Recessed SiO2 or Si3N4 overcoat for GMR head in magnetic disk drive

Abstract

A giant magnetoresistive (GMR) head contains an overcoat layer consisting of silicon dioxide or silicon nitride. These materials have a coefficient of thermal expansion (CTE) that is less than alumina, which is conventionally used for the overcoat layer. As a result, the overcoat layer exhibits a smaller temperature-induced protrusion when the head heats up from friction with the passing air stream. The process of forming the head includes forming a recess in the overcoat layer that reduces the stress on the poles and improves the performance of the head. The process includes depositing a seed layer over the overcoat layer in preparation to plating a metal mask layer with an opening where the recess is to be formed, wet chemical etching the seed layer through the opening in the mask layer and performing an ion milling process to remove any remaining traces of the seed layer. With the seed layer completely removed, a trench having smooth sidewalls and bottom can be etched in the overcoat layer by a reactive ion etch (RIE) process. The saw that is used to separate the head elements in the wafer can be passed through the clean trench without contacting the overcoat layer, thereby avoiding the chipping and cracking that might otherwise result from the use of a silicon dioxide or silicon nitride overcoat layer.

1 . A GMR head comprising: 
 a substrate;    a bottom magnetic pole disposed on said substrate and including a bottom pole-tip;    a top magnetic pole disposed over said bottom magnetic pole and including a top pole-tip, said bottom and top pole-tips being separated by a non-magnetic gap layer;    a coil positioned such that a current through said coil induces a magnetic field between said pole-tips;    an overcoat layer overlying said top pole, said overcoat layer being formed of a material selected from the group consisting of silicon dioxide and silicon nitride, a recess being formed in said overcoat layer, said recess having a bottom and a sidewall that are substantially smooth and devoid of spikes or projections.    
   
   
       2 . The GMR head of  claim 1  wherein overcoat layer has a thickness in the range of 15 μm to 45 μm.  
   
   
       3 . The GMR head of  claim 2  wherein said recess has a width of from 1 μm to 5 μm.  
   
   
       4 . A method of fabricating a GMR head comprising: 
 providing a wafer element comprising a plurality of GMR head elements, each of said GMR head elements comprising a pair of magnetic pole-tips and a coil;    forming an overcoat layer over said GMR head elements;    forming a seed layer on said overcoat layer;    forming a mask layer on said seed layer, said mask layer having an opening at a location where a trench is to be formed in said overcoat layer, said opening exposing an exposed section of said seed layer;    etching said exposed section of said seed layer through said opening in said mask layer using a wet chemical;    directing an ion milling beam into said opening in said mask layer to remove remaining portions of said exposed section of said seed layer; and    etching said overcoat layer through said opening in said mask layer to create a trench in said overcoat layer.    
   
   
       5 . The method of  claim 4  wherein said opening in said mask layer is configured such that etching said overcoat layer creates a rectilinear lattice of trenches in said overcoat layer.  
   
   
       6 . The method of  claim 5  wherein said plurality of GMR head elements are separated from each other by said rectilinear lattice of trenches.  
   
   
       7 . The method of  claim 6  comprising separating said GMR head elements.  
   
   
       8 . The method of  claim 7  wherein separating said GMR head elements comprises running a dicing saw blade over a plurality of linear saw paths, each of said linear paths lying within said trenches.  
   
   
       9 . The method of  claim 8  wherein said saw blade makes no substantial contact with said overcoat layer.  
   
   
       10 . The method of  claim 4  wherein etching said overcoat layer comprises reactive ion etching.  
   
   
       11 . The method of  claim 4  wherein forming an overcoat layer comprises forming a layer comprising a material selected from the group consisting of silicon dioxide and silicon nitride.  
   
   
       12 . The method of  claim 11  wherein forming a mask layer comprises: 
 depositing a photoresist layer on said seed layer;    patterning said photoresist layer so as to leave sections of said photoresist layer remaining;    depositing said mask layer between said sections of said photoresist layer; and    removing said sections of said photoresist layer so as to form said opening.    
   
   
       13 . The method of  claim 12  wherein depositing said mask layer comprises plating.  
   
   
       14 . The method of  claim 12  wherein depositing said mask layer comprises physical vapor deposition.  
   
   
       15 . The method of  claim 11  wherein forming said mask layer comprises forming a NiFe layer.  
   
   
       16 . The method of  claim 15  wherein forming said seed layer comprises evaporation or physical vapor deposition.  
   
   
       17 . The method of  claim 16  wherein forming said seed layer comprises forming a layer comprising a material selected from the group consisting of Ta/Cu/NiFe, CoFe, CoFeN and NiCr.  
   
   
       18 . The method of  claim 17  wherein said wet chemical comprises a mixture of H 2 SO 4  and ammonium sulfate.  
   
   
       19 . The method of  claim 18  wherein said ion milling process is performed for 5 to 10 minutes.  
   
   
       20 . The method of  claim 19  wherein said ion milling process is performed with an ion beam set at an angle of from −10° to −70° with respect to normal of the surface of said overcoat layer.  
   
   
       21 . The method of  claim 11  wherein forming said mask layer comprises forming a layer comprising a material selected from the group consisting of CoFe and CoNiFe.  
   
   
       22 . The method of  claim 21  wherein forming said seed layer comprises evaporation or physical vapor deposition.  
   
   
       23 . The method of  claim 22  wherein forming said seed layer comprises forming a layer comprising NiCr.  
   
   
       24 . The method of  claim 23  wherein said ion milling process is performed for 5 to 10 minutes.  
   
   
       25 . The method of  claim 24  wherein said ion milling process is performed with an ion beam set at an angle of from −10° to −70° with respect to normal of the surface of said overcoat layer.  
   
   
       26 . The method of  claim 11  wherein forming said mask layer comprises forming a Cu layer.  
   
   
       27 . The method of  claim 26  wherein forming said seed layer comprises evaporation or physical vapor deposition.  
   
   
       28 . The method of  claim 27  wherein forming said seed layer comprises forming a layer comprising a material selected from the group consisting of AuCr, Cu and NiFe/Cu.  
   
   
       29 . The method of  claim 28  wherein said wet chemical comprises a mixture of NaH 4 OH and ammonium persulfate.  
   
   
       30 . The method of  claim 29  wherein said ion milling process is performed for 5 to 10 minutes.  
   
   
       31 . The method of  claim 30  wherein said ion milling process is performed with an ion beam set at an angle of from −10° to −70° with respect to normal of the surface of said overcoat layer.