The success of an ALD process depends largely on the control of the chemistry of the interactions between the precursor molecules and the deposition surfaces. A detailed understanding, at the atomic scale, of the mechanisms at play during ALD growth cycles is thus a crucial point for the implementation and optimisation of the process. ALD must lead to high quality materials (conformal layers, purity, stoichiometry). The hindsight of almost two decades of research in the field clearly shows that this understanding must be based on advanced means of ad hoc in situ and ex situ characterisation, together with the use of multi-scale modelling. The questions that are addressed are multiple, choice of precursors, identification and quantification of growth mechanisms during the early stages of deposition and during the steady state, modification/preparation of surfaces before deposition, to name the main ones. The literature often shows a complex reality, leading to deviations from the conceptual foundations of ALD: complexity of reaction mechanisms, incomplete dissociation, gas phase reactions, layer contamination, steric hindrance of grafted precursors, more complex intra-layer reactions for ionic oxides... In order to reduce these differences, to anticipate the choice of precursors, to evaluate the quality of the layers produced, their structuring at the atomic scale, but also to provide the elements of understanding and parameters for the models at the reactor scale, the means of modelling and characterisation at the nanometric scale must be used in synergy.

This is the objective of this GDR axis: bring together expertise at the national level, in situ and ex situ characterisation (IR, XPS, LEIS, XRD, etc.), modelling techniques at the atomic scale such as DFT (scale of the elementary chemical reaction), Monte Carlo Kinetics (mesoscopic scale and process simulation) and at the reactor scale. These pooled tools should make it possible to answer the fundamental questions of the relationships between nanostructures/properties and performances of devices resulting from ALD processes.

ALD reaction chamber adapted for in situ characterization by synchrotron radiation developed in collaboration between LMGP and SIMAP (source JL Deschanvres, LMGP)