Plasma processing apparatus

A plasma processing apparatus comprising:

• a chamber;
• a substrate support disposed in the chamber and including a lower electrode;
• an RF generator that generates a pulsed RF signal in order to generate plasma in the chamber, the pulsed RF signal having a first power level in a first period in each cycle and having a second power level smaller than the first power level in a second period in each cycle;
• a pulsed voltage generator that is electrically connected to the lower electrode and that generates a pulsed voltage signal, the pulsed voltage signal having a reference voltage level in a delay period in the first period, having a sequence of a plurality of voltage pulses having a first voltage level in the first period excluding the delay period, and having the reference voltage level in the second period, the first voltage level having an absolute value larger than an absolute value of the reference voltage level, the delay period falling within a range of 2 to 7% of a total period in each cycle;
• a microwave interferometer that monitors an electron density of plasma in the chamber;
• and
• controller circuitry configured to control the RF generator to adjust at least one of the first power level and the delay period based on an electron density of plasma monitored in the delay period.

A plasma control method comprising:

• generating plasma in a chamber by supplying a pulsed RF signal to a substrate support disposed in the chamber and including a lower electrode, the pulsed RF signal having a first power level in a first period in each cycle and having a second power level smaller than the first power level in a second period in each cycle;
• supplying a pulsed voltage signal to the lower electrode, the pulsed voltage signal having a reference voltage level in a delay period in the first period, having a sequence of a plurality of voltage pulses having a first voltage level in the first period excluding the delay period, and having the reference voltage level in the second period, the first voltage level having an absolute value larger than an absolute value of the reference voltage level, the delay period falling within a range of 2 to 7% of a total period of each cycle;
• measuring an electron density of the plasma;
• and
• adjusting at least one of the first power level and the delay period based on the electron density measured in the delay period.