Method and apparatus for plasma processing with control of ion energy distribution at the substrates

摘要

In plasma processing, a bias voltage is provided from a power supply through a DC blocking capacitor to a platform on which a substrate to be treated is supported within a plasma reactor. The periodic bias voltage applied to the DC blocking capacitor has a waveform comprised of a voltage pulse peak followed by a ramp down of voltage from a first level lower than the pulse peak to a second lower level, the period of the bias waveform and the ramp down of voltage in each cycle selected to compensate for and substantially cancel the effect of ion accumulation on the substrate so as to maintain a substantially constant DC self-bias voltage on the substrate between the voltage pulse peaks. The waveform may include a single voltage pulse peak followed by a ramp down in voltage during each cycle of the bias voltage such that the ion energy distribution function at the substrate has a single narrow peak centered at a selected ion energy. The waveform may also comprise two voltage pulse peaks each followed by a ramp down of voltage selected to provide a bias voltage at the substrate comprising two voltage peaks during each cycle with DC self-bias voltages following each pulse peak at two different substantially constant DC levels, resulting in an ion energy distribution function at the substrate that includes two peaks of ion flux centered at two selected ion energies with substantially no ion flux at other ion energies. The ion energy distribution function may thus be tailored to best accommodate the desired plasma treatment process and can be used to reduce the effects of differential charging of substrates.