Abstract:
Plural carbon-containing overcoats are formed on a media-facing surface of an information storage system head. The plural carbon-containing overcoats can mitigate corrosion without increasing head-media spacing. A first of the overcoats may be formed prior to creation of contact or air bearing features on the media-facing surface, with a second overcoat formed after creation of air bearing features. The first overcoat may be etched back substantially or completely prior to formation of the second overcoat. Laminated carbon-containing overcoats may have greater strength and/or coverage than non-laminated overcoats of the same thickness. The overcoats may be formed of several forms of diamond-like carbon (DLC) or silicon-carbide (SiC).

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to information storage system transducers. It is well known in the field of magnetic information storage systems that a means for increasing storage density and signal resolution is to reduce the separation between a transducer and associated media. For many years, devices incorporating flexible media, such as floppy disk or tape drives, have employed a head in contact with the flexible media during operation in order to reduce the head-media spacing. Recently, hard disk drives have been designed which can operate with high-speed contact between the hard disk surface and the head. 
     Another means for increasing signal resolution that has become increasingly icommon is the use of magneto resistive (MR) or other sensors for a head. MR elements may be used along with inductive writing elements, or may be separately employed as sensors. While MR sensors offer greater sensitivity than inductive transducers, they are more prone to damage from high-speed contact with a hard disk surface, and may also suffer from corrosion. For these reasons, air bearing surfaces (ABS) for heads containing MR sensors are conventionally coated with a hard, durable carbon or carbon-based overcoat. During etching of the ABS that creates relieved features for interacting with the rapidly moving media surface, the MR sensors are covered with a mask. 
     The overcoats may be formed before or after etching of the ABS. Current methods for making ABS overcoats include sputtering or ion beam chemical vapor deposition (IBCVD) to form diamond-like carbon (DLC) films. More recently, cathodic arc deposition has been used to form tetrahedral-amorphous carbon (ta-C) films having even greater hardness. Employment of harder films allows the thickness of the films to be reduced, which can help to reduce head-media spacing. 
     DLC and ta-C films have a high stress as well as high hardness, and do not adhere well to slider ABS or magnetic layers, and so an adhesion layer of Si or Si 3 N 4  is conventionally formed to help with stress relief and adhesion. The DLC coating  20  conventionally has a thickness that is about four times that of the adhesion layer. Thus a 80 Å layer of DLC may be formed on a 20 Å adhesion layer of Si 3 N 4 , to create a minimum head-media spacing of 100 Å. Further head-media spacing conventionally occurs due to penetration of energetic interlayer ions into underlying magnetic layers, deadening a portion of those magnetic layers. 
     It is not clear that the minimum head-medium spacing due to these layers can be reduced substantially without encountering problems in overcoat durability and adhesion layer continuity. For example, a 10 Å adhesion layer may be only a few atoms thick, and may not provide adequate adhesion even if one assumes that the somewhat thicker carbon overcoat can withstand high-speed head-disk contact without damage or removal. Further, the possibility of corrosion may increase as conventional overcoats are made thinner, risking failure of the head. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention plural carbon-containing overcoats are formed on a media-facing surface of a head. The plural carbon-containing overcoats may serve to avoid corrosion without increasing head-media spacing. A first of the overcoats may be formed prior to creation of air bearing features on the media-facing surface, with a second overcoat formed after creation of air bearing features. The first overcoat may be etched back substantially or completely prior to formation of the second overcoat. The overcoats may be formed of several forms of diamond-like carbon (DLC) or silicon-carbide (SiC). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cutaway cross-sectional view of a head formed in accordance with the present invention having dual carbon-based overcoats. 
     FIG. 2 is a cutaway cross-sectional view of a stage in the formation of the head of FIG.  1 . 
     FIG. 3A is a cutaway cross-sectional view of plural layers forming a spin-valve sensor for the head of FIG.  1 . 
     FIG. 3B is a cutaway cross-sectional view of plural layers forming a top synthetic spin-valve sensor for the head of FIG.  1 . 
     FIG. 3C is a cutaway cross-sectional view of plural layers forming a bottom synthetic spin-valve sensor for the head of FIG.  1 . 
     FIG. 3D is a cutaway cross-sectional view of plural layers forming a dual synthetic spin-valve sensor for the head of FIG.  1 . 
     FIG. 4 is a perspective view of a wafer substrate with multiple transducers formed thereon being diced into rows for processing in accordance with the present invention. 
     FIG. 5 is a perspective view of one of the transducer-bearing rows of FIG.  4 . 
     FIG. 6 is a perspective view of a head showing a media-facing surface formed in accordance with the present invention. 
     FIG. 7A is a cutaway cross-sectional view of some steps in the production of an embodiment of a head in accordance with the present invention, showing a transducer of FIG. 3B covered with an adhesion layer and a first carbon-containing overcoat. 
     FIG. 7B is a cutaway cross-sectional view of some later steps in the production of the head of FIG. 7A, including first and second carbon-containing overcoats. 
     FIG. 7C is a cutaway cross-sectional view of some later steps in the production of the head of FIG. 7A, in which the first carbon-containing overcoat has been removed and a second carbon-containing overcoat has been formed. 
     FIG. 8A is a cutaway cross-sectional view of some steps in the production of an embodiment of a head in accordance with the present invention, showing a transducer of FIG. 3B covered with a first carbon-containing overcoat without an adhesion layer. 
     FIG. 8B is a cutaway cross-sectional view of some later steps in the production of the head of FIG. 8A, including first and second carbon-containing overcoats. 
     FIG. 8C is a cutaway cross-sectional view of some later steps in the production of the head of FIG. 8A, including a second carbon-containing overcoat, with first carbon-containing overcoat removed. 
     FIG. 9 is a cross-sectional view of a portion of a head including a microscopic pad on a media-facing surface. 
     FIG. 10 is a perspective view of the head of FIG. 9 showing a plurality of pads on the media-facing surface. 
     FIG. 11 is a cross-sectional view of a portion of a head having a media-facing surface that is slightly recessed adjacent a MR sensor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a cutaway cross-sectional view of a head  20  formed in accordance with the present invention. As discussed in detail below, the head  20  includes a transducer  22  that has been formed on a wafer substrate  25  along with thousands of other transducers, which are diced into rows and further processed to create a media-facing surface  27 , including forming plural carbon-containing overcoats  30  and  33 . The media-facing surface is relieved for interaction with a media such as a disk, with a projection  37  containing the transducer  22  and a recess  39  adjacent the projection. The recess  39  is formed by etching after formation of the first overcoat  30 , during which the projection  37  is covered with a mask, so that the first overcoat does not cover the recess. The second overcoat  33 , on the other hand, is formed after the etching that creates the recess  39 , and so the second overcoat is disposed on the recess as well as the projection  37 . This has an advantage of providing a carbon-containing overcoat that covers the entire media-facing surface, but which is thickest on media-facing surface projections that are most likely to contact the media and, in the absence of the overcoat, be damaged by that contact. Independent control of the coating thickness on the projection relative to the coating thickness on the recess allows those thicknesses to be independently optimized. 
     The transducer  22  in this embodiment includes a magnetically permeable shield layer  35  and a magnetically permeable first pole layer  40 , which are sandwiched about a MR sensor  44 . First and second non-ferromagnetic, electrically insulating read gap layers  42  and  46  separate the sensor  44  from the shield layer  35  and first pole layer  40 , respectively, and a back gap layer  48  abuts the sensor distal to the media-facing surface  27 . A magnetically permeable second pole layer  50  is separated from the first pole layer  40  by a write gap  52  formed of non-ferromagnetic, electrically insulating material. Also disposed between the first and second poles  40  and  50  is an electrically conductive coil  55  and an electrically insulating spacer material  57 . A protective layer  60  coats a trailing end  62  of the head  20 , which may also be thinly covered with overcoats  30  and  33 . 
     FIG. 2 shows some initial, wafer-level steps in forming the head of FIG.  1 . On the wafer substrate  25 , which may be made of AlTiC, SiC or other known materials and which has been polished and cleaned, the first magnetically permeable shield layer  35  is formed, for instance of permalloy (Ni 80 Fe 20 ). An optional surface layer, not shown, may be formed on the wafer prior to forming the shield layer to provide a smooth, defect-free surface. The first read gap layer  42  of nonmagnetic, electrically insulating material such as alumina or DLC is then formed, on top of which a magnetoresistive (MR) sensor  44  is formed. The MR sensor  44  may be an anisotropic magnetoresistive (AMR) sensor, canted current sensor, spin valve (SV) sensor, giant magnetoresistive (GMR) sensor, or other known sensor. After the MR sensor  44  has been defined, the back gap  48  and second read gap  46  of nonmagnetic material such as alumina are formed, optionally at the same time. The first pole layer  40  of magnetically permeable material such as permalloy that also serves as a shield for the sensor  44  is then formed. The nonmagnetic, electrically insulating write gap  52  of material such as alumina is formed on the first pole layer  40 , and the conductive coil  55  is formed on the write gap  52 , the coil surrounded by nonmagnetic, electrically insulating material  57  such as baked photoresist. The second pole layer  50  of magnetically permeable material is then formed, and the protective coating  60  of alumina, DLC or other materials is conventionally formed. The substrate and thin film layers are then diced along line  64  and other lines, as discussed below with regard to FIG. 4, forming perhaps thousands of heads from a single wafer. 
     FIG. 3A provides greater detail for an embodiment in which the MR sensor  44  is a spin valve (SV) sensor. For this embodiment, a ferromagnetic free layer may be formed by depositing for instance a CoFe layer  70  and then a NiFe layer  72 . A thin conductive spacer layer  74  is then formed, for example of Cu. A ferromagnetic layer  76  is then formed of a material such as CoFe, having a magnetic moment pinned by an antiferromagnetic layer  78 . The layers  70 ,  72 ,  74  and  76  may each have a thickness in a range between a few angstroms and one hundred angstroms, whereas the antiferromagnetic layer  78 , which may be made of PtMn for example, may be thicker. 
     FIG. 3B depicts an embodiment in which the MR sensor  44  is a top synthetic spin valve (TSSV) sensor. Much as before, a ferromagnetic free layer may be formed by depositing for instance a CoFe layer  80  and then a NiFe layer  82 . A thin conductive spacer layer  84  is then formed, for example of Cu. A first coupled ferromagnetic layer  86  is then formed, followed by a thin layer  88  of a platinum group element such as ruthenium (Ru), iridium (Ir) or rhodium (Rh). Layer  88  may for example be made Ru that is less than 10 Å-thick, which is then covered with a second coupled ferromagnetic layer  90  having a thickness substantially matching that of first coupled layer  86 , such that the ferromagnetic layers  86  and  90  are magnetostatically coupled about the platinum group layer  88 . An antiferromagnetic layer  92 , which may be made of PtMn for example, is formed on and pins ferromagnetic layer  90 , also pinning coupled layer  86 . 
     FIG. 3C illustrates an embodiment in which the MR sensor  44  is a bottom synthetic spin valve (BSSV) sensor. In this case, an antiferromagnetic layer  100 , which may be made of PtMn for example, is first formed. First and second ferromagnetic layers  102  and  106 , which may contain CoFe, are magnetically coupled about noble metal layer  104 , which may contain Ru. Antiferromagnetic layer  100  pins the coupled layers  102  and  106 . A conductive spacer layer  108 , which may contain Cu. is formed on coupled layer  106 , followed by a pair of ferromagnetic free layers  110  and  112 , which may contain CoFe and NiFe, respectively. 
     FIG. 3D illustrates an embodiment in which the MR sensor  44  is a dual synthetic spin valve (DSSV) sensor. In this case, an antiferromagnetic layer  120 , which may be made of PtMn for example, is first formed. First and second ferromagnetic layers  122  and  126 , which may contain CoFe, are magnetically coupled about noble metal layer  124 , which may contain Ru. Antiferromagnetic layer  120  pins the coupled layers  122  and  126 . A conductive spacer layer  128 , which may contain Cu, is formed on coupled layer  126 , followed by a ferromagnetic free layers  130 ,  132  and  134 , which may contain CoFe, NiFe and CoFe, respectively. A thin conductive spacer layer  136  is then formed, for example of Cu. A first coupled ferromagnetic layer  138  is then formed, followed by a thin (preferably less than 10 Å-thick) layer  140  of Ru; and then a second coupled ferromagnetic layer  142  having a thickness substantially matching that of first coupled layer  138 , such that the ferromagnetic layers  138  and  142  are magnetostatically coupled about the noble metal layer  140 . An antiferromagnetic layer  144 , which may be made of PtMn for example, is formed on and pins ferromagnetic layer  142 , also pinning coupled layer  138 . 
     The synthetic spin valve sensors depicted in FIG. 3B, FIG.  3 C and FIG. 3D have the advantage of providing a more stable pinning structure than that illustrated in FIG.  3 A. It has been discovered, however, that these synthetic spin valve embodiments suffer from corrosion, particularly during a test procedure known as “hot-wet” testing. A hot-wet test that heads or disk drives may have to pass to be considered reliable may include running for 100-200 hours in an environment of 80% humidity at a temperature of 90° C. When heads having MR sensors such as those represented by FIG. 3B, FIG.  3 C and FIG. 3D were exposed to a hot-wet test, a loss of amplitude and increase in resistance were discovered that were traced to corrosion and/or depletion of the copper layers in the sensors, resulting in failure of a substantial fraction of those heads. Providing dual carbon-based overcoats in accordance with the present invention has solved this problem. 
     FIG. 4 shows the wafer substrate  25  with a multitude of transducers formed thereon, including transducer  22 . After formation of the multiple layers described above with regard to FIGS. 1-3, the substrate  25  and thin film layers are then cut along a number of lines such as lines  64  and  66 , forming a row  150  along with perhaps one hundred other rows of heads from a single wafer  25 . 
     FIG. 5 shows row  150  after separation from the other rows, with the recently formed transducer  22  visible through the transparent protective coating. Row  150  may be held in a chuck for processing of surface  64 , which will become the media-facing surface of the heads in row  150 . Surface  64  may be lapped while resistive leads are monitored to obtain a desired height of transducers including transducer  22 . After lapping, surface  64  is coated with a first carbon-containing overcoat, which protects the transducers from damage during processing of surface  64 . A carbon-containing overcoat is defined in the present disclosure to have an atomic concentration of carbon that is about one-fourth or more. Surface  64  is then masked and etched to create relieved features for a media-facing surface. Reactive ion etching (RIE) or ion beam etching (IBE) is used to create the relieved features of the media-facing surface. After these features are created, a second carbon-containing overcoat is formed, and the row  150  is separated into individual heads. 
     FIG. 6 shows such a head  160  with a transducer  162  and a media-facing surface  180  after creation of relieved features and plural carbon-containing overcoats. The head in this example has three rails  182 ,  184  and  186  that project slightly compared to a recessed area- 188  of the media-facing surface  180 . The media-facing surface  180  also has a shelf  190  that is intermediate in height between the recessed area and rails. The rails may project a few microns or less beyond the recessed areas. The rails, recessed areas and shelf are designed to position the head  160  at a small but substantially constant distance that may be between about one microinch and one-half microinch from the surface of a rapidly spinning rigid disk. 
     FIG. 7A shows the formation of a first carbon-containing overcoat  200  on a media-facing surface of the MR sensor of FIG. 3B. A silicon-containing adhesion layer  202 , which may for example be made of Si, SiC or Si 3 N 4 , is first deposited to a thickness of, for example 10 Å to 20 Å. The first carbon-containing overcoat  200  in this embodiment is formed of DLC and may have a thickness in a range-between about 15 Å and 100 Å. 
     As shown in FIG. 7B, after formation of the rails, recessed areas and shelf, the first carbon-containing overcoat  200  is at least partially removed, and a second silicon-containing adhesion layer  205  is deposited, followed by a second carbon-containing overcoat  210 . Removal or thinning of the first carbon-containing overcoat may be accomplished for example by sputtering an ion beam on the overcoat. The beam may contain argon (Ar) ions which are directed at a small angle (e.g., ≦45°) from normal to the media-facing surface, with the beam rotating about the normal. The silicon-containing adhesion layer  205  may be formed to a thickness of 10 Å to 20 Å and may, for example, be made of Si, SiC or Si 3 N 4 . The second carbon-containing overcoat  210  in this embodiment may be formed of DLC and has a thickness in a range between about 15 Å and 70 Å. The first or second carbon-containing overcoats  200  and  210  may contain m-DLC, e-DLC, a-DLC or t-aC, where the prefixes “m” “e” and “a” indicate diamond like carbon coatings made from ion beam chemical vapor deposition (IBCVD) using precursors of methane, ethylene, and acetylene, respectively. These precursors have different concentrations of hydrogen that result in differing characteristics of DLC films. Tetrahedral-amorphous carbon (ta-C) can be formed by filtered cathodic arc deposition to have primarily sp 3  bonds, to be essentially free of defects and to have a hydrogen concentration that can be zero or greater. The first or second carbon-containing overcoats  200  and  210  may instead be formed of dense, nonporous, essentially defect-free SiC, as disclosed in U.S. patent application Ser. No. 09/352,544 to Han et al., incorporated by reference herein. 
     Alternatively, as shown in FIG. 7C, the first carbon-containing overcoat and first silicon-containing adhesion layer may be completely removed prior to formation of a second carbon-containing overcoat  212  and second silicon-containing adhesion layer  215 . In this example, the second carbon-containing overcoat  212  has a thickness of 45 Å, and the second silicon-containing adhesion layer  215  has a thickness of 15 Å. Instead of removing all of the first adhesion layer, the first carbon-containing overcoat may be completely removed, while some or all of the first adhesion layer may remain for providing adhesion for the second carbon-containing overcoat  212 . The silicon layer may optionally provide an etch-stop for RIE removal, such as oxygen ashing, or a signal for IBE removal that stops the removal. 
     In FIG. 8A, a first carbon-containing overcoat  220  has been formed on a media-facing surface of the MR sensor of FIG.  3 B. The first carbon-containing overcoat  220  may contain dense, nonporous SiC, e-DLC, a-DLC or t-aC, and may be formed to a thickness in a range between about 10 Å and 100 Å. In this embodiment a silicon-containing adhesion layer does not necessarily have to be formed to ensure adhesion of the first carbon-containing overcoat  220  to the media-facing surface of the MR sensor. This interlayer-free layer of DLC may be formed with carbon ions that nucleate ceramic layers as well as magnetic layers. 
     As shown in FIG. 8B, after formation of the rails, recessed areas and shelf, the first carbon-containing overcoat  220  may be partially removed, and a second carbon-containing overcoat  222  is formed. For the case in which the first carbon-containing overcoat  220  was formed to be relatively thin, for example having a thickness in a range between about 10 Å and 20 Å, the first carbon-containing overcoat need not be partially removed prior to formation of the second carbon-containing overcoat  222 . The second carbon-containing overcoat  222  may contain dense, nonporous SiC, e-DLC, a-DLC, t-aC or other forms of DLC. 
     In addition to reducing corrosion, the formation of a laminated overcoat made of two or more carbon-containing layers may provide lower overall stress than an overcoat made of a single carbon-containing layer of the same thickness as the laminated overcoat, which may improve adhesion. Also, it may be advantageous to form a laminated overcoat from different types of carbon-containing layers, for example with a first layer of e-DLC and a second layer of a-DLC. Forming the first carbon-containing layer of dense, nonporous SiC and the second carbon-containing layer of m-DLC, eDLC, a-DLC or t-aC may be advantageous, in that the first layer also contains silicon, and can provide adhesion for the second carbon-containing layer. Alternatively, the dense, nonporous SiC can be employed for the second carbon-containing layer, with the first carbon-containing layer formed of m-DLC, e-DLC, a-DLC, t-aC or SiC, which may improve an interface with a disk coating. 
     FIG. 8C shows an embodiment in which a first carbon-containing layer formed prior to creation of relieved features on a media-facing surface has been removed, and a second carbon-containing layer  225  has been formed after creation of the relieved features. Any optional silicon-containing adhesion layer that may have been formed has also been removed. The second carbon-containing layer  225  may be formed of dense, nonporous SiC, e-DLC, a-DLC or t-aC to a thickness in a range between about 15 Å and 80 Å. The dense, nonporous SiC in this case may be formed by sputtering SiC at a media-facing surface during bombardment of that surface with neutral atoms. 
     FIG. 9 is a cross-sectional view of a portion of a head  240  having a media-facing surface  242  that is shown in a perspective view in FIG.  10 . The media-facing surface  242  has at least one pad  244  located distal to a transducer  246  on an air bearing rail  250 , like that disclosed in U.S. patent application Ser. No. 09/239,594 to Han et al., incorporated by reference herein. Pad  244  may be formed of SiC, m-DLC, e-DLC, a-DLC or t-aC that is deposited through a mask disposed atop a first carbon-containing overcoat  252  that was formed on the media-facing surface  242  prior to relieving the surface via etching or the like. A recessed area  255  is then formed by RIE or IBE, leaving rail  250  projecting above the recessed area, in which first carbon-containing overcoat  252  has been removed. A second carbon-containing overcoat  262  is then formed on the media-facing surface  242 . Thus plural carbon-containing coatings surround the pads  244 , ensuring that the pads do not break free from the media facing is surface  242 . 
     FIG. 11 is a cross-sectional view of a portion of a head  300  having a merged transducer  303  similar to that shown in FIG. 1, with like elements sharing the same numbers in the two figures. An amagnetic, electrically insulating layer  301 , which for conciseness was omitted from the description of FIG. 1, is disposed between the substrate  25  and the first shield layer  35 . A media-facing surface  305  of head  300  has a slightly recessed area  310  adjacent metallic elements such as the MR sensor  44  and magnetically permeable yokes  40  and  50 , compared with a slightly projecting area  315  disposed adjacent the substrate and ceramic layers. A much more recessed area  320  of the media-facing surface  305  is disposed distal to the transducer  303 , the recessed area  320  being similar to recessed area  255  shown in FIG.  10 . Thin film layers including the MR sensor  44  may be recessed relative to the substrate  25  in order to avoid wear and thermal asperities that may otherwise occur due to contact with a media surface, not shown. Formation of the head  300  of FIG. 11 proceeds similarly to that described above, however, the thin film layers including the MR sensor  44  may be initially recessed by chemical, mechanical and/or ion beam processes that preferentially remove those layers relative to the substrate  25 . A first carbon-containing coating  322  is then formed prior to shaping the media-facing surface  305  with features such as recessed area  320 . A second carbon-containing coating  325  may be formed after the formation of recessed areas such as area  320 . 
     In accordance with the present invention, we have disclosed forming plural carbon-containing overcoats on a media-facing surface of a head, which may have benefits including corrosion avoidance. Although we have focused on teaching the preferred embodiment, other embodiments and modifications of this invention will be apparent to persons of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.