A self-consistent modeling of feature profile evolution under competition between etching and deposition

Radical deposition is one of the important issues for SiO$_2$ etching as the radicals contribute to the protection of side wall as well as the acceleration of etching by the formation of a mixing layer on the bottom. We investigate the relationship among local wall charging, etching and deposition in a SiO$_2$ trench etching, by considering the transport of electrons, positive ions, and neutral radicals in the two-dimensional sheath structure in a two frequency-capacitively coupled plasma in CF$_4$/Ar. Emphasis is given on the influence of both charging and neutral radical accumulation inside the SiO$_2$ trench during plasma etching. Feature profiles of the SiO$_2$ trench are estimated by the Level Set method under conditions with/without charging and neutral deposition. In particular, the effect of the bias amplitude on the profile evolution is discussed under the competition between etching and deposition.