Thermal adsorption-enhanced atomic layer etching of Si3N4

Atomic layer etching (ALE) is an alternative method for nanopatterning in which atomic layers of material are removed by sequential self-limiting surface reactions. In this study, the authors report a new cyclic process for atomic layer etching of Si3N4 films achieved by alternating exposure steps of CH3F gas adsorption and Ar+ bombardment. Self-limiting etching characteristics of the ALE process are demonstrated as a function of both CH3F etchant flow rate and CH3F exposure time. From comparative studies on the amount of Si3N4 etched using the ALE mode versus pure Ar+ ion sputtering, it is found that the ALE process operates with an ALE synergy factor of ∼67% and also removes Si3N4 with better uniformity due to cooperative interactions between the self-limited CH3F chemisorption and the Ar+ ion sputtering. Based on both the chemical bonding changes following the CH3F etchant exposure and reaction product analyses during the Ar+ plasma step, possible etch reaction steps for the ALE Si3N4 process are proposed.