The near-field microwave technique for deep profiling of free carrier concentration in semiconductors

We describe a technique for profiling of layered samples via near-field (NF) microwave measurements. This technique is based on a recently developed theory of the NF microscopy of layered media. The deep profilometry involves solution of a nonlinear inverse problem in which sample properties are mathematically reconstructed from a set of experimental data obtained with a system of NF probes. We have built an effective computer algorithm that yields a fairly accurate solution of this ill-conditioned problem. As an example, we analyze retrieval of a carrier concentration profile in a semiconductor. The process of retrieving some forms of profiles with the characteristic spatial scales of 10-100 nm, which are typical for semiconductor technologies, is simulated. A satisfactory accuracy (better than 10%-15%) is achieved for millimeter-wave microscopes with the probe apertures of 3-15 mu m. We simulate the measuring characteristics for a possible NF microscope circuit, which provide the basis for realization of the proposed method. (C) 2011 American Institute of Physics. [doi:10.1063/1.3580167]