Abstract:
A method for forming a magnetic write pole with a trapezoidal cross-section is described. The method consists of first forming a magnetic seedlayer on a base followed by depositing a removable material layer on the seedlayer, and then a resist layer on the removable material layer. A trench is then formed in the resist, and the resist is heated to cause the cross-sectional profile of the trench to assume a trapezoidal shape. The resist is then capped with another resist layer and further heated to cause the width of the trapezoidal trench to become narrower. The cap layer and removable material layer at the bottom of the trench are then removed and the trench filled with magnetic material by electroplating. The resist and seedlayer external to the trench are finally removed to form a write pole with a trapezoidal cross-section.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     This invention was made with United States Government support under Agreement No. 70NANB1H3056 awarded by the National Institute of Standards and Technology (NIST). The United States Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to magnetic recording heads and more particularly to the fabrication of a trapezoidal write pole. 
     BACKGROUND 
     Magnetic recording heads have utility in a magnetic disc drive storage system. Most magnetic recording heads used in such systems today are “longitudinal” magnetic recording heads. Longitudinal magnetic recording in its conventional form has been projected to suffer from superparamagnetic instabilities at densities above approximately 40 Gbit/in 2 . It is believed that reducing or changing the bit cell aspect ratio will extend this limit up to approximately 100 Gbit/in 2 . However, for recording densities above 100 Gbit/in 2 , different approaches will likely be necessary to overcome the limitations of longitudinal magnetic recording. 
     An alternative to longitudinal recording that overcomes at least some of the problems associated with the superparamagnetic effect is “perpendicular” magnetic recording. Perpendicular magnetic recording is believed to have the capability of extending recording densities well beyond the limits of longitudinal magnetic recording. Perpendicular magnetic recording heads for use with a perpendicular magnetic storage medium may include a pair of magnetically coupled poles, including a main write pole having a relatively small bottom surface area and a flux return pole having a larger bottom surface area. A coil having a plurality of turns is located adjacent to the main write pole for inducing a magnetic field between the pole and a soft underlayer of the storage media. The soft underlayer is located below the hard magnetic recording layer of the storage media and enhances the amplitude of the field produced by the main pole. This in turn allows the use of storage media with higher coercive force. Consequently, more stable bits can be stored in the media. In the recording process an electrical current in the coil energizes the main pole, which produces a magnetic field. The image of this field is produced in the soft underlayer to enhance the field strength produced in the magnetic media. The flux density that diverges from the tip into the soft underlayer returns through the return flux pole. The return pole is located sufficiently far apart from the main write pole such that the material of the return pole does not affect the magnetic flux of the main write pole, which is directed vertically into the hard layer and the soft underlayer of the storage media. 
     A magnetic recording system such as, for example, a perpendicular magnetic recording system may utilize a write pole with a square or rectangular cross-section. Under certain circumstances, the increased magnetic field concentration at the sharp corners can cause writing or erasure on adjacent tracks. 
     Another development that overcomes at least some of the problems associated with the superparamagnetic effect is heat assisted magnetic recording (HAMR), sometimes referred to as optical or thermal assisted recording. Heat assisted magnetic recording generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. The heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased aerial densities, with a larger magnetic anisotropy at room temperature and assuring a sufficient thermal stability. 
     More specifically, super paramagnetic instabilities become an issue as the grain volume is reduced in order to control media noise for high aerial density recording. The superparamagnetic effect is most evident when the grain volume V is sufficiently small that the inequality K u V/k b T&gt;40 can no longer be maintained. K u  is the magnetic crystalline anisotropy energy density of the material, k b  is Boltzman&#39;s constant, and T is absolute temperature. When this inequality is not satisfied, thermal energy demagnetizes the individual grains and the stored data bits will not be stable. Therefore, as the grain size is decreased, in order to increase the aerial density, a threshold is reached for a given material K u  and temperature T such that stable data storage is no longer feasible. 
     The thermal stability can be improved by employing a recording medium formed of a material with a very high K u . However, with the available materials, the recording heads are not able to provide a sufficient or high enough magnetic writing field to write on such a medium. Accordingly, it has been proposed to overcome the recording head field limitations by employing thermal energy to heat a local area on the recording medium before or at about the time of applying the magnetic write field to the medium. By heating the medium, the K u  or the coercivity is reduced such that the magnetic write field is sufficient to write to the medium. Once the medium cools to ambient temperature, the medium has a sufficiently high value of coercivity and assures thermal stability of the recorded information. When applying a heat or light source to the medium, it is desirable to confine the heat or light to the track where writing is taking place, and to generate the write field in close proximity to where the medium is heated to accomplish high aerial density recording. The separation between the heated spot and the write field spot should be minimal or as small as possible so that the writing may occur while the medium temperature is substantially above ambient temperature. This also provides for the efficient cooling of the medium once the writing is completed. 
     Accordingly, there is identified a need for an improved write pole with a shape and dimensions that overcome the limitations and shortcomings of known magnetic recording heads and heat assisted magnetic recording heads. 
     SUMMARY 
     In one aspect of the invention, a method of forming a magnetic write pole with a trapezoidal cross-section is presented. The method comprises forming a magnetic seedlayer on a base, forming a removable material layer on the seedlayer, forming a resist layer on the removable layer and forming a trench in the resist and heating the structure for a first amount of time at a first temperature to form a predetermined slope in the first and second sidewalls of the trench. The method further comprises capping the trench with another resist layer and heating the capped trench for a second amount of time at a second temperature to shrink the separation of the first and second sidewalls of the trench, removing the cap layer and the removable material at the bottom of the trench, electroplating a magnetic material in the trench and removing the resist by stripping the resist and finally removing the seed material outside the pole area by ion-beam etching to form the magnetic pole. 
     In accordance with another aspect of the invention, a magnetic write pole with a multilayer structure and a trapezoidal cross-section comprises a base and a multilayer magnetic seedlayer on the base. A magnetic layer on the seedlayer has a trapezoidal cross-section, a bottom width W b  less than or equal to about 100 nm, a top width of about 1.25 to 3 times W b , a height h, and an aspect ratio h/W b  of about 1:1 to about 10:1. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional view from the air bearing surface (ABS) plane showing a prior art HAMR write pole. 
         FIG. 1B  is a cross-sectional view from the ABS plane showing a trapezoidal write pole of the current invention. 
         FIG. 2  is a diagram illustrating the steps to form a trapezoidal pole. 
         FIG. 3  is a cross-sectional view of a trench in a resist layer on a substrate before (A) and after (B) a thermal bake process. 
         FIG. 4  is a cross-sectional view of a capped trench in a resist layer on a substrate before (A) and after (B) a thermal shrink process. The resist cap is removed in (C). 
         FIG. 5A  are SEM images showing different trench profiles achieved at different temperatures during thermal bake process.  FIG. 5B  is a graph showing bottom and top spacing and beveled angle as a function of bake temperature. 
         FIG. 6A  are SEM images showing different trench profiles after baking for different times.  FIG. 6B  is a graph showing bottom and top spacing and beveled angle as a function of bake time. 
         FIG. 7  are SEM images showing trench profiles after combinations of thermal bake (Process A) and thermal shrink (Process B). 
         FIG. 8  are SEM images showing trench profiles after combinations of thermal bake (Process B) and thermal shrink (Process A). 
         FIG. 9  is a cross-sectional view of resist layer  300  on easily removable resist layer  290  on magnetic seed layer  210  on substrate  220  (not to scale). 
         FIG. 10A  are magnetic hysteresis loops for a 1000 Å single CoNiFe layer. 
         FIG. 10B  are magnetic hysteresis loops for a 1000 Å laminated seedlayer with a Ni 80 Fe 20  cap layer. 
         FIG. 11  is a chart of corrosion resistance of CoNiFe seedlayers with and without Ni 80 Fe 20  cap layer. 
         FIG. 12  are SEM images of 100 nm wide plated trapezoidal poles using (a) a CoNiFe seedlayer and (b) a CoNiFe seedlayer with Ni 80 Fe 20  anti corrosion cap layer. 
         FIG. 13  is a diagram illustrating the steps to electroplate magnetic trapezoidal pole. 
         FIG. 14  is a schematic of an Ms gradient trapezoidal pole configuration. 
         FIG. 15  is a cyclic voltammetry plot of current density versus applied potential for the single bath electrolyte shown in Table 2. 
         FIG. 16  is a graph showing how composition and magnetic moment of a plated pole can be tailored by adjusting plating current density for the single bath electrolyte shown in Table 2. 
         FIG. 17  are SEM images of the microstructures of 0.5T NiCu (left) and 0.3T NiCu (right) plated from the single bath shown in Table 2. 
         FIG. 18  are magnetic hystresis loops of a plated graded Ms stack containing a CoNiFe laminate seed. 
         FIG. 19A  is a schematic of a trapezoidal pole before seed removal. 
         FIG. 19B  is a schematic of a trapezoidal pole after seed removal. 
         FIG. 20  is a FIB-SEM image of a cross-sectioned trapezoidal pole after seed removal. 
         FIG. 21  is a schematic of a static ion beam etch method. 
         FIG. 22  is a SEM image of a cross-sectioned trapezoidal pole after seed removal by static ion beam etch. 
         FIG. 23  is a SEM image of a cross-sectioned trapezoidal pole after backfilling with Comptech sputtered alumina. 
         FIG. 24  is a SEM image of a cross-sectioned trapezoidal pole after backfilling with IBD aluminum. 
         FIG. 25  are SEM images of sectioned (top row) and unsectioned (bottom row) trapezoidal poles with three different designs. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to the problem of side writing or erasure on adjacent tracks due to magnetic field concentrations at sharp corners in prior art write poles with rectangular cross-sections as seen from the air bearing surface (ABS) of a recording media.  FIG. 1A  shows a cross-section of prior art write pole  10  as seen from the ABS. Write pole  10  has three sections,  20 ,  30 , and  40 . The shading on  FIG. 1  illustrates magnetic field concentrations capable of side writing or erasure. The embodiment of the invention is to replace sections  20  and  30  with a single pole  50  having a trapezoidal cross-section with a bottom spacing  70  at its tip and a top spacing  80  to form write pole  60  as shown in  FIG. 1B . Furthermore, by making the spacing of section  90  in  FIG. 1B  equal to top spacing  80 , the corners responsible for magnetic field leakage are eliminated. In another embodiment of the invention, the aspect ratio H/W of the trapezoidal pole  50  is about 1:1 to about 10:1 to keep the wider portions away from the bottom edge (front edge) of the pole that does the writing. In another embodiment of the invention, the magnetization of the trapezoidal pole  50  is graded to ensure that the field from the top of the pole is lower than the field from the bottom of the pole since writing is done at the bottom of the pole. 
     Prior art trapezoidal poles have been fabricated using high angle ion-beam etching with masking to create the trapezoidal shape. This process is not compatible with the process used to form heat assisted magnetic recording (HAMR) heads. A process that is compatible with the HAMR process is electroplating in a resist trench with a trapezoidal shape. 
     The disclosed invention solves the following issues. 1) The trench has a trapezoidal shape. 2) The trench width at the bottom is less than 100 nm. 3) The aspect ratio h/W b  is about 1:1 to about 10:1. 4) Removing the seedlayer without leaving a footing or redepositing seedlayer material on the sides of the pole. 5) Backfilling with alumina without leaving voids in the alumina. 6) The process needs to be compatible with standard processes in industry fabs. 
     The invention discloses how to form a narrow trench with a controlled trapezoidal shape and controllable top and bottom separations. In summary the method is a hybrid thermal flow process consisting of a resist post-development thermal bake treatment process that allows a sub-100 nm high aspect ratio trench with a trapezoidal shape to be formed that can then be used as a template for electroplating writer pole materials. 
     Lithographic Process 
     The steps to form a magnetic pole with a trapezoidal cross-section are given in  FIG. 2 . First, a substrate is provided (step  100 ). The substrate can be a ceramic composite used to form sliders such as an aluminum oxide/titanium oxide composite or other materials known in the art. A plating seedlayer is deposited on the substrate (step  102 ). Suitable seedlayers are selected from a group but are not limited to FeCo, NiFe, CoNiFe, Ru, Ta, CoZrTa, CoNbTa, and Cu. 
     A thin, easily removable, resist layer is deposited on the seedlayer (step  104 ). The removable layer is preferably about 10 nm to about 30 nm thick and is preferably a polymethylglutarimide (PMGI) layer. The removable layer is then given a post-apply bake (step  106 ). A thicker top resist layer is then deposited on the PMGI layer with a thickness of from about 0.5 μm to about 4.0 μm depending on the requirements for the top pole design (step  108 ). The resist is then given a post-apply bake (step  110 ). The resist is then exposed using e-beam or other lithographic tools e.g. G-line, I-line, DUV, 193 nm scanner, electron beam direct write, EUV, x-ray lithography or others (step  112 ). The exposed wafer is then given a post exposure bake (step  114 ). The exposed wafer is then developed in standard tetramethyl ammonium hydroxide (TMAH) developer to form a rectangular trench (step  116 ). The developed wafer is then put through a hybrid thermal flow process, described later, to produce the proper trapezoidal shape and spacing of the trench (step  118 ). Magnetic material is then electroplated in the trench to form a magnetic trapezoidal pole (step  120 ). 
     Hybrid Thermal Flow Process 
     The hybrid thermal flow process is composed of two processes, a thermal bake process and a thermal shrink process. In the thermal bake process, the resist is baked at a temperature close to the glass transition temperature, Tg, of the resist. This causes the walls of the trench to slope into a trapezoidal cross-section as shown in  FIG. 3 .  FIG. 3A  shows resist layer  220  with trench  221  on substrate  230  before thermal bake process.  FIG. 3B  shows resist layer  220  after thermal bake. Trench  221  with rectangular cross-section has transformed into trench  222  with trapezoidal cross-section after the bake. 
     The thermal shrink process is illustrated in  FIG. 4  where resist layer  240  on substrate  230  with a rectangular trench is capped with resist layer  242 . Resist layer  242  is applied by spin coating and fills the trench during the process. The spacing of the trench is “a”. The resist is then baked at a temperature less than, equal to, or greater than that used for the thermal bake process. This thermal shrink process causes the separation of the two walls of the trench to decrease giving an added dimension to the control of the trapezoidal trench forming process. The new spacing is “b” where b&lt;a. The thermal shrink process can be repeated at will to obtain the required trench separation. The thermal bake process and thermal shrink process can be interchanged as needed to obtain required trapezoidal trench shapes and dimensions. By combining the two processes, trenches with high aspect ratios of 1:1 to 10:1 and sub-100 nm spacing have been produced. The process is very manufacturable. The addition of the hybrid thermal bake process to an overall manufacturing process can be done using resist development track tools that are standard in most industry fabs. The actual time it takes to incorporate these processes into the lithographic step is minimal compared to the results that can be achieved. In addition, the cost of the added material is attractively small in relation to the cost of updating and maintaining advanced lithographic equipment such as DUV, 193 nm scanners, electron beam direct write, or EUV tools that are needed to reduce trench dimensions to the sub-100 nm regime. It should be mentioned that this method or process is not limited to the application of magnetic pole fabrication. In principle it can be used in any device fabrication in the case where a narrow trapezoidal trench pattern is needed. 
     An example of how a trapezoidal shape is formed in a 1.3 μm thick resist with a rectangular trench during a thermal bake is shown in  FIG. 5A . Scanning electron microscope (SEM) images of the trench are shown at different temperatures after a 60 second bake at different temperatures in  FIG. 5A . The bottom and top spacing, of the trench as well as the bevel angle are shown in  FIG. 5B  as a function of temperature for a 60 second baking time. The top spacing and bevel angle are smoothly varying functions of temperature while the bottom spacing remained constant. 
       FIGS. 6A and 6B  show the time dependence of the thermal bake process at 145° C. on trench dimensions in a 1.3 μm thick resist. The top spacing and bevel angle are smoothly varying functions of time while the bottom spacing remained constant. Combinations of the thermal bake process and the thermal shrink process can give considerable latitude to the shaping of a trapezoidal trench. 
       FIG. 7  shows SEM images of trenches in a 1.3 μm thick resist given three exposures (increasing from top to bottom). Process A was a thermal bake at 155° C. for 60 seconds and process B was a thermal shrink process at 120° C. for 90 seconds. The shrinking of the wall separation after multiple thermal shrink treatments (A+B, A+2B, A+3B, and A+4B) is evident. Other combinations of treatments were carried out with similar results. 
       FIG. 8  shows trapezoidal shape formation in a 1.3.mu·m thick resist given three exposure levels again. In this case the originals were given two thermal shrink treatments (Process B) of 60 seconds each at 120.degree. C. and then given one thermal bake treatment (Process A) for 90 seconds at 130.degree. C., 140.degree. C., and 150.degree. C. The large control over the shape of the trench is apparent from  FIG. 8 . 
     Plating Process 
     The plating process to form a trapezoidal pole starts with step  102  in  FIG. 2 , deposit seedlayer. Although the seedlayer used in this process is described in detail, other seedlayers and combinations of seedlayers can be used. A schematic showing the layer structure of the seed and resist layers is shown in  FIG. 9  where the relative dimensions are not to scale. All layers in seedlayer  310  can be formed by physical vapor deposition (PVD), e-beam vapor deposition, sputtering and other means known to those in the art. The seedlayer has two characteristics, a laminated layer structure and an anticorrosion cap. Seedlayer  310  is shown on substrate  320  and includes first or bottom layer  330  on substrate  320 . First layer  330  is NiFe about 15 Å thick. Second layer  340  is CoNiFe about 350 Å thick. Third layer  350  on CoNiFe layer  340  is Ta about 12 Å in thickness. Fourth layer  360  includes three NiFe layers about 15 Å thick each. Fifth layer  370  on NiFe layer  360  is CoNiFe about 250 Å thick. Sixth or cap layer  380  is Ni 80 Fe 20  about 50 Å thick and is added for anticorrosion protection as will be discussed below. Easily removable resist layer  390  is on cap layer  380 . Layer  390  is preferably a PMGI layer about 10 nm to 30 nm thick and is applied to protect the seedlayer at the base of the trench during subsequent thermal processing. Thick resist layer  400  is on thin easily removable layer  390 . Resist layer  400  is from 0.5 μm to 4.0 μm thick depending on the requirements of the pole design. 
     Magnetic properties of laminate seedlayer  310  are compared with a single CoNiFe layer in  FIGS. 10A and 10B .  FIG. 10A  shows B versus H hysteresis loops for a solid 1000 Å CoNiFe film and  FIG. 10B  shows B versus H hysteresis loops for a 1000 Å laminate film. The hard axis loop of the laminate shows almost no hysteresis. 
     In another embodiment of this invention, the magnetization of each magnetic layer in the seedlayer can be different such that the seedlayer exhibits a vertical magnetization gradient which can contribute to the magnetization gradient in the write pole. 
       FIG. 11  shows the corrosion resistance of a capped seedlayer to be superior to that of an uncapped layer. This corrosion protection is important in defining the shape of the pole. The formation of the trapezoidal resist shape as shown earlier involves thermal baking and shrinking which results in undercut features at the resist/seedlayer interface. During the pre-plate and plating processes, the corrosive plating solution can be trapped in this crevice and cause corrosion. This is evident in  FIG. 12  which shows SEM images of 100 nm wide plated trapezoidal poles using a CoNiFe seedlayer without (a) and with (b) Ni 80 Fe 20  anticorrosion cap  280 . The SEM images on the right were taken after the poles were sectioned to show the trapezoidal shape. With the Ni 80 Fe 20  cap layer  280 , the corrosive solution trapped in the photoresist could not visibly corrode the seedlayer. Since the plating process is on top of an intact (uncorroded) seedlayer, the pole morphology is visibly improved and the depression in the center of the pole is eliminated. 
     Trapezoidal Pole Plating 
     The plating process flow to form a trapezoidal pole is shown in  FIG. 13  which shows the steps to electroplate a magnetic trapezoidal pole. At step  500 , removable layer  390  at the bottom of the trench is removed to expose the seedlayer. This is carried out by O 2  reactive ion etching to clear trench bottom. Next, etching removes surface oxide on the seedlayer (step  502 ). An acid spray etch performs this process. At step  504 , the trench is filled with magnetic material by electroplating. Solid FeCoNi, FeCo and graded magnetization poles can be formed. Following electroplating, the plated trench is rinsed and dried to remove plating solution (step  506 ). In the next step, the photoresist is removed by oxygen ashing and solvent stripping (step  508 ). As discussed later, in the final step, the exposed seedlayer is removed by ion beam etching (step  510 ). 
     The solid CoNiFe pole is electroplated using the parameters shown in Table 1. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Solid CoNiFe trapezoidal pole plating chemistry and parameters. 
               
             
          
           
               
                   
                 Chemical 
                 Concentration (g/l) and parameters 
               
               
                   
                   
               
             
          
           
               
                   
                 NiCl 2 •6H 2 O 
                 40 
               
               
                   
                 CoCl 2 •6H 2 O 
                 31 
               
               
                   
                 FeCl 2 •4H 2 O 
                 4 
               
               
                   
                 H 3 BO 3   
                 40 
               
               
                   
                 NH 4 Cl 
                 40 
               
               
                   
                 STJ additive 
                 0.65 
               
               
                   
                 Sodium LaurlelSulfate 
                 0.1 
               
               
                   
                 (SLS) 
               
               
                   
                 PH 
                 2.8 
               
               
                   
                 Current 
                 2.8-3 mA/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 1, the organic STJ additive acts as a leveling agent and plays an important role in controlling the grain size and surface morphology of the plated pole. Its adsorption to the narrow trench surface can be preferentially enhanced due to radial transportation at the current crowding points thereby increasing plating uniformity. Due to the trapezoidal profile of the trench cross-section, the accessibility of the small trench by the diffusing metal ions can be increased. This improves the uniformity of the plated pole cross-section along the length of the pole. 
     Graded Ms Poles 
     As illustrated in  FIG. 1A , prior art poles  10  are solid, plated, high Ms CoFeNi material for sections  20 ,  30 , and  40 . This high Ms configuration results in a magnetic field spike at the back of the pole  10 . In order to reduce this field spike, trapezoidal poles with an Ms gradient can be employed. A schematic of a trapezoidal graded Ms pole is shown in  FIG. 14 . 
     Three different pole materials with different magnetization can be plated to form this pole. For example, in the current seedlayer configuration (sputtered Si on substrate)/NiFe 15 Å/CoNiFe 250 Å/Ta 12 Å/NiFe 15 Å) 3 /CoNiFe 250 Å/Ni 80 Fe 20  50 Å, it is possible to subsequently plate 100 nm of 1T NiFe layer using a regular NiFe bath, and 50 nm of 0.5T NiCu on the 1T NiFe layer, and 50 nm of 0.3T NiCu layer on the 0.5T NiCu layer using another bath. 
     The 0.3T and 0.5T NiCu layers can be plated from a single bath using the novel developed bath chemistry shown in Table 2. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 0.3T and 0.5T NiCu plating chemistry and parameters. 
               
             
          
           
               
                   
                 Chemical 
                 Concentration (g/l) and parameters 
               
               
                   
                   
               
             
          
           
               
                   
                 NiCl 2 •6H 2 O 
                 119 
               
               
                   
                 CuSO 4 •5H 2 O 
                 0.5 
               
               
                   
                 Sodium citrate dehydrate 
                 29.4 
               
               
                   
                 H 3 BO 3   
                 25 
               
               
                   
                 STJ additives 
                 0.6 
               
               
                   
                 SLS 
                 0.1 
               
               
                   
                 PH 
                 55 
               
               
                   
                 Current (0.3T/0.5T) 
                 2.5/10 mA/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     In the single bath method, deposition is carried out using a single electrolyte while varying deposition parameters such as voltage or current to produce compositional, structural and magnetic modulations of the plated structure. For example, current density is shown as a function of applied voltage in cyclic voltammetry measurements made using the bath given in Table 2 where ions of two metals, Cu and Ni, with Cu being more noble than Ni, are present. At certain potentials (or currents) that are sufficiently negative, Cu will be reduced and Ni will not. In this region, region I in  FIG. 15 , Cu will be plated and Ni will not. As the potential is decreased into region II, both Cu and Ni will plate and the amounts of each will depend on the applied potential. As shown in  FIG. 15 , a 0.3T NiCu alloy will plate at a current density of about −2.5 mA/cm 2  and a 0.5T NiCu alloy will plate at a current density of −10.0 mA/cm 2 . Since the deposition rate of Cu is diffusion limited and hence constant, by varying the potential (or current) during plating, composition and magnetic modulations of the plated structure can be achieved. 
     The current control technique is employed in the wafer scale embodiment described here.  FIG. 16  shows the composition and magnetic moment variation in NiCu plated layers as a function of plating current. As shown in the figure, the magnetic moment, Bs, can be conveniently tailored by adjusting the plating current. Specifically, 2.5 and 10 mA/cm 2  currents can be applied to obtain 0.3T and 0.5T NiCu. The composition uniformity ( 1   a ) for 0.5T and 0.3T NiCu plated layers are 0.1 at / 0  (0.5T) and 0.7 at / 0  (0.3T) respectively. 
     The microstructure of the 0.5T and 0.3T NiCu are shown in  FIG. 17  as characterized by scanning electron microscopy (SEM). The surface looks sound and glossy and the grains are refined due to the use of the STJ organic additive in the bath. The magnetic hysteresis loop of an actual rated Ms stack is shown in  FIG. 18 . The stack consists of 50 nm of 0.3T NiCu on 50 nm of 0.5T NiCu on 100 nm of 1T NiFe on 100 nm of CoNiFe laminate seed. 
     Seed Removal and Pole Backfilling 
       FIG. 19A  is a schematic of the trapezoidal pole before ion beam etching.  FIG. 19B  is a schematic of the trapezoidal pole after ion beam etching.  FIG. 19B  indicates that the seed material redeposits on the sidewalls of the pole when standard rotating ion mill etching procedures are used.  FIG. 20  shows a focused ion beam scanning electron micrograph (FIB-SEM) of a cross-sectioned trapezoidal pole after seed removal by the standard rotating beam ion mill etching process. The redeposited layer is indicated by the dashed lines. 
     A seed removal method that works best is a static etch with the wafer stationary with the poles at a 30° angle with respect to the ion beam (i.e. α=30°) as shown in  FIG. 21 . In another embodiment, the wafer can be swept through a range of angles e.g. from about 20° to about 40°. As shown in the figure, the wafer is also set at 50° (i.e. θ=50°) to the ion beam. 
     Successful seed removal using this process is shown in  FIG. 22 .  FIG. 22  is an SEM image of a seed with an 86° wall angle with no redeposited seed material on the wall of the seed. The bottom, middle and top widths of the pole are 90 nm, 130 nm and 185 nm respectively. 
     Conventional sputtering such as with Alcatel Comptech equipment cannot be used to backfill the pole with alumina.  FIG. 23  is an SEM image of a pole that was backfilled with sputtered alumina using Comptech equipment. There are voids along the sides of the pole as indicated by the arrows. However, ion beam deposition can be used to backfill the pole.  FIG. 24  shows two magnifications of SEM images of a pole backfilled with 1.2 μm of ion beam deposited (IBD) alumina deposited at θ=60° with the wafer rotating. There are no voids in the alumina. 
     EXAMPLE 
     SEM images of three trapezoidal poles with different dimensions that have been fabricated by the invention disclosed herein are shown in  FIG. 25 . The top images are end-on views of vertical cross-sections of the poles. The bottom images are perspective views of the unsectioned poles. The bottom and top widths (i.e., critical dimension or CD) are indicated on the figure. 
     In summary, a novel hybrid thermal flow method to form trapezoidal shape resist trench structures has been invented that allows the production of trapezoidal write poles by electroplating. This process has been used to manufacture heat-assisted magnetic recording heads (HAMR). 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.