Uniformity of VHF plasma produced with ladder shaped electrode

The uniformity of very high frequency (VHF) plasma produced with the ladder shaped electrode was examined by changing VHF power feeding positions for different discharge frequencies. It was found that the plasma uniformity strongly depends on how to feed the VHF power. Potential distributions on the ladder shaped electrode were calculated using the moment method and compared with measured spatial profiles of the ion saturation current. It was found that when the number of feeding positions are increased, the plasma uniformity is improved.