Angular Dependence of Si3N4 Etching in C4F6/CH2F2/O2/Ar Plasmas

The dependence of Si3N4 etching on ion-incident angles is investigated at various CH2F2 flow rates in C4F6/CH2F2/O2/Ar plasmas. A Faraday cage system is used to control the angles at which ions impact the surface of the substrate. The normalized etch yield (NEY) curves for Si3N4 exhibit maxima at ion-incident angles ranging from 50 to 70° at all CH2F2 flow rates, implying 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, affecting both the maximum NEYs and the corresponding ion-incident angles. Systematic analyses on deposition and etching of the passively deposited fluorocarbon films on Si3N4 in a C4F6/CH2F2/O2/Ar plasma show that the normalized deposition rate (NDR) of the fluorocarbon film is nearly the same and unaffected by the CH2F2 flow rate while etching of fluorocarbon films is similar to etching of Si3N4. This indicates that etching of the fluorocarbon film, rather than its deposition, limits Si3N4 etching in C4F6/CH2F2/O2/Ar plasmas.