Plasma monitoring

For precise control of a plasma process, the condition of the plasma must be monitored during the ongoing process. Generally, two methods are available:

1. Spectroscopic monitoring:
   A low-pressure plasma emits the colour typical for the process gas , i.e. the wavelength of the electromagnetic radiation. The colour changes with the increasing proportion of residual gases. This means that additional wavelengths (spectral lines) are observed in a spectroscopic measurement. The intensity of the radiation changes with the pressure of the low-pressure plasma.
   It can be normal that the spectrum of a plasma changes over the course of the process because reaction products accumulate in the plasma. However, checks are required to ensure that the changes do not exceed the specified tolerances.
2. Measurement and monitoring of pressure, gas flow, voltage, time, and other process parameters.