Measurable Range of Bulk Carrier Lifetime for a Thick Silicon Wafer by Induced Eddy Current Method

Abstract

In contactless measurement for a wide range of bulk carrier lifetime τ_bwith a single wafer, it is preferable to use the thickest possible wafer since the maximum bulk lifetime is determined by the thickness of the wafer. For thick wafers with short bulk lifetime, the bulk lifetime must be determined after a reasonable time delay of photoconductive decay to avoid the effect of higher-order-mode recombination with shorter time constants. The appropriate range is examined in terms of the voltage signal during the photoconductive decay by computer simulations and experiments. It is shown that the measurable range is between 1/10 and 1/20 of the maximum voltage, i.e., τ_b=0.73-11 ms for p-type and τ_b=2.1-32 ms for n-type Si wafers with thickness 20 mm subject to non-monochromatic illumination of long duration.