Applications of carrier de-smearing of photoluminescence images on silicon wafers

Lateral carrier diffusion can lead to significant smearing in photoluminescence (PL) images of silicon wafers with high lifetime or localised recombination centres. A method to de-smear the PL image by applying the continuity equation in two dimensions has been proposed previously and demonstrated on a virtual wafer with simulated carrier diffusion and artificial random Gaussian noise. This work will demonstrate the de-smearing method experimentally by using a partially shaded monocrystalline silicon wafer. A criterion for determining the noise filter parameters is also proposed based on the convergence of multiple images measured under the same settings and filtered and de-smeared in parallel. The results show that the de-smearing method is effective across most of the wafer, with the exception of regions very close to the shaded edge where the signal to noise ratio is poor. The de-smearing method was also applied to PL images on a high lifetime n-type multicrystalline wafer and for Fe imaging of p-type multicrystalline silicon. De-smearing of the PL images suggests that the intra grain lifetime of the n-type multicrystalline silicon can reach up to 800 mu s, but is limited by recombination in the grain boundaries. The application of de-smearing for Fe imaging results in a sharper Fe profile near the grain boundaries. Copyright (c) 2016 John Wiley & Sons, Ltd.