Abstract:
A method of fabricating a c-aperture or E-antenna plasmonic near field source for thermal assisted recording applications in hard disk drives is disclosed. A c-aperture or E-antenna is built for recording head applications. The technique employs e-beam lithography, partial reactive ion etching and metal refill to build the c-apertures. This process strategy has the advantage over other techniques in the self-alignment of the c-aperture notch to the c-aperture internal diameter, the small number of process steps required, and the precise and consistent shape of the c-aperture notch itself.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates in general to thermal assisted recording (TAR) applications and, in particular, to an improved system, method and apparatus for fabricating a c-aperture or IS-antenna plasmonic near field source for thermal assisted recording applications in hard disk drives. 
     2. Description of the Related Art 
     In magnetic recording disk drives, the magnetic material (or media) for the recording layer on the disk is chosen to have sufficient coercivity such that the magnetized data bits are written precisely and retain their magnetization state until written over by new data bits. As the areal data density (the number of bits that can be recorded on a unit surface area of the disk) increases, the magnetic grains that make up the data bits can be so small that they can be demagnetized simply from thermal instability or agitation within the magnetized bit (the so-called “superparamagnetic” effect). To avoid thermal instabilities of the stored magnetization, media with high magneto-crystalline anisotropy (K u ) may be required. However, increasing K u  also increases the short-time switching field, H 0 , which is the field required to reverse the magnetization direction, which for most magnetic materials is somewhat greater than the coercivity or coercive field measured on much longer time-scales. However, H 0  cannot exceed the write field capability of the recording head, which currently is limited to about 15 kOe for perpendicular recording. 
     Since it is known that the coercivity of the magnetic material of the recording layer is temperature dependent, one proposed solution to the thermal stability problem is thermally-assisted recording (TAR), wherein the magnetic material is heated locally to near or above its Curie temperature during writing to lower the coercivity enough for writing to occur, but where the coercivity/anisotropy is high enough for thermal stability of the recorded bits at the ambient temperature of the disk drive (i.e., the normal operating or “room” temperature). Several TAR approaches have been proposed, primarily for the more conventional longitudinal or horizontal recording, wherein the magnetizations of the recorded bits are oriented generally in-the-plane of the recording layer. However, TAR is also applicable for perpendicular recording, wherein the magnetizations of the recorded bits are oriented generally out-of-the-plane of the recording layer. TAR is also usable with patterned media. 
     In TAR, it is important to avoid heating data tracks adjacent to the data track where data is to be written because the stray magnetic field from the write head can erase data previously recorded in the adjacent tracks. Also, even in the absence of a magnetic field, heating of adjacent data tracks accelerates the thermal decay over that at ambient temperature and thus data loss may occur. A proposed solution for this adjacent-track interference problem is the use of an optical channel with a small aperture that directs heat from a radiation source, such as a laser, to heat just the data track where data is to be written. This type of TAR disk drive is described in U.S. Pat. No. 5,583,727 and U.S. Pat. No. 6,982,844. 
     In conventional (non-TAR) disk drives, each read/write head is located on an air-bearing slider that is maintained in close proximity to its associated disk surface as the disks rotate. The films making up the read and write heads are deposited on a wafer containing a large number, e.g., 40,000, of rectangular regions arranged in rows, with each region ultimately becoming an individual slider. After formation of the read and write heads at the wafer level, the wafer is cut into rows and the rows cut into individual sliders. The sliders are then “lapped” in a plane perpendicular to the wafer surface, with this plane becoming the slider&#39;s air-bearing surface (ABS). However, for sliders used for TAR disk drives, the only proposed methods for forming an optical channel and/or aperture structure have been to fabricate the optical channel and/or aperture structure on the slider at the row level, i.e., after the wafer has been cut into rows, or at the individual slider level. These are costly and time-consuming methods. 
     TAR requires small focused light spots that are much smaller than the diffraction limit of the light source. Therefore, regular optical components are not viable for these types of applications. Nanoscale near field plasmonic sources are being considered for use in TAR for fabricating the required optical structures. One of the most promising optical structures is the c-aperture, which can be thought of as an E-antenna. To clarify, the dielectric aperture in this structure looks like the letter “c”, while the metal surrounding that dielectric forms an antenna in the shape of a capital letter “E”. EA improved wafer-level process for forming optical channels and aperture structures on air-bearing sliders for use in TAR disk drives would be desirable. 
     SUMMARY OF THE INVENTION 
     Embodiments of a system, method, and apparatus for fabricating a c-aperture or E-antenna plasmonic near field source for thermal assisted recording applications in hard disk drives are disclosed. The invention comprises a technique for building a c-aperture in a manner that is consistent with and appropriate for recording head applications. The technique employs e-beam lithography, partial reactive ion etching (RIE) and metal refill to build the c-apertures. This process strategy has the advantage over other techniques in the self-alignment of the c-aperture notch to the c-aperture internal diameter, the small number of process steps required, and the precise and consistent shape of the c-aperture notch itself. 
     The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic sectional side view of one embodiment of a thermal assisted recording (TAR) head for a hard disk drive, and is constructed in accordance with the invention; 
         FIG. 2  is an enlarged schematic sectional air bearing surface (ABS) view of one embodiment of a c-aperture writer for the TAR head of  FIG. 1 , rotated 90 degrees, and is constructed in accordance with the invention; 
         FIGS. 3-13  are schematic sectional and top views of various embodiments of a method of fabricating the c-aperture of  FIG. 2 , and are constructed in accordance with the invention; 
         FIG. 14  is a sectional view through one embodiment of a portion of an air-bearing slider and associated perpendicular magnetic recording disk for a TAR disk drive that uses an optical channel and aperture structure to direct heat to the recording layer of the disk in accordance with the invention; 
         FIG. 15  is an illustration of one embodiment of the radiation exit face of an aperture structure having a generally c-shaped aperture with a characteristic dimension “d,” and is constructed in accordance with the invention; 
         FIG. 16  is a perspective view of one embodiment of a portion of a wafer showing a plurality of generally rectangular regions in accordance with the invention; and 
         FIG. 17  is a perspective view of one embodiment of an aperture structure on a rectangular region of the wafer in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-17 , embodiments of a system, method and apparatus for fabricating a c-aperture or E-antenna plasmonic near field source for thermal assisted recording applications in hard disk drives are disclosed. 
     For example,  FIG. 14  is a sectional view through a portion of an air-bearing slider  110  and associated perpendicular magnetic recording disk for a TAR disk drive of the type that uses an optical channel for directing heat to the disk. The disk  140  includes a substrate  142 , an optional “soft” or relatively low-coercivity magnetically permeable underlayer (SUL)  144 , and a perpendicular magnetic recording layer (RL)  146 . The SUL  144  is not required for a TAR disk drive but if used is typically any alloy material suitable as the magnetically-permeable flux-return path, such as NiFe, FeAlSi, FeTaN, FeN, CoFeB and CoZrNb. The RL  146  may be any media with perpendicular magnetic anisotropy, such as a cobalt-chromium (CoCr) alloy granular layer grown on a special growth-enhancing sublayer, or a multilayer of alternating films of Co with films of platinum (Pt) or palladium (Pd). The RL  146  may also be an L1 0  ordered alloy such as FePt or FeNiPt. The disk  140  would also typically include a protective overcoat (not shown) over the RL  146 . 
     The slider  110  has a trailing surface  111  and an air-bearing surface (ABS) surface  112  oriented generally perpendicular to trailing surface  111 . The slider  110  is typically formed of a composite material, such as a composite of alumina/titanium-carbide (Al 2 O 3 /TiC), and supports the read and write elements typically formed as a series of thin films and structures on its trailing surface  111 . The surface  111  is called the trailing surface because of the direction  123  of the disk  140  relative to slider  110 . The ABS  112  is the recording-layer-facing surface of the slider that faces the disk and is shown without the thin protective overcoat typically present in an actual slider. The recording-layer-facing surface or ABS shall mean the surface of the slider that is covered with a thin protective overcoat, the actual outer surface of the slider if there is no overcoat, or the outer surface of the overcoat.  FIG. 14  is not drawn to scale because of the difficulty in showing the very small features. 
     The slider  110  supports a conventional magnetoresistive read head  115  located between shields S 1  and S 2 , and a conventional perpendicular write head that includes a magnetic yoke  120  with a write pole  120   a , a flux return pole  120   b , and an electrically conductive coil  125 . The write pole  120   a  is formed of conventional high-moment material, such as a FeCoNi alloy. The write coil  125  is shown as wrapped around yoke  120  with the electrical current directions being shown as into the paper by the coil cross-sections marked with an “X” and out of the paper by the coil cross-sections marked with a solid circle. When write-current pulses are directed through coil  125 , the write pole  120   a  directs magnetic flux, represented by arrow  122 , to the RL  146 . The dashed line  130  with arrows show the flux return path through the SUL  144  back to the return pole  120   b . As known in the art, the coil may also be of the helical type. 
     Because the disk drive is a TAR disk drive, the slider  110  also includes a waveguide or optical channel  150  with an aperture structure  160  near the ABS  112 . The optical channel  150  with aperture structure  160  is depicted in  FIG. 14  as extending through the yoke  120  and being located between the write pole  120   a  and the return pole  120   b . However, for the method of fabrication of this invention, the optical channel  150  with aperture structure  160  may be fabricated on the trailing surface  111  at other locations, such as between shield S 2  and return pole  120   b , or between the write pole  120   a  and the outer face  131  of slider  110 . The optical channel  150  is formed of a core material  151  such as a high-index-of-refraction dielectric material that is transmissive to radiation at the wavelength of the laser radiation source. Typical radiation-transmissive materials include TiO 2  and Ta 2 O 5 . The radiation-transmissive material  151  is surrounded by cladding material  152   a ,  152   b  that has a lower refractive index than the optical channel material  151  and is transmissive to radiation at the wavelength of the laser radiation source. Typical cladding materials include SiO 2  and Al 2 O 3 . The optical channel  150  directs radiation to the aperture structure  160 . Aperture structure  160  includes the opening or aperture  161  that is filled with radiation-transmissive material and that is surrounded by metal layer  162 . Preferably the aperture  161  is filled with a low index of refraction material such as SiO 2  or Al 2 O 3  The aperture structure  160  has a radiation entrance face  163  and a radiation exit face  164  that are generally parallel to one another and to the ABS. The aperture structure  160  directs radiation, as represented by wavy arrow  166 , to the RL  146  to heat the RL nearly to or above the Curie temperature of the material making up the RL. During writing, the RL  146  moves relative to the slider  110  in the direction shown by arrow  123 . In TAR, heating from radiation through aperture structure  160  temporarily lowers the coercivity H c  of the RL  146  so that the magnetic regions may be oriented by the write field from write pole  120   a . The magnetic regions become oriented by the write field if the write field H w  is greater than H c . After a region of the RL in the data track has been exposed to the write field from the write pole  120   a  and heat from the aperture structure  160  it becomes written or recorded when it cools to below the Curie temperature. The transitions between recorded regions (such as previously recorded regions  127 ,  128  and  129 ) represent written data “bits” that can be read by the read head  115 . 
     If the radiation source is light from a CD-RW type laser diode, then the wavelength is approximately 780 nm. The laser diode may be located on the slider  110 . Alternatively, laser radiation may be delivered from a source off the slider through an optical fiber or waveguide. The aperture  161  at radiation exit face  164  acts as a near-field optical transducer. The aperture  161  is subwavelength-sized, i.e., the dimension of its smallest feature is less than the wavelength of the incident laser radiation and preferably less than one-half the wavelength of the laser radiation. 
       FIG. 15  is a view of radiation exit face  164  with aperture  161  surrounded by metal  162 . The aperture  161  shown in  FIG. 15  is a “C”-shaped aperture with a characteristic dimension “d.” The near-field spot size is determined by the characteristic dimension “d,” which is the width of the ridge of the aperture. The resonant wavelength depends on the characteristic dimension of the aperture as well as the electrical properties and thickness of the thin film surrounding the aperture. This is discussed by J. A. Matteo et. al.,  Applied Physics Letters , Volume 85(4), pp. 648-650 (2004) for a C-shaped aperture. 
     For sliders used in conventional (non-TAR) disk drives, the films making up the read and write heads are deposited on a wafer containing a large number, e.g., 40,000, of rectangular regions arranged in rows, with each region ultimately becoming an individual slider and the wafer surface of each region becoming the trailing surface of the individual slider, like trailing surface  111  of slider  110 . After formation of the read and write heads at the wafer level, the wafer is cut into rows and the rows cut into individual sliders. The sliders are then “lapped” in a plane perpendicular to the wafer surface, with this plane becoming the slider ABS. However, for sliders used for TAR disk drives, the only proposed methods for forming the aperture structures have been to fabricate the aperture structure on the slider at the row level, i.e., after the wafer has been cut into rows, or at the individual slider level. These are costly and time-consuming methods. 
     In the present invention, the aperture structures, as well as the optical channels, are fabricated at the wafer level. Thus, after the wafer is cut into rows and the rows into the individual sliders, each slider contains not only the read and write heads, but the aperture structure and optical channel required for TAR, like the slider shown in  FIG. 14 . 
       FIG. 16  is a perspective view of a portion of a wafer  170 . The wafer  170  has a generally planar upper surface and a plurality of generally rectangular regions  180  arranged in generally parallel rows  190 , with each region  180  being shown bounded by dashed lines  191 ,  192 . Each region  180  has an optical channel  150  and aperture structure  160 . After all the processing steps for forming the read and write heads, and the optical channels  150  and aperture structures  160  in the manner described below, the wafer  170  is cut into rows  190  along planes represented by dashed lines  191 , and the rows  190  then cut along planes represented by dashed lines  192 , to form the individual sliders. The sliders are lapped, either at the row level or the individual slider level, along planes parallel to planes represented by dashed lines  191 , to define the ABS. The wafer  170  has a thickness “t” which is the “length” of the individual sliders. 
       FIG. 17  is a perspective view, not to scale, of an aperture structure  160  on a rectangular region  180  of wafer  170 . The aperture structure  160  includes the aperture  161  surrounded by metal  162 , which may be a pure metal, such as Au or Cu, or an alloy of two or more metals, like a AuCu alloy. The aperture structure  160  has parallel faces  163 ,  164  that are generally parallel to the plane  191  along which the wafer will be cut into rows of rectangular regions. At faces  163  and  164 , the aperture  161  has a generally C-shape defined by a ridge  165  of metal  162  that extends between faces  163  and  164 . 
       FIG. 17  also shows one embodiment of dimensions for the aperture structure  160 , which are meant to be merely representative of typical dimensions and do not limit the scope of the invention. The aperture structure  160  has a width parallel to plane  191  and to the “length” of rectangular region  180  of about 400 to 800 nm and a thickness of about 200 to 400 nm in the direction perpendicular to the wafer surface. The ridge  165  has a width of about 30 nm and a thickness of about 30 nm, with the characteristic dimension “d” of the C-shaped aperture being the width of ridge  165 . The size of the ridge  165  and the characteristic dimension “d” essentially define the spot size of the radiation incident on the recording layer, and for the dimensions shown the areal bit density on the disk would be greater than about 1 Terabit/in 2 . 
       FIG. 1  depicts an embodiment of a thermal assisted recording (TAR) head  21  for a hard disk drive. TAR head  21  comprises a main pole  23 , a core  25  and cladding  27 ,  29 ,  31  formed thereon and therebetween. The cladding  27 ,  29 ,  31  may comprise Al 2 O 3  having a thickness on the order of 1 to 2 μm. One embodiment of the core  25  has a thickness of about 300 nm and an aperture and lip thickness of about 525 nm. Another separate layer of cladding  33  (e.g., SiO 2 ) having a thickness of about 200 nm may be located between core  25  and cladding  29 . TAR head  21  may further comprise a stitch pole  35  having a thickness of about 1 μm, and an aperture  41  having an aperture and lip throat height of about 90 nm, in one embodiment. 
       FIG. 2  is an enlarged schematic sectional ABS view of one embodiment of the aperture  41 . For example, aperture  41  may comprise a c-aperture or E-antenna writer. In the embodiment shown, aperture  41  comprises a substrate (e.g., formed from NiFe), a stitch pole  45 , and a base layer or magnetic lip  47  which may be formed from a core of CoFe or similar magnetic material. An insulation layer  49  is formed on the magnetic lip  47 , is encased in a conductive material  51 , and has cladding  27 . In some embodiments, the insulation layer  49  is formed from SiO 2 , has a thickness of about 60 nm, and has a central rectangular notch  53  (e.g., 30×30 nm) formed therein opposite the magnetic lip  47 . The conductive material  51  may comprise Au and have a width of about 500 nm. The thickness of magnetic lip  47  is about 300 nm, and conductive material  51  has a thickness of about 120 nm. 
     Referring now to  FIGS. 3-13 , schematic sectional and top views of various embodiments of a method of fabricating the aperture  41  depicted in  FIG. 2  are shown. The method fabricates a plasmonic near field source for thermal assisted recording applications in, for example, hard disk drives. In one embodiment, the method initially comprises depositing an insulator  61  (which will ultimately be the insulation layer  49 ) on a “base layer”  63  (which will ultimately be the magnetic lip  47 ). As shown in  FIG. 4 , an e-beam resist layer  65  is applied on the insulator  61 .  FIGS. 5 and 6  depict sectional side and top views of e-beam lithography and liftoff on the e-beam resist layer to form a pair of parallel hard mask features  67  separated by a gap  69 . 
     As shown in  FIG. 7 , the insulator layer  61  is then reactive ion etched (RIE) to form a notch  53  in the insulation layer  49  below the gap  69 . The hard mask features  67  protect the insulator material beneath them from the RIB. Next,  FIGS. 8 and 9  depict performing e-beam lithography and liftoff to add an additional hard mask  71  over the gap  69  and notch  53 . Although this second e-beam step must be reasonably well-aligned to the first e-beam step, as shown in  FIG. 9 , the features  67  and  71  can be designed such that there is ample misalignment tolerance, making the alignment easy to achieve with existing e-beam tool capabilities. Specifically, feature  71  must completely protect the gap  69 , but be narrower than the outer edges of feature  67 . There is significant margin for vertical misalignment in  FIG. 9 , as most of the top and bottom of the features are subsequently removed (see  FIG. 13 ). 
     Referring to  FIG. 10 , another RIE is performed to completely remove all of the insulator layer not protected by either hard mask features  67  or  71 . In another variation of this process, a thin layer of insulating material (e.g., less than 5 nm) may remain following this second RIE step. The advantage of leaving this insulating layer is that it may serve as a protective layer to avoid potential corrosion of the magnetic lip material  47 . Leaving a small amount of insulating material would have little impact on the E-antenna performance. For example, see related U.S. patent application Ser. No. 12/347,084, titled Thermally Assisted Recording Head Having Recessed Waveguide with Near Field Transducer and Methods of Making Same; and U.S. patent application Ser. No. 12/347,194, titled Thermally Assisted Recording Head Having an Optical Waveguide and a Near Field Transducer with a Tuned Backedge; U.S. patent application Ser. No. 12/347,134, titled Thermally Assisted Recording Head Having an Electrically Isolated Magnetic Layer and a Near Field Transducer, which are incorporated herein by reference in their entirety. 
     In  FIG. 11 , a wet chemical etch is used to remove the extraneous hard mask features  67  and  71 , and then form a structure comprising only the insulation layer  49  on the base layer  63 . As shown in  FIG. 12 , a conductive layer  73  is deposited on the structure  49 ,  63 . As a result of this process, the notch  53  is exactly centered in aperture  49 . 
     Finally, as shown in  FIG. 13 , a throat and trackwidth of the c-aperture  41  are formed from the structure  49 ,  63 . This step may comprise defining a back wall  75  of the c-aperture and a waveguide trackwidth  77  by separate photolithography processes (e.g., labeled T 4  and T 5 , respectively) on the structure. In the T 4  and T 5  processes, aligned photolithography creates a protective resist mask, ion milling removes extraneous material, and a solvent lift-off process removes the residue photoresist. The air bearing surface (ABS) edge  79  is defined by lapping the structure. 
     In some embodiments, the insulator layer is deposited as 60 nm of SiO 2  and the base layer is 300 nm of CoFe. The e-beam resist layer may comprise applying polymethylmethacrylate (PMMA) on the insulator layer. The liftoff steps may comprise using Cr liftoff, and forming the pair of hard mask features from Cr in rectangular shapes, with the gap having a width of approximately 30 nm. The thickness of the insulator layer may be reactive ion etched using CF 4 , both outside of the pair of parallel features and in the gap. The second hard mask  71  also may comprise lift-off Cr. The wet etching step may comprise Cr etching, that does not attack either the base layer or the insulator, such that all of the Cr is removed and only the notched insulator layer and the base layer remain. The conductive layer step may comprise depositing approximately 120 nm of Au on the structure. 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.