Patent ID: 7537671

Claim:
A plasma monitor for a vacuum processing system, the monitor comprising: a vacuum tight housing connectable to a plasma processing chamber with an inside thereof in communication with a vacuum pressure environment within the chamber, the housing having at least two line-of-sight signal paths therethrough, including a monitoring signal path and a reference signal path; at least two windows in the housing, including a first window located in the monitoring signal path and a second window located in the reference signal path, each window having a side thereof in contact with the vacuum pressure environment and exposed to deposits thereon of film forming material from the vacuum pressure environment; a reference signal source located along the reference signal path; at least two optical sensors including a first sensor located outside of the first window in the monitoring signal path and a second sensor located outside of the second window in the reference signal path and oriented to receive and measure signals in the respective paths; the monitoring signal path extending from a plasma volume in the processing chamber when the housing is coupled thereto, through the housing and the first window, to the first sensor, and the reference signal path extending from the reference signal source, through the housing and the second window, to the second sensor; means including a central cavity within the housing at a point of intersection of the monitoring signal and reference signal paths for affecting the flow of the film forming material from the plasma volume and through the central cavity within the housing and equally along each of the monitoring signal and the reference signal paths to and onto the respective first and second windows so as to deposit film of the film forming material from the vacuum pressure environment substantially equally on the first and second windows; and a processor programmed to derive a measurement of emissions from the plasma volume in response to outputs from the first and second sensors.