Detecting chemiluminescent radiation in the cleaning of a substrate processing chamber

In a substrate processing apparatus, a substrate processing chamber has a substrate support to support a substrate, a gas delivery system to provide an energized cleaning gas to the chamber to clean process residues formed on surfaces in the chamber during processing of the substrate, and an exhaust to exhaust the cleaning gas. A detector monitors a chemiluminescent radiation emitted from about a surface during cleaning of the process residues by the energized cleaning gas and generates a signal in relation to the monitored chemiluminescent radiation. A controller receives the signal and evaluates the signal to determine an endpoint of the cleaning process.