US Patent 6972524 Plasma processing system control

A method of approximating an ion energy distribution function (IEDF) at a substrate surface of a substrate, the substrate being processed in a plasma processing chamber. There is included providing a first voltage value, the first voltage value representing a value of a first voltage that represents a DC potential (VDC) at the substrate surface. There is also included providing a peak low frequency RF voltage value (VLFRF(PEAK)) during plasma processing, the peak low frequency RF voltage (VLFRF(PEAK)) value representing a peak value of a low frequency RF voltage (VLFRF) supplied to the plasma processing chamber. There is further included providing a computing device configured to compute the IEDF from the first voltage value and the peak low frequency RF voltage value (VLFRF(PEAK)) in accordance withf⁡(E)≡(ⅆVLFⅆt)-1,whereinVLF⁡(t)=[(VLFRF⁡(PEAK)-Vdc2)1/2-(VLFRF⁡(PEAK)-Vdc8)1/2⁢sin⁢⁢ω⁢⁢t]2.