ION-BOMBARDMENT ENERGY-DISTRIBUTIONS IN A RADIO-FREQUENCY INDUCTION PLASMA

Ion bombardment energy distributions to a grounded substrate in a low pressure, rf induction plasma source are measured. The plasma source consists of a planar, spiral coil driven at 13.56 MHz which is separated from a low pressure discharge vessel by a quartz vacuum window. Ion bombardment spectra were determined using a differentially pumped retarding grid energy analyzer which samples the plasma through an 80 mum diam grounded, conducting orifice. The ion flux was found to be nearly monoenergetic for heavier ionic species such as Ar and oxygen. A double-peaked distribution was observed in water vapor plasmas where the sheath transit time of light ions is much less than the rf period. The average ion energy follows the average plasma potential and the width of the ion energy distribution correlates with the rf component of the floating probe potential, which is typically 2-6 V(p-p).