Contactless Measurement of Photoinduced Carrier Lifetime and Injection Level in Silicon Wafer Using Additional Eddy Current

A new contactless method for measuring the lifetime and the injection level of photoinduced excess carriers in silicon wafer is described. In order to flow measuring current in the wafer, a pair of high frequency magnetic fluxes in opposite directions are used so as to concentrate the induced eddy current in the central part even for narrow wafer. The voltage in the wafer caused by eddy current and the photoconductivity are analyzed, and it is shown that the injection level of excess carriers can be calculated from the relation between the above voltage and lifetime measured for the different illumination intensity. The dependence of lifetime on the injection level for NTD Si and normally doped n-C.Z Si wafers are found to be considerably different. The measurement sensitivity and the spatial resolution of this method are discussed.