Semiconductor device manufacturing method

This semiconductor device manufacturing method is provided with: a film-forming step wherein a silicon nitride layer or a silicon oxide layer is formed such that a side wall portion of a silicon-containing layer, which is formed on a substrate and patterned, is covered with the silicon nitride layer or the silicon oxide layer; and a plasma etching step wherein the silicon-containing layer is selectively removed, and the silicon nitride layer or the silicon oxide layer formed on the side wall portion is left. In the plasma etching step, an etching gas containing SF6 gas is used.