Electrical impedance tomography applied to semiconductor wafer characterization

A new method is described for determining the distribution of resistivity of semiconductor wafers and thin conducting films. It uses peripheral electrodes to inject small direct currents into the wafer or film and to measure the resultant potential differences, from which the distribution of resistivity is calculated. The usable area of the wafer is not degraded and, because the wafer is scanned electrically, the method is much faster than conventional methods. Results obtained on silicon wafers and conducting films are presented, which demonstrate the sensitivity and reproducibility of the method.