Plasma processing apparatus and plasma etching method

A method of plasma etching comprising:

• obtaining a plurality of etching rates respectively corresponding to a plurality of negative DC bias potentials using an apparatus of plasma processing, which includes a chamber, a substrate support disposed in the chamber and including a lower electrode, a radio-frequency power supply electrically coupled to the lower electrode, and a focus ring disposed on the substrate support to surround a substrate wherein the focus ring has a first region and a second region, the first region includes an inner top surface of the focus ring, the second region includes an outer top surface of the focus ring, the inner top surface and the outer top surface extend in a circumferential direction around a central axis of the focus ring, and the inner top surface extends at a position closer to the central axis than the outer top surface, and wherein in said obtaining the plurality of etching rates, a sequence, including a process of etching the substrate mounted on the substrate support by generating plasma in the chamber and generating a negative DC bias potential in the first region of the focus ring and a process of obtaining an etching rate in a central region of the substrate in the process of etching the substrate as an etching rate corresponding to the negative DC bias potential generated in the first region among the plurality of etching rates, is repeated while the plurality of negative DC bias potentials are sequentially set as the negative DC bias potential in the first region;
• determining a lower limit of an absolute value of the negative DC bias potential in the first region, wherein the lower limit is determined using a relationship between the plurality of negative DC bias potentials and the plurality of etching rates corresponding thereto so that the etching rate in the central region of the substrate does not substantially change when the negative DC bias potential in the first region is greater than or equal to the lower limit;
• and
• etching the substrate mounted on the substrate support by generating plasma in the chamber and generating the negative DC bias potential having the absolute value greater than or equal to the lower limit in the first region of the focus ring.