RF plasma power supply combining technique for increased stability

An RF plasma system comprising:

• an RF signal generator which during operation generates an RF signal;
• a splitter having an input line receiving the RF derived from said RF signal, and a second output line carrying a second output signal derived from said RF signal;
• a first branch circuit receiving said first output signal and generating a first derived signal therefrom, said first branch circuit comprising a first power amplifier;
• a second branch circuit receiving said second output signal and generating a second derived signal therefrom, said second branch circuit comprising a second power amplifier having an output line;
• a combiner having a first input, a second input, and an output, said first input receiving said first derived signal and said second input receiving said second derived signal, said combiner combining said first and second derived signals to produce a power output signal therefrom;
• and
• a plasma processing chamber in which a plasma is formed during operation, said plasma receiving the power output signal from the combiner,
• wherein with a plasma present in the chamber, the first power amplifier is characterized by a first forward power curve surface and the second power amplifier is characterized by a second forward power curve surface and wherein the first and second power curve surfaces are oriented with respect each other such that changes in the load that produce an increase in forward power level for the first power amplifier produce a decrease in forward power level for the second power amplifier and vice versa.

A plasma processing apparatus comprising:

• a plasma processing chamber;
• and
• an RF power amplifier supplying power to the plasma processing chamber;
• an RF signal generator connected to said RF power amplifier and supplying an RF signal having a frequency r.sub.RF ;
• said RF power amplifier comprising:
• a splitter having an input line receiving said RF signal, a first output line carrying a first output signal derived from said RF signal, and a second output line carrying a second output signal derived from said RF signal;
• a first branch circuit receiving said first output signal and generating a first derived signal therefrom, said first branch circuit comprising a first power amplifier and a phase shifting element, said first power amplifier having an output line;
• a second branch circuit receiving said second output signal and generating a second derived signal therefrom, said second branch circuit comprising a second power amplifier having an output line;
• a combiner having a first input and a second input, said first input receiving said first derived signal and said second input receiving said second derived signal, said combiner combining said first and second derived signals to produce a power output signal therefrom,
• wherein said phase shifting element is connected between the output line of the first power amplifier and the first input of the combiner and produces a first phase shift in a signal passing from the first power amplifier to the combiner relative to a signal passing from the second power amplifier to the combiner, and wherein said first and second branch circuits also produce at frequency r.sub.RF a total phase shift in the first derived signal relative to the second derived signal that is equal to one of the following two values:
• s(360.degree.)+360.degree. and s(360.degree.)+180.degree., wherein s is an integer which may take on any positive value or zero.

A method of supplying RF power to a plasma in a plasma processing chamber, said method comprising:

• splitting an RF signal into a first output signal and a second output signal;
• power amplifying the first output signal to produce a first amplified signal;
• power amplifying the second output signal to produce a second amplified signal;
• phase shifting the second amplified signal relative to the first amplified signal to produce a phase shifted signal;
• combining the first amplified signal and the phase shifted signal to produce a power output signal therefrom;
• and
• delivering the power output signal to the plasma in the plasma processing chamber.