Abrading – Abrading process – Combined abrading
Reexamination Certificate
2000-06-07
2002-02-19
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Combined abrading
C451S005000, C451S008000, C451S010000, C451S041000, C451S908000, C029S603100, C029S603060
Reexamination Certificate
active
06347983
ABSTRACT:
BACKGROUND
During the fabrication of magnetic heads for use in magnetic data storage applications, an array of transducers and auxiliary circuits are fabricated on a common substrate. To establish adequate performance for high efficiency recording heads, it is desirable to achieve the specified magnetoresistive element (MRE) sensor height within a very tight tolerance. One common practice is to use electrical lap guides (ELGs) and online bending mechanisms to form a closed-loop controlled lapping process as disclosed in U.S. Pat. No. 5,023,991. Such ELGs can be fabricated with the actual transducers through the same wafer processing. The ELGs predict the magnetoresistive (MR) transducer height, also known as the stripe height (SH), and feed this information to the bar lapping machine. The machine can take corrective action by adjusting the bending mechanism to minimize SH variation based on the predicted SH profile of the ELGs.
Thin film deposition techniques are often used to fabricate magnetic read/write transducers. In a typical process, an array of transducers and ELGs are formed on a common substrate by a deposition of metallic and nonmetallic layers. The patterning of the array of transducers and ELGs is accomplished using photolithography in combination with etching and lift-off processes. The finished array or wafer is then optically and electrically inspected and then sliced to produce bars, with one row of transducers in a side-by-side pattern on each bar. The bars are then lapped at the air bearing surface (ABS), which will eventually face the recording medium, to establish a specified sensor height. The bars of sliders are machined to obtain a desired SH or a desired inductive transducer height, also known as the throat height (TH). After diamond-like carbon processing, which protects the transducer from damage, and advanced air bearing processing, the bars are diced to produce individual transducers, heads, or sliders.
During machining of a particular row of transducers and ELGs, the machined surface moves from a beginning position to a final position while reducing the height of the transducers. The primary function of the ELGs is to control the machining process such that the desired transducer height is achieved. After a particular row of transducers is machined to the desired transducer height as controlled by the ELGs, the rows or bars are cut or diced into individual recording heads or sliders. After this process, the ELGs can be destroyed if desired.
Typically, each ELG includes one or more resistive elements, which are fabricated in the deposition of layers along with the sliders. A simple ELG design has one resistor that is aligned with a transducer such that the machining process reduces the height of both the transducer and the resistor at the same time. The resistance of the machined resistor (frequently referred to as the analog resistor) is monitored to determine when the desired height of the transducer has been achieved so that the machining process can be halted. Other ELG designs include at least two resistive components, one machined (analog) and typically one or two non-machined reference resistors. In some ELG designs, the resistance of each of the reference resistors is measured before lapping and used to calculate the local sheet resistance for the bar. The resistance of the machined resistor is compared to the constant resistance of one of the reference resistors during the machining process. When the resistance of the machined resistor equals the resistance of the reference resistor, the machining process is halted, presumably at the point where the height of the machined resistor is approximately equal to the desired transducer height.
FIG. 1
shows an ELG for a magnetoresistive or giant magnetoresistive transducer machining from U.S. Pat. No. 5,722,155. Measurements of reference resistor R
2
102
and R
3
103
are used to calculate local sheet resistance (Q), which is then combined with R
1
101
(exposed and machined) measurement to estimate the MRE
104
sensor height.
The SH estimation is insensitive to sheet resistance (Q) variation or feature size variation (edge movement) caused in wafer processing. Continuously monitoring R
2
102
and R
3
103
allows compensation for resistance measurement variation caused by thermal effect or other sources during lapping. The three resistors are connected to each other and to terminals T
1
105
, T
2
106
, and T
3
107
, which is connected to a controller or data acquisition unit. The controller (not shown) measures the resistance of the resistors and controls the machining process as a function of the measured resistances and the desired machined height of the transducer
14
.
ELG measurement accuracy—which is decreased due to errors introduced by the existence of mask or contact edge movement and noise—and ELG measurement resolution directly affect finished slider SH and TH variations. As higher density and lower cost requirements continuously drive the data storage industry, the transducer height tolerance continues to decrease, while the number of sliders and transducers per bar increases. This increased bar densification leads to thinner and more flexible bars with more sliders per bar. To maintain and improve transducer height control during the lapping process, more accurate ELG measurement and electrical resistance monitoring techniques are required.
SUMMARY
The present invention relates generally to the batch fabrication of sliders, which produce magnetoresistive and giant magnetoresistive read/write transducers for data storage applications. More particularly, the present invention relates to an improved ELG, which controls the machining process such that the transducers are machined to a specified height or resistance target.
Accordingly, the present invention provides a method of lapping a magnetic transducer. The method includes rough lapping the transducer based on a first signal and fine lapping the transducer based on a second signal from a dummy transducer. The dummy transducer can have electrical properties substantially similar to electrical properties of the magnetic transducer. The first signal can include a stripe height calculated as a function of a reference resistor element and an analog resistor element. The first signal can also include the stripe height calculated as a function of the reference resistor element's width, length, and resistance, and the analog resistor element's length and resistance. The analog resistor element can be exposed to machining before the stripe height is calculated. The reference resistor element can be approximately 40 &mgr;m wide and 700 &mgr;m long. The analog resistor element can be approximately 25 &mgr;m wide and 70 &mgr;m long. The stripe height can also be further calculated using a third resistor. The first signal can also include local sheet resistance calculated as a function of the reference resistor element's resistance, width, and length. The second signal can also include lap to reader resistance from the dummy transducer and a stripe height calculated from a reference resistor element and an analog resistor element. The dummy transducer can also provide process noise monitoring capability during lapping.
In another embodiment, the invention provides an electrical lap guide system for use in lapping a magnetic transducer. The system includes resistor elements and a dummy transducer. The resistor elements are used to control rough lapping and the dummy transducer is used to measure the electrical properties of the transducer to control fine lapping. The resistor elements can further include an analog resistor element and a reference resistor element. The reference resistor element can be used to calculate local sheet resistance as a function of the reference resistor element's resistance, width, and length. The analog resistor element can be machined before being used to calculate a stripe height as a function of the reference resistor's width, length, and resistance, and the analog resistor's length
Hao Shanlin
Liu Dongming
Price James K.
Clifford Chance Rogers & Wells
Feller Mitchell S.
Hail III Joseph J.
McDonald Shantese
Seagate Technology LLC
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