Enhanced silicon nitride etching in the presence of F atoms: Quantum chemistry simulation

Dry etching of silicon nitride (SiN) is a challenging process in the semiconductor industry and requires high etch selectivity. Fluorine containing chemistry is widely used to etch silicon based materials, and one of the methods to increase the etch selectivity is to use reactants enhancing SiN etching in the presence of atomic fluorine. In this paper, quantum chemistry simulations have been carried out using the density functional theory method [B3LYP, 6-31 + G(d,p)] in order to determine such reactants. These simulations are based on the assumption that such reactants, for example, NO, can increase SiN etch rate via interacting with F–N bonds of the modified SiNFx surface. Silicon nitride cluster with F–N bonds is used here as a model of the modified SiNFx surface. Several new reactants (HF, Cl, H, Br, and FNO) enhancing SiN etch rate have been found by these simulations. The fact that such species as NO, HF, and H atoms can enhance SiN etching explains qualitatively some previously published experimental data.