Etching method and substrate processing apparatus

A method comprising:

• loading, into a process chamber, a substrate on which a multilayered film is foiined, the multilayered film including (i) a silicon-containing insulating layer, (ii) undercoat layers provided in the silicon-containing insulating layer, the undercoat layers being respectively located at different depths, and (iii) a mask layer provided on the silicon- containing insulating layer;
• supplying a first process gas into the process chamber, the first process gas containing a fluorocarbon gas and a second noble gas;
• forming a plasma from the first process gas in the process chamber, thereby causing the multilayered film to be etched to a first depth at which a first undercoat layer among the undercoat layers is located;
• after causing the multilayered film to be etched to the first depth, changing the second noble gas to a first noble gas to supply a second process gas into the process chamber, the second process gas containing the fluorocarbon gas and the first noble gas;
• and
• forming a plasma from the second process gas in the process chamber, thereby causing the multilayered film to be etched to a second depth at which a second undercoat layer among the undercoat layers is located, the second depth being deeper than the first depth;
• wherein
• the first noble gas has higher ionization energy than Ar gas,
• momentum of an ionized particle of the first noble gas is less than momentum of an ionized particle of Ar gas, and
• the second noble gas contains Ar gas or a gas having lower ionization energy than Ar gas.