Molecular dynamics simulations for the scattering of neon, argon, and xenon ions on silicon and silicon dioxide surfaces were performed at grazing incidence to examine how the angular distribution of reflected ions deviates from that of the ideal specular reflection, depending on the ion mass, incident angle, and surface material and its roughness. This study is motivated to understand how energetic ions interact with the sidewalls of high-aspect-ratio (HAR) channels when reactive ion etching (RIE) is used to form such HAR channels in semiconductor manufacturing. It is found that the higher the ion mass is, the less grazing the ion incident angle is, or the rougher the surface is, the larger the angular distribution of reflected ions becomes around the corresponding specular reflection angles. Quantitative information on such reflected ions can be used to predict the profile evolution of HAR channels in RIE processes.