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

Energy and time-dependent mass spectrometry is used to determine the relative number density of singly- and multiply-charged metal-ion fluxes incident at the substrate during high-power 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 Ti n+ ( n = 1, 2, …) ions incident at the film growth surface. We find that the flux of Ti n+ with n > 2 is insignificant; thus, we measure the Ti 2+ /Ti + integrated flux ratio J T i 2 + / J T i + 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, J T i 2 + varies by more than two orders of magnitude with only a small change in J T i + . This allows the ratio J T i 2 + / J T i + to be continuously tuned from less than 0.01 with Xe, which has a low first-ionization potential IP 1 , to 0.62 with Ne which has a high IP 1 . The value for Xe, I P X e 1 = 12 . 16 eV , is larger than the first ionization potential of Ti, I P T i 1 = 6 . 85 eV , but less than the second Ti ionization potential, I P T i 2 = 13 . 62 eV . For Ne, however, I P N e 1 = 21 . 63 eV is greater than both I P T i 1 and I P T i 2 . Therefore, the high-energy tail of the plasma-electron energy distribution can be systematically adjusted, allowing J T i 2 + / J T i + to be controllably varied over a very wide range. [ABSTRACT FROM AUTHOR]