Effect of bias voltage waveform on ion energy distribution

Ion energy distribution (IED) is one of the primary factors governing the e tching or deposition characteristics in plasma-aided microelectronics manuf acturing processes. This article explores the influence of rf bias voltage waveform and frequency on the IED. It is demonstrated that the sheath volta ge above the wafer is reasonably similar to the rf voltage on the biased su bstrate. Since the IED correlates well with the sheath voltage if the ion t ransit time through the sheath is smaller than the rf time period, the IED can be controlled by means of the rf bias voltage. The voltage waveform con trols the shape of the distribution while the frequency determines its widt h. The sinusoidal waveform leads to a distribution that peaks at high energ ies and gradually decreases with decreasing energy. Square wave results in a sharp step in the IED at high energies, the width of which can be control led by means of the blocking capacitance. The triangular waveform generates a constant IED over a considerable range of energy. It is also demonstrate d that, by utilizing the correlation between the IED and applied voltage wa veform, one can design voltage waveforms that produce distributions with sp ecific features. (C) 2000 American Institute of Physics. [S0021-8979(00)011 11-7].