Method for fault identification in a plasma process

A method of fault identification in a plasma process powered by an RF source, comprising the steps of:

• (a) determining, in respect of a given baseline plasma process performed in advance of a production run, the changes in magnitude of a plurality of Fourier components of the RF source resulting from known changes in a plurality of the process input parameters from their baseline values,
• (b) storing said parameter changes and corresponding Fourier component magnitude changes as reference data,
• (c) running the plasma process during a subsequent production run,
• (d) during said production run, determining if there is a fault in the plasma process,(e) if there is a fault, repeating the baseline process with input parameter values nominally the same as the baseline values of step (a),
• (f) determining the magnitudes of the said Fourier components in respect of the repeat baseline process, and
• (g) comparing the data determined at step (f) with the reference data to determine which input parameter(s) have changed.