Mechanism study of H₂-plasma assisted Si₃N₄ layered etch

The cyclic two-step process, comprised of energetic H₂ plasma followed by HF wet clean or in situ NF₃ plasma, demonstrates Si₃N₄ layer-by-layer removal capability exceeding 10 nm per cycle, surpassing typical atomic layer etch methods by an order of magnitude. In this paper, we investigated the surface reaction mechanisms via first principle density functional theory simulations and surface analysis. The results unveiled that energetic H₂ plasma, in the first step, selectively removes nitrogen (N) in preference to silicon (Si), generating ammonia (NH_x) and transforming Si₃N₄ into SiON upon exposure to air, which becomes removable by HF wet clean in the second step. For the second step employing in situ NF₃ plasma, it further leverages H-passivated surfaces to enhance NF₃ dissociation and provide alternative reaction pathways to yield volatile byproducts such as SiHF₃ and SiF_x, thereby significantly improving nitride removal efficiency.