Micro-Scale Sheet Resistance Measurements on Ultra Shallow Junctions

Abstract

The paper reports 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. The authors 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. The findings indicate that such local sheet resistance in-homogeneities 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