Molecular Dynamics Analysis of Surface Reaction Kinetics during Si Etching in Cl-based Plasmas: Effects of Etch By-Products Ion Incidence

Profile anomalies and surface roughness are critical issues to be resolved in plasma etching of nanometer-scale microelectronic devices, which in turn requires a better understanding of the effects of ion incident energy and angle on surface reaction kinetics. This paper presents a classical molecular dynamics (MD) simulation of Si etching by energetic Cl$^{+}$ and SiCl$_{x}^{+}$ ($x=$ 1--4) ion beams at normal incidence with different energies $E_{i}=$ 20--500 eV, where the improved Stillinger-Weber interatomic potential was used for Si/Cl system. Emphasis is placed on differences in the etching mechanisms between the etchant and etch by-products ion incidences. Numerical results indicated that in Cl$^{+}$ incidence, the Si etch yield increases with increasing $E_{i}$; on the other hand, in SiCl$^{\mathrm{+}}$ incidence, the deposition of Si atoms (or minus Si etch yield) occurs at lower $E_{i}\le $ 300 eV while the etching occurs at high $E_{i}$ \textgreater\ 300 eV. In addition, in Cl$^{+}$ incidence, the thickness of surface reaction layers and the coverage (or concentration) of Cl atoms therein increase with increasing $E_{i}$, while in SiCl$^{\mathrm{+}}$ incidence, the surface layer thickness and the Cl coverage are large at lower $E_{i}$ owing to deposition.