Radial waveguide systems and methods for post-match control of microwaves

A system for plasma processing of a workpiece, comprising:

• a process chamber configured to create a plasma for the plasma processing;
• a radial waveguide, adjacent to the process chamber, configured to generate microwaves for transmission to the process chamber to supply energy for the plasma;
• a signal generator that provides a first microwave signal and a second microwave signal, the first and second microwave signals having a common frequency, wherein the signal generator adjusts a phase offset between the first and second microwave signals in response to a digital correction signal;
• a first electronics set and a second electronics set, wherein each of the first and second electronics sets:
• amplifies a respective one of the first and second microwave signals to provide an amplified microwave signal,
• transmits the respective one of the first and second amplified microwave signals into the radial waveguide to produce microwaves therein;
• and
• matches an impedance of the respective one of the first and second amplified microwave signals to an impedance presented by the radial waveguide;
• at least two monitoring antennas disposed within the radial waveguide that produce analog signals in response to the microwaves;
• and
• a signal controller that:
• receives the analog signals from the at least two monitoring antennas,
• determines the digital correction signal based at least on the analog signals, and
• transmits the digital correction signal to the signal generator;
• and wherein the first electronics set includes:
• a tuner that matches the impedance of the first amplified microwave signal to the impedance presented by the radial waveguide,
• a dummy load, and
• a circulator that shunts power reflected back from the radial waveguide toward the first electronics set, into the dummy load;
• and
• the signal generator adjusts the phase offset, and the tuner matches the impedance, concurrently with one another.

A method for controlling a plasma within a process chamber, comprising:

• generating, with a signal generator, a first microwave signal and a second microwave signal, the first and second microwave signals having a common frequency, and a phase offset therebetween that is determined at least in part by the signal generator responding to a digital correction signal;
• amplifying the first and second microwave signals to provide respective first and second amplified microwave signals;
• transmitting the first and second amplified microwave signals into a radial waveguide proximate the process chamber, such that microwaves propagate from the radial waveguide into the process chamber to provide energy for the plasma;
• generating analog signals from the microwaves with at least two monitoring antennas disposed within the radial waveguide;
• determining the digital correction signal based at least on the analog signals from the at least two monitoring antennas;
• and
• transmitting the digital correction signal to the signal generator.