the accumulation of air occurs, which hinders the formation of an uneven pattern having a proper configuration. 
     In the sixth embodiment, however, the width W 2  of the linear projection  16   b  is made smaller than the width W 3  of the linear projections  16   a . With this arrangement, when the stamper  1 E (see  FIG. 13 ) is pressed against the resin layer of the magnetic disc D, only a small amount of resin flows into between the guard band pattern portion  11  (recesses  11   c  formed between the linear projections  11   a ) and the servo pattern portion  12  (recess  16   c ), and air flows smoothly. Thus, excessive supply or insufficient loading of resin is prevented, so that the performance of pattern transfer is not deteriorated. 
       FIG. 14  is a perspective view depicting a principal portion of a stamper according to the seventh embodiment of the present invention. In this stamper  1 F, a linear projection  18   a  is integrally connected to the ends  11   b  of the linear projections  11   a  of the guard band pattern portion  11 . The linear projection  18   a  extends in the radial direction. The height H of the linear projection  18   a  is lower than the height B of the linear projections  11   a.    
     Since the height of the linear projection  18   a  is lower than that of the linear projections  11   a  in the seventh embodiment, resin or air readily flows between the guard band pattern portion  11  (recesses  11   c  formed between the linear projections  11   a ) and the servo pattern portion  12  (recess  18   b ) when the stamper  1 F (see  FIG. 14 ) is pressed against the resin layer of the magnetic disc D. Thus, similarly to the sixth embodiment, insufficient loading of resin is prevented, so that the performance of pattern transfer is not deteriorated. 
     It is difficult to manufacture the stamper  1 F of the seventh embodiment by a conventional etching technique, because the linear projection  18   a  and the linear projections  16   a  differ from each other in height. Preferably, therefore, the stamper  1 F is manufactured by the method described below. 
     First, application of a resist, light exposure by electronic beams and development are performed with respect to a surface of a material substrate of the stamper  1 F prepared in advance. A first etching step is performed using the applied resist as a mask. Then, resist is applied again. In this process, the recesses formed by the first etching process are filled with the resist applied later. Then, light exposure and development are performed. Then, a second etching step is performed on the conditions different from those of the first etching (e.g. different etching time) using the resist as a mask. By this process, a stepped portion is formed on the material substrate of the stamper  1 F so that the linear projection  18   a  and the linear projections  16   a  having different heights are formed. 
     The present invention is not limited to the foregoing embodiments. For instance, the object to which the uneven pattern is to be transferred is not limited to a discrete track media. The present invention is also effective in making another stamper by transferring the uneven pattern of the stamper  1  by nanoimprinting. Further, in duplicating a stamper by a technique other than nanoimprinting, such as plating, a force opposite from that of nanoimprinting is applied to the stamper  1  in removing the duplicated stamper from the stamper  1 . This causes the deformation or damage of the stamper similarly to the problem which the present invention aims to solve. Thus, the present invention is also effective for such duplication. The stamper  1  of the foregoing embodiments is applicable to other situations where a fine uneven pattern needs to be formed.