Anomalous plasma event detection and mitigation in semiconductor processing

A semiconductor processing tool comprising:

• a semiconductor processing chamber;
• an RF generator configured to provide RF power to the semiconductor processing chamber to generate and maintain a plasma;
• a photodetector configured to detect an optical signal indicative of a plasma's luminescence in the semiconductor processing chamber, the photodetector configured to convert the optical signal to an analog voltage signal;
• and
• a slope change detection unit configured to:
• receive the analog voltage signal,
• filter the analog voltage signal to form a low-pass filtered voltage signal,
• compare the low-pass filtered voltage signal with the analog voltage signal to determine whether changes associated with the low-pass filtered voltage signal exceed a threshold, and
• in response to the determination, cause a signal to be sent to the RF generator that is configured to cause an adjustment to the RF generator.

A method of detecting an anomalous plasma event comprising:

• forming a plasma utilizing a signal from an RF generator;
• detecting a fluctuating optical signal generated by the plasma;
• computing a spectral density of the fluctuating optical signal;
• and
• determining that the spectral density of the fluctuating optical signal differs from one or more reference spectral densities of a fluctuating optical signal, generated by the plasma, by a threshold amount, wherein computing the spectral density of the fluctuating optical signal comprises determining the spectral density of the fluctuating optical signal at a frequency of about 400 kHz or between about 400 kHz and about 4 MHz.