Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-08-12
2004-11-16
Tugbang, A. Dexter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S603070, C029S603130, C029S603140, C029S603160, C029S603180, C360S324000, C360S325000, C360S326000, C360S327000, C216S062000, C216S065000, C216S066000, C204S192150, C427S079000, C427S080000
Reexamination Certificate
active
06817086
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photolithographic process for extreme resolution of a track width definition for a read head and, more particularly, to a bilayer lift off photolithographic process which obviates fencing after backfilling with one or more read head layers.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a magnetic disk, a slider that has read and write heads, a suspension arm and an actuator arm that swings the suspension arm to place the read and write heads adjacent selected circular tracks on the disk when the disk is rotating. The suspension arm biases the slider into contact with the surface of the disk or parks it on a ramp when the disk is not rotating but, when the disk rotates and the slider faces the rotating disk, 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 field signals to and reading magnetic field signals 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.
An exemplary high performance read head employs a spin valve sensor for sensing the magnetic field signals from the rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer structure and a ferromagnetic free layer structure. An antiferromagnetic pinning layer interfaces the pinned layer structure for pinning a magnetic moment of the pinned layer structure 90° to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer structure is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic field signals from the rotating magnetic disk. The quiescent position, which is parallel to the ABS, is the position of the magnetic moment of the free layer structure with the sense current conducted through the sensor in the absence of field signals.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layer structures are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with the pinned and free layer structures. When the magnetic moments of the pinned and free layer structures are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. Changes in scattering changes the resistance of the spin valve sensor as a function of cos &thgr;, where &thgr; is the angle between the magnetic moments of the pinned and free layer structures. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in the resistance of the sensor as the magnetic moment of the free layer structure rotates from a position parallel with respect to the magnetic moment of the pinned layer structure to an antiparallel position with respect thereto and R is the resistance of the sensor when the magnetic moments are parallel.
In addition to the spin valve sensor the read head includes nonmagnetic electrically nonconductive first and second read gap layers and ferromagnetic first and second shield layers. The spin valve sensor is located between the first and second read gap layers and the first and second read gap layers are located between the first and second shield layers. In the construction of the read head the first shield layer is formed first followed by formation of the first read gap layer, the spin valve sensor, the second read gap layer and the second shield layer. Spin valve sensors are classified as a top or a bottom spin valve sensor depending upon whether the pinning layer is located near the bottom of the sensor close to the first read gap layer or near the top of the sensor close to the second read gap layer. Spin valve sensors are further classified as simple pinned or antiparallel pinned depending upon whether the pinned layer structure is one or more ferromagnetic layers with a unidirectional magnetic moment or a pair of ferromagnetic layers that are separated by a coupling layer with magnetic moments of the ferromagnetic layers being antiparallel. Spin valve sensors are still further classified as single or dual wherein a single spin valve sensor employs only one pinned layer and a dual spin valve sensor employs two pinned layers with the free layer structure located therebetween.
The areal density of a read head is a measure of the number of bits per square inch that the read head is capable of sensing on the rotating magnetic disk. Areal density is a product of linear density, which is the number of bits per inch along a circular track of the rotating magnetic disk, and track width density, which is the number of tracks per inch along a radius of the rotating magnetic disk. The linear density is quantified as bits per inch (BPI) and the track width density is quantified as tracks per inch (TPI).
The track width of a read head is typically formed with a bilayer photoresist. After forming sensor material layers a first layer of inorganic or organic material, such as photoresist, which is a non-actinic polymer, is applied by spin coating on the wafer and then subjected to a soft bake to remove casting solvents. Next, a second inorganic or organic material, such as photoresist, which is an actinic photoresist, is spun onto the wafer and soft baked. Assuming that the second photoresist layer is a positive photoresist the second photoresist layer is light imaged with a mask preventing exposure of the light to the second photoresist layer portion that is to be retained. The first and second photoresist layers are then subjected to a dissolver, which is a basic solution. The dissolver first dissolves the light exposed portions of the second photoresist layer down to the first photoresist layer and then proceeds to dissolve the first photoresist layer causing an undercut below the second photoresist layer. The dissolution is terminated when a desired undercut is obtained with the second photoresist layer overhanging the first photoresist layer on each side of the first photoresist layer. Accordingly, the width of the second photoresist layer defines the track width of the read head and the first photoresist layer permits the first and second photoresist layers to be lifted off with any layers deposited thereon, which is described hereinbelow.
After forming the bilayer photoresist on the sensor material layers ion milling is implemented to remove exposed portions of the sensor material layers leaving a sensor material layer portion below the bilayer photoresist that has a width equal to the desired track width of the read head. The space on each side of the bilayer photoresist is then backfilled with read head layers, such as first and second hard bias layers and first and second lead layers, with the first hard bias layer and the first lead layer abutting a first side surface of the sensor and the second hard bias layer and the second lead layer abutting a second side surface of the sensor. The hard bias layers and the lead layers are typically deposited by ion beam deposition since the deposition is more collimated than sputter deposition. Even so, a portion of the deposition enters the undercut on each side of the bilayer photoresist and overlaps first and second end portions of the sensor. Even when the thic
Emilio Santini Hugo Alberto
Lu Jennifer Qing
MacDonald Scott Arthur
Johnston Ervin F.
Kim Paul D
Tugbang A. Dexter
LandOfFree
Photolithographic process for extreme resolution of track... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photolithographic process for extreme resolution of track..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photolithographic process for extreme resolution of track... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3315395