Tuning the stress in TiN films by regulating the doubly charged ion fraction in a reactive HiPIMS discharge

In the present study, we investigate the impact of pulse power (P-pulse) on the ion flux and the properties of TiN films using reactive high-power impulse magnetron sputtering. P-pulse was adjusted in the range of 5-25kW, while keeping the total average power constant through regulating the pulsing frequency. It is found that the required N-2 flow, to produce stoichiometric TiN, decreases as P-pulse is increased, which is due to a decrease in the deposition rate. The plasma conditions when stoichiometric TiN is formed were investigated in detail. In situ ion mass spectrometry measurements of the ion energy distribution functions reveal two distinct ion populations, ions originating from sputtered atoms (Ti+, Ti2+, and N+) and ions originating from the working gas (Ar+, Ar2+, and N-2(+)). The average ion energies (E-ave) of the sputtered ions show an increase with increasing P-pulse, while E-ave for the gas ions remains almost unaffected. The relative flux intensity Ti2+/Ti+ showed an increasing trend, from 0.28 to 0.47, as P-pulse was increased from 5 to 25kW. The ion flux changes affect the growth of the TiN film such that 111-textured films are grown for low P-pulse while higher P-pulse results in mixed orientations. In addition, the hardness of the deposited film increases with increasing P-pulse, while the compressive film stress increases significantly at a higher P-pulse. In this way, optimum deposition conditions were identified at P-pulse=8.3kW, where a relatively low compressive stress of 0.89GPa and high hardness of 22.67GPa were measured.