Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to thin film magnetic heads used to read and write data onto magnetic media, and more particularly to the use of ion milling, such as with the use of a focused ion beam (FIB) tool, to trim the pole tip lateral edges to achieve a narrow track width. 
     2. Description of the Prior Art 
     Thin film magnetic recording heads are generally utilized in the data storage industry to record data onto magnetic media, such as magnetic hard disks. It is an industry-wide goal to store ever increasing quantities of data upon the magnetic media by increasing the areal density of the data stored on the media. The areal data storage density is typically increased by increasing the linear density of the data bits (bits per inch, BPI), and/or by writing the data in narrower tracks (tracks per inch, TPI). With regard to hard disks, where the data is written in narrower circular tracks on the disk, more data tracks per inch can be written and therefore more data can be stored on the disk when the TPI is increased. 
     The width of the data track that is written by a recording head is generally determined by the width of the second magnetic pole, termed the P 2  pole, of the write head, and efforts have been undertaken in the prior art to devise methods for reducing the width of the base of the P 2  pole, commonly referred to as the P 2 B dimension. These prior art methods have included the use of ion beams to irradiate selected areas of the P 2  pole to remove material and thereby reduce the P 2 B dimension. 
     With particular regard to the present invention, the use of a focused ion beam (FIB) to mill portions of the P 2  pole to reduce the P 2 B dimension is known. Such prior art efforts have indeed reduced the P 2 B dimension, however the use of the FIB tool, particularly where the P 2 B dimension is quite small can be problematic. Specifically, owing to the current density distribution within the FIB tool ion beam, the edges of a milled P 2  pole tip are rounded, rather than being sharp edges. The rounded edges of the P 2  pole result in a P 2 B dimension that is unpredictable and a P 2  pole that is non-optimum. There is therefore a need for an improved method for conducting the FIB milling of the write head which results in a P 2  pole having sharp milled lateral edges and a clearly defined P 2 B dimension. Where the milled lateral edges of the P 2  pole are sharp, a clearly defined track width is created and unwanted side writing from the pole tip is significantly reduced, such that narrower data tracks are produced and the data tracks can be written closer together, thus resulting in increased TPI and increased areal density of the data upon the magnetic media. 
     SUMMARY OF THE INVENTION 
     In the present method for manufacturing a magnetic head a focused ion beam (FIB) tool is utilized to mill the side edges of a P 2  pole, in order to provide a narrowed track width. Prior to milling, a thin film layer of material is deposited upon the air bearing surface (ABS) including the P 2  pole tip. The milling boxes of the FIB tool are properly aligned upon the layer with reference to the location of the P 2  pole tip, and milling of the lateral edges of the P 2  pole tip is then conducted to the appropriate depth. The layer of material is then removed. The resulting P 2  pole tip has sharp lateral edges, rather than the rounded edges that are produced in prior art FIB processing methods that do not utilize the thin film layer. In a preferred implementation, a hardened photoresist is utilized to form the thin film layer. However, in an alternative embodiment the FIB tool is utilized first to deposit the thin film layer and thereafter to perform the milling operation. 
     It is an advantage of the present invention that the areal density of data written on magnetic media is increased. 
     It is another advantage of the present invention that the track width of data written on magnetic media is decreased. 
     It is a further advantage of the present invention that side writing from a pole tip is reduced. 
     It is a yet another advantage of the present invention that data tracks can be written closer together upon magnetic media. 
     It is yet a further advantage of the present invention that the focused ion beam milling of the lateral edges of pole tips results in sharp edges of the milled sides of the pole tip. 
     It is still another advantage of the present invention that a thin film is deposited upon a pole tip in selected areas, such that the milling boxes of the FIB tool can be accurately aligned relative to the pole tip structures. 
     It is still a further advantage of the present invention that the ion milling step does not create pole tip recession, as the upper surface of the pole tip is not exposed to the ion beam during the milling step. 
    
    
     These and other objects and advantages of the present invention will become well understood by those skilled in the art upon reading the following detailed description which makes reference to the several figures of the drawing. 
     IN THE DRAWINGS 
     FIG. 1 is a top plan view of a hard disk drive of the present invention including a magnetic head of the present invention; 
     FIG. 2 is a top plan view of a typical pole tip as is well known in the industry; 
     FIG. 3 is an enlarged view of the pole tip depicted in FIG. 2 showing FIB tool milling boxes disposed thereon; 
     FIG. 4 is a graph generally illustrating the current distribution of a FIB tool ion beam; 
     FIG. 5 is a side cross-sectional view of a milled P 2  pole tip of the prior art, taken along lines  5 — 5  of FIG. 3; 
     FIG. 6 is a top plan view of a pole tip, similar to FIG. 2, having a FIB milling layer of the present invention deposited thereon; 
     FIG. 7 is a side cross-sectional view taken along lines  7 — 7  of FIG. 6 of the FIB milled P 2  pole of the present invention; 
     FIG. 8 is a further view of the pole tip of the present invention depicted in FIG. 7 having the milling layer removed; and 
     FIG. 9 is a top plan view of a preferred deposition pattern of the FIB milling layer of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The magnetic heads of the present invention are utilized to read and write data to magnetic media, such as hard disks in hard disk drive devices. A simplified top plan view of a hard disk drive  10  is presented in FIG. 1, wherein at least one magnetic media hard disk  12  is rotatably mounted upon a spindle  14 . A magnetic head  16 , typically termed a slider, of the present invention, is mounted upon an actuator arm  18  to fly above the surface  19  of each rotating hard disk  12 , as is well known to those skilled in the art. It is an object of the magnetic head  16  of the present invention to achieve a high areal data storage density on the magnetic media  12 . 
     To achieve high density areal data storage on magnetic media  12  it is necessary to record data in narrow bands, termed tracks, on the magnetic media. Generally, the track width is determined by the width of the magnetic poles of the magnetic head  16 , and the present invention relates to the use of ion milling in particular by use of a focused ion beam tool to trim the lateral edges of the poles to thereby achieve narrower poles and thus a narrower track width. Where the data tracks are narrower, more tracks per inch (TPI) can be recorded, thus achieving a higher areal data storage density. 
     FIG. 2 is a plan view of a portion of a prior art pole tip structure of a magnetic head configuration  20  that is well known in the industry. As depicted therein, the magnetic head  20  includes thin film layers that are typically deposited proximate the rear edge of the air bearing surface (ABS)  21  of the head  20 . The magnetic head  20  includes a write head element  22  having a first magnetic pole  23  (P 1 ) and a second magnetic pole (P 2 ) having a pole tip  24 . The P 1  pole and P 2  pole tip are separated by a thin film write gap layer  26  composed of a non-magnetic material, and the P 1  pole, the P 2  pole and the write gap layer are exposed on the ABS surface  21  of the head  20 . Generally, the width of the written data track on the magnetic media is determined by the width of the base  28  of the P 2  pole tip  24 , typically known as the P 2 B dimension. Therefore, the present invention is primarily directed towards reducing the P 2 B dimension of the P 2  pole tip  24 , such that the track width can be reduced, and the TPI (and thus the areal data storage density on the disk) can be thereby increased. 
     FIG. 3 is an enlarged view of FIG. 2 having super-imposed focused ion beam milling areas, termed milling boxes, shown thereon in phantom. More specifically, as depicted in FIG. 3, a first generally rectangular focused ion beam milling box  36  and a second focused ion beam milling box  38  overlay the P 2  pole tip  24  in a generally symmetrical manner about the center line  40  of the P 2  pole tip. The milling boxes  36  and  38  outline rectangular areas on the ABS surface  21  in which the ion beam of a focused ion beam tool will be directed in a raster-like manner to remove write head material. It is therefore to be understood that following the usage of the FIB tool that the remaining central portion  42 , and importantly base portion  44  of the P 2 B base  28 , of the P 2  pole tip located between the milling boxes  36  and  38  will remain unmilled. The width W of the base portion  44  of the milled P 2  pole tip  24  will then primarily determine the track width of the head  20  following the FIB tool milling. It is also significant to note that the lower portion  60  of the milling boxes  36  and  38  can be extended into the P 1  pole  23  to notch the P 1  pole, thereby increasing the performance of the head  10 , as is known to those in the art. The use of a FIB tool and the milling box configuration shown in FIG. 3, to trim the lateral edges of the P 2  pole tip, and to notch the P 1  pole is prior art that is known to those skilled in the art. 
     In attempting to create narrow track widths through the use of FIB tool milling of the P 2  pole tip, certain limitations have been reached. Specifically, as depicted in FIG. 4, the current density distribution I around the center B of the ion beam of the FIB tool has a generally Gaussian distribution, such that the edges b of the ion beam have a generally reduced current density as compared to the central portions B of the beam. As a result, the focused ion beam does not remove material, or cut, in a precise straight edge. Rather, the cut edge is somewhat rounded, which can result in inefficient data writing by the magnetic head, as is next discussed. 
     FIG. 5 is a cross sectional view taken along lines  5 — 5  of FIG. 3 proximate the base portion  44  of the P 2  pole tip that remains after a prior art FIB milling process to a depth D. The milled P 2  pole tip is shown in an operational setting proximate the surface  19  of a magnetic media hard disk  12 . The milled base portion  44  of the P 2  pole tip of FIG. 5, results from a FIB tool beam having the typically Gaussian current density distribution depicted in FIG.  4 . The significant deleterious features of the P 2  pole tip depicted in FIG. 5 are the rounded edges  90  of the pole tip that result from the FIB milling process. In particular, the rounded edges  90  of the projecting base portion  44  of the P 2  pole tip result in media writing inefficiencies that the present invention described below seeks to improve. Specifically, where the nominal gap distance from the P 2  pole tip base portion  44  to the media surface  19  is denoted as x, at the edges  94  of the pole tip base  44  the gap distance is y owing to the increased distance t of the rounded edges  90  at each edge  94  of the pole tip. This increase in the gap distance (from x to y) results in a weakening of the write signal transmitted to the media  12  and also increases unwanted side writing from the pole tip. As is known, pole tip side writing necessarily increases the spacing between tracks on magnetic media, thereby acting as a limiting factor in increasing the TPI and thus the areal data storage density that can be achieved. Additionally, the rounded edges  90  cause a reduction in the desired pole tip width W by an amount z on each side of the pole tip  44 , such that a reduced effective pole tip width W′ is created that has the expected nominal gap distance x to the media surface  19 . The notches that are cut into the P 1  pole  23  through the lower ends  60  of the milling boxes  36  and  38  (as depicted in FIG. 3) will also have problematic rounded edges (not shown). Additionally, although not shown in FIG. 5, the prior art P 2  pole FIB milling process results in some exposure of the ABS surface  21  of the head  20  to the focused ion beam, thus resulting in some milling of the ABS surface  23  of the head  20  and a recession of the P 1  pole, P 2  pole tip and other important components (not shown) relative to the ABS surface. The pole tip recession can result in degrading the performance of the magnetic head  20 . 
     It is therefore to be understood that significant limitations exist in the prior art methods for using a FIB tool to mill the P 2  pole tip, particularly where the width W of the unmilled base portion  44  of the P 2  pole tip is small enough to be comparable to the dimension z of the rounded edges  90  that result from the use of the FIB tool having the generally Gaussian current density distribution of its beam. As described below, the present invention results in the elimination of the rounded edges  90  of the pole tip  44  when using a FIB tool, thereby providing an improved pole tip trimming process that results in an improved pole tip, and thus an improved magnetic head  16  of the present invention for a disk drive  10 . 
     A first step of the present invention is the deposition of a thin film layer  100  upon the pole tip ABS surface  21  of the prior art head  20 , as is depicted in FIGS. 6 and 7, wherein FIG. 6 is a plan view similar to FIG.  3  and FIG. 7 is a cross-section view, similar to FIG.  5 . Specifically, FIG. 6 depicts the prior art magnetic head  20  having a surface layer  100  of the present invention deposited thereon, such that the features of the head  20 , such as the P 2  pole tip  24 , are shown in phantom. Additionally, the FIB tool milling boxes  36  and  38  are shown disposed in the identical location to that shown in FIG.  3 . Following the deposition of the protective layer  100 , the FIB tool is utilized to mill the areas within the milling boxes  36  and  38 , as was done in the prior art. The improvement that results from the protective layer  100  of the present invention is best seen in FIG.  7 . Specifically, the rounded edges  90  that result from the ion beam milling are now formed within the protective layer  100 . Thus, the thickness T of the protective layer  100  is at least equal to the distance t (see FIG. 5) of the rounded edge effect  90  that the FIB tool creates. Additionally, the overall depth of milling conducted in the present invention is necessarily increased from D of the prior art by the thickness T of the protective layer to achieve a resulting pole tip  108  of the present invention (described in detail herebelow with the aid of FIG. 8) having the same vertical dimension D as the prior art pole tip depicted in FIG.  5 . Following the FIB milling step, the protective layer  100  is removed from the head by such means as a chemical etch, burnishing or other generally known methods. 
     A cross sectional view of the improved pole tip  108  of the head  16  of the present invention is depicted in FIG. 8 proximate the surface  19  of a magnetic media  12 . As depicted therein, the pole tip  108  has generally square edges  112  which result in a uniform gap distance x throughout the entire width W of the pole tip  108 . Also, although not shown, the P 1  notches will also be formed with substantially square edges. As a result, the improved pole tip  108  produces the desired track width upon the media surface  19  with substantially reduced side writing as compared to the prior art pole tip depicted in FIG.  5 . Due to the reduced side writing, data tracks on the media surface  19  can be written closer together, thereby increasing the TPI and the areal density of data written upon the media. Additionally, where the protective layer  100  of the present invention is utilized, the width W of the P 2  pole tip can be reduced relative to the prior art, because edge rounding of the milled pole tip does not occur. 
     In a specific example of the present invention, as is known in the prior art, a 100 pico-Amp Ga+ion beam at 50 keV energy for a nominal dose 4.0 nC/micron 2  results in a pole tip rounding having a distance t of approximately 0.1 microns. Therefore, to counteract this ion beam rounding effect, a protective layer  100  of the present invention having a thickness T of at least approximately 0.1 microns is utilized. The protective layer  100  can be composed of various materials that are capable of protecting the edges of the pole tip while being easily removed from the pole tip following the FIB milling process, without contaminating the pole tip. A layer material such as a hardened photoresist is preferred, as the properties of such resists are well known in the head fabrication art, however materials such as tungsten, and platinum that form alloys with gallium ions of the FIB tool may be suitable. 
     The protective layer  100  of the present invention is preferably utilized where the wafer substrates containing a plurality of heads have been sliced into rows of heads, such that the heads can be more easily manipulated for individual sequential fabrication utilizing the FIB tool. A generally suitable range of FIB tool parameters includes a 10 pico-Amp to 30 nano-Amp Ga+ion beam at 50 keV energy with a dose in the range of 0.01 nC/micron 2  to 10 nC/micron 2 . The tendency in the industry towards smaller write head features generally results in a tendency towards lower ion beam currents and doses. The utilization of the protective layer  100  of the present invention results in exceedingly square edges for the P 2  pole tip as well as for notches in the P 1  pole. Generally, the squareness of the P 2  pole tip edges of the present invention will have a radius of curvature of from 0.10 nm to less than 100 nm depending upon the beam current and dosage levels, where the lower ion beam current and dosage levels generally result in substantially square edges having a radius of curvature of approximately 1 nm. 
     Most advanced FIB milling tools have the capability of depositing a substance upon a surface as well as removing material from a surface. Specifically, current FIB tools have the ability to deposit tungsten and/or platinum, typically as alloys with gallium where gallium ions are utilized in the deposition process. Therefore, in a two step process utilizing a FIB tool, the protective layer  100  of tungsten or platinum alloys with gallium can be deposited onto the pole tip surface utilizing the FIB tool, and thereafter the FIB tool can be utilized to mill the pole tip surface within the milling boxes. 
     In attempting to perform the milling step of the present invention upon the protective layer  100 , it can be difficult to accurately align the milling boxes  36  and  38  where the surface features of the pole tip are rendered invisible by the protective layer  100 . To solve this problem, an upper portion  120  of the P 2  pole tip  24  can be left uncovered during the protective layer deposition process as is depicted in FIG.  9 . With a knowledge of the physical dimensions of the head  16 , the milling boxes  36  and  38  can be oriented appropriately by the FIB tool operator based upon the visualization of the top portion  120  of the P 2  pole tip. Improved accuracy of the FIB tool milling process of the present invention with the deposited layer  100  is thereby obtained. 
     While the present invention has been shown and described with reference to certain preferred embodiments, it is to be understood that those skilled in the art will no doubt devise alterations and modifications in form and detail which nevertheless include the basic spirit and scope of the invention. It is therefore intended that the following claims cover all such alterations and modifications.

Technology Category: 4