Abstract:
A method is presented for fabricating a CPP read head having a CPP read head sensor and a hard bias layer which includes forming a strip of sensor material in a sensor material region, and depositing strips of fast-milling dielectric material in first and second fast-milling dielectric material regions adjacent to the sensor material region. A protective layer and a layer of masking material are deposited on the strip of sensor material and the strips of fast-milling dielectric material to provide masked areas and exposed areas. A shaping source, such as an ion milling source, is provided which shapes the exposed areas. Hard bias material is then deposited on the regions of sensor material and fast-milling dielectric material to form caps on each of these regions. The caps of hard bias material and the masking material are then removed from each of these regions.

Description:
The following is a continuation in part of pending application Ser. No. 11/081,222, entitled “METHOD TO IMPROVE ABILITY TO PERFORM CMP-ASSISTED LIFTOFF FOR TRACKWIDTH DEFINITION,” filed Mar. 15, 2005 now U.S. Pat. No. 7,270,758, having at least one common inventor; and, claims priority from and incorporates by reference pending application Ser. No. 11/081,222. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to magnetic heads for reading data written to storage media, and more particularly to magnetic read heads for disk drives. 
     2. Description of the Prior Art 
     In recent years there has been a constant drive to increase the performance of hard disk drives by increasing the areal data storage density of the magnetic hard disk. This is done by reducing the written data track width, such that more tracks per inch can be written on the disk. This naturally requires that the width of the read head be reduced so magnetic field interference from adjacent data tracks is not picked up. 
     Read sensors, of which one type is referred to as a “spin valve”, developed to read trackwidths smaller than 130 nm depend upon the ability to ion mill the sensor to these very small dimensions, and to reliably lift-off the deposited layer materials. A common problem with the fabrication of such small sensors is illustrated in  FIGS. 5-15 . 
     The sensor is typically formed of a stack of layers, which are generally formed as a region of magnetic material bounded by strips of dielectric or insulating materials.  FIG. 5  shows a top plan view of a portion of a wafer  41  as it is being prepared for shaping into a sensor  40 . The sensor material region  42  is shown to be bounded by a first dielectric material region  44  and a second dielectric material region  46 . These first and second dielectric material regions  44 ,  46  are chosen to be of non-conducting material. In the prior art, these are preferably chosen to be alumina so that these make up first and second alumina regions  54 ,  56 . A band of masking material  48  such as photoresist is then deposited to protect the material of the sensor material region  42 , and first and second dielectric material regions  44 ,  46  from being cut away during shaping processes such as ion milling. The width of the band of masking material  48  establishes the eventual width of the read head sensor  40  and thus the magnetic read width (MRW)  50 , which is approximately the same as, but somewhat less than, the trackwidth of the recorded track on the magnetic disk. The height of the sensor material region  42  establishes the stripe height  52  of the sensor  40 . 
     The difficulty arises when the exposed portions of sensor material region  42  and first and second alumina regions  54 ,  56  are subjected to ion milling, since the sensor material  42  and the first and second alumina regions  54 ,  56  have different milling rates, the sensor material  42  is removed faster than the alumina  54 ,  56 . A series of views of cross-sections of the sensor region  42 , as taken through line  6 - 6  in  FIG. 5 , and the first alumina region, as taken through line  7 - 7  of  FIG. 5  are shown side-by-side for comparison in  FIGS. 6-15 . Comparable stages of fabrication of a sensor layer stack  58  in the sensor region  42  are shown in  FIGS. 6 ,  8 ,  10 ,  12  and  14 , and of an alumina stack  60  in the alumina region  54  in  FIGS. 7 ,  9 ,  11 ,  13  and  15 , respectively. Since the relative heights of the layers at each stage of fabrication are at issue, the bottom of the sensor layer stack  58  and the bottom of the alumina layer stack  60 , are aligned in the pairs of drawings. 
     In the first stage,  FIG. 6  shows the layer of sensor material  62 , protective layer  64 , preferably composed of material such as Diamond-like carbon (DLC), and then a layer of masking material  48 , and  FIG. 7  shows the layer of alumina  66 , protective layer  64  and masking material  48 . 
     Next Reactive Ion Etching (RIE) is performed to shape the protective layer material  64  in both  FIGS. 8-9 . 
       FIGS. 10-11  show the effect of ion milling, which narrows the sensor material  62  to the dimensions of the mask material  48  and establishes the magnetic read width (MRW)  50 .  FIG. 11  shows that due to its slower milling rate, the alumina layer remaining  68  may be 200-300 Å thick, as compared to a typical sensor  62  thickness of 400 Å. 
       FIGS. 12 and 13  show the effects of depositing the hard bias/leads material  70  on both the sensor material region  42 , and the first alumina region  54 . The hard bias/leads are used to magnetically bias magnetic domains in certain layers of the sensor material  42 , and also to supply electric current to the sensor  40 . Therefore, in order to maintain the function of the sensor, it is important that the leads are not shorted together. The hardbias/leads material  70  is deposited in a blanketing layer over both the sensor material region  42  and alumina regions  54 ,  56 , (see  FIG. 5 ). In the sensor region  42 , the height of the masking material  48  is such that the hard bias/leads material  70  on the masking material  48  is removed vertically far enough from the material  72  deposited on the sides of the sensor that a gap  74  remains, so that three separate elements are formed, namely a first side lead  76  and second side lead  78 , and a hard bias/lead material cap  80 . 
     However in the alumina region  54 , shown in  FIG. 13 , since the residual step  68  remains, the hard bias/leads material  70  is raised vertically by this step height  82 , as shown by the two set of arrows  82 . Consequently, there is not enough vertical displacement of the side leads  76  and the cap  80 , so that there is no gap, and side material  72  commonly forms bridges  84  between them. First and second leads  76 ,  78  are thus no longer electrically isolated, and are thus shorted together. 
     The next process, shown in  FIGS. 14 and 15 , is a CMP (Chemical Mechanical Polishing) assisted liftoff. As shown in  FIG. 14 , this is intended to remove the cap  80  and the masking material  48  from the sensor  62 , leaving the first and second leads  76 ,  78  electrically isolated from each other, except for the conductive path through the sensor  62 , as it should be. However, as shown in  FIG. 15 , in the alumina region  54 , the masking material  48  has been unintentionally encapsulated by the hard bias/lead layer  70 , which is not removed by the CMP assisted process. Thus, this leaves an electrical short between the first and second side leads  76 ,  78 , which must be removed if the sensor  62  is to function properly. 
     Thus, there is a need for a fabrication method that prevents the formation of bridges in hardbias/lead material layer that produces electrical short circuits in disk drive read sensors. 
     SUMMARY OF THE INVENTION 
     A preferred embodiment of the present invention is a method for fabricating a CPP read head for a hard disk drive having a CPP read head sensor and a hard bias layer. The method includes depositing a strip of sensor material in a sensor material region, and depositing strips of fast-milling dielectric material in first and second fast-milling dielectric material regions adjacent to the sensor material region. Next, a protective layer is deposited on the sensor material region and the first and second fast-milling material regions. A layer of masking material is deposited on the strip of sensor material and the strips of fast-milling dielectric material to provide masked areas and exposed areas. A shaping source, such as an ion-milling source, is provided which shapes the exposed areas. Hard bias material is then deposited on the regions of sensor material and fast-milling dielectric material to form caps of hard bias material on each of these regions. The caps of hard bias material and the masking material are then removed from each of these regions. 
     It is an advantage of the present invention that the production of short circuits between hard bias/leads is minimized, thus increasing production yields. 
     It is another advantage that photoresist is not encapsulated by hard bias/lead material and is thus more easily removed. 
     It is a further advantage of the present invention that more uniform topography is produced, thus simplifying subsequent processing steps. 
     It is another advantage of the present invention that corner shunting is reduced or eliminated. 
     It is yet another advantage of the present invention that a negative residual step height can be produced, allowing for easier CMP operations. 
     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  shows a top plan view of an exemplary disk drive; 
         FIG. 2  illustrates a perspective view of view of an exemplary slider and suspension; 
         FIG. 3  shows a top plan view of an exemplary read/write head; 
         FIG. 4  is a cross-section view of an exemplary CIP read/write head; 
         FIG. 5  shows a top plan view a portion of a CIP read sensor showing strips of alumina and sensor material and photoresist material; 
         FIG. 6-15  show parallel pairs of cross-section views of the sensor region and the alumina region of the prior art at various stages of fabrication; and 
         FIG. 16-25  show parallel pairs of cross-section views of the sensor region and the alumina region of the present invention at various stages of fabrication; 
         FIG. 26  is a cross-section view of an exemplary CPP read/write head; 
         FIG. 27  is an isometric top view of a CPP read sensor of the prior art in an intermediate stage of fabrication illustrating corner shunting; 
         FIG. 28  is a detail view of the portion enclosed in detail box A of  FIG. 27  illustrating corner shunting; 
         FIG. 29  is an isometric top view of a CPP read sensor of the present invention in an intermediate stage of fabrication illustrating how corner shunting is avoided; 
         FIG. 30  is a detail view of the portion enclosed in detail box B of  FIG. 29  illustrating how corner shunting is avoided; 
         FIG. 31  shows a top plan view a portion of a CPP read sensor showing strips of alumina and sensor material and photoresist material; 
         FIG. 32-41  show parallel pairs of cross-section views of the sensor region and the alumina region of the prior art at various stages of fabrication; and 
         FIG. 42-51  show parallel pairs of cross-section views of the sensor region and the alumina region of the present invention at various stages of fabrication. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment of the present invention is a method of fabrication of read sensors that utilizes fast-milling dielectric material that more closely matches the milling rate of sensor material. The present invention is also a disk drive including a magnetic head having a read head having milled sensor layers above the dielectric layer, and a method for producing this read head. 
     A hard disk drive  2  is shown generally in  FIG. 1 , having one or more magnetic data storage disks  4 , with data tracks  6  which are written and read by a data read/write device  8 . The data read/write device  8  includes an actuator arm  10 , and a suspension  12  that supports one or more magnetic heads  14  included in one or more sliders  16 . 
       FIG. 2  shows a slider  16  in more detail being supported by suspension  12 . The magnetic head  14  is shown in dashed lines, and in more detail in  FIGS. 3 and 4 . The magnetic head  14  includes a coil  18  and P 1  pole, which also acts as S 2  shield, thus making P 1 /S 2   20 . P 1 /S 2  may also be made as two discrete layers. The second pole P 2   22  is separated from P 1 /S 2  by write gap  23 . 
     The read sensor  40  is sandwiched between the first shield S 1   30  and the second shield P 1 /S 2   20 . There is generally included an insulation layer  32  between the rest of the length of SI  30  and P 1 /S 2   20 . The magnetic head  14  flies on an air cushion between the surface of the disk  4  and the air-bearing surface (ABS)  24  of the slider  16 . The write head portion  26  and the read head portion  28  are generally shown, with the read head sensor  40  and the ABS  24 . 
     There are two configurations of read head in common use in the industry today. These are called Current Perpendicular to the Plane (CPP), and Current In the Plane (CIP). In the CPP configuration, Shield S 1  and P 1 /S 2  are made of conducting material which act as electrodes supplying current to the read sensor which lies between them. 
     The first embodiment of the present invention uses a CIP configuration, in which the current flows from side to side through the elements. For CIP read heads, the read sensor  40  is generally sandwiched between two insulation layers, usually designated G 1   34  and G 2   36  which are made of non-conductive material, to keep the circuit from shorting out. 
     Note that this structure is strictly for illustration only, and one skilled in the art will appreciate that sensor structures can vary dramatically from the one shown in  FIG. 4 , the methodology of the present invention being applicable to formation of all such heads. 
     The novelty of the present invention is best understood in comparison to processes of the prior art, as discussed above. A common problem with the fabrication of sensors of the prior art is illustrated in  FIGS. 5-15 . The sensor is typically formed of a stack of layers that are generally formed as a region of magnetic material bounded by strips of dielectric or insulating materials.  FIG. 5  shows a top plan view of a portion of a wafer  41  as it is being prepared for shaping into a CIP sensor  40 . The sensor material region  42  is shown to be bounded by a first dielectric material region  44  and a second dielectric material region  46 . These first and second dielectric material regions  44 ,  46  are chosen to be of non-conducting material. In the prior art, these are preferably chosen to be alumina so that these make up first and second alumina regions  54 ,  56 . A band of masking material  48  such as photoresist is then deposited to protect the material of the sensor material region  42 , and first and second dielectric material regions  44 ,  46  from being cut away during shaping processes such as ion milling. The width of the band of masking material  48  establishes the eventual width of the read head sensor  40  and thus the magnetic read width (MRW)  50 . The height of the sensor material region  42  establishes the stripe height  52  of the sensor  40 . 
     The difficulty arises when the exposed portions of sensor material region  42  and first and second alumina regions  54 ,  56  are subjected to ion milling, since the sensor material  42  and the first and second alumina regions  54 ,  56  have different milling rates, the sensor material  42  being removed faster than the alumina  54 ,  56 . A series of views of cross-sections of the sensor region  42 , as taken through line  6 - 6  in  FIG. 5 , and the first alumina region, as taken through line  7 - 7  of  FIG. 5  are shown side-by-side for comparison in  FIGS. 6-15 . Comparable stages of fabrication of a sensor layer stack  58  in the sensor region  42  are shown in  FIGS. 6 ,  8 ,  10 ,  12  and  14  and of an alumina stack  60  in the alumina region  54  in  FIGS. 7 ,  9 ,  11 ,  13  and  15 , respectively. Since the relative heights of the layers at each stage of fabrication are at issue, the bottom of the sensor layer stack  58  and the bottom of the alumina layer stack  60 , are aligned in the pairs of drawings. 
     In the first stage,  FIG. 6  shows the layer of sensor material  62 , protective layer  64 , preferably of material such as DLC, and then a layer of masking material  48 , and  FIG. 7  shows the layer of alumina  66 , protective layer  64  and masking material  48 . 
     Next Reactive Ion Etching (RIE) is performed to shape the protective layer material  64  in both  FIGS. 8-9 . 
       FIGS. 10-11  show the effect of a shaping operation such as ion milling, which narrows the sensor material  62  to the dimensions of the mask material  48  and establishes the magnetic read width (MRW)  50 .  FIG. 11  shows that due to its slower milling rate, the alumina layer remaining  68  may be 200-300 Å thick, as compared to a typical sensor  62  thickness of 400 Å. 
       FIGS. 12 and 13  show the effects of depositing the hard bias/leads material  70  on both the sensor material region  42 , and the first alumina region  54 . The hard bias/leads are used to magnetically bias magnetic domains in certain layers of the sensor material  42 , but also to supply electric current to the sensor  40 . Therefore, in order to maintain the function of the sensor, it is important that the leads are not shorted together. The hardbias/leads material  70  is deposited in a blanketing layer over both the sensor material region  42  and alumina regions  54 ,  56 , (see  FIG. 5 ). In the sensor region  42 , the height of the masking material  48  is such that the hard bias/leads material  70  on the masking material  48  is removed vertically far enough from the material  72  deposited on the sides of the sensor that a gap  74  remains, so that three separate elements are formed, namely a first side lead  76  and second side lead  78 , and a hard bias/lead material cap  80 . 
     However in the alumina region  54 , shown in  FIG. 13 , since the residual step  68  remains, the hard bias/leads material  70  is raised vertically by this step height  82 , as shown by the two set of arrows. Consequently, there is not enough vertical displacement of the side leads  76  and the cap  80 , so that there is no gap, and side material  72  commonly forms bridges  84  between them. First and second leads  76 ,  78  are thus no longer electrically isolated, and are thus shorted together. 
     The next process, shown in  FIGS. 14 and 15 , is a CMP (Chemical Mechanical Polishing) assisted liftoff. As shown in  FIG. 14 , this is intended to remove the cap  80  and the masking material  48  from the sensor  62 , leaving the first and second leads  76 ,  78  electrically isolated from each other, except for the conductive path through the sensor  62 , as it should be. However, as shown in  FIG. 15 , in the alumina region  54 , the masking material  48  has been unintentionally encapsulated by the hard bias/lead layer  70 , which is not removed by the CMP assisted process. Thus, this leaves an electrical short between the first and second side leads  76 ,  78 , which must be removed if the sensor  62  is to function properly. 
     In contrast,  FIGS. 16-25  show the method of fabrication of the present invention. In place of alumina, a dielectric material having a milling rate more closely comparable to that of the sensor material is used. This material shall be referred to, purposes of this discussion, and in  FIGS. 16-25 , which follow, as fast-milling dielectric  90 . Ideally, the milling rate of this fast milling dielectric would exactly match that of the sensor material. However, an exact match is not necessary, as long as the milling rates are close enough that a step height from residual material is small enough that bridges do not form in the hard bias/lead material which then interfere with the CMP assisted removal of the masking material and excess hard bias/lead material. It is estimated that a step height of 50 Å or less in the residual dielectric, which might be achieved through either full or partial mill, including a combination of mill angles, will provide satisfactory results. A partial list of materials which may be used as the fast-milling dielectric include Ta 2 O 5 , SiO 2 , Si 3 N 4 , AlN, variable compositions of Al—Si—O—N, HfO 2 , ZrO 2 , and Hf 1-x Si x O 2 . It will be understood by those skilled in the art that this list is not to be considered limiting and that many other materials would fit the definition of fast-milling dielectrics. 
     In a similar manner to that shown before,  FIG. 5  will be used to show the regions of sensor material, and a first region of fast-milling dielectric material  94  and second region of fast-milling dielectric material  96 . As before, a series of views of cross-sections of the sensor region  42 , as taken through line  6 - 6  in  FIG. 5 , and the first fast-milling material region  94 , as taken through line  7 - 7  of  FIG. 5  are shown, this time in  FIGS. 16-25 . Comparable stages of fabrication of a sensor layer stack  58  in the sensor region  42  are shown in  FIGS. 16 ,  18 ,  20 ,  22  and  24  and of a fast-milling dielectric stack  92  in the first fast-milling dielectric material region  94  in  FIGS. 17 ,  19 ,  21 ,  23  and  25 , respectively. Once again, the bottom of the sensor layer stack  58  and the fast-milling dielectric stack  92 , are level in the pairs of drawings. 
     In the first stage,  FIG. 16  shows the layer of sensor material  62 , protective layer  64 , preferably of material such as DLC, and then a layer of masking material  48 , and  FIG. 17  shows the fast-milling dielectric stack  92 , including the layer of fast-milling dielectric material  90 , protective layer  64  and masking material  48 . 
     Next Reactive Ion Etching (RIE) is performed to shape the protective layer material  64  in both the sensor layer stack  58  and the fast-milling dielectric stack  92  as seen in  FIGS. 18-19 . 
       FIGS. 20-21  show the effect of ion milling, using any of a variety of ion-beam, etch tools, and which narrows the sensor material  62  to the dimensions of the mask material  48  and establishes the magnetic read width (MRW)  50 .  FIG. 21  shows that the fast-milling dielectric stack  92 , due to its faster, but not exactly matching milling rate, still retains a reduced residual step  98  having a residual step height  99  which is 10-20 Å in height, compared to typical thickness of 400 Å of the sensor material  62 . As referred to above, it is estimated that a step height of 50 Å or less in the residual dielectric will provide satisfactory results. This also compares favorably with a height of 100-200 Å of the residual step  68  of the prior art (see  FIG. 13 ). 
       FIGS. 22 and 23  show the effects of depositing the hard bias/leads material  70  on both regions  42 ,  94  (see  FIG. 5 ). In the sensor region  42 , the height of the masking material  48  is such that the hard bias/leads material  70  on the masking material  48  is removed vertically far enough from the material  72  deposited on the sides of the sensor  62  that a gap  74  remains, so that three separate elements are formed, namely a first side lead  76  and second side lead  78 , and a hard bias/lead material cap  80 . In comparison, in the fast-milling dielectric stack  92  of the present invention, the reduced residual step  98  has a residual step height  99 , which is small enough that there is still enough distance that the material  72  deposited on the sides of the sensor does not join with the material in the first side lead  76  and second side lead  78 , and a gap  74  remains. Now there are three separate elements are formed, namely a first side lead  76  and second side lead  78 , and a hard bias/lead material cap  80 , as in the sensor layer stack  58 . 
     When CMP assisted liftoff is completed, as shown in  FIGS. 24 and 25 , the cap  80  and the masking material  48  are removed from both the sensor  62 , and the fast-milling dielectric stack  92  leaving both sets of first and second leads  76 ,  78  electrically isolated from each other, except for the conductive path through the sensor  62 , as it should be. 
     As discussed above, there are two configurations of read head in common use in the industry today. These are called Current Perpendicular to the Plane (CPP), and Current In the Plane (CIP). The detailed description above had concerned a read head of the CIP configuration. 
     However, an alternative embodiment of the present invention concerns a read head of the CPP configuration. As a general convention, in the following discussion, when elements are similar to those used in the prior discussion, the same element numbers will be used. Elements that differ in the CPP configuration from those in the CIP configuration will use a numbering convention using elements in the 100s, wherever possible. Thus, the CIP read sensor was referred to as “40” and the CPP sensor will be referred to as “140”. 
     In the CPP configuration, shields S 1  and S 2  are made of conducting material that act as electrodes supplying current to the read sensor that lies between them. The slider shown in  FIG. 26  is of a Current Perpendicular to Plane (CPP), configuration wherein current flows vertically in the pictured figure rather than horizontally. The magnetic head  14  includes a coil  18 , P 1  pole  20 , and a second pole P 2   22  that is separated from P 1  pole  20  by write gap  23 . The P 1  pole  20 , second pole P 2   22  and write gap  23  can be considered together to be included in the write head  26 . 
     A read sensor  140  is sandwiched between a first shield, designated as S 1   130  and a second shield S 2   134 , and these elements together make up the read head  128 . In this configuration of read head  128  where Current is Perpendicular to the Plane (CPP), shields S 1   130  and S 2   134  act as top electrode  159  and bottom electrode  160 , respectively, supplying current to the read sensor  140  that lies between them. An insulation layer  32  also separates the S 1   130  and S 2   134  electrical leads in the area behind the read sensor  140 , so that the leads do not shunt current away from sensor. As before, the magnetic head  14  flies on an air cushion between the surface of the disk  4  and the air-bearing surface (ABS)  24  of the slider  16 . 
     Note that this structure is strictly for illustration only, and one skilled in the art will appreciate that sensor structures can vary dramatically from the one shown in  FIG. 26 , the methodology of the present invention being applicable to formation of all such heads. In particular, an insulating layer (not shown) between S 2   134  and P 1   20  is present in the so-called “piggy-back” head design, whereas such an insulating layer is absent from the so-called “merged” head design shown in  FIG. 26 . The former “piggy-back” head design is that which is preferred in CPP sensors. 
     As in the CIP configuration discussed above, the fabrication process for a read head of CPP configuration can experience problems when the dielectric material surrounding the sensor mills at a slower rate than that of the sensor material. The CPP configuration, however, has different potential problems, one of which is illustrated in  FIGS. 27 and 28  (prior art) and will be discussed below. 
     A common type of CPP sensor, called a TMR sensor, has an insulating tunnel barrier layer that separates two ferromagnetic layers. Sense current flows perpendicular to the surfaces of the ferromagnetic layers. In the TMR sensor, the sense current flowing through the tunnel barrier layer is strongly dependent upon a spin-polarization state of the two ferromagnetic layers. When the magnetizations of the two ferromagnetic layers are antiparallel to each other, the tunnel current is lowered, so that a high junction resistance is obtained. Alternately, when the magnetizations of the two ferromagnetic layers are parallel to each other, the tunnel current is heightened; and, thus, a low junction resistance is obtained. 
     In order to simplify the following discussion, the various layers of the TMR sensor are not illustrated with the exception of the tunnel barrier layer. The important point to note is that current flows from an upper electrode to a lower electrode through the sensor material. There should not be any other conductive path linking the electrodes directly to the tunnel junction layer aside from the conductive layers in the sensor itself, because this will shunt current away from the sensor with an attendant loss of its sensitivity, in effect partially, or completely, “shorting out” the sensor. 
     Reference is now made to  FIGS. 27 and 28  (prior art), which show exactly this condition happening.  FIG. 28  is an enlarged detail view of the detail box A enclosed by dashed lines in a portion of  FIG. 27 . These figures show isometric views of a CPP read head sensor  140  in an intermediate stage of fabrication. The sensor material  142  has been formed on the lower electrode  160 , and surrounding layers of conventional dielectric material  45 ,  47  have been formed around the sensor material  142  in a similar manner to that discussed above. The sensor material  142  and dielectric material  45 ,  47  to the left and the right of the sensor, respectively, have been milled to form the magnetic read width (MRW) dimension  50  and the stripe height  52  of the sensor  140 . Note that the stripe height  52  that exists at wafer-level processing differs from the final stripe height of the sensor after the wafer has been cut into rows in the so-called slider-fabrication process, where the stripe height is further reduced by lapping to the required dimension of a functioning sensor in the read head, as is known in the art. As shown more clearly in  FIG. 28 , the conventional dielectric material  44  has milled at a slower rate than the sensor material  142 , leaving a step height  82 , as in the discussion above. The tunnel barrier layer  150  is shown as part of the sensor material  142 . 
     In the course of milling operations, residual material  100  is generated, which can be partly composed of small particles of the sensor material  142 , and hence may be electrically conductive. This residual material  100  is especially difficult to remove from the corner areas of the sensor  140 . In the prior art, using conventional dielectric  45 , generally alumina, the milling rate of the dielectric does not closely match the milling rate of the sensor material  142 , and thus a residual step height  82  remains between the alumina  45  and the sensor material  142 . The step height  82  of the conventional dielectric  45  allows the residual material  100  to accumulate in the corners until it bridges across the tunnel barrier material  150  and creates an unwanted electrical path to the lower electrode  160  by creating an electrical shunt that “shorts out” the sensor. This is known as “corner shunting”. This is, of course, undesirable, and the following  FIGS. 29 and 30  show how this problem is solved by the use of the method of the present invention. 
       FIG. 30  is an enlarged detail view of the detail box B enclosed by dashed lines in a portion of  FIG. 29 . These figures again show isometric views of a CPP read head sensor  140  in the same intermediate stage of fabrication. Once again, the sensor material  142  and dielectric material, this time using fast-milling dielectric material  90 , on the left of the sensor  95 , and on the right of the sensor  97 , have been milled to form the magnetic read width (MRW) dimension  50  and the stripe height  52  of the sensor  140 . The fast-milling dielectric material  90 ,  95 ,  97  as used in the present invention, results in a much reduced residual step height  99 . Accumulated milling residue  100  which builds up in the corner cannot bridge across the tunnel barrier layer  150 , and thus corner shunting of this type is eliminated. As will be discussed below, it is possible that this residual step height  99  can be a negative value if the dielectric material is completely removed, and the underlying electrode material  160  is milled into slightly. 
     In a similar manner to that discussed above,  FIG. 31  shows a top plan view of a portion of a wafer  141  as it is being prepared for shaping into a CPP sensor  140 . The sensor material region  142  is shown to be bounded by first dielectric material region at the back side of the sensor  44  and second dielectric material region at the front of the sensor  46  as before. In the prior art, these are preferably chosen to be alumina so that these make up first and second alumina regions  54 ,  56 . A band of masking material  48  such as photoresist is then deposited to protect the material of the sensor material region  142 , and first and second dielectric material regions  44 ,  46  from being cut away during shaping processes such as ion milling. The width of the band of masking material  48  establishes the eventual width of the read head sensor  140  and thus the magnetic read width (MRW)  50 . The height of the sensor material region  142  establishes the stripe height  52  of the sensor  140  during the wafer process. 
     In a similar manner to that discussed above, the following series of figures will depict the cross-sectional views of the material stacks of the CPP sensor as taken through section lines  8 - 8  and  9 - 9 . The series of views of cross-sections of the sensor region  142 , as taken through line  8 - 8  in  FIG. 31 , and the first alumina region  54 , as taken through line  9 - 9  of  FIG. 31  are shown side-by-side for comparison in  FIGS. 32-41 .  FIGS. 32-41  show the cross-sections as seen in the prior art, using alumina as the dielectric material, and  FIGS. 42-51  show the cross-sectional views of a first fast-milling dielectric material  94  region, as in the method of the present invention. 
     Comparable stages of fabrication of a sensor layer stack  158  in the sensor material region  142  are shown in  FIGS. 32 ,  34 ,  36 ,  38 , and  40  and of an alumina stack  60  in the alumina region  54  in  FIGS. 33 ,  35 ,  37 ,  39  and  41 , respectively. Since the relative heights of the layers at each stage of fabrication is of interest here, the bottom of the sensor layer stack  158  and the bottom of the alumina layer stack  60 , are aligned in the pairs of drawings. 
     In the first stage,  FIG. 32  shows the electrode layer  160  upon which are formed a layer of sensor material  162 , including the tunnel barrier layer  150 , a protective layer  64 , and a layer of masking material  48 .  FIG. 33  shows the electrode layer  160  followed by a layer of alumina  66 , a protective layer  64  and masking material  48 . 
     Reactive Ion Etching (RIE) is next performed to shape the protective layer material  64  in both  FIGS. 34 and 35 . 
       FIGS. 36 and 37  show the effect of a shaping operation such as ion milling, which narrows the sensor material  162  to the dimensions of the mask material  48  and establishes the magnetic read width (MRW)  50 .  FIG. 37  shows that due to its slower milling rate, the alumina layer remaining as a residual step  68  may be 150-300 Å thick, as compared to a typical sensor  162  material thickness of 300˜400 Å. A layer of insulating material  176  is formed on both the sensor stack  158  and the alumina layer stack  60 . This insulating material prevents electrical shorts and is another important difference from the structure of the CIP read head discussed earlier. 
       FIGS. 38 and 39  show the effects of depositing hard bias material  170  on both the sensor material region  142 , and the first alumina region  54 . The hard bias material  170  is used to magnetically bias magnetic domains in certain layers of the sensor material  142 . It is also generally electrically conductive, and this is the reason that the insulating layer  176  is important in a CPP configuration, to maintain electrical isolation. The hard bias material  170  is deposited in a blanketing layer over both the sensor material region  142  and alumina region  54 . In the sensor region  142 , the height of the masking material  48  is such that the hard bias material  170  on the masking material  48  is removed vertically far enough from the material  172  deposited on the sides of the masking material  48  that a gap  74  remains or a thin separation layer separates the hard bias material cap  180  from the other hard bias material  170 . 
     However, in the alumina region  54 , shown in  FIG. 39 , since the residual step  68  remains, the hard bias material  170  is raised vertically by this step height  82 , as shown by the two set of arrows. Consequently, there is not enough vertical displacement and no gap remains. The side material  172  commonly forms bridges  84  between the cap  180  and the remaining hard bias material  170 . 
     The next process, shown in  FIGS. 40 and 41 , is a CMP (Chemical Mechanical Polishing) assisted liftoff. As shown in  FIG. 40 , this is intended to remove the cap  180  and the masking material  48  from the sensor  162 . However, as discussed above with reference to  FIG. 39 , in the alumina region  54 , the masking material  48  has been unintentionally encapsulated by the hard bias material  170 , which may not be removed by the CMP assisted process. Thus, this leaves material behind the sensor, which must be removed if the sensor  162  is to function properly. This is not shown here, but is analogous to the condition discussed above with reference to the CIP configuration and shown in  FIG. 15  above. 
     Alternatively, the CMP process may indeed remove the cap  180 , and plane the hard bias material  170  down to the level of the protective layer  64 , as seen in  FIGS. 40 and 41 . However, due to the residual step  66  of the alumina layer  68 , the hard bias material  170  is raised higher then it should be, so when the CMP process laps it down to the level of the protective layer  64 , the hard bias layer  170  is reduced by the same thickness of the step height  82  of excess alumina  66  below it. The effectiveness of the hard bias material  170  to bias the free layer (not shown) of the sensor is dependent upon the thickness of material included. Since the thickness is thus reduced, the effectiveness of the hard bias material  170  is likewise reduced and performance of the sensor  140  may be compromised. 
     In contrast,  FIGS. 42-51  show the method of fabrication of a CPP sensor of the present invention. In place of alumina, a dielectric material having a milling rate more closely comparable to that of the sensor material is used. As previously discussed, this material shall be referred to as fast-milling dielectric  90 . A partial list of materials, which may be used, include Ta 2 O 5 , SiO 2 , Si 3 N 4 , AlN, variable compositions of Al—Si—O—N, HfO 2 , ZrO 2 , and Hf 1-x Si x O 2 . It will be understood by those skilled in the art that this list is not to be considered limiting and that many other materials would fit the definition of fast-milling dielectrics. 
     In a similar manner to that shown before,  FIG. 31  shows the regions of sensor material, and a first region of fast-milling dielectric material  94  and second region of fast-milling dielectric material  96 . As before, a series of views of cross-sections of the sensor region  42 , as taken through line  8 - 8  of  FIG. 31  and the first fast-milling material region  94 , as taken through line  9 - 9  of  FIG. 31  are shown, this time in  FIGS. 42-51 . Comparable stages of fabrication of a sensor layer stack  158  in the sensor region  142  are shown in  FIGS. 42 ,  44 ,  46 ,  48 , and  50  and of a fast-milling dielectric stack  92  in the first fast-milling dielectric material region  94  in  FIGS. 43 ,  45 ,  47 ,  49 , and  51 , respectively. Once again, the bottom of the sensor layer stack  158  and the fast-milling dielectric stack  92 , are coincident lying within the same plane in the pairs of drawings. 
     In the first stage,  FIG. 42  shows the electrode layer  160  upon which are formed a layer of sensor material  162 , including the tunnel barrier layer  150 , a protective layer  64 , and a layer of masking material  48 .  FIG. 43  shows the fast-milling dielectric stack  92  of the first fast-milling region  94 , including the electrode layer  160  followed by a layer of fast-milling dielectric material  90  a protective layer  64  and masking material  48 . 
     Next Reactive Ion Etching (RIE) is performed to shape the protective layer material  64  in both the sensor layer stack  158  and the fast-milling dielectric stack  92  as seen in  FIGS. 44-45 . 
       FIGS. 46-47  show the effect of ion milling, using any of a variety of ion-beam, etch tools, and which narrows the sensor material  162  to the dimensions of the mask material  48  and establishes the magnetic read width (MRW)  50 . The fast-milling dielectric stack  92 , due to its faster, but not exactly matching milling rate, may still retain a reduced residual step  98  having a residual step height  99  in a similar manner to that shown in  FIG. 21  of the CIP configuration. This is much reduced compared to the residual step  68  of the prior art having residual step height  82  (see  FIG. 39 ). The layer of insulating material  176  is formed on both the sensor layer stack  158  and the fast-milling dielectric stack  92 , as described above. 
     Alternatively, the fast-milling dielectric material  90  may mill even slightly faster then the material of the sensor stack  158 . This may allow all of the fast-milling dielectric  90  in this region to be removed, as well as thin layer of the electrode material  160 . This results in a negative step height  182 , which is shown in  FIGS. 47 ,  49  and  51 . It is believed that this negative step height, or reduced electrode thickness will not negatively affect performance of the read head, if the negative step height is within the range of 0 to 300 Å. 
       FIGS. 48 and 49  show the effects of depositing the hard bias material  170  on both regions  142 ,  94 . In the sensor region  142 , the height of the masking material  48  is such that the hard bias material  170  on the masking material  48  is removed vertically far enough that a gap  74  or a thin area remains, allowing for easy removal of the bias material cap  180 . In comparison, in the fast-milling dielectric stack  92  of the present invention, the reduced residual step  98  has a residual step height  99 ,  182 , which is small enough, (or even negative, as shown in the figure) that an even larger gap  74  or a thin area again remains. The hard bias material cap  180  is thus easily removed. Also, the thickness of the hard bias material  170  is not compromised as in the case of the prior art discussed above, and thus the biasing effect of the hard bias layer  170  is also not reduced. 
     When CMP assisted liftoff is completed, as shown in  FIGS. 50 and 51 , the cap  180  and the masking material  48  are removed from both the sensor  162 , and the fast-milling dielectric stack  92 . The result is a read sensor  140  that does not encounter the problems discussed above pertaining to corner shunting. 
     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.