This article contains a broad overview of etch process as one of the most important top-down technologies widely used in semiconductor manufacturing and surface modification of nanostructures. In plasma etching process, the complexity comes from the introduction of new materials and from the constant reduction in dimensions of the structures in microelectronics. The emphasis was made on two types of etching processes: dry etching and wet etching illustrated by three dimensional (3D) simulation results for the etching profile evolution based on the level set method. The etching of low-k dielectrics has been demonstrated via modelling the porous materials. Finally, simulation results for the roughness formation during isotropic etching of nanocomposite materials as well as smoothing of the homogeneous materials have also been shown and analyzed. Simulation results, presented here, indicate that with shrinking microelectronic devices, plasma and wet etching interpretative and predictive modeling and simulation have become increasingly more attractive as a tool for design, control and optimization of plasma reactors.