Patent Publication Number: US-2007108163-A1

Title: Stamper, imprinting method, and method of manufacturing an information recording medium

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a stamper used when manufacturing an information recording medium, an imprinting method that presses a stamper into a resin layer formed on a surface of a substrate to transfer a concave/convex form of the stamper, and a method of manufacturing an information recording medium using a concave/convex pattern transferred to a resin layer.  
      2. Description of the Related Art  
      Optical lithography is conventionally known as a method of forming a fine concave/convex pattern (a resist pattern) in a resist layer (a resin layer) formed on a surface of a substrate during a process that manufactures an information recording medium or the like. When optical lithography is carried out, a resist layer formed on a subs-rate is irradiated with light to form an exposure pattern and then the resist layer is developed to form a concave/convex pattern on the substrate. In recent years, electron-beam lithography that draws a pattern of nanometer size using an electron beam instead of light to form a concave/convex pattern has been developed as a technique for forming an even finer pattern. However, electron-beam lithography has a problem in that a long time is required to draw a pattern on the resist layer, making such technique unsuited to mass production.  
      As a method of solving this problem, U.S. Pat. No. 5,772,905 discloses a nano-imprint lithography method (i.e., an imprinting method that forms a concave/convex pattern of nanometer size: hereinafter simply “imprinting method”) that forms a concave/convex pattern of nanometer size on a substrate by pressing a stamper on which a concave/convex pattern of nanometer size has been formed onto a resin layer on the substrate to transfer the concave/convex form of the stamper to the resin layer. With this imprinting method, first as shown in FIG. 1A of U.S. Pat. No. 5,772,905, a stamper (“mold”) 10z (hereinafter component elements disclosed in the specification of the U.S. Pat. No. 5,772,905 are indicated by reference numerals appended with “z”) that has a concave/convex pattern of nanometer size (as one example, with a minimum width of around 25 nm) formed in a transfer surface thereof is manufactured. More specifically, an electron beam lithography apparatus is used to draw a desired pattern on a resin layer formed so as to cover a thin film (“molding layer”) 14z made of silicon oxide or the like that has been formed on the surface of a silicon substrate 12z, and then the thin film 14z is etched by a reactive ion etching apparatus with the resin layer as a mask to form a concave/convex pattern with a plurality of convex parts (features) 16z within the thickness of the thin film 14z. By doing so, the stamper 10z is manufactured.  
      Next, as one example, polymethyl methacrylate (PMMA) is spin coated on the surface of a silicon substrate 18z to form a resin layer (a “thin film layer”) 20z with a thickness of around 55 nm. Next, after heating both the stamper 10z and a multilayer structure composed of the substrate 18z and the resin layer 20z to around 200° C., as shown in FIG. 1B of the U.S. Pat. No. 5,772,905, the convex parts 16z of the stamper 10z are pressed into the resin layer 20z on the substrate 18z with a pressure of 13.1 MPa (133.6 kgf/cm 2 ). After this, the multilayer structure is left to cool to room temperature in a state where the stamper 10z is still pressed in (i.e., a cooling process is carried out), and then the stamper 10z is separated from the resin layer 20z. By doing so, as shown in FIG. 1C of the U.S. Pat. No. 5,772,905, the convex parts 16z of the concave/convex pattern of the stamper 10z are transferred to the resin layer 20z to form a plurality of concave parts (“regions”) 24z, thereby forming a concave/convex pattern of nanometer size (in the resin layer 20z) on the substrate 18z.  
     SUMMARY OF THE INVENTION  
      By investigating the conventional imprinting method described above, the present inventors found the following problems. That is, with this imprinting method, as shown in FIGS. 1A and 1B of the U.S. Pat. No. 5,772,905, a stamper 10z formed so that the heights from the bottom surfaces of the concave parts in the concave/convex pattern to the protruding ends of the convex parts 16z are uniform across the entire stamper (that is, a stamper formed so that the protruding ends of the respective convex parts 16z lie on substantially the same plane) is pressed into the resin layer 20z to form the concave/convex pattern on the substrate 18z. Various types of convex parts 16z with different lengths along a direction that corresponds to a circumferential direction (i.e., the direction of rotation) of the information recording medium (hereinafter simply “lengths in the circumferential direction”) and/or different lengths along a direction corresponding to a radial direction of the information recording medium (hereinafter simply “lengths in the radial direction”) are formed on the stamper 10z in accordance with the form of the data track patterns and the servo patterns to be formed. However, with the conventional imprinting method, since the concave/convex pattern is pressed onto the resin layer 20z with a substantially uniform pressing force across the entire stamper 10z, parts where convex parts 16z that are long in the radial direction and comparatively long in the circumferential direction, for example, have been formed are difficult to press sufficiently deeply into the resin layer 20z.  
      More specifically, as shown in  FIG. 28 , the convex parts 16z for forming the data track patterns on the information recording medium, for example, are comparatively long in the circumferential direction but have comparatively short lengths L11 in the radial direction across the entire range from the inner periphery to the outer periphery of the information recording medium. Accordingly, at data track pattern forming regions where convex parts 16z with comparatively short lengths L11 in the radial direction are formed, the PMMA (the resin material forming the resin layer 20z) can smoothly move inside the concave parts in the periphery of the convex parts 16z when the convex parts 16z are pressed in, and therefore the convex parts 16z can be pressed sufficiently deeply into the resin layer 20z. As a result, in the data track pattern forming regions, it is possible to form concave/convex patterns on the substrate 18z with a sufficiently small thickness T11 for the residue between the protruding ends of the convex parts 16z and the substrate 18z (i.e., at the bottoms of the concave parts 24z).  
      On the other hand, as shown in  FIG. 29 , as examples the convex parts 16z for forming preamble patterns and sector address patterns of servo patterns on the information recording medium have comparatively long lengths in the radial direction from the inner periphery to the outer periphery of the information recording medium and also comparatively long lengths L12 in the circumferential direction at positions corresponding to the outer periphery of the information recording medium. Accordingly, in servo pattern forming regions where the convex parts 16z with comparatively long lengths L12 in the circumferential direction are formed (in this example, the outer peripheries of the preamble pattern forming regions and the sector address pattern forming regions), the PMMA cannot smoothly move inside the concave parts in the periphery of the convex parts 16z when the convex parts 16z are pressed in, making it difficult to press the convex parts 16z sufficiently deeply into the resin layer 20z. As a result, in the outer peripheries of regions where servo patterns (preamble patterns and the like) are to be formed, it is difficult to make the thickness of the residue T12 between the protruding ends of the convex parts 16z and the substrate 18z sufficiently thin.  
      Convex parts 16z for forming burst patterns, where individual burst regions are composed of convex parts, out of the servo patterns on the information recording medium (i.e., convex parts 16z for forming the concave parts between the individual burst regions in the burst patterns) are set so that the lengths thereof in the circumferential direction between the concave parts corresponding to the individual burst regions become gradually longer from the inner periphery to the outer periphery. Similarly, convex parts 16z for forming burst patterns, where individual burst regions are composed of concave parts, out of the servo patterns on the information recording medium (i.e., convex parts 16z for forming the individual burst regions in the burst patterns) are set so that the lengths of the convex parts 16z in the outer periphery in the circumferential direction become longer than those of the convex parts 16z in the inner periphery. Accordingly, in servo pattern forming regions in which convex parts 16z that are comparatively long in the circumferential direction are formed (in this example, the cuter peripheries of the burst pattern forming regions), it is difficult for the PMMA to move smoothly into the concave parts in the periphery of the convex parts 16z when the convex parts 16z are pressed in, making it difficult to press the convex parts 16z sufficiently deeply into the resin layer 20z. As a result, in the outer peripheries of regions where servo patterns (i.e., burst patterns) are to be formed, it is difficult to make the thickness of the residue between the protruding ends of the convex parts 16z and the substrate 18z sufficiently thin. In addition, since the surface area of the convex parts 16z for forming burst patterns where the individual burst regions are composed of convex parts is large relative to the concave parts in the burst pattern forming regions, there is the risk of difficulty in pressing the convex parts 16z sufficiently deeply into the resin layer even in the inner peripheries where the lengths of the convex parts 16z in the circumferential direction are comparatively short.  
      When manufacturing an information recording medium using the concave/convex pattern formed on the substrate 18z, it is necessary to remove the residue from the substrate 18z at the bottoms of the concave parts 24z of the concave/convex pattern by carrying out an etching process or the like. Accordingly, when the concave/convex pattern has been formed on the substrate 18z by the conventional imprinting method, there is the problem that a long time is required to remove the residue with the thickness T12 at positions (e.g., the outer peripheries of the regions for forming the preamble patterns and the like) where the convex parts 16z with long lengths L12 in the circumferential direction, for example, have been pressed in. Also, as described earlier, the thickness T11 of the residue at positions (i.e., the data track pattern forming regions) where convex parts 16z with short lengths L11 in the radial direction, for example, are pressed in is sufficiently thinner than the thickness T12. Accordingly, if the etching process is carried out for sufficient time to reliably remove the residue with the thickness T12, the removal of the residue with the thickness T11 will be completed before the removal of the residue with the thickness T12 is completed. As a result, at positions (i.e., the concave parts 24z with the length L11 in the radial direction) where the residue with the thickness T11 has been removed, the etching will continue until the removal of the residue with the thickness T12 is completed, so that the inner side walls of the concave parts 24z are eroded, resulting in the length in the radial direction of the concave parts 24z (this length is hereinafter referred to as the “opening length”) becoming wider. This means that with the conventional imprinting method, there is another problem in that when a concave/convex pattern is formed on the substrate 18z, it is difficult to form the lengths (i.e., opening length) of the concave parts 24z after the residue is removed (i.e., after the etching process) with the desired widths.  
      The present invention was conceived in view of the problems described above and it is a principal object of the present invention to provide a stamper, an imprinting method, and a method of manufacturing an information recording medium that can precisely form concave/convex patterns including concave parts with desired opening lengths.  
      A stamper according to the present invention has stamper-side concave/convex patterns formed thereupon and is capable of manufacturing an information recording medium on which data track patterns and servo patterns are formed by concave/convex patterns, wherein a plurality of types of convex parts with different heights from a reference plane, which is set between a front surface and a rear surface of the stamper, to protruding ends of the convex parts are formed in the stamper-side concave/convex patterns, and second convex parts, at least one part of which has the height that is higher than the height of a highest first convex part out of the convex parts formed in regions corresponding to the data track patterns, are formed in regions corresponding to the servo patterns. Note that the expression “the front surface of the stamper” in this specification refers to “bottom surfaces of concave parts in the stamper-side concave/convex patterns”, that is, the “formation surface of the stamper-side concave/convex patterns”. Here, when the bottom surfaces of the concave parts in the stamper-side concave/convex patterns do not lie on the same plane, a bottom surface of any of the concave parts (as one example, a bottom surface that is closest to the rear surface of the stamper out of the bottom surfaces of the concave parts) is set as the “front surface of the stamper” for the present invention. In addition, the expression “between the front surface and the rear surface” for the present invention includes both the “front surface of the stamper” and the “rear surface of the stamper”. The expression “reference plane” in this specification refers to a freely chosen plane set between the front surface and the rear surface of the stamper.  
      According to the stamper according to the present invention and an imprinting method described later that uses such stamper, the stamper-side concave/convex patterns are constructed so that second convex parts, at least one part of which has the height that is higher than the height of a highest first convex part out of the convex parts formed in regions corresponding to the data track patterns, are formed in regions corresponding to the servo patterns. By doing so, when the entire region (i.e., the data track pattern forming regions and the servo pattern forming regions) of the stamper is pressed into the resin layer with a uniform pressing force during imprinting, it is possible to press the convex parts in the servo pattern forming regions, which include a large number of convex parts that are difficult to press into the resin layer, sufficiently deeply into the resin layer. Accordingly, the convex parts in the data track pattern forming regions and the convex parts in the servo pattern forming regions can be pressed into the resin layer to a similar extent and sufficiently deeply, thereby making it possible to make the thickness of the residue on the substrate uniform across the entire substrate. Accordingly, since it is possible to make the time required to remove the residue substantially equal across the entire substrate, it is possible to avoid a situation where the concave parts in the concave/convex pattern transferred to the resin layer in the regions corresponding to the data track pattern regions are formed with unintentionally wide openings due to the side wall surfaces of the concave parts being eroded. By doing so, it is possible to precisely form concave/convex patterns including concave parts with the desired opening widths across the entire data track pattern forming regions and the entire servo pattern forming regions. By manufacturing an information recording medium using the concave/convex patterns that have been formed with high precision, it is possible to manufacture an information recording medium that is not susceptible to recording/reproducing errors.  
      On a stamper according to the present invention, in the stamper-side concave/convex patterns, third convex parts that are continuously formed along a direction corresponding to a radial direction of the information recording medium may be formed as the second convex parts, and the third convex parts may be formed so that the height thereof is higher than the height of the first convex part at positions where the length of the third convex parts in a direction corresponding to a circumferential direction of the information recording medium is longer than the length of the first convex part in the direction corresponding to the radial direction. Note that the expression “the length (of the convex parts) in the direction corresponding to the circumferential direction” in this specification refers to “the distance in the circumferential direction between opposite side wall surfaces of one convex part”. Also, the expression “the length (of the convex parts) in the direction corresponding to the radial direction” in this specification refers to “the distance in the radial direction between opposite side wall surfaces of one convex part”.  
      According to the stamper according to the present invention and an imprinting method described later that uses such stamper, by forming the third convex parts so that the height thereof is higher than the height of the first convex part at positions where the length of the third convex parts in a direction corresponding to a circumferential direction of the information recording medium is longer than the length of the first convex part the direction corresponding to the radial direction, it becomes possible to press the third convex parts, such as the convex parts for forming the preamble patterns and the convex parts for forming the sector address patterns whose lengths in the circumferential direction in the outer peripheries thereof are longer than the length in the radial direction of the first convex part for forming the data track patterns, into the resin layer to a similar extent to the first convex part for forming the data track patterns and sufficiently deeply into the resin layer. This means that the thickness of the residue in the regions corresponding to the data track pattern regions (i.e., in the data track pattern forming regions) and the thickness of the residue in the regions corresponding to the servo pattern regions (i.e., in the servo pattern forming regions) can be made substantially uniform.  
      On the stamper according to the present invention, in the stamper-side concave/convex patterns, parts corresponding to individual burst regions in burst patterns out of the servo patterns may be composed of concave parts and fourth convex parts may be formed around the concave parts as the second convex parts, and the fourth convex parts may be formed so that the height thereof is higher than the height of the first convex part in at least one part of each of the fourth convex parts. Note that the expression “individual burst regions” in this specification refers to a plurality of convex parts or a plurality of concave parts that are substantially parallelogram-shaped or substantially oval (which includes circular forms) and are disposed in the circumferential direction of the information recording medium.  
      According to the stamper according to the present invention and an imprinting method described later that uses such stamper, by forming the fourth convex parts so that the height thereof is higher than the height of the first convex part in at least one part of each of the fourth convex parts, it is possible to press the outer peripheries of the fourth convex parts for forming the burst patterns that are difficult to press into the resin layer during the imprinting process into the resin layer to a similar extent as the first convex part for forming the data track patterns and sufficiently deeply into the resin layer. This means that the thickness of the residue in the regions corresponding to the data track pattern regions (i.e., in the data track pattern forming regions) and the thickness of the residue in the regions corresponding to the burst pattern regions (i.e., in the burst pattern forming regions) can be made substantially uniform.  
      On the stamper according to the present invention,  
      the fourth convex parts may be formed so that the height thereof is higher than the height of the first convex part across the entire forth concave parts.  
      According to the stamper according to the present invention and an imprinting method described later that uses such stamper, by forming the fourth convex parts so that the height thereof is higher than the height of the first convex part across the entire forth concave parts, the fourth convex parts for forming the burst patterns that are difficult to press into the resin layer due to their surface area being large relative to the concave parts can be pressed into the resin layer sufficiently deeply across the entire range from the inner periphery to the outer periphery.  
      An imprinting method according to the present invention carries out a stamper pressing process, which presses the stamper-side concave/convex patterns of any of the stampers described above onto a resin layer formed by applying a resin material onto a surface of a substrate, and a stamper separating process, which separates the stamper from the resin layer, in the mentioned order to transfer a concave/convex form of the stamper-side concave/convex patterns to the resin layer.  
      A method of manufacturing an information recording medium according to the present invention uses a concave/convex pattern transferred to the resin layer by the imprinting method described above.  
      According to the method of manufacturing an information recording medium according to the present invention, by manufacturing the information recording medium using the concave/convex pattern transferred to the resin layer by the imprinting method described above, it is possible to manufacture an information recording medium where servo signals can be reliably obtained and a magnetic head can be properly kept on a desired data recording track so that data can be properly recorded on the data recording tracks and data can be properly read from the data recording tracks.  
      It should be noted that the disclosure of the present invention relates to a content of Japanese Patent Application 2005-329601 that was filed on 15 Nov. 2005 and the entire content of which is herein incorporated by reference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other objects and features of the present invention will be explained in more detail below with reference to the attached drawings, wherein:  
       FIG. 1  is a block diagram showing the construction of an imprinting apparatus;  
       FIG. 2  is a plan view of an information recording medium;  
       FIG. 3  is a cross-sectional view of the information recording medium;  
       FIG. 4  is a cross-sectional view of a preform;  
       FIG. 5  is a cross-sectional view of a stamper;  
       FIG. 6  is a plan view of data track pattern forming regions and a servo pattern forming region of the stamper;  
       FIG. 7  is a plan view of a data track pattern forming region of the stamper;  
       FIG. 8  is a plan view of a preamble pattern forming region inside a servo pattern forming region of the stamper;  
       FIG. 9  is a plan view of a burst pattern forming region inside a servo pattern forming region of the stamper;  
       FIG. 10  is a cross-sectional view in the circumferential direction of a stamper where bottom surfaces of concave parts lie on the same plane;  
       FIG. 11  is a cross-sectional view in the circumferential direction of a stamper where bottom surfaces of concave parts do not lie on the same plane;  
       FIG. 12  is a correspondence chart showing the relationship between the lengths of the convex parts and the height from a reference plane to the protruding ends of the convex parts;  
       FIG. 13  is a cross-sectional view along the circumferential direction of a disk-shaped base plate in a state where a nickel layer has been formed on a surface in the manufacturing process of a stamper;  
       FIG. 14  is a cross-sectional view along the circumferential direction of the disk-shaped base plate in a state where an exposure pattern has been drawn (i.e., a latent image has been formed) by irradiating a resist layer formed on the nickel layer with an electron beam;  
       FIG. 15  is a cross-sectional view along the circumferential direction of the disk-shaped base plate in a state where a concave/convex pattern has been formed on the nickel layer by developing the resist layer in the state shown in  FIG. 14 ;  
       FIG. 16  is a cross-sectional view along the circumferential direction of the disk-shaped base plate in a state where a mask pattern has been formed by etching the nickel layer using the resist layer (the concave/convex pattern) in the state shown in  FIG. 15  as a mask;  
       FIG. 17  is a cross-sectional view along the circumferential direction of the disk-shaped base plate in a state where a concave/convex pattern has been formed by carrying out an etching process using the mask pattern;  
       FIG. 18  is a cross-sectional view along the circumferential direction of the disk-shaped base plate in a state where an electrode film has been laminated to cover the concave/convex pattern shown in  FIG. 17 ;  
       FIG. 19  is a cross-sectional view along the circumferential direction of the disk-shaped base plate in a state where a nickel layer has been formed to cover the electrode film shown in  FIG. 18 ;  
       FIG. 20  is a cross-sectional view of a state where the stamper has been pressed onto a resin layer of the preform;  
       FIG. 21  is a cross-sectional view of the peripheries of positions where convex parts have been pressed in the state shown in  FIG. 20 ;  
       FIG. 22  is a cross-sectional view of the peripheries of positions where convex parts have been pressed in the state shown in  FIG. 20 ;  
       FIG. 23  is a cross-sectional view of a state where a concave/convex pattern has been formed by separating the stamper from the preform in the state shown in  FIG. 20 ;  
       FIG. 24  is a cross-sectional view of a state where a concave/convex pattern has been formed by etching a metal layer using the concave/convex pattern shown in  FIG. 23 ;  
       FIG. 25  is a plan view of a burst pattern forming region inside a servo pattern forming region of another stamper;  
       FIG. 26  is a plan view of a burst pattern forming region inside a servo pattern forming region of another stamper;  
       FIG. 27  is a plan view of a burst pattern forming region inside a servo pattern forming region of yet another stamper;  
       FIG. 28  is a cross-sectional view of a state where convex parts with short lengths on a conventional stamper have been pressed into a resin layer; and  
       FIG. 29  is a cross-sectional view of a state where convex parts with long lengths on the conventional stamper have been pressed into the resin layer. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of a stamper, an imprinting method, and a method of manufacturing an information recording medium according to the present invention will now be described with reference to the attached drawings.  
      First, the construction of an imprinting apparatus  100  for manufacturing an information recording medium using the stamper according to the present invention will be described with reference to the drawings.  
      The imprinting apparatus  100  shown in  FIG. 1  includes a press  110  and a control unit  120  and is constructed so as to be capable of forming a concave/convex pattern  36  (see  FIG. 23 ) by pressing a stamper  20  (see  FIG. 5 ) onto a preform  10  (see  FIG. 4 ) when manufacturing the information recording medium  1  shown in  FIGS. 2 and 3  in accordance with the imprinting method according to the present invention. The information recording medium  1  is a discrete-track type magnetic recording medium and as shown in  FIG. 2 , servo pattern regions As are provided between data track pattern regions At so that the data track pattern regions At and the servo pattern regions As are alternately disposed in the direction of rotation (the “circumferential direction”, shown by the arrow R in  FIG. 2 ) of the information recording medium  1 . Also, as shown in  FIG. 3 , in each data track pattern region At, a data track pattern composed of a large number of concentric data recording tracks, which are produced by dividing the region with a predetermined arrangement pitch, and guard band parts is formed by concave/convex patterns  5  (concave/convex patterns  5   t ) including a plurality of convex parts  5   a  and a plurality of concave parts  5   b . Similarly, in each servo pattern region As, various types of servo patterns for tracking servo control are formed by concave/convex patterns  5  (concave/convex patterns  5   s ) including a plurality of convex parts  5   a  and a plurality of concave parts  5   b . Note that in  FIGS. 3 and 5 , for ease of understanding the present invention, the lengths of the convex parts and the concave parts have been shown differently to the actual lengths. In this specification, a region sandwiched by two data track pattern regions At that are disposed in the direction of rotation (i.e., a region from a downstream end in the direction of rotation of one data track pattern region At to an upstream end in the direction of rotation of another data track pattern region At) is referred to as a “servo pattern region As”.  
      Also, as shown in  FIG. 4 , as one example the preform  10  is constructed by laminating (forming) a magnetic layer  12 , a metal layer  13 , and a resin layer  14  in the mentioned order on a disk-shaped base plate  11  formed in a circular plate shape from alumina, silicon, glass, ceramic, or the like. In reality, various functional layers such as a soft magnetic layer and an oriented layer are provided between the disk-shaped base plate  11  and the magnetic layer  12 , but for ease of understanding the present invention, such layers have been omitted from the description and drawings. It should be noted that in this example, the disk shaped base plate  11 , the magnetic layer  12  and the metal layer  13  together construct the “substrate” for the present invention. As examples, polystyrene resin, methacrylate resin (such as PMMA), polystyrene, phenol resin, novolac resin, and the like should preferably be used as the resin material that forms the resin layer  14  since a favorable concave/convex form is achieved for the concave/convex pattern  36  formed when the stamper  20  is separated as described later. For the preform  10  described here, as one example, the resin layer  14  is formed using novolac resin so that the thickness of the resin layer  14  is in a range of 40 nm to 100 nm, inclusive (as one example, 70 nm).  
      On the other hand, as shown in  FIG. 5 , the stamper (mold)  20  is formed in a circular plate shape with a thickness of around 300 μm by laminating an electrode film  21  and a nickel layer  22 . The rear surface of the stamper  20  (the upper surface in  FIG. 5 ) is formed so as to be flat and concave/convex patterns  35  (one example of the “stamper-side concave/convex patterns” for the present invention) for forming the concave/convex pattern  36  in the resin layer  14  of the preform  10  are formed on the front surface of the stamper  20  (i.e., the surface that forms the bottom surfaces of the concave parts  35   b  in the concave/convex pattern  35 : the lower surface in  FIG. 5 ). In addition, as described later, to prevent the resin material from adhering to the stamper  20  when the stamper  20  is separated from the resin layer  14 , an adhesive force reducing film  23  is formed by coating the surface of the electrode film  21  (the surface of the concave/convex patterns  35 ) with a fluorochemical material, for example. In this case, the material that forms the adhesive force reducing film  23  is not limited to a fluorochemical coating material, and any material that can reduce adhesion to the resin layer  14  may be used. The concave/convex patterns  35  of the stamper  20  include convex parts  35   a  formed corresponding to the concave parts  5   b  of the concave/convex patterns  5  (the concave/convex patterns  5   t ,  5   s ) of the information recording medium  1  and concave parts  35   b  formed corresponding to the convex parts  5   a  of the concave/convex patterns  5 .  
      More specifically, as shown in  FIG. 6 , on the stamper  20 , data track pattern forming regions Ats, in which the concave/convex patterns  35   t  for forming the concave/convex patterns  5   t  (data track patterns) in the data track pattern regions At of the information recording medium  1  are formed, and servo pattern forming regions Ass, in which the concave/convex patterns  35   s  for forming the concave/convex patterns  5   s  (servo patterns) in the servo pattern regions As of the information recording medium  1  are formed, are set corresponding to the data track pattern regions At and the servo pattern regions As of the information recording medium  1 . Note that in  FIG. 6  and in FIGS.  7  to  9  and  25  to  27  described later, the formation positions of the convex parts  35   a  have been obliquely shaded. A preamble pattern forming region Aps in which a concave/convex pattern  35   s  for forming a preamble pattern is formed, an address pattern forming region in which a concave/convex pattern  35   s  for forming an address pattern is formed (not shown), and a burst pattern forming region Abs in which a concave/convex pattern  35   s  for forming a burst pattern is formed are set in each servo pattern forming region Ass. In addition, four regions Ab 1   s  to Ab 4   s  corresponding to signal regions in a burst pattern on the information recording medium  1  are set in each burst pattern forming region Abs.  
      Here, the convex parts  35   a  formed in the data track pattern forming regions Ats and the convex parts  35   a  formed in the servo pattern forming regions Ass have lengths (hereinafter, “lengths in the radial direction”) in a direction corresponding to the radial direction of the information recording medium  1  (hereinafter, a direction for the stamper  20  that corresponds to the radial direction of the information recording medium  1  is also referred to as the “radial direction”) and lengths (hereinafter, “lengths in the circumferential direction”) in a direction corresponding to the circumferential direction (i.e., direction of rotations of the information recording medium  1  (hereinafter, a direction for the stamper  20  that corresponds to the circumferential direction of the information recording medium  1  is also referred to as the “circumferential direction”) set in accordance with the forms of the data track patterns and servo patterns of the information recording medium  1 . More specifically, as shown in  FIG. 7 , the convex parts  35   a   1  formed in the data track pattern forming regions Ats are convex parts  35   a  for forming the guard band parts (inter-track concave parts) of the data track patterns of the information recording medium  1  and are continuously formed along a direction corresponding to the circumferential direction (i.e., the direction of rotation) of the information recording medium  1  as belt-like shapes elongated in the circumferential direction. These convex parts  35   a   1  are one example of “first convex parts” for the present invention and have lengths in the circumferential direction that are set corresponding to the lengths along the circumferential direction of the data track pattern regions At of the information recording medium  1 . Also, as shown in  FIG. 12 , the convex parts  35   a   1  (the “data track pattern convex parts” in  FIG. 12 ) are formed so that the length thereof in the radial direction (the length L 1  shown in  FIG. 7 ) is 100 nm, for example, across the entire range from the region corresponding to an inner periphery Ai of the information recording medium  1  to a region corresponding to an outer periphery Ao. Note that the concave parts  35   b   1  shown in  FIG. 7  are concave parts  35   b  for forming the convex parts  5   a  used as the data recording tracks on the information recording medium  1 , and as one example are formed so that the length thereof in the radial direction is substantially equal to the length in the radial direction of the convex parts  35   a   1 .  
      Also, as shown in  FIG. 8 , the convex parts  35   a   2  formed in the preamble pattern forming region Aps in each servo pattern forming region Ass are convex parts  35   a  for forming the concave parts  5   b  used as a preamble pattern on the information recording medium  1 , and are continuously formed along a direction corresponding to the radial direction of the information recording medium  1  as belt-like shapes elongated in the radial direction. The convex parts  35   a   2  are one example of “third convex parts” for the present invention (one type of “second convex parts” for the present invention) and are formed so that the length thereof in the radial direction corresponds to the length from the inner periphery Ai to the outer periphery Ao of the information recording medium  1 . Also, as shown in  FIG. 12 , the convex parts  35   a   2  (indicated as “preamble pattern convex parts (length=two bits)” in  FIG. 12 ) are set so that the length thereof in the circumferential direction (the length L 2  shown in  FIG. 8 ) gradually increases from the inner periphery to the outer periphery, so that in a region corresponding to the inner periphery Ai of the information recording medium  1  (at a position 5.0 mm from the center, for example), the length L 2  in the circumferential direction is 56 nm, for example, and in a region corresponding to the outer periphery Ao of the information recording medium  1  (at a position 13.0 mm from the center, for example), the length L 2  in the circumferential direction is 147 nm, for example. Note that the concave parts  35   b   2  shown in  FIG. 8  are concave parts  35   b  for forming the convex parts  5   a  used as preamble patterns on the information recording medium  1  and as one example are formed with the length thereof in the circumferential direction set substantially equal to the length in the circumferential direction of the convex parts  35   a   2  at positions with the same radius. Here, the expression “length=two bits” in  FIG. 12  refers to a length in the circumferential direction that is recognized as a two-bit signal in an address pattern or the like at positions with the same radius. In the same way, the expression “length=eight bits” refers to a length in the circumferential direction that is recognized as an eight-bit signal in an address pattern or the like at positions with the same radius.  
      In addition, the convex parts  35   a  (not shown) formed in a sector address pattern forming region of each servo pattern forming region Ass are convex parts for forming the concave parts  5   b  used as sector address patterns of the information recording medium  1 , and in the same way as the convex parts  35   a   2  for forming the concave parts  5   b  used as the preamble patterns described earlier, are continuously formed along the direction corresponding to the radial direction of the information recording medium  1  as belt-like shapes elongated in the radial direction. Accordingly, in the following description, the convex parts  35   a  for forming the sector address patterns are assigned the same reference numerals as the convex parts  35   a   2  for forming the preamble patterns. The convex parts  35   a   2  are another example of “third convex parts” for the present invention (one type of “second convex parts” for the present invention) and the lengths thereof in the radial direction are set corresponding to the length from the inner periphery Ai to the outer periphery Ao of the information recording medium  1 . The convex parts  35   a   2  for forming the sector address patterns have lengths thereof in the circumferential direction (the length L 2  shown in  FIG. 8 ) set so as to gradually increase from the inner periphery to the outer periphery. More specifically, as shown in  FIG. 12 , out of the convex parts  35   a   2 , convex parts  35   a   2  that are two bits long are formed so that the length L 2  thereof in the circumferential direction is 56 nm, for example, in regions corresponding to the inner periphery Ai of the information recording medium  1  and is 147 nm, for example, in regions corresponding to the outer periphery Ao of the information recording medium  1 . Similarly, out of the convex parts  35   a   2  for forming the sector address patterns, convex parts  35   a   2  that are eight bits long are formed so that the length L 2  thereof in the circumferential direction is 226 nm, for example, in regions corresponding to the inner periphery Ai of the information recording medium  1  and is 587 nm, for example, in regions corresponding to the outer periphery Ao of the information recording medium  1 . Note that the concave parts  35   b  (not shown) formed in the sector address pattern forming regions are concave parts  35   b  for forming the convex parts  5   a  for the sector address patterns of the information recording medium  1 , and as one example are formed so that lengths thereof in the circumferential direction are two bits long, eight bits long and the like in the same way as the convex parts  35   a   2  for forming the sector address patterns.  
      As shown in  FIG. 9 , the convex parts  35   a   3  formed in the burst pattern forming regions Abs (as one example, the region Ab 1   s ) of the servo pattern forming regions Ass are examples of “fourth convex parts” for the present invention (another type of “second convex parts” for the present invention) and are constructed so as to be capable of forming the concave parts  5   b  of the burst patterns of the information recording medium  1 . In this case, in the burst pattern forming regions Abs of the stamper  20 , as one example, a plurality of concave parts  35   b   3 , which are parallelogram-shaped when viewed from above and can manufacture an information recording medium  1  including burst patterns where the individual burst regions are composed of convex parts, are formed at positions corresponding to the individual burst regions. As one example, the convex parts  35   a   3  are formed as a single convex part in each burst pattern forming region Abs so as to surround a plurality of concave parts  35   b   3  in the regions Ab 1   s  to Ab 4   s . Also, as shown in  FIG. 12 , the convex parts  35   a   3  (the “burst pattern convex parts” in  FIG. 12 ) are formed so that the length (the length L 3  shown in  FIG. 9 ) thereof in the circumferential direction between two concave parts  35   b   3  that are adjacent in the circumferential direction inside the regions Ab 1   s  to Ab 4   s  is set so as to gradually increase from the inner periphery to the outer periphery. Here, the length L 3  is 56 nm in a region corresponding to the inner periphery Ai of the information recording medium  1  and is 147 nm in a region corresponding to the outer periphery Ao of the information recording medium  1 . Note that as one example, the length in the circumferential direction of the concave parts  35   b   3  is set substantially equal to the length between two concave parts  35   b   3  at positions with the same radius in the circumferential direction (i.e., substantially equal to the length L 3 ).  
      Also, as shown in  FIG. 10 , on the stamper  20 , the bottom surfaces of the concave parts  35   b  between the convex parts  35   a  that construct the concave/convex patterns  35  are formed so as to lie on substantially the same plane as the concave/convex pattern formation surface (the “front surface” for the present invention) of the stamper  20 . Note that in this specification the bottom surfaces of the concave parts  35   b  (that is, the concave/convex pattern formation surface) are referred to in the following description as a “reference plane” (a reference plane X) for the present invention. The “reference plane” for the present invention is not limited to the reference plane X whose position matches the bottom surfaces of the concave parts  35   b  (i.e., position on a plane that includes the bottom surfaces), and any chosen position between the rear surface of the stamper and the concave/convex pattern formation surface (that is, any position in a range of the thickness of the stamper) can be set as the reference plane X. Also, as shown in  FIG. 11 , according to this method of manufacturing, in some cases the bottom surfaces of the respective concave parts  35   b  do not lie on the same plane, and in this case a plane including the bottom surface of any of the concave parts  35   b  (in the example in  FIG. 11 , the concave parts  35   b  formed on both sides of the convex part  35   a   1 ) can be set as the reference plane X. Also, as shown in  FIG. 10 , the convex parts  35   a  in the concave/convex patterns  35  are formed so that the respective heights from the reference plane X to the protruding ends of the respective convex parts are set in accordance with the respective lengths in the radial direction and the lengths in the circumferential direction of the convex parts.  
      More specifically, as shown in  FIG. 12 , the convex parts  35   a   1  for forming the data track patterns whose length L 1  in the radial direction is 100 nm in the entire range from the inner periphery to the outer periphery are formed so that the height from the reference plane X to the protruding ends of the convex parts  35   a   1  (that is, the height H 1  shown in  FIGS. 10 and 11 : the protruding length of the convex parts  35   a   1 ) is 85 nm in the entire range from the inner periphery to the cuter periphery. The convex parts  35   a   2  for forming the preamble patterns whose length L 2  in the circumferential direction in the inner periphery is 56 nm and whose length L 2  in the circumferential direction in the outer periphery is 147 nm are formed so that the height from the reference plane X to the protruding ends of the convex parts  35   a   2  (that is, the height H 2  shown in  FIGS. 10 and 11 : the protruding length of the convex parts  35   a   2 ) gradually increases from the inner periphery to the cuter periphery so as to be 80 nm in the inner periphery and 88 nm in the outer periphery. In the same way, the convex parts  35   a   2  for the sector address patterns (that are two bits long) whose length in the circumferential direction in the inner periphery is 56 nm and whose Length in the circumferential direction in the outer periphery is 147 nm are formed so that the height from the reference plane X to the protruding ends of the convex parts  35   a   2  (that is, the protruding length of the convex parts  35   a   2 ) gradually increases from the inner periphery to the outer periphery so as to be 80 nm in the inner periphery and 88 nm in the outer periphery. In addition, the convex parts  35   a   2  for the sector address patterns (that are eight bits long) whose length in the circumferential direction in the inner periphery is 226 nm and whose length in the circumferential direction in the outer periphery is 587 nm are formed so that the height from the reference plane X to the protruding ends of the convex parts  35   a   2  (that is, the protruding length of she convex parts  35   a   2 ) gradually increases from the inner periphery to the outer periphery so as to be 90 nm in the inner periphery and 95 nm in the outer periphery. In this way, on the stamper  20 , the convex parts  35   a   2  that are continuously formed along the radial direction are formed so that the height from the reference plane X to the protruding ends of the convex parts  35   a   2  is higher than the height H 1  of the convex parts  35   a   1  at positions where the length of the convex parts  35   a   2  in the circumferential direction is longer than the length in the radial direction of the convex parts  35   a   1  formed in the data track pattern forming regions Ats.  
      Also, the convex parts  35   a   3  for forming the burst patterns whose length L 3  in the circumferential direction between two adjacent concave parts  35   b   3  (the concave parts  35   b  that correspond to the individual burst regions) is 56 nm in the inner periphery and 147 nm in the outer periphery are formed so that the height from the reference plane X and the protruding end of the convex part  35   a   3  between two concave parts  35   b   3  (that is, the height H 3  shown in  FIGS. 10 and 11 : the protruding length of positions between the adjacent concave parts  35   b   3 ) increases toward the outer periphery so as to be 92 nm in the inner periphery and 101 nm in the outer periphery. In this way, on the stamper  20 , the convex parts  35   a  formed continuously in both the radial direction and the circumferential direction to surround a plurality of concave parts  35   b   3  are formed so that the height from the reference plane X to the protruding ends of the convex parts  35   a  are higher than the heights H 1  of the convex parts  35   a   1  across the entire convex parts  35   a . Note that the difference between the largest and smallest heights of the convex parts  35   a  should preferably be 50 nm or below so that the convex parts  35   a  can be reliably pressed into the resin layer  14  as described later.  
      On the other hand, as shown in  FIG. 1 , the press  110  includes hot plates  111 ,  112  and a raising/lowering mechanism  113 . The hot plates  111 ,  112  heat the preform  10  and the stamper  20  under the control of the control unit  120 . Also, as shown in  FIG. 20 , the hot plate  111  is constructed so as to be capable of holding the preform  10  in a state where the surface on which the resin layer  14  has been formed faces upward, and the hot plate  112  is constructed so as to be capable of holding the stamper  20  in a state where the formation surface of the concave/convex patterns  35  faces downward. The raising/lowering mechanism  113  moves (lowers) the hot plate  112  toward the preform  10  held by the hot plate  111  to press the stamper  20  held by the hot plate  112  into the resin layer  14  of the preform  10 . Also, the raising/lowering mechanism  113  separates (raises) the hot plate  112  from the hot plate  111  to separate the stamper  20  pressed into the resin layer  14  from the resin layer  14 . The control unit  120  controls the hot plates  111 ,  112  to heat both the preform  10  and the stamper  20  and controls the raising/lowering mechanism  113  to press the stamper  20  onto the preform  10  (the “stamper pressing process” for the present invention) and to separate the stamper  20  pressed into the preform  10  from the preform  10  (the “stamper separating process” for the present invention).  
      Next, the method of manufacturing the stamper  20  will be described with reference to the drawings.  
      First, as shown in  FIG. 13 , by vapor-depositing nickel onto a disk-shaped base plate  25  that is made of silicon and has been polished so that its surface is flat, a nickel layer  26  with a thickness of around 10 nm is formed. It should be noted that the base plate used when manufacturing the stamper  20  is not limited to a silicon base plate, and various kinds of base plate, such as a glass base plate or a ceramic base plate, may be used. Next, as shown in  FIG. 14 , by spin coating a resist (as one example “ZEP52CA” made by ZEON CORPORATION of Japan) onto the nickel layer  26  that has been formed, a resist layer  27  with a thickness of around 100 nm is formed on the surface of the nickel layer  26 . The resist used for forming the resist layer  27  is also not limited to the resist given above, and any freely chosen resist material can be used. After this, an electron beam lithography apparatus is used to irradiate the resist layer  27  with an electron beam to draw a desired exposure pattern  31  (in this example, a pattern corresponding to the convex parts  35   a  of the stamper  20 ). Next, by developing the resist layer  27  in this state, parts corresponding to a latent image  27   a  are removed. By doing so, as shown in  FIG. 15 , a concave/convex pattern  32  is formed on the nickel layer  26 . After this, by etching the nickel layer  26  using the concave/convex pattern  32  (the resist layer  27 ) as a mask, as shown in  FIG. 16 , the mask pattern  33  composed of the nickel layer  26  is formed on the disk-shaped base plate  25 .  
      Next, by carrying out reactive ion etching using a mixture of CF 4  and O 2 , for example, with the nickel layer  26  (a mask pattern  33 ) en the disk-shaped base plate  25  as a mask, the disk-shaped base plate  25  is etched as shown in  FIG. 17  to form a plurality of concave parts  34   a  and thereby form a concave/convex pattern  34 . When doing so, the mixed proportions (the flow ratio) of the CF 4  and O 2 , the pressure inside the processing apparatus, the amount of applied energy, the processing time, and the like are appropriately adjusted so that the concave parts  34   a  formed at positions where the lengths in the radial direction or the circumferential direction of parts exposed from the mask pattern  33  are long (i.e., “parts where the openings are wide”: for example, positions where the convex parts  35   a   3  and the like of the stamper  20  will be formed) are etched more deeply than the concave parts  34   a  formed at positions where the lengths in the radial direction or the circumferential direction of parts exposed from the mask pattern  33  are short (i.e., “parts where the openings are narrow”: for example, positions where the convex parts  35   a   1  and the like of the stamper  20  will be formed). As a specific example, a 25-second etching process is carried out with the flow ratio of the CF 4  and O 2  etching gases set at 35:15 (flow rates of CF 4 : 35 sccm, O 2 : 15 sccm), the pressure inside the processing chamber set at 0.3 Pa, the microwave power set at RF1kW, and the bias power applied to the disk-shaped base plate  25  set at RF50W. As a result, as shown in  FIG. 17 , the concave/convex pattern  34  is formed so that the concave parts  34   a  with wide openings (i.e., where the length in the radial direction or the circumferential direction is long) are deeper than the concave parts  34   a  with narrow openings (where the length in the radial direction or the circumferential direction is short).  
      Next, the disk-shaped base plate  25  in this state is soaked in potassium permanganate solution, for example, to oxidize the surface of the concave/convex pattern  34  (the surface of the nickel layer  26  on the disk-shaped base plate  25 ). By doing so, a master matrix (not shown) is completed. Next, as shown in  FIG. 18 , after an electrode film  21  for electroforming has been formed along the concave/convex form of the concave/convex pattern  34  of the master matrix, electroforming is carried out using the electrode film  21  as an electrode to form the nickel layer  22  on the electrode film  21  as shown in  FIG. 19 . After this, the multilayer structure composed of the electrode film  21  and the nickel layer  22  (the parts that form the stamper  20 ) is separated from the multilayer structure composed of the disk-shaped base plate  25  and the nickel layer  26 . When doing so, since the surface of the concave/convex pattern  34  has been oxidized, the multilayer structure composed of the electrode film  21  and the nickel layer  22  can be easily separated. By doing so, the concave/convex pattern  34  of the master matrix is transferred to the electrode film  21  and the nickel layer  22  to form the concave/convex patterns  35  (see  FIG. 10 ). After this, the rear surface of the nickel layer  22  is polished to make the rear surface flat and the surface of the electrode film  21  is coated with a fluorochemical material to form the adhesive force reducing film  23 . This completes the stamper  20  on which the concave/convex patterns  35  including a plurality of convex parts  35   a  of different lengths in the radial direction, different lengths in the circumferential direction, and different heights from the reference plane X to the protruding ends of the convex parts are formed as shown in  FIG. 10 .  
      Next, a process that forms a concave/convex pattern on the preform  10  using the stamper  20  described above in accordance with the imprinting method according to the present invention will be described with reference to the drawings.  
      First, the preform  10  and the stamper  20  are set in the press  110 . More specifically, the preform  10  is attached to the hot plate  111  with the formation surface of the resin layer  14  facing upward and the stamper  20  is attached to the hot plate  112  with the formation surface of the concave/convex patterns  35  facing downward. After this, the control unit  120  controls the hot plates  111 ,  112  so that both the preform  10  and the stamper  20  are heated. At this time, the hot plates  111 ,  112  heat both the preform  10  and the stamper  20  to around 170° C., which is around 100° C. higher than the glass transition point (in this example, around −70° C.) of the novolac resin forming the resin layer  14 . By doing so, the resin layer  14  softens and becomes easy to mold. Here, heating to a temperature in a range of 70° C. to 120° C., inclusive higher than the glass transition point of the resin material is preferable, with heating to at least 100° C. higher than the glass transition point being more preferable. By doing so, as described later, it becomes easy to press the stamper  20  onto the resin layer  14 .  
      Next, the control unit  120  controls the raising/lowering mechanism  113  to lower the hot plate  112  toward the hot plate  111  to press, as shown in  FIG. 20 , the concave/convex patterns  35  of the stamper  20  onto the resin layer  14  of the preform  10  on the hot plate  111  (the “stamper pressing process” for the present invention). Note that in  FIG. 20  and in  FIGS. 21 and 22  described later, for ease of understanding the present invention, the lengths of the convex parts  35   a  and the opening widths of the concave parts  35   b  in the concave/convex patterns  35  have been illustrated with different lengths and opening widths to the actual concave/convex patterns  35 . At this time, in accordance with control by the control unit  120 , as one example the raising/lowering mechanism  113  maintains a state where a load of 34 kN is applied across the entire stamper  20  for five minutes. In accordance with control by the control unit  120 , the hot plates  111 ,  112  continuously carry out a heating process so that the temperatures of the preform  10  and the stamper  20  do not fall while the stamper  20  is being pressed onto the preform  10  by the raising/lowering mechanism  113 . It should be noted that during the heating process, the temperature should preferably be maintained in a range of 170° C.±1° C. (as one example, a temperature that only changes in a range of ±0.2° C.). By doing so, the concave/convex patterns  35  of the stamper  20  are transferred to the resin layer  14  to form the concave/convex pattern  36 .  
      Here, as described earlier, on the stamper  20  used by the imprinting apparatus  100 , the concave/convex patterns  35  are formed so that out of the convex parts  35   a  that are formed in the servo pattern forming regions Ass, the convex parts  35   a   2  whose lengths in the circumferential direction are longer than the length in the radial direction of the convex parts  35   a   1  in the data track pattern forming regions Ats (i.e., out of the convex parts  35   a   2 , convex parts  35   a   2  whose length in the circumferential direction is longer than the length in the radial direction of the convex parts  35   a   1 ) have higher heights from the reference plane X to the protruding ends of the convex parts. Accordingly, when the stamper  20  is pressed onto the resin layer  14  with uniform pressing force being applied across the entire stamper  20 , the convex parts  35   a  with the longer lengths in the circumferential direction (in this example, the convex parts  35   a   2 ) are pressed deeply into the resin layer  14  in the same way as the convex parts  35   a   1  and the like. Also, as described earlier, the convex parts  35   a   3  for forming the burst patterns are formed so that the height from the reference plane X to the protruding ends of the convex parts between two adjacent concave parts  35   b   3  in the circumferential direction gradually increases from the inner periphery to the outer periphery and is higher than the height H 1  of the convex parts  35   a   1  across the entire range from the inner periphery to the outer periphery. Accordingly, when the stamper  20  is pressed onto the resin layer  14  with uniform pressing force being applied across the entire stamper  20 , the convex parts  35   a   3  that are difficult to press into the resin layer  14  due to their large surface area relative to the concave parts  35   b   3  are also deeply pressed into the resin layer  14  in the same way as the convex parts  35   a   1 ,  35   a   2 , and the like described above. As a result, the convex parts  35   a  with different lengths in the radial direction and different lengths in the circumferential direction are pressed into the resin layer  14  substantially uniformly.  
      As a specific example, as shown in  FIG. 21 , in the data track pattern forming regions Ats in which a plurality of convex parts  35   a   1  with a length L 1  in the radial direction of 100 nm are formed, the resin layer  14  at the positions where the convex parts  35   a   1  are pressed in moves smoothly toward the concave parts  35   b   1  of the stamper  20 , resulting in the convex parts  35   a   1  being pressed sufficiently deeply into the resin layer  14  of the preform  10 . Accordingly, the thickness T 1  of the residue (the resin layer  14  between the bottom surfaces of the concave parts  36   b   1  and the surface of the metal layer  13 ) at positions where the convex parts  35   a   1  are pressed in is around 28 nm±3 nm. On the other hand, as shown in  FIG. 22 , in the servo pattern forming regions Ass in which the convex parts  35   a   2  with a length L 2  in the circumferential direction in the outer periphery of around 147 nm are formed (in this example, the preamble pattern forming regions Aps and the sector address pattern forming regions in which the two-bit length sector address patterns are formed), the height H 2  from the reference plane X to the protruding ends of the convex parts  35   a   2  in the outer periphery of the convex parts  35   a   2  is 85 nm that is around 3 nm higher than the height H 1  of the convex parts  35   a   1 , and therefore the wide convex parts  35   a   2  that are more difficult to press into the resin layer  14  than the concave parts  35   a   1  are pressed sufficiently deeply into the resin layer  14 . Accordingly, the thickness T 2  of the residue (the resin layer  14  between the bottom surfaces of the concave parts  36   b   2  and the surface of the metal layer  13 ) at positions where the convex parts  35   a   2  are pressed in is around 29 nm±3 nm.  
      Also, on the stamper  20 , in the servo pattern forming regions Ass in which the convex parts  35   a   2  for forming the (eight bits long) sector address patterns with a length in the circumferential direction of 226 nm in the inner periphery and of 587 nm in the outer periphery are formed (in this example, sector address pattern forming regions in which the eight-bit long sector address patterns are formed), the convex parts are formed so that the height thereof from the reference plane X so the protruding ends of the convex parts gradually increases from the inner periphery to the outer periphery from 90 nm to 98 nm, meaning that the convex parts  35   a   2  protrude further out than the convex parts  35   a   1 . This means that the convex parts  35   a   2  can be pressed sufficiently deeply and to a similar extent as the convex parts  35   a   1  into the resin layer  14 . In addition, in the servo pattern forming regions Ass (the burst pattern forming region Abs) where the length in the circumferential direction of the convex parts  35   a   3  for forming burst patterns between two adjacent concave parts  35   b  in the circumferential direction is 56 nm in the inner periphery and is 147 nm in the outer periphery, the convex parts are formed so that the height from the reference plane X to the protruding ends of the convex parts gradually increases from the inner periphery to the outer periphery from 92 nm to 101 nm, meaning that the protruding ends of the convex parts  35   a   3  protrude further out than the convex parts  35   a   1 . This means that the convex parts  35   a   3  can be pressed sufficiently deeply and to a similar extent as the convex parts  35   a   1  into the resin layer  14 . Accordingly, the thickness of the residue at positions where the various types of convex parts  35   a  with different lengths in the circumferential direction and the radial direction are pressed in is substantially equal across the entire range of the data track pattern forming regions Ats and the servo pattern forming regions Ass. Next, while controlling the hot plates  111 ,  112  to have the heating process continued (to keep the temperature in a range of 170° C.±1° C.), as shown in  FIG. 23 , the control unit  120  controls the raising/lowering mechanism  113  to raise the hot plate  112  and thereby separate the stamper  20  from the preform  10  (the resin layer  14 ) (the “stamper separating process” for the present invention). By doing so, the concave/convex form of the concave/convex patterns  35  of the stamper  20  is transferred to the resin layer  14  of the preform  10 , thereby forming the concave/convex pattern  36  on the metal layer  13 . This completes the imprinting process.  
      Next, the process for manufacturing the information recording medium  1  according to the method of manufacturing an information recording medium according to the present invention will be described with reference to the drawings.  
      First, the resin material (residue) remaining on the bottom surfaces of the concave parts in the concave/convex pattern  36  in the resin layer  14  is removed by an oxygen plasma process. When doing so, since the thickness of the residue on the metal layer  13  is substantially even in a range of 25 nm to 32 nm, inclusive, across the entire preform  10 , it is possible to avoid a situation where the openings of the concave parts change to unintentionally wide openings (that is, where the side wall surfaces of the concave parts are badly eroded) when the residue is removed. Next, an etching process that uses a metal-etching gas is carried out with the concave/convex pattern  36  (i.e., the convex parts) as a mask. When doing so, as shown in  FIG. 24 , the parts of the metal layer  13  at the bottom surfaces of the concave parts of the concave/convex pattern  36  are removed so that concave/convex patterns  37  composed of the metal material are formed on the magnetic layer  12 . Next, an etching process is carried out using a gas for etching the magnetic material, with the concave/convex patterns  37  (the remaining metal layer  13 ) being used as a mask. By doing so, parts of the magnetic layer  12  that are exposed from the concave/convex patterns  37  are removed.  
      Next, the metal layer  13  remaining on the magnetic layer  12  is removed by carrying out an etching process using a metal-etching gas. By doing so, as shown in  FIG. 3 , the concave/convex patterns  5  (the concave/convex patterns  5   t ,  5   s ) are formed. In such concave/convex patterns  5 , grooves corresponding to the concave parts in the concave/convex pattern  36  produced by transferring the concave/convex form of the stamper  20  are formed in the magnetic layer  12 . Next, a surface treatment process is carried out. During this surface treatment process, after the grooves have first been filled with silicon dioxide (not shown), for example, the surface is smoothed by carrying out ion-beam etching. After this, a protective film composed of DLC (Diamond-Like Carbon), for example, is formed on the smoothed surface and finally a lubricant is applied. By doing so, the information recording medium  1  is completed. In this case, since the information recording medium  1  is manufactured using the concave/convex patterns  37  formed using the concave/convex pattern  36  whose concave parts are formed so that the openings have the desired widths, the concaves  5   b  in the concave/convex patterns  5  (the data recording tracks, servo patterns, and the like) formed using the concave/convex patterns  36 ,  37  also have openings with the desired widths. As a result, the occurrence of recording errors and reproduction errors is avoided for the information recording medium  1 .  
      In this way, according to the stamper  20  and the imprinting method that uses the stamper  20 , the concave/convex patterns  35  are constructed so that in at least part of the servo pattern forming regions Ass, convex parts  35   a  (in this example, the convex parts  35   a   2 ,  35   a   3 , and the like) are formed with higher heights than the highest convex parts  35   a  (in this example, the convex parts  35   a   1 ) out of the convex parts  35   a  formed in the data track pattern forming regions Ats. By doing so, when the stamper  20  is pressed into the resin layer  14  with a uniform pressing force across the entire stamper  20  (the data track pattern forming regions Ats and the servo pattern forming regions Ass) during imprinting, the convex parts  35   a  in the servo pattern forming regions Ass, which includes a large number of convex parts  35   a  that are difficult to press into the resin layer  14 , can be pressed sufficiently deeply into the resin layer  14 . Since the convex parts  35   a  in the data track pattern forming regions Ats and the convex parts  35   a  in the servo pattern forming regions Ass can be pressed in to a similar extent and sufficiently deeply into the resin layer  14 , the thickness T of the residue on the metal layer  13  can be made uniform across the entire preform  10 . Accordingly, since the time required to remove the residue can be made substantially equal across the entire preform  10 , it is possible to avoid a situation where the concave parts  36   b  in the concave/convex pattern  36  transferred to the resin layer  14  in the regions corresponding to the data track pattern regions are formed with unintentionally wide openings due to the side wall surfaces of the concave parts  36   b  being eroded. By doing so, it is possible to form the concave/convex pattern  36  including concave parts with the desired opening widths across the entire range of both the data track pattern regions and the servo pattern regions. In addition, by manufacturing the information recording medium  1  using the concave/convex pattern  36  that has been formed with high precision, it is possible to manufacture an information recording medium that is not susceptible to recording/reproducing errors.  
      Also, according to the stamper  20 , by forming the “third convex parts” for the present invention (in this example, the convex parts  35   a   2 ) in the servo pattern forming regions Ass so that the third convex parts are higher than the convex parts  35   a   1  at positions where the length in the circumferential direction of the convex parts  35   a   2  is longer than the length L 1  in the radial direction of the convex parts  35   a   1 , as examples convex parts  35   a  (such as the convex parts  35   a   2  for forming the preamble patterns and the convex parts  35   a   2  for forming the sector address patterns) whose lengths in the circumferential direction in the outer periphery are longer than the length L 1  in the radial direction of the convex parts  35   a   1  for forming the data track patterns can be pressed into the resin layer  14  to a similar extent as the convex parts  35   a   1  for forming the data track patterns and sufficiently deeply into the resin layer  14 . This means that the thickness of the residue inside the regions corresponding to the data track pattern regions (i.e., the data track pattern forming regions Ats) and the thickness of the residue inside the regions corresponding to the servo pattern regions (i.e., the servo pattern forming regions Ass) can be made substantially uniform.  
      In addition, according to the stamper  20 , by forming the fourth convex parts (in this example, the convex parts  35   a   3 ) for the present invention in the burst pattern forming regions Abs inside the servo pattern forming regions Ass so as to be higher than the convex parts  35   a   1  across the entire stamper  20 , it becomes possible to press the convex parts  35   a   3  for forming the burst pattern regions that are difficult to press into the resin layer  14  due to their large surface area compared to the concave parts  35   b   3  sufficiently deeply into the resin layer  14  across the entire range from the inner periphery to the outer periphery.  
      Also, according to the method of manufacturing 
          the information recording medium  1  using the stamper  20 , by manufacturing the information recording medium  1  using the concave/convex pattern  36  transferred to the resin layer  14  by the imprinting method described above, it is possible to manufacture an information recording medium  1  where servo signals can be reliably obtained and therefore the magnetic head can be properly kept on a desired track. As a result, data can be properly recorded on the data recording tracks and data can be properly read from the data recording tracks.        

      Note that the present invention is not limited to the construction and method described above. For example, although an example has been described where the convex parts  35   a   3  inside the burst pattern forming regions Abs are formed higher than the convex parts  35   a   1  inside the data track pattern forming regions Ats across the entire range from the inner periphery to the outer periphery, if the length in the circumferential direction between the adjacent concave parts  35   b   3  in the inner periphery (i.e., the length in the circumferential direction of the convex parts  35   a   3 ) is shorter than on the stamper  20  described above, for example, the convex parts  35   a   3  can be formed lower than the convex parts  35   a   1  in such positions. In such example, the positions (the outer peripheries of the convex parts  35   a   3 ) where the convex parts  35   a   3  are formed higher than the height H 1  of the convex parts  35   a   1  correspond to the “at least one part” for the present invention. In this way, by forming the fourth convex parts for the present invention in the burst pattern forming regions Abs inside the servo pattern forming regions Ass so that the fourth convex parts (in this example, the convex parts  35   a   3  or the like) are higher than the convex parts  35   a   1  in at least one part of each of the fourth convex parts, during the imprinting process, it is possible to press the outer peripheries of the convex parts  35   a   3  for forming the burst patterns that are difficult to press into the resin layer  14  reliably into the resin layer  14  to a similar extent as the convex parts  35   a   1  for forming the data track patterns and sufficiently deeply into the resin layer  14 . This means that the thickness of the residue inside regions corresponding to the data track pattern regions (i.e., inside the data track pattern forming regions Ats) and the thickness of the residue inside regions corresponding to the burst pattern regions (i.e., inside the burst pattern forming regions Abs) can be made substantially uniform.  
      Also, although the stamper  20  with the concave/convex patterns  35  where parts corresponding to the individual burst regions of the information recording medium  1  are constructed by the concave parts  35   b   3  has been described, like the stamper  20 A shown in  FIG. 25 , it is possible to form the concave/convex patterns  35  where parts corresponding to the individual burst regions of the information recording medium  1  are constructed by convex parts  35   a . Here, like the burst pattern forming regions Abs of the stamper  20 A, for convex parts  35   a  where at least one of the length L 4  in the circumferential direction and the length L 5  in the radial direction is much longer than the length in the radial direction of the convex parts  35   a   1 , the height from the reference plane X to the protruding ends of the convex parts  35   a  should preferably be set higher than the height H 1  of the convex parts  35   a   1 . By doing so, the convex parts  35   a  that are difficult to press into the resin layer  14  during the imprinting process (i.e., the convex parts  35   a  where one of the lengths L 4  and L 5  is much longer than the length L 1 ) can be pressed into the resin layer  14  to a similar extent as the convex parts  35   a   1  and sufficiently deeply into the resin layer  14 , in the same way as with the convex parts  35   a   2 ,  35   a   3  described earlier.  
      Also, although the stampers  20 ,  20 A with burst patterns where parallelogram-shaped individual burst regions are disposed in the circumferential direction have been described, it is possible to apply the present invention to a stamper that can form burst patterns where approximately oval or circular individual burst regions are arranged in the circumferential direction. In addition, like the stamper  20 B shown in  FIG. 26 , for example, it is possible to apply the present invention to a construction where the burst patterns are formed by concave/convex patterns  35  in which a plurality of convex parts  35   a  (a plurality of concave parts  35   b ) shaped as zigzags in the circumferential direction are disposed in the radial direction. The convex parts  35   a  of the stamper  20 B are one example of third convex parts for the present invention and have a part shown by the arrow B in  FIG. 26  that is “formed continuously in the radial direction”. Accordingly, at parts where the length in the circumferential direction of the convex parts  35   a  (i.e., the length L 6  shown in  FIG. 26 ) is longer than the length L 1  in the radial direction of the convex parts  35   a   1  described earlier, the height H from the reference plane X to the protruding ends of the convex parts  35   a  should preferably be higher than the height H 1  of the convex parts  35   a   1 . By doing so, during the imprinting process, it is possible to press the convex parts  35   a  sufficiently deeply into the resin layer  14 . Note that as shown in  FIG. 26 , the expression “formed continuously in the radial direction” for the present invention is not limited to a state where parts are formed continuously along a direction perpendicular to the circumferential direction (i.e., along a direction shown by the arrow R in  FIG. 26 ) and includes a state where parts are formed continuously along a direction that intersects the radial direction at an acute angle.  
      In addition, like the stamper  20 C shown in  FIG. 27 , it is possible to use a construction that forms burst patterns by disposing a plurality of convex parts  35   a  (a plurality of concave parts  35   b ) that are parallelogram-shaped in a checkerboard pattern. Here, like the burst pattern forming regions Abs of the stamper  20 C, for convex parts  35   a  where at least one of the length L 7  along the circumferential direction and the length L 8  along the radial direction is much longer than the length in the radial direction of the convex parts  35   a   1 , the height from the reference plane X to the protruding ends of the convex parts  35   a  should preferably be higher than the height H 1  of the convex parts  35   a   1 . By doing so, like the convex parts  35   a   2 ,  35   a   3  described earlier, convex parts  35   a  that are difficult to press into the resin layer  14  during the imprinting process (i.e., convex parts  35   a  where one of the lengths L 7  and L 8  is much longer than the length L 1 ) can be pressed into the resin layer  14  to a similar extent as the convex parts  35   a   1  and sufficiently deeply.  
      Also, although the stamper  20  is manufactured by the method of manufacturing described above forming the electrode film  21  and the nickel layer  22  so as to cover the concave/convex pattern  34  formed by etching the disk-shaped base plate  25  using the nickel layer  26  (the mask pattern  33 ) as a mask, the method of manufacturing the stamper according to the present invention is not limited to this. As one example, it is also possible to manufacture the stamper  20  by forming the resist layer  27  on the disk-shaped base plate  25 , forming a concave/convex pattern (not shown) by forming concave parts with different depths in the resist layer  27 , and then forming the electrode film  21  and the nickel layer  22  so as to cover the concave/convex pattern. In addition, it is also possible to manufacture the stamper according to the present invention by using a stamper manufactured by transferring the concave/convex form of the stamper  20  described above to a stamper forming material as a master stamper and transferring the concave/convex form of the master stamper to another stamper forming material, or in other words, by transferring the concave/convex form of the stamper  20  described above an even number of times.  
      In addition, although a heating process is continuously carried out on both the preform  10  and the stamper  20  from before the start of the process that presses the stamper  20  onto the preform  10  until the process that separates the stamper  20  is completed in the imprinting method that uses the imprinting apparatus  100  described above (i.e., in the method of manufacturing the information recording medium  1 ), the present invention is not limited to this and it is possible to use a process that stops the heating process for the preform  10  and the stamper  20  after the stamper  20  has been sufficiently pressed onto the preform  10 , and separates the stamper  20  afterward. In addition, it is possible to cool both the stamper  20  and the preform  10  to the glass transition point of the resin layer  14  or below before the stamper  20  is separated. It is also possible to use a method that forms the resin layer for the present invention using a resin material whose glass transition point is lower than room temperature (as one example, around 25° C.) and forms concave/convex patterns in the resin layer without carrying out a heating process or a cooling process from the stamper pressing process to the stamper separating process. In addition, it is possible to use a method that forms a concave/convex pattern in a resin layer by forming the resin layer using a UV-curing resin or an electron-beam curing resin as the “resin material” for the present invention, and irradiating the resin layer with UV rays or an electron beam after the stamper pressing process to harden (or semi-harden) the resin layer, and then carrying out the stamper separating process.  
      Concave/convex patterns formed by the imprinting method according to the present invention are not limited to being applied to manufacturing discrete track type information recording media and can be used when manufacturing a patterned medium with patterns aside from track-type patterns and/or when manufacturing various types of information recording media aside from magnetic recording media, such as optical recording media and magneto-optical recording media.