Methods and apparatus for processing a substrate

An apparatus configured to couple to a processing chamber for processing a substrate comprising:

• a first voltage/current (V/I) probe configured to connect to an input side or an output side of a matching network of the processing chamber comprising capacitors arranged in a voltage divider network configured to detect a voltage of an RF signal generated by an RF generator at a target RF frequency, and an inductor configured to detect a current of the RF signal generated by the RF generator at the target RF frequency;
• a processor coupled to the first V/I probe configured to determine a phase angle of the RF signal generated by the RF generator based on a voltage detected by the first voltage/current (VI) probe of the RF signal generated by the RF generator, and a current detected by the first voltage/current (VI) probe of the RF signal generated by the RF generator;
• the processor further configured to generate a plurality of offset RF reference signals at the target RF frequency of the RF generator, each of the offset RF reference signals having a known offset phase angle from −180° to +180° relative to the RF signal generated by the RF generator at the target RF frequency;
• the processor further configured to:
• i) determine a phase angle difference equal to a difference between the determined phase angle of the RF signal generated by the RF generator and the phase angle of each of the plurality of offset RF reference signals generated by the processor;
• ii) determine an absolute value of each phase angle difference;
• iii) determine the minimum absolute value of the plurality of phase angle differences;
• iv) determine a correction factor offset equal to the phase angle of the offset RF reference signal which produced the minimum absolute value phase angle difference out of the plurality of phase angle differences;
• v) determine a correction factor equal to a sum of the correction factor offset, and the phase angle difference between the offset RF reference signal which produced the minimum absolute value of the plurality of phase angle differences and the determined phase angle of the RF signal generated by the RF generator;
• and
• determining at a phase angle equal to the correction factor an impedance at output and controlling impedance tuning of the matching network based at least in part on at least one of the voltage of the RF signal generated by the RF generator and the current of the RF signal generated by the RF signal generator, detected by the first V/I probe.