Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-06-18
2004-09-07
Tugbang, A. Dexter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S603130, C029S603150, C029S603180, C029S603120, C029S603230, C216S022000, C216S038000, C360S313000, C360S122000, C360S125020
Reexamination Certificate
active
06785953
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of protecting a second pole tip thickness during fabrication of a write head and, more particularly, to preventing a reduction in the thickness of the second pole tip during subsequent processing steps, such as seed layer removal, sputter cleaning the wafer and formation of studs for terminals.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
A write head typically employs ferromagnetic first and second pole pieces which are capable of carrying flux signals for the purpose of writing magnetic impressions into a track on a magnetic medium, such as a rotating magnetic disk. Each of the first and second pole pieces has a yoke region which is located between a pole tip region and a back gap region. The pole tip region is located at the ABS and the back gap region is spaced from the pole tip region at a recessed location within the write head. At least one coil layer is embedded in an insulation stack which is located between the first and second pole pieces in the yoke region. A nonmagnetic write gap layer is located between the pole tip regions of the first and second pole pieces. The thinner the thickness of the write gap layer, the greater the number of bits the write head can write into the track of a rotating magnetic disk. The first and second pole pieces are magnetically connected at the back gap. Processing circuitry digitally energizes the write coil which induces flux into the first and second pole pieces so that flux signals bridge across the write gap at the ABS to write the aforementioned magnetic impressions or bits into the track of the rotating disk. The second pole piece has a second pole piece yoke (P2 yoke) which is magnetically connected to the second pole tip (P2 tip) and extends to the back gap for connection to the first pole piece.
A write head is typically rated by its areal density which is a product of its linear bit density and its track width density. The linear bit density is the number of bits which can be written per linear inch along the track of a rotating magnetic disk and the track width density is the number of tracks that can be written per inch along a radius of the rotating magnetic disk. The linear bit density is quantified as bits per inch (BPI) and the track width density is quantified as tracks per inch (TPI). As discussed hereinabove, the linear bit density depends upon the thickness of the write gap layer. The track width density is directly dependent upon the width of the second pole tip at the ABS. Efforts over the years to increase the areal density of write heads has resulted in computer storage capacities increasing from kilobytes to megabytes to gigabytes.
The first and second pole pieces, including the second pole tip, are typically fabricated by plating techniques. The strong-felt need to fabricate second pole tips with submicron widths is limited by the resolution of the fabrication techniques. The second pole tip is typically fabricated by frame plating. Photoresist is employed to provide the frame and a seed layer is employed to provide a return path for the plating operation. A typical sequence for fabricating a second pole tip, as well as other components of the first and second pole pieces, is to sputter clean the wafer, sputter deposit a seed layer, such as nickel iron, on the wafer, spin a layer of photoresist on the wafer, light-image the photoresist layer through a mask to expose areas of the photoresist that are to be removed (assuming that the photoresist is a positive photoresist), develop the photoresist to remove the light-exposed areas to provide an opening in the photoresist at the pole tip region and then plate the second pole tip in the opening up to a desired height.
It is necessary that a second pole tip have a sufficient amount of volume at the ABS in order to conduct the required amount of flux for writing the signals into the magnetic disk. If the second pole tip is made thinner, it must be made higher in order to provide the necessary volume of magnetic material. Unfortunately, as the track width becomes narrower the resolution of the photoresist decreases. Resolution is quantified as aspect ratio which is the width of the second pole tip versus the thickness of the photoresist. As the thickness of the photoresist increases the light penetration during the light-imaging step loses its columnation as it travels toward the bottom of the photoresist. The result is that the side walls of the photoresist frame are jagged which results in jagged side walls of the second pole tip.
The aforementioned problems are particularly manifested when the second pole tip and the yoke of the second pole piece are plated simultaneously in a common photoresist frame. In addition to loss of resolution with an increasing height of the second pole tip, there is also notching of the side walls of the photoresist frame, and consequently the second pole tip, due to reflection of light from a seed layer on the insulation stack immediately behind the pole tip region. One method to overcome this problem has been to employ a stitched “T”-shaped second pole piece which is fabricated by first making only the second pole tip portion with a photoresist frame and then subsequently making the yoke portion of the second pole piece with a second photoresist frame with the yoke portion being stitched (magnetically connected) to a stitch region at the top of the second pole tip. This type of second pole piece is referred to as a stitched “T” because the yoke portion extends laterally across the top of the pole tip portion, forming the configuration of a “T”. The yoke portion can be stitched across the entire top surface of the second pole tip in which case it is exposed at the ABS or it may be recessed from the ABS, as desired.
Unfortunately, processing steps subsequent to the construction of the second pole tip decrease the height of the second pole tip and can seriously damage its side walls. When the second pole piece is a continuous pole tip and yoke combination these processing steps are removal of the seed layer by sputter etching after removal of the photoresist frame and the fabrication of studs for write head and read head terminals which involves sputter etching to clean the wafer, depositing a seed layer, photoresist framing the areas involved, plating the studs, removing the photoresist layer and sputter etching the exposed seed layer. While these steps lessen the height of the second pole tip of the continuous second pole tip and yoke combination, it is even more aggravated with the stitched “T” type of second pole piece. After the second pole tip of the stitched “T” is fabricated, sputter etching is required to remove the seed layer employed to fabricate the pole tip which further reduces the height of the second pole tip. Further, if chemical mechanical polishing (CMP) is employed for planarizing the wafer, preparation steps for this operation can further reduce the height of the second pole tip.
In order to overcome the loss of height of the second pole tip while maintaining a narrow track width (wid
Johnston Ervin F.
Tugbang A. Dexter
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