Abstract: A method of processing a substrate that includes: flowing nitrogen-containing (N-containing) gas, dioxygen (O2), a noble gas, and a fluorocarbon into the plasma processing chamber, the plasma processing chamber configured to hold a substrate including a dielectric layer as etch target and a patterned hardmask over the target layer; while flowing the gases, generating a fluorine-rich and nitrogen-deficient plasma in the plasma processing chamber, fluorine-rich and nitrogen-deficient plasma being made of more number of fluorine species than nitrogen species; and forming a high aspect ratio feature by exposing the substrate to the fluorine-rich and nitrogen-deficient plasma to etch a recess in the dielectric layer.