Magnetic head slider having a protective coating thereon
FIELD OF THE INVENTION 
     This invention relates to magnetic heads, and in particular to thin film magnetic heads and to the method for making the thin film magnetic heads. 
     DESCRIPTION OF THE PRIOR ART 
     Thin film magnetic heads have been in use for many years, and these heads are conventionally formed on a substrate in a series of rows each having a plurality of heads. Once the heads are fabricated, the substrate is cut to form a row of heads in a side-by-side orientation. While still in a row format, the thin film magnetic heads are lapped to a predetermined throat height dimension which is very critical to head performance. Once the desired lapped throat height dimension is achieved, this should not be affected by subsequent processing of the head. 
     One of the subsequent steps in the processing of the heads is the production of a pattern of rails on the lapped surface to form an air bearing surface (ABS). The desired pattern of rails on the ABS has gotten progressively more complex in shape so that a dry processing technique such as an etching process is generally used. Protection of the thin film magnetic head during the etching process requires a protective coating which is generally thick and which is removed after completion of the etching process. 
     The row of magnetic heads is then separated into individual magnetic head sliders, and, in operation, the slider &#34;flies&#34; with the ABS and the attached thin film magnetic head a small uniform spacing, usually less than ten microinches, from the magnetic recording medium. In the normal operation of a magnetic disk recording system, the head sometimes comes into inadvertent contact with the magnetic recording medium. 
     In the prior art various protective layers were deposited on the magnetic head slider to protect the ABS from mechanical wear caused by contact between the head and magnetic recording medium during flying. 
     For example, U.S. Pat. No. Re 32,464 discloses a magnetic recording system in which a rigid magnetic recording disk has a protective layer of carbon to protect it from wear. The magnetic transducer is coated with carbon, preferably in the form of graphite, to provide a low friction wear resistant contacting surface with the recording medium. The thickness of the coating is between 2 and 10 microinches. 
     IBM TDB, December, 1982, p. 3173 describes a magnetic head slider having a protective layer of silicon carbide or diamond-like carbon. The thickness of the protective layer is within the range of 500 to 1000 angstroms. 
     IBM TDB, June, 1976, p. 351 describes a magnetic head having a protective layer of silicon nitride in layers of about 200 to 5000 angstroms. 
     Unexamined Japanese patent application, 58-150,122, published Sep. 6, 1983, describes a magnetic head having a thin film of a material having a lubricating effect on the surface of the head which faces the magnetic recording medium. A list of suitable materials is given which includes carbon, and the thickness of the film is within the range of 200 to 800 angstroms. 
     U.S. Pat. No. 4,130,847 describes a magnetic head slider having a protective coating over at least the magnetic head. The coating is produced in a recess within the slider body to a thickness as small as 10 microinches. 
     German patent application DE 3,714,787, published Nov. 24, 1988, describes a storage system in which the magnetic disk surface is coated with friction reducing carbon and the rails of the magnetic head slider are coated with a friction reducing lubricant comprising carbon. The thickness of the carbon is 10 to 1000 angstroms. 
     Patent application serial number PCT/US88/00438, published Aug. 25, 1988, discloses a magnetic head slider in which a magnetic head is built within one of the side rails. A wear layer is provided over the slider which comprises a 50 angstroms thick chromium layer and a 200 angstroms thick carbon layer. Either of the two components of the wear layer can be omitted. 
     None of the references disclose a protective layer for a magnetic head slider which is effective to protect a thin film magnetic head not only during the normal operation of the magnetic head slider in a magnetic disk storage system but also during the fabrication process. 
     SUMMARY OF THE INVENTION 
     It is therefore the principal object of this invention to provide a thin protective coating on a magnetic head slider which protects the magnetic head not only in the normal operation of the magnetic head slider in a magnetic recording system but also during the fabrication process. 
     In accordance with the invention, a magnetic head slider is provided having leading and trailing ends and at least two rails on an air bearing surface. The rails have a protective coating on their surface comprising a thin adhesion layer and a thin layer of amorphous hydrogenated carbon. 
     In a specific embodiment the adhesion layer comprises silicon about 10 to 50 angstroms thick and the thickness of the protective coating is about 250 angstroms or less. 
     The method for making the magnetic head slider, after the air bearing surface is formed to provide a chosen magnetic head dimension, comprises the steps of depositing a protective coating on the air bearing surface, the protective coating comprising a thin adhesion layer and a thin layer of amorphous hydrogenated carbon, forming a pattern of rails on the air bearing surface by removing material from the air bearing surface to a chosen depth in areas of the air bearing surface other than the rails, and retaining the protective coating on the rails during normal operation of the magnetic head slider in a magnetic recording system so that the magnetic head slider is protected from wear and corrosion damage. 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a partial row of thin film magnetic heads. 
     FIG. 2 is a bottom plan view of a specific embodiment of a magnetic head slider. 
     FIG. 3 is a bottom plan view of an alternate embodiment of a magnetic head slider. 
     FIGS. 4A-D comprise views of a partial row of thin film magnetic heads showing successive steps in the process for making a magnetic head slider according to the present invention. 
     FIG. 5 is a plan view of the trailing end of a specific embodiment of a magnetic head slider according to the present invention. 
     FIG. 6 is a plan view of the trailing end of an alternate embodiment of a magnetic head slider according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention relates to a magnetic recording system which includes a magnetic head slider. The slider supports a thin film magnetic read/write head, and the head is formed by depositing layers of magnetic material, electrically conductive material, and electrically insulating material to form the well known pole pieces and magnetic gap necessary for the transducing function with a magnetic coating on a magnetic recording medium. During fabrication, a plurality of thin film magnetic heads are deposited onto a wafer which is then cut to form rows of transducers with the transducers set in a side-by-side relationship. The thin film magnetic heads are lapped to a predetermined throat height dimension which is very critical to head performance. A pattern of rails is produced on the lapped surface to form an air bearing surface (ABS), and the row is separated into individual magnetic head sliders. 
     Each slider is mounted onto a suspension system which in turn is mounted onto an accessing system for locating the magnetic heads onto tracks formed by the magnetic heads when writing onto a rotating magnetic disk, for example. During normal operation the slider flies at a small spacing, in the range of a few microinches, over the magnetic recording medium. 
     It has been discovered that the prior art process of forming the ABS can produce a significant loss in yield in the manufacturing process due to corrosion damage to the sensitive head components. This has been found to be due in some cases to insufficient coverage of critical components during the etching operation and in other cases to damage to some head components during the removal of the masking layer used to protect the head during the etching process. 
     It has also been discovered that prior art protective layers deposited after ABS formation have not met the lifetime requirements of current thin film magnetic heads in operation. This degradation of head/slider life in operation has been discovered to be due, in part, to mechanical wear caused by the inadvertent contact between the head and magnetic recording medium during flying. In addition to the mechanical wear, the thin film magnetic heads contain a variety of materials that are attacked by the normal constituents of the atmosphere. Prolonged exposure of the head to the atmosphere can result in degradation of the head performance due to oxidation and resulting in corrosion of the head materials. 
     It was unexpectedly observed, according to the present invention, that a protective coating comprising a thin adhesion layer and a thin layer of amorphous hydrogenated carbon is effective to protect the thin film magnetic head from damage not only in the processing to form the pattern of rails on the ABS, but also during normal operation of the head in a magnetic disk file. This was unexpected since in prior art processes, the protective coating used during processing was made very thick since it was progressively eroded during the etching process for forming the ABS. On the other hand, the total thickness of the protective layer on the slider during operation is constrained to a very thin dimension since its thickness adds directly to the spacing between the thin film magnetic head and the magnetic recording medium. In a specific embodiment a thickness of amorphous hydrogenated carbon as little as 50 angstroms thick was shown to produce significant improvement to both manufacturing yield and lifetime of the head in operation. 
     Referring to FIG. 1, there is shown a view of a partial row 11 having a plurality of thin film magnetic heads 20. The row 11 is lapped on surface 19 so that each of the thin film magnetic heads 20 has a chosen throat height. A pattern of rails is produced on surface 19 to form an air bearing surface (ABS), and the row is then separated into individual magnetic head sliders 10. 
     The pattern of rails may be as shown in FIG. 2 in which a pair of outside rails 12, 14 is produced along with a center rail 16. The side rails extend from the leading end 15 of the slider 10 part way to the trailing end 17, while the center rail extends from the leading end 15 to the trailing end 17. The thin film magnetic head 20 is located at the trailing end of the center rail 16. 
     The pattern of rails may also be as shown in FIG. 3, and this embodiment corresponds to the arrangement shown in row 11 of FIG. 1. In this case the outside rails 12, 14 extend from the leading end 15 of the slider 10 to the trailing end 17. The thin film magnetic heads 20 are located at the trailing end 17 of the side rails 12, 14. 
     The rail pattern produced in individual sliders 10 is at the same level on the ABS 19 as the lapped pole pieces of the thin film magnetic heads 20, and the remainder is a recessed area 18 which is recessed from the ABS 19 by a distance chosen to produce a combined pressure profile with a moving magnetic recording medium so that the slider 10 flies at the chosen flying height or spacing over the magnetic recording medium. 
     According to the present invention, at a time after the heads are lapped to the selected throat height and before the rail pattern is produced on the ABS, a protective coating is produced over the ABS. This protective coating protects the thin film magnetic heads in three ways. The protective coating is effective to protect the thin film magnetic head during the processing of the head/slider to form the pattern of rails on the ABS. The protective coating is also effective, during normal operation of the head in a magnetic disk file, for example, to protect the head and the ABS from mechanical wear caused by inadvertent contact between the head/slider and the magnetic recording medium during flying. In addition to mechanical wear, the protective coating also is effective to protect the variety of materials in the magnetic head that are attached by the normal constituents of the atmosphere from oxidation and corrosion in normal operation of the system. 
     The protective coating 22 (FIGS. 5 and 6) comprises two layers, the first layer being a suitable adhesion layer 24 and the second layer being a thin layer of amorphous hydrogenated carbon 26. In a specific embodiment the adhesion layer 24 is silicon about 50 angstroms thick, and the total thickness of the protective coating is about 250 angstroms. In another specific embodiment the adhesion layer 24 is silicon about 30 angstroms thick and the total thickness of the protective coating is about 125 angstroms. 
     The process for making the magnetic head slider, according to the present invention, will be described by reference to FIG. 4. The process starts with either a single slider 10 or preferably a substrate 13 comprising a row 11 having a plurality of sliders in a side-by-side relationship. The thin film magnetic heads 20 are fabricated on a first surface 21 of the row 11, and first surface 21 is at substantially ninety degrees to the ABS 19. ABS 19 is lapped until the thin film magnetic heads reach a predetermined throat height. The lapping can be by any suitable technique such as that described in commonly assigned U.S. Pat. No. 4,912,883, for example. Alternatively, should the thin film magnetic heads 20 include a magnetoresistive (MR) read transducer, the lapping can be as described in commonly assigned U.S. Pat. No. 4,914,868 in which the ABS is lapped until the MR read transducer reaches a chosen MR element height. 
     The lapped row of thin film magnetic heads 20 is shown in FIG. 4A. The protective coating 22 is then deposited over the ABS 19 in two layers (FIG. 4B) comprising an adhesion layer 24 and a layer of amorphous hydrogenated carbon 26. In a specific embodiment, adhesion layer 24 comprises a deposited layer of amorphous silicon. Typically, the silicon is deposited to a thickness of about 10-50 angstroms, although a possible range is from a monolayer to about 500 angstroms. However, from the standpoint of limiting the increase in spacing between the magnetic head and magnetic recording medium, the thinner layer (less than 50 angstroms) of silicon is preferred. 
     The layer of hydrogenated amorphous carbon 26 is deposited to a thickness of about 50-1000 angstroms. A layer of hydrogenated amorphous carbon 26 as little as 50 angstroms thick has been shown to provide a significant improvement in both wear and corrosion rates. However, a thicker layer is preferable since it provides increased protection, so the thickness is chosen based on the permissible increase in spacing between the magnetic head and the magnetic recording medium. 
     The two layers of the protective coating 22 can be deposited by any suitable technique such as plasma assisted chemical vapor deposition, ion beam or laser techniques. The preferred technique is by the use of a DC biased substrate in an RF plasma deposition apparatus. The film properties of the carbon layer 26 can be controlled by the appropriate choice of deposition parameters. These include controlling temperature and bias of the parts during deposition, RF power, hydrogen content in the argon sputtering gas, sputtering gas pressure, and target to substrate spacing. 
     Once the protective coating 22 is deposited over the row 11, a thick layer of a patternable material 30 is deposited over the row 11. The preferred material is a photoresist material, and this material is exposed through an appropriate mask (not shown) to produce a negative image of the desired rail pattern in the patternable material layer 30. The patternable material is developed to produce a mask in the image of the desired rail pattern. 
     The masked row 11 is then subjected to a suitable etching process (FIG. 4C) such as reactive ion etching, sputter etching, ion milling, or laser etching, for example, as depicted by the arrows in FIG. 4C. The exposed part of protective coating 22 is etched away and the ABS 19 of row 11 is then etched to a depth chosen to provide the desired flying characteristics for the slider 10 in normal operation with a magnetic recording medium. 
     The remainder of the patternable material 30 is then removed (FIG. 4D) by the use of a suitable solvent, for example, to produce a row 11 of sliders. The remaining part of the protective coating 22 covers the rails of the sliders 10 and has protected the slider during the slider rail fabrication process. The sliders 10 in the row 11 are then parted to form individual sliders as shown in FIGS. 5 and 6. The protective coating also protects the thin film magnetic head 20 and the ABS from wear and corrosion damage during normal operation of the slider 10 in a magnetic recording system. 
     A magnetic head slider has been disclosed having a thin protective coating thereon which protects the magnetic head from damage not only during fabrication but also in normal operation in a magnetic disk file, for example, and the protective coating comprises a thin adhesion layer and a thin layer of amorphous hydrogenated carbon. This structure is in contrast to prior art techniques in which a thick protective coating was used during fabrication and then removed, and a thin protective coating was deposited after fabrication of the slider to serve as a protective coating during usage. The present invention produces greater manufacturing yields and a longer lifetime in operation in a magnetic recording system. 
     While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.