The present application claims priority from Japanese application JP 2009-262450 filed on Nov. 18, 2009, the content of which is hereby incorporated by reference into this application.
The present invention relates to a manufacturing method for a magnetic head slider equipped with a reader element and a writer element.
A recent increase in an amount of information to be processed with a magnetic read/write apparatus has made a rapid progress in high recording density. Under this circumstance, a high sensitivity and high output magnetic head is required. In order to meet this requirement, many efforts have been made to shorten the distance between a magnetic disc and a reader element and writer element of a magnetic head. A distance between the magnetic head and the magnetic disc includes: a thickness of an over coat formed on the surfaces of the magnetic head and magnetic disc for corrosion resistance and abrasion resistance; and a clearance avoiding likelihood contact due to a warp and irregularity of a magnetic disc and an irregularity of the head surface. For the former case, it is necessary that the over coat has a thickness sufficient to some extent to protect the surfaces of the magnetic head and magnetic disc. For the latter case, the clearance is able to be reduced by smoothing roughness of a head air bearing surface (ABS).
Lapping techniques have been improved heretofore in order to smooth the roughness of the head ABS. As illustrated in JP-A-2002-231452, a lapping process is divided into several processes, and fixed grain lapping is performed at a finishing lapping process by fixing abrasive grains to a lapping plate, to thereby reduce scratches. Further, the abrasive grains are made fine to reduce the roughness of a lapping plane.
As disclosed in JP-A-2002-331452, using fine abrasive grains has the effect of reducing the roughness of the lapping plane to some extent, although some disadvantages occur. One of the disadvantages is a considerable reduction in lapping rate. Another manifested problem is that since the abrasive grains are fine, the embedded abrasive grains are likely to be dropped off and the dropped-off abrasive grains may cause generation of scratches.
The scratch problem may be suppressed by preliminarily lapping the lapping plate to remove beforehand abrasive grains likely to be dropped off. However, as apparent from an experiment example illustrated in
As also apparent from
As described above, even under the contradictory relation between the lapping rate and the lapping surface roughness, it is required to lap the ABS of a magnetic head to a desired shape in as short time as possible.
Since the lapping process for magnetic heads functions also as a size control of the magnetic read/write element, a lowered process time prolongs a time taken to obtain a target processing or lapping amount, resulting in a lowered productivity. In order to avoid this, the lapping process is separated into a size control process and a surface roughness reducing process. The size control lapping process is executed at high speed until 1 to 5 nm remained to a target processing amount, whereas the roughness reducing process is executed at a lapping rate reduced to the extent that the both the lapping surface roughness and the lapping rate are satisfied.
In order to settle the above-described issue of the present invention, even in the surface roughness reducing process, the element portion is made in contact with the abrasive grains of the lapping plane to lap the element portion surface. Namely, the magnetic head to which the size controlling process was completed is subjected to a heating process to release a processing strain remained in the element and allow the writer element and reader element to swell. A specific heating method is preferably a method of uniformly heating a whole work, for example, by using an oven. A magnetic head is placed in an oven set at a temperature of 100° C. to 200° C. and heated for 10 minutes or longer to cause the element surface to swell by 1 to 5 nm.
After this heating process, the element surface protruding beyond the ceramic substrate by several nm is made in contact with the abrasive grains on the lapping plate to progress the lapping process even during the surface roughness process. In this case, the abrasive grains on the lapping plate apply a small surface pressure relative to the ceramic substrate and will not cut into the ceramic substrate, so that the ceramic substrate will not be worked. However, in a softer element region, the cut process of the abrasive grains into the element surface progresses. Since the abrasive grains will not cut into the ceramic region, blade edges of the abrasive grains will not fed further in a depth direction.
The surface roughness reducing process operates only to remove the element region surface protruding beyond the ceramic substrate surface. The abrasive grains which were not fed pass along the element surface to remove convex portions on the element surface without forming new concave portions. It is therefore possible to reduce the surface roughness of the whole ABS. In addition, a recess is hardly formed between the ceramic substrate portion and element portion.
Another method of settling the above-described issue is a method of executing the surface roughness reducing process by slanting the lapping plane by an extremely slight angle. Namely, a solid film having a thickness of 50 nm to several hundred nm is formed in a partial area of ABS at a position spaced apart by 500 μm or more from the element portion of the magnetic head after the size control process. In this state, the surface roughness reducing lapping process is executed to allow the lapping plate surface to be inclined by 0.006 degree to 0.02 degree because the solid film serves as a crosstie. Thus the lapping plate surface contacts the solid film and element portion surface, so that the element portion surface is able to be lapped while a lapping rate is retained.
After the element region is lapped to a depth of 2 to 4 nm at the position of the writer element in the element region, the lapping plate surface contacts the edge of the ceramic substrate so that the lapping process is stopped. Similar to the method described previously, with this method, the abrasive grains which were not fed pass along the element portion surface to remove convex portions on the element portion surface without forming new concave portions. It is therefore possible to reduce a surface roughness.
It is also possible to control the recess between the element portion and the ceramic substrate portion and the recess between the writer and reader in the element region.
According to the present invention, as compared to a general magnetic head manufacturing method using coarse lapping and finishing lapping, it is possible to improve further the roughness of the surface of the magnetic head facing the magnetic disc. It is therefore possible to realize a magnetic head slider applicable to a magnetic disc having a large storage capacity.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
Prior to describing specific embodiments, description will be made first on the results of a relation between lapping rate and lapping surface roughness calculated by using the Monte Carlo method. The lapping surface roughness was calculated by using abrasive grain density, lapping rate and others as parameters and at a time when the abrasive grains have passed through with cutting the work surface.
It was assumed that the blade edge of each abrasive grain is of a semisphere shape, and a surface region contacting the blade edge is removed in the blade edge shape. Positions where the abrasive grains pass were determined randomly by using random numbers, heights were set so as to obtain a predetermined variation, and an average position of the blade edges of the abrasive grains was changed so as to obtain a predetermined lapping rate.
The relation when the lapping rate comes to zero as near as possible was calculated more precisely. The calculation results are illustrated in
In the experiment example illustrated in
On the basis of the above-described knowledge, description will be made on lapping of the air bearing surface of a magnetic head according to the first embodiment.
As described earlier, it is desirable from the viewpoint of productivity that, in the magnetic head manufacturing process, a lapping process to control the magnetic head size is executed at high speed, whereas a lapping process to reduce the surface roughness is executed at a lapping rate equal to or faster than a predetermined value. The following method was used as a method of lowering the lapping rate of the surface roughness reducing lapping process.
The air bearing surface of a magnetic head to be worked is constituted of a ceramic substrate portion and an element portion made of alumina and magnetic material, and both the portions are worked at the same time. Since the ceramic substrate portion has a higher hardness than that of the element portion, the lapping rate is determined by a cut amount of abrasive grains into the ceramic surface. This means that if the abrasive grains are unable to cut into the ceramic surface, the feed of the blade edges in the depth direction is stopped.
The conditions of eliminating the cut-in of the ceramic surface are able to be realized microscopically by setting a load upon each abrasive grain lower than a threshold value at which the cut-in (surface plastic deformation) starts, and macroscopically by lowering a surface pressure between the lapping plate and the work or increasing the density of the abrasive grains acting upon a work.
In a practical case of usual lapping, the lapping rate of the lapping plate lowers as a use time lapses. This is because the heights of the abrasive grains on the lapping plate become gradually uniform and the number of abrasive grains associated with lapping increases, so that a load upon each abrasive grain lowers and the cut-in lowers. The lapping plate in this state has no practical value for the size control because of its lower productivity, although it may be reused for the surface roughness reduction.
Although the lapping rate can be lowered by the above-described method, it is impossible to perform a desired work if the lapping plate with the lowered lapping rate is used for a magnetic head surface work after the size control work. The reason is as follows. In a conventional lapping process having a certain degree of lapping rate, there is a surface pressure allowing the abrasive grains to cut into the ceramic surface of the substrate portion, and the cut-in of abrasive grains becomes larger in the softer element portion. This may result in forming an average recess of several nm on the element portion relative to the average recess on the substrate portion. Even if the lapping plate unable to obtain a lapping rate sufficient for the ceramic portion surface is used for lapping the element portion surface, the blade edges of abrasive grains will not reach the element portion and the surface thereof will not be lapped. In other words, this will not lead to further improvement of the lapping surface roughness.
Next, in order to protect the surface of the air bearing surface which was lapped flat, a generally well-known hard carbon thin film is formed by about 3 nm (an air bearing surface protective film forming process 116), and thereafter an air bearing surface step forming process 117 is executed by dry etching to stabilize a floating amount of the magnetic disc slider floating above a magnetic disc. Lastly, each row bar is cut off into individual magnetic head sliders (a magnetic head slider cut-off process 118), and thereafter a magnetic recording apparatus is completed by combining the magnetic head slider with a magnetic disc, a driver and the like.
A characteristic process of the present invention is an element heating process 114 not used by conventional manufacture processes and provided between the element size control lapping process 113 and the surface roughness reducing lapping process 115. Detailed description will now be made on the role, operation, effects and others of the element heating process 114, with reference to the accompanying drawings.
The element size control lapping process 113 executes a multi stage lapping process including coarse lapping and precise lapping, in order to satisfy both the productivity and size precision because of the large lapping amount of the element. In this embodiment, the coarse lapping executes a free abrasive lapping while abrasive grains 11 having an average grain diameter of 250 nm are supplied as slurry to the lapping plate 10. When the size of the reader element from the lapping plane in the depth direction becomes about 500 nm, the next step of the precise lapping is executed. Specifically, by using the lapping plate 10 embedding abrasive grains having an average grain diameter of 100 nm in the surface layer thereof, applying a lapping surface pressure of 0.2 MPa or larger between the lapping plate and the row bar, and at a practical production lapping rate, e.g., at 0.1 nm/sec, the lapping was executed until to an element size of 85 nm, leaving 5 nm to be removed to a final target element size, 80 nm, by the heating process and surface roughness reducing lapping process to be described later (refer to
In the outline shape of the magnetic head slider after the heating process illustrated in
The surface shape of the element portion before the heating process (at the completion stage of the element size control lapping process 113, refer to
Next, the surface roughness reducing lapping process 115 as the objective of the present invention is executed (refer to
As different from the lapping plate used by the element size control lapping process 113, it is important to use a lapping plate 13 having a very low lapping rate relative to the ceramic substrate portion 1. In this embodiment, the lapping plate was adjusted to have a lapping rate of 0.001 nm/sec or slower at a lapping surface pressure of 0.1 MPa. An average height of the abrasive grains embedded in the lapping plate is 20 nm or lower, and an average abrasive grain density is 0.4 grain/μm2 or higher.
The average abrasive grain height is defined as in the following. An area of 5 μm square at each of 10 arbitrary positions (preferably, 24 positions at a 45-degree interval on inner, middle and outer circumferences) is measured with an atomic force microscope, 10 heights from the highest of the embedded abrasive grains at each measuring point are selected, and the average height of abrasive grains selected in all the areas is calculated. The abrasive grain density is measured on the lapping plate surface by an atomic force microscope (AFM), and the grain density of 0.4 grain/μm2 means that 10 protrusions corresponding to the abrasive grains were observed in an area of 5 μm square.
The lapping plate has a lapping rate of 0.001 nm/sec or slower relative to the ceramic substrate portion of the magnetic head slider as described above. However, this lapping plate has a lapping ability with regard to the element portions 2, 5 and 6 having a far smaller hardness than that of the ceramic substrate portion 1. As the row bar having the element portion protruded by the heating process 114 is lapped with this lapping plate, the protruded element portion 12 is lapped being contacted with the abrasive grains of the lapping plate. It is therefore possible to planarize the element portion (refer to
In this state described above,
The cut-in of abrasive grains relative to the element portion is 5 nm at the maximum at the start of lapping. However, since the blade edges of abrasive grains are not able to be cut into the ceramic substrate portion 1, the blade edges move to the element portion at the same position as the surface of the ceramic substrate portion 1. Since the blade edges of abrasive grains will not cut into the element portion deeper than the ceramic substrate portion surface but remove the protruded portions protruding beyond the ceramic substrate portion, the surface roughness is reduced.
Lapping continues for about 30 seconds also after the protruded portion of 5 nm is removed by lapping. In this state, the lapping rate is 0.001 nm/sec being restricted by the ceramic substrate portion. The size change by lapping during the last half of 30 seconds is 0.03 nm or smaller and is negligible. The element size reaches the target size of 80 nm after the lapping.
The processes after the surface roughness reducing lapping process 115 are also illustrated in
In order to partially form the hard film 23 near at the end of the magnetic head slider opposite to the element portion air bearing surface 3, the hard film forming mask 21 with the opening at the area corresponding to the hard film is disposed. Thereafter, a carbon film having a thickness of 70 nm to 200 nm is formed in the predetermined area by the above-described well-known film forming method. In this embodiment, the hard film 23 was formed to a thickness of 70 nm to 200 nm by using methane plasma gas CVD. An area where the hard film is formed is the area of about 300 μm from a position spaced apart from the edge of the magnetic head element portion by about 500 μm to the opposite end of the ceramic substrate portion 1.
Next, in the surface reducing lapping process 215, lapping was performed by slanting the magnetic head slider (row bar) relative to the lapping plate 13 as illustrated in
On the other hand, since the hardness of the material constituting the element portion is lower than that of ceramics, cut-in by the abrasive grains occur and the lapping progresses. When the end portion of the element portion 2 is lapped by about 3 nm, the area where the abrasive grains on the lapping plate contact the magnetic head slider reaches a boundary area between the ceramic substrate portion 1 and element portion 2, and the abrasive grains start contacting the ceramic substrate portion 1. Since the lapping plate 13 has a lower lapping ability relative to the ceramic substrate portion 1, the position of an abrasive grain blade edge will not enter deeper than the edge of the ceramic substrate portion 1. An element portion protruding beyond a tangent line 14 between the abrasive grain blade edge and the lapping plate is removed without cutting into further. The surface roughness of the element portion air bearing surface is therefore reduced (refer to
As illustrated in
The present invention provides a manufacture method capable of improving the surface roughness of the air bearing surface of the magnetic head facing the magnetic disc surface. It is therefore possible to contribute to the performance improvement and the cost reduction of the magnetic head slider having large storage capacity, and also to industrial use largely.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
Number | Date | Country | Kind |
---|---|---|---|
2009-262450 | Nov 2009 | JP | national |