Semiconductor device manufacturing method

A semiconductor device manufacturing method comprising:

• a step of holding a substrate to be processed in a processing chamber, the substrate having a resist layer formed in a predetermined pattern on a main surface of a silicon layer;
• a first etching step in which a mixed gas having a deposition gas and an etching gas mixed at a predetermined ratio is introduced into a processing chamber and the substrate is plasma etched in the mixed gas atmosphere by using the resist layer as a mask;
• and
• a repetition step of repeating a plurality of times a deposition step in which the deposition gas is introduced into the processing chamber and the substrate that has been plasma etched in the first etching step is subjected to deposition treatment in an atmosphere having the deposition gas as a main component and a second etching step in which the etching gas is introduced into the processing chamber and the substrate that has been subjected to the deposition treatment in the deposition step is plasma etched in an atmosphere having the etching gas as a main component.