US Patent 9412617 Plasma processing method and plasma processing apparatus

Plasma etching is performed while suppressing bowing during etching of a multi-layer film. The plasma etching is performed multiple times using a processing gas containing HBr gas and C4F8 gas, and the etching gradually forms recesses from a SiN layer through a laminated film. By adding a gas containing boron to the processing gas during the etching at a predetermined timing and at a predetermined flow ratio while etching the laminated film, a protective film is formed on side walls of the SiN layer that are exposed to the recess.