Atomic-Scale Etching Mechanism of Aluminum with Fluorine-Based Plasma

A first-principles density functional theory study has been carried out to investigate the etching and corrosion of aluminum with fluorine-based plasma. Aluminum is modeled with the (111) surface of aluminum metal and (0001) surface of alumina, which forms as a thin layer on aluminum. The adsorption of plasma gases, for example, CF4, CHF3, and F2, on both surfaces is investigated. CF4 and CHF3 are very weakly adsorbed on both surfaces. On the other hand, a F2 molecule dissociates on both surfaces, which leads to the interaction of more F atoms to the same Al atom. Maximum three F atoms are allowed to adsorb on a single surface Al atom, which paves the way to form an AlF3 molecule. For all F adsorption, the interaction between F and surface Al is much stronger with aluminum surface compared to alumina surface, which explains the relative difficulty of etching alumina. The isopropyl alcohol, which is used to clean the plasma chamber and removed nonvolatile AlF3, itself adsorb on Al(111) and Al2O3(0001) surfaces. This preadsorbed isopropyl alcohol further activates the neighboring surface Al atoms and thus induces stronger interaction between F and surfaces.