Multi-stage heterodyne control circuit

A method for controlling an RF generator, the method comprising:

• sensing a characteristic of an RF signal output from the RF generator and outputting a sensor signal in response to the sensed characteristic;
• mixing the sensor signal with a first mix signal to generate a first heterodyne signal;
• filtering the first heterodyne signal through a low pass filter;
• mixing the filtered first heterodyne signal with a second mix signal to generate a second heterodyne signal;
• filtering the second heterodyne signal through a band pass filter;
• detecting the filtered second heterodyne signal to generate a DC signal;
• and
• controlling the RF signal in response to the DC signal.

An RF generator comprising:

• an RF generator configured to generate an RF signal;
• a signal sensor configured to sense a characteristic of the RF signal and output a sensor signal in response thereto;
• and
• a control circuit operationally coupled to the RF generator, the control circuit comprising:
• a first heterodyne stage receiving the sensor signal, with the first heterodyne stage configured to:
• mix the sensor signal with a first mix signal to generate a first heterodyne signal;
• and
• filter the first heterodyne signal through a low pass filter;
• a second heterodyne stage receiving the filtered first heterodyne signal, the second heterodyne stage configured to:
• mix the filtered first heterodyne signal with a second mix signal to generate a second heterodyne signal;
• and
• filter the second heterodyne signal through a band pass filter;
• and
• a detection stage configured to convert the filtered second heterodyne signal to a DC signal;
• wherein the control circuit is configured to control the RF signal in response to the DC signal.

A semiconductor fabrication system comprising:

• an RF generator configured to generate an RF signal;
• a plasma chamber operationally coupled to the RF generator to receive the RF signal;
• a signal sensor operationally coupled between the RF generator and the plasma chamber, the signal sensor configured to sense a characteristic of the RF signal and output a sensor signal in response thereto;
• and
• a control circuit operationally coupled to the RF generator and to the signal sensor, the control circuit comprising:
• a first heterodyne stage receiving the sensor signal, with the first heterodyne stage configured to:
• mix the sensor signal with a first mix signal to generate a first heterodyne signal;
• and
• filter the first heterodyne signal through a low pass filter;
• a second heterodyne stage receiving the filtered first heterodyne signal, the second heterodyne stage configured to:
• mix the filtered first heterodyne signal with a second mix signal to generate a second heterodyne signal;
• and
• filter the second heterodyne signal through a band pass filter;
• and
• a detection stage configured to convert the filtered second heterodyne signal to a DC signal;
• wherein the control circuit is configured to control the RF signal in response to the DC signal.

A control circuit comprising:

• a first heterodyne stage receiving an input signal, the input signal being based on a characteristic of a pulsed RF signal, with the first heterodyne stage configured to:
• mix the input signal with a first mix signal to generate a first heterodyne signal;
• and
• filter the first heterodyne signal through a low pass filter;
• a second heterodyne stage receiving the filtered first heterodyne signal, the second heterodyne stage configured to:
• mix the filtered first heterodyne signal with a second mix signal to generate a second heterodyne signal;
• and
• filter the second heterodyne signal through a band pass filter;
• a detection stage configured to convert the filtered second heterodyne signal to a DC signal;
• and
• a power control stage receiving the DC signal and configured to control the pulsed RF signal in response to the DC signal.