Etching method and plasma processing apparatus

A plasma processing apparatus comprising:

• a chamber;
• a substrate support in the chamber;
• a gas supply configured to supply a process gas into the chamber;
• a plasma generator configured to generate plasma from the process gas in the chamber;
• and
• a control circuitry;
• wherein the plasma generator includes a radio frequency power supply configured to supply a pulse of a source radio frequency power and a bias power supply configured to supply a pulse of bias power to the substrate support,
• the control circuitry is configured to, in a state where a substrate including a mask having a sparse-dense pattern and a silicon layer located below the mask is supported by the substrate support, control the gas supply and the plasma generator to:
• form a recess overlapping an opening of the mask by etching the silicon layer using first plasma generated from a first process gas,
• form a protective layer on at least a side wall of the recess, and
• etch a bottom of the recess using second plasma generated from a second process gas,
• in a case where the protective layer is formed, the control circuitry is configured to control the gas supply and the plasma generator such that a precursor layer is formed on at least the side wall of the recess and then the precursor layer is modified into the protective layer using a third process gas, and
• in a case where the bottom of the recess is etched, the control circuitry is configured to control the radio frequency power supply and the bias power supply such that the pulse of the source radio frequency power is supplied in a first period and the pulse of the bias power is supplied to the substrate support in a second period that does not overlap with the first period.