The one-dimensional transport of the neutral reactive species in the planar reactor is studied theoretically to draw conclusions on the reactor performance at maximum etching rate. The etching rate is calculated as a function of the reactant flux entering the reactor for various flux densities of desorbing product from the etched surface. An influence of the mutual diffusion of reactant and product on the etching rate is shown together with respective concentrations of reactant and reaction product in the reactor. The theory is compared with experimental results corresponding to etching of aluminium by chlorine. A method of in situ monitoring of the etching rate uniformity is also presented.