Abstract:
A GMR read head is described. The device comprises a spin valve stack whose top layer is a first capping layer. On the first capping layer are two additional layers, a lead overlay layer and a second capping layer. These are divided into two opposing portions, separated from each other by a trench that is filled with a dielectric. A bias layer and a conductive lead layer contact the stack on its sidewalls.

Description:
This is a division of patent application Ser. No. 09/747,234, filing date Dec. 26, 2000 now U.S. Pat. No. 6,634,087, Spin Valve Head Having Lead Overlay, assigned to the same assignee as the present invention. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the general field of magnetic read heads with particular reference to GMR structures for use in reading data recorded at densities in the 100 Gb per sq. in. range. 
     BACKGROUND OF THE INVENTION 
     Requirements on transducers for ultra-high recording densities (greater than 60 Gb/in 2 ) place certain constraints on the properties of the read and write heads needed to achieve this. These fundamental constraints have a profound influence on the design and fabrication of the read/write transducers. To achieve extremely high recording densities, Giant Magnetoresistance (GMR) reader design has to be capable of very high linear bit density (BPI) and also very high track density (TPI). Consequently, GMR devices continue to be pushed to narrower track widths and to thinner free layers to maintain high signal output in spite of reductions in track width and reduced gap length. 
     A critical issue for a very narrow track width is possible large amplitude and sensor stability loss. One approach that has been proposed to alleviate the amplitude loss and sensor stability concern is to use a lead overlay design. In lead overlay design, MR sensor track width is defined by conductor lead edge while the contiguous hard bias junction is placed outside the lead overlay. 
     For reader device situated within a reduced gap (i.e. thin upper dielectric layer), lead overlay topography becomes very critical. The bi-layer resist structure for conductor lift-off is normally made with an undercut in the bottom resist layer. For a very narrow track width, there is no room for creating this resist undercut so conductor lead structures formed using conventional lift-off process are exposed to a high probability of ending up with bridging conductor leads as well as conductor lead fencing. The former results in current shunting, while the latter leads to sensor to shield shorts. Additionally, lead overlays formed during a conductor lead lift-off process is usually associated with poor contact resistance at the lead overlay and GMR interface. 
     In the present invention the bias and conductor lead substructures are formed without the use of a liftoff process. 
     A routine search of the prior art was performed with the following references of interest being found: U.S. Pat. No. 5,985,162 (Han et al.), U.S. Pat. No. 6,103,136 (Han et al.), and U.S. Pat. No. 6,007,731 (Han et al.) all show lead lift off processes. In U.S. Pat. No. 5,966,273, Matsumoto et al. show a lead process while in U.S. Pat. No. 5,491,600, Chen et al. show a multi-layered lead and associated process. 
     SUMMARY OF THE INVENTION 
     It has been an object of the present invention to provide a spin valve magnetic read head suitable for use with ultra-high recording densities, 
     Another object of the invention has been to provide a process for the manufacture of said read head. 
     A further object has been that said process produce a product that is free of conductor lead bridging, conductor lead fencing, and contact resistance at the lead overlayer and GMR structure interface. 
     These objects have been achieved by means of a process wherein a first capping layer is deposited through DC sputtering and, without breaking vacuum, a lead overlay layer is then deposited on the first capping layer. This is followed by deposition, also by DC sputtering, of a second capping layer which is patterned so that it becomes a hard mask. Then, using this hard mask, the lead overlay layer is removed from the center of the structure by means of ion beam etching. The hard bias and conductor lead layers are then formed inside parallel trenches with the use of liftoff processes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the basic layer structure of the spin valve portion of the device that constitutes the present invention. 
         FIG. 2  shows the structure of  FIG. 1  after the addition of a lead overlay layer that is sandwiched between two capping layers. 
         FIGS. 3–5  illustrate how the central trench is etched with the upper cap layer used as a hard mask. 
         FIG. 6  shows the etching of the two outer trenches. 
         FIG. 7  shows  FIG. 6  after deposition of the hard bias and conductor lead layers. 
         FIG. 8  shows the completed structure. 
         FIG. 9  shows both edges of the completed structure. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is important to note that the order in which the various layers of the present invention are deposited as well as the thicknesses specified for them are critical, as opposed to optimal. A structure having the same set of layers as the present invention, but having one or more whose thicknesses lie outside the specified ranges, will not operate properly. It may also be possible to form structures having the same layers, with the same thicknesses in the same order, as those of the present invention but formed using one or more different sub-processes (such as liftoff instead of subtractive etching). Such structures will, in general, have a production yield and operating reliability that is different from that of devices made by following all the teachings of the present invention. 
     We now describe the present invention in terms of the process used for its manufacture. This description will also serve to clarify the structure of the present invention. For convenience, only the right hand side of the device has been shown in  FIGS. 1 through 8 . A fuller visualization of the structure may be obtained by jumping ahead to  FIG. 9  which shows both ends of the structure. 
     We begin our description by referring to  FIG. 1 . The process begins with the provision of lower magnetic shield layer  15 . On this is deposited the lower dielectric layer  17  to a thickness between about 120 and 160 Angstroms. More specifically, layer  17  is formed by first depositing a layer of tantalum (not shown), converting it to tantalum oxide, and then depositing a layer of aluminum oxide on this tantalum oxide layer. With layer  17  in place, the next step is the deposition of seed layer  10  (for which we have used nickel-chromium but other materials such as nickel-iron-chromium could also have been used). The thickness of layer  10  is between about 40 and 60 Angstroms. 
     The next layer to be deposited is free layer  11  onto which is deposited layer of non-magnetic material  12  (typically copper). This is followed by synthetic antiferromagnetic pinned layer  13  onto which is deposited the final layer (for the basic spin valve portion of the device) which is manganese platinum layer  14 . Layer  13  consists of a layer of cobalt iron between about 15 and 25 Angstroms thick followed by a spacer layer (not shown) that is a layer of ruthenium between about 6 and 9 Angstroms thick and a layer of cobalt-iron (also not shown) between about 15 and 25 Angstroms thick. Layers  13  and  14  together form the pinned layer portion of the device. 
     Referring now to  FIG. 2 , capping layer  23  is deposited onto layer  14 . A requirement for capping layer  23  is that it have a low IBE (ion beam etching) rate while still being subject to RIE (reactive ion etching). Our preferred material for this has been tantalum because it is already one of the components of a GMR configuration, but similar materials such titanium or tungsten could also have been used. It is between about 50 and 70 Angstroms thick, and it is a key feature of the invention that this layer be deposited through DC sputtering and that, without breaking vacuum, lead overlay layer  24  is deposited onto capping layer  23  and, again through DC sputtering and still without breaking vacuum, a second capping layer  26  (also of tantalum between about 150 and 250 Angstroms thick) is deposited onto lead overlay layer  24 . More specifically, the term ‘without breaking vacuum’, as used here, implies maintaining a pressure (other than the partial pressure of the sputtering gases) that is no greater than about 10 −6  torr. Our preferred material for lead overlay layer  24  has been gold deposited to a thickness between about 200 and 300 Angstroms, but other materials, such as copper (between about 150 and 250 Angstroms thick) could also have been used. 
     Next, as illustrated in  FIG. 3 , capping layer  26  is coated with photoresist layer  31  which is patterned to define a centrally located trench following which layer  26  is RIE etched using trifluoro methane, so that it becomes a hard mask as shown in  FIG. 4 . Then, using this hard mask, IBE is used to form centrally located trench  55 , as shown in  FIG. 5 . Trench  55  has sidewalls that slope by no more than 45 degrees away from vertical and its depth is such that all unprotected portions of lead overlay layer  24  are removed as well as portions of both capping layers. This is the result of intentionally over-etching so that about 70% of layer  26  and about 50% of layer  23  get removed during this step. 
     At this stage in the process the wafer (of which the device is a part), is annealed so that the pinned layer direction can be set up. Annealing conditions are heating for between about 5 and 10 hours at a temperature between about 250 and 280° C. in the presence of a magnetic field whose strength is between about 6,000 and 10,000 Oersted. Additionally, this heat treatment causes some diffusion of both tantalum capping layers into overlay layer  24  which results in a strengthening of the overlay layer. 
     Referring now to  FIG. 6 , the GPC (GMR/Permant magnet/Conductor lead) process is used for the formation of the hard bias and conductor leads. Using a lift-off resist pattern to define trenches  65 , IBE is used to form the trenches  65 . These are two trenches that run parallel to trench  55 , being symmetrically disposed on either side thereof and separated therefrom by between about 0.1 and 0.15 microns. Trenches  65 , being formed by IBE, extend downwards to a depth such that a small portion of lower dielectric layer  17  is removed. These trenches have sloping sidewalls that slopes no more than 30 degrees below horizontal. 
     Referring now to  FIG. 7 , a layer of hard bias material  71  is then deposited inside trenches  65  to a thickness sufficient to partly fill these trenches and to also fully coat sloping sidewalls  66 . After hard bias layer deposition, conductor lead layers such as Ta/Au/Ta are then deposited. The conductive lead layers being confined to inside trenches  65  except for a small amount of overlap  75  of upper capping layer  26 , as shown in  FIG. 7 . The conductor lead layer  72  is selectively deposited over bias layer  71  to a thickness that is sufficient to overfill trenches  65  without increasing the magnitude of overlap  75 . To minimize the overlap, hard bias and conductive lead layers are, preferably, deposited through ion beam deposition (IBD). 
     The process of the present invention then concludes with successive depositions of upper dielectric layer  81  and upper magnetic shield  82 , over the entire wafer. 
     Experimental Confirmation 
     After completing a device using the lead overlay process described above, magnetic performance properties of this device was compared with a reference GMR unit. The results are listed in TABLE I below: 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Structure: 
                   
                   
                   
                   
                   
                   
                   
               
               
                 NiFe 82%, MnPt 43% 
                 Bs 
                 Hc 
                 He 
                 Hk 
                 Rs 
                 Dr/r 
                 Dr 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 NiCr55/BCL5/Cu5/NiFe15/ 
                 0.23 
                 7.7 
                 −3.4 
                 6.4 
                 19.1 
                 12.6 
                 2.40 
               
               
                 CoFe10/Cu20/Cofe19/ 
               
               
                 Ru7.5/CoFe21/MnPt120/ 
               
               
                 Ta50(reference) 
               
               
                 NiCr55/BCL5/Cu5/NiFe15/ 
                   
                   
                   
                   
                 1.5 
               
               
                 CoFe10/Cu20/Cofe19/ 
               
               
                 Ru7.5/CoFe21/MnPt120/ 
               
               
                 Ta50/Cu250/Ta200 
               
               
                 After removing 200 Å of 
                   
                   
                   
                   
                 1.6 
               
               
                 Ta by reactive ion etching 
               
               
                 After ion beam etching 
                 0.24 
                 7.7 
                 −2.2 
                 9.0 
                 18.9 
                 13.2 
                 2.49 
               
               
                 to remove copper 
               
               
                   
               
               
                 where Bs = free layer moment, 
               
               
                 Hc = coercivity, 
               
               
                 He = inter-layer coupling field, 
               
               
                 Hk = anisotropy field, 
               
               
                 Rs = GMR sheet resistance, 
               
               
                 BCL = Ru 
               
             
          
         
       
     
     With the presence of the lead overlay layers, the sheet resistance is 1.5 ohm/sq. After IBE to remove Cu lead overlay, Rs of the GMR stack is 18.9 ohm/sq. The Rs is equivalent to that of the reference GMR stack. Other magnetic properties of the lead overlaid wafer are also equivalent to the reference wafer. Thus, the subtractive lead overlay process does not create damage to the GMR sensor. 
     For a 150Å Cu lead overlay, the resistance aspect ratio between the GMR and Exchange/Lead Overlay is around 6.0. Thus, the lead overlay is a low resistance path for conducting the sensor current. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.