Аннотация:A numerical model of dry etching of a cavity below a planar mechanical element (e.g. a mirror or a solid gear) through a set of holes is presented. From simulations using the developed model, it is shown that complex geometries of MEMS devices and low pressure dry etching may lead to limitation of the etching rate by gas transport under mechanical elements related to a strongly inhomogeneous distribution of gas concentration under the planar element; some criteria of distinction between the systems with and without the transport limitation effect are provided. The influence of the operating mode and parameters of the etching reactor is also discussed; the models of well-stirred (continuous-flow) reactor and batch (periodic) reactor are considered.