Molecular dynamics analysis of silicon chloride ion incidence during Si etching in Cl-based plasmas: Effects of ion incident energy, angle, and neutral radical-to-ion flux ratio

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(100) etching by energetic Cl$_{x}^{+}$ ($x=$ 1--2) and SiCl$_{x}^{+}$ ($x=$ 0--4) ion beams with different incident energies $E_{\mathrm{i}}=$ 20--500 eV and angles $\theta_{\mathrm{i}}=$ 0--85$^{\circ}$, with and without low-energy neutral Cl radicals (neutral-to-ion flux ratios $\Gamma _{\mathrm{n}}$/$\Gamma_{\mathrm{i}}=$ 0 and 100). An improved Stillinger-Weber interatomic potential was used for the Si/Cl system. Numerical results indicated that in Cl$^{+}$, Cl$_{2}^{+}$, SiCl$_{3}^{+}$, and SiCl$_{4}^{+}$ incidences for $\theta _{\mathrm{i}}=$ 0$^{\circ}$ and $\Gamma_{\mathrm{n}}$/$\Gamma _{\mathrm{i}}=$ 0, the etching occurs in the whole $E_{\mathrm{i}}$ range investigated; on the other hand, in SiCl$^{+}$ and SiCl$_{2}^{+}$ incidences, the deposition occurs at low $E_{\mathrm{i}}$\textless 300 and 150 eV, respectively, while the etching occurs at further increased $E_{\mathrm{i}}$ [1]. For SiCl$^{+}$ and SiCl$_{2}^{+}$, the transition energies from deposition and etching become lowered for $\Gamma_{\mathrm{n}}$/$\Gamma _{\mathrm{i}}=$ 100. Numerical results further indicated that in the SiCl$^{+}$ incidence for $\Gamma_{\mathrm{n}}$/$\Gamma _{\mathrm{i}}=$ 0, the etching occurs in the whole $\theta _{\mathrm{i}}$ range investigated for $E_{\mathrm{i}}\ge $ 300 eV; on the other hand, for $E_{\mathrm{i}}=$ 100 and 150 eV, the deposition occurs at low $\theta_{\mathrm{i}}$\textless 60$^{\circ}$ and 40$^{\circ}$, respectively, while the etching occurs at further increased $\theta_{\mathrm{i}}$; in addition, for $E_{\mathrm{i}}\le $ 50 eV, the deposition occurs in the whole $\theta_{\mathrm{i}}$ range investigated.\\[4pt] [1] N. Nakazaki \textit{et al}., Jpn. J. Appl. Phys. \textbf{53}, 056201 (2014).