The results of a study of SiNx, SiO2, and Si etching in a high-density electron cyclotron resonance plasma using mixtures containing SF6, NF3, N-2, O-2, and Ar are presented. Higher selectivities of SiNx, etching over SiO2 (up to similar to100) were achieved with NF3, while higher selectivities over Si (up to 5-10) were obtained with SF6-based mixtures. Plasma and surface processes responsible for etching are analyzed, and mechanisms of nitride etching in NF3-based plasmas are proposed. (C) 2004 American Vacuum Society.