Patent ID: 8154209

Claim:
A method of operating a plasma processing system having a space for receiving gas, an electrode portion and an RF driver, the RF driver being operable to provide a driving signal to the electrode portion, said method comprising: providing a gas into the space; providing the driving signal to the electrode portion, the driving signal being based on a first signal portion and a second signal portion; and generating, from the gas, a plasma in the space, wherein the plasma has a plasma sheath, wherein the plasma sheath has a plasma sheath potential, wherein the plasma sheath potential is based on the driving signal, wherein the plasma sheath potential as a function of time based on a first plasma sheath potential function portion and a second plasma sheath potential function portion, wherein the first plasma sheath potential function portion comprises a continuous sinusoidal portion having a first amplitude and a first frequency, wherein the second plasma sheath potential function portion comprises a sinusoidal portion having a maximum amplitude interval, and a minimum amplitude interval and a duty cycle, wherein the maximum amplitude interval has a second frequency, a first duration and a first interval amplitude, wherein the minimum amplitude interval has a second duration and a second interval amplitude, wherein the first interval amplitude is larger than the second interval amplitude, wherein the duty cycle is the ratio of the first duration to the sum of the first duration and the second duration, and wherein the second plasma sheath potential function portion is amplitude-modulated at a frequency equal to a harmonic of the first frequency.