Molecular dynamics simulations of Si etching in Cl- and Br-based plasmas: Cl+ and Br+ ion incidence in the presence of Cl and Br neutrals

Abstract

Classical molecular dynamics (MD) simulations have been performed for Cl+ and Br+ ions incident on Si(100) surfaces with Cl and Br neutrals, respectively, to gain a better understanding of the ion-enhanced surface reaction kinetics during Si etching in Cl- and Br-based plasmas. The ions were incident normally on surfaces with translational energies in the range Ei = 20–500 eV, and low-energy neutrals of En = 0.01 eV were also incident normally thereon with the neutral-to-ion flux ratio in the range Γn0/Γi0 = 0–100, where an improved Stillinger--Weber potential form was employed for the interatomic potential concerned. The etch yields and thresholds presently simulated were in agreement with the experimental results previously reported for Si etching in Cl2 and Br2 plasmas as well as in Cl+, Cl2+, and Br+ beams, and the product stoichiometry simulated was consistent with that observed during Ar+ beam incidence on Si in Cl2. Moreover, the surface coverage of halogen atoms, halogenated layer thickness, surface stoichiometry, and depth profile of surface products simulated for Γn0/Γi0 = 100 were in excellent agreement with the observations depending on Ei reported for Si etching in Cl2 plasmas. The MD also indicated that the yield, coverage, and surface layer thickness are smaller in Si/Br than in Si/Cl system, while the percentage of higher halogenated species in product and surface stoichiometries is larger in Si/Br. The MD further indicated that in both systems, the translational energy distributions of products and halogen adsorbates desorbed from surfaces are approximated by two Maxwellians of temperature T1 ≈ 2500 K and T2 ≈ 7000–40 000 K. These energy distributions are discussed in terms of the desorption or evaporation from hot spots formed through chemically enhanced physical sputtering and physically enhanced chemical sputtering, which have so far been speculated to both occur in the ion-enhanced surface reaction kinetics of plasma etching.