Abstract:
In a perpendicular recording head, a notch is formed in the top write gap at a location on top of the main pole. A perpendicular head with this notched top write gap structure has less transition curvature and better writability while reducing the adjacent track interference (ATI). Also, the process used to fabricate the head ensures that the trailing edge (writing edge) of the main pole is extremely flat with no corner rounding.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to perpendicular recording on a magnetic recording disk and in particular to a perpendicular recording head having a notched wrap around shield. 
       BACKGROUND OF THE INVENTION 
       [0002]    In perpendicular recording, data are recorded on a magnetic recording disk by magnetizing the recording medium in a direction perpendicular to the surface of the disk. In this type of recording the magnetic easy axes of the magnetic grains which store the recorded data are arranged perpendicular to the disk surface, instead of parallel to the disk surface as is the case in longitudinal recording. Perpendicularly recorded data are more stable than longitudinal data, and the data can be recorded at a higher density than longitudinal data. The coercivity of the medium is higher, since the magnetic recording layer is in effect “inside the gap” between the head and a soft underlayer (SUL) that is located under the magnetic layer. 
         [0003]    In addition, for the same read head design, perpendicular data provide a greater read back amplitude. The disk has a higher magnetic moment-thickness product (MrT). For the same physical width of the read head, the magnetic read width is narrower. 
         [0004]    High track density heads require narrow pole widths. A sufficiently short flare length is necessary to maintain the write field strength of a narrow track PMR write head. As a result, the widened portion behind the flare point of the pole piece is close to the medium and can produce undesired fields to the extent that the data in adjacent tracks are erased. A high track density write head inevitably needs to balance writability and adjacent track interference (ATI). 
         [0005]    The wrap around shield (WAS) design is a very promising approach for high track density application. As shown in  FIG. 1 , the WAS design has a trailing shield  16  placed in the proximity of the trailing side of the pole  10 , separated from pole  10  by a small gap  12 , and side shields  18  which drape down along the sides of the pole  10 . In the WAS design, the fringe fields are mostly confined between the pole and side shields and therefore the fringe fields create much less interference with adjacent tracks. 
         [0006]    Nonetheless, there is a need for further improvements and fabrication method for achieving less transition curvature and less flux shunting and therefore better writability while reducing ATI. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with this invention, the effects of adjacent track interference (ATI) are reduced by the use of a perpendicular magnetic head including a wrap around shield in which a notch is formed in the top write gap on top of the main pole. In addition, a perpendicular head by the use of this notched wrap around shield structure of this invention has less transition curvature and better writability. The reduced transition curvature is due to the modification of the main pole field contour by the notched top write gap. And the better writability is due to less flux shunting to the shield. Also, the process used to fabricate the head ensures that the trailing edge of the main pole is extremely flat with no corner rounding. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention will be better understood by reference to the following drawings, which are not necessarily drawn to scale. 
           [0009]      FIG. 1  illustrates an prior art magnetic recording head with a wrap around shield, viewed from the air-bearing surface (ABS). 
           [0010]      FIG. 2  illustrates an ABS view of a magnetic recording head with a wrap around shield and a notched top write gap over the main pole in accordance with the invention. 
           [0011]      FIGS. 3A-3K  illustrate a process of fabricating a magnetic recording head with a notched top write gap. 
           [0012]      FIGS. 4A-4K  illustrate an alternative process of fabricating a magnetic recording head with a notched top write gap. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 2  illustrates a main pole with a notched top write gap above the main pole according to the invention, viewed from the air-bearing surface (ABS). Shown are a main pole  20 , a wrap around shield  22  and a top write gap  24  between main pole  20  and wrap around shield  22 . Wrap around shield  22  includes a trailing shield  26  and side shields  28 . In accordance with this invention, a notch  30  is formed in the top write gap  24  at a location on the top of main pole  20 . As is apparent from  FIG. 2 , side shields  28  extend in a direction perpendicular to trailing shield  26 . The formation of the notch  30  in the top write gap  24  creates recesses  32  in trailing shield  26  on either side of notch  30 . 
         [0014]      FIGS. 3A-3K  illustrate a process for fabricating the structure shown in  FIG. 2 . The illustrated process begins after a layer  302  of a magnetic material such as CoFe, CoNiFe, NiFe, or laminated magnetic materials such as CoFe/Cr/CoFe/NiCr, which will form the main pole, has been deposited, as shown in  FIG. 3A . The process sequence up to this point is well known to persons of skill in the art and therefore will not be described here. A photoresist mask layer  304  is then deposited on layer  302  and patterned, as shown in  FIG. 3B , to a dimension which will determine the width of the main pole, often referred to as the critical dimension (CD). Mask layer  304  may deposited as a series of sublayers. In one embodiment mask layer  304  consists of 193 TIS 250 nm, Durimide 60 nm, SiO2 100 nm, and Durimide 1000 nm. The total thickness of mask layer  304  may be ˜1.5 μm, for example. 
         [0015]    Using layer  304  as a mask, magnetic layer  302  is etched, preferably using a ion milling process, to form main pole  20 , as shown in  FIG. 3C . The ion milling undercuts the mask layer  302  to give main pole  20  a trapezoidal shape, with its sides slanted at an angle Θ. An alumina layer  306  is then deposited. As shown in  FIG. 3D , alumina layer  306  is subjected to a chemical mechanical planarization (CMP) to provide a flat surface  308 . A process using an Al 2 O 3  abrasive, APS oxidizer, BTA corrosion inhibitor, and a chemical at a pH of 10 may be employed. The resulting structure is shown in  FIG. 3E , which shows that the main pole  20  remains covered by alumina layer  306 . It should be noted in the prior art, the CMP process exposes the main pole  20  and as a result the upper corners of main pole  20  become rounded. This detracts from the performance of the finished head. 
         [0016]    A reactive ion milling process is applied to reduce the surface of alumina layer  306  and expose the top of mask layer  304 , as shown in  FIG. 3F . Following the ion milling, the surface  309  of alumina layer  306  may be 50 nm above the top surface of main pole  20 . Another photoresist mask layer  310  is deposited and patterned as shown in  FIG. 3G , with openings  312  on each side of photoresist layer  304 . Using layer  310  as a mask, another reactive ion milling process is performed, side openings  312  creating cavities  314  in alumina layer  306  on each side of main pole  20 . The resulting structure is shown in  FIG. 3H . Because the portion of photoresist layer  310  between the openings  312  is wider than main pole  20 , the ion milling process produces upward projecting ridges  316  on each side of main pole  20 . The vertical dimension of ridges  316  could be 50 nm. 
         [0017]    Mask layers  304  and  310  are then removed. A reactive ion etch (RIE) and ion milling may be applied, which causes the inner sides of ridges  316  to become slightly angled for better gap and shield deposition, as shown in  FIG. 3I . 
         [0018]    Next, as shown in  FIG. 3J , top write gap  24  is deposited on the exposed surfaces of main pole  20  and alumina layer  306 . Top write gap  24  is preferably deposited by sputtering and may have a thickness of 30 nm, for example. The top write gap material could be Rh or Ru. As is shown in  FIG. 3K , the deposition of top write gap  24  over ridges  316  forms notch  30  in top write gap  24 . 
         [0019]    Following the deposition of a seed layer (not shown), a NiFe layer  320  is deposited by plating as shown in  FIG. 3K . NiFe layer  320  fills cavities  314  and notch  30 , thereby forming side shields  28  and trailing shield  26 . Because the same photoresist layer  304  that was used to form main pole  20  is also used to define the location of ridges  316 , the resulting notch  30  is self-aligned to main pole  30 . Ridges  316  and the overlying top write gap  24  also form recesses  32  in trailing shield  26 . 
         [0020]    A CMP process may be performed on the top surface of NiFe layer  320  to form wrap around shield  22 , similar in structure to the wrap around shield shown in  FIG. 2 . An alumina overcoat (not shown) is normally deposited on the top surface of the finished trailing shield  26 . 
         [0021]      FIGS. 4A-4G  illustrate an alternative process for fabricating a notched wrap around shield having a notched top write gap in accordance with this invention. In this process, as shown in  FIGS. 4A and 4B , a hard mask layer  402 , which in this embodiment is made of alumina, is deposited on magnetic layer  302  prior to the deposition of photoresist mask layer  304 . Hard mask layer  402  may be 20 nm thick, for example. After photoresist mask layer  304  has been patterned, the exposed portions of hard mask layer  402  are etched, as shown in  FIG. 4C . The presence of alumina layer  402  on top of magnetic layer  302  allows better pole width control in the ion milling process that is used to form main pole  20 . This also permits the formation of a larger angle Θ than is possible with only a photoresist mask protecting magnetic layer  302 . As noted above, the trapezoidal shape of main pole  20  is advantageous in preventing data erasure on the adjacent track. The finished shape of main pole  20  is shown in  FIG. 4D . 
         [0022]    After main pole  20  has been formed, alumina layer  306  is deposited and planarized, as shown in  FIGS. 4E and 4F , and then subjected to a reactive ion milling process to lower the surface of alumina layer  306  so that it intersects an edge of photoresist layer  304 , as shown in  FIG. 4G . A second photoresist layer  404  is deposited and patterned with an opening  406  that encloses photoresist layer  304 . 
         [0023]    Another photoresist mask layer  404  is deposited and patterned as shown in  FIG. 4G , with openings  406  on each side of photoresist layer  304 . Using layer  406  as a mask, another ion milling process is performed, side openings  406  creating cavities  408  on each side of main pole  20 . The resulting structure is shown in  FIG. 4H . Because the portion of photoresist layer  310  between the openings  406  is wider than main pole  20 , the ion milling process produces upward projecting ridges  410  on each side of main pole  20 . The vertical dimension of ridges  410  could be 50 nm. 
         [0024]    After cavities  408  have been formed, photoresist layers  304  and  404  are stripped, resulting in the structure shown in  FIG. 4I . An RIE process is performed on the exposed surfaces of alumina layers  306  and  402 . Top write gap  24  (Rh or Ru) is deposited on the exposed surfaces of alumina layers  306  and  402 , as shown in  FIG. 4J . Assuming that the thickness of hard mask layer  402  is 20 nm and the thickness of top write gap  24  is 10 nm, the total gap thickness is 30 nm. The presence of ridges  410  and the overlying top write gap  24  create notch  30  in top write gap  24  at a location on top of write pole  20 . NiFe layer  320  is deposited by plating and planarized as described above, resulting in wrap around shield  408 , shown in  FIG. 4K . Recesses  32  are formed in wrap around shield  408  on either side of notch  30 . 
         [0025]    While specific embodiments of this invention have been described, it should by understood that these embodiments or illustrative only, and not limiting. Many different and alternative embodiments in accordance with this invention will be apparent to persons of skill in the art.