Mapping current paths in integrated circuits (IC) is expected to be important for design debug and failure analysis. Due to the rapid development of IC technology with higher transistor densities and smaller feature sizes, accurate location of the current paths buried under several layers of conducting interconnect is expected to have several important applications. Magnetic force microscope (MFM) holds great promise to meet this challenge and this work focuses on MFM based techniques for mapping current in conductors with over layers.;Extensive numerical modeling of the magnetic fields and the MFM images has shown that the simple point probe approximation is insufficient to model MFM mapping of current flow in ICs for the conductors used in this work. An extended model, which considers realistic MFM probe geometries and the forces acting on the whole probe including along the cantilever of the probe, has been shown to he necessary. Qualitative and quantitative comparison of the experimental results and simulation results with this model are in agreement to within experimental uncertainty. Analysis of the comparison suggested that the thickness of Cobalt coating is not uniform on different regions of the probe, which was verified by scanning electron microscope (SEM) cross section images of the probes cut by a focused ion beam (FIB). The thickness of the CoCr coating varies from 60 nm to 130 nm on the surface of the cantilever and from 30 nm to 110 nm on the surface of the tip. Correcting for film thickness variation in the model produced images for current flowing in buried conductors in very close agreement with the experimental results.;Based on the simulation and experimental results, we have devised a method to locate accurately the internal current path from MFM images with submicrometer uncertainty for simple model circuits. The method was tested for different patterns of model conducting lines. It was shown to be a useful technique for fault location in IC failure analysis when current flows through the devices buried under several layers and no topographic features are on the surface to provide clues about the positions of the devices.;This thesis presents a systematic study of MFM based mapping of current in model circuits by using force and force gradient techniques. In comparing these two techniques with respect to signal to noise ratio as a function of the tip height above the surface of conducting lines, force was found to have a much higher SNR (from ∼150 to ∼580 times) than force gradient. As a result, force based techniques will have better sensitivity and are able to detect much smaller minimum currents. For model circuits that mimic ICs, we have achieved a measurement sensitivity of approximately 1.02 muA/ Hz for force and 0.29 mA/ Hz for force gradient in air without magnet to maintain the orientation of the magnetic moments of the probe during the measurement (∼0.64 muA/ Hz in air and ∼0.095 muA/ Hz in vacuum for force with a magnet), this was achieved with a probe to circuit separation of one micron. We can conclude that the force measurement technique is superior for the application of MFM current imaging of buried conductors in ICs. However, this comes at the price of reduced spatial resolution.
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