Bias waveform adjustment to substrate for mono-energetic ion energy distribution

A mono-energetic ion energy distribution has a narrow the angular distribution of ions, for resulting in vertical etching profile. For the mono energetic ion energy distribution, a feedback system between ion density and the applied voltage waveform is developed. When applying a waveform to the substrate, the potential of the substrate increases due to the increase in ion flux to the substrate which leads to a broaden the ion energy distribution. The substrate potential increase depends on the incident ion flux. Therefore, the ion flux is measured with a probe and the waveform is adjusted. Through this feedback mono energetic ion energy distribution can be achieved.