Lifetime mapping of Si wafers by an infrared camera

We present a fast and contact-free method to map the effective minority carrier lifetime tau (eff) of silicon wafers at a high spatial resolution. An infrared camera measures the infrared light absorbtion induced by optically excited free carriers. A single camera measurement yields a map of the areal density of excess minority carriers which we convert into a map of the effective minority carrier lifetime tau (eff). The infrared measurement results agree with the results of established techniques, such as microwave detected photoconductance decay and quasi steady state photoconductance lifetime measurements. The novel infrared lifetime mapping technique is sufficiently fast for in-line process control.