Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2001-02-16
2003-02-04
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C029S603090
Reexamination Certificate
active
06515475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods for determining the track width of magnetoresistive sensors of magnetic heads at the wafer level, and more particularly to the utilization of electrical resistance measurements of the magnetoresistive sensor while applying a magnetic field to determine the track width of the sensor.
2. Description of the Prior Art
Magnetic heads are fabricated in large quantities upon wafer substrates in an expensive fabrication process involving many steps. The magnetoresistive sensor of the read head portion of the magnetic heads is fabricated early in the overall head fabrication process, and a critical parameter to magnetic head performance is the track width of the fabricated magnetoresistive sensor. Therefore, following the fabrication of the magnetoresistive sensors on the wafer substrate, efforts are undertaken to measure the fabricated track width. Where the fabricated track width of the magnetoresistive sensors is not within product design parameters, time and expense can be saved by halting further fabrication of magnetic heads on such a wafer that has magnetoresistive sensors having an unacceptable track width.
Presently, optical inspection methods are utilized to determine the track width of the fabricated magnetoresistive sensors on the wafer. However, efforts to increase the areal data storage density of magnetic disks have resulted in efforts to decrease the track width of the hard disk data tracks, such that more data tracks per inch can be written onto the magnetic disk. In conjunction therewith, the track width of the magnetoresistive sensor has likewise been reduced in order to properly read data from the narrow data tracks, and current magnetoresistive sensors are fabricated with track widths of less than 0.5 microns. At this dimension, current optical scanning methods incur substantial resolution problems in accurately determining the track width of the magnetoresistive sensors upon the wafer surface, and a non-optical method for determining the track width of the magnetoresistive sensors is desirable.
The present invention utilizes the electrical and magnetic properties of the magnetoresistive sensors to determine the track width of the magnetoresistive sensors upon the wafer, as will be understood from the detailed description that follows.
SUMMARY OF THE INVENTION
In fabricating magnetic heads on a wafer surface, magnetoresistive sensors having two different stripe heights and the same stripe width are formed. Additionally, two different electronic lapping guides (ELGs) having different stripe heights and the same stripe width are also formed. While the design widths and heights of the sensors and ELGs are known, the actually fabricated widths and heights of the sensors and ELGs is unknown, due to the windage in the fabrication process. In the present invention, to determine the actual track width of the sensors, the change in electrical resistance of the sensors and ELGs is experimentally determined during the application of a magnetic field to the sensors and ELGs. Through a mathematical analysis, the actual track width of the fabricated sensors is determined utilizing the design widths and heights of the sensors and ELGs, together with the experimentally determined changes in electrical resistance of the sensors and ELGs.
It is an advantage of the method for determining the track width of magnetoresistive sensors of the present invention that a non-optical method for determining the actual track width of the magnetoresistive sensors is provided.
It is another advantage of the method for determining the track width of magnetoresistive sensors of the present invention that the actual track width of magnetoresistive sensors can be determined where the track width is so narrow that optical track width measuring techniques are inaccurate.
It is a further advantage of the method for determining the track width of magnetoresistive sensors of the present invention that electrical measurements of sensors and ELGs can be utilized to determine the actual track width of the sensors.
It is yet another advantage of the method for determining the track width of magnetoresistive sensors of the present invention that a rapid, accurate method for determining the actual track width of the sensors is provided.
It is yet a further advantage of the method for determining the track width of magnetoresistive sensors of the present invention that the actual track width of the sensors can be rapidly determined at various locations throughout the wafer surface, such that wafer process parameters can be analyzed.
These and other features and advantages of the present invention will no doubt become apparent to those skilled in the art upon reviewing the following detailed description which makes references to the several figures of the drawings.
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IEEE Transactions on Magnetics, vol. 30, No. 6, Nov. 1994, “Design, Fabrication & Testing of Spin-Valve Heads for High Density Recording,” by Ching Tsang, Robert E. Fontana, Tsann Lin, D.E. Heim, Virgil S. Speriosu, Bruce A. Gurney & Mason L. Williams, IBM Research Division.
Goubau Wolfgang
Marley Arley Cleveland
Guillot Robert O.
Intellectual Property Law Offices
International Business Machines - Corporation
Snow Walter E.
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