Tunable eddy current device for the contactless characterization of a large variety of semiconductor materials

This paper concerns the development of an innovative device for the characterization of the some transport properties of semiconductors using contactless eddy current probes. The eddy current probe, interacting with a semiconductor wafer, is constituted of a coil connected to a transmission line. The original approach, compared to the existing techniques, consists in measuring the impedance of the semiconductor wafer by reflectometry using a tunable signal over a wide frequency range thus allowing the characterization of a large variety of semiconductor materials. Using an additional electromagnetic model of the coil-wafer interaction, the conductivity of the wafer was consequently estimated. The fast electronic device developed in this work also exhibits very high sampling rates thus allowing the measurement of the photoconductivity of semiconductor materials in fast transient conditions. This process results in a new contactless conductivity measurement device not dedicated to a single material. As a practical example, the measurement capacity of our device is demonstrated by estimating the conductivity of a set of doped silicon wafers.