Abstract:
A substrate having an arrangement of self-assembling magnetic domains and a method of fabrication therefor. In some embodiments, a substrate is patterned with a plurality of chemically contrasted alignment features, and a block copolymer having a magnetic component and a non-magnetic component is deposited onto the substrate. The block copolymer self-assembles into a sequence of magnetic domains responsive to the alignment features. The period of the alignment features is between about 2 times and about 10 times the period of the magnetic domains.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of copending U.S. patent application Ser. No. 12/273,791 filed Nov. 19, 2008 and which issues Mar. 31, 2015 as U.S. Pat. No. 8,993,060, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    Structures having components with dimensions on a nanometer scale are being considered for use in the areas of optics, electronics, mechanics, magnetism and so forth. Nanostructures encompass various structures referred to as, for example, nanoparticles, nanotubes or quantum dots, and may potentially be used as building blocks for ordered and complex materials. 
         [0003]    For data storage media, including bit patterned media (BPM) and discrete track media (DTM), the patterning of ultra-high density dot array or line array, with a periodicity as small as 25 nm or less is desirable. However, since optical lithography is limited by the diffraction limit, the resolution of conventional optical lithography is usually limited to about 50 nm half-pitch. Thus conventional optical lithography may not be suitable for fabricating such nanostructures for bit patterned magnetic storage media. 
         [0004]    A high-throughput patterning method is desired for forming nanostructures on a substrate. Self-assembly technology has the potential to provide both ultrahigh-density patterning and high throughput. 
       SUMMARY 
       [0005]    Various embodiments of the present disclosure are generally directed to a substrate having an arrangement of self-assembling magnetic domains and a method therefor. 
         [0006]    In some embodiments, a method includes pattering a substrate with a plurality of chemically contrasted alignment features, and depositing a block copolymer having a magnetic component and a non-magnetic component onto the substrate. The block copolymer self-assembles into a sequence of magnetic domains responsive to the alignment features. The period of the alignment features is between about 2 times and about 10 times the period of the magnetic domains. 
         [0007]    In other embodiments, a method includes forming a photoresist layer on a disc-shaped rigid substrate having a polymer brush layer thereon. A lithographic process is used to form a first plurality alignment features in a servo area and a second plurality of alignment features in a bit area of the photoresist layer. A self-assembling copolymer material comprising a magnetic component and a non-magnetic component is deposited on at least a portion of the bit area. The position of curvilinearly shaped domains of the self-assembled material is directed by the second plurality of alignment features to form a nanostructure pattern in the bit area having a period from two to ten times a period of the second plurality of alignment features. The curvilinearly shaped domains are formed by the magnetic component of the copolymer material. 
         [0008]    In other embodiments, a bit patterned magnetic recording medium is formed by the foregoing steps. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic representation of a fabrication process in accordance with one aspect of the present disclosure. 
           [0010]      FIG. 2  is a schematic representation of a block copolymer. 
           [0011]      FIG. 3  is a cross-sectional view of a substrate. 
           [0012]      FIG. 4  is a cross-sectional view of a substrate. 
           [0013]      FIGS. 5-7  are schematic representations of dot patterns. 
           [0014]      FIGS. 8-11  are schematic representations of portions of patterned media constructed in accordance with some aspects of the present disclosure. 
           [0015]      FIG. 12  is a photomicrograph of a portion of a patterned media in accordance with an aspect of the present disclosure. 
           [0016]      FIG. 13  is a schematic cross-sectional view of a portion of another patterned media constructed in accordance with an aspect of the present disclosure. 
           [0017]      FIG. 14  is a schematic cross-sectional view of a portion of another patterned media constructed in accordance with an aspect of the present disclosure. 
           [0018]      FIG. 15  is a photomicrograph of a portion of another patterned media in accordance with an aspect of the present disclosure. 
           [0019]      FIG. 16  is a plan view of a patterned surface that can be used in the fabrication of the patterned media of  FIG. 15 . 
           [0020]      FIGS. 17-19  are schematic representations of a cross-section of another patterned media constructed in accordance with an aspect of the present disclosure. 
           [0021]      FIG. 20  is a schematic representation of a data storage disc template in accordance with an aspect of the present disclosure. 
           [0022]      FIG. 21  is a flow diagram that illustrates the method of an aspect of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The present disclosure generally relates to methods of fabricating nanostructured devices and to devices fabricated using such methods. In one aspect, the disclosure sets forth a method for achieving long-range order and precise positional control in naturally self-assembled nanostructures. 
         [0024]    Some embodiment are directed to data storage media and the fabrication thereof. Data storage media generally include a servo area and a bit area. The servo area includes information that is used to control the position of a recording head and the timing of read and write operations. The bit area is used to store information that is written to and read from the media. In one aspect, various embodiments allow the integration of self-assembly processes into nano-imprint template fabrication of bit patterned media (BPM) for both a bit area having high-density periodic dot patterns and a servo area having medium-to-high density periodic/non-periodic dot/line patterns. 
         [0025]    In another aspect, some embodiments use a substrate structure with a chemical contrast surface pattern that can be used to direct the self-assembly, or self-organization, of an array of nanostructures. As used in this description, a chemical contrast substrate refers to a substrate having regions or materials that exhibit different chemical preferences, or affinities, for different components of a block copolymer. The regions or materials can have little topographic difference. The regions or materials serve as alignment features that direct the self-assembly of the nanostructures. Self-assembly means the formation of periodic nanostructures of self-assembling materials, such as bloc copolymers and nanoparticles. The periodic nanostructures can form spontaneously in a relatively large area according to thermodynamic properties. 
         [0026]    A substrate having a chemical contrast can be used to direct the positioning of block copolymer spherical or cylindrical nanodomains with domain periods of  25  nm or less, corresponding to an areal density of z 1 Tdot/in 2  as desired for the template fabrication of bit patterned media (BPM). Referring to the drawings,  FIG. 1  schematically illustrates a fabrication process in accordance with one aspect of the disclosure. 
         [0027]    In  FIG. 1 , a disc  10  includes a substrate  12  and has a surface pattern  14  formed on the substrate. The surface pattern includes a chemical contrast surface pattern having a plurality of regions  16  in or on a surface  18 . The regions  16  serve as alignment features for subsequently deposited nanostructures. While only a few regions  16  are shown in  FIG. 1  for clarity, it will be appreciated that many more regions  16  may be used in a practical device. The regions and surface have different affinities for material that are to be subsequently deposited on the substrate, and serve to direct the position and/or orientation of nanostructures. The regions  16  can be created by conventional lithography, such as e-beam lithography, nano-imprinting, extreme-ultraviolet (EUV) lithography, 193 nm lithography, 248 nm lithography, X-ray lithography, etc. 
         [0028]    The half-pitch of the surface pattern  14  can be, for example, tens to hundreds of nanometers. In this example, the regions  16  have a substantially circular shape in the plane of the surface  18 . The regions  16  are also referred to as dots. 
         [0029]    A self-assembled material is used to fabricate a pattern  20 , whose long-range order and positional accuracy is directed by surface pattern  14 . In one example, the self-assembled pattern is fabricated using block copolymers. The components of the block copolymer will position themselves on the surface of the substrate in a pattern that is directed by the chemical contrast pattern of the substrate. One domain of the block copolymer can be removed to leave the domains  22  in the pattern  20 . In one example, the remaining domains  22  have a substantially spherical shape. 
         [0030]    The period ratio between substrate pattern and block copolymer pattern can vary in a range from 1:1 to 10:1. In addition, the lattice structure in substrate chemical contrast pattern is not necessarily the same as that in the block copolymer pattern. Furthermore, the chemical contrast pattern need not be periodic. 
         [0031]    In one example, the size of the alignment dots  16  is smaller than the size of the block copolymer domain  22  when measured in a lateral direction, and the volume of the alignment dots is much smaller than that of the block copolymer domains. 
         [0032]      FIG. 2  is a schematic representation of a block copolymer  30 . The block copolymer includes a major component  32  and a minor component  34 . 
         [0033]      FIG. 3  is a cross-sectional view of a portion of a chemically patterned substrate  40 . A polymer brush layer  42  is formed on a surface  44  of the substrate. In this example, openings  46 ,  48  are formed in the polymer brush layer. The substrate is formed of a material having an affinity to a first component of a block copolymer, and the polymer brush layer  42  is formed of a material having an affinity to a second component of the block copolymer. When the block copolymer is subsequently applied to the substrate, the positions of the domains of the block copolymer will be controlled by the affinities of the block copolymer components with the substrate and the polymer brush layer. The example of  FIG. 3  includes a concave substrate pattern. 
         [0034]      FIG. 4  is a cross-sectional view of a portion of a chemically patterned substrate  50 . A polymer brush layer  52  is formed on a surface  54  of the substrate. In this example, nanoposts  56 ,  58  are formed on the polymer brush layer. The polymer brush layer is formed of a material having an affinity to a first component of a block copolymer, and the nanoposts are formed of a material having an affinity to a second component of the block copolymer. When the block copolymer is subsequently applied to the substrate, the positions of the domains of the block copolymer will be controlled by the affinities of the block copolymer components with the polymer brush layer and the nanoposts. The example of  FIG. 4  includes a convex substrate pattern. 
         [0035]    In the examples described herein, the polymer brush layer can be comprised of polystyrene (for copolymers with polystyrene as the major blocks). In the example of  FIG. 4 , the nanoposts can be comprised of SiOx or various metals, such as tantalum, chromium, titanium, etc. 
         [0036]    To form the pattern, a block copolymer can be deposited on the patterned surface via spin-coating from a dilute solution in general solvents like toluene, forming monolayered spheres (for sphere-form block copolymers) or lying-down cylinders (for cylinder-form block copolymers), and one domain of the block copolymer can be removed, using one of several known techniques, to leave a plurality of nanostructures in the form of dots (or holes) or lines (or trenches). 
         [0037]    Block copolymer nanostructures can be used to form structures having half-pitch domain sizes in the order of about 5 TIm to about 50 TIm. However, these block copolymer nanostructures usually lack long-range order. In one aspect, this disclosure addresses the poor long-range order issue by using a substrate having a surface pattern with a chemical contrast to promote long-range order in block copolymer nanostructures. 
         [0038]    The block copolymer can include two organic blocks (e.g., polystyreneblock-polymethylmethacrylate), or one organic block and one inorganic block (e.g., polystyrene-block-polydimethylsiloxane). One of the domains can be removed by UV degradation followed by a wet rinse. For example, upon UV exposure, polymethylmethacrylate is degraded while polystyrene is cross-linked. In another example, oxygen plasma can be used to remove organic components. Polydimethylsiloxane has good resistance to oxygen plasma. 
         [0039]    The substrate pattern with chemical contrast and customized pattern layout can be used to direct the positioning of self-assembled nanodomains with domain periods of 25 TIm or less (˜1 Tdot/in 2 ). This substrate chemical pattern can be generated by various advanced lithographic techniques, such as e-beam, nano-imprint, EUV, 193 TIm, 248 TIm, X-ray, etc. Although block copolymers are used as examples here, the self-assembled material is not limited to block copolymers, and it can be any self-assembling materials with at least two chemically distinct components, e.g., chemically functionalized nanoparticles and nanotubes. In a chemically functionalized Nan particle, besides the organic Nan particle inner core, there is an outer shell comprised of organic polymer chains which have a distinct chemical property compared with the inner core. One example of a chemically functionalized Nan particle is: 3-aminopropyl-(3oxobutanoic acid) functionalized silica Nan particle.  FIGS. 5-7  are schematic representations of substrate dot patterns with various periodic lattice structures, where Ls is the period (i.e., the distance between alignment dots) in substrate pattern, Lsx is the period in an X direction, and Lsy is the period in a Y direction of a Cartesian co-ordinate system. 
         [0040]      FIG. 5  shows a hexagon pattern of alignment dots positioned such that Lsy=0.866 Lsx.  FIG. 6  shows a stagger pattern of alignment dots positioned such that Lsy=Lsx.  FIG. 7  shows a square pattern of alignment dots positioned such that Lsy=Lsx. 
         [0041]    The period of the substrate pattern is not necessarily equal to the domain period (IX) in a natural block copolymer pattern, which is helpful to release the pressure of conventional lithographic technology used to generate the substrate pattern, for example bye-beam lithography or optical lithography. The natural pattern of self-assembled materials refers to the self-assembled nanostructure formed without the guidance of external fields, such as a substrate topographic pattern or chemical contrast pattern. With a method described here, only a sparse substrate pattern (e.g., chemical contrast) needs to be generated by conventional lithography, which will be used to direct a dense self-assembled pattern. Thus, self-assembly releases the resolution pressure of conventional lithography. 
         [0042]    The pattern multiplication (i.e., the ratio of substrate pattern period and block copolymer pattern period) ranges from about one to about 10. For example, the ratio of 10 can be used if a single grain of 1 O×10 block copolymer domains can be typically formed in a natural block copolymer nanopattern without any surface guidance and thus in the form of multi-grain structures. 
         [0043]    Such a pattern multiplication is useful for patterned media fabrication having an areal dots density of 1-2 Tdot/in 2  and beyond. The patterning resolution of this method is only limited by the properties of available self-assembling materials, which have half-pitch dimensions of about 4 nm to about 50 nm for block copolymers, about 3 run to about 10 run for nanoparticles, and about 1 run to about 5 run for nanotubes, corresponding to areal densities 1-50 Tdot/in 2 . 
         [0044]      FIGS. 8-10  are schematic representations of block copolymer patterns directed by periodic substrate patterns with same or different lattice structures. 
         [0045]      FIG. 8  shows a pattern of nanostructures formed on a substrate having alignment dots at the positions indicated by item number  60 . The alignment dots are positioned such that Lsy=0.866 Lsx.  FIG. 8  shows a hexagonal pattern of alignment dots with 3 times (3X) multiplication, wherein Ls=nLo(±10%), for n=1, 2, . . . , 10, and where Lo is the period in a natural (i.e., un-directed) block copolymer pattern. However, the pattern of alignment dots in  FIG. 8  is not limited to a 3× multiplication. 
         [0046]      FIG. 9  shows a pattern of nanostructures formed on a substrate having alignment dots at the positions indicated by item number  62 . The alignment dots are positioned such that Lsy=Lsx.  FIG. 9  shows a stagger pattern of alignment dots with 3× multiplication, wherein Ls=nLo(+10%), for n=1, 2, . . . , 10. However, the pattern of alignment dots in  FIG. 9  is not limited to a 3× multiplication. 
         [0047]      FIG. 8  shows a pattern of nanostructures formed on a substrate having alignment dots at the positions indicated by item number  64 . The alignment dots are positioned such that Lsy=Lsx. 
         [0048]      FIG. 10  shows a square pattern of alignment dots with 4 times (4×) multiplication, wherein Ls=2nLo(±10%), for n =1, 2, . . . , 5. However, the pattern of alignment dots in  FIG. 10  is not limited to a 3× multiplication. 
         [0049]    In the structures of  FIGS. 8-10 , a natural lattice structure is assumed to be obtainable in a block copolymer pattern without any substrate guidance. 
         [0050]    The lattice structure of the substrate pattern can also be different from that of naturally self-assembled structures. For example, substrate patterns with hexagon, stagger, or square array are all able to align block copolymer spherical/cylindrical domains with a naturally hexagon lattice. Furthermore, the substrate pattern need not be periodic, as long as it can direct long-range ordering of block copolymer domain structures by pinning some block copolymer nanodomains to the underlying substrate at some spots. 
         [0051]      FIG. 11  is a schematic representation of a block copolymer pattern directed by a non-periodic substrate pattern having alignment dots at the positions indicated by item number  66 . In this example, the average dimension for Ls is &lt;Ls&gt;, and &lt;Ls&gt; is in a range from about 2 Lo to about 10 Lo. 
         [0052]    The substrate pattern can be created by optical lithography. A substrate having a chemical contrast surface can include alternating hydrophobic/hydrophilic regions or alternating polar/non-polar regions having a distinct affinity to distinct blocks in the copolymer. 
         [0053]    Self-assembled nanodot arrays can be directed by a substrate chemical pattern with pattern pitches that are much larger than the pitches of the nanodot array. By using a carefully designed self-assembly system, a spherical block copolymer self-assembled on a substrate hexagon dot pattern with a low-topography chemical contrast, highly addressable block copolymer dot arrays with 24 nm pitch (1.3 Tdot/in 2 ) directed by substrate dot arrays with a periodicity of 24 nm/48 nm/72 nm/96 nm have been fabricated. In addition, directed &gt;2 Tdot/in 2  dot arrays have also been successfully demonstrated. In this example, the dots are arranged in the array format of  FIG. 5 . 
         [0054]    While others have studied perpendicularly oriented cylindrical block copolymers, a neutral surface wetting condition is required to achieve domain orientation perpendicular to both substrate/copolymer interface and copolymer/air interface in the case of cylindrical block copolymers. In one aspect, this disclosure includes a spherical block copolymer without the concern of neutral surface wetting to generate an addressable dot array, which is in thermodynamic equilibrium and thus intrinsically has a low defect density and long-term stability. 
         [0055]      FIG. 12  is a photomicrograph of a portion of a patterned media in accordance with an aspect of the present disclosure.  FIG. 12  shows a 1.3 Tdot/in 2  spherical PSPDMS block copolymer pattern directed by a hexagon substrate pattern with 3× period. 
         [0056]      FIG. 13  is a schematic cross-sectional view of a portion of a patterned media similar to that shown in  FIG. 12 . In the example of  FIG. 13 , a substrate  70  with a chemically contrasting surface  72  includes a polymer brush layer  74  and openings  76 ,  78  in the polymer brush layer. A block copolymer  80  is deposited on the chemically contrasting surface. The block copolymer includes a plurality of substantially spherical domains  82 ,  84 ,  86  and  88  of a first component in a second component  90 . Domains  82  and  88  have an affinity to the substrate and therefore form at the locations of the openings in the brush layer. 
         [0057]      FIG. 14  is a schematic cross-sectional view of the portion of the patterned media of  FIG. 13 , after the second component has been substantially removed. 
         [0058]    In another aspect of the present disclosure, by combining a substrate chemical pattern with a cylindrical block copolymer, highly ordered dense line patterns can be fabricated.  FIG. 15  is a photomicrograph of a cylindrical poly(styrene-dimethyl siloxane) (PS-PDMS) block copolymer pattern directed by a substrate dot pattern.  FIG. 15  shows a patterned portion  92  and an unpatterned portion  94 , without an underlying substrate pattern. There is no obvious domain orientation in the unpatterned area. 
         [0059]    The chemical contrast pattern on the substrate includes a plurality of dots  96  as shown in  FIG. 16 . In the pattern of  FIG. 16 , Ls=n.J3Lo(±10%), with n=1, 2, . . . , 5, and where Lo is the period in natural (i.e., un-directed) block copolymer pattern. 
         [0060]    When a cylindrical block copolymer is deposited on the patterned surface, the cylinders attach to the pattern dots and lie in a direction substantially parallel to the patterned surface. 
         [0061]      FIGS. 17-19  are schematic representations of a cross-section of a patterned media constructed with a cylindrical block copolymer in accordance with an aspect of the present disclosure. 
         [0062]      FIG. 17  shows a cross-sectional schematic view in cross-track direction. In the example of  FIG. 17 , a substrate  100  with a chemically contrasting surface  102  includes a polymer brush layer  104  and openings  106  in the polymer brush layer. A cylindrical block copolymer  108  is deposited on the chemically contrasting surface. The block copolymer includes a plurality of substantially cylindrical domains  110 ,  112  and  114  of a first component in a second component  116 . Domains  110  and  114  have an affinity to the substrate and therefore form at the locations of the openings in the brush polymer layer. 
         [0063]      FIG. 18  is a schematic cross-sectional view of the portion of the patterned media of  FIG. 17 , after the second component has been substantially removed. 
         [0064]      FIG. 19  is a cross-sectional schematic view of the structure of  FIG. 18  in the down-track direction. 
         [0065]    The block copolymer materials can be any spherical (for a dot array of nanostructures) or cylindrical (for a dot or line array of nanostructures) block copolymers with two (or more) highly immiscible blocks/components, A and B (or more), which can form nanostructures with domain spacings of 25 nanometers, nm or less, such as polystyrene polymethylmethacrylate (PS-PMMA) (down to ˜20-25 nm), poly(styrene-dimethyl siloxane) (PS-PDMS)(down to about 10 nm), polystyrene-poly(ethylene oxide) (PS-PEO) (down to about 15 nm), PS-P2VP (down to about 12 nm), polystyrene-block-poly (4-vinylpyridine) (PS-P4VP) (down to about 15 nm), etc. 
         [0066]    In one example, the block copolymer nanostructure can be directly used as a recording media if one component/block includes magnetic elements, such like cobalt, iron, etc. 
         [0067]    The self-assembled nanodomains can be integrated into BPM nanoimprint template fabrication including both a regular bit pattern and a non-regular servo pattern as shown in  FIG. 20 . 
         [0068]      FIG. 20  is a schematic representation of a data storage disc template  120  in accordance with an aspect of the present disclosure. The disc template includes a plurality of tracks  122 , only one of which is shown. Each track includes a plurality of data bit areas  124 , and a plurality of servo areas  126 . The data bit areas can be fabricated using the process described herein. The servo areas can be fabricated using a lithographic process, such as e-beam writing. 
         [0069]      FIG. 21  is a process flow diagram illustrating a method for using directed self-assembled block copolymer nanostructures in BPM template fabrication including both a bit pattern and a servo pattern. In this method, e-beam writing (EBW) is used to generate a servo pattern in the servo area, and a self-assembly material/process is used to prepare a high-density dot array in the bit area. Block  130  shows that the method starts by coating a substrate with a thin polymer brush layer. In one example, the thin polymer brush layer can have a thickness of about 1 nm to about 10 nm. 
         [0070]    The thin polymer brush layer is then coated with a photoresist layer having, for example, a thickness of about 20 nm to about 50 nm. The photoresist can be patterned using known techniques to include a regular dot pattern (in a bit area) and a non-regular servo pattern (in a servo area). The photoresist can be patterned using, for example, e-beam lithography, optical lithography, etc. (block  132 ). 
         [0071]    Next, a first evaporation and liftoff process can be used to form a first hard mask pattern in both the bit and servo areas (using for example, chromium, tantalum, etc.). 
         [0072]    The regular dot pattern in the bit area will be used as a substrate pattern to guide a subsequently applied block copolymer pattern and the non-regular servo pattern in servo area will be used as final servo pattern (block  134 ). 
         [0073]    Block  136  shows that the block copolymers are coated and annealed (e.g., via a thermal/solvent process) to form a highly ordered block copolymer pattern in the bit area directed by the hard mask dot pattern formed previously. 
         [0074]    Block  138  shows that a second evaporation and liftoff process can be used to form a second hard mask pattern in the bit area, which may partially overlap with a first hard mask pattern in some spots. 
         [0075]    Next, the final hard mask patterns, including a bit pattern (from the second hard mask pattern) and a servo pattern (from the first hard mask pattern) are transferred into the substrate (that may be quartz, for an ultraviolet (UV) imprint) by etching (or other methods), and all hard mask patterns can be removed by a wet etch, as shown in block  140 . 
         [0076]    The method illustrated in  FIG. 21  can be integrated into the fabrication of BPM nanoimprint master templates including both a bit pattern (having a regular period, high pattern density, single shape, tight size/position sigma) and a servo pattern (that can be non-periodic or periodic, with a moderate-to-high pattern density, flexible shape, etc.). A directed self-assembled pattern can be used for the bit region and an e-beam defined pattern can be used for the servo region. 
         [0077]    The block copolymer can include two organic blocks (e.g., polystyreneblock-polymethylmethacrylate) or one organic block, one inorganic block (e.g., polystyrene-block-polydimethylsiloxane). One of the domains can be removed by UV degradation followed by a wet rinse. For example, upon UV exposure, polymethylmethacrylate is degraded while polystyrene is cross-linked. In another example, oxygen plasma can be used to remove organic components in a hybrid organic/inorganic block copolymer. The inorganic block (i.e., polydimethylsiloxane) has good resistance to oxygen plasma. 
         [0078]    In one example, spherical block copolymers are directed by a chemical contrast substrate pattern with a customized dot pattern layout to generate highly ordered dense dot arrays with ultra-high pattern densities. 
         [0079]    In another example, cylindrical block copolymers are directed by a chemical contrast substrate pattern with a customized dot pattern layout to generate highly ordered line arrays with high pattern densities. 
         [0080]    In one aspect, the highly ordered dot array generated by using the directed self-assembly method described above can be integrated with an e-beam lithography process to fabricate a full-disc BPM template including both a servo pattern and a bit pattern. 
         [0081]    In another aspect, this disclosure provides apparatus fabricated using one of the described methods. 
         [0082]    While the present disclosure has set forth various aspects described in terms of several examples, it will be apparent to those skilled in the art that various changes can be made to the disclosed examples without departing from the scope of the disclosure as defined by the following claims. The implementations described above and other implementations are within the scope of the claims.