Patent Publication Number: US-2006002023-A1

Title: Magnetic head having a deposited second magnetic shield and fabrication method therefor

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to read heads for use in magnetic heads for hard disk drives, and more particularly to a read head which includes deposited second magnetic shield and a fabrication method therefor.  
      2. Description of the Prior Art  
      Magnetic heads for hard disk drives typically include a read head portion and a write head portion. In a commonly used read head, a magnetoresistive read sensor layered structure is located in a read region, while a magnetic hard bias element and an electrical lead element are located in each of two side regions. The sensor is fabricated between two magnetic shields that shield it from ambient magnetic fields, and the space between the two magnetic shields defines the sensor read gap in which it senses magnetic data bits on the rotating hard disk of the disk drive. The magnetic shields are typically fabricated in an electroplating process in which an electrically conductive seed layer is first deposited across the wafer surface upon an insulation layer, followed by a photolithographically patterned photoresist with openings created at desired magnetic shield locations. The magnetic shield is next electroplated upon the exposed seed layer within a magnetic shield opening in the photoresist. Following the electroplating of the magnetic shield, the photoresist and exposed seed layer are removed and an insulating fill layer is deposited across the wafer surface. A portion of the seed layer therefore remains beneath the magnetic shield that was electroplated upon it. A chemical mechanical polishing (CMP) step is next conducted to remove the insulating fill layer down to the surface of the electroplated magnetic shield, such that a flat surface is created for the subsequent fabrication of further magnetic head components.  
      In modern magnetic heads, the size of the magnetoresistive sensor is constantly being reduced to read ever smaller data bits on hard disks having greater areal data storage densities. The size of the read gap between the magnetic shields is likewise reduced in order to match the reduced data bit size. Improvements in the properties of the magnetic shields are also desirable to improve the performance of the heads.  
      Current magnetic shields are electroplated with NiFe80/20 material, but this material has a low Hk of around 2.5 Oe, which is a potential cause of write induced instability. Because of the low anisotropy field of the second magnetic shield, magnetic domain walls within the shield can be easily excited into unwanted movement by external fields as well as the stray fields from the write head poles. The domain wall motion in the second magnetic shield can cause noise in the read out signal from the read sensor, and result in write induced sensor instability when the magnetic domain walls in the second magnetic shield are located close to the sensor. The insulation layer between the sensor and the second magnetic shield must be thick enough to avoid this problem, and if the thickness of the insulation layer is reduced the noise can increase, such that the signal-to-noise ratio of the magnetic head will decrease. It is known that other soft magnetic films can offer higher anisotropy fields and can be excellent shield materials, like the CoZrTa alloy films that have been widely used as sensor shields in tape heads. However, many of these alloy films, like the CoZrTa films, cannot be electroplated in an aqueous environment, and have to be deposited by other methods like plasma vapor deposition (PVD).  
      For prior art electroplated thick shields, the seed layer is deposited and the shield is electroplated into a patterned photo-resist. But a deposited shield, which involves a full film deposition across the surface of the wafer, must be patterned by using etching methods, such as wet etching, ion milling, etc. For second magnetic shield patterning, there are two additional constraints that we have to be taken into consideration during the patterning process. The first constraint is that the very thin layer of insulation of the second gap, such as Al2O3, which may be less than 20 nm, should not be removed during the patterning. This automatically rules out ion milling, since severe over milling must be applied to ensure an acceptable vertical edge of the second magnetic shield. The second constraint is that the second magnetic shield patterning process should not necessitate an additional non-magnetic layer between the second gap and the second magnetic shield, which would add to the total shield to shield distance.  
      With regard to patterning a deposited second magnetic shield, wet etching might seem to be a good way to pattern it. However, the shield would have to be wet etched twice, since the ˜2 um shield would not allow for an accurate alignment right after deposition. The two wet etching steps would be: a first etch to open the alignment marks, and a second etch to define the shield island with accurate alignment. However, there would need to be a large tolerance because the wet etch process has a large variation and windage. Wet etching therefore is unsatisfactory, particularly when the shield dimensions are becoming smaller and smaller.  
     SUMMARY OF THE INVENTION  
      The hard disk drive of the present invention includes the magnetic head of the present invention having an improved read head. The improved read head includes a second magnetic shield that is fabricated in a deposition process. This differs from prior art second magnetic shields that are electroplated, wherein an electrically conductive seed layer is first deposited, followed by the electroplating of the second magnetic shield within a suitably patterned opening in a photoresist layer. The present invention therefore does not require the deposition of the electrically conductive seed layer. In a preferred embodiment, the deposited second magnetic shield is comprised of cobalt zirconium tantalum (CZT). The CZT magnetic shield is preferably deposited within an opening formed in a relatively hard RIEable material such as Ta 2 O 5 , SiO 2 , Si 3 N 3 , and SiO x N y . Because the CZT material is relatively soft, it is important that it is deposited within a relatively hard material such that a subsequent chemical mechanical polishing (CMP) step can be conducted down to the surface of the relatively hard layer. In an alternative embodiment, the relatively hard layer in which the CZT magnetic shield is deposited is comprised of a hard baked photoresist. The magnetic head of the present invention has an improved signal-to-noise ratio, and promotes the manufacture of hard disk drives having a greater areal data storage density.  
      It is an advantage of the magnetic head of the present invention that it has a read head sensor having improved magnetic shields.  
      It is another advantage of the magnetic head of the present invention that it has a read head sensor with a second magnetic shield that is comprised of a deposited material.  
      It is a further advantage of the magnetic head of the present invention that it includes a read head sensor having a second magnetic shield that is deposited within an opening formed within a RIEable material.  
      It is yet another advantage of the magnetic head of the present invention that it includes a read head sensor having a second magnetic shield that is comprised of deposited CZT.  
      It is an advantage of the hard disk drive of the present invention that it includes a magnetic head of the present invention which has a read head sensor having improved magnetic shields.  
      It is another advantage of the hard disk drive of the present invention that it includes a magnetic head of the present invention that it has a read head sensor with a second magnetic shield that is comprised of a deposited material.  
      It is a further advantage of the hard disk drive of the present invention that it includes a magnetic head of the present invention that it includes a read head sensor having a second magnetic shield that is deposited within an opening formed within a RIEable material.  
      It is yet another advantage of the hard disk drive of the present invention that it includes a magnetic head of the present invention that it includes a read head sensor having a second magnetic shield that is comprised of deposited CZT.  
      These and other features and advantages of the present invention will no doubt become apparent to those skilled in the art upon reading the following detailed description which makes reference to the several figures of the drawing. 
    
    
     IN THE DRAWINGS  
      The following drawings are not made to scale as an actual device, and are provided for illustration of the invention described herein.  
       FIG. 1  is a top plan view generally depicting a hard disk drive of the present invention that includes a magnetic head of the present invention;  
       FIG. 2  is a side cross-sectional view depicting a typical prior art magnetic head;  
       FIG. 3  is an elevational view taken from the air bearing surface of the read head portion of the magnetic head depicted in  FIG. 2 ;  
       FIGS. 4-8  are side cross-sectional views depicting steps in a fabrication process for a first embodiment of a magnetic head of the present invention;  
       FIG. 9  is a side elevational view of a first magnetic head embodiment of the present invention;  
       FIGS. 10-15  are side cross-sectional views depicting fabrication steps for a second magnetic head embodiment of the present invention;  
       FIG. 16  is a side elevational view of a second magnetic head embodiment of the present invention;  
       FIGS. 17-21  are side cross-sectional views depicting fabrication steps for a third magnetic head embodiment of the present invention; and  
       FIG. 22  is a side elevational view of a third magnetic head embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  is a top plan view that depicts significant components of a hard disk drive which includes the magnetic head of the present invention. The hard disk drive  10  includes a magnetic media hard disk  12  that is rotatably mounted upon a motorized spindle  14 . An actuator arm  16  is pivotally mounted within the hard disk drive  10  with a magnetic head  20  of the present invention disposed upon a distal end  22  of the actuator arm  16 . A typical hard disk drive  10  may include a plurality of disks  12  that are rotatably mounted upon the spindle  14  and a plurality of actuator arms  16  having a magnetic head  20  mounted upon the distal end  22  of the actuator arms. As is well known to those skilled in the art, when the hard disk drive  10  is operated, the hard disk  12  rotates upon the spindle  14  and the magnetic head  20  acts as an air bearing slider that is adapted for flying above the surface of the rotating disk. The slider includes a substrate base upon which the various layers and structures that form the magnetic head are fabricated. Such heads are fabricated in large quantities upon a wafer substrate and subsequently sliced into discrete magnetic heads  20 .  
      A typical prior art magnetic head structure is next described with the aid of  FIGS. 2 and 3  to provide a basis for understanding the improvements of the present invention. As will be understood by those skilled in the art,  FIG. 2  is a side cross-sectional view that depicts portions of a prior art magnetic head  30 , termed a longitudinal magnetic head, and  FIG. 3  is an elevational view of the read head portion of the magnetic head depicted in  FIG. 2 , taken from the air bearing surface of  FIG. 2 .  
      As depicted in  FIGS. 2 and 3 , a typical prior art magnetic head  30  includes a substrate base  32  with an insulation layer  34  formed thereon. An electrically conductive seed layer  35  is next deposited upon the insulation layer  34  and a first magnetic shield (S 1 )  36  is fabricated upon the seed layer  35 . In fabricating the first magnetic shield  36 , following the deposition of the seed layer  35 , a photoresist is deposited across the surface of the wafer and patterned to create openings that expose the seed layer in the desired location of the first magnetic shield. Thereafter, an electroplating process is conducted in which the first magnetic shield is electroplated upon the seed layer in the openings formed through the photoresist. Following the electroplating process, the photoresist is removed and the portion of the seed layer that was disposed beneath the photoresist is also removed. The portion of the seed layer that is disposed beneath the first magnetic shield  36  remains. An insulative fill layer  37  is then deposited across the surface of the wafer, and a chemical mechanical polishing (CMP) step is then conducted to remove the excess insulator fill layer  37  down to the upper surface of the first magnetic shield, such that a flat surface is created for the subsequent fabrication of further read head components, as are next described.  
      A first insulation layer (G 1 )  38  of the read head is then deposited upon the wafer and the S 1  magnetic shield  36 . A magnetoresistive sensor  40 , comprising a plurality of layers of specifically chosen materials, is then fabricated upon the G 1  layer  38 . Thereafter, electrical leads  54  are fabricated from the sensor towards magnetic head electrical contacts (not shown) to conduct the electrical sense current to the sensor for providing magnetic data bit signals from the sensor  40 . A second insulation layer (G 2 )  56  is subsequently deposited across the top of the sensor  40  and electrical leads  54 .  
      An electrically conductive seed layer  57  is next deposited upon the G 2  insulation layer  56  and a second magnetic shield (S 2 )  58  is fabricated upon the seed layer  57 . The second magnetic shield  58  is fabricated in a similar manner to the first magnetic shield  36 . That is, in fabricating the second magnetic shield  58 , following the deposition of the seed layer  57 , a photoresist is deposited across the surface of the wafer and patterned to create openings that expose the seed layer  57  in the desired location of the second magnetic shield. Thereafter, an electroplating process is conducted in which the second magnetic shield  58  is electroplated upon the seed layer  57  in the openings formed through the photoresist. Following the electroplating process, the photoresist is removed and the portion of the seed layer  57  that was disposed beneath the photoresist is also removed. The portion of the seed layer that is disposed beneath the magnetic shield  58  remains in place. An insulative fill layer  55  is then deposited across the surface of the wafer, and a chemical mechanical polishing (CMP) step is then conducted to remove the excess insulator fill layer  55  down to the upper surface of the second magnetic shield  58 , such that a flat surface is created for the subsequent fabrication of further magnetic head components, specifically, components of the write head portion of the magnetic head, as are next described.  
      Returning to  FIG. 2 , an electrical insulation layer  59  is then deposited upon the S 2  shield  58 , and a first magnetic pole (P 1 )  60  is fabricated upon the insulation layer  59 . Following the fabrication of the P 1  pole  60 , a write gap layer typically composed of a non-magnetic material such as alumina  72  is deposited upon the P 1  pole  60 . This is followed by the fabrication of a P 2  magnetic pole tip  76  and an induction coil structure, including coil turns 80, that is then fabricated within insulation  82  above the write gap layer  72 . Thereafter, a yoke portion  84  of the second magnetic pole is fabricated in magnetic connection with the P 2  pole tip  76 , and through back gap element  90  to the P 1  pole  60 . Electrical leads (not shown) to the induction coil are subsequently fabricated and a further insulation layer  114  is deposited to encapsulate the magnetic head. The magnetic head  30  is subsequently fabricated such that an air bearing surface (ABS)  116  is created.  
      It is to be understood that there are many detailed features and fabrication steps of the magnetic head  30  that are well known to those skilled in the art, and which are not deemed necessary to describe herein in order to provide a full understanding of the present invention.  
      In the prior art magnetic heads  30 , as depicted in  FIGS. 2 and 3 , the read gap, which is the distance between the first and second magnetic shield  36  and  58  respectively, is desirably small, such that ambient magnetic fields will be shielded from the sensor to reduce sensor noise. A problem with the read gap size becomes significant in advanced magnetic head designs where the size of the read head structures (such as the thickness of the G 2  insulation layer  56 ) is decreased in order to read smaller data bits that are formed on magnetic disks having increased areal data storage density. Particularly, the closeness of the second magnetic shield  58  to the sensitive sensor layers  40  allows for unwanted domain movement within the second magnetic shield to create noise within the sensor signal. A new second magnetic shield material with higher anisotropy and higher Hk is desired. A deposited material, such as CZT is acceptable, however, CZT is so mechanically soft that its use presents a problem. The present invention provides a solution to this problem.  
       FIGS. 4-8  are side cross-sectional views depicting steps in a read head fabrication process for a first embodiment  104  of a magnetic head of the present invention, and  FIG. 9  is a side elevational view of a completed read head portion  100  of the first magnetic head embodiment  104  of the present invention.  FIGS. 4-8  are presented as cross-sectional views in that they depict fabrication steps that are conducted on a wafer substrate, where  FIGS. 4-8  are taken from the location of the future air bearing surface (ABS) of the magnetic head;  FIG. 9  is taken from the ABS of the completed magnetic head  104 . As will be understood from the following description, the significant differences between the various magnetic heads of the present invention and the prior art magnetic head  30  depicted in  FIGS. 2 and 3  relates to the structure of the second magnetic shield  58 , and other features and structures of the magnetic heads of the present invention may be similar to those of the prior art magnetic head  30 , and similar structures are numbered identically for ease of understanding.  
      With reference to  FIG. 4 , the initial fabrication steps of a read head portion  100  of a first embodiment of a magnetic head  104  of the present invention are depicted. As depicted in  FIG. 4 , the read head portion  100  includes a substrate base  32  with an insulation layer  34  formed thereon. An electrically conductive seed layer  35  is next deposited upon the insulation layer  34  and a first magnetic shield (S 1 )  36  is fabricated upon the seed layer  35 .  
      A first insulation layer (G 1 )  38  of the read head  100  is then deposited upon the wafer and the S 1  magnetic shield  36 . A magnetoresistive sensor  40 , comprising a plurality of layers of specifically chosen materials, is then fabricated upon the G 1  layer  38 . Thereafter, electrical leads  54  are fabricated from the sensor towards magnetic head electrical contacts (not shown) to conduct the electrical sense current to the sensor for providing signals from the sensor  40 . A second insulation layer (G 2 )  56  is subsequently deposited across the top of the sensor  40  and electrical leads  54 .  
      As is next depicted in  FIG. 5 , a nonmagnetic, insulative layer  108  is then deposited across the wafer surface on top of the G 2  insulation layer  56 . The insulative layer  108  is comprised of a material that is etchable in a reactive ion etch (RIE) process, termed a RIEable material herein, and such materials include Ta 2 O 5 , SiO 2 , Si 3 N 3 , and SiO x N y  as examples. The silicon based nonmagnetic, insulative materials are etchable in a fluorine ion based RIE process  
      Following the deposition of the layer  108 , a photoresist layer  112  is deposited across the surface of the wafer and photolithographically patterned to create openings  116  of the desired shape and at the location at which the second magnetic shield is to be created. Thereafter, as depicted in  FIG. 6 , an RIE process is conducted in which the photoresist  112  acts as an etching mask, and in which the layer  108  is etched through the openings  116  in the photoresist layer  112  down to the G 2  insulation layer  56  to create a magnetic shield trench  120  within the layer  108 . The G 2  insulation layer  56  acts as an etch stop layer, and therefore, where the layer  108  is comprised of a silicon based material, the G 2  insulation layer  56  can be comprised of a material such as alumina or any other materials having an RIE chemistry that has a low selectivity as compared to the material comprising the RIEable layer  108 .  
      With reference to  FIG. 7 , the material  124  that comprises the second magnetic shield  128  is next deposited across the surface of the wafer in sufficient thickness to fill the etched magnetic shield openings  120  and  116  above the thickness of the photoresist  112 . The deposited magnetic shield material  124  must have appropriate magnetic properties to function as a magnetic shield for the sensor  40 , and a suitable material for the deposited second magnetic shield is cobalt zirconium tantalum, known as CZT.  
      As depicted in  FIG. 8 , a chemical mechanical polishing (CMP) is next conducted to remove the excess CZT material  124  and photoresist mask  112 , down to the surface of the insulative layer  108 . CZT is known to be a mechanically soft material, and the CMP process therefore relies on the hardness of the insulative material  108  as a polishing stop layer. The insulative layer materials identified hereabove provide sufficient hardness to protect the softer CZT during the CMP process. However, where the hardness of the RIEable material layer  108  is deemed insufficient, a thin chemical mechanical polish (CMP) stop layer (not shown) such as diamond like carbon (DLC) can be deposited upon the RIEable layer  108  prior to the deposition of the photoresist layer  112 .  
      As will be understood by those skilled in the art, a desirable CMP slurry is a silicon based slurry with hydrogen peroxide as an oxidizer; a preferred slurry utilizes MH817 plus H 2 O 2 . A recommended CMP pad is an IC 1000 KXY pad, and the CMP conditions include a 4 psi pressure at a 45 rpm polishing table rotation speed.  
      Where it is desirable that the RIEable insulation layer  108  be replaced with an insulation material such as alumina, following the CMP step, a second RIE step can be conducted to remove the remaining RIEable insulation material  108 . Thereafter, a layer of alumina can be deposited, and a second CMP step is then conducted to reexpose the surface of the CZT second magnetic shield  128 .  
      Following the CMP step the fabrication of the second magnetic shield  128  is completed. The CMP process results in a flat surface  132  upon which the further magnetic head components, as described hereabove, can be fabricated, including the fabrication of the write head components the dicing of the wafer substrate and the subsequent creation of the air bearing surface of the magnetic head, all as described hereabove.  FIG. 9  depicts the read head portion  100  of the first magnetic head embodiment  104  of the present invention as taken from the ABS surface. As depicted therein, the read head portion  100  includes the substrate base  32 , insulation layer  34 , seed layer  35 , first magnetic shield  36 , G 1  insulation layer  38 , sensor  40 , electrical leads  54 , G 2  insulation layer  56 , second magnetic shield  128 , RIEable insulative layer  108 , and the electrical insulation layer  59  that is deposited upon the second magnetic shield  128  and RIEable insulative layer surface  132 . Thereafter, the write head portion (not shown in  FIG. 9 ) of the first magnetic head embodiment  104  is fabricated. This write head portion may be identical to the write head portion of the prior art magnetic head  30  as described hereabove. However, the magnetic head of the present invention is not to be so limited, and may include virtually any write head design that is compatible with the read head portion  100  described herein.  
      A significant feature of the first magnetic head embodiment  104  of the present invention is that the second magnetic shield  128  is comprised of a material having a higher anisotropy and higher Hk than the prior art electroplated NiFe shield. The deposited CZT material of the second magnetic shield of the present invention therefore creates less signal noise, and the head has a higher signal-to-noise ratio. Additionally, it is advantageous in that a thinner G 2  insulation layer  56  can be possibly be used. This would allow the magnetic shields  36  and  128  to be advantageously fabricated closer together, such that the read gap of the magnetic head  104  is reduced as compared to the prior art. The magnetic head  104  may be thus utilized with hard disk drives including hard disks having a greater data areal storage density, which necessitates the creation of smaller data bits and requires the utilization of magnetic heads having the smaller read gap of the magnetic head  104  of the present invention.  
      A second embodiment  204  of a magnetic head of the present invention is depicted in  FIGS. 10-16 , wherein  FIGS. 10-15  are side cross-sectional views depicting steps in a read head fabrication process for the second magnetic head embodiment  204 , and  FIG. 16  is a side elevational view of a completed read head portion  200  of the second magnetic head embodiment  204 .  FIGS. 10-15  are presented as cross-sectional views in that they depict fabrication steps that are conducted on a wafer substrate, where  FIGS. 10-15  are taken from the location of the future air bearing surface (ABS) of the magnetic head;  FIG. 16  is taken from the ABS of the completed magnetic head  204 . As will be understood from the following description, the significant differences between the various magnetic heads of the present invention and the prior art magnetic head  30  depicted in  FIGS. 2 and 3  relates to the structure of the second magnetic shield, and other features and structures of the magnetic heads of the present invention may be similar to those of the prior art magnetic head  30 , and similar structures are numbered identically for ease of understanding.  
      With reference to  FIG. 10 , the initial fabrication steps of a read head portion  200  of a second embodiment of a magnetic head  204  of the present invention are depicted. As depicted in  FIG. 10 , the read head portion  200  includes a substrate base  32  with an insulation layer  34  formed thereon. An electrically conductive seed layer  35  is next deposited upon the insulation layer  34  and a first magnetic shield (S 1 )  36  is fabricated upon the seed layer  35 .  
      A first insulation layer (G 1 )  38  of the read head  200  is then deposited upon the wafer and the S 1  magnetic shield  36 . A magnetoresistive sensor  40 , comprising a plurality of layers of specifically chosen materials, is then fabricated upon the G 1  layer  38 . Thereafter, electrical leads  54  are fabricated from the sensor towards magnetic head electrical contacts (not shown) to conduct the electrical sense current to the sensor for providing magnetic data bit signals from the sensor  40 .  
      As is next depicted in  FIG. 11 , a nonmagnetic, insulative layer  208  is next deposited across the wafer surface on top of the electrical leads  54  and upper surface of the sensor  40 . The insulative layer  208  is comprised of a material that is etchable in a reactive ion etch (RIE) process, termed a RIEable material herein, and such materials include Ta 2 O 5 , SiO 2 , Si 3 N 3 , SiO x N y , as examples. The silicon based nonmagnetic insulative materials are etchable in a fluorine ion based RIE process. Following the deposition of the nonmagnetic, insulative layer  208 , a photoresist layer  212  is deposited across the surface of the wafer and photolithographically patterned to create openings  216  of the desired shape and at the location at which the magnetic shield is to be created. Thereafter, as depicted in  FIG. 12 , an RIE process is conducted in which the photoresist  212  acts as an etching mask, and in which the nonmagnetic, insulative layer  208  is etched through the openings  216  in the photoresist layer  212  down to the surface of the electrical leads  54  and the upper surface of the sensor  40  to create a magnetic shield trench  220  within the insulative layer  208 .  
      As is next seen in  FIG. 13 , the photoresist layer  212  is removed, such as by a wet chemical stripping process, and an insulation layer  222 , which functions as the G 2  insulation layer, is next deposited across the surface of the wafer. The G 2  insulation layer  222  is therefore deposited into the magnetic shield trench  220  and on top of the insulative layer  208 . With reference to  FIG. 14 , the material  224  that comprises the second magnetic shield  228  is next deposited across the surface of the wafer upon the G 2  insulation layer  222  in sufficient thickness to fill the etched magnetic shield openings  220  and  216  above the thickness of the G 2  insulation layer  222 . The deposited magnetic shield material  224  must have appropriate magnetic properties to function as a magnetic shield for the sensor  40 , and a suitable material for the deposited second magnetic shield is cobalt zirconium tantalum, known as CZT.  
      As depicted in  FIG. 15 , a chemical mechanical polishing (CMP) is next conducted to remove the excess CZT material  124 , down to the surface of the G 2  insulation layer  222 . CZT is known to be a mechanically soft material, and the CMP process therefore relies on the hardness of the G 2  insulation layer  222  as a polishing stop layer. As will be understood by those skilled in the art, a desirable CMP slurry is a silicon based slurry with hydrogen peroxide as an oxidizer; a preferred slurry utilizes MH817 plus H 2 O 2 . A recommended CMP pad is an IC 1000 KXY pad, and the CMP conditions include a 4 psi pressure at a 45 rpm polishing table rotation speed.  
      Following the CMP step the fabrication of the second magnetic shield  228  is completed. The CMP process results in a flat surface  232  upon which the further magnetic head components, as described hereabove, can be fabricated, including the fabrication of the write head components the dicing of the wafer substrate and the subsequent creation of the air bearing surface of the magnetic head, all as described hereabove.  FIG. 16  depicts the read head portion  200  of a completed second magnetic head embodiment  204  of the present invention as taken from the ABS surface. As depicted therein, the read head portion  200  includes the substrate base  32 , insulation layer  34 , seed layer  35 , first magnetic shield  36 , G 1  insulation layer  38 , sensor  40 , electrical leads  54 , RIEable insulative layer  208 , G 2  insulation layer  222 , second magnetic shield  228  and the electrical insulation layer  59  that is deposited upon the second magnetic shield and outer portion of the G 2  insulation layer surface  222 . Thereafter, the write head portion (not shown in  FIG. 16 ) of the second magnetic head embodiment  204  is fabricated. This write head portion may be identical to the write head portion of the prior art magnetic head  30  as described hereabove. However, the magnetic head of the present invention is not to be so limited, and may include virtually any write head design that is compatible with the read head portion  200  described herein.  
      A significant feature of the second magnetic head embodiment  204  of the present invention is that the writer induced noise in the sensor signal is reduced due to the improved material that comprises the second magnetic shield. Additionally, the read gap between the magnetic shields  36  and  228  may be reduced as compared to the prior art magnetic head  30 , in that the improved second magnetic shield material may allow for a thinner G 2  insulation layer to be used, as has been discussed above. This would allow the magnetic shields  36  and  228  to be advantageously fabricated closer together, such that the read gap of the magnetic head  204  is reduced as compared to the prior art. The magnetic head  204  may be thus utilized with hard disk drives including hard disks having a greater data areal storage density, which necessitates the creation of smaller data bits and requires the utilization of magnetic heads having a smaller read gap.  
      A third embodiment  304  of a magnetic head of the present invention is depicted in  FIGS. 17-22 , in which  FIGS. 17-21  are side cross-sectional views depicting steps in a read head fabrication process for the third embodiment  304  of a magnetic head of the present invention, and  FIG. 22  is a side elevational view of a completed read head portion  300  of the third magnetic head embodiment  304  of the present invention.  FIGS. 17-21  are presented as cross-sectional views in that they depict fabrication steps that are conducted on a wafer substrate, where  FIGS. 17-21  are taken from the location of the future air bearing surface (ABS) of the magnetic head;  FIG. 22  is taken from the ABS of the completed magnetic head  304 . As will be understood from the following description, the significant differences between the various magnetic heads of the present invention and the prior art magnetic head  30  depicted in  FIGS. 2 and 3  relates to the structure of the second magnetic shield, and other features and structures of the magnetic heads of the present invention may be similar to those of the prior art magnetic head  30 , and similar structures are numbered identically for ease of understanding.  
      With reference to  FIG. 17 , the initial fabrication steps of a read head portion  300  of a first embodiment of a magnetic head  304  of the present invention are depicted. As depicted in  FIG. 4 , the read head portion  300  includes a substrate base  32  with an insulation layer  34  formed thereon. An electrically conductive seed layer  35  is next deposited upon the insulation layer  34  and a first magnetic shield (S 1 )  36  is fabricated upon the seed layer  35 .  
      A first insulation layer (G 1 )  38  of the read head  300  is then deposited upon the wafer and the S 1  magnetic shield  36 . A magnetoresistive sensor  40 , comprising a plurality of layers of specifically chosen materials, is then fabricated upon the G 1  layer  38 . Thereafter, electrical leads  54  are fabricated from the sensor towards magnetic head electrical contacts (not shown) to conduct the electrical sense current to the sensor for providing magnetic data bit signals from the sensor  40 . A second insulation layer (G 2 )  56  is subsequently deposited across the top of the sensor  40  and electrical leads  54 .  
      As is next depicted in  FIG. 18 , a photoresist layer  306  is next deposited across the surface of the wafer and photolithographically patterned to create openings  316  within which the second magnetic shield is to be created. Thereafter, as depicted in  FIG. 19 , the wafer is subjected to a baking process in order to hard bake the photoresist. This is necessary to bake off moisture and volatile compounds within the resist layer that will otherwise interfere with the CZT material deposition process that follows. The hard baking of the photoresist in this step can create some dimensional problems, in that the edges of the photoresist shrink and become distorted during a hard bake process, such as from the dashed original unbaked profile  318  to the somewhat shrunken hard baked profile  320 . Due to the dimensional constraints of a magnetic head, the precise location of the second magnetic shield may be a significant parameter, and the first and second magnetic head embodiments described hereabove, which utilize a RIEable insulator layer, are somewhat favored over this third embodiment, in that the location of the second magnetic shield can be established with greater precision where an RIE process is used. However, where the possible amount of change in the magnetic shield location due to the hard baking of the photoresist is not a significant parameter, this third head embodiment is adaptable.  
      With reference to  FIG. 20 , the material  324  that comprises the second magnetic shield  328  is next deposited across the surface of the wafer in sufficient thickness to fill the magnetic shield opening  316  above the thickness of the hard baked photoresist  306 . The deposited magnetic shield material  324  must have appropriate magnetic properties to function as a magnetic shield for the sensor  40 , and a suitable material for the deposited second magnetic shield is cobalt zirconium tantalum, known as CZT.  
      As depicted in  FIG. 21 , a chemical mechanical polishing (CMP) is next conducted to remove the excess CZT material  324  down to the surface of the hard baked photoresist layer  306 . CZT is known to be a mechanically soft material, and the CMP process therefore relies on the hardness of the hard baked resist  306  as a polishing stop layer. As will be understood by those skilled in the art, a desirable CMP slurry is a silicon based slurry with hydrogen peroxide as an oxidizer; a preferred slurry utilizes MH817 plus H 2 O 2 . A recommended CMP pad is an IC 1000 KXY pad, and the CMP conditions include a 4 psi pressure at a 45 rpm polishing table rotation speed Following the CMP process the fabrication of the second magnetic shield  328  is completed. The CMP process results in a flat surface  332  upon which the further magnetic head components, as described hereabove, can be fabricated, including the fabrication of the write head components the dicing of the wafer substrate and the subsequent creation of the air bearing surface of the magnetic head, all as described hereabove.  FIG. 22  depicts the read head portion  300  of the third magnetic head embodiment  304  of the present invention as taken from the ABS surface. As depicted therein, the read head portion  300  includes the substrate base  32 , insulation layer  34 , seed layer  35 , first magnetic shield  36 , G 1  insulation layer  38 , sensor  40 , electrical leads  54 , G 2  insulation layer  56 , second magnetic shield  328 , hard baked resist  306 , and the electrical insulation layer  59  that is deposited upon the second magnetic shield and photoresist layer surface  332 . Thereafter, the write head portion (not shown in  FIG. 22 ) of the third magnetic head embodiment  304  is fabricated. This write head portion may be identical to the write head portion of the prior art magnetic head  30  as described hereabove. However, the magnetic head of the present invention is not to be so limited, and may include virtually any write head design that is compatible with the read head portion  300  described herein.  
      As with other embodiments of the present invention, a significant feature of the third magnetic head embodiment  304  of the present invention is that the improved material of the second magnetic shield results in reduced sensor signal noise. Also, the improved second magnetic shield may allow for the use of a thinner G 2  insulation layer, as described above. This would allow the magnetic shields  36  and  328  to be advantageously fabricated closer together, such that the read gap of the magnetic head  304  is reduced as compared to the prior art.  
      While the present invention has been shown and described with regard to certain preferred embodiments, it is to be understood that modifications in form and detail will no doubt be developed by those skilled in the art upon reviewing this disclosure. It is therefore intended that the following claims cover all such alterations and modifications that nevertheless include the true spirit and scope of the inventive features of the present invention.