Patent Publication Number: US-7910011-B2

Title: Method of manufacturing magnetic head for perpendicular magnetic recording

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of manufacturing a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system. 
     2. Description of the Related Art 
     The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system. 
     Magnetic heads for perpendicular magnetic recording typically have, as do magnetic heads for longitudinal magnetic recording, a structure in which a read head having a magnetoresistive element (hereinafter also referred to an MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head includes a pole layer that generates a magnetic field in the direction perpendicular to the plane of the recording medium. The pole layer includes, for example, a track width defining portion having an end located in a medium facing surface that faces toward the recording medium, and a wide portion that is coupled to the other end of the track width defining portion and that is greater in width than the track width defining portion. The track width defining portion has a nearly uniform width. 
     For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, as the track width is reduced, the write characteristics, such as overwrite property that is a parameter indicating overwriting capability, suffer degradation. It is therefore required to achieve better write characteristics as the track width is reduced. Here, the length of the track width defining portion taken in the direction perpendicular to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property. 
     A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs in accordance with the position of the magnetic head across the tracks. 
     In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits better capability of writing on a recording medium compared with that of the longitudinal magnetic recording system, the occurrence of the skew mentioned above results in problems such as a phenomenon in which, when data is written on a certain track, data stored on a track adjacent thereto is erased (this phenomenon is hereinafter referred to as adjacent track erasing), and unwanted writing between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between two adjacent tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal. 
     As one of techniques for preventing the above problems resulting from the skew, there is known a technique in which the end face of the track width defining portion located in the medium facing surface is formed into such a shape that the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side, as disclosed in, for example, U.S. Pat. No. 6,710,973 B2, U.S. Patent Application Publication No. US2003/0151850 A1, and U.S. Patent Application Publication No. US2006/0077589 A1. In the medium facing surface of a magnetic head, typically, the end farther from the substrate is located forward along the direction of travel of the recording medium (that is, located closer to the air outflow end of the slider). Therefore, the shape of the end face of the track width defining portion located in the medium facing surface mentioned above is such that the side closer to the substrate is shorter than the side farther from the substrate. 
     Consideration will now be given to a method of forming a pole layer in which the end face of the track width defining portion located in the medium facing surface has such a shape that the side closer to the substrate is shorter than the side farther from the substrate, as mentioned above. U.S. Pat. No. 6,710,973 and U.S. Patent Application Publication No. US2003/0151850 A1 each disclose a method including forming a groove in an inorganic insulating film by selectively etching the inorganic insulating film using a mask made of photoresist, and forming the pole layer in this groove. U.S. Patent Application Publication No. US2006/0077589 A1 discloses a method including forming a nonmagnetic conductive layer on a nonmagnetic layer, forming an opening in the nonmagnetic conductive layer by selectively etching the nonmagnetic conductive layer using a mask made of photoresist, forming a groove in the nonmagnetic layer by selectively etching a portion of the nonmagnetic layer exposed from the opening of the nonmagnetic conductive layer by reactive ion etching (hereinafter also referred to as RIE), and forming the pole layer in this groove. 
     If formed by any of the methods disclosed in U.S. Pat. No. 6,710,973 B2, U.S. Patent Application Publication No. US2003/0151850 A1 and U.S. Patent Application Publication No. US2006/0077589 A1, the resultant pole layer has such a shape that, along the entire perimeter of the pole layer, the side surface of the pole layer is mostly inclined with respect to the direction perpendicular to the top surface of the substrate. The pole layer having such a shape is smaller in area of the cross section thereof perpendicular to the direction in which magnetic flux flows, as compared with a case in which the entire side surface of the pole layer is perpendicular to the top surface of the substrate. The pole layer having the above-described shape cannot allow a magnetic flux of great magnitude to pass through a portion near the boundary between the track width defining portion and the wide portion, in particular, and this results in degradation of the write characteristics such as overwrite property. For this reason, in the pole layer having the above-described shape, the neck height must be reduced in order to suppress degradation of the write characteristics. 
     A portion of the side surface of the pole layer near the boundary between the track width defining portion and the wide portion is difficult to form accurately. Consequently, in the pole layer, the portion near the boundary between the track width defining portion and the wide portion tends to have such a shape that the width gradually increases with increasing distance from the medium facing surface. Accordingly, as the neck height is reduced, it becomes difficult to accurately define the width of the track width defining portion in the medium facing surface, that is, the track width. 
     For the above-described reasons, conventionally, it has been difficult to form a pole layer that is capable of preventing the problems resulting from the skew, capable of defining the track width accurately, and capable of improving the write characteristics. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method of manufacturing a magnetic head for perpendicular magnetic recording that makes it possible to form a pole layer capable of preventing the problems resulting from the skew, capable of defining the track width with precision, and capable of improving the write characteristics. 
     A magnetic head for perpendicular magnetic recording manufactured by a first or a second manufacturing method of the present invention includes: 
     a medium facing surface that faces toward a recording medium; 
     a coil that generates a magnetic field corresponding to data to be written on the recording medium; 
     a pole layer that allows a magnetic flux corresponding to the magnetic field generated by the coil to pass and generates a write magnetic field for writing the data on the recording medium by means of a perpendicular magnetic recording system; 
     a bottom forming layer made of a nonmagnetic material; 
     an encasing layer made of a nonmagnetic material, disposed on the bottom forming layer, and having a groove that opens at a top surface of the encasing layer and that accommodates the pole layer; and 
     a substrate on which the bottom forming layer, the encasing layer, the pole layer and the coil are stacked, the substrate having a top surface. 
     The pole layer includes: a track width defining portion having an end face that is located in the medium facing surface and that defines a track width, and having an end opposite to the end face; and a wide portion connected to the end of the track width defining portion and having a width greater than that of the track width defining portion. The end face of the track width defining portion located in the medium facing surface has a width that decreases with decreasing distance from the top surface of the substrate. The groove includes: a first portion for accommodating at least part of the track width defining portion of the pole layer; and a second portion for accommodating at least part of the wide portion of the pole layer, the second portion being farther from the medium facing surface than the first portion. The first portion has a width that decreases with decreasing distance from the top surface of the substrate. The second portion penetrates the encasing layer. 
     The first manufacturing method for the magnetic head for perpendicular magnetic recording of the present invention includes the steps of: 
     forming the bottom forming layer; 
     forming a nonmagnetic layer on the bottom forming layer, the nonmagnetic layer being intended to undergo formation of the groove therein later to thereby become the encasing layer; 
     forming a groove defining layer on the nonmagnetic layer, the groove defining layer having a penetrating opening that has a shape corresponding to a plane geometry of the groove to be formed later; 
     forming the groove in the nonmagnetic layer so that the nonmagnetic layer becomes the encasing layer; 
     forming the pole layer such that the pole layer is accommodated in the groove of the encasing section; and 
     forming the coil. 
     In the first manufacturing method of the present invention, the step of forming the groove in the nonmagnetic layer includes: a first etching step for taper-etching the nonmagnetic layer by reactive ion etching so as to form an initial groove in the nonmagnetic layer, the initial groove including the first portion of the groove of the encasing layer; a step of forming an initial groove mask that covers the first portion of the initial groove; and a second etching step for etching the nonmagnetic layer by reactive ion etching, with the initial groove mask and the groove defining layer used as an etching mask, so as to complete the groove. Each of the bottom forming layer and the groove defining layer is lower in etching rate in the first and second etching steps than the nonmagnetic layer. 
     In the first etching step, the nonmagnetic layer is etched such that an initial sidewall is formed by the initial groove in a region in which the second portion is to be formed, the initial sidewall being intended to be etched in the second etching step later to thereby become a sidewall of the second portion, and such that part of the nonmagnetic layer remains on the bottom forming layer in the region in which the second portion is to be formed. In the second etching step, the initial sidewall is etched to thereby form the sidewall of the second portion. 
     In the first manufacturing method of the present invention, the nonmagnetic layer may be formed of Al 2 O 3 , and each of the bottom forming layer and the groove defining layer may be formed of a nonmagnetic metal material. 
     In the first manufacturing method of the present invention, in the second etching step, the initial sidewall may be etched so that an angle formed by the sidewall of the second portion with respect to a direction perpendicular to the top surface of the substrate will be smaller than an angle formed by the initial sidewall with respect to the direction perpendicular to the top surface of the substrate. 
     In the first manufacturing method of the present invention, the step of forming the groove in the nonmagnetic layer may further include a step of forming a mask on the nonmagnetic layer before the first etching step so that, in the region in which the second portion is to be formed, part of the nonmagnetic layer will remain on the bottom forming layer in the first etching step. 
     The second manufacturing method for the magnetic head for perpendicular magnetic recording of the present invention includes the steps of: 
     forming the bottom forming layer; 
     forming a nonmagnetic layer on the bottom forming layer, the nonmagnetic layer being intended to undergo formation of the groove therein later to thereby become the encasing layer; 
     forming a groove defining layer on the nonmagnetic layer, the groove defining layer having a penetrating opening that has a shape corresponding to a plane geometry of the groove to be formed later; 
     forming the groove in the nonmagnetic layer so that the nonmagnetic layer becomes the encasing layer; 
     forming the pole layer such that the pole layer is accommodated in the groove of the encasing section; and 
     forming the coil. 
     In the second manufacturing method of the present invention, the step of forming the groove in the nonmagnetic layer includes: a first etching step for taper-etching the nonmagnetic layer by reactive ion etching so as to form an initial groove in the nonmagnetic layer, the initial groove including the first portion of the groove of the encasing layer; a step of forming an initial groove mask that covers the first portion of the initial groove; and a second etching step for etching the nonmagnetic layer by reactive ion etching, with the initial groove mask and the groove defining layer used as an etching mask, so as to complete the groove. Each of the bottom forming layer and the groove defining layer is lower in etching rate in the first and second etching steps than the nonmagnetic layer. 
     In the first etching step, the nonmagnetic layer is etched such that an initial sidewall is formed by the initial groove in a region in which the second portion is to be formed, the initial sidewall being intended to be etched in the second etching step later to thereby become a sidewall of the second portion, and such that a top surface of the bottom forming layer is exposed in the region in which the second portion is to be formed. In the step of forming the initial groove mask, the initial groove mask is formed such that the initial groove mask covers, in addition to the first portion, part of the top surface of the bottom forming layer exposed by the initial groove in the region in which the second portion is to be formed. In the second etching step, the initial sidewall is etched to thereby form the sidewall of the second portion. 
     In the second manufacturing method of the present invention, the nonmagnetic layer may be formed of Al 2 O 3 , and each of the bottom forming layer and the groove defining layer may be formed of a nonmagnetic metal material. 
     In the second manufacturing method of the present invention, in the second etching step, the initial sidewall may be etched so that an angle formed by the sidewall of the second portion with respect to a direction perpendicular to the top surface of the substrate will be smaller than an angle formed by the initial sidewall with respect to the direction perpendicular to the top surface of the substrate. 
     According to the first or second manufacturing method of the present invention, the step of forming the groove in the nonmagnetic layer includes the first etching step, the step of forming the initial groove mask, and the second etching step. This makes it possible to form a pole layer that is capable of preventing the problems resulting from the skew, capable of defining the track width with precision, and capable of improving the write characteristics. In particular, the second etching step of the present invention prevents formation of a sidewall-protecting film on the sidewall of the second portion of the groove, and thereby serves to suppress an increase in the angle formed by the sidewall of the second portion with respect to the direction perpendicular to the top surface of the substrate. This allows the above-listed advantageous effects of the invention to be exerted more remarkably. 
     Other objects, features and advantages of the present invention will become fully apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of the medium facing surface of a magnetic head of a first embodiment of the invention. 
         FIG. 2  is a cross-sectional view showing the configuration of the magnetic head of the first embodiment of the invention. 
         FIG. 3  is a top view of a pole layer of the magnetic head of the first embodiment of the invention. 
         FIG. 4  is a perspective view showing a portion of the pole layer of the magnetic head of the first embodiment of the invention. 
         FIG. 5A  to  FIG. 5C  are illustrative views showing a groove of an encasing layer of the magnetic head of the first embodiment of the invention. 
         FIG. 6A  to  FIG. 6C  are illustrative views showing a step of a method of forming the groove of the encasing layer of the first embodiment of the invention. 
         FIG. 7A  to  FIG. 7C  are illustrative views showing a step that follows the step of  FIG. 6A  to  FIG. 6C . 
         FIG. 8A  to  FIG. 8C  are illustrative views showing a step that follows the step of  FIG. 7A  to  FIG. 7C . 
         FIG. 9A  to  FIG. 9C  are illustrative views showing a step that follows the step of  FIG.8A  to  FIG. 8C . 
         FIG. 10A  to  FIG. 10C  are illustrative views showing a step that follows the step of  FIG. 9A  to  FIG. 9C . 
         FIG. 11A  to  FIG. 11C  are illustrative views showing a step of a groove-forming method of a comparative example. 
         FIG. 12A  to  FIG. 12C  are illustrative views showing a step that follows the step of  FIG. 11A  to  FIG. 11C . 
         FIG. 13A  to  FIG. 13C  are illustrative views showing a step that follows the step of  FIG. 12A  to  FIG. 12C . 
         FIG. 14A  to  FIG. 14C  are illustrative views showing a step that follows the step of  FIG. 13A  to  FIG. 13C . 
         FIG. 15A  to  FIG. 15C  are illustrative views showing a step of a method of forming the groove of the encasing layer of a second embodiment of the invention. 
         FIG. 16A  to  FIG. 16C  are illustrative views showing a step that follows the step of  FIG. 15A  to  FIG. 15C . 
         FIG. 17A  to  FIG. 17C  are illustrative views showing a step that follows the step of  FIG. 16A  to  FIG. 16C . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Embodiments of the present invention will now be described in detail with reference to the drawings. Reference is first made to  FIG. 1  and  FIG. 2  to describe the configuration of a magnetic head for perpendicular magnetic recording of a first embodiment of the invention.  FIG. 1  is a front view of the medium facing surface of the magnetic head for perpendicular magnetic recording of the first embodiment.  FIG. 2  is a cross-sectional view showing the configuration of the magnetic head for perpendicular magnetic recording of the first embodiment.  FIG. 2  shows a cross section perpendicular to the medium facing surface and the top surface of the substrate. In  FIG. 2  the arrow marked with T shows the direction of travel of the recording medium. 
     As shown in  FIG. 1  and  FIG. 2 , the magnetic head for perpendicular magnetic recording (hereinafter simply referred to as the magnetic head) of the present embodiment includes: a substrate  1  made of a ceramic material such as aluminum oxide and titanium carbide (Al 2 O 3 —TiC); an insulating layer  2  made of an insulating material such as alumina (Al 2 O 3 ) and disposed on the substrate  1 ; a bottom shield layer  3  made of a magnetic material and disposed on the insulating layer  2 ; a bottom shield gap film  4  that is an insulating film disposed on the bottom shield layer  3 ; a magnetoresistive (MR) element  5  as a read element disposed on the bottom shield gap film  4 ; a top shield gap film  6  that is an insulating film disposed on the MR element  5 ; and a first top shield layer  7  made of a magnetic material and disposed on the top shield gap film  6 . 
     An end of the MR element  5  is located in the medium facing surface  30  that faces toward the recording medium. The MR element  5  may be an element made of a magneto-sensitive film that exhibits a magnetoresistive effect, such as an AMR (anisotropic magnetoresistive) element, a GMR (giant magnetoresistive) element, or a TMR (tunneling magnetoresistive) element. The GMR element may be of a CIP (current-in-plane) type wherein a current used for detecting magnetic signals is fed in a direction nearly parallel to the planes of layers constituting the GMR element, or may be of a CPP (current-perpendicular-to-plane) type wherein a current used for detecting magnetic signals is fed in a direction nearly perpendicular to the planes of the layers constituting the GMR element. 
     The magnetic head further includes a nonmagnetic layer  81  and a second top shield layer  82  that are disposed in this order on the first top shield layer  7 . The nonmagnetic layer  81  is made of a nonmagnetic material such as alumina. The second top shield layer  82  is made of a magnetic material. The portion from the bottom shield layer  3  to the second top shield layer  82  makes up a read head. 
     The magnetic head further includes: an insulating layer  83  made of an insulating material and disposed on the second top shield layer  82 ; a coil  9  disposed on the insulating layer  83 ; an insulating layer  10  made of an insulating material and disposed around the coil  9  and in the space between the respective adjacent turns of the coil  9 ; and an insulating layer  11  made of an insulating material and disposed around the insulating layer  10 . The coil  9  is planar spiral-shaped. The top surfaces of the coil  9  and the insulating layers  10  and  11  are planarized. The insulating layers  83  and  11  are made of alumina, for example. The insulating layer  10  is made of photoresist, for example. The coil  9  is made of a conductive material such as copper. 
     The magnetic head further includes: a nonmagnetic layer  41  made of a nonmagnetic material and disposed on the planarized top surfaces of the coil  9  and the insulating layers  10  and  11 ; a bottom forming layer  42  disposed on the nonmagnetic layer  41 ; and an encasing layer  43  disposed on the bottom forming layer  42 . The nonmagnetic layer  41  is made of alumina, for example. The bottom forming layer  42  can be made of, for example, a nonmagnetic metal material such as Ru, NiB, NiP, NiCr, Pd. V, Cr, Nb, Te, Rh, Ir, Re, Rb, Cs or NiCu. The encasing layer  43  has a groove  43   a  that opens at the top surface of the encasing layer  43  and that accommodates a pole layer described later. The encasing layer  43  is made of, for example, an insulating material such as alumina, silicon oxide (SiO x ) or silicon oxynitride (SiON). 
     The magnetic head further includes a groove defining layer  13  disposed on the top surface of the encasing layer  43 . The groove defining layer  13  is a layer for defining the shape of the groove  43   a . The groove defining layer  13  has a penetrating opening  13   a  that has a shape corresponding to the plane geometry of the groove  43   a . The edge of the opening  13   a  is located directly on the edge of the groove  43   a  located at the top surface of the encasing layer  43 . The groove defining layer  13  is made of, for example, a nonmagnetic metal material such as Ta, Mo, W, Ti, Ru, Rh, Re, Pt, Pd, Ir, NiCr, NiP, NiB, WSi 2 , TaSi 2 , TiSi 2 , TiN or TiW. 
     The magnetic head further includes a nonmagnetic film  14  made of a nonmagnetic material, a polishing stopper layer  15 , and the pole layer  16  that are disposed in the groove  43   a  of the encasing layer  43  and in the opening  13   a  of the groove defining layer  13 . The nonmagnetic film  14  is disposed to touch the surface of the groove  43   a . The pole layer  16  is disposed apart from the surface of the groove  43   a . In the groove  43   a  the nonmagnetic film  14  is disposed to be sandwiched between the encasing layer  43  and the pole layer  16 . In the groove  43   a  the polishing stopper layer  15  is disposed to be sandwiched between the nonmagnetic film  14  and the pole layer  16 . 
     The nonmagnetic film  14  is made of a nonmagnetic material. The material of the nonmagnetic film  14  may be an insulating material or a semiconductor material, for example. Examples of the insulating material usable as the material of the nonmagnetic film  14  include alumina, silicon oxide (SiO x ), and silicon oxynitride (SiON). Examples of the semiconductor material usable as the material of the nonmagnetic film  14  include polycrystalline silicon and amorphous silicon. 
     The polishing stopper layer  15  is made of a nonmagnetic metal material. The polishing stopper layer  15  may be made of the same nonmagnetic metal material as that used for the groove defining layer  13 . 
     The pole layer  16  is made of a magnetic metal material. The pole layer  16  can be made of any of CoFeN, CoNiFe, NiFe, and CoFe, for example. 
     The magnetic head further includes a gap layer  18  disposed on the top surfaces of the groove defining layer  13 , the nonmagnetic film  14 , the polishing stopper layer  15  and the pole layer  16 . The gap layer  18  has an opening located away from the medium facing surface  30 . The gap layer  18  may be made of an insulating material such as alumina or a nonmagnetic metal material such as Ru, NiCu, Ta, W, NiB or NiP. 
     The magnetic head further includes a shield  20 . The shield  20  includes: a first layer  20 A disposed on the gap layer  18 ; a second layer  20 C disposed on the first layer  20 A; a yoke layer  20 B disposed on a portion of the pole layer  16  where the opening of the gap layer  18  is formed; a coupling layer  20 D disposed on the yoke layer  20 B; and a third layer  20 E disposed to couple the second layer  20 C to the coupling layer  20 D. The first layer  20 A, the yoke layer  20 B, the second layer  20 C, the coupling layer  20 D and the third layer  20 E are each made of a magnetic material. These layers  20 A to  20 E can be made of any of CoFeN, CoNiFe, NiFe and CoFe, for example. 
     The magnetic head further includes a nonmagnetic layer  21  made of a nonmagnetic material and disposed around the yoke layer  20 B. Part of the nonmagnetic layer  21  is disposed on a side of the first layer  20 A. The nonmagnetic layer  21  is made of, for example, an inorganic insulating material such as alumina or coating glass. Alternatively, the nonmagnetic layer  21  may be made up of a layer of a nonmagnetic metal material and a layer of an insulating material disposed thereon. In this case, the nonmagnetic metal material may be, for example, a refractory metal such as Ta, Mo, Nb, W, Cr, Ru, NiCu, Pd or Hf. 
     The magnetic head further includes: an insulating layer  22  disposed on regions of the top surfaces of the yoke layer  20 B and the nonmagnetic layer  21  above which a coil  23  described later is to be disposed; the coil  23  disposed on the insulating layer  22 ; an insulating layer  24  disposed around the coil  23  and in the space between the respective adjacent turns of the coil  23 ; an insulating layer  25  disposed around the insulating layer  24 ; and an insulating layer  26  disposed on the coil  23  and the insulating layers  24  and  25 . The coil  23  is planar spiral-shaped. Part of the coil  23  passes between the second layer  20 C and the coupling layer  20 D. The coil  23  is made of a conductive material such as copper. The top surfaces of the second layer  20 C, the coupling layer  20 D and the insulating layers  24  and  25  are planarized. The insulating layer  24  is made of photoresist, for example. The insulating layers  22 ,  25  and  26  are made of alumina, for example. 
     The portion from the coil  9  to the third layer  20 E of the shield  20  makes up a write head. The magnetic head further includes a protection layer  27  formed to cover the shield  20 . The protection layer  27  is made of alumina, for example. 
     As described so far, the magnetic head of the present embodiment includes the medium facing surface  30  that faces toward the recording medium, the read head, and the write head. The read head and the write head are stacked on the substrate  1 . The read head is disposed backward along the direction T of travel of the recording medium (that is, disposed closer to the air inflow end of the slider), while the write head is disposed forward along the direction T of travel of the recording medium (that is, disposed closer to the air outflow end of the slider). 
     The read head includes: the MR element  5  as the read element; the bottom shield layer  3  and the top shield layer  7  for shielding the MR element  5 , portions of the shield layers  3  and  7  closer to the medium facing surface  30  being opposed to each other with the MR element  5  located in between; the bottom shield gap film  4  disposed between the MR element  5  and the bottom shield layer  3 ; and the top shield gap film  6  disposed between the MR element  5  and the top shield layer  7 . 
     The write head includes the coil  9 , the nonmagnetic layer  41 , the bottom forming layer  42 , the encasing layer  43 , the groove defining layer  13 , the nonmagnetic film  14 , the polishing stopper layer  15 , the pole layer  16 , the gap layer  18 , the shield  20 , and the coil  23 . The coils  9  and  23  generate a magnetic field corresponding to data to be written on the recording medium. The coil  9  is not an essential component of the write head and may be dispensed with. The nonmagnetic film  14  may also be dispensed with. 
     The pole layer  16  has an end face located in the medium facing surface  30 . The pole layer  16  allows a magnetic flux corresponding to the magnetic field generated by the coil  23  to pass, and generates a write magnetic field for writing the data on the recording medium by means of the perpendicular magnetic recording system. 
     The shield  20  has an end face located in the medium facing surface  30 , and is coupled to a portion of the pole layer  16  away from the medium facing surface  30 . The gap layer  18  is made of a nonmagnetic material, and is provided between the pole layer  16  and the shield  20 . 
     In the medium facing surface  30 , the end face of the shield  20  is disposed forward of the end face of the pole layer  16  along the direction T of travel of the recording medium, with a predetermined distance provided therebetween by the thickness of the gap layer  18 . The thickness of the gap layer  18  is within a range of 20 to 50 nm, for example. At least part of the coil  23  is located between the pole layer  16  and the shield  20  and insulated from the pole layer  16  and the shield  20 . 
     The encasing layer  43  has the groove  43   a  that opens at the top surface of the encasing layer  43  and that accommodates the pole layer  16 . The groove  43   a  penetrates the encasing layer  43 . The pole layer  16  is disposed in the space surrounded by the top surface of the bottom forming layer  42 , the groove  43   a  of the encasing layer  43  and the opening  13   a  of the groove defining layer  13 . In the groove  43   a  the nonmagnetic film  14  is disposed to be sandwiched between the encasing layer  43  and the pole layer  16 . In the groove  43   a  the polishing stopper layer  15  is disposed to be sandwiched between the nonmagnetic film  14  and the pole layer  16 . The nonmagnetic film  14  has a thickness within a range of 20 to 80 nm, for example. However, the thickness of the nonmagnetic film  14  is not limited to this range and can be appropriately chosen according to the track width. The polishing stopper layer  15  has a thickness within a range of 20 to 80 nm, for example. 
     The shield  20  includes: the first layer  20 A disposed adjacent to the gap layer  18 ; the second layer  20 C located on a side of the first layer  20 A farther from the gap layer  18 ; the yoke layer  20 B disposed on the portion of the pole layer  16  where the opening of the gap layer  18  is formed; the coupling layer  20 D disposed on the yoke layer  20 B; and the third layer  20 E disposed to couple the second layer  20 C to the coupling layer  20 D. The second layer  20 C is disposed between the medium facing surface  30  and at least part of the coil  23 . The coil  23  is wound around the coupling layer  20 D. In the example shown in  FIG. 2 , part of the yoke layer  20 B is disposed between the pole layer  16  and part of the coil  23 . However, in place of such a yoke layer  20 B, there may be provided a coupling layer that has a plane geometry the same as that of the coupling layer  20 D and that couples the pole layer  16  to the coupling layer  20 D. 
     The first layer  20 A has a first end located in the medium facing surface  30  and a second end opposite to the first end. The second layer  20 C also has a first end located in the medium facing surface  30  and a second end opposite to the first end. Throat height TH is the distance between the medium facing surface  30  and a point at which the space between the pole layer  16  and the shield  20  starts to increase as seen from the medium facing surface  30 . In the present embodiment, the throat height TH is the distance between the medium facing surface  30  and an end of the first layer  20 A farther from the medium facing surface  30 . The throat height TH is within a range of 0.05 to 0.3 μm, for example. 
     Reference is now made to  FIG. 3  and  FIG. 4  to describe the shape of the pole layer  16  in detail.  FIG. 3  is a top view of the pole layer  16 .  FIG. 4  is a perspective view showing a portion of the pole layer  16  in the vicinity of the medium facing surface  30 . 
     As shown in  FIG. 3  and  FIG. 4 , the pole layer  16  includes a track width defining portion  16 A and a wide portion  16 B. The track width defining portion  16 A has an end face located in the medium facing surface  30  and an end opposite to the end face. The wide portion  16 B is connected to the end of the track width defining portion  16 A and has a width greater than that of the track width defining portion  16 A. The width of the track width defining portion  16 A does not change substantially in accordance with the distance from the medium facing surface  30 . For example, the wide portion  16 B is equal in width to the track width defining portion  16 A at the boundary with the track width defining portion  16 A, and gradually increases in width as the distance from the medium facing surface  30  increases and then maintains a specific width to the end of the wide portion  16 B. In the present embodiment the track width defining portion  16 A is defined as a portion of the pole layer  16  that extends from the end face located in the medium facing surface  30  to the point at which the width of the pole layer  16  starts to increase. Here, the length of the track width defining portion  16 A taken in the direction perpendicular to the medium facing surface  30  is called a neck height. The neck height is within a range of 60 to 200 nm, for example. 
     As shown in  FIG. 4 , the end face of the track width defining portion  16 A located in the medium facing surface  30  has: a first side A 1  closest to the substrate  1 ; a second side A 2  opposite to the first side A 1 ; a third side A 3  connecting an end of the first side A 1  and an end of the second side A 2  to each other; and a fourth side A 4  connecting the other end of the first side A 1  and the other end of the second side A 2  to each other. The second side A 2  defines the track width. The end face of the track width defining portion  16 A located in the medium facing surface  30  has a width that decreases with decreasing distance from the first side A 1 . Each of the third side A 3  and the fourth side A 4  forms an angle of, for example, 8 to 15 degrees, with respect to the direction perpendicular to the top surface of the substrate  1 . The length of the second side A 2 , that is, the track width, is within a range of 0.05 to 0.20 μm, for example. The thickness of the pole layer  16  taken in the medium facing surface  30  is within a range of 0.15 to 0.3 μm, for example. 
     As shown in  FIG. 3 , the pole layer  16  has: a first side surface S 1  and a second side surface S 2  located opposite to each other in a first region R 1  that extends from the medium facing surface  30  to a position 10 to 300 nm away from the medium facing surface  30 ; and a third side surface S 3  and a fourth side surface S 4  located in a second region R 2  other than the first region R 1 . The first side surface S 1  and the third side surface S 3  are located on the same side as seen from the center of the pole layer  16  taken in the track width direction. The second side surface S 2  and the fourth side surface S 4  are located such that the locations of the second and fourth side surfaces S 2 , S 4  and the locations of the first and third side surfaces S 1 , S 3  are symmetric with respect to the center of the pole layer  16  taken in the track width direction. 
     The distance between the first side surface S 1  and the second side surface S 2  taken in the track width direction decreases with decreasing distance from the top surface of the substrate  1 . The distance between the third side surface S 3  and the fourth side surface S 4  taken in the track width direction may be uniform regardless of the distance from the top surface of the substrate  1 , or may decrease or increase with decreasing distance from the top surface of the substrate  1 . The angle formed by the third side surface S 3  with respect to the direction perpendicular to the top surface of the substrate  1  is smaller than the angle formed by the first side surface S 1  with respect to the direction perpendicular to the top surface of the substrate  1 . The angle formed by the fourth side surface S 4  with respect to the direction perpendicular to the top surface of the substrate  1  is smaller than the angle formed by the second side surface S 2  with respect to the direction perpendicular to the top surface of the substrate  1 . In the case where the distance between the third side surface S 3  and the fourth side surface S 4  taken in the track width direction decreases with decreasing distance from the top surface of the substrate  1 , it is preferred that each of the angle formed by the third side surface S 3  with respect to the direction perpendicular to the top surface of the substrate  1  and the angle formed by the fourth side surface S 4  with respect to the direction perpendicular to the top surface of the substrate  1  be as close as possible to zero degree. 
       FIG. 4  shows an example in which the distance from the medium facing surface  30  to the boundary between the first region R 1  and the second region R 2  is greater than the distance from the medium facing surface  30  to the boundary between the track width defining portion  16 A and the wide portion  16 B, that is, the neck height. However, the distance from the medium facing surface  30  to the boundary between the first region R 1  and the second region R 2  may be equal to or smaller than the neck height. 
     Reference is now made to  FIG. 5A  to  FIG. 5C  to describe the bottom forming layer  42 , the encasing layer  43  and the groove defining layer  13  in detail.  FIG. 5A  is a top view of a stack of the bottom forming layer  42 , the encasing layer  43  and the groove defining layer  13 .  FIG. 5B  is a cross-sectional view of the stack of  FIG. 5A  taken along line  5 B- 5 B.  FIG.5C  is a cross-sectional view of the stack of  FIG. 6A  taken along line  5 C- 5 C. 
     As shown in  FIG. 5A  to  FIG. 5C , the encasing layer  43  is disposed on the bottom forming layer  42 , and has the groove  43   a  that opens at the top surface of the encasing layer  43  to accommodate the pole layer  16 . The groove defining layer  13  is disposed on the encasing layer  43 , and has the penetrating opening  13   a  that has a shape corresponding to the plane geometry of the groove  43   a . The edge of the opening  13   a  is located directly on the edge of the groove  43   a  located at the top surface of the encasing layer  43 . 
     The groove  43   a  of the encasing layer  43  includes: a first portion  43   a   1  for accommodating at least part of the track width defining portion  16 A of the pole layer  16 ; and a second portion  43   a   2  for accommodating at least part of the wide portion  16 B of the pole layer  16 . The second portion  43   a   2  is farther from the medium facing surface  30  than the first portion  43   a   1 . The first portion  43   a   1  is to accommodate the portion of the pole layer  16  located in the region R 1  shown in  FIG. 4 . The second portion  43   a   2  is to accommodate the portion of the pole layer  16  located in the region R 2  shown in  FIG. 4 . The first portion  43   a   1  has a width that decreases with decreasing distance from the top surface of the substrate  1 . Of the groove  43   a , at least the second portion  43   a   2  penetrates the encasing layer  43 .  FIG. 5A  to  FIG. 5C  show an example in which the whole of the groove  43   a  penetrates the encasing layer  43 . 
     Here, as shown in  FIG. 5B , the first portion  43   a   1  has a sidewall SW 1  that forms an angle θ 1  with respect to the direction perpendicular to the top surface of the substrate  1 . The angle θ 1  is equal or nearly equal to the angle formed by each of the third side A 3  and the fourth side A 4  shown in  FIG. 4  with respect to the direction perpendicular to the top surface of the substrate  1 . The angle θ 1  is within the range of 8 to 15 degrees, for example. 
     The second portion  43   a   2  has a sidewall SW 2  that may be perpendicular to the top surface of the substrate  1  or may be inclined with respect to the direction perpendicular to the top surface of the substrate  1 . Here, as shown in  FIG. 5C , θ 2  represents the angle formed by the sidewall SW 2  of the second portion  43   a   2  with respect to the direction perpendicular to the top surface of the substrate  1 . The angle θ 2  is smaller than the angle θ 1 . The angle θ 2  is within a range of 0 degree to 3.5 degrees, for example. 
     Reference is now made to  FIG. 6A  to  FIG. 10C  to describe a method of manufacturing the magnetic head of the present embodiment.  FIG. 6A  to  FIG. 10C  are illustrative views showing a method of forming the groove of the encasing layer of the embodiment. The portions closer to the substrate  1  than is the bottom forming layer  42  are omitted in  FIG. 6A  to  FIG. 10C . 
     In the method of manufacturing the magnetic head of the embodiment, first, as shown in  FIG. 2 , the insulating layer  2 , the bottom shield layer  3  and the bottom shield gap film  4  are formed in this order on the substrate  1 . Next, the MR element  5  and leads (not shown) connected to the MR element  5  are formed on the bottom shield gap film  4 . Next, the MR element  5  and the leads are covered with the top shield gap film  6 . Next, the top shield layer  7 , the nonmagnetic layer  81 , the second top shield layer  82  and the insulating layer  83  are formed in this order on the top shield gap film  6 . Next, the coil  9  and the insulating layers  10  and  11  are formed on the insulating layer  83 . Next, the top surfaces of the coil  9  and the insulating layers  10  and  11  are planarized by, for example, chemical mechanical polishing (hereinafter referred to as CMP). Next, the nonmagnetic layer  41  is formed on the planarized top surfaces of the coil  9  and the insulating layers  10  and  11 . 
       FIG. 6A  to  FIG. 6C  show the next step.  FIG. 6A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 6B  is a cross-sectional view of the stack of  FIG. 6A  taken along line  6 B- 6 B.  FIG. 6C  is a cross-sectional view of the stack of  FIG. 6A  taken along line  6 C- 6 C. In this step, first, the bottom forming layer  42  is formed on the nonmagnetic layer  41 . Next, a nonmagnetic layer  43 P is formed on the bottom forming layer  42 . The nonmagnetic layer  43 P will undergo formation of the groove  43   a  therein later and will thereby become the encasing layer  43 . Next, a nonmagnetic metal layer  13 P is formed on the nonmagnetic layer  43 P. The nonmagnetic metal layer  13 P will undergo formation of the opening  13   a  therein later and will thereby become the groove defining layer  13 . 
     Next, a photoresist mask  51  to be used for forming the opening  13   a  in the nonmagnetic metal layer  13 P is formed on the nonmagnetic metal layer  13 P. The photoresist mask  51  has an opening  51   a  having a shape corresponding to the opening  13   a  and the groove  43   a . The photoresist mask  51  is formed by patterning a photoresist layer by photolithography. Next, the nonmagnetic metal layer  13 P is selectively etched using the photoresist mask  51 , whereby the penetrating opening  13   a  is formed in the nonmagnetic metal layer  13 P. This etching is performed by, for example, ion beam etching (hereinafter referred to as IBE). Next, the photoresist mask  51  is removed.  FIG. 7A  to  FIG. 7C  show the state in which the opening  13   a  has been formed in the nonmagnetic metal layer  13 P. 
       FIG. 7A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 7B  is a cross-sectional view of the stack of  FIG. 7A  taken along line  7 B- 7 B.  FIG. 7C  is a cross-sectional view of the stack of  FIG. 7A  taken along line  7 C- 7 C. As shown in  FIG. 7A  to  FIG. 7C , the nonmagnetic metal layer  13 P becomes the groove defining layer  13  as a result of the formation of the opening  13   a.    
     Next, photoresist masks  52  and  53  are formed on the groove defining layer  13 . The photoresist masks  52  and  53  are formed at the same time by patterning a photoresist layer by photolithography. The photoresist mask  52  has a penetrating opening  52   a  wider than the opening  13   a  of the groove defining layer  13 , and is formed on the groove defining layer  13  such that the opening  13   a  is exposed from the opening  52   a . The distance between the edge of the opening  13   a  and the edge of the opening  52   a  is preferably within a range of 0.1 to 0.3 μm. The photoresist mask  53  is formed into an island shape on the groove defining layer  13  in a region in which the second portion  43   a   2  of the groove  43   a  is to be formed, except a ring-like region near the edge of the opening  13   a . The distance between the perimeter of the photoresist mask  53  and the edge of the opening  13   a  is preferably within a range of 0.1 to 1 μm. 
     Next, the nonmagnetic layer  43 P is taper-etched by reactive ion etching (hereinafter referred to as RIE), with the photoresist masks  52  and  53  and the groove defining layer  13  used as etching masks. This step will be called a first etching step. Next, the photoresist masks  52  and  53  are removed.  FIG. 8A  to  FIG. 8C  show the state after the removal of the photoresist masks  52  and  53 . 
       FIG. 8A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 8B  is a cross-sectional view of the stack of  FIG. 8A  taken along line  8 B- 8 B.  FIG. 8C  is a cross-sectional view of the stack of  FIG. 8A  taken along line  8 C- 8 C. As shown in  FIG. 8A  to  FIG. 8C , the taper-etching of the nonmagnetic layer  43 P results in formation of an initial groove  43 Pa in the nonmagnetic layer  43 P. In the case where the nonmagnetic layer  43 P is made of alumina (Al 2 O 3 ), an etching gas containing at least BCl 3  out of BCl 3  and Cl 2  and further containing CF 4  or N 2  is used for RIE to taper-etch the nonmagnetic layer  43 P in the first etching step. BCl 3  and Cl 2  are main components that contribute to the etching of the nonmagnetic layer  43 P. CF 4  and N 2  are gases for forming, during etching of the nonmagnetic layer  43 P, a sidewall-protecting film on the sidewall of the groove formed by the etching. The etching gas containing CF 4  or N 2  serves to form the sidewall-protecting film on the sidewall of the groove during the etching of the nonmagnetic layer  43 P, thereby serving to accomplish taper-etching of the nonmagnetic layer  43 P. 
     The edge of the opening  13   a  of the groove defining layer  13  is located directly on the outer edge of the initial groove  43 Pa located at the top surface of the nonmagnetic layer  43 P. The initial groove  43 Pa includes the first portion  43   a   1  of the groove  43   a , and an initial sidewall forming portion  43 Pa 2 . The initial sidewall forming portion  43 Pa 2  is formed in a ring-like region near the perimeter of the region in which the second portion  43   a   2  of the groove  43   a  is to be formed. After the first etching step, as shown in  FIG. 8A  to  FIG. 8C , a portion of the nonmagnetic layer  43 P, that is, the portion of the nonmagnetic layer  43 P that was covered with the photoresist mask  53  in the first etching step, remains on the bottom forming layer  42  in a region that is inward relative to the initial sidewall forming portion  43 Pa 2 . As shown in  FIG. 8C , the initial sidewall forming portion  43 Pa 2  has an initial sidewall SW 2 P that will be etched in a second etching step to be performed later and will thereby become the sidewall SW 2  of the second portion  43   a   2 . 
       FIG. 9A  to  FIG. 9C  show the next step.  FIG. 9A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 9B  is a cross-sectional view of the stack of  FIG. 9A  taken along line  9 B- 9 B.  FIG. 9C  is a cross-sectional view of the stack of  FIG. 9A  taken along line  9 C- 9 C. In this step, first formed is an initial groove mask  54  that covers the first portion  43   a   1  of the initial groove  43 Pa. The initial groove mask  54  is formed by patterning a photoresist layer by photolithography. Next, the nonmagnetic layer  43 P is etched by RIE with the initial groove mask  54  and the groove defining layer  13  used as an etching mask. This step will be called the second etching step. Next, the initial groove mask  54  is removed.  FIG. 10A  to  FIG. 10C  show the state after the removal of the initial groove mask  54 . 
       FIG. 10A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 10B  is a cross-sectional view of the stack of  FIG. 10A  taken along line  10 B- 10 B.  FIG. 10C  is a cross-sectional view of the stack of  FIG. 10A  taken along line  10 C- 10 C. As shown in  FIG. 10A  to  FIG. 10C , the groove  43   a  is completed by the second etching step. As a result of completion of the groove  43   a , the nonmagnetic layer  43 P becomes the encasing layer  43 . 
     In the second etching step, the initial sidewall SW 2 P is etched to thereby form the sidewall SW 2  of the second portion  43   a   2 , and the portion of the nonmagnetic layer  43 P remaining on the bottom forming layer  42  in the region inward relative to the initial sidewall forming portion  43 Pa 2  is removed by etching. As shown in  FIG. 9C  and  FIG. 10C , in the second etching step, the initial sidewall SW 2 P is etched so that the angle formed by the sidewall SW 2  of the second portion  43   a   2  with respect to the direction perpendicular to the top surface of the substrate  1  will be smaller than the angle formed by the initial sidewall SW 2 P with respect to the direction perpendicular to the top surface of the substrate  1 . Furthermore, in the second etching step, an etching gas containing BCl 3  and Cl 2 , for example, is used for RIE to etch the nonmagnetic layer  43 P. 
     Process steps subsequent to the completion of the groove  43   a  will be described with reference to  FIG. 1  and  FIG. 2 . Subsequent to the completion of the groove  43   a , first, the nonmagnetic film  14  is formed over the entire top surface of the stack shown in  FIG. 10A  to  FIG. 10C . The nonmagnetic film  14  is also formed in the groove  43   a . The nonmagnetic film  14  is formed by sputtering or chemical vapor deposition (hereinafter referred to as CVD), for example. The thickness of the nonmagnetic film  14  is precisely controllable. In the case of forming the nonmagnetic film  14  by CVD, it is preferred to employ, in particular, so-called atomic layer CVD (hereinafter referred to as ALCVD) in which formation of a single atomic layer is repeated. In this case, it is possible to control the thickness of the nonmagnetic film  14  with higher precision. In the case of forming the nonmagnetic film  14  by ALCVD, it is preferable to use alumina, in particular, as the material of the nonmagnetic film  14 . In the case of using a semiconductor material to form the nonmagnetic film  14 , it is preferred that the nonmagnetic film  14  be formed by ALCVD at low temperatures (around 200° C.) or by low-pressure CVD at low temperatures. The semiconductor material for use as the material of the nonmagnetic film  14  is preferably undoped polycrystalline silicon or amorphous silicon. 
     Next, the polishing stopper layer  15  is formed over the entire top surface of the stack by, for example, sputtering or ALCVD. The polishing stopper layer  15  is also formed in the groove  43   a . The polishing stopper layer  15  indicates the level where to stop polishing in a polishing step to be performed later. 
     Next, a magnetic layer (not shown) that will become the pole layer  16  later is formed. This magnetic layer is formed such that the top surface thereof is located higher than the top surfaces of the groove defining layer  13 , the nonmagnetic film  14  and the polishing stopper layer  15 . The magnetic layer may be formed by frame plating or by making an unpatterned plating layer and then patterning the plating layer through etching. 
     Next, a coating layer made of, for example, alumina, is formed over the entire top surface of the stack. Next, the coating layer and the magnetic layer are polished by, for example, CMP, until the polishing stopper layer  15  becomes exposed, and the top surfaces of the polishing stopper layer  15  and the magnetic layer are thereby planarized. When CMP is employed to polish the coating layer and the magnetic layer, such a slurry is used that polishing is stopped when the polishing stopper layer  15  becomes exposed, such as an alumina-base slurry. 
     Next, a portion of the polishing stopper layer  15  exposed at the top surface of the stack is selectively removed by RIE or IBE, for example. Next the nonmagnetic film  14 , the polishing stopper layer  15  and the magnetic layer are polished by, for example, CMP, until the groove defining layer  13  becomes exposed, and the top surfaces of the groove defining layer  13 , the nonmagnetic film  14 , the polishing stopper layer  15  and the magnetic layer are thereby planarized. As a result, the remainder of the magnetic layer becomes the pole layer  16 . When CMP is employed to polish the nonmagnetic film  14 , the polishing stopper layer  15  and the magnetic layer, such a slurry is used that polishing is stopped when the groove defining layer  13  becomes exposed, such as an alumina-base slurry. It is possible to control the thickness of the pole layer  16  with precision by stopping the polishing when the groove defining layer  13  becomes exposed, as thus described. 
     Next, the gap layer  18  is formed over the entire top surface of the stack. The gap layer  18  is formed by sputtering or CVD, for example. In the case of forming the gap layer  18  by CVD, it is preferred to employ ALCVD, in particular. In the case of forming the gap layer  18  by ALCVD, it is preferred to use alumina, in particular, as the material of the gap layer  18 . 
     Next, a portion of the gap layer  18  away from the medium facing surface  30  is selectively etched to form an opening in the gap layer  18 . Next, the first layer  20 A is formed on the gap layer  18 , and the yoke layer  20 B is formed on a portion of the pole layer  16  where the opening of the gap layer  18  is formed. The first layer  20 A and the yoke layer  20 B may be formed by frame plating or by making a magnetic layer through sputtering and then selectively etching this magnetic layer. Next, the nonmagnetic layer  21  is formed over the entire top surface of the stack. Next, the nonmagnetic layer  21  is polished by, for example, CMP, until the first layer  20 A and the yoke layer  20 B become exposed, and the top surfaces of the first layer  20 A, the yoke layer  20 B and the nonmagnetic layer  21  are thereby planarized. 
     Next, the insulating layer  22  is formed on regions of the top surfaces of the yoke layer  20 B and the nonmagnetic layer  21  above which the coil  23  is to be disposed. Next, the coil  23  is formed by, for example, frame plating, such that at least part of the coil  23  is disposed on the insulating layer  22 . Next, the second layer  20 C and the coupling layer  20 D are formed by frame plating, for example. Alternatively, the coil  23  may be formed after the second layer  20 C and the coupling layer  20 D are formed. 
     Next, the insulating layer  24  made of, for example, photoresist, is selectively formed around the coil  23  and in the space between the respective adjacent turns of the coil  23 . Next, the insulating layer  25  is formed over the entire top surface of the stack. Next, the insulating layer  25  is polished by, for example, CMP, until the second layer  20 C, the coupling layer  20 D and the coil  23  become exposed, and the top surfaces of the second layer  20 C, the coupling layer  20 D, the coil  23 , and the insulating layers  24  and  25  are thereby planarized. 
     Next, the insulating layer  26  is formed on the coil  23  and the insulating layers  24  and  25 . Next, the third layer  20 E is formed by frame plating, for example. The shield  20  is thus completed. 
     Next, the protection layer  27  is formed to cover the entire top surface of the stack. Wiring, terminals and so on are then formed on the protection layer  27 , the substrate is cut into sliders, and processes including lapping of the medium facing surface  30  and fabrication of flying rails are performed to thereby complete the magnetic head. 
     The functions and effects of the magnetic head of the present embodiment will now be described. In the magnetic head, the write head writes data on a recording medium while the read head reads data written on the recording medium. In the write head, the coil  23  generates a magnetic field that corresponds to data to be written on the recording medium. The pole layer  16  and the shield  20  form a magnetic path for passing a magnetic flux corresponding to the magnetic field generated by the coil  23 . The pole layer  16  allows the magnetic flux corresponding to the magnetic field generated by the coil  23  to pass, and generates a write magnetic field used for writing the data on the recording medium by means of the perpendicular magnetic recording system. The shield  20  takes in a disturbance magnetic field applied from outside the magnetic head to the magnetic head. It is thereby possible to prevent erroneous writing on the recording medium caused by the disturbance magnetic field intensively taken into the pole layer  16 . The shield  20  also has a function of returning a magnetic flux that has been generated from the end face of the pole layer  16  (the track width defining portion  16 A) located in the medium facing surface  30  and that has magnetized the recording medium. 
     According to the present embodiment, in the medium facing surface  30 , the end face of the shield  20  is located forward of the end face of the pole layer  16  along the direction T of travel of the recording medium (that is, located closer to the air outflow end of the slider), with a specific small distance provided therebetween by the gap layer  18 . The position of an end of the bit pattern to be written on the recording medium is determined by the position of the end of the pole layer  16  that is closer to the gap layer  18  and located in the medium facing surface  30 . The shield  20  takes in a magnetic flux that is generated from the end face of the pole layer  16  located in the medium facing surface  30  and that expands in directions except the direction perpendicular to the plane of the recording medium, so as to prevent this flux from reaching the recording medium. It is thereby possible to prevent a direction of magnetization of the bit pattern already written on the recording medium from being changed due to the effect of the above-mentioned flux. The present embodiment thereby makes it possible to improve linear recording density. 
     According to the present embodiment, as shown in  FIG. 4 , the end face of the track width defining portion  16 A located in the medium facing surface  30  has a width that decreases with decreasing distance from the first side A 1 , that is, with decreasing distance from the top surface of the substrate  1 . This makes it possible to prevent the problems resulting from the skew. 
     In the present embodiment, the pole layer  16  is disposed in the groove  43   a  of the encasing layer  43  made of a nonmagnetic material, with the nonmagnetic film  14  and the polishing stopper layer  15  disposed between the pole layer  16  and the groove  43   a . The width of the pole layer  16  is therefore smaller than that of the groove  43   a . This makes it easy to form the groove  43   a  and to reduce the width of the pole layer  16  and the width of the top surface of the track width defining portion  16 A that defines the track width, in particular. As a result, according to the embodiment, it is possible to easily implement a track width that is smaller than the minimum track width that can be formed by photolithography, and to control the track width with accuracy. 
     In the present embodiment, the pole layer  16  has: the first and second side surfaces S 1  and S 2  located opposite to each other in the first region R 1  that extends from the medium facing surface  30  to the position 10 to 300 nm away from the medium facing surface  30 ; and the third and fourth side surfaces S 3  and S 4  located in the second region R 2  other than the first region R 1 . The distance between the first side surface S 1  and the second side surface S 2  taken in the track width direction decreases with decreasing distance from the top surface of the substrate  1 . The angle formed by the third side surface S 3  with respect to the direction perpendicular to the top surface of the substrate  1  is smaller than the angle formed by the first side surface S 1  with respect to the direction perpendicular to the top surface of the substrate  1 . The angle formed by the fourth side surface S 4  with respect to the direction perpendicular to the top surface of the substrate  1  is smaller than the angle formed by the second side surface S 2  with respect to the direction perpendicular to the top surface of the substrate  1 . According to the present embodiment, the area of the cross section of the wide portion  16 B of the pole layer  16  perpendicular to the direction in which magnetic flux flows is greater as compared with a case in which the angle formed by the third side surface S 3  with respect to the direction perpendicular to the top surface of the substrate  1  is equal to the angle formed by the first side surface Si with respect to the direction perpendicular to the top surface of the substrate  1 , and the angle formed by the fourth side surface S 4  with respect to the direction perpendicular to the top surface of the substrate  1  is equal to the angle formed by the second side surface S 2  with respect to the direction perpendicular to the top surface of the substrate  1 . Consequently, the present embodiment makes it possible to allow a magnetic flux of greater magnitude to pass through the portion near the boundary between the track width defining portion  16 A and the wide portion  16 B, in particular, thereby making it possible to improve the write characteristics such as overwrite property. Furthermore, according to the present embodiment, since it is unnecessary to extremely reduce the neck height in order to improve the write characteristics, it becomes possible to precisely define the track width by allowing a great neck height. 
     A description will now be given on the advantageous effects of the groove-forming method of the present embodiment in comparison with a groove-forming method of a comparative example. Reference is now made to  FIG. 11A  to  FIG. 14C  to describe the groove-forming method of the comparative example. The groove-forming method of the comparative example is the same as that of the present embodiment up to the step of forming the penetrating opening  13   a  in the nonmagnetic metal layer  13 P. The nonmagnetic metal layer  13 P becomes the groove defining layer  13  as a result of the formation of the opening  13   a.    
       FIG. 11A  to  FIG. 11C  show the next step.  FIG. 11A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 11B  is a cross-sectional view of the stack of  FIG. 11A  taken along line  11 B- 11 B.  FIG. 11C  is a cross-sectional view of the stack of  FIG. 11A  taken along line  11 C- 11 C. In this step, first, a photoresist mask  62  is formed on the groove defining layer  13 . The photoresist mask  62  is formed by patterning a photoresist layer by photolithography. The photoresist mask  62  has a penetrating opening  62   a  wider than the opening  13   a  of the groove defining layer  13 , and is formed on the groove defining layer  13  such that the opening  13   a  is exposed from the opening  62   a.    
     Next, the nonmagnetic layer  43 P is taper-etched by RIE with the photoresist mask  62  and the groove defining layer  13  used as an etching mask. This step will be called a first etching step. Next, the photoresist mask  62  is removed.  FIG. 12A  to  FIG. 12C  show the state after the removal of the photoresist mask  62 . 
       FIG. 12A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 12B  is a cross-sectional view of the stack of  FIG. 12A  taken along line  12 B- 12 B.  FIG. 12C  is a cross-sectional view of the stack of  FIG. 12A  taken along line  12 C-  12 C. As shown in  FIG. 12A  to  FIG. 12C , the taper-etching of the nonmagnetic layer  43 P results in formation of an initial groove  43 Pa in the nonmagnetic layer  43 P. 
     The edge of the opening  13   a  of the groove defining layer  13  is located directly on the edge of the initial groove  43 Pa located at the top surface of the nonmagnetic layer  43 P. The initial groove  43 Pa includes the first portion  43   a   1  of the groove  43   a , and an initial sidewall forming portion  43 Pa 2 . The initial sidewall forming portion  43 Pa 2  of the comparative example is formed in the entire region in which the second portion  43   a   2  of the groove  43   a  is to be formed, not in the ring-like region as in the case of the initial sidewall forming portion  43 Pa 2  of the embodiment. As shown in  FIG. 12C , the initial sidewall forming portion  43 Pa 2  has an initial sidewall SW 2 P that will be etched in a second etching step to be performed later and will thereby become the sidewall SW 2  of the second portion  43   a   2 . In the comparative example, the top surface of the bottom forming layer  42  is exposed in the entire region surrounded by the initial sidewall SW 2 P. 
       FIG. 13A  to  FIG. 13C  show the next step.  FIG. 13A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 13B  is a cross-sectional view of the stack of  FIG. 13A  taken along line  13 B- 13 B.  FIG. 13C  is a cross-sectional view of the stack of  FIG. 13A  taken along line  13 C- 13 C. In this step, first formed is an initial groove mask  63  that covers the first portion  43   a   1  of the initial groove  43 Pa. The initial groove mask  63  is formed by patterning a photoresist layer by photolithography. Next, the nonmagnetic layer  43 P is etched by RIE with the initial groove mask  63  and the groove defining layer  13  used as an etching mask. This step will be called the second etching step. Next, the initial groove mask  63  is removed.  FIG. 14A  to  FIG. 14C  show the state after the removal of the initial groove mask  63 . 
       FIG. 14A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 14B  is a cross-sectional view of the stack of  FIG. 14A  taken along line  14 B- 14 B.  FIG. 14C  is a cross-sectional view of the stack of  FIG. 14A  taken along line  14 C- 14 C. As shown in  FIG. 14A  to  FIG. 14C , the groove  43   a  is completed by the second etching step. In the second etching step, the initial sidewall SW 2 P is etched to thereby form the sidewall SW 2  of the second portion  43   a   2 . As shown in  FIG. 13C  and  FIG. 14C , in the second etching step, the initial sidewall SW 2 P is etched so that the angle formed by the sidewall SW 2  of the second portion  43   a   2  with respect to the direction perpendicular to the top surface of the substrate  1  will be smaller than the angle formed by the initial sidewall SW 2 P with respect to the direction perpendicular to the top surface of the substrate  1 . 
     Here, as shown in  FIG. 14B , θ 11  represents the angle formed by the sidewall SW 1  of the first portion  43   a   1  of the comparative example with respect to the direction perpendicular to the top surface of the substrate  1 . The angle θ 11  is within a range of, for example, 8 to 15 degrees, like the angle θ 1  of the present embodiment. Furthermore, as shown in  FIG. 14C , θ 12  represents the angle formed by the sidewall SW 2  of the second portion  43   a   2  of the comparative example with respect to the direction perpendicular to the top surface of the substrate  1 . The angle θ 12  is smaller than the angle θ 11 , but greater than the angle θ 2  of the present embodiment. The angle θ 12  is within a range of, for example, 6.5 to 10 degrees. 
     As described above, according to the comparative example, the angle θ 12  is relatively great. The reason for this is as follows. According to the comparative example, the top surface of the bottom forming layer  42  is exposed in the entire region surrounded by the initial sidewall SW 2 P. As a result, during the second etching step, a larger amount of substances fly off due to etching of the bottom forming layer  42 , so that a larger amount of reaction product is generated due to those substances. The reaction product adheres to the sidewall SW 2  of the second portion  43   a   2  of the groove  43   a , and thereby forms a sidewall-protecting film. The angle θ 12  becomes relatively great due to the formation of the sidewall-protecting film. Consequently, according to the comparative example, the area of the cross section of the wide portion  16 B of the pole layer  16  perpendicular to the direction in which magnetic flux flows cannot be made sufficiently great, and as a result, it is not possible to satisfactorily improve the write characteristics such as overwrite property. 
     In contrast, according to the present embodiment, a portion of the top surface of the bottom forming layer  42  located inward relative to the initial sidewall forming portion  43 Pa 2  of the initial groove  43 Pa is covered with the nonmagnetic layer  43 P when the second etching step starts. Consequently, according to the present embodiment, it is possible to suppress formation of the sidewall-protecting film on the sidewall SW 2  of the second portion  43   a   2  of the groove  43   a  caused by the substances flying off due to etching of the bottom forming layer  42  during the second etching step. This serves to prevent an increase in the angle formed by the sidewall SW 2  with respect to the direction perpendicular to the top surface of the substrate  1 . As a result, according to the present embodiment, the advantageous effects of being capable of preventing the problems resulting from the skew, capable of defining the track width with precision and capable of improving the write characteristics are exerted more remarkably. 
     Second Embodiment 
     A description will now be given on a manufacturing method for a magnetic head of a second embodiment of the invention. The manufacturing method for the magnetic head of the second embodiment is the same as that of the embodiment up to the step of forming the penetrating opening  13   a  in the nonmagnetic metal layer  13 P. The nonmagnetic metal layer  13 P becomes the groove defining layer  13  as a result of the formation of the opening  13   a.    
       FIG. 15A  to  FIG. 15C  show the next step.  FIG. 15A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 15B  is a cross-sectional view of the stack of  FIG. 15A  taken along line  15 B- 15 B.  FIG. 15C  is a cross-sectional view of the stack of  FIG. 15A  taken along line  15 C- 15 C. In this step, first, a photoresist mask  72  is formed on the groove defining layer  13 . The photoresist mask  72  is formed by patterning a photoresist layer by photolithography. The photoresist mask  72  has a penetrating opening  72   a  wider than the opening  13   a  of the groove defining layer  13 , and is formed on the groove defining layer  13  such that the opening  13   a  is exposed from the opening  72   a . The shape of the photoresist mask  72  is the same as that of the photoresist mask  52  of the first embodiment. 
     Next, the nonmagnetic layer  43 P is taper-etched by RIE with the photoresist mask  72  and the groove defining layer  13  used as an etching mask. This step will be called a first etching step. Next, the photoresist mask  72  is removed.  FIG. 16A  to  FIG. 16C  show the state after the removal of the photoresist mask  72 . 
       FIG. 16A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 16B  is a cross-sectional view of the stack of  FIG. 16A  taken along line  16 B- 16 B.  FIG. 16C  is a cross-sectional view of the stack of  FIG. 16A  taken along line  16 C- 16 C. As shown in  FIG. 16A  to  FIG. 16C , the taper-etching of the nonmagnetic layer  43 P results in formation of an initial groove  43 Pa in the nonmagnetic layer  43 P. The conditions for RIE of the first etching step are the same as those of the first embodiment. 
     The edge of the opening  13   a  of the groove defining layer  13  is located directly on the edge of the initial groove  43 Pa located at the top surface of the nonmagnetic layer  43 P. The initial groove  43 Pa includes the first portion  43   a   1  of the groove  43   a , and an initial sidewall forming portion  43 Pa 2 . The initial sidewall forming portion  43 Pa 2  has an initial sidewall SW 2 P that will be etched in a second etching step to be performed later and will thereby become the sidewall SW 2  of the second portion  43   a   2 . In the present embodiment, the top surface of the bottom forming layer  42  is exposed in the entire region surrounded by the initial sidewall SW 2 P. 
       FIG. 17A  to  FIG. 17C  show the next step.  FIG. 17A  is a top view of a stack of layers formed in the process of manufacture of the magnetic head.  FIG. 17B  is a cross-sectional view of the stack of  FIG. 17A  taken along line  17 B- 17 B.  FIG. 17C  is a cross-sectional view of the stack of  FIG. 17A  taken along line  17 C- 17 C. In this step, an initial groove mask  73  is first formed. The initial groove mask  73  covers the first portion  43   a   1  of the initial groove  43 Pa. In the present embodiment, the initial groove mask  73  further covers a portion of the top surface of the bottom forming layer  42  exposed by the initial groove  43 Pa within a region in which the second portion  43   a   2  of the groove  43   a  is to be formed. Specifically, the initial groove mask  73  covers the top surface of the bottom forming layer  42  in the region in which the second portion  43   a   2  of the groove  43   a  is to be formed, except a ring-like region near the initial sidewall SW 2 P. The top surface of the bottom forming layer  42  is exposed in the ring-like region near the initial sidewall SW 2 P. The initial groove mask  73  is formed by patterning a photoresist layer by photolithography. 
     Next, the nonmagnetic layer  43 P is etched by RIE with the initial groove mask  73  and the groove defining layer  13  used as etching masks. This step will be called the second etching step. The conditions for RIE of the second etching step are the same as those of the first embodiment. In the second etching step, the initial sidewall SW 2 P is etched to thereby form the sidewall SW 2  of the second portion  43   a   2 . The groove  43   a  is completed by the second etching step. Next, the initial groove mask  73  is removed. The state after the removal of the initial groove mask  73  is as shown in  FIG. 10A  to  FIG. 10C , as in the first embodiment. The steps that follow are the same as the first embodiment. 
     According to the second embodiment, when the second etching step starts, the top surface of the bottom forming layer  42  is covered with the initial groove mask  73  in the region in which the second portion  43   a   2  of the groove  43   a  is to be formed, except the ring-like region near the initial sidewall SW 2 P. Consequently, according to the present embodiment, it is possible to suppress formation of the sidewall-protecting film on the sidewall SW 2  of the second portion  43   a   2  of the groove  43   a  caused by the substances flying off due to etching of the bottom forming layer  42  during the second etching step. This serves to prevent an increase in the angle formed by the sidewall SW 2  with respect to the direction perpendicular to the top surface of the substrate  1 . As a result, according to the present embodiment, the advantageous effects of being capable of preventing the problems resulting from the skew, capable of defining the track width with precision and capable of improving the write characteristics are exerted more remarkably. 
     The remainder of configuration, function and effects of the second embodiment are similar to those of the first embodiment. 
     The present invention is not limited to the foregoing embodiments but can be carried out in various modifications. For example, in each of the foregoing embodiments, a coil helically wound around the pole layer  16  may be provided in place of the planar spiral-shaped coils  9  and  23 . 
     While the foregoing embodiments have been described with reference to a magnetic head having a structure in which the read head is formed on the base body and the write head is stacked on the read head, the read head and the write head may be stacked in the reverse order. 
     It is apparent that the present invention can be carried out in various forms and modifications in the light of the foregoing descriptions. Accordingly, within the scope of the following claims and equivalents thereof, the present invention can be carried out in forms other than the foregoing most preferred embodiments.