Developments in ultrashallow spreading resistance analysis

Spreading resistance analysis on ultrashallow structures is complicated by the interaction of bevel rounding with geometric effects associated with lateral boundaries. When a spreading resistance probe is stepped from the original sample surface, across the rounded region at the bevel edge and onto the bevel, the resistance increases. Some of the increase is the result of approaching the lateral boundary represented by the bevel, and some is the result of increasing local sheet resistance as the probes begin to move below the original surface. We remove the geometric effect by solving the boundary value problem involving a sheet resistance which varies with distance along the direction of probe travel. Having obtained the local sheet resistance, we assign a depth for each point from profilometer data, and the usual depth-dependent analysis is used to obtain the resistivity profile.