Towards accurate atom scale characterisation of hydrogen passivation of interfaces in TOPCon architectures
Passivated contact cell architectures have the potential for higher efficiencies than the currently dominant PERC technology. Further development requires greater understanding of the passivation mechanism and potential surface related degradation, especially at polysilicon-oxide-crystalline silicon contacts. In particular, the hydrogenation provided by high temperature firing of dielectrics has been shown to govern both initial passivation and subsequent degradation at this interface.
Given the nanoscale dimensions of the tunnelling oxide, assessing the concentration of hydrogen at the interface is a complex task. In this work* we use atom probe tomography to demonstrate the capacity to resolve hydrogen atoms at this interface. Atom probe tomography can provide improved depth resolution via 3D reconstructions of the elemental atomic distributions at the interface.
We propose a route towards atomic scale measurements of hydrogen across a thin tunnelling oxide, which can enable further understanding of charge carrier flow at or near this interface. We show that the ability to characterise hydrogen at the nanoscale is crucially limited by the residual gas present during the atom probe measurement. Deuterium, as a surrogate for naturally abundant hydrogen, is therefore recommended to accurately provide less ambiguous determination of hydrogen concentrations at the atom scale in such structures. Even with the use of deuterium, however, challenges remain, and the analysis and interpretation of the data must be undertaken with care. Such atom scale characterisation can provide critical information on the role that hydrogen plays in passivating contact interfaces.
