Etching method and plasma processing system

An etching method comprising:

• (a) providing a substrate on a substrate support in a chamber, the substrate including a silicon-containing film and a mask on the silicon-containing film, the silicon-containing film including silicon and nitrogen;
• (b) supplying a process gas to the chamber, the process gas containing a single or mixed gas and a chlorine-containing gas that contains carbon and hydrogen, the single or mixed gas containing fluorine and hydrogen, where a flow rate of the chlorine-containing gas is 1.5 volume % or more and 5 volume % or less of a total flow of the process gas excluding an inert gas;
• and
• (c) generating a plasma from the process gas to etch the silicon-containing film, where the plasma contains active species of hydrogen fluoride.