Fundamental size limitations of micro four-point probes

The continued down-scaling of integrated circuits and magnetic tunnel junctions (MTJ) for hard disc read heads presents a challenge to current metrology technology. The four-point probes (4PP), currently used for sheet resistance characterization in these applications, therefore must be down-scaled as well in order to correctly characterize the extremely thin films used. This presents a four-point probe design and fabrication challenge. We analyze the fundamental limitation on down-scaling of a generic micro four-point probe (M4PP) in a comprehensive study, where mechanical, thermal, and electrical effects are considered. We show that the most severe limits on down-scaling from a state of the art M4PP are set by electromigration, probe fracture or material strength, and thermal effects. Compared to current state of the art probes, however, there is still room for down-scaling.