Accurate Metrology for the Width of the Probes for Perpendicular Recording Inductives
Original Publication Date: 2002-Jul-28
Included in the Prior Art Database: 2003-Jun-21
Disclosed is a design and method of electrical metrology to measure a large number of widespread points on a wafer. This method gives an exact trackwidth value instead of one which is modified by milling redeposition, and dramatically improves the measurement time, as compared with the time required using conventional FIB/SEM tools. The design part consists of placing an identical probe element in the curf area, very close to the actual device. The curf area has an added element, consisting of a thin layer of an electrically resistive material. Said layer is placed in the critical dimension area and is formed as an exact replica of the top of the probe's dimension. Once the resistor is shaped in the probes similitude it can then be probed after a few process steps (to provide contacts and etch the underlying probe layer). This method gives a possible methodology of creating not just a copy of the probes for size sampling, but also (because of the potential of having such a large number of sites available) adding reference resistors that will aid in the calculation of sheet resistance of the resistive material. Because the Focused Ion Beam (FIB) cut is only a very localized section, if it is not done in the exact place, it could give wrong information. Second, the Ion Milling redeposition of underlying material tends to pile up onto the sides of the probe, causing the SEM metrology to obtain a modified size measurement. Finally, because the FIB/SEM combination is so slow, for productivity sake, it is undesirable to do many sites across the wafers. Fig. 1 As shown in Fig. 1, the first step is ion milling and shaping the probe, the second removing the resist while protecting the vias, third etch the pads and lastly four point probe the feature. The four point probe can then pass voltage through two points, and from sheet resistivity data given for the substrate material, the trackwidth can be computed. It is understood that the metrology aids do not need all the process steps listed (they pertain to the progression for the fabrication of the device as well). It is also understood that this technique becomes invaluable to set up critical process steps leading to the fabrication/ process of the perpendicular heads. Furthermore, it can be used as process control to normalize materials as well as tooling changes.