Minority Carrier Lifetime Estimation by Photoconductance Decay for Silicon Wafers Immersed in HF

The measurement of minority carrier bulk lifetimes of Si wafers immersed in HF is known to have an immersion time dependence, which is specially strong for high lifetime wafers and can vary significantly for different surface treatments performed previously. These complications can make the lifetime measurement become difficult to interpret and inaccurate. Therefore, a method for extracting the bulk lifetime from the measured curves of lifetime versus immersion time is suggested. A model of the reaction between Si and HF is considered, consisting in a first-order reaction between Si and HF for polished wafers and two first-order reactions for textured wafers. Experiments on polished and textured p-type Si wafers were conducted with the photoconductance decay technique to test the model proposed and to show that it is more adequate to estimate the bulk lifetime by using the reactions models than to report it as the lifetime measured at a particular immersion time, which is the usual procedure.