We report a new method for measuring sheet resistance on implanted wafers by using micro-fabricated four-point probes with a tip-to-tip spacing of a few microns. These microscopic probes have a contact force five orders of magnitude smaller than conventional probes, and can perform local non-destructive Ultra Shallow Junction (USJ) sheet resistance measurements on both blanket and patterned wafers. We demonstrate this new technique on laser annealed wafers, measuring micro-scale sheet resistance variations on wafers that appear homogeneous when mapped with conventional four-point probes. The microscopic four-point probes detect stitching effects caused by laser spot overlap/misalignment during the annealing process. Our findings indicate that such local sheet resistance inhomogeneities average out in conventional four-point measurements, and that new metrology is therefore needed to fully characterize USJ wafers activated by laser anneal and other diffusion-less methods.
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