Understanding time-resolved processes in atomic-layer etching of ultra-thin Al₂O₃film using BCl₃and Ar neutral beam

We scrutinize time-resolved processes occurring in atomic-layer etching (ALET) of ultra-thin Al₂O₃film using BCl₃gas and Ar neutral beam by employing density functional theory calculations and experimental measurements. BCl₃gas is found to be preferentially chemisorbed on Al₂O₃(100) in trans form with the surface atoms creating O-B and Al-Cl contacts. We disclose that the most likely sequence of etching events involves dominant detachment of Al-associated moieties at early etching stages in good agreement with our concurrent experiments on tracking Al₂O₃surface compositional variations during Ar bombardment. In this etching regime, we find that ALET requires half the maximum reaction energy of conventional plasma etching, which greatly increases if the etching sequence changes.