Patent Publication Number: US-7712207-B2

Title: Method of manufacturing a wrap around shield for a perpendicular write pole using a laminated mask with an endpoint detection layer

Description:
FIELD OF THE INVENTION 
     The present invention relates to perpendicular magnetic recording and more particularly to a novel trailing wrap around magnetic shield design and a method for manufacturing such a shield design. 
     BACKGROUND OF THE INVENTION 
     The heart of a computer&#39;s long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. 
     The write head traditionally includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic transitions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk. 
     In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current, therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. 
     The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos Θ, where Θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals. 
     When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When a spin valve employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. An AP spin valve includes first and second magnetic layers separated by a thin non-magnetic coupling layer such as Ru. The thickness of the spacer layer is chosen so as to be antiparallel coupled to the magnetizations of the ferromagnetic layers of the pinned layer. A spin valve is also known as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed alter the free layer) or at the bottom (before the free layer). 
     The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers. 
     Magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (API) with a layer of antiferromagnetic material such as PtMn. While an antiferromagnetic (AFM) material such as PtMn does not in and of itself have a magnetization, when exchange coupled with a magnetic material, it can strongly pin the magnetization of the ferromagnetic layer. 
     In order to meet the ever increasing demand for improved data rate and data capacity, researchers have recently been focusing their efforts on the development of perpendicular recording systems. A traditional longitudinal recording system, such as one that incorporates the write head described above, stores data as magnetic bits oriented longitudinally along a track in the plane of the surface of the magnetic disk. This longitudinal data bit is recorded by a fringing field that forms between the pair of magnetic poles separated by a write gap. 
     A perpendicular recording system, by contrast, records data as magnetizations oriented perpendicular to the plane of the magnetic disk. The magnetic disk has a magnetically soft underlayer covered by a thin magnetically hard top layer. The perpendicular write head has a write pole with a very small cross section and a return pole having a much larger cross section. A strong, highly concentrated magnetic field emits from the write pole in a direction perpendicular to the magnetic disk surface, magnetizing the magnetically hard top layer. The resulting magnetic flux then travels through the soft underlayer, returning to the return pole where it is sufficiently spread out and weak that it will not erase the signal recorded by the write pole when it passes back through the magnetically hard top layer on its way back to the return pole. 
     One of the features of perpendicular recording systems is that the high coercivity top layer of the magnetic medium has a high switching field. This means that a strong magnetic field is needed to switch the magnetic moment of the medium when writing a magnetic bit of data. In order to decrease the switching field and increase recording speed, attempts have been made to angle or “cant” the write field being emitted from the write pole. Canting the write field at an angle relative to the normal of the medium makes the magnetic moment of the medium easier to switch by reducing the switching field. Modeling has shown that a single pole writer in a perpendicular recording system can exhibit improved transition sharpness (i.e. better field gradient and resolution), achieve better media signal to noise ratio, and permit higher coercive field media for higher areal density magnetic recording if, according to the Stoner-Wohlfaith model for a single particle, the effective flux field is angled. A method that has been investigated to cant the magnetic field has been to provide a trailing magnetic shield adjacent to the write head, to magnetically attract the field from the write pole. 
     The trailing shield can be a floating design, in that the magnetic trailing shield is not directly, magnetically connected with the other structures of the write head. Magnetic field from the write pole results in a flux in the shield that essentially travels through the magnetic medium back to the return pole of the write head. Alternatively, the trailing shield can be magnetically connected with other magnetic portion of the write head such as the write pole and return pole. 
     Various dimensions of the shield are critical for the trailing shield to operate correctly. For instance, effective angling or canting of the effective flux field is optimized when the write pole to trailing shield separation (gap) is about equal to the head to soft underlayer spacing (HUS) and the trailing shield throat height is roughly equal to half the track-width of the write pole. This design improves write field gradient at the expense of effective flux field. To minimize effective flux field lost to the trailing shield and still achieve the desired effect, the gap and shield thickness are adjusted to minimize saturation at the shield and effective flux field lost to the shield respectively. In order for a trailing shield to function optimally, the thickness of the trailing shield gap must be tightly controlled. Therefore, there is a need for a means for accurately controlling such trailing gap thickness during manufacture. 
     In addition, the track width and shape of the write pole must be tightly controlled. The write pole is preferably configured with a trapezoidal shape and preferably has a straight fiat trailing edge. The write pole can be formed by ion milling a magnetic material at such an angle or combination of angles that a write pole having the desired trapezoidal shape is formed. A challenge to creating such a well defined pole structure is that the mask used during ion milling must be thick and robust to withstand the aggressive ion mill and form a write pole having a well controlled track width and flat, straight trailing edge. Such a mask structure does not lend itself well to functioning as a trailing shield gap, because, alter the ion milling, the remaining mask is not flat and does not have the desired small, well controlled thickness to function as a trailing shield gap. 
     Therefore, there is a need for a method for manufacturing a perpendicular write head that can produce a write pole having a well controlled track width and flat trailing edge, while still producing a trailing, wrap around shield that has a trailing gap with a well controlled thickness and shape. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for manufacturing a magnetic write head for perpendicular recording having a wrap around trailing shield. The method includes depositing a magnetic write pole material over a substrate and then forming mask structure over the magnetic write pole material. The mask structure includes a hard mask-layer with an end point detection layer embedded therein at a desired elevation within the hard mask layer. The end point detection layer can be a material that is essentially the same as the rest of the hard mask except with a small amount of an easily detectable element added therein. 
     An ion milling operation is performed to remove magnetic write pole material not covered by the mask structure, to form the write pole. A non-magnetic material is then deposited and a reactive ion mill is performed to remove the non-magnetic material until the end point detection layer has been reached and removed. 
     The present invention provides end point detection while reducing the number of mask layers that, must be deposited, while maximizing the amount of ion mill resistant, material in the hard mask structure. The invention uses innovative hard mask materials, which have the end point detection marker embedded in the hard mask material in low-concentration. In this way, the hard mask material retains its low ion mill rate properties while also serving as an end point detection marker. 
     These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale. 
         FIG. 1  is a schematic illustration of a disk drive system in which the invention might be embodied; 
         FIG. 2  is an ABS view of a slider, taken from line  2 - 2  of  FIG. 1 , illustrating the location of a magnetic head thereon; 
         FIG. 3  is a cross sectional view, taken from line  3 - 3  of  FIG. 2  and rotated 90 degrees counterclockwise, of a magnetic head according to an embodiment of the present invention; 
         FIG. 4  is an ABS view of the write head taken from line  4 - 4  of  FIG. 3   
         FIG. 5  is an enlarged view of a write pole and surrounding structure; 
         FIGS. 6-15  are ABS views similar to that of  FIGS. 4 and 5 , showing a magnetic head in various intermediate stages of manufacture and illustrating a method of manufacturing a magnetic head according to an embodiment of the invention; and 
         FIGS. 16-18  are views of a magnetic write head in various intermediate stages of manufacture illustrating a method of manufacturing a write head according to an alternate embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description is of the best embodiments presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein. 
     Referring now to  FIG. 1 , there is shown a disk drive  100  embodying this invention. As shown in  FIG. 1 , at least one rotatable magnetic disk  112  is supported on a spindle  114  and rotated by a disk drive motor  118 . The magnetic recording on each disk is in the form of annular patterns of concentric data tracks (not shown) on the magnetic disk  112 . 
     At least one slider  113  is positioned near the magnetic disk  112 , each slider  113  supporting one or more magnetic head assemblies  221 . As the magnetic disk rotates, slider  113  moves radially in and out over the disk surface  122  so that the magnetic head assembly  121  may access different tracks of the magnetic disk where desired data, are written. Each slider  113  is attached to an actuator arm  119  by way of a suspension  115 . The suspension  115  provides a slight spring force which biases slider  113  against the disk, surface  122 . Each actuator arm  119  is attached to an actuator means  127 . The actuator means  127  as shown in  FIG. 1  may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by controller  129 . 
     During operation of the disk storage system, the rotation of the magnetic disk  112  generates an air bearing between the slider  113  and the disk surface  122  which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension  115  and supports slider  113  off and slightly above the disk surface by a small, substantially constant spacing during normal operation. 
     The various components of the disk storage system are controlled in operation by control signals generated by control unit  129 , such as access control signals and internal clock signals. Typically, the control unit  129  comprises logic control circuits, storage means and a microprocessor. The control unit  129  generates control signals to control various system operations such as drive motor control signals on line  123  and head position and seek control signals on line  128 . The control signals on line  128  provide the desired current profiles to optimally move and position slider  113  to the desired data track on disk  112 . Write and read signals are communicated to and from write and read heads  121  by way of recording channel  125 . 
     With reference to  FIG. 2 , the orientation of the magnetic head  121  in a slider  113  can be seen in more detail.  FIG. 2  is an ABS view of the slider  113 , and as can be seen the magnetic head including an inductive write head and a read sensor, is located at a trailing edge of the slider. The above description of a typical magnetic disk storage system, and the accompanying illustration of  FIG. 1  are for representation purposes only. It should be apparent that disk storage systems may contain a large number of disks and actuators, and each actuator may support a number of sliders. 
     With reference now to  FIG. 3 , the magnetic head  221  for use in a perpendicular magnetic recording system is described. The head  221  includes a write element  302  and a read element  304  that includes a magnetoresistive sensor  305 . The read sensor  305  is preferably a giant magnetoresistive (GMR) sensor and is preferably a current perpendicular to plane (CPP) GMR sensor. CPP GMR sensors are particularly well suited for use in perpendicular recording systems. However, the sensor  305  could be another type of sensor such as a current in plane (CIP) GMR sensor or, a tunnel junction sensor (TMR) or some other type of sensor. The sensor  305  is located between and insulated from first and second magnetic shields  306 ,  308  and embedded in a dielectric material  307 . The magnetic shields, which can be constructed of for example CoFe or NiFe, absorb magnetic fields, such as those from up-track or down track data signals, ensuring that the read sensor  304  only detects the desired data track located between the shields  306 ,  308 . A non-magnetic, electrically insulating gap layer  309  may be provided between the shield  308  and the write head  302 . 
     With continued reference to  FIG. 3 , the write element  302  includes a write pole  310  that is magnetically connected with a magnetic shaping layer  312 , and is embedded within an insulation material  311 . The write pole  310  has a small cross section at the air bearing surface and is constructed of a material having a high saturation moment, such as NiFe or CoFe. The shaping layer  312  is constructed of a magnetic material such as CoFe or NiFe. 
     The write element  302  also has a return pole  314  that preferably has a surface exposed at the ABS and has a cross section parallel with the ABS surface that is much larger than that of the write pole  310 . This can be seen more clearly with reference to  FIG. 4 , which shows the head  221  as viewed from the air bearing surface (ABS). The return pole  314  is magnetically connected with the shaping layer  312  by a back gap portion  316 . The return pole  314  and back gap  316  can be constructed of, for example, NiFe, CoFe or some other magnetic material. 
     An electrically conductive write coil  317 , shown in cross section in  FIG. 3 , passes through the write element  302  between the shaping layer  312 , and the return pole  314 . The write coil  317  is surrounded by an electrically insulating material  320  that electrically insulates the turns of the coil  317  from one another and electrically isolates the coil  317  from the surrounding magnetic structures  310 ,  312 ,  316 ,  314 . When a current passes through the coil  317 , the resulting magnetic field causes a magnetic flux to flow through the return pole  314 , back gap  316 , shaping layer  312  and write pole  310 . This magnetic flux causes a write field to be emitted toward an adjacent magnetic medium (not shown in  FIGS. 3 and 4 ). The shaping layer  312  is also surrounded by an insulation layer  321  which separates the shaping layer  312  from the ABS. The insulation layers  320 ,  321 ,  311  can all be constructed of the same material, such as alumina (Al 2 0 3 ) or of different electrically insulating materials. 
     The write head element  302  also includes a trailing shield  322 . With reference to  FIG. 4 , the trailing shield  322  wraps around the write pole  310  to provide side shielding as well as trailing shielding from stray magnetic fields. These stray magnetic fields can be from portions of the write head  302  itself, or could also be from adjacent track signals or from magnetic fields from external sources. 
     With reference now to  FIG. 5  the configuration of the write pole  310  and the surrounding portions of the trailing shield  322  are shown enlarged and in greater detail. The write pole  310  has a trailing edge  402  and a leading edge  404 . The terms trailing and leading are with respect to the direction of travel along a data track when the write head  302  is in use. The write pole  310  also preferably has first and second laterally opposing sides  406 ,  408  that are configured to define a width at the leading edge  404  that is narrower than the width at the trailing edge  402 , forming a write pole  310  having a trapezoidal shape. This trapezoidal shape is useful in preventing adjacent track writing due to skew of the write head  302  when the head  302  is located at extreme outer or inner positions over the disk, however, this trapezoidal shape of the write head  310  is not necessary to practice the present invention. 
     With continued reference to  FIG. 5 , the magnetic trailing shield  322  is separated from each side  406 ,  408  of the write pole  310  by a side gap  410 . The trailing shield  322  is also separated from the trailing edge  402  of the write pole  310  by a trailing gap  412 . The thickness of each of the side gaps  410  is preferably about 2 to 4 or about 3 times the thickness of the trailing gap  412 . The materials defining and filling the side and trailing gaps  410 ,  412  are non-magnetic materials. The trailing gap  412  is filled with a non-magnetic material  416 , which may be alumina or may be some other non-magnetic material. Similarly, the side gaps  410  include a non-magnetic side gap material  414  which may be, for example, conformally deposited alumina. 
     As can be seen with reference to  FIG. 5 , the trailing shield  322  may or may not be configured with notches  418  at either side of the write pole  310 . The notches can be described as extensions of the side gaps  410  that extend in the trailing direction slightly beyond the trailing edge gap  412 . These optional notches  418  can be constructed by a manufacturing process that will be described below, and can improve the magnetic performance of the write element  302 . Preferably the notches have a notch depth (ND) that is less than or equal to 30 nm. The trailing shield  322  can be constructed, of a magnetic material such as NiFe. 
     With reference now to  FIGS. 6 through 15 , a method for constructing a write pole and a wrap around trailing shield according to an embodiment is described. The method described with reference to  FIGS. 6-15  can form a trailing shield with notches  418  and with a very well controlled trailing gap thickness  412  as described above with reference to  FIG. 5 . 
     With particular reference to  FIG. 6 , a substrate layer  600  is provided. The substrate  600  can include the non-magnetic fill layer  321  and the shaping layer  312  on which the write pole  310  is to be formed ( FIG. 3 ). One or more layers of write pole material  602  are deposited over the substrate  600 . The write pole layer  604  preferably is a lamination of magnetic layers such as CoFe with thin layers of non-magnetic material sandwiched between the magnetic layers. 
     A plurality of mask layers  604  are deposited over the write pole layer (lamination)  602 . The mask layers include a first hard mask structure  603 . The first hard mask layer  603  includes a first sub-layer  606  constructed of a material that has a high resistance ion milling, preferably alumina (Al 2 O 3 ). The first sub-layer is constructed to a thickness to define a trailing gap thickness in the finished trailing shield. For example, the first sub-layer  606  can be constructed to a thickness of 15-25 nm or about 20 nm. The first hard mask layer further includes a second sub-layer  608 . The second sub-layer is preferably constructed of a material that is resistant to ion milling, but is removal by a process such as reactive ion etching (RIE). The second sub-layer  608  can, therefore, be constructed of, for example, Si 3 N 4 . The second sub-layer  608  (which can also be referred to as a RIEable layer) has a thickness that is chosen to define the size of a trailing shield notch such as the notch  418  described with reference to  FIG. 5 . Therefore, the second sub-layer  608  can have a thickness of 25-35 nm or about 30 nm. In addition, the first hard mask layer  603  includes a third sub-layer  610 . The third sub-layer is constructed of a material that functions both as a hard mask material and also as an end point detection layer. Therefore, the third sub-layer  610  should be constructed of a material that can be easily detected, such as by Secondary Ion Mass Spectroscopy (SIMS) and which also is very resistant ion milling. The third sub-layer can, therefore, be constructed of hard mask material such as alumina with a small amount of a detectable material such as Ti, (ie. AlTiO). The third sub-layer  610  can have, for example 2-10 atomic percent or about 5 atomic percent Ti. The use of alumina in the hard mask sub-layers  606 ,  610  is by way of example only, however. Other hard ion mill resistant materials such as Diamond Like Carbon (DLC), BeO, etc. could be used as well. In addition, the use of Ti as a detectable material in the third sub-layer is by way of example only. The detectable material element can be any element on the periodic table that does not have isotopic overlap with the milling gas (used in a reactive ion milling operation to be described below), atmospheric gases nor the layers below the hard mask layer. Other detectable materials that could be used include Ta, V, Cr, Cu, Zr, Nb, Mo, Ru, Rh, Hr, W, Re, Os, Ir, Pt and Au. The third sub-layer advantageously maintains the hard mask properties of it majority material (for example alumina) while also being detectable by the incorporation of a small amount of detectable material. 
     With continued reference to  FIG. 6 , the mask layers  604  further include a first image transfer layer  612 , which can be a soluble polyimide layer such as DURIMIDE®. The first image transfer layer can be, for example, 1000 to 1400 nm or about 1200 nm. Another hard mask layer  614  such as, for example silicon dioxide (SiO 2 ) can be deposited over the first image transfer layer, and an antireflective layer  616 , which can also be a soluble polyimide such as DURIMIDE® can be formed over the second hard mask  614 . The top hard mask  614  can be 60 to 1.50 nm thick or about 90 nm thick. The second, or top, image transfer layer  616  can be 100 to 130 nm thick or about 115 nm thick. A layer of resist material such as photoresist or e-beam resist  618  is deposited at the top of the mask layers  604 . 
     With reference now to  FIG. 7 , the resist layer is photolithographic-ally patterned, such as by photolithography or electron beam (e-beam) lithography. After exposure, the photo layer is developed in an appropriate developing solution. The photo layer  618  is patterned to have a width to define a desired write pole track width, as will be further described herein below. 
     With reference now to  FIG. 8 , a reactive ion etch (RIE)  802  is performed to transfer the image of the photoresist mask  618  onto the underlying image transfer layers  612 ,  618  and top hard mask  616 , by removing portions of the layers that are not covered by the photo mask  802 . The RIE  802  can be performed in several steps using both oxygen chemistry such as O 2  and CO 2  and fluorine chemistry such as a CF 4  or CHF 3 . Then, with reference to  FIG. 9 , a reactive ion mill  902  is performed to transfer the image of the overlying mask layers  612 ,  614 ,  616  and  618  onto the underlying first hard mask structure  603 . The reactive ion milling  902  can be performed with an Ar or CHF 3  based process depending on the materials used in the hard mask layers  606 ,  610  and end point detection layer  608 . The above described material removal processes are by way of example, however. The choice of which material removal processes are used to transfer the image of the photo layer  618  onto the underlying mask layers  606 - 616  will depend upon the materials used for these layers  606 - 616 . 
     With reference now to  FIG. 10 , an ion milling operation  1002  is performed to remove portions of the write pole material  602  that are not protected by the mask layers  604 . The ion milling is preferably performed at an angle (or various angles) with respect to normal in order to configure the write pole  602  with the desired trapezoidal shape as shown. This is, however, not necessary to the practice of the present invention. It can be seen that the ion milling  1002  removes the photo layer  618  top image transfer layer  616  top hard mask  614  and at least a portion of the image transfer  612  in the process of forming the write pole  602 . Then, with reference to  FIG. 11 , the remaining image transfer layer  612  is removed such as by a tetraethylammonium hydroxide (TMAH) based etching followed by an N-methylpyrrolidinone (NMP) photoresist strip. This leaves the first hard mask structure  603 . 
     With reference now to  FIG. 12 , a layer of non-magnetic, side gap material  1202  is deposited. The side gap material  1202  is preferably alumina, although other non-magnetic materials could be used as well. This layer  1202  is preferably deposited by a conformal deposition method such as atomic layer deposition, chemical vapor deposition, etc. Although various material and deposition method could be used for the layer  1202 , the layer will be referred to herein as ALD layer  1202 . 
     Then, with reference to  FIG. 13 , a material removal process  1302  is performed to remove a portion of the ALD layer  1202 . The material removal process is preferably an ion mill, performed in an Ar chemistry with end point detection (EPD). The third sub-layer  610  ( FIG. 12 ) can be used to indicate when the ion milling  1302  should be terminated. As mentioned above, the third sub-layer  610  includes an element, such as Ti, that can be easily detected, such as by SIMS. Therefore, when it has been determined that the third sub-layer  610  has been removed, the ion milling  1302  can be terminated. The ton milling  1302  is preferably performed at an angle that is chosen remove material at a high etch rate to form an upper surface on the layers  1202 ,  608  that is as flat as possible. It has been found that an optimal ion mill angle for this purpose is about 45 to 65 degrees or about 55 degrees with respect to normal. When the end point detection layer  608  has been reached, its presence can be easily detected in the ion mill tool, indicating that ion milling  1302  can be terminated. 
     Then, with reference to  FIG. 14 , a reactive ion etch (RIE)  1402  is performed to remove the third sub-layer  608  leaving the first sub-layer  606  exposed, and having a straight fiat surface. The RIE  1402 , which may be performed in a fluorine based chemistry, preferentially removes the end point detection layer  608 , so that very little if any of the first hard mask layer  606  is removed. This results, not only in the layer  606  having a straight, fiat, surface, but also in the layer  606  having a very well controlled thickness, which thickness can be controlled at deposition of the layer  606 . With reference now to  FIG. 15 , a wrap around trailing shield  1502  can be formed by first depositing an electrically conductive, magnetic seed layer and then electroplating to deposit a magnetic material. The seed layer and magnetic material can both be, for example, NiFe. It can be seen that the thickness of the first sub-layer  606  defines the trailing gap thickness. However, the deposition of the magnetic material  1502  can include first depositing a non-magnetic seed layer  1501  such as Rh or some other electrically conductive, non-magnetic material. In that case the first sub-layer would be deposited to a such as thickness that the thickness of the first sub-layer  606  plus the thickness of the seed layer  1501  together equal a desired trailing gap thickness. Therefore, the first sub-layer is preferably deposited to a thickness that is less than or equal to (ie. not greater than) a desired trailing gap thickness of the finished write head. 
       FIGS. 16-18  illustrate a method of constructing a wrap around trailing magnetic shield according to an alternate embodiment of the invention. As shown in  FIG. 16 , a mask structure  1602  is formed over the magnetic write pole material layer  602 . 
     The mask structure  1602  includes a multi-layer first hard mask structure  1604 . This first hard mask structure  1604  includes a first sub-layer constructed of a non-magnetic material that is resistant to ion milling, preferably alumina (Al 2 O 3 ). The first hard mask also includes a second sub-layer formed over the first sub-layer, the second sub-layer being constructed primarily of a material that is resistant to ion milling, but which also contains a material that can be easily detected, such as by SIMS. The second sub-layer  1608  can be constructed of for example alumina with a small amount of a detectable material such as Ti (ie. AlTiO with 1-10 atomic percent Ti). Such material, when used in the second sub-layer, behave much like a simple alumina hard mask (having excellent ion milling resistance) while also being easily detectable. 
     As in the previously described example, the mask structure  1602  can include an image transfer layer  612  formed over the hard mask layer and may include a second, or top, hard mask layer  614 , and second image transfer layer  616 . As before, the first and second image transfer layers  612 ,  616  can be constructed of a soluble polyimide such as DURAMIDE®, and the top hard mask  614  can be constructed of SiO 2  or some other suitable material. The first image transfer layer  612  can have a thickness of 1000 to 1400 nm or about 1200 nm. The top hard mask can have at thickness of 100 to 130 nm or about 115 nm, and the top, or second, image transfer layer  616  can have a thickness of 60 to 150 or about 90 nm. A photo mask  618  at the top of the mask structure  1602  defines the width of the mask structure  1602 . 
     As described in the above previous embodiment, an ion mill process can be performed to form the write pole  602  and a layer of non-magnetic material (ALD layer)  1202  such as alumina can be deposited by a conformal deposition method, as described previously with reference to  FIGS. 12 and 13 . 
     With reference now to  FIG. 17 , a reactive ion milling  1302  is performed while detecting for the presence of the second sub-layer  1608 . When it has been determined that the second sub-layer  1608  has been removed, then milling  1302  can be terminated. The remaining first sub-layer  1606  can then be left intact to provide non-magnetic trailing gap. Then, with reference to  FIG. 17 , a magnetic material can be deposited to form a trailing wrap around shield  1802  that does not have a notch as the previously described trailing shield did. 
     While various embodiments have been described, it should be understood that they have been presented by way of example only, and not limitation. Other embodiments failing within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.