A two-dimensional fluid/Monte Carlo simulation was developed to study plasma molding over deep trenches and the resulting ion and energetic (fast) neutral distributions, with emphasis on neutral beam sources. Plasma molding occurs when the sheath thickness is comparable to or smaller than the trench width. Using the electric field profiles predicted by the self-consistent fluid simulation, ions and energetic neutrals (resulting mainly by ion neutralization on the sidewall) were followed by the Monte Carlo simulation. The dominant energetic species at the bottom of a high aspect ratio trench were neutrals. A thin sheath (compared to the trench width), favored a larger energetic neutral flux at the bottom, at the expense of neutral energy and directionality. A relatively thick sheath produced neutrals of higher directionality at the expense of neutral flux. Neutral energy and directionality both increased by increasing the sheath potential. (C) 2003 American Vacuum Society.