Atomic layer etching of silicon nitride film by oxygen gas cluster ion beam with acetylacetone

The atomic layer etching (ALE) of silicon nitride (SiN x ) film was demonstrated using an oxygen gas cluster ion beam (O2-GCIB) with acetylacetone (Hacac) as the adsorption gas. A GCIB is a beam of aggregates of several thousand atoms, and it enables high energy density irradiation with little damage. In this study, we characterized the ALE to reveal the etching mechanism. The XPS results indicated the following etching process: (i) O2-GCIB irradiation oxidizes the surface of SiN x film; (ii) the oxynitride layer reacts with Hacac vapor; (iii) the reaction layer is removed by the GCIB. The ALE can be executed by the sequential repetition of the processes (i) to (iii). This technique enables highly accurate control of thickness of SiN x film with little irradiation damage.