Atomic-scale characterization of plasma-induced damage in plasma-enhanced atomic layer deposition

Plasma-enhanced atomic layer deposition (PE-ALD) has many advantages for the deposition of thin films. However, an appropriate control of the plasma frequency in the PE-ALD process is required to reduce the plasma-induced damage of the thin films during deposition. In this study, we comparatively studied the effects of conventional 13.56 MHz, radio frequency (RF) and 60 MHz, very high frequency (VHF) plasma reactants in the PE-ALD during the deposition of Al ₂ O ₃ . The plasma damage and the degree of strain of the substrate are investigated by transmission electron microscopy at the atomic scale. In addition, a correlation between the atomic structure and plasma damage at RF and VHF is suggested. Compared to the RF PE-ALD, Al ₂ O ₃ thin films deposited with VHF PE-ALD show a clearly effective reduction of the plasma-induced damage. Moreover, the Al ₂ O ₃ thin films are grown into a tetrahedral structure near the surface and are then further grown into an octahedral structure, indicating the presence of an increased number of ions and radicals during the plasma-enhanced process. It is evident that the VHF PE-ALD is a more important deposition process for reducing plasma-induced damage to thin films than its RF counterpart.