Abstract:
A process (and the structure resulting therefrom) is described for manufacturing a magnetic write head in which there is no physical interface between the first and second trailing shields. This is achieved by laying down a sacrificial layer which is patterned to extend inwards towards the top yoke whereby the dimensions and shapes of the shields are defined.

Description:
FIELD OF THE INVENTION 
     The invention relates to the general field of perpendicular magnetic write heads with particular attention to the formation of the first and second trailing shields. 
     BACKGROUND OF THE INVENTION 
     In perpendicular magnetic recording (PMR), a trailing shield, as well as side shields and a leading shield, are used in order to produce a greater on-track field gradient thereby achieving a better signal to noise ratio together with high linear density and lower fringing fields for this high track density. 
       FIG. 1  is a cross-sectional view of a magnetic write head of the prior art. As can be seen, interface  11  is present between first trailing shield  12  and second trailing shield  13 . Also shown in the figure are leading shield  14 , main pole  15 , top yoke  16 , and field coils  17 . 
       FIGS. 2   a - 2   c  show air-bearing surface (ABS) views of  FIG. 1  for three of several different arrangements of the shields that are possible. In all three figures unlabeled diagonal arrows indicate wherever there is a physical interface between two regions (such as  11  in  FIG. 1 ) while the presence of broken lines separating two regions having different functions (e.g. between side shields  21  and first trailing shield  12  in  FIG. 2   a . Note the presence of physical interface  11  in all three figures. Although no corresponding figure has been provided, write heads that are otherwise similar to those shown in  FIG. 2 , but having no side shields, are also sometimes used. 
     Unfortunately, the various shields shown in  FIGS. 1 and 2  often cause unintended data erasure that is largely dependent on the geometry of the shields. The present invention has determined the source of the unintended erasure and discloses how this problem may be overcome. 
     A routine search of the prior art was performed with the following representative reference of interest being found: 
     In U.S. Pat. No. 7,477,481, Guthrie et al. show only one trailing shield. Note that no references teaching first and second trailing shields nor of the use of a sacrificial material in forming the trailing shield, were found. 
     SUMMARY OF THE INVENTION 
     It has been an object of at least one embodiment of the present invention to fix the far track accidental erasure problem in a shielded writer. 
     Another object of at least one embodiment of the present invention has been to eliminate domain wall collisions at the shield interfaces, thereby preventing the formation of the hot spots that are responsible for far track erasure. 
     Still another object of at least one embodiment of the present invention has been to eliminate as many interfaces as possible between multiple shield layers by providing a single piece seamless trailing shield. 
     A further object of at least one embodiment of the present invention has been to provide a method of forming said seamless trailing shield. 
     These objects have been achieved by the introduction of a sacrificial layer immediately after the top yoke plating has been done and the photoresist mold stripped. This sacrificial layer defines the shape and dimensions of the first trailing shield. Its later removal facilitates formation of the first and second trailing shields in a single step. 
     Another important feature of the invention is that the seed layer, once it has served its primary purpose of enabling the electroformation of the top yoke, is only partly removed (by ion milling or by liftoff). This feature allows the seed layer to remain on top of the write gap layer so that it may protect the latter when the sacrificial layer is removed later on. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a perpendicular magnetic write head of the prior art. 
         FIGS. 2   a - 2   c  show ABS views of three possible versions of  FIG. 1 . 
         FIG. 3  illustrates the initial structure that is the starting point for manufacturing the invention. 
         FIG. 4  shows how a sacrificial layer, which defines the shape and dimensions of the first trailing shield, is introduced. 
         FIG. 5  shows the formation of insulation to separate the shields from the main pole. 
         FIGS. 6 and 7  illustrate removal of the sacrificial layer and the formation of the upper field coils. 
         FIG. 8  shows formation of the coil housing and the laying down of both the first and second trailing shields in a single deposition. 
         FIG. 9  shows the final structure as manufactured according to the process of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although there are methods that allow one step formation of leading shield and side shield, or side shields and first trailing shield, or even leading shield, side shields and first trailing shield, what is common to all these examples of the prior art is that the first trailing shield and the second trailing shield are always formed separately. In today&#39;s standard practice, the first trailing shield is formed and planarized, following which the second trailing shield is formed on top of the first trailing shield. Inevitably, this results in the presence of a physical interface between the two trailing shields. 
     The relationship between this physical interface and the unintended erasure of data by the shield(s), that was mentioned earlier, was investigated using Magnetic Force Microscopy (MFM) images of two writers, at air bearing surfaces (ABS). Both writers had side shields as well as first and second trailing shields. In both cases, domain walls that originated near the main pole were seen to propagate until they collided with the horizontal domain wall at the interface between the first and second trailing shields. 
     Further investigation determined that these domain wall collisions were the cause of the (unintended) far track erasure. This demonstrated that, if this type of far track erasure is to be eliminated, it is critical to remove the possibility for domain wall collision to occur inside the shields. It was further determined that the best way to achieve this was to make it impossible for the horizontal domain wall (caused by the physical discontinuity between the first and second trailing shields) to form at all. 
     This is accomplished by the invention through the formation of both the first trailing shield and the second trailing shield in a single process that eliminates the possibility of any physical interface forming between them so that the trailing shield becomes a single seamless piece. This process, that we describe immediately below, will also serve to make clear the structure of the present invention. 
     The disclosed process has the additional advantage that it remains compatible with, and may be applied to, prior art processes for eliminating interfaces between leading shield and side shield, and between side shield and first trailing shield. Consequently, all shield layers (leading, side, first trailing, and second trailing) may be formed into a single seamless piece. 
     Referring now to  FIG. 3 , the process of the invention starts with main magnetic pole  15  which has upper and lower horizontal top surface portions, connected by a sloping portion. The broken line that passes through the approximate center of the sloping portion marks the future location of the ABS. 
     Also shown in  FIG. 3  are non-magnetic write gap layer  31  and electrically conductive seed layer  32 . Photoresist mold  33  is formed on seed layer  32 , using standard photolithographic techniques, and top yoke  16  is electroformed therein on seed layer  32 . Photoresist mold  33  is then stripped away in the usual way. 
     Now follows a key novel step: As shown in  FIG. 4 , sacrificial layer  43  is laid down on seed layer  32  following which it is patterned to terminate beyond the sloping portion about 2 microns therefrom, which causes write gap layer  31  to extend about half way into space  41  that separates sacrificial layer  43  from top yoke  16 . Thus sacrificial layer  43  defines the shape and dimensions of the first trailing shield. 
     Sacrificial layer  43  may be photoresist or it could of any material that can be selectively removed later. Examples include, but are not limited to, NiFe, CoNiFe, silicon nitride, and Cu. With the sacrificial layer in place, the exposed portion of seed layer  32  is selectively removed using ion beam etching. 
     Moving on to  FIG. 5 , after removing all parts of seed layer  32  that are not covered by sacrificial layer  43  (or by top yoke  16 ), insulating layer  51  is deposited to an initial thickness that exceeds that of sacrificial layer  43 , following which the full structure is planarized until there is no longer any insulating material on either top yoke  16  or sacrificial layer  43 . Examples of possible materials for layer  51  include, but are not limited to, alumina. Layer  51  is deposited to a thickness in a range of from 0.3 to 1.5 microns. 
     Next, as illustrated in  FIG. 6 , insulating layer  61  is deposited on top yoke  16  and insulating layer  51 . Examples of suitable materials for layer  61  include, but are not limited to, alumina. Layer  61  is deposited to a thickness in a range of from 0.05 to 0.5 microns. Part of insulating layer  61  then removed (through ion beam milling or through a liftoff process) and is given beveled edge  62  which is located between 0.2 and 2 microns from the outer edge of layer  51 . 
     Then, as shown in  FIG. 7 , part of field coil  17  is formed on insulating layer  61  over top yoke  16 . Now follows the removal of sacrificial layer  43  with seed layer  32  remaining in place to protect write gap layer  31 . 
     As seen in  FIG. 8 , the process concludes by covering field coils  17  and insulating layer  61  with insulating material  82 , whose melting/softening point is below about 200° C. This is followed by heating layer  82  until it softens (or has been softened by chemical means) so that it assumes a lenticular shape. After layer  82  has been allowed to harden (through cooling or by some other means, if appropriate), magnetic layer  81  is deposited to fully contact layers  32 ,  51 ,  61 , and  82 , thereby forming seamlessly connected first and second trailing shields. 
     A comparison of  FIGS. 1 and 9  shows them to be essentially the same except for the absence of physical interface  11  in  FIG. 9 . 
     ALTERNATIVE EMBODIMENTS 
     Since the sacrificial layer (commonly a dummy photoresist) will be removed later, other materials, such as SiN, which are selectively removable relative to Al 2 O 3  and magnetic metal, may be substituted. In that case, the removal method of this alternative sacrificial material will be different, for example, RIE (reactive ion etching). Alternatively, appropriate metal materials could be used for the sacrificial material. In this case, the selective removal process could be implemented using a wet etch procedure.