Structure size dependent etch rates that lead to reactive ion etching lags and microloading are one of the big problems in microelectronics for structure transfer with plasma etch processes at high aspect ratios. This paper deals with the general role of neutral particles and ions in plasma etching processes. Starting from the fundamental laws of gas dynamics and vacuum technology, formulas are derived for the maximum etch rate of an unstructured surface as well as for the aspect ratio dependence of the etch rates of cylindrical trench holes. The theoretical results are compared with experimental results obtained from single-crystal silicon etching for generating trench capacitors for memory cells in multi-Mbit dynamic random access memory.