Abstract:
The magnetic writing head of the present invention includes a P 2  pole tip having a novel profile. This profile, as viewed from the air bearing surface (ABS) can generally be described an hour glass shape in that the minimum width of the pole tip is disposed away from the base of the P 2  pole tip. The negative profile results in a significant reduction in magnetic side writing that emanates from the write head. A novel method for producing the negative profiled pole tip involves control of the photoresist processing parameters and pole tip plating parameters. Specifically, the photoresist is baked at particular temperatures for particular periods of time, such that the cross linking within the photoresist is produced to the extent that the photoresist will controllably swell during the plating operation. The result is that as the P 2  pole tip is plated, the photoresist swells to cause the negative profile along the thickness of the pole tip.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to magnetic pole tip configurations for magnetic write heads, and more specifically to pole tip configurations that reduce magnetic side writing. 
     2. Description of the Prior Art 
     For very high density magnetic recording it is necessary to record magnetic domains very close together. The bit packing is done in both the linear direction (Bits per Inch (BPI)) and in the radial direction (Tracks per Inch (TPI)). The TPI is generally determined by two parameters, the size of the written bit that is primarily determined by the second pole tip&#39;s lateral dimension (P 2 W), and the inter-track guard band that is mostly composed of magnetic noise. The width of the inter-track band is determined by how well the drive can servo, the accuracy of the actuator system, and by the extent of the side writing of the poles. The side writing is one of the easier parameters to control, and reduce, because it is an intrinsic function of the way pole tips are constructed. 
     To reduce side writing, pole tips of various shapes have been developed, such as rectangular and trapezoidal shapes. Additionally, write heads have been developed that include a notched first pole tip, as described in U.S. Pat. No. 5,901,432, in an effort to reduce sidewriting. As the width of the base of the P 2  pole has been reduced, in order to produce narrower track widths, the effect of side writing has become more pronounced in relation to the narrowed track widths. The side writing produced by the P 2  pole tips therefore requires further reduction, and the P 2  pole tip of the present invention, with its negative profile, provides such a side writing reduction. 
     SUMMARY OF THE INVENTION 
     The magnetic writing head of the present invention includes a P 2  pole tip having a novel profile. This profile, as viewed from the air bearing surface (ABS) can generally be described an hour glass shape in that the minimum width of the pole tip is disposed away from the base of the P 2  pole tip. The negative profile results in a significant reduction in magnetic side writing that emanates from the write head. 
     A novel method for producing the negative profiled pole tip involves control of the photoresist processing parameters and pole tip plating parameters. Specifically, the photoresist is baked at particular temperatures for particular periods of time, such that the cross linking within the photoresist is produced to the extent that the photoresist will controllably swell during the plating operation. The result is that as the P 2  pole tip is plated, the photoresist swells to cause the negative profile along the thickness of the pole tip. 
     It is an advantage of the present invention that a magnetic write head has been developed that produces reduced magnetic side writing. 
     It is another advantage of the present invention that a magnetic pole tip has been developed that produces reduced side writing with no additional manufacturing steps over the existing manufacturing methods. 
     It is a further advantage of the present invention that an improved magnetic write head has been developed that is simple to manufacture. 
     It is yet another advantage of the present invention that the manufacturing method for a magnetic write head has been developed which produces an improved write head with no additional manufacturing steps. 
     These and other features 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 drawings. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a plan view of a prior art merged thin film magnetic head having a notched P 1  pole; 
     FIG. 2 is a plan view depicting the effect upon the prior art P 2  pole tip of ion beam etching undertaken to create the prior art head depicted in FIG. 1; 
     FIG. 3 is a plan view of a hard disk drive including the magnetic head of the present invention; 
     FIG. 4 is a perspective view with cut-away portions that depicts the magnetic head of the present invention; 
     FIG. 5 is a plan view of the magnetic head of the present invention taken from the ABS surface side; 
     FIG. 6 is a perspective view with cut-away portions of the photoresist profile for the P 2  pole tip depicted in FIG. 4; and 
     FIG. 7 is a plan view of the photoresist profile depicted in FIG. 6 taken from the ABS surface side. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Various attempts have been made to reduce side writing from thin film magnetic heads in order to increase the areal density of data written on magnetic disks. Recent advances in write head designs include the prior art notched pole tip design depicted in FIG. 1, from which the novel features and advantages of the present invention can be advantageously explained. The notched write head of FIG. 1 is described fully in the inventor&#39;s prior U.S. Pat. No. 5,901,432 and is briefly described herein. As depicted in FIG. 1, the prior art head  10  includes a P 1  pole  14 , a write gap layer  18 , a seed layer  22  and a P 2  pole tip  26  having a thickness  30  that is significantly greater than its base width  34 ; these components being formed within an encapsulating layer  38 . To reduce side writing between the P 2  pole tip  26  and the P 1  pole  14 , notches  42  are etched into the P 1  pole  14 . Such heads  10  typically are formed to include a read head portion  46  disposed between shield layers  50  and  54 . Where the shield layer  50  also serves as a pole, such as P 1  pole  14 , the head  10  is termed a merged head. 
     In manufacturing the prior art notched pole  14  depicted in FIG. 1, the P 1  layer is deposited, followed by the gap layer  18  having a thickness of approximately from 900 Å to 3,000 Å, depending upon the size of the data bits, and therefore the bits per inch (BPI) areal density to be written by the write head  10 . A seed layer  22  of approximately 800 Å is deposited upon the gap layer  18  and the P 2  pole tip  26  is plated onto the seed layer  22 . Typically, where the P 2  pole tip width is approximately 0.5 microns, the thickness of the P 2  pole tip will be initially plated up to approximately 4 microns thick. The P 2  pole tip trench that is formed in the photolithographic resist layer, that is created to plate up the P 2  pole tip, will then typically have a thickness of approximately 4.5 microns. Therefore, the aspect ratio of the prior art P 2  pole tip trench is approximately 9 to 1 (thickness to width), which can create difficult plating problems, as is known to those skilled in the art. After the P 2  pole tip has been plated up within the photoresist trench, the photoresist is removed using a wet chemical removal process. Then, using ion beam etching techniques with suitable masking techniques, the pole tip area is etched using the P 2  pole tip as part of the mask, such that the seed layer  22 , gap layer  18  and portions of the P 1  pole  14  are removed to create the notches  42 , as depicted in FIG.  1 . Typically, the depth of notching is approximately 1.5 to 2 gap thicknesses. The portions of the seed layer  22  and gap layer  18  located beneath the P 2  pole tip  26  are not removed due to the shielding thereof by the P 2  pole tip. 
     The ion etching process is typically conducted at an angle of approximately 10° from normal to perform the material etching process and at an angle of approximately 70° from normal to clean up material that becomes redeposited along the sides of the gap layer  18 , seed layer  22  and P 2  pole tip  26  during the etching process. This necessary removal of redeposited material can present a problem, because if the etching at the 70° angle is too great the P 2  pole tip width can be reduced, whereas if the etching at the 70° angle is not sufficient then redeposited material will remain on the sides of the gap layer  18  and other side surfaces, which can lead to device performance problems. 
     The etching process step that is undertaken to notch the P 1  pole  14  also significantly reduces the thickness of the initially plated P 2  pole tip. Specifically, as depicted in FIG. 2, where the initially plated pole tip  60  has a thickness of approximately 4 microns, as a result of the etching step, a significant upper portion  64  of the pole tip  60  is etched away, such that the thickness of the remaining portion  68  of the P 2  pole tip corresponds to thickness  30  of the P 2  pole tip  26  of approximately 2.5 microns. As will be understood by those skilled in the art after reading the following detailed description of the present invention, the P 2  pole tip manufacturing process of the present invention does not require a notched P 1  pole tip. Thus, the etching step of the prior art is not required, and, significantly, it is not necessary to plate up the P 2  pole tip to a height such as 4 microns, and then to etch away the top portion of it. Therefore, the photolithographic trench for plating the P 2  pole tip of the present invention is not as deep as the trench of the prior art P 2  pole tip  60 , thus simplifying the P 2  pole tip plating process. 
     A simplified depiction of a disk drive  70  that includes the thin film magnetic head  74  of the present invention is presented in FIG.  3 . The disk drive  70  includes one or more hard disks  78 , one or more actuator arms  82  that have a magnetic head  74  of the present invention mounted thereto, together with additional electromechanical and computerized components (not shown) that are well known in the hard disk drive prior art. 
     A merged magnetic head  74  of the present invention is depicted in FIGS. 4 and 5, wherein FIG. 4 is a perspective view with cut-away portions that depicts the novel profile of the P 2  pole tip  100 , and FIG. 5 is an ABS surface plan view of the P 2  pole tip  100 . The write head portion of the magnetic head  74  includes a first pole layer (P 1 )  114 , that is typically formed by plating, a gap layer  118  having a thickness G that is deposited upon the P 1  layer  114 , a seed layer  122  that is deposited upon the gap layer  118 , and a P 2  pole  126  that is plated onto the seed layer  122  in a process that is described in detail herebelow. The P 2  pole  126  has a back portion (yoke)  130  and a P 2  pole tip  138  that is formed with an ABS surface profile that includes a pole tip base (P 2 B)  146  having a width W and two sides  150  that each include an indentation  156 , such that a distinctive reduction in width along the thickness of the ABS surface profile exists, thereby creating an hour glass, necked shape having a minimum width w disposed at a point  160  away from the P 2 B base  146 . This “hour glass” profile, also referred to as a negative profile, has been demonstrated to produce significant side writing reduction because the fringing magnetic fields  166  (see FIG. 5) start from receding lateral surfaces  170  of the indentations  156  of the pole tip  138 . Even where the P 1  pole tip  114  is much wider than the width W of the base  146  of the P 2  pole tip  138  the reduction in side writing is significant. 
     The disclosed P 2  pole tip ABS surface profile is controllably produced in a preferred manufacturing embodiment using a negative resist process. It has been found that the negative resist material properties, with its polar resin stabilized via chemically enhanced cross linking, can be manipulated towards producing such a plated profile in the ABS surface of P 2  pole tip  138 . This result is unexpected because the profile is not present at the photoresist level. Instead, the preferred plated profile is produced by controllably allowing the resist to change its lateral dimensions while the plating process takes place. The novel steps in the process of the present invention are explained with the aid of FIGS. 6 and 7, wherein FIG. 6 is a perspective view with cut-away portions of the photoresist profile for the P 2  pole tip  138  of the present invention, and FIG. 7 is a plan view of the ABS surface side of the photoresist profile depicted in FIG.  6 . 
     As depicted in FIGS. 6 and 7, the manufacturing process of the magnetic head of the present invention has proceeded with the formation of the P 1  pole layer  114  with the gap layer  118  having been deposited thereon to a thickness G, and with a seed layer  122  having been deposited upon the gap layer  118 . A photoresist layer  180  has been deposited upon the seed layer  122 . As is well known, the bottom portions (not shown for ease of depiction) of the photoresist layer  180  as well as the bottom portions (not shown) of the P 1  pole layer  114 , gap layer  118  and seed layer  122  extend downwardly during manufacturing, and are later removed to establish the ABS surfaces depicted in FIGS. 4 and 5. Following the deposition of the photoresist layer  180 , a standard photo exposure step is conducted, followed by a typical two step baking cycle (soft bake and post exposure bake), followed by a developing step in which the unexposed photoresist is chemically removed. FIGS. 6 and 7 depict the photoresist layer  180  following the bake cycle and the removal of unexposed photoresist which then creates the photoresist trench profile  188  for the hour glass shaped P 2  pole tip  138  of the present invention. As depicted in FIGS. 6 and 7, the photoresist trench  188  includes straight, flat side walls  192  for the plating process that will produce the hour glass shaped P 2  pole tip  138 . It is noteworthy that the straight, flat sidewalls  192  facilitate the measurement of the P 2 W pole tip width W prior to the plating operation, which can be measured very precisely utilizing a top down scanning electron microscope or similar tool. 
     It is therefore to be understood that the hour glass shaped P 2  pole tip  138  of the present invention is controllably formed in a plating process that utilizes a photoresist profile that initially has straight, fiat sidewalls  192 . The sidewalls  192  are thereafter controllably allowed to change shape, by absorption of the plating solution during the plating process. The sidewall  138  by an inward swelling of the sidewalls  192  during the P 2  pole tip plating process, as is next discussed. 
     The polar resin of the photoresist  180  and its solvent contribute to the controlled absorption of the plating solution (typically H2O/H2SO4) and its surfactant formulation, as is commonly used in the art. The degree of swelling of the resist  180  is controlled in the present invention by the amount of cross linking that is created in the negative resist by the photo initiation generation of acid, and the degree of cross linking developed during the post exposure bake cycle. Specifically, the bake time t and bake temperature T of the post exposure bake step are selected to control the amount of fluid the resin can accommodate, which is reflected in the amount of swelling and thus lateral necking  160  on the pole tip  138 . Experimentation has shown that for a short post exposure bake time t of approximately 5 min. at relatively low bake temperature T of approximately 95 degrees C. the amount of lateral necking  160  is approximately 0.15 μm per edge. The necking  160  will reduce to approximately 0.5 μm if the post exposure bake temperature T is increased to 105 deg. C., or if the post exposure bake time t is, extended to 30 mins. For a 105 deg. C. post exposure bake temperature that is 30 min. in length, the amount of swelling in the resist is no longer measurable. The general range of necking  160  of each side edge is preferably in the range of 2.5% to 20% of W with a preferred necking of approximately 15% of W per side edge. It is obvious that the amount of swelling can not be so large as to cause closure of the open space profile where the pole tip  138  is formed, so the amount of swelling for extremely small pole tip widths W must controlled to be less than for larger pole tip widths. 
     The location of the necking  160 , and the amount of necking can be further controlled by controlling the plating rate P. That is, where a relatively slow plating rate is utilized, the degree of swelling will be maximized and the location of the maximum necking  160  (minimum width w) will be closest to the P 2 B pole tip base  146 . Conversely, where the plating rate is more rapid, the maximum necking point  160  will tend to be higher; that is, away from the P 2 B pole tip base  146 . For a deposition rate of 400 Å/min. the point of maximum necking  160  is located approximately 0.3 microns away from the seed layer, at 600 Å per minute the maximum necking point  160  is located approximately 0.6 microns from the seed layer, at 800 Å per minute the point  160  is approximately 0.9 microns from the seed layer, and at approximately 1,000 Å per minute the maximum swelling point is approximately 1.2 microns from the seed layer. In examining the relationship between side writing and the location of the maximum necking, it appears that minimal side writing occurs where the point  160  of minimum necking width w is located at one to five gap thickness G away from the P 2 B base  146 , with a preferred location at two to three gap thicknesses. For instance, where the gap layer thickness is 0.3 microns, maximum necking is preferred at approximately 0.6 microns from the seed layer, and a deposition rate of approximately 600 Å per minute is indicated. 
     Because the negative profiled P 2  pole tip of the present invention significantly reduces sidewriting, the P 1  notching step of the prior art device described hereabove is no longer required ,in order to achieve the same areal data storage density. Therefore, it is not necessary to plate the P 2  pole tip  138  of the present invention to an increased thickness in order for it to be subsequently etched away, as depicted in FIG.  2  and described hereabove, to a final desired thickness. Rather, the thickness of the resist  180 , and therefore the depth of the trench  188  into which the P 2  pole tip of the present invention is plated can be significantly reduced. Specifically, where a P 2  pole tip base width W of 0.5 microns, and a P 2  pole tip thickness of 2.5 microns is desired, a resist trench  188  having a depth of approximately 3.0 microns is suitable. Such a trench will have an aspect ratio of approximately 6 to 1 (thickness to width) as compared to the prior art P 2  pole tip trench with its aspect ratio of 9 to 1 (as described hereabove). Therefore, the P 2  pole tip plating process of the present invention is somewhat easier to accomplish because the aspect ratio of the P 2  pole tip trench can be reduced. Additionally, implementation of the necked profile P 2  pole tip  138  of the present invention facilitates the use of generally narrower pole tip widths with acceptable side writing minimization because the P 1  pole tip notching ion etch step, which can have a significant impact upon a narrow width pole tip, is not performed. In this regard, a preferred embodiment of a plated pole tip  138  has been experimentally demonstrated as having a 0.28 micron width W at the P 2 B base with a negative profile of 0.05 microns per edge maximum necking point  160  occurring at a 0.6 microns of the 3.0 micron total thickness of the pole tip  138 . A significant advantage of the negative profile method and design described herein to the prior art is the simplicity of processing, the use of a thinner resist layer  180 , together with a lower aspect ratio of the plating trench  188 , and the availability of measurement of the P 2 W pole tip width W prior to plating. 
     While the plating process described hereinabove utilizes a negative photoresist to obtain the sidewall swelling during the plating process, there is no apparent reason why a positive photoresist process cannot be implemented, and the present invention is therefore not to be limited to the use of negative photoresist to achieve the sidewall swelling during the plating process that results in the hour glass shaped P 2  pole tip profile of the present invention. 
     While the invention has been shown and described with reference to various preferred embodiments, it is to be understood that those skilled in the art will no doubt develop various alterations and modifications therein. It is therefore intended that the following claims cover all such alterations and modifications that nevertheless include the true spirit and scope of the invention.