One- and two-dimensional carrier profiling in semiconductors by nanospreading resistance profiling

Measurement of the carrier concentrations in silicon with lateral and in-depth resolution on the sub-100 nm scale has been demonstrated with an atomic force microscope (AFM) using conducting tips. The technique determines the local spreading resistance and hence inherits the attractive features of the conventional spreading resistance profiling (SRP) technique and will be referred to as nano-SRP. For instance, the calibration curve established by measuring homogeneously doped substrates indicates a dynamic range of concentrations between 10(14) and 10(19) cm(-3) and a monotonic relation between resistance and resistivity, similar to a conventional SRP calibration curve. In the present study, W-coated diamond tips are used at a precisely controlled force of 70 mu N, leading to a contact radius of 50 nm as determined from AFM analysis of the resulting imprints. The drastic reduction of the contact size implies that one can measure directly on a vertical cross section of the structure and overcome some limitations created by the beveling step. Moreover, the applicability to a cross section implies that one can determine with high resolution the in-depth as well as the lateral carrier distributions, which is not feasible with conventional SRP. The nano-SRP technique has been applied to measure the carrier distribution in several types of submicron structures: pn junctions, two-dimensional implanted and diffused layers. A comparison shows that the different measurement geometries (bevel versus cross section) lead to the expected differences in carrier spilling. (C) 1996 American Vacuum Society.