Abstract:
This invention relates to near field assemblies with improved optical coupling efficiency suitable for near field photolithography and heat assisted magnetic recording with fluid bearing structures. Masters for photolithography are fabricated using a fluid bearing suspended at a near field distance using hydrostatic bearings. Near field features fabricated on a fluidized slider emit a radiated laser to develop a photo-resist layer deposited on the master replicator. A plurality of near field assemblies is etched on a wafer. Each of the near field assemblies includes a planar solid immersion mirror, at least one grating, and a near field transducer. The features created during the etching step are used to guide at least one milling tool to machine at least one surface on one or more of the planar solid immersion mirror, the at least one grating, and the near field transducer. The features created during the machining step are used to guide at least one polishing tool to polish at least one surface on one or more of the planar solid immersion mirror, the at least one grating, and the near field transducer. The wafer is cut to create a plurality of discrete near field assemblies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 61/172,685 filed Apr. 24, 2009, which is entitled “Plasmon Head with Hydrostatic Gas Bearing for Near Field Photolithography” which is hereby incorporated herein in its entirety by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to near field assemblies with improved optical coupling efficiency suitable for near field photolithography and heat assisted magnetic recording with fluid bearing structures. 
       BACKGROUND OF THE INVENTION 
       [0003]    The efficiency of energy transfer between the incident radiation and near field transducers is relatively low. The coupling efficiency from the amount of incoming light from the laser with respect to the amount of light received by the near field transducer is about 2 percent versus a theoretical efficiency of about 30 percent to about 40 percent. Increased efficiency of coupling light energy to near field assemblies has applications in both heat assisted magnetic recording and nano-photolithography. 
         [0004]    Heat assisted magnetic recording (“HAMR”) has been proposed to increase the recording density of hard disc drives to 1 Terabyte/inch 2  higher. The magnetic anisotropy of the recording medium, i.e. its resistance to thermal demagnetization, is greatly increased when heated, while still allowing the data to be recorded with standard recording fields. In application, a laser beam heats the area on the disc that is to be recorded and temporarily reduces the anisotropy in just that area sufficiently so that the applied recording field is able to set the magnetic state of that area. After cooling back to the ambient temperature, the anisotropy returns to its high value and stabilizes the magnetic state of the recorded mark. U.S. Pat. No. 7,272,079 (Challener) discloses an apparatus for heat assisted magnetic recording, which is incorporated by reference. 
         [0005]    With regard to nano-photolithography, the continuing size reduction of integrated circuits to nanometer (nm) scale dimensions requires the development of new lithographic techniques. The ultimate resolution of conventional photolithography is restricted by the diffraction limit. It is becoming increasingly difficult and complex to use the established method of optical projection lithography at the short optical wavelengths required to reach the desired feature sizes. For example, the use of wavelengths in the deep ultraviolet, the extreme ultraviolet (EUV), or the X-ray regime requires increasingly difficult adjustments of the lithographic process, including the development of new light sources, photo-resists, and optics. 
         [0006]    U.S. Pat. Publication No. 2003/0129545 (Kik et al.) discloses a method for performing nanolithography using a photo-mask with conductive nanostructures disposed thereon. The nanostructures have a plasmon resonance frequency that is determined by the dielectric properties of the surroundings and of the nanostructures, as well as the nanostructure shape. The nanostructures are illuminated with light at or near the frequency of the plasmon resonance frequency, which causes collective oscillations of the electrons at the surface of the nanostructure. These oscillations can have wavelengths that are much shorter than the wavelength of the light that excited them, which are sufficient to modify adjacent portions of the resist layer. The resist layer is developed to create plasmon printed, subwavelength patterns. Creating the photo-mask, however, is time intensive, expensive, and does not easily permit design changes. 
         [0007]    The commercialization of nanoscale devices requires the development of high-throughput nanofabrication technologies that allow frequent design changes. Maskless nanolithography, including electron-beam and scanning-probe lithography, offers the desired flexibility, but is limited by low throughput and extremely high cost. 
         [0008]    U.S. Pat. Publication No. 2007/0069429 (Albrecht et al.) is directed to a system and method for patterning a master disk to be used for nanoimprinting magnetic recording disks. An air-bearing created by a rotating master disk substrate supports a slider with an aperture structure within the optical near-field of a resist layer. The fly height of the slider is typically about 10 to about 20 nanometers. A liquid lubricant and/or a protective film, such as a carbon film, may be provided on the resist layer to improve the flyability of the slider supporting the plasmonic head. The timing of the laser pulses is controlled to form a pattern of exposed regions in the resist layer, with this pattern ultimately resulting in the desired pattern of data islands and non-data islands in magnetic recording disks when they are nanoimprinted by the master disk. 
         [0009]    The spinning master disk of Albrecht is essential to establish the air bearing between the slider and the photo-resist. The spinning master disk, however, is subject to vibration and spindle run-out errors that lead to patterning errors and potential collisions between the slider and the photo-resist. Roughness of the photo-resist and media needs to be closely controlled to enable the slider to fly without crashing. If the plasmonic lens contacts the master disk it can be coated with photo-resist, potentially smearing the lens and causing patterning errors. Finally, a spinning master disk is not a practical method of making more complex structures, such as for example micro electrical mechanical systems (MEMS). 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    The present invention is directed to near field heads with improved optical coupling efficiency suitable for heat assisted magnetic recording and near field photolithography. 
         [0011]    The near field assemblies are first patterned using photo lithography methods. A vision system uses the features created by the etching process as a reference for subsequent machining and polishing operations. The machining and polishing steps are primarily directed to the sidewalls of the planar solid immersion mirror, the gratings and the near field transducer. The top surface of the wafer can also be polished prior to gold/silver deposition. Wafer level machining operations are capable of generating near vertical sidewall profiles and smooth surface in the range of less than about 10 nanometers. 
         [0012]    The preset invention is also directed to micromachining tools for fabricating the near field assemblies. The cutting surfaces of the tools are preferably coated with nano-scale diamonds. The diamonds can be prepared by engaging the spinning cutting surface with one or more abrasive surfaces of various roughness. 
         [0013]    One embodiment is directed to a method of fabricating a near field assembly. A plurality of near field assemblies are etched on a wafer. Each of the near field assemblies includes a planar solid immersion mirror, at least one grating, and a near field transducer. The features created during the etching step are used to guide at least one milling tool to machine at least one surface on one or more of the planar solid immersion mirror, the at least one grating, and the near field transducer. The features created during the machining step are used to guide at least one polishing tool to polish at least one surface on one or more of the planar solid immersion mirror, the at least one grating, and the near field transducer. The wafer is cut to create a plurality of discrete near field assemblies. 
         [0014]    The present invention is also directed to a low-cost approach to near field nano-scale photolithography using a near field assembly with hydrostatic gas bearings. The hydrostatic gas bearing flies the near field assembly at less than 100 nm, and more preferably less than 25 nm, above the photo-resist without the need to spin the substrate. The near field assembly concentrates short-wavelength surface plasmons into about sub-100 nm regions on the photo-resist and can pattern features of about 80 nm or less. This nanofabrication system has the potential to provide desktop, maskless nanophotolithography at several orders of magnitude lower cost than current maskless techniques. Nano-scale typically refers to features with dimensions of less than one micrometer (1×10 −6  meters). 
         [0015]    At least one near field assembly is preferably located at the trailing edge of the slider. Alternatively, one or more lenses are mounted on the slider. For commercial applications, a plurality of near field assemblies are provided on each slider. 
         [0016]    The slider is supported by a suspension assembly fabricated with air channels connected to an external air supply. The channels are fluidly coupled to openings in the air bearing surface of the slider. In one embodiment, channels are etched in the suspension assembly and a polyamide cover is applied over the channels to form gas conduits. The channels can be on the top or the bottom of the suspension assembly. 
         [0017]    The hydrostatic gas bearing provides a controlled clearance between the substrate and the slider. The clearance is maintained by externally pressurizing a plurality of pads located on the air bearing surface of the slider in proximity with the substrate. Once the desired clearance is attained between the hydrostatic slider and the substrate, a laser is directed at a near field transducer located on the slider. The resulting emission from the near field transducer exposes the photo-resist. 
         [0018]    In one embodiment, the externally pressurized gas bearing design allows for independently controlling the pressure on each pad of the hydrostatic bearing. Independent control of each gas port permits the pitch and roll of the slider to be adjusted to optimize the photolithographic process. 
         [0019]    The clearance of the slider is preferably calibrated ex-situ on an optical fly height tester prior to usage. Each hydro-static pad pressure is calibrated to assure a near field gap. A sensor is preferably provided on the slider to monitor flying height. Heaters may also be provided to adjust the position of the near field assembly relative to the photo-resist. 
         [0020]    The system includes an X-Y stage to accurately locate a substrate relative to the slider. A controller operating the X-Y stage and the laser assembly accurately expose the photo-resist to form the desired pattern. Since the substrate is not required to spin to maintain a gas bearing, transfer of vibration and spindle run-out errors to the pattern are minimized. 
         [0021]    Micro electro mechanical systems (MEMS) methods are well suited for fabricating the present hydrostatic slider. For example, a silicon wafer is patterned with the gas bearing features. A series of through holes for the gas ports are machined with a deep reactive ion etch process (DRIE) or simply machined. Once the silicon wafers are patterned and fabricated, a series of slider bars are sliced to expose the slider sides for further processing. A thick dielectric such as alumina is sputtered at the end of slider. A planar solid immersion mirror with a dual offset grating used to focus a waveguide mode onto the near-field transducer (NFT) is fabricated onto the trailing edge of the slider. 
         [0022]    The photolithography system includes a head suspension assembly with a load beam having a flexure at a distal end and a plurality of channels. A covering layer extends over the channels to form gas conduits. The slider includes a first surface attached to the flexure and a second surface facing the substrate. The first surface of the slider includes a plurality of ports fluidly coupled to the gas conduits. The ports extend through the slider and exit through holes in at least one air bearing surface located on the second surface. A near field assembly on the slider emits radiation onto a region of the photo-resist in response to incident radiation. A laser assembly supplies the incident radiation. A source of pressurized gas delivered to the gas conduits maintains a clearance between the near field assembly and the photo-resist layer. A controller synchronizes activation of the laser assembly with the position of the substrate relative to the near field assembly to form the desired pattern on the photo-resist layer. 
         [0023]    The substrate must meet flatness requirements in order to establish a nanometer level gap without interference and smearing of the near field elements. The laser assembly supplies radiation at a first wavelength and the near field assembly emits radiation at a second shorter wavelength in response to incident radiation. 
         [0024]    The present invention is also directed to a near field assembly for near field photolithography. 
         [0025]    The present invention is directed to fabricating masters that can be used for further pattern transfers for feature replication purpose. A master is first fabricated with the present invention. Additional slaves are fabricated by photo-imprinting. The slaves are then used to fabricate pattern on finished magnetic media or substrates. 
         [0026]    The present invention is also directed to a method for forming a pattern in photo-resist layer on a substrate using a photolithography system. A pressurized gas is delivered through conduits in a head suspension to ports on a slider. The pressurized gas is ejected from the ports in the slider to create a hydrostatic gas bearing with a clearance between a near field assembly and a photo-resist layer. Incident radiation is directed from a laser assembly to the near field assembly. Activation of the laser assembly is synchronized with a position of the substrate relative to the near field assembly to form the pattern. 
         [0027]    The present invention is directed to fabricating a heat assisted magnetic head to render the edges of the gratings, near field sensor and edges of the optical tools smooth and free from defects rendered during the etching process. Milling operation heals the roughness and defects generated by the etching process. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0028]      FIG. 1  is a schematic illustration of a maskless, nano-photolithography system with a hydrostatic gas bearing in accordance with an embodiment of the present invention. 
           [0029]      FIG. 2A  illustrates a near field assembly formed on an edge of a slider in accordance with an embodiment of the present invention. 
           [0030]      FIG. 2B  is a perspective view of the slider of  FIG. 2A . 
           [0031]      FIG. 2C  is a schematic illustration of an alternate near field transducer in accordance with an embodiment of the present invention. 
           [0032]      FIG. 3  is an exploded view of a head suspension in accordance with an embodiment of the present invention. 
           [0033]      FIG. 4  is a top view of the head suspension of  FIG. 3 . 
           [0034]      FIG. 5  is a bottom exploded view of the head suspension of  FIG. 3 . 
           [0035]      FIG. 6  is a perspective view of an alternate head suspension in accordance with an embodiment of the present invention. 
           [0036]      FIG. 7  is a bottom view of the slider of  FIG. 6 . 
           [0037]      FIG. 8  is a schematic illustration of a near field assembly made using the methods of the present invention. 
           [0038]      FIG. 9  is a side sectional view of a near field transducer of  FIG. 8  positioned opposite a magnetic media in accordance with an embodiment of the present invention. 
           [0039]      FIGS. 10 and 11  illustrate common defects in prior art near field assemblies. 
           [0040]      FIG. 12  is a sectional view of a side wall of a planar solid immersion mirror on the near field assembly of  FIG. 8 . 
           [0041]      FIGS. 13 and 14  are side sectional views of milling tools coated with nano-scale diamonds used in the method of the present invention. 
           [0042]      FIGS. 15A-15C  illustrate a method of preparing a tool for use in an embodiment of the present invention. 
           [0043]      FIG. 16  is a top view of a wafer containing a plurality of near field assemblies in accordance with an embodiment of the present invention. 
           [0044]      FIG. 17  is a perspective view of the present near field assembly used in a heat assisted magnetic recording application in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0045]      FIG. 1  is a schematic illustration of the system  50  for maskless, nano-scale, photolithography in accordance with an embodiment of the present invention. A master  52  including a substrate  54  with photo-resist layer  56  supported on a linear stage  58 . Slider  60  has an air-bearing surface (ABS)  62  that is oriented toward the master  52 . 
         [0046]    The slider  60  is mounted on a suspension  64  similar to a conventional suspension like that used in magnetic recording disk drives, with a head gimbal assembly or flexure  66  that permits the slider  60  to “pitch” and “roll” relative to the master  52 . The suspension  64  is connected to support arm  68  that is supported by controller  70 . The support arm  68  applies a preload to the suspension  64  to maintain the flying ability of the slider  60 . 
         [0047]    In one embodiment, the support arm  68  is fixedly mounted on controller  70 . In another embodiment, the support arm  68  is adapted to translate relative to the controller  70 . Translation can include linear movement in the X, Y, and/or Z directions, as well as rotation around a fixed point. For example, a linear actuator can move the support arm  68  in the X-direction and/or Y-direction. Alternatively, a rotary actuator, such as a rotary voice-coil-motor (VCM) actuator, rotates the support arm  68  along a generally radial or arcuate path. 
         [0048]    The slider  60  includes a near field assembly  72  that directs radiation from laser assembly  74  to the resist layer  56 . The laser assembly  74  typically includes a laser, a modulator and one or more lenses. Alternatively, one or more lenses may be located on the slider  60 . The laser assembly  74  is supported by armature  76  attached to the controller  70 . In embodiments where the support arm  68  is permitted to translate relative to the controller  70 , the armature  76  preferably translates with the support arm  68  so that the position of the laser assembly  74  relative to the near field assembly  72  is maintained. The master  52  is movable relative to the slider  60  by X-Y stage  58 . 
         [0049]    Radiation  80  from the laser assembly  74  may be directed to the near field assembly  72  using a variety of techniques, such as for example the system disclosed in U.S. Pat. No. 5,497,359 or U.S. Pat. Publication 2007/0069429, which are hereby incorporated by reference. Alternatively, the radiation  80  from laser assembly  74  may be delivered to the near field assembly  72  by optical fibers. 
         [0050]    Most commonly used lasers are diode-pumped solid state lasers, e.g., Nd:YAG or Nd:YLF. These may be frequency multiplexed to give radiation at higher harmonics. For example a Nd:YAG laser with frequency multiplexing may be used to generate radiation at 1064 nm, 532 nm, 355 nm or 266 nm. Additionally, the radiation from the laser may be modulated using external modulators. Mode-locked lasers also provide rapid pulses with frequencies up to about 100 MHz. Other lasers such as pulsed diode lasers may also be used. 
         [0051]    The controller  70  can be a specialty computer, a conventional PC, or a combination thereof. The controller  70  is programmed with the desired pattern to be created in the photo-resist  56 . The control system  70  controls the X-Y stage  58  and activation of the laser assembly  74  to form the desired pattern in the resist layer  56  of master  52 . In another embodiment, the laser assembly  74  delivers pulses on demand, in response to a trigger signal. 
         [0052]      FIG. 2A  is an enlarged view of a near field assembly  102  located on a side surface of a slider  100  in accordance with one embodiment of the present invention. Planar solid immersion mirror  104  with dual offset gratings  106 A,  106 B focuses radiation  80  onto near field transducer  108 . The dual offset grating  106 A,  106 B are offset by half a wavelength of the radiation  80  causing a phase shift. The near field transducer  108  is located at the focus of the planar solid immersion mirror  104 . When the near field transducer  108  is excited to surface plasmon resonance, tip  110  couples the light into the photo-resist  56 . The tip  110  provides a lightning rod effect for field confinement. A near field assembly suitable for use in the present embodiment is disclosed in Challener, et al.  Heat - assisted Magnetic Recording by a Near - field Transducer with Efficient Optical Energy Transfer , DOI: 10.1038 Nature Photonics (2009) and U.S. Pat. No. 7,272,079 (Challener), which are incorporated by reference. 
         [0053]    Surface plasmons (SPs) are collective oscillations of surface charge that are confined to an interface between a dielectric and a metal. When surface plasmons are resonantly excited by the external optical field  80 , the field amplitude of the output radiation  112  in the vicinity of the region  114  may be orders of magnitude greater than that of the incident radiation  80 . 
         [0054]    The region  114  of output radiation  112  is tightly confined, with a cross-sectional area much smaller than the incident wavelength  80 . The region  114  is typically circular or oval in shape, although a variety of other shapes are possible. The region  114  preferably covers an area with a major dimension of less than about 100 nanometers, and more preferably less than about 80 nanometers, and more preferably less than about 60 nanometers. 
         [0055]    The output radiation  112  from the near field transducer  108  heats the photo-mask  56  to form exposed regions  115  with different properties than the unexposed regions  119  of the photo-mask  56 . The exposed regions  115  are depicted as corresponding to the size of the region  114  created from a single laser pulse. The size of the exposed regions  115 , however, can be modified by varying the on-time of the laser, clearance  118 , and a variety of other factors. 
         [0056]    After exposure to heat from the output radiation  112 , the photo-resist  56  forms a new material different from the unexposed regions. By controlling the position of the master  52  and the pulses from the laser assembly  74 , the controller  70  can generate a predetermined pattern. The master  52  is then etched, such as by chemical etchants or reactive-ion-etching (RIE). The exposed regions  115  are resistant to the etching acting as a mask. The exposed regions  115  are resistant to hydrochloric acid mixtures (HCl:H.sub.2O.sub.2:H.sub.2O, 1:1:48) and nitric acid mixtures, while the unexposed regions  119  are removed in the same acid mixture. 
         [0057]    The etching is performed into the substrate  54  so that after removal of the remaining photo-resist  56 , the substrate  54  has the desired pattern features  121 . The present system permits features  121  with dimensions less than the wavelength of the incident radiation  80 . The features  121  preferably have a size less than about 50%, more preferably less than about 30%, and most preferably less than about 20%, of the wavelength of the incident radiation. The features  121  preferably have a maximum dimension of less than about 80 nanometers, and more preferably less than about 60 nanometers, and more preferably less than about 40 nanometers. 
         [0058]    Due to the exponential decay of the evanescent field of surface plasmons, the tightly focused region  114  only exists at the near field of the near field transducer  108 , normally less than about 100 nanometers. To achieve high-speed scanning, clearance  118  between distal end  116  of the tip  110  and surface  57  of the photo-resist  56  is preferably less than about 50 nanometers, and more preferably less than about 20 nanometers to about 10 nanometers, above the photo-resist layer  56 . 
         [0059]    As best illustrated in  FIG. 2B , distal end  116  of the tip  110  is flush with air bearing surface  130 C so that the clearance  118  is controlled by the gas bearing. In another embodiment, the tip  110  extends beyond the air bearing surface  130 C toward the master  52 . This embodiment permits the plasmon field to be closer to the photo-mask  56 , while maintaining a greater clearance between the slider  60  and the surface  57  of the photo-resist  56 . 
         [0060]      FIG. 2C  is a schematic illustration of an alternate near field transducer  108 C in accordance with an embodiment of the present invention. Distal end  116 C includes pointed tip  110 C. The tip  110 C concentrates energy from the transducer  108 C. A variety of other shapes are possible for the tip  110 C, depending on the shape and size of the desired exposed regions  115  (see  FIG. 2A ). 
         [0061]      FIGS. 3 through 5  illustrate a suspension assembly  200  capable of generating a hydrostatic gas bearing in accordance with an embodiment of the present invention. Stainless steel suspension  202  is etched to create channels  204 A,  204 B,  204 C,  204 D (collectively “ 204 ”). In the illustrated embodiment, distal ends of the channels  204  terminate in through holes  206 A,  206 B,  206 C,  206 D (collectively “ 206 ”). The through holes  206  are configured to align with ports  208 A,  208 B,  208 C,  208 D (collectively “ 208 ”) in slider  210 . 
         [0062]    While the illustrated embodiment includes four channels and four ports  208  in the slider  210 , a variety of other configurations are possible. In one embodiment, the channels  204 A and  204 B are combined into a single channel, as are  204 C and  204 D. As will be discussed herein, the number and/or the locations of ports  208  can also vary. In another embodiment, the channels  204  may be formed in the bottom surface of the suspension  202 , making the holes  206  unnecessary. 
         [0063]    Sealing layer  212  is located over the top of the channels  204  to form a substantially air-tight seal. In one embodiment, the sealing layer  212  is a polyamide sheet with a pressure sensitive adhesive on one surface. Pressurized gas can be delivered to the channels  204  from base plate  214  attached to load beam  216 . In one embodiment, a multi-layered polyamide sheet  215  delivers pressurized gas from the controller  70  to the base plate  214 . The polyamide sheet  215  includes conduits  217 A,  217 B,  217 C,  217 D (collectively “ 217 ”) fluidly coupled to through holes  228 A,  228 B,  228 C,  228 D in the base plate  214  and the load beam  216 . The pressurized gas travels down the respective channels  204  to flexure  218 , out through holes  206 , and into the ports  208  on the slider  210 . 
         [0064]    As best illustrated in  FIG. 5 , bottom surface  230  of the flexure  218  includes recesses  232  around the through holes  206 . These recesses  232  mate with the ports  208  on the top of the slider  210 . Each port  208  is fluidly coupled to a respective plurality of holes  234 A,  234 B,  234 C,  234 D (collectively “ 234 ”) formed in respective air bearing surfaces  236 A,  236 B,  236 C,  236 D (collectively “ 236 ”) on the base of the slider  210 . The pressurized gas exits these holes  234  to form a gas bearing between the slider  210  and the master  52 . 
         [0065]    The controller  70  monitors gas pressure delivered to the slider  60 . Gas pressure to each of the four channels  204  is preferably independently controlled so that the pitch and roll of the slider  60  can be adjusted. In another embodiment, the same gas pressure is delivered to each of the channels  204 . While clean air is the preferred gas, other gases such as for example argon may also be used. The gas pressure is typically in the range of about 2 atmospheres to about 4 atmospheres. 
         [0066]    The slider  210  includes an alternate near field assembly  250  in accordance with another embodiment of the present invention. The near field assembly  250  includes aperture  252  formed of a material, such as glass, quartz or another dielectric material, that is transmissive to radiation  80  at the wavelength of the laser assembly  74 . A film  254  of material substantially reflective to the radiation  80  at the wavelength of the laser assembly  74  is located on the disk-facing side  256  around the aperture  252 . The aperture  252  is preferably subwavelength-sized, i.e., its diameter if it is circularly-shaped or its smallest feature if it is non-circular, is less than the wavelength of the incident laser radiation  80  and preferably less than one-half the wavelength of the laser radiation  80 . A suitable near field assembly  250  is disclosed in U.S. Pat. Publication No. US 2007/0069429. 
         [0067]    Optical transmission through a subwavelength aperture in a metal film is enhanced when the incident radiation is resonant with surface plasmons at a corrugated metal surface  250  surrounding the aperture  252 . Thus features such as ridges or trenches in the metal film  250  serve as a resonant structure to further increase the emitted radiation output from the aperture  252  beyond what it would be in the absence of these features. The effect is a frequency-specific resonant enhancement of the radiation emitted from the aperture  252 , which is then directed onto the photo-resist  56  positioned within the near-field. This resonant enhancement is described by Thio et al.,  Enhanced Light Transmission Through A Single Subwavelength Aperture , Optics Letters, Vol. 26, Issue 24, pp. 1972-1974 (2001) and in US 2003/0123335. 
         [0068]      FIGS. 6 and 7  illustrate the slider  100  of  FIGS. 2A and 2B  as part of a suspension assembly  120  in accordance with an embodiment of the present invention. Top surface  122  of the suspension  120  is etched to form three channels  124 A,  124 B, and  124 C (collectively “ 124 ”). The channels  124  terminate in through holes  126 A,  126 B,  126 C (collectively “ 126 ”) fluidly coupled to ports through the slider  100 . As best illustrated in FIG.  7 , bottom surface  128  of the slider  100  includes three air bearing surfaces  130 A,  130 B, and  130 C, each with a plurality of holes  132  fluidly coupled to the channels  124 . The single pad  130 C near the near field assembly  102  optimizes the tracking of the tip  110  with the waviness of the master  52 . The four-pad design of  FIG. 5 , by contrast, averages the waviness of the master  52  across the entire lower surface of the slider  210 . 
         [0069]    The substrate  54  may be any suitable material, such as a wafer of single-crystal silicon. The photo-resist  56  is preferably a photo-resist that is generally insensitive to light with a wavelength greater than about 400 nm so that it can be handled in room light. The photo-resist is a material that changes its optical or chemical etching properties when heated by exposure to laser radiation. 
         [0070]      FIG. 8  illustrates an embodiment of a near field assembly  400  in accordance with an embodiment of the present invention. Dual offset gratings  402 A,  402 B (“ 402 ”) redirect incident electromagnetic radiation  408  to sidewalls  414  of planar solid immersion mirror  404 . The near field transducer  406  is located at the focus of the planar solid immersion mirror  404 . The dual offset gratings  402 A,  402 B are offset by half a wavelength of the incident radiation  408  causing a phase shift. When the near field transducer  406  is excited to surface plasmon resonance, tip  410  couples the radiation  408  onto the recording media  412 . 
         [0071]    Near field assemblies are typically fabricated in an Alumina base material using ion milling or reactive ion etching. As illustrated in  FIG. 10 , non-perpendicular side walls  414  on the planar solid immersion mirror  404  divert light from reaching the near field transducer  406 . As illustrated in  FIG. 11 , surface roughness  416  due to etching on any of the reflective surfaces, such as the offset grating  402  and the sidewalls  414  of the planar solid immersion mirror  404 , also contributes to light scattering and thus reduced transmission efficiency. Theoretical formulations do not account for side wall slope  414  and wall roughness  416  in estimating the coupling efficiency of the incident radiation  408 . There are no known ion bombardment processes known to resolve both the roughness issue and the wall slope. 
         [0072]    The present near field assembly  400  is fabricated using conventional etching processes to remove the bulk of the material. The side walls  414  and the grating  402  are then micro machined with specially fabricated diamond tip coated miniature tool coated with nano diamonds or tools equipped with a single diamond tip. The single diamond tip provides very accurate but lengthy machining time. A machined tip coated with nano diamond is preferred in most cases due to the speed of the operation. 
         [0073]    Specially shaped machining tools can be fabricated to machine the gratings requiring a particular angle. Conical tools can be readily fabricated and coated with nano diamonds to perform such operations. Various tooling and machining techniques for producing optical quality surfaces are disclosed in U.S. Pat. Nos. 6,581,286 (Cambell et al.); 7,445,409 (Trice et al.); and 7,510,462 (Bryan et al.), which are hereby incorporated by reference. 
         [0074]    Near vertical side wall  414 , such as illustrated in  FIG. 12 , are attained with the milling operation. A vision based system can be used to guide the milling operation to machine the side walls  414  of the parabolic planar solid immersion mirror  404 , the edges of the near field transducer, and the gratings  402 . Roughness and streaks of the critical surfaces  402 ,  406 ,  414  can be substantially reduced by a high speed machining operation involving nano diamonds attached to the milling tool. For best performance it is preferred to have machining tool with adhered nano diamonds to control surface finish. 
         [0075]      FIGS. 13 and 14  are cross sectional views of milling tool  430 ,  432  with nano-scale diamonds  434  adhered to the milling tips  436 ,  438 . The nano-scale diamonds  434  can be adhered to the tools  430 ,  432  using a variety of techniques, such as for example adhesives or fusing. Alternatively, the tools  430 ,  432  can be coated with SiC, Titanium, diamond-like-carbon, and a variety of other materials. A multi-step machining cycle may be desirable to first machine vertical sidewalls and then polish to reduce surface roughness. 
         [0076]      FIGS. 15A-15C  illustrate a sequence of steps to prepare the tool  430  for machining optical surfaces on near field assemblies according to an embodiment of the present invention. Rotating cutting surface  440  is brought into engagement with a flat abrasive surface  442 . The abrasive surface can be a hard metal or SiC. In one embodiment, the abrasive surface  442  has a layer of nano-scale diamonds  446 . Multiple abrasive surfaces  442  with increasing smoothness can be used to prepare the cutting surface  440 . Once the cutting surface  440  is polished, nano-scale diamonds are attached. An optional hard coat can be applied over the diamonds. The cutting tip  444  preferably has a diameter of about 300 micrometers to about 100 micrometers. 
         [0077]      FIG. 16  illustrates a wafer  450  populated with a plurality of near field assemblies  452 . The devices  452  are first patterned using photolithography methods. A vision system uses the features created by the etching process as a reference for the machining and polishing operations. The machining and polishing steps are primarily directed to the sidewalls  456  of the planar solid immersion mirror  458 , the gratings  460  and the near field transducer  462 . The top surface of the wafer can also be polished prior to gold/silver deposition. Wafer level machining operations are capable of generating near vertical sidewall profiles and smooth surface in the range of less than about 10 nanometer. Each cell  454  includes a complete near field assembly  452 . The wafer  450  is subsequently cut into discrete components. 
         [0078]    The high precision optical surfaces on near field assemblies made according to the present invention increase the efficiency of coupling light energy by about one order of magnitude, from about 2 percent to about 20 percent or more. These higher efficiency near field assemblies have application in nano-photolithography and heat assisted magnetic recording for hard disc drives. Various ways of employing the present near field assemblies for heat assisted magnetic recording on hard disc drives are disclosed in U.S. Pat. Nos. 6,944,112 (Challener); 7,106,935 (Challener); 7,272,079 (Challener); 7,330,404 (Peng et al.); 7,440,660 (Jin et al.); and U.S. Patent Publication Nos. 2006/0182393 (Sendur et al.) and 2008/0002298 (Sluzewski), which are hereby incorporated by reference. 
         [0079]      FIG. 17  illustrates a near field assembly  452  employed in a HAMR application in accordance with an embodiment of the present invention. The near field transducer  452  is attached to a read/write head  470  positioned above spinning magnetic media  472 . Incident radiation  474  is preferably directed perpendicular to the gratings  460 . The gratings  460  are preferably fabricated with about 45 degree surfaces to direct the incident radiation  470  into the planar solid immersion mirror  458 , and ultimately the near field transducer  462 . 
         [0080]      FIGS. 18-19  illustrate a multi-layered gimbal assembly  530  in accordance with an embodiment of the present invention. In the illustrated embodiment, center layer  532  includes traces  534  that deliver compressed air from inlet ports  536  in the top layer  538  to exit ports  540  on the bottom layer  542 . The exit ports  540  are fluidly coupled to the ports  508  on the button bearings  504 . As best illustrated in  FIG. 19 , the inlet ports  536  are offset and mechanically decoupled from the gimbal mechanism  544 . 
         [0081]    Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the inventions. The upper and lower limits of these smaller ranges which may independently be included in the smaller ranges is also encompassed within the inventions, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the inventions. 
         [0082]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. 
         [0083]    The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. 
         [0084]    Other embodiments of the invention are possible. Although the description above contains much specificity, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above. 
         [0085]    Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.