Ionization fraction in sputter-based copper ion sources for plasma immersion ion implantation

This paper reports on ionization fraction in sputter-based copper ion sources for plasma immersion ion implantation (PIII). Deposition rate of copper thin film on a silicon substrate was measured, and A Cu+ ion flux fraction to overall Cu species was obtained from the effects of the substrate bias on the deposition rate. The ion flux fraction increased with Ar pressure and the fraction reached ∼100%. The fraction was also compared with that obtained from quadrupole mass spectroscopy (QMS) and Langmuir probe measurements; and these results showed a fairly good agreement. The ionization fraction increased with the discharge pressure and a flight length of the sputtered copper atoms in the plasma column, suggesting that a long interaction time of the copper atoms with the plasma is a crucial condition for the enhancement of the ionization fraction.