Selective suppression of dry-etch rate of materials containing both silicon and nitrogen

A method of etching a patterned substrate in a substrate processing region of a substrate processing chamber, wherein the patterned substrate has an exposed silicon-and-nitrogen-containing region and exposed silicon, the method of etching the patterned substrate comprising sequential steps of:

• (1) a first dry etch stage comprising:
• flowing each of nitrogen trifluoride and hydrogen (H2) into a remote plasma region fluidly coupled to the substrate processing region while forming a first plasma in the plasma region to produce first plasma effluents, and
• forming protective solid by-product on the exposed silicon-and-nitrogen-containing region to form a protected silicon-and-nitrogen-containing region by flowing the first plasma effluents into the substrate processing region through through-holes in a showerhead;
• (2) a second dry etch stage comprising
• flowing a fluorine-containing precursor into the remote plasma region while forming a second plasma in the plasma region to produce second plasma effluents, wherein essentially no hydrogen (H2) is flowed into the substrate processing region during the second dry etch stage, and
• etching the exposed silicon faster than the protected silicon-and-nitrogen-containing region by flowing the second plasma effluents into the substrate processing region through the through-holes in the showerhead;
• and
• (3) sublimating the protective solid by-product from the protected silicon-and-nitrogen-containing region by raising a temperature of the patterned substrate.