Plasma etching, a purely chemical dry etching technique, basically consists of the following steps: 1) generation of reactive species in a plasma; 2) diffusion of these species to the surface of the material being etched; 3) adsorption of these species on the surface; 4) occurrence of chemical reactions between the species and the material being etched, forming volatile byproducts; 5) desorption of the byproducts from the surface; and 6) diffusion of the desorbed byproducts into the bulk of the gas.