Abstract:
Methods and structures for the fabrication of a thin film, perpendicular recording write head are disclosed. The structure provides a pole tip separated from a rear pole by a non-magnetic separation layer located adjacent the flare point. The rear pole contains an imbedded non-magnetic layer. The separated pole tip and imbedded layer aid in the high data rate recording as well as the erasure performance of the write pole structure. The fabrication involves the deposition of two different oxide layers which have mutually high etch selectivities. This characteristic allows a write pole structure to be built wherein the track width is independent of the location of the flare point. The process also produces a structure wherein the placement of the throat height of the shield is self aligned to the flare point of the write pole.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to structures and methods for fabricating thin film magnetic write heads. More specifically, the invention relates to structures and methods for fabricating a thin film write head for perpendicular recording having independent control of track width, flare point, wrap around shield throat height self aligned to flare point, and stepped wrap around shields wherein the thickness or depth of the wrap around shield increases in the back region the write main pole. The methods and structure also provide for a back pole region having an imbedded non-magnetic layer and a separation layer between back pole and front pole regions to form de-coupled pole tip. 
     2. Description of the Related Art 
     As areal densities for magnetic storage hard disk drives continue to increase, the critical dimensions for thin film write heads are driven to smaller levels. For future designs, track widths (TW), flare points (FP), and wrap around shield throat heights (TH) will be on the order of 60 nm. Holding these dimensions provides a significant challenge for conventional processing, as will be illustrated in  FIG. 1 .  FIG. 1  (Prior Art) is a partial plan view  100  of a typical thin film perpendicular write pole  212 . Write pole  212  is typically imbedded in oxide layer  112 , and is deposited after imaging the shape of the pole and etching oxide layer  112 . Alternatively, write pole layer  212  can be blanket deposited, then imaged to define the final shape, etched or ion milled to define the pole, with areas around the pole subsequently filled with an oxide layer and both layers planarized. In either case, current imaging and etching processes can create errors with respect to the location of the flare point  102 , since the position where the flare point is located by lithography FP d  ref  104  will not be the actual location of the flare point FP a  ref  106  subsequent to etching/milling of the pole material  212 , or oxide layer within which the pole material is deposited. Errors can also be introduced with respect to the track width TW. The imaged track width TW d  ref  108  may be larger or smaller than the actual value TW a  ref  110 . These errors also impact the location of the flare point. As dimensions are reduced, the location errors of the flare point can significantly impact the performance of the write head. Similar errors are introduced when locating and etching the cavities for the wrap around shield. The throat height, or the depth or thickness of the wrap around shield from the ABS, is critical to the performance of the write head. More particularly, the location of the rear of the wrap around shield relative to the flare point is critical, and is subject to significant errors when conventional lithography and etching processes are utilized to fabricate the shield. What is needed is a better process for producing perpendicular thin film write heads. 
       FIG. 2  (Prior Art) is a partial, cross sectional view of a typical thin film perpendicular write head  200 . The head comprises shield layers  202 ,  204 , shaping layer  210 , coil structure  208 , main pole  212 , lower return pole layer  206 , wrap around shield  214 , and upper return pole layer  216 . Alternatively, structure  214  may also be a trailing shield. Main pole  212  is typically deposited over spacer layer  112 . Details of wrap around shields and trailing shields, as applied to perpendicular recording heads, can be found in, for example, US Patent Application Publications 2007/0146930, 2007/0115584, 2006/0174474, 2006/0044682, and 2007/0137027. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a thin film perpendicular magnetic head including a write pole having a first flare point, a second flare point, and a separation layer, the write pole having a first portion extending from an air bearing surface to the separation layer, the first portion having a constant first width, the write pole having a second portion extending from the first flare point to the second flare point, the second portion having a constant second width greater than the first width, the separation layer dividing the first portion from the second portion. 
     It is another object of the present invention to provide a method for making a thin film perpendicular magnetic head including depositing a first oxide layer, a separation layer, and a second oxide layer on a surface, a portion of the separation layer interposed between the first oxide layer and said second oxide layer, the portion of the separation layer oriented approximately perpendicular to the surface; depositing a mask layer over a first portion of the first oxide layer and over a first portion of the second oxide layer; creating an opening in the mask layer, the opening exposing a second portion of the first oxide layer and a second portion of the second oxide layer, the opening extending across the portion of the separation layer; isotropically etching, with a first process, the second portion of the first oxide layer to form a first trench; and, anisotropically etching, with a second process, the second portion of the second oxide layer, subsequent to isotropically etching the first oxide layer with the first process, to form a second trench, wherein the second portion of the second oxide layer is exposed to conditions of the first process, and the width of the first trench is greater than the width of the second trench. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein: 
         FIG. 1  (Prior Art) is a partial plan view of a typical thin film perpendicular write pole; 
         FIG. 2  (Prior Art) is a partial cross section view of a typical thin film perpendicular write head structure; 
         FIG. 3   a  is a partial plan view of a substrate subsequent to the deposition of a blanket etch stop layer in accordance with an embodiment of the present invention; 
         FIG. 3   b  is a cross section view through section A-A of  FIG. 3   a  in accordance with an embodiment of the present invention; 
         FIG. 4  is a cross section view of  FIG. 3   b  subsequent to the deposition of a blanket layer of oxide  1  and a metal mask layer in accordance with an embodiment of the present invention; 
         FIG. 5   a  is a plan view of  FIG. 4  subsequent to the etching of oxide 1 in accordance with an embodiment of the present invention; 
         FIG. 5   b  is cross section view through section B-B of  FIG. 5   a  in accordance with an embodiment of the present invention; 
         FIG. 6  is a cross section view of  FIG. 5   b  subsequent to the blanket deposition of oxide  2  in accordance with an embodiment of the present invention; 
         FIG. 7   a  is a plan view of  FIG. 6  subsequent to the planarization of oxide 2 in accordance with an embodiment of the present invention; 
         FIG. 7   b  is a cross section view through section C-C of  FIG. 7   a  in accordance with an embodiment of the present invention; 
         FIG. 8  is a cross section view of  FIG. 7   b  subsequent to the blanket deposition of an etch mask layer and a CMP stop layer in accordance with an embodiment of the present invention; 
         FIG. 9   a  is a cross section view of  FIG. 8  subsequent to the blanket deposition of a photo resist layer in accordance with an embodiment of the present invention; 
         FIG. 9   b  is a plan view of  FIG. 9   a  subsequent to the patterning of mask and CMP stop layer  804  in accordance with an embodiment of the present invention; 
         FIG. 10  is a plan view of  FIG. 9   b  subsequent to the selective isotropic etching of oxide 1 in accordance with an embodiment of the present invention; 
         FIG. 11  is a cross section view through section D-D of  FIG. 10  in accordance with an embodiment of the present invention; 
         FIG. 12  is a cross section view through section E-E of  FIG. 10  in accordance with an embodiment of the present invention; 
         FIG. 13  is a cross section view of  FIG. 11  subsequent to the deposition of a spacer layer in accordance with an embodiment of the present invention; 
         FIG. 14  is a cross section view of  FIG. 12  subsequent to the deposition of a spacer layer in accordance with an embodiment of the present invention; 
         FIG. 15  is a cross section view of  FIG. 13  subsequent to the deposition of magnetic layer  1502  and non-magnetic core layer  1504  in accordance with an embodiment of the present invention; 
         FIG. 16  is a cross section view of  FIG. 14  subsequent to the deposition of magnetic layer  1502  and non-magnetic core layer  1504  in accordance with an embodiment of the present invention; 
         FIG. 17  is a cross section view of  FIG. 15  subsequent to planarization in accordance with an embodiment of the present invention; 
         FIG. 18  is a cross section view of  FIG. 16  subsequent to planarization in accordance with an embodiment of the present invention; 
         FIG. 19  is a cross section view of  FIG. 17  subsequent to removal of spacer layer  1302  in accordance with an embodiment of the present invention; 
         FIG. 20  is a cross section view of  FIG. 18  subsequent to removal of spacer layer  1302  in accordance with an embodiment of the present invention; 
         FIG. 21  is a cross section view of  FIG. 19  subsequent to the an-isotropic etching of oxide  2  in accordance with an embodiment of the present invention; 
         FIG. 22  is a cross section view of  FIG. 21  subsequent to the removal of CMP stop layer  804  in accordance with an embodiment of the present invention; 
         FIG. 23  is a plan view of the structure in  FIG. 22  in accordance with an embodiment of the present invention; 
         FIG. 24  is a cross section view of  FIG. 19  subsequent to the deposition of magnetic material  2402  in accordance with an embodiment of the present invention; 
         FIG. 25  is a cross section view of  FIG. 22  subsequent to the deposition of magnetic material  2402  in accordance with an embodiment of the present invention; 
         FIG. 26  is a cross section view of  FIG. 24  subsequent to planarization in accordance with an embodiment of the present invention; 
         FIG. 27  is a cross section view of  FIG. 25  subsequent to planarization in accordance with an embodiment of the present invention; 
         FIG. 28  is a plan view of the structure of  FIG. 26 ,  27  in accordance with an embodiment of the present invention; 
         FIG. 29  is a cross section view of  FIG. 26  subsequent to the deposition of a second layer of oxide  2  in accordance with an embodiment of the present invention; 
         FIG. 30  is a cross section view of  FIG. 27  subsequent to the deposition of a second layer of oxide  2  in accordance with an embodiment of the present invention; 
         FIG. 31  is a plan view of the structures of  FIG. 29 ,  30  subsequent to the etching of oxide  2  layers in accordance with an embodiment of the present invention; 
         FIG. 32  is a cross section view through section F-F in  FIG. 31  in accordance with an embodiment of the present invention; 
         FIG. 33  is a cross section view through section G-G in  FIG. 31  in accordance with an embodiment of the present invention; 
         FIG. 34   a  is a cross section view of  FIG. 32  subsequent to the deposition of a side gap layer in accordance with an embodiment of the present invention; 
         FIG. 34   b  is a cross section view of  FIG. 34   a  subsequent to the removal of portions of side gap layer  3402  in accordance with an embodiment of the present invention; 
         FIG. 35   a  is a cross section view of  FIG. 33  subsequent to the deposition of a side gap layer in accordance with an embodiment of the present invention; 
         FIG. 35   b  is a cross section view of  FIG. 34   a  subsequent to the removal of portions of side gap layer  3402  in accordance with an embodiment of the present invention; 
         FIG. 36  is a cross section view of  FIG. 34   b  subsequent to the deposition of a shield gap layer in accordance with an embodiment of the present invention; 
         FIG. 37  is a cross section view of  FIG. 35   b  subsequent to the deposition of al shield gap layer in accordance with an embodiment of the present invention; 
         FIG. 38  is a cross section view of  FIG. 36  subsequent to shield deposition in accordance with an embodiment of the present invention; 
         FIG. 39  is a cross section view of  FIG. 38  subsequent to lapping in accordance with an embodiment of the present invention; 
         FIG. 40  is an ABS view of the structure of  FIG. 39  in accordance with an embodiment of the present invention; and, 
         FIG. 41  is a plan view of the structure of  FIG. 39  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  (Prior Art) have been discussed above in the Background section. Details of the embodiments of the present invention are best described via a sequential process of construction disclosed in  FIGS. 3-41  below. 
       FIG. 3   a  is a partial plan view  300  of a substrate subsequent to the deposition of a blanket etch stop layer  306  in accordance with an embodiment of the present invention.  FIG. 3   b  is a cross section view  301  through section A-A of  FIG. 3   a . Support layer  304  is typically a spacer layer comprising a dielectric material similar to layer  112  of  FIG. 2  (Prior Art). Etch stop layer  306  may comprise a metal or dielectric, preferably layer  306  is a metal. Typically, etch stop layer  306  may comprise a metal such as Ru, Rh, or Cr, but other materials may be suitable as are well known to those skilled in the art. 
       FIG. 4  is a cross section view  400  of  FIG. 3   b  subsequent to the deposition of a blanket layer of oxide 1 (ref  402 ) and a metal mask layer  404  in accordance with an embodiment of the present invention. Material composition of oxide 1 layer  402  is disclosed in detail below. Subsequent to the deposition of mask layer  404 , a photo resist layer is deposited, imaged, and developed in accordance with processes well known to those skilled in the art (not shown). Portions of mask layer  404  is then etched in accordance with the pattern developed in the photo resist (not shown). After patterning mask layer  404 , portions of oxide 1 layer  402  are removed by RIE in accordance with processes known in the art. 
       FIG. 5   a  is a plan view  500  of  FIG. 4  subsequent to the etching of portions of oxide 1 layer  402  in accordance with an embodiment of the present invention.  FIG. 5   b  is cross section view  501  through section B-B of  FIG. 5   a . Following the etching of oxide 1 layer  402 , metal mask layer  404  and portions of etch stop layer  306  not covered by remaining portions of oxide 1 layer  402  are removed by processes well known in the art. 
       FIG. 6  is a cross section view  600  of  FIG. 5   b  subsequent to the blanket deposition of oxide  2  layer  602  and separation layer  604  in accordance with an embodiment of the present invention. Separation layer  604  preferably comprises (but is not limited to) a metal such as Pt, Pd, Rh, Ru, Cr, their mixtures and alloys. Oxide 1 and oxide 2 are chosen to have unique selectivities when undergoing a reactive ion etch (RIE) processing. That is, when oxide 1 is being etched, oxide 2 is minimally affected. Likewise, when oxide 2 is being etched, oxide 1 is minimally affected. Some examples of oxide 1/oxide 2 pairs include, but are not limited to: 
     I. Oxide 2:SiO 2 ; Oxide 1:Si 3 N 4    
     II. Oxide 2:SiO 2 ; Oxide 1:Al 2 O 3    
     For pair I, SiO2 etching is performed with carbon rich fluorocarbon gases such as C 3 F 8  and C 4 F 8 . Si 3 N 4  etching is performed with mixtures of CF 4 /O 2 /N 2 , or SF 6 /CH 4 /N 2 /O 2 . When etching SiO 2  in the presence of Si 3 N 4 , selectivities range from 4:1 up to 30:1. When etching Si 3 N 4  in the presence of SiO 2 , selectivity is about 6:1. For pair II, SiO 2  etching is performed with mixtures of CHF 3 /CF 4  with a SiO 2 /Al 2 O 3  selectivity of about 10:1. Al 2 O 3  etching is performed in BCl 3  with a Al 2 O 3 /SiO 2  selectivity of about 10:1. 
     In an alternate embodiment of the present invention, pair I can be Oxide 1:SiO 2 ; Oxide 2:Si 3 N 4 . Pair 2 can be Oxide 1:SiO 2 ; Oxide 2:Al 2 O 3  . The foregoing limitations on the etch chemistries and selectivities apply. 
       FIG. 7   a  is a plan view  700  of  FIG. 6  subsequent to the planarization of oxide 2 layer  602  and removal of a portion of layer  604  in accordance with an embodiment of the present invention.  FIG. 7   b  is a cross section view  701  through section C-C of  FIG. 7   a . Layer  604 ′ represents the portion of separation layer  604  that provides a boundary between oxide 1 layer  402  and oxide 2 layer  602 . 
       FIG. 8  is a cross section view  800  of  FIG. 7   b  subsequent to the blanket deposition of an etch mask layer and CMP stop layer  804  in accordance with an embodiment of the present invention. Layer  804  performs a dual function and acts a both a mask and CMP stop layer. Layer  804  is preferably comprised of a precious metal such as Pd, Pt, Ru, Rh, and Cr, but other materials may be suitable as are known in the art. 
       FIG. 9   a  is a cross section view  900  of  FIG. 8  subsequent to the blanket deposition of a photo resist layer  902  in accordance with an embodiment of the present invention. After imaging and developing photo resist layer  902 , mask and CMP stop layer  804  are patterned to removed a portion of layer  804 . Photo resist layer  902  is then stripped (not shown).  FIG. 9   b  is a plan view  901  of  FIG. 9   a  subsequent to the patterning of mask and CMP stop layer  804  in accordance with an embodiment of the present invention. Portions of oxide 1 layer  402  and oxide 2 layer  602  are now exposed for further processing. 
       FIG. 10  is a plan view  1000  of  FIG. 9   b  subsequent to the selective isotropic etching of a portion of oxide 1 layer  402  in accordance with an embodiment of the present invention. Due to the selection of oxide 1 and oxide 2, combined with the aforementioned etch conditions, oxide 2 is minimally affected during the etch of oxide 1. After removal of the exposed portion of oxide 1 layer  402 , a portion of underlying layer  306  is exposed. 
       FIG. 11  is a cross section view  1100  through section D-D of  FIG. 10  in accordance with an embodiment of the present invention.  FIG. 12  is a cross section view  1200  through section E-E of  FIG. 10 . Isotropic etching of oxide 1 layer  402  has undercut the oxide near the mask opening TW′ (ref  1102 ) by a distance D (ref  1104 ). This undercutting during isotropic etching creates a self aligned flare point (see  FIG. 28  below) at the boundary of separation layer  604 ′. Typically, distance D is about 50% of mask opening TW′, but can be as large as 100% of TW′. The opening TW′ in mask and CMP stop layer  804  situated over oxide 2 layer  602  will later define the track width of the write pole. 
       FIG. 13  is a cross section view  1300  of  FIG. 11  subsequent to the deposition of spacer layer  1302  in accordance with an embodiment of the present invention.  FIG. 14  is a cross section view  1400  of  FIG. 12  subsequent to the deposition of a spacer layer  1302 . Spacer layer  1302  is deposited to fill in opening TW′ to protect the mask opening over oxide 2 layer  602  from damage or unintended dimensional change during a subsequent CMP planarization step ( FIG. 14 ). Preferably, the deposition is carried out with a “line of sight” type deposition process such as sputtering or vapor deposition, the conditions of which are well known to those skilled in the art. Layer  1302  comprises a reactive ion etchable material such as aluminum oxide. The deposition process also deposits layer  1302 ′ in the trench previously etched in oxide 1 layer  402  of  FIG. 12 . 
       FIG. 15  is a cross section view  1500  of  FIG. 13  subsequent to the deposition of magnetic layer  1502  and non-magnetic core layer  1504  in accordance with an embodiment of the present invention. Both layers  1502  and  1504  are deposited with “line of sight” type deposition processes such as sputtering. Deposition produces magnetic layer  1502 ′ and non-magnetic core layer  1504 ′ situated within the trench previously etched in oxide 1 layer  402 . The thickness of magnetic layer  1502 ′ is utilized to position the horizontal location (as viewed in  FIG. 15 ) of the non-magnetic core layer  1504 ′. Magnetic layers  1502 ,  1502 ′ comprise magnetic alloys of Fe, Ni, and Cr, as are well known to those skilled in the art. Non-magnetic core layer  1504 ,  1504 ′ may be any non-magnetic material, oxide or metal. Preferably, layer  1504 ,  1504 ′ comprises a precious metal such as Rh, Ru, Pt, Pd; or an oxide such as alumina or silica.  FIG. 16  is a cross section view  1600  of  FIG. 14  subsequent to the deposition of magnetic layer  1502  and non-magnetic core layer  1504 . 
       FIG. 17  is a cross section view  1700  of  FIG. 15  subsequent to planarization in accordance with an embodiment of the present invention. Layers  1300 ,  1502 , and  1504  have been removed by CMP, to stop layer  804 .  FIG. 18  is a cross section view  1800  of  FIG. 16  subsequent to planarization in accordance with an embodiment of the present invention. Note a portion of layer  1302  remains to protect the pole defining opening in layer  804 . An optional process (not shown) may be utilized to protect the open trench in  FIG. 17  from debris created during the CMP process. This process requires filling of the trench with proto resist after the processes completed in  FIG. 15 , and prior to the planarization by CMP. The entire trench need not be filled completely, only the opening defined by layer  804 . After planarization, the protective photo resist is removed by standard dry photo resist stripping processes. 
       FIG. 19  is a cross section view  1900  of  FIG. 17  subsequent to removal of spacer layer  1302  in accordance with an embodiment of the present invention.  FIG. 20  is a cross section view  2000  of  FIG. 18  subsequent to removal of spacer layer  1302 . Layer  1302  is removed by RIE in accordance with processes well known to those skilled ion the art. 
       FIG. 21  is a cross section view  2100  of  FIG. 19  subsequent to the an-isotropic etching of oxide 2 layer  602  in accordance with an embodiment of the present invention. Note that a portion of separation layer  604 ′ is visible due to removal of a portion of oxide layer  602 . The cavity is not filled with layer  604 ′. 
       FIG. 22  is a cross section view  2200  of  FIG. 21  subsequent to the removal of CMP stop layer  804  in accordance with an embodiment of the present invention. 
       FIG. 23  is a plan view  2300  of the structure in  FIG. 22  in accordance with an embodiment of the present invention. Non-magnetic core layer  1504 ′ extends up to separation layer  604 ′. 
       FIG. 24  is a cross section view  2400  of  FIG. 19  subsequent to the deposition of magnetic material  2402  in accordance with an embodiment of the present invention. Magnetic layer  2402  may be deposited by sputtering or vapor deposition. Layer  2402  may also be deposited by electroplating following the deposition of a conformal magnetic seed layer (not shown). Magnetic layer  2402  is composed of the same material as layer  1502 ′.  FIG. 25  is a cross section view  2500  of  FIG. 22  subsequent to the deposition of magnetic material  2402 . 
       FIG. 26  is a cross section view  2600  of  FIG. 24  subsequent to planarization in accordance with an embodiment of the present invention. The cavity etched in oxide 1 layer  402  contains magnetic material layers  2402   a  and  1502 ′. Non-magnetic core layer  1504 ′ is completely imbedded in magnetic material, except for the portions bounded by separation layer  604 ′.  FIG. 27  is a cross section view of  FIG. 25  subsequent to planarization. The cavity etched in oxide 2 layer  602  is filled with magnetic layer  2402   b.    
       FIG. 28  is a plan view  2800  of the structure of  FIG. 26 ,  27  in accordance with an embodiment of the present invention. Several important features of the write pole of the present invention are notable. The pole is divided into three regions; a pole tip region comprising magnetic layer  2402   b , a rear pole region, divided from the pole tip region by separation layer  604 ′, and comprising imbedded nonmagnetic layer  1504 ′ and magnetic material layers  1502 ′ and  2402   a;  and, a third region comprising magnetic material layer  2402   c.  The rear pole region has two flare points,  2802  and  2804 . The first flare point  2802  dominates the performance of the write pole, and is specifically located at the boundary of separation layer  604 ′ and oxide  402 . This location is independent of the track width dimension TW′ (ref  1102 ) of the pole tip. 
       FIGS. 29-38  describe the fabrication of the laterally stepped wrap around shield. 
       FIG. 29  is a cross section view  2900  of  FIG. 26  subsequent to the deposition of a second layer  2902  of oxide 2 in accordance with an embodiment of the present invention.  FIG. 30  is a cross section view  3000  of  FIG. 27  subsequent to the deposition of oxide layer  2902 . Following deposition of oxide layer  2902 , a blanket RIE mask layer is deposited and patterned in accordance with processes known in the art (not shown). Portions of oxide 2 layer  2902  and  602  are then removed by a selective RIE process designed to remove oxide 2 without etching oxide 1 layer  402 , as disclosed above.  FIG. 31  is a plan view  3100  of the structures of  FIG. 29 ,  30  subsequent to the selective etching of oxide 2 layers  2902  and  602  in accordance with an embodiment of the present invention. 
       FIG. 32  is a cross section view  3200  through section F-F in  FIG. 31 .  FIG. 33  is a cross section view  3300  through section G-G in  FIG. 31 .  FIG. 34   a  is a cross section view  3400  of  FIG. 32  subsequent to the deposition of a side gap layer  3402  in accordance with an embodiment of the present invention.  FIG. 35   a  is a cross section view  3500  of  FIG. 33  subsequent to the deposition of a side gap layer  3402 . Side gap layer  3402  preferably comprises alumina, but also comprise a non-magnetic metal such as Rh, or Ru. Side gap layer  3402  is deposited by atomic layer deposition, ALD, to provide conformal coverage on all exposed surfaces. The processes involved in ALD are known to those skilled in the art.  FIG. 34   b  is a cross section view  3401  of  FIG. 34   a  subsequent to the removal of portions of side gap layer  3402  in accordance with an embodiment of the present invention.  FIG. 35   b  is a cross section view  3501  of  FIG. 34   a  subsequent to the etching of portions of side gap layer  3402 . Typically, removal of side gap layer  3402  on horizontal surfaces (as viewed in  FIGS. 34   a ,  35   a ) is performed by ion milling, in accordance with processes well known in the art. 
       FIG. 36  is a cross section view  3600  of  FIG. 34   b  subsequent to the blanket deposition of shield gap layer  3602  in accordance with an embodiment of the present invention.  FIG. 37  is a cross section view of  FIG. 35   b  subsequent to the deposition of shield gap layer  3602 . Shield gap layer  3602  is deposited by ALD, in accordance with processes well known in the art. Shield gap layer may comprise a metal such as Rh, Ru, Pd, Pt; or a dual layer comprising a first layer of an oxide such as alumina, covered in a seed layer of magnetic material such as alloys of Ni, Fe, and Cr (not shown). In any case, the upper exposed layer must be conductive to facilitate electroplating of the shield. Following the deposition of gap layer  3602 , a photo resist layer is deposited, imaged, and developed (not shown) to provide a boundary for the shield during electroplating. After electroplating, the photo resist layer is removed, along with a portion of gap layer  3602  (not shown). A blanket oxide layer is then deposited and planarized by CMP (not shown).  FIG. 38  is a cross section view  3800  of  FIG. 36  subsequent to shield  3802  deposition, filler oxide  3804  deposition, and planarization, in accordance with an embodiment of the present invention. The structure is then lapped to form the air bearing surface (ABS).  FIG. 39  is a cross section view  3900  of  FIG. 38  subsequent to lapping in accordance with an embodiment of the present invention. Lapping determines the throat height of the shield, which is the length of the forward pole layer  2402   b  between the ABS and the vertical boundary with separation layer  604 ′, less the thickness of the two added layers  3402  and  3602  (not shown). See the plan view of  FIG. 31  and process steps shown in  FIGS. 34   a - 37 .  FIG. 39  also shows the rear pole comprising magnetic layers  1502 ′,  2402   a , and imbedded nonmagnetic layer  1504 ′. 
       FIG. 40  is an ABS view  4000  of the structure of  FIG. 39  in accordance with an embodiment of the present invention.  FIG. 41  is a plan view  4100  of the structure of  FIG. 39  in accordance with an embodiment of the present invention. 
     The foregoing features described in embodiments of the present invention provide for a number of advantages in the write performance. The rear pole (yoke) having embedded non-magnetic core layer  1504 ′ promotes a transverse closure domain under small driving magnetic fields, therefore minimizing the effect of any remnant field. It also enables fast field response to the driving field through a magnetization rotation mechanism. De-coupling the pole tip from the rear pole (via separation layer  604 ′) leads to an independent relaxation process inducing more instantaneous head field relaxation after writing, essential for magnetic recording data rates over 1 GHz. 
     The present invention is not limited by the previous embodiments heretofore described. Rather, the scope of the present invention is to be defined by these descriptions taken together with the attached claims and their equivalents.