Effects of Dipping in an Aqueous Hydrofluoric Acid Solution before Oxidation on Minority Carrier Lifetimes in p-Type Silicon Wafers

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Abstract
A scanning photon microscope is successfully applied to measure ac surface photovoltages which correspond to apparent minority carrier lifetimes (τPCD) measured by the microwave-detected photoconductive decay (µ-PCD) method, using oxidized p-type silicon wafers pre-treated with or without dipping in an aqueous hydrofluoric acid (HF) solution. The dipping in HF solution causes a larger fixed oxide charge, resulting in a strongly inverted layer beneath the oxide. This situation gives longer τPCD than the bulk lifetime (τPV) by an ac photovoltaic method, while if the fixed oxide charge is small, τPCD gives an apparently smaller lifetime than τPV, implying that τPCD is influenced by the surface charge state or the surface potential. Hence, the process diagnosis by lifetime requires the measurements by both surface photovoltages and the µ-PCD method.