Characteristics and mechanism of NF3 plasma-modulated modification in atomic layer etching of silicon nitride

Plasma-enhanced atomic layer etching (PE-ALE) is a promising technique for achieving low-damage, highly selective SiN x etching. Although remote plasma (RP)-based ALE offers advantages over conventional direct plasma (DP) processes, systematic comparisons of the surface-modification mechanisms between DP and RP remain limited. Herein, the effects of DP and RP configurations during the surface-modification step of NF 3 plasma-based SiN x ALE were investigated in terms of the etching behavior, plasma-induced surface modification, and post-etch surface morphology. Both DP-ALE and RP-ALE exhibited a self-limiting ALE window at substrate bias voltages of 30–40 V, with a stable etch per cycle (EPC) of approximately 0.33 nm/cycle. Additionally, the cumulative etch thickness increased linearly with the number of cycles, confirming that self-limiting surface reactions stably governed the NF 3 plasma-based modification process. Although DP-ALE and RP-ALE exhibited similar EPC and ALE synergy values, they showed distinct differences in post-etch surface chemistry and surface damage. X-ray photoelectron spectroscopy (XPS) analysis revealed that RP-ALE suppressed both defect fluoride formation and distortion of the Si-N network more than DP-ALE. Atomic force microscopy (AFM) analysis showed that both processes reduced the surface roughness of the SiN x and SiO 2 films relative to the pristine surfaces, with RP-ALE exhibiting superior surface smoothing. These results demonstrate that the RP configuration maintains self-limiting reactions through radical-mediated surface fluorination during modification while effectively suppressing plasma-induced surface damage.