Patent Publication Number: US-6215630-B1

Title: Diamond-like carbon and oxide bilayer insulator for magnetoresistive transducers

Description:
This is a divisional of application Ser. No. 08/571,469, filed Dec. 13, 1995. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is directed to a process for fabricating a thin film magnetic structure and the magnetic structure fabricated thereby. 
     Many magnetic transducers employ magnetic layers, or soft adjacent layers (SALs), adjacent an insulating material. In inductive heads, the insulating material might be used for a gap for the magnetic transducer. Typically, the insulating material is deposited first (such as on another magnetic layer or on a substrate) and the magnetic layer is patterned on top of the insulating layer. Typically, a photoresist is patterned in the desired shape of the magnetic layer and a wet chemical etchant is applied to the exposed portions of the magnetic layer to shape the magnetic layer into the desired pole. The etchant employed in removing unwanted portions of the magnetic layer also often attacks the desired insulating layer, resulting in a reduction of the thickness of the insulating layer and a compromise of the characteristics of the transducer. There is, accordingly, a need for an etchant stop to protect the insulating layer and to form a part of the resulting gap. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a magnetic structure having a magnetic layer and a layer of insulating material with a layer of diamond-like carbon sandwiched between the magnetic layer and the insulating layer. In one form of the invention, the structure is a magnetic transducer that includes a second magnetic layer and the insulating layer and layer of diamond-like carbon form a gap for the transducer. 
     According to one aspect of the present invention, a layer of diamond-like carbon is deposited onto the exposed surface of an insulating layer and a layer of magnetic material is deposited onto the layer of diamond-like carbon. A photoresist is applied to the exposed surface of the magnetic layer and is patterned to a desired shape. The exposed portions of the magnetic layer are removed with a wet chemical etchant that does not attack the diamond-like carbon layer. Thereafter, any remaining photoresist is removed. In one form of the invention, the insulating layer is deposited onto a base magnetic layer, and the insulating layer and layer of diamondlike carbon together form a gap for a magnetic transducer 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section view taken at line  1 — 1  at FIG. 2, near the air bearing surface of a magnetic head in accordance with the present invention. 
     FIGS. 2A and 2B illustrate the process of forming the patterned magnetic pole in accordance with the present invention. 
     FIGS. 3A and 3B illustrate the process of milling a soft adjacent layer in an MR head using diamond-like carbon as part of the insulating underlayer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, a magnetic structure includes a lower magnetic layer  10 , and upper magnetic layer  12  and a layer  14  of insulating oxide such as silicon dioxide (SiO 2 ) or aluminum oxide (Al 2 O 3 ). Layer  15  of diamond-like carbon is formed over layer  14 . Layers  10  and  12  are typically a nickel/iron metal alloy, such as Sendust or Permalloy. Layer  12  may be a soft adjacent layer (SAL) for a magnetoresistive (MR) head (not shown) above layer  12 , and layer  10  may be a bottom shield (with layers  14  and  15  providing an insulating layer between them). Alternatively, layers  10  and  12  may be poles separated by a gap formed of layers  14  and  15 , such as for a read or write head. In any case, the structure employs a layer of insulating oxide material such as SiO 2  or Al 2 O 3  below a to-be patterned layer of magnetic material However, pinholes are formed in deposited layers of SiO 2  and Al 2 O 3 . 
     Prior use of only insulating SiO 2  or Al 2 O 3  layers over the magnetic layer did not always protect the magnetic layer from etching when the magnetoresistive layer was etched. More particularly, if the insulating layer was not adequately thick, i.e., greater than about 750 to 1000 Angstroms, pinholes formed in the SiO 2  or Al 2 O 3  layer allowed etchant to pass through the layer and attack the magnetic layer below. The present invention applies a diamond-like carbon layer over the insulating layer to protect the insulating layer and lower magnetic layer during subsequent processing. 
     FIGS. 2A and 2B illustrate the process of forming the head structure shown in FIG. 1 in accordance with the presently preferred embodiment of the present invention. As shown in FIG. 2A, insulating layer  14  is deposited over the top surface of magnetic layer  10 . Typically, layer  14  has a thickness of less than about 750 Angstroms, and therefore may have pinholes that could allow penetration of etchant. A layer of diamond-like carbon  15  is applied over layer  14 , and magnetic layer  12  is applied over layer  15 . Layer  15  may be quite thin, about 200 Angstroms being adequate in most cases. A layer of photoresist  20  is applied over the entirety of layer  12  and is patterned as shown in FIG. 2A to the desired shape of the SAL to be formed in layer  12 . A wet acid etchant, such as one based on hydrochloric acid, is applied to the exposed portions of layer  12  to etch and remove the exposed portions of layer  12 . 
     Most insulating materials, such as SiO 2  and Al 2 O 3 , form pinholes which permit passage of etchant. At thicknesses less than about 750 Angstroms, such insulating materials are poor etchant stops. One characteristic of diamond-like carbon is that it is substantially free of pinholes, even at thicknesses of about 200 Angstroms. Since the wet acid etchant does not attack the diamond-like carbon, the etchant cannot reach the insulating layer  14 . As a result, the SiO 2  or Al 2 O 3  insulating layer  14  is protected from the wet etchant by the diamond-like carbon layer  15  which is not attacked by that etchant. Upon completion of the etching of layer  12 , the remaining photoresist  20  is dissolved, leaving the structure illustrated in FIG.  2 B and ready for encapsulation as shown in FIG.  1 . 
     Diamond-like carbon is commercially known as “DLC” and is commercially available from a variety of sources. The diamond-like carbon is similar to diamond in physical properties. The material is a hydrogenated carbon typically having a hydrogen content between about 30 to 50 percent and a large fraction of sp 3  carbon-carbon bonds rather than sp 2  found in ordinary graphite. The material is typically formed from a hydrogenated carbon feedstock, such as methane (CH 4 ), processed by any of a variety of processes, such as an ion beam deposition process. It is theorized that during formation of diamond-like carbon, hydrogen is removed from the feedstock material forming a network of SP 3  bonded carbon atoms, rather than an ordered array of Sp 2  bonded carbon, i.e. graphite. The material resembles a hard, highly cross-linked polymer and exhibits a higher thermal conductivity than common electrical insulating material (such as SiO 2  or Al 2 O 3 ) and a high electrical resistivity, of the order of about 10 10  Ω-cm. Diamond-like carbon films are similar to-diamonds in that they exhibit very high hardness ranges (1,000 to 5,000 on the Vickers hardness scale), a low coefficient of friction (of the order of less than 0.1) and densities between about 1.7 and 2.2. The material is commercially referred to as “diamond-like” because of its similarity in characteristics to natural and synthetic diamond. Moreover, like natural and synthetic diamond, the diamond-like carbon exhibits a high resistivity. 
     Diamond-like carbon is a good electrical insulator, although it is also highly thermally conductive. Hence, diamond-like carbon layer  15  forms part of the insulating or gap layer and provides dissipation of heat from the resulting head. Another advantage of the diamond-like carbon layer is that the layer is not susceptible to attack by the etchants used to etch the oxide layer, so the integrity of the oxide layer is maintained. Moreover, etchants ordinarily used in subsequent processing of the head do not attack diamond-like carbon. Thus, wet etchants used in shaping Ni/Fe magnetic films do not attack the diamond-like carbon etchant stop layer. As a result, the head is less susceptible of delamination during subsequent processing. 
     FIGS. 3A and 3B illustrate the use of a diamond-like carbon layer to control ion milling where the diamond-like carbon is left in the transducer as part of the insulating layer. FIG. 3A illustrates an MR head having a metal reader bottom shield  60  and an insulating layer  62  on layer  60 . Insulating layer  62  is an insulating oxide, such as Al 2 O 3  or SiO 2 . A layer  64  of diamond-like carbon is deposited over layer  62 , and a soft adjacent layer (SAL)  66  is formed over layer  64 . A layer  68  of tantalum is formed over SAL  66 , and a layer  70  of magnetic material forms the magnetoresistive element. Conductive layers  72  and  74  are formed of a cobalt-platinum alloy and provide electrical connection between gold or copper contacts  76  or  78  and opposite sides of MR element  70 . Optionally, an additional insulating layer may be formed between SAL  66  and layer  68  to form a free SAL FIG. 3B illustrates the process of patterning SAL  66 . 
     As shown in FIG. 3B, the magnetic material to form the SAL  66  is deposited on the top surface of the diamond-like carbon layer  64 . A layer of photoresist  80  is formed on SAL layer  66  and patterned into the shape of the SAL The exposed portions of the photoresist layer  80  and SAL layer  66  are then ion milled to remove most photoresist and to mill to a depth at least equal to the thickness of SAL layer  66 . The photoresist and SAL layer have approximately the same mill rate. However, the diamond-like carbon has a mill rate one-fifth that of the SAL Consequently, there is very little milling into the insulating layer formed of layer  62  and diamond-like carbon layer  64 , thereby resulting in a well formed SAL fully patterned by ion milling without significant milling into the underlayer insulation. After the milling is completed, any remaining photoresist is exposed, dissolved and washed away. Moreover, since the diamond-like carbon is itself a good insulator, it may remain as part of the underlayer. 
     One feature of the invention is the fact that the diamond-like carbon is applied by an ion beam deposition directly onto layer  14  or  64 . The simplicity of the ion beam process permits the formation of low defect films in the diamond-like carbon. Other techniques for applying the diamond-like carbon to layer  14  or  64  include radio frequency and direct current magnetron sputtering, carbon-arc deposition, laser ablation, and plasma enhanced chemical vapor deposition (PECVD). 
     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.