Patent ID: 8101906

Claim:
An apparatus for adjusting a parameter setting in a substrate processing chamber, the apparatus comprising: a memory, the memory configured to store and to retrieve data and instructions; a processor, enabled to retrieve instructions from the memory and execute the instructions to: record a measurement with a reference spectrometer a reference optical intensity of radiation from a light source transmitted through a first reference optical path in a reference chamber other than the substrate processing chamber; record a measurement of a second optical intensity of radiation from the light source through at least a second optical path of the substrate processing chamber, the second optical path causing attenuation to the radiation different from attenuation of the first reference optical path; compare the reference optical intensity with the second optical intensity to obtain a correction factor for the second optical path; record a measurement through a second reference optical path in the substrate processing chamber of a reference optical plasma intensity generated in the substrate processing chamber; record a measurement through the second optical path of the substrate processing chamber of a second optical plasma intensity generated in the substrate processing chamber; and compare the second optical plasma intensity adjusted in accordance with the correction factor with the reference optical plasma intensity.