Strategy for tuning the average charge state of metal ions incident at the growing film during HIPIMS deposition

Energyand time-dependent mass spectrometry is used to determine the relative number density of singlyand multiply-charged metal-ion fluxes incident at the substrate during highpower pulsed magnetron sputtering (HIPIMS) as a function of the average noble-gas ionization potential. Ti is selected as the sputtering target since the microstructure, phase composition, properties, and stress-state of Ti-based ceramic thin films grown by HIPIMS are known to be strongly dependent on the charge state of Tin+ (n = 1, 2, ...) ions incident at the film growth surface. We find that the flux of Tin+ with n > 2 is insignificant; thus, we measure the Ti2+/Ti+ integrated flux ratio / at the substrate position as a function of the choice of noble gas -Ne, Ar, Kr, Xe, as well as Ne/Ar, Kr/Ar, and Xe/Ar mixtures -supporting the plasma. We demonstrate that by changing noble-gas mixtures, varies by more than two orders of magnitude with only a small change in . This allows the ratio / to be continuously tuned from less than 0.01 with Xe, which has a low first-ionization potential , to 0.62 with Ne which has a high . The value for Xe, = 12.16 eV, is larger than the first ionization potential of Ti, = 6.85 eV, but less than the second Ti ionization potential, = 13.62 eV. For Ne, however, = 21.63 eV is greater than both and . Therefore, the high-energy tail of the plasma-electron energy distribution can be systematically adjusted, allowing / to be controllably varied over a very wide range. corresponding author: [email protected]; phone: +46 13 28 1213