Patent Publication Number: US-2010108639-A1

Title: Imprinting mold and method of producing imprinting mold

Description:
TECHNICAL FIELD 
     The present invention relates to a mold used in nano-imprint lithography (NIL) and a method of producing the same. 
     BACKGROUND ART 
     As a lithography technology usually used for patterning, there exists photolithography, and for the manufacture of a variety of products in small quantities, there exist direct writing by an electron beam, and so on. However, with these lithography technologies, there are respective problems. First, because the photolithography has a limit to its resolution due to the light wavelength, it is difficult to form pattern features of 100 nm or less. The direct writing by an electron beam is lacking in throughput per unit time and hence is not suitable for mass production. In order to overcome the fine-pattern limit and processing capacity of the lithography technology that is the core of these fine structure device making technologies, research into lithography by new means is being actively conducted. In particular, research into nano-imprint lithography technology, which can create design rules of the order of a nanometer and which is a technology suitable for mass production, is attracting attention. This technology is to press a mold having a nanometer-scale recess/protrusion structure onto a resist on a wafer to transfer the structure of the mold to the resist, thereby forming a fine recess/protrusion structure in the resist and, by removing the remaining film, forming a pattern as with the conventional lithography. Because the pattern transfer finishes with the pressing of the mold and the removal of the remaining film, the time required for patterning can be reduced, thus improving throughput, which means that this technology is suitable for mass production. 
     Patent Literature 1: Japanese Patent Kokai No. 2005-539393   
     Patent Literature 2: Japanese Patent Kokai No. 2005-283814   
     DISCLOSURE OF THE INVENTION 
     [Problem to be Solved by the Invention] 
     However, in the case of forming a recess/protrusion surface in subject-to-shaping material such as a resist using a conventional mold, when forming a recess/protrusion pattern with regions where the area occupied by recesses is larger than that occupied by protrusions and regions where the former is smaller than the latter being mixed, namely, when forming a recess/protrusion surface having a plurality of regions different in recess/protrusion area ratio by imprint, it is difficult to form a desired pattern in subject-to-shaping material. Details thereof will be described below with reference to  FIGS. 1 and 2 . 
       FIGS. 1 and 2  are cross-sectional views showing an imprint process of forming a single recess/protrusion surface having three regions different in recess/protrusion area ratio. In the nano-imprint process, first, subject-to-shaping material is prepared. A substrate  3  made of desired material and uniformly coated with a resist  2  of, e.g., thermoplastic resin is used as the subject-to-shaping material ( FIG. 1  ( a )). 
     Then, after the substrate  3  coated with the resist  2  is heated to soften the resist, a mold  1  is put in contact with the resist  2 , and by applying pressure, the resist  2  is deformed. The mold  1  has a recess/protrusion surface made up of three regions different in recess/protrusion area ratio. That is, region  1  is a region where the recess area percentage is relatively large; region  2  is a region where the recess area percentage is medium; and region  3  is a region where the recess area percentage is relatively small. The recess area percentage refers to the ratio of the recess area to the area of the entire recess/protrusion surface of each of the regions of the mold and can be expressed as: 
     Recess area percentage r=Recess area of the region/(Recess area of the region+Protrusion area of the region), where the recess area refers to the area of recesses of the recess/protrusion surface formed in the mold, and the protrusion area refers to the area of protrusions of the recess/protrusion surface formed in the mold. 
     Next, keeping the mold  1  pressed onto the resist  2 , the substrate temperature is lowered to harden the resist  2 , thereby transferring the recess/protrusion pattern of the mold  1  to the resist  2  ( FIG. 1  ( b )). 
     Then, after the resist  2  has hardened sufficiently, the mold  1  is separated from the substrate  3  ( FIG. 1  ( c )). At this time, a remaining film  2   a  from the resist is left on parts of the substrate  3  corresponding to the protrusions of the mold  1 . The thickness of this remaining film  2   a  is greater in a region of the mold having a smaller recess area percentage. That is, the thickness of the remaining film  2   a  increases in the order of region  1 , region  2 , and region  3 . This is because a region of the mold having a smaller recess area percentage is smaller in the amount of resist going into the space in a recess of the mold than a region having a larger one. Then, after the mold  1  is separated from the substrate  3 , the remaining film  2   a  is removed by reactive ion etching (RIE) to finish the imprint ( FIG. 1  ( d )). Here, the etching is performed to completely remove the remaining film  2   a  left in a region (region  3 ) of the mold having a relatively small recess area percentage. However, because the thickness of the remaining film is greater in this region than in the other regions as mentioned above, if the etching is performed to completely remove all of this, the etching continues even after the remaining film  2   a  is completely removed in regions of the mold having a relatively large recess area percentage (regions  1 ,  2 ), so that protrusions of the recess/protrusion pattern imprinted in the resist  2  are etched excessively. Thus, there is the problem that in regions of the mold having a relatively large recess area percentage (regions  1 ,  2 ), enough recess/protrusion depth (or height) in the patterned recess/protrusion surface cannot be secured. 
       FIG. 2  shows a case where the initial thickness of the resist  2  coated over the substrate  3  is smaller than in  FIG. 1 . The process performed in each step is the same as in  FIG. 1 , and hence description thereof is omitted. In this case, the remaining film  2   a  from the resist left on the portions corresponding to the protrusions of the mold  1  is substantially uniform over all the regions, but the recess/protrusion depth of the recess/protrusion pattern imprinted in the resist  2  becomes smaller as the recess area percentage becomes larger. That is, the recess/protrusion depth of the recess/protrusion pattern formed in the resist  2  decreases in the order of region  3 , region  2 , and region  1  ( FIG. 2  ( c )). Thereafter, the remaining film  2   a  is etched to finish the imprint, but there is the problem that in the region (region  3 ) of the mold having a relatively large recess area percentage, the recess/protrusion depth of the recess/protrusion pattern formed in the resist  2  at mold pressing is small and that thus enough recess/protrusion depth cannot be secured. 
     As described above, with the conventional mold having a recess/protrusion surface made up of a plurality of regions different in recess/protrusion area ratio, the recess/protrusion depth of the recess/protrusion surface is uniform over all the regions, hence causing the above problem. 
     The present invention was made in view of the above facts, and an object thereof is to provide a mold that, when forming a plurality of regions different in recess/protrusion area ratio in subject-to-shaping material by imprint, can form a recess/protrusion surface having enough recess/protrusion depth in each region, and a method of producing the same. 
     [Means for Solving the Problem] 
     According to the present invention, there is provided an imprinting mold having a recess/protrusion surface. The recess/protrusion surface is made up of a plurality of regions different in the ratio of the area of recesses to the area of protrusions, and a recess/protrusion surface of a region where the area ratio is small is deeper in recess/protrusion depth than a recess/protrusion surface of a region where the area ratio is large. 
     Further, according to the present invention, there is provided a method of producing the above imprinting mold. The method comprises the steps of preparing a mold substrate having a transfer layer laid over a substrate material; preparing a reference mold having a recess/protrusion surface made up of a plurality of recess/protrusion patterns different in the ratio of the area of recesses to the area of protrusions, corresponding to the plurality of regions respectively, where recess/protrusion depth of its recess/protrusion surface is uniform; pressing the reference mold to transfer the recess/protrusion patterns of the reference mold to the transfer layer and to make the thickness of a remaining film from the transfer layer that is left on parts of the substrate material corresponding to protrusions of the reference mold be different for each of the regions; coating a coating material such as thermoset material over the mold substrate to fill the inner spaces of recesses of the recess/protrusion patterns formed in the transfer layer and then solidifying the coating material such as thermoset material; etching back the coating material such as thermoset material until the tops of protrusions of the recess/protrusion patterns formed in the transfer layer are exposed; and selectively etching the transfer layer with the coating material such as thermoset material as a mask. 
     Yet further, according to the present invention, there is provided a method of producing the above imprinting mold. The method comprises the steps of preparing a mold substrate having a transfer layer laid over a substrate material; preparing a reference mold having a recess/protrusion surface made up of a plurality of recess/protrusion patterns different in the ratio of the area of recesses to the area of protrusions, corresponding to the plurality of regions respectively, where recess/protrusion depth of its recess/protrusion surface is uniform; pressing the reference mold to transfer the recess/protrusion patterns of the reference mold to the transfer layer and to make the thickness of a remaining film from the transfer layer that is left on parts of the substrate material corresponding to protrusions of the reference mold be different for each of the regions; removing all of the remaining film by etching while, by the etching, making the height of a protrusion of the recess/protrusion patterns formed in the transfer layer be different for each of the regions; coating a coating material such as thermoset material over the mold substrate to fill the inner spaces of recesses of the recess/protrusion patterns formed in the transfer layer and then solidifying the coating material such as thermoset material; etching back the coating material such as thermoset material until the tops of protrusions of the recess/protrusion patterns formed in the transfer layer are exposed; and selectively etching the transfer layer with the coating material such as thermoset material as a mask. 
     Still further, according to the present invention, there is provided a method of producing the above imprinting mold. The method comprises the steps of preparing a mold substrate having a transfer layer laid over a substrate material; preparing a reference mold having a recess/protrusion surface made up of a plurality of recess/protrusion patterns different in the ratio of the area of recesses to the area of protrusions, corresponding to the plurality of regions respectively, where recess/protrusion depth of its recess/protrusion surface is uniform; pressing the reference mold to transfer the recess/protrusion patterns of the reference mold to the transfer layer and to make the thickness of a remaining film from the transfer layer that is left on parts of the substrate material corresponding to protrusions of the reference mold be different for each of the regions; removing part of the remaining film by etching; coating a coating material such as thermoset material over the mold substrate to fill the inner spaces of recesses of the recess/protrusion patterns formed in the transfer layer and then solidifying the coating material such as thermoset material; etching back the coating material such as thermoset material until the tops of protrusions of the recess/protrusion patterns formed in the transfer layer are exposed; and selectively etching the transfer layer with the coating material such as thermoset material as a mask. 
     Further, according to the present invention, there is provided a method of producing the above imprinting mold. The method comprises the steps of preparing a mold substrate having a transfer layer laid over a substrate material; preparing a reference mold having a recess/protrusion surface made up of a plurality of recess/protrusion patterns different in the ratio of the area of recesses to the area of protrusions, corresponding to the plurality of regions respectively, where recess/protrusion depth of its recess/protrusion surface is uniform; pressing the reference mold to transfer the recess/protrusion patterns of the reference mold to the transfer layer; removing, by etching, all of a remaining film from the transfer layer that is left on parts of the substrate material corresponding to protrusions of the reference mold; coating a coating material such as thermoset material over the mold substrate to fill the inner spaces of recesses of the recess/protrusion patterns formed in the transfer layer and then solidifying the coating material such as thermoset material; etching back the coating material such as thermoset material until the tops of protrusions of the recess/protrusion patterns formed in the transfer layer are exposed; and selectively etching the transfer layer with the coating material such as thermoset material as a mask. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is cross-sectional views showing an imprint process using a conventional mold; 
         FIG. 2  is cross-sectional views showing an imprint process using the conventional mold; 
         FIG. 3  is a cross-sectional view of an imprinting mold according to the present invention; 
         FIG. 4  is cross-sectional views showing an imprint process using the mold according to the present invention; 
         FIG. 5  is cross-sectional views showing an imprint process using a mold according to the present invention; 
         FIG. 6  is a process chart showing the method of producing an imprint mold according to a first embodiment of the present invention; 
         FIG. 7  is a process chart showing the method of producing an imprint mold according to a second embodiment of the present invention; 
         FIG. 8  is a process chart showing the method of producing an imprint mold according to a third embodiment of the present invention; 
         FIG. 9  is a process chart showing the method of producing an imprint mold according to a fourth embodiment of the present invention; 
         FIG. 10  is a perspective view showing the structure of a discrete track medium; and 
         FIG. 11  is a process chart for producing a discrete track medium using a mold according to the present invention. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1  Mold 
           10  Mold 
           10   a  to  10   d  Mold 
           20  NIL resist 
           20   a  Resist remaining film 
           30  Substrate 
           40  SOG 
           50   a  Nickel film 
           50   b  Nickel film 
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are used to denote substantially the same or equivalent constituents or parts throughout the figures cited below. For convenience of description for each region, the regions are shown separately, but in practice they are integrally formed. 
     First, the configuration of the mold according to the present invention will be described.  FIG. 3  is a cross-sectional view showing the configuration of the mold  10  according to the present invention. In the mold  10 , there is formed a recess/protrusion surface made up of, e.g., three regions different in recess/protrusion area ratio. In  FIG. 3 , region  1  is a region of the mold where the recess area percentage is relatively large; region  2  is a region of the mold where the recess area percentage is medium; and region  3  is a region of the mold where the recess area percentage is relatively small. The recess area percentage refers to the ratio of the recess area to the area of the entire recess/protrusion surface of each of the regions of the mold  10  and can be expressed as: 
     Recess area percentage r=Recess area of the region/(Recess area of the region+Protrusion area of the region), where the recess area refers to the area of recesses of the recess/protrusion surface formed in the mold  10 , and the protrusion area refers to the area of protrusions of the recess/protrusion surface formed in the mold. In this embodiment, the recess area percentage r of region  1  is, for example, 0.75; the recess area percentage of region  2  is, for example, 0.5; and the recess area percentage of region  3  is, for example, 0.25. Meanwhile, the recess/protrusion depth d of the recess/protrusion surface formed in the mold  10  differs between regions  1  to  3 . That is, the recess/protrusion depth d of the recess/protrusion surface formed in the mold  10  is larger in a region having a smaller recess area percentage and smaller in a region having a larger recess area percentage. Specifically, it is desirable that the recess/protrusion surface of the mold  10  be formed so as to establish an inversely proportional relationship between the recess/protrusion depth d and the recess area percentage r. That is, since the recess area percentage r of regions  1  to  3  is 0.75, 0.5, and 0.25 respectively as mentioned above, it is desirable that the recess/protrusion surface be formed such that, as to the recess/protrusion depth d of the recess/protrusion surface, a ratio relationship of 1.33:2:4 is established between regions  1  to  3 . In other words, the recess/protrusion depth d should be set such that the volume of the inner space of each recess of the recess/protrusion surface is the same over all the regions. 
       FIG. 4  is cross-sectional views showing the imprint process of forming a recess/protrusion pattern in subject-to-shaping material using the mold  10  having the recess/protrusion surface whose recess/protrusion depth differs according to the recess area percentage as described above. A recess/protrusion pattern obtained by using the mold  10  will be described below with reference to  FIG. 4 . 
     First, subject-to-shaping material is prepared. A substrate  30  uniformly coated with an NIL resist  20  is used as the subject-to-shaping material ( FIG. 4  ( a )). 
     Then, after the substrate  30  coated with the NIL resist  20  is heated to soften the resist, a mold  10  is put in contact with the resist  20 , and by applying pressure, the resist  20  is deformed. Then, keeping the mold pressed, the substrate temperature is lowered to harden the resist  20 , thereby transferring the recesses/protrusions of the mold  10  to the resist  20  ( FIG. 4  ( b )). 
     Then, after the resist  20  has hardened sufficiently, the mold  10  is separated from the substrate  30  ( FIG. 4  ( c )). At this time, a remaining film  20   a  from the resist  20  is left on parts of the substrate  30  corresponding to the protrusions of the mold  10 . By using the mold  10  according to the present invention, the thickness of the remaining film  20   a  is substantially uniform over regions  1  to  3 . This is because the recess/protrusion depth d of each region of the mold  10  is adjusted according to the recess area percentage r. That is, the reason is that because the recess/protrusion depth d has an inversely proportional relationship with the recess area percentage r, the volume of resist going into the space in a recess of the mold  10  is substantially the same for each region. 
     Then, after the mold  10  is separated from the substrate  30 , etching is performed using reactive ion etching (RIE) to remove all of the remaining film  20   a , thereby finish the imprint ( FIG. 4  ( d )). In this embodiment, because the thickness of the remaining film  20   a  is substantially uniform over regions  1  to  3 , there is solved the problem that in regions of the mold having a relatively large recess area percentage (regions  1 ,  2 ), the recess/protrusion pattern imprinted in the resist  20  is over-etched and that thus enough recess/protrusion depth (or height) cannot be secured. The final recess/protrusion pattern of the resist  20  obtained after the etching process is a precise duplicate of the recess/protrusion pattern formed in the mold  10 , over all the regions. 
     As such, when forming a recess/protrusion surface having a plurality of regions different in recess/protrusion area ratio in subject-to-shaping material by imprint, by using a mold where in regions of the mold having a relatively small recess area percentage the recess/protrusion depth is made deeper and where in regions of the mold having a relatively large recess area percentage the recess/protrusion depth is made shallower, the volume of resist going into a recess of the mold when imprinted is substantially the same over the regions, and thus the thickness of the remaining film from the resist left on parts corresponding to the protrusions of the mold is substantially uniform over all the regions. Therefore, there is solved the problem with the conventional art that because the thickness of the remaining film is different for each region, an over-etched region occurs and that thus enough recess/protrusion depth of the recess/protrusion pattern formed in the region cannot be secured. 
     In the above embodiment, the case where the cross-section shape of the recess/protrusion pattern formed in the mold is rectangular has been described, but the present invention is not limited to this.  FIG. 5  is cross-sectional views showing the production process when imprinting in subject-to-shaping material using a mold  10 ′ having a recess/protrusion surface made up of a plurality of regions different in cross-section shape. Also in this case, by setting the recess/protrusion depth such that the volume of the inner space of each recess of the recess/protrusion surface formed in the mold  10 ′ is the same over the regions, the thickness of the remaining film  20   a  can be made uniform over all the regions, thus solving the problem with the conventional art as described above. 
     Next, a method of producing a mold where the recess/protrusion depth varies according to the recess/protrusion area ratio as shown in  FIG. 3  will be described below. Although the above description has mentioned that it is desirable that the recess/protrusion surface of the mold  10  be formed so as to establish an inversely proportional relationship between the recess/protrusion depth d and the recess area percentage r, this is not exactly implemented in the mold produced by the producing method described below. A method of producing a mold having a tendency where a region having a smaller recess area percentage has a larger recess/protrusion depth will be described below. Even with this mold, the effect of improving to some extent the above problem as occurs with the use of the conventional mold can be expected. 
     Embodiment 1 
     A first embodiment of the method of producing a mold according to the present invention will be described with reference to  FIG. 6 . First, a mold substrate forming the base of the mold to be produced is prepared. A substrate  30  made of, e.g., silicon, ceramic, or the like and uniformly coated with an NIL resist  20  as a transfer layer by, e.g., a spin coat method is used as the mold substrate. As the NIL resist  20 , light curing resin or thermoplastic resin can be used, and in this embodiment, thermoplastic resin is used. As the thermoplastic resin, for example, polymethyl methacrylate (PMMA) or polystyrene (PS) can be used ( FIG. 6  ( a )). 
     Then, the substrate  30  coated with the NIL resist  20  is heated to about 200° C. to soften the NIL resist  20 . Next, a conventional mold  1 , where a recess/protrusion surface made up of a plurality of regions different in recess/protrusion area ratio is formed, is put in contact with the softened NIL resist  20 , and by applying pressure, the NIL resist  20  is deformed. Then, keeping the mold pressed, the substrate temperature is lowered to harden the resist  20 , thereby transferring the recess/protrusion pattern of the mold  1  to the NIL resist  20  ( FIG. 6  ( b )). Here, the mold  1  has, e.g., three regions different in recess/protrusion area ratio, and region  1  is a region of the mold where the recess area percentage is relatively large; region  2  is a region of the mold where the recess area percentage is medium; and region  3  is a region of the mold where the recess area percentage is relatively small. The recess/protrusion depth of the recess/protrusion surface is uniform over regions  1  to  3 . Note that the mold  1  is formed by coating a resist over, e.g., a thermally oxidized silicon film and patterning the resist by electron beam direct writing and, with the resist as a mask, performing dry etching, and that the widths of the protrusions and recesses of the recess/protrusion surface thereof are 1 μm or less. 
     After the NIL resist  20  has hardened sufficiently, the mold  1  is separated from the substrate  30  ( FIG. 6  ( c )). At this time, a remaining film  20   a  from the NIL resist  20  is left on parts of the substrate  30  corresponding to the protrusions of the mold  1 . The thickness of this remaining film  20   a  is greater in a region of the mold  1  having a smaller recess area percentage. That is, the thickness of the remaining film  20   a  increases in the order of region  1 , region  2 , and region  3 . Note that the initial thickness of the NIL resist  20  is set so as to produce these differences in the thickness of the remaining film  20   a.    
     Then, SOG (Spin On Glass) is coated over the subject-to-shaping material having the recess/protrusion pattern formed therein to form an SOG film  40 . At this time, the SOG is coated such that the spaces in the recesses formed in the NIL resist  20  are filled with SOG and that the thickness (indicated by an arrow in  FIG. 6  ( d )) of the SOG film measured from the top of a protrusion of the NIL resist  20  is uniform over the regions. Next, the solvent of the SOG film  40  is dried at a temperature (60 to 120° C., preferably 80 to 100° C.) less than or equal to a glass transition temperature Tg of the NIL resist  20  to cause a partial polymerization reaction ( FIG. 6  ( d )). 
     Then, the SOG film  40  is etched back by dry etching using fluorocarbon such as CF 4  or CHF 3  as etching gas until the tops of the protrusions of the NIL resist  20  below are exposed ( FIG. 6  ( e )). 
     Next, only the NIL resist  20  is selectively etched by reactive ion etching (RIE) with O 2  plasma or the like ( FIG. 6  ( f )). By undergoing the above steps, a mold  10   a  is finished. Thereafter, the substrate  30  may be etched with the SOG film  40  as a mask as needed. 
     The recess/protrusion pattern formed in each region of the mold  10   a  produced by the above producing method takes on the recess/protrusion area ratio of the recess/protrusion pattern formed in the original mold  1  as it is. The recess/protrusion depth is different for each region according to the thickness difference of the resist remaining film  20   a  formed when the original mold  1  is pressed. That is, a recess/protrusion surface having a plurality of regions different in recess/protrusion area ratio is formed in the mold  10   a,  and the recess/protrusion depth of the recess/protrusion surface is deeper in a region having a smaller recess area percentage. The widths of the protrusions and recesses of the recess/protrusion surface thereof are 1 μm or less as in the original mold  1 . 
     Using the finished mold  10   a  as a master, a nickel mold in the same shape as this, may be produced.  FIG. 6  ( g ) to ( i ) show the steps until obtaining a nickel mold  10   a ′ from the finished mold  10   a.  The nickel mold  10   a ′ is obtained by performing electroforming two times. That is, a nickel film  50   a  is electrodeposited over the surface of the mold  10   a  as a master by electroforming ( FIG. 6  ( g )). Then, the nickel film  50   a  is separated from the master. Thereby, a mold having the inverse of the recess/protrusion pattern of the master can be obtained. Next, a nickel film  50   b  is electrodeposited over the surface of the nickel film  50   a  by electroforming ( FIG. 6  ( h )). Then these are separated to finish the nickel mold  10   a ′. By this means, a mold having completely the same shape as the mold  10   a  that is a master and further having heat resistance can be obtained. 
     Embodiment 2 
     A second embodiment of the method of producing a mold according to the present invention will be described with reference to  FIG. 7 . First, a mold substrate forming the base of the mold to be produced is prepared. A substrate  30  uniformly coated with an NIL resist  20  as a transfer layer by, e.g., a spin coat method is used as the mold substrate. As the NIL resist  20 , light curing resin or thermoplastic resin can be used, and in this embodiment, thermoplastic resin is used. As the thermoplastic resin, for example, polymethyl methacrylate (PMMA) or polystyrene (PS) can be used ( FIG. 7  ( a )). 
     Then, the substrate  30  coated with the NIL resist  20  is heated to about 200° C. to soften the NIL resist  20 . Next, a conventional mold  1 , where a recess/protrusion surface made up of a plurality of regions different in recess/protrusion area ratio is formed, is put in contact with the softened NIL resist  20 , and by applying pressure, the NIL resist  20  is deformed. Then, keeping the mold pressed, the substrate temperature is lowered to harden the resist  20 , thereby transferring the recess/protrusion pattern of the mold  1  to the NIL resist  20  ( FIG. 7  ( b )). The mold  1  has, e.g., three regions different in recess/protrusion area ratio, and region  1  is a region of the mold where the recess area percentage is relatively large; region  2  is a region of the mold where the recess area percentage is medium; and region  3  is a region of the mold where the recess area percentage is relatively small. The recess/protrusion depth of the recess/protrusion surface is uniform over regions  1  to  3 . Note that the mold  1  is formed by coating a resist over, e.g., a thermally oxidized silicon film and patterning the resist by electron beam direct writing and, with the resist as a mask, performing dry etching, and that the widths of the protrusions and recesses of the recess/protrusion surface thereof are 1 μm or less. 
     After the NIL resist  20  has hardened sufficiently, the mold  1  is separated from the substrate  30  ( FIG. 7  ( c )). At this time, a remaining film  20   a  from the NIL resist is left on parts of the substrate  30  corresponding to the protrusions of the mold  1 . The thickness of this remaining film  20   a  is greater in a region of the mold  1  having a smaller recess area percentage. That is, the thickness of the remaining film  20   a  increases in the order of region  1 , region  2 , and region  3 . Note that the initial thickness of the NIL resist  20  is set so as to produce these differences in the thickness of the remaining film  20   a.    
     Next, etching is performed so as to completely remove the remaining film  20   a  formed in region  3  by reactive ion etching (RIE) with O 2  plasma or the like ( FIG. 7  ( d )). By this etching process, in regions  1  and  2 , even after their remaining film  20   a  is completely removed, etching continues so that the protrusions of the patterned NIL resist  20  are further etched. Thus, the height thereof decreases in the order of region  3 , region  2 , and region  1 . 
     Then, SOG (Spin On Glass) is coated over the subject-to-shaping material having the recess/protrusion pattern formed therein, filling the recesses to form an SOG film  40 . At this time, the SOG is coated such that the thickness (indicated by an arrow in  FIG. 7  ( e )) measured from the top of a protrusion of the patterned NIL resist  20  is uniform over the regions. Next, the solvent of the SOG film  40  is dried at a temperature (60 to 120° C., preferably 80 to 100° C.) less than or equal to a glass transition temperature Tg of the NIL resist  20  to cause a partial polymerization reaction ( FIG. 7  ( e )). 
     Then, the SOG film  40  is etched back by dry etching using fluorocarbon such as CF 4  or CHF 3  as etching gas until the tops of the protrusions of the NIL resist  20  below are exposed ( FIG. 7  ( f )). 
     Next, only the NIL resist  20  is selectively etched by reactive ion etching (RIE) with O 2  plasma or the like ( FIG. 7  ( g )). By undergoing the above steps, a mold  10   b  is finished. Thereafter, the substrate  30  may be etched with the SOG film  40  as a mask as needed. Further, by using a light transmissive material such as glass as the substrate  30 , the mold  10   b  could also be used as a mold with which to form a pattern in light curing resin. 
     The recess/protrusion pattern formed in each region of the mold  10   b  produced by the above producing method takes on the recess/protrusion area ratio of the recess/protrusion pattern formed in the original mold  1  as it is. The recess/protrusion depth is different for each region according to the thickness difference of the resist remaining film  20   a  formed when the original mold  1  is pressed. That is, a recess/protrusion surface having a plurality of regions different in recess/protrusion area ratio is formed in the mold  10   b,  and the recess/protrusion depth of the recess/protrusion surface is deeper in a region having a smaller recess area percentage. The widths of the protrusions and recesses of the recess/protrusion surface thereof are 1 μm or less as in the original mold  1 . 
     Using the finished mold  10   b  as a master, a nickel mold in the same shape as this, may be produced.  FIG. 7  ( h ) to ( j ) show the steps until obtaining a nickel mold  10   b ′ from the finished mold  10   b.  The nickel mold  10   b ′ is obtained by performing electroforming two times. That is, a nickel film  50   a  is electrodeposited over the surface of the mold  10   b  as a master by electroforming ( FIG. 7  ( h )). Then, the nickel film  50   a  is separated from the master. Thereby, a mold having the inverse of the recess/protrusion pattern of the master can be obtained. Next, a nickel film  50   b  is electrodeposited over the surface of the nickel film  50   a  by electroforming ( FIG. 7  ( i )). Then these are separated to finish the nickel mold  10   b ′. By this means, a mold having completely the same shape as the mold  10   b  that is a master and further having heat resistance can be obtained. 
     Embodiment 3 
     A third embodiment of the method of producing a mold according to the present invention will be described with reference to  FIG. 8 . First, a mold substrate forming the base of the mold to be produced is prepared. A substrate  30  uniformly coated with an NIL resist  20  as a transfer layer by, e.g., a spin coat method is used as the mold substrate. As the NIL resist  20 , light curing resin or thermoplastic resin can be used, and in this embodiment, thermoplastic resin is used. As the thermoplastic resin, for example, polymethyl methacrylate (PMMA) or polystyrene (PS) can be used ( FIG. 8  ( a )). 
     Then, the substrate  30  coated with the NIL resist  20  is heated to about 200° C. to soften the NIL resist  20 . Next, a conventional mold  1 , where a recess/protrusion surface made up of a plurality of regions different in recess/protrusion area ratio is formed, is put in contact with the softened NIL resist  20 , and by applying pressure, the NIL resist  20  is deformed. Then, keeping the mold pressed, the substrate temperature is lowered to harden the resist  20 , thereby transferring the recess/protrusion pattern of the mold  1  to the NIL resist  20  ( FIG. 8  ( b )). The mold  1  has, e.g., three regions different in recess/protrusion area ratio, and region  1  is a region of the mold where the recess area percentage is relatively large; region  2  is a region of the mold where the recess area percentage is medium; and region  3  is a region of the mold where the recess area percentage is relatively small. The recess/protrusion depth of the recess/protrusion surface is uniform over regions  1  to  3 . Note that the mold  1  is formed by coating a resist over, e.g., a thermally oxidized silicon film and patterning the resist by electron beam direct writing and, with the resist as a mask, performing dry etching, and that the widths of the protrusions and recesses of the recess/protrusion surface thereof are 1 μm or less. 
     After the NIL resist  20  has hardened sufficiently, the mold  1  is separated from the substrate  30  ( FIG. 8  ( c )). At this time, a remaining film  20   a  from the NIL resist  20  is left on parts of the substrate  30  corresponding to the protrusions of the mold  1 . The thickness of this remaining film  20   a  is greater in a region of the mold  1  having a smaller recess area percentage. That is, the thickness of the remaining film  20   a  increases in the order of region  1 , region  2 , and region  3 . Note that the initial thickness of the NIL resist  20  after coated is set so as to produce these differences in the thickness of the remaining film  20   a.    
     Next, etching is performed so as to completely remove the remaining film  20   a  formed in region  1  by reactive ion etching (RIE) with O 2  plasma or the like ( FIG. 8  ( d )). That is, while the relatively thin remaining film formed in region  1  is completely removed by this etching process, in regions  2  and  3 , the remaining film  20   a  still remains after this etching process. The thickness of the remaining film  20   a  after this etching process is greater in region  3  than in region  2 . 
     Then, SOG (Spin On Glass) is coated over the subject-to-shaping material having the recess/protrusion pattern formed therein, filling the recesses to form an SOG film  40 . At this time, the SOG is coated such that the thickness (indicated by an arrow in  FIG. 8  ( e )) measured from the top of a protrusion of the patterned NIL resist  20  is uniform over the regions. Next, the solvent of the SOG film  40  is dried at a temperature (60 to 120° C., preferably 80 to 100° C.) less than or equal to a glass transition temperature Tg of the NIL resist  20  to cause a partial polymerization reaction ( FIG. 8  ( e )). 
     Then, the SOG film  40  is etched back by dry etching using fluorocarbon such as CF 4  or CHF 3  as etching gas until the tops of the protrusions of the NIL resist  20  below are exposed ( FIG. 8  ( f )). 
     Next, only the NIL resist  20  is selectively etched by reactive ion etching (RIE) with O 2  plasma or the like ( FIG. 8  ( g )). By undergoing the above steps, a mold  10   c  is finished. Thereafter, the substrate  30  may be etched with the SOG film  40  as a mask as needed. 
     The recess/protrusion pattern formed in each region of the mold  10   c  produced by the above producing method takes on the recess/protrusion area ratio of the recess/protrusion pattern formed in the original mold  1  as it is. The recess/protrusion depth is different for each region according to the thickness difference of the resist remaining film  20   a  formed when the original mold  1  is pressed. That is, a recess/protrusion surface having a plurality of regions different in recess/protrusion area ratio is formed in the mold  10   c,  and the recess/protrusion depth of the recess/protrusion surface is deeper in a region having a smaller recess area percentage. The widths of the protrusions and recesses of the recess/protrusion surface thereof are 1 μm or less as in the original mold  1 . 
     Using the finished mold  10   c  as a master, a nickel mold in the same shape as this, may be produced.  FIG. 8  ( h ) to ( j ) show the steps until obtaining a nickel mold  10   c ′ from the finished mold  10   c.  The nickel mold  10   c ′ is obtained by performing electroforming two times. That is, a nickel film  50   a  is electrodeposited over the surface of the mold  10   c  as a master by electroforming ( FIG. 8  ( h )). Then, the nickel film  50   a  is separated from the master. Thereby, a mold having the inverse of the recess/protrusion pattern of the master can be obtained. Next, a nickel film  50   b  is electrodeposited over the surface of the nickel film  50   a  by electroforming ( FIG. 8  ( i )). Then these are separated to finish the nickel mold  10   c ′. By this means, a mold having completely the same shape as the mold  10   c  that is a master and further having heat resistance can be obtained. 
     Embodiment 4 
     A fourth embodiment of the method of producing a mold according to the present invention will be described with reference to  FIG. 9 . First, a mold substrate forming the base of the mold to be produced is prepared. A substrate  30  uniformly coated with an NIL resist  20  as a transfer layer by, e.g., a spin coat method is used as the mold substrate. The thickness of the NIL resist  20  is set smaller than in the above embodiments. To be specific, as shown in  FIG. 9  ( b ), the thickness is set at a minimum necessary value to completely fill the insides of the mold recesses formed in region  3  of a mold  1  described later with the NIL resist  20 . That is, the initial thickness is set such that the inner spaces of the mold recesses in regions  1  and  2  are not completely filled with the NIL resist  20 . As the NIL resist  20 , light curing resin or thermoplastic resin can be used, and in this embodiment, thermoplastic resin is used. As the thermoplastic resin, for example, polymethyl methacrylate (PMMA) or polystyrene (PS) can be used ( FIG. 9  ( a )). 
     Then, the substrate  30  coated with the NIL resist  20  is heated to about 200° C. to soften the NIL resist  20 . Next, a conventional mold  1 , where a recess/protrusion surface made up of a plurality of regions different in recess/protrusion area ratio is formed, is put in contact with the softened NIL resist  20 , and by applying pressure, the NIL resist  20  is deformed. Then, keeping the mold pressed, the substrate temperature is lowered to harden the resist  20 , thereby transferring the recess/protrusion pattern of the mold  1  to the NIL resist  20  ( FIG. 9  ( b )). The mold  1  has, e.g., three regions different in recess/protrusion area ratio, and region  1  is a region of the mold where the recess area percentage is relatively large; region  2  is a region of the mold where the recess area percentage is medium; and region  3  is a region of the mold where the recess area percentage is relatively small. The recess/protrusion depth of the recess/protrusion surface is uniform over regions  1  to  3 . Note that the mold  1  is formed by coating a resist over, e.g., a thermally oxidized silicon film and patterning the resist by electron beam direct writing and, with the resist as a mask, performing dry etching, and that the widths of the protrusions and recesses of the recess/protrusion surface thereof are 1 μm or less. 
     After the NIL resist  20  has hardened sufficiently, the mold  1  is separated from the substrate  30  ( FIG. 9  ( c )). At this time, a remaining film  20   a  from the NIL resist is left on parts of the substrate  30  corresponding to the protrusions of the mold  1 . The thickness of this remaining film  20   a  is substantially uniform over all the regions unlike in the above embodiments 1 to 3. Meanwhile, the thickness (indicated by an arrow in  FIG. 9  ( c )) measured from the top of this remaining film  20   a  to the top of a protrusion of the patterned NIL resist  20  is different for each region and increases in the order of region  1 , region  2 , and region  3 . 
     Next, etching is performed so as to completely remove the remaining film  20   a  formed in each region by dry etching with O 2  plasma or the like ( FIG. 9  ( d )). By this means, protrusions of the NIL resist  20  whose thickness is different for each region remain on the substrate  30 , and the thickness thereof increases in the order of region  1 , region  2 , and region  3 . 
     Then, SOG (Spin On Glass) is coated over the subject-to-shaping material having the recess/protrusion pattern formed therein, filling the recesses to form an SOG film  40 . At this time, the SOG is coated such that the thickness (indicated by an arrow in  FIG. 9  ( e )) measured from the top of a protrusion of the patterned NIL resist  20  is uniform over the regions. Next, the solvent of the SOG film  40  is dried at a temperature (60 to 120° C., preferably 80 to 100° C.) less than or equal to a glass transition temperature Tg of the NIL resist  20  to cause a partial polymerization reaction ( FIG. 9  ( e )). 
     Then, the SOG film  40  is etched back by dry etching using fluorocarbon such as CF 4  or CHF 3  as etching gas until the tops of the protrusions of the NIL resist  20  below are exposed ( FIG. 9  ( f )). 
     Next, only the NIL resist  20  is selectively etched by reactive ion etching with O 2  plasma or the like ( FIG. 9  ( g )). By undergoing the above steps, a mold  10   d  is finished. Thereafter, the substrate  30  may be etched with the SOG film  40  as a mask as needed. Further, by using a light transmissive material such as glass as the substrate  30 , the mold  10   d  could also be used as a mold with which to form a pattern in light curing resin. 
     The recess/protrusion pattern formed in each region of the mold  10   d  produced by the above producing method takes on the recess/protrusion area ratio of the recess/protrusion pattern formed in the original mold  1  as it is. The recess/protrusion depth is different for each region according to the difference in the recess/protrusion depth of the recess/protrusion pattern formed in the resist  20  when the original mold  1  is pressed. That is, a recess/protrusion surface having a plurality of regions different in recess/protrusion area ratio is formed in the mold  10   d,  and the recess/protrusion depth of the recess/protrusion surface is deeper in a region having a smaller recess area percentage. The widths of the protrusions and recesses of the recess/protrusion surface thereof are 1 μm or less as in the original mold  1 . 
     Using the finished mold  10   d  as a master, a nickel mold in the same shape as this, may be produced.  FIG. 9  ( h ) to ( j ) show the steps until obtaining a nickel mold  10   d ′ from the finished mold  10   d.  The nickel mold  10   d ′ is obtained by performing electroforming two times. That is, a nickel film  50   a  is electrodeposited over the surface of the mold  10   d  as a master by electroforming ( FIG. 9  ( h )). Then, the nickel film  50   a  is separated from the master. Thereby, a mold having the inverse of the recess/protrusion pattern of the master can be obtained. Next, a nickel film  50   b  is electrodeposited over the surface of the nickel film  50   a  by electroforming ( FIG. 9  ( i )). Then these are separated to finish the nickel mold  10   b ′. By this means, a mold having completely the same shape as the mold  10   d  that is a master and further having heat resistance can be obtained. 
     The SOG used in the above embodiments is preferably, for example, AZ Spinfill (trademark) (component: polysilazane) or DowCorning Fox (trademark) (component: hydrogen silsesquioxane (HSQ)). 
     Although in the above embodiments description has been made taking as an example a case where SOG that is thermosetting is used as coating material for the recess/protrusion structure, a material which can coat the recess/protrusion pattern and has etching selectivity in a subsequent step can be used as the coating material, not being limited to SOG. For example, if light curing resin or water-soluble resin is used, when being coated, the resin can be coated without dissolving the NIL resist of the recess/protrusion pattern. 
     As apparent from the above description, according to the method of producing a mold according to the present invention, by using a conventional mold having a recess/protrusion surface made up of a plurality of regions different in recess/protrusion area ratio where the recess/protrusion depth of the recess/protrusion surface is uniform over the regions, a new mold can be produced which has a recess/protrusion surface of the same recess/protrusion area ratio as that of the recess/protrusion surface of the conventional mold for each region and whose recess/protrusion depth differs according to the recess/protrusion area ratio. Further, when a recess/protrusion pattern of a different recess/protrusion depth is formed in each region, the thickness difference of the remaining film or the difference in the recess/protrusion depth of the recess/protrusion pattern, which is formed in the resist by using the conventional mold, is used. Hence, it is easy to adjust it by etching or so on. 
     The mold according to the present invention as described above can be used in the manufacture of, for example, discrete track media.  FIG. 10  shows the structure of a discrete track medium. The discrete track medium is a record medium configured to have grooves formed between data tracks  100  of magnetic material, where by filling these grooves with nonmagnetic material  101 , the data tracks are separated physically and magnetically. With this structure, the record density of discrete track media can be improved without causing a harmful effect such as side write or crosstalk. In this discrete track medium, a servo pattern as position control information such as track addresses and sector addresses as well as the data tracks is formed, and by reading the position control information written in the servo pattern, the magnetic head is positioned with accuracy on the order of a nanometer. The data tracks and the servo pattern may be formed in respective predetermined areas at different pitches respectively. That is, recess/protrusion patterns of different recess/protrusion area ratios may be respectively formed in the data track formed area and the servo pattern formed area. In forming these recess/protrusion patterns, the nano-imprint lithography technology can be used, and the mold according to the present invention described above can be used. 
     A method of producing a discrete track medium using the mold according to the present invention will be described below with reference to  FIG. 11 . First, a discrete track medium substrate having a glass substrate  200 , a soft magnetic layer  201 , and a magnetic layer  202  laid one over another is prepared and is uniformly coated with an NIL resist  20  by, e.g., a spin coat method ( FIG. 11  ( a )). As the NIL resist  20 , light curing resin or thermoplastic resin can be used, and in this embodiment, thermoplastic resin is used. As the thermoplastic resin, for example, polymethyl methacrylate (PMMA) or polystyrene (PS) can be used. 
     Then, the substrate  30  coated with the NIL resist  20  is heated to about 200° C. to soften the NIL resist  20 . Next, the mold  10  according to the present invention is put in contact with the softened NIL resist  20 , and by applying pressure, the NIL resist  20  is deformed. Then, keeping the mold pressed, the substrate temperature is lowered to harden the resist  20 , thereby transferring the recess/protrusion pattern of the mold  10  to the NIL resist  20  ( FIG. 11  ( b )). In the mold  10 , a recess/protrusion surface made up of two regions different in recess/protrusion area ratio, corresponding to the data track formed area and the servo pattern formed area is formed. Specifically, the region corresponding to the data track formed area has a relatively small recess area percentage, and the region corresponding to the servo pattern formed area has a relatively large recess area percentage. The magnitude relationship in recess/protrusion area ratio between the regions may be the opposite of the above one. 
     After the NIL resist  20  has hardened sufficiently, the mold  10  is separated from the substrate  30  ( FIG. 11  ( c )). At this time, a remaining film  20   a  from the resist  20  is left on parts of the substrate  30  corresponding to the protrusions of the mold  10 . The thickness of this remaining film  20   a  is uniform over the data track formed area and the servo pattern formed area. 
     Next, the remaining film  20   a  is completely removed by reactive ion etching (RIE) with O 2  plasma or the like ( FIG. 11  ( d )). The patterned NIL resist  20  forms a mask on the magnetic layer  202  for forming the data track and the servo pattern. 
     Then, with the NIL resist  20  as a mask, grooves  202   a  are formed in the magnetic layer  202  by dry etching ( FIG. 11  ( e )). Subsequently, the grooves  202   a  are filled with nonmagnetic material  203  of, e.g., SOG ( FIG. 11  ( f )). By this means, the float stability of the magnetic head is secured. Then, by forming a protective, lubricant film  204  on the magnetic layer  202 , a discrete track medium is finished. 
     In this way, a discrete track medium having the data track formed area and the servo pattern formed area that are different in track pitch can be produced using a mold according to the present invention.