Abstract:
A method of manufacturing a near-field optical head. A first projection shaped in a quadrangular pyramid is formed on a surface of a substrate for providing a near-field optical element of the near-field optical head. A second projection shaped in a frustum of quadrangular pyramid is formed on the surface of the substrate for providing an air bearing surface of the near-field optical head. A metal film is formed on at least one surface of the first projection and the metal film is connected with a resistance meter through a conduction wiring for detecting an electrical resistance of the metal film. The first and second projections and the metal film are polished while the resistance meter detects an electrical resistance of the metal film and until the detected electrical resistance reaches a predetermined value such that a top surface of the first projection has a specified size and becomes flush with a surface of the second projection providing the air bearing surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of International Application No. PCT/JP2007/063258, filed Jul. 3, 2007, claiming a priority date of Aug. 1, 2006, and published in a non-English language. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a fabrication method and a fabrication apparatus of a head using near field light mounted with a near field optical element. 
     2. Background Art 
     For information recording and reproducing apparatuses requiring an increase in capacity and reduction in size, magnetic recording techniques are demanded to achieve higher recording density. The higher the recording density becomes, the smaller a recording area per bit becomes, and the energy of one bit of information comes close to thermal energy at room temperature resulting in thermal fluctuations causing recorded information to be reversed or erased, for example. 
     In the in-plane recording method generally used in magnetic recording techniques, magnetism is recorded so that the magnetization direction is oriented in the in-plane direction of a recording medium. However, in this method, recorded information loss, for example, tends to occur because of thermal fluctuations as described above. Then, in order to avoid such failure, the recording method is shifting to the use of a perpendicular recording method in which magnetization signals are recorded in the direction perpendicular to the recording medium. This method is the method in which magnetic information is recorded according to the principles that a magnetic monopole is brought close to a recording medium. According to this method, a recording magnetic field is directed to the direction almost perpendicular to a recording film. Information recorded with the perpendicular magnetic field tends to keep stable energy because it is difficult that the north pole and the south pole form a loop in the recording film surface. Thus, this perpendicular recording method is more resistant to thermal fluctuations than the in-plane recording method. 
     However, recent information recording and reproducing apparatuses are demanded for much higher density. On this account, in order to suppress the influence of the magnetic domains adjacent to each other and thermal fluctuations to a minimum, such a recording medium having a stronger coercivity is being adopted as a recording medium. Because of this, even according to the perpendicular recording method described above, it becomes difficult to record information on the recording medium. 
     Then, in order to solve this problem, a hybrid magnetic recording method (near field light assisted magnetic recording method) is provided in which near field light locally heats a magnetic domain to temporarily reduce the coercivity for writing during this period. This hybrid magnetic recording method is the method that uses near field light generated by the interaction between a micro-area and a near field optical element formed on a near field optical head. The near field light is used to produce a light spot having a diameter of a few tens nm or below, which cannot be carried out by existent light because of diffraction limits, and to generate a heat spot in almost the same size. 
     In the near field optical element, a main problem is to obtain a strong micro-spot of the near field light. To this problem, some shapes are already proposed. In application 1 (JP-A-2001-118543), such a structure is formed in which the outline shape of an optical aperture provided at the tip end of a near field optical element is formed in a triangle and the polarization direction of the incident light is orthogonal to one side of the triangle, whereby a strong near field light is generated, which is localized on that one side (triangular aperture method). In the application 1 (Technical Digest of 6th international conference on near field optics and related techniques, the place country-region Netherlands, Aug. 27-31, 2000, p 100) and application 2 (JP-A-2002-221478), a metal film is formed on two surfaces facing to each other among four side surfaces of a quadrangular pyramid, these two surfaces have a gap below optical wavelengths near the top of the quadrangular pyramid, each of the metal films on the two surfaces has a top with the radius of curvature of a few tens nm or below in the gap part, and a strong near field light localized in the gap part is generated (bow tie antenna method).
     Application 1: JP-A-2001-118543   Application 2: JP-A-2002-221478   Non-Patent Publication 1: Technical Digest of 6th international conference on near field optics and related techniques, the place country-region Netherlands, Aug. 27-31, 2000, p 100   

     In the foregoing techniques described above, for the near field optical element of the triangular aperture method in application 1, the fabrication method is already disclosed, and the element can be relatively easily fabricated. However, for the near-filed light element of the bow tie antenna method in Non-Patent Publication 1 and application 2, because the element requires processing of about a few nm to a few tens nm for shapes of the metal film top and the gap part, extremely advanced micromachining techniques such as an electron beam stepper (electron beam lithography system) and a focused ion beam apparatus are generally needed. For this, a simple fabrication method suited for mass production is sought. 
     In addition, it is also necessary that a near field optical element is incorporated in a head having an air bearing surface (ABS: air bearing surface) in accuracy of order of a few nm for floating in the air from a medium at a clearance from about a few nm to a few tens, and thus it is demanded to solve this by a fabrication method suited for mass production. 
     SUMMARY OF THE INVENTION 
     In order to solve the problems, according to the present invention, a head using near field light including a near field optical element formed of a truncated pyramid having a top face and a plurality of side surfaces and a metal film and including a floating projection having an air bearing surface is fabricated as follows. 
     First, on one surface of a substrate, a first projection in a pyramid or a truncated pyramid to be the near field optical element after processing and a second projection to be the floating projection similarly after processing are formed. 
     Subsequently, a metal film is formed on at least one side surface of the first projection. 
     Subsequently, a sacrificial interconnect is provided on one surface of the substrate, a conductive interconnect electrically connected to the sacrificial interconnect is provided on one surface of the substrate, and the conductive interconnect is electrically connected to an electrical resistance detecting unit. 
     Subsequently, a flat polishing material is arranged so as to face to one surface of the substrate. The polishing material is used to polish the first projection, the second projection and the sacrificial interconnect while the conduction resistance value is measured by the electrical resistance detecting unit so that the top face of the near field optical element is in a predetermined size and the top face and the air bearing surface are in the same plane. 
     In addition, in the invention, the metal film can be formed as described below. 
     A sacrificial layer is deposited on one side surface of the first projection from the direction perpendicular to one side surface, a metal film is deposited on the other side surface facing to at least one side surface, the sacrificial layer deposited on one side surface is removed together with the overlapping metal film, whereby the metal film can be formed on the other side surface. 
     Moreover, in the invention, in addition to the first projection, the second projection and the sacrificial interconnect, the metal film formed near the top of the first projection is also polished, whereby the end surface of the polished metal film and the top face are in the same plane. 
     Moreover, in the invention, the sacrificial interconnect can be formed on the first projection, on the second projection, and on a third projection provided near the first projection. 
     Moreover, in the invention, a metal film placed on two side surfaces of the first projection facing to each other can be the sacrificial interconnect. 
     According to the invention, because the end point in the polishing step can be detected by the electrical resistance detecting unit, the size of the top face of the truncated pyramid configuring the near field optical element can be a few tens nm or below. Thus, the size of a near field light spot generated from the near field optical element can be a few tens nm or below. Accordingly, the recording density of an information recording and reproducing apparatus mounted with the head using near field light can be improved. 
     In addition, according to the invention, because the top face of the truncated pyramid configuring the near field optical element and the air bearing surface are formed on the same plane, in operating the information recording and reproducing apparatus, the distance between the top face and the recording medium can be almost the same as the distance between the air bearing surface and the recording medium. Thus, the distance between the top face and the recording medium is a few tens nm or below, and the energy of the near field light generated from the near field optical element can be efficiently transmitted to the recording medium. Accordingly, the recording density and the SN ratio of the information recording and reproducing apparatus can be improved. 
     In addition, according to the invention, because the near field optical element and the head using near field light having the performance described above can be fabricated with processing techniques at relatively low level, they can be fabricated at low costs as compared with the techniques before. 
     In addition, according to the invention, the metal film can be formed on the side surfaces of the truncated pyramid configuring the near field optical element. This metal film can further localize the near field light, or the metal film is formed to be the magnetic pole to meet the hybrid magnetic recording method. 
     In addition, the clearance near the top face of a plurality of the metal films can be a few tens nm or below. The near field light can be further localized, or the leakage flux due to the magnetic pole can be localized. Accordingly, the recording density of the information recording and reproducing apparatus can be improved. 
     In addition, according to the invention, the sacrificial interconnect is included in the metal film, whereby the end point in the polishing step can be detected highly accurately. 
     In addition, according to the invention, the sacrificial interconnect is provided on the projection to be the floating projection after processing and on the projection provided near the near field optical element, whereby the end point in the polishing step can be detected highly accurately. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view depicting an information recording and reproducing apparatus using near field light according to embodiment 1 of the invention; 
         FIGS. 2A-2B  show bottom and cross-sectional side views, respectively, of a near field optical head according to embodiment 1 of the invention; 
         FIG. 3  is a perspective view depicting a near field optical element according to embodiment 1 of the invention; 
         FIG. 4  shows cross-sectional views depicting a method of fabricating the near field optical element and the near field optical head according to embodiment 1 of the invention; 
         FIG. 5  shows cross-sectional views depicting another method of fabricating the near field optical element and the near field optical head according to embodiment 1 of the invention; 
         FIGS. 6A-6B  are cross-sectional views depicting another method of fabricating the near field optical element and the near field optical head according to embodiment 1 of the invention; 
         FIG. 7  is a bottom view depicting a near field optical head according to embodiment 2 of the invention; 
         FIG. 8  is a perspective view depicting a near field optical element according to embodiment 2 of the invention; 
         FIG. 9  are cross-sectional views depicting a method of fabricating the near field optical element and the near field optical head according to embodiment 2 of the invention; 
         FIG. 10  is a bottom view depicting a near field optical head according to embodiment 2 of the invention; 
         FIG. 11  is a cross-sectional view depicting another method of fabricating the near field optical element and the near field optical head according to embodiment 2 of the invention; and 
         FIG. 12  is a block diagram depicting the schematic configuration of a fabrication apparatus according to a modification of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the best method for carrying out the invention will be described with reference to the drawings. 
     Embodiment 1 
     A near field optical element according to embodiment 1 of the invention, a near field optical head mounted with the near field optical element, and an information recording and reproducing apparatus mounted with the near field optical head will be described with reference to  FIGS. 1 to 3 . 
     As shown in  FIG. 1 , an information recording and reproducing apparatus  1  in the embodiment has a near field optical head  2 , a suspension  3  that is movable in parallel with the surface of a recording medium (hereinafter, referred to as a disk) D and supports the near field optical head  2  on the tip end side thereof in the pivotable state about two axes parallel with the surface of the disk D and orthogonal to each other, an optical signal controller (light source)  5  that leads a light beam L from the base end side of an optical waveguide  4  into the optical waveguide  4 , an actuator  6  that supports the base end side of the suspension  3  and moves the suspension  3  to scan in the direction parallel with the surface of the disk D, a spindle motor (rotating and driving unit)  7  that rotates the disk D in a certain direction, a control unit  8  that processes signals for recording and reproduction and controls the operations of the optical signal controller  5 , the actuator  6  and the spindle motor  7 , and a housing  9  that accommodates these individual components therein. In addition, the near field optical head  2  and the suspension  3  configure a head gimbal assembly  12 . 
     The housing  9  is formed of a metal material such as aluminum in a rectangular shape seen from the top, and has a recessed part  9   a  formed therein that accommodates the individual components. In addition, to the housing  9 , a cover, not shown, is detachably fixed so as to block the aperture of the recessed part  9   a . In almost the center of the recessed part  9   a , the spindle motor  7  is mounted, and the center hole of the disk D is fit into the spindle motor  7  to detachably fix the disk D. At the corner of the recessed part  9   a , the actuator  6  is mounted. On the actuator  6 , a carriage  11  is mounted through a bearing  10 , and the suspension  3  is mounted at the tip end of the carriage  11 . Then, the carriage  11  and the head gimbal assembly  12  are movable together by drive of the actuator  6  as described above. 
     In addition, the optical signal controller  5  is mounted in the recessed part  9   a  so as to be next to the actuator  6 . Then, as adjacent to the actuator  6 , the control unit  8  is mounted. 
       FIG. 2  shows the head gimbal assembly  12  according to the embodiment. In addition,  FIG. 2(   a ) shows a bottom view depicting the near field optical head  2 , and  FIG. 2(   b ) shows a cross section depicting the near field optical head  2 , the suspension  3 , and the optical waveguide  4 . In  FIG. 2 , for clarity of explanations the scale of the individual components of the head gimbal assembly  12  is adjusted for illustration purpose only, and it does not match with the actual dimensions of these components. The same applies for drawings as further described below. 
     The near field optical head  2  configuring the head gimbal assembly  12  has a slider  15  having an opposed surface  15   a  facing to the surface of the disk D, a near field optical element  16  that is fixed to the slider  15  and generates near field light, and a light beam guiding unit that leads a light beam L into the near field optical element  16 . 
     The slider  15  is shaped in a rectangular parallelepiped of an optically transparent material such as quartz glass and the size is about a 1 mm square. This slider  15  is supported so as to hang from the tip end of the suspension  3  through a gimbal part  25  in the state in which the opposed surface  15   a  is faced on the disk D side. This gimbal part  25  is the component whose motion is controlled as it is displaced only about two axes parallel with the flat surface of the disk D. 
     On the opposed surface  15   a  of the slider  15 , two projections are formed, having an ABS (air bearing surface: Air Bearing Surface)  15   b  formed thereon which generates pressure for floating due to the viscosity of an air flow produced by the rotating disk D. The length of each of the projections in the moving direction of the disk D is almost equal to the length of one side of the slider  15 , the width is about 100 to 500 μm, and the height is about 1 to 10 μm. In the embodiment, a step flat type ABS is taken as an example, having two projections arranged in parallel with the moving direction of the disk D, but the embodiment is not limited to this case, which may be other schemes such as a step-taper type, and a tri-pad type. 
     The slider  15  receives the force to float above the disk D by the ABS  15   b , and also receives the force that holds the slider down to the disk D side by the suspension  3 . The slider  15  floats in the state in which it is apart from the surface of the disk D at a few tens nm or below by the balance between forces of these two. In addition, by the function of the gimbal part  25 , the slider  15  can stably float even though the surface of the disk D has waviness. 
     In addition, on the top surface of the slider  15 , a lens  26  is formed at the position right above the near field optical element  16 . Moreover, on the top surface of the slider  15 , the optical waveguide  4  such as an optical fiber is mounted. The tip end of this optical waveguide  4  is a mirror surface  4   a  at an angle of 45 degrees, and the mounting position is adjusted so that the mirror surface  4   a  is positioned right above the lens  26 . Then, the optical waveguide  4  is connected to the optical signal the controller  5  through the suspension  3 , the carriage  11  and the like. 
     Thus, the optical waveguide  4  is configured to guide the light beam L incident from the optical signal controller  5  to the tip end side, reflect the light in the mirror surface  4   a  to change the direction, and then emit the light to the lens  26 . In addition, the emitted light beam L is condensed by the lens  26 , transmitted through the slider  15 , and led into the near field optical element  16 . In other words, the optical waveguide  4  and the lens  26  configure the light beam guiding unit described above. 
     To each of two side surfaces of the near field optical element  16  aligned as orthogonal to the moving direction M of the disk D and facing to each other, a conductive interconnect  18  is connected, which is arranged on the opposed surface  15   a  of the slider  15 . The remaining end of the conductive interconnect  18  is extended to the end of the slider  15 . 
       FIG. 3  shows the outline of the near field optical element according to the embodiment. A truncated quadrangular pyramid  301  is placed on the opposed surface  15   a  of the slider  15 . The truncated quadrangular pyramid  301  is formed of an optically transparent material such as quartz glass. The truncated quadrangular pyramid  301  is formed of four side surfaces  301   a ,  301   b ,  301   c , and  301   d  and a top face  301   e  facing to the disk D. Among the four side surfaces, on the two side surfaces  301   a  and  301   b  arranged orthogonal to the moving direction M of the disk D and facing to each other, a first metal film  303  and a second metal film  304  are formed, respectively. For the first metal film  303  and the second metal film  304 , a metal material such as Au or Ag is used. The first metal film  303  and the second metal film  304  form a bow tie antenna. The top face  301   e  is a rectangle, and the length of each side is a few tens nm or below. Therefore, the first metal film  303  and the second metal film  304  have a clearance near the top face  301   e , and the size is also a few tens nm or below. 
       FIG. 4  shows cross sections depicting a method of fabricating the near field optical element and the near field optical head according to the embodiment. As shown in  FIG. 2 , a cross section A is a section crossing the two ABSs  15   b , crossing the first metal film  303 , the second metal film  304  and the top face  301   e , and perpendicular to the top face  301   e . A cross section B is a section crossing the two side surfaces  301   c  and  301   d , not covered with the first metal film  303  and the second metal film  304 , and the top face  301   e  and perpendicular to the top face  301   e . In  FIG. 4 , cross sections in the cross section A are shown on the left in the drawing, and in  FIG. 4 , cross sections in the cross section B are shown on the right in the drawing. 
     First, as shown in Step S 401 , a quadrangular pyramid  401  (first projection) to be the truncated quadrangular pyramid  301  after the fabrication process steps are finished, and truncated quadrangular pyramids  402  (second projection) having the top face to be the ABS  15   b  after the fabrication process steps are finished are formed on the opposed surface  15   a  of the slider  15  with photolithography. Although the quadrangular pyramid  401  has the side surface  301   a ,  301   b ,  301   c , and  301   d , it does not have the top face  301   e  yet. In addition, although for convenience of processing by photolithography, the quadrangular pyramid  402  also has the side surfaces with a slope, it does not influence the operation of the near field optical head because it is smaller than the size of the ABS  15   b . Although the heights of the quadrangular pyramid  401  and the quadrangular pyramid  402  are 1 to 10 μm, it is unnecessary here that the height of the two pyramids have to be aligned. 
     Subsequently, as shown in Step S 402 , on the side surface  301   b , a deposition method of high directivity such as vacuum deposition is used to form a sacrificial layer  403  from the direction perpendicular to the side surface  301   b . At this time, the sacrificial layer  403  is also formed not only on the side surface  301   b  but also on the side surfaces  301   c  and  301   d  adjacent to the side surface  301   b . The sacrificial layer  403  is not formed on the side surface  301   a  facing to the side surface  301   b  because the side surface  301   a  is hidden because of the directivity of the deposition method. In addition, among the surfaces configuring the truncated quadrangular pyramid  402 , the sacrificial layer  403  is formed on the side surfaces nearly parallel with the side surface  301   b , the side surfaces adjacent to the side surface  301   b , and the top face. The sacrificial layer  403  is formed of an Al film, and the film thickness ranges from a few tens nm to a few hundreds nm. 
     Subsequently, as shown in Step S 403 , on the side surface  301   a , a metal film forming method of high directivity such as vacuum deposition is used to form the first metal film  303  from the direction perpendicular to the side surface  301   a . At this time, the first metal film  303  is formed not only on the side surface  301   a  but also on a part of the sacrificial layer  403  and on the side surfaces of the truncated quadrangular pyramid  402  nearly parallel with the side surface  301   a.    
     Subsequently, as shown in Step S 404 , the sacrificial layer  403  is removed. At this time, the first metal film  303  placed on the sacrificial layer  403  is also removed, and only the first metal film  303  placed on the side surface  301   a  and on the side surfaces of the truncated quadrangular pyramid  402  nearly parallel with the side surface  301   a  is left (lift-off process). For removing the sacrificial layer  403 , an aqueous solution having a main component of a phosphoric acid is used. 
     Subsequently, as shown in Step S 405 , the similar steps as steps from Steps S 403  to S 404  are repeated to form the second metal film  304  placed on the side surface  301   b . Here, the first metal film  303  placed on the side surface  301   a  and the second metal film  304  placed on the side surface  302   b  are electrically connected to each other near the top of the quadrangular pyramid  401 . In addition, also on the side surfaces of the truncated quadrangular pyramid  402  nearly parallel with the side surface  301   b , the second metal film  304  is formed. 
     Subsequently, as shown in Step S 406 , the first metal film  303  and the second metal film  304  placed on the side surfaces of the truncated quadrangular pyramid  402  are removed. For this step, photolithography is used. 
     Subsequently, as shown in Step S 407 , a polishing material is arranged in parallel with the slider  15 , and as indicated by X in  FIG. 4 , the polishing material  404  is moved in parallel with one surface of the substrate to polish the surface of the slider  15  for removing the metal film formed near the top thereof. At this time, to the first metal film  303  and the second metal film  304 , an ohmmeter  405  is connected through the conductive interconnect  18 . Near the top of the quadrangular pyramid  401 , the first metal film  303  and the second metal film  304  are electrically connected to each other. However, when polishing is conducted until the top of the quadrangular pyramid  401  is brought into contact with the polishing material  404 , the first metal film  303  and the second metal film  304  do not conduct to each other. More specifically, the first metal film  303  and the second metal film  304  configure a sacrificial interconnect that changes electrical resistance by being polished. At this time, because the resistance value measured by the ohmmeter  405  suddenly rises, the moment at which the top of the quadrangular pyramid  401  is brought into contact with the polishing material  404  can be determined. 
     When the polishing is continued slightly from the moment, as shown in Step S 408 , the top of the quadrangular pyramid  401  is cut to form the top face  301   e . In addition, the top face of the truncated quadrangular pyramid  402  is also similarly cut to from the ABS  15   b . At this time, the top face  301   e  and the ABS  15   b  are in the same plane. For example, the polishing material  404  is used to polish the quadrangular pyramid  401  and the truncated quadrangular pyramids  402  until the value of the electrical resistance reaches a predetermined value so that the top face  301   e  of the quadrangular pyramid  401  is formed in a predetermined size and the top face  301   e  and the ABSs  15   b  (air bearing surface) are arranged on the same plane. This predetermined value indicates the resistance value of the metal film (sacrificial interconnect) when the top face  301   e  and the ABSs  15   b  (air bearing surface) are arranged on the same plane. 
     After that, the formation of the lens  26  and connection to the optical waveguide  4  are conducted, and then the near field optical head  2  is completed. 
     According to the embodiment, because the timing of terminating polishing can be known by the ohmmeter  405 , the size of one side of the top face  301   e  can be a few tens nm or below. More specifically, the clearance between the first metal film  303  and the second metal film  304  near the top face  301   e  can be a few tens nm or below, and the size of the near field light spot generated between the first metal film  303  and the second metal film  304  can be a few tens nm or below. Thus, the recording density of the information recording and reproducing apparatus  1  using the near field light can be improved. 
     In addition, according to the embodiment, because the top face  301   e  and the ABSs  15   b  can be formed on the same plane, in operating the information recording and reproducing apparatus  1 , the distance between the top face  301   e  and the disk D can be almost the same as the distance between the ABS  15   b  and the disk D. Therefore, the distance between the top face  301   a  and the disk D is a few tens nm or below, and the energy of the near field light generated between the first metal film  303  and the second metal film  304  can be efficiently transmitted to the disk D. Accordingly, the recording density and the SN ratio of the information recording and reproducing apparatus  1  can be improved. 
     In addition, according to the embodiment, because the near field element in the order of a few tens nm or below can be prepared with techniques at relatively low level, the near field element can be prepared at low costs as compared with the techniques before. 
     Further, for the deposition of the first metal film  303  in Step S 403 , a deposition method of high directivity such as vacuum deposition is used. However, as shown in Step S 403   a  in  FIG. 5 , deposition may be conducted by using a deposition method of low directivity such as a sputtering method. In addition, also for deposition of the second metal film  304 , deposition of low directivity such as a sputtering method may be similarly used. Therefore, the yields and the productivity in preparation can be improved. 
     In addition, in Step S 406 , the first metal film  303  and the second metal film  304  placed on the side surfaces of the truncated quadrangular pyramid  402  are removed. However, without doing this, as shown in Step S 406   a  in  FIG. 6 , a sacrificial interconnect  601  is formed on the top face of the truncated quadrangular pyramid  402 , whereby the conduction may be achieved between the first metal film  303  and the second metal film  304  placed on the side surfaces of the truncated quadrangular pyramid  402 . After that, as shown in Step S 407   a , an ohmmeter  602  is connected to the first metal film  303  and the second metal film  304  placed on the side surfaces of the truncated quadrangular pyramid  402 , and as similar to Step S 407 , the ohmmeter  405  is connected to polish the surface of the slider  15  with the polishing material  404 . In polishing, because the film thickness of the sacrificial interconnect  601  becomes thinner and thinner, the electrical resistance gradually becomes greater. This can be monitored by the ohmmeter  602 , and thus the polishing step can be more stably performed. 
     Although a magnetic element is not shown in the near field optical head  2  according to the embodiment, the head can of course meet recording and reproduction by light as well as meet the hybrid magnetic recording method by the combination of the magnetic element. 
     Embodiment 2 
     Next, embodiment 2 of the invention will be described with reference to  FIGS. 7 to 9 . In addition, in embodiment 2, for the same configuration as that in embodiment 1, the same numerals and signs are designated to omit the explanations. 
       FIG. 7  shows a bottom view depicting a near field optical head  700  according to the embodiment. In addition,  FIG. 8  shows a schematic diagram depicting a near field optical element  800  according to the embodiment. Although the embodiment has almost the similar configuration of embodiment 1, the main difference is in that yokes  701  and  702  and a coil  703  are added. 
     An truncated quadrangular pyramid  301  arranged on an opposed surface  15   a  of a slider  15  is configured of four side surfaces  301   a ,  301   b ,  301   c , and  301   d  and a top face  301   e  facing to a disk D. Among the four side surfaces, on the two side surfaces  301   c  and  301   d  arranged along the moving direction M of the disk D and facing to each other, a first metal film  801  and a second metal film  802  are formed, respectively. For the first metal film  801  and the second metal film  802 , a soft magnetic material is used. At this time, when a soft magnetic material having a high saturation magnetic flux density is used, it is suited for recording at high recording density. The first metal film  801  and the second metal film  802  configure a magnetic head that generates leakage flux. The top face  301   e  is a rectangle, and the length of each side ranges from a few hundreds nm to a few tens nm or below. Thus, the first metal film  801  and the second metal film  802  have a clearance (magnetic gap) near the top face  301   e , and the size ranges from a few hundreds nm to a few tens nm or below. In addition, on the side surface  301   a  adjacent to the side surface  301   c  and the side surface  301   d , a third metal film  803  is formed. The third metal film  803  is formed of a metal material such as Au or Ag. At the side contacted with the top face  301   e  of the third metal film  803 , near field light is localized. 
     To the first metal film  801  and the second metal film  802 , the yokes  701  and  702  provided on the opposed surface  15   a  of the slider  15  are connected, respectively. The yokes  701  and  702  are connected to each other on the opposed surface  15   a  of the slider  15 , and the connecting portion thereof is a vertical circuit part (not shown in the drawing) bent along the direction vertical to the opposed surface  15   a  of the slider  15 . The coil  703  is provided on the opposed surface  15   a  of the slider  15  so as to spirally wind around the vertical circuit part. At this time, the coil  703  is insulated between the adjacent wire materials, the yokes  701  and  702 . The yokes  701  and  702  are a soft magnetic material. For them, a material such as permalloy may be used, because a high saturation magnetic flux density is unnecessary as the first metal film  801  and the second metal film  802  are required. In addition, for the coil  703 , a material having a small electrical resistance such as Cu is used. In addition, this coil  703  is electrically connected to a control unit  8  through a suspension  3  and a carriage  11 , and current modulated according to information is supplied thereto from the control unit  8 . In other words, the yokes  701  and  702  and the coil  703  configure an electromagnet as a whole. Therefore, the leakage flux is generated between the first metal film  801  and the second metal film  802 , and the hybrid magnetic recording method is implemented together with the near field light generated by the third metal film  803 . In addition, on the end surface (outlet end) on the downstream side of the moving direction M of the head  700 , a magnetic resistance element  704  is provided to read magnetic information on the disk D. 
       FIG. 9  shows cross sections depicting a method of fabricating the near field optical element and the near field optical head according to the embodiment. Here, for clarifying the main points of the embodiment, as shown in  FIG. 7 , a section crossing two ABSs  15   b , crossing the first metal film  801 , the second metal film  802  and the top face  301   e , and perpendicular to the top face  301   e  is a cross section α. In addition, a section crossing the third metal film  803 , the side surface  301   b  not covered with the metal film, and the top face  301   e , and perpendicular to the top face  301   e  is a cross section β. In  FIG. 9 , cross sections in the cross section α are shown on the left in the drawing, and in  FIG. 9 , cross sections in the cross section β are shown on the right in the drawing. 
     First, as shown in Step S 901 , it is the same in embodiment 1 that the slider  15  is prepared, which is formed on the surface with a quadrangular pyramid  401  to be the truncated quadrangular pyramid  301  after the fabrication process steps are finished, and the top face of a truncated quadrangular pyramid  402  to be the ABS  15   b  after the fabrication process steps are finished. 
     Subsequently, as shown in Step S 902 , the first metal film  801 , the second metal film  802 , and the third metal film  803  are formed. As similar to embodiment 1, this can be implemented in which deposition of the sacrificial layer, deposition of the metal film, and the lift-off process are repeated, and lastly, only the metal film on the quadrangular pyramid  401  is left. 
     Subsequently, as shown in Step S 903 , a polishing material  404  is arranged in parallel with the slider  15 , and as indicated by X in  FIG. 9 , the polishing material  404  is moved in parallel with one surface of the substrate to polish the surface of the slider  15  for removing the metal film formed near the top. At this time, an ohmmeter  405  is connected to the first metal film  801  and the second metal film  802 . As similar to embodiment  1 , this connection is performed through a conductive interconnect (not shown in the drawing) arranged on the opposed surface  15   a  of the slider  15 . Although the first metal film  801  and the second metal film  802  are electrically connected to each other near the top of the quadrangular pyramid  401 , as different from embodiment 1, the first metal film  801  and the second metal film  802  are electrically connected to each other also through the third metal film  803 . However, when polishing is conducted until the top of the quadrangular pyramid  401  is brought into contacted with the polishing material  404 , the first metal film  801  and the second metal film  802  are not contacted with each other. At this time, because the resistance value measured by the ohmmeter  405  is changed, the moment at which the top of the quadrangular pyramid is brought into contacted with the polishing material  404  can be determined. 
     When the polishing is continued slightly from the moment, as shown in Step S 904 , the top of the quadrangular pyramid  401  is cut to form the top face  301   e . In addition, the top face of the truncated quadrangular pyramid  402  is similarly cut to form the ABSs  15   b . At this time, the top face  301   e  and the ABSs  15   b  are in the same plane. 
     According to the embodiment, even though any of the side surfaces are covered with the metal film among four side surfaces of the truncated quadrangular pyramid  301  of the near field optical element  800 , the advantages similar to those of embodiment 1 are provided. 
     The change in the resistance value measured by the ohmmeter  405  in Step S 903  in the embodiment is smaller than that in embodiment 1. Then, similarly to embodiment 1, a sacrificial interconnect is provided on the ABS  15   b  to more reliably determine the moment at which the top of the quadrangular pyramid  401  is brought into contact with the polishing material  404 . 
     Moreover, as shown in  FIG. 10 , near the near field optical element  800 , truncated quadrangular pyramids  1001  (different projections) are provided for measurement having a height almost the same height of the quadrangular pyramid  401 , and a sacrificial interconnect  1002  is provided thereon, whereby the moment at which the top of the quadrangular pyramid  401  is brought into contact with the polishing material  404  can be determined more accurately. The sacrificial interconnect is provided from above the truncated quadrangular pyramid  1001  for measurement to over the opposed surface  15   a  of the slider  15 , reaching the end part of the slider  15 . As shown in Step S 903   a  in  FIG. 11 , the sacrificial interconnect  1002  is connected to an ohmmeter  1003  for similar polishing. In polishing, because the film thickness of the sacrificial interconnect  1002  on the truncated quadrangular pyramid  1001  for measurement becomes thinner and thinner, the electrical resistance becomes gradually greater. Because this can be monitored by the ohmmeter  1003 , the polishing step can be more stably performed. In  FIG. 10 , two rectangular truncated quadrangular pyramids  1001  for measurement seen from the top are provided. However, some configurations can be selected such as the provision of three square truncated quadrangular pyramids  1001  for measurement seen from the top so as to surround the near field optical element  800 . 
     In addition, the method of fabricating the near field optical element described in each of the embodiments can be adapted to a fabrication apparatus as it is. As shown in  FIG. 12 , more specifically, a fabrication apparatus  2000  of the near field optical element has a projection forming unit  2010 , a sacrificial interconnect providing unit  2020 , and a polishing unit  2030 . On one surface of the substrate, the projection forming unit  2010  forms a first projection to be a truncated pyramid after processing, and second projections to be a floating projection after processing. The sacrificial interconnect providing unit  2020  arranges at least a part of the sacrificial interconnect on the top of any one of the first projection and the second projection. The polishing unit  2030  uses a polishing material to polish the first projection, the second projection, and the sacrificial interconnect until the value of electrical resistance of the sacrificial interconnect reaches a predetermined value so that the top face of the near field optical element is in a predetermined size and the top face and the air bearing surfaces are arranged on the same plane. Since the fabrication method discussed in each of the embodiments described above can be adapted to the fabrication apparatus  2000  as it is, the detailed descriptions are omitted. 
     According to the invention, the near field optical element can be fabricated with high accuracy and in large quantity.