Pulse windowing optical sensor

A method of collecting optical data of a pulsed plasma using a photosensitive charge transfer array of sensor columns comprising an active column and at least one storage column, the method comprising:

• performing a sampling step and a reset step for each plasma pulse Pm of M>1 plasma pulses,
• the sampling step comprising performing a collection step and a transfer step for each sampling interval Tn of N sampling intervals comprising a sampling interval T1,
• the collection step comprising accumulating photoelectrons corresponding to the plasma pulse Pm into column charges Qn stored in the active column during the sampling interval Tn, wherein the sampling interval Tn has a same predetermined temporal relationship ΔTn with each of the plasma pulses,
• the transfer step comprising shifting stored charge in each of the sensor columns to respective adjacent columns to transfer the column charges Qn out of the active column,
• the reset step comprising, for m<M, shifting stored charge in each of the sensor columns to respective adjacent columns to transfer column charges Q1 corresponding to the sampling interval T1 to the active column;
• and
• reading out stored charge in each of the sensor columns as the optical data after accumulating photoelectrons corresponding to the last plasma pulse PM during the last sampling interval TN.

An optical emission spectroscopy (OES) system comprising:

• a pulsed plasma apparatus comprising a processing chamber and configured to generate a plasma having M>1 plasma pulses in the processing chamber;
• an OES detection device optically coupled to the plasma and comprising
• an optical collector configured to receive an optical signal;
• a photosensitive charge transfer array of sensor columns comprising an active column and at least one storage column;
• and
• an optically dispersive element configured to generate a dispersed optical signal from the optical signal, the dispersed optical signal being incident on and localized to the active column;
• and
• a control and data acquisition circuit electrically coupled to the photosensitive charge transfer array and configured to
• perform a sampling step and a reset step for each plasma pulse Pm of the M>1 plasma pulses,
• the sampling step comprising performing a collection step and a transfer step for each sampling interval Tn of N sampling intervals comprising a sampling interval T1,
• the collection step comprising accumulating photoelectrons corresponding to the plasma pulse Pm into column charges Qn in the active column during the sampling interval Tn, wherein the sampling interval Tn has a same predetermined temporal relationship ΔTn with each of the plasma pulses,
• the transfer step comprising shifting stored charge in each of the sensor columns to respective adjacent columns to transfer the column charges Qn out of the active column,
• the reset step comprising, for m<M, shifting stored charge in each of the sensor columns to respective adjacent columns to transfer column charges Q1 corresponding to the sampling interval T1 to the active column, and
• read out stored charge in each of the sensor columns as optical data after accumulating photoelectrons corresponding to the last plasma pulse PM during the last sampling interval TN.