Low-energy argon ion bombardment-induced decomposition of physisorbed hydrofluorocarbons on silicon nitride surfaces: A computational mechanistic study

Using a combination of tight binding molecular dynamics and ab initio molecular dynamics simulations, we study the mechanisms of bombardment-induced decomposition of hydrofluorocarbons (HFCs) physisorbed on silicon nitride for ion energies of ≤35 eV. We propose three key mechanisms by which bombardment-driven HFC decomposition can occur, focusing on the two pathways observed at these low ion energies: "direct decomposition" and "collision assisted surface reactions (CASRs)." Our simulation results clearly demonstrate the importance of the presence of favorable reaction coordinates for enabling CASR, which dominates at lower energies (≈11 eV). At higher energies, direct decomposition becomes more favored. Our work also predicts that the primary decomposition pathways for CH3F and CF4 are CH3F → CH3 + F and CF4 → CF2 + 2F, respectively. The fundamental details of these decomposition pathways and the decomposition products formed under ion bombardment have implications for plasma-enhanced atomic layer etching process design that will be discussed.