Mechanisms determining uniformity across the wafer in low-energy plasma etching for microelectronic applications: Ion energy distribution function and edge effects

This study investigates the spatial distribution of the plasma sheath characteristics and radial non-uniformity of plasma parameters across the wafer in inductively coupled plasma etching tools for advanced microelectronic applications. The work focuses on the mechanisms controlling uniformity of hafnium oxide (HfO2) parasitic sputtering relevant for plasma-assisted atomic layer etching (ALE) with ultra-low energy ions. The study utilized a combination of hydrodynamic modeling for the plasma volume and a more detailed model for the plasma sheath near the wafer, incorporating field-dependent ion mobility. The developed models are based on parameters obtained by plasma diagnostics, and the results were validated in sputtering experiments. We show that sheath disturbance near the wafer edge systematically shifts the ion energy distribution to higher values, increasing sputtering rates at the periphery of the wafer for low-energy bombarding ions. Taking account of this effect is important in the development of monolayer-precision plasma technologies in microelectronics, such as ALE.