The dependence of Si3N4 etching on ion-incident angles is investigated at various CH2F2 flow rates in C4F6/CH2F2/O-2/Ar plasmas. The normalized etch yield (NEY) curves for Si3N4 imply that physical sputtering is a major contributor to Si3N4 etching. An increase in the amount of CH2F2 in the plasma produces thicker and more etch-resistant fluorocarbon films. Systematic analyses on deposition and etching of the passively deposited fluorocarbon films on Si3N4 in a C4F6/CH2F2/O-2/Ar plasma show that the normalized deposition rate of the fluorocarbon film is nearly the same and unaffected by the CH2F2 flow rate whileetching of fluorocarbon films is similar to etching of Si3N4, thus, etching ofthe fluorocarbon film, rather than its deposition, limits Si3N4 etching in C4F6/CH2F2/O-2/Ar plasmas.