A study of MgF2 thin film growth in the atomic layer deposition process by multi-scale simulations

Metal fluoride thin film enhances cyclability and capacity retention of a battery by protecting electrodes and reducing side reactions at the interface. In this work, growth mechanism for MgF2 thin film by ALD is investigated by multi-scale approach of density functional theory (DFT) and the kinetic monte carlo (KMC) method. Bis (ethylcyclopentadienyl)magnesium, Mg(EtCp)(2), and hydrogen fluoride, HF, are selected as a precursor and reactive gas, respectively. DFT is adopted to reveal and find dominant reaction pathways calculating adsorption and activation energies of surface reactions. F on a clean MgF2 surface is a major reaction site for the precursor adsorption, and sequential and concurrent ligand decompositions are equally predicted during HF pulse. The KMC model is developed to reproduce the MgF2 deposition process with calculated energetics from DFT. Mass gain of the film, growth rate, and surface HF coverage calculated by KMC show a good agreement with experimentally measured values. Ligand molecules remaining on the surface are suggested to be a critical factor for a low surface HF coverage and carbon impurity. We believe the multi-scale simulation presented in this work can be a useful guide for the fundamental understanding of the reaction mechanism as well as the optimization of film quality.