Systems and methods for detection of plasma instability by optical diagnosis

A method for plasma processing of a wafer, comprising:

• having a wafer on a wafer support apparatus, the wafer support apparatus positioned beneath an electrode such that a plasma generation region exists between the wafer and the electrode;
• supplying a process gas to the plasma generation region;
• supplying radiofrequency power to the electrode to transform the process gas into a plasma within the plasma generation region;
• collecting optical emissions from the plasma using one or more optical emission collection devices;
• determining an intensity of optical emission at a first optical emission wavelength corresponding to excited neutral atoms of the process gas within the collected optical emissions over time, wherein first optical emission wavelength is selected such that the intensity of optical emission at the first optical emission wavelength corresponding to excited neutral atoms of the process gas remains substantially unchanged when a plasmoid is present within the plasma;
• determining an intensity of optical emission at a second optical emission wavelength corresponding to excited ions of the process gas within the collected optical emissions over time, wherein the second optical emission wavelength is selected such that the intensity of optical emission at the second optical emission wavelength corresponding to excited ions of the process gas increases when the plasmoid is present within the plasma, wherein the first optical emission wavelength is different than the second optical emission wavelength;
• determining an indicator ratio of the intensity of optical emission at the second optical emission wavelength corresponding to excited ions of the process gas to the intensity of optical emission at the first optical emission wavelength corresponding to excited neutral atoms of the process gas over time;
• identifying an increase in the indicator ratio over time by a threshold amount that indicates a presence of the plasmoid within the plasma;
• in response to identifying the increase in the indicator ratio over time by the threshold amount, operating a direct current power supply to supply electrical current to the wafer support apparatus and from the wafer support apparatus directly to an underside of the wafer during plasma processing of the wafer to mitigate formation of the plasmoid within the plasma.