Abstract:
An enhanced inductive coil design for use in data storage magnetic disk drives with areal density over 35 Gb/in 2 , features a double wound twin coil that is able to achieve a yoke length of 15 μm or less by reducing the insulation spacing between the two coils. The coil further presents improved reliability by reducing the possibility of occurrence of electrical shorting. The coil is made by forming two interleafing conductors on the same layer with a demesne process. A tri-level process is implemented in the layout of the first conductor to ensure that the coil width and spacing are uniform and even, in order for the second conductor to be wound therebetween. A conformal dielectric layer of approximately 0.1 to 0.2 μm in thickness is deposited between the two conductors and serves as insulation. The two conductors are formed by a copper seed layer plating process that eliminates potential damage to the conductors during production.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to data storage systems such as disk drives, and it particularly relates to a thin film read/write head for use in such data storage systems. More specifically, the present invention relates to an advanced inductive coil design and manufacturing process for thin film heads. The new inductive coil design features a double wound twin coil having a shorter yoke length relative to a conventional design while maintaining at least the same number of coil turns. The new coil design and process enable the disk drive to achieve a greater areal density, hence greater storage capacity than a conventional coil design. 
     BACKGROUND OF THE INVENTION 
     In a conventional magnetic storage system, a thin film magnetic head includes an inductive read/write transducer mounted on a slider. The thin film head is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk. In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. An exemplary thin film magnetic head includes a plurality of write poles, also known as P 1  and P 2 , that encapsulate a magnetically inductive coil disposed by a recess from the air bearing surface (ABS). During a write operation, the inductive coil cooperates with the poles P 1  and P 2  to generate a magnetic field that directs the magnetic flux from the pole P 1  to the pole P 2  through the magnetic disk onto which digital data are to be recorded. 
     In a conventional magnetic media application, the magnetic recording disk is comprised of several concentric tracks onto which magnetization bits are deposited for data recording. Each of these tracks is further divided into sectors wherein the digital data are registered. As the demand for large capacity magnetic storage continues to grow at an ever increasing pace, the current trend in the magnetic storage technology has been proceeding toward a high track density design of magnetic storage media. In order to maintain the industry standard interface, magnetic storage devices increasingly rely on reducing track width as a means to increase the areal density without significantly altering the geometry of the storage media. 
     As the track width becomes smaller, the size of the thin film head must also be reduced accordingly. This reduction necessitates an accompanied decrease in the physical dimension allowance of the inductive coil, also known as the yoke length. While the coil yoke length decreases, the demand for high areal density continues to impose the same or greater requirement for the coil density, which is the number of coil turns per coil area. 
     To address the coil size and density requirements, various attempts have been developed. One such attempt is exemplified by U.S. Pat. No. 4,416,056 to Takahashi, which discloses a conventional inductive coil comprising of two plane coil layers that are formed by a plurality of spirally wound conductors arranged in an alternating pattern. By doubling the number of coil layers, the coil density increases proportionally. 
     In general, the conventional inductive coil according to the Takahashi patent is manufactured using a chemical wet etching process to create the pattern of the coil winding. Prior to the wet etch, the coil pattern is formed by a photolithographic process involving the deposition of a photo resist layer onto a conductor substrate surface. By exposing the photo resist layer to an ultraviolet light source through a photo mask, the coil pattern photographic image is formed. The wet etch is then applied to the exposed photo resist to remove the exposed photo resist material, leaving behind on the substrate the patterned conductors that form the coil winding. 
     The inductive coil process according to the Takahashi patent presents a number of disadvantages that significantly offset the benefit of high areal density of the conventional coil design. Some of these disadvantages are described as follows: 
     During the preparation process prior to the photolithography, a layer of dielectric material is deposited onto the conductor substrate surface to provide insulation between the coil layers prior to the deposition of the photo resist layer. With reference to  FIG. 1 , which illustrates a conventional coil process, due to the physical imperfection of the dielectric material, there likely exist various tiny openings or pinholes  1 , formed in the dielectric layer  3 . Thus, during the wet etch process which is designed to remove the exposed photo resist material, the etching solution may seep through the pin holes  1  in the dielectric layer  3  to permeate into the underlying conductor surface  5 , thereby likely resulting in a damage to the coil. In some instances, the etching solution may penetrate far enough to cause damage to the write pole P 1 . As a consequence, a considerable endeavor is required to ensure that the dielectric layer is free of pinholes  1 , which in itself is a difficult task to accomplish. 
     Yet another disadvantage with the Takahashi design is the coil size limitation due to the alignment process and the physical limitation of the photo resist. The coil windings are separated by a gap of width “d.” This gap is formed after a wet etch during which the exposed photo resist material is removed therefrom. In order to form this gap, a photo mask  7  must be aligned with the photo resist layer with high precision. As the demand for high coil density increases, the coil size becomes smaller and so does the gap width “d.” As a result, the alignment becomes more challenging, resulting in a potential misalignment which could adversely affect the quality and production of the conventional inductive coils. 
     Furthermore, the photo resist typically reaches a physical limitation of about 0.2 μm. Thus, both the alignment problem and the photo resist limitation impose a size constraint on the conventional inductive coil. As a result, conventional inductive coils as exemplified by the Takahashi patent, may not be further enhanced beyond their maximum limit as dictated by the foregoing size constraint, thus preventing these coils from meeting the demand for greater areal density in high capacity disk drives. Currently, a conventional coil design may have reached its size limitation of 17 μm with a coil density of 9 turns per coil. 
     As the demand for high capacity magnetic storage continues to grow, the size of inductive coils needs to be reduced in order to increase the areal density, while the coil density remains the same or greater. Consequently, a demand for an improved inductive coil design and process is needed. This improved coil design preferably utilizes an enhanced process that would promote high magnetic efficiency for high areal density recording without potentially causing damage to the coil conductors. Moreover, the improved coil design should be able to meet the demand for a decreased coil size imposed by the technology advancement without being affected by the size constraints currently faced by conventional inductive coil design. 
     SUMMARY OF THE INVENTION 
     It is a feature of the present invention to present a new enhanced inductive coil design for use in data storage magnetic disk drives with areal density over 35 Gb/in 2 . The enhanced inductive coil design of the present invention features a double wound twin coil concept using the following process:
         1. The twin coil is built on the same layer with a demesne process.   2. A tri-level process is implemented in the layout of the first coil to ensure that the coil width and spacing are uniform and even, in order for the second coil to be wound therebetween.   3. A conformal dielectric layer of approximately 0.1 to 0.2 μm in thickness is deposited between the two coils to serve as insulation.   4. The coils are formed by a copper (Cu) seed layer plating process which eliminates the potential damage to the coils during production.       

     The foregoing and other features of the present invention are realized by a coil and method the same by forming an insulation layer. Then, using a reaction ion etching process (RIE), the first coil pattern is formed, followed by a deposition process and/or plating process to form the first coil (also referred to as first coil elements). It should be understood that the first coil could alternatively be formed using another conventional or available process. 
     Subsequently, the first coil is planarized using a chemical-mechanical polishing process, followed by a RIE process which is inert relative to the metallic composition of the first coil to remove the remaining insulation layer. A Plasma-Enhanced Chemical Vapor Deposition (PECVD) process is used to form a second insulation layer to cover the first coil. The PECVD process is highly conformal and is pinhole free. 
     The second coil is then formed on the second insulation layer using a deposition process and/or plating process. A chemical-mechanical polishing process is then used to planarize the second coil. In an alternative embodiment, the insulation layer separating the first and second coils is removed by a reactive ion etching process. 
     Using the enhanced process of the present invention, the new coil design is able to achieve a smaller yoke length of 15 μm or less while maintaining at least the same number of coils per turn as a result of the reduction in the insulation spacing between the two coils. A further advantage of the enhanced coil design of the present invention is the improved reliability by reducing the electrical shorting possibility realized by the seed layer ion milling process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the present invention and the manner of attaining them, will become apparent, and the invention itself will be understood by reference to the following description and the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional view of a prior art inductive coil including a coil gap and a photo mask; 
         FIG. 2  is a fragmentary perspective view of a data storage system utilizing a read/write head of the present invention; 
         FIG. 3  is a perspective view of a head gimbal assembly comprised of a suspension and a slider to which the read/write head of  FIG. 2  is secured, for use in a head stack assembly; 
         FIG. 4  is an enlarged perspective view of a thin film read/write element (with the top yoke removed for clarity of illustration) forming part of the read/write head of  FIGS. 2 and 3 ; 
         FIG. 5  is a cross-sectional view of the write head of the read/write element of  FIG. 4  taken along line  4 — 4 , illustrating a double winding twin coil of the present invention; 
         FIG. 6  is a top view of the double winding twin coil made according to the present invention of  FIG. 5 ; 
         FIGS. 7 through 15  illustrate a manufacturing sequence for fabricating first coil elements of the double winding twin coil of  FIGS. 5 and 6  according to a preferred embodiment of the present invention; 
         FIGS. 8 through 19  illustrate a manufacturing sequence for fabricating second coil elements of the double winding twin coil of  FIGS. 5 and 6  according to a preferred embodiment of the present invention; and 
         FIG. 20  illustrates an optional reactive ion etching process for removing an insulating dielectric layer interposed between the first and second coil elements. 
     
    
    
     Similar numerals in the drawings refer to similar elements. It should be understood that the sizes of the different components in the figures might not be in exact proportion, and are shown for visual clarity and for the purpose of explanation. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 2  illustrates a disk drive  10  comprised of a head stack assembly  12  and a stack of spaced apart magnetic data storage disks or media  14  that rotate about a common shaft  15 . The head stack assembly  12  is pivoted about an actuator axis  16  in the direction of the arrow C. The head stack assembly  12  includes a number of actuator arms, only three of which  18 A,  18 B,  18 C are illustrated, which extend into spacings between the disks  14 . 
     The head stack assembly  12  further includes an E-shaped block  19  and a magnetic rotor  20  attached to the block  19  in a position diametrically opposite to the actuator arms  18 A,  18 B,  18 C. The rotor  20  cooperates with a stator (not shown) for rotating in an arc about the actuator axis  16 . Energizing a coil of the rotor  20  with a direct current in one polarity or the reverse polarity causes the head stack assembly  12 , including the actuator arms  18 A,  18 B,  18 C, to rotate about the actuator axis  16  in a direction substantially radial to the disks  14 . 
     A head gimbal assembly (HGA)  28  is secured to each of the actuator arms, for instance  18 A. With reference to  FIG. 2 , the HGA  28  is comprised of a suspension  33  and a read/write head  35 . The suspension  33  includes a resilient load beam  36  and a flexure  40  to which the head  35  is secured. 
     The head  35  is formed of a slider  47  secured to the free end of the load beam  36  by means of the flexure  40 , and a read/write element  50  supported by the slider  47 . The read/write element  50  is mounted at the trailing edge  55  of the slider  47  so that its forwardmost tip is generally flush with the air bearing surface (ABS)  65  of the slider  47 . 
     The details of the read/write element  50  will now be described with reference to  FIGS. 4 and 5 . The read/write element  50  integrates a write section  60  and a read section  61 . The read section  61  is formed of a first shield layer (Shield  1 )  80  preferably made of a material that is both magnetically and electrically conductive. An insulating layer  82  is formed over substantially the entire surface of the first shield layer  80  to define a non-magnetic, transducing read gap  87 . 
     The read section  61  is also comprised of a read sensor  83  formed within the insulation layer  82 . The read sensor  83  can be any suitable sensor, including but not limited to a magnetoresistive (MR) element, a giant magnetoresistive (GMR) element, a spin valve, or a Current In the Plane mode (CIP) sensor. Further, the read section  61  also includes a second shield layer (Shield  2 )  85  that is made of an electrically and magnetically conductive material, which may be similar or equivalent to that of the first shield layer  80 . The second shield layer  85  is formed over substantially the entire surface of the insulating layer  82 . 
     The write section  60  typically includes a thin film write head with a bottom pole  90  (P 1 ) and a top pole  96  (P 2 ). The bottom pole P 1  is made of magnetically conductive material, and be for example only, similar or equivalent to that of the first shield layer  80 . The pedestal region  120  is formed on the bottom pole P 1  from the ABS to the back face  92  which defines the zero throat level with extreme accuracy. The pole tip region is defined as the region between the ABS and the zero throat level. 
     The top pole P 2  is made of a magnetically conductive material, and be for example only, similar or equivalent to that of the first shield layer  80  and the bottom pole P 1 . The top pole P 2  is formed over, and is separated from the pedestal  120 , to define a write gap  98  therewith. The thickness of the top pole P 2  can be substantially the same as, or similar to that of the first shield layer  80 . The write gap  98  can be filled with a material similar or equivalent to that of the insulating layer  82 . 
     With reference to  FIGS. 5 and 6 , a write twin coil  94  made according to the present invention, forms part of the write section  60 , and includes a plurality of multi-layered conductive first coil elements (or conductors)  97  and second coil elements  99 , only a few of which are illustrated. The twin coil  94  is topologically divided into a front region  120  disposed adjacent to the top pole P 2 , an aft region  122 , and a central region  124 . 
     The coil elements  97  and  99  are formed in an alternating manner within an insulating layer  95  and are spirally wound starting from the front region  120  and terminating in the aft region  122 . The width of the coil elements  97  and  99  generally varies from approximately 1.0 μm in the front region  120  to approximately 3.0 μm in the aft region  122 . A thin layer of dielectric material  126  is interposed between the coil elements  97  and  99  to serve as insulation. 
     The forward-facing portions of the coil elements  97  and  99  are generally flattened in the front region  120  and reduced to a smallest width, for the coil elements  97  and  99  to fit in a very limited yoke length, for reducing the coil size. The central region  124  is generally made of a dielectric material and provides the necessary physical separation between the front region  120  and aft region  122  for magnetic induction during a write operation. 
     With reference to  FIG. 5 , the top pole P 2  extends into a yoke  104 . The yoke  104  covers substantially the entire front region  120  of the write coil  94 . The yoke  104  is made of a material such as Al 2 O 3 . The length of the yoke  104  is referred to as the yoke length which determines the size of the coil  94 . The coil  94  is formed over an insulation layer  112 , which is made of a material such as Al 2 O 3 . During fabrication, the insulation layer  112  serves as a protective layer for the bottom pole P 1  for potential damage during the coil fabrication. 
     With reference to  FIG. 6 , an output electrical lead  128  is connected to an outer terminal end of the first coil  97  in the aft region  122 , and an input electrical lead  129  is connected to an inner terminal end of the second coil  99  in the central region  124 . Additionally, an interconnect  600  provides an electrical connection between an outer terminal end of the second coil  99  in the aft region  121 , and an inner terminal end of the first coil  97  in the central region  124 . 
     During a write operation, a voltage difference between the input lead  129  and output lead  128  causes an electrical current I W  to flow through the coil  94  to induce a magnetic flux flow through the write gap  98 . Changes in the flux flow across the write gap  98  produce the different magnetic orientations of vertical magnetized regions or domains in the disk  14  during a write operation. 
     The process for fabricating the enhanced inductive double winding twin coil  94  according to a preferred embodiment of the present invention will now described in connection with  FIGS. 7  to  20 . 
     With reference to  FIG. 7 , the fabrication of the inductive coil  94  begins with the deposition of a stopping layer  112  preferably made of Al 2 O 3  on top of the bottom pole P 1 . The stopping layer  112  prevents the etchant from permeating through the bottom pole P 1  to cause damage during the fabrication of coil  94 . 
     With reference to  FIG. 8 , a layer  130  of photo resist material is deposited over the entire surface of the stopping layer  112 . The photo resist material is photo-sensitive, so that upon exposure to a light source, its chemistry is altered to allow the exposed material to be removed by a developer solution, leaving behind the unexposed material which forms the coil elements  97  and  99 . 
     With reference to  FIG. 9 , a photo mask layer  132  is placed over the photo resist layer  130 . A pattern of coil elements is formed on the photo mask layer  132 , and is comprised of masked areas  134  and unmasked areas  136 . The masked areas  134  are made of a photo mask material that blocks light transmission therethrough, preventing the underlying areas of the photo resist layer  130  from being exposed. The unmasked areas  136  are formed as opening in the photo mask layer  132  with the purpose of allowing light to transmit through and expose the areas in the photo resist layer  130 . In a preferred embodiment, a masked area  134  and its separation gap are of equal width “I” which typically ranges from approximately 0.2 to 1 μm. 
     With reference to  FIG. 10 , an ultraviolet light source  140  is directed toward the photo resist layer  130  through the photo mask layer  132 . The light source  140  transmits through the unmasked areas  136  to the exposed areas  142  of the photo resist layer  130 , while the shielded areas  144  of the photo resist layer  132  are unaffected as they are optically shielded by the masked areas  134  of the photo mask  132 . 
     With reference to  FIG. 11 , the photo mask layer  132  is removed and a developer solution is applied to the photo resist layer  130 . The developer solution chemically reacts with the photo resist material in the exposed areas  142  of the photo resist layer  130  and allows them to be removed. Consequently, a patterned photo resist layer  130  is formed by the remaining unexposed areas  144 . 
     With reference to  FIG. 12 , a copper (Cu) seed layer  146  is deposited over the patterned photo resist layer  130  in preparation for the plating step to form the first coil elements  97 . 
     With reference to  FIG. 13 , a copper plating layer  148  is formed over the patterned copper seed layer  146  and fills in the gaps  145  in between the copper covered unexposed areas  144  of the photo resist layer  130  to a height above the top of the copper seed layer  146 . The copper seed layer  146  is then integrally fused into the copper plating layer  148 . 
     With reference to  FIG. 14 , a planarization step involving a chemical milling polishing (CMP) process is used to remove the excess copper material, and to form a level surface on the copper plating layer  148  to the same height as the patterned photo resist layer  130 . 
     With reference to  FIG. 15 , the patterned photo resist layer  130  is removed using a photo stripping solution that is not chemically reactive with the copper material of the copper plating layer  148 . This is in contrast with the prior art where wet chemical solution is use for pattern formation, which solution may etch damage to the copper material. 
     Furthermore, the stopping layer  112  is impervious to the photo stripping solution, thus preventing potential damage to the bottom pole P 1 . Subsequent to the planarization and the removal of the patterned photo resist layer  130 , the first coil elements  97  are formed from the copper plating layer  148 . 
     With reference to  FIG. 16 , a layer  150  of dielectric material, preferably made of SiO 2 , is formed over the first coil elements  97  to serve as the insulating layer  126  between the first coil elements  97  and the second coil elements  99  to be made in the following steps. The enhanced coil process of the present invention uses the dielectric layer  126  between the coils elements  97 ,  99 , which dielectric layer  126  is preferably deposited by a PECVD (Plasma-Enhanced Chemical Vapor Deposition) process. 
     The present invention does not use chemical or wet etching processes that attack the metallic first coil elements  97 , and thus avoiding damage to the first coil elements  97 . Instead, the current process uses a photo stripping process or a reactive ion etching (RIE) process to remove the excess first coil pattern after completion of the planarization of the first coil elements  97 . 
     With reference to  FIG. 17 , a copper seed layer  152  is deposited over the dielectric layer  150  in preparation of the plating step to form the second coil elements  99 . 
     With reference to  FIG. 18 , a copper plating layer  154  is deposited over the copper seed layer  152  and fills in the gaps  157  in between the first coil elements  97  to a height above the top of the dielectric layer  150 . The copper seed layer  152  is then integrally fused into the copper plating layer  154 . 
     With reference to  FIG. 19 , the copper plating layer  154  undergoes a planarization step using Chemical Mechanical Polishing (CMP) to form a level surface of the copper plating layer  154  at the same level as the top of the first coil elements  97  with the dielectric layer  150  above the top of the first coil elements  97  completely removed. The second coil elements  99  are now formed from the copper plating layer  154  and separated from the first coil elements  97  by the vertical portion  156  of the dielectric layer  150 . The double winding twin coil  94  of the present invention is thus complete with a resulting double packing coil density to maximize the size constraint utilization of the twin coil  94 . 
     With reference to  FIG. 20 , a distinguishing feature of the present invention is the optional use of reactive ion etching (RIE) to remove the dielectric material from the vertical portions  156  of the dielectric layer  150  interposed between the first and second coils elements  97  and  99 , if there is a quality assurance concern with the dielectric separation. The use of RIE does not pose harm to the enhanced inductive coil design of the present invention as REI is known to be chemically inert to and thus does not attack copper. 
     Another distinguishing feature of the present invention is the elimination of a second photo mask process for forming the second coil elements  99 , thereby effectively creating a self-alignment process. This is a significant improvement over the conventional coil fabrication process whereby a second photo mask process is used to form the second coil elements, thus requiring the pattern on the photo mask to accurately aligned with the already formed first coil elements. 
     The alignment process of the conventional coil process becomes exasperated as the coil size is reduced, thus creating a potential misalignment which could adversely affect the quality and the production of the conventional inductive coils. As a result, the enhanced coil process of the present invention has greatly increased the quality of the inductive coils, while reducing the production cost as the fabrication process has become more efficient than the convention process. 
     It should be understood that the geometry, compositions, and dimensions of the elements described herein can be modified within the scope of the invention and are not intended to be the exclusive; rather, they can be modified within the scope of the invention. Other modifications can be made when implementing the invention for a particular environment.