Modeling and Simulation of Nanoscale Surface Rippling during Plasma Etching of Si under Oblique Ion Incidence

A three-dimensional atomic-scale cellular model (ASCeM-3D) has been developed to reproduce the evolution of feature profiles on atomic or nanometer scale during plasma etching. Emphasis was placed on the evolution of nanoscale surface features and roughness during Si etching in Cl 2 plasmas, with further attention being given to that of ripple structures on etched surfaces. Simulations were carried out for different ion incident angles from θ i = 0 to 85°, with an ion incident energy E i = 100 eV, flux Γ i 0 = 1.0 ×10 16 cm -2 s -1 , and neutral-to-ion flux ratio Γ n 0 /Γ i 0 = 100, which are typical in high-density plasma etching environments. Numerical results indicated that as the angle θ i is increased, nanoscale concavo-convex features drastically change and ripple structures occur on etched surfaces. For θ i = 0° or normal ion incidence, the surfaces are randomly roughened. For increased θ i = 30–45° or oblique ion incidence, the ripples are formed perpendicular to the direction of ion incidence, while they are parallel to the direction of ion incidence for further increased θ i = 75–80°. Analysis of ion trajectories implied that the ion reflection and concentration on microscopically roughened surfaces largely affect the surface roughening and rippling during plasma etching. These numerical approaches would become important to predict the nanoscale surface features and roughness, especially the line edge roughness (LER) formed on feature sidewalls, because experiments of oblique incidence of ions on surfaces are difficult in plasma environments.