Results of a comparative study of SiNx SiO2 and Si etching in high- and low-density O-2-N-2 based plasmas with small additions of SF6 are presented. Higher selectivities of SiNx etching over both SiO2 (up to 50-70) and Si (up to 20) are obtained in a high-density reactor as compared with low-density reactive ion etching. Plasma and surface processes responsible for etching are analyzed. Kinetics of NO molecules responsible for enhanced nitride etching is shown to be distinctly different for low- and high-density plasma conditions. Possible ways of further optimization of the process are discussed. (C) 2003 American Vacuum Society.